Vibration wave motor

Abstract

To provide a vibration wave motor capable of yielding excellent driving characteristics even at a low density.SOLUTION: A vibration wave motor 10 of the present invention comprises: an electromechanical conversion element 13; an elastic body 12 on a driving surface of which a vibration wave is generated by vibration of the electromechanical conversion element 13; and a relative motion member 15 that is in contact with the driving surface of the elastic body 12 and is driven to rotate by the vibration wave. The electromechanical conversion element 13 has a density of 4.2 to 6.0×103 kg / m3. A plurality of grooves 12c are provided on the side of the driving surface of the elastic body 12. When a depth of at least one of the plurality of grooves 12c is defined as T, a thickness from a bottom of each groove 12c to a bonding surface of the elastic body with which the electromechanical conversion element is in contact is defined as B, and a thickness of the electromechanical conversion element 13 is defined as C, a value of T / (B+C) is within a range of 1.3 to 2.8.SELECTED DRAWING: Figure 10

Description

[Technical field]

[0001] The present invention relates to a vibration wave motor and an optical device. [Background technology]

[0002] A vibration wave motor generates a traveling vibration wave (hereafter abbreviated as a traveling wave) on the driving surface of an elastic body by utilizing the expansion and contraction of a piezoelectric body (see Patent Document 1). The vibrator of such a vibration wave motor is generally composed of an electromechanical conversion element (hereafter referred to as a piezoelectric body) and an elastic body. Conventionally, piezoelectric bodies are generally composed of a material such as lead zirconate titanate, commonly known as PZT, but in recent years, lead-free materials have been researched due to environmental concerns, and their incorporation into vibration wave motors is being considered (see Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Special Publication No. 1-17354 Summary of the Invention

[0004] The present invention provides an oscillatory wave motor including an electromechanical conversion element, an elastic body in which an oscillatory wave is generated on a drive surface by vibration of the electromechanical conversion element, and a relative moving member in contact with the drive surface of the elastic body and rotated by the oscillatory wave, wherein the electromechanical conversion element has a density of 4.2 to 6.0×10 3 kg / m 3 A plurality of grooves are provided on the driving surface side of the elastic body, and the depth of at least one of the plurality of grooves is defined as T, the thickness from the bottom of the groove to the joint surface of the elastic body with which the electromechanical conversion element comes into contact is defined as B, and the thickness of the electromechanical conversion element is defined as C, whereby the value of T / (B+C) is in the range of 1.3 to 2.8. Further, an optical device according to the present invention includes the above-mentioned vibration wave motor. [Brief description of the drawings]

[0005] [Figure 1] 1 is a schematic cross-sectional view of a lens barrel 20 incorporating a vibration wave motor 10 of an embodiment, and a camera 1. FIG. [Diagram 2] FIG. 2 is a perspective view in which a part of a vibrator 11 and a moving element 15 are cut away. [Diagram 3] FIG. 1 shows a piezoelectric body 13, where (a) is the bonding surface with the elastic body and (b) is the back surface. [Figure 4] 2 is a block diagram illustrating a drive device 80 of the vibration wave motor 10 according to the embodiment. FIG. [Diagram 5] 1A and 1B are diagrams illustrating an equivalent circuit of a vibrator 11 of a vibration wave motor 10, where (a) is the equivalent circuit and (b) is a formula for calculating a mechanical quality factor Qm. [Figure 6] 1 is a graph showing the results of calculating the Lm value through CAE analysis while varying the T value, B value, and C value. [Figure 7] 1 is a graph showing the relationship between T / (B+C) and driving voltage. [Figure 8] 13A and 13B are diagrams for explaining the relationship between T / (B+C) and the behavior of protrusion 12d of transducer 11, where (a) is when T / (B+C) is small, and (b) is when T / (B+C) is large. [Figure 9] This is a sequence for starting the vibration wave motor 10. [Figure 10] This is a diagram in which numerical values ​​have been added to the graph in Figure 7. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0006] Hereinafter, an embodiment of a vibration wave motor 10 will be described in detail with reference to the accompanying drawings. Fig. 1 is a schematic cross-sectional view of a lens barrel 20 and a camera 1 incorporating a vibration wave motor 10 of the embodiment.

