JPH03243183A - Ultrasonic motor device - Google Patents

Abstract

PURPOSE:To follow the output frequency of a VCO by a method wherein the rotation and stop of an ultrasonic motor is detected by a rotation and/or stopping detecting means while a reference voltage for rectifying a current for monitoring of the motor is controlled variably. CONSTITUTION:The current of the piezo-electric element of an ultrasonic motor 1 is monitored by a current monitoring means 2 and the wave form of the current is rectified and amplified to effect the feed-back of it. In this case, the rotation and/or stopping of the motor 1 is detected by a rotation and/or stopping detecting means 6. A reference voltage for the above-described rectification and amplification is controlled variably by the output signal through a reference voltage control means 7. According to this method, a reference voltage for rectifying and amplifying the wave form of the current of the motor 1 can be controlled automatically so as to be optimum even when the motor 1 is stopped by the change of a resonance frequency due to the change of the heat generation of the motor 1, an ambient temperature, the abutting force of a moving body, the magnitude of an impressing signal and the like. Accordingly, the output frequency of a VCO can be followed and the motor 1 can be driven again.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a drive circuit for an ultrasonic motor using a piezoelectric element.

[Summary of the invention]

The present invention monitors the current flowing through the piezoelectric element of the ultrasonic motor, rectifies and amplifies the current waveform, feeds it back as a control voltage of the voltage controlled oscillation means, and uses the output signal of the voltage controlled oscillation means to control the ultrasonic motor. In an ultrasonic motor circuit that generates a drive signal, a rotation stop detection means for detecting rotation stop of the ultrasonic motor from a signal obtained by rectifying and amplifying the current waveform is provided, and the rotation stop detection means detects rotation stop of the ultrasonic motor from a signal obtained by rectifying and amplifying the current waveform, and detecting the rectification and amplification from the output signal of the rotation stop detection means. This is to variably control the reference voltage for rectification.

[Conventional technology]

An ultrasonic motor applies a frequency voltage to a piezoelectric element to excite a traveling wave or a standing wave on an elastic pair surface, thereby driving a moving body that is pressed into contact with the piezoelectric element. The frequency of the applied signal must be at or close to the resonant frequency (fr) of the ultrasonic motor.

Conventionally, fr was measured in advance and a drive signal was applied to the ultrasonic motor using a reference oscillator or the like.

Further, as a device for stably driving an ultrasonic motor, the present applicant has proposed an ultrasonic motor device in Japanese Patent Application No. 63-271387.

[Problem to be solved by the invention]

It is not practical to measure fr in advance and obtain a drive signal using a reference oscillator or the like. This is because configuring an oscillator suitable for fr would be difficult to mass-produce due to variations in the constants of the electric elements, and furthermore, if the drive frequency was fixed with a reference oscillator, the ultrasonic motor would generate heat due to energy loss and the environment This is because if there is a change in f' or current consumption due to changes in temperature, pressure contact force of the moving body, magnitude of applied signal, etc., the operation will stop.

The ultrasonic motor device disclosed in Japanese Patent Application No. 63-271387 takes advantage of the fact that the current flowing through the piezoelectric element reaches its maximum at fr, and uses a resistor to convert the current into a voltage signal and rectifies the converted current waveform. Amplify and use voltage controlled oscillation means (VCO)
The ultrasonic motor is driven by inputting feedback as a control voltage to the VCO and setting the base voltage for rectification and amplification so that the output frequency of the VCO is near fr. In addition, this method is based on changes in the environmental temperature, the magnitude of the applied signal, etc.
The output frequency of the VCO can follow changes in the current and current, and is suitable for, for example, driving a stationary ultrasonic motor with little load fluctuation. However, the output frequency of the VCO cannot follow changes in fr or current due to changes in the pressure contact force of a moving object (for example, shock caused by an unexpected drop when applied to a wristwatch, etc.), and in some cases, the output frequency of the VCO
There is also a possibility that the output frequency of O becomes stable when it deviates from fr, and the ultrasonic motor stops forever. Furthermore, changes in the current of rr due to changes in the environmental temperature, the magnitude of the applied signal, etc. differ for each motor, so V
It became necessary to adjust the tracking characteristics of CO.

[Means to solve the problem]

In order to solve the above problems, the present invention includes a rotation stop detection means for detecting rotation stop of the ultrasonic motor, and a reference voltage for controlling the reference voltage for rectifying and amplifying the current waveform of the ultrasonic motor. A control means is provided to detect stoppage of the ultrasonic motor and automatically adjust the reference voltage to an optimum value.

