JP2010104181A - Surface acoustic wave actuator - Google Patents

Abstract

In a surface acoustic wave actuator, a simple structure maintains a thin structure and suppresses an increase in area, enabling accurate measurement of the relative position of a stator and a mover, and reducing size and cost. Plan.
An actuator (1) includes a stator (2) made of a piezoelectric substrate having excitation means (20) for exciting a surface acoustic wave, and is driven by the surface acoustic wave excited by the excitation means (20) to the stator (2). And a pair of position detection electrodes 4 and 5 for detecting a change in position due to the relative movement of the stator 2 and the mover 3 by a change in capacitance. And the mover 3 are provided. The electrodes 4 and 5 can be formed in the same process as the process for forming the excitation means 20 in the left and right empty areas of the surface acoustic wave propagation area in a plane and close to each other. It is easily provided without increasing the area without impairing the area.
[Selection] Figure 1

Description

  The present invention relates to an actuator that uses a driving force generated by a surface acoustic wave.

  2. Description of the Related Art Conventionally, a linear motor type surface acoustic wave actuator that moves a moving element relative to a stator made of a piezoelectric substrate by using a driving force generated by a surface acoustic wave propagating on the surface of the piezoelectric substrate is known. The driving force generated by the surface acoustic wave is transmitted from the stator to the moving element by friction. The configuration is composed of a piezoelectric substrate and a mover, and can be easily reduced in thickness. The surface acoustic wave is excited by applying high-frequency power to the interdigitated electrode formed on the surface of the piezoelectric substrate. In order to control the actuator, it is necessary to grasp the relative position of the movable element with respect to the stator. However, since friction is accompanied by slip, the magnitude of relative movement cannot always be derived from the magnitude of driving input power. That is, in order to grasp the position of the moving element, position measurement that is not based on the magnitude of input power is required.

  Therefore, the position of the moving element and the moving speed are measured by a laser distance meter or laser speedometer that detects the reflected laser light from the moving element by irradiating the moving element with laser light from the direction along the moving direction of the moving element. And is used for measurement (for example, see Non-Patent Document 1, FIG. 2. (a)).

In addition to the surface acoustic wave for driving, a surface acoustic wave for position detection is generated, and the position of the movable body is detected by detecting the reflected wave from the movable body of the surface acoustic wave. A surface acoustic wave actuator that controls movement is known (for example, see Patent Document 1).
M. Kay. Kurosawa et al., “Elastic friction drive of surface acoustic wave motor”, Ultrasonics 41, pp 271-275 (2003) JP 2007-259670 A

  However, in the position measurement using the laser beam as described above, a measuring device is separately attached, so that the surface acoustic wave actuator is limited in size, in particular, thinning, in order to secure the external place. Therefore, mechanical adjustment is required. Also, in position measurement using surface acoustic waves for position detection, a region for creating a cross finger electrode for surface acoustic wave excitation is added to the piezoelectric substrate, so that the surface acoustic wave actuator can be made thin. However, the area is widened and size reduction is limited.

  The present invention solves the above-described problems, and is a small size that can achieve a precise measurement of the relative position of the stator and the mover while maintaining a thin structure and suppressing an increase in area with a simple structure. An object of the present invention is to provide a low-cost surface acoustic wave actuator.

  In order to achieve the above object, a first aspect of the present invention provides a stator comprising a piezoelectric substrate having excitation means for exciting a surface acoustic wave, and the piezoelectric driven by the surface acoustic wave excited by the excitation means. In a surface acoustic wave actuator comprising a mover that moves relative to a substrate, a pair of position detections for detecting a change in position due to a relative movement of the stator and the mover by a change in capacitance Are provided on the stator and the movable body.

  According to a second aspect of the present invention, in the surface acoustic wave actuator according to the first aspect, the width of the stator-side electrode in the direction perpendicular to the moving direction changes along the moving direction.

  According to a third aspect of the present invention, in the surface acoustic wave actuator according to the second aspect, the length of the moving side electrode in the moving direction is shorter than that of the stator side.

  According to a fourth aspect of the present invention, in the surface acoustic wave actuator according to any one of the first to third aspects, the electrode includes two pairs for detecting a large displacement and for detecting a small displacement. On the stator side of the electrode pair for use, electrodes having a shorter length in the moving direction than the stator side of the electrode pair for detecting large displacement are repeatedly arranged along the moving direction.

  According to a fifth aspect of the present invention, in the surface acoustic wave actuator according to the first aspect, the electrodes on the stator side are formed by repeatedly arranging electrodes of a predetermined length at regular intervals along the moving direction. The electrode is composed of one electrode having the same length as the predetermined length.

  According to a sixth aspect of the present invention, in the surface acoustic wave actuator according to the fifth aspect of the present invention, a strip-like electrode extending in the moving direction in parallel with the repeatedly arranged electrode is further provided on the stator side, Are connected in series across the electrodes arranged repeatedly and the strip electrode, and the change in position is detected by the change in the capacitance connected in series.

  A seventh aspect of the present invention is the surface acoustic wave actuator according to the fifth or sixth aspect, wherein the electrode arranged repeatedly has a capacitance of a sine wave function due to relative movement of the electrode on the movable element side. The shape changes according to the above.

  The invention according to claim 8 is the surface acoustic wave actuator according to claim 1, wherein the stator side of the position detecting electrode is configured by repeatedly arranging a predetermined length of electrode along the moving direction at regular intervals. The electrode on the mover side has a length straddling the two adjacent electrodes arranged repeatedly, and the change in position is connected in series with each other formed by the electrode on the mover side and the two electrodes straddling the electrode. It is detected by a change in the capacitance.

