JP2014195382A - Vibration actuator, barrel, and camera - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a vibration actuator capable of preventing generation of abnormal noise or occurrence of trouble caused by unstable drive even in the case where a high-order vibration mode is included within a drive range, a barrel, and a camera.SOLUTION: A vibration actuator 30 comprises: a vibrator 110 which is vibrated by vibration of an electromechanical energy conversion element 112 to which two driving signals of phases different from each other are inputted; a mover 120 which is pressurized by the vibrator 110 and moved relatively to the vibrator 110 by vibration of the vibrator 110; and drive voltage regulation means 205 capable of regulating voltages of the driving signals. In the case where frequencies of the driving signals are settled within a resonant frequency band including a resonant frequency of the vibration actuator 30, the drive voltage regulation means 205 lowers the voltages of the driving signals so as to fall below a voltage in the case where the frequency of the driving signal is settled within any other band than the resonant frequency band.

Description

  The present invention relates to a vibration actuator, a lens barrel, and a camera.

Conventionally, in order to drive the vibration actuator, two drive signals having different phases are applied to the piezoelectric element. The frequency of the drive signal starts from the high frequency side where the vibration actuator rotates at a low speed, and decreases to the low frequency side where the vibration actuator rotates at a high speed.
When the frequency of the drive signal includes the resonance frequency of the higher-order vibration mode, there is a possibility that abnormal noise may be generated when the resonance frequency is exceeded or the drive may become unstable.
Therefore, start from the frequency (startup frequency) between the drive frequency used to drive the vibration actuator and the resonance frequency of the next higher-order vibration mode of the vibration mode (drive mode) including that drive frequency. The driving frequency is gradually lowered (for example, see Patent Document 1).

JP-A-3-22873

  However, the start-up frequency is limited to a frequency between the drive frequency and the resonance frequency of the next higher-order vibration mode of the drive mode, and thus has a limited range. For this reason, the resonance frequency of the higher-order vibration mode cannot be avoided due to the drive target and the drive control request, and the drive range may include the frequency range of the higher-order vibration mode.

  An object of the present invention is to provide a vibration actuator, a lens barrel, and a camera that can suppress the occurrence of abnormal noise.

The present invention solves the above problems by the following means.
According to the first aspect of the present invention, a vibrator that vibrates due to vibration of an electromechanical energy conversion element to which two drive signals having different phases are input, and the vibrator is pressurized, and the vibration is caused by vibration of the vibrator. A vibration actuator comprising: a moving element that moves relative to a vibrator; and a drive voltage adjusting unit that can adjust a voltage of the drive signal, wherein the frequency of the drive signal includes a resonance frequency of the vibration actuator. When in the frequency band, the drive voltage adjusting means lowers the voltage of the drive signal from a voltage in a band other than the resonance frequency band.
A second aspect of the present invention is the vibration actuator according to the first aspect, wherein the drive voltage adjusting means changes the voltage of the drive signal in response to a change in impedance of the vibration actuator during driving. This is a vibration actuator characterized by the above.
A third aspect of the present invention is the vibration actuator according to the first or second aspect, wherein the drive voltage adjusting means is configured to reduce the voltage of the drive signal when the frequency of the drive signal is the resonance frequency. The vibration actuator is characterized by lowering the most.
A fourth aspect of the present invention is a lens barrel including the vibration actuator according to any one of the first to third aspects.
A fifth aspect of the present invention is a camera including the lens barrel according to the fourth aspect.

  In addition, the said structure may be improved suitably, and at least one part may substitute for another structure.

  According to the present invention, it is possible to provide a vibration actuator, a lens barrel, and a camera that can suppress the generation of abnormal noise and the occurrence of problems due to unstable driving even when the driving range includes a higher-order vibration mode.

It is a conceptual block diagram of the camera in this embodiment. It is a longitudinal cross-sectional view of the ultrasonic motor which is one Embodiment of the vibration actuator which concerns on this invention. It is a block block diagram of the drive circuit in an ultrasonic motor. It is a figure which shows the drive area | region of an ultrasonic motor, the vibration mode, and the voltage of a drive signal. It is a flowchart of the voltage adjustment control by a voltage adjustment part. FIG. 5 is a diagram corresponding to FIG. 4 in which the driving area of the ultrasonic motor is different.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a conceptual configuration diagram of a camera 1 in the present embodiment.
The camera 1 includes a camera body 10 and a lens barrel 20. The lens barrel 20 is an interchangeable lens that can be attached to and detached from the camera body 10. In the present embodiment, an example in which the lens barrel 20 is replaceable is shown. However, the present invention is not limited to this. For example, the camera body and the lens barrel may be an integrated camera.

