JPH0191678A - Speed controller for ultrasonic wave motor - Google Patents

Abstract

PURPOSE:To obtain a speed controller for moving a mover stably at a specified speed, by detecting the moving speed of the moving body, and by setting a speed detecting means for generating the output of signal in proportion to a moving speed. CONSTITUTION:When a variable oscillation circuit 1 is worked and AC voltage is applied to an ultrasonic wave motor 5 via a 90 deg. phase-shifting circuit 2 and power amplifying circuits 3, 4, then a moved 14 is rotationally driven. The speed of the mover 14 is converted to the pulse signal of frequency in proportion to the speed, by a frequency generator (FG) 6, and the pulse signal is converted to DC voltage in proportion to its frequency, by an F-V converter circuit 7, and the input of this DC voltage to the circuit 1 via a compensating filter 8 is provided. The oscillatory frequency of the circuit 1 is controlled according to this veltage. Then, by the circuit 1, the oscillator frequency is changed in proportion to a speed difference between the moving speed of the mover 14 and a specified speed, and by controlling mechanical arm current, the speed of the moving body 14 is controlled to be constant.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a speed control device for an ultrasonic motor that generates driving force using a piezoelectric body.

BACKGROUND OF THE INVENTION In recent years, a driving voltage of several tens of kHz is applied to a vibrating body using a piezoelectric material such as piezoelectric ceramic to excite elastic vibration, causing the vibrating body to undergo stretching vibration or thickness vibration, and this vibration is used as a driving force to drive a rotor. An ultrasonic motor that rotates or linearly moves a driven body (moving body) by pressing and driving the driven body (moving body) is attracting attention.

Hereinafter, the conventional technology of an ultrasonic motor will be explained with reference to the drawings.

FIG. 3 is a perspective view of the annular ultrasonic motor 5, in which an annular piezoelectric material 9 is bonded to an annular elastic body 10 to create a vibrating body 1.
1. 12 is a friction material made of wear-resistant material, 13
are elastic bodies, and are bonded together to form the moving body 14. The moving body 14 is in contact with the vibrating body 11 via the friction material 12. When a voltage is applied to the piezoelectric body 9, bending vibration is excited in the circumferential direction of the vibrating body 11, and this becomes a traveling wave, thereby driving the movable body 14. Note that a protrusion 15 for extracting mechanical output is installed on the vibrating body 11 in the figure.

FIG. 4 shows an example of the electrode structure of the piezoelectric body 9 used in the ultrasonic motor of FIG. In the figure, the structure is such that nine elastic waves are placed in the circumferential direction. In the same figure, A
and B are electrode groups each consisting of a small region corresponding to a half wavelength, C is an electrode group corresponding to a three-quarter wavelength, and D is an electrode group corresponding to a quarter wavelength.

Electrodes C and D create a positional phase difference of 1/4 wave length (90°) between electrode groups A and B. Adjacent small electrode parts in electrodes A and B are electrodes used when polarizing the piezoelectric body 9,
The adhesive surface of the elastic body 10 of the piezoelectric body 9 is the surface opposite to the surface shown in FIG. 4, and the electrodes on that surface are entirely flat electrodes. During use, electrode groups A and B are short-circuited, as indicated by diagonal lines in FIG. 4.

V1=V□-5in (ll, Jt) for the electrodes A and B of the piezoelectric body 9 of the ultrasonic motor configured as above.
---(1) V2=V, ) -cos(ωt)
---(2> However, ■o: Instantaneous value of voltage ω: Angular frequency t - If voltages ■1 and ■2 expressed in time are applied, respectively,
The vibrating body has ξ=ξo ・(cos(ωt) ・cos(kX)+5
in(ωt) −5in(kX) )=ξO・cos(
ωt−kX) ---(3) However, ξ:
Bending vibration amplitude value ξ0: Instantaneous value of bending vibration: Wave number (2π/λ) λ: Wavelength

FIG. 5 shows that point A on the surface of the vibrating body 11 moves in an ellipse with a long axis 2W and a short axis 2U due to the excitation of the traveling wave, and the movable body 14 placed under pressure on the vibrating body 11 moves in an ellipse. The figure shows how the waves move at a rotational speed of .omega..omega.xU in the opposite direction to the direction of wave propagation due to frictional force due to contact near the apex. Further, when there is slippage between the vibrating body 11 and the movable body 14, this speed becomes smaller than the above-mentioned (2). Arrow B in the same figure shows the traveling direction of the moving body 14, and arrow A shows the traveling direction of this traveling wave. Also, the speed ■ of the moving body 14 mentioned above is proportional to the instantaneous value ξ0 of this bending vibration. do.

