JPH01110071A - Driving method for supersonic motor - Google Patents

Abstract

PURPOSE:To obtain a thin, high speed, high torque motor, by exciting standing waves of longitudinal vibration and odd order bending vibration simultaneously in an elastic body. CONSTITUTION:A piezoelectric board 12 polarized in the direction of thickness is stuck to the rear face of a rectangular elastic board 11, and metallic electrode films 15 are provided on the opposite main faces thereof. A pair of electrode terminals 16 are led out from these electrode films 15. A moving sheet member 13 is placed on the surface of the rectangular elastic board 11 and pressure contacted with the elastic board 11 through a roller 14 rotatable around the central axis. When AC voltage is applied onto the electrode terminal 16 and the elastic board 11 is resonated, the sheet member 13 is moved in the direction of an arrow with high speed.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a motor that utilizes ultrasonic vibration energy.

(Prior art) Ultrasonic motors that utilize traveling waves have the characteristics of generating high torque at low speeds.
A motor as shown in FIG. 6 has been proposed.

In FIG. 6, a bending wave traveling in the direction A is excited in the elastic body 11. In this case, the surface particles of the elastic body vibrate elliptically, so if the moving body 13 is pressed onto the elastic body, the moving body moves in the direction B.

(Problem to be solved by the invention) However, when constructing a linear motor using the motor as described above,
In order to excite pure traveling waves, special consideration must be taken to prevent reflected waves from the ends. For example, it is necessary to attach special vibration absorbers to both ends of the elastic plate to completely absorb traveling waves.

Furthermore, since the transverse vibration component of the elliptical vibration on the surface of the elastic body is small, the moving speed and torque of the moving body cannot be increased very much.

The object of the present invention is to provide an ultrasonic motor for paper feeding which eliminates such conventional drawbacks.

(Means for Solving the Problems) The present invention is characterized in that elliptical vibration is excited on the surface of the elastic body by simultaneously exciting standing waves of longitudinal vibration and odd-numbered bending vibration in the elastic body.

(Function) When two standing waves as described above are excited simultaneously, since they are standing waves, a special device for suppressing reflected waves is not required.

Furthermore, since the standing wave of longitudinal vibration is excited separately from the bending vibration, the transverse vibration component is larger than that of the traveling wave. Therefore, high speed and high torque can be achieved.

FIG. 3(a) shows one method for simultaneously exciting standing waves of longitudinal vibration and one-dimensional bending vibration. Elastic plate 11
A piezoelectric ceramic plate that is uniformly polarized in the thickness direction is bonded to the back surface of the piezoelectric ceramic plate, and metal electrode films are provided on both sides of the piezoelectric ceramic plate. When alternating current electrical signals at resonance frequencies of two vibration modes are input between the electrodes, standing waves of longitudinal vibration and -dimensional bending vibration are excited in the elastic body. The figure shows a displacement distribution 31 of longitudinal vibration standing waves and a displacement distribution 32 of one-dimensional bending vibration standing waves. Also, Fig. 3(b)
shows the motion of particles on the surface of an elastic body when two standing waves are excited simultaneously. In areas A and C and areas B and D, elliptical vibrations in opposite directions are excited, and the amplitudes are different between A and B and between C and D.

In an ultrasonic motor, the more rollers that press against the moving body, the greater the thrust of the motor can be.

An example of a dual mode vibrator with 11th-order bending vibration and 2nd-order longitudinal vibration will be explained. Figure 4(a) shows the amplitude displacement distributions of two types of vibrations. In the figure, 11 is the rectangular metal elastic plate, and 41 and 42 are the amplitude displacements of the second-order longitudinal vibration and the 11th-order bending vibration, respectively. It shows the distribution. As is clear from the figure, the amplitude displacements of the two vibrations are approximately equal at each point A, B, and C of the rectangular elastic plate. As a result, as shown in FIG. 4(b), the two vibrations are combined at each of the above points, and elliptical vibrations having substantially equal amplitude and the same direction of rotation are excited.

Therefore, if the rollers are pressed against the three points mentioned above, each roller will rotate at the same rotation speed and in the same direction.