[Effect]

According to the above configuration, the ultrasonic motor stops due to changes in fr or current due to changes in the heat generated by the ultrasonic motor itself, the environmental temperature, the pressure contact force of the moving object, the magnitude of the applied signal, etc. Even if the current waveform of the ultrasonic motor is rectified and amplified, the reference voltage is automatically controlled to the optimum value, and the VCO
The output frequency is tracked, and the ultrasonic motor can be driven again.

〔Example〕

Embodiments of the present invention will be described below based on the drawings. There are various types of ultrasonic motors using piezoelectric elements, such as a standing wave method and a traveling wave method (for example, "Key Points of New Method/New Principle Motor Development and Practical Application" published by Japan Industrial Technology Center in 1982). ), the ultrasonic motor of the present invention may be any one of the following.

FIG. 1 shows a typical embodiment of the present invention in a functional block diagram.

The principle by which the drive circuit of the present invention stably drives an ultrasonic motor will be explained using the ultrasonic motor 1, current monitor means 2, rectifier amplification means 3, VCO 4, drive means 5, and reference voltage generation means 8 shown in FIG. do. The slope of the output frequency with respect to the control voltage of the VCO 4 may be either positive or negative, but in the description, it is assumed that the VCO has a negative slope. FIG. 3 shows an example of a VCO circuit, and FIG. 4 shows the output characteristics of the VCO. The output characteristics of the VCO are 1
When approximated by the following equation, it can be expressed by equation (1).

f= a−νin+ b −−−−−−−−−1−(1
) formula r = frequency of the signal to be applied to the ultrasonic motor 1 by dividing the output signal of vc○4 Vin = control Ilt pressure of VCO a = slope coefficient b - offset frequency. The control wit pressure at which f=fr is assumed to be Vr.

The current i of the ultrasonic motor l is determined by the resistance Rm of the current detection means 2.
is converted into a voltage signal by a compensating capacitor C
1 and is input to the amplification means 3.

The rectifying and amplifying means 3 rectifies and amplifies the IT current waveform based on the reference voltage Vref, and the rectified and amplified signal Vin is outputted to the VCO.
4 as a control voltage. Vin at this time can be calculated using the following equation (2).

Vin=Sref-An-i-Rm------
(2) where An is the amplification degree of the amplification means. When the rectified and amplified AC signal Vin is input to the VCO4,
The output frequency changes in accordance with Vin within one period of Vin, but by dividing the frequency by 1/4, the frequency after division becomes constant. This situation is shown in FIG. Further, even if a signal Vm obtained by smoothing Vtn is manually applied instead of the AC signal Vtn, the frequency f after frequency division does not change. onwards,
The control voltage of the VCO will be explained using Vm. Vm can be calculated using the following equation (3).

Vm=Vref−An−i−Rm/π−−−−−−(
3) Substitute equation (3) into equation (1).

f=a(Vref-An-i-Rs/π)+b-(4
) Here, when the switch S of the reference voltage generation means 8 changes from the ON state to the OFF state, the reference voltage Vref of the rectification and amplification increases to Vl with a time constant of R3·C2. The relationship between the applied frequency f of the ultrasonic motor 1 and the current i is shown in FIG.

The moment the switch S turns OFF, the reference voltage Vref
is OV, and since f is sufficiently higher than fr, the current i is very small, and Vm in equation (4) can be expressed as V m # Vref. In other words, immediately after switch S is turned on, V
Vm approaches Vr as ref changes. As f also approaches fr, the current i increases as shown in FIG. As the current i increases, from equation (4), V
m becomes smaller than Vref by An-i - Rm/π. Here, the maximum current of the ultrasonic motor is i yla
x, the maximum value of the feedback term due to current is An-im
a becomes ・Rm/π.

Here, Vl is set so as to satisfy the condition of equation (5).

Vr<Vl≦Vr+An-1Ilax-Rm/π-
(5) If Vl is set as shown in equation (5), Vref
When Vm reaches the final voltage V1, Vm becomes stable at a voltage lower than Vr. Therefore, the frequency f applied to the ultrasonic motor 1 is stabilized at a frequency higher than the resonance frequency fr, and the ultrasonic motor can be driven. Figure 7 shows the V after the switch S changes from the ON state to the OFF state.
The changes in ref and Vm are shown.

