JP2522286B2 - Ultrasonic motor drive circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION A. Field of Industrial Application The present invention relates to an elastic body in which a progressive vibration wave is formed by an electrostrictive element, and the progressive vibration wave when the elastic body is pressed by a predetermined pressing force. The present invention relates to a drive circuit of an ultrasonic motor having a moving body driven by.

B. Conventional Technology This type of ultrasonic motor drives a moving body by supplying a frequency signal (for example, an AC signal) to an electrostrictive element to cause it to vibrate, which causes the elastic body to form a progressive vibration wave. is there. At this time, since the moving body catalyzes the elastic body with a predetermined pressing force, when the load of the moving body becomes large, the two come into sliding contact with each other. Therefore, it is preferable to stop the ultrasonic motor when the load of the moving body is large in order to prevent wear of both and to improve the life.

C. Problems to be Solved by the Invention Therefore, it is possible to stop the ultrasonic motor by providing a sensor such as a rotary encoder on the moving body side to detect that a large load is acting from the movement of the moving body. However, the sensor is required separately from the motor component, which is not preferable because the configuration is complicated. It is also not possible to detect the motor load by detecting overcurrent as in conventional DC motors.

An object of the present invention is to provide an ultrasonic motor drive circuit capable of detecting the drive state of an ultrasonic motor and performing a protection operation without separately providing a sensor or the like.

D. Means for Solving Problems The present invention will be described with reference to FIGS. 1 and 2 (a) and (b) showing an embodiment. Ultrasonic motor 10 according to the present invention
Is a progressive vibration wave is formed in the elastic body 11 by the electrostrictive element 13 to which a frequency signal (such as an AC signal) is applied, and the moving body 12 is driven by the progressive vibration wave of the elastic body 11. is there. Referring also to FIG. 3, in the present invention, a difference calculation means AND for calculating the difference between the signal correlated with the voltage phase of the frequency signal and the signal correlated with the current phase flowing into the electrostrictive element.
And a phase difference detection means COD that integrates the calculated difference to detect the phase difference between the voltage phase of the frequency signal and the current phase flowing into the electrostrictive element, and the vibration wave based on the detected phase difference. The determination means 28 for determining whether the load amount of the moving body driven by the predetermined amount or more, and when it is determined by the determination of the determination means 28 that the driving state of the ultrasonic motor is abnormal, the ultrasonic motor is turned on. Protective means 22 for performing protective operation for protection
And resetting the integrated value every cycle of the frequency signal solves the above-mentioned problem.

E. Action The integrated value of the phase difference between the drive voltage and current correlates with the load. When the determination means 28 determines that the load of the ultrasonic motor is not less than the predetermined amount based on the integrated value, the protection means 28 protects the ultrasonic motor. The integrated value is reset every cycle.

F. Embodiment An embodiment of the present invention will be described with reference to FIGS.

In FIG. 1, reference numeral 10 denotes an ultrasonic motor, and in this embodiment, a rotary ultrasonic motor is shown. As shown in FIGS. 2 (a) and 2 (b), the ultrasonic motor 10 is constructed by pressing a moving body 12 having the same shape against an annular elastic body 11 with a predetermined pressing force by a spring member (not shown). Have been. An electrostrictive element 13 is attached to the back surface of the elastic body 11, and the surface of the electrostrictive element 13 is
On 13a, segment electrodes 14a to 14d are formed. The electrostrictive elements 13 below the segment electrodes 14b and 14d are alternately polarized.

In FIG. 1, the output of the AC power supply 21 is input to a 90-degree phase delay circuit 23, a current phase detection circuit 24, and a phase difference detection circuit 25 via a switch 22. 90 degree phase delay circuit
23 delays the phase of the input AC signal by 90 degrees and outputs the delayed AC signal. The output is supplied to the segment electrode 14d via the amplifier 26. The current phase detection circuit 24 detects the current phase of the input AC signal, and its output is input to the phase difference detection circuit 25 and also to the segment electrode 14b via the amplifier 27. The phase difference detection circuit 25 detects the phase difference between the phase of the voltage applied to the electrostrictive element 13 and the phase of the current flowing into the electrostrictive element 13 due to the application of the voltage. The detected phase difference is input to the determination circuit 28, and when it is determined that the phase difference is equal to or greater than a predetermined value, a determination signal is output to a terminal 29. The terminal 29 has a latch circuit 30 for latching the judgment signal.
, And the latch output opens and closes the switch 22. That is, when the difference between the two phases is more than a predetermined value, the switch
22 is open. The latch circuit 30 is not essential to the present invention.

When the switch 22 is closed, the AC power supply 21 is connected to the segment electrodes 14b and 14d of the electrostrictive element 13 via the amplifiers 26 and 27.
AC signals 90 degrees out of phase are supplied. Therefore, a progressive vibration wave is generated on the surface of the elastic body 11, and the moving body 12 is rotationally driven. When the switch 22 is opened, the power supply to the electrostrictive element 13 is stopped, so that the electrostrictive element 13 does not vibrate and the moving body 12
Stops.

