WO2015163406A1 - Drive device, drive method, and image pickup device - Google Patents

Abstract

In a drive device, drive method, and image pickup device of the present invention, a drive unit has a bridge circuit wherein a switching element is used, said drive unit supplying electric energy to an electromechanical conversion element that transmits mechanical energy to a drive member, and the drive unit starts supplying power at a drive voltage having a threshold voltage value of the switching element in the cases of starting supplying the electric energy to the electromechanical conversion element.

Description

DRIVE DEVICE, DRIVE METHOD, AND IMAGING DEVICE

The present invention relates to a driving device using an electromechanical transducer that converts electrical energy into mechanical energy, a driving method thereof, and an imaging device using the driving device.

In a mechanical device including a movable part, an actuator is usually incorporated to drive the movable part. This actuator is a device that converts input energy into mechanical motion, one of which is referred to as SIDM (Smooth Impact Drive Mechanism, “SIDM” is a registered trademark), for example, an electromechanical conversion such as a piezoelectric element. A driving device using an element is known.

This SIDM drive device is typically an electromechanical conversion element that converts electrical energy into mechanical energy, a drive member that is fixed to one end of the electromechanical conversion element and that transmits the mechanical energy, and the drive member. A moving member and the like engaged with a predetermined friction force are provided. The electromechanical transducer is, for example, a piezoelectric element in which a plurality of piezoelectric layers made of a piezoelectric material are stacked via internal electrodes between each piezoelectric layer. A pair of external electrodes for supplying the electric energy is respectively formed on a pair of side surfaces facing each other along the stacking direction of the piezoelectric elements, and the pair of external electrodes is connected to the plurality of internal electrodes. They are connected alternately one after another. In such a SIDM drive device, when a sawtooth or pulsed drive voltage is applied from an external drive circuit via the pair of external electrodes, the piezoelectric element expands and contracts in the stacking direction. The drive member reciprocates in the longitudinal direction according to the expansion and contraction of the piezoelectric element. Here, when the electromechanical conversion element (here, the piezoelectric element) is repeatedly expanded and contracted so that the moving speed of the driving member is asymmetric between the forward path and the backward path, the moving member is moved by the asymmetric reciprocating motion of the driving member. Moving along the longitudinal direction, electrical energy is converted into movement of the moving member.

Such a driving device is disclosed in, for example, Patent Document 1 and Patent Document 2. The drive mechanism disclosed in Patent Document 1 includes an electro-mechanical conversion element, a drive member fixedly coupled to the electro-mechanical conversion element, a driven member frictionally coupled to the drive member, and the electro-mechanical element. Drive pulse generating means for imparting expansion / contraction displacement to the conversion element, and the driven pulse generation means generates expansion / contraction displacements having different expansion and contraction speeds in the electro-mechanical conversion element and is frictionally coupled to the drive member A drive mechanism using an electro-mechanical conversion element that generates a movement in the drive pulse, wherein the drive pulse generating means includes means for controlling the time for applying the drive pulse to the electro-mechanical conversion element, and controls the application time. Thus, the driving speed is controlled by controlling the electric charge applied to the electromechanical conversion element. The drive pulse generating means is applied to the electromechanical conversion element by gradually increasing the time for applying the drive pulse to the electromechanical conversion element at the start of driving of the drive mechanism and gradually increasing the application time. The electric charge is controlled so that the driving speed gradually increases. On the other hand, the drive pulse generating means is applied to the electro-mechanical conversion element by gradually decreasing the application time of the drive pulse to the electro-mechanical conversion element when the drive mechanism is stopped and gradually decreasing the application time. The electric charge is controlled so that the driving speed is gradually reduced. According to Patent Document 1, in a driving mechanism using a conventional piezoelectric element (prior art in Patent Document 1), when driving / stopping / reversing, a driving pulse is controlled to be ON / OFF for the piezoelectric element. The driving member and the moving member are suddenly moved / stopped / reversed to cause a significant speed change, and an impact sound is generated. However, since the drive mechanism configured as described above controls to gradually increase / decrease the charge of the drive pulse applied to the piezoelectric element, the drive member and the moving member are smoothly moved / stopped / reversed, and a significant speed is achieved. Since no change occurs, it is possible to prevent impact sound, resonance sound, and the like.

The drive device disclosed in Patent Document 2 includes an electromechanical transducer that expands and contracts when a drive voltage is applied, a drive member that is driven by the electromechanical transducer, and a predetermined frictional force applied to the drive member. An engaging member; a driving circuit that drives the electromechanical conversion element with a rectangular wave driving voltage; and drive control means that controls the operation of the driving circuit, and the expansion of the electromechanical conversion element. And a reduction device that causes the drive member and the engagement member to move relative to each other at different speeds, and further includes a member sensor that detects the position of the engagement member, and the drive control means includes: The electromechanical transducer element outputs a drive pulse having a predetermined duty ratio based on a signal from the member sensor, and the drive circuit generates the rectangular wave in response to the drive pulse. It is obtained so as to drive.

By the way, in recent years, image sensors using solid-state image sensors such as CCD (Charged Coupled Device) type image sensors and CMOS (Complementary Metal Oxide Semiconductor) type image sensors have been developed and miniaturized. Digital devices such as mobile phones and personal digital assistants equipped with such image pickup devices using image pickup devices are becoming widespread. Further, there is a demand for enhancement of functions of an image pickup apparatus mounted on the digital device, and an AF (Auto Focus) function, a scaling (zoom) function, and the like are also mounted. In order to realize the AF function, the scaling function, and the like, the SIDM driving device is used.

For example, the driving device disclosed in Patent Document 2 can detect the position of the engaging member, drive the engaging member at high speed and accurately position it, and can realize the AF function and the zooming function. However, since the speed of the engaging member is high, the acceleration of the engaging member becomes large when the drive device is started or stopped (the movement start or stop of the engagement member), and as a result, a relatively loud sound is generated. Will occur. In other words, since the driving member and the engaging member are frictionally engaged, when the actuator is started or stopped, the engaging member swings back and forth along the driving direction due to the inertial mass of the engaging member. Repetitively colliding with the drive member, a relatively loud noise is generated. The image pickup apparatus mounted on the digital device is required to reduce the noise substantially the same as that of a compact digital camera or the like with respect to the sound. In the driving apparatus disclosed in Patent Document 2, the noise is reduced. It is difficult to realize

On the other hand, it is conceivable to use the drive mechanism disclosed in Patent Document 1 for noise reduction. However, since the drive mechanism disclosed in Patent Document 1 controls to gradually increase or decrease the electric charge of the drive pulse applied to the piezoelectric element, the speed of AF and zooming becomes slow. May end up.