On the contrary, it is the basis of rectification and amplification! ! When the lightning voltage ref (='V1) becomes the relationship shown in equation (6), the final The stable frequency of the drive frequency f becomes a frequency lower than fr, and the ultrasonic motor stops.

Vl>Vr+An-imax-Rm/π-1--(6)
As explained above, if Vl, which is the reference voltage for rectifying and amplifying the current waveform, is set to an appropriate value, the output frequency of the VCO can be stabilized at a frequency higher than fr, and the ultrasonic motor can be driven. can do.

Next, the main operation of the present invention will be explained using FIG. 2.

Simply put, the operation of the present invention is to sweep the drive frequency from higher to lower than fr, and when the rotation of the ultrasonic motor stops, the reference voltage for rectification and amplification is varied and the sweep drive is performed again. Thus, the reference voltage for rectification and amplification is varied until the condition of equation (5) is satisfied.

Details are given below.

The rotation detecting means 6 is a circuit that detects the stopped state of the ultrasonic motor, and the smoothing means 61 receives the current waveform signal Vin rectified and amplified by the rectifying and amplifying means 3 using a voltage follower, and smooths it using a resistor R4 and a capacitor C3. It is. Differentiating means 62 differentiates the smoothed signal Vm. Then, when there is a steep change in Vm, a pulse signal is output. As shown in FIG. 7, since the change in Vm is steep when the ultrasonic motor comes to a stop, it is possible to detect the stoppage of the ultrasonic motor from the output signal of the differentiating means 62. FIG. 8 shows the change in Vm and the output signal of the rotation stop detection means 6 when the ultrasonic motor stops rotating. Let A be the output signal of the rotation stop detection means 6 at this time.

Upon receiving the rotation stop detection signal A, the reference signal V1 for rectification and amplification is
The reference voltage is what generates the data F for varying the !
11?11 Means 7. FIG. 13 shows a circuit example of the up/down counter control means 71 in the reference voltage control means 7, and FIG. 14 shows a timing diagram showing the operation of the circuit of FIG. 13. FIG. 12 shows an example of a circuit of a DA converter that receives data F generated by the reference voltage control means 7 and generates a reference voltage 1 that matches the data F.

In FIGS. 13 and 14, signal C is a motor drive enable signal, which cancels the recency of each FF and initializes the up/down counter 712. up/down counter 7
12, all data becomes 1, and the output signal V1 of the reference voltage generating means 8 becomes the maximum value. Figure 14, 1st
This is the operating area.

Also, when the signal C changes from 1 to 0, the reference voltage Vref for rectification and amplification gradually changes from OV to Vl, but since Vl is now set to the maximum, the condition of equation (6) is satisfied. If not satisfied, Vref+An-i-Rm
When /π becomes higher than Vr, an ultrasonic motor rotation stop detection signal A is output. Upon receiving the rotation stop detection signal A of the ultrasonic motor, a subtraction signal E is input to the up/down counter 712, data F is deleted by l, and data 1 is also reduced in accordance with data F. Also, switch S
Control signal B is also generated, and switch/7ch S is temporarily turned on.
state, and the charge in the capacitor C2 is discharged. Therefore, Vref is when the switch S is in the OFF state.
It will gradually change from Ov to vl again. Furthermore, when the motor rotation stop detection signal A is output again, the above operation is repeated until the condition of equation (5) is satisfied. The operation region (2) in FIG. 14 shows the above operation.

Furthermore, if the rotation of the ultrasonic motor does not stop for a predetermined period of time, the addition/subtraction wI of the up/down counter 712
The control signal becomes 1, the data F of the up/down counter 712 is added by 1, and Vl becomes higher by that amount. At this time, the switch S is not in the ON state. This operation is shown in the operation region (2) in FIG.

FIG. 15 is a circuit diagram showing an example of the reference signal generating means 711. For example, if there is no rotation stoppage for 128 seconds corresponding to a half cycle of 1/256 Hz, the above-mentioned operation (2) is performed. .

The data F of the up/down counter 712 is added to V
When l becomes high and the condition of equation (5) is no longer satisfied and the motor rotation stop detection signal A is output, the addition/subtraction signal is changed to Ol, that is, the up/down counter 71.
2 is used as a subtraction counter, and the operation is repeated from step (2). The 2nd operating area repeats the 2nd operating area.

