JP6659995B2 - Vibration wave motor and optical equipment - Google Patents

Description

  The present invention relates to a vibration wave motor and an optical device.

  Conventionally, there is a lens barrel provided with a vibration wave motor. The vibration wave motor includes an electromechanical transducer, a vibrator vibrated by the electromechanical transducer, and a movable element that is brought into pressure contact with the vibrator and that rotates and moves by vibrating the vibrator (see Patent Document 1). . Such a vibration wave motor may generate abnormal noise if the dynamic range is raised too much.

JP 2006-333679 A

A vibration wave motor according to the present invention has an annular shape including a vibrator that vibrates due to vibration of an electromechanical transducer, and a mover that is in pressure contact with the vibrator and moves relatively to the vibrator. The vibrator has a base portion in contact with the electromechanical transducer, and a comb-shaped portion formed in a comb shape extending from the base portion to the mover side. The height from the electromechanical transducer toward the mover is Kh, the height of the base is Bh, the radial widths of the comb teeth and the base are Kr, and are input to the electromechanical transducer. When the wavelength of the drive signal is λ, the coefficient C = (Kh / Bh) × (Kr / λ) is configured to be 0.17 to 0.5.
Further, an optical apparatus according to the present invention is configured to include the vibration wave motor.

It is a figure explaining camera 1 provided with a lens barrel provided with a vibration wave motor of an embodiment. FIG. 2 is a diagram illustrating a lens barrel 20 according to the embodiment of the present invention. FIG. 3 is a diagram illustrating a vibrator 11 of the vibration wave motor 10 of the embodiment. FIG. 3 is a block diagram illustrating a driving device 40A of the vibration wave motor 10. It is a sectional view of vibration wave motor 10 of an embodiment. 4 is a graph showing a relationship between a force coefficient and a coefficient C. 4 is a graph showing a relationship between an electromechanical coupling coefficient and a coefficient C. 6 is a graph showing a result of measuring a startable voltage while changing a value of a coefficient C.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 is a diagram illustrating a camera 1 including a lens barrel 20 including the vibration wave motor according to the embodiment.
The camera 1 is a camera capable of capturing a still image and a moving image, and includes a lens barrel 20 which is an imaging optical system, an imaging element 30, an AFE (Analog front end) circuit 60, an image processing unit 70, and an audio processing unit. It comprises a detection unit 80, an operation member 90, a CPU 100, a buffer memory 110, a recording interface 120, a memory 130, and a monitor 140, and can be connected to a PC 150 of an external device.

  The lens barrel 20 includes a plurality of optical lens groups L, and forms a subject image on a light receiving surface of the image sensor 30. In FIG. 1, the plurality of optical lens groups L are simplified and shown as single lenses. Of the optical lens group L, a third lens group L3 for AF (shown in FIG. 2) described later is driven by the vibration wave motor 10.

  The imaging device 30 is configured by a CMOS image sensor or the like in which light receiving elements are two-dimensionally arranged on a light receiving surface. The imaging device 30 generates an analog image signal by photoelectrically converting a subject image by a light beam that has passed through the lens barrel 20.

  The analog image signal is input to the AFE circuit 60. The AFE circuit 60 performs gain adjustment (signal amplification according to ISO sensitivity) for an analog image signal. Specifically, the imaging sensitivity is changed within a predetermined range in response to a sensitivity setting instruction from CPU 100. The AFE circuit 60 further converts the image signal after analog processing into digital data by a built-in A / D conversion circuit. The digital data is input to the image processing unit 70.

The image processing unit 70 performs various types of image processing on digital image data.
The buffer memory 110 temporarily stores image data in a process before or after image processing by the image processing unit 70.

  The sound detection unit 80 includes a microphone and a signal amplification unit. The sound detection unit 80 mainly detects and captures sound from the direction of a subject when capturing a moving image, and transmits the data to the CPU 100.

  The operation member 90 indicates a mode dial, a cross key, an enter button, and a release button, and sends an operation signal corresponding to each operation to the CPU 100. The setting of still image shooting and moving image shooting is set by the operation member 90.