[0007] In the embodiment, a circular vibration wave motor 10 will be described as an example of the vibration wave motor. The lens barrel 20 has an outer fixed barrel 31 and an inner fixed barrel 32. Between the outer fixed barrel 31 and the inner fixed barrel 32, a mechanism is provided for fixing a motor unit having a vibration wave motor 10.

[0008] The drive circuit 40 is provided between the outer fixed cylinder 31 and the inner fixed cylinder 32 of the lens barrel 20, and drives and controls the vibration wave motor 10, detects the number of rotations, and performs detection by the vibration sensor.

[0009] Next, a description will be given of the vibration wave motor 10. The vibration wave motor 10 has a vibrator 11 and a moving element 15. Fig. 2 is a perspective view of the vibrator 11 and the moving element 15 with parts cut away.

[0010] The oscillator 11 is composed of an electromechanical conversion element (hereinafter referred to as a piezoelectric body 13), such as a piezoelectric element or an electrostrictive element that converts electrical energy into mechanical energy, and an elastic body 12 to which the piezoelectric body 13 is bonded. The oscillator 11 is designed to generate traveling waves, and in this embodiment, nine traveling waves will be described as an example.

[0011] The elastic body 12 is made of a metal material with high resonance sharpness and has a circular ring shape. A groove 12c is cut in the surface of the elastic body 12 opposite to the surface to which the piezoelectric body 13 is joined. The tip surface of the protrusion 12d (where there is no groove 12c) becomes the driving surface 12a and is in pressure contact with the slider 15. The reason for cutting the groove 12c is to bring the neutral surface of the traveling wave as close as possible to the piezoelectric body 13 side, thereby amplifying the amplitude of the traveling wave on the driving surface 12a. A flange portion 12e extending radially is provided on the inner peripheral side of the elastic body 12, and a notch portion (not shown) is provided in the flange portion 12e. The notch portion fits into a protrusion portion (not shown) provided on the fixing portion 14, thereby regulating the circumferential movement of the elastic body 12.

[0012] 3 is a diagram showing the piezoelectric body 13, where (a) is the bonding surface with the elastic body and (b) is the back surface. The bonding surface of the piezoelectric body 13 is divided into two phases (phase A and phase B) along the circumferential direction. In each phase, elements with alternating polarizations at 1 / 2 wavelength intervals are arranged, with a 1 / 4 wavelength interval between phase A and phase B. The electrodes and electrode patterns provided on the surface will be described later.

[0013] The slider 15 is made of a light metal such as aluminum, and a sliding material is provided on the sliding surface 15a to improve wear resistance. On the surface of the slider 15 opposite the oscillator 11, a vibration absorbing member 23 such as rubber is disposed to absorb vertical vibrations of the slider 15, and an output transmission member 24 is disposed thereon.

[0014] A vibration absorbing member 23 such as rubber is disposed on the moving element 15 in order to absorb vibrations of the moving element 15 in the vertical direction, and an output transmission member 24 is disposed thereon.

[0015] The output transmission member 24 is regulated in the pressure direction and radial direction by a bearing 25 provided on the fixed part 14, thereby regulating the pressure direction and radial direction of the moving element 15. The output transmission member 24 has a protrusion 24a, from which a fork 35 connected to a cam ring 36 is engaged, and the cam ring 36 rotates together with the rotation of the output transmission member 24.

[0016] A key groove 37 is cut obliquely into the cam ring 36. A fixing pin 38 provided on the AF ring 34 fits into the key groove 37, and when the cam ring 36 is driven to rotate, the AF ring 34 is driven in a straight direction along the optical axis, so that it can be stopped at a desired position.

[0017] A vibration transmission prevention member 16 such as nonwoven fabric or felt is provided between the piezoelectric body 13 and the pressure spring 18 to prevent the vibration of the vibrator 11 from being transmitted to the pressure spring 18, the pressing ring 19, etc. The pressure spring 18 is composed of a disc spring or a wave washer. The retaining ring 19 is attached to the fixed portion 14 by a screw, and by attaching this, the output transmission member 24, the moving element 15, the vibrator 11, and the pressure spring 18 can be configured as one motor unit.