JP-A-9-191676 JP 2010-260054 A

The present invention has been made in view of the above-described circumstances, and its object is to realize a high-speed movement and accurate positioning, and a driving device capable of reducing sound generated at the time of starting and stopping, and driving thereof A method and an imaging device using the driving device are provided.

In the driving apparatus, the method, and the imaging apparatus according to the present invention, the driving unit that supplies electric energy to the electromechanical transducer that transmits mechanical energy to the driving member includes a bridge circuit using a switching element, and the electric machine When power supply to the conversion element is started, power supply is started with a driving voltage having a threshold voltage value of the switching element. Therefore, the drive device, the method, and the imaging device according to the present invention can reduce the sound that is generated at the time of starting and stopping while realizing rapid movement.

The above and other objects, features and advantages of the present invention will become apparent from the following detailed description and the accompanying drawings.

It is a figure which shows the external appearance structure of the mobile telephone carrying the imaging device using the drive device of embodiment. It is a block diagram which shows the electrical structure of the said imaging device. It is a typical section side view showing the structural composition of the imaging device. FIG. 4 is a cross-sectional view corresponding to the line AA in FIG. 3 in the imaging apparatus. FIG. 4 is a cross-sectional view corresponding to the line BB in FIG. 3 in the imaging apparatus. It is a typical cross-sectional side view which shows the structural structure of the said drive device. It is a figure which shows the displacement of the rectangular-wave-shaped drive pulse supplied to the said drive device, and a piezoelectric element. It is a circuit diagram which shows an example of the drive part in the said drive device. It is a circuit diagram which shows another example of the drive part in the said drive device. It is a figure for demonstrating the threshold voltage of the switching element in the said drive device. It is a figure for demonstrating the drive voltage and threshold voltage in the said drive device. It is a figure which shows the sawtooth-shaped drive pulse supplied to the said drive device.

Hereinafter, an embodiment according to the present invention will be described with reference to the drawings. In addition, the structure which attached | subjected the same code | symbol in each figure shows that it is the same structure, The description is abbreviate | omitted suitably. In this specification, when referring generically, it shows with the reference symbol which abbreviate | omitted the suffix, and when referring to an individual structure, it shows with the reference symbol which attached the suffix.

The driving device in the embodiment is usually incorporated in various devices including the movable part in order to drive the movable part. Here, as an example, the driving apparatus is an imaging device mounted on a mobile phone called a smartphone. The drive device used will be described.

FIG. 1 is a diagram showing an external configuration of a mobile phone equipped with an imaging device using the driving device of the embodiment. FIG. 1A shows the front surface and FIG. 1B shows the back surface. FIG. 2 is a block diagram illustrating an electrical configuration of the imaging apparatus. FIG. 3 is a schematic cross-sectional side view showing a structural configuration of the imaging apparatus. 4 is a cross-sectional view taken along the line AA of FIG. 3 in the imaging apparatus, and is a cross-sectional view seen from the lower side of the drawing. FIG. 5 is a cross-sectional view taken along the line BB of FIG. 3 in the imaging apparatus, and is a cross-sectional view seen from the upper side of the drawing. FIG. 6 is a schematic cross-sectional side view showing a structural configuration of the driving device. 6A is an overall configuration diagram, and FIG. 6B is an exploded perspective view of a lens holding frame. FIG. 7 is a diagram showing a rectangular-wave drive pulse supplied to the drive device and displacement of the piezoelectric element. FIG. 7A shows a drive pulse when the lens holding frame (moving member) is moved in one direction of travel, and FIG. 7B shows displacement of the piezoelectric element (electromechanical conversion element) in the case of FIG. 7A. The horizontal axis in FIG. 7A represents time, the vertical axis represents drive voltage, the horizontal axis in FIG. 7B represents time, and the vertical axis represents the displacement of the piezoelectric element (electromechanical transducer). FIG. 7C shows a driving pulse when the lens holding frame (moving member) is moved in the other direction, which is the opposite direction of the one direction of travel, and FIG. 7D shows the piezoelectric element (electromechanical conversion in the case of FIG. 7C). The displacement of the element. The horizontal axis in FIG. 7C represents time, the vertical axis represents drive voltage, the horizontal axis in FIG. 7D represents time, and the vertical axis represents the displacement of the piezoelectric element (electromechanical transducer).

<Mobile phone SP>
For example, as shown in FIG. 1, the mobile phone SP performs a telephone function by communicating with a display unit OT that displays predetermined information, an input operation unit IN that receives an input of a predetermined instruction, and a mobile phone network. The communication unit MC (not shown) that realizes the above, each unit OS, IS, IG, IB, IP, AD, CT, ME, IF shown in FIG. 2 and these units OT, IN, MC, OS, IS, IG, IB , IP, AD, CT, ME, and IF, and a thin plate-like housing HS that houses the IF. A rectangular display surface of the display unit OT faces one main surface (front surface) of the housing HS, and an input operation unit IN is disposed on one end side (lower side) of the display surface. The display surface of the display unit OT is provided with a touch panel that accepts input by touching the display surface with a fingertip or a pen, and an instruction input that cannot be input by the input operation unit IN is displayed on the touch panel and the display unit OT. It is realized by combining with information to be processed. For example, on the display unit OT, an image shooting mode start button, an image shooting button for switching between still image shooting and moving image shooting, a shutter button, and the like are displayed, and the display surface of the displayed button position is touched. The instruction indicated by the button is input to the mobile phone SP. The touch panel may be of a known type such as a so-called capacitance type. The imaging unit ID of the imaging apparatus faces the other main surface (back surface) facing the one main surface of the housing HS.

<Imaging device ID>
The electrical configuration of the imaging device ID will be described. For example, as illustrated in FIG. 2, the imaging device ID includes an imaging optical system OS, an imaging element IS, an image generation unit IG, an image data buffer IB, an image processing unit IP, and a drive unit AD for the drive unit. A control unit CT, a storage unit ME, and an interface unit (I / F unit) IF.