  The CPU 100 controls the overall operation of the camera 1 by executing a program stored in a ROM (not shown). For example, AF (auto focus) operation control, AE (auto exposure) operation control, auto white balance control, and the like are performed.

  The recording interface 120 has a connector (not shown), and a recording medium such as a memory card 121 is connected to the connector, and writes data into and reads data from the connected recording medium. .

The memory 130 records a series of image data subjected to image processing. The camera 1 of the present embodiment captures an image corresponding to a moving image.
The monitor 140 includes a liquid crystal panel, and displays an operation menu, a still image, a moving image, and the like in accordance with an instruction from the CPU 100.

Next, the lens barrel 20 will be described.
FIG. 2 is a diagram illustrating the lens barrel 20 of the embodiment. FIG. 3 is a diagram illustrating the vibrator 11 of the vibration wave motor 10 according to the embodiment.
The lens barrel 20 includes an outer fixed barrel 31 that covers an outer peripheral portion of the lens barrel 20, and an inner fixed barrel 32 that is located on an inner circumferential side of the outer fixed barrel 31. The vibration wave motor 10 is provided between the cylinder 32.

  A first lens unit L1, a second lens unit L2, a third lens unit L3, which is an AF lens held by an AF ring 34, and a fourth lens unit L4 are arranged on the inner fixed barrel 32 from the object side. The first lens unit L1, the second lens unit L2, and the fourth lens unit L4 are fixed to the inner fixed cylinder 32. The third lens unit L3 is configured to be movable with respect to the inner fixed cylinder 32 by moving the AF ring 34.

As shown in FIG. 2, the vibration wave motor 10 includes a vibrator 11, a mover 15, a pressurizing member 18, and the like. The vibrator 11 is fixed, and the mover 15 is driven to rotate.
The vibrator 11 will be described. As shown in FIG. 3, the vibrator 11 includes an electromechanical conversion element (hereinafter, referred to as a piezoelectric body 13) such as a piezoelectric element or an electrostriction element that converts electric energy into mechanical energy, and a piezoelectric body 13. And an elastic body 12 joined to the elastic body 12. A traveling wave is generated in the vibrator 11.

The elastic body 12 is made of a metal material having a large resonance sharpness. The shape of the elastic body 2 is an annular shape. On the surface of the elastic body 12 opposite to the surface with which the piezoelectric body 13 is in contact, a comb-tooth portion 12a having a groove 12c is formed. 15 is contacted under pressure.
The vibration wave motor 10 drives the third lens unit L3 by driving the moving element 15 using a driving force generated on a driving surface by excitation of the piezoelectric body 13. The reason for cutting off the groove 12c is to make the neutral plane of the traveling wave as close to the piezoelectric body 13 as possible, thereby amplifying the amplitude of the traveling wave on the driving surface. In the elastic member 12, a portion of the elastic member 12 from the contact surface where the piezoelectric member 13 contacts to the contact surface where the moving element 15 contacts is not cut by the groove 12c, and is referred to as a base portion 12b in the present embodiment.

  The piezoelectric body 13 is arranged in contact with the surface of the base portion 12b opposite to the comb tooth portion 12a. The driving surface of the elastic body 12 is subjected to a lubricating surface treatment.

  The piezoelectric body 13 is generally formed of a material such as lead zirconate titanate, which is generally called PZT, but may be other materials than PZT. For example, it may be composed of a lead-free material such as potassium sodium niobate, potassium niobate, sodium niobate, barium titanate, sodium bismuth titanate, and potassium bismuth titanate.

  As shown in FIG. 2, a nonwoven fabric 16, a pressing plate 17, and a pressing member 18 are arranged below the piezoelectric body 13. The nonwoven fabric 16 is made of felt, for example, and is arranged below the piezoelectric body 13 so that the vibration of the vibrator 11 is not transmitted to the pressing plate 17 and the pressing member 18.

  The pressure plate 17 is configured to receive the pressure of the pressure member 18. The pressing member 18 is formed of a disc spring, is disposed below the pressing plate 17, and generates a pressing force. In the present embodiment, the pressing member 18 is a disc spring, but may be a coil spring or a wave spring instead of the disc spring. The pressing member 18 is held by the holding ring 19 being fixed to the fixing member 14.

