Vibration wave motor

Abstract

To provide a vibration wave motor that can achieve good driving characteristics even at low density. [Solution] The vibration wave motor 10 of the present invention comprises an electromechanical conversion element 13, an elastic body 12 on which vibration waves are generated on the drive surface by the vibration of the electromechanical conversion element 13, and a relative motion member 15 that contacts the drive surface of the elastic body 12 and is rotationally driven by the vibration waves. The electromechanical conversion element 13 has a density of 4.2 to 6.0 × 10³ kg / m³, and a plurality of grooves 12c are provided on the drive surface side of the elastic body 12. If the depth of at least one of the plurality of grooves 12c is T, the thickness from the bottom of the groove 12c to the joint surface of the elastic body on which the electromechanical conversion element contacts is B, and the thickness of the electromechanical conversion element 13 is defined as C, then the value of T / (B+C) is in the range of 1.3 to 2.8.

Description

Technical Field

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

Background Art

[0002] A vibration wave motor generates a progressive vibration wave (hereinafter abbreviated as a progressive wave) on the driving surface of an elastic body by utilizing the expansion and contraction of a piezoelectric body (see Patent Document 1). Such a vibrator of a vibration wave motor generally includes an electromechanical conversion element (hereinafter referred to as a piezoelectric body) and an elastic body. Conventionally, the piezoelectric body is generally composed of a material such as lead zirconate titanate commonly called PZT. However, in recent years, lead-free materials have been studied due to environmental problems, and their mounting on vibration wave motors has been considered (see Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

[0004] The vibration wave motor of the present invention comprises an electromechanical conversion element, an elastic body on which vibration waves are generated on the drive surface due to the vibration of the electromechanical conversion element, a relative motion member that contacts the drive surface of the elastic body and is rotationally driven by the vibration waves, and a drive circuit that provides a repeatedly fluctuating drive signal to the vibration wave motor, wherein the electromechanical conversion element has a density of 4.2 to 6.0 × 10³ kg / m³, a plurality of grooves are provided on the drive surface side of the elastic body, the depth of at least one of the plurality of grooves is T, and the electromechanical conversion element is located from the bottom of the groove When the thickness to the joint surface of the elastic body in contact with the child is defined as B, and the thickness of the electromechanical conversion element is defined as C, the value of T / (B+C) is in the range of 1.3 to 2.8, and when the vibration wave motor is started from speed 0 to speed greater than 0 by the drive signal provided by the drive circuit, the frequency change amount of the frequency sweep is set to 0.7 kHz / msec or less when T / (B+C) is in the range of 1.3 to 1.7, and to 0.5 kHz / msec or less when T / (B+C) is in the range of 1.7 to 2.8. Furthermore, the optical instrument of the present invention is configured to include the above-mentioned vibration wave motor. [Brief explanation of the drawing]

[0005] [Figure 1] This is a schematic cross-sectional view of the lens barrel 20 and camera 1 incorporating the vibration wave motor 10 of the embodiment. [Figure 2] This is a perspective view with parts of the oscillator 11 and the moving element 15 cut out. [Figure 3] In the figure showing the piezoelectric element 13, (a) is the bonding surface with the elastic body, and (b) is its back surface. [Figure 4] This is a block diagram illustrating the drive device 80 of the vibration wave motor 10 according to the embodiment. [Figure 5] This diagram illustrates the equivalent circuit of the oscillator 11 of the vibration wave motor 10, where (a) is the equivalent circuit and (b) is the formula for calculating the mechanical quality factor Qm. [Figure 6] This graph shows the results of calculating the Lm value using CAE analysis while varying the T-value, B-value, and C-value. [Figure 7]This graph shows the relationship between T / (B+C) and the drive voltage. [Figure 8] This diagram illustrates the relationship between T / (B+C) and the behavior of the projection 12d of the oscillator 11, where (a) shows the case when T / (B+C) is small, and (b) shows the case when T / (B+C) is large. [Figure 9] This is the sequence for starting the vibration wave motor 10. [Figure 10] This is a graph with numerical values ​​added to it, as shown in Figure 7. [Modes for carrying out the invention]

[0006] The embodiment of the vibration wave motor 10 will be described in detail below with reference to the attached drawings. Figure 1 is a schematic cross-sectional view of the lens barrel 20 and camera 1 incorporating the vibration wave motor 10 of the embodiment.