The imaging optical system OS includes one or a plurality of optical elements such as lenses and optical filters, and forms an optical image of an object (subject) on the light receiving surface of the imaging element IS. A lens LZ attached to a moving member 14 of a lens holding frame to be described later is an optical element that moves along the optical axis C among the one or more optical elements in the imaging optical system OS. The lens LZ may be a single lens or a lens group including a plurality of lenses. The lens LZ may be, for example, an AF lens that moves along the optical axis C to perform focusing (focusing). For example, the lens LZ moves along the optical axis C to perform zooming (magnification). It may be a variable power lens. An optical image of the object is guided along the optical axis C to the light receiving surface of the imaging element IS by the imaging optical system OS including such a lens LZ, and the optical image of the object is captured by the imaging element IS. The imaging element IS is an element that converts the optical image into an electrical signal. More specifically, as described above, the imaging element IS converts the optical image of the subject formed by the imaging optical system OS into electrical signals (image signals) of R, G, and B color components, and R , G, and B are output as image signals to the image generation unit IG. In the imaging element IS, the imaging operation such as imaging of either a still image or a moving image or reading of output signals of each pixel (horizontal synchronization, vertical synchronization, transfer) in the imaging element IS is controlled by the control unit CT. . The imaging element IS is, for example, a CCD type image sensor, a CMOS type image sensor, or the like.

The image generation unit IG performs amplification processing, digital conversion processing, etc. on the analog output signal from the image sensor IS, and determines an appropriate black level, γ correction, and white balance adjustment (WB adjustment) for the entire image. Then, known image processing such as contour correction and color unevenness correction is performed to generate image data from the image signal. The image data generated by the image generation unit IG is output to the image data buffer IB. The image data buffer IB is a memory that temporarily stores image data and is used as a work area for performing later-described processing on the image data by the image processing unit IP. For example, the image data buffer IB is a volatile storage element. It is composed of a certain RAM (Random Access Memory).

The image processing unit IP is a circuit that performs predetermined image processing such as resolution conversion on the image data in the image data buffer IB. Further, the image processing unit IP may include a known distortion correction process, a known peripheral illuminance drop correction process, and the like as necessary.

The driving unit AD is a driving device AD, and operates as described later based on a control signal output from the control unit CT, thereby, for example, arranging an optical element for realizing an AF function or a zooming function in the optical axis direction. Move along.

The control unit CT includes, for example, a microprocessor and its peripheral circuits, and includes an imaging element IS, an image generation unit IG, an image data buffer IB, an image processing unit IP, a driving device AD, a storage unit ME, and an I / F unit. The operation of each part of the IF is controlled according to its function. In other words, the imaging device ID is controlled by the control unit CT so as to execute at least one of still image shooting and moving image shooting of the subject.

The storage unit ME is a storage circuit that stores image data generated by shooting a still image or moving image of a subject. For example, a ROM (Read Only Memory) that is a nonvolatile storage element or a rewritable nonvolatile memory It comprises an EEPROM (Electrically Erasable Programmable Read Only Memory) that is a storage element, RAM, and the like. That is, the storage unit ME has a function as a memory for still images and moving images.

The I / F unit IF is an interface that transmits and receives image data to and from an external device, and is an interface that conforms to standards such as USB (Universal Serial Bus) and IEEE1394.

In such an imaging operation, in such a cellular phone SP, when the start button of the image capturing mode is operated, a control signal indicating the operation content is output to the control unit CT, and the control unit CT has a function of image capturing. When the image shooting button is operated, a control signal indicating the operation content is output to the control unit CT. The control unit CT starts and executes the still image shooting mode and starts the moving image shooting mode. The operation according to the operation content such as execution is executed. When the shutter button is operated, a control signal indicating the operation content is output to the control unit CT, and the control unit CT executes an operation corresponding to the operation content such as still image shooting or moving image shooting. .

More specifically, when taking a still image, the control unit CT controls the imaging element IS to take a still image, and uses the AF optics of the imaging optical system OS via the drive device AD. Focusing is performed by operating the element. As a result, a focused optical image is periodically and repeatedly formed on the light receiving surface of the image sensor IS, converted into image signals of R, G, and B color components, and then output to the image generation unit IG. . The image signal is temporarily stored in the image data buffer IB, and after image processing is performed by the image processing unit IP, an image based on the image signal is displayed on the display unit OT. The photographer can adjust the main subject so as to be within a desired position in the screen by referring to the display unit OT. By operating a so-called shutter button (not shown) in this state, image data is stored in the storage unit ME as a still image memory, and a still image is obtained.

When performing moving image shooting, the control unit CT controls the imaging element IS to perform moving image shooting. Thereafter, in the same manner as in the case of still image shooting, the photographer refers to the display unit OT and adjusts so that the image of the subject obtained through the image sensor IS falls within a desired position on the screen. be able to. Movie shooting is started by operating a shutter button (not shown). Then, at the time of moving image shooting, the control unit CT controls the image pickup element IS to take a moving image and operates the AF optical element of the image pickup optical system OS via the driving device AD to perform focusing. As a result, a focused optical image is periodically and repeatedly formed on the light receiving surface of the image sensor IS, converted into image signals of R, G, and B color components, and then output to the image generator IG. . The image signal is temporarily stored in the image data buffer IB, and after image processing is performed by the image processing unit IP, an image based on the image signal is displayed on the display unit OT. Then, by operating the shutter button (not shown) once again, moving image shooting is completed. The captured moving image is guided and stored in the storage unit ME as a memory for moving images.

On the other hand, when zooming is instructed, a control signal indicating the instruction content is output to the control unit CT, and the control unit CT operates the zooming lens of the imaging optical system OS via the driving device AD to change the zoom. Do it twice. As a result, the scaled optical image is formed on the light receiving surface of the image sensor IS.

<Image pickup device ID, structure of drive device AD>
Next, the structural configurations of the imaging device ID and the driving device AD will be described. In this description, the xyz rectangular coordinate system is set as follows. In each figure, the z direction means the vertical direction (the direction of the optical axis C) in a side view, the origin side is the image side, and the side facing this origin side is the object side. The x and y directions mean the vertical and horizontal directions orthogonal to the z direction and orthogonal to each other in plan view.

