JP2699299B2 - Ultrasonic motor drive circuit - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a driving circuit for an ultrasonic motor. 2. Description of the Related Art A piezoelectric body operates most efficiently when excited at a mechanical resonance frequency, and its efficiency decreases when the frequency deviates from the resonance frequency. For this reason, it is preferable that the frequency of the frequency voltage that causes the piezoelectric body to oscillate accurately matches the resonance frequency of the piezoelectric body, but the resonance frequency of the piezoelectric body fluctuates depending on changes in load and environmental conditions. Therefore, a vibration feedback type driving circuit for automatically tracking the frequency of the frequency voltage to the resonance frequency has been invented. This drives the piezoelectric body at a constant frequency voltage,
By taking out an output voltage proportional to the vibration amplitude of the piezoelectric body by an appropriate method and feeding it back to the input terminal of the amplifier, the resonance frequency of the piezoelectric body always tracks the resonance frequency even if it fluctuates ( Handbook of Ultrasonic Techniques, published on July 20, 1978, pages 565 to 566). [0004] However, it is not always desirable to drive the ultrasonic motor at the resonance frequency. Therefore, even if this type of drive circuit is applied to an ultrasonic motor, it will be described above. As described above, only the resonance frequency can be tracked, and the frequency voltage cannot be set to an arbitrary frequency. Accordingly, an object of the present invention is to provide an ultrasonic motor driving circuit which can set the frequency of the frequency voltage for driving the ultrasonic motor arbitrarily without being limited to only the resonance frequency. . [0006] To achieve the above object, the present invention provides an electromechanical transducer and an elastic body,
In a drive circuit of an ultrasonic motor having a vibrator that generates vibration when a drive signal is applied to the electromechanical transducer and a relative motion member that performs relative motion between the vibrator and the vibration element, A voltage generating means for generating a voltage in accordance with the vibration state of the vibrator from a portion of the element to which the drive signal is not applied, and a phase difference between a voltage obtained from the voltage generating means and a voltage of the drive signal. And a control means for controlling the frequency of the drive signal based on the output of the phase difference calculation means. According to the present invention, the phase difference calculating means calculates the phase difference between the voltage obtained from the voltage generating means and the voltage of the drive signal,
The control means controls the frequency of the drive signal based on the calculation result. Thus, the ultrasonic motor can be driven at any frequency, not limited to the resonance frequency. FIG. 1 and FIG. 2 show an embodiment of the present invention.
Shows a drive circuit diagram of the ultrasonic motor, and FIG. 2 shows a characteristic diagram of the drive circuit. In FIG. 1, an oscillator 1 outputs a pulse having a frequency f to a waveform shaper 2, and the waveform shaper 2
The waveform of the input pulse is shaped into a sine wave and output to the amplifier 4 and the phase shifter 3. The phase shifter 3 shifts the phase of the input sine wave by π / 2 and outputs the shifted sine wave. The amplifiers 4 and 5 amplify and output the input sine waves, respectively. Then, the amplified sine wave is input to the electrodes 6a and 6b formed on the surface of the piezoelectric body of the stator 6 (comprising a piezoelectric body and an elastic body) of the ultrasonic motor. The electrodes of the stator 6 are divided into four regions 6a to 6d. Sine waves having different phases are input to the electrodes 6a and 6b as described above, and the ground is connected to the electrode 6c.
The electrode 6d is a portion where no input voltage is applied. Matching inductances 7 and 8 are connected in parallel between the electrodes 6a and 6c and between the electrodes 6b and 6c. The phase difference detection circuit 9 detects an input voltage to the electrode 6a and a voltage (hereinafter referred to as a monitor voltage) generated by excitation of the electrode 6d to which no input voltage is applied, and detects a phase difference θ. Is calculated. The phase difference detection circuit 9
The detected phase difference θ is input to the comparator 10. The comparator 10 outputs the output θ from the phase difference detection circuit 9 and the preset optimal phase difference θ output from the reference 11.
_OPT and outputs the deviation amount Δθ. The optimum phase difference θ _OPT is a value uniquely determined by the polarization direction of the piezoelectric portion below the electrode 6c, the damping of the stator, the pressure contact force of the rotor driven by the stator, and the like (that is, the value unique to each ultrasonic motor). Value). The θ _OPT is experimentally obtained, and can be set in the referrer 11 at an initial stage and used stably. The optimum phase difference θ _OPT obtained experimentally may be a phase difference at which the ultrasonic motor has the maximum number of revolutions, or a phase difference at which the ultrasonic motor has a desired speed. The θf converter 12 receives the deviation Δθ of the phase difference and calculates the displacement direction and the displacement amount of the input frequency f in order to optimize the input frequency f.