The camera body 10 includes an image sensor 11, a control device 12, an AF sensor 13, and the like.
The imaging element 11 is a photoelectric conversion element such as a CCD or CMOS, for example, which converts an image formed on the imaging surface by the lens barrel 20 into an electrical signal and outputs the electrical signal.
The control device 12 calculates the movement amount of the focus group in the lens barrel 20 and controls the entire camera 1.
The AF sensor 13 is, for example, a CCD line sensor or the like for performing focus detection.

The lens barrel 20 includes an imaging optical system including a lens group (not shown) including a focusing lens 21, a cam barrel 22 that moves the focusing lens 21 provided therein, and an ultrasonic wave that rotationally drives the cam barrel 22. A motor 30 and a detection unit 23 that detects the position and speed of the focusing lens 21 are provided.
The ultrasonic motor 30 is a drive source that drives the focusing lens 21. The rotational force of the ultrasonic motor 30 is transmitted to the cam cylinder 22 via the idle gear 24, and the cam cylinder 22 moves and drives the focusing lens 21 provided therein by rotation. The ultrasonic motor 30 is driven based on a focusing command input from the control device 12 of the camera 1. The ultrasonic motor 30 will be described in detail later.
The detection unit 23 includes an optical encoder, a magnetic encoder, and the like, and detects the position and speed of the focusing lens 21. In this embodiment, the position and speed of the focusing lens 21 are detected by detecting the position and speed of the cam cylinder 22.

  In the camera 1 configured as described above, a subject image is formed on the imaging surface of the imaging element 11 in the camera body 10 by the imaging optical system including the focusing lens 21 in the lens barrel 20. The image of the subject image formed by the image sensor 11 is converted into an electrical signal, and the signal is A / D converted and image processed to obtain (photograph) image data. A series of operations related to photographing in the camera 1 is controlled by a control device 12 included in the camera body 10. Further, at the time of shooting, the control device 12 drives the ultrasonic motor 30 of the lens barrel 20 based on the detection information of the AF sensor 13 to perform focus adjustment.

Next, the ultrasonic motor 30 will be described in detail with reference to FIGS. 2 and 3.
FIG. 2 is a longitudinal sectional view of an ultrasonic motor 30 which is an embodiment of the vibration actuator according to the present invention. FIG. 3 is a block configuration diagram of the drive circuit 200 of the ultrasonic motor 30.
The ultrasonic motor 30 includes a motor main body 100 and a drive circuit 200.
The motor main body 100 includes a vibrator 110, a mover 120, an output shaft 130, a pressure member 140, an output gear 150, and the like. The vibrator 110 side is fixed and the mover 120 is rotated.

The vibrator 110 is a substantially annular member having an elastic body 111 and a piezoelectric body 112 bonded to the elastic body 111.
The elastic body 111 is formed of a metal material having a high resonance sharpness, and has a substantially annular shape. The elastic body 111 includes a comb tooth portion 111a, a base portion 111b, and a flange portion 111c.
The comb tooth portion 111a is formed by cutting a plurality of grooves on the surface opposite to the surface to which the piezoelectric body 112 is bonded, and the tip surface of the comb tooth portion 111a is in pressure contact with the moving element 120. It becomes a driving surface for driving the moving element 120. This drive surface is subjected to a lubricious surface treatment such as Ni-P (nickel-phosphorus) plating.

The base portion 111b is a portion that is continuous in the circumferential direction of the elastic body 111, and the piezoelectric body 112 is bonded to the surface of the base portion 111b opposite to the comb tooth portion 111a.
The flange portion 111c is a hook-like portion protruding in the inner diameter direction of the elastic body 111, and is disposed at the center of the base portion 111b in the thickness direction. The vibrator 110 is fixed to the fixing member 101 by the flange portion 111c.