A substantially rectangular fixed base 3 in which the imaging element IS for converting an optical image of a subject into an electrical signal is fixed at the center is arranged, and the front of the optical axis C (+ z direction) with respect to the fixed base 3 ) Is provided with a substantially rectangular movable table 4.

The movable table 4 is supported by the fixed table 3 via the suspension wire 5 so as to be swingable in the direction perpendicular to the optical axis C. The movable table 4 includes an upper frame portion 4a and four arm portions 4b extending from the four sides of the upper frame portion 4a in the direction of the fixed table 3.

More specifically, one end of each of the four suspension wires 5 facing the z direction (the direction of the optical axis C) is fixed to the four corners of the fixed base 3, and the other end of each suspension wire 5 is movable. The four corners of the upper frame portion 4a of the table 4 are joined and fixed with an adhesive. The suspension wire 5 is bent in the x direction and the y direction, so that the movable table 4 is translated in the direction perpendicular to the optical axis C with respect to the fixed table 3.

As shown in FIG. 5, elliptical coils 8 are fixed to the four sides of the upper surface of the fixed base 3, and magnets 9 facing the coils 8 are attached to the lower surfaces of the arm parts 4 b of the movable base 4. It has been. The coil 8 and the magnet 9 constitute an electromagnetic actuator 7 of an optical camera shake correction mechanism.

A base body (weight member) 11 of an AF driving device AD (11 to 17) is fixed to one corner of the lower surface of the upper frame portion 4a of the movable base 4.

<Drive device AD>
The drive device AD includes a base body 11, an electromechanical conversion element 12, a drive member 13, a moving member 14, and a drive unit EC. More specifically, as shown in FIG. 3, the base 11, the piezoelectric element as an example of the electromechanical transducer 12, and the driving member 13 are coupled in the direction of the optical axis C from the top, and the driving member 13. Is extended in the direction of the fixed base 3. The drive member 13 is in a cantilever support state. The lens holding frame 14 as an example of the moving member 14 is frictionally engaged with the driving member 13. Note that a reinforcing member 30 may be fitted into the adhesive fixing portion between the electromechanical conversion element 12 and the driving member 13 as shown by a broken line in FIG. 6A and may be adhesively fixed with an epoxy adhesive or the like.

<Electromechanical transducer 12>
The electromechanical transducer 12 is an element that converts input electrical energy into mechanical energy that expands and contracts, that is, mechanical motion. For example, a piezoelectric that converts input electrical energy into mechanical elastic motion by the piezoelectric effect. Elements and the like. Such a piezoelectric element includes, for example, a laminate and a pair of external electrodes. The laminated body is formed by alternately laminating a plurality of thin film (layer) piezoelectric layers made of a piezoelectric material and a thin film (layer) internal electrode layer having conductivity. The plurality of internal electrode layers are respectively formed so as to face the outside with a pair of outer peripheral side surfaces facing each other. The pair of external electrodes are formed along the stacking direction on the pair of outer peripheral side surfaces in the stacked body, and supply the electric energy to the stacked body, and are sequentially and alternately connected to the plurality of internal electrodes. . Examples of the piezoelectric material include lead zirconate titanate (PZT), crystal, lithium niobate (LiNbO ₃ ), potassium tantalate niobate (K (Ta, Nb) O ₃ ), barium titanate (BaTiO ₃ ), and tantalum. Inorganic piezoelectric materials such as lithium oxide (LiTaO ₃ ) and strontium titanate (SrTiO ₃ ).

<Drive member 13>
The drive member 13 is fixedly connected to an end surface of one end in the expansion / contraction direction of the electromechanical conversion element (piezoelectric element in the present embodiment) 12, and mechanical energy converted from electric energy is transmitted by the electromechanical conversion element 12. It is a member. More specifically, in the present embodiment, the drive member 13 is a columnar (shaft-shaped) member (drive shaft) that is bonded and fixed to the end surface of one end of the laminate in the piezoelectric element with an adhesive. As the material of the driving member 13, for example, any material such as metal, resin, and carbon can be used. The cross section perpendicular to the longitudinal direction of the drive member 13 may be any shape such as a rectangle, a polygon, an ellipse, and a circle, but in this embodiment, the moving member 14 is easy along the longitudinal direction of the drive member 13. This cross section is circular so that it can be relatively moved. In addition, when this cross section is a rectangle or a polygon, it is preferable that it is chamfered from the said viewpoint.

<Substrate 11>
The base 11 is a member that is fixedly connected to the end surface of the other end in the expansion / contraction direction of the electromechanical transducer element (piezoelectric element in this example) 12 and supported by the lower surface of the upper frame portion 4a. The base 11 has an inertial mass that is greater than the inertial mass of the drive member 13. More specifically, the base 11 has a cylindrical shape having a diameter that matches the outer shape of the electromechanical conversion element 12, and is bonded and fixed to the electromechanical conversion element 12 by an adhesive at one end face thereof. Thus, the electromechanical conversion element 12 is supported. Since the base body 11 has an inertial mass larger than that of the drive member 13, the base body 11 is stationary with respect to the expansion and contraction motion of the electromechanical conversion element 12 by being fixed to the upper frame portion 4 a. The expansion / contraction motion of the mechanical conversion element 12 is mainly transmitted to the drive member 13. The base body 11 is a member for increasing the output of the drive device AD as described above, and is not always necessary. In this case, the electromechanical conversion element 12 is fixed to the lower surface of the upper frame portion 4a. become.

<Moving member 14>
The moving member 14 is a member engaged with the driving member 13 with a predetermined frictional force, and slides with respect to the driving member 13 below the upper frame portion 4a of the movable base 4. In the present embodiment, the moving member 14 is a lens holding frame that supports and holds an AF lens LZ for realizing an AF function, which is an example of an optical element. As shown in FIG. 6B, a slider block 14a is formed on the moving member 14 of the lens holding frame by extending a part of the outer periphery. A through opening is formed in the slider block 14a along the direction of the optical axis AX, and the drive member 13 is inserted through the through opening. The direction of the optical axis C and the axial direction of the drive member 13 are parallel. A notch portion 14b is formed at the center of the slider block 14a, and the radial half of the drive member 13 is exposed at the notch portion 14b. A pad 15 that is in contact with the half of the driving member 13 in the radial direction is fitted into the notch 14b. The driving member 13 is pressed into the pad 15 by a pressing spring 16 screwed to the slider block 14a with screws 17, 17. An urging force in a direction toward 13 is given. With such a structure, the lens holding frame 14 including the pad 15 and the driving member 13 are pressed against each other by the urging force of the pressing spring 16 and are frictionally engaged by a predetermined frictional force. Note that the structure in which the lens holding frame (moving member) 14 and the driving member 13 are frictionally engaged is not limited to such a structure. The slider block 14a is integrally formed with the lens holding frame 14, but may be connected as a separate body from the lens holding frame 14 with a separate part.