[0018] 3A and 3B are diagrams showing the piezoelectric body 13 as described above, with (a) showing the bonding surface with the elastic body and (b) showing the back surface. A plurality of electrode portions 131 are provided on the first surface 13A, which is the bonding surface of the piezoelectric body 13. In this embodiment, 16 electrode portions 131, each having a length equivalent to 1 / 2 the wavelength of the traveling wave, are provided along the circumferential direction. The electrode parts 131 are divided into two groups of eight on each side. One group is designed to transmit a driving voltage of phase A, and the other group is designed to transmit a driving voltage of phase B. Between phase A and phase B, an electrode part 131C of 1 / 4 wavelength and an electrode part 131D of 3 / 4 wavelength are provided, making a total of 18 electrode parts 131. In this embodiment, the side on which the eighteen electrode portions 131 are provided is joined to the elastic body 12.

[0019] On the other hand, on the second surface, which is the surface opposite to the first surface shown in FIG. 3(b), an electrode formed by combining a group of A-phase electrodes is provided at the position where the A-phase electrode portion is present on the first surface. Similarly, an electrode that combines the B phase electrode group is provided at the position of the B phase electrode group, and an electrode portion 132C of 1 / 4 wavelength and an electrode portion 132D of 3 / 4 wavelength are provided between the A phase and B phase, for a total of four electrode portions 132. In this embodiment, an A-phase drive signal and a B-phase drive signal are applied to this second surface, and the 1 / 4 wavelength portion is short-circuited to the elastic body 12 by conductive paint, so as to be grounded.

[0020] The material of the piezoelectric body 13 used in the embodiment is a so-called lead-free material, which is a material containing potassium sodium niobate, potassium niobate, sodium niobate, and barium titanate as main components.

[0021] FIG. 4 is a block diagram illustrating a drive device 80 of the vibration wave motor 10 according to the embodiment. First, the drive / control unit 68 of the vibration wave motor 10 will be described. The oscillator 60 generates a drive signal of a desired frequency in response to a command from the controller 68. The phase shifter 62 splits the drive signal generated by the oscillator 60 into two drive signals with different phases. The amplifier 64 boosts the two drive signals separated by the phase shifter 62 to desired voltages. The drive signal from the amplifier 64 is transmitted to the vibration wave motor 10, and application of this drive signal generates a traveling wave in the oscillator, thereby driving the moving element 15.

[0022] The rotation detection unit 66 is composed of an optical encoder, a magnetic encoder, or the like, and detects the position and speed of a driven object driven by the driving of the slider 15, and transmits the detected value to the control unit 68 as an electric signal.

[0023] The control unit 68 controls the driving of the vibration wave motor 10 based on a driving command from the CPU in the lens barrel 20 or the main body of the camera 1. The control unit 68 receives a detection signal from the rotation detection unit 66, obtains position information and speed information based on the value, and controls the frequency of the oscillation unit 60 so as to position the motor at a target position. The control unit 68 changes the phase difference of the phase shift unit 62 when switching the rotation direction.

[0024] Next, the operation of the vibration wave motor 10 according to the embodiment will be described. When a drive command is issued from the control unit 68, the oscillator unit 60 generates a drive signal. The drive signal is split by the phase shift unit 62 into two drive signals with a phase difference of 90 degrees, and then amplified by the amplifier unit 64 to a desired voltage.

[0025] The drive signal is applied to the piezoelectric body 13 of the vibration wave motor 10, and the piezoelectric body 13 is excited. The excitation generates a ninth-order bending vibration in the elastic body 12. The piezoelectric body 13 is divided into an A phase and a B phase, and the drive signals are applied to the A phase and the B phase, respectively. The 9th bending vibration generated from phase A and the 9th bending vibration generated from phase B are shifted in positional phase by 1 / 4 wavelength, and the A-phase drive signal and the B-phase drive signal are shifted in phase by 90 degrees, so the two bending vibrations are combined to become a 9-wave traveling wave.

[0026] An elliptical motion occurs at the crest of the traveling wave. Therefore, the slider 15, which is in pressure contact with the driving surface 12a, is frictionally driven by this elliptical motion. An optical encoder is disposed in the driving body driven by the driving of the slider 15, and an electric pulse is generated from there and transmitted to the control unit 68. Based on this signal, the control unit 68 can obtain the current position and the current speed.

[0027] In this embodiment, as described above, a lead-free material is used as the piezoelectric body 13 in consideration of environmental issues. However, after careful investigation by the inventors, it was found that when a lead-free piezoelectric body 13 is installed in a vibration wave motor 10, it is difficult to obtain driving performance similar to that of a PZT (lead zirconate titanate) piezoelectric body under the same conditions.