By the way, if this ultrasonic motor 5 is shown as an equivalent circuit, the sixth
It is known that the result will be as shown in the figure. In the same figure, C8
is the electrical capacitance of the vibrating body 11, and C1 is the electric capacitance of the vibrating body 11.
, Ll corresponds to the mass, and R1 corresponds to the braking coefficient and load. This circuit composed of C1, L, , R, is related to mechanical operations such as vibration, and is called a mechanical bowl, and the current i flowing through this mechanical bowl out of the current i supplied to the electrodes of the piezoelectric body 9. , is called the mechanical arm current. As described above, the magnitude of this mechanical arm current i is proportional to the vibration amplitude of the vibrating body 11, and therefore proportional to the moving speed of the moving body 14.

Now, drive the ultrasonic motor 5 configured as above,
When controlling the moving speed of the moving body 14 to a predetermined constant value,
As mentioned earlier, the mechanical arm current i is proportional to the moving speed, so conventionally the value of this mechanical arm current i is detected using well-known technology and the applied voltage is controlled so that this value remains constant. However, an attempt was made to keep the moving speed of the moving body 14 constant.

Problems to be Solved by the Invention However, in the above configuration, if the contact state between the movable body 14 and the vibrating body 11 and the load state received from the outside are always constant, the moving speed of the movable body 14 will also be constant; This mechanical arm current 17 constant force type is an oven loop for the moving speed, so the contact state between the moving body 14 and the vibrating body 11 may fluctuate due to changes in temperature and humidity, or if the external load changes. , the proportional state between the moving speed and the mechanical arm current i changes due to these fluctuations, so the moving speed of the moving body 14 changes in accordance with these fluctuations. Therefore, it is difficult to control the moving speed of the moving body 14 to a predetermined constant value using the conventional method in which the mechanical arm current i is controlled only to a constant set value.

In view of this, an object of the present invention is to provide a speed control device for an ultrasonic motor that always moves a moving body at a predetermined constant speed.

Means for Solving the Problems The present invention drives a piezoelectric body with an alternating current voltage to excite an elastic wave in a vibrating body composed of the piezoelectric body and an elastic body, thereby bringing the piezoelectric body into contact with the vibrating body. an ultrasonic motor that moves an installed moving object; a speed detection means that detects the moving speed of the moving object and outputs a signal proportional to the moving speed;
A speed control device for an ultrasonic motor includes variable oscillation means for controlling the frequency of the alternating voltage.

Operation According to the above-described configuration, the present invention controls the speed of the moving body by changing the frequency of the applied AC voltage using the variable oscillation means whose output frequency is controlled by the output of the speed detection means.

Embodiment Before describing the embodiment of the present invention, the characteristics of the ultrasonic motor 5 will be added.

When the level of the alternating voltage applied to the ultrasonic motor 5 is kept constant and its frequency is varied, the magnitude of the mechanical arm current i exhibits a frequency characteristic as shown in FIG. 2. As can be seen from this figure, at frequencies higher than the resonance point (the peak of the characteristic curve), the magnitude of the lti arm current 11 corresponds one-to-one depending on the frequency value, except for the unstable region near the resonance point. If the frequency f1 is changed from f, . . . to f + a2, the mechanical arm current i will change from i to 1 + a
2 range changes.

Furthermore, as mentioned earlier, changing the mechanical arm current 11 changes the speed of the moving body 14, so speed control is performed by changing the frequency f of the drive voltage in accordance with the fluctuation in speed. Can be done.

