JP2011024312A - Ultrasonic motor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce the cost and size of an ultrasonic motor of a self-sensing type. <P>SOLUTION: In the ultrasonic motor 1 in which a piezoelectric element rotates by the pressure contact of a moving body 13 to a vibrator 12 performing high-frequency vibration in response to a drive signal, and which periodically forms a part for changing the vibration state of a groove or the like at the contact part of the vibrator and the moving body, and eliminates the use of a sensor by an effect that a detection circuit 31 detects the change of the vibration state caused by the passage of the part, a signal converter 32 generates a pulsation waveform accompanied by the passage of the part from a change of a phase with respect to the drive signal of a detection voltage of a detection electrode, a band filter 33 extracts a pulsation component form the pulsation waveform, and at least either of a rotation position and a rotation speed is detected by counting by a counter 35. Then, since a frequency setter 36 changes a block frequency of the band filter 33 according to a frequency of the drive signal, an AC component periodically appearing at the pulsation component due to a variation of a pressurizing force at each rotation is eliminated. By this, the accuracy of assembling is alleviated. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an ultrasonic motor, and more particularly, to a small-sized super motor used for a lens driving mechanism of a micro camera unit (MCU) that can be mounted on a DSC (digital still camera), a mobile phone, or an optical pickup unit such as a DVD. The present invention relates to a sonic motor.

  Compared with electromagnetic motors, the ultrasonic motor has high torque, high holding power when stopped, and high speed (about 3 times that of stepping motors). Have. However, when speed control or position control is performed, it is necessary to separately install a position detection sensor. For mounting on a small device as described above, an electromagnetic stepping motor or voice is required in terms of arrangement and size. There are disadvantages compared to coil motors and the like, and if this point is improved, it will be very advantageous in terms of torque and efficiency over the electromagnetic type.

  Therefore, Patent Document 1 has been proposed to deal with such a problem. According to the prior art, a non-uniform structure (protrusions or the like is provided on the moving body) is provided at the contact portion between the moving body (rotor) and the vibrating body (stator), and the detection piezoelectric element is sandwiched between the piezoelectric elements. The amount of rotation of the moving body can be detected from the signal component corresponding to the positional relationship between the non-uniform structure and the detection piezoelectric element, which appears in the output of the detection piezoelectric element due to uneven surface pressure generated in the uniform structure. Self-sensing ultrasonic motors have been proposed.

JP-A-6-133570

  The above-described conventional technique is an excellent technique in which a means for detecting the rotation amount and the rotation position of an encoder or the like need not be provided separately. However, since the change in the vibration state of the vibrating body due to the change in the contact state between the moving body and the vibrating body is detected by the detecting piezoelectric element, the pressing force of the pressing member (winding spring) that presses the moving body against the vibrating body is uneven. If the output take-out shaft attached to the moving body is inclined, the pressing force of the moving body to the vibrating body is uneven due to the site, and there is a problem that accurate detection cannot be performed.

  Specifically, FIG. 16 is a diagram for explaining the waveform change of the position pulse due to the uneven pressing force. The detection voltage of the detection piezoelectric element is compared with the drive signal from the drive unit to obtain a pulsation waveform as indicated by reference numeral α1 in FIG. 16B. Amplitude changes are caused by passing through the uniform structure (detection unit) and the uniform structure (drive unit) (in the example of FIG. 16, the one higher than the reference voltage indicated by reference numeral α2 becomes the detection unit and lower) The number of pulses of the non-uniform structure (detection unit) is counted by counting the number of pulses of the non-uniform structure (detection unit). Can be detected.

  However, when the pressing unevenness occurs, as shown in FIG. 16A, the pulsation waveform indicated by the reference symbol α3 has a low-frequency periodic component (the one rotation cycle) as indicated by the reference symbol α4. (swells repeated at τ) are superimposed. The amplitude of the low frequency component may reach half of the amplitude of the pulsation waveform, which significantly reduces the S / N.

  On the other hand, in the case of an ultrasonic motor used for the micro camera unit (MCU) or the like, the rotation speed is greatly different between a case where the error is large because it is far from the target position and a case where the error near the target position is small. Varies between 2400 rpm and 120 rpm. Therefore, the frequency of the periodic component also changes in the range of 40 to 2 Hz. On the other hand, the number of the detection units is, for example, 24 per rotation period τ, and the frequency of the pulsation waveform is 960 to 48 Hz. For this reason, when the periodic component is removed by filter separation, there is a problem that a pulsation waveform having a relatively small amplitude change cannot be detected with good S / N. For this reason, high assembly accuracy is required, and the motor is increased in size and costs are increased.