[0028] In order to investigate the cause, CAE (computer aided engineering) analysis and other methods were used, and it was found that the density of the lead-free piezoelectric body 13 and PZT were different. The density of the lead-free piezoelectric body 13 is, for example, 4.2 to 4.7×10 in the case of a niobium-based material. 3 kg / m 3 , and 5.5 to 6.0 × 10 for barium titanate-based materials. 3 kg / m 3 In contrast, PZT is 7.7 to 7.8 × 10 3 kg / m 3 It is. That is, the lead-free piezoelectric body 13 has a density that is 20% to 40% smaller than that of PZT.

[0029] (Equivalent circuit) FIG. 5 is a diagram for explaining an equivalent circuit of the vibrator 11 of the vibration wave motor 10, where (a) is the equivalent circuit and (b) is a formula for calculating the mechanical quality factor Qm. In the figure, Lm is the equivalent inductance, Cm is the equivalent capacitance, R is the resonance resistance, and Cd is the electrostatic capacitance of the piezoelectric body 13. The values ​​of Lm and Cm affect the resonance characteristics of the vibrator 11. The mechanical quality factor Qm is a measure of the resonance characteristics, and a larger Qm value indicates better resonance characteristics. As shown in Equation 1, Qm increases as the Lm value increases.

[0030] Table 1 shown below shows the Lm and Cm values ​​calculated by CAE analysis when each material was used as the piezoelectric body 13. Here, the model of the piezoelectric body 13 is as follows. Outer diameter: 62mm, Inner diameter: 55mm, Thickness of transducer 11: 4.22 mm, Number of grooves 12c provided on the drive surface 12a side: 48 Depth of groove 12c: 1.92mm, [Table 1]

[0031] As shown in Table 1, the Lm value of PZT is 0.341, whereas the Lm value of barium titanate is 0.325 and the Lm value of niobate is 0.313. That is, the lower the density, the smaller the Lm value. When a lead-free piezoelectric body 13 is incorporated in the vibrator 11, the Lm value is smaller than when a PZT piezoelectric body is incorporated. That is, the mechanical quality factor Qm when a lead-free piezoelectric body 13 is incorporated is smaller than when a PZT piezoelectric body is incorporated. For this reason, it was found that it was more difficult to obtain the desired resonance characteristics when a lead-free piezoelectric body 13 was incorporated than when a PZT piezoelectric body 13 was incorporated.

[0032] Since the vibration wave motor 10 is based on the principle of utilizing resonance, if the vibrator 11 does not have the desired vibration characteristics, it is difficult to obtain the driving performance when combined with the moving element 15. Therefore, with the vibrator 11 using the lead-free piezoelectric body 13, it tends to be difficult to obtain the desired driving performance.

[0033] Therefore, in order to improve the resonance characteristics of the vibrator 11 using the lead-free piezoelectric body 13, the tendency of the dimensions of the vibrator 11 that improve the Lm value was investigated. Here, the depth of groove 12c provided in the comb teeth of elastic body 12 is T, the thickness from the bottom of groove 12c to the joint surface with piezoelectric body 13 is B, and the thickness of piezoelectric body 13 is C. Figure 6 shows T value: 1.9-2.8, B value: 1.3~1.8, C value: 0.25~0.5, 13 is a graph showing the results of calculating the Lm value by CAE analysis while changing the Lm value within the range of

[0034] The calculation results show that there is a correlation between the value of T / (B+C) and Lm. This is because the larger the value of T, the larger the value of Lm becomes, while the smaller the value of B or the smaller the value of C, the larger the value of Lm becomes.

[0035] Therefore, we compared PZT and niobium-based materials with a density smaller than that of PZT (4.2 to 4.7 × 10 3 kg / m 3 ) and the Lm value of the vibrator 11 was calculated by CAE for each piezoelectric material when the T / (B+C) value was changed. The calculated values ​​for T / (B+C) of 1.2, 1.3, 2, and 2.8 are shown in Table 2. [Table 2]

[0036] In addition, Table 2 is T value: 1.9-3.5, B value: 1.0~2.2, C value: 0.25~0.8, The results of calculating the Lm value by CAE analysis are shown below. 4.2~4.7×10 3 kg / m 3 Since this range is the density range of common niobium-based piezoelectric materials, the CAE analysis was performed using the upper and lower density limits.