  The piezoelectric body 112 is an electromechanical conversion element that converts electrical energy into mechanical energy. For example, a piezoelectric element or an electrostrictive element is used. The piezoelectric body 112 is divided into ranges in which electric signals of two phases (A phase and B phase) are input along the circumferential direction of the elastic body 111. In each phase, elements in which polarization is alternated every ½ wavelength are arranged, and an interval of ¼ wavelength is provided between the A phase and the B phase.

A drive signal having a predetermined voltage and frequency is supplied to the piezoelectric body 112 from a drive circuit 200 described later via the flexible printed circuit board 102 connected to the electrodes of the respective phases. The piezoelectric body 112 expands and contracts by this drive signal, and a traveling wave is generated on the drive surface of the elastic body 111. In this embodiment, four traveling waves are generated.
The moving element 120 is a member that is formed of a light metal such as aluminum and is rotationally driven by a traveling wave generated on the driving surface of the elastic body 111. In the moving element 120, a surface treatment such as alumite for improving wear resistance is applied to the surface of the moving element 120 that contacts the vibrator 110 (the driving surface of the elastic body 111).

The output shaft 130 is a substantially cylindrical member. The output shaft 130 is provided so that one end thereof is in contact with the moving element 120 via the rubber member 103 and rotates integrally with the moving element 120.
The rubber member 103 is a substantially ring-shaped member made of rubber. The rubber member 103 has a function of allowing the moving element 120 and the output shaft 130 to rotate integrally with rubber viscoelasticity, and a function of absorbing vibration so as not to transmit vibration from the moving element 120 to the output shaft 130. And butyl rubber, silicon rubber, propylene rubber and the like are used.

The pressurizing member 140 is a member that generates a pressing force that pressurizes the vibrator 110 and the moving member 120, and is provided between the output gear 150 and the bearing receiver 104. In this embodiment, the pressure member 140 uses a compression coil spring, but is not limited thereto.
The output gear 150 is inserted so as to fit in the D cut of the output shaft 130, is fixed by a stopper 106 such as an E ring, and is provided so as to be integrated with the output shaft 130 in the rotation direction and the axial direction. The output gear 150 rotates with the rotation of the output shaft 130 and transmits driving force to the idle gear 24 (see FIG. 1).
The bearing receiver 104 is disposed on the inner diameter side of the bearing 105, and the bearing 105 is disposed on the inner diameter side of the fixed member 101.

  The pressing member 140 pressurizes the vibrator 110 toward the moving element 120 in the axial direction of the output shaft 130, and the moving element 120 pressurizes and contacts the driving surface of the vibrator 110 due to the applied pressure. Driven by rotation. A pressure adjusting washer may be provided between the pressure member 140 and the bearing receiver 104 so that an appropriate pressure can be obtained for driving the ultrasonic motor 30.

  The motor body 100 configured as described above generates a traveling wave in the vibrator 110 by a drive signal supplied from a drive circuit 200 described later, whereby the moving element 120 is rotationally driven, and rotational force is generated from the output gear 150. Output. The speed of the moving element 120 (that is, the number of rotations of the output gear 150) changes according to the frequency of the drive signal.

Next, the drive circuit 200 in the ultrasonic motor 30 will be described.
As shown in FIG. 3, the drive circuit 200 includes a control unit 201, an oscillation unit 202, a phase shift unit 203, amplification units 204A and 204B, a voltage adjustment unit 205, and a vibration detection unit 206. Yes.
The control unit 201 controls the driving of the motor main body 100 based on the driving command from the control device 12 in the lens barrel 20 or the camera 1 main body and the position and speed information of the focusing lens 21 by the detecting unit 23. To do. That is, the control unit 201 receives the detection signal from the detection unit 23, obtains position information and speed information based on the values, and causes the focusing lens 21 to be positioned at the target position commanded from the control device 12. The drive frequency of the drive signal generated by the oscillator 202 is controlled.

The oscillating unit 202 generates a drive signal having a desired frequency according to a command from the control unit 201. The drive signal is asymmetric in one direction in the + direction when the potential is zero.
The phase shifter 203 divides the drive signal generated by the oscillator 202 into two drive signals having a phase difference of 90 degrees.
The amplification units 204A and 204B boost the two drive signals divided by the phase shift unit 203 to desired voltages, respectively. The drive signals from the amplifiers 204A and 204B are applied to the piezoelectric body 112 of the motor body 100, whereby a traveling wave is generated in the vibrator 110 and drives the moving element 120.

