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WO2000005593A1 - Transducteur de position dielectrique variable et son procede d'utilisation - Google Patents

Transducteur de position dielectrique variable et son procede d'utilisation Download PDF

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Publication number
WO2000005593A1
WO2000005593A1 PCT/US1999/016744 US9916744W WO0005593A1 WO 2000005593 A1 WO2000005593 A1 WO 2000005593A1 US 9916744 W US9916744 W US 9916744W WO 0005593 A1 WO0005593 A1 WO 0005593A1
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WO
WIPO (PCT)
Prior art keywords
plate
capacitance
transducer
plates
signal
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Ceased
Application number
PCT/US1999/016744
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English (en)
Inventor
Philip T. Dempster
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Life Measurement Instruments Inc
Original Assignee
Life Measurement Instruments Inc
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Filing date
Publication date
Application filed by Life Measurement Instruments Inc filed Critical Life Measurement Instruments Inc
Priority to AU51265/99A priority Critical patent/AU5126599A/en
Publication of WO2000005593A1 publication Critical patent/WO2000005593A1/fr
Anticipated expiration legal-status Critical
Ceased legal-status Critical Current

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B7/00—Measuring arrangements characterised by the use of electric or magnetic techniques
    • G01B7/30—Measuring arrangements characterised by the use of electric or magnetic techniques for measuring angles or tapers; for testing the alignment of axes
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B7/00—Measuring arrangements characterised by the use of electric or magnetic techniques
    • G01B7/003—Measuring arrangements characterised by the use of electric or magnetic techniques for measuring position, not involving coordinate determination
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B7/00—Measuring arrangements characterised by the use of electric or magnetic techniques
    • G01B7/02—Measuring arrangements characterised by the use of electric or magnetic techniques for measuring length, width or thickness
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01D—MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR
    • G01D5/00—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable
    • G01D5/12—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means
    • G01D5/14—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means influencing the magnitude of a current or voltage
    • G01D5/24—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means influencing the magnitude of a current or voltage by varying capacitance
    • G01D5/2405—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means influencing the magnitude of a current or voltage by varying capacitance by varying dielectric

