JPH04347588A - Circuit for driving single-phase resonance mode ultrasonic motor - Google Patents

Abstract

PURPOSE:To automatically track an optimum driving frequency, to reduce variation in rotation and to obtain arbitrarily set dynamic characteristic. CONSTITUTION:A frequency signal synchronized with rotation of a moving element such as a rotor, is obtained by a detected frequency generator 5, phase- compared with a frequency signal representing set rotation of an ultrasonic motor to be output from set frequency generating means 1 by a phase comparator 6, and an oscillator 8 which outputs a driving frequency is controlled by altering the frequency in a direction in which its difference becomes '0'. Eventually, the driving frequency is altered by an amount corresponding to a variation in rotation of the rotor, i.e., f, and brought into coincidence with a resonance frequency.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to ultrasonic motors. More specifically, the present invention relates to a drive circuit that automatically tracks the optimum drive frequency of a single-phase resonant mode ultrasonic motor.

0002

[Prior Art] In an ultrasonic motor, when the temperature of the vibrating body (including the piezoelectric vibrator) changes, the resonance frequency changes, causing a deviation from the preset drive frequency, resulting in a decrease in dynamic characteristics. cause Therefore, in order to prevent this, a correction circuit is provided so that the rate of change in the frequency of the drive oscillator with temperature is equal to the rate of change in the resonant frequency of the piezoelectric material, and the oscillation frequency is changed by changing the frequency of the oscillator according to the temperature. A technique has been proposed in which the temperature change is made to match the temperature change of the drive frequency (Japanese Patent Application Laid-Open No. 1983-1999).
No. 171175).

[0003] Furthermore, by calculating the phase difference between the input voltage input to the piezoelectric body and the monitor voltage generated by excitation from the part of the piezoelectric body to which no input voltage is applied,
A technology has also been proposed in which the direction and amount of deviation from the optimum value of the frequency of the input voltage is known, and the frequency of the input voltage is controlled based on this knowledge, thereby making it possible to maintain the drive of the ultrasonic motor in the optimum state at all times. (Unexamined Japanese Patent Publication No. 61-25
No. 1490).

0004

[Problems to be Solved by the Invention] However, all of the prior art drive circuits are of a two-phase drive type, which is not a drive type that can be applied to the single-phase resonant mode ultrasonic motor that is the object of the present invention. That is, conventionally, no driving method for a single-phase resonant mode ultrasonic motor has been proposed.

SUMMARY OF THE INVENTION An object of the present invention is to provide a drive circuit that can automatically set the optimum drive frequency for a single-phase resonant mode ultrasonic motor.

[0006]

[Means for Solving the Problems] In order to achieve the above object, a drive circuit for a single-phase resonant mode ultrasonic motor of the present invention includes a vibrating body driven by an ultrasonic vibrator, an end portion of the vibrating body, In a single-phase resonant mode ultrasonic motor consisting of a moving body that is in contact and moved by the vibration of the vibrating body,
a detection frequency generator that generates a frequency signal synchronized with the movement of the moving body; a set frequency generation means that generates a frequency signal indicating a set speed of the ultrasonic motor; the set frequency generation means and the detection frequency generator; and an oscillator that outputs a drive frequency of the ultrasonic motor based on the output of the phase comparator, the output of the oscillator being applied to the vibrating body. The above moving body is moved.

[0007]

[Operation] The temperature of a vibrating body containing piezoelectric ceramics rises or falls due to changes in load, etc., causing the resonance frequency to fluctuate and deviate from the driving frequency. For example, as shown in FIG. 3, when the temperature increases from A to B, the resonance frequency shifts from f to f1, resulting in a shift of Δf (=f-f1). As shown in Fig. 3, this deviation of △f appears as a change in the motor rotation speed (N→N1), so a frequency signal synchronized with the rotation of the rotating body is obtained, and it is used to rotate the ultrasonic motor at the set rotation speed. The oscillator is controlled to change the frequency in a direction in which the difference becomes 0 and output it as a drive frequency. Finally, the drive frequency is changed by an amount corresponding to the rotational unevenness of the rotating body, that is, Δf, to match the resonance frequency.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the structure of the present invention will be explained in detail based on embodiments shown in the drawings.