  According to a ninth aspect of the present invention, in the surface acoustic wave actuator according to any one of the fifth to eighth aspects, the electrical signal accompanying the change in the capacitance is acquired and the electrical signal intensity is binarized. A measurement output circuit for outputting a signal is provided.

  According to a tenth aspect of the present invention, in the surface acoustic wave actuator according to any one of the fifth to ninth aspects, the position detection electrode includes two pairs, and the predetermined length and repetition of the one pair of electrodes. The interval is different from the predetermined length and repetition interval of the other pair of electrodes.

  An eleventh aspect of the invention is the surface acoustic wave actuator according to any one of the fifth to ninth aspects, wherein two pairs of the position detecting electrodes are provided, and the arrangement phases of the repetitive electrodes of the two pairs are set to each other. It is different.

  According to the first aspect of the present invention, since the pair of position detection electrodes can be configured to be planar and close to each other, the entire surface acoustic wave actuator (hereinafter simply referred to as an actuator) can be made thin. Can be formed. In general, the propagation direction of the surface acoustic wave is parallel to the direction of relative movement of the stator and the mover, and the position detection electrode is, for example, either the left or right of the propagation region of the surface acoustic wave on the surface of the piezoelectric substrate. In the empty area and the buffer area, an increase in the area of the entire actuator can be suppressed. In addition, since the position detection electrodes can be formed simultaneously by the same film forming process or etching process as the process for forming the excitation means such as the interdigitated electrodes on the piezoelectric substrate, it can be formed with high accuracy, easy and low cost. In addition, the device for measuring the capacitance needs only to be electrically wired to the position detection electrode separately from the actuator. Installation space for sensors when using a laser distance meter, additional mechanism, adjustment during installation And the like, and an increase in cost due to an increase in the number of parts, an increase in material cost accompanying an increase in the size of the piezoelectric substrate material, an increase in assembly man-hours, etc. can be suppressed.

  According to the invention of claim 2, by setting the electrode shape, and hence the capacitance between the electrodes, to a specific shape in a specific region of the relative movement position, the position measurement sensitivity in that region is increased or decreased. Thus, position measurement according to the usage application of the actuator can be easily realized at low cost.

  According to the invention of claim 3, since the position detecting electrode on the movable element side can be made small, the electrode arrangement portion on the movable element side can be made a small space.

  According to the invention of claim 4, the usability of the actuator is improved by combining the position measurement with a low resolution by the electrode for detecting a large displacement and the position measurement with a high resolution by an electrode for detecting a small displacement. For example, long distance movement and high position accuracy stop can be performed at higher speed.

  According to the invention of claim 5, the area of the moving element can be made smaller than the area of the stator. In addition, an analog signal having a constant period corresponding to the movement position obtained by moving the electrode on the mover side in a fixed direction with respect to the electrode on the stator side arranged repeatedly can be used for the position control of the actuator. In this case, the position of relative movement can be compensated based on the periodic phenomenon.

  According to the invention of claim 6, since it is not necessary to connect a lead wire for taking out an electric signal to the electrode on the moving element side, the structure of the electric circuit can be simplified, and a highly reliable actuator free from problems of wiring. Can be realized.

  According to the invention of claim 7, various control methods based on a sine wave signal generally used in AC electric appliances can be used.

  According to the eighth aspect of the present invention, since it is not necessary to connect a lead wire for taking out an electric signal to the electrode on the moving element side, the structure of the electric circuit can be simplified, and a highly reliable actuator free from wiring defects and the like. Can be realized.

  According to the ninth aspect of the present invention, digital control using a binarized signal can be performed. For example, the relative movement position can be measured by counting the number of pulses, and can be easily controlled by a CPU having a small processing capability. In addition, the influence of noise can be reduced by digital control.

  According to the tenth aspect of the present invention, the movement direction of the relative movement can be determined by comparing the position detection signals from the two pairs of position detection electrodes, so that the movement position can be uniquely determined.

  According to the eleventh aspect of the present invention, the movement direction of the relative movement can be determined by comparing the phases of the position detection signals from the two pairs of position detection electrodes, so that the movement position can be uniquely determined.

(First embodiment)
Hereinafter, a surface acoustic wave actuator according to an embodiment of the present invention will be described with reference to the drawings. The surface acoustic wave actuator 1 according to the first embodiment includes a stator 2 composed of a piezoelectric substrate having excitation means 20 for exciting a surface acoustic wave as shown in FIGS. And a mover 3 which is arranged on the surface of the piezoelectric substrate and is driven by the surface acoustic wave excited by the excitation means 20 to move relative to the stator 2, and by relative movement of the stator 2 and the mover 3. Position detection electrodes 4 and 5 are provided on the stator 2 and the movable element 3 to detect a change in position by a change in capacitance. Here, the stator 2 and the mover 3 move relative to each other, and there is no limitation on which is fixed and which is moved regardless of the name. Further, in this specification, the relative position of the mover 3 with respect to the stator 2 is represented by a coordinate value on the x coordinate defined by being fixed to the stator 2. The direction of relative movement is the positive or negative direction of the x-axis (this is also referred to as the left-right direction, the front-rear direction, or the length direction). Hereafter, each structure is explained in full detail.

The piezoelectric substrate constituting the stator 2 is a substrate made of a piezoelectric body itself such as LiNbO ₃ (lithium niobate), for example. The piezoelectric substrate may be a non-piezoelectric substrate formed with a piezoelectric thin film, for example, a PZT thin film (lead, zirconium, titanium alloy thin film). A surface acoustic wave is excited in the surface portion of the piezoelectric thin film on the surface. Accordingly, the piezoelectric substrate may be any substrate provided with a piezoelectric body portion on which the surface acoustic wave is excited, and the surface shape is not limited to a flat surface as shown in the present embodiment, but may be a cylindrical surface or a general surface. It may be a non-planar shape made of a curved surface.