Definitions

  • the position transducer is normally used as the feedback component of a servo system.
  • a servo system that utilizes a linear motor such as a linear solenoid or voice coil system.
  • Another example would be control of a butterfly type air valve, in which application a rotary transducer is used to measure angular position.
  • An example of a monitoring system is liquid level detection using a float in conjunction with a linear or rotary transducer.
  • Another example is a two-axis joystick. In this case, the transducer is configured to have two outputs to describe coordinate position.
  • the position transducer includes first and second electrically conductive plates separated from a third electrically conductive plate.
  • the first plate has a first capacitance relative to the third plate and the second plate has a second capacitance relative to the third plate.
  • the position transducer includes a fourth moveable nonconductive plate, having a dielectric constant greater than unity, that is interposed between the first, second and third plates and that covers a portion of the first and second plates.
  • the position transducer includes means for translating or rotating the fourth nonconductive plate between the first, second and third conductive plates, so that movement of the fourth plate produces approximately complementary changes in the first capacitance and the second capacitance, and means for generating a transducer signal representative of the changed first and second capacitances by means of a nulling technique.
  • the position transducer includes an array of four fixed conductive plates separated from a fifth fixed conductive plate. Each of the four conductive plates has a capacitance relative to the fifth plate, which are denoted as Cl, C2, C3, and C4, respectively.
  • the position transducer includes a sixth moveable nonconductive plate interposed between the group of four plates and the fifth plate.
  • This embodiment includes a means for moving the sixth nonconductive plate between the group of four conductive plates and the fifth conductive plate along each of two axes, so that with movement along one axis, the sum (Cl + C2) varies in approximately complementary fashion to the sum (C3 + C4), and with movement along the other axis, the sum (Cl + C3) varies in approximately complementary fashion to the sum (C2 + C4).
  • FIG. 1 shows a schematic representation of an arrangement of fixed conductive plates and moveable nonconductive plate according to the present invention.
  • FIG. 2 A shows a circuit including the variable capacitances formed between pairs of conductive plates shown in FIG. 1.
  • FIG. 2B shows some representative waveforms at various points of the circuit shown in FIG. 2A with movement of the nonconductive plate.
  • FIG. 3 shows a schematic representation of the arrangement of the fixed conductive plates and moveable nonconductive plate in a transducer suitable for two axis sensing.
  • FIG. 4 shows a circuit including the variable capacitances formed between pairs of conductive plates shown in FIG. 3.
  • FIG. 5 shows some representative waveforms at various points in the circuit of FIG. 4.
  • FIGS. 6A, 6B, 6C, and 6D show some possible arrangements of the fixed conductive plates and moveable nonconductive plate shown in FIG. 1 that are suitable for linear position sensing.
  • FIGS. 7A, 7B, 1C, and 7D show some possible arrangements of the fixed conductive plates and moveable nonconductive plate shown in FIG. 1 that are suitable for rotary position sensing.
  • FIG. 8 shows another arrangement of the fixed conductive plates and moveable nonconductive plate according to the present invention.
  • FIG. 9 shows a circuit including the variable and fixed capacitances formed between pairs of conductive plates shown in FIG. 8.
  • FIGS. 10A, 10B, and IOC show some possible arrangements of the fixed conductive plates and moveable nonconductive plate of FIG. 8 that are suitable for linear position sensing.
  • FIG. 11 shows some of the possible configurations of fixed conductive plates and moveable nonconductive plate of FIG. 3 that are suitable for sensing position in a plane.
  • FIG. 12A shows an exploded view of some of the components of the present invention as configured for linear sensing.
  • FIG. 12B shows a side view of the implementation of FIG. 12A.
  • FIGS. 13A and 13B show an implementation for rotary sensing with the present invention.
  • FIGS. 14A and 14B illustrates the exceptional linearity and repeatability of a linear transducer example according to the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
  • the present invention uses the principle that the capacitance between two conductive plates which are separated by an air gap is increased if the air in between is replaced with a nonconductive material having a dielectric constant greater than unity.
  • the proportion by which capacitance increases is the dielectric constant of the nonconductive material.
  • a position transducer includes at least two separated conductive plates having a sheet of nonconductive material that may partially fill the space between those two plates. If the sheet of nonconductive material is moved so that more of the space between two separated conductive plates is filled, the capacitance between the two conductive plates will increase.