The voltage adjustment unit 205 identifies the resonance frequency band of the higher-order vibration mode of the vibrator 110 in the motor main body 100 based on the detection result of the vibration detection unit 206. In the resonance frequency band in the higher-order vibration mode, the amplification unit 204A, The voltage of the drive signal supplied from 204B to the motor main body 100 (piezoelectric body 112) is changed to be lower than the rated voltage.
The voltage adjustment unit 205, higher-order vibration mode, and resonance frequency band will be described later.
The voltage adjustment unit 205 includes a variable resistor, for example. The voltage adjustment unit 205 will be described in detail later.
The vibration detection unit 206 detects a voltage generated by the piezoelectric effect of the piezoelectric body 112 in the motor main body 100.

The motor main body 100 operates as follows by the drive circuit 200 having the above configuration.
When the movement target position of the focusing lens 21 is input from the control device 12 in the camera body 10 to the control unit 201, the control unit 201 detects the input target position and the position of the focusing lens 21 input from the detection unit 23. Based on the information, the driving amount of the motor main body 100 is calculated and a driving signal is generated from the oscillation unit 202. From the drive signal generated by the oscillating unit 202, the phase shift unit 203 generates two drive signals having a 90 ° phase difference, and amplifies them to a desired voltage by the amplifiers 204A and 204B.

The drive signal is applied to the A phase and the B phase of the piezoelectric body 112 of the motor main body 100, respectively. As a result, the piezoelectric body 112 is excited, and the elastic body 111 generates a fourth-order bending vibration in which the positional phases of the A phase and the B phase are shifted by ¼ wavelength. The A phase drive signal and the B phase drive signal are 90 ° out of phase, and the two bending vibrations are combined into four traveling waves.
An elliptical motion is generated at the wavefront of the traveling wave, and the moving element 120 that is in pressure contact with the driving surface of the elastic body 111 is frictionally driven by the elliptical motion. That is, the mover 120 rotates, and the rotational force is output from the output gear 150 via the output shaft 130.

As described above, the output rotation speed of the motor main body 100 varies depending on the frequency of the drive signal. That is, when the frequency changes from a high frequency to a low frequency, the rotation speed changes from a low rotation speed to a high rotation speed. The control unit 201 controls the output rotation speed by changing the frequency of the drive signal generated by the oscillation unit 202.
The range of the output rotation speed of the motor main body 100 is set so that the focusing lens 21 to be driven can move from the movement start (speed 0) to the maximum movement speed (maximum speed).

Next, voltage control by the voltage adjusting unit 205 in the drive circuit 200 will be described with reference to FIGS.
4A and 4B are diagrams showing the drive region, vibration mode, and drive signal voltage of the ultrasonic motor 30, wherein FIG. 4A shows the vibration mode of the vibrator 110, the vertical axis represents impedance, and the horizontal axis represents frequency. It is. (B) shows the voltage of the drive signal corresponding to (a), the vertical axis is voltage, and the horizontal axis is frequency. (C) is a figure which shows the example of the voltage change of the drive signal different from (b).
FIG. 5 is a flowchart of voltage adjustment control by the voltage adjustment unit 205.
FIG. 6 is a diagram corresponding to FIG. 4 in which the drive region of the ultrasonic motor 30 is different.

  Here, as shown in FIG. 4A, a vibration mode mainly used in driving the ultrasonic motor 30 is referred to as a drive vibration mode. The vibration mode next to the drive vibration mode is referred to as a high-order vibration mode. A certain range including the resonance point and the antiresonance point of the higher order vibration mode and in which the impedance changes greatly is called a resonance frequency band of the higher order vibration mode.

As described above, the voltage adjustment unit 205 in the drive circuit 200 identifies the resonance frequency band of the higher-order vibration mode of the vibrator 110 in the motor main body 100 based on the detection result of the vibration detection unit 206, and in the higher-order vibration mode. In the resonance frequency band, the voltage of the drive signal supplied from the amplifiers 204A and 204B to the motor body 100 (piezoelectric body 112) is changed to be lower than the rated voltage.
That is, as shown in FIG. 4A, when the frequency of the drive signal applied to the motor main body 100 (vibrator 110) is in the resonance frequency band of the higher-order vibration mode, the drive is performed as shown in FIG. The voltage of the signal is set to a predetermined adjustment voltage (0 V or higher) lower than the rated voltage.

