Ultrasonic motor and electronic device with ultrasonic motor

• US 6,586,860 B1
• Filed: 10/26/2000
• Issued: 07/01/2003
• Est. Priority Date: 11/01/1999
• Status: Active Grant

• Current Assignee: Seiko Instruments Incorporated (Seiko Group)
• Original Assignee: Seiko Instruments Incorporated (Seiko Group)
• Inventors: Suzuki, Kenji, Kasuga, Masao, Iino, Akihiro
• Primary Examiner(s): BUDD, MARK OSBORNE
• Application Number:
  US09/696,790
• Time in Patent Office: 978 Days
• Field of Search: 310/316.01, 310/316.02, 310/316.03, 310/317
• US Class Current: 310/316.02
• CPC Class Codes: H02N 2/0075 Electrical details, e.g. drive or control circuits or methods

Abstract

In a self-excited oscillator circuit, a buffer is connected to an electrode or electrodes, and a buffer and an inverter are connected to an electrode or electrodes. Each of the inverters and and the buffer has a tri-state configuration and is capable of setting an output terminal in a high-impedance state, i.e., turning off an output signal, according to a signal input to a control terminal. Therefore, it is possible to turn off a drive circuit and the ultrasonic motor by setting the inverter in the high-impedance state. It is also possible to change the direction of movement of the moving member by setting one of the buffer and the inverter in the high-impedance state.

Claims

1. An ultrasonic motor comprising:

a piezoelectric element having a plurality of driving electrodes and a common electrode;

a vibrating body driven by the piezoelectric element to undergo vibration in response to a signal applied across the driving electrodes and the common electrode of the piezoelectric element;

a moving body driven by vibration of the vibrating body;

a self-excited oscillating circuit having an amplifier circuit for amplifying an output signal of the piezoelectric element and feeding back the amplified output signal as a driving signal to the driving electrodes of the piezoelectric element to cause self-excited oscillation of the vibrating body;

a common connecting point provided between the amplifier circuit and the plurality of driving electrodes of the piezoelectric element for connecting the plurality of driving electrodes to one point so that all of the driving electrodes are simultaneously driven; and

an inverter provided between the common connecting point and at least one of the driving electrodes of the piezoelectric element for selectively inverting the phase of the driving signal supplied to the at least one driving electrode to control a direction of movement of the moving body.

2. An ultrasonic motor according to claim 1;

wherein the self-excited oscillating circuit has an LC resonant circuit comprising the piezoelectric element and a capacitive element, and the inverter is provided between the piezoelectric element and the capacitive element.

3. An ultrasonic motor according to claim 1;

wherein the piezoelectric element has the driving electrodes provided on a first surface and the common electrode provided on a second surface opposite,the first surface.

4. An ultrasonic motor according to claim 3;

wherein the piezoelectric element has a disc shape.

5. An ultrasonic motor according to claim 1;

wherein the piezoelectric element comprises a plurality of stacked piezoelectric elements, the common electrode comprises interconnected electrodes formed on a first surface of each of the stacked piezoelectric elements and the driving electrodes comprise interconnected electrodes formed on a second surface, opposite the first surface, of each of the stacked piezoelectric elements.

6. An ultrasonic motor according to claim 1;

wherein the piezoelectric element has a detection electrode provided on the first surface where the plurality of driving electrodes are provided, and the amplifier circuit amplifies a detection signal output from the detection electrode and outputs the amplified detection signal as a driving signals to the driving electrodes.

7. An ultrasonic motor according to claim 1;

wherein the amplified output signal supplied to the driving electrodes has a constant level whether or not the phase is inverted by the inverter.

8. An ultrasonic motor according to claim 1;

further comprising a driving signal adjusting circuit for adjusting the driving signal so that driving signals having substantially the same level are supplied to each of the driving electrodes whether or not the phase is inverted by the inverter.

9. An ultrasonic motor according to claim 1;

further comprising a spring member for resiliently urging the moving body into contact with the vibrating body.

