JP2008072831A - Vibrating actuator, drive unit for the vibrating actuator, lens barrel, and camera - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a vibrating actuator which can enlarge the starting torque, even if the outside diameter of a vibrator is small. <P>SOLUTION: This vibrating actuator is equipped with an annular vibrator 201 which vibrates by a drive signal, and a relative motion member 205 which performs relative motion to the vibrator by the vibration of the vibrator, and the outside diameter of the vibrator is 10-15 mm, and the force factor is 0.05 or larger. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a vibration actuator that generates vibration energy by generating vibration in a vibrating body, extracts the vibration energy as an output, and obtains a driving force.

Conventionally, this type of vibration actuator is provided in, for example, an interchangeable lens of a camera, and has been put into practical use as a drive motor for driving an autofocus lens. In order to drive the vibration actuator by vibrating the vibration body of the vibration actuator, a drive device that provides a drive signal with a frequency corresponding to the drive speed for driving the vibration actuator, that is, the rotation speed is used (see Patent Document 1).
JP-A-9-163767

  However, the vibration actuator having a small outer diameter of the vibrating body has a problem that the starting torque is small. In particular, there has been a problem that it may not start when used in a low temperature environment.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a vibration actuator capable of increasing the starting torque even when the outer diameter of the vibrating body is small, a driving device for the vibration actuator, a lens barrel using the vibration actuator, and a camera.

  In order to solve the above problem, the vibration actuator according to claim 1 is a ring-shaped vibrating body that vibrates according to a drive signal, and a relative motion that performs a relative motion with respect to the vibrating body by the vibration of the vibrating body. A vibration member having an outer diameter of 10 to 15 mm and a force coefficient of 0.05 or more.

  The vibration actuator according to claim 2 is the vibration actuator according to claim 1, wherein the vibration body includes an annular base portion and an elastic body provided on the relative motion member side with respect to the base portion. A piezoelectric element provided on a surface of the base portion opposite to the surface on which the elastic body is provided, and a convex portion is provided on the surface of the base portion on the side on which the piezoelectric element is provided. Features.

  According to a third aspect of the present invention, there is provided a drive device for a vibration actuator, wherein the drive voltage output means supplies a drive voltage to the vibration actuator, and controls the sudden drop of the drive voltage in the middle of a predetermined cycle. In the middle, the drive voltage is controlled to drop rapidly, and when the time from the start point to the sudden drop point in the predetermined cycle is a, and when the time from the sudden drop point to the end point in the predetermined cycle is b, Control means for performing control so that / b is 1.7 or less.

  The vibration actuator driving apparatus according to claim 4, wherein a DC power source is connected to the primary winding, a transformer that supplies a voltage from the secondary winding to the vibrating body of the vibration actuator, and a primary side of the transformer A first switching means for turning on and off the current flowing through the winding; a second switching means for turning on and off the current flowing through the secondary winding of the transformer; and the first switching means within a predetermined period of time a. Switching control means for performing control to turn on the first switching means for the time b, then turn on the second switching means, and turn on the second switching means, so that a / b is 1.7 or less. It is characterized by.

  6. The vibration actuator driving apparatus according to claim 5, wherein a DC power source is connected to the primary side winding, a transformer for supplying a voltage from the secondary side winding to the vibrating body of the vibration actuator, and a primary side of the transformer Control means for turning on and off the current flowing in the winding or the secondary winding, and when the capacitance Cd of the piezoelectric element of the vibration actuator is 1 [nF] <Cd <1.25 [nF] The secondary winding has an inductance value L of 1.9 [mH] <L <2.5 [mH].

  According to a sixth aspect of the present invention, there is provided the vibration actuator driving apparatus according to the fifth aspect, wherein the input voltage of the transformer is 3 V and the transformer step-up ratio is 1:24.

  The vibration actuator drive device according to claim 7 is the vibration actuator drive device according to any one of claims 3 to 6, wherein the vibration actuator has an outer diameter of a vibrating body of 10 to 15 mm, The force coefficient is 0.05 or more.

  A lens barrel according to an eighth aspect includes the vibration actuator according to the first or second aspect and a lens driven by the vibration actuator.

  The lens barrel according to claim 9 is a driving device for the vibration actuator according to any one of claims 3 to 6, a vibration actuator driven by the driving device, and a lens driven by the vibration actuator. It is characterized by comprising.

    A camera according to a tenth aspect includes the vibration actuator according to the first or second aspect and a lens driven by the vibration actuator.

  A camera according to an eleventh aspect includes the vibration actuator driving device according to any one of claims 3 to 6, a vibration actuator driven by the driving device, and a lens driven by the vibration actuator. It is characterized by having.

  According to the present invention, the starting torque of the vibration actuator can be increased even when the outer diameter of the vibrating body is small.