  The excitation means 20 is constituted by a so-called comb-shaped electrode (interstitial electrode, IDT: inter digital transducer) formed by engaging two electrodes on the surface of the piezoelectric substrate. Two excitation means 20 are provided on both the front and rear sides of the moving element 3 for forward movement and backward movement. Each excitation means 20 is provided with a comb-shaped electrode 21 for reflecting and effectively utilizing the surface acoustic wave. Comb teeth adjacent to each other of the comb-shaped electrodes of the excitation means 20 belong to different electrodes, and are arranged at a pitch that is half the wavelength of the surface acoustic wave to be excited. By applying a high frequency (MHz band) voltage from the high frequency voltage power source E between the two comb electrodes, the electrical energy is converted into mechanical waves by the comb electrodes, and surface acoustic waves are excited on the surface of the piezoelectric substrate. Is done. The amplitude of the excited surface acoustic wave is determined by the magnitude of the excitation voltage applied to the electrode. The length of the wave packet of the excited surface acoustic wave corresponds to the length of voltage application time.

  The mover 3 is made of, for example, a hard material such as silicon, and a plurality of protrusions 32 are provided on a surface (FIG. 1B) that contacts the piezoelectric substrate. Such a protrusion 32 is manufactured by, for example, a silicon etching method. The material for forming the mover 3 may be a hard material as long as it is not silicon. The mover 3 is applied with a preload F by the preload applying means 31 and is pressed against the surface of the surface acoustic wave propagation region in the piezoelectric substrate (stator 2). When the surface acoustic wave is excited by one of the excitation means 20 in a state where the movable element 3 is pressed, the driving force accompanying the elliptical vibration of the surface acoustic wave is transmitted to the movable element 3 through the frictional force. Then, the movable element 3 is driven to move in a direction opposite to the propagation direction of the surface acoustic wave, that is, in a direction approaching the excitation means 20 that excites the wave. For example, when the right excitation means 20 shown in FIG. 1A is operated, the movable element 3 moves forward to the right by the surface acoustic wave propagating in the negative direction of the x axis, and the left excitation means 20 is operated. The mover 3 moves backward to the left.

  The protrusion on the bottom surface of the movable element 3 is for efficiently transmitting the driving force of the surface acoustic wave to the movable element 3. Further, if the driving force of the surface acoustic wave can be efficiently transmitted to the moving element 3 without the protrusion, the protrusion on the bottom surface is unnecessary. Depending on the magnitude of the preload F, the moving speed and acceleration of the moving element 3 change. The moving speed of the moving element 3 is a function of the magnitude of the excitation voltage, and the moving distance is a function of the magnitude of the excitation voltage and the excitation duration. Further, the movable distance of the movable element 3, that is, the stroke (movement range) of the surface acoustic wave actuator 1, is determined from the length in the x-axis direction of the surface area of the piezoelectric substrate sandwiched between the left and right excitation means 20. This is a length obtained by subtracting the length in the x-axis direction of the ground contact surface with respect to the stator 2.

  The position detection electrode 4 on the stator 2 side is a rectangular surface electrode whose one side is parallel to the x-axis, and is provided in a region on the surface of the piezoelectric substrate that does not hinder the propagation of surface acoustic waves. The electrode 5 for position detection on the side of the moving element 3 is a surface electrode facing the surface of the piezoelectric substrate, and is formed on a holding member 50 fixed to the moving element 3 so as to form a parallel plane electrode capacitor together with the electrode 4. It is configured. The shape of the electrode 5 is the same as the shape of the electrode 4. However, more generally, in the shape of the electrodes 4 and 5, the overlapping area of the electrodes 4 and 5 in plan view changes due to the relative movement of the stator 2 and the mover 3 in the stroke range of the surface acoustic wave actuator 1. Any shape is acceptable. Further, the electrode 4 does not need to be provided between the left and right excitation means 20, and therefore the length of the electrode 4 in the x direction is not limited to the distance between the left and right excitation means 20.

  A change in position, that is, a movement distance due to relative movement of the stator 2 and the mover 3 in the surface acoustic wave actuator 1 is detected by detecting a change in capacitance between the position detection electrodes 4 and 5. For example, a measurement output circuit 10 such as a capacitance measuring device or a charge measuring device can be connected to the electrodes 4 and 5, and the moving distance can be obtained based on the circuit output. Moreover, although the sensitivity can be improved as the distance between the electrodes 4 and 5 becomes shorter, it is limited by mechanical accuracy. That is, as the distance between the surfaces is shorter, the variation in the measured value is affected by the variation in the distance between the surfaces. Therefore, the distance between the surfaces may be determined in consideration of the allowable variation and the machine accuracy.

  Next, the principle of the above-mentioned movement distance measurement will be described with reference to FIGS. As shown in FIGS. 3A and 3B, when the electrode 5 on the mover 3 side moves in the x-axis direction from the maximum overlap state to the zero overlap state in a plan view with respect to the electrode 4 on the stator 2 side. The capacitance between the electrodes, and hence the amount of charge Q accumulated between the electrodes under a constant voltage, varies from the maximum value to the minimum value zero as shown in FIG. By measuring in advance such a functional relationship Q = Q (x) between the x-coordinate value representing the position of the movable element 3 relative to the stator 2 and the charge amount Q, the relative movement position of the movable element 3 can be determined. Can be sought. In the case of the relationship of Q = Q (x) shown in FIG. 4, the charge amount Q is a linear function of x, and the position of the mover 3 is uniquely determined. When the lengths of the electrodes 4 and 5 in the x-axis direction (moving direction) are the same as in the present embodiment, the distance corresponding to the electrode length is the stroke length that can determine the position of the moving element 3.