[0037] As shown in Table 2, it was found that the lower the density, the smaller the Lm value, while by increasing the T / (B+C) value, a value equivalent to that of transducer 11 equipped with PZT can be obtained.

[0038] However, there may be some drawbacks when the T / (B+C) value is increased. For this reason, we decided to prototype a vibration motor equipped with a niobium-based material and investigate its resonance characteristics as a vibration motor.

[0039] The material of the piezoelectric body 13 was mainly potassium sodium niobate, and the elastic body 12 was stainless steel. Twelve prototypes were made by changing the T and B values ​​of the elastic body 12 and the C of the piezoelectric body 13, and the voltage of the drive signal (drive voltage) that could be used to drive each prototype was investigated. The prototype is T value: 1.5~2.0 B value: 0.35~0.75 C value: 0.25~0.5 The density of the prototype piezoelectric body 13 was set to 4.4×10 3 kg / m 3 It is.

[0040] It is believed that the lower the drive voltage at which the vibration motor can be driven, the better the resonance characteristics of the actual vibration motor, and the higher the drive voltage, the worse the resonance characteristics of the actual vibration motor.

[0041] The measurement results are shown in Figure 7. When the T / (B+C) value was 1.2, the vibration wave motor 10 did not start even when a drive voltage of 100 V was applied. When the T / (B+C) value was in the range of 1.3 to 2.8, the device could be driven at an appropriate driving voltage of 100 V or less. When the T / (B+C) value was 3.33, the moving element 15 was driven, but the rotational state of the moving element 15 was somewhat unstable.

[0042] Increasing the T / (B+C) value increases the Lm value of the vibrator 11 and improves the Qm value. However, this may result in a decrease in the electromechanical coupling coefficient Kvn of the vibrator 11, resulting in a drawback in that the efficiency of conversion from electrical energy to mechanical energy decreases. It is believed that when the T / (B+C) value was set to 3.33, this caused a problem, and the rotational state of the slider 15 became slightly unstable.

[0043] (First embodiment) Based on the above study results, the first embodiment of the present invention has the following configuration. The piezoelectric body 13 is made of a material mainly composed of potassium sodium niobate, and its density is 4.2 to 4.7 × 10 3 kg / m 3 The elastic body 12 is made of stainless steel, and the T / (B+C) value is in the range of 1.3 to 2.8.

[0044] By adopting such a configuration, even if the density of the piezoelectric body 13 is reduced, the resonance characteristics of the vibrator 11 can be ensured, and the driving performance when combined with the moving element 15 can be ensured.

[0045] When T / (B+C) is 1.3, the calculation results of the CAE analysis show that the Lm value of the transducer 11 is approximately 0.41, and when T / (B+C) is 2.8, the Lm value of the transducer 11 is approximately 0.74.

[0046] Second embodiment Next, a second embodiment will be described. In the second embodiment, the piezoelectric body 13 is made of a material mainly composed of barium titanate, and its density is 5.5 to 6.0 × 10 3 kg / m 3 The elastic body 12 was made of stainless steel, and the T / (B+C) value was in the range of 1.3 to 2.8.

[0047] Even when the piezoelectric body 13 is made of barium titanate, its density is smaller than that of PZT, so the Lm value of the vibrator 11 decreases and sufficient resonance characteristics cannot be obtained as the vibrator 11. Even if the moving element 15 is combined in this state, no driving performance can be obtained.

[0048] Therefore, in this embodiment, the T / (B+C) value was changed and the Lm value of the transducer 11 was calculated by CAE analysis.

[0049] Table 3 shows the density of 5.5×10 3 kg / m 3 Time and 6.0×10 3 kg / m 3 13 shows the results of calculating the Lm value of each transducer 11 when the T / (B+C) value is changed to 1, 2, 1.3, 2, and 2.8. 5.5~6.0×10 3 kg / m 3 Since this range is the density range of common barium titanate piezoelectric materials, the CAE analysis was performed using the upper and lower density limits. The CAE analysis was also performed with a T value of 1.9 to 3.5, a B value of 1.0 to 2.2, and a C value of 0.25 to 0.8. [Table 3]

[0050] When the T / (B+C) value is 1.3, the Lm value is approximately 0.42, and when T / (B+C) is 2.8, the Lm value of the transducer 11 is approximately 0.75. The density of the piezoelectric body 13 is 5.5 to 6.0 × 10 3 kg / m 3 For the material, the relationship between the T / (B+C) value and Lm is 4.2~4.7×10 3 kg / m 3 This is almost the same value as that of the material. Therefore, the appropriate range for the T / (B+C) value is considered to be 1.3 to 2.8.

