JPH0755067B2 - Ultrasonic motor device - Google Patents

Description

TECHNICAL FIELD The present invention relates to a drive circuit for an ultrasonic motor using a piezoelectric element. In particular, it relates to a circuit for intermittently driving an ultrasonic motor.

[Outline of Invention]

The present invention monitors a current flowing through a piezoelectric element of an ultrasonic motor, rectifies and amplifies the current waveform, feeds it back to a voltage controlled oscillator as a control voltage, and outputs the ultrasonic motor from an output signal of the voltage controlled oscillator. In the ultrasonic motor drive circuit for generating the drive signal of, the rotation stop detection means for detecting the rotation stop of the ultrasonic motor is provided, and the output of the rotation stop detection means is output from the output signal of the rotation stop detection means and the intermittent drive signal. The reference voltage for the rectification and amplification is variably controlled so that a signal is generated near the end of the intermittent drive, and an almost maximum rotation speed of the ultrasonic motor is obtained near the end of the intermittent drive.

[Conventional technology]

The ultrasonic motor applies a frequency voltage to a piezoelectric element to excite a traveling wave or a standing wave on the surface of an elastic body to drive a moving body that is in pressure contact. The frequency of the applied signal must be the resonance frequency of the ultrasonic motor (hereinafter referred to as fr) or a frequency close to this. Conventionally, fr is measured in advance,
The 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, Japanese Patent Application No. 63-271387 and an ultrasonic motor device have been proposed by the present applicant.

[Problems 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 the oscillator that fits in fr is not suitable for mass production because the constants of electric elements vary, and if the drive frequency is fixed by the reference oscillator, heat generation and environmental temperature due to energy loss of the ultrasonic motor itself will occur. This is because the maximum rotation speed of the ultrasonic motor cannot be obtained during intermittent driving when there is a change in fr or current consumption due to changes in the pressure contact force of the moving body or the magnitude of the applied signal.

The ultrasonic motor device of Japanese Patent Application No. 63-271387 utilizes the fact that the current flowing through the piezoelectric element is maximized at fr, and rectifies and amplifies the resistance for converting the current into a voltage signal and the converted current waveform. Then, it is fed back to the voltage controlled oscillator (hereinafter referred to as VCO) as a control voltage, and the ultrasonic motor is driven by setting the reference voltage for rectification amplification so that the output frequency of the VCO is near fr. is there. In addition, this method
The output frequency of the VCO can follow changes in fr and changes in current due to changes in the magnitude of the applied signal, and is suitable for driving stationary ultrasonic motors, for example, where load fluctuations are small. However, the output frequency of the VCO cannot follow the change in fr or the change in current due to the change in the pressure contact force of the moving body (for example, the shock caused by an unexpected drop when applied to a wristwatch etc.), and in some cases the VCO When the output frequency deviates from fr, the output frequency becomes stable and the ultrasonic motor may remain stopped. Furthermore, since the changing characteristics of the fr current due to changes in the environmental temperature and the magnitude of the applied signal are different for each ultrasonic motor, it is necessary to individually combine the VCO tracking characteristics. .
When the ultrasonic motor is driven intermittently by this method, and when the maximum number of rotations of the ultrasonic motor is to be obtained near the end of intermittent driving of the intermittent driving time, the driving state of the ultrasonic motor changes due to the above problems. In that case, the maximum rotation speed of the ultrasonic motor may not be obtained.

[Means for Solving the Problems]

In order to solve the above problems, in the present invention, a rotation stop detection means for detecting rotation stop of an ultrasonic motor, a rectification amplification means for a current waveform of the ultrasonic motor, and a reference voltage of the rectification amplification means. A reference voltage control means for controlling the ultrasonic motor is detected, and the reference voltage is automatically adjusted to an optimum one so that the ultrasonic motor rotation is stopped at the end of the intermittent driving. It was done like this.

[Action]

According to the above-mentioned configuration, the ultrasonic motor is stopped due to the heat generation due to the energy loss of the ultrasonic motor itself, the environmental temperature, the pressure contact force of the moving body, the change of fr due to the change of the magnitude of the applied signal and the change of the current. Even if occurs, the reference voltage for rectifying and amplifying the current waveform of the ultrasonic motor is automatically controlled to the optimum voltage, and the rotation of the ultrasonic motor stops near the end of intermittent driving. With this, almost the maximum rotation of the ultrasonic motor can be obtained.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings. There are various possible ultrasonic wave motors that use piezoelectric elements, such as the standing wave method and the traveling wave method (for example, “Points of new system / principle motor development / practical application” published by Japan Industrial Technology Center in 1984). ), Any of the ultrasonic motors of the present invention may be used.