<Driver EC>
The drive unit EC is a circuit that supplies electric energy to the electromechanical transducer 12 in order to drive the electromechanical transducer 12. The drive unit EC will be described in more detail later. For the drive unit EC, for example, a known oscillation circuit that oscillates a sawtooth drive pulse shown in FIG. 12 can be used. The horizontal axis in FIG. 12 is time, and the vertical axis is voltage. When a sawtooth pulse as shown in FIG. 12 is applied to the piezoelectric element 12 from the drive unit EC, the piezoelectric element 12 gently extends (reverses) in the thickness direction at a gently rising portion of the sawtooth pulse, The drive member 13 is also gently displaced in the same direction. At this time, the slider block 14 a of the lens holding frame 14 that is frictionally coupled to the drive member 13 moves in the reverse direction together with the drive member 13. Next, at the rapidly falling portion of the sawtooth pulse, the piezoelectric element 12 is rapidly contracted (moved forward) in the thickness direction, and the driving member 13 is also rapidly displaced in the same direction. At this time, the slider block 14a frictionally coupled to the drive member 13 overcomes the frictional coupling force by the inertial force and stays at that position, and does not substantially move in the forward direction. In this way, by continuously applying the sawtooth pulse to the piezoelectric element 12, the lens holding frame 14 can be gradually moved in the reverse direction together with the slider block 14a. Conversely, in order to gradually move the lens holding frame 14 together with the slider block 14a in the forward direction, the direction of the waveform of the sawtooth pulse applied to the piezoelectric element 12 may be changed. In addition, for example, in order to reduce the manufacturing cost and the like, the drive unit EC is supplied with a rectangular pulse having a predetermined duty ratio (for example, 3: 7 or 7: 3) as shown in FIG. 7A or 7C. It is possible to use a known H-bridge circuit with four switching elements that oscillate as a half-bridge circuit with two switching elements. When a rectangular wave pulse having a duty ratio as shown in FIG. 7A or FIG. 7C is applied from the drive unit EC to the piezoelectric element 12, the displacement waveform of the piezoelectric element 12 has a sawtooth shape as shown in FIG. 7B or 7D. In the same manner as described above, the lens holding frame 14 can be gradually moved together with the slider block 14a.

Here, the suspension wire 5 can serve as a transmission path of a rectangular wave pulse applied to the electromechanical transducer 12. That is, the rectangular wave pulse generated by the drive unit EC is transmitted through the conductive suspension wire 5 (see arrow a in FIG. 3) and then supplied to the electromechanical transducer 12 via the lead wire 20a. it can. What is necessary is just to connect the earth | ground side of the electromechanical conversion element 12 to the earth | ground part of the drive part EC via the another suspension wire 5 from the earth wire 20b (refer arrow b of FIG. 3).

The lead wire 20a is arranged on the movable table 4 side so as to be away from the imaging device IS on the fixed table 3 side. This lead wire 20a is formed by insert-molding a conductive metal foil in a movable base 4 made of an insulating synthetic resin, one end is connected to the suspension wire 5 inside the movable base 4, and the other end is movable base 4 It can also be pulled out from and connected to the electromechanical transducer 12. In this way, it is possible to further reduce noise in the image sensor IS due to rectangular wave pulses.

Thus, the AF lens LZ is autofocused by driving the lens holding frame 14 forward or backward by the driving device AD. Although not specifically shown, a rotation prevention mechanism is provided to prevent rotation of the lens holding frame 14 that is cantilevered by the drive member 13. As shown in FIGS. 3 and 4, the position detection magnet 23 is attached to the lens holding frame 14, and the Hall element 22 is attached to the movable base 4, thereby detecting the forward / backward (focus) position of the lens holding frame 14. I am doing so. Further, by holding the zoom lens LZ with the lens holding frame 14 instead of the AF lens LZ, similarly, the forward / backward (magnification) position of the lens holding frame 14 can be detected and zoomed.

Simultaneously with this autofocus, the electromagnetic actuator 7 of the optical camera shake correction mechanism is driven, and the movable base 4 is translated in the direction orthogonal to the optical axis C, whereby camera shake correction is performed. Here, the behavior of the lens holding frame 14 during the camera shake correction drive will be described. Note that the lens holding frame 14 exhibits the same behavior in the x direction and the y direction. The magnet 9 is magnetized with an N pole on the top surface and an S pole on the bottom surface. When no current is flowing through the coil 8, no electromagnetic force is generated between the magnet 9 and the coil 8, so that the four suspension wires 5 remain in a state parallel to the z direction. On the other hand, when a current is passed through the coil 8 in the direction of the arrow in FIG. 5, an electromagnetic force is generated between the magnet 9 and the coil 8, so the magnet 9 is mounted and supported by the four suspension wires 5. The movable table 4 is moved in the −x direction. At the time of actual camera shake correction driving, the direction and magnitude of the current flowing through the coil 8 change according to a predetermined control signal, and accordingly, the movable base 4 is ensured to be parallel to the image sensor 2 in the x direction. Shift driven in the state. The posture of the movable table 4 supported by the four suspension wires 5 as in the present embodiment is secured by a support mechanism having no spring property, such as the drive member 13 of the drive device AD. Therefore, the movable table 4 is driven to shift in a state in which the parallelism in the x and y directions is ensured with respect to the imaging device 2.

Next, the electrical configuration of the drive device AD, that is, the drive unit EC that feeds electrical energy to the electromechanical conversion element (in this example, the piezoelectric element) 12 will be described more specifically. The drive unit EC uses a bridge circuit using a switching element.

FIG. 8 is a circuit diagram showing an example of a drive unit in the drive device. The drive unit ECa shown in FIG. 8 is configured using a half-bridge circuit. The drive unit ECa includes a charging circuit 41 that charges the electromechanical transducer 12 in the polarization direction, a discharge circuit 42 that discharges the electric charge accumulated by charging, and a control circuit 40 that controls driving of these circuits 41 and 42. ing.

