JPH01148082A - Driving method for ultrasonic motor - Google Patents

Abstract

PURPOSE:To facilitate the start of an ultrasonic motor even at the time of outputting a high torque and to enhance the efficiency and the stability of the motor by controlling the amplitude of an applied voltage at the time of starting with respect to an applied voltage at the time of operating in response to its output torque. CONSTITUTION:When a start signal is generated from a start controller 1, a signal of driving frequency is generated from an oscillator 2. This signal is applied through a voltage control amplifier 5 and a resistor 8 to piezoelectric ceramics 10, and also applied through a 90 deg. phase shifter 3, a voltage control amplifier 4 and a resistor 6 to the ceramics 10. when the currents flowing to the resistors 6, 8 are varied according to output torque, this is detected by differential amplifiers 7, 9, and the amplifiers 4, 5 are controlled by the detected output.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Applications Prior Art In recent years, ultrasonic motors have attracted attention, in which elastic vibrations are excited in a vibrating body using a piezoelectric material such as a piezoelectric ceramic, and this vibration is used as a driving force.

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

FIG. 3 is a perspective view of a conventional ultrasonic motor, in which a piezoelectric ceramic 1 as a piezoelectric body is attached to one of the annular surfaces of an elastic body 11.
The vibrating body 12 is constructed by pasting together the 0 pieces. 13 is a friction material made of a wear-resistant material, and 14 is an elastic body, which are pasted together to form a moving body 15. The moving body 15 is in contact with the vibrating body 12 via the friction material 13. When an electric field is applied to the piezoelectric ceramic 10, a traveling wave of bending vibration is excited in the circumferential direction of the vibrating body 12, thereby driving the movable body 15. Note that the arrow in the figure indicates the rotation direction of the moving body 15.

FIG. 4 shows an example of the electrode structure of the piezoelectric ceramic 10 used in the ultrasonic motor of FIG.

In the figure, nine elastic waves are placed in the circumferential direction. In the figure, A and B are electrode groups each consisting of a small area corresponding to a half wavelength, C is an electrode group having a length of three-quarters of a wavelength, and D is an electrode having a length of a quarter of a wavelength. Electrodes C and D create a positional phase difference of 1/4 wavelength (=90 degrees) between electrode groups A and B. Adjacent small electrode portions in electrodes A and B are polarized oppositely to each other in the thickness direction. The bonding surface of the piezoelectric ceramic 10 with the elastic body 11 is the surface opposite to the surface shown in FIG. 4, and the electrode is a solid electrode. In use, electrode groups A and B are arranged as indicated by diagonal lines in FIG.
They are used by short-circuiting each.

In the electrodes A and B of the piezoelectric ceramic 10 of the ultrasonic motor configured as above, V
(1) V2-VOXC05(ωt)
---(2) However, if vo: instantaneous value of voltage ω: angular frequency t: voltages v1 and v2 expressed in time are applied,
The vibrating body 12 has ξ−ξox(cos(ωt)xcos(kx)+5in
(ωt)xsin(kx)) -vo Xcos(ωt-kx) ---(
2) However, ξ: amplitude value of bending vibration ξ0: instantaneous value of bending vibration k: wave number (2π/λ) λ: wavelength .

FIG. 5 shows that point A on the surface of the vibrating body 12 moves in an ellipse with the major axis 2w and the minor axis 2u due to the excitation of the traveling wave, and the vibrating body 1
The moving body 15 placed under pressure on the ellipse 2 contacts the ellipse near the apex and moves at a speed of V-ωxu in a direction opposite to the direction of wave propagation due to frictional force.

Problems to be Solved by the Invention In order to increase the output of the ultrasonic motor, it is sufficient to increase the kinetic energy of the imaging object. Since kinetic energy is proportional to the square of the mass and speed of the vibrating body, the output can be increased by increasing the mass or speed of the vibrating body. Note that the speed V is proportional to the instantaneous value ξ0 of the bending vibration of the vibrating body 12, and the instantaneous value ξ0 of the bending vibration is proportional to the current value flowing through the piezoelectric ceramic 10 forming the vibrating body 12.
By driving near the resonance frequency of the vibrating body 12 where a large current can be obtained with a small voltage, a large speed can be obtained and the output of the ultrasonic motor can be increased. However, the resonant frequency of an ultrasonic motor varies depending on the load, so when outputting low torque, it is easy to start even if the driving frequency deviates from the vicinity of the resonant frequency, but when outputting high torque, the driving frequency is close to the resonant frequency. If it deviates from the starting point (
There is a problem with this.

The present invention has been made in view of the above problems, and an object of the present invention is to provide an ultrasonic motor that can be stably started regardless of the output torque and is highly efficient.