[0007] The embodiment will describe a ring-type vibration wave motor 10 as a vibration wave motor. The lens barrel 20 has an outer fixed cylinder 31 and an inner fixed cylinder 32. A motor unit having a vibration wave motor 10 is fixed between the outer fixed cylinder 31 and the inner fixed cylinder 32.

[0008] The drive circuit 40 is installed between the outer fixing cylinder 31 and the inner fixing cylinder 32 of the lens barrel 20, and performs functions such as driving and controlling the vibration wave motor 10, detecting the rotation speed, and detecting vibrations with the vibration sensor.

[0009] Next, the vibration wave motor 10 will be described. The vibration wave motor 10 has an oscillator 11 and a moving element 15. Figure 2 is a perspective view with parts of the oscillator 11 and moving element 15 cut out.

[0010] The oscillator 11 is composed of an electromechanical conversion element (hereinafter referred to as piezoelectric body 13), such as a piezoelectric element or electrostrictive element, which converts electrical energy into mechanical energy, and an elastic body 12 to which the piezoelectric body 13 is joined. 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 a high resonance sharpness and has an annular shape. A groove 12c is cut into the opposite side of the elastic body 12 to which the piezoelectric body 13 is joined. The tip surface of the projection 12d (where there is no groove 12c) becomes the driving surface 12a and is pressed into contact with the moving element 15. The reason for cutting the groove 12c is to bring the neutral plane 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. The inner circumference of the elastic body 12 is provided with a radially extended flange portion 12e, and the flange portion 12e is provided with a notch (not shown), which fits into the notch with a projection (not shown) provided on the fixing portion 14, thereby restricting the circumferential movement of the elastic body 12.

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

[0013] The movable element 15 is made of a light metal such as aluminum, and a sliding material is provided on the surface of the sliding surface 15a to improve wear resistance. On the side of the movable element 15 opposite to the vibrator 11, a vibration absorbing member 23, such as rubber, is placed to absorb the vertical vibration of the movable element 15, and an output transmission member 24 is placed on top of it.

[0014] A vibration-absorbing member 23, such as rubber, is placed on top of the movable element 15 to absorb vertical vibrations of the movable element 15, and an output transmission member 24 is placed on top of that.

[0015] The output transmission member 24 is regulated in the pressing direction and the radial direction by the bearing 25 provided on the fixing portion 14, whereby the pressing direction and the radial direction of the mover 15 are regulated. The output transmission member 24 has a protruding portion 24a, and the fork 35 connected to the cam ring 36 engages therewith. As the output transmission member 24 rotates, the cam ring 36 is rotated.

[0016] A key groove 37 is cut obliquely in the cam ring 36. The fixing pin 38 provided on the AF ring 34 engages with the key groove 37, and when the cam ring 36 is rotationally driven, the AF ring 34 is driven in the straight-ahead direction in the optical axis direction so that it can stop at a desired position.

[0017] A vibration transmission prevention member 16 such as a non-woven fabric or felt is provided between the piezoelectric body 13 and the pressing spring 18 so that the vibration of the vibrator 11 is not transmitted to the pressing spring 18, the retaining ring 19, etc. The pressing spring 18 is composed of a disc spring or a wave washer. The fixing portion 14 has a retaining ring 19 attached by screws, and by attaching this, it becomes possible to configure the output transmission member 24, the mover 15, the vibrator 11, and the pressing spring 18 as one motor unit.

[0018] FIG. 3 is a diagram showing the piezoelectric body 13 as described above, where (a) is the joint surface with the elastic body and (b) is its back surface. A plurality of electrode portions 131 are provided on the first surface 13A which is the joint surface of the piezoelectric body 13. In the present embodiment, 16 electrode portions 131 having a length corresponding to 1 / 2 wavelength of the traveling wave along the circumferential direction are provided. The electrode portions 131 are divided into groups of eight on the left and right. One group is configured to transmit the driving voltage of the A phase, and the other group is configured to transmit the driving voltage of the B phase. Between the A phase and the B phase, electrode portions 131C for 1 / 4 wavelength and electrodes 131D for 3 / 4 wavelength are provided, and a total of 18 electrode portions 131 are provided. In the embodiment, the side where the 18 electrode portions 131 are provided is joined to the elastic body 12.