FIG. 1 shows a block diagram of a speed control device for an ultrasonic motor according to a first embodiment of the present invention. In Figure 1, 1 is a variable oscillation circuit that generates an AC signal whose output frequency is controlled by the input voltage value, and 2 is a variable oscillation circuit 90 that generates two signals with a 90° phase difference from the output of the variable oscillation circuit 1. The phase shift circuit 3.4 amplifies each signal with a 90° phase difference to a voltage level sufficient to drive the ultrasonic motor 5 and applies the power to each electrode of the piezoelectric body 9. The amplifier circuit 6 is a well-known frequency power generator 11f that detects changes in magnetic flux proportional to the moving speed from a magnetized plastic magnet attached around the moving object 14 using a magnetoresistive element and outputs a pulsed signal! l (
FG), 7 is a frequency-voltage (F-V) conversion circuit that outputs a voltage proportional to the output frequency of FG, 8 is a compensation filter to stabilize the speed control loop, and its output is the input of variable oscillation circuit 1 connected to.

The operation of the ultrasonic motor speed control device of this embodiment configured as described above will be described below.

The variable oscillator 1 operates and AC voltage is applied to the ultrasonic motor 5 (piezoelectric body 9) through the 90° phase shifter and power amplifier 3.4.
When applied, the movable body 14 is rotationally driven. The speed of the rotationally driven moving body 14 is converted by the FG 6 into a pulse signal with a frequency proportional to the speed, and this pulse signal is converted into a DC voltage proportional to the frequency by the F-V conversion circuit 7, and this DC voltage is input to the variable oscillation circuit 1 via the compensation filter. The oscillation frequency of the variable oscillation circuit 1 is controlled according to this input voltage.

Here, the variable oscillation circuit 1 uses a signal proportional to the moving speed of the moving body 14 outputted by the F-V conversion circuit 7 (compensation filter 8) to generate a mechanical arm current i if the speed is lower than a predetermined speed. To increase the oscillation frequency, fml
conversely, if the speed is high, the oscillation frequency is increased to reduce the mechanical arm current is. In this way, the variable oscillation circuit 1 changes the oscillation frequency in proportion to the speed difference from the predetermined speed, and controls the mechanical arm current, so that the speed of the moving body 14 is kept constant.

As described above, according to this embodiment, the drive frequency is controlled to a predetermined speed based on the speed information of the moving body 14, so that it can operate stably and always at a predetermined speed. Instead of changing the mechanical arm current depending on the voltage level, the mechanical arm current is changed by changing the frequency, so it is possible to realize an ultrasonic motor speed control device that does not require the application of a higher voltage than in the past.

As described in detail, according to the present invention, the moving speed of the movable body can be stabilized at a predetermined speed even if there are load fluctuations due to changes in the contact state between the movable body and the elastic body or external load fluctuations. We can provide speed control device for ultrasonic motor to drive,
Its practical effects are great.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a speed control device for an ultrasonic motor according to an embodiment of the present invention, FIG. 2 is a frequency characteristic diagram of mechanical arm current, and FIG. 3 is a cutaway perspective view of an annular ultrasonic motor.
Figure 4 is a plan view showing the shape and electrode structure of the piezoelectric body used in the ultrasonic motor in Figure 3, Figure 5 is an explanatory diagram of the operating principle of the ultrasonic motor, and Figure 6 is an equivalent circuit of the ultrasonic motor. It is a diagram. 1... variable oscillation circuit, 2... 90° phase shift circuit, 3...
4... Power amplifier circuit, 5... Ultrasonic motor, 6...
...FG, 7...F-V conversion circuit, 8...compensation filter. Name of agent: Patent attorney Toshio Nakao (1 person) Figure 3 Figure 4

Claims (1)

[Claims] (1) A piezoelectric body is driven with an alternating current voltage to excite an elastic wave in a vibrating body composed of the piezoelectric body and an elastic body, thereby moving a movable body placed in contact with the vibrating body. It comprises an ultrasonic motor, a speed detection means for detecting the moving speed of the moving body and outputting a signal proportional to the moving speed, and a variable oscillation means for controlling the frequency of the alternating voltage according to the output of the speed detecting means. A speed control device for an ultrasonic motor characterized by: