JPH04140077A - Drive control of ultrasonic motor - Google Patents

Abstract

PURPOSE:To make a smooth start-up of a motor at all times by a method wherein the frequency of a.c. signals which are applied at the time of motor start-up is so swept that it may come near the resonance frequency of a piezoelectric body and the sweeping is stopped when the level of signals detected by a piezoelectric sensor gets larger than the specified value during sweeping. CONSTITUTION:When start up signals are inputted, the output of a start up timer 23 comes to the 'H' level. Therefore, the sweeping voltage of a start voltage Vs is inputted into VOC 30 from a voltage sweep circuit 24 and the frequency of a.c. signals applied to an ultrasonic motor M is swept toward the resonance frequency accordingly. Along with this, an elastic wave amplitude of the ultrasonic motor M increases and the level of signals detected by a piezoelectric sensor 6 increases, too. The actual rotation speed of the motor increases slowly. However, when the level of the signals detected by the piezoelectric sensor 6 exceeds a reference voltage Vr at time t2, the start-up sweep circuit 24 stops sweeping, keeping a voltage Vc inputted into the VCO 30 at a value Vp and the frequency of the a.c. signals applied to the ultrasonic motor M at a value fp.

Description

DETAILED DESCRIPTION OF THE INVENTION Industrial Application Field of the Present Invention The present invention relates to an ultrasonic motor drive device.

Prior Art> In recent years, ultrasonic motors, which are small, have large torque, and do not generate magnetism, have been widely used in place of conventional DC motors.

As shown in Fig. 4, the ultrasonic motor has a rotating shaft 1 at the center.
A disk-shaped rotor 2 having a plurality of piezoelectric bodies 31 to 3n arranged in an annular shape,'! 11 to 4n, 5 and a stator 8 having an elastic body 7 adhered to the upper surface of the piezoelectric sensor 6.

The piezoelectric bodies 31 to 3n and 41 to 4n are arranged so that their polarities are alternated, and as shown in FIG. When an AC signal with a 90 degree phase at a frequency close to the resonance frequency of the body is applied from the electrodes 9a, 9b, 10a, 10b, the piezoelectric bodies 3] to 3n and 41 to 4n bend and vibrate in the circumferential direction, causing left and right vibrations. The waves interfere through the intermediate piezoelectric body 5, and as shown in FIG. 6, an elastic wave is generated on the surface of the elastic body 7 that travels along the circumferential direction.

Therefore, the rotor 2, which is in pressure contact with the elastic body 7 from above, is driven to rotate in a direction opposite to the direction in which the elastic waves travel.

Note that the rotation speed of the rotor 20 becomes faster as the amplitude of the elastic wave becomes larger, as the speed of the elastic wave becomes less dependent on the traveling speed of the elastic wave.As shown in FIG. The closer the frequency of the signal is to the resonance frequency fO of the piezoelectric bodies 31-3n141-4n, the higher it becomes.

Therefore, as in the drive control device shown in FIG. If the signal is applied as a signal to the piezoelectric bodies 31 to 3n and 41 to 4n of the ultrasonic motor M, the ultrasonic motor M can be rotated at a rotational speed corresponding to the value of the voltage Vc.

Note that the frequency of the AC signal applied to the ultrasonic motor M is generally fj"f, which is higher than the resonance frequency fO in FIG.
Two frequency ranges are used.

If the voltage VC is increased, the frequency of the alternating current signal becomes higher, and the rotational speed of the motor becomes slower. Conversely, if the voltage VC is lowered, the rotational speed becomes faster.

Problems to be Solved> However, when starting the ultrasonic motor M in an IH setting using the drive control described above, suddenly starting it with a voltage corresponding to the rotation speed of the steady frequency will shorten the life of the motor. This may interfere with the smooth movement of the mechanical system driven by the motor.

Therefore, when starting the motor, a method can be considered in which the voltage VC is changed from a high value to a low value to start the ultrasonic motor M at a slow rotational speed and gradually increase the rotational speed.

However, the ultrasonic motor M has a rotor 2 as described above.
Since the rotor 2 is in pressure contact with the stator 8, the state in which the rotor 2 is buried in the surface of the elastic body 7 is inevitable. When the motor is started from this state, the motor rotation speed is Tracking is extremely slow.

For this reason, the voltage VC is varied to the extent that the frequency of the applied alternating current signal is equal to or less than the resonant frequency f of the piezoelectric body, making it impossible to start the motor.

In this case, the complicated work and control of returning the frequency of the alternating current signal to a predetermined frequency higher than the resonant frequency fO and starting again is required.

An object of the present invention is to provide a drive control device for an ultrasonic motor that solves this problem.