  Hereinafter, embodiments of the vibration actuator will be described in detail with reference to the accompanying drawings. In the present embodiment, an ultrasonic motor using an ultrasonic vibration region will be described as an example of the vibration actuator.

  FIG. 1 is a diagram illustrating a camera system 101 according to an embodiment of the present invention. The camera system 101 according to the present embodiment includes a camera body 102 having an image sensor 108 and a lens barrel 103 having a lens 107. The lens barrel 103 is an interchangeable lens that can be attached to and detached from the camera body 102. In the present embodiment, the lens barrel 103 is an interchangeable lens. However, the present invention is not limited to this. For example, the lens barrel 103 may be a lens barrel integrated with the camera body. The lens barrel 103 includes a lens 107, a cam barrel 106, gears 104 and 105, an ultrasonic motor 110, and the like. In the present embodiment, the ultrasonic motor 110 is used as a driving source for driving the lens 107 during the focusing operation of the camera system 101, and the driving force obtained from the ultrasonic motor 110 is transmitted via the gears 104 and 105. This is transmitted to the cam cylinder 106. The lens 107 is held by the cam cylinder 106 and is a focus lens that moves in the optical axis direction by the driving force of the ultrasonic motor 110 to adjust the focus.

  FIG. 2 is a cross-sectional view showing the configuration of the ultrasonic motor of this embodiment. The ultrasonic motor 110 includes a vibrating body 201, a rotor 205, and the like, with the vibrating body 201 side being fixed and the rotor 205 side being rotationally driven. The vibrating body 201 is a stator having an elastic body 202 and a piezoelectric body 203 joined to the elastic body 202, and the piezoelectric body 203 is excited on the surface of the piezoelectric body 203 opposite to the elastic body 202 side. A flexible printed circuit board 204 that supplies a drive signal is connected. The vibrating body 201 generates a progressive vibration wave (hereinafter referred to as “traveling wave”) by the excitation of the piezoelectric body 203. As an example, a description will be given with 9 traveling waves per round.

  The vibrating body 201 is a substantially annular member having an elastic body 202 and a piezoelectric body 203 joined to the elastic body 202. The elastic body 202 is made of a metal material having a high resonance sharpness and has a substantially annular shape. The elastic body 202 includes a comb tooth portion 202a, a base portion 202b, a flange portion 202c, and a convex portion 202d. The elastic body 202 has a comb-tooth portion 202a having a groove formed on the surface opposite to the surface to which the piezoelectric body 203 is bonded. This tip surface serves as a driving surface and is in pressure contact with the rotor 205. . The reason for providing the comb-tooth portion 202a is to amplify the amplitude of the traveling wave on the drive surface by bringing the neutral surface of the traveling wave as close as possible to the piezoelectric body 203 side.

  The base portion 202b is a portion that is continuous in the circumferential direction of the elastic body 202, and the piezoelectric body 203 is bonded to the surface of the base portion 202b opposite to the comb tooth portion 202a. The convex portion 202d is provided on the inner diameter side of the base portion 202b and on the piezoelectric body 203 side with respect to a flange portion 202c described later. In the present embodiment, it is formed so as to slightly protrude from the bonding surface of the piezoelectric body 203 so as to facilitate positioning when the piezoelectric body 203 is bonded. The flange portion 202c is provided on the inner diameter side of the convex portion 202d, is a hook-like portion protruding in the inner diameter direction of the elastic body 202, and is disposed at the center in the thickness direction of the base portion 202b. The elastic body 202 is attached to the stator mount 206 by a flange portion 202c. An output shaft 213 (described later) is rotatably attached to the stator mounting base 206 via a bearing 207.

  The piezoelectric body 203 is an electromechanical conversion element that converts electrical energy into mechanical energy. For example, an electrostrictive element or a piezoelectric element is used. The piezoelectric body 203 has a range in which electrical signals of two phases (A phase and B phase) are input along the circumferential direction of the elastic body 202, and in a range corresponding to each phase, every 1/2 wavelength The elements in which the polarizations are alternately arranged are arranged, and an interval of ¼ wavelength is provided between the A phase and the B phase. The flexible printed circuit board 204 is connected to electrodes of each phase of the piezoelectric body 203, and the piezoelectric body 203 expands and contracts by the drive signal supplied from the outside to the flexible printed circuit board 204 to excite the elastic body 202. To do.

  The rotor 205 is formed of, for example, a light metal such as aluminum, and rotates by an elliptical motion caused by a traveling wave generated on the driving surface of the elastic body 202 that is the tip surface of the comb tooth portion 202a by being in pressure contact with the vibrating body 201. A relative motion member to be driven. The rotor 205 is a rotating body formed with a rotation center line as a central axis, and a substantially cylindrical through-hole portion 205a is formed at the center thereof. The through-hole portion 205a is fitted to an output shaft 213, which will be described later, and its diameter is larger by a tolerance than the diameter of the output shaft 213.