The charging circuit 41 applies the power supply voltage Vm to the external electrode 122 of the electromechanical conversion element 12 to charge the electromechanical conversion element 12 in the polarization direction (charge in a direction in which the polarization is increased). The discharge circuit 42 grounds the external electrode 121 of the electromechanical conversion element 12 (that is, applies a potential in the opposite direction to the voltage between the terminals of the piezoelectric member 3), and discharges the electric charge accumulated in the electromechanical conversion element 12. Discharge.

The charging circuit 41 includes a switching element Q1 composed of a P-channel MOS type FET (field effect transistor) and a power source 49 connected thereto. The discharge circuit 42 is composed of a switching element Q2 made of an N-channel MOS type FET (field effect transistor) connected to the ground. In the present embodiment, an FET is used as the switching element, but other electronic switching elements such as a bipolar transistor may be used.

Based on the polarization direction of the electromechanical transducer 12 (direction indicated by arrow P in FIG. 8), the negative external electrode 121 is grounded, and the positive external electrode 122 is connected to the drains of the switching elements Q1 and Q2. Has been. The gates of the switching elements Q1 and Q2 are connected to the control terminals C1 and C2 of the control circuit 40, the source of the switching element Q1 is connected to the power source 49, and the source of the switching element Q2 is grounded. Drive control signals Sc1 and Sc2 are input from the control circuit 40 to the charging circuit 41 and the discharging circuit 42, respectively. The control circuit 40 drives the charging circuit 41 and the discharging circuit 42 (that is, the charging circuit 41 and the discharging circuit 42). Connection with the electromechanical transducer 12) is controlled.

The control circuit 40 controls driving of the charging circuit 41 and the discharging circuit 42. The control circuit 40 alternately drives the charging circuit 41 and the discharging circuit 42 with drive control signals Sc1 and Sc2 that are pulse signals having a predetermined duty ratio that make the drive times different from each other (see FIG. 7). The capacitor 43 arranged in series with the electromechanical conversion element 12 will be described later.

FIG. 9 is a circuit diagram showing another example of a drive unit in the drive device. The drive unit ECb shown in FIG. 9 is configured using a full bridge circuit. The bridge circuit 50 of the drive unit ECb includes a first switch circuit 501 having a switching element Q1 and a second switch circuit 502 having a switching element Q2 connected in series, and a third switch circuit 503 having a switching element Q3. The fourth switch circuit 504 having the switching element Q4 is connected in series. The switching elements Q1 and Q4 are N channel MOS type FETs, and the switching elements Q2 and Q3 are P channel MOS type FETs. A power supply (not shown) is connected between a connection point a between the second switch circuit 502 and the third switch circuit 503 and a connection point c between the first switch circuit 501 and the fourth switch circuit 504, and the first switch circuit 501. The electromechanical transducer 12 is connected between the connection point b of the second switch circuit 502 and the connection point d of the third switch circuit 503 and the fourth switch circuit 504. Drive control signals Sc1, Sc2, Sc3, and Sc4 are input from the control terminals C1, C2, C3, and C4 of the control circuit 40 to the switch circuits 501, 502, 503, and 504 (that is, the gates of the FETs), respectively. It is like that.

The positive and negative polarities of the power source connected between the connection points a and c and the polarization direction of the electromechanical transducer 12 connected between the connection points b and d can be arbitrarily set. For example, as shown in FIG. 9, it is assumed that the connection point a is the positive electrode of the power source, the electromechanical transducer 12 is polarized in the direction of the arrow P, and the + polarization side is connected to the connection point b. In this case, the second switch circuit 502 and the fourth switch circuit 504 are charged until the power supply voltage Vm is applied to the electromechanical conversion element 12 in the polarization direction (the direction in which polarization is increased) and the inter-terminal voltage Vs becomes + Vm. The first switch circuit 501 and the third switch circuit 503 apply the power supply voltage Vm to the electromechanical conversion element 12 in the direction opposite to the polarization direction to discharge the charge, and the inter-terminal voltage Vs. Constitutes a circuit for charging until becomes −Vm.

If the connection direction of the electromechanical conversion element 12 is reversed, the second switch circuit 502 and the fourth switch circuit 504 become a circuit that charges the electromechanical conversion element 12 in the polarization direction, and the first switch circuit 501 and the third switch circuit 504 The switch circuit 503 is a circuit that charges the electromechanical transducer 12 in the direction opposite to the polarization direction. That is, the first switch circuit 501 and the third switch circuit 503 constitute a circuit that applies the power supply voltage Vm in the polarization direction to the electromechanical conversion element 12 and charges it until the inter-terminal voltage Vs becomes + Vm. The switch circuit 502 and the fourth switch circuit 504 apply the power supply voltage Vm in the direction opposite to the polarization direction to the electromechanical transducer 12 to discharge the charge, and charge until the inter-terminal voltage Vs becomes −Vm. Configure the circuit.

When the drive unit EC is configured by a full bridge circuit having four switching elements, a charging voltage of −Vm to + Vm is applied to the electromechanical conversion element 12, so that the drive voltage of the electromechanical conversion element 12 is equivalently used. Is 2 Vm, the driving voltage is twice that of the driving unit ECa shown in FIG. 8, and there is an advantage that a piezoelectric actuator with a low voltage and a large displacement can be configured. The capacitor 51 arranged in series with the electromechanical conversion element 12 will be described later.

<Start voltage value>
When driving / stopping / reversing a driving device using a piezoelectric element, if the driving pulse is controlled to ON / OFF with respect to the piezoelectric element, the driving member or moving member suddenly moves / stops / reverses and the speed changes significantly. Occurs, and an impact sound is generated. Therefore, for example, the drive device described in Patent Document 1 controls the drive pulse applied to the piezoelectric element to gradually increase / decrease the charge, and smoothly moves / stops / moves the drive member and the moving member. By reversing, it is possible to prevent impact sound, resonance sound, and the like without causing a significant speed change.