  The moving element 15 is made of a light metal such as aluminum, and the surface 15a of the sliding surface is subjected to a surface treatment such as a sliding material for improving abrasion resistance (see FIG. 3).

  A vibration absorbing member 23 made of rubber or the like is arranged on the movable element 15 to absorb vertical vibration of the movable element 15, and an output transmission member 24 is arranged thereon. .

  The output transmission member 24 regulates the pressing direction and the radial direction by a bearing 25 provided on the fixed member 14, whereby the pressing direction and the radial direction of the movable element 15 are regulated. I have.

  The output transmission member 24 has a projection 24a from which a fork 35 connected to a cam ring 36 is fitted. The cam ring 36 rotates with the rotation of the output transmission member 24.

  A key groove 37 is cut in the cam ring 36 at an angle to the circumferential direction. A fixing pin 38 is provided on the outer peripheral side of the AF ring 34. The fixed pin 38 is fitted in the key groove 37, and the AF ring 34 is driven in the optical axis straight traveling direction by rotating the cam ring 36, so that the AF ring 34 can be stopped at a desired position.

  A holding ring 19 is attached to the fixing member 14 with a screw. By attaching the holding ring 19 to the fixed member 14, the components from the output transmission member 24 to the moving element 15, the vibrator 11, and the pressing member 18 can be configured as one motor unit.

Next, a driving device 40A for driving the vibration wave motor 10 will be described.
FIG. 4 is a block diagram illustrating a driving device 40A of the vibration wave motor 10. The driving device 40A is provided on the substrate 40 (see FIG. 2).
The driving device 40A is connected to the vibration wave motor 10 as shown in FIG. 4, receives rotation speed information of the vibration wave motor 10 from a rotation detection unit 45 provided in the vibration wave motor 10, and The control of the motor 10 is also performed.

The drive device 40A includes a drive control unit 41, an oscillation unit 42, a phase shift unit 43, and an amplification unit 44.
The drive control unit 41 controls the drive of the vibration wave motor 10 based on a drive command from the lens barrel 20 or the CPU 100 of the camera 1 body. The drive control unit 41 receives rotation information of the vibration wave motor 10 as control information from a rotation detection unit 45 attached to the vibration wave motor 10.

The oscillating unit 42 generates a drive signal having a desired wavelength and frequency according to a command from the drive control unit 41.
The phase shifter 43 divides the drive signal generated by the oscillator 42 into two drive signals having different phases.
The amplifier 44 boosts the two drive signals divided by the phase shifter 43 to desired voltages.
The two driving signals from the amplifying unit 44 are transmitted to the vibration wave motor 10, and a traveling wave is generated in the vibrator 11 by applying the two driving signals, and the moving element 15 is driven.

  The rotation detection unit 45 is configured by an optical encoder, a magnetic encoder, or the like, detects the position and speed of a driven object driven by driving the movable element 15, and outputs the detected value to the drive control unit 41 as an electric signal. .

  In the drive device 40A having the above configuration, the drive control unit 41 controls the drive of the vibration wave motor 10 based on a drive command from the lens barrel 20 or the CPU 100 of the camera 1 body. That is, upon receiving the detection signal from the rotation detection unit 45, the drive control unit 41 obtains position information and speed information based on the values, and controls the drive signal so that the drive signal is positioned at the target position. . That is, the frequency of the oscillating unit 42, the phase difference of the phase shift unit 43, and the voltage of the amplifying unit 44 are controlled.

  In the present embodiment, in order to improve the performance of the lens barrel 20 having the above-described configuration, the dynamic range of the rotation speed of the vibration wave motor 10 is extended. The expansion of the dynamic range of the rotation speed of the vibration wave motor 10 is to expand the range of the rotation speed that can be used in the vibration wave motor 10.

