HK1210111B - Ejector devices, methods, drivers, and circuits therefor - Google Patents

Description

Ejector apparatus, method, driver and circuit therefor

RELATED APPLICATIONS

The present application claims benefit from the filing date of U.S. application No. 61/647,359 entitled Methods, Drivers and computers for Ejector Devices and Systems, filed On 5/2012, U.S. application No. 61/722,556 entitled Ejector Device and reaction Function Driver for, filed On 11/5 2012, and U.S. application No. 61/722,584 entitled On Demand Driver generation Device, filed On 11/5 2012, all of which are incorporated herein by reference in their entirety.

Technical Field

The systems, methods, and apparatus disclosed herein relate generally to the field of electromechanical systems. More specifically, the systems, methods, and apparatus described herein may be used to drive, monitor, and control a droplet (drop) generating ejector system.

Background

Piezoelectric actuators are electronic components that undergo mechanical deformation when a voltage is applied across them. Under the influence of a voltage, the crystal structure of the piezoelectric material (e.g. ceramic) is affected such that the piezoelectric material will change shape. For example, if an alternating electric field is applied to a piezoelectric material, the piezoelectric material will vibrate (contract and expand) at the frequency of the applied signal. This property of piezoelectric material can be used to create an effective actuator-an electronic component that can be used to displace mechanical loads. When a voltage is applied to the piezoelectric actuator, the resulting change in shape and size of the piezoelectric material shifts the mechanical load. The electrical signal applied to the piezoelectric actuator is typically either a single tone (i.e., single frequency) or a square wave input.

In some configurations, when a drive signal having a sufficient voltage and one or more appropriate frequencies is applied to a piezoelectric actuator, the piezoelectric actuator may induce motion in a mechanical load, such as a fluid, generating droplets of the fluid, which may be ejected as a stream of droplets. Improved piezoelectric drivers, drive systems, and drive methods are generally desirable during generation of a stream of ejected droplets.

Disclosure of Invention

The present disclosure is directed to droplet ejector devices and methods of driving such devices. The droplet ejector apparatus may include an actuator coupled to a droplet generator plate to define an ejector assembly, a driver and a feedback circuit. The droplet generator plate may include a plurality of openings in fluid communication with a fluid reservoir to be loaded with fluid. The drive circuit is in signal communication with the actuator and is configured to drive the actuator based on the drive waveform. A feedback circuit is in signal communication with the actuator and the drive circuit and is configured to determine a relaxation time based on a feedback signal indicative of oscillation of the fluid-loaded droplet generator plate. The drive waveform includes a first drive sequence separated from a second drive sequence by a relaxation time period that is based on relaxation times of the actuator and the fluid-loaded droplet generator plate.

Further in accordance with the present disclosure, a drive circuit and a drive signal or drive waveform are provided for a piezoelectric ejector device or for a drop generator that may be included in a piezoelectric device.

Drawings

FIG. 1 illustrates a cross-sectional view of an embodiment of an injector assembly of the present disclosure.

Fig. 2A and 2B are cross-sectional views of one embodiment of an activated injector plate for an injector assembly of the present disclosure.

FIG. 3A is a schematic view of an embodiment of an ejector mechanism in a symmetric configuration for an ejector assembly of the present disclosure.

Fig. 3B is a disassembled view of an embodiment of a symmetric ejector mechanism of the present disclosure.

Fig. 3C is a plan view of an embodiment of a symmetric ejector mechanism of the present disclosure.

FIG. 4 is a cross-sectional view through a portion of an embodiment of an injector mechanism of the present disclosure.

Figure 5 is a block diagram of one embodiment of a system for driving and controlling a piezoelectric actuator according to the present disclosure.

Fig. 6 is a schematic circuit diagram of a modified buck-boost converter of the present disclosure.

Fig. 7 is a schematic circuit diagram of one embodiment of a modified boost converter of the present disclosure for converting battery voltage from 2 to 3 volts to up to a 60V output to drive a full bridge and/or resonant converter.

Fig. 8 is a schematic circuit diagram of one embodiment of a driven resonant converter of the present disclosure.

Fig. 9 is a block diagram of one embodiment of a driver of the present disclosure using a boost converter.

FIG. 10 is a block diagram of one embodiment of a multi-tone driver and resonance detection and control circuit according to the present disclosure.

Figure 11 illustrates a time-varying voltage output of one embodiment of a two-tone driver according to the present disclosure.

Fig. 12 is a block diagram of another embodiment of a multi-tone driver and resonance detection and control circuit according to the present disclosure.

Fig. 13 is a block diagram of yet another embodiment of a multi-tone driver and resonance detection and control circuit according to the present disclosure.

Fig. 14 is a block diagram of yet another embodiment of a multi-tone driver and resonance detection and control circuit according to the present disclosure.

Fig. 15 is a schematic circuit diagram of one embodiment of a driver according to the present disclosure.

Fig. 16 is a block diagram of another embodiment of a multi-tone driver and resonance detection and control circuit according to the present disclosure.

FIG. 17 is a circuit diagram of one embodiment of a full bridge circuit with a TEP measurement circuit.

Fig. 18 is an enlarged view of the TEP measurement portion of the circuit of fig. 17.

Fig. 19 is a waveform showing the voltage vs time for resonance and non-resonance decay.

FIG. 20 is a flow chart illustrating one embodiment of a method of determining a resonance of an electromechanical mechanism.

FIG. 21 is a flow chart illustrating another embodiment of a method of determining electromechanical resonance.

Fig. 22 shows a sample waveform (amplitude versus frequency) of an integrated signal according to one embodiment of a mechanism of the present disclosure.

Fig. 23 shows a sample waveform (amplitude versus frequency) of an integrated signal according to another embodiment of a mechanism of the present disclosure.

FIG. 24 is a block diagram of another embodiment of a driver and resonance detection and control circuit according to the present disclosure.

FIG. 25 is a block diagram of yet another embodiment of a driver and resonance detection and control circuit according to the present disclosure.

FIG. 26 is a block diagram of yet another embodiment of a driver and resonance detection and control circuit according to the present disclosure.

FIG. 27 is a block diagram of one embodiment of a TEP resonance detection circuit.

FIG. 28 is a block diagram of one embodiment of a bypass for a resonance detection and control circuit according to the present disclosure.

FIG. 29 shows drive signals and resonance detection and control circuit signals according to one embodiment of the present disclosure.

Fig. 30 is a schematic circuit diagram of one embodiment of a level-shifting driver that takes complementary waveform generator outputs to drive the levels necessary for full-bridge operation according to the present disclosure.

FIG. 31 is a waveform of mass deposition vs. frequency variation for one implementation of the present disclosure.

Fig. 32 is a graph of integrated voltage vs frequency for a resonant measurement output according to one implementation of the present disclosure.

Fig. 33 is a schematic circuit diagram of one embodiment of a gated oscillator boost circuit for a drive system.

FIG. 34A is a graph of an exemplary fluid relaxation waveform.

Fig. 34B is an expanded view of the fluid relaxation waveform of fig. 34A.

Fig. 35A-D are diagrams of example waveforms for ring-down damping.

Fig. 36 is a diagram of a relaxation waveform following removal of a drive signal.

Fig. 37 is a graph of a relaxation waveform following a soft ramp down of a drive signal.

Fig. 38A is a diagram of a relaxation waveform after five-cycle excitation, showing harmonic generation ("beating") of the ring-down signal.

FIG. 38B is an expanded view of the relaxation waveform of FIG. 38A.

FIG. 39A is a graph of fluid relaxation waveforms after ten cycles of excitation with the addition of a damping signal, showing reduced relaxation time and harmonic generation.

FIG. 39B is an expanded view of the relaxation waveform of FIG. 39A.

FIG. 40 is a graph of relaxation waveforms after ten cycle square wave excitation with a damped signal.

FIG. 41 is a graph of a relaxation waveform without a damping signal.

Fig. 42 is a diagram of a relaxation waveform after ten-cycle square wave driving with two periods of the damping signal and relaxation dead time.

FIG. 43 is a block diagram of one embodiment of a drive signal generator.

FIG. 44 is a schematic circuit diagram of one embodiment of a level shifter circuit.

FIG. 45 is a schematic circuit diagram of one embodiment of an IR level detection circuit.

Fig. 46 is a schematic circuit diagram of one embodiment of a 2X charge pump.

Fig. 47 is a schematic circuit diagram of one embodiment of two boost converters acting as charge pumps and piezoelectric ceramic (piezo) drivers in accordance with the present disclosure.

FIG. 48 is a schematic circuit diagram of one embodiment of a microcontroller of the present disclosure.

Fig. 49 shows a circuit diagram of one embodiment of a set of level shifters driving a full bridge loaded with a resonant tank (tank) (including piezo).

FIG. 50 illustrates one embodiment of a TEP pull down/drop on demand circuit.

Detailed Description

The present disclosure relates generally to ejector devices, and methods of their use in fluid delivery. In particular, the present disclosure relates to ejector devices and methods useful in fluid delivery for ocular, topical, oral, nasal, or pulmonary use, including delivery of ocular fluid to the eye. In drop-on-demand operation, using the systems and methods described herein, one or more drops of fluid may be ejected at a given time to achieve the ejector displacement and velocity necessary to deliver fluid in drop form with a desired mass transfer rate and fluid dosage, and with reduced bubbling (beading) and ejector clogging.

By way of background, in very high volume droplet generation and ejector systems, the fluid may bubble on the surface of the ejector, block the droplet generation opening and reduce mass transport, sometimes for periods of up to several seconds or even minutes. Thus, fluid foaming and related effects can make it difficult to provide the necessary fluid ejection velocity over the pattern of ejector openings or nozzles. These challenges are particularly relevant when operating in low speed mode or unfavorable eigenmode shapes. The eigenmode or normal mode of an oscillating system is a vibration or motion mode in which all parts of the system move sinusoidally at the same frequency and with a fixed phase relationship. The motion described by the normal mode is called resonance. The frequency of the normal mode of the system is referred to as its natural or resonant frequency. A physical object such as a building, bridge or molecule or as in this example a fluid ejector mechanism has a set of normal modes depending on its structure, materials and boundary conditions. The ejected fluid may also form an evaporative film on the ejector surface, which can greatly degrade ejector performance.

In certain embodiments, an ejector apparatus includes an ejector mechanism (e.g., an ejector plate and a drop generator plate coupled to an actuator) that generates a directed stream of fluid drops, and a fluid supply arrangement for loading the ejector mechanism. For ease of reference, the combination of the ejector mechanism and the fluid supply arrangement will be referred to herein as an ejector assembly. Suitable fluids include, but are not limited to: solutions, suspensions and emulsions having viscosities in the range that droplets can be formed using an ejector mechanism. Suitable fluids also include, but are not limited to, fluids containing drugs and pharmaceutical products.

To achieve mass deposition of fluid droplets in high volume droplet generation and ejection systems, ejected continuous fluid ejection may be utilized. Continuous ejection allows mass deposition of larger volumes of fluid (e.g., in the range of 0.5-30 uL) by the generation and ejection of large numbers of small droplets.

However, jetting a stream of droplets in a continuous mode can cause bubbling due to, among other reasons, chaotic jetting, satellite recovery, and inductive and triboelectric effects. Once formed, a fluid bubble located above the ejector opening may grow, e.g., due to the pumping action, eventually wetting the outer surface of the ejector opening, e.g., due to Coulomb attraction or mechanical movement. In addition to the momentum of the oscillating ejector mechanism, the fluid itself also increases momentum, which may be established during continuous injection mode or when insufficient relaxation time periods are provided between the oscillation and injection time periods, as discussed below.

Thus, in accordance with the present disclosure, improved droplet generation and ejection techniques are provided for driving a piezoelectric actuator (or other actuator) to reduce, minimize, or eliminate fluid bubbling on the surface of the injector and over the injector opening. The present disclosure also provides improved droplet generation and ejection techniques that inhibit or prevent the formation of an incomplete ejection of fluid film on the surface of the ejection assembly and on other components, which is necessary to maintain performance over an extended period of use.

Various techniques are disclosed to stop or reduce fluid momentum build-up during continuous jetting operations in order to suppress or prevent bubbling through electrical drive signal timing and piezoelectric energy cancellation or active damping. These techniques may be applied to a range of suitable drive signal types including, but not limited to, sinusoidal, square, ramp, chirp (chirp), amplitude modulated and frequency modulated drive signals and waveforms, and combinations of such waveforms.

In embodiments of these techniques, the droplets may be formed from a fluid contained in a reservoir coupled to the ejector mechanism. The sprayer mechanism and reservoir may be disposable or reusable, and the components may be packaged in a housing of the sprayer device, such as those described in U.S. provisional application nos. 61/569,739, 61/636,559, 61/636,565, 61/636,568, 61/642,838, 61/642,867, 61/643,150, and 61/584,060, and in U.S. patent application nos. 13/184,446, 13/184,468, and 13/184,484, the contents of which are incorporated herein by reference.

Referring to fig. 1, for example, an ejector assembly 100 may include an ejector mechanism 101 and a reservoir 120. The ejector mechanism 101 may comprise an oscillating plate arrangement with an ejector plate 102, wherein the ejector plate 102 is integrally formed with a centrally located generator plate portion comprising the ejector opening 126, as in this embodiment, or the ejector plate 102 may be coupled to a separate generator plate that may be activated by a piezoelectric actuator 104 forming part of the ejector mechanism. For convenience, both embodiments will be referred to as having a drop generator 132. Actuator 104 vibrates or otherwise displaces ejector plate 102 to deliver fluid 110 from reservoir 120 in direction 114, either as individual droplets 112 from one or more openings 126 (droplet on demand) or as a stream of droplets 112 ejected from one or more openings 126.

In some applications, the ocular fluid may be sprayed toward the eyes 116 (e.g., of an adult or child or animal). The fluid may contain an agent for treating a human or animal discomfort, condition or disease (either in the eye or on the skin surface, or in nasal or pulmonary applications).

