Abstract:
A vibration detection piezoelectric element and a driving piezoelectric element are connected to each other without sandwiching an insulation member or a ground electrode therebetween. vibration wave motor accurately detects a vibration state of the motor by arranging a cancel circuit for canceling a driving frequency signal component included in an output from the detection piezoelectric element.

Description:
This application is a continuation of application Ser. No. 08/324,969, filed Oct. 18, 1994, now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a driving device for a vibration type motor which utilizes a resonance of a vibration member. 
     2. Related Background Art 
     In recent years, a vibration type motor called an ultrasonic wave motor, a piezoelectric motor, or a vibration wave motor has been developed, and has been put into practical applications by the present applicants. As is well known, the vibration type motor is a non-electromagnetic driven type motor, in which AC voltages are applied to electro-mechanical energy conversion elements such as piezoelectric elements or electrostrictive elements to cause such elements to generate a high-frequency vibration, and the vibration energy is picked up as a continuous mechanical motion. 
     FIG. 13 is a side view which shows a conventional bar-shape ultrasonic wave motor, and also shows the arrangement of wiring lines for supplying voltages to piezoelectric elements arranged in the motor, and for extracting an output voltage therefrom. A vibration member  1  constitutes the bar-shape ultrasonic wave motor, and comprises a coupled structure of piezoelectric or electrostrictive elements and an elastic member. 
     The piezoelectric element portion of the vibration member  1  is constituted by A- and B-phase driving piezoelectric elements a 1 , a 2 , b 1 , and b 2 , and a vibration detection piezoelectric element S. When an A-phase applied voltage is applied to a portion sandwiched between the A-phase piezoelectric elements a 1  and a 2 , and a B-phase applied voltage is applied to a portion sandwiched between the B-phase piezoelectric elements b 1  and b 2 , the piezoelectric elements are driven. Also, the rear sides of the A- and B-phase piezoelectric elements a 1 , a 2 , b 1 , and b 2  are connected to the GND potential. One surface of the vibration detection piezoelectric element S is similarly connected to the GND potential, and a signal is output from the other surface thereof. The signal output surface of the vibration detection piezoelectric element S contacts a metal block. The block is insulated from the GND potential by an insulation sheet. Therefore, the vibration detection piezoelectric element S can directly output an electric power voltage corresponding to a vibration generated therein. A resonance frequency or the like is calculated on the basis of the magnitude of the output voltage or its phase difference from a driving voltage. 
     FIG. 14 shows a driving circuit for such a vibration wave motor. The driving circuit comprises driving electrodes A and B for applying AC voltages to the piezoelectric or electrostrictive elements, an oscillator  2  for generating an AC voltage, a 90° phase shifter  3 , switching circuits  4 A and  5 B for switching AC voltages from the oscillator and the phase shifter by a power supply voltage, and booster coils  6  and  7  for amplifying pulse voltages switched by the switching circuits  4 A and  5 B. The driving circuit also includes a phase difference detector  8  for detecting a signal phase difference between the driving electrode A and a vibration detection electrode S. 
     The driving circuit further includes a control microcomputer  10 . FIG. 15 is a waveform chart showing signals from the driving electrode A and the vibration detection electrode S shown in FIG.  14 . 
     The control microcomputer  10  supplies a command to the oscillator  2  to generate an AC voltage having a given frequency at which the vibration wave motor is to be driven. The signals output from the driving electrode A and the vibration detection electrode S have regular sine waveforms, as shown in FIG.  15 . Therefore, the phase difference detector  8  can output a signal corresponding to the phase difference at that time to the microcomputer  10 . The microcomputer  10  detects a current difference from a resonance frequency on the basis of the input signal, and controls a drive of the motor at an optimal frequency. In this manner, the driving frequency can be controlled. 
     When such a bar-shape vibration wave motor includes an odd number of driving piezoelectric elements, as shown in FIG. 16, a driving voltage is undesirably applied to a vibration member portion, and an appropriate detection output cannot be obtained even if a vibration detection piezoelectric element is simply stacked on the driving piezoelectric elements. 
     Also, a problem of an increase in driving voltage is posed since the vibration wave motor uses piezoelectric elements. As a countermeasure against this problem, a method which adopts a floating structure shown in FIG. 17 to halve the conventional driving voltage has been proposed. 
     FIG. 18 shows a driving circuit for such a vibration wave motor. The driving circuit comprises driving electrodes A, A′, B, and B′ for applying AC voltages to the piezoelectric or electrostrictive elements, an oscillator  2  for generating an AC voltage, a 90° phase shifter  3 , switching circuits  4 A,  4 A′,  5 B, and  5 B′ for switching AC voltages from the oscillator and the phase shifter by a power supply voltage, and booster coils  6  and  7  for amplifying pulse voltages switched by the switching circuits  4 A,  4 A′,  5 B, and  5 B′. 