FIG. 3 shows details of the phase difference detection circuit 25 and the determination circuit 28. In FIG. 3, the phase difference detection circuit 25 has two input terminals IN1 and IN2, and a voltage phase is applied to the input terminal IN1.
The current phase is input to the input terminal IN2. The input terminal IN1 is connected to the AND gate AND and the inverter INV1, and the input terminal IN2 is connected to the inverter INV2.
The AND output is connected to the non-inverting input terminal of the comparator COM via the resistor RE, and is grounded via the capacitor CON and the transistor TR. An integrating circuit is constituted by the resistor RE and the capacitor CON. The output of the inverter INV1 is input to the base of the transistor TR. The inverting input terminal of the comparator COM is connected to the power supply BA and Vba
The reference voltage indicated by is applied.

The operation of the phase difference detection circuit 25 and the determination circuit 28 will be described with reference to FIG. Incidentally, the segment electrode 14 of the electrostrictive element 13
It is assumed that AC signals having a phase difference of 90 degrees are supplied to b and 14d, a progressive vibration wave is formed in the elastic body 11, and the moving body 12 is rotationally driven.

The voltage phase A is input to the input terminal IN1, and the current phase B is input to the input terminal IN2. The difference between the two phases increases in accordance with the load on the ultrasonic motor 10. When a load is applied to the moving body 12 and the two phases are shifted from each other, the AND output C is generated only while the voltage phase A rises and the current phase B falls.
Stands up. At this time, the capacitor CON is charged by the AND output C. Then, when the voltage phase A falls, a high level output is obtained from NIV1 and the transistor TR
Is turned on, the capacitor CON is discharged. Therefore, the input voltage D at the non-inverting input terminal of the comparator COM is as shown in FIG. Since the reference voltage of the inverting input terminal of the comparator COM is now set to Vba, when the input voltage D of the non-inverting input terminal exceeds Vba, the output E of the comparator COM goes high and the output E of the terminal 2
It is taken out from 9 and latched by the latch circuit 30. Since the latch circuit 30 outputs a high level latch signal, the switch 22 is opened. As a result, the power supply to the electrostrictive element 13 is stopped and the ultrasonic motor 10 is stopped. The load of the moving body 12 is released and the latch circuit is opened by a reset switch (not shown)
If the switch 30 is reset, the switch 22 is closed, the ultrasonic motor 10 is supplied with power again, and the ultrasonic motor 10 is started.

In the above description, the electrostrictive element is driven by the AC signal, but the electrostrictive element may be driven by any signal as long as it is a frequency signal such as a pulse signal in which the voltage periodically changes. . Further, although the power supply to the ultrasonic motor is stopped when the comparator outputs the high level signal, an alarm lamp or a warning sound may be used to notify that the load on the moving body has increased. Furthermore, set the comparator of the reference voltage Vba to 1
Although only one comparator is used, a plurality of comparators having different reference voltages may be provided to determine the magnitude of the load on the moving body based on which comparator outputs the load. Furthermore, the present invention can be applied to linear ultrasonic motors as well as rotary ultrasonic motors.

G. Effect of the Invention According to the present invention, the difference between the drive voltage and the phase of the current of the frequency signal supplied to the electrostrictive element is integrated, and the load of the ultrasonic motor is determined based on the integrated value. The ultrasonic motor can be protected with a simple structure without using a separate sensor, and the load detection response is improved by resetting the integral value every cycle. Further, as in the embodiment, when the load exceeds a predetermined value, the power supply to the ultrasonic motor is stopped and the ultrasonic motor is stopped, so that undesired friction between the moving body and the elastic body at the time of heavy load is eliminated. It is possible to obtain an ultrasonic motor with a long life.

[Brief description of drawings]

1 to 4 are diagrams for explaining one embodiment of the present invention, and FIG. 1 is a block diagram showing the overall configuration, and FIG. 2 (a).
2 is a plan view of the ultrasonic motor, FIG. 2 (b) is a bb cross-sectional view thereof, FIG. 3 is a detailed view of a phase difference detection circuit and a judgment circuit, and FIG. 4 is a time chart of signals of each section. 10: Ultrasonic motor, 11: Elastic body 12: Moving body, 13: Electrostrictive element 21: AC power supply, 22: Switch 23: 90 degree phase delay circuit 24: Current phase detection circuit 25: Phase difference detection circuit, 28: Judgment circuit 30: Latch circuit

Claims (1)

(57) [Claims] 1. A drive circuit of an ultrasonic motor for forming a vibration wave in an elastic body by an electrostrictive element to which a two-phase frequency signal having a phase difference is applied, and driving the moving body by the vibration wave. Difference calculating means for calculating the difference between the signal correlated with the voltage phase of the signal and the signal correlated with the current phase flowing into the electrostrictive element, integrating the calculated difference, and the voltage phase of the frequency signal Phase difference detection means for detecting a phase difference with the current phase flowing into the electrostrictive element, and determination means for determining whether or not the load amount of the ultrasonic motor is a predetermined amount or more based on the detected phase difference. When the drive unit of the ultrasonic motor is determined to be abnormal by the determination of the determination unit, a protection unit that performs a protection operation to protect the ultrasonic motor is provided, and the integrated value is the frequency signal. 1 cycle of Driving circuit of the ultrasonic motor, characterized in that the reset and.