The location of attachment of the actuator 104 to the ejector plate 102 may also affect the operation of the ejector assembly 100, as well as the generation of individual droplets or streams of droplets. In the implementation of fig. 1, for example, the actuator 104 (or a plurality of individual actuator components 104) may be coupled to a peripheral region of the ejector plate 102 on a surface 122 opposite the reservoir 120.

In this embodiment, central region 130 of ejector plate 102 includes an ejection region 132 having one or more openings 126 through which fluid 110 flows to form droplets 112. The jetting region (or drop generator) 132 can occupy a portion of the central region 130, such as a center thereof, or the jetting orifice pattern of the jetting region 132 can occupy substantially the entire area of the central region 130. Further, the open end 138 of the reservoir may substantially correspond to the size of the jetting region 132, or as in this embodiment, the open area 138 may be larger than the jetting region 132.

As shown in fig. 1, the ejector plate 102 is disposed over or in fluid communication with an open end 138 of the reservoir 120 containing the fluid 110. For example, the reservoir 120 may be coupled to the ejector plate 102 along the peripheral region 146 of the first major surface 125 using a suitable seal or coupling, such as an O-ring 148a, disposed in a groove formed in the reservoir wall 150. A portion 144 of the reservoir housing may also be provided in the form of a removable bladder. However, the present disclosure is not so limited and any suitable bladder or reservoir may be used.

When a voltage is applied across electrodes 106a and 106B located on opposite surfaces 136 and 134 of actuator 104, ejector plate 102 deflects to become a relatively more concave shape 170 or a relatively more convex shape 172 as shown in fig. 2A and 2B, respectively, depending on the polarity of the voltage.

When driven with an alternating voltage, actuator 104 operates to alternately reverse the convex and concave shapes 170 and 172 of ejector plate 102, including the periodic motion (oscillation) of ejector plate 102. The droplets 112 are formed at the orifice or opening 126, as described above, wherein the oscillating motion of the ejection region 132 causes one or more droplets 112 to be ejected along the fluid delivery (ejection) direction 114, for example in a single-droplet (drop-on-demand) application or as a stream of droplets.

The drive voltage and frequency may be selected for improved performance of the ejection mechanism, as described above. In some embodiments, the oscillation frequency of actuator 104 may be selected at or near the resonant frequency of ejector plate 102, or at one or more frequencies selected to oscillate ejector plate 102 at such resonance via superposition, interference, or resonant coupling.

When operating at or near the resonant frequency, the ejector plate 102 may amplify the displacement of the ejector region (drop generator) 132, reducing the relative power requirements of the actuator, as compared to a directly coupled design. The damping factor of the resonant system (including actuator 104, ejector plate 102, and any fluid-filled drop generator) may also be selected to be greater than the piezoelectric actuator input power in order to reduce fatigue and increase service life without significant failure.

An example of an eductor assembly is described in U.S. provisional patent application No. 61/569,739 entitled "Ejector Mechanism, Ejector Device, and Methods of Use", filed 12 months and 12 days 2011, which is incorporated herein by reference. In one particular embodiment, the Ejector plate Mechanism 100 may include a rotationally Symmetric Ejector plate 102 coupled to an annular actuator 104, as shown in FIG. 3A, and as described in U.S. provisional patent application No. 61/636,565 entitled "Central-symmetry Lead Free Ejector Mechanism, Ejector Device, and Methods of use," filed 4/20/2012, which is also incorporated herein by reference. However, the present disclosure is not so limited.

In the particular configuration of fig. 3A, the ejector mechanism 300 includes a separate generator plate 301 attached to an ejector plate 302. The actuator 304 incorporates one or more separate piezoelectric devices or other actuator elements for driving the rotationally symmetric ejector plate 302, as described above, but in this embodiment the actuator 304 comprises an annular structure. A drop generator (ejector) region 332 of the ejector plate 302 includes a pattern of openings 326 in a central region 330 and is driven via the actuator 304 by a suitable drive signal generator circuit as described below. An example of a technique for generating drive voltages is described in U.S. provisional patent application No. 61/647,359, filed on 5/15/2012 and entitled "Methods, Drivers and Circuits for ejection devices and Systems," which is incorporated herein by reference.

Fig. 3B is a disassembled view of the symmetric injector mechanism 300. In this embodiment, the ejector plate 302 uses discrete (individual) drop generator elements (ejector regions) 301, as shown from the back (downward facing) surface 325 and the front (upward facing) surface 322, respectively, to the left and right of fig. 3B. The drop generator element 301 is mechanically coupled to the ejector plate 302 over a central aperture 352 and includes a pattern of openings 326 configured to generate a stream of fluid drops when driven by a generator plate type actuator 304, as described above.

Fig. 3C is a plan view of the symmetric injector mechanism 300. The ejector mechanism 300 includes an ejector plate 302, and an actuator 304 and a droplet generator 301 are attached to the ejector plate 302. The drop generator includes a pattern of openings 326 in the central region 330, as described above. The ejector mechanism 300 may be coupled to a fluid reservoir or other ejection device component via an aperture 351 in a symmetrically arranged plate-like mechanical coupling element 355, or with another suitable connection as described above with respect to fig. 1.

As shown in fig. 3C, depending on the application, the injector plate 302 may have a dimension 354 of about 21mm, or in the range of about 10mm or less to about 25mm or more. Suitable materials for the ejector plate 302 and drop generator 301 include, but are not limited to, flexible stress and fatigue resistant metals (such as stainless steel).

For orientation purposes, the various elements of the ejector mechanism 300 as shown in fig. 3A-3C may be described with respect to the position of a reservoir (such as the reservoir 320 described above with respect to fig. 1). In general, the proximal element of the mechanism 300 is positioned closer to the fluid reservoir 120 (fig. 1) and the distal element is positioned further from the fluid reservoir 120, as defined along the droplet stream or spray direction 114.

In the particular embodiment of fig. 4, the ejector assembly 400 includes an ejector mechanism 400, the ejector mechanism 400 including an oscillating ejector plate 402, the oscillating ejector plate 402 having a first major (proximal) surface 425 adjacent to the fluid reservoir 420 and a second major (distal) surface 422 opposite the fluid reservoir 420. In this embodiment, piezoelectric actuator 404 is formed as a distal member with reservoir 420 attached to a proximal surface 425 of oscillating plate 402. Alternatively, actuator 404 may be coupled to ejector plate 402 on distal surface 425 around reservoir 420.

The proximal and distal surfaces 436 and 434 of the actuator 404 are provided with conductive layers 460, for example, to provide the bottom and top electrodes 106a and 106b (FIG. 1) for the drive signals, as described above. As shown in fig. 4, a conductive layer 460 on the proximal surface 436 of the actuator 404 is separated from the distal surface or side 422 of the injector plate 402 by a dielectric layer 462, allowing the oscillating injector plate 402 to be grounded and electrically isolated from the conductive layer 460 of the actuator 404. On the distal side 434 of the actuator, an additional dielectric layer 462 may be provided to separate the metallization layer 461 from the top conductive layer (or drive electrode) 460. In certain embodiments of the present disclosure, this electrically isolates the metallization layer 461, allowing the metallization layer to act as an electrically isolated electrode for back EMF (electromotive force) measurements. In other embodiments, the separate contact for back EMF measurement may be eliminated by using the voltage level on the electrodes 106a, 106b, as discussed further below.

As shown in fig. 4, oscillating ejector plate 402 is positioned in fluid communication with reservoir 420, and proximal surface or side 425 is in contact with fluid 410. An additional coating 463 may be formed on the exposed (top and side) surfaces of the actuator 404 and may include at least a portion of the distal surface 422 of the ejector plate 402 to prevent contact between the actuator 404 and any fluid 410 ejected from the reservoir 420. In some implementations, one or both of the ejector plate 402 and generator plate (or ejector region) 432 may also be coated with an inert, medical-grade, non-toxic, non-reactive, and optionally acid-, base-, and solvent-resistant material 465, or other material having a suitable combination of such properties.

The coatings 463 and 465 may be the same or different and are applied individually or in any combination, such as by sputtering, vapor deposition, physical vapor deposition (PAD), chemical vapor deposition (COD), electrostatic powder deposition, or any suitable combination of such techniques. The coatings 463 and 465 may include materials such as polypropylene, nylon, and High Density Polyethylene (HDPE),Materials and other polymeric materials that are conformally coated, and metallic coating materials including, but not limited to, gold, platinum, and palladium. In the case where the coatings 463 and 465 are applied to the oscillating ejector plate 402 either individually or together in a thickness range of about 0.1 μm or less to about 500 μm or more,In any combination of generator plate 432 and surface of actuator 404, coatings 463 and 465 may be selected to be sufficiently adhesive to prevent delamination when vibrated at high frequencies.

In order to drive the actuator of the piezoelectric mechanism, a drive signal or a drive waveform needs to be generated by a drive circuit. In providing such a drive signal, a number of factors are considered in accordance with the present disclosure. In particular, a wide variety of factors may affect the speed of the displaced mechanical load, including the drive signal frequency and amplitude and the quality factor of the mechanical resonance at that frequency. As the drive signal frequency, amplitude, or both increase, the displacement speed of the mechanical load increases. However, higher operating frequencies also have higher average power while increasing displacement speed. The additional power required to operate at high frequencies may be undesirable in certain applications. Piezoelectric materials and piezoelectrically driven devices exhibit a resonance region where mechanical actuation becomes maximized. It is often desirable to provide electrical actuation at these frequencies to produce the maximum displacement of a piezoelectric element or piezoelectric mechanism (e.g., a piezoelectric element coupled to a load such as an ejector plate and a fluid-filled generator plate) with the least amount of electrical energy possible. However, at resonance, the piezoelectric device becomes either fully or partially resistive, thereby dissipating a significant amount of the energy in the piezoelectric. They also lose the beneficial energy dissipation properties of capacitive mode operation and reduce their efficiency in resonant converter circuits. Thus, there remains a need for improved devices, methods, and systems as described herein that provide maximum displacement and displacement speed of a mechanical load coupled to a piezoelectric actuator while enhancing the energy efficiency of the system. This is particularly important in battery operated systems where available power may be limited. According to the present invention, the ejector mechanism filled with the fluid is regarded as a membrane having a vibration membrane mode different from that of the piezoelectric ceramics (piezo) itself. While the resonance of the piezoceramic is the frequency with the highest motion/mechanical drive power of the ceramic itself, there are membrane modes that are not based on the ceramic/piezoceramic resonance itself. The piezoelectric ceramic only generates a force application function and the smaller the losses in the membrane, the higher the motion. When the system is driven in one of these membrane modes, the piezoelectric ceramic may be an almost perfect capacitor, allowing high Q amplification of the input voltage or current by the piezoelectric ceramic acting as a capacitor. This greatly reduces energy consumption and allows much higher voltage and current delivery to the device without heating the piezoelectric body.

In addition, a wide variety of factors may change the resonant properties and electrical characteristics of the piezoelectric device, such as the drive signal applied to the piezoelectric body, the mechanical load coupled to the piezoelectric body, or even the ambient temperature, pressure, and humidity surrounding the piezoelectric body. Due to one or more of these factors, a piezoelectric that is initially driven to operate at a resonant frequency may drift out of resonance, which results in less efficient operation of the piezoelectric, and potentially reduced displacement of mechanical loads. Thus, there remains a need for an apparatus, method and system as described herein that can detect the resonance of an electromechanical system including a piezoelectric actuator and its associated mechanical load, and provide corrective action to bring the piezoelectric actuator and/or mechanical load back to resonance when these systems are no longer operating in a resonant mode.

In accordance with the present disclosure, methods and circuits are provided to track maximum displacement or resonance modes in order to compensate for temperature, humidity and pressure variations and manufacturing tolerances. Further, using the actuator electrode as part of the feedback portion of the resonant system, tracking of resonance without using an isolated feedback electrode is described herein. By eliminating a separate isolated feedback electrode, the spray was significantly increased by 10-50% depending on the equipment. In one embodiment, this technique is used with a full bridge circuit and a Q-factor sweep (sweep) with resonant converter circuits, as discussed in more detail below.

In certain embodiments of the present disclosure, means are provided for exciting, detecting and characterizing electrical and/or mechanical resonances of a piezoelectric element or several coupled elements, or of an ejector mechanism. When an electromechanical mechanism, such as an injector mechanism, becomes resonant, energy is stored in the electromechanical mechanism and released at a different rate than a non-resonant electromechanical, electrical, or mechanical mechanism. Furthermore, the resonance of the electromechanical mechanism will act as an integrator of the electrical signal over time, allowing a plurality of unique signatures (signatures) to be generated in dependence on the applied electrical signal.

In certain embodiments, an electrical signal, which may be a single tone, a polyphonic tone, a chirp, any waveform, or any electrical signal containing one or more frequencies, is applied to the piezoelectric element. The electrical circuit that generates the electrical signal may be any circuit that delivers power or voltage and current at the desired frequency of the electrical signal. The electrical signal is applied for a defined amount of time and then abruptly stopped. The electrical signal remaining in the piezo is then measured by current, voltage or power measurements and either recorded for mathematical processing such as by FFT (fourier transform) or applied directly to an analog energy integrating circuit. The analog integrator may be switched on and off to correlate against a defined waveform, or may simply integrate all of the energy stored in the injector. A signature of the electromechanical resonance is obtained, which is dependent on the original electrical signal and the mechanical and electrical properties of the electromechanical system.

Furthermore, and particularly with respect to droplet ejector systems, in order to generate droplets of appropriate size and with sufficient ejection speed, the drive signal to the piezoelectric must be quite large. A battery that can be conveniently attached to the drop generator spray system does not produce sufficient voltage to drive the piezoelectric body. Thus, there remains a need for systems, methods, and devices that power droplet-generating ejection systems while maintaining the convenience and portability of battery packs.