FIG. 1 is a typical embodiment of the present invention and is shown in a functional block diagram. FIG. 2 is an embodiment of the functional block diagram of FIG.

Before explaining the operation, FIG. 6 shows the relationship between the applied frequency f of the ultrasonic motor 1 and the current i. As shown in the figure, the ultrasonic motor has the maximum current i at the resonance frequency fr and the maximum rotation speed. Also, the ultrasonic motor is not driven unless the driving frequency is higher than fr.

The slope of the output frequency with respect to the control voltage of VCO4 may be either positive or negative, but in the description, it is assumed that the VCO has a negative slope. Third
The VCO circuit example is shown in the figure, and the VCO output characteristic is shown in FIG. VC
If the output characteristic of O is approximated by a linear equation, it can be expressed by equation (1).

f = a · Vin + b Equation (1) where, f is the frequency of the signal applied to the ultrasonic motor 1 by dividing the output signal of VCO4 by 1/4 Vin = VCO frequency control voltage a = Slope coefficient b = Offset frequency. Here, the control voltage for f = fr is Vr. Second
In the figure, the current i of the ultrasonic motor 1 is the resistance of the current detecting means 2.
Converted to voltage signal by Rm, coupling capacitor
It is input to the amplification means 3 through C1. The rectifying / amplifying means 3 rectifies and amplifies the current waveform with the reference voltage V1 as a boundary. The rectified and amplified signal Vin is input to VCO4 as a control voltage. Vin at this time can be expressed by the following equation (2).

Vin = V1−An · i · Rm (2) Here, An is the amplification degree of the amplification means. When the rectified and amplified AC signal Vin is input to VCO4, the output frequency fout changes according to Vin within one cycle of Vin, but by dividing by 1/4, the frequency f after division is constant. Becomes This is shown in FIG. FIG. 12 shows an example of the frequency dividing means for dividing the output frequency four by 1 in the driving means 5.
Further, even if the signal Vm obtained by smoothing Vin is input instead of the AC signal Vin, the frequency f hardly changes. Hereinafter, the VCO control voltage will be described as Vm. Vm can be expressed by the following equation (3).

Vm = V1−An · i · Rm / π (3) Expression (3) is substituted into Expression (1).

f = a (V1−An · i · Rm / π) + b Equation (4) where the An · i · Rm / π term is a feedback term due to the current of the ultrasonic motor.

Next, the case where the data of the up / down counter 72 is added from 0 will be postponed.

As the data of the up / down counter 72 increases, the output voltage V1 of the reference voltage generating means 8 increases.

When the data of the up / down counter 72 is 0, V1 is 0V, so f is sufficiently higher than fr and the current i is very small. Therefore, the change of f almost follows the change of V1. (This is shown in Fig. 7 Area. ) As V1 changes, Vm approaches Vr and f also approaches fr. Accordingly, the current i increases as shown in FIG. When the current i increases, Vm is larger than V1 from Equation (4).
・ Since i · Rm / π becomes smaller, the control voltage Vm of VCO becomes lower than Vr even if V1 becomes higher than Vr. (This is shown in Fig. 7 Area. Here, if the up-down counter 72 is further added to increase V1, f becomes closer to fr, the current i also increases, and the feedback amount by the current i becomes maximum when f = fr. At this time, the expression (5) is established.

Vr = Vm = V1−An · imax · Rm / π (5) where imax is the maximum current of the ultrasonic motor. Also,
At this time, the number of rotations of the ultrasonic motor becomes almost maximum.

Further, as V1 is increased, Vm becomes higher than Vr even with the maximum feedback amount due to the current of the ultrasonic motor, and the drive frequency f becomes lower than fr. In such a state, the ultrasonic motor stops rotating. (This is shown in Fig. 7 Area. That is, when the reference voltage V1 for rectification and amplification has a relationship as shown in equation (6), the ultrasonic motor stops.