First, the principle of the single-phase resonant mode ultrasonic motor according to the present invention will be explained.

In FIG. 5, a prismatic member indicated by reference numeral 11 is a vibrating body made of an elastic material. Here, the length L of the vibrating body 11 was 40 mm, and the height H was 10 mm. Ultrasonic vibrators 12 and 12 made of piezoelectric ceramics are bonded to the upper and lower surfaces of the vibrating body 11. Electrodes 13 and 14 made of metal thin films are provided on both the front and back surfaces of the ultrasonic vibrators 12 and 12, and one electrode film 13 or 14 is bonded to the vibrating body 11. Note that the ultrasonic transducers 12, 12 may be attached only to one surface of the vibrating body 11. When the length of the ultrasonic transducers 12, 12 is a, and the amount of protrusion (overhang amount) of the vibrating body 11 from the ultrasonic transducers 12, 12 is b, the relationship between a and b is a:
The relationship was set so that b=2:1 (that is, L=a+2b).

Now, the electrodes 13 of the ultrasonic transducers 12, 12
, 14, an alternating signal is applied via a predetermined drive circuit, and the frequency of this alternating signal is continuously changed, so that the admittance of the ultrasonic transducers 12, 12 increases rapidly at a specific frequency. shows the peak value. This is actually measured and shown in FIG. 4, where the admittance rapidly increases and peaks at frequencies f0, f1, and f2. A rapid increase in admittance means that a large current is flowing, and each becomes a resonance mode. Among these resonance modes, in the f1 resonance mode, as shown in FIG. 6, the parts of the vibrating body 11 that protrude from the ultrasonic transducers 12, 12 are bent in the vertical direction and in mutually opposite directions, vibrating in a undulating manner. The vibrating body 11 in the f2 resonance mode vibrates so as to expand and contract in the longitudinal direction of the vibrating body 1, as shown in FIG. Although the amplitude in this case changes depending on the applied voltage, the tip of the vibrating body 11 usually vibrates with an amplitude of about several μm. Note that f0 is a standing wave mode.

[0012] The single-phase resonance mode ultrasonic motor utilizes the difference in behavior due to the resonance mode of the vibrating body 11 described above, and by switching the resonance mode, the moving direction of the moving body can be arbitrarily moved in the forward direction or the reverse direction. This made it possible to switch to

That is, as shown in FIG.
A movable body 15 is installed that contacts one end edge X of the movable body 15, and the movable body 15 and the vibrating body 11 constitute an ultrasonic motor. In the case of this embodiment, the moving body 15 is a rotating body that can rotate around a rotation axis 15A, and is arranged so that the circumferential surface of the rotating body 15 and the end edge X of the moving body 1 are parallel to each other. . Furthermore, preferably, the edge portion X and the rotating shaft 15 of the rotating body 15
The arrangement is such that the angle θ formed by the line connecting A and the surface of the vibrating body 1 to which the ultrasonic transducer 12 is attached is approximately 45°.

A frequency generator plate (FG plate) 15B is coaxially fixed to the rotating body 15, and rotates integrally with the rotating body 15, forming a part of the drive circuit. ) is provided so that a pulse synchronized with the rotation of the rotating body 15 can be obtained. Although not specifically illustrated, the FG plate 15B is a disk having, for example, a slit for optical detection, a magnetic pattern for magnetic detection, and the like.

The ultrasonic vibrators 12, 12 are made of piezoelectric ceramics, for example, and are caused to vibrate by applying an alternating signal from the drive circuit shown in FIG. This drive circuit includes a set frequency generating means 1 which generates a frequency signal indicating the set speed of the ultrasonic motor, a detection frequency generator 5 which generates a frequency signal synchronized with the rotation of a rotating body 15, and a set frequency generating means 1. and a phase comparator 6 that compares the phases of signals A and B output from the detection frequency generator 5, respectively, and a low-pass filter 7 to remove the influence of high frequency noise. The output of the oscillator 8 is amplified by a power amplifier 9 and then applied to the ultrasonic vibrators 12, 12 of the vibrating body 11 of the ultrasonic motor 10 to rotate it. It constitutes a feedback system that rotates the body 15.

