JPH03218277A - Driving method of ultrasonic motor - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for driving an ultrasonic motor that generates driving force by exciting elastic waves using a piezoelectric material such as a piezoelectric ceramic.

2. Description of the Related Art Ultrasonic motors, which excite elastic vibrations in a vibrating body using a piezoelectric material such as piezoelectric ceramic, and use this as driving force, are attracting attention.

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

FIG. 3 is a partially cutaway perspective view of an annular ultrasonic motor.
A vibrating body 3 is formed by bonding a toroidal piezoelectric ceramic 2 as a piezoelectric body to one of the toric surfaces of a toroidal elastic body 1.

Reference numeral 5 denotes an annular elastic body, which forms a movable body 6 by bonding it to a friction material 4 made of a wear-resistant material. This movable body 6 is brought into pressure contact with the vibrating body 3 via the friction material 4 .

When an AC voltage is applied to a drive electrode (not shown) provided on the piezoelectric body 2, a radial first-order, circumferential third-order or higher flexural vibration progresses with a radial displacement distribution as shown in FIG. Waves are excited in the vibrating body 3.

The moving body 6 is frictionally driven by the lateral component of the wave crest of this traveling wave and rotates.

Figure 5 shows that due to the traveling wave of bending vibration excited in the vibrating body,
It is an explanatory view showing the principle by which a moving body is frictionally driven. Any point A+ on the surface of the vibrating body 3. lt. Due to the excitation of the traveling wave of bending vibration, it moves in an ellipse with a major axis 2w and a minor axis 2U.

The movable body 6 placed under pressure on the vibrating body 3 comes into contact with the vibrating body near the apex of the elliptical locus, and moves in the opposite direction to the traveling direction of the traveling wave due to the frictional force of the contact surface. The vibration amplitude of the vibrating body is determined by the drive current flowing into the piezoelectric body, and the lateral component U of the wave front of the traveling wave is determined by the vibration amplitude of the vibrating body. The moving speed of the moving body 6 is determined by the product of the lateral component U of the wave crest of the traveling wave described above and the angular frequency ω of the bending vibration as shown in the following formula, and the output torque is determined by the following formula: -ω × u determined by the frictional force between

Ultrasonic motor 1, shifted by a predetermined position to the piezoelectric body 2
By configuring a pair of drive electrodes, taking out the drive terminals, and applying alternating current voltages with predetermined different phases to these two drive terminals, two standing waves of flexural vibrations with different positions are excited in the vibrating body. As a result, a traveling wave of bending vibration can be excited. At this time, if the amplitudes of the two standing waves are equal, a traveling wave with a small standing wave component can be obtained, and the moving object can be driven more efficiently than the operating principle. The vibrating body has the same number as when using a single piezoelectric body.When viewed from the drive terminal, there is resonance.
Exhibits anti-resonance characteristics. Therefore, driving near the resonant frequency allows efficient driving with low voltage.

Problems to be Solved by the InventionDuring normal operation, the conventional ultrasonic motor 1 described above uses the lateral component of the crest of a traveling wave to uniformly drive the contact surface of a moving body with frictional force, thereby improving stability. It has good characteristics. However, if the external mechanical load becomes large or uneven, or an abnormal situation occurs such as a foreign object entering the contact surface between the moving body and the vibrating body, the speed of the moving body may decrease or, in severe cases, it may stop. do. If voltage continues to be applied to the drive electrode in such a situation, the vibrating body will come into contact with the contact surface of the moving body unevenly, causing the friction material formed on the contact surface of the moving body to deteriorate and the vibrating body to heat up. In order to solve the above-mentioned problems, the present invention has the problem that the vibrating body itself deteriorates. detection and
Applying a drive voltage to the piezoelectric body when either of the following is detected: the drive current value has fallen below a predetermined value, or the phase of the drive current has changed for a predetermined period of time or more. It is intended to stop.

Operation Method of driving an ultrasonic motor of the present invention (1) Applying a driving voltage to the driving electrode of the piezoelectric body to excite a traveling wave in the vibrating body. On the other hand, by detecting either that the current value flowing into the drive electrode has fallen below a predetermined value or that the phase of the drive current has changed with respect to the drive FEl [pressure], an abnormality is detected in the ultrasonic motor. By detecting the occurrence of an abnormal situation and stopping the application of drive voltage to the piezoelectric body within a certain period of time after the occurrence of this abnormal situation, deterioration of the vibrating body and the friction material can be prevented.

Example Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1(A) is a block diagram showing an embodiment of the ultrasonic motor driving method of the present invention. A voltage controlled oscillator 101 generates an alternating current signal for driving the ultrasonic motor. 102 is a dividing circuit, and voltage controlled oscillator 10
One output signal is divided into two drive signals having a predetermined phase difference. The output of the dividing circuit 102 is amplified by power amplifiers 103 and 104 to a level sufficient to drive the ultrasonic motor, and is applied to two drive terminals of the ultrasonic motor 106, respectively, to cause bending vibrations in the vibrating body of the ultrasonic motor 106. Excite the traveling wave of During normal operation (
Good stability is achieved by uniformly driving the contact surface of the moving body with frictional force using the lateral component of the wave crest of the main traveling wave. Reference numeral 107 is an encoder that outputs a signal corresponding to the rotational movement speed of the moving body of the ultrasonic motor, and a rotation reduction detector 108 detects the speed of the moving body based on the output signal of the encoder 107.