[0019] On the other hand, on the second surface, which is the opposite surface to the first surface shown in Figure 3(b), an electrode is provided that is formed by combining a group of A-phase electrodes at the position where the A-phase electrode portion is located on the first surface. Similarly, an electrode is provided at the position of the B-phase electrode group, such that it is formed by coupling the B-phase electrode group, and between the A-phase and B-phase, an electrode section 132C for 1 / 4 wavelength and an electrode section 132D for 3 / 4 wavelength are provided, for a total of four electrode sections 132. In this embodiment, the A-phase drive signal and the B-phase drive signal are applied to this second surface, and the quarter-wavelength portion is short-circuited with the elastic body 12 using conductive paint to provide GND.

[0020] The piezoelectric material 13 used in the embodiment is a lead-free material, mainly composed of potassium sodium niobate, potassium niobate, sodium niobate, and barium titanate.

[0021] Figure 4 is a block diagram illustrating the drive device 80 of the vibration wave motor 10 according to the embodiment. First, let's describe the drive / control unit 68 of the vibration wave motor 10. The oscillator 60 generates a drive signal of a desired frequency according to a command from the control unit 68. The phase shift unit 62 splits the drive signal generated by the oscillator 60 into two drive signals with different phases. The amplification unit 64 boosts the two drive signals separated by the phase shift unit 62 to the desired voltage. The drive signals from the amplification unit 64 are transmitted to the vibration wave motor 10, and the application of these drive signals generates a traveling wave in the vibrating body, driving the moving element 15.

[0022] The rotation detection unit 66 is composed of an optical encoder, a magnetic encoder, etc., and detects the position and speed of the driven object driven by the drive of the moving element 15, and transmits the detected values ​​as electrical signals to the control unit 68.

[0023] The control unit 68 controls the drive of the vibration wave motor 10 based on drive commands from the CPU in the lens barrel 20 or the camera body 1. The control unit 68 receives a detection signal from the rotation detection unit 66, obtains position information and velocity information based on its value, and controls the frequency of the oscillation unit 60 so that it is positioned at the target position. When switching to the rotation direction, the control unit 68 changes the phase difference of the phase shift unit 62.

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

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

[0026] Elliptical motion occurs at the wavefront of the traveling wave. Therefore, the moving element 15, which is pressurized and in contact with the driving surface 12a, is driven frictionally by this elliptical motion. An optical encoder is positioned on the driving body driven by the driving of the moving element 15, from which electrical pulses are generated and transmitted to the control unit 68. Based on this signal, the control unit 68 can obtain the current position and current velocity.

[0027] In this embodiment, as described above, lead-free material is used as the piezoelectric element 13, taking environmental issues into consideration. However, as a result of diligent research by the inventors, it was found that when a lead-free piezoelectric material 13 is mounted on a vibration wave motor 10, it is difficult to obtain the same driving performance as a PZT (lead zirconate titanate) piezoelectric material under the same conditions.

[0028] In order to investigate the cause, we used CAE (computer-aided engineering) analysis and other methods to find that the density of the lead-free piezoelectric material 13 and the PZT were different. The density of lead-free piezoelectric material 13 is, for example, 4.2 to 4.7 × 10³ kg / m³ for niobium-based materials and 5.5 to 6.0 × 10³ kg / m³ for barium titanate-based materials. In contrast, PZT has a density of 7.7 to 7.8 × 10³ kg / m³. In other words, the lead-free piezoelectric material 13 has a density that is 20% to 40% lower than that of PZT.

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

[0030] Table 1 below shows the Lm and Cm values ​​calculated by CAE analysis when each material is treated as piezoelectric material 13. The model of the piezoelectric element 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, Groove depth 12c: 1.92mm, [Table 1]

[0031] As shown in Table 1, the Lm value for PZT is 0.341, while the Lm value for barium titanate is 0.325 and the Lm value for niobium is 0.313. In other words, the Lm value decreases as the density decreases. When the lead-free piezoelectric material 13 is incorporated into the oscillator 11, the Lm value is smaller compared to when the PZT piezoelectric material is incorporated. That is, the mechanical quality coefficient Qm when the lead-free piezoelectric material 13 is incorporated is smaller than when the PZT piezoelectric material is incorporated. For this reason, it was found that it was more difficult to obtain the desired resonance characteristics when the lead-free piezoelectric material 13 was incorporated compared to when the PZT piezoelectric material 13 was incorporated.