However, in this prior art, when the application of voltage to the piezoelectric element is started, generation of a drive pulse is started from a state where the output voltage is zero. FIG. 11 is a diagram for explaining a drive voltage and a threshold voltage when a rectangular wave pulse is applied to the electromechanical transducer 12. The horizontal axis is time, and the vertical axis is the voltage of the piezoelectric element to which the drive pulse is applied. FIG. 11A shows the case of the prior art, and FIG. 11B shows the case of the present embodiment. As shown by the solid line graph in FIG. 11A, in the prior art, when the driving of the piezoelectric element is started, a high voltage is gradually applied from zero to the piezoelectric element, so the voltage of the piezoelectric element also starts from zero, and when stopped, Since the voltage is gradually lowered to zero and applied, the voltage of the piezoelectric element also gradually decreases to zero.

In the driving device AD of the embodiment, since the driving member 13 and the moving member 14 are frictionally engaged, when the moving member 14 starts to move, there is a dead zone that does not start moving below a predetermined voltage value. To do. Therefore, in the driving device AD, when the moving speed V of the moving member 14 is zero, that is, the voltage value (start voltage value) at the start of applying a voltage to the electromechanical transducer 12 is set to a predetermined voltage value. Thus, the time from zero voltage to start voltage application can be shortened, and the speed of AF and zooming can be increased. For example, as shown in FIG. 11B, the start voltage is set to voltage A.

The larger start voltage value is desirable because the time during which the voltage is applied to the electromechanical transducer 12 is shortened. However, on the other hand, when the start voltage value is increased, the piezoelectric element of the electromechanical transducer 12 has good response, and thus suddenly starts to vibrate with a large amplitude and gives an impact force to the moving member. This will excite the resonance and generate sound.

Therefore, more specifically, in the driving device AD according to the embodiment, for example, as shown in FIG. 11B, the start voltage value is set to the threshold value of the switching element constituting the driving unit EC.

FETs used for the switching elements Q1 to Q4 have “threshold” as their characteristics. FIG. 10 is a graph for explaining the threshold voltages of the switching elements Q1 to Q4 in the drive unit EC of the drive device AD. The horizontal axis of the graph of FIG. 10 is the gate-source voltage Vgs, and the vertical axis is the drain current Id.

As shown in the graph of FIG. 10, the threshold voltage value is a voltage value at which the switching element is turned on when the switching element is energized and current starts to flow. In the graph of FIG. 10, when the gate-source voltage Vgs is higher than 0.75, a drain current flows. That is, the threshold voltage of the switching elements Q1 to Q4 is “0.75V”.

For example, in the bridge circuit 50 of FIG. 9, drain currents of the switching elements Q2 and Q4 flow, and the second switch circuit 502 and the fourth switch circuit 504 supply power to the electromechanical conversion element 12 in the polarization direction (direction in which polarization is increased). A charging circuit for applying the voltage Vm is configured. Further, when the difference between the power supply voltage Vm and the drive control signals Sc1, 3 from the control circuit 40 becomes greater than “0.75V”, the drain currents of the switching elements Q1, Q3 flow, and the first switch circuit 501 and The third switch circuit 503 constitutes a circuit that applies the power supply voltage Vm to the electromechanical conversion element 12 in the direction opposite to the polarization direction to discharge the charge, and charges the inter-terminal voltage Vs to −Vm. It will be.

That is, when the gate-source voltage Vgs is less than “0.75 V”, the switch is in the OFF state, and no voltage is applied to the electromechanical transducer 12. Further, when the gate-source voltage Vgs is “0.75 V” or more, the switch is turned on, and the voltage is applied to the electromechanical transducer 12.

As described above, even if the start voltage value is gradually increased from zero, the voltage is not applied to the electromechanical transducer 12 unless the gate-source voltage Vgs becomes “0.75 V” or more. Therefore, if the start voltage value is set to the threshold value “0.75 V” of the switching elements Q1 to Q4, it is possible to achieve both the silencing as much as possible and the quick movement of the moving member ( (See arrow 121 in FIG. 11B). The drive unit EC applies a drive voltage indicated by a solid line in FIG. 11B to the electromechanical transducer 12.

Thus, by setting the start voltage value as the threshold voltage of the switching element constituting the drive unit EC, the electromechanical conversion element (piezoelectric element in this example) is obtained from the lowest voltage value that can be output by the switching element. Therefore, the vibration of the moving member 14 caused by the rapid vibration of the electromechanical transducer 12 can be suppressed to the maximum, and the generation of sound can be prevented to the maximum. In addition, it is possible to improve the speed of AF and zooming.

In addition, when the charge of the drive pulse applied to the electromechanical conversion element 12 is reduced, the charge of the drive pulse is gradually reduced to the threshold voltage value to the threshold voltage value of the switching element. When the voltage decreases, the voltage value may be zero (see arrow 122 in FIG. 11B). Since the voltage value has been gradually lowered to the lowest voltage value that the switching element can output, even if the voltage value is gradually lowered further, the vibration of the moving member 14 due to the sudden vibration of the electromechanical transducer 12 is Because it doesn't change.

Also, by not setting the start voltage value to zero, it is possible to shorten the time until the next drive voltage application (see arrow 123 in FIG. 11B). That is, the next drive voltage can be applied without waiting for the time T1 indicated by the double-ended arrows in FIG. 11B.

Note that if the start voltage value is too large, sound will be generated, and if it is too small, the speed of AF and zooming will not be improved. If it is in the range of%, the influence is slight, and it is known that the quality of the imaging device IS equipped with the driving device AD is not affected.

<Modification>
As described above, since the piezoelectric element of the electromechanical conversion element 12 has good responsiveness, it is applied to the piezoelectric element in order to suddenly start vibration with a large amplitude so as not to give an impact force to the moving member. It is desirable that the voltage be as small as possible. However, the start voltage value is limited by the threshold voltage of the switching element Q constituting the drive unit EC.

Therefore, a voltage value applied to the piezoelectric element can be adjusted by disposing a capacitor (the capacitor 43 in FIG. 8 and the capacitor 51 in FIG. 9) in series with the piezoelectric element and dividing the drive voltage.

For example, in FIG. 9, the capacitance of the electromechanical transducer 12 is 30 nF (nanofarad), and the capacitance of the capacitor 51 is 100 nF.

The combined capacitance C when the capacitances are connected in series is
1 / C = Σni = 1 (1 / Ci)
So
1 / C = 1/30 + 1/100
And C = 23 nF. Therefore, the voltage applied to the electromechanical transducer 12 is divided into 23/30 of the drive voltage.