  An object of the present invention is to provide an ultrasonic motor that can be reduced in cost and size.

  The ultrasonic motor of the present invention includes a driving unit, a vibrating body in which a piezoelectric element performs high-frequency vibration in response to a driving signal from the driving unit, and a movable body that is in pressure contact with the vibrating body and is rotationally driven by the high-frequency vibration. And a portion that is formed in a contact portion between the vibrating body and the moving body and is structurally periodically non-uniform with respect to a moving direction of the moving body for changing a vibration state of the vibrating body, and the vibration Detecting a change in the vibration state of the vibrating body due to the passage of the periodically non-uniform portion from a detection electrode for detecting a voltage generated along with piezoelectric deformation of the body and a detection voltage of the detection electrode, A detection unit that detects at least one of a rotational position and a rotation speed of the moving body, and the detection unit is configured to detect the periodically non-uniform portion from a change in phase of the detection voltage of the detection electrode with respect to the drive signal. The pulsation waveform accompanying the passage of A rotating signal converter (rotation amount) and a rotation speed are detected by counting the pulse of the pulsating component from the output of the filter, and a signal converter that outputs the pulsating component from the pulsating waveform. It includes a counter and a frequency setter that changes the cutoff frequency of the filter in accordance with the frequency of the drive signal.

  According to the above configuration, the driving unit, the vibrating body (stator) in which the piezoelectric element performs high-frequency vibration in response to a driving signal from the driving unit, and press-contacting the vibrating body are driven to rotate by the high-frequency vibration. At least one of the rotational position (rotation amount) and rotational speed of the moving body based on the detection voltage of the moving body (rotor), the detection electrode for detecting the voltage generated by the piezoelectric deformation of the vibrating body, and the detection voltage of the detection electrode A contact portion between the vibrating body and the moving body is structurally non-uniform with respect to the moving direction of the moving body in order to change a vibration state of the vibrating body such as a groove. In such a case, the detection unit detects the change in the vibration state of the vibrating body due to the passage of the non-uniform part from the detection voltage by the detection electrode, and the sensorless movement such as an encoder is performed. Said rotation of the body In a self-sensing ultrasonic motor that can detect at least one of a position (amount of rotation) and a rotation speed, the detection unit is periodically disabled from a change in phase of the detection voltage with respect to the drive signal. A signal converter that outputs a pulsation waveform associated with the passage of a uniform portion, a filter that extracts a pulsation component from the pulsation waveform, and a position of the moving body by counting pulses of the pulsation component from the output of the filter And a counter for detection. Further, it should be noted that the filter has a variable cutoff frequency, and correspondingly, a frequency setting unit is provided that changes the cutoff frequency of the filter in accordance with the frequency of the drive signal.

  Therefore, there is unevenness in the pressing force from the pressing member that presses the moving body to the vibrating body, or the output take-out shaft of the moving body is inclined, and the pressing force of the moving body to the vibrating body is Even if there is non-uniformity due to the non-uniformity, the frequency setting device changes the cut-off frequency of the filter according to the frequency of the drive signal, that is, the rotational speed, of the AC component that periodically appears in the pulsating component due to the non-uniformity. Therefore, it can be appropriately removed. As a result, when a waveform shaper is provided in the counter or preceding stage, the amplitude level of the input pulse to the waveform shaper can be kept within a predetermined range, and the S / N can be improved. In this way, the pressing force of the moving body on the vibrating body and the inclination of the output take-out shaft of the moving body, that is, the allowable range (tolerance) for the assembly accuracy can be expanded, and the cost and size can be reduced.

  In the ultrasonic motor of the present invention, the filter includes a capacitive element in a resistor and an amplifier connected to a connection point thereof, and a cutoff frequency is determined by a resistance value of the resistor and a time constant depending on a capacitance of the capacitive element. The resistor further includes a current control unit that controls a current flowing through the resistor in response to an output from the frequency setter, the resistance value of the resistor changing according to a passing current. To do.

  According to said structure, while being able to implement | achieve the said filter with an analog simple circuit called a current control part as a passive element, a fine adjustment is attained and the said pulsation component can be removed favorably.

  Furthermore, in the ultrasonic motor of the present invention, the current control unit includes a field effect transistor, the resistor is connected in series to a drain current path of the field effect transistor, and the frequency setting device includes the field effect transistor. The voltage applied to the gate is changed.