  The output shaft 213 is a substantially cylindrical member made of resin. The output shaft 213 is an output extraction member that fits into the through-hole portion 205a of the rotor 205 and rotates with the rotor 205 to extract the rotational motion of the rotor 205. is there. The output shaft 213 has a D-cut at least at a part of the end fitting with the through-hole part 205a of the rotor 205, the other end is joined to the gear 104, and the gear 104 is output to the driven member. Tell. The flange ring 211 is a member that is fitted to the output shaft 213, is movable in the direction of the rotation center line of the output shaft 213, and rotates together with the output shaft 213. A buffer member 210 is provided between the flange ring 211 and the rotor 205. The buffer member 210 is a substantially ring-shaped member made of rubber or the like, for example, is fitted to the output shaft 213 and absorbs vibration in the rotation center line direction of the rotor 205.

  The E ring 212 is fitted in a groove 213a provided at the end of the output shaft 213, and a regulating member that regulates the positions of the flange ring 211 and the rotor 205 with respect to the output shaft 213 in the pressurizing direction of the pressurizing unit 209 described later. It is. The pressurizing unit 209 is a mechanism that pressurizes the vibrating body 201 and the rotor 205, and is provided on the output shaft 213. The pressurizing unit 209 is configured by a spring that generates a pressurizing force. The pressurizing unit 209 pressurizes the vibrating body 201 and the rotor 205 in the direction of the rotation center line of the output shaft 213.

  FIG. 3 is a diagram illustrating a configuration of a vibrating body of the ultrasonic motor. FIG. 3A is a diagram showing a vibration body of a comparative example, and FIG. 3B is a diametrical straight line passing between the comb tooth portions of the vibration body of FIG. It is sectional drawing. FIG. 3C is a view showing the vibrating body 201 of the ultrasonic motor (FIG. 2) of the present embodiment, and FIG. 3D is a view of FIG. 3B of the vibrating body of FIG. It is similar sectional drawing. In both cases, the outer diameter (outer diameter) is 12 mm.

  As can be seen by comparing FIG. 3B and FIG. 3D, the comb teeth 202a of the vibrating body 201 of the present embodiment has a length in the radial direction as compared with the comparative example (FIG. 3B). Is long. Further, the vibrating body 201 of the present embodiment has a convex portion 202d. With such a configuration, the vibrating body 201 has a larger volume and consequently a larger mass than the vibrating body of the comparative example. With such a configuration, the vibrating body 201 of the present embodiment achieves a force coefficient of 0.05 or more.

  Here, the force coefficient will be described.

The behavior of an ultrasonic motor using piezoelectric ceramics as the piezoelectric body of the vibrator is described by the following equation.
-F = AV-Zv (1)
I = YdV + Av (2)
A: Force coefficient F: Force of mechanical terminal v: Speed of mechanical terminal V: Voltage of electrical terminal I: Current of electrical terminal Z: Mechanical impedance of piezoelectric ceramics Yd: Suppressing admittance A times of applied voltage V is inside piezoelectric ceramics The value obtained by subtracting the impedance drop due to the product of the internal mechanical impedance Z and the speed v from the AV value indicates the magnitude of the force that can be extracted to the outside.

Further, when the equivalent circuit of the ultrasonic motor is shown in FIG. 4 and the impedance curve of the equivalent circuit of FIG. 4 is shown in FIG.
fm: resonance frequency fn: anti-resonance frequency m: mass of vibrator k: electromechanical coupling coefficient Cd: capacitance of piezoelectric ceramic L: inductance
L = m / A ² (3)
L = {1 / (2π) ² } × (1 / Cd) × {1 / (fn ² −fm ² )} (4)
Can be expressed as

  That is, from the equation (3), the force coefficient A can be changed by the mass m of the vibrator. If the mass m is increased, the force coefficient A is also increased. If the Cd value is constant, the force coefficient can be changed by the resonance frequency fm and antiresonance frequency fn in the impedance curve of FIG.

  In the present embodiment, in order to increase the force that can be taken out of the ultrasonic motor, the radial length of the comb tooth portion is extended in the inner diameter direction, and the convex portion 202d is provided on the piezoelectric element bonding surface (base portion 202b). The mass was increased by increasing the volume of the elastic body, and the force coefficient was increased. As a result, in the annular ultrasonic motor having an outer diameter of 10 to 15 mm, the generated starting torque is increased, and the performance is improved particularly at low temperatures.

  The measurement for calculating the force coefficient was as follows. The Cd value was measured using an LCR meter for each phase. The resonance frequency fm and the anti-resonance frequency fn were obtained based on measurement values measured with an impedance measuring instrument (applied with 1 Vrms) in a stator single body state (without contact pressure with the rotor). The mass m is approximated by using the mass of the stator.