V1> Vr ＋ An ・ imax ・ Rm / π ・ ・ ・ Equation (6) When you want to obtain the maximum rotation of the ultrasonic motor near the end of each driving during intermittent driving, the control voltage at the end of driving is Change V1 so that

In the present invention, the control voltage of the VCO is fed back with the current of the ultrasonic motor. As shown in FIG. 8, when V1 is directly changed to VCO as a control voltage at a constant speed without performing current feedback of the ultrasonic motor, the driving frequency f changes according to V1. The time required to pass through the drive range of the motor is shortened, and the number of rotations of the ultrasonic motor does not become so high due to the influence of the moment of inertia of the rotor. When current feedback is applied as in the present invention,
Even if V1 is changed at a constant speed as shown in Fig. 9,
The control voltage Vm actually applied to the VCO has a slower rate of change due to an increase in current. Therefore, the change in the drive frequency f also becomes gentle and the drive time of the ultrasonic motor becomes long,
The rotation speed of the ultrasonic motor can rise to almost the maximum rotation speed. Next, the main operation of the present invention will be described with reference to FIG.
Briefly, the operation of the present invention sweeps the drive frequency from higher to lower than fr, stores the data of the up / down counter 72 when the rotation of the ultrasonic motor is stopped, and pauses the intermittent drive. The count data is subtracted by a predetermined number of times, and the counter is counted up so as to reach the above-mentioned stopped storage data in the intermittent drive time. In addition, the counter is decremented by 1 when the rotation is stopped within the driving time, and the counter is incremented by 1 when the rotation is not stopped within the driving time. This is designed to obtain almost the maximum number of rotations of the sonic motor. Details are given below.

In FIG. 2, the rotation detecting means 6 is a circuit for detecting the stopped state of the ultrasonic motor, and receives the voltage waveform signal Vin rectified and amplified by the rectifying / amplifying means 3 by the voltage follower and smoothes it by the resistor R4 and the capacitor C3. Is the smoothing means 61. Differentiating means 62 differentiates the smoothed signal Vm. Then, when there is a sharp change in Vm, a pulse signal is output. 7th
As shown in the figure, when the ultrasonic motor stops,
Since the change of Vm is abrupt, the stop of the ultrasonic motor can be detected from the output signal of the differentiating means 62. FIG. 7 shows the change in Vm and the output signal of the rotation stop detecting means 6 when the ultrasonic motor stops rotating. The output signal of the rotation stop detecting means 6 at this time is A.

The reference voltage control means 7 receives the rotation stop detection signal A and generates data F for varying the reference signal V1 for rectification and amplification.

FIG. 10 is a circuit diagram showing another embodiment of the rotation stop detecting means 6, and FIG. 11 shows conditions such as the output timing of the rotation stop detecting signal A in the rotation stop detecting means 6 of FIG. It is a figure.

FIG. 14 shows a circuit example of the up / down counter control means 71 in the reference voltage control means 7, and FIG. 15 is a timing chart showing the operation of the circuit of FIG. FIG. 13 shows a circuit example of a DA converter which receives the counter data generated by the reference voltage control means 7 and generates the reference voltage V1 according to the counter data.

In FIGS. 14 and 15, the Reset signal is a drive enable signal for the motor, and intermittent drive is started when the drive signal changes from 1 to 0. It also resets the up / down counter 72 and each FF. The operation of the circuit will be described below in order.

(A). For the first drive signal, the up / down counter 72
Is counted up until the rotation stop signal A of the ultrasonic motor is output.

(B). When the rotation stop signal A is output, drive is stopped,
Only 1 is subtracted from the up / down counter 72, and the data is stored (latched) in the storage means 73. The storage timing is latched by the Latch signal.

(C). After latching Up-down counter 72 to a predetermined number N
Just reduce. In the example, it is -16.

(D). After that, if the drive signal is turned ON, it will be N within the ON time.
Count up at a frequency that counts up only (N = 16 in the example). In the example, drive ON time is 1 second, N = 16
So it is counting up at 16Hz.

(E). When the stop signal A is not output within the driving time, when the count data of the up / down counter 72 matches the data stored in the storage unit 73, the comparison unit
The 74 outputs a coincidence signal and stops driving. When the driving is stopped, the counter 72 is incremented by 1 and stored (latched) in the storage means 73.

(F). Same as (c).

(G). Same as (d).

(H). When the stop signal A is output within the drive time, the counter 72 is decremented by 1 when the drive is stopped and stored (latched) in the storage means 73.

(I), (j), (k). After that, it is repeated from (c).

FIG. 16 is a circuit diagram showing an example of the storage means 73, and FIG. 17 is a circuit diagram showing an example of the comparison means 74.

〔The invention's effect〕

According to the present invention, the maximum rotation speed of the ultrasonic motor can be obtained near the end of intermittent driving. In addition, even if there is a change in fr or current due to temperature, drive voltage fluctuations, load fluctuations, etc., the ultrasonic motor is automatically driven so that the maximum rotation speed of the ultrasonic motor is obtained near the end of intermittent driving. Thus, the circuit constant (reference voltage of the rectifying / amplifying means) is adjusted.