  According to the above configuration, the frequency setter changes the voltage applied to the gate of the field effect transistor, so that the current passing through the resistor changes and the resistance value of the resistor changes. The cutoff frequency can be changed. The frequency setter comprises, for example, a frequency-voltage converter, and changes the voltage applied to the gate of the field effect transistor according to the frequency of the drive signal. In this way, the current control unit can be realized with an analog and simple circuit as described above.

  Furthermore, in the ultrasonic motor of the present invention, the piezoelectric element is formed by laminating a plurality of piezoelectric layers in which electrodes are formed at equal intervals in the circumferential direction, and a drive signal given from the drive unit to each electrode is The piezoelectric element revolves at the tip of the piezoelectric element because the phases corresponding to the equal intervals are shifted from each other, and the moving body is moved by the contact member attached to the tip of the piezoelectric element. The movable body is configured to include a shaft for taking out the rotation, a movable body main body fixed to the shaft, and a cover plate stacked on the movable body main body. In the surface on the cover plate side, the grooves that extend in the radial direction and are formed at equal intervals in the circumferential direction are the structurally non-uniform portions.

  According to said structure, the ultrasonic motor of the same shape as the normal cylindrical motor from which an output shaft extends from a cylindrical main body is realizable.

  As described above, the ultrasonic motor according to the present invention is driven to rotate when the moving body (rotor) comes into pressure contact with the vibrating body (stator) in which the piezoelectric element performs high-frequency vibration in response to the drive signal. In addition, a structurally non-uniform portion for changing the vibration state of the vibrating body, such as a groove, is periodically formed in the contact portion between the vibrating body and the moving body. By detecting the change in the vibration state of the vibrating body from the detection voltage of the detection electrode, it is possible to detect at least one of the rotational position (rotation amount) and rotational speed of the moving body without using a sensor such as an encoder. In the self-sensing ultrasonic motor, the detection unit outputs a pulsation waveform accompanying the passage of the non-uniform portion periodically from a change in phase of the detection voltage with respect to the drive signal; , A filter that extracts a pulsating component from the pulsating waveform, and a counter that detects the position of the moving body by counting pulses of the pulsating component from the output of the filter, and further, a cutoff frequency of the filter A frequency setting device is provided that is variable and changes the cutoff frequency of the filter in accordance with the frequency of the drive signal.

  Therefore, there is unevenness in the pressing force from the pressing member that presses the moving body to the vibrating body, or the output take-out shaft of the moving body is inclined, and the pressing force of the moving body to the vibrating body is reduced. Even if there is unevenness due to the part, the frequency setting device changes the cut-off frequency of the filter according to the frequency of the drive signal, that is, the rotational speed, of the alternating current component that periodically appears in the pulsation component due to the unevenness. By doing so, it can be appropriately removed. As a result, when a waveform shaper is provided in the counter or preceding stage, the amplitude level of the input pulse to the waveform shaper can be kept within a predetermined range, and the S / N can be improved. In this way, the pressing force of the moving body on the vibrating body and the inclination of the output take-out shaft of the moving body, that is, the allowable range (tolerance) for the assembly accuracy can be expanded, and the cost and size can be reduced.

It is a schematic block diagram of the lens drive unit using the ultrasonic motor which concerns on one Embodiment of this invention. It is an axial direction sectional view showing the structure of the ultrasonic motor. 6 is a six-sided view of a vibrating body in the ultrasonic motor. FIG. It is the top view and bottom view which show the front and back both surfaces per layer of the lamination type piezoelectric element in the said vibrating body. It is a perspective view which shows the mode of a deformation | transformation of the bending primary mode of the said piezoelectric element. It is a figure which shows the mode of the vibration of a vibrating body by the deformation | transformation of the said piezoelectric element. It is a perspective view of the moving body in the ultrasonic motor. It is an expanded view for demonstrating the drive of the moving body by the vibration of the said vibrating body. It is a graph for demonstrating the detection mechanism of the drive and rotation position of the said mobile body. It is a block diagram of a drive circuit and a detection circuit of an embodiment of the present invention. It is a block diagram which shows one structural example of the band filter in the said detection circuit. It is a block diagram which shows one specific structural example of the frequency setting device in the said detection circuit. It is a wave form diagram for demonstrating operation | movement of the frequency setting device shown in FIG. It is a graph for demonstrating operation | movement of the said frequency setting device. It is a wave form diagram for demonstrating operation | movement of the band filter by which the frequency setting was carried out. It is a wave form diagram for demonstrating the fluctuation of the position detection waveform by the press nonuniformity to the vibrating body of the said mobile body.

