JPH0755068B2 - 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 continuously 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, and feeds it back to a voltage controlled oscillating means (hereinafter referred to as VCO) as a control voltage.
In an ultrasonic motor drive circuit that generates a drive signal for the ultrasonic motor from an output signal of CO, a rotational speed detection unit and a rotational speed setting unit that detect the rotational speed of the ultrasonic motor are provided, and the rotational speed detection unit The reference voltage for rectifying and amplifying the rectifying and amplifying means is variably controlled so that the output signal is within the setting range of the rotating speed setting means, and the rotation speed of the ultrasonic motor is controlled.

[Conventional technology]

The ultrasonic motor drives a rotor that is in pressure contact with a piezoelectric element by applying a frequency voltage to excite a traveling wave or a standing wave on the surface of the elastic body. 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 impossible to control the rotation speed of the ultrasonic motor by a method of measuring fr in advance and obtaining a drive signal using a reference oscillator or the like. Furthermore, if the drive frequency is fixed by the reference oscillator, if there is a change in fr or current consumption due to heat generation due to energy loss of the ultrasonic motor itself, environmental temperature, pressure contact force of moving body, change in applied signal magnitude, etc. The rotation speed of the sonic motor changes greatly.

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 converted current waveform and the resistance for converting the current into a voltage signal. Is fed back to the VCO as a control voltage, and the ultrasonic motor is driven by setting a reference voltage for rectification amplification so that the output frequency of the VCO is near fr. This method allows the output frequency of the VCO to follow changes in fr and changes in current due to changes in environmental temperature and the magnitude of the applied signal, but it cannot control the rotation speed of the ultrasonic motor.

[Means for Solving the Problems]

In order to solve the above problems, in the present invention, a rotation speed detection means for detecting the rotation speed of an ultrasonic motor, a rotation speed setting means, a rectification amplification means for a current waveform of the ultrasonic motor, and the rectification amplification. Reference voltage control means for controlling the reference voltage of the means is provided to compare the output of the rotation speed detection means with the set amount of the rotation speed setting means, and the output value of the rotation speed detection means is the rotation speed. The reference voltage is automatically adjusted to an optimum value so that it falls within the setting range of the setting means.

[Action]

According to the above configuration, the rotation speed of the ultrasonic motor changes due to changes in fr and current due to changes in heat generation due to energy loss of the ultrasonic motor itself, environmental temperature, pressure contact force of moving body, magnitude of applied signal, etc. Even if it changes, the reference voltage for rectifying and amplifying the current waveform of the ultrasonic motor is automatically controlled to the optimum value, and the rotation speed of the ultrasonic motor is set to a predetermined speed.

〔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 circuit diagram showing a typical embodiment of the present invention.

Before explaining the operation, FIG. 5 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.

In FIG. 1, the slope of the output frequency with respect to the control voltage of VCO4 may be positive or negative, but in the description, it is assumed that the VCO has a negative slope. Fig. 2 shows a VCO circuit example, and Fig. 3 shows the VCO output characteristics. If the output characteristic of VCO 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. First
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, within one cycle of Vin
VCO output frequency fout changes according to Vin, but is 1/4
By dividing the frequency, the frequency f after the division becomes constant.
This is shown in FIG. FIG. 11 shows an example of the frequency dividing means for dividing the output frequency four by 1/4 in the driving means 5. Also, instead of the AC signal Vin, a signal obtained by smoothing Vin
The frequency f hardly changes even if Vm is input. 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, in FIG. 6, the case where the data of the up / down counter 72 is added from 0 will be extended.

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. 6 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. 6 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 driving frequency f becomes lower than fr. In such a state, the ultrasonic motor stops rotating.
(This is shown in Fig. 6 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 (6) Formula In the present invention, the current of the ultrasonic motor is fed back to the control voltage of the VCO. As shown in FIG. 7, it can be seen that when V1 is directly input as a control voltage to the VCO without performing current feedback of the ultrasonic motor, the control range of the rotational speed of the ultrasonic motor by V1 is very narrow. If the control range is very narrow, the setting resolution of V1 must be increased, and ultra high precision DA
You need a converter.