Thus, the voltage value applied to the electromechanical transducer 12 can be adjusted by arranging an appropriate capacitor in series.

In this case, it is possible to achieve more silence. In other words, a capacitor having an appropriate capacity is provided depending on the desired balance between noise reduction and speedup.

This specification discloses various modes of technology as described above, and the main technologies are summarized below.

A driving apparatus according to one aspect includes an electromechanical conversion element that converts electric energy into mechanical energy that expands and contracts, a driving member that is coupled to one end in the expansion and contraction direction of the electromechanical conversion element, and transmits the mechanical energy; A moving member engaged with the driving member with a predetermined frictional force, and a driving unit that has a bridge circuit using a switching element and supplies the electric energy to the electromechanical conversion element. When starting feeding of the electric energy to the electromechanical transducer, feeding is started with a driving voltage having a threshold voltage value of the switching element.

The driving method according to another aspect includes an electromechanical conversion element that converts electrical energy into mechanical energy that expands and contracts, and a drive member that is coupled to one end in the expansion and contraction direction of the electromechanical conversion element and that transmits the mechanical energy A driving member that includes a moving member that is engaged with the driving member with a predetermined frictional force, and a driving unit that supplies a bridge circuit using a switching element and supplies the electric energy to the electromechanical transducer. In the driving method, when feeding of the electric energy to the electromechanical transducer is started, feeding is started with a driving voltage having a threshold voltage value of the switching element.

In such a driving apparatus and driving method, when feeding electric energy to the electromechanical conversion element, feeding starts from a driving voltage at which the switching element is turned on, so that the moving member can be quickly moved. it can. The driving device and the driving method start feeding electric energy at a driving voltage at which the switching element is turned on, that is, a driving voltage as low as possible, with respect to the electromechanical conversion element having good response. A sudden change in the amplitude of can be suppressed. Therefore, the impact force applied to the moving member by the electromechanical conversion element is kept low, the occurrence of resonance of the moving member is suppressed, and the generation of sound is reduced.

In another aspect, in the above-described drive device, when the drive unit stops the supply of the electric energy to the electromechanical transducer, the drive voltage of the supplied electric energy is switched to the switching device. The electric energy supply is stopped by gradually lowering the threshold voltage value of the element.

Such a driving device does not supply electric energy with a driving voltage equal to or lower than the threshold voltage value when stopping electric power supply to the electromechanical transducer, and therefore starts supplying the next electric energy. It is possible to shorten the time until. Therefore, the drive device can cause the drive member to reach the target position in a shorter time.

In another aspect, the above-described driving device includes a capacitor connected in series with the electromechanical conversion element.

In such a drive device, since the capacitor is connected in series to the electromechanical conversion element, the drive voltage can be divided and applied to the electromechanical conversion element. That is, the drive device can apply a voltage lower than the threshold voltage of the switching element to the electromechanical conversion element even when the threshold voltage of the switching element is applied as the drive voltage. The sudden large amplitude of the mechanical conversion element can be further suppressed, and the generation of sound can be further reduced. In addition, by changing the capacitance of the capacitor, it is possible to adjust the voltage at which power supply to the electromechanical conversion element is started while maintaining the power supply voltage constant (without adjusting the power supply voltage).

An imaging apparatus according to another aspect includes any one of the above-described driving apparatuses, an imaging element that converts an optical image into an electrical signal, and one or a plurality of optical elements, and captures an optical image of an object. An imaging optical system that forms an image on a light receiving surface of the element, and the optical element that moves along the optical axis direction of the one or more optical elements in the imaging optical system is the moving member of the drive device Is attached.

Since such an imaging apparatus includes any one of the above-described driving devices, it is possible to reduce the sound generated at the time of starting and stopping while realizing high-speed movement and accurate positioning. In particular, when the imaging device is a model that can shoot a moving image, recording of noise of the driving device is reduced, and thus such an imaging device can capture (capture) a more preferable moving image.

This application is based on Japanese Patent Application No. 2014-91670 filed on April 25, 2014, the contents of which are included in this application.

In order to express the present invention, the present invention has been properly and fully described through the embodiments with reference to the drawings. However, those skilled in the art can easily change and / or improve the above-described embodiments. It should be recognized that this is possible. Therefore, unless the modifications or improvements implemented by those skilled in the art are at a level that departs from the scope of the claims recited in the claims, the modifications or improvements are not covered by the claims. To be construed as inclusive.

According to the present invention, it is possible to provide a driving device, a driving method, and an imaging device using the same.

Claims (5)

An electromechanical transducer that converts electrical energy into elastic mechanical energy;
A driving member connected to one end of the electromechanical conversion element in the direction of expansion and contraction, to which the mechanical energy is transmitted;
A moving member engaged with the driving member with a predetermined frictional force;
A bridge circuit using a switching element, and a drive unit that feeds the electric energy to the electromechanical transducer,
The drive unit starts feeding at a driving voltage having a threshold voltage value of the switching element when starting feeding of the electric energy to the electromechanical transducer.
Drive device. When the drive unit stops the supply of the electric energy to the electromechanical conversion element, the drive unit gradually decreases the drive voltage of the supplied electric energy to the threshold voltage value of the switching element. , Stop feeding the electric energy,
The drive device according to claim 1. Comprising a capacitor connected in series with the electromechanical transducer,
The drive device according to claim 1 or claim 2. A drive device according to any one of claims 1 to 3,
An image sensor that converts an optical image into an electrical signal;
An imaging optical system that includes one or a plurality of optical elements, and that forms an optical image of an object on a light receiving surface of the imaging element;
An optical element that moves along the optical axis direction among the one or more optical elements in the imaging optical system is attached to the moving member of the drive device.
Imaging device. An electromechanical conversion element that converts electrical energy into expandable mechanical energy, a drive member that is connected to one end in the expansion / contraction direction of the electromechanical conversion element, and that transmits the mechanical energy, and a predetermined frictional force applied to the drive member A driving device driving method comprising: a moving member engaged with the driving device; and a driving circuit that has a bridge circuit using a switching element and supplies the electric energy to the electromechanical transducer.
When starting feeding of the electrical energy to the electromechanical transducer, start feeding with a driving voltage having a threshold voltage value of the switching element,
Driving method.

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