In this way, by using a dual mode vibrator with 11th order bending vibration and 2nd order longitudinal vibration, the roller can be driven at three points. Therefore, if the vibrator is used as a stator, an ultrasonic motor with a large thrust can be realized.

In addition to the combinations of vibration modes described above, there are many dual mode vibrators that can be driven at three points, and generally odd-order bending vibration and second-order longitudinal vibration may be combined.

(Example) Examples of the present invention will be described below with reference to the drawings.

FIG. 1 is a sectional view showing the configuration of an ultrasonic motor in which a stator is a dual-mode vibrator for primary longitudinal vibration and primary bending vibration. A piezoelectric ceramic plate 12 polarized in the thickness direction is bonded to the back surface of the rectangular elastic plate 11, and a metal electrode film 15 is provided on both sides of the piezoelectric plate. A pair of electrode terminals 16 are taken out from these electrode films.
has been done. A sheet-like moving body 13 is placed on the surface of the rectangular elastic plate 11, and is pressed against the elastic plate by a roller 14 that can rotate around a central axis. When an AC voltage is applied to the electrode terminal 16 to cause the elastic plate to resonate, the sheet-like moving body 13 moves at high speed in the direction of the arrow. Note that the roller may be pressed at any position other than the vibration node.

Next, other embodiments will be described. FIG. 5(a) shows a stress distribution 52 of the second-order longitudinal vibration and a stress distribution 53 of the eleventh-order bending vibration excited in the elastic plate 11 in the stator. This relationship determines a method for efficiently exciting the two types of vibrations at the same time, and the results are shown in FIG. 5(b). A piezoelectric ceramic plate 12 is bonded to the back surface of the elastic plate 11 as shown. Each piezoelectric ceramic plate is polarized in the direction of the arrow, and has metal electrode films 15 on the front and back surfaces.
is provided. As shown in the figure, two sets of electrode terminals 54 and 55 are taken out from the elastic plate 11 and each piezoelectric ceramic plate. When an AC voltage is applied to the electrode terminal 54, a second order longitudinal vibration can be excited, and when an AC voltage is applied to the electrode terminal 55, an 11th order bending vibration can be excited. When alternating current voltages with phases different by 90 degrees are applied to the respective terminals, the vibrator becomes a dual mode vibrator with second-order longitudinal vibration and eleventh-order bending vibration.

FIG. 2 shows a configuration including the stator and rollers. A sheet-like moving body 13 is placed on the surface of the dual mode vibrator shown in FIG. 2, and is pressed against it by three freely rotatable rollers 14. The pressure contact positions of the rollers are A and B shown in Figure 4.
, C. When alternating voltages having a phase difference of 90 degrees are applied to the two pairs of electrode terminals of the vibrator to cause resonance, the sheet-like moving body 13 moves in the direction of the arrow. The thrust in this case was approximately three times that of a conventional motor using one roller.

In this example, the dimensions are 120 x 30 x 2 mm.
A 5 mm thick PZT piezoelectric ceramic plate was bonded to a stainless steel elastic plate to form a dual mode vibrator. Further, the frequency of the driving AC voltage was 42.2 kHz.

(Effects of the Invention) According to the present invention, a vibration absorbing device is not required, and an ultrasonic motor that is high speed, high torque, thin, and has a large thrust can be realized.

[Brief explanation of the drawing]

FIG. 1 and FIG. 2 are diagrams showing embodiments of the present invention. FIG. 3, FIG. 4, and FIG. 5 are diagrams showing standing wave excitation states of longitudinal vibration standing waves and odd-order bending vibrations. FIG. 6 is a diagram showing the principle of a conventional ultrasonic motor. In the figure, 11... elastic plate, 12... piezoelectric ceramic plate, 13... moving body, 14... roller, 15...
Electrode, 16.54°55... Electrode terminal, 31, 41,
52...Longitudinal vibration displacement distribution, 32.42°53...Bending vibration displacement distribution, respectively.

Claims (1)

[Claims] A method for driving an ultrasonic motor characterized by simultaneously exciting longitudinal vibration and odd-order bending vibration.