[0032] Because the vibration wave motor 10 operates on the principle of resonance, if the desired vibration characteristics cannot be obtained in the vibrator 11, it is difficult to obtain the desired driving performance when combined with the moving element 15. Therefore, vibrators 11 using lead-free piezoelectric material 13 tend to have difficulty obtaining the desired driving performance.

[0033] Therefore, in order to improve the resonance characteristics of the oscillator 11 using lead-free piezoelectric material 13, we investigated the trend of the dimensions of the oscillator 11 that improve the Lm value. Here, let T be the depth of the groove 12c provided in the comb teeth of the elastic body 12, B be the thickness from the bottom of the groove 12c to the bonding surface with the piezoelectric body 13, and C be the thickness of the piezoelectric body 13. Figure 6 shows T-value: 1.9~2.8 B value: 1.3~1.8 C value: 0.25~0.5 This graph shows the results of calculating the Lm value using CAE analysis for each of the following variations within the specified range.

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

[0035] Therefore, we used CAE to calculate what the Lm value of the oscillator 11 would be for each piezoelectric material when the T / (B+C) value was changed for PZT and niobium-based materials with a lower density than PZT (4.2~4.7 × 10³ kg / m³). The results are shown in Table 2, where the calculated values ​​are for T / (B+C) of 1.2, 1.3, 2, and 2.8. [Table 2]

[0036] 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 using CAE analysis for each of the following variations are shown. The density range of 4.2 to 4.7 × 10³ kg / m³ is typical for niobium-based piezoelectric materials, so CAE analysis was performed using the upper and lower density limits within this range.

[0037] As shown in Table 2, it was found that the Lm value decreases as the density decreases, while increasing the T / (B+C) value yields a value equivalent to that of the oscillator 11 equipped with PZT.

[0038] However, there are potential drawbacks to increasing the T / (B+C) value. Therefore, we decided to fabricate a prototype vibration motor using niobium-based materials and investigate its resonance characteristics as a vibration motor.

[0039] The piezoelectric element 13 was made primarily of potassium sodium niobate, and the elastic element 12 was made of stainless steel. Twelve prototypes were fabricated by changing the T and B values ​​of the elastic element 12 and the C value of the piezoelectric element 13, and the drive signal voltage (drive voltage) that could be driven by 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 range was defined as follows. Furthermore, the density of the prototype piezoelectric material 13 is 4.4 × 10³ kg / m³.

[0040] It is believed that the lower the drive voltage, the better the resonance characteristics of the vibration motor in actual use, and the higher the drive voltage, the worse the resonance characteristics of the vibration motor in actual use.

[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 100V was applied. When the T / (B+C) value was in the range of 1.3 to 2.8, the device could be driven with an appropriate drive voltage of 100V or less. When the T / (B+C) value was 3.33, the device was driven, but the rotation of the moving element 15 was somewhat unstable.

[0042] Increasing the T / (B+C) value increases the Lm value of the oscillator 11, improving the Qm value. However, this can lead to a decrease in the electromechanical coupling coefficient Kvn of the oscillator 11, resulting in a drawback of reduced efficiency in converting electrical energy to mechanical energy. When the T / (B+C) value was set to 3.33, it is thought that this resulted in a drawback, causing the rotation state of the moving element 15 to become somewhat unstable.

[0043] (First Embodiment) Based on the above findings, the first embodiment of the present invention has the following configuration. The piezoelectric material 13 is made of a material mainly composed of potassium sodium niobate, with a density of 4.2 to 4.7 × 10³ kg / m³, and the elastic material 12 is made of stainless steel with a T / (B+C) value in the range of 1.3 to 2.8.

[0044] This configuration ensures that even with a reduced density of piezoelectric material 13, the oscillator 11 maintains its resonant characteristics, and thus ensures driving performance when combined with the moving element 15.

[0045] When T / (B+C) is 1.3, the Lm value of oscillator 11 is approximately 0.41 according to the CAE analysis calculation, and when T / (B+C) is 2.8, the Lm value of oscillator 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, with a density of 5.5 to 6.0 × 10³ kg / m³, and the elastic body 12 is made of stainless steel with a T / (B+C) value in the range of 1.3 to 2.8.