Fig. 5 illustrates one embodiment of a system 500 for using a piezoelectric actuator 540, such as may be used in a drop generator system. As shown on fig. 5, the system 500 may include a power source 510, such as a battery; an electronic driver 520, i.e., circuitry responsible for generating a drive voltage or signal 530 to a piezoelectric actuator 540; a piezoelectric actuator 540; and a mechanical load 550 to which piezoelectric actuator 540 is coupled. The piezoelectric actuator 540 may be used to drive a wide variety of mechanical loads 550, such as a droplet generator plate, to form fluid droplets, as described in U.S. provisional application nos. 61/569,739, 61/636,559, 61/636,565, 61/636,568, 61/642,838, 61/642,867, 61/643,150, and 61/584,060, and in U.S. patent application nos. 13/184,446, 13/184,468, and 13/184,484, the contents of which are incorporated herein by reference and described above.

In some embodiments, as shown on fig. 5, it may also be desirable to couple a resonance detection and control circuit 560 to the piezoelectric actuator 540. This circuit 560 can be used to detect when the entire electromechanical mechanism 570 (actuator 540 and load 550) is no longer operating in a resonant mode, i.e., a mode in which the mechanism 570 produces a maximum or increased mechanical displacement of the load 550. The circuit 560 may also provide feedback to the driver 520 to control the frequency, for example, to bring the frequency back to the resonant frequency. Other embodiments of power supplies, drivers, converters, and waveforms according to the present disclosure are given in the incorporated references.

As discussed in further detail below, in one embodiment, a full bridge circuit is used to drive the piezoelectric injector mechanism. The potential (voltage) on each side of the piezoelectric element alternates between a supply voltage, which may be the output of a boost converter, a resonant converter, a buck-boost converter, a transformer or a voltage converter, and ground to allow portable operation at a given frequency. By driving the piezo at a single frequency down to one cycle (cycle), energy is stored in the piezo ejector mechanism, which is released back into the circuit in the form of a voltage if the drive signal ceases.

Thus, when the drive signal is suspended, the piezoelectric body operates mainly as a signal source rather than a load. The energy of the electromechanical mechanism (ejector mechanism with its piezoelectric element) must either be returned as a voltage into the electronic circuitry or dissipated by friction and electrical losses in the mechanical system.

There are three situations for determining how the electromechanical energy is removed and/or dissipated. If the circuit attached to the injector is open-circuited (tri-stated), the piezo will exchange energy capacitively (trade) with the driver FET through oscillation or simply dissipate through mechanical and internal electrical losses. The circuit connected to the injector may also be short circuited, which allows the injector to quickly dump (dump) its energy to system ground. Instead, the circuit may give the injector a limited electrical load, which produces a controlled evanescent oscillation.

Sampling the output voltage of the injector provides a measure of the injector mechanism motion associated with the fluid injection under open circuit and limited load conditions. Current sampling may be used to provide motion tracking in the event of a short circuit. In any of these cases, no feedback electrode is required, thereby avoiding having to provide a separate metallization layer, such as layer 461 in the embodiment of fig. 4.

The power supply 510 may be any suitable power source capable of powering the driver 520, including a suitable battery. Although not shown, the system 500 may include more than one power source, or an alternative or backup power source, if desired. Depending on the characteristics of the power supply 510, it may be necessary to raise the output voltage of the power supply 510 in order to ultimately power the piezoelectric actuator 540.

As discussed above, in some embodiments according to the present disclosure, the output voltage from power supply 510 may be boosted, for example, by a boost converter or buck-boost converter loaded with piezoelectric actuator 540. One embodiment of a modified buck-boost converter of the present disclosure is shown in fig. 6.

Such converters perform DC-AC rather than DC-DC conversion. It is used to dump charge onto a capacitor (defined by the piezoelectric actuator 600) and then take all of this charge and return it to the battery 602. Fast recovery diodes D1, D3 may be included to prevent body diode failure. The driver may include a P-MOSFET T1 connected in series with an inductor L1 from a power supply input to ground, a piezo connected between the series connection of inductor L1 and P-MOS T1, and an N-MOS T2 connected to ground. N-MOS T2 should have a fast recovery diode D1 to prevent body diode failure. When the P-MOSFET T1 is turned off, current continues to flow through the inductor L1, causing the output voltage drop across the N-MOSFET T2 to be negative and current to conduct through the diode D1 in parallel with the N-MOSFET. All of the current is deposited on the piezo and the voltage on the piezo goes from zero to a value determined by the current ramping through inductor L1. The voltage may be calculated according to the equation V-Q/C based on the charge contained by the current in inductor L1, where Q is the charge and C is the capacitance (V is the voltage). In one embodiment, at the end of the cycle, N-MOSFET T2 may be turned on to bring the piezoelectric voltage back to ground. This cycle may be repeated at the desired drive frequency. A circuit with its buck-boost converter can be more efficient (using 50% less current or better) in generating an equivalent voltage than a boost converter. This circuit uses much less current for the same drive voltage. However, a drawback to using this configuration is that it is limited to an amplitude signal of about 80-100 volts due to the limitations of the drain-to-source voltage Vds of the FET.

In another embodiment, a modified boost converter (shown in FIG. 7) used with a full bridge (discussed further below with respect to FIG. 15) and driving a resonant converter (shown in FIG. 8) is used to increase the signal amplitude and provide the desired overshoot capability (i.e., 100 volts and 170 volts). The embodiment of the resonant converter shown in fig. 8 includes one or more inductors 800. An inductor is added to create a resonant converter for voltage amplification added through a piezoelectric actuator (depicted by capacitor 802), where the piezoelectric actuator acts as a load. Thus, in this embodiment, the full bridge is used to drive a resonant tank that acts as a resonant converter, without the last DC part of the DC-AC-DC transition.

One embodiment of a drive circuit using a boost converter is shown in fig. 9. Like elements will be indicated with like reference numerals in the various embodiments discussed below. As shown in the embodiment of fig. 9, the power supply 510 may be coupled to a boost converter 900, the boost converter 900 in turn including or being coupled to a charge holding capacitor 910. The boost converter 900 may be used to step up the supply voltage from the power supply 510 and charge the capacitor 910 to supply the charge and voltage necessary to drive the piezoelectric actuator 540. The boost converter 900 varies the voltage to allow the correct electric field to be applied to the piezoelectric actuator 540, and thus, the voltage, rather than the power, can be boosted. As a non-limiting example, the power supply 510 may supply 2.7V to the boost converter 900, providing an output voltage of up to 60V for the capacitor 910. Other embodiments of power supplies according to the present disclosure are presented herein. The feedback signal 580 is used by the resonance detection and control circuit 560 to determine the resonant frequency and optionally provide feedback to control the frequency provided by the driver 520.

A driver 520 according to the present disclosure may generally be configured to generate and control a drive signal 530 to a piezoelectric actuator 540. Additional embodiments of drivers 520 according to the present disclosure are discussed below. The driver 520 may operate in any of several different modes depending on the desired characteristics of the overall mechanism 570. For example, in certain embodiments, the driver 520 as described herein may be configured to generate a multi-tone drive signal 530 that operates (1) at two or more frequencies other than mechanical/electrical resonance, with the beat frequency at mechanical resonance, as described in more detail below in the section entitled "envelope mode", or (2) at two or more frequencies at individual mechanical resonances, as described in more detail below in the section entitled "Bessel mode". Of course, it will be appreciated that these drivers may also be configured to drive a single frequency, such as a single resonant frequency. The driver may also provide a square wave to drive a single mode or multiple modes with square wave harmonics to induce increased mechanical speed. Specific implementations are now discussed.

In one embodiment, it may be desirable to drive the piezoelectric actuator 540 such that the displacement of the mechanical load 550 is increased while preserving the capacitive effect of the piezoelectric actuator 540 and minimizing overall power consumption. In one embodiment, the driver may operate in an "envelope mode". In such embodiments, the driver 520 may be configured to operate at two or more frequencies outside of the mechanical/electrical resonance, with the beat frequency at the mechanical resonance.

As previously described, in certain implementations, the piezoelectric actuator may be driven resonantly to provide maximum displacement of the mechanical load. Thus, the drive signal 530 may be based on an integer multiple of the resonant frequency, i.e., the piezoelectric actuator 540 may be driven harmonically. However, without being limited by theory, those skilled in the art will appreciate that signals with higher fundamental operating frequencies may result in increased electrical power consumption, as certain higher operating frequencies may have the effect of making the piezoelectric actuator behave more like a resistor than a capacitor as the impedance of the load varies with frequency. In certain embodiments of the present disclosure, the driver 520 may alternatively combine two or more signals to drive the piezoelectric actuator 540. The frequency and amplitude of the input signal may be selected so as to produce an increased displacement of the mechanical load while retaining beneficial energy and circuit benefits, such as nearly ideal capacitive behavior. The signal characteristic selection may depend on, for example, the desired displacement of the mechanical load.

In general, as shown on fig. 10, a driver 520 according to the present disclosure may include two or more input signals 1010a, 1010b, 1010c, etc. coupled to a combining circuit 1020. The combining circuit 1020 may be any form of electronic device suitable for combining two or more electrical signals into a combined two-or multi-tone drive signal 530, e.g., an electronic device suitable for generating sums and/or differences of all or a subset of the input signals 1010a, 1010b, 1010c, etc. The combined drive signal 530 may be coupled directly to the piezoelectric actuator 540 or, alternatively, to an impedance matching circuit (not shown) which is in turn coupled to the piezoelectric actuator 540. This allows impedance matching (i.e., impedance matching of the piezoelectric actuator 540 to the output impedance of the driver circuit).

The frequencies of the input signals 1010a, 1010b, 1010c, etc. may be selected so as to optimize certain characteristics of the system. For example, by driving the piezoelectric actuator 540 with two (or more) non-resonant frequencies, energy dissipation in the piezoelectric actuator 540 can be minimized. In one particular embodiment, it may be desirable to indirectly drive piezoelectric actuator 540 into resonance by selecting input signals 1010a, 1010b, 1010c, etc., such that the difference or sum of two or more frequencies, i.e., the frequency of one or more combined drive signals 530, is equal to one or more resonant frequencies of piezoelectric actuator 540. Without being limited by theory, it is understood that when two or more electrical signals having different frequencies are combined, they will periodically constructively and destructively interfere at the difference, sum and cross-modulation frequencies.

This property of interference may be employed in conjunction with amplitude and phase weighting such that the resulting constructive and destructive interference occurs to provide one or more resonant frequencies of the piezoelectric actuator 540 and produce a maximum physical displacement x of the load 550. In this manner, the driver 520 may indirectly cause resonant mechanical motion in the piezoelectric actuator 540. Fig. 11 shows a time-varying voltage output 530 of one example of the two-tone driver 520. In one embodiment, two or more input signals 1010a, 1010b, 1010c, etc. (each having a non-resonant frequency) may be driven with the same combined maximum amplitude as the single mode drive. This may result in reduced electrical power consumption compared to single mode driving, since the individual signals are at a frequency lower than the resonance frequency. Thus, the piezoelectric material benefits from the higher frequencies of the combination because the piezoelectric material has a higher impedance at frequencies lower than the resonant frequency.

Furthermore, by driving the piezoelectric actuator 540 with two or more non-resonant frequencies, the electrical properties of the piezoelectric actuator 540 can remain fully capacitive while still producing mechanical resonance and increased displacement. This allows the piezoelectric actuator 540 to be used directly in a resonant converter, further reducing energy losses in the piezoelectric actuator 540 by recovering energy in one or more inductors.

Drivers operating in "envelope mode" according to embodiments of the present disclosure may improve drop ejection in a piezoelectric drop ejector system and reduce power consumption in the system. They may additionally expand the range of fluid viscosities that may be ejected from a droplet ejector system. Exemplary operating frequencies in such applications may range from 1KHz to 5MHz, such as, for example, 43KHz and 175 KHz. With the actuator as described herein, the system can support multiple high displacement frequencies that reduce fluid foaming and increase the range of viscosities that the system can eject.

In another embodiment, a driver according to the present disclosure may operate in a "Bessel mode". The driver 120 may be configured to operate at two or more frequencies of separate mechanical resonances.

Similar to the operational modes described above and as shown on fig. 10, a driver 520 according to the present disclosure may include two or more input signals 1010a, 1010b, 1010c, etc. coupled to a combining circuit 1020. The combining circuit 1020 may be any form of electronic device suitable for combining two or more electrical signals into a combined two-or multi-tone drive signal 530, such as an electronic device suitable for generating sums and/or differences of all or a subset of the input signals 1010a, 1010b, 1010c, etc. The combined drive signal 530 may be coupled directly to the piezoelectric actuator 540 or, alternatively, to an impedance matching circuit (not shown) which is in turn coupled to the piezoelectric actuator 540. This allows matching of the impedance of the load (i.e., the piezoelectric actuator 540) to the impedance of the drive circuit 520. To determine resonance, feedback signal 580 is used by resonance detection and control circuit 560 to determine the resonance frequency and optionally provide feedback to control the frequency provided by driver 520.

In embodiments where the driver 520 operates in the Bessel mode, the frequency of the input signals 1010a, 1010b, 1010c, etc. is different from the frequencies described above for the envelope mode, so that different characteristics of the system are optimized. In an envelope mode implementation, the input signals 1010a, 1010b, 1010c, etc. are specifically selected at non-resonant frequencies that will combine to produce a resonant beat frequency as shown in fig. 11. In the Bessel mode embodiment, the input signals 1010a, 1010b, 1010c, etc. are themselves at different resonant frequencies of the piezoelectric actuator 540 and the mechanical load 550, for reasons described further below. Furthermore, drivers operating in Bessel mode are optimized to work specifically with non-rectangular loads 550.