The set frequency generating means 1 includes an oscillator 2 that outputs a signal of a constant frequency, and an integer n inputted from an external control means such as a microcomputer through an IO port 3.
The frequency divider 4 divides the frequency signal input from the oscillator 1 into 1/n using a digital signal of 1, and outputs a frequency signal A indicating the set speed of the ultrasonic motor. The phase of this signal A is indicated by Wr. On the other hand, the detection frequency generator 5
In the case of this embodiment, a frequency generator (FG) that detects the rotation of an FG plate 15B that rotates integrally with the rotating body 15 constituting the ultrasonic motor 10 is employed. The output signal B of the detection frequency generator 5 consists of a frequency and phase Wd synchronized with the motor rotation.

Further, the phase comparator 6 compares the phase difference between the phase Wr of the signal A and the phase Wd of the signal B, and outputs a DC voltage proportional to the frequency difference and phase difference. As the oscillator 8, a voltage controlled oscillator whose output frequency is controlled by the error voltage output from the phase comparator 6 is employed. The alternating signal output from the voltage controlled oscillator 8 is amplified by the amplifier 9 and applied between the electrodes 13 and 14 of the two ultrasonic transducers 12 and 12. Each electrode 13, 14 of the two ultrasonic transducers 12 is connected in parallel to a drive circuit amplifier 9 serving as a power source. The alternating signal applied from the drive circuit is determined by the elastic properties of the entire vibrating body 11 and the ultrasonic transducers 12, 12, and the f1 resonance mode and f1.
2 This is an electrical signal with a frequency that becomes a resonance mode.

The ultrasonic motor constructed as described above operates as follows.

Now, when the frequency of the resonance mode f1 is set in the set frequency generating means 1, this is outputted as a signal A with a frequency indicating the set speed of the ultrasonic motor.
The vibrating body 11 is driven to rotate the rotating body 15 in a predetermined direction.

On the other hand, the rotational speed of the rotating body 15 rotated by the motor 10 is output as a signal B by the output of the FG5. Here, when a change occurs in the resonant frequency of the vibrating body 11 and deviates from the driving frequency, a phase difference occurs between the set speed signal A and the actual speed signal B, and this is phase-compared in the phase comparator 6. The phase difference is converted into a voltage and output to the voltage controlled oscillator 8. For example, the frequency signal that determines the set speed is fixed, but the resonant frequency of the motor changes, so the phase difference is obtained by comparing the phase difference with a periodic signal obtained from an encoder or the like using the above-mentioned fixed signal as a reference. That is, signals are compared based on the amount of shift (phase difference) rather than the magnitude of the voltage value. Then, in order to set this error voltage to 0, the drive frequency Sig. c to the ultrasonic transducers 12, 12. Then, when there is no longer a phase difference between the phase Wr of the reference signal A and the phase Wd of the rotation signal B of the rotating body 15 rotated by the motor 10, a phase lock is activated in the feedback system, and the ultrasonic wave is transmitted at the speed indicated by the signal A. The motor 10 will rotate evenly. In this manner, the vibrating body 11 is vibrated in a undulating manner while changing the driving frequency to match the resonant frequency. As a result, the end edge X of the vibrating body 11 vibrates in the diagonal stroke range shown by arrow A in FIG. Then, when the vibrating body 11 is deformed obliquely upward, the edge portion X is oriented to bite into the circumferential surface of the rotating body 15, thereby pushing the rotating body 15 clockwise. On the other hand, vibrator 1
When the rotor 1 deforms diagonally downward, the end edge X runs away from the circumferential surface of the rotor 15, so that it does not apply any rotational force to the rotor 15. As a result, in the f1 resonance mode, the rotating body 5 is rotated clockwise in FIG. 6.