  Next, modified examples of the position detection electrodes 4 and 5 will be described with reference to FIGS. In this modified example, as shown in FIGS. 5A, 5B, and 5C, the electrode 5 on the moving element 3 side overlaps the electrode 4 on the stator 2 side from the state of zero overlap in plan view. When moving in the x direction to the state of zero overlap through the overlap state, the charge amount Q accumulated between the electrodes changes from zero to zero after reaching the maximum value as shown in FIG. In the case of this modification, if the lengths of the electrodes 4 and 5 in the x direction are the same as described above, a distance that is twice the electrode length is a stroke length that can determine the position of the movable element 3. However, in the case of the functional relationship of Q = Q (x) shown in FIG. 6, the charge amount Q is locally a linear function of x. Since coordinate values exist, the position of the mover 3 cannot be uniquely determined. In such a configuration of the electrodes 4 and 5 and the position measuring method, the moving element 3 is moved by grasping by which means the position of the moving element 3 is on the side of the peak value in the graph of Q = Q (x). The position of the child 3 can be determined uniquely.

  According to the surface acoustic wave actuator 1 of the present embodiment, the pair of position detection electrodes 4 and 5 can be configured to be planar and close to each other, so that the entire surface acoustic wave actuator 1 is not thinned. It can form without. In general, the propagation direction of the surface acoustic wave and the relative movement direction of the stator 2 and the mover 3 are parallel to each other, and the electrodes 4 and 5 are piezoelectric as shown in FIG. It can be provided in an empty region or a buffer region on either the left or right side of the surface acoustic wave propagation region on the substrate surface without increasing the area of the entire actuator. Further, since the electrodes 4 and 5 can be simultaneously formed by the same film forming process or etching process as the process for forming the excitation means 20 such as the interdigitated electrode on the piezoelectric substrate, the electrodes 4 and 5 can be formed with high accuracy, easy and low cost. In addition, the measurement circuit for measuring the capacitance may be separated from the surface acoustic wave actuator 1 and electrically wired to the electrode for position detection, and the installation space for the sensor when using the laser distance meter in the conventional example, An additional mechanism and adjustment at the time of installation are unnecessary, and an increase in cost due to an increase in the number of parts, an increase in material cost accompanying an increase in the size of the piezoelectric substrate material, and an increase in assembly man-hours can be suppressed.

  By the way, since the measurement sensitivity improves as the overlap of the electrodes 4 and 5 in plan view increases, it is desirable to increase the area of the electrodes 4 and 5. Therefore, for example, the electrodes 4 and 5 in FIG. 1 (a) have substantially the entire length of the region where the excitation means 20 is separated, and the electrode 5 on the movable element 3 side is excited when the movable element 3 is at the right end of the stroke. The comb electrode of the means 20 can be covered. This is because the length in the x-axis direction of the electrode 5 formed on the holding member 50 fixed to the moving element 3 can be set without being limited by the length of the moving element 3. In this case, care must be taken so that the electrode 5 does not receive noise from the excitation means 20.

(Second Embodiment)
The surface acoustic wave actuator according to the second embodiment will be described with reference to FIGS. The surface acoustic wave actuator 1 according to the present embodiment is different from the first embodiment shown in FIG. 1 described above in terms of position detection electrodes 4 and 5, and the other points are the same. In the following embodiments, only the electrodes 4 and 5 are different and will be described with reference to FIGS. 1 and 2 as appropriate.

  As shown in FIGS. 7A, 7B, and 7C, the electrode 4 on the stator 2 side in the surface acoustic wave actuator 1 of the present embodiment is on the negative side of the x-axis of the electrode 4 in the first embodiment. It is a triangular electrode in which one side is replaced with a vertex, and the electrode 5 on the movable element 3 side is the same rectangle as the electrode 5 in the first embodiment. The relative movement of the electrodes 4 and 5 is the same as that of the modification of the first embodiment shown in FIG. 5, and the distance of twice the length of the electrodes 4 and 5 in the x-axis direction is moved. The stroke length is such that the position of the child 3 can be determined. When the electrode 5 on the mover 3 side moves in the x direction from the zero overlap state to the zero overlap state in plan view from the zero overlap state with respect to the stator 2 side electrode 4, it is accumulated between the electrodes. As shown in FIG. 8, the charge amount Q varies from zero to a maximum value to zero. A curve indicating a change in the charge amount Q is a part of a parabola, and Q is a quadratic function of x. Whether or not the position of the movable element 3 can be determined uniquely is limited and unique as in the modification of the first embodiment.

  More generally describing the shape of the electrode 4 on the stator 2 side in this embodiment, the width of the electrode 4 in the direction orthogonal to the moving direction (x-axis direction) of the moving element 3 (hereinafter simply referred to as the width) moves. It is a shape that varies rather than constant along the direction. Further, as described above, since the stator 2 and the mover 3 move relative to each other, the width of the electrode 5 on the mover 3 side is not constant along the x-axis direction. Can do. Furthermore, the widths of both electrodes 4 and 5 can be changed along the x-axis direction. By changing the widths of the electrodes 4 and 5 in this way, the functional relationship Q = Q (x) between the x coordinate value representing the position of the movable element 3 and the charge amount Q can be set to a desired function. .