[Brief description of drawings]

FIG. 1 is a functional block diagram showing a typical embodiment of the present invention, FIG. 2 is a circuit diagram showing a concrete example of the present invention, and FIG. 3 is a circuit diagram showing an example of a VCO used in the present invention. 4, FIG. 4 is a diagram showing the output characteristics of the VCO of FIG. 3, FIG. 5 is a diagram showing the current waveform Vi of the ultrasonic motor, the rectified waveform Vin, the output signal of the VCO, and the signal after frequency division, FIG. Is a diagram showing the relationship between the driving frequency of the ultrasonic motor, the current consumption, and the number of revolutions, and FIG. 7 is the change of V1 and Vm, the driving frequency f, and the current consumption i when the up-down counter 72 is added from 0, FIG. 8 shows the generation of the rotation stop detection signal A when the ultrasonic motor is stopped.
The figure which shows the rotation characteristic when not applying the ultrasonic motor current feedback to the control voltage of the VCO, and FIG. 9 is the figure which shows the rotation characteristic when applying the ultrasonic motor current feedback to the control voltage of the VCO.
FIG. 11 is a circuit diagram showing another embodiment of the rotation stop detecting means, 11th
10 is a diagram showing the rotation stop detection signal A of the rotation stop detecting means of FIG. 10, FIG. 12 is a circuit diagram showing an example of the frequency dividing means in the driving means 5, and FIG. 13 is a counter of the up / down counter 72. FIG. 14 is a circuit diagram showing an example of reference voltage generation means (DA converter) for receiving the data and generating the reference voltage V1, and FIG. 14 is an up / down counter control means 71 in the reference voltage control means 7.
FIG. 15 is a circuit diagram showing an example, FIG. 15 is a timing diagram showing the operation of the up / down counter control means 71 and the change of the reference voltage V1 in FIG. 14, and FIG. 16 is a storage means in the reference voltage control means 7.
FIG. 17 is a circuit diagram showing an example of 73, and FIG. 17 is a circuit diagram showing an example of a comparison unit 74 in the reference voltage control unit 7. 1 ... Ultrasonic motor Rm ... Current monitor resistance C1 ... Coupling capacitors D1, D2 ... Rectifying diode L1, L2 ... Boost coil T1, T2 ... Switching transistor

Claims (6)

[Claims] 1. A traveling wave or a standing wave is excited on the surface of the elastic body by applying a frequency voltage to a piezoelectric element of a vibrating body in which the piezoelectric element is attached to the elastic body, and the traveling wave or the standing wave is excited. In an ultrasonic motor for driving a moving body that is pressed against the elastic body by waves, current detecting means for detecting current consumption of the piezoelectric element, amplifying means for amplifying an output signal of the current detecting means, and the amplifying means Voltage-controlled oscillation means whose output frequency changes in accordance with the output signal, drive means for intermittently generating a drive signal to be applied to the piezoelectric element from the output signal of the voltage-controlled oscillation means, and a reference for amplification by the amplification means. A reference voltage generating means for generating a signal, a rotation stop detecting means for detecting a rotation stop of the intermittent drive of the ultrasonic motor by the drive signal, and an output signal of the rotation stop detecting means, Ultrasonic motor apparatus characterized by having a reference voltage control means for controlling the reference voltage generating means. 2. The ultrasonic motor device according to claim 1, wherein the amplifying means is a rectifying / amplifying means for amplifying a signal on one side of a reference signal of the reference voltage generating means. 3. The rotation stop detecting means has a smoothing means for smoothing an output signal of the amplifying means, and a differentiating means for differentiating an output signal of the smoothing means or an output signal of the smoothing means for the reference voltage. The ultrasonic motor device according to claim 1, further comprising one of comparison means for comparing the reference signal of the generation means with a second reference voltage obtained by dividing the reference signal. 4. The reference voltage control means stores an up / down counter of a multi-bit increment, a storage means for storing output data of the up / down counter, an output data of the up / down counter and storage data of the storage means. The ultrasonic motor device according to claim 1, further comprising a comparing unit that outputs a coincidence signal when they are compared with each other and an up-down counter control unit that controls the up-down counter and the storage unit. 5. The up / down counter control means includes reference signal generation means such as a crystal oscillator, addition / subtraction control means for controlling addition / subtraction of the up / down counter, and count signal generation for generating a count signal of the up / down counter. 5. The ultrasonic motor device according to claim 4, comprising: means and an intermittent drive signal generation means for generating a drive signal for intermittently driving the ultrasonic motor. 6. The ultrasonic motor device according to claim 4, wherein said reference voltage generating means has a DA converter whose output voltage is controlled by the count data of said up / down counter.