<1! Means for Solving the Problem> In order to solve the above problem, the drive control @ of the ultrasonic motor of the present invention is as follows. In an ultrasonic motor drive control device that drives an ultrasonic motor with a piezoelectric sensor for detection using an alternating current signal whose frequency can be varied, the ultrasonic motor starts! At 1J, a starting sweep means sweeps the frequency of the AC signal in the direction of the resonant frequency of the piezoelectric body, a level detector detects the signal level from the piezoelectric sensor, and the signal level detected by the level detector is set to the AC signal. It is equipped with a comparator that detects when the frequency becomes larger than a predetermined value during sweeping, and a line-drawing regulating means that receives the detection signal from the comparator and visually controls the investigation of the frequency of the AC signal by the starting line-drawing means. .

Therefore, when starting the motor, the frequency of the applied AC signal is swept in the direction of the resonant frequency of the piezoelectric body, and during this sweep, if the signal level detected from the piezoelectric sensor becomes larger than a predetermined value, this Yuibiki is abbreviated.

<Example of the present invention> Hereinafter, one embodiment of the present invention will be described based on the drawings.

FIG. 1 shows the drive side w of an ultrasonic motor according to an embodiment of the present invention.
FIG. 2 is a block diagram showing the configuration of a J device (hereinafter abbreviated as a drive control device) 2o.

In FIG. 1, 21 is a speed setting circuit that sets the rotational speed of the ultrasonic motor M after starting, and outputs a voltage Va corresponding to the set speed.

22 is a startup sweep circuit, which turns “H” upon receiving a startup signal.
Start-up timer 2 that outputs a level timer signal for a predetermined time
3, and a voltage sweep circuit 24 that outputs a sweep voltage vb that decreases at a predetermined speed from a predetermined start voltage VS while receiving a timer signal via the companion control switch 25.

This start voltage Vs is preset to a voltage at which the frequency of the applied AC signal becomes a frequency fs higher than the frequency f2 shown in FIG. 7.

26 is a changeover switch that selects either the voltage Va of the speed setting circuit 21 or the sweep voltage Vb of the voltage sweep circuit 24 as the control wJ voltage VC for co3o;
While the timer signal is at "H" level, the output voltage vb is selected, and while the timer signal is at "L" level, the output voltage Va is selected.

The VCO 30 outputs to the phase shift circuit 31 a pulse signal whose frequency changes in proportion to a change in the input control IP lightning voltage a.

The phase shift circuit 31 divides the frequency of the input pulse signal by 1/4 and outputs a two-phase signal with a 90-degree phase.

32.33 is a driver that drives the primary coils 34a, 35a of the transformer 34.35 with current using a two-phase signal, and the secondary coils 34b, 35b of the transformer 34.35 drive the two-phase alternating current to a predetermined voltage. The signal is output to each piezoelectric body 31-3n, 41-4n of the ultrasonic motor M.

4o is a level detection circuit that detects the level of the signal detected by the piezoelectric sensor 6 of the ultrasonic motor M, and 41 is a level detection circuit that detects the level detected by the level detection circuit 40 at a predetermined reference voltage V.
This is a comparator that outputs an "H" level signal when the signal is larger than the current value.

The "H" level output of this comparator 41 turns off the sweep control switch 25 of the startup sweep circuit 22, and the sweep of the voltage sweep circuit 24 is stopped.

42 is a reference voltage generator that outputs a reference voltage Vr to the comparator 41, and the ultrasonic motor M is connected to a phase shifter 31 corresponding to the voltage Va output from the speed setting circuit 21.
It always outputs a reference voltage Vr that is slightly higher than the output level of the level detection circuit 40 when it is rotating steadily at an output frequency of .

Next, the operation of this drive control 1 device will be explained.

When the activation signal shown in (a) of FIG. 2 is input at time t1, the output of the activation timer 23 becomes 1 as shown in (b) of the same figure.
Time becomes “H Rubel”.

Therefore, as shown in FIG. In response to the pull, the frequency is swept from the frequency fs in the direction of the resonance frequency, as shown in (d) of the figure.

Along with this frequency sweep, the elastic wave amplitude of the ultrasonic motor M increases, and the level of the detection signal from the piezoelectric sensor 6 also increases as shown in (e) of the figure.

In response to this level increase, the actual motor rotation speed increases slowly as shown in (f) in the figure due to the pressure contact state of the rotor 2 and stator 8. When the level of the signal exceeds the reference voltage V', the sweep of the startup sweep circuit 24 is stopped, the voltage VC input to the VCO 30 is held at ■p, and the frequency of the AC signal applied to the ultrasonic motor M also increases. It is held in fp.