  • the position transducer provides a transducer signal or signals representative of the changed capacitance between one or several pairs of plates.
  • transducer that simply consisted of pairs of conductive plates with a moveable sheet of nonconductive material in between would be practical, it would also suffer from various problems, chief among them, dependency on temperature, critical dependency on dimensions, and susceptibility to stray capacitance . It would be desirable to configure a transducer so that both baseline and span were inherently independent of temperature. In addition, it would be desirable to configure the transducer so that its calibration were independent of the dielectric constant of the moveable sheet of nonconductive material between the plates. It would also be desirable to configure the transducer so that close tolerances were not required for good performance. It would also be desirable that the transducer be insensitive to stray capacity.
  • a first embodiment is a symmetric configuration with an inherently stable midscale output, and cancellation of some non-linearities, but whose span is dependent on spacing and dielectric constant.
  • the second main embodiment is a refinement of the first that addresses dependency on both spacing and dielectric constant of the moveable plate, for more critical applications.
  • the third main embodiment senses position along two axes. This embodiment may also include the refinements of the second embodiment, and thus reduce dependency on spacing and dielectric constant of the moveable plate.
  • the three embodiments may be further subdivided into multiple embodiments, as will be seen.
  • the first and second embodiments may be configured for either linear or rotary movement. Particular examples involving the use of printed circuit boards will be shown.
  • electrically conductive plates 101 and 102 are separated from a third electrically conductive plate 103.
  • Moveable nonconductive plate 104 which has a dielectric constant greater than unity, is interposed so that it fills part of the space between plates 101 and 103, and part of the space between plates 102 and 103.
  • the capacitance of plate 101 relative to plate 103 is denoted by
  • C101 and the capacitance of plate 102 relative to plate 103 by C102.
  • capacitance C102 increases and C101 decreases.
  • the variation of capacitances C101 and C102 may be a linear function of the movement of plate 104, and the sum (C101 + C102) may remain approximately constant.
  • other (non-linear) functions relating capacitance and movement may be obtained as desired by the application designer.
  • FIG. 2A shows a circuit that includes the various plates shown in FIG. 1.
  • Clock circuit 112 (not detailed) generates squarewave E clk which operates double pole electronic switches 108, 109, and 110.
  • the frequency of the squarewave could be 5 kHz, but other frequencies or asymmetric waveforms would also work.
  • Reference voltage V r which may be a power supply voltage or generated in some other manner, is connected to one pole of switch 108 while the other pole of switch 108 is connected to the output voltage E 0 of integrator 111.
  • switch 109 has one pole connected to an electrically neutral point and the other to E 0 . It can be seen that the action of switch 108 produces an excitation squarewave E ⁇ , at point B in FIG.
  • any AC voltage on plate 103 is amplified in its power by buffer amplifier 107, whose output drives capacitor 140.
  • the other side of capacitor 140 is alternately grounded and connected to the input of integrator 111 by switch 110, synchronous with the AC voltage on plate 103, because all three switches 108, 109, and 110 are driven by E dk .
  • the effect is that capacitor 140 will deliver a charge to integrator 1 11 during each cycle that is equal to the amplitude of the voltage at the output of buffer 107 times the value of capacitor 140, and that the sign of this charge will change the output E 0 of integrator 111 in a direction tending to drive E 0 towards the voltage y which would result in no AC voltage on plate 103.
  • step response to change in position of plate 104 may be about one millisecond.
  • the transducer may be designed to respond faster or slower by choice of component values and clock frequency.
  • the null condition in terms of the capacitances and signals means that the signals applied to conductive plate means are such that, given the capacitances associated with each plate of the plate means, the voltage capacitively induced on the reference plate is zero. In other words, when the reference plate is at 0 volts (null), the currents through the two capacitors are equal in magnitude and opposite in sign, cancelling each other out. The effect is that as capacity diminishes due to movement of the non-conductive plate, its associated voltage increases and visa versa.
  • the first embodiment although adequate for many applications, may have the following deficiency: span of output is dependent on spacing of the conductive plates, as well as on the thickness and dielectric constant of plate 104. This creates the potential for unwanted temperature dependencies and variable performance due to manufacturing tolerances. A method to reduce these dependencies will now be described.
  • capacitors 105 and 106 refer to the capacitance of plate 101 to plate 103 and of plate 102 to plate 103, respectively, as shown in FIG. 8.