  As described above, it is possible to increase the starting torque by increasing the force coefficient. In this case, it has been found that it is necessary to limit the waveform of the drive signal applied to the piezoelectric body. When it was outside the limitation, it was found that the ultrasonic motor did not drive normally, especially at low temperatures.

  Hereinafter, the driving apparatus of the ultrasonic motor in this embodiment will be described. FIG. 6 is a diagram illustrating the configuration of the ultrasonic motor driving apparatus according to the present embodiment. An annular vibrator of an ultrasonic motor is composed of an annular elastic body and an annular piezoelectric element (electromechanical energy conversion element) joined to the elastic body. The electrode is appropriately polarized (for example, about 12 poles). Two alternating current signals whose phases are shifted by 90 degrees are combined with their inverted signals and supplied alternately to the polarized electrodes as appropriate for each polarized electrode. As a result, the piezoelectric element is vibrated to generate a traveling wave vibration in the elastic body. The relative motion member in pressure contact with the elastic body is driven to rotate by receiving the vibration of the traveling wave generated in the elastic body.

  In FIG. 6, in order to simplify the drawing, two alternating signals whose phases are shifted by 90 degrees are described as being supplied to the two piezoelectric elements 1a and 1b. However, the piezoelectric element 1a means all polarized piezoelectric elements to which one AC signal and its inverted signal are supplied, and the piezoelectric element 1b is a polarized piezoelectric element to which the other AC signal and its inverted signal are supplied. It shall mean all elements.

  In FIG. 6, the ultrasonic motor driving device includes a DC power supply circuit 2, a pulse generation circuit 3, switching control circuits 4 and 5, and driving circuits 6 a and 7 a. The drive circuit 6 a includes a transformer 11, MOSFETs 12, 13 and 41, diodes 14, 15, 42 and 43, and an inverter 16. Similarly to the drive circuit 6a, the drive circuit 7a includes a transformer 21, MOSFETs 22, 23, 51, diodes 24, 25, 52, 53, and an inverter 26.

  FIG. 7 is a diagram showing an internal configuration of the switching control circuit 4. As shown in FIG. 7, the switching control circuit 4 includes a resistor 31, a diode 32, a Schmitt trigger buffer 33, a resistor 34, a capacitor 35, a Schmitt trigger inverter 36, an inverter 37, a flip-flop 38, and a NAND gate 39. The operation of the switching control circuit 4 will be described later. The switching control circuit 5 has the same configuration as the switching control circuit 4.

  FIG. 8 is a diagram showing the driving frequency versus rotational speed (rotational speed) characteristics of the ultrasonic motor. f0 is a drive frequency at which the ultrasonic motor starts rotating, f1 is a drive frequency at which the maximum rotation speed of the control range is reached, and fr is a drive frequency at which mechanical resonance occurs in the vibrator of the ultrasonic motor. In the present embodiment, in consideration of control stability and the like, a characteristic that is lower than the drive frequency fr corresponding to the mechanical resonance of the vibrator of the ultrasonic motor is used. That is, control is performed to increase the rotational speed of the ultrasonic motor by lowering the drive frequency from the drive frequency f0.

  In the drive device configured as described above, the pulse generation circuit 3 includes two phase shifts of the phase of the drive frequency f corresponding to the desired rotational speed N by 90 degrees in order to rotate the ultrasonic motor at the desired rotational speed N. Pulse signals P1 and P2 are output. The pulse signals P1 and P2 output from the pulse generation circuit 3 become the signals B1 and B2 through the switching control circuits 4 and 5, and turn on / off the MOSFETs 12 and 22 of the drive circuits 6a and 7a. When the MOSFETs 12 and 22 are on / off controlled, boosted signals C1 and C2 having the same frequency f as the pulse signal are generated on the secondary winding side of the transformers 11 and 21.

  The boosted signals C1 and C2 generated on the secondary winding side are supplied to the piezoelectric elements 1a and 1b, and the piezoelectric elements 1a and 1b vibrate at the same frequency f as the pulse signal. The signals C1 and C2 are 90 degrees out of phase. As described above, the piezoelectric element 1a is a set of a plurality of polarized piezoelectric elements, and is a set of piezoelectric elements to which the signal C1 and the signal -C1 are supplied. Similarly, the piezoelectric element 1b is a set of a plurality of polarized piezoelectric elements, and is a set of piezoelectric elements to which the signal C2 and the signal -C2 are supplied. The signal -C1 and the signal -C2 are signals that are wired with the ground and each signal wiring reversed with respect to the signals C1 and C2. When the signals C1 and C2 are thus supplied to the piezoelectric elements 1a and 1b, traveling waves are generated in the elastic bodies joined to the piezoelectric elements 1a and 1b. The relative motion member in pressure contact with the elastic body receives vibrations of traveling waves generated in the elastic body and is rotationally driven at a rotational speed N corresponding to the drive frequency f.