  FIG. 1 is a schematic configuration diagram of a lens driving unit 2 using an ultrasonic motor 1 according to an embodiment of the present invention. The lens driving unit 2 is used for zooming of a DSC (digital still camera) or digital video camera, or for correcting aberrations of a DVD pickup lens, and is a small ultrasonic motor having a thickness W1 of, for example, 3 to 5 mm. It is. The cylindrical ultrasonic motor 1 is attached to a frame 3 of a lens unit, and an output shaft thereof serves as a lead screw 11 to constitute a linear motion lens feed mechanism. The frame 3 is also provided with guide shafts 4 and 5 in parallel with the lead screw 11, and a lens 7 is held by a guide member 6 slidable on the guide shafts 4 and 5. The lead screw 11 is engaged with the guide member 6, and when the lead screw 11 is rotated, the guide member 6, and thus the lens 7, is connected to the lead screw 11 (ultrasonic motor 1) and the guide shafts 4, 5. Is displaced in the direction of the axis (left and right in the figure).

  FIG. 2 is an axial sectional view showing the structure of the ultrasonic motor 1. The ultrasonic motor 1 includes a vibrating body (stator) 12 in which a piezoelectric element 12a performs high-frequency vibration, a moving body (rotor) 13 that is in pressure contact with the vibrating body 12 and moved by the high-frequency vibration, and the vibration. A pressure member 14 that presses the body 12 against the moving body 13, a bottomed cylindrical case 15 that accommodates them, the lead screw 11 that is fixed to the moving body 13 integrally or by caulking, and the lead A pair of bearing members 16 and 17 that pivotally support the screw 11 are provided.

  One bearing member 16 closes the open end of the bottomed cylindrical case 15, supports the base end portion 11a of the lead screw 11 in the radial direction, and the other bearing member 17 is attached to the frame. It consists of a ball bearing that fits into the cap 18, and a concave surface 11c formed on the free end portion 11b of the lead screw 11 fits in to support the free end portion 11b in the radial direction and the thrust direction.

  The vibrating body 12 includes the piezoelectric element 12a, a contact member 12b on the moving body 13 side, and a weight member 12c for stability on the opposite side. While the rotation of the case 15 is restricted, the axis with the moving body 13 is positioned and held. The pressure member 14 biases the vibrating body 12 toward the moving body 13 (right side in the figure), and the contact member 12 b is pressed against the moving body 13. On the other hand, the second bearing member 17 receives the reaction force from the cap 18 due to the pressing force from the moving body 13 to the lead screw 11 at the center of rotation, and the friction loss can be minimized. ing. The cap 18 is engraved with a screw 18a between the frame 3 and the cap 18 is moved to the ultrasonic motor 1 side (left side in the figure) by the amount of rotation of the screw 18a. The cap 18 is fixed to the frame 3 by adhesion after the adjustment.

  FIG. 3 is a six-sided view of the vibrating body 12, wherein (a) is a plan view, (b) is a front view, (c) is a side view, and (d) is a bottom view. . As described above, the vibrating body 12 includes the laminated piezoelectric element 12a, the contact member 12b on the moving body 13 side, and the weight member 12c on the opposite side, and these are coupled with an adhesive. For the adhesive, an epoxy adhesive having high rigidity and high adhesive strength is used. The contact member 12b is made of ceramics such as alumina and zirconia having high wear resistance. In this contact member 12 b, three spherical contact portions 12 d are formed at equal intervals (120 ° intervals) in the circumferential direction of the piezoelectric element 12, and the spherical shape is formed by the pressing force of the pressure member 14 described above. Each vertex 12e of the contact portion 12d contacts the moving body 13. The weight member 12c is made of tungsten having a high specific gravity or a copper or iron-based tungsten alloy or the like in order to suppress the deflection on the base end side caused by bending vibration of the piezoelectric element 12a as will be described later.

  FIG. 4 is a plan view and a bottom view showing both the front and back surfaces per layer of the multilayer piezoelectric element 12a. Each layer 12f sandwiches a piezoelectric layer 12g made of PZT (lead zirconate titanate), and on one surface (FIG. 4 (a)), a drive circuit, which will be described later, at equal intervals (90 ° intervals) in the circumferential direction. The drive electrodes IA, IB, IC, ID to which the drive signal is input are formed, and the detection electrode IS that outputs the detection signal to the detection circuit, which will be described later, is formed at the position where the bending displacement is the largest as much as possible. The solid GND electrode IG is formed on the other surface (FIG. 4B) in common. These internal electrodes IA, IB, IC, ID; IS and IG are formed by silver palladium printing or the like, and between the stacked piezoelectric layers 12g, the drive electrodes IA, IB, IC, ID and detection electrodes IS and GND electrodes IG are alternately formed.