  • Resistances 113, 114, 122, and capacitor 116 may be chosen so that, in the absence of moveable nonconductive plate 104, the current through capacitor 116 would exactly null the current through ClOl or C102.
  • Capacitor 1 16 may be constructed to be part of the structure of ClOl and C102. Referring now to FIG. 8, plate 131 is aligned opposite plate 104, as are plates 101 and 102. Plates 101, 102, and 131 might be mounted on the same insulating structure, for example, epoxy fiberglass board. As such, variations in spacing due to temperature or manufacturing tolerance will affect all three capacitances equally, maintaining cancellation of air capacitance. A disadvantage is that the transducer becomes larger. Where size is critical, capacitor 1 16 may be a standard component, or it may be created on a circuit board by juxtaposition of conductive areas, usually on opposite sides of a circuit board.
  • guard 132 may be placed behind plate 103 with guard 132 driven by the output of buffer amplifier 107. In FIG. 9 this connection is indicated by an arrow pointing to the capital letter 'G'.
  • circuits utilize squarewaves driving plates 101 and 102, and a particular form of synchronous detection (switch 110, capacitor 140, integrator 1 11), it would be appreciated by one skilled in the art that sine waves or other waveforms, as well as detectors of different design, could be substituted without altering the fundamental operation of the circuit.
  • the essential operation of the circuit is that the detector output alters the voltages applied to plates 101 and 102 in accordance with equations (1) and (2) in an arrangement that drives the voltage on plate 103 towards a null condition.
  • a separate amplifier and capacitor could be used to null the air capacitance ClOl and C102.
  • the ground of switch 109 with some other voltage, for example with (-V r ).
  • the output voltage in the center position of plate 104 would be zero.
  • Buffer amplifier 107 is shown as an operational amplifier. It could be some other type of device, for example a source follower FET. Other integrators besides the simple circuits shown in FIGS.
  • integrator 111 could be replaced with a high gain amplifier that had a 6db/octave roll off at high frequencies, with no significant degradation of performance.
  • the first two embodiments may be configured to respond to a variety of movements.
  • the most common types of movement are linear translation and rotation, but it is not intended that the invention be restricted to these two movements.
  • An example of a movement other than linear or rotary is a trajectory constrained to the surface of a sphere. Because linear and rotary applications will be the most common, several embodiments of these two types of movement will now be described.
  • FIGS. 6A, B, C, and D show four arrangements of nonconductive plate 104 for the first preferred embodiment.
  • FIGS. 10A, B, and C show three arrangements of nonconductive plate 104 for the second preferred embodiment. Note that these figures do not show conductive plate 103, since to do so would obscure the relationship of plates 101, 102, and 104. These arrangements all have in common that as plate 101 is uncovered by plate 104, plate 102 is correspondingly covered and vice versa.
  • One skilled in the art would be able to devise other variations within the spirit of the invention.
  • FIGS. 7 A, B, C, and D show four arrangements for rotary sensing for the first embodiment. As in the case of FIGS. 6A-D and 10A-C, and for the same reason, plate 103 is not shown.
  • plates 101 and 102 are symmetric half disks and nonconductive plate 104 is a half disk that covers a portion of each of plates 101 and 102.
  • the output of such a transducer is a symmetric sawtooth waveform that repeats every 360 degrees.
  • plates 101 and 102 are nesting spirals and nonconductive plate 104 is a section of a disk.
  • This configuration may have geometry allowing linear response to rotation greater than 180 degrees.
  • FIG. 7C is a variation in which plate 104 is a spiral and plates 101 and 102 are pie-shaped sections. Like FIG. 7B, this configuration may have geometry allowing linear response to rotation over more than 180 degrees.
  • FIG. 7D is similar to FIG. 7A except that plates 101 and 102 have been shaped so as to produce a sinusoidal output with continuous rotation. This is just one example in which geometry of the plates may be designed to create a specific functional relationship between motion and transducer output.
  • FIGS. 7A-D Adaptation of the arrangements of FIGS. 7A-D to the second configuration is not shown in the figures. Many ways to add a compensating plate 131 to those arrangements will occur to those skilled in the art.
  • plate 131 could be a ring-shaped flat conductor surrounding plates 101 and 102.
  • capacitance 116 would be realized by a component or by juxtaposition of conductive areas on a printed circuit board.
  • a preferred linear configuration of either the first or second embodiments is an assembly comprising two printed circuit boards. These boards, separated by simple spacers and three or four electrical connections that may be the spacers themselves, contain the entire transducer, including the circuitry.
  • circuit board 124 may be a one or two layer board in which plates 101, 102, and 131 are etched onto layer 120 by standard printed circuit board techniques.