When current feedback is applied as in the present invention, the control range of the rotation speed of the ultrasonic motor by V1 becomes wider as shown in FIG. 8, and the setting resolution of V1 may be lower than the former. That is,
This means that it is easy to control the rotation speed.

Next, the main operation of the present invention will be described. In short, the operation of the present invention counts up the up / down counter 72 until the analog voltage value or digital value corresponding to the rotation speed of the ultrasonic motor falls within the preset voltage value or digital value range. It is something to go. The up / down counter 72 counts when the set voltage or digital value is changed, or when the voltage value or digital value corresponding to the rotation speed of the ultrasonic motor is outside the set range due to changes in environmental temperature or load. The rotation speed is always controlled within the set range by increasing or counting down. The details are given below.

The rotation speed detecting means 6 in FIG. 1 is a circuit for detecting the rotation speed of the ultrasonic motor, and an example is shown in FIG. In Figure 9,
A light emitting means 63 and a light receiving means 64 are arranged so as to face each other with the surface of a rotation detection disk 61 integrated with the rotor and having a slit on the circumferential surface sandwiched therebetween. The light emitting means 63 is controlled so as to turn on when the ultrasonic motor is driven. When the ultrasonic motor rotates and the slit 62 of the rotation detection disk 61 passes through the light emitting means 63, the light of the light emitting means 63 is transmitted to the light receiving means 64.
The light receiving means 64 is a light sensitive element such as a phototransistor. Output a1 of the light receiving means 64 in response to the light of the light emitting means 63
Changes as shown in FIG. The result of comparing the signal of A1 with the reference voltage Va is the output a2 of the comparator A2.
The frequency of a2 is proportional to the rotation speed of the ultrasonic motor, and the frequency-voltage converting means 65 outputs the analog voltage value or digital value A corresponding to the frequency.

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

The rotation speed setting means 73 in the reference voltage control means 7 is shown in FIG.
The circuit diagram which shows an example is shown. In the figure, the voltage Vcomp2 is set by the volume resistance Rv. Vcomp1 becomes a voltage lower than Vcomp2 by dV. In the example, Vcomp1 is 0.1V lower than Vcomp2. FIG. 14 is a circuit example of the up / down counter control means 71, and FIG. 15 is a timing chart showing the operation of the circuit of FIG. FIG. 12 shows a circuit example of a DA converter that receives the counter data generated by the reference voltage control means 7 and generates the reference voltage V1 that matches the counter data.

In FIG. 14 and FIG. 15, the Reset signal is a drive enable signal for the motor, and the drive is started when it changes from 1 to 0.
Further, the reset of the up / down counter 72 and each FF is released, and the light emitting means 61 in the rotation speed detecting means 6 is turned on. The operation of the circuit will be described below in order with reference to FIGS. 14 and 15.

(A) When the Reset signal falls, the up / down counter 72 is counted up until the output signal A of the rotation detection means 6 is within the set voltage range of the rotation speed setting means 73 (Vcomp1 <A <Vcomp2). I will do it.

(B). When the rotation speed signal A falls within the set voltage range of the rotation speed setting means 73, the up-down count 72 stops counting up.

(C). When the rotation speed signal A becomes higher than Vcomp2 (when the rotation speed becomes too high), the up / down counter 72 is counted down. (Addition / subtraction control signal UD is set to Low
Then, the count signal CK is input. ) (D). When the rotation speed signal A falls within the set voltage range of the rotation speed setting means 73, the up / down counter 72 stops counting down.

(E). When the rotation speed signal A becomes lower than Vcomp1 (when the rotation speed becomes too slow), the up / down counter 72 is counted up again. (Add / subtract control signal UD
The count signal CK is input to High. ) (F). When the rotation speed signal A falls within the set voltage range of the rotation speed setting means 73, the up / down counter 72 stops counting up.