  Electrodes IA, IB, IC, ID; IS and IG in each layer 12f are commonly connected by external electrodes OA, OB, OC, OD; OS and OG formed by screen printing or vapor deposition of silver or gold. Is done. The external electrodes OA, OB, OC, OD; OS and OG are joined with a lead wire or a flexible substrate (lead wire 12h in the example of FIG. 3) with solder or a conductive adhesive, etc. A drive signal and a detection signal are input to and from the circuit. Due to the formation of these external electrodes OA, OB, OC, OD; OS and OG, the piezoelectric element 12a is preferably a quadrangular prism. Each layer 12f and the electrodes IA, IB, IC, ID; IS and IG formed thereon are polarized in the same direction after lamination.

  With respect to the piezoelectric element 12a configured as described above, phases corresponding to the equal intervals (90 ° intervals) are mutually connected between the drive electrodes IA, IB, IC, ID and the GND electrode IG from the drive circuit. By applying a high-frequency drive signal that is shifted by 90 °, each of the drive electrodes IA, IB, IC, and ID performs stretching vibration that is 90 ° out of phase. When the frequency of the drive signal is brought close to a resonance frequency, for example, 180 kHz, the piezoelectric element 12a generates a vibration in the bending primary mode as shown in FIG. Here, as described above, the weight member 12c is attached to the proximal end side of the piezoelectric element 12a, and is fixed to the case 15 via the pressure member 14, and the contact portion 12d on the distal end side is caused by the bending vibration. Performs a revolving motion (swing vibration). As a result, elliptical vibrations whose phases are shifted from each other by 120 ° are generated at the apexes 12e of the contact portion 12d, as indicated by reference numeral 12r in FIG. The frictional force generated by the elliptical vibration 12r is rotationally driven around the axis of the piezoelectric element 12a. Similar to FIG. 3, FIG. 6 (a) is a plan view of the vibrating body 12, and FIG. 6 (b) is a front view.

  On the other hand, FIG. 7 is a perspective view of the moving body 13, and FIG. 8 is a cross-sectional view showing the vicinity of the contact portion between the moving body 13 and the contact member 12 b of the vibrating body 12. Note that FIGS. 7 and 8 are upside down with respect to FIGS. 3 and 6. The moving body 13 includes the lead screw 11 as a shaft for taking out the rotation, a moving body main body 13a fixed to the lead screw 11, and a cover plate 13b stacked on the moving body main body 13a. In the surface of the movable body 13a on the cover plate 13b side, grooves 13c are formed at equal intervals in the circumferential direction extending in the radial direction. And this groove | channel 13c is a structurally non-uniform | heterogenous part, and becomes the detection area 13d. Further, the portion where the groove 13c is not formed is a structurally uniform portion, and becomes a drive (normal) region 13e.

  The moving body 13 is produced by forming a groove 13c on a moving body main body 13a made of metal such as stainless steel by machining or etching, and then laminating a thin cover plate 13b made of stainless steel or the like. The cover plate 13b is subjected to nitriding treatment or the like in order to improve wear resistance. Lamination of the cover plate 13b to the movable body main body 13a is performed by joining with a thin adhesive layer or by joining the vicinity of the center by spot welding or the like, so that the movable body main body 13a and the cover plate 13b are not misaligned. It only needs to be able to rotate integrally. By comprising in this way, the ultrasonic motor 1 of the same shape as the normal cylindrical motor from which an output shaft extends from a cylindrical main body is realizable. The same effect can be obtained even when a protrusion is used in place of the groove 13c as the structurally non-uniform portion.

  In the ultrasonic motor 1 configured as described above, FIG. 8 is a diagram schematically showing how the movable body 13 is driven by the vibrating body 12. Referring to this, when the piezoelectric element 12a is driven in a resonance state, the movable body 13 is moved (rotated) to the left in the figure indicated by the arrow 13f by the elliptical vibration 12r of the vertex 12e of the contact portion 12d, and the vertex 12e alternately passes over the drive area 13e and the detection area 13d of the moving body 13. Here, the groove 13c, that is, the detection area 13d, is arranged so that the vertex 12e passes at the same timing, that is, the detection area 13d is 120 ° / n (n is an integer, with respect to the vertex 12e every 120 °. 8 is formed every n = 4).