In other words, according to the present invention, as long as the output frequency range of the ultrasonic motor is set to include the range of changes in fr due to changes in temperature, drive voltage, load changes, etc., when the ultrasonic motor starts driving, The circuit constant (reference voltage of the rectifier amplification means) is adjusted so that the ultrasonic motor is automatically driven.

〔Effect of the invention〕

According to the present invention, when driving an ultrasonic motor, even if the drive circuit becomes unable to drive the ultrasonic motor due to changes in temperature or drive voltage, or even load changes, In order to automatically adjust the drive constant of the drive circuit to the optimum one in accordance with fluctuations, etc., the drive circuit is driven again.

[Brief explanation of drawings]

FIG. 1 is a functional block diagram showing a typical embodiment of the invention, FIG. 2 is a circuit diagram showing a specific example of the invention, and FIG. 3 is a circuit diagram showing an example of a VCO used in the invention. , Fig. 4 is a diagram showing the output characteristics of the VCO in Fig. 3, Fig. 5 is a diagram showing the current waveform Vt of the ultrasonic motor, the rectified waveform Vin, the output signal of the VCO, and the signal after frequency division. is a diagram showing the relationship between the drive frequency and current consumption of the ultrasonic motor, Figure 7 is a diagram showing the change in Vref, drive frequency, and consumption after turning off the switch S in Figure 2, and Figure 8 is a diagram showing the relationship between the drive frequency and current consumption of the ultrasonic motor. FIG. 9 is a circuit diagram showing another embodiment of the rotation stop detection means 6, and FIG. FIG. 11 is a circuit diagram showing an example of frequency dividing means in the drive means 5, and FIG. 12 is a diagram showing the rotation stop detection signal A of the rotation stop detection means of the rotation stop detection means. ), and FIG. 13 shows an example of the up/down counter control means 71 in the reference voltage control means 7. The circuit diagram, FIG. 14 is a timing diagram showing the operation of the 77 pull-down force counter @ control means of FIG. 13, and FIG. 15 is an example of the reference signal generation means 1301 in the up-down counter control means 71 of FIG. FIG. 1... Ultrasonic motor Rm... Current monitor resistor CI... Camping capacitors Di, D2... Rectifying diodes Ll, L2... Boosting coils Tl, T2... More than switching transistors

Claims (5)

[Claims] (1) By applying a frequency voltage to the piezoelectric element of a vibrating body in which a piezoelectric element is attached to an elastic body, a traveling wave or a standing wave is excited on the surface of the elastic body, and the traveling wave or standing wave causes the elastic In an ultrasonic motor that drives a moving body that is pressed against a body, the current detecting means detects the current consumption of the piezoelectric element, the amplifying means amplifies the output signal of the current detecting means, and the output signal of the amplifying means Voltage controlled oscillation means whose output frequency changes, driving means which generates a signal to be applied to the piezoelectric element from the output signal of the voltage controlled oscillation means, and reference voltage generation means which generates a reference signal for amplification of the amplification means. an ultrasonic motor comprising: a rotation stop detection means for detecting rotation stop of the ultrasonic motor; and a reference voltage control means for receiving an output signal of the rotation detection means and controlling the reference voltage generation means. Device. (2) The ultrasonic motor device according to claim 1, wherein the amplification means is a rectification amplification means that amplifies the signal to one side with respect to the reference signal of the reference voltage generation means. (3) The rotation stop detection means includes a smoothing means for smoothing the output signal of the amplification means, and the output signal of the smoothing means is differentiated by the reference voltage generating means. 2. The ultrasonic motor device according to claim 1, further comprising comparison means for comparing the reference signal with a second reference voltage obtained by dividing the reference signal. (4) The reference voltage control means includes a multi-bit up/down counter and an up/down counter control means that receives the output signal of the rotation stop detection means and generates a control signal for addition/subtraction of the up/down counter and a count signal. The ultrasonic motor device according to claim 1, characterized in that the ultrasonic motor device comprises: (5) The reference voltage generating means is configured to control the output voltage by the count data of the up/down counter.
an A converter, and a resistance element provided in series between the output end of the DA converter and one end of the rectifying and amplifying means;
2. The ultrasonic motor device according to claim 1, wherein a capacitive element and a switching element are provided in parallel between an end point of the resistive element on the rectifying and amplifying means side and ground.