Therefore, the lower limit of the number of revolutions will be examined.
By manipulating the driving frequency and the phase difference of the vibration wave motor 10, the rotation speed of the vibration wave motor 10 can be reduced. However, when the rotation speed falls below a certain value, the driving force from the vibrator 11 to the moving member 15 is reduced. Cannot be transmitted, and the rotation of the movable element 15 stops.

Here, the force coefficient A and the electromechanical coupling coefficient Kvn will be described.
The force coefficient A is a parameter represented by an inductance when the piezoelectric body 13 is represented by an equivalent circuit and a mass m of a stator including the piezoelectric body 13 and the elastic body 12.
The electromechanical coupling coefficient Kvn is a square root of a ratio of electrical energy applied to the vibration wave motor 10 that can be converted into mechanical energy. The electromechanical coupling coefficient Kvn indicates a conversion efficiency (electromechanical coupling coefficient) from electric energy to mechanical energy. The larger this value is, the higher the conversion efficiency from electrical energy to mechanical energy is.

  It is considered that by increasing the force coefficient A or the electromechanical coupling coefficient Kvn, the conversion efficiency between electric energy and mechanical energy is improved, so that the lower limit of the rotation speed of the vibration wave motor 10 can be reduced. .

FIG. 5 is a cross-sectional view of the vibrator 11 provided in the vibration wave motor 10 of the embodiment. As shown in the figure, the height of the comb tooth portion 12a: Kh, the height of the base portion 12b: Bh, the radial width of the comb tooth portion 12a and the base portion 12b (difference between the inner diameter and the outer diameter): Kr, The wavelength of the input voltage oscillated by the oscillator 42 and input to the piezoelectric body 13 is λ.
Then, the following coefficient C calculated from these values is introduced.
C = (Kh / Bh) × (Kr / λ)
Here, the height Kh of the comb teeth 12a is the distance (length) from the contact surface of the comb teeth 12a with which the piezoelectric body 13 contacts to the contact surface with which the moving element contacts. The height Bh of the base portion 12b is a distance of a portion (length) from the contact surface of the elastic body 12 with which the piezoelectric body 13 contacts to the contact surface of the movable member, excluding the height of the comb teeth portion 12a. (Length).

The relationship between the coefficient C, the force coefficient, and Kvn was determined by simulation.
FIG. 6 is a graph showing the relationship between the force coefficient and the coefficient C. FIG. 7 is a graph showing the relationship between the electromechanical coupling coefficient and the coefficient C.
As shown in FIG. 6, as the value of the coefficient C increases, the force coefficient A also increases .

That is, at C = (Kh / Bh) × (Kr / λ), the height of the comb tooth portion 12a: Kh, the height of the base portion 12b: Bh, and the radial width of the comb tooth portion 12a and the base portion 12b ( The difference between the inner diameter and the outer diameter): Kr and the wavelength of the input voltage: λ are adjusted to increase the value of the coefficient C, whereby the force coefficient A can be increased.

The rotation speed of the vibration wave motor 10 is low when the driving voltage is low and becomes high when the driving voltage is high. However, when the driving voltage is too low, the driving force is not transmitted to the moving element 15 and the motor 15 does not rotate.
However, as described above, when the coefficient C is increased, the force coefficient A is increased, and the conversion efficiency from electrical energy to mechanical energy is improved. Therefore, when the force coefficient A increases, the number of rotations can be obtained even with smaller electric energy. Therefore, it is considered that by increasing the coefficient C, the lower limit voltage (startable voltage) at which the rotational force can be transmitted can be reduced, and the dynamic lens of the rotational speed can be increased.

FIG. 8 is a graph showing the result of measuring the startable voltage while changing the actual value of the coefficient C.
Here, as a result of the actual measurement, at the coefficient C <0.17, abnormal noise was generated from the vibration wave motor 10. It is considered that the reason for this is that as the coefficient C decreases, the pressing force between the vibrator 11 and the moving element 15 in the vibration wave motor 10 decreases.
Also, when 0.5 <coefficient C, abnormal noise was generated from the vibration wave motor 10. When the coefficient C is larger than 0.5, a vibration mode other than the vibration mode for driving the movable element 15 to rotate is generated in the comb tooth portion 12a, and the vibration wave motor 10 It is considered that the behavior of is not stable.
Therefore, the coefficient C is preferably set to 0.17 ≦ C ≦ 0.5 in order to drive the vibration wave motor 10 so that no abnormal noise is generated.