[0051] Niobium-based (density: 4.2-4.7×10 3 kg / m 3) and barium titanate (density: 5.5 to 6.0 × 10 3 kg / m 3 ) has a similar relationship when the T / (B+C) value is between 1.3 and 2.8, so the Lm value is between 4.2 and 6.0×10 3 kg / m 3 In this case, a T / (B+C) value of 1.3 to 2.8 is considered to be in the appropriate range.

[0052] Third embodiment Next, a third embodiment of the present invention will be described. 8 is a diagram for explaining the relationship between T / (B+C) and the behavior of protrusion 12d of vibrator 11. Fig. 8(a) shows the behavior of protrusion 12d of vibrator 11 when T / (B+C) is small (for example, when groove 12c is shallow), and Fig. 8(b) shows the behavior of protrusion 12d of vibrator 11 when T / (B+C) is large (for example, when groove 12c is deep).

[0053] When a traveling vibration wave is generated in the vibrator 11, bending occurs when the thickness of the adhesive surface of the piezoelectric body 13 is combined with the bottom of the groove 12c of the elastic body 12 and the thickness of the piezoelectric body 13 (i.e., bending deformation occurs in the absence of the protrusion 12d). The neutral plane of bending exists between the bottom of groove 12c of elastic body 12 and the bottom surface of piezoelectric body 13. Then, protrusion 12d is subjected to bending vibration generated when the thickness of the adhesive surface of piezoelectric body 13 is combined with the thickness of piezoelectric body 13 from the bottom of groove 12c of elastic body 12, and moves like a swing in the driving direction.

[0054] When T / (B+C) is small, the movement of the tip (driving part) of the protrusion 12d in the driving direction is small, and when T / (B+C) is large, the movement in the driving direction is large. To roughly estimate the magnitude of this speed, if the movement in the driving direction occurring when the thickness of the adhesive surface of the piezoelectric body 13 combined with the thickness of the piezoelectric body 13 from the bottom of the groove 12c of the elastic body 12 is taken as ((B+C) / 2), then the movement in the driving direction of the driving surface 12a is (T+(B+C) / 2) / ((B+C) / 2) times larger. For example, if T is made larger, the swing of the driving surface 12a becomes larger accordingly.

[0055] When T / (B+C) is large, the movement in the drive direction is large, and therefore the force applied from the moving element 15 to the drive surface 12a is large. For example, if the displacement of the movement in the drive direction is doubled, the speed and acceleration are also doubled, and when an attempt is made to move the moving element 15 in contact with the drive surface 12a, twice the force (load) is applied to the drive surface 12a. As a result, there is a possibility that the vibration wave motor 10 will not be able to drive when there is a large change in speed, such as when it is started.

[0056] In the embodiment, when a piezoelectric body 13 made of a lead-free material with a low density is incorporated into the vibrator 11, T / (B+C) is made larger than when a piezoelectric body 13 made of PZT is incorporated in order to improve Lm of the vibrator 11. Therefore, in this case, the above-mentioned situation is likely to occur. As a result of the inventors' investigation, it was found that this problem could be solved by lengthening the time for which the frequency is changed when sweeping the frequency at the start of the vibration wave motor 10.

[0057] FIG. 9 shows a sequence when the vibration wave motor 10 is started. In a state where there is no drive command from the control unit 68 (t0), Drive frequency: fs0 Driving voltage: Voltage V0 (=0V) Phase difference between A and B phases: 0 degrees It is as follows.

[0058] When a drive command is received from the control unit 68 (t1) Drive frequency: remains at fs0 Driving voltage: Voltage V1 Phase difference between A and B phases: 90 degrees (-90 degrees when inverted) At this time, the rotation speed is set to 0.

[0059] The driving frequency is gradually lowered, and when it reaches the frequency f0 at time t2, the moving element 15 is driven.

[0060] At time t4, the frequency becomes flow and the rotation speed reaches the target speed Rev1.