10. An ultrasonic motor according to claim 1;

wherein the amplified output signal is supplied to all of the driving electrodes when the inverter is not selected so that a standing wave produced in the vibrating body causes the moving body to move in a first direction, and the amplified output signal is supplied to some of the driving electrodes while an output of the inverter is supplied to other driving electrodes when the inverter is selected so that a standing wave produced in the vibrating body causes the moving body to move in a second direction opposite the first direction.

11. An ultrasonic motor according to claim 1;

wherein the first surface of the piezoelectric element on which the driving electrodes are provided is divided into a plurality of sectors, adjacent pairs of the sectors being polarized in opposite directions, each sector having one of the driving electrodes provided thereon, and the vibrating body is fixed to the first surface of the piezoelectric element on which the driving electrodes are formed and has protrusions each disposed at selected sectors for transmitting driving power to the moving body.

12. An ultrasonic motor according to claim 1;

further comprising a first buffer disposed between the common connection point and a first group of the driving electrodes, and a parallel connection of the inverter and a second buffer connected between the common connection point and a second group of the driving electrodes.

13. An electronic device having a motor and an output mechanism driven by the motor;

wherein the ultrasonic motor comprises the ultrasonic motor according to claim 1; and

the output mechanism is driven by the moving body.

14. An ultrasonic motor comprising:

a vibrating body having a piezoelectric element provided with a plurality of driving electrodes on one surface and a common electrode on another surface;

a moving body in frictional contact with the vibrating body to undergo movement in response to vibration of the vibrating body;

a self-excited oscillation circuit having an amplifier for amplifying an output signal of the piezoelectric element and feeding back the amplified output signal to the driving electrodes of the piezoelectric element, a filter circuit for filtering the amplified output signal, and an inverter for selectively inverting the amplified output signal and producing an inverted signal;

wherein all of the driving electrodes of the piezoelectric element are simultaneously driven by either the amplified output signal or the inverted signal.

15. An ultrasonic motor according to claim 14;

further comprising a spring member for resiliently urging the moving body into contact with the vibrating body.

16. An ultrasonic motor according to claim 14;

wherein the amplified output signal is supplied to all of the driving electrodes when the inverter is not selected so that a standing wave produced in the vibrating body causes the moving body to move in a first direction, and the amplified output signal is supplied to some of the driving electrodes while the inverted signal is supplied to other driving electrodes when the inverter is selected so that a standing wave produced in the vibrating body causes the moving body to move in a second direction opposite the first direction.

17. An ultrasonic motor according to claim 14;

wherein the self-excited oscillation circuit has a resonant circuit comprised of the piezoelectric element and a capacitor.

18. An ultrasonic motor according to claim 14;

wherein the surface of the piezoelectric element on which the driving electrodes are provided is divided into a plurality of sectors, each sector having one of the driving electrodes provided thereon and adjacent pairs of the sectors being oppositely polarized.

19. An ultrasonic motor according to claim 18;

wherein the vibrating body is fixed to the surface of the piezoelectric element on which the driving electrodes are formed and has protrusions each disposed at one of the sectors for transmitting a driving power to the moving body.

20. An ultrasonic motor according to claim 19;

wherein the piezoelectric element has a disc shape.

21. An ultrasonic motor according to claim 20;

wherein the common electrode covers substantially an entire surface of the piezoelectric element.

22. An ultrasonic motor according to claim 14;

wherein the self-excited oscillation circuit further comprises a first buffer disposed between an output of the amplifying circuit and a first group of the driving electrodes, and a parallel connection of the inverter and a second buffer connected between the output of the amplifying circuit and a second group of the driving electrodes.

23. An ultrasonic motor according to claim 14;

wherein the piezoelectric element becomes inductive between a resonance point and an anti-resonance point.

24. An ultrasonic motor according to claim 14;

wherein the signals supplied to the driving electrodes have a constant level whether or not the phase is inverted by the inverter.