  According to this, the voltage and the phase of the detection voltage output from the detection electrode IS are as shown in FIG. 9A and FIG. 9B, respectively. First, FIG. 9A shows the amplitude value of the detection voltage. Reference numeral α11 corresponds to the drive area 13e, and reference numeral α12 corresponds to the detection area 13d. The frequency f0 at which the detected voltage is the maximum value, that is, the distortion is the maximum, is the resonance point, and the driving is performed at the frequency f0 'in the vicinity thereof. When entering the detection region 13d, the resonance frequency shifts to f0 ″ on the low frequency side, and the amount of distortion of the piezoelectric element 12a also decreases. This reduces the amplitude by ΔV. This is because the spring constant of the contact portion of the moving body 13 is different between the drive area 13e and the detection area 13d. In the drive area 13e, since the moving body main body 13a is located directly below the cover plate 13b, the rigidity at the contact point is high. On the other hand, in the detection area 13d, the space immediately below the cover plate 13b is a space, and the structure is such that the pressure at the contact point is supported by the elasticity of the cover plate 13b, and the rigidity is reduced. Thus, the resonance frequency of the piezoelectric element 12a is lowered, and the resonance state of the piezoelectric element 12a changes between the drive area 13e and the detection area 13d.

  FIG. 9B shows the phase difference of the detected voltage with respect to the drive signal. Reference numeral α21 corresponds to the drive area 13e, and reference numeral α22 corresponds to the detection area 13d. For the same reason as described above, when entering the detection region 13d and the resonance frequency is shifted to the low frequency side, the phase of the detection voltage advances by Δθ.

  Utilizing this, the drive circuit 21 and the detection circuit 31 of the ultrasonic motor 1 are configured as shown in FIG. The drive circuit 21 and the detection circuit 31 are integrated with the control IC 20 of the ultrasonic motor 1.

  First, in the drive circuit 21, a pulse (moving speed signal) is input from a controller 22 such as a micro camera unit (MCU). What is represented by this pulse (movement speed signal) is an instruction of 2400 rpm to 200 rpm, for example, as the rotation speed of the moving body 13 as described above, and is composed of, for example, the 24 pulses per rotation. . The input pulse (movement speed signal) is input to the counter 23, and the movement speed at which the moving body 13 is to be driven is detected from the number of pulses. The movement speed information is input to the deviation counter 24, and a difference from the current movement speed information given from the detection circuit 31 as described later is obtained. The deviation counter 24 outputs a drive pulse corresponding to the difference. To do. The drive pulse is amplitude-amplified corresponding to the difference by the speed adjusting unit 25, that is, the drive pulse having a larger amplitude is generated as the deviation between the target rotation speed and the current rotation speed is larger. Input to the unit 26. The drive voltage generation unit 26 also receives a signal having a resonance frequency of 180 kHz from an oscillator 27. The drive voltage generation unit 26 modulates the signal having the resonance frequency with the drive pulse, and further has a phase. By generating signals that are shifted from each other by 90 °, the drive signals corresponding to the drive electrodes IA, IB, IC, and ID are generated as described above.

  On the other hand, the detection voltage from the detection electrode IG is input to the signal converter 32 of the detection circuit 31. The signal converter 32 also receives a reference signal among the four drive signals from the drive voltage generator 26, and the signal converter 32 outputs the detection voltage of the detection electrode IG. From the change in the phase with respect to the drive signal, a pulsation waveform as shown in FIG. 16 having different amplitudes in the detection area 13d and the drive area 13e is output. The pulsation waveform is input to a band-pass filter (high-pass filter) 33, and the low-frequency periodic component (swell) indicated by reference numeral α4 in FIG. 16A is removed, and the pulsation component as shown in FIG. Only is extracted. The pulsating component is input to the waveform shaper 34, and only the portion related to the detection area 13d is output as a detection pulse. The detection pulse is input to the counter 35, and the moving speed information indicating the actual rotational speed is generated and input to the deviation counter 24.

  In such a friction drive actuator, since the moving body 13 is driven so as to overcome the friction force (inertial force), the detection voltage at the detection electrode IG from the input of the drive signal (input pulse) to the piezoelectric element 12a. The deviation counter 24 calculates the amount of speed deviation from the target movement speed information based on the input pulse from the counter 23 and the current movement speed information from the counter 35. It can be immediately reflected in the drive signal. Thus, when the difference between the target moving speed information and the current moving speed information is less than or equal to a predetermined value, the counter 23 cuts off the switch 28 interposed between the oscillator 27 and the drive voltage generator 26, Sonic drive is stopped.