Next, when the frequency of the f2 resonance mode is set in the set frequency generating means 1, the vibrating body 11 is moved as shown in FIG. , vibrate in the direction of expansion and contraction. As a result, the end edge X of the vibrating body 1 bites into the circumferential surface of the rotating body 15 when it is extended, pushing the rotating body 15 counterclockwise. On the other hand, when the vibrating body 11 contracts, the edge portion X runs away from the circumferential surface of the rotary body 15, so the frictional force between the vibrating body 11 and the rotary body 15 is reduced, and the rotary body 15 is interlocked. do not. As a result, in the f2 resonance mode, the rotating body 15 is rotationally driven in the counterclockwise direction in the illustrated case.

According to the ultrasonic motor configured as described above, the rotational speed of the rotating body 15 can be changed by changing the voltage of the signal applied to the ultrasonic transducers 12, 12, or by changing the resonance frequency f1, Vibrating body 11 by fine adjustment of f2
All you have to do is change the vibration amplitude. Furthermore, arbitrarily switching the rotational direction of the movable body 5 between forward and reverse directions can be achieved by an extremely simple means of causing the vibrating body 11 to resonate in a different mode f1 or f2.

[0023] Although the above-described embodiment is an example of a preferred implementation of the present invention, the present invention is not limited thereto, and various modifications can be made without departing from the gist of the present invention. For example, in addition to detecting the rotational speed of the rotating body, the speed of the rotating body may be detected, or the temperature of the vibrating body may be detected and corrected. Further, the drive circuit 9 of FIG.
A digital servo may be configured by employing a digital low-pass filter and a digital oscillator instead of the phase comparator 6, low-pass filter 7, and voltage-controlled oscillator 8. Further, in this embodiment, a rotating object is used as the moving object 15, but the present invention is not limited to this, and it is also possible to use a linear motor that uses an object that moves in a straight line.

[0024]

[Effects of the Invention] As is clear from the above explanation, the present invention controls the driving frequency by giving negative feedback of the deviation of the resonance frequency from the vibrating body and constantly comparing the phase with the frequency indicating the motor setting speed. Therefore, the optimal drive frequency of the single-phase resonance mode ultrasonic motor can be automatically tracked, rotational unevenness can be reduced, and arbitrary set dynamic characteristics can be obtained.

Further, although the conventional drive circuit corrects the first-order mode resonance frequency, the drive circuit of the present invention can cover even the n-order resonance mode.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of a drive circuit for a single-phase resonant mode ultrasonic motor of the present invention.

FIG. 2 is a graph showing the relationship between resonance frequency and rotation speed.

FIG. 3 is a graph showing the relationship between temperature and resonant frequency number.

FIG. 4 is a graph showing the relationship between the frequency of a signal applied to an ultrasonic transducer and admittance for explaining the resonance mode of a vibrating body.

FIG. 5 is an explanatory diagram showing the arrangement relationship between the vibrating body and the ultrasonic vibrator of the single-phase resonance mode ultrasonic motor of the present invention.

FIG. 6 is a schematic diagram showing the configuration of a single-phase resonance mode ultrasonic motor to which the present invention is directed, and shows behavior in the f1 resonance mode.

FIG. 7 is a schematic diagram showing behavior in the f2 resonance mode.

[Explanation of symbols]

1 Setting frequency generation means 5 Detection frequency generator 6 Phase comparator 8 Drive signal oscillator 10 Ultrasonic motor 11 Vibrating body 12 Ultrasonic vibrator 13 Ultrasonic vibrator 15 Rotating body (moving body) 15B Configuring the detection frequency generator frequency generator board

Claims (1)

[Claims] 1. A single-phase resonant mode ultrasonic motor comprising a vibrating body driven by an ultrasonic vibrator, and a moving body that comes into contact with an end of the vibrating body and moves by the vibration of the vibrating body, a detection frequency generator that generates a frequency signal synchronized with the movement of the moving body; a set frequency generating means that generates a frequency signal indicating a set speed of the ultrasonic motor; the set frequency generating means and the detected frequency generator; a phase comparator that compares the phases of signals respectively output from the oscillator, and an oscillator that outputs a driving frequency of the ultrasonic motor based on the output of the phase comparator, and adds the output of the oscillator to the vibrating body. A drive circuit for a single-phase resonant mode ultrasonic motor that moves the above-mentioned moving body.