  FIG. 9 shows a modification of the electrodes 4 and 5. As shown in FIGS. 9A, 9B, and 9C, each of the electrodes 4 and 5 has a triangular shape, and the width changes along the x-axis direction. Such a functional relationship Q = Q (x) in the electrodes 4 and 5 is a symmetrical parabola as shown in FIG. 9D.

  According to the surface acoustic wave actuator 1 of the present embodiment, the shape of the electrodes 4 and 5, and hence the capacitance between the electrodes and the charge amount Q are specified in a specific region of the relative movement position, that is, a specific range of the x coordinate. The position measurement sensitivity in the specific area is increased or decreased by setting the shape of the surface acoustic wave, so that the position measurement having the accuracy according to the usage and usage of the surface acoustic wave actuator 1 can be easily performed at low cost. realizable. For example, the sensitivity increases when the slope at Q = Q (x) is large. Thus, the slope of the Q (x) characteristic varies depending on the electrode shape of the position detection electrodes 4 and 5, and the resolution can be changed depending on the location.

(Third embodiment)
A surface acoustic wave actuator according to a third embodiment will be described with reference to FIGS. As shown in FIGS. 10A, 10B, and 10C, the surface acoustic wave actuator 1 according to the present embodiment moves in the moving direction of the electrode 5 on the mover side according to the second embodiment shown in FIG. Is different from the second embodiment in that the length is shorter than the electrode 4 on the stator side, and the other points are the same.

  When the electrode 5 moves in the x-axis direction with respect to the electrode 4, the capacitance between the electrodes or the accumulated charge amount Q shows x-coordinate dependency divided into three as shown in FIG. 11. The three sections include a state in which the rear edge of the electrode 5 in the x-axis direction protrudes from the rear end of the electrode 4 in a plan view, a state in which the entire length of the electrode 5 is included in the length of the electrode 4, 5 corresponds to a state in which the front edge in the x-axis direction protrudes from the front end of the electrode 4. In each section, Q = Q (x) becomes a quadratic curve, a primary curve, and a quadratic curve in order.

  According to the surface acoustic wave actuator 1 of the present embodiment, since the position detecting electrode 5 on the movable element 3 side can be made small, the electrode arrangement portion on the movable element side, that is, the holding member 50 can be formed in a small space. In addition, by using the portion where Q (x) shown in FIG. 11 is a linear function of x for the position control of the moving element 3, it is possible to realize control that is intuitively easy to understand.

(Fourth embodiment)
A surface acoustic wave actuator according to a fourth embodiment will be described with reference to FIGS. As shown in FIG. 12, the surface acoustic wave actuator 1 in the present embodiment has a triangular electrode similar to the electrodes 4 and 5 in the surface acoustic wave actuator 1 of the third embodiment described above and a rectangular shape with a short length. There are provided two pairs of electrodes 4 and 5 for detecting minute displacements and electrodes 6 and 7 for detecting large displacements. The electrode 4 for detecting minute displacement on the stator 2 side repeats the element electrode 41 having a shorter moving direction (x-axis direction) along the moving direction than the electrode 6 for detecting large displacement on the stator 2 side. It is arranged and configured. The electrodes 5 and 6 on the side of the moving element 3 are fixed to the moving element 3 and integrally move along the x-axis direction. Each pair of the electrodes 4 and 5 and the electrodes 6 and 7 is independently connected to the measurement output circuits 10 and 11 to measure capacitance and charge. The measurement results by the measurement output circuits 10 and 11 are output to the control circuit 12 that integrates these results and controls the position of the moving element 3.

  When the electrode 5 moves in the x-axis direction with respect to the electrode 4, the charge amount Q between the electrodes varies according to a sawtooth waveform as a curve q1 shown in FIG. The unit waveform of the sawtooth waveform corresponds to the roughly triangular waveform shown in FIG. 11 in the third embodiment described above. When the electrode 7 moves in the x-axis direction with respect to the electrode 6, the charge amount Q between the electrodes has a large roughly triangular waveform as shown by a curve q2 shown in FIG. In the case of this embodiment, the total length of the row of the plurality of element electrodes 41 and the length of the electrodes 6 are equal. Therefore, the range of the curve q1 and the range of the curve q2 on the x coordinate axis in FIG. 13 are the same. However, the total length of the row and the length of the electrode need not be limited in this way, and can be in an arbitrary relationship.

  According to the surface acoustic wave actuator 1 of this embodiment, an actuator is obtained by combining position measurement with low resolution by the electrodes 6 and 7 for detecting large displacement and position measurement with high resolution by the electrodes 4 and 5 for detecting minute displacements. The convenience of 1 is improved. For example, long distance movement and high position accuracy stop can be performed at higher speed.

(Fifth embodiment)
A surface acoustic wave actuator according to a fifth embodiment will be described with reference to FIGS. As shown in FIG. 14, the electrode 4 on the stator 2 side of this embodiment is configured by repeatedly arranging rectangular element electrodes 41 having a predetermined length along the x-axis direction at regular intervals. The electrode 5 is composed of one electrode having the same length as the predetermined length. This corresponds to a configuration in which the electrode 4 in the first embodiment is repeatedly arranged as the element electrode 41 at regular intervals along the x-axis direction, and the electrode 5 is left as it is. However, in the case where the entire electrode 4 composed of the row of element electrodes 41 is disposed in the separation region of the excitation means 20, the entire electrodes 4 and 5 are reduced in a certain proportion in the length direction.

  When the electrode 5 moves in the x-axis direction with respect to the electrode 4, the charge amount Q between the electrodes 4 and 5 varies according to a triangular waveform repetition curve as shown in FIG. When the length of the electrode 5 in the x-axis direction is equal to or shorter than the distance between the element electrodes 41, the minimum value of the charge amount Q is zero.