[0047] Even when the piezoelectric material 13 is made of barium titanate, its density is lower compared to PZT, which lowers the Lm value of the oscillator 11, and sufficient resonance characteristics cannot be obtained for the oscillator 11. In this state, even if the moving element 15 is combined, driving performance cannot be obtained.

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

[0049] Table 3 shows the results of calculating the Lm value for each oscillator 11 when the density was changed to 5.5 × 10³ kg / m³ and 6.0 × 10³ kg / m³, and the T / (B+C) value was changed to 1, 2, 1.3, 2, and 2.8. The density range of 5.5 to 6.0 × 10³ kg / m³ is typical for barium titanate-based piezoelectric materials, so CAE analysis was performed using the upper and lower density limits within this range. Furthermore, CAE analysis was conducted with T values ​​ranging from 1.9 to 3.5, B values ​​from 1.0 to 2.2, and C values ​​from 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 oscillator 11 is approximately 0.75. Even for piezoelectric materials 13 with a density of 5.5 to 6.0 × 10³ kg / m³, the relationship between the T / (B+C) value and Lm is almost the same as for materials with a density of 4.2 to 4.7 × 10³ kg / m³. Therefore, the appropriate range for the T / (B+C) value is considered to be 1.3 to 2.8.

[0051] Since the Lm values ​​for both niobium-based materials (density: 4.2-4.7 × 10³ kg / m³) and barium titanate-based materials (density: 5.5-6.0 × 10³ kg / m³) show a similar relationship in the T / (B+C) value range of 1.3-2.8, it can be considered that a T / (B+C) value of 1.3-2.8 is appropriate for densities of 4.2-6.0 × 10³ kg / m³.

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

[0053] When a progressive vibration wave is generated in the oscillator 11, the bending occurs with the thickness of the piezoelectric element 13 combined with the thickness of the adhesive surface of the piezoelectric element 13, starting from the bottom of the groove 12c of the elastic body 12 (i.e., bending deformation occurs without the protrusion 12d). The neutral plane of the bending exists between the bottom of the groove 12c of the elastic body 12 and the lower surface of the piezoelectric body 13. The projection 12d, under the influence of the bending vibration generated when the thickness of the bonding surface of the piezoelectric body 13 is combined with the thickness of the piezoelectric body 13, experiences a swing-like motion in the driving direction.

[0054] When T / (B+C) is small, the movement of the tip (drive unit) of the projection 12d in the driving direction is small, and when T / (B+C) is large, the movement in the driving direction is large. To estimate the magnitude of the velocity, if the motion in the driving direction that occurs when the thickness of the adhesive surface of the piezoelectric element 13 is combined with the bottom of the groove 12c of the elastic body 12 is ((B+C) / 2), then the driving surface 12a experiences a motion in the driving direction that is (T+(B+C) / 2) / ((B+C) / 2) times greater. For example, if T is increased, the swing of the driving surface 12a will increase accordingly.

[0055] When T / (B+C) is large, the motion in the driving direction is large, and therefore the force applied from the moving element 15 to the driving surface 12a becomes large. For example, if the displacement of motion in the driving direction doubles, the velocity and acceleration also double, and when attempting to move the moving element 15 that is in contact with the driving surface 12a, twice the force (load) is applied to the driving surface 12a. As a result, there is a possibility that the motor may not be able to drive when there are large changes in speed, such as when the vibration wave motor 10 is started up.

[0056] In this embodiment, when a lead-free piezoelectric element 13 with low density is incorporated into the oscillator 11, T / (B+C) is increased compared to when a PZT piezoelectric element 13 is incorporated, in order to improve the Lm of the oscillator 11. Therefore, in this case, the situation described above is likely to occur. The inventors then investigated and found that the problem could be solved by increasing the time the frequency is changed when sweeping the frequency during startup of the vibration wave motor 10.

[0057] Figure 9 shows the sequence for starting the vibration wave motor 10. In the state where there is no drive command from the control unit 68 (t0), Drive frequency: fs0 Driving voltage: Voltage V0 (=0V) Phase difference between phase A and phase B: 0 degrees That's how it is.