  In the present embodiment, when the ultrasonic motor is driven in this way, it is provided on the series circuit of the secondary windings of the transformers 11 and 21 and the piezoelectric elements 1a and 1b in the cycle of the driving frequency f. By switching off the MOSFETs 13 and 23 for a certain period, free vibrations generated between the transformers 11 and 21 and the piezoelectric elements 1a and 1b are suppressed. Hereinafter, this control will be described in more detail.

  FIG. 9 is a diagram showing a timing chart for driving the ultrasonic motor. The operation for suppressing free vibration in the drive circuit 6a and the drive circuit 7a is based on the same principle. Therefore, the operation in the drive circuit 6a, that is, the supply of signals to the piezoelectric element 1a will be described as a representative.

  As shown in FIG. 9A, the pulse generation circuit 3 outputs a pulse signal P1 having a desired frequency (period t1-t4). The switching control circuit 4 receives the pulse signal P1 and the drive waveform feedback signal from the primary side of the transformer 11 of the drive circuit 6a, and receives the signal B1 shown in FIG. 9B and the signal A1 shown in FIG. 9C. Is output. The generation of the signal B1 and the signal A1 will be described later. The time t1-t2 of the signal B1 is a value determined by circuit constants such as the transformer 11 of the drive circuit 6a and cannot be controlled from the outside. That is, the value depends on the inductance L of the secondary winding of the transformer 11 and the resonance frequency fc of the electrostatic capacitance C of the piezoelectric element 1a, and does not depend on the drive frequency f. On the other hand, the time t1 to t4 of the signal B1 is a time determined by the drive frequency and is a value that can be controlled from the outside. Accordingly, when the time t1 to t4 becomes longer, the time t1 to t2 becomes constant, and therefore the time t2 to t4 becomes longer.

  As shown in FIG. 6, the signal B1 is input to the gate terminal of the MOSFET 12, the signal B1 is low (t1-t2), the MOSFET 12 is turned off, and the signal B1 is high (t2-t4). ), And the MOSFET 12 is controlled to be turned on. On the other hand, the signal B1 is inverted by the inverter 16 and input to the gate terminal of the MOSFET 13, the MOSFET 13 is turned on while the signal B1 is low (t1-t2), and the MOSFET 13 is turned off while the signal B1 is high (t2-t4). The switching is controlled as follows.

  The signal A1 is input to the gate terminal of the MOSFET 41, the signal A1 is low (t1-t2, t3-t4), the MOSFET 41 is turned on, and the signal A1 is high (t2-t3). The MOSFET 41 is controlled to be turned off. Although the MOSFETs 12 and 14 are Nch-MOSFETs, but the MOSFET 41 is a Pch-MOSFET, the on / off operation with respect to the gate signal is reversed.

  While the MOSFET 12 is on, the current I1 tends to flow from the DC power supply circuit 2 to the primary winding of the transformer 11. However, the MOSFET 41 is turned off between t2 and t3 by the signal A1, and the primary winding of the transformer 11 is turned on. No current flows through the wire. While the signal A1 is low (t3-t4), a current flows through the primary winding of the transformer 11 (FIG. 9D), and energy is stored in the primary winding of the transformer 11. In this manner, the MOSFET 12 is controlled to be turned on / off, whereby a driving voltage as shown in FIG. 9E is supplied to the piezoelectric element 1a.

  The driving voltage supplied to the piezoelectric element 1a is considered to generate free vibration after timing t2. However, in the present embodiment, this free vibration is suppressed by turning off the MOSFET 13 after the timing t2. That is, the occurrence of free vibration is suppressed by inserting the switching element of the MOSFET 13 on the series circuit between the piezoelectric element 1a, the secondary winding of the transformer 11 and the ground, and turning off the MOSFET 12.

  The relationship between the drive frequency and the drive voltage applied to the piezoelectric element 1a will be described. As shown in FIG. 9, since the MOSFET 12 is on from t2 to t4, the current I1 tends to flow from t2, but the current I1 is prevented from flowing from t2 to t3 by the signal A1. If the current I1 continues to flow from t2 to t4, the energy stored in the transformer 11 increases and the voltage applied to the piezoelectric element 1a also increases. When the drive frequency is changed, the time from t2 to t4 changes as described above, so that the time from t2 to t4 becomes longer as the drive frequency is lowered. As a result, the voltage applied to the piezoelectric element 1a increases, the amplitude of the piezoelectric element 1a increases, and the rotational speed of the ultrasonic motor increases. However, even if the voltage applied to the piezoelectric element 1a is increased more than necessary, it only becomes thermal energy and is inefficient. Therefore, in the present embodiment, the MOSFET 41 is turned off by the signal A1 so that no current flows through the primary winding of the transformer 11 so that the voltage applied to the piezoelectric element 1a is not unnecessarily increased.