Without being limited by theory, it is generally understood that the resonant modes of an electromechanical system are assumed to be integer multiples of the resonant frequency, i.e., at harmonics. However, when either the mechanical load 550 or the piezoelectric actuator 540 itself is non-rectangular, the eigenmodes of the injector mechanism, i.e., the frequencies at which the entire mechanism vibrates simultaneously, do not occur at integer multiples that can be readily generated using the harmonic electrical signal 530. For shapes other than rectangular, this prevents optimal driving of the piezoelectric actuator 540 and the mechanical load 550. More specifically, for a circular or substantially circular mechanical load 550, the resonant frequency occurs at the Bessel frequency, i.e., the resonant frequency is multiplied by the solution of the Bessel function. Thus, for embodiments operating in Bessel mode, the driver 520 may be optimized to provide maximum displacement of the circular or substantially circular mechanical load 550 by using two or more input signals 1010a, 1010b, 1010c, etc. having Bessel frequencies.

In certain embodiments, the amplitude and frequency of the input signals 1010a, 1010b, 1010c, etc. may be selected such that the system 500 provides improved displacement of the mechanical load 550 at lower resonant frequencies and improved displacement speed of the mechanical load 550 at higher resonant frequencies. For example, in a drop generator application, Bessel mode input signals 1010a, 1010b, 1010c, etc. may be driven with amplitude weighting between different eigenmodes having desired shape factors to optimize both the mechanical displacement of the liquid drug and the velocity of the drop displacement while maintaining an optimal phasing relationship with electrical drive signal 520 to facilitate maximizing fluid ejection. By combining two (or more) input signals 1010a, 1010b, 1010c, etc. in this manner, the overall quality of the system can be enhanced-lower frequency modes can enhance higher frequency modes-and the overall power in each signal can be reduced, as compared to single mode signals.

By way of example only, the drop ejector mechanism may have Bessel resonant modes at 50kHz and 165 kHz. A single drive at 50kHz provided a displacement of the ejector mechanism of 5 μm; driving alone at 165kHz provided a displacement of 800nm but also provided higher speeds and improved spray characteristics. However, in a system according to the present disclosure, both modes may be driven simultaneously. Running both signals at half the power provides a 2.5 μm displacement from the 50kHz mode and another 400nm displacement from the 165kHz mode, equivalent to a total of 2.9 μm, significantly higher than the 800nm that the 165kHz signal alone can provide, but with improved displacement speed and spray characteristics associated with the 165kHz signal. In addition, the spray is periodically raised at a beat frequency of 215kHz (i.e., the sum of the signals) and 115kHz (i.e., the difference between the signals). This increases the peak velocity of the system and the range of viscosities that the droplet ejector mechanism can eject while suppressing fluid bubbling.

Those of ordinary skill in the art will appreciate that this is merely one example of a combination of modes and that many other modes of operation may be selected to meet different system requirements. Each Bessel mode (different frequency) has a specific velocity and displacement. Thus, the lower frequency mode has a lower velocity, but may have a higher displacement.

According to the present disclosure, the spray is due to a combination of displacement and frequency (velocity). Both of these aspects can be enhanced by using multiple frequencies. In one embodiment, for example, by reducing the amplitude of each electrical drive frequency by half, the aggregate displacement seen with a droplet ejector mechanism operating at 391kHz can be increased beyond 1700nm due to the lower frequency, higher displacement, low spray mode, while maintaining proper electrical and mechanical phasing for resonant ejection. In addition, the amount of energy required to power the high viscosity fluid jet is reduced compared to the use of a single mode driver.

As shown with respect to fig. 10, drivers operating in both envelope mode and Bessel mode may be implemented with the same logic and electronic components, as described herein. As described above, the operation of system 500, i.e., in envelope mode or Bessel mode, is a function of the frequency and amplitude of the signals applied to the circuitry and the mechanical resonance quality factor.

Other embodiments of the driver are discussed below. In the embodiment of fig. 12, the driver 520 provides electrical signals 1210a, 1210b by means of Alternating Current (AC) sources 1200a, 1200b, which are then summed by a mixer 1220. These AC sources may be selected so as to generate each signal 1210a, 1210b with a desired frequency and amplitude. In one embodiment, the combined signal 1220 may be coupled to an amplifier 1230, the amplifier 1230 may be powered by the power supply 510, or alternatively by a separate power supply 1240, wherein the power supply 1240 may be coupled to a power converter 1250 such as an AC/DC converter or DC/DC converter in cases where a large output voltage, current, or power is required for actuation of the piezoelectric actuator 540. Such an amplifier 1230 may be linear or non-linear and may be single-ended or differential. The feedback signal 580 is used by the resonance detection and control circuit 560 to determine the resonant frequency and optionally provide feedback to control the frequency provided by the AC sources 1200a, 1200 b.

Fig. 13 illustrates another implementation of a driver 520 according to the present disclosure. In this embodiment, the driver 520 may include one or more power supplies or Numerically Controlled Oscillators (NCO)1300, 1302 having different frequencies 410a, 410 b. The signals 1310a, 1310b generated by these sources 1300, 1302 may then be digitally summed in an OR gate OR other digital logic 1320 to produce a multi-frequency signal, similar to performing Pulse Width Modulation (PWM). The resulting signal 1330 may then be used to drive a half-bridge circuit 1340 to generate the single-ended drive signal 130 across the piezoelectric 150, as shown in fig. 13. Bridge circuit 1340 may be fed from power supply 110 or a separate power supply 1342, optionally via power converter 1350. Feedback signal 580 is used by resonance detection and control circuit 560 to determine the resonant frequency and optionally provide feedback to control the frequency provided by NCO 1300, 1302.

In another embodiment shown in fig. 14, the driver 520 may again include one or more power supplies or digitally controlled oscillators (NCO)1400, 1402 having different frequencies 1410a, 1410 b. The signals 1410a, 1410b generated by these sources 1400, 1402 may be digitally summed in an OR gate OR other digital logic 1420 to produce a multi-frequency Pulse Width Modulated (PWM) signal. The resulting signal 1430 can then be used to drive two half bridge circuits 1440a and 1440b, as shown in fig. 14, the half bridge circuit 1440b being fed through an inverter 1480 to provide an inverted version of the output 1430 so as to form a full bridge drive. The bridge circuits 1440a, 1440b may be fed from the power supply 110 or a separate power supply 1442, optionally via a power converter 1450. Feedback signal 580 is used by resonance detection and control circuit 560 to determine the resonant frequency and optionally provide feedback to control the frequency provided by NCO 1400, 1402.

Those skilled in the art will appreciate that two separate sources and appropriate logic may be used to control the phasing and dead time (dead time) between the half-bridge drives. Fig. 15 shows one embodiment of a circuit diagram implementing such a full bridge drive 1501, in which multiplexers 1590a, 1590b receive additional non-inverted control line inputs 1592a, 1592b, respectively, from the NCO and inverted control line inputs 1594a, 1594b, respectively. The multiplexers 1590a, 1590b allow either mixed two frequency signals to drive the full bridge or separate frequencies to drive each half of the full bridge. The control lines allow different modes of operation, for example using a single NCO and inverter to drive both half bridges of a full bridge at a single frequency or using both NCO in the illustrated configuration at the same frequency but in anti-phase. Fig. 16 illustrates yet another embodiment of a driver 520 according to the present disclosure. In this embodiment, driver 520 includes a waveform database 1600, for example, in conjunction with a digital representation of drive signal 530. Waveform database 1600 may be used to generate any single-tone or multi-tone digital waveform signal for digital-to-analog converter (DAC)1610 for conversion into a corresponding electrical signal 1620. This signal 1620 may be boosted by an appropriately powered amplifier 1630 (powered by the power supply 510 or by a separate power supply 1640, as shown in fig. 16). The amplifier 1630 may be linear or non-linear and may be single-ended or differential. The resulting drive signal 530 is then applied to piezoelectric actuator 540 to drive a mechanical load 550, such as a fluid-loaded ejector plate or an ejector plate with a fluid-filled drop generator. Feedback signal 580 is used by resonance detection and control circuit 560 to determine the resonance frequency and optionally provide feedback to control the frequency selection provided by database 1600.

Fig. 17 shows a circuit diagram of one embodiment of a driver 120 circuit according to the present disclosure, providing a full bridge driver and a resonance measurement circuit. In this embodiment, the driver 120 includes a first PMOS/NMOS pair 1800, 1802 that switches a positive voltage Vboost between the electrodes of the piezoelectric actuator (injector) at the system drive frequency using a drive signal 1804 and an inverted drive signal 1806. The first PMOS/NMOS pair 1800, 1802 drives a first or positive side of the actuator via signal 1810. The drive frequency may range, for example, from 1Hz to 10MHz, and the Vboost voltage may range, for example, from 6 volts to 75 volts. The voltage on output 1810 is controlled by transistor 1812, which is controlled by time-energy-product (TEP) feedback signal 1814 that is part of the TEP measurement circuit shown in the enlarged view of fig. 18. This allows the signal from the driver to be decoupled for monitoring the output signal from the piezoelectric actuator, as discussed in more detail below.

The driver also includes a second PMOS/NMOS pair 1814, 1816 to drive the second or negative side of the actuator via signal 1820. The drive signal 1820 to the driver is controlled by turning off transistor 1822. During monitoring of the output voltage from the piezoelectric actuator, transistor 1822 briefly turns on to prevent the driver voltage from passing through to the ADC (not shown, but its location is indicated by reference 1850). As discussed in more detail below, then transistor 1822 is turned off and transistor 1824 is turned off by the TEP enable signal 1832 to allow the output voltage to pass through to the ADC (not shown). Transistor 1824 may also be driven at the original signal drive frequency via the TEP enable signal 1832 to provide an associated output signal.

Fig. 18 shows the voltage control circuitry of fig. 17 in an enlarged view. The circuit is differentially balanced by providing equal resistors R1 and R2. TEP _ enable 1832 keeps T7 transistor 1824 on during driving. This prevents 45V + from reaching the ADC, which has a maximum input of VDD < ═ 6V. Resistor R2 and capacitor C1 form an integrator circuit that measures injector ring down (ringdown).

After the drive is cut off, the signals TEP _ n 1814 and TEP _ p 1830 short the signals Ejector _ p 1810 and Ejector _ n 1820, respectively, for a brief period of time to leak the voltage low enough to avoid damaging the ADC. Thereafter, TEP _ n 1814 keeps the emitter _ p 1810 connected to ground through transistor T51812. The signal TEP _ p 1830 switches off transistor T61822, switching Ejector _ n 1820 into the ADC port path. For correlation, TEP _ enable 1832 either disables transistor T71824 or drives it at the original drive frequency. An RC integrator before the ADC simply integrates the output signal and the ADC samples at specified times to obtain values for the energy amplitude in the TEP signal.

Regardless of the amplitude and/or frequency of the drive signal 130, when the piezoelectric actuator 540 is driven by the drive signal 530, some amount of energy will be both stored and released in the electromechanical mechanism 500. That is, the question of how much energy is stored and dissipated in the piezoelectric actuator 540 is a function of, among other things, the frequency of the drive signal 530, the ambient temperature, and the nature of the mechanical load 550. As previously described, piezoelectric actuators are often driven in a resonant mode to provide increased or maximum displacement of mechanical loads. At the resonant frequency of the piezoelectric actuator 540, energy is stored and released at a different rate than when the piezoelectric is in a non-resonant mode. When the mechanism is in resonance, energy will remain in the mechanism and dampen oscillations (ring) in the piezoelectric body for a certain (measurable) period of time before it eventually decays, and the mechanism returns to its original resting state. When the mechanism is not at resonance, energy leakage from the mechanism may be almost immediate. For example, fig. 19 shows the time-varying voltage during this decay period in resonant and non-resonant modes in accordance with one embodiment of the system of the present disclosure. It is possible to use this property of the electromechanical system to determine when a mechanism is at resonance and when it is not.

Fig. 20 and 21 illustrate examples of methods of the present disclosure for generating an energy profile of a mechanism 500 that may be used to determine whether the mechanism is at resonance. For simplicity, similar steps in the flowcharts are depicted by the same reference numerals. As shown on fig. 20, at step 2000, the drive signal 530 may be applied to the piezoelectric actuator 540 for a limited period of time. Piezoelectric actuator 540 may or may not be coupled to a mechanical load (not depicted) depending on the overall mechanism requirements and the type of characteristic to be detected. In general, to obtain a detectable signal, the drive signal 530 should be applied to the piezoelectric actuator 540 for at least one time period of the waveform for the piezoelectric mode (where the piezoelectric actuator is not coupled to a load) and the drive signal 530 should be applied to the piezoelectric actuator 540 for at least two time periods of the waveform for the membrane mode (where the piezoelectric actuator is coupled to a load such as a fluid-filled injector mechanism), regardless of frequency. The energy in the load accumulates for a period of time dictated by the quality factor of the resonance and can be driven for any amount of time greater than a minimum required number of time periods.

At step 2010, signal 530 is no longer applied to piezoelectric actuator 540. This "stop" may be caused by simply de-energizing the driver 520, turning off the driver 520 (e.g., electrically, by a tri-state drive FET), or some other action sufficient to prevent the signal 530 from being applied to the piezoelectric actuator 540. At this point, mechanism 570 will return to its original resting state, i.e., piezoelectric actuator 540 will no longer be actuated to displace mechanical load 550, and the energy remaining in the mechanism will dissipate. As discussed previously, how quickly the signal 580 decays depends on whether the mechanism is at resonance. To make signal 580 more easily detectable, it may be desirable to increase the amplitude of signal 580 by stopping the drive waveform at the peaks of drive signal 530, rather than at the zero crossings. However, it should be noted that stopping the drive signal 530 at the zero crossing is more detrimental to measuring mechanical resonance than piezoelectric resonance.