The oscillator 1 is controlled by calculating from θ. In this embodiment, the control means 13 is constituted by the comparator 10, the referrer 11, and the θf converter 12. Further, the piezoelectric body functions as an electromechanical transducer, and the rotor functions as a relative motion member. Next, the operation of the embodiment when the optimum phase difference θ _opt which becomes the maximum number of revolutions of the ultrasonic motor is selected will be described with reference to FIG. In FIG. 2, the horizontal axis indicates the frequency f, and the vertical axis indicates the rotational speed N of the ultrasonic motor and the phase difference θ output from the phase difference calculating circuit 9. Now, it is assumed that the characteristics of the ultrasonic motor are indicated by a curve NA as the frequency characteristics of the rotational speed N of the ultrasonic motor and by the curve θA as the frequency characteristics of the phase difference θ output from the phase difference calculating circuit 9. At this time, that is, at time A, the comparator 10 compares the phase difference θ output from the phase difference calculating circuit 9 with the optimum phase difference θopt, and receives the output to receive the θf converter 1
2 controls the oscillator 1 to output the optimum frequency.
At that time, in the curve θA, the frequency corresponding to the optimal phase difference θopt becomes the optimal input frequency. The optimum value of the input frequency is indicated by the frequency fA. Then, at time B, the rotation speed N is changed due to changes in various conditions (changes caused by driving the ultrasonic motor and changes in external conditions applied to the surface wave motor).
Is changed like a curve NB. However, since the input frequency is fA, the rotation speed is N1.
(N1 <Nmax). At this time, the phase difference θ
Is shifted according to the shift of the frequency characteristic of the rotation speed, so that the frequency characteristic of the phase difference θ is as shown by a curve θB. As a result, at time B, the input frequency is fA as described above, so that the phase difference calculation circuit 9 outputs the phase difference θ1 at time B to the comparator 10. The comparator 10 compares the input phase difference θ1 with the optimum phase difference θopt,
The deviation amount Δθ is output to the θf converter 12. The θf converter 12 converts the deviation Δθ into a frequency deviation Δf and feeds it back to the oscillator 1. Then, the oscillator 1 outputs the input frequency fB based on the deviation amount Δf. That is, by controlling the phase difference θ output from the phase difference calculation circuit 9 to always coincide with the optimum frequency θopt, the driving efficiency of the ultrasonic motor is maintained at high efficiency. Similarly, at the next time, the phase difference θ and the optimal phase difference θopt
The operation of obtaining the amount of deviation Δθ by comparing with the above and feeding back to the oscillator 1 to output the optimum input frequency is repeated. Since the curves .theta.A and .theta.B are curves indicating an increase or a decrease, when the deviation .DELTA..theta. Is obtained, the displacement direction and the magnitude of the input frequency f based on the deviation .DELTA.f are determined. Therefore, it is possible to know in which direction and how much the input frequency f should be changed based on the deviation amount Δθ. Therefore, by obtaining the shift amount Δθ, the input frequency that determines the shift amount Δf of the frequency and feeds back to the oscillator 1 to give the maximum rotation speed can be determined. Therefore, the ultrasonic motor always rotates at the maximum rotation speed. Highly efficient driving is possible. As described above, according to the present invention, the phase difference calculating means detects the phase difference between the voltage obtained from the voltage generating means and the voltage of the drive signal, and the control means calculates the result of this calculation. Control the frequency of the drive signal based on Therefore, the ultrasonic motor can be driven at an arbitrary frequency without being limited to the resonance frequency, so that the ultrasonic motor can be driven with high efficiency or at a desired speed. Further, the drive signal for driving the ultrasonic motor can be limited to a desired frequency band.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a circuit diagram of an embodiment of a driving circuit for an ultrasonic motor according to the present invention. FIG. 2 is a diagram illustrating a frequency characteristic of a rotation speed and a frequency characteristic of a phase difference of the driving circuit. [Description of Signs] 1 ··· Oscillator 6 ··· Stator of ultrasonic motor 9 ··· Phase difference calculation circuit 11 ··· Referencer

Claims (1)

(57) [Claims] A vibrator that includes an electromechanical transducer and an elastic body, and generates a vibration when a drive signal is applied to the electromechanical transducer, and a relative motion member that performs relative motion between the vibrator and the vibrator. A drive circuit for the ultrasonic motor, comprising: a voltage generating means for generating a voltage according to a vibration state of the vibrator from a portion of the vibrator to which the drive signal is not applied; An ultrasonic wave comprising: a phase difference calculating unit that calculates a phase difference between a voltage and a voltage of the driving signal; and a control unit that controls a frequency of the driving signal based on an output of the phase difference calculating unit. Motor drive circuit.