  FIG. 10 is a timing chart showing a process in which the signal A1 and the signal B1 are generated in the switching control circuit 4 of FIG. FIG. 10A shows a drive waveform feedback signal from the drive circuit 6a, and shows a signal waveform at a terminal opposite to the terminal connected to the DC power supply circuit 2 of the primary winding of the transformer 11. . The drive waveform feedback signal is shaped as shown in FIG. 10B through the resistor 31 and the diode 32, and further, the pulse signal as shown in FIG. 10C is outputted via the Schmitt trigger buffer 33. .

  The pulse signal shown in FIG. 10C has the waveform shown in FIG. 10D after passing through the integrating circuit of the resistor 34 and the capacitor 35, and the Schmitt trigger inverter 36 outputs the pulse signal having the timing shown in FIG. Is done. The constants of the resistor 34 and the capacitor 310 are determined so that the rise of the output of the Schmitt trigger inverter 36 comes at the timing t2, that is, around the lower limit point of the drive waveform feedback signal in FIG.

  The output of the Schmitt trigger inverter 36 is input to the clock terminal (CLK) of the flip-flop 38. At this time, the D terminal of the flip-flop 38 is always at ground. On the other hand, the pulse signal P1 (FIG. 10 (f)) from the pulse generation circuit 3 is inverted by the inverter 37 and input to the preset terminal (PRE) of the flip-flop 38.

  The flip-flop 38 to which such a signal is input outputs an inverted Q signal shown in FIG. 10G and outputs it as a signal A1. On the other hand, the non-inverted signal Q is NANDed by the output of the inverter 37 and the NAND gate 39, and the NAND gate 39 outputs the signal B1.

  Note that the ultrasonic motor driving apparatus of the present embodiment turns on the MOSFET 12 to store energy on the primary side of the transformer 11 and turns off the MOSFET 12 to generate a vibration signal (attenuation signal) generated on the secondary side of the transformer 11. ), Only the first waveform is used for driving the piezoelectric element 1a, and the subsequent waveforms are excluded as free vibration. It can be said that the switching control circuit 4 extracts the first waveform as an effective signal. The first waveform is a signal of the first half cycle of the vibration signal, and signals after the first half cycle are free vibration signals.

  The operations of the drive circuit 7a side and the switching control circuit 5 can be described in the same manner using the timing charts of FIGS.

  Here, the waveform of the drive voltage in FIG. FIG. 11 is a diagram showing a waveform of one cycle of the driving voltage in the ultrasonic motor driving apparatus of the present embodiment. The waveform in FIG. 11 is a so-called pseudo sine wave. In one cycle of the waveform shown in FIG. 11, the time from the start point of the cycle to the point where the sudden drop in voltage starts is a, and the time from the point where the voltage drop starts to the end point of the cycle is b. Further, the difference between the voltage at the point where the voltage in the cycle is maximum (in FIG. 11, the start point of the cycle) and the voltage at the point where the voltage is minimum (in FIG. 11, the minimum point in the interval b) is c. And In this case, in the section a, energy is stored in the transformers 11 and 21 as described in the description of the driving device in FIG. In the section b, the stored energy is supplied to the ultrasonic motor.

  In the case of an ultrasonic motor with a large force coefficient, the vibration amplitude trajectory (Lissajous shape) varies depending on the waveform of the drive voltage supplied to the ultrasonic motor, and as a result, the vibration energy of the stator transmitted to the rotor of the ultrasonic motor differs. .

  Hereinafter, the relationship between the waveform of the drive voltage and the locus of vibration amplitude will be described in more detail. First, measurement of the vibration amplitude trajectory will be described. FIG. 12 is a diagram for explaining measurement points of vibration amplitude. As shown in FIG. 12B, the trajectory of vibration at the measurement point of the vibrating body is elliptical with respect to the rotation direction (horizontal axis) and the rotation axis direction (vertical axis). In this embodiment, the vibration amplitude trajectory is measured by measuring the speed of the vibration surface shown in FIG. 12A near the sliding surface of the vibrating body with the rotor by means of a laser interferometer. The vibration amplitude in the direction of the axis (rotation axis) was calculated, and a Lissajous shape created by synthesizing the vibration amplitude in two directions was obtained. However, this vibration amplitude indicates the fourth-order bending mode used as the drive mode.

  FIG. 13 is a diagram illustrating an electrode pattern of a piezoelectric element provided on the surface of the vibrating body opposite to the sliding surface with the rotor. The electrodes are divided into a plurality of regions, and the four electrodes on the right side in the figure correspond to the piezoelectric element 1a in FIG. 6, and the four electrodes on the left side correspond to 1b. GND indicates grounding. Also, the electrodes marked with black circles in the figure are polarized in the opposite direction with respect to the electrodes without black circles.