  In the ultrasonic motor 1 configured as described above, it should be noted that the cut-off frequency of the band-pass filter 33 of the detection circuit 31 can be changed. In the embodiment, there is provided a frequency setter 36 that changes the cutoff frequency of the band-pass filter 33 in accordance with the frequency of the input pulse proportional to it.

  FIG. 11 is a block diagram showing a configuration example of the band filter 33. The band-pass filter 33 includes a high-pass filter 332 that includes resistors R1 and R2 and a capacitive element C1, and an amplifier 331 connected to a connection point between the resistor R2 and the capacitive element C1, and a current control unit 333. It is configured with. The pulsating waveform from the signal converter 32 is input to the inverting input terminal of the amplifier 331 via the input resistor R1, and is input to the non-inverting input terminal of the amplifier 331 via the capacitive element C1 and the resistor R2. The The amplifier 331 is negatively fed back. On the other hand, the source-drain resistance of the current control unit 333 is a function R333 (v) that depends on the voltage v of the frequency setter. Accordingly, the high-pass filter 332 has a cutoff frequency fc as shown in the following equation according to a time constant based on a function R333 (v) of the resistance value of the resistor R2, the capacitance of the capacitive element C1, and the source-drain resistance of the current controller 333. It is determined.

fc = 1 / {2πC1 × R2 × R333} (v)
Meanwhile, the resistance value of the resistor R2 changes according to the passing current, and the current control unit 333 controls the current flowing through the resistor R2 in response to the output from the frequency setter 36. In the present embodiment, the current control unit 333 is composed of a field effect transistor, the resistor R2 is connected in series to the drain current path, and the frequency setting unit 36 changes the voltage applied to the gate.

  FIG. 12 is a block diagram showing a specific configuration example of the frequency setting unit 36. First, an input pulse signal V1 from the controller 22 serving as an input speed instruction signal shown in FIG. 13A is given to one input of the NAND gate U1, and its output V2 is as shown in FIG. 13B. The inverted pulse signal V2 of the input pulse signal V1. The inverted pulse signal V2 is supplied to a series circuit of a capacitor Ct and a resistor Rt, and charging of the capacitor Ct is started. Therefore, the potential V3 at the connection point between the capacitor Ct and the resistor Rt rises at the moment when the inverted pulse signal V2 rises, as shown in FIG. The voltage gradually decreases according to a time constant determined by the capacitance of the capacitor Ct and the resistance value of the resistor Rt. The potential V3 is input to the inverter U2, and therefore the output V4 of the inverter U2 is a period in which the input potential V3 exceeds the threshold voltage Vth set in the inverter U2, as shown in FIG. Only goes high. The output V4 of the inverter U2 is integrated by a resistor R and a capacitor C. Thus, the input pulse is subjected to frequency-voltage conversion, and a direct current voltage proportional to the frequency of the pulse is applied to the current control unit 333, and a NAND gate. Returned to the other input of U1.

  With this configuration, as shown in FIG. 14, as the frequency of the input pulse signal V1 from the controller 22 increases (Fa → Fb → Fc), the frequency setting unit 36 outputs V4 to the current control unit 333. Is increased (Va → Vb → Vc), thereby changing the resistance value of the resistor R2 of the bandpass filter 33, and the bandpass filter 33 cutoff frequency fc is increased as shown in FIG. (Fca → fcb → fcc).

  Therefore, as shown in FIG. 16A, the pulsation waveform for position detection indicated by the reference symbol α3 has a pulsation waveform for detecting the position indicated by the reference symbol α4 due to unevenness in the pressing force of the movable body 13 on the vibrating body 12. Even if a low-frequency periodic component accompanying the rotation (swelling repeated at one rotation period τ) is superimposed, the periodic component is appropriately removed by the band filter 33 as indicated by reference numeral α1 in FIG. be able to. As a result, when the waveform shaper 34 is provided in the counter 35 or the preceding stage, the amplitude level of the input pulse to the waveform shaper 34 falls within a predetermined range, and the S / N can be improved. . In this way, the pressing force of the moving body 13 to the vibrating body 12 and the inclination of the output take-out shaft (lead screw 11) of the moving body 13, that is, the allowable range (tolerance) for the assembly accuracy can be expanded. Miniaturization can be achieved.