At step 2020, for example, resonance detection and control circuit 560 coupled to piezoelectric actuator 540 as shown in fig. 5 may be activated to measure various characteristics associated with the attenuation of the signal remaining in piezoelectric mechanism 570. At step 2030, the resonance detection and control circuit 560 may integrate the detected signal 580. At the resonant frequency of mechanism 570, the integrated signal will have the largest amplitude, reflecting the largest physical movement of piezoelectric actuator 540 and the corresponding displacement of mechanical load 550. The resonance detection and control circuit 560 may be synchronized with the driver 520 to window the integration of the measured signal 580 over the relevant time period of the decay. For example, if the integration starts too early, it will retrieve the original drive signal 530, which is not of interest at that time in the analysis.

In the embodiment of fig. 20, a resonance determination is made at step 2040 based on the detected signal 580 increasing compared to the signal 580 taken at the previous input signal 530 frequency. If no such increase is detected, the frequency of the input signal 530 is changed at step 2050 to monitor for an effect on the piezoelectric mechanism 170. Thus, at step 2040, an assessment may be made as to whether the mechanism is at resonance. In certain embodiments, the process of steps 2000-2040 may be repeated several times to actually determine the resonant frequency of the system. The drive frequency 520 may be adjusted at step 2050 each time it is determined at step 2040 that the mechanism is not in a resonant mode. For example, the frequency of the drive signal 530 applied to the piezo may be varied in steps, e.g., 1kHz apart, so that the response of the mechanism 500 is observed at the varied drive frequency until a clear spike in amplitude, i.e., resonant response, is observed.

In the embodiment of fig. 21, the defined set of frequencies is tested on the input signal 530 by counting down the number of frequencies tested and determining whether the defined number of frequencies has been tested at step 2160 and if not changing the frequencies and applying a new input signal 530 at step 2050. Once the requisite number of frequencies have been run, a determination is made at step 2170 as to the frequency at which the highest amplitude detection signal 580 was obtained. Thus, in the embodiment of fig. 21, the order of the steps may be varied slightly such that the determination as to whether a resonant response is observed occurs at the end of the process. At step 2000, drive signal 530 may be applied to piezoelectric actuator 540, which may then be removed at step 2010. The resonance detection and control circuit may be activated at step 2020 and the measured signal 580 may be integrated at step 2030. At step 2160, the method may determine whether it has tested sufficient frequencies; for example, 10 different frequencies may need to be tested. If only one (or any number less than 10) is tested, the method can jump to step 2050 and change the drive signal frequency. This process may be repeated until the requisite number of frequencies have been tested, at which point it may be determined whether one of the tested frequencies has proven resonant behavior, as shown at step 2170.

The previous examples have assumed that the resonant frequency is located using a single tone drive frequency. However, those of ordinary skill in the art will appreciate that these processes may be accelerated by, for example, using the multi-tone drive signal 530. For example, the drive signal may have 10 tones starting at 45kHz, spaced 1kHz apart, with equal amplitude. In this manner, each of the 10 frequencies can be analyzed simultaneously, i.e., the 10 frequency signals are transmitted before waiting and evaluating the output signal 580. In yet another embodiment, the drive signal 530 may be a chirp or arbitrary waveform.

Fig. 22 and 23 show sample waveforms (amplitude versus frequency) after processing (integrated value at each frequency) of the integrated signals of two exemplary systems according to the present disclosure. In particular, fig. 22 shows sample waveforms for a correlator-based system, i.e., as shown in fig. 26 and described further below, while fig. 23 shows sample waveforms for a Fast Fourier Transform (FFT) -based system, i.e., as shown in fig. 24 and 25 and described further below.

The previous examples have assumed the use of a single tone drive frequency. However, those of ordinary skill in the art will appreciate that these processes may be accelerated by, for example, using the multi-tone drive signal 530. For example, the drive signal may have 10 tones starting at 45kHz, spaced 1kHz apart, with equal amplitude. In this way, each of the 10 frequencies can be analyzed simultaneously. In yet another embodiment, the drive signal 130 may be a chirp or arbitrary waveform. For the purposes of this application, a chirp is a signal in which the frequency of the signal is continuously scanned at a specified rate. The rate may be a linear or non-linear function.

The foregoing description describes how such a system operates at high levels. One of ordinary skill in the art will appreciate that there are a wide variety of suitable electronic implementations. For example, suitable resonance detection and control circuitry 160 may be implemented in many different ways. In both embodiments, as shown in fig. 24 and 25, the resonance detection and control circuit 560 may include a fast fourier transform circuit. In the embodiment of fig. 24, the analog FFT circuit 2400 is coupled to an analog-to-digital converter (ADC) 2410. In the embodiment of fig. 25, the resonance detection and control circuit 560 may include an ADC 2500 coupled to a digital FFT 2510. Digital FFT may be preferred over analog FFT implementations because of the convenience of implementation in a standard microprocessor or microcontroller, such as a PIC microprocessor.

In yet another embodiment, as shown in fig. 26, the resonance detection and control circuit 560 may receive the output signal 580 after the output signal 580 is amplified in the preamplifier stage 2630. In this embodiment, the resonance detection and control circuit 560 includes a mixer 2600 coupled to an integrator 2610. The mixer 2600 may be any form of digital or analog circuitry capable of multiplying the drive signal 530 with the measured signal 580. Such an implementation may be preferred in situations where very fast processing is required, as the mixer may be able to perform calculations in real time. The integrator 2610 may then be coupled to an ADC2620 or any other amplitude measurement or tracking circuit.

One of ordinary skill in the art will appreciate that it may be desirable to include some optional pre-processing components, depending on the characteristics of the overall system. For example, as shown on fig. 26 and discussed above, it may be desirable to place a preamplifier 2630 between the piezoelectric actuator 540 and the resonance detection and control circuit 560 so that the measured signal 580 and/or the drive signal 530 are amplified prior to processing. Alternatively, a resistive or capacitive voltage divider (not depicted) may be coupled to the resonance detection and control circuit 560 to, for example, convert the output 580 of the piezoelectric actuator 540 to a voltage suitable for input to the components implementing the resonance detection and control circuit 560. It is to be understood that these components may also be desirable with respect to other implementations, including but not limited to the implementations shown in fig. 24 and 25.

FIG. 27 is a block diagram of one embodiment of a resonant frequency detection circuit according to the present disclosure. As shown in fig. 27, the piezoelectric element (or piezoelectric ceramic) 540 is coupled to an isolation impedance 2740, a sampling FET 2750, a capacitor 2760, and an ADC 2720.

The sampling FET 2750 may be used to maintain the circuit in its dynamic range, thereby ensuring that the circuit operates in its linear, operable range. The isolation impedance 2740 may be configured to allow a drive signal (e.g., a 45V drive signal) to be isolated from a point a between the isolation impedance 2740 and the sampling FET 2750, the capacitor 2760, and the ADC2720, such that the point a does not exceed a certain limit voltage (e.g., 3V) in order to protect other components, including the ADC 2720.

Thus, the drive signal may range up to a signal voltage SV (e.g., about 45V), as illustrated by the square wave input to piezoelectric ceramic 540. After the drive signal, a TEP signal (depicted by an evanescent wave) is emitted by piezoelectric ceramic 540. The signal passes through an isolation impedance to give a reduced amplitude version at point a. The voltage at the voltage limit or isolation point a defined between the isolation impedance 2740 and one or more of the sampling FET 2750, the capacitor 2760, and the ADC2720 has a maximum value MV (e.g., about 3V). For piezoelectric resonance detection and characterization, a time-energy product (TEP) signal is also shown, as disclosed herein and as described in the incorporated references. To enable analysis of discrete samples of the drive signal, the sampling FET 2750 is selectively turned off or on. It will be appreciated from the above discussion that TEP (time-energy product) is the energy stored in the piezoelectric/membrane combination, i.e., in the fluid-filled ejector mechanism. Depending on the quality factor of the pattern, more or less energy will be stored. The smaller the damping in the mode, the longer the system will continue to move after the drive signal has terminated. This means that the piezo will output a signal (based on the load circuit) after the drive signal is turned off. Thus, during this ring down time, the generated signal will have a maximum amplitude and ringing (ringing) time based on the quality factor of the mode and whether it is in piezoelectric mode or system (membrane) mode. The TEP signal charges the capacitor and is used by an analog-to-digital converter (ADC)2720 to determine the ring-down time. Thus, the TEP signal may be correlated or integrated to determine energy storage in the mode.

FIG. 28 illustrates selected components of one embodiment of a resonance detection and control circuit 560 with an optional bypass switch 2800. The bypass switch 2800 may be used to select between direct input to the ADC2810 or first through the preamplifier 2820, mixer 2830, and integrator 2840. When the entire resonance detection and control circuit 560 is enabled, the NCO or oscillator is turned on in a single frequency mode and sweeps through the frequency. The resonance detection and control circuit 2810 defines a resonance if its output is greater than a defined value or maximum value. The strength of the resonance is determined by the amplitude of the output of the resonance detection and control circuit 2810. A boost converter (not shown) is controlled by a gated oscillator using an analog-to-digital converter (ADC) output to sample the output voltage. With the inductor added to the full bridge output, the piezoelectric actuator voltage is monitored to control the boost voltage output. In contrast to conventional resonant matching, which results in the actual power transfer rather than the energy storage in the resonant element, the boosted voltage output is further amplified by the resonant converter consisting of the piezoelectric ceramic and the inductor without increasing the input current. In this embodiment, the measurement circuit is implemented as a resistor divider and a peak detector to monitor the voltage in the loop, both for voltage control, and also to sweep the electrical resonance loop during the quality factor. This feeds the ADC. TEP cannot be used with resonant converters because the magnitude of the electrical resonance is stronger.

In another embodiment, referring to FIG. 18, the resonance detection and control circuit operates such that the N-channel device T7 is turned on throughout the full bridge drive cycle to ground the measurement node while the high drive voltage applied to the piezoelectric actuator (injector) is activated (to protect the ADC). When the high voltage drive signal is stopped, the N-channel devices T5 and T6 are enabled (turned on) to temporarily short the piezoelectric actuator. Both of which leak high drive voltages to the piezoelectric actuator (which masks the piezoelectric motion voltage) and allow the voltage induced by the actuator motion to be unmasked and directed to the ADC node. The N-channel device T5 is turned on for the entire measurement cycle, while T6 is disabled (turned off) after a short amount of time (1ns-50us) to force the piezoelectric motion to output a voltage to the ADC node. If there is no short circuit of T6, energy is not necessarily directed to the ADC measurement port. When T6 is disabled, T7 is also disabled, allowing the output of the piezos to be voltage divided by R3/(R2+ R3) and integrated by the capacitances from C1 and T7. The ADC samples the voltage a specified time after T7 is disabled, typically between 1 and 500 μ s. Transistor T7 may be switched at the rate of the original drive signal so as to be related to the frequency of the signature.

Examples of driving signals for both sides of the piezoelectric actuator and corresponding signals applied to T5, T6, and T7 are shown in fig. 29. This sequence and ADC measurements may be made in defined frequency steps (e.g., 150kHz, 10MHz, etc.) from 1Hz to 150 MHz. The maximum integral value may be selected as the spray frequency, but mathematical corrections to the specific spray dynamics may also be applied (such as the increase in injector velocity with frequency, and piezoelectric vs. membrane mode displacement) and the voltage coupling coefficient may be applied to make the mechanism more accurate.

In one embodiment, an electromechanical system according to the present disclosure may determine the frequency and quality factor of its resonance. In another embodiment, an electromechanical system as described herein may allow for tracking of its resonance as it changes due to mechanical loading, applied drive signals, and ambient temperature, or any combination thereof. Such aspects and resonance tracking may be achieved without the need for feedback electrodes, the use of which may affect drop generation, efficiency, and mass deposition on a desired target in a fluid ejection system. Additional benefits in specific applications may also be realized in accordance with the present disclosure.

For example, in certain embodiments, resonance tracking as described herein may be used in any drop generator device of the present disclosure. Thus, the droplet generator device can be made to bring itself back to the resonant mode. Short duration drives at different frequencies are used to map the resonance amplitude across a range of frequencies. (this range of frequencies can be calculated by determining the maximum statistical difference between parts in the fabrication/manufacturing process.) the output after spraying can be compared to the original resonance map of the droplet generator device to fix any drift and used for spray verification. In such use, resonance tracking can be achieved without the need for feedback electrodes, which will have the effect of reducing mass deposition in the fluid ejection mechanism, as described herein.

Charge-isolated ejectors (double-layer flex circuit, 50 μm SS316L annular gold-plated 40X 160, 57 hole ejector element, 19mm OD X13 mm ID 250 μm thick PZT) were driven to eject at frequencies from 10kHz to 150 kHz. Mass deposition and electrical waveforms were recorded at the same time at each frequency.

The level-shift driver circuit shown in fig. 30 is driven by MICROCHIPPIC16LF1503 from an internal complementary waveform generator. The level-shift driver drives a full bridge of actuating piezoelectric elements. MICROCHIP PIC16LF1503 waits 10 seconds between each frequency to allow the OHAUS PA214 scale to reach equilibrium during mass deposition measurements. MICROCHIPPIC16LF1503 also provides all the necessary drive signals (for T5-T7 referenced in FIG. 18). The electrical signals were recorded on an agllient 3014A oscilloscope and processed sequentially in MATLAB by integrating the signals up to the measurement time of PIC16LF1503 to demonstrate the operation of resonance measurement and control (various analog filters were implemented digitally to determine the optimal circuit components).

