Vibration wave motor

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.

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 a1, a2, b1, and b2, 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 a1 and a2, and a B-phase applied voltage is applied
 to a portion sandwiched between the B-phase piezoelectric elements b1 and
 b2, the piezoelectric elements are driven. Also, the rear sides of the A-
 and B-phase piezoelectric elements a1, a2, b1, and b2 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.degree. phase shifter 3, switching
 circuits 4A and 5B 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 4A and 5B.
 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.degree. phase shifter 3,
 switching circuits 4A, 4A', 5B, and 5B' 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 4A, 4A', 5B, and 5B'.
 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 4A, 4A' having a
 180.degree. phase difference to applied voltages therebetween, and 5B, 5B'
 also having a 180.degree. 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.

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, A0, A', B0, and B', and the output from the vibration
 detection electrode S in FIG. 5. A signal AO from a switching circuit 4A
 has a 180.degree. phase difference from a signal A' from a switching
 circuit 4A'. Signals B0 and B' from switching circuits 5B and 5B' have a
 90.degree. phase difference from the signal from the circuit 4A, and they
 have a 180.degree. 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 B0 having a
 phase opposite to that of the signal B' is added to the output from the
 electrode S. Also, a signal A0 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.sub.1 and
 S.sub.2 are arranged, and an electrode S is extracted from the middle
 position between the elements S.sub.1 and S.sub.2. Note that piezoelectric
 elements S.sub.1 and S.sub.2 having the same characteristics are used.
 Referring to FIG. 11, a signal B' is applied to one detection piezoelectric
 element S.sub.1, and a voltage BO having a phase opposite to the signal B'
 is applied to the other detection piezoelectric element S.sub.2, thereby
 mutually canceling the signals B0 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.