〔The invention's effect〕

According to the present invention, the rotation speed of the ultrasonic motor can be easily controlled, and a stable rotation speed can be obtained. In addition, even if the rotation speed is out of the setting range due to changes in fr and current due to temperature and drive voltage fluctuations, load fluctuations, etc., the circuit constants (reference voltage of the rectifying / amplifying means) are automatically adjusted, and the ultrasonic motor The rotation speed of is corrected.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a typical embodiment of the present invention, FIG. 2 is a circuit diagram showing an example of a VCO used in the present invention, and FIG. 3 is a diagram showing output characteristics of the VCO of FIG. FIG. 4 is a diagram showing the current waveform Vi, the rectified waveform Vin, the output signal of the VCO and the signal after frequency division of the ultrasonic motor, and FIG. 5 shows the relationship between the driving frequency of the ultrasonic motor, the consumption current and the rotation speed. 6 and 6 show changes in V1 and Vm, drive frequency f, consumption current i, and rotation speed of the ultrasonic motor when the up / down counter 72 is added from 0, and FIG. 7 is a control voltage of the VCO. Fig. 8 shows the rotation characteristics of the ultrasonic motor without current feedback, Fig. 8 shows the VCO
Showing the rotation characteristics when the ultrasonic motor current feedback is applied to the control voltage of FIG. 9, FIG. 9 is a circuit diagram showing an embodiment of the rotation speed detecting means 6, and FIG. 10 is the rotation speed and rotation speed of the ultrasonic motor. FIG. 11 is a circuit diagram showing an example of the frequency dividing means 51 in the driving means 5, and FIG. 12 is a circuit diagram showing an output relationship of the detecting means. FIG.
FIG. 13 is a circuit diagram showing an example of a reference voltage generating means (DA converter) for generating the, FIG. 13 is a circuit diagram showing an example of the rotation speed setting means 73, and FIG. FIG. 15 is a timing chart showing changes in the output A of the up-down counter control means 71 and the operation rotational speed detection means 6 of FIG. 1 ... Ultrasonic motor Rm ... Current monitor resistance C1 ... Coupling capacitors D1, D2 ... Rectifying diode L1, L2 ... Boost coil T1, T2 ... Switching transistor

Claims (5)

[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 Of the output signal of the voltage control oscillation means, a driving means for generating a drive signal to be applied to the piezoelectric element from the output signal of the voltage control oscillation means, and a reference signal for amplification of the amplification means. Receiving the output signal of the rotation speed detecting means, the rotation speed detecting means for detecting the rotation speed of the ultrasonic motor based on the drive signal, and the reference voltage generating means. It has a reference voltage control means for controlling,
The ultrasonic wave motor device, wherein the amplifying means is a rectifying / amplifying means that amplifies the signal on one side of the reference signal of the reference voltage generating means. 2. The rotation speed detecting means is integrated with a rotor of an ultrasonic motor, and has a rotation detecting plate having slits or stepped faces which are multi-divided on a circumferential surface, and is transmitted or reflected by the rotation detecting plate. A light emitting means for outputting the light, a light receiving means for receiving the transmitted light or the reflected light and outputting a frequency signal corresponding to the rotation speed of the rotor, and an output from the light receiving means for changing the rotation speed of the rotor. The ultrasonic motor device according to claim 1, comprising frequency-voltage conversion means for outputting an analog voltage value or a digital value. 3. The reference voltage control means, an up / down counter for advancing a plurality of bits, a rotation speed setting means for controlling the rotation speed of the rotor, outputs of the rotation speed setting means and the rotation speed detecting means. 3. The ultrasonic motor device according to claim 2, further comprising an up-down counter control means for controlling the up-down counter. 4. 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. 4. The ultrasonic motor device according to claim 3, further comprising: means for comparing the output signal of the rotation speed detection means with a comparison means for comparing the output signal of the rotation speed setting means. 5. The ultrasonic motor device according to claim 3, wherein said reference voltage generating means has a DA converter whose output voltage is controlled by the count data of said up / down counter.