This state continues during the timer time of the startup timer 22, but during this time, the rotational speed of the ultrasonic motor M approaches the speed Sp corresponding to the frequency fp of the AC signal, and at 13:00 when the timer time ends, the rotational speed of the ultrasonic motor M approaches the speed Sp. Voltage from setting circuit 21■
An alternating current signal of a frequency corresponding to a (frequency much higher than fp) is applied.

Therefore, the rotational speed of the ultrasonic motor M becomes slightly slower, reaching a speed Sa corresponding to the voltage (a).

In this state of steady rotation, the speed setting circuit 2
If the first output type E is varied, the motor rotational speed will smoothly change following the variation of this voltage.

In addition, when shifting to steady rotation, the ultrasonic motor M
Since the rotation speed of the level detection circuit 40 becomes slightly slower, the level detection circuit 40
The level from the voltage will not exceed the reference voltage, and there is no risk of returning to the activated state.

Other Embodiments of the Present Invention In the above embodiments, a drive control device that can vary the motor rotation speed during steady rotation has been described. However, if the motor rotation speed during steady rotation is fixed, the standard There is no need to link the voltage "■" to the set voltage of the speed setting circuit 21.

In addition, in the above embodiment, the startup time was set by the startup timer, but as shown in FIG. The voltage Vr- may be output from the speed setting port M21', and the sweep of the voltage sweep circuit 24 may be controlled by the output of the flip-flop 45 set by the activation signal.

In this case, the speed cannot be changed during steady rotation as in the above embodiment, but if the flip-flop 45 is configured to be reset at the rise of the output of the comparator 41, the frequency of the AC signal will give the desired rotation speed. Since the frequency is swept and fixed, it is possible to cope with cases where the rotation start of the rotor is extremely slow.

Effects of the Present Invention> As described above, the ultrasonic motor drive side 'a device of the present invention sweeps the frequency of the applied alternating current signal so as to approach the resonant frequency of the piezoelectric body when starting the motor, If the level of the detection signal from the piezoelectric sensor becomes higher than a predetermined value during this sweep, this sweep is regulated, so there is no failure to start the motor due to excessive sweeping, and smooth startup is always possible. can.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention;
FIG. 2 is a timing diagram for explaining the operation of one embodiment, and FIG. 3 is a block diagram showing the configuration of another embodiment of the present invention. FIG. 4 is a perspective view showing the configuration of the ultrasonic motor, FIG. 5 is a front view of the main parts of the ultrasonic motor, FIG. 6 is a schematic diagram for explaining the operation of the ultrasonic motor, and FIG. The figure is a characteristic diagram showing changes in elastic wave amplitude with respect to the applied frequency of an ultrasonic motor, and FIG. 8 is a block diagram showing the configuration of a conventional device. M... Ultrasonic motor, 33~3n, 4r~4n
...Piezoelectric body, 6...Piezoelectric sensor, 7.
...Elastic body, 2o...Ultrasonic motor drive control device, 21...Speed setting circuit, 2
2... Start sweep circuit, 23... Start timer, 24... Voltage sweep circuit, 25...
・Sweep control switch, 26...changeover switch,
30...■C0131... Phase shift circuit,
40...Level detection circuit, 41...Comparator, 42...1 quasi-voltage generator. Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Procedural amendment (voluntary) December 3, 1990 Director General of the Patent Office Toshi Yuzu 1, Indication of the case 1990 Patent Application No. 261872 2, Title of the invention: Ultrasonic motor drive control device 3, relationship with the person making the amendment case Patent applicant address: 5-10-27 Minami-Azabu, Minato-ku, Tokyo Name (0
57) Anritsu Corporation Representative: Shinto Sugai 4, Agent: 141 Telephone: 490-4516 Address: 1-17-5 Osaki, Parts Ward, Tokyo 6. Contents of amendment

Claims (1)

[Scope of Claims] An ultrasonic motor that is rotationally driven by an elastic wave generated by an alternating current signal applied to a piezoelectric body and has a piezoelectric sensor that detects the elastic wave vibration is driven by an alternating current signal whose frequency can be varied. In the drive control device for a sonic motor, the ultrasonic motor includes: a starting sweep means for sweeping the frequency of the alternating current signal in the direction of the resonance frequency of the piezoelectric body when starting the ultrasonic motor; and a level detector for detecting the signal level from the piezoelectric sensor. and a comparator for detecting that the signal level detected by the level detector becomes larger than a predetermined value during the sweep of the alternating current signal; A drive control device for an ultrasonic motor, comprising: a sweep regulating means for regulating the frequency sweep of the alternating current signal.