[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 phase A and phase B: 90 degrees (-90 degrees during inverted drive) This is the setting. At this time, the rotation speed = 0.

[0059] The drive frequency is gradually reduced, and when the frequency at time t2 becomes f0, the moving element 15 is driven.

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

[0061] In this embodiment, the time taken for frequency changes during frequency sweep is increased according to the T / (B+C) value. Specifically, a relationship is established between the frequency difference of flow-fs0 and the time difference between t4 and t2. Furthermore, when the T / (B+C) value is small, the time difference between t4 and t2 is shortened, and when the T / (B+C) value is large, the time difference between t4 and t2 is lengthened. In this way, increasing the rise time reduces the reaction force from the moving element 15 acting on the vibrator 11 of the vibration wave motor 10 during startup.

[0062] In the case of the vibration wave motor 10 equipped with PZT (T / (B+C):1.08), the frequency change rate of the frequency sweep during startup is set to approximately 1 kHz / m sec. When T / (B+C) is in the range of 1.2 to 1.7, the motion of the drive surface 12a in the driving direction increases by approximately 1.1 to 1.4 times compared to T / (B+C) = 1.08. Therefore, the t4-t2 time is multiplied by 1.4. In other words, if the frequency change rate of the frequency sweep is set to about 1 / 1.4 of that, or 0.7 kHz / m sec, the load on the vibration wave motor 10 will be about the same as or less than when the 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 motion of the drive surface 12a in the driving direction increases by approximately 1.4 to 2.0 times compared to T / (B+C): 1.08. Therefore, if the t4-t2 time is doubled, that is, if the frequency change rate of the frequency sweep is reduced to about 1 / 2.0 of that, or 0.5 kHz / msec, the load on the vibration wave motor 10 will be about the same as or less than when the PZT is installed (T / (B+C): 1.08).

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

[0065] In this embodiment, a vibration wave motor 10 using progressive vibration waves is disclosed for cases with 4 or 9 wavenumbers. However, similar effects can be obtained with other wavenumbers such as 5 to 8 waves, or 10 or more waves, by using a similar configuration and control.

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

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

[0068] The embodiments and variations can be used in combination as appropriate, but a detailed explanation is omitted. Furthermore, 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: Projection, 12e: Flange, 13: Piezoelectric body, 13A: First surface, 14: Fixing part, 15: Moving part, 15a: Sliding surface, 16: Vibration transmission prevention member, 18: Pressure spring, 19: Retaining ring, 20: Lens barrel, 23: Vibration absorption member, 24: Output transmission member, 25: Bearing 31: Outer fixing cylinder, 32: Inner fixing cylinder, 34: Ring, 35: Fork, 36: Cam ring, 37: Keyway, 38: Fixing pin, 40: Drive circuit, 60: Oscillator, 62: Phase shift unit, 64: Amplifier, 66: Rotation detection unit, 68: Control unit, 80: Drive device, 131: Electrode unit, 131C: Electrode unit, 131D: Electrode, 132: Electrode unit, 132C: Electrode unit, 132D: Electrode unit

Claims

1. Electromechanical conversion element, An elastic body in which vibration waves are generated on the driving surface due to the vibration of the electromechanical conversion element, A relative motion member that contacts the driving surface of the elastic body and is rotationally driven by the vibration wave, The system includes a drive circuit that provides a repeatedly fluctuating drive signal to the vibration wave motor, The electromechanical conversion element has a density of 4.2 to 6.0 × 10³ kg / m³. Multiple grooves are provided on the drive surface side of the elastic body. Let T be the depth of at least one of the plurality of grooves. Let B be the thickness from the bottom of the groove to the bonding surface of the elastic body in contact with the electromechanical conversion element. When the thickness of the electromechanical conversion element is defined as C, the value of T / (B+C) is in the range of 1.3 to 2.

8. When the drive circuit uses the drive signal to start the vibration wave motor from speed 0 to a speed greater than 0, the frequency change amount of the frequency sweep is determined based on the T / (B+C) value. If T / (B+C) is in the range of 1.3 to 1.7, then it should be 0.7 kHz / msec or less. When T / (B+C) is in the range of 1.7 to 2.8, it was set to 0.5 kHz / msec or less. Vibration wave motor.

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