  • Circuit board 125 is a multi-layer board of typically four circuit layers, indicated as structures 127, 117, 118, and 119 in FIG. 12B.
  • Layer 127 has plate
  • Layer 117 includes guard 132. Extra space is dedicated to ground for shielding. Layers 118 and 119 are both used for circuit traces, and layer 119 also carries the electronic components.
  • the bottom and top circuit boards are fixed to each other by standoffs 126, so that clearance exists to insert nonconductive plate 104.
  • electrical connections are integrated with standoffs 126.
  • a variation would use three circuit boards or two circuit boards and an ASIC (application specific integrated circuit).
  • the bottom circuit board would be as described.
  • the middle circuit board would contain plate 103 and guard 132.
  • the top circuit board would contain the electronics circuit.
  • the top board would be replaced by an ASIC and the middle board would have a few traces and components.
  • FIGS. 13A and 13B A configuration of the first embodiment for the rotary case is shown in FIGS. 13A and 13B. The arrangement is very similar to the linear case. The rotary configuration shown is that of FIG. 7A.
  • the bottom board 124 contains plates 101 and 102, whereas the top board 125 contains plate 103, the guard, and the circuitry.
  • Moveable plate 104 is mounted on a shaft 128 that passes through bushing 121 mounted to lower board 124.
  • the bottom and top circuit boards are fixed to each other by standoffs (not shown), so that clearance exists to insert nonconductive plate 104.
  • each conductive plate 1 through 4 has a capacitance relative to plate 5, which are denoted Cl through C4, respectively.
  • Cl through C4 the capacitance relative to plate 5
  • a method of generating such voltages X and Y will be described.
  • the method is stable, simple, and uses no transformers or inductors.
  • the method is based on the fact that it is possible to apply four non-zero AC voltages to each of plates 1 through 4, with phase and amplitude such that the voltage on plate 5 is null.
  • Squarewave A controls S.P.D.T. (Single Pole Double Throw) analog switches 12, 13 so that at the common point of switch 12 there is a squarewave whose amplitude is equal to reference voltage V+ minus output voltage X, and at the common point of switch 13 there is a squarewave whose amplitude is equal to output voltage X minus reference voltage V-. Note that these two squarewaves are 180 degrees out of phase.
  • the squarewave of switch 12 is inverted by amplifiers 8, 11 and applied to plates 2, 4.
  • the squarewave of switch 13 is inverted by amplifiers 9, 10 and applied to plates 1, 3.
  • squarewave B controls S.P.D.T. analog switches 14, 15 so that at the common point of switch 14 there is a squarewave whose amplitude is equal to reference voltage V+ minus output voltage Y, and at the common point of switch 15 there is a squarewave whose amplitude is equal to output voltage Y minus reference voltage V-, and these two squarewaves are 180 degrees out of phase.
  • the squarewave of switch 14 is inverted by amplifiers 8, 9 and applied to plates 1 and 2.
  • the squarewave of switch 15 is inverted by amplifiers 10, 11 and applied to plates 3 and 4.
  • each plate is driven by a composite waveform that is the sum of two squarewaves in quadrature phase relationship. Representations of these waveforms are to be found at the bottom of FIG. 5.
  • the change in voltage on plate 5 may be considered to represent an error in output voltage X, since there is a unique voltage for X at which the change will be zero, and we would like voltage X to be this value.
  • the voltage on plate 5 is amplified by unity voltage gain amplifier 16.
  • the output of amplifier 16 drives capacitor 29 whose 5 other connection is alternately grounded and connected to integrator 19 by analog switch 17. That switch is controlled by waveform C which is generated as the NAND result of the non-inverted outputs of flip flops 22, 23. When this waveform is negative, capacitor 29 is connected to the integrator, and when it is positive, it is connected to ground.
  • the effect is to deliver a charge to the integrator that is o proportional to any change in voltage on plate 5 that occurs in the transition from state IV to state I (see FIG. 5). That charge drives the integrator in a fashion that changes voltage X in the direction that tends to reduce the error. For a given position of plate 6, voltage X will approach the value that corresponds to a null transition on plate 5 with an arbitrarily small error.
  • the change in voltage on plate 5 may be considered to represent an error in output voltage Y, since there is a unique voltage for Y at which the transition will be zero, and we would like voltage Y to be this value.
  • the voltage on plate 5 is amplified by unity voltage gain amplifier 16.
  • the output of amplifier 16 drives capacitor 30 whose other connection is alternately grounded and connected to integrator 20 by analog switch 18. That switch is controlled by waveform D which is generated as the NAND result of the inverted output of flip flop 22 and the non-inverted output of flip flop 23. When this waveform is negative, capacitor 30 is connected to integrator 20, and when it is positive, it is connected to ground.