Sampling the integrated piezoelectric output signal for 30 μ s from when T7 was disabled closely tracks the motion and mass deposition of the mechanism across frequency, as shown in fig. 31 and 32. Fig. 31 shows mass deposition in membrane mode and piezoelectric mode, while fig. 32 shows resonance measurement output. The output is stronger for the piezoelectric mode (where only the piezoelectric actuator is involved) than for the membrane mode (where the actuator is coupled to the membrane, which may take the form of a fluid-filled ejector mechanism), and the output must be corrected with motion to the voltage coupling parameter for both the piezoelectric mode and the membrane mode. The coupling parameters are determined by sinusoidal excitation of the actuator and measurement of the movement using Digital Holographic Microscopy (DHM). The coupling parameters merely scale (weight) the results in a given frequency region to provide optimal injection. In addition, the frequency and amplitude of the motion can be used to calculate the injector velocity, which can be used to determine the optimal spray. If operation is limited to piezoelectric or membrane mode, i.e. hybrid operation is not allowed, the circuit can be used without correction. The circuit only tracks system displacements that are loosely related to the spray. Accurate spray calculations require coupling constants and velocity calculations. The resonance measurement and control system may be configured in any manner.

While specific embodiments of determining and providing a resonant signal to an actuator (piezo mode) or to an ejector mechanism (membrane mode) have been discussed above, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the spirit and scope of the invention. In addition, modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof.

While the above discussion discusses the value of determining and using the resonant frequency in driving a piezoelectric actuator, the particular drive signal or drive waveform also affects the stability and repeatability of the ejector device by affecting bubbling and wetting on the front face or front surface of the ejector mechanism.

Fig. 33 is a schematic circuit diagram of one embodiment of a circuit 3300 for implementing a droplet generation system in any of the configurations described above. In this particular embodiment, circuit 3300 is configured as a gated oscillator boost implementation for a driver (e.g., driver 520), as described herein and as disclosed in the incorporated references.

As shown in FIG. 33, circuit 3300 includes one or more additional electronic components including, but not limited to, switching components S1-S4, capacitors C1-C4, diode D1, comparator U1, inverter U3, a pulse width modulation circuit (PWM), where the PWM includes PW envelope generator V2, inverter U5-U6, logic NAND gates U2 and U4, and NOR gate U8, to control the gate of transistor Q1 to control comparator U1 to feed the PWM circuit and to control the voltage of the power rail to switches S1-S4. These additional components are used to generate delays, phase shifts, gating, summing, signal boosting, and other power and signal conditioning effects to generate a pulse width modulated PWM signal for driving an actuator, such as actuator 540 discussed above. As described above, the mechanical load (e.g., load 550) may include, for example, an actuator attached to the fluid-loaded ejector plate or to an ejector plate coupled to the fluid-loaded generator plate based on a single-tone or multi-tone Numerically Controlled Oscillator (NCO) signal.

FIG. 34A, B is a graph of fluid relaxation waveforms versus time using one embodiment of the apparatus of the present disclosure. The drive signal voltage is supplied in two pulse trains from about 25ms to just over 25.5ms in the time axis (horizontal axis) and from about 27.5ms to just over 28ms in the time axis.

As shown in fig. 34A, the back EMF signal follows the drive signal and then decays at a characteristic time scale of a few tenths of a millisecond, e.g., at an exponential decay constant in the range of about 0.1-0.5ms or about 0.2-0.3 ms. Thus, there may be fluid ejection from the device after the drive signal is terminated. There may also be a residual bias that decays over a slightly longer timescale of about 1ms or more, as shown by the separation between the drive signal voltage (at zero) and the back EMF signal between the first and second pulse trains.

Figure 34B is an expanded view of the fluid relaxation waveform diagram of figure 34A showing back EMF ring drop after termination of the drive signal. As shown in fig. 34B, there may be a large movement of the ejector plate after the drive signal is terminated, resulting in continued droplet formation as described above. There is also a phase shift between the drive signal and the back EMF, which can cause the fluid-loaded ejector plate motion to lag behind (or in this case, lead) the drive signal waveform.

The ejector plate assembly begins from a rest state in which there is no mechanical motion before being energized by the drive waveform. When an electrical drive signal is applied to induce motion, there is a finite time lag before the droplet is ejected. When there is more than one opening in the drop generator, each opening may have a different characteristic time to achieve a desired velocity of fluid ejection depending on the oscillation mode(s) and corresponding resonance frequency(s). Thus, the characteristic lead time before droplet formation is a function of the drive voltage, frequency, orifice position and eigenmode shape, as defined by the oscillating ejector plate or droplet generator.

Foaming can occur when the fluid is extruded through the opening before sufficient velocity for droplet generation is reached, further delaying the onset of droplet formation and reducing mass deposition and fluid transport. Fluid bubbling can also increase wetted ejector plate momentum, lengthening the characteristic ring-down time after the drive signal terminates.

To reduce foaming, the ejector system may be actuated for a selected time, also referred to herein as a sustained actuation length. In particular, depending on the eigenmodes of the particular structure, the time may be selected to bring the ejector plate to a velocity sufficient to eject the droplet(s) from one or more openings in an ejection zone located in various locations on the droplet generator or in a central region of the ejector plate. According to an aspect of the present disclosure, the drive signal may be selected to operate in a drop on demand mode. In this mode, the actuator is driven for a certain number of cycles determined by the fluid properties, then the drive is stopped to allow the system to relax, and then the continuous drive length sequence is repeated. This may be performed a desired number of times to achieve a desired fluid mass transfer. The drop-on-demand mode has the effect of reducing fluid bubbling and thus reducing the momentum of the ejector mechanism, thereby increasing mass transfer to the drop stream and reducing the ring-down time after the drive signal is turned off. The sustained drive length is also selected depending on the desired dose, fluid viscosity, oscillation mode, and injector configuration, among other parameters, and may range from about 1ms or less to about 10ms or more or in the range of about 1-2ms or less or about 2-5ms or more.

Fluid bubbling may be reduced or suppressed by driving the piezoelectric actuator for a selected number of cycles. The number of cycles is sufficient to allow one or more droplets to be ejected from the one or more openings. The number of cycles is also selected based on parameters including, but not limited to, the desired dose, fluid viscosity, oscillation mode, and injector configuration, for example in the range of about 1 cycle to about 10 cycles, for example in the range of about 2-5 cycles. Alternatively, the actuator 1604 may be driven for 10 cycles or more, such as about 10-20 cycles, or in the range of about 10-60 cycles or more, such as about 10, 20, 30, 40, 50, or 60 cycles.

In other applications, a continuous fluid jet of the jet is necessary in order to deliver a relatively larger amount of liquid (e.g., in the range of 0.5-30 μ l or more). However, jetting in a sustained mode (i.e., with a sustained drive signal) may also result in bubbling. As described above, without being limited to any particular theory, bubbling may occur due to chaotic ejection, satellite recovery, induction, and electrification effects. Also, as fluid bubbles form on the opening, the amount of bad fluid may tend to increase with additional cycles of the actuator, e.g., via pumping action and associated hydrodynamic effects. Continued pumping may eventually lead to wetting on the distal surface of the oscillating ejector plate (or drop generator plate), resulting in increased momentum, Coulomb attraction, and related mechanical and electromechanical effects.

The piezoelectric actuator may also be driven for a selected number of cycles, followed by a period of time between drive signals, which may be characterized as a relaxation time or relaxation period. The cessation of the oscillating drive voltage during the relaxation time period causes the fluid-filled ejector plate oscillations to decay through a characteristic ring-down time. The ring down time depends on, for example, the magnitude of the ejector plate and actuator motion and the mass of the ejector system that the fluid is wetting. Depending on the application, the relaxation time period selected based on the ring down time may reduce blistering. This intermittent driving of the actuator will be referred to herein as a pulsed mode of operation. Depending on the drive pulse width and the relaxation time, the mass injection rate (per unit time) can be reduced in the pulsed mode of operation, for example by about one-third, about one-half or about two-thirds, compared to the continuous injection mode of operation.

In some embodiments, the movement of the piezoelectric actuator after the drive signal ceases may be monitored by detecting a back EMF (or a back voltage) induced by the residual movement of the piezoelectric actuator, wherein the piezoelectric actuator is mechanically coupled to the ejector plate. For example, the back EMF may be monitored via a metallization layer or electronic sensor that is electrically isolated from the actuator surface, as described above with reference to FIG. 4, or with a back voltage induced on the drive signal circuitry, such as via a drive electrode or other conductive layer that is in direct contact with the actuator surface.

Thus, based on the back EMF signal, the ring down time may be determined by the residual ejector plate and the time required for the fluid oscillation to fall below a particular threshold. This has an advantage over fixed relaxation time applications because the relaxation times are automatically adjusted for droplet formation, wetting, fluid viscosity, and the effect of other factors on the ring down time of the fluid-wetted ejector assembly.

For example, the relaxation time may be defined by the time required for the back EMF voltage to become less than a selected fraction of its initial value (e.g., about one tenth (10%) of the initial value) after the drive signal is stopped. Alternatively, different scores may be selected, for example, about one twentieth (5%) or less, or about one fifth (20%), about one third (33%), about one half (50%), or a different ratio such as 1/e, or multiples thereof. In additional applications, the relaxation time period may be selected based on an absolute threshold, for example, based on a correlation of the back EMF signal to a selected magnitude or velocity at which the fluid-loaded ejector plate oscillates.

FIG. 35 is a set of amplitude versus time plots of a drive signal waveform and a corresponding piezoelectric motion waveform, showing the phase shift between the two waveforms over time. 35A-D illustrate different methods for generating a ring down damping signal to reduce residual motion after termination of the drive signal. Based on the magnitude and phase of the observed ring-down feedback signal, a cancellation waveform may be generated in the form of an active damping or braking signal. For example, in fig. 35A, the cancellation signal includes only half waves that generate an opposite or 180 degree phase shift relative to the original wave signal. In fig. 35B, in addition to generating the opposite half-wave, the amplitude of the opposite waveform is also adjusted. In fig. 35C, the opposite half wave is also time shifted to achieve an additional phase shift. In fig. 35D, small pulses of higher frequency and opposite phase are generated.

In general, the damping signal may be offset in phase with respect to the drive signal and reduced in magnitude (combination of fig. 35B and 35C). The magnitude is determined based on the magnitude of the back EMF signal, e.g., using an actuator sensor or a back voltage in the drive circuit to generate a ring down or feedback signal 580 for the resonance detection and control circuit 560, as shown in the piezo system above. Relaxation waveform and ring-down analysis is performed on the back EMF signal to generate a Pulse Width Modulation (PWM) damping signal having an appropriate magnitude and phase delay, e.g., as described above with respect to the various components of circuit 3300 of fig. 33.

Depending on the application, the fluid oscillations on the drop generator may or may not occur at the same frequency as the ring drop oscillations of the ejector plate itself. To the extent that this occurs, or in any case where multiple modes are excited, the back EMF signal will exhibit multiple frequencies and beat frequencies, as described below, and the active damping signal may be modified accordingly, for example by providing a combination of two or more different damping signals having different magnitudes, phases and frequencies.

Alternatively, a single short pulse or "chirp" signal may be utilized based on the desired level of signal complexity and the desired effect on the ring-down signal. For example, an "inverse" cancellation or damping signal may be applied, either based on the phase of the drive waveform itself or based on the timing of the back EMF signal. In such applications, smaller opposite polarity damping signals of selected timing and amplitude may be provided to absorb or cancel residual oscillatory energy and cause the actuator and load to brake in a manner similar to a vehicle.

Once any cancellation waveform or active damping (braking) signal is applied, the relaxation time period may be used before applying another drive signal, as described above. Thus, the drop generator may be driven in a pulsed or continuously pulsed mode, with or without a damping waveform following each pulse.

The droplets may also be generated in a single-pulse mode, where the fluid is delivered through a single finite drive waveform extending over a certain number of cycles, with or without an active damping signal followed. In this single-pulse mode of operation, the relaxation time may be considered arbitrary, extending until activation by an independently triggered (e.g., user-selected) device.

Thus, a range of different methods may be used to generate the damping signal. For example, waveforms of equal amplitude may be applied, with an amplitude based on the energy stored in the piezo and a 180 ° phase shift (opposite polarity) based on the phase of the back EMF signal. Alternatively, one or more pulses of unequal amplitude may be applied with opposite polarity or different phase shifts based on the available positive or negative supply voltage. In a single pulse or "chirped" damping waveform, the energy in the waveform can be selected to match the energy of the fluid-loaded ejector plate and actuator system, and delivered with an opposite polarity or other phase shift selected to maximize energy absorption, thereby taking advantage of the time-energy balance to counteract residual oscillation and reduce the ring-down time.

In a pulsed or "limited cycle" mode of operation, the actuator may be driven a limited number of cycles, below the characteristic bubble time of the ejector system, followed by a relaxation period based on the characteristic ring down time, and repeated as necessary to achieve the desired fluid dose or mass deposition. Although the mass spray per unit time is nominally reduced, as described above, this can be offset by the benefit of reduced foaming. The relaxation or "dead" time between delivery pulses may be reduced by application of a suitable damping signal.

In this mode, the drop generator may be driven a limited number of cycles, below the characteristic bubble time of the ejector plate system, followed by application of an inverse (opposite polarity) waveform, based on the corresponding phase of the back EMF signal. The amplitude and phase may be selected for energy balance to absorb a substantial portion of the residual oscillation energy in a single pulse, or the amplitude and phase may be varied as described above. The damping waveform or "brake" signal may be controlled to reduce the motion of the actuator and injector plate membrane, followed by an additional ring-down of the fluid itself, during which no new drive signal is applied.

Thus, a complete waveform includes a limited cycle drive signal followed by a damping signal and relaxation or dead time for fluid ring-down, and repeated as necessary to achieve the desired fluid dose or mass deposition. Based on the reduced ring-down time, this mode provides both reduced bubbling and increased fluid delivery rate, as defined in terms of fluid mass per unit time, as compared to limited cycle driving without active damping or braking signals.