     The driving circuit also includes a control microcomputer  10 . The control microcomputer  10  supplies a command to the oscillator  2  to generate an AC voltage having a given frequency at which the vibration wave motor is to be driven. At this time, the switching circuits  4 A,  4 A′ having a 180° phase difference to applied voltages therebetween, and  5 B,  5 B′ also having a 180° phase difference of applied voltages therebetween, switch input signals to electrodes A, A′ or B, B′ at the input timings. In this case, a voltage twice the power supply voltage is apparently applied to the driving electrodes A, A′, B, and B′ via the coils. Therefore, the piezoelectric elements can be driven by a voltage half that required in the conventional motor. However, even when the floating structure is adopted, the above-mentioned problem is posed upon arrangement of the detection piezoelectric element. 
     As described above, in the vibration type motor structure shown in FIG. 16 or  17 , even when the vibration detection piezoelectric element S is simply stacked on the driving piezoelectric elements as in the conventional method, a vibration cannot be appropriately detected. 
     SUMMARY OF THE INVENTION 
     One aspect of the present invention has been made in consideration of the above situation, and has as its object to provide a driving device for a vibration type motor, which comprises a cancel circuit for canceling a voltage of a driving frequency signal component included in the output from a vibration detection piezoelectric element so as to obtain an appropriate vibration detection output. 
     One aspect of the present invention is to provide, based on the above object, a vibration type device which synthesizes or subtracts between a driving frequency signal applied to driving piezoelectric elements and a detection piezoelectric element output to obtain an accurate-detection output as the driving piezoelectric element output. 
     Other objects of the present invention will become apparent from the following description of the embodiments taken in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side view of a bar-shape ultrasonic wave motor according to the first embodiment of the present invention; 
     FIG. 2 is a block diagram showing a circuit according to the first embodiment of the present invention; 
     FIG. 3 is a waveform chart showing the outputs from electrodes A and S in the first embodiment; 
     FIG. 4 is a side view of a bar-shape ultrasonic wave motor according to the second embodiment of the present invention; 
     FIG. 5 is a block diagram showing a circuit according to the second embodiment of the present invention; 
     FIG. 6, including FIGS.  6 ( a ) to  6 ( f ) is a waveform chart for explaining the operation of the second embodiment; 
     FIG. 7 is a block diagram showing a circuit according to the third embodiment of the present invention; 
     FIG. 8 is a block diagram showing a circuit according to the fourth embodiment of the present invention; 
     FIG. 9 is a block diagram showing another embodiment of the present invention; 
     FIG. 10 is a side view of a bar-shape ultrasonic wave motor according to the fifth embodiment of the present invention; 
     FIG. 11 is a block diagram showing a circuit according to the fifth embodiment of the present invention; 
     FIG. 12 is a side view of a bar-shape ultrasonic wave motor according to the sixth embodiment of the present invention; 
     FIG. 13 is a side view of a conventional bar-shape ultrasonic wave motor; 
     FIG. 14 is a block diagram showing a conventional circuit; 
     FIG. 15 is a waveform chart for explaining the operation of the motor shown in FIG. 14; 
     FIG. 16 is a side view showing another conventional bar-shape ultrasonic wave motor; 
     FIG. 17 is a side view showing the floating structure of the conventional bar-shape ultrasonic wave motor; and 
     FIG. 18 is a block diagram showing a circuit of the conventional floating structure. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 is a side view which shows a bar-shape ultrasonic wave motor according to the first embodiment of the present invention, and also shows the arrangement of wiring lines for supplying voltages to piezoelectric elements arranged in the motor and for extracting an output voltage therefrom. 
     FIG. 2 is a block diagram showing a circuit portion for driving the motor shown in FIG. 1 and a circuit portion for detecting a vibration generated therein. The driving portion in FIG. 1 is the same as that in the prior art shown in FIG.  16 . In this embodiment, a vibration detection piezoelectric element s is arranged on a surface, to which a B-phase voltage is applied, of a B-phase driving piezoelectric element, and an electrode S for extracting a signal from the vibration detection piezoelectric element s is arranged at the opposite surface. 
     A difference between the circuit in FIG.  2  and the prior art is that a differential amplifier  11  is arranged between a driving electrode B and the vibration detection electrode S. FIG. 3 is a waveform chart showing the outputs from the driving electrode A and the vibration detection electrode S. 
     The output from the vibration detection electrode S has a waveform obtained by superposing a voltage component applied to the opposite side of the piezoelectric element on a sine waveform. More specifically, the output from the vibration detection electrode S has a waveform obtained by superposing a vibration detection signal and a B-phase driving waveform. Therefore, by removing the superposed waveform component by the differential amplifier  11 , the same sine waveform as that shown in FIG. 15 can be obtained. When this signal is used as the vibration detection signal, the motor can be driven at an optimal frequency as in the prior art. 
     FIG. 4 is a side view which shows a bar-shape ultrasonic wave motor according to the second embodiment of the present invention, and also shows the arrangement of wiring lines for supplying voltages to piezoelectric elements arranged in the motor and for extracting an output voltage therefrom. 
