JPS61224885A - Vibration wave motor - Google Patents

Abstract

PURPOSE:To facilitate a mode rejection by providing detecting means for detecting two vibrations at a vibrator, adding or subtracting the output signals to form a signal indicating the vibration of the vibrator. CONSTITUTION:A piezoelectric element 18 has piezoelectric elements 18c, 18c' disposed at the position displaced by integer number times of lambda/2 in A- and B-phases of drive piezoelectric element groups 18a, 18b for detecting a vibration. The elements 18c, 18c' are polarized in the same direction. Thus, a counterelectromotive force E generated at the detecting terminal becomes the sum of the elements 18c, 18c', and a drive circuit follows the resonance point that the detecting terminal voltage takes the maximum value. When the elements 18c, 18c' are symmetrical with respect to the center of the cylinder, a mode rejection can be performed completely for the vibration mode of odd order.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a vibration wave motor driven by progressive vibration waves.

(Prior art) As disclosed in Japanese Patent Publication No. 58-32518, for example, a vibration wave motor uses the vibration motion generated when a frequency voltage is applied to a piezoelectric vibrator for driving, and is different from a conventional electromagnetic motor. In comparison, it has attracted attention in recent years because it does not require winding, so it has a simple and compact structure, and it has the advantage of being able to obtain high torque even when rotating at low speeds.

As means for exciting vibrations in the vibrating body, an electro-mechanical transducer that deforms periodically, such as a piezoelectric element, an electrostrictive element, and a magnetostrictive element, may be used, but for the sake of simplicity, the piezoelectric element will be explained below.

By the way, in order to efficiently frictionally drive a movable body by the vibration of a vibrating body, a vibration wave motor is used by causing the vibrating body to resonate in a desired vibration mode and generating large vibrations in the vibrating body. However, the resonant frequency of the vibrating body fluctuates depending on changes in the environment such as temperature and pressure, as well as the pressing force and contact area between the vibrating body and the moving body. A drive circuit that follows changes in the body's resonant frequency is required.

Normally, the drive circuit for driving a device that uses strong ultrasonic vibrations is a so-called positive feedback oscillation circuit that detects the resonance point of the vibrating body and feedback-controls the drive frequency in order to stably follow the resonance frequency. used.

Therefore, the drive circuit requires a means for detecting the vibration state of the vibrating body, and such a means may include, for example, bonding a piezoelectric element for vibration detection to the vibrating body, and causing the reverse piezoelectric effect of the piezoelectric element to occur. By detecting the electromotive force,
In some cases, vibration of the vibrating body is detected. In this case, the drive frequency at which the drive amplitude is maximum, that is, the back electromotive force is at its maximum value, is determined.However, there are many resonance points of the vibrating body due to various vibration modes, and mode rejection other than the desired vibration mode is necessary. action is required. For this reason, 1. For example, Japanese Patent Application Laid-Open No. 59-204477 discloses a technique in which mode rejection is performed by passing the output from the vibration detection terminal through a band-pass filter, but the resonance frequencies are very close to each other. In some cases, a bandpass filter with a narrow band width was required to perform complete mode rejection. However, it is difficult to manufacture a filter with sufficient characteristics, and even if it were manufactured, it would be expensive.

<Object of the Invention> An object of the present invention is to realize a vibration wave motor that can perform mode rejection well.

Based on this objective, the present invention provides vibration detection means at a plurality of positions of the vibration wave motor, each of which vibrates in a different phase,
A second object of the present invention is to provide a vibration wave motor that performs feedback control of the oscillation frequency of a drive circuit using the result obtained by adding or subtracting the outputs of the means.

<Example> First, before a detailed explanation of the present invention, a vibration wave motor will be explained. Figure 1 is a perspective view showing the configuration of a so-called surface wave type vibration wave motor, which uses progressive surface waves generated by the bending motion of an elastic body, among rotary vibration wave motors, and Figure 2 is a cross-sectional view thereof. .

In FIGS. 1 and 2, reference numeral 1 indicates that the fixed cover 2
3 is a spring for pressing the movable body 6 against the elastic body 7 via the rotating disk 5, 4 is a thrust bearing, 7 is an elastic body mainly made of metal, and 8 is the elastic body 7 6 is the moving body that presses into contact with the elastic body 7, 5 is the rotating disk (rotating shaft), 9 is a supporting vibration absorber, and 10 is the fixed body.