[0061] In this embodiment, the time for changing the frequency when sweeping the frequency is lengthened according to the T / (B+C) value. Specifically, a relationship is established between the frequency difference of flow-fs0 and the time difference of t4-t2. When the value of T / (B+C) is small, the time difference between t4 and t2 is shortened, and when the value of T / (B+C) is large, the time difference between t4 and t2 is lengthened. In this way, by increasing the rise time, the reaction force from the moving element 15 acting on the vibrator 11 of the vibration wave motor 10 at the time of startup can be reduced.

[0062] In the case of the oscillatory wave motor 10 equipped with a PZT (T / (B+C): 1.08), the frequency change rate of the frequency sweep at the time of startup is set to about 1 kHz / m sec. When T / (B+C) is in the range of 1.2 to 1.7, the movement of the driving surface 12a in the driving direction increases by about 1.1 to 1.4 times compared to T / (B+C): 1.08. Therefore, the time t4-t2 is increased by 1.4 times. In other words, if the frequency change rate of the frequency sweep is set to about 1 / 1.4, 0.7 kHz / ms, the load on the vibration wave motor 10 will be the same as or less than when a PZT is installed (T / (B+C): 1.08).

[0063] Furthermore, when T / (B+C) is in the range of 1.7 to 2.8, the movement of the driving surface 12a in the driving direction increases by approximately 1.4 to 2.0 times compared to when T / (B+C) is 1.08. Therefore, if the t4-t2 time is increased by 2.0, that is, if the frequency change rate of the frequency sweep is set to about 1 / 2.0, or 0.5 kHz / msec, the burden on the vibration wave motor 10 will be the same as or less than when a PZT is installed (T / (B+C): 1.08).

[0064] By changing the amount of change in frequency according to T / (B+C), it becomes possible to ensure reliable startup even when there is a large change in speed, such as when the vibration wave motor 10 is started up (i.e., when the load on the vibrator 11 of the vibration wave motor 10 is large).

[0065] In this embodiment, a vibration wave motor 10 using a progressive vibration wave is disclosed in which the wave number is 4 or 9. However, similar effects can be obtained with other wave numbers, such as 5 to 8 waves or 10 waves or more, by using a similar configuration and controlling in a similar manner.

[0066] Furthermore, when T / (B+C) is 1.7, the amount of change in frequency may be set to 0.7 kHz / msec or less, or the amount of change in frequency may be set to 0.5 kHz / msec or less.

[0067] Regarding T / (B+C) described in the first and second embodiments, when T / (B+C) is in the range of 1.76 to 2.8 as shown in Fig. 10, the driving voltage is preferably about 60 V. Furthermore, when T / (B+C) is in the range of 1.76 to 2.50, the driving voltage becomes lower, which is even more preferable.

[0068] The embodiments and modifications may be used in appropriate combination, but detailed description thereof will be omitted. The present invention is not limited to the embodiments described above. [Explanation of symbols]

[0069] 1: camera, 10: vibration wave motor, 11: vibrator, 12: elastic body, 12a: drive surface, 12c: protrusion, 12e: flange, 13: piezoelectric body, 13A: first surface, 14: fixed portion, 15: slider, 15a: sliding surface, 16: vibration transmission prevention member, 18: pressure spring, 19: pressure ring, 20: lens barrel, 23: vibration absorbing member, 24: output transmission member, 25: bearing , 31: outer fixed barrel, 32: inner fixed barrel, 34: ring, 35: fork, 36: cam ring, 37: key groove, 38: fixed pin, 40: drive circuit, 60: oscillator, 62: phase shifter, 64: amplifier, 66: rotation detector, 68: control unit, 80: drive device, 131: electrode unit, 131C: electrode unit, 131D: electrode, 132: electrode unit, 132C: electrode unit, 132D: electrode unit

Claims

[Claim 1] An electromechanical conversion element; an elastic body in which a vibration wave is generated on a driving surface by vibration of the electromechanical conversion element; a relative moving member that contacts the drive surface of the elastic body and is rotationally driven by the vibration wave; In an oscillatory wave motor comprising: The electromechanical transducer has a density of 4.2 to 6.0×10 ３ kg / m ３ and A plurality of grooves are provided on the driving surface side of the elastic body, A depth of at least one of the plurality of grooves is T; A thickness from the bottom of the groove to the first surface is B, When the thickness of the electromechanical transducer is defined as C, The value of T / (B+C) is in the range of 1.3 to 2.8; Oscillatory wave motor.

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