     FIG. 5 is a block diagram showing a circuit portion for driving the motor shown in FIG. 4 and a circuit portion for detecting a vibration. The driving portion in FIG. 4 is the same as that in the prior art shown in FIG.  17 . In this embodiment, a vibration detection piezoelectric element s is arranged on a surface, to which a B′-phase voltage is applied, of a B-phase driving piezoelectric element, and an electrode S for extracting a signal from the vibration detection piezoelectric element s is arranged at the opposite surface. 
     A difference between the circuit in FIG.  5  and the conventional circuit shown in FIG. 18 is that differential amplifiers  11  and  12  are respectively arranged between driving electrodes A and A′, and between a driving electrode B′ and the vibration detection electrode S. FIG. 6, including FIGS.  6 ( a ) to  6 ( f ) is a waveform chart showing the outputs from portions A, A 0 , A′, B 0 , and B′, and the output from the vibration detection electrode S in FIG. 5. A signal AO from a switching circuit  4 A has a 180° phase difference from a signal A′ from a switching circuit  4 A′. Signals B 0  and B′ from switching circuits  5 B and  5 B′ have a 90° phase difference from the signal from the circuit  4 A, and they have a 180° phase difference therebetween. The outputs from the driving electrode A and the vibration detection electrode S have waveforms each obtained by superposing a voltage component (i.e., A or B′) applied to the opposite side of the corresponding piezoelectric element on a sine waveform. Therefore, by removing the superposed waveform components using the differential amplifiers  11  and  12 , regular sine waveforms like waveforms A-A′ and S-B′ in FIG.  6 ( f ) can be obtained. 
     In this manner, a voltage applied across the two terminals of the driving piezoelectric element and a voltage obtained across the two terminals of the vibration detection piezoelectric element s are obtained, and a phase difference between these voltages is detected by a phase difference detector  8 , thus detecting regular phase difference characteristics. The microcomputer  10  detects the current difference from a resonance frequency on the basis of the signal from the detector  8 , and controls the motor to drive it at an optimal frequency. 
     FIG. 7 is a block diagram showing a circuit according to the third embodiment of the present invention. 
     In the third embodiment, a voltage across the two terminals of the piezoelectric element is detected without using any differential amplifier. In place of subtracting a signal, a signal having a phase opposite to the signal is added to the signal after impedance matching. More specifically, in the second embodiment, a voltage B′ applied to the opposite side of the vibration detection piezoelectric element s is subtracted from the output from the electrode S of the vibration detection piezoelectric element s. In place of subtraction, a signal B 0  having a phase opposite to that of the signal B′ is added to the output from the electrode S. Also, a signal A 0  having a phase opposite to that of a signal A′ is added to the output from the driving electrode A. In this manner, by utilizing original signals, a resonance frequency can be detected by a simple circuit which does not require any differential amplifier. 
     In FIG. 7, as an impedance element, only one resistor is connected to each signal extraction portion. However, in practice, a voltage-dividing circuit for decreasing a voltage, and impedance elements such as coils, capacitors, and the like may often be connected to achieve impedance matching. 
     FIGS. 8 and 9 are block diagrams each showing a circuit portion for driving a motor shown according to the fourth embodiment of the present invention and a circuit portion for detecting a vibration. In FIGS. 5 and 7, the signal from the vibration detection electrode S is compared with an A phase, while in this embodiment, a signal to be compared is changed to a B phase contacting the vibration detection piezoelectric element s. With this arrangement, since an electrode B′ can be commonly used, the number of lines extracted from the motor can be decreased. 
     FIGS. 10 and 11 are respectively a side view of a motor and a block diagram of a circuit according to the fifth embodiment of the present invention. In FIG. 10, two vibration detection piezoelectric elements S 1  and S 2  are arranged, and an electrode S is extracted from the middle position between the elements S 1  and S 2 . Note that piezoelectric elements S 1  and S 2  having the same characteristics are used. 
     Referring to FIG. 11, a signal B′ is applied to one detection piezoelectric element S 1 , and a voltage BO having a phase opposite to the signal B′ is applied to the other detection piezoelectric element S 2 , thereby mutually canceling the signals B 0  and B′. Therefore, a regular vibration detection signal can be obtained from the vibration detection electrode S without requiring any circuitry processing. Thus, the number of circuit components can be decreased. 
     FIG. 12 is a side view which shows a bar-shape ultrasonic wave motor according to the sixth embodiment of the present invention, and also shows the arrangement of wiring lines for supplying voltages to piezoelectric elements arranged in the motor and for extracting an output voltage therefrom. In this embodiment, one end face of a vibration detection piezoelectric element is connected to the GND potential. With this arrangement, a regular vibration detection signal can be obtained from a vibration detection electrode S without requiring any circuitry processing. Therefore, vibration detection can be realized without increasing the number of piezoelectric elements unlike in the fifth embodiment. 
     In the above embodiments, conversion element for detection and conversion element for drive are provided in a different positions along a thickness direction, respectively. However, the element for detection, may be provided in a portion of the element for drive.