Force that increases external mechanical load＼ Force that causes unevenness＼
Alternatively, if an abnormal situation occurs such as a foreign object entering the contact surface between the moving body and the vibrating body, the speed of the moving body decreases or stops. If the driving voltage is continued to be applied in this situation, the vibrating body will contact the contact surface of the moving body unevenly, the friction material formed on the contact surface of the moving body will deteriorate, and the vibrating body will heat up. The vibrating body itself deteriorates. Therefore, the rotation drop detector 108 detects that the moving body has fallen below a predetermined speed with respect to the driving voltage of 1 novel while exciting a traveling wave to the vibrating body, and the time circuit 109 detects that the speed has continued for a certain period of time. After confirming this, the oscillation of the voltage controlled oscillator 101 is stopped, and the driving of the ultrasonic motor 106 is stopped.

Here, the time circuit 109 detects an instantaneous rotation stop state.
Alternatively, the rotation of the moving body is checked for a certain period of time to prevent noise from entering the rotation drop detector 108 and causing a malfunction and drive stoppage. As the confirmation time (Dai), set a time that does not cause deterioration of the ultrasonic motor.

FIG. 1(B) is a time chart at terminals A, B, and C in FIG. 1(A), showing the operation of the circuit. As shown by the waveform at terminal A, when the operation of the ultrasonic motor starts at time 1+, a constant output is obtained from the voltage controlled oscillator 101 and drives the ultrasonic motor 106. time t2
If an abnormal situation occurs and the speed of the moving object decreases, terminal B
The rotation drop detector 108 detects this as shown by the waveform at terminal C, and at the same time the time circuit 108 detects this as shown by the waveform at terminal C.
9 begins measuring the time this anomaly lasts. When the time circuit 109 detects that the abnormality has continued for a certain period of time (Δt),
At time t3, the output of the voltage controlled oscillator 101 is stopped.

Here, the speed reduction is detected based on the driving voltage level, but it is also possible to detect the speed reduction based on the driving current level.

FIG. 2 is a block diagram showing another embodiment of the ultrasonic motor driving method of the present invention.

A voltage controlled oscillator 118 generates an AC signal to drive the ultrasonic motor. The dividing circuit 119 divides the output signal of the voltage controlled oscillator 118 into two drive signals having a predetermined phase difference. The output of divider circuit 119 is connected to power amplifiers 120 and 1
21 to a level sufficient to drive the ultrasonic motor, and is applied to two drive terminals of the ultrasonic motor 123, respectively. When the speed of the moving body decreases or stops in an abnormal situation, the drive current relative to the drive voltage decreases, or the phase of the drive current relative to the drive voltage changes. Among these, the value of the drive current is detected by the current detector 124 connected between the human output terminals of the resistor 122, and the current drop detector 125 detects that the current value has become below a predetermined value with respect to the drive voltage level. After the time circuit 126-9 confirms that this has continued for a certain period of time, the voltage controlled oscillator 118 stops oscillating, and the ultrasonic motor 123 stops driving.

In this embodiment, the voltage and current are used instead of the current drop detector 125. It is also possible to stop driving the ultrasonic motor by detecting a change in the phase of the drive voltage and current by using a phase change detector that detects a change in the phase of the drive voltage and current.

In the above example (Table 1) Stopping or reducing the speed of a moving object in an abnormal situation When the speed of the moving object falls below a predetermined value while exciting the moving object to the vibrator The force that the current value flowing into the By combining circuits, the present invention can be realized in the same way by detecting any one of the above-mentioned detection means.Also, since the vibration of the piezoelectric body is proportional to the inflow current, 10. In addition, the present invention can also be realized by providing a sensor electrode for vibration detection and detecting a decrease in current value or a change in phase by observing changes in the vibration state of the vibrating body.

Effects of the Invention As described above, the driving method of the present invention prevents permanent deterioration of the vibrating body and friction material by accurately detecting an abnormal situation in the ultrasonic motor and stopping the driving of the vibrating body. A highly reliable ultrasonic motor can be provided.

[Brief explanation of drawings]

FIG. 1(A) is a block diagram of a drive circuit according to an embodiment of the present invention. FIG. 1(B) is a time chart of each part of FIG. 1(A), and FIG. Fig. 3 is a partially cutaway perspective view of an annular ultrasonic motor; Fig. 4 is a diagram showing radial vibration displacement of the vibrating body of an annular ultrasonic motor; Fig. 5 is an explanatory diagram of the operating principle of the ultrasonic motor. 101, 118...voltage controlled oscillation pins 102, 11
9...Division section 11 103, 104, 120, 121...Power amplifier 106, 123...Ultrasonic motor 107...Encoder 2 108...Rotation drop detection bolt 109, 126... Time cycle 122... Resistance 124... Current detector 125... Current drop detector

Claims (1)

[Claims] a vibrating body formed by adhering a piezoelectric body to one surface of an elastic body; a movable body that is brought into pressure contact with the surface of the vibrating body that does not have the piezoelectric body; In a method of driving an ultrasonic motor equipped with a set of drive electrodes, driving voltages having a predetermined phase difference are applied to each of the drive electrodes to excite a traveling wave in the vibrating body to move the movable body. , the speed of the moving body during the application of the drive voltage has decreased to a predetermined value or less; the current value flowing into the drive electrode has decreased to a predetermined value or less;
and a method for driving an ultrasonic motor, characterized in that application of the drive voltage to the piezoelectric body is stopped when any one of the above changes in the phase of the current with respect to the drive voltage is detected for a predetermined period of time or more. .