  As described above, in the frequency band of the high-order vibration mode, by setting the voltage of the drive signal to an adjustment voltage lower than the rated voltage, power is supplied to the piezoelectric body 112 but the driving force is reduced. As a result, vibration is suppressed, and generation of abnormal noise due to the elastic body 111 of the vibrator 110 colliding with the moving element 120 can be suppressed. Moreover, since the driving force is reduced even when the rotation becomes unstable, the occurrence of problems due to driving can be suppressed.

  Here, the voltage adjustment unit 205 identifies the frequency band of the higher-order vibration mode as the adjustment voltage, for example, by setting a threshold value of a voltage value (deformed voltage value) generated by the deformation of the piezoelectric body 112, and this threshold value, The deformation voltage value of the piezoelectric body 112 detected by the vibration detection unit 206 is sequentially compared, and if the deformation voltage value exceeds the threshold value, it is determined that the higher-order vibration mode.

  FIG. 5 shows a flowchart of such resonance frequency band identification and voltage adjustment control. In the following description and FIG. 5, step is also abbreviated as “S”.

First, a drive signal having a rated voltage is applied to the piezoelectric body 112 at a frequency (higher than or equal to the resonance frequency band) f1 of the higher-order vibration mode, a frequency sweep is started, and the frequency is gradually lowered (S501).
At the same time, the deformation voltage Vx of the piezoelectric body 112 is read (S502) and compared with the threshold value Vs1 (S503).
When a drive signal having a rated voltage is applied to the piezoelectric body 112, when the frequency of the drive signal enters the resonance frequency band (f2), the amount of voltage generated by the deformation of the piezoelectric body 112 increases. The threshold value Vs1 is a threshold value for determining whether or not this deformation has occurred.

If it is determined in step 503 that the deformation voltage: Vx is smaller than the threshold value: Vs1 (Yes), the reading of the voltage: Vx in step 502 is repeated.
On the other hand, if it is determined in step 503 that the voltage: Vx has become equal to or greater than the threshold value: Vs1 (No), it is determined that resonance is occurring, and the voltage of the drive signal supplied to the piezoelectric body 112 is set to the rated voltage. A lower adjustment voltage is set (S504).

Further, the frequency of the drive signal is lowered and compared with the deformation voltage: Vx of the piezoelectric body 112 and the threshold value: Vs2 (S505).
When a drive signal of an adjustment voltage is applied to the piezoelectric body 112, if the frequency of the drive signal becomes higher than the resonance frequency band (f3), the amount of voltage generated due to the deformation of the piezoelectric body 112 decreases. The threshold value Vs2 is a threshold value for determining whether or not this deformation has occurred. When smaller than the threshold value Vs2, it indicates that the resonance frequency band has been exceeded.

If it is determined in step 505 that the deformation voltage: Vx is not less than or equal to the threshold value: Vs2 (No), the reading of the voltage: Vx in step 505 is repeated.
If it is determined that the deformation voltage: Vx is equal to or lower than the threshold value: Vs (Yes), it is determined that the resonance has ended, and the voltage of the drive signal supplied to the piezoelectric body 112 is returned to the rated voltage (S506).

  In addition to the above, the voltage adjustment control by the voltage adjustment unit 205 is stored in advance in, for example, a memory (not shown) provided in the drive circuit 200, and the stored information is referred to during driving. Therefore, the adjustment voltage may be used in the corresponding frequency band. In other words, the identification of the frequency band of the higher-order vibration mode is performed by driving the motor body 100 in the entire drive region (frequency band) after assembly of the lens barrel 20 and detecting the piezoelectric body detected by the vibration detection unit 206. The frequency band of the higher order vibration mode is set based on the voltage value of 112, and the frequency band of the higher order vibration mode is stored in a memory or the like.