FIG. 3 is a plan view showing the structure of the piezoelectric element 8, in which the fan-shaped portion indicated by the dotted line is polarized in the thickness direction with polarities indicated by (+) and (-) symbols. Here, an AC voltage V=Vosinωt is applied to the A-phase piezoelectric element group represented by 8a, and V=±V, ) cosωt is applied to generate a traveling surface wave in the elastic body 7 bonded to the piezoelectric element 8. (The direction of movement is changed depending on the direction of movement.) The moving body 6 is brought into pressure contact with the elastic body 7 via the thrust bearing 4 by the spring 3, and the frictional force due to the traveling surface wave acts on the moving body 6, which joins the moving body 6. The rotating shaft 5 rotates.

The fixed cover 2 is fixed to the fixed body 10 with screws 1, and a vibration absorber 9 is inserted between the piezoelectric element 8 and the fixed body 10, so that vibrations generated in the elastic body are not transmitted to the fixed body 10. .

Figure 4 shows a brass elastic body 7 (inner diameter φ38, outer diameter φ
46. When a piezoelectric element 8 for six waves as shown in FIG. It is a figure which shows the relationship between the frequency and amplitude obtained by measuring the displacement amplitude of the elastic body 7 in an axial direction. It can be seen that various resonance points exist when the applied voltage is constant at 30 Vpp and the driving frequency is varied. The amplitude peaks shown in a to f are the resonance points of the second to seventh order out-of-plane amplitudes, and e corresponds to the sixth order (there is no first-order out-of-plane vibration).

When such vibrations are detected by the detection terminal, mode rejection other than e must be performed because the negative body 7 is configured to be most efficient when producing sixth-order vibrations. .

FIG. 5 is a plan view of a piezoelectric element 18 showing one embodiment of the present invention. 18a and 18b are piezoelectric element groups for driving, and are phase A and phase B, respectively.

18c and l 8 c' are piezoelectric elements for vibration detection, and λ
It is placed at a position shifted by an integer multiple of /2 (λ is the wavelength in the desired vibration mode), and in this case it is a symmetrical position with respect to the center of the cylinder, and at a position shifted by 6 times input /2, or 3λ. As mentioned above, the piezoelectric element 18 is a piezoelectric element that is most efficient when a sixth-order vibration is generated (that is, a six-wave piezoelectric element), and 18c and 18♂ are Polarized in the same direction.

FIG. 6 is a diagram showing the connection of piezoelectric elements for vibration detection arranged as shown in FIG. 5, for example.

The arrows drawn inside the piezoelectric elements in the figure indicate the direction of polarization. Similar to FIG. 5, FIG. 6(a) shows a case where the detection piezoelectric elements 18c and 18c' are polarized in the same direction, and the electrodes on the same side are connected to each other.
The back electromotive force E generated at the detection terminal is caused by the piezoelectric elements 18c and 18
It becomes the sum of c′. Here, the elements 18c and 18c' are separated by λ/2 exposure n (n: an integer), so when n is an even number, the elements 18c and 18c' are in phase, and when n is an odd number, the elements 18c and 18c' are in phase. A back electromotive force of opposite phase is generated, and the sum thereof takes a maximum value when n is an even number, and becomes zero when n is an odd number. (However, this is the case where the back electromotive forces of 18c and 18C' are equal.

) Since the drive circuit tracks the resonance point where the detection terminal voltage takes the maximum value, the arrangement of the piezoelectric elements 18 c and l 8 c' is determined so that n is an even number in the case shown in FIG. 6(a). do. In the case of a six-wave vibrator whose resonance frequency is shown in FIG. 4, the maximum detected voltage is shown at the resonance point of e, which is the six-wave vibration mode, and the detected voltage is lower than that in other modes. However, when 18c and 18C' are at symmetrical positions with respect to the center of the cylinder as shown in Figure 5, the voltage generated at the detection terminal becomes zero when vibration in an odd-order vibration mode occurs, so the drive circuit It does not operate, and completely mode rejection is possible for odd-order vibration modes. Other even-order vibration modes remain without mode rejection, but since the interval between the resonance frequencies of these even-order vibration modes is relatively wide, the desired vibration mode can be detected by using a normal bandpass filter. Getting just the resonant frequency...comes.

FIG. 6(b) shows another embodiment for obtaining a detection voltage, in which the polarization directions of the detection piezoelectric elements 18c and 18c' are reversed, and the wiring connections are the same as in FIG. 6(a). However, in this case, the piezoelectric elements 18c and l8c are arranged so that n is an odd number.
All you have to do is decide on the placement of '.