  14 and 15 show a case where the vibrating body (force factor 0.05 or more) in FIG. 3B is driven using the driving device in FIG. The driving waveform (the waveform of the driving voltage supplied to the electrode in FIG. 13) in the state without contact pressure with the rotor and the locus of the vibration amplitude near the sliding surface of the vibrating body (see FIG. 12) at that time FIG.

  The sine wave in FIG. 14 corresponds to a voltage effective value of 75 Vrms. Waveform (1) is for the case where the secondary inductance value of the transformers 11 and 21 in FIG. 6 is 1.8 mH, the input voltage is 3 V, and the step-up ratio is 1:22. Waveform (2) shows that the secondary inductance value of the transformers 11 and 21 in FIG. 6 is 1.8 mH, the input voltage is 3 V, the step-up ratio is 1:22, and a 200 pF capacitor is connected in parallel to each of the piezoelectric elements 1 a and 1 b in FIG. This is the case. Waveform (3) in FIG. 15 shows a secondary inductance value of 1.8 mH of transformers 11 and 21 in FIG. 6, an input voltage of 3 V, a step-up ratio of 1:22, and a 500 pF capacitor for each of piezoelectric elements 1a and 1b in FIG. Is added in parallel. Waveform (4) is for the case where the secondary inductance value of the transformers 11 and 21 in FIG. 6 is 2.2 mH, the input voltage is 3 V, and the step-up ratio is 1:24.

  FIG. 16A shows the relationship between the drive waveform and the a / b value by obtaining the value of a / b from the sections a and b described in FIG. 11 in the drive waveforms of FIGS. It is a figure. FIG. 16B shows the circumferential (rotation direction) amplitude and the axial (rotation axis) direction amplitude of the stator (vibration body) vibration amplitude in each drive waveform of FIGS. 14 and 15, and the drive waveform and the stator (vibration). (Body) It is the figure which showed the relationship with a vibration amplitude. FIG. 17 is a diagram showing the relationship between the value of a / b of the vibration waveform and the stator (vibrating body) vibration amplitude based on the relationship of FIGS. FIG. 17 shows that the vibration amplitude decreases as the value of a / b of the vibration waveform increases.

  When the ultrasonic motor is driven with the drive waveforms of waveforms (1) to (4) of FIGS. 14 and 15 using the drive device of FIG. 6, the superstructure using the vibrating body of FIG. The sonic motor can be driven normally with any driving waveform (1) to (4). However, the ultrasonic motor using the vibrating body having a large force coefficient shown in FIG. 3B may not be driven with the waveform (1). As can be seen from FIG. 16A, the waveform (1) has a large a / b value, and as a result, the vibration amplitude becomes small as can be seen from FIG. Therefore, in order to drive an ultrasonic motor having a force coefficient of 0.05 or more as in this embodiment, the value of a / b needs to be 1.7 or less.

  The value of a / b becomes large when the value of b is small. However, it is considered that the cause of the decrease in the vibration amplitude is not only due to the decrease in the value of b and the increase in the value of a / b as a result. It is also conceivable that the vibration amplitude decreases as the voltage value c shown in FIG. 11 decreases. Conversely, it is considered that the vibration amplitude increases as the value of c increases. Therefore, if the value of a / b is greater than 1.7, the ultrasonic motor can be driven normally by using a drive waveform having a large value of c.

  In this way, for an ultrasonic motor with a large force coefficient, the starting torque of the ultrasonic motor is increased by driving with a drive signal in which the value of a / b of the drive waveform or the value of c is adjusted. Appropriate driving can be performed.

  As described above, in this embodiment, the force coefficient of the ultrasonic motor is increased and the waveform of the driving voltage is limited to increase the starting torque of the ultrasonic motor and perform appropriate driving. be able to.

  In addition, the fact that the secondary inductance value L of the transformers 11 and 21 in the drive device of FIG. 6 and the Cd value, which is the electrostatic capacitance of the piezoelectric element of the ultrasonic motor, match, also indicates that the ultrasonic motor is driven normally. It is important to let In the present embodiment, the capacitance Cd value of the piezoelectric ceramic (piezoelectric element) of the ultrasonic motor is in the range of 1 [nF] <Cd <1.25 [nF], whereas the transformer of the drive device It is preferable that the secondary inductance value L of 11 and 21 is in the range of 1.9 [mH] <L <2.5 [mH], the transformer input voltage Vin = 3 V, and the transformer step-up ratio 1:24.

  Thus, for an ultrasonic motor having a large force coefficient, the range of the Cd value of the ultrasonic motor is specified, and the secondary inductance value L of the transformer on the drive device side is specified, whereby the L and Cd values are obtained. By adapting, it is possible to increase the starting torque of the ultrasonic motor and perform appropriate driving.