Examples of the invention

Example 1:an ejector mechanism. In this example, a symmetrical (e.g., 21mm diameter stainless steel) ejector plate 104 is used, with a pattern of openings 126 provided in a drop generator 132 formed in a central region of the ejector plate 104. A drive circuit 520 is used to generate the drive signal and an oscillation or feedback circuit 560 is used to measure the back EMF or feedback voltage signal from the (e.g., piezoelectric) actuator and control the drive circuit to provide a damping signal after each drive waveform. Other techniques for generating different drive waveforms and damping signals are also contemplated, as described above and as disclosed in the incorporated references.

The ejector mechanism operates in contact with a fluid reservoir and is provided with a drive signal (e.g., sinusoidal or square wave) to pump fluid through an opening of a drop generator and eject the fluid in the form of a stream of drops. When the continuous drive signal can cause the fluid to bubble, a short burst or limited cycle time can be used, such as about 150ms or less, about 100ms or less, about 50ms or less, or about 25ms or less. An electrically isolating pad or back EMF sensor may be attached to the actuator to monitor movement of the injector assembly with respect to the drive signal and provide a residual oscillation cancellation signal after termination of the drive signal to reduce the ring down time and increase the net fluid delivery rate.

Example 2:piezoelectric relaxation and fluid relaxation. In this example, an actuator driven in resonance mode will continue to oscillate for a given period of time defined by the relaxation time after the drive signal stops. Even when the motion of the actuator and ejector system is reduced, the membrane or drop generator will continue to oscillate due to the additional energy in the fluid-loaded mechanism. If the piezo is driven before the fluid has been allowed to relax, fluid bubbling will occur, and if the dead time between cycles is insufficient, bubbling and fluid oscillation will increase with repeated cycles.

FIG. 36 is a graph of a fluid relaxation waveform illustrating these phenomena after drive signal removal. As described above, the piezoelectric back EMF voltage (ordinate) is generated by the motion of the piezoelectric actuator and may be taken from an electrically isolated metal pad on top of the piezoelectric body or a back EMF sensor. Depending on the relative amplitude threshold, the back EMF indicates that ring-down of the actuator assembly occurs on a time scale of around one millisecond, such as about half a millisecond or less, or about 0.2-0.3 ms. Over this relaxation period, the magnitude of the oscillation may result in a significant period of fluid ejection after termination of the drive signal, e.g., up to 1 to 10 times the length of the drive signal waveform itself.

Depending on the ejector design, fluid loading, orifice size, and other factors, the fluid relaxation time of the fluid-filled mechanism (or also referred to herein as the ejector mechanism) may be two to three times the ring down time of the actuator itself, e.g., 1 millisecond or more, or in the range of about 1-2ms or about 2-4 ms. The fluid must be allowed to relax over this generally slow relaxation time to prevent foaming.

FIG. 37 is a graph of a fluid relaxation waveform after a soft ramp down, illustrating how the actuator assembly reacts as the drive signal linearly decreases. Due to the energy stored in the actuator itself (e.g. in a piezoelectric element, which may be a ceramic element), the amplitude of the residual oscillation actually increases during the ramp down period and even after the drive signal reaches zero. This energy dissipates relatively slowly, e.g., over hundreds of harmonic oscillation cycles.

Fig. 38A is a diagram of a relaxation waveform after five-cycle excitation, in which the drive signal is abruptly stopped. FIG. 38B is an expanded view of the relaxation waveform of FIG. 38A, illustrating harmonic generation ("beat frequency") in the ring down signal. As shown in fig. 38A and 38B, not only does the actuator assembly continue to move after the drive signal is terminated, but it also generates relatively large harmonics and cross-modulation products, which in turn generate motion in a resonant mode ("eigenmode") having a shape that is favorable for bubbling.

Example 3:a cancellation waveform. In this example, a cancellation waveform is used to reduce thisResidual motion and ring down time.

FIG. 39A is a graph of a fluid relaxation waveform with an active damping waveform after ten cycles excitation. FIG. 39B is an expanded view of the relaxation waveform of FIG. 39A illustrating reduced relaxation time and harmonic generation. As shown in fig. 39A, the damping signal is generated after the drive signal in order to absorb the energy stored in the (piezoelectric) actuator. Although the injector mechanism continues to move after the damping signal is applied, the relaxation time is greatly reduced and harmonics and cross-modulation products ("beat frequencies") are suppressed. This allows for higher mass deposition rates with reduced blistering.

FIG. 40 is a graph of a relaxation waveform with an active damping signal after ten cycles square wave excitation. As shown, both the drive signal and the damping signal may be provided as a substantially square wave.

FIG. 41 is a graph illustrating a relaxation waveform for the same square wave excitation as used in FIG. 40, but without the damping signal.

FIG. 42 is a graph illustrating piezoelectric and fluid relaxation with active damping signal and relaxation dead time after two periods of a ten cycle square wave drive signal. FIG. 42 shows two full cycles of a fully assembled waveform, including a ten cycle square wave drive signal, an active damping signal for braking the piezoelectric actuator, and fluid relaxation (dead time) times between repetitions.

Example 4:foaming of the fluid. This example uses the ejector mechanism according to example 1 above, where bubbling is observed when the drive signal is a simple sine or square wave. In this particular example, the drive signal waveform is 50ms long.

To illustrate the benefits of relaxation time and active damping signal, two different viscous liquids were utilized: distilled water and latanaprost (latanaprost), pictures of ejectors at various stages were taken, where latanaprost is a topical drug used to reduce intraocular pressure.

Distilled water and latanoprost images were captured at high speed (75000 frames per second). For both liquids, the initial spray demonstrates the resonant mode of the generator plate, but not every hole ejects a droplet. At 30% by spray signal, a sustained spray that does not allow relaxation or "ring down" results in the formation of large bubbles. At 60% pass spray signal, satellite droplets are generated due to chaotic spray collisions, which increase when there is no slack time, and the level of foaming and collisions increases as the spray continues. After the cycle is complete, large satellite droplets and bubbles are observed.

Example 5:foaming and suppression of satellite formation. This example also uses the ejector mechanism according to example 1 above, but bubbling is suppressed by utilizing one or more of the limited cycle (repetitive pulses), relaxation time, and active damping techniques described above.

Again, water was compared to latanoprost, but active damping and relaxation was utilized. The initial spray image again shows the resonant mode of the generator plate, but not every well ejects fluid. This demonstrates that the pattern is non-trivial and must be carefully determined in combination with the selected hole pattern and ejector plate geometry. In the mid cycle, the droplets are ejected from most of the ejection locations (openings) in a linear stream. There is less turbulent flow, thereby reducing satellite formation compared to spray patterns that exhibit poor spray. In this example, foaming is suppressed for both fluids, and larger bubbles are substantially absent or not observed. After the cycle is complete, the large satellite droplets are significantly reduced and substantially no bubbling is observed in the opening. Some satellite droplets may be observed, but are substantially absent at the droplet formation site.

In various additional examples, a method is provided that applies a first alternating voltage one or more cycles to a piezoelectric actuator, wherein the piezoelectric actuator is operable to oscillate an ejector mechanism to generate droplets of fluid, stop the first alternating voltage and apply a cancellation waveform or active damping signal, wait a first relaxation time period, apply a second alternating voltage one or more cycles to the piezoelectric actuator, stop the second alternating voltage and apply a cancellation waveform, and wait a second relaxation time period. The ejector mechanism may include an ejector plate having a proximal surface in contact with the fluid and one or more openings, the piezoelectric actuator oscillating the ejector plate upon application of the drive voltage. These steps may be repeated one or more times to generate or deliver a selected amount of fluid, for example in the form of a stream of droplets. The amount may be selected between about 5. mu.l and about 30. mu.l. The ejector mechanism may also be configured to eject the stream of droplets with an average ejected droplet diameter greater than about 15 microns.

The ejector may be configured for passivation and charge isolation with respect to the drive voltage. The cancellation waveform may be phase shifted with respect to the drive voltage and have an amplitude substantially equal to or different from the drive voltage. The phase shift may be 180 degrees so that the cancellation waveform has opposite polarity with respect to one or both of the alternating drive voltages. Alternatively, the cancellation waveform may be substantially in phase with one or both of the alternating drive voltages, or with a time delay selected for a different phase shift with respect to one or both of the alternating voltages.

The cancellation waveform may also have an amplitude that is unequal with respect to one or both of the alternating voltages, e.g. a smaller amplitude than one or both of the alternating drive voltages. The cancellation waveform may also have an amplitude selected for a waveform having energy substantially equal to the energy stored in the piezoelectric actuator.

Any one or more of the first and second alternating voltages and the counteracting waveform may be pulse width modulated or comprise or consist essentially of a substantially square wave or a substantially sinusoidal wave. For example, both alternating voltages may be substantially sinusoidal or substantially square wave, or a combination of sinusoidal and square wave.

One or both of the relaxation periods may be monitored based on the resonance of the actuator, for example by detecting the back EMF voltage. The one or two relaxation periods may be proportional to a frequency of one or two of the alternating voltages, and the frequency may be between one and about thirty. One or both relaxation time periods may also be determined when the back EMF has a certain threshold, e.g. as part of an initial value, or one or both relaxation time periods may be proportional to the number of cycles of the alternating voltage or voltages.

Example 6:

in one embodiment, the ejector device is implemented as a two-part device, comprising an ejector assembly with a fluid reservoir (also referred to herein as a cartridge) and a base system. The base system is configured to receive and engage with a cartridge in a complementary manner. When the user inserts the cartridge into the base system, electrical contact is made and the cartridge becomes activated. In one embodiment, the cartridge EEPROM is read to begin counting down the disabled cartridges.

A front rotary seal may be provided that covers the ejector mechanism of the cartridge and is configured to be turned so as to open the ejector mechanism or provide line-of-sight access to the ejector orifice of the ejector mechanism. The rotation also triggers a magnetic switch in the box which is relayed to the microcontroller unit to bring it out of sleep mode. The aiming system (blue LED) is also turned on and the boost converter is started.

An auto-tune or mass sweep (Q-sweep) is initiated to set the spray frequency. In this embodiment, the Q-scan involves the generation of three cycles of each of a range of frequencies within a predetermined frequency range and obtains TEP feedback to find the optimal spray frequency region. This is discussed in more detail below. Initiation of the scan may be triggered either by turning the front rotary seal or by activating a spray button, and in one embodiment, the activation mechanism may be software selectable. After the Q-scan is complete, a boost converter configured to act as a charge pump boosts the ring (piezo ejector) voltage to the voltage specified for the product by charging the boost rail to the desired voltage. This range may be, for example, 0 to 120V.

The second switch is triggered when the user presses the spray button. After this event, the gated Complementary Waveform Generator (CWG) drives a level shifter circuit, which in turn drives the full bridge to drive the piezoelectric actuator and deliver the drug. The ejector mechanism ejects via a constant voltage drive (a boost duty cycle) that is constantly adjusted to balance the boost output voltage and hence the amplification in the resonant tank) or an overshoot drive by charging the boost (boost up) followed by turning on the drive to cause a large overshoot on the high speed spray. While a constant voltage can be used in a continuous or drop-ON-demand mode (x cycles ON-y cycles OFF-repeats), overshoot can only be used with drop-ON-demand.

In addition, the drive signal frequency may be a constant frequency or a dither. Dithering means that the frequency is swept (like a chirp) over a set of bandwidths (3k, 5k, 10k, 20 k). Fluttering causes a sharp velocity change in the piezoelectric motion, resulting in better ejection. Dithering can be performed, for example, quickly (within the decay time of the resonant tank) to generate a constant multi-tone signal.

An IR-based quantity detection circuit may be included to measure the amount of liquid delivered during spraying and extend or shorten the spraying time to deliver the correct dose. After a predefined period of time (in this embodiment, after 10 seconds), all LEDs are turned off and the device returns to sleep mode until the user turns off and reopens the front rotary seal.

Since auto-tuning comprises an aspect of the present invention, specific implementations will be described in more detail below.

The purpose of the auto-tuning system is to allow the piezo ejector system to dynamically adjust itself to slight material differences and changing environmental variables, and is critical to a reliable and manufacturable product.

The frequency generated by the Numerically Controlled Oscillator (NCO) and CWG is incremented by a set amount over a defined range of up to 1kHz to 200kHz, but is often incremented by 1kHz or 0.5kHz over 80-150 kHz. The battery voltage is compensated to account for the gradual depletion of the battery, after which the boost rail is charged to a constant voltage using analog-to-digital (ADC) sampling feedback. The loop (resonant structure defined by the capacitive piezoelectric actuator (piezo ceramic) and one or more inductors) is then driven for a brief period of time, preferably the smallest possible sample size, for example, 1.5-2.5 cycles at a single frequency. The drive signal is repeated 3-5 times in rapid succession at this frequency in order to charge the capacitor in the integrating peak detector with the same amplitude factor (voltage) each time. The amplitude coefficient is recorded and the process is repeated at the next frequency. Repetition of such low voltage signals significantly improves the signal-to-noise ratio of the measurements and prevents system ejection while determining the optimum resonant frequency of the ejection.

Auto-tuning is achieved by driving the injector at low voltage and measuring the piezo ceramic/inductor loop response (Q-factor). When completed across a wide frequency range, the auto-tune characterizes the injector system and finds the peak frequency.

For the Q-scan to work properly, the drive voltage needs to be high enough to drive the energy into the piezo properly, but it must be low enough not to cause unwanted ejection. Therefore, the drive voltage must be closely monitored by the microcontroller.

The analog-to-digital converter (ADC) used to monitor the drive voltage is mathematically compensated to maintain accurate measurements as the battery goes down (de-rate) and the voltage drops.

In this embodiment, the sweep is software controlled by an algorithm that first checks the output range to ensure that the correct voltage threshold has been met. The sweep will be a constant output, without a high enough voltage for fluid ejection, so if the output range is too low, the voltage is increased slightly and the sweep repeats.