  In FIG. 4B, the voltage adjustment unit 205 immediately changes the rated voltage to the adjustment voltage in the frequency band in which the vibrator 110 is in the high-order vibration mode. However, the adjustment voltage may be gradually changed in accordance with the state of the higher-order vibration mode (for example, change in impedance value). That is, for example, as shown in FIG. 4C, the voltage is lowest at the frequency of the resonance point of the higher-order vibration mode that can be read from the change in impedance shown in FIG. It is set low, and its vicinity is gradually changed so as to be continuous with the rated voltage. Thereby, the influence by lowering the voltage of the drive signal can be minimized.

FIG. 6 is a diagram showing the drive region and vibration mode of the ultrasonic motor 30 as in FIG. 4. In this example, the drive region of the ultrasonic motor 30 is different, and two higher-order vibrations are present in the drive region. There are modes (A, B).
In such a case as well, as shown in (b), the voltage of the drive signal is reduced to the adjustment voltage in the frequency region (resonance frequency bands A and B) corresponding to the higher order vibration modes (A and B). .

As described above, this embodiment has the following effects.
(1) In the ultrasonic motor 30 according to the present embodiment, the voltage adjustment unit 205 in the drive circuit 200 sets the resonance frequency band of the higher-order vibration mode of the vibrator 110 in the motor main body 100 based on the detection result of the vibration detection unit 206. In the resonance frequency band of the higher-order vibration mode, the voltage of the drive signal supplied from the amplifiers 204A and 204B to the motor body 100 (piezoelectric body 112) is changed to an adjustment voltage lower than the rated voltage.
Thereby, although electric power is supplied to the piezoelectric body 112, the driving force is reduced. As a result, vibration is suppressed, and generation of abnormal noise due to the elastic body 111 of the vibrator 110 colliding with the moving element 120 can be suppressed. In particular, even in the case where the high-order vibration mode is set in the vicinity of the rotation start frequency, it is possible to suppress generation of annoying abnormal noise at the start of rotation. Further, even if the rotation becomes unstable, the driving force is reduced, so that the occurrence of problems can be suppressed.

(Deformation)
The present invention is not limited to the above-described embodiment, and various modifications and changes as described below are possible, and these are also within the scope of the present invention.
(1) In the present embodiment, the ultrasonic motor 30 that uses vibration in the ultrasonic region is described as an example of the vibration actuator. However, the present invention is not limited to this, and the vibration actuator that uses vibration outside the ultrasonic region is used. You may apply.

(2) In the present embodiment, the ultrasonic motor 30 is provided in the lens barrel 20 and used as a drive unit that performs a focus operation. However, the present invention is not limited thereto, and for example, a drive unit that performs a zoom operation. You may use for.
(3) In this embodiment, the camera 1 includes the image sensor 11 and records (shoots) an image as electronic information. However, the present invention is not limited to this, and is applied to, for example, a camera using a film. You can do it.
In addition, although embodiment and a deformation | transformation form can also be used in combination as appropriate, detailed description is abbreviate | omitted. Further, the present invention is not limited to the embodiment described above.

  DESCRIPTION OF SYMBOLS 1: Camera, 20: Lens barrel, 23: Detection part, 30: Ultrasonic motor, 100: Motor main body, 110: Vibrator, 120: Mover, 200: Drive circuit, 201: Control part, 205: Voltage adjustment Unit 206: Vibration detection unit

Claims (5)

A vibrator that vibrates due to vibration of an electromechanical energy conversion element to which two drive signals having different phases are input;
A mover that is pressurized by the vibrator and moves relative to the vibrator by the vibration of the vibrator;
Drive voltage adjusting means capable of adjusting the voltage of the drive signal;
A vibration actuator comprising:
When the frequency of the drive signal is in a resonance frequency band that includes the resonance frequency of the vibration actuator, the drive voltage adjusting means lowers the voltage of the drive signal to a voltage that is in a band other than the resonance frequency band. about,
Vibration actuator characterized by The vibration actuator according to claim 1,
The drive voltage adjusting means changes the voltage of the drive signal in response to a change in impedance of the vibration actuator during driving;
Vibration actuator characterized by The vibration actuator according to claim 1 or 2,
The drive voltage adjusting means reduces the voltage of the drive signal most when the frequency of the drive signal becomes the resonance frequency;
Vibration actuator characterized by   A lens barrel comprising the vibration actuator according to any one of claims 1 to 3.   A camera comprising the lens barrel according to claim 4.

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