1 is a configuration diagram of a camera system according to an embodiment of the present invention. Sectional drawing which shows the structure of the ultrasonic motor of embodiment of this invention. The figure which shows the structure of the vibrating body (stator) of an ultrasonic motor. The figure which shows the equivalent circuit of an ultrasonic motor. The figure which shows the impedance curve of the equivalent circuit of FIG. The figure which shows the structure of the drive device of the ultrasonic motor of embodiment of this invention. The figure which shows the structure of the switching circuit of FIG. The figure which shows the drive frequency versus rotational speed characteristic of an ultrasonic motor. The figure which shows the timing chart of the drive of an ultrasonic motor. The figure for demonstrating the process in which signal A1, B1 used with the drive device of the ultrasonic motor of embodiment of this invention is produced | generated. The figure which shows the waveform of 1 period of the drive voltage in the drive device of the ultrasonic motor of embodiment of this invention. The figure for demonstrating the measurement point of a drive amplitude. The figure which shows the pattern of the electrode of the piezoelectric element provided in the vibrating body. The figure which shows the locus | trajectory of a drive waveform and vibration amplitude at the time of driving the vibrating body of FIG.3 (b). The figure which shows the locus | trajectory of a drive waveform and vibration amplitude at the time of driving the vibrating body of FIG.3 (b). (A) is a figure which shows the relationship between the value of a / b of a drive waveform and a vibration waveform, and the figure which shows the relationship between a vibration waveform and vibration amplitude. The figure which shows the relationship between the value of a / b of a vibration waveform, and the amplitude of a vibration waveform.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1a, 1b: Piezoelectric element, 2: DC power supply circuit, 3: Pulse generation circuit, 4, 5: Switching control circuit, 6a, 7a: Drive circuit, 11, 21: Transformer, 12, 13, 22, 23: MOSFET, DESCRIPTION OF SYMBOLS 101: Camera system, 102: Camera body, 103: Lens barrel, 107: Lens, 110: Ultrasonic motor, 201: Vibrating body (stator), 202: Elastic body, 202a, comb-tooth part, 202b: Base part, 202d: convex part, 203: piezoelectric body, 205: rotor.

Claims (11)

A ring-shaped vibrating body that vibrates in response to a drive signal;
A relative motion member that performs relative motion with respect to the vibrating body by vibration of the vibrating body,
A vibration actuator characterized in that an outer diameter of the vibrating body is 10 to 15 mm and a force coefficient is 0.05 or more. The vibration actuator according to claim 1,
The vibrating body is provided on an annular base portion, an elastic body provided on the relative motion member side with respect to the base portion, and a surface of the base portion opposite to a surface on which the elastic body is provided. A vibration actuator comprising: a piezoelectric element, wherein a convex portion is provided on a surface of the base portion on which the piezoelectric element is provided. Drive voltage output means for supplying a drive voltage to the vibration actuator;
In the middle of a predetermined cycle, control is performed to rapidly drop the drive voltage, a time from the start point to the sudden drop point in the predetermined cycle is a, and time from the sudden drop point to the end point in the predetermined cycle is b And a control unit that performs control so that a / b is 1.7 or less. A transformer for supplying a voltage from the secondary winding to the vibrating body of the vibration actuator, connecting a DC power source to the primary winding;
First switching means for turning on and off the current flowing in the primary winding of the transformer;
Second switching means for turning on and off the current flowing in the secondary winding of the transformer;
Within a predetermined period, the first switching means is turned on for a time a, then the first switching means is turned off for a time b, and the second switching means is turned on, and a / b is 1.7. A vibration actuator driving device comprising: a switching control unit that controls the following: A transformer for supplying a voltage from the secondary winding to the vibrating body of the vibration actuator, connecting a DC power source to the primary winding;
Control means for turning on and off the current flowing in the primary side winding or the secondary side winding of the transformer;
When the capacitance Cd of the piezoelectric element of the vibration actuator is 1 [nF] <Cd <1.25 [nF], the inductance value L of the secondary winding of the transformer is 1.9 [mH] <L <2.5 [mH] The drive device for the vibration actuator, In the drive device of the vibration actuator according to claim 5,
A drive device for a vibration actuator, wherein an input voltage of the transformer is 3V and a transformer step-up ratio is 1:24. In the drive device of the vibration actuator as described in any one of Claim 3 to 6,
The vibration actuator has a vibration body having an outer diameter of 10 to 15 mm and a force coefficient of 0.05 or more. The vibration actuator according to claim 1 or 2,
A lens barrel comprising a lens driven by the vibration actuator. A drive device for a vibration actuator according to any one of claims 3 to 6,
A vibration actuator driven by the driving device;
A lens barrel comprising a lens driven by the vibration actuator. The vibration actuator according to claim 1 or 2,
And a lens driven by the vibration actuator. A drive device for a vibration actuator according to any one of claims 3 to 6,
A vibration actuator driven by the driving device;
And a lens driven by the vibration actuator.

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