The sweep is repeated in a pulse train to find a consistent peak frequency between measurements. If the peaks do not coincide, the voltage is slightly increased and the pulse train repeats. If the two peaks remain equal, the microcontroller will select the peak for injection within the optimum frequency range previously programmed.

The means for generating the drive signal are depicted in the block diagram of fig. 43, which shows a full bridge driver with integrated drive gates. A Numerically Controlled Oscillator (NCO)4300 generates a drive signal with high frequency resolution. The second numerically controlled oscillator 4302 is gated with the first NCO by logic 4304 to periodically disable the Complementary Waveform Generator (CWG)4306 without a significant software load on the processor resources. This allows both extended FET life and relaxation of the injector system at any frequency to prevent (combat) spray "bubbling" problems as discussed above. A timer may also be used for this purpose. The logically combined signals are input to a complementary waveform generator 4306, the complementary waveform generator 4306 outputs two inverted square waves with adjustable dead zone to a level shifter circuit 4308, the level shifter circuit 4308 converts 2.0V-3.5V to +35 for PMOS (not shown) and +10 for NMOS (not shown) of full bridge 4310 to minimize switching losses and ON resistance. CWG 4306 effectively alternates the number of "on" cycles of piezoelectric ceramic with the number of "off" cycles that allow the fluid to relax.

A circuit diagram of one embodiment of a level shifter circuit 4308 for driving NMOS and PMOS is shown in fig. 44.

It drives the actuator differentially with a 45V Boost converter output (V _ Boost) and is driven with inverted square waves (CWG _ P and CWG _ N) from CWG, which control the gates of FETs T1 and T10. The PMOS outputs (FB _ P1 and FB _ P2) are +45V to +35V, while the NMOS outputs (FB _ N1 and FB _ N2) are 0V to + 10V.

As discussed above, this embodiment also provides Infrared (IR) spray volume detection. The IR LED was driven with a forward voltage drop of up to 1.8V and a current of 65 mA. The phototransistor measures the light intensity and provides an analog output voltage between 0V and the battery voltage, which is read by the ADC. The spray has been shown to have a substantially linear voltage response to spray volume.

One embodiment of such an IR spray amount detection circuit is shown in fig. 45.

In the present embodiment, three batteries each providing about 1.5V are used as the portable power source. In another embodiment, only two batteries are used, so that a 2X charge pump needs to be used to raise the battery voltage high enough to drive the high brightness aiming system LEDs. One embodiment of such a charge pump uses pulse width modulated signals from a microcontroller peripheral. A schematic circuit diagram of one embodiment of a charge pump circuit for targeting LEDs is shown in fig. 46.

As another aspect of this embodiment, the device provides a cartridge enable/disable/timer. This is implemented in this embodiment as a two-wire serial interface EEPROM provided on the cartridge to allow unique identification, for example by serial number. After a predefined period of use, the serial number may be erased to permanently disable the cartridge. The serial number may be configured in different ways, for example, the first few bits may be the manufacturer's identifier, while the remaining bits may provide a unique serial number for the device to identify the medication in the reservoir. The microcontroller in this embodiment can keep track of up to 30 devices for up to 60 days.

The electronics, which may be implemented in the ASIC, may be configured to receive input from the temperature sensor, or the ASIC may have an internal temperature sensor for disabling the cassette if the drug temperature exceeds a predefined temperature.

As discussed above, to provide the appropriate voltage to the actuator, the boost rail is charged to the desired voltage using a boost converter configured to act as a charge pump. Fig. 47 is a circuit diagram of two boost converters, one of which powers a piezoelectric driver and the other of which provides a prescribed low current ring charge (voltage). The monitoring is performed by the ADC in conjunction with the microcontroller. FIG. 48 is a circuit diagram of one embodiment of a microcontroller. ADC, NCO, CWG, PWM are all internal to the section. In this embodiment, the ADC is an integrated device and can be switched between various pins internally in the chip. Initially, it starts on pin RC2 where it is used to monitor and maintain the boost voltage during Q-scan (auto-tune). As discussed above, the voltage must be almost constant, otherwise the result of the frequency sweep will provide an erroneous result. The ADC is then switched to RA4, which will allow the actuator (ring) voltage to be charged and calibrated. Finally, the ADC is switched to RA0 where the integrating peak detector compresses the peak voltage to the voltage range of the ADC. The measurements from the peak detector can be used to maintain a constant loop voltage or rob the amplitude factor from the Q-scan.

Fig. 49 shows a circuit diagram of one embodiment of a set of level shifters driving a full bridge loaded with a resonant tank (including piezo-ceramic). It also has peak detector feedback.

Fig. 50 shows one embodiment of a TEP pull down/drop on demand pull down circuit consisting of one level shifter and two NMOS FETs leaking the loop instead of letting it float when the full bridge is off.

While the invention has been described with reference to specific embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the spirit and scope of the invention. In addition, modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular examples disclosed, but that the invention will include all embodiments falling within the scope of the appended claims.

Claims (36)

1. A drop ejection system, comprising:

a drop ejector assembly including a piezoelectric actuator coupled to a drop generator plate having a plurality of openings therethrough, the drop generator plate defining a fluid-filled drop generator plate when the openings are filled with a fluid;

a drive signal generator electrically coupled to the piezoelectric actuator, the drive signal generator configured to generate a drive signal for driving the piezoelectric actuator; and

a controller electrically coupled to the actuator and the drive signal generator, wherein the controller is configured to control the drive signal to drive the piezoelectric actuator at a resonant frequency of the droplet ejector assembly and to determine the resonant frequency based on an attenuation signal from the piezoelectric actuator, and wherein the controller includes a capacitor and an ADC to determine a time-energy product of the attenuation signal.

2. The system of claim 1, wherein the controller comprises a resonance measurement and control circuit configured to determine a resonance frequency of the droplet ejector assembly by controlling the drive signal generator to generate a set of frequency signals across a range of frequencies and monitoring an effect on the decay signal.

3. The system of claim 2, wherein each frequency signal is repeated a plurality of times and the resulting time-energy product signal is monitored each time to ensure consistency.

4. The system of claim 1, wherein the drive signal comprises at least two different frequency signals, the resonant frequency being defined by interference between the at least two different frequency signals.

5. The system of claim 4, wherein each different frequency signal is non-resonant with respect to the droplet ejector assembly.

6. A method of operating a droplet ejector assembly, the method comprising:

applying a drive signal to a droplet ejector assembly, wherein the droplet ejector assembly comprises a piezoelectric actuator coupled to a fluid-loaded droplet generator plate;

determining a resonant frequency of the injector assembly based on an accumulated magnitude or peak of a feedback signal from the piezoelectric actuator; and

the drive signal is controlled to drive the piezoelectric actuator at a resonant frequency of the injector assembly,

wherein the feedback signal is defined by an attenuation signal following a drive or test signal to the actuator.

7. A method as claimed in claim 6, wherein the determination of the resonant frequency is done following the test signal or following the drive signal.

8. The method of claim 7, wherein the drive signal is adjusted to account for changes in the resonant frequency of the injector assembly due to changes in one or more of: characteristics of the fluid loaded into the droplet generator plate, amount of fluid loading of the droplet generator plate, temperature, humidity, and pressure.

9. The method of claim 8, wherein the change in resonant frequency is based on at least a resonance shift induced by one or more of temperature, humidity, pressure, and drive voltage.

10. The method of claim 6, wherein the determining of the resonant frequency comprises integrating the attenuation signal to determine an energy magnitude.

11. The method of claim 6, wherein determining the resonant frequency is done following different test frequency signals, the method further comprising applying different frequency test signals to the actuator across a range of frequencies.

12. The method of claim 11, wherein determining the resonant frequency is based on a time-energy product signal from the actuator and is obtained by integrating the time-energy product signal.

13. The method of claim 6, wherein applying the drive signal to the actuator comprises generating at least first and second different drive frequency signals that are non-resonant individually with respect to the fluid-loaded drop generator plate but together are resonant with respect to the fluid-loaded drop generator plate.

14. A droplet ejection apparatus comprising:

a fluid reservoir or ampoule;

an ejector assembly comprising a droplet generator plate and a piezoelectric actuator coupled to the droplet generator plate, wherein the droplet generator plate is in fluid communication with the reservoir such that the droplet generator plate is loaded with fluid; and

a driver coupled to the piezoelectric actuator, wherein the driver is configured to generate at least first and second drive signals at different first and second drive frequencies, wherein the drive signals are coupled to the piezoelectric actuator to oscillate the ejector assembly at one or more resonant frequencies; and

a controller configured to determine a shift in one or more of the resonant frequencies and to control at least one of the first drive frequency and the second drive frequency based on the shift such that the injector assembly is oscillated at the resonant frequency,

wherein the controller is configured to determine the shift in the resonant frequency based on the attenuation signal from the actuator in the absence of the drive signal.

15. The droplet ejection device of claim 14, wherein the drive signal is non-resonant with respect to the fluid-loaded droplet generator plate such that the actuator oscillates the ejector assembly at a resonant frequency based on interference between the first drive frequency and the second drive frequency.

16. A method for detecting when an electromechanical system including a piezoelectric actuator is operating in a resonant mode, the method comprising:

a. applying a drive signal to the piezoelectric actuator for a limited period of time;

b. removing the drive signal from the piezoelectric actuator;

c. activating a measurement circuit coupled to the piezoelectric actuator;

d. receiving the detected signal from the piezoelectric actuator in the measurement circuit; and

e. determining whether the electromechanical system is in a resonant mode based on a property of the detected signal,

wherein the resonance mode is determined based on a duration of a decay signal from the actuator following removal of the drive signal or based on a peak or total energy of the decay signal.

17. The method of claim 16, further comprising the step of varying the frequency of the drive signal and repeating steps a through e without the electromechanical system operating in a resonant mode.

18. The method of claim 16, further comprising the step of integrating the attenuated signal.

19. The method of claim 16, wherein the electromechanical system is operable in a plurality of resonant modes, and the method further comprises determining an optimal mode of the plurality of resonant modes for operation of the electromechanical system.

20. A method of providing a drive waveform to maximize physical displacement of a mechanical load coupled to a piezoelectric actuator, the method comprising:

providing two or more input signals; and

the input signals are combined to produce a combined drive signal, wherein the two or more input signals are selected such that the combined drive signal has a frequency equal to at least one resonant frequency of a mechanical load coupled to the piezoelectric actuator.

21. The method of claim 20, wherein at least one input signal is amplitude and phase weighted such that the piezoelectric actuator achieves maximum physical displacement of the mechanical load.

22. The method of claim 20, wherein the two or more input signals are selected such that one signal has a frequency at which the piezoelectric actuator provides an increased mechanical load displacement and another signal has a frequency at which the piezoelectric actuator provides an increased mechanical load displacement velocity.

23. The method of claim 22, wherein at least one input signal is selected to be at a resonant frequency of a mechanical load coupled to the piezoelectric actuator.

24. The method of claim 22, wherein the mechanical load is non-rectangular, and wherein the at least one input signal operates at a Bessel mode frequency, and wherein the Bessel mode frequency is a solution of the resonance frequency multiplied by a Bessel function.

25. A piezoelectric ejector device for ejecting droplets of a fluid, comprising:

an ejector mechanism including a piezoelectric actuator and a droplet generator plate; and

driver electronics for driving the actuator, the electronics including a microcontroller configured to perform auto-tuning of the injector mechanism by identifying and setting an optimal spray frequency,

wherein the auto-tuning involves generating at least one cycle for each of a range of drive signal frequencies over a predefined frequency range and obtaining time-energy product feedback from an attenuation signal emitted by the actuator following each frequency generation.

26. The piezoelectric ejector device of claim 25, wherein individual cycles are generated rapidly and continuously for each frequency so that the capacitor in the integrating peak detector is charged with the same voltage for each cycle, the voltage is recorded and the process repeats below the next frequency.

27. The piezoelectric ejector device of claim 25, further comprising at least one Numerically Controlled Oscillator (NCO) for incrementing the frequency over a predefined frequency range.

28. The piezoelectric ejector device of claim 25, wherein power is provided to the actuator from at least one battery, the microcontroller being configured to monitor the battery voltage and compensate for gradual depletion of the battery.

29. The piezoelectric ejector device of claim 25, further comprising at least one inductor to define a resonant tank with the piezoelectric actuator, wherein the piezoelectric actuator acts as a capacitor.

30. The piezoelectric ejector device of claim 26, wherein the microcontroller is configured to maintain a constant voltage at each drive signal frequency during auto-tuning, the drive voltage being monitored using the ADC to ensure a drive voltage high enough to properly drive energy into the piezoelectric actuator while maintaining the voltage at a level low enough to avoid unwanted ejection.

31. The piezoelectric ejector device of claim 29, wherein the boost circuit is configured to act as a charge pump to boost the piezoelectric actuator voltage to a specified voltage after auto-tuning.

32. The piezoelectric injector device of claim 31, wherein the drive electronics comprises a drive circuit comprising two NCO, logic for combining signals from the two NCO to define a combined signal, a complementary waveform generator CWG for receiving the combined signal, a level shifter circuit connected to the CWG, and a full bridge connected to the level shifter and operable to drive the piezoelectric actuator with the drive signal to inject fluid.

33. The piezoelectric ejector device of claim 32, wherein the microcontroller is configured to constantly adjust the boost operating cycle to balance the boost output voltage and thus balance the amplification in the resonant tank to provide a constant voltage drive.

34. The piezoelectric ejector device of claim 32, wherein the microcontroller is configured to maintain the drive signal at a constant frequency.

35. The piezoelectric ejector device of claim 32, wherein the microcontroller is configured to dither the drive signal by sweeping the frequency of the drive signal over a defined bandwidth.

36. The piezoelectric ejector device of claim 32, wherein the logic combines signals from the two NCO to define a combined signal that periodically disables the CWG to provide two anti-phase square waves with adjustable dead band to the level shifter circuit.