FIG. 6(c) shows another embodiment in which the polarization directions of the detection piezoelectric elements 18c and 18 are opposite, and the electrodes on opposite sides are connected. However, in this case, the arrangement of the piezoelectric elements 18c and 18(' may be determined so that n is an even number.

FIG. 6(d) shows another embodiment in which the polarization directions of the detection piezoelectric elements 18c and 18C' are the same, and the wires are connected between the electrodes on opposite sides so that n is an odd number. The placement of the doto has been decided.

The same applies when exciting odd-numbered vibration modes, but as shown in FIG. 5, the detection piezoelectric element 18c.

When 18c' is placed at a symmetrical position with respect to the center of the cylinder, in odd-order vibration modes, the piezoelectric elements 18c and 18
Since c' vibrates in opposite phase, the electromotive force also has opposite phase. Therefore, Fig. 6 shows (b) or (d)
), the detection voltage is zero in the even wave vibration mode, and complete mode rejection is possible.In this embodiment, other odd wave vibration modes remain, but the drive frequency Since there is a resonance point at a frequency that is quite far away from the oscilloscope, if you use a normal bandpass filter as mentioned above, you can obtain the resonance frequency of the desired vibration mode and prevent it from vibrating in a different vibration mode. can.

FIG. 7 is a plan view of a piezoelectric element 28 showing another embodiment. 28a, 28b, 28c are piezoelectric element groups for driving;
Assuming the human phase, B phase, and C phase, respectively, the phase is 120 in order.
It is driven by applying alternating current voltages shifted by degrees. (3 phase drive) 28d.

28 d' and 28 d are piezoelectric elements for vibration detection, and their connection method corresponds to that shown in FIG. 6(a). This is also 6
This piezoelectric element is for waves, but since there are three piezoelectric elements for vibration detection, further mode rejection is possible compared to the embodiment shown in FIG.

In the embodiments described above, piezoelectric elements typified by PZT etc. were used as electro-mechanical conversion elements, but PM
An electrostrictive element such as N may be used, however, in that case, the concept of polarization processing described above corresponds to a bias DC electric field. Further, it may be a magnetostrictive element, that is, an electro-mechanical transducer that periodically deforms.

In addition, in this embodiment, a rotary type was explained, but the same applies to a linear motor, and the vibration mode used for driving is not limited to out-of-plane vibration.Furthermore, the number of vibration detection elements is limited to two. First, as mentioned above, if there are two or more, mode rejection becomes easier.

(Effects of the Invention) As explained above, the vibrating body is provided with a detection means for detecting at least two vibrations at an interval of an integral multiple of 172 wavelengths of vibration waves, and each output signal from the detection means is added or subtracted. By using the signal as a signal indicating the vibration of the vibrating body, there is an effect of facilitating other mode rejections.

[Brief explanation of drawings]

Figure 1 is a perspective view showing the structure of the ultrasonic motor, Figure 2 is its cross-sectional view, Figure 3 is a plan view of the piezoelectric element, Figure 4 is a diagram showing each resonance point of the vibrating body, and Figure 5 is a diagram showing the resonance points of the vibrating body. A plan view of a piezoelectric element of a vibration wave motor according to an embodiment of the present invention, FIG. 6 is a diagram showing the connection of the piezoelectric element shown in FIG. 5, and FIG. 7 is a diagram of a vibration wave motor according to another embodiment of the invention FIG. 3 is a plan view of a piezoelectric element. 8.18.28 is a piezoelectric element, 7 is an elastic body, 9 is a vibration absorber,
6 is a moving body. , production area 1b monme i4i otsu

Claims (1)

[Scope of Claims] 1) An electro-mechanical transducer that periodically deforms is bonded to an elastic body to generate a progressive vibration wave in the elastic body to form a vibrating body, and the progressive vibration wave causes the above-mentioned A vibrated motor that frictionally drives a movable body brought into pressurized contact with a vibrating body, comprising detection means for detecting at least two vibrations at an interval of an integral multiple of 1/2 wavelength of the vibration wave generated in the vibrating body. . A vibration wave motor, characterized in that the vibration wave motor is configured to add or subtract each output signal from the detection means to obtain a signal indicating the vibration of the vibrating body. 2) The vibration wave motor according to claim 1, wherein the electro-mechanical conversion element and the detection means are piezoelectric elements, electrostrictive elements, or magnetostrictive elements. 3) The vibration wave motor according to claim 1, wherein the electro-mechanical conversion element for driving and the detection means are arranged on the same surface of the vibrating body. 4) The vibration wave motor according to claim 1, wherein the vibrating body is a cylinder, and the detection means is located at a symmetrical position with respect to the center of the cylinder.