Then, in a further range of 0.17 ≦ C ≦ 0.2 in the usable range of the coefficient C, 0.17 ≦ C ≦ 0.5, the coefficient C increases as shown in FIG. The startable voltage also decreases as time goes on.
This is probably because as the coefficient C increases as described above, the force coefficient A increases and the transmission efficiency increases.

  As shown, when the coefficient C exceeds 0.2, the startable voltage does not decrease as the value of the coefficient C increases, but when the coefficient C is up to about 0.36, the drivable voltage is slightly less than 25V. It is a large value. Therefore, a more preferable range of the coefficient C in consideration of the startable voltage is 0.2 ≦ C ≦ 0.36. Further, the startable voltage is maintained at about 20 V until the coefficient C is about 0.28. Therefore, a more preferable range of the coefficient C is 0.2 ≦ C ≦ 0.28.

  However, when the coefficient C becomes 0.28 or more, the startable voltage increases. This is because, as described above, when the coefficient C increases, a vibration mode other than the vibration mode for driving the movable member 15 to rotate is generated in the comb teeth portion 12a, and the vibration mode interferes with the other vibration modes. It is considered that the behavior of the wave motor 10 becomes unstable.

As described above, according to the present embodiment, the coefficient C is preferably 0.17 ≦ C ≦ 0.5, more preferably 0.2 ≦ C ≦ 0.36, and still more preferably 0.2 ≦ C ≦ 0. 28. In the present embodiment, the height of the comb tooth portion 12a: Kh, the height of the base portion 12b: Bh, the comb tooth portion 12a, and the base portion 12b so that the coefficient C has a desired value within these ranges. Is adjusted in the radial direction (difference between the inner diameter and the outer diameter): Kr, and the wavelength of the input voltage: λ.
By performing such adjustment, the startable voltage of the vibration wave motor 10 can be reduced, the dynamic range can be expanded, and the performance of the lens barrel can be improved.

(Modified form)
The present invention is not limited to the embodiments described above, 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, an example is described in which the lens barrel 20 including the vibration wave motor of the embodiment is detachable from the camera body. However, the present invention is not limited to this. It may be one.
(2) In the present embodiment, the vibration wave motor 10 in which the driven body is provided inside the annular elastic body 12 has been described. However, the invention is not limited thereto, and the shaft member is disposed inside the elastic body 12. Alternatively, the driven member may be rotated by the rotation of the shaft member.
The embodiments can be used in appropriate combinations, but detailed description is omitted. Further, the present invention is not limited by the embodiments described above.

  1: Camera, 10: Vibration wave motor, 11: Vibrator, 12: Elastic body, 12a: Comb part, 12b: Base part, 13: Piezoelectric body, 15: Moving element

Claims (5)

A vibrator vibrated by the electromechanical transducer,
A mover driven by the vibration of the vibrator,
The vibrator,
A base portion in contact with the electromechanical transducer,
And a comb portion formed on the side of the mover from the base portion,
The height of the comb tooth portion is Kh, the height of the base portion is Bh, the radial width of the comb tooth portion and the base portion is Kr, and the wavelength of the drive signal input to the electromechanical transducer is λ. Where the coefficient C = (Kh / Bh) × (Kr / λ) is not less than 0.17 and not more than 0.5;
A vibration wave motor. The vibration wave motor according to claim 1,
The coefficient C that is 0.2 to 0.3 6,
A vibration wave motor. The vibration according to claim 1 or 2 is a motor,
The vibrator is characterized in that the vibrator has an annular shape, and the width of the comb teeth and the width of the base are radial widths of the comb teeth and the base. The vibration according to any one of claims 1 to 3, wherein the vibration is a motor,
The vibration wave motor according to claim 1, wherein the comb teeth extend from the base toward the movable element.   An optical device comprising the vibration wave motor according to any one of claims 1 to 4.

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