  • the effect is to deliver a charge to the integrator that is proportional to any step change in voltage on plate 5 that occurs in the transition from state I to state II (see FIG. 5). That charge drives the integrator in a fashion that changes voltage Y in the direction that tends to reduce the error. For a given position of plate 6, voltage Y will approach the value that corresponds to a null transition on plate 5 with an arbitrarily small error.
  • the voltage X and Y that would be required to achieve null voltage changes on plate 5 may be calculated.
  • the voltage X and Y that would be required to achieve null voltage changes on plate 5 may be calculated.
  • output voltage is proportional to capacitive change, (C2 + C4) - (Cl + C3) or (Cl + C2) - (C3 + C4), relative to total capacity (Cl + C2 + C3 + C4). Therefore, output is dependent on plate spacing and the thickness and dielectric constant of plate 6. If it were possible to remove those effects of capacitive coupling to plate 5 that are due to air gap only, dependency on the properties of plate 6 and the spacing of the plates would be largely nullified.
  • inverting amplifier 27 applies the inverted sum of the voltages on plates 1 through 4 to capacitor 28.
  • the other end of this capacitor is connected to a point electrically common to sensing plate 5. If, for example, the capacitance of capacitor 28 were just equal to the sum of Cl through C4 and the gain of amplifier 27 exactly equal to -0.25, cancellation of the effects of air coupling would be achieved.
  • Capacitor 28 may be a part of the structure of the transducer so that its capacitance varies automatically with the spacing of plates 1 through 4 from plate 5, or it may be a conventional capacitor. Full, partial, or no cancellation may be appropriate, depending on the design requirements for a given application and the tolerances and materials used.
  • FIGS. 11A-D configurations of the fixed and moving plates 1-6 will now be discussed.
  • plates 1 through 4 will be rectangular or square as seen in FIG. 11A.
  • Movable nonconductive plate 6 may be rectangular in form and mechanically accessed by slender extensions as illustrated.
  • FIG. 1 IB Another approach is illustrated in FIG. 1 IB.
  • plate 6 consists of a strip with a rectangular hole. In this case, as the plate moves upward, sum (Cl + C2) decreases whereas sum (C3 + C4) increases.
  • capacitive change is as described above. So output X is as described previously, but output Y is inverted relative to up and down movement.
  • FIG. 11C illustrates an arrangement in which attachment to moveable plate 6 is by a central rod normal to the plate. Plates 1 through 4 have a cutout for protrusion of the rod.
  • FIG. 1 ID is a non-orthogonal version of FIG. 4C illustrating that coordinate axes need not be constrained to a 90- degree relationship
  • FIGS. 11A-D are far from exhaustive. They are intended to be illustrative of the fact that the invention is not dependent on some particular arrangement or shape of plates 1-6.
  • plate 6 is a very high impedance point in the circuit. It is desirable to shield this part of the circuit from external fields, yet at the same time keep stray capacity between this part of the circuit to ground at a minimum.
  • plate 7 is placed behind plate 5 as seen in
  • FIG. 3 this plate is driven by the output of buffer amplifier 16.
  • the capacitance between plates 6 and 7 may be large in comparison with Cl through C4, it has virtually no effect because buffer amplifier 16 maintains this plate at the same potential as plate 5.
  • plate 7 is not grounded, it is not significantly affected by external fields because the output of amplifier 16 has a low impedance.
  • the position transducer includes several air gap capacitors which have their values varied by movement of an insulator between them of dielectric constant greater than unity, and means to convert the capacitor values into one or two transducer outputs that are representative of the changed capacitance.
  • the position transducer includes a circuit that feeds back signals based on output voltage or output voltages to the capacitors such that a null voltage at their electrical junction results.
  • the position transducer may include a guard system to shield sensitive parts of the transducer.
  • the position transducer may further include a circuit board system, two examples of which were described above and are illustrated in FIGS. 12A-B and 13A-B.
  • the position transducer may further include conducting and nonconducting plates in the forms shown in FIGS. 6A-D, 7A-D, 10A-C, and 11A- D.
  • the position transducer may further include an air capacitance nulling system.
  • the present invention provides a position transducer which combines high accuracy, low moving mass, virtually unlimited life span and very low cost for many new applications that were not practical before now because of high cost, low performance, or limitation to one axis of available transducers.
  • FIGS. 14A and 14B data collected from a transducer according to the present invention is presented in FIGS. 14A and 14B.
  • the example transducer is a linear, single axis transducer of the second main embodiment. Plate configuration is illustrated in FIG. 10A. Data was collected over a displacement range of 0.350 inches in 0.050-inch increments, and five complete test runs were conducted.
  • FIG. 14A illustrates the excellent linearity of response
  • FIG. 14B demonstrates excellent repeatability by inspection of mean voltage output and standard deviation over the repeated trials.

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Abstract

L'invention concerne un transducteur diélectrique variable comprenant une première et une deuxième plaques électriquement conductrices (A, B), séparées d'une troisième plaque électriquement conductrice (D) de sorte que la première plaque (A) présente une première capacité (CA) relative à la troisième plaque (D), la deuxième plaque (B) présentant une seconde capacité (CB) relative à la troisième plaque (D). Ce transducteur est également pourvu d'une quatrième plaque mobile non conductrice (P), dont la constante diélectrique est supérieure à l'unité intercalée entre la première, la deuxième, et la troisième plaques (A, B, C), cette quatrième plaque recouvrant par ailleurs une partie de la première et de la deuxième plaques (A, B). Des organes sont en outre destinés à déplacer la quatrième plaque (P) entre la première, la deuxième, et la troisième plaques (A, B, C), modifiant ainsi en conséquence la première (CA) et la seconde (CB) capacités. Ce transducteur comporte enfin des organes permettant de générer un signal de transducteur représentant cette première et cette seconde capacités une fois celles-ci modifiées, grâce à l'utilisation d'une méthode de zéro.
PCT/US1999/016744 1998-07-24 1999-07-23 Transducteur de position dielectrique variable et son procede d'utilisation Ceased WO2000005593A1 (fr)

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AU51265/99A AU5126599A (en) 1998-07-24 1999-07-23 Variable dielectric position transducer and method

Applications Claiming Priority (2)

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US12223798A 1998-07-24 1998-07-24
US09/122,237 1998-07-24

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Cited By (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2817033A1 (fr) * 2000-11-23 2002-05-24 Hitachi Comp Products Europ Sa Disposistif de mesure exploitant une mesure indirecte de permettivite comprenant des moyens de compensation en derive
FR2817035A1 (fr) * 2000-11-23 2002-05-24 Hitachi Comp Products Europ Sa Dispositif de mesure exploitant une mesure indirecte de permittivite a sondes mulitiples
FR2817034A1 (fr) * 2000-11-23 2002-05-24 Hitachi Comp Products Europ Sa Dispositif de mesure exploitant une mesure indirecte de permettivite a reponse rapide
FR2817036A1 (fr) * 2000-11-23 2002-05-24 Hitachi Comp Products Europ Sa Dispositif de mesure exploitant une mesure indirecte de permettivite a grande dynamique
FR2817032A1 (fr) * 2000-11-23 2002-05-24 Hitachi Comp Products Europ Sa Perfectionnements aux dispositifs de mesure exploitant une mesure indirecte de permittivite
WO2002042721A1 (fr) * 2000-11-23 2002-05-30 Hitachi Computer Products (Europe) S.A. Dispositif de mesure capacitif
WO2008064501A3 (fr) * 2006-12-01 2008-07-31 Hsr Hochschule Fuer Technik Ra Système pour mesurer une grandeur physique
EP2876407A1 (fr) * 2013-11-26 2015-05-27 Semtech Corporation Interface de détection capacitive pour une détection de proximité
EP2865282B1 (fr) 2013-09-03 2018-04-18 Hauni Maschinenbau GmbH Système et procédé de contrôle d'articles en forme de tige de l'industrie de traitement du tabac

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US3312892A (en) * 1964-05-04 1967-04-04 Technology Instr Corp Of Calif Contactless electrical transducer having moving parts
US3702957A (en) * 1970-01-23 1972-11-14 Peter Caleb Frederick Wolfenda Variable capacitance displacement transducers
US4339709A (en) * 1979-04-09 1982-07-13 Facom Device for measuring the relative position of two objects
US4584885A (en) * 1984-01-20 1986-04-29 Harry E. Aine Capacitive detector for transducers
US5767686A (en) * 1995-03-30 1998-06-16 Fife Corporation Device for contactless detection of the position of a moving web

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3312892A (en) * 1964-05-04 1967-04-04 Technology Instr Corp Of Calif Contactless electrical transducer having moving parts
US3702957A (en) * 1970-01-23 1972-11-14 Peter Caleb Frederick Wolfenda Variable capacitance displacement transducers
US4339709A (en) * 1979-04-09 1982-07-13 Facom Device for measuring the relative position of two objects
US4584885A (en) * 1984-01-20 1986-04-29 Harry E. Aine Capacitive detector for transducers
US5767686A (en) * 1995-03-30 1998-06-16 Fife Corporation Device for contactless detection of the position of a moving web

Cited By (11)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2817033A1 (fr) * 2000-11-23 2002-05-24 Hitachi Comp Products Europ Sa Disposistif de mesure exploitant une mesure indirecte de permettivite comprenant des moyens de compensation en derive
FR2817035A1 (fr) * 2000-11-23 2002-05-24 Hitachi Comp Products Europ Sa Dispositif de mesure exploitant une mesure indirecte de permittivite a sondes mulitiples
FR2817034A1 (fr) * 2000-11-23 2002-05-24 Hitachi Comp Products Europ Sa Dispositif de mesure exploitant une mesure indirecte de permettivite a reponse rapide
FR2817036A1 (fr) * 2000-11-23 2002-05-24 Hitachi Comp Products Europ Sa Dispositif de mesure exploitant une mesure indirecte de permettivite a grande dynamique
FR2817032A1 (fr) * 2000-11-23 2002-05-24 Hitachi Comp Products Europ Sa Perfectionnements aux dispositifs de mesure exploitant une mesure indirecte de permittivite
WO2002042721A1 (fr) * 2000-11-23 2002-05-30 Hitachi Computer Products (Europe) S.A. Dispositif de mesure capacitif
JP2004514883A (ja) * 2000-11-23 2004-05-20 ヒタチ、コンピュータ、プロダクツ、（ユーロプ）、ソシエテ、アノニム 静電容量型測定デバイス
WO2008064501A3 (fr) * 2006-12-01 2008-07-31 Hsr Hochschule Fuer Technik Ra Système pour mesurer une grandeur physique
EP2865282B1 (fr) 2013-09-03 2018-04-18 Hauni Maschinenbau GmbH Système et procédé de contrôle d'articles en forme de tige de l'industrie de traitement du tabac
EP2865282B2 (fr) † 2013-09-03 2024-07-24 Körber Technologies GmbH Système et procédé de contrôle d'articles en forme de tige de l'industrie de traitement du tabac
EP2876407A1 (fr) * 2013-11-26 2015-05-27 Semtech Corporation Interface de détection capacitive pour une détection de proximité

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