  According to the surface acoustic wave actuator 1 of the present embodiment, since the length of the electrode 5 can be made smaller than that of the electrode 4, the area of the moving element 3 can be made smaller than the area of the stator 2. Further, an analog signal based on the charge amount Q periodically generated according to the electrode 4 on the stator 2 side that is repeatedly arranged can be used for position control of the actuator. In this case, the position of the relative movement can be compensated by the periodic behavior on the assumption that the moving direction of the moving element 3 is known. Further, the moving direction of the moving element 3 can be grasped naturally when moving only in a certain direction during a series of operations, and can be grasped by referring to the moving limit when there is a moving limit.

(Sixth embodiment)
A surface acoustic wave actuator according to a sixth embodiment will be described with reference to FIGS. As shown in FIG. 16, the electrode 4 on the stator 2 side of the present embodiment is electrostatically coupled to the rectangular element electrode 41 in the fifth embodiment described above by the relative movement of the electrode 5 on the mover 3 side. The capacity changes according to a sine wave function. When the electrode 5 moves in the x-axis direction with respect to the electrode 4, the charge amount Q between the electrodes 4 and 5 varies according to a sinusoidal repeating curve as shown in FIG. When the length of the electrode 5 in the x-axis direction is equal to or shorter than the distance between the element electrodes 41, the minimum value of the charge amount Q is zero.

  According to the surface acoustic wave actuator 1 of the present embodiment, various control methods based on a sine wave signal generally used in AC electric equipment and the like can be easily incorporated in the control of the surface acoustic wave actuator 1.

(Seventh embodiment)
The surface acoustic wave actuator according to the seventh embodiment will be described with reference to FIGS. On the stator 2 side of the present embodiment, as shown in FIG. 18A, an electrode 4 similar to the electrode 4 in the above-described fifth embodiment is provided, and in addition to the electrode 4, it is repeatedly arranged. A strip electrode 40 extending in the movement direction is provided in parallel with the element electrode 41. The electrode 5 on the movable element 3 side has the same length as the electrode 5 in the fifth embodiment, and the capacitance is connected in series across the element electrode 41 and the strip electrode 40 that are repeatedly arranged. Thus, the electrode is widened. Accordingly, the change in the position of the movable element 3 in the x-axis direction is caused by the capacitance C1 changing between the electrodes 4 and 5 and the band electrode 40 and the electrode 5 as shown in the equivalent circuit of FIG. The constant capacitance C0 is detected by a change in capacitance connected in series. Further, as shown in FIG. 19, the same configuration as that shown in FIGS. 18A and 18B can be realized by adding the strip electrode 40 in the sixth embodiment in the same manner as described above.

  According to the surface acoustic wave actuator 1 of the present embodiment, it is not necessary to connect a lead wire for extracting an electric signal to the electrode 4 on the movable element 3 side. A highly reliable actuator can be realized.

(Eighth embodiment)
A surface acoustic wave actuator according to an eighth embodiment will be described with reference to FIGS. In this embodiment, instead of the strip electrode 40 in the seventh embodiment, every other element electrode 41 is used as an electrode for capacitive coupling. Therefore, instead of the electrode 5 widened in the width direction in the seventh embodiment, the electrode 5 is extended in the length direction. That is, as shown in FIG. 20A, the stator 2 side of the position detection electrode is configured by repeatedly disposing element electrodes 41 having a predetermined length at regular intervals along the moving direction. The electrode 5 has a length that extends over two adjacent element electrodes 41 that are repeatedly arranged.

  Further, the change in the position of the movable element 3 in the x-axis direction is such that the capacitances C1 and C2 that increase and decrease between the two element electrodes 41 and the electrode 5 as shown in the equivalent circuit of FIG. Is detected by a change in capacitance connected in series. When the electrode 5 moves in the x-axis direction with respect to the electrode 4, the charge amount Q between the electrodes 4 and 5 is formed by connecting capacitances C1 and C2 that increase and decrease to each other in series as shown in FIG. It fluctuates according to a repetitive curve of a chevron waveform that reflects a change in capacitance.

  According to the surface acoustic wave actuator 1 of this embodiment, as in the seventh embodiment, it is not necessary to connect a lead wire for extracting an electric signal to the electrode 4 on the moving element 3 side. A simple and reliable actuator with no wiring defects can be realized.

(Ninth embodiment)
A surface acoustic wave actuator according to a ninth embodiment will be described with reference to FIGS. In the present embodiment, as shown in FIG. 22, the measurement output circuit 10 in the eighth embodiment acquires an electrical signal associated with the change of the capacitance C, C = C1 + C2, and at the same time, the binary of the electrical signal strength. This is a surface acoustic wave actuator 1 having a function of outputting an activating signal. The measurement output circuit 10 includes a resistor R, a voltage source V, and a comparator CP. The resistor R is connected to one terminal a of both terminals a and b of the capacitor C and the positive electrode of the constant voltage source V, and the negative electrode of the constant voltage source V is connected to the ground terminal b. An electric signal is input from the terminal a to the positive input terminal of the comparator CP, and a threshold voltage Vref is input to the negative input terminal. When the input voltage from the terminal a is larger than the threshold voltage Vref, the binarized signal Vs is output from the output terminal of the comparator CP.

  The electric signal accompanying the change in the capacitance C is binarized by a threshold value TH corresponding to the threshold voltage Vref as shown in the graph of the charge amount Q in FIG. The binarized signal shown in b) is output.

  According to the surface acoustic wave actuator 1 of the present embodiment, digital control using a binarized signal can be performed. For example, the relative movement position can be measured by counting the number of pulses accompanying the periodic change of the capacitance C and the charge amount Q, and can be easily controlled even by a CPU having a small processing capability. In addition, the influence of noise can be reduced by digital control.

(Tenth embodiment)
The surface acoustic wave actuator according to the tenth embodiment will be described with reference to FIGS. The present embodiment corresponds to an arrangement including two pairs of electrode positions for detecting the moving position in the eighth embodiment. In this case, as shown in FIG. 24, the length of the element electrode 41 and the electrode 5 in one pair of electrodes 4 and 5, the repetition interval of the element electrode 41, and the element electrode 61 in the other pair of electrodes 6 and 7 are used. The length of the electrode 7 and the repetition interval of the element electrode 61 are different from each other between the pairs. The electrodes 5 and 7 move together with the moving element 3.

  According to the surface acoustic wave actuator 1 of this embodiment, by comparing the position detection signals from the two pairs of position detection electrodes 4 and 5 and the electrodes 6 and 7, the moving direction of the relative movement can be determined. The moving position can be uniquely determined. That is, as shown in FIG. 25, the x coordinate value indicating the same Q (x) value on both sides of the peak value in each waveform indicated by the curve q1 can be identified by Q (x) in the curve q2. Therefore, by setting the repeated arrangement of the element electrodes 41 and 61 so that the peaks of the curves q1 and q2 do not overlap with the same x coordinate value, the x coordinate value of the movable element 3 can be uniquely determined over a wide range.

(Eleventh embodiment)
The surface acoustic wave actuator according to the eleventh embodiment will be described with reference to FIGS. The present embodiment corresponds to the two pairs of electrode positions for detecting the moving position in the fifth embodiment (FIG. 14) and the seventh embodiment (FIG. 19), and the arrangement phase of the repeated electrodes of both pairs. Are different from each other. That is, according to the configuration based on FIG. 14 of the fifth embodiment, as shown in FIG. 26, the pair of electrodes 4 and 5 and the pair of electrodes 6 and 7 have the same shape in the length direction and the repeated structure. These electrode pairs are arranged, for example, by shifting the electrode arrangement phase by a quarter. The width of each electrode of the electrodes 4 and 5 and the width of each electrode of the electrodes 6 and 7 may be the same or different as in this example. Measurement output circuits 10 and 11 are individually connected to each electrode pair to measure capacitance and charge. The measurement results by the measurement output circuits 10 and 11 are output to the control circuit 12 that integrates these results and controls the position of the moving element 3.

  When the electrodes 5 and 7 move in the x-axis direction with respect to the electrodes 4 and 6, respectively, the charge amount Q in each electrode pair is out of phase with each other as shown by the curves q1 and q2 having a periodic triangular waveform shown in FIG. It will be in a shifted state. The electrodes 5 and 7 move together with the moving element 3.

  Further, according to the configuration based on FIG. 19 of the seventh embodiment, as shown in FIG. 28A, a pair of electrodes 4 and 5 having the strip electrode 40 and a pair of electrodes 6 and 7 having the strip electrode 60 are formed. Are electrode pairs having the same shape in the length direction and a repetitive structure, and these electrode pairs are arranged, for example, by shifting the electrode arrangement phase by a quarter (interval δ in the figure). Measurement output circuits 10 and 11 are individually connected to each electrode pair to measure capacitance and charge. The measurement results by the measurement output circuits 10 and 11 are output to the control circuit 12 that integrates these results and controls the position of the moving element 3. An equivalent circuit of these electrode pairs and the measurement circuit has a configuration shown in FIG.

  When the electrodes 5 and 7 move in the x-axis direction with respect to the electrodes 4 and 6, the charge amount Q in each electrode pair is out of phase with each other as shown by the curves q1 and q2 having a sine waveform shown in FIG. It becomes a state. The electrodes 5 and 7 move together with the moving element 3.

  According to the surface acoustic wave actuator 1 of this embodiment, the moving direction of the relative movement can be determined by comparing the phases of the position detection signals from the two pairs of position detection electrodes. Coordinate value) can be uniquely determined. 30A shows a configuration in which the strip electrodes 40 and 60 in FIG. 28A are shared, and FIG. 30B shows an equivalent circuit thereof.

  The present invention is not limited to the configurations shown in the above embodiments, and various modifications can be made. For example, the configurations of the above-described embodiments can be combined with each other. Moreover, the excitation means 20 can also be only one of the forward movements.