  Further, the band-pass filter 33 can be realized by an analog and simple circuit called a current control unit (FET) in the passive elements (R1, R2, C1), and can be finely adjusted. It can be removed well.

  In the above example, in the band-pass filter 33, the change in the cut-off frequency fc is realized by using the resistor R2 whose resistance value changes according to the change in the passing current, but any element having the same type of function can be used. Application to is possible. Further, in place of the FET, any element whose current is changed by a control voltage can be applied to the present invention.

  The scope of the present invention should not be limited by the above-described embodiments, and various modifications are possible within the scope of the description of the claims and the equivalents thereof, and it has ordinary knowledge in the art. It is clear to the person.

DESCRIPTION OF SYMBOLS 1 Ultrasonic motor 2 Lens drive unit 3 Frame 6 Guide member 7 Lens 11 Lead screw 12 Vibrating body (stator)
12a Piezoelectric element 12b Contact member 12c Weight member 12d Contact portion 12e Vertex 12g Piezoelectric layer 13 Moving object (rotor)
13a Mobile body 13b Cover plate 13c Groove 13d Detection area 13e Drive (normal) area 14 Pressure member 15 Case 16, 17 Bearing member 20 Control IC
21 drive circuit 22 controller 23 counter 24 deviation counter 25 speed adjustment unit 26 drive voltage generation unit 27 oscillator 28 switch 31 detection circuit 32 signal converter 33 band filter 331 amplifier 332 high pass filter 333 current control unit 34 waveform shaper 35 counter 36 frequency Setter C, Ct Capacitor C1 Capacitance element IA, IB, IC, ID Drive electrode IG GND electrode IS Detection electrode OA, OB, OC, OD; OS; OG External electrode R, R1, R2, Rt Resistance U1 NAND gate U2 Inverter

Claims (5)

A drive unit;
A vibrating body in which the piezoelectric element performs high-frequency vibration in response to a driving signal from the driving unit;
A movable body that is in pressure contact with the vibrating body and is rotationally driven by the high-frequency vibration;
A portion that is formed at a contact portion between the vibrating body and the moving body, and is structurally periodically non-uniform with respect to a moving direction of the moving body for changing a vibration state of the vibrating body;
A detection electrode for detecting a voltage generated with piezoelectric deformation of the vibrating body;
Detection that detects at least one of the rotational position and the rotational speed of the moving body by detecting a change in the vibration state of the vibrating body due to the passage of the periodically non-uniform portion from the detection voltage of the detection electrode. With
The detector is
A signal converter that outputs a pulsation waveform accompanying the passage of the periodically non-uniform portion from a phase change of the detection voltage of the detection electrode with respect to the drive signal;
A filter for extracting a pulsation component from the pulsation waveform;
A counter that detects at least one of a rotational position and a rotational speed of the moving body by counting pulses of the pulsating component from the output of the filter;
An ultrasonic motor comprising: a frequency setter that changes a cutoff frequency of the filter according to a frequency of the drive signal. The filter is a high-pass filter including a capacitive element in a resistor and an amplifier connected to a connection point thereof, and a cutoff frequency is determined by a time constant depending on a resistance value of the resistor and a capacitance of the capacitive element,
The resistance value of the resistor changes according to the passing current,
The ultrasonic motor according to claim 1, further comprising a current control unit that controls a current flowing through the resistor in response to an output from the frequency setter. The current control unit includes a field effect transistor, and the resistor is connected in series to a drain current path of the field effect transistor,
The ultrasonic motor according to claim 2, wherein the frequency setting unit changes a voltage applied to a gate of the field effect transistor.   The ultrasonic motor according to claim 3, wherein the frequency setting unit includes a frequency-voltage converter, and changes a voltage applied to a gate of the field effect transistor according to a frequency of the driving signal. The piezoelectric element is formed by laminating a plurality of piezoelectric layers in which electrodes are formed at equal intervals in the circumferential direction, and the drive signals given to the electrodes from the driving unit are shifted in phase corresponding to the equal intervals. By being a high-frequency signal, the tip of the piezoelectric element revolves, and the moving body is rotated around the axis of the piezoelectric element by a contact member attached to the tip of the piezoelectric element.
The movable body includes a shaft for taking out the rotation, a movable body main body fixed to the shaft, and a cover plate stacked on the movable body main body, and a surface on the cover plate side of the movable body main body. 5. The ultrasonic motor according to claim 1, wherein grooves that extend in the radial direction and are formed at equal intervals in the circumferential direction are the structurally nonuniform portions. 6.