Means for Solving the Problems An ultrasonic motor driving method is used in which the height of the applied voltage at startup with respect to the applied voltage during operation is controlled in accordance with the output torque.

By increasing the applied voltage at startup compared to the applied voltage during operation according to the torque to be output, it is easy to start, and efficient and stable ultrasonic motor drive can be achieved even when high torque is output. can.

EXAMPLE Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a block diagram of an ultrasonic motor drive circuit according to an embodiment of the present invention. A starting control unit 1 that issues a starting signal for the ultrasonic motor is connected to an oscillator 2.
The output of is connected via a 90-degree phase shifter 3 to a voltage-controlled amplifier A4 whose amplification factor can be changed by an external signal, and to a voltage-controlled amplifier B5 on the other hand.

The output side of the voltage control amplifier A4 is applied to the piezoelectric ceramic 10 constituting the driver of the ultrasonic motor via a resistor R16, and the output side of the voltage control amplifier B5 is applied to the piezoelectric ceramic 10 via a resistor R27. be done. Further, both ends of the resistor R16 are connected to two input sides of a differential amplifier A7, and the output side of the differential amplifier A7 is connected to a voltage control amplifier A4. Similarly, both ends of the resistor R28 are connected to two input sides of a differential amplifier B9, and the output side of the differential amplifier B9 is connected to a voltage-controlled amplifier B5.

FIG. 2(a) shows the change in the current flowing through the resistor R1 and resistor R2 in FIG. 1 in response to a change in torque, and FIG. 2(b) shows the change in the current flowing through the differential amplifier A in response to a change in torque. ? , and the output signal of differential amplifier B9.

In FIG. 1, when the activation control section 1 generates a activation signal, the oscillator 2 generates a driving frequency signal. Here, the above signal is divided into two, one being the above 9
The voltage passes through the 0 degree phase shifter 3 and is boosted by the voltage control amplifier A4 to a voltage that drives the ultrasonic motor. On the other hand, the signal is boosted to the voltage by the voltage control amplifier B5. Furthermore, the signal issued from the voltage controlled amplifier A4 is applied to the piezoelectric ceramic 10 through the resistor R16. Here, as shown in FIG. 2(a), when the current flowing through the resistor R16 changes due to the output torque, the differential amplifier A7 detects the change in the current, and the voltage control amplifier A4 detects the change in the current. emit a signal. This signal changes the output of the voltage control amplifier A4, and as shown in FIG. 2(b), at startup, Sl
, a voltage such as S2 is applied to the piezoelectric ceramic 10 during driving. Similarly, if the current flowing through the resistor R28 changes depending on the output torque, the differential amplifier B
9 detects the change in the current, and the voltage control amplifier B5
send a signal to. This signal changes the output of the voltage control amplifier B5, and as shown in FIG. 2(b), voltages such as Sl during startup and S2 during driving are applied to the piezoelectric ceramic 10. With the drive control method for the ultrasonic motor as described above, the applied voltage at startup changes depending on the torque to be output, so that stable and efficient drive is possible even when high torque is output.

Effects of the Invention According to the present invention, it is possible to provide an ultrasonic motor that is stable and efficient even when outputting high torque.

[Brief explanation of the drawing]

Fig. 1 is a block diagram and a second perspective view of a drive circuit using an ultrasonic motor driving method according to an embodiment of the present invention, and Fig. 4 shows the shape and shape of the piezoelectric ceramic used in the ultrasonic motor of Fig. 3. , a plan view showing the electrode structure, and FIG. 5 is an explanatory diagram of the operating principle of the ultrasonic motor. 1... Start-up control section, 2... Oscillator, 3
...90 degree phase shifter, 4...Voltage control amplifier A, 5...Voltage control amplifier B, 6...
...Resistor R1, 7...Differential amplifier A, 8...
... Resistor R2, 9... Differential amplifier B, 10.
...Piezoelectric ceramic, 11...Elastic body,
12... Vibrating body, 13... Friction material, 1
4...Elastic body, 15...Moving body. Name of agent: Patent attorney Toshio Nakao and one other person Figure 1 Figure 2 Figure 3 Figure 4 5tIJ font ff'7

Claims (1)

[Claims] By driving a piezoelectric body with an alternating current voltage and exciting an elastic traveling wave in a vibrating body composed of the piezoelectric body and an elastic body,
In a method of driving an ultrasonic motor that moves a moving body placed in contact with the vibrating body, the height of the applied voltage at startup is controlled in accordance with the torque to be output, with respect to the applied voltage during operation. A method of driving an ultrasonic motor characterized by the following.