(A) is a top view of the surface acoustic wave actuator which concerns on the 1st Embodiment of this invention, (b) is the sectional view on the AA line of (a). The perspective view of a surface acoustic wave actuator same as the above. (A) (b) is a perspective view which shows the structure and position measurement principle of the position detection electrode of a surface acoustic wave actuator same as the above. The graph which shows the electric charge change with respect to the position change of the electrode for position detection same as the above. (A) (b) (c) is a perspective view which shows the modification of the position detection electrode of a surface acoustic wave actuator same as the above, and the position measurement principle. The graph which shows the electric charge change with respect to the position change of the electrode for position detection same as the above. (A) (b) (c) is a perspective view which shows the structure and position measurement principle of the position detection electrode of the surface acoustic wave actuator which concern on 2nd Embodiment. The graph which shows the electric charge change with respect to the position change of the electrode for position detection same as the above. (A) (b) (c) is a plan view showing a modification of the position detection electrode and the position measurement principle of the position detection electrode, (d) is a graph showing the charge change with respect to the position change of the position detection electrode. . (A) (b) (c) is a perspective view which shows the structure and position measurement principle of the position detection electrode of the surface acoustic wave actuator which concern on 3rd Embodiment. The graph which shows the electric charge change with respect to the position change of the electrode for position detection same as the above. The top view which shows the structure and position measurement principle of the position detection electrode of the surface acoustic wave actuator which concern on 4th Embodiment. The graph which shows the electric charge change with respect to the position change of the electrode for position detection same as the above. The top view which shows the structure and position measurement principle of the position detection electrode of the surface acoustic wave actuator which concern on 5th Embodiment. The graph which shows the electric charge change with respect to the position change of the electrode for position detection same as the above. The top view which shows the structure and position measurement principle of the position detection electrode of the surface acoustic wave actuator which concern on 6th Embodiment. The graph which shows the electric charge change with respect to the position change of the electrode for position detection same as the above. (A) is a top view which shows the structure and position measurement principle of the position detection electrode of the surface acoustic wave actuator which concern on 7th Embodiment, (b) is an equivalent circuit schematic of the position measurement circuit of (a). The top view which shows the other structural example and position measurement principle of the position detection electrode same as the above. (A) is a top view which shows the structure and position measurement principle of the position detection electrode of the surface acoustic wave actuator which concern on 8th Embodiment, (b) is an equivalent circuit schematic of the position measurement circuit of (a). The graph which shows the electric charge change with respect to the position change of the electrode for position detection same as the above. The circuit diagram of the measurement output circuit connected to the position detection electrode of the surface acoustic wave actuator which concerns on 9th Embodiment. (A) is a graph which shows the charge change with respect to the position change of a position detection electrode same as the above, (b) is a graph which shows the position change of the binarization signal obtained by processing the charge change of (a). The top view which shows the structure and position measurement principle of the position detection electrode of the surface acoustic wave actuator which concern on 10th Embodiment. The graph which shows the electric charge change with respect to the position change of the electrode for position detection same as the above. The top view which shows the structure and position measurement principle of the position detection electrode of the surface acoustic wave actuator which concern on 11th Embodiment. The graph which shows the electric charge change with respect to the position change of the electrode for position detection same as the above. (A) is a top view which shows the modification and position measurement principle of the position detection electrode of a surface acoustic wave actuator same as the above, (b) is an equivalent circuit diagram of the position measurement circuit of (a). The graph which shows the electric charge change with respect to the position change of the electrode for position detection same as the above. (A) is a top view which shows the modification of the electrode for position detection of Fig.29 (a), (b) is an equivalent circuit schematic of the position measurement circuit of (a).

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Surface acoustic wave actuator 2 Stator 3 Mover 4, 41, 6, 61 Electrode for position detection (stator side)
5,7 Position detection electrode (moving element side)
10, 11 Measurement output circuit 20 Excitation means 40, 60 Strip electrode

Claims (11)

Elasticity comprising: a stator composed of a piezoelectric substrate having excitation means for exciting a surface acoustic wave; and a movable element driven by the surface acoustic wave excited by the excitation means and moved relative to the piezoelectric substrate. In surface wave actuators,
A surface acoustic wave characterized in that a pair of position detection electrodes for detecting a change in position caused by relative movement of the stator and the mover by a change in capacitance is provided on the stator and the mover. Actuator.   2. The surface acoustic wave actuator according to claim 1, wherein a width of the stator-side electrode in a direction perpendicular to the moving direction changes along the moving direction.   The surface acoustic wave actuator according to claim 2, wherein a length of the moving side electrode in the moving direction is shorter than that of the stator side.   The electrodes include two pairs for detecting large displacement and detecting small displacement, and the stator side of the electrode pair for detecting small displacement is longer in the moving direction than the stator side of the electrode pair for detecting large displacement. 4. The surface acoustic wave actuator according to claim 1, wherein electrodes having short lengths are repeatedly arranged along the moving direction. 5.   The stator-side electrode is formed by repeatedly arranging electrodes having a predetermined length along the moving direction at regular intervals, and the electrode on the stator side is formed by one electrode having the same length as the predetermined length. The surface acoustic wave actuator according to claim 1. Further provided on the stator side with a strip-like electrode extending in the moving direction in parallel with the repeatedly arranged electrodes,
The electrode on the moving element side is connected in series with capacitance across the electrode repeatedly disposed and the strip electrode,
6. The surface acoustic wave actuator according to claim 5, wherein the change in position is detected by a change in the capacitance connected in series.   7. The electrode according to claim 5, wherein the electrode arranged repeatedly has a shape in which an electrostatic capacitance changes according to a sine wave function as a result of relative movement of the electrode on the movable element side. Surface acoustic wave actuator. The stator side of the electrode for position detection is configured by repeatedly arranging electrodes of a predetermined length along the movement direction at a constant interval, and the electrode on the mover side is formed by two adjacent electrodes arranged repeatedly. It is said to be the length to straddle,
2. The elastic surface according to claim 1, wherein the change in position is detected by a change in capacitance connected in series formed by an electrode on the movable element side and two electrodes straddling the electrode. Wave actuator.   9. The measurement output circuit according to claim 5, further comprising a measurement output circuit that acquires an electric signal associated with the change in the capacitance and outputs a binarized signal of the electric signal intensity. The surface acoustic wave actuator described.   The two pairs of position detection electrodes are provided, and a predetermined length and a repetition interval of the one pair of electrodes are made different from a predetermined length and a repetition interval of the other pair of electrodes. Item 10. The surface acoustic wave actuator according to any one of Items 9 to 9.   10. The surface acoustic wave actuator according to claim 5, wherein two pairs of the position detection electrodes are provided, and the arrangement phases of the pairs of repeated electrodes are made different from each other. 11.

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