Piezoelectric motor drive circuit and method

• US 20060244339A1
• Filed: 04/29/2005
• Published: 11/02/2006
• Est. Priority Date: 04/29/2005
• Status: Active Grant

• Current Assignee: Microvision, Inc.
• Original Assignee: Symbol Technologies, Inc. (Zebra Technologies Corporation)
• Inventors: Yavid, Dmitriy, Wood, Frederick F., Mazz, Thomas
• Granted Patent: US 7,227,294 B2
• Time in Patent Office: Days
• US Class Current: 310/317
• CPC Class Codes: G09G 2340/145 related to small screens
• CPC Class Codes: G09G 3/002 to project the image of a two-dimensional display, such as an array of light emitting or modulating elements or a CRT
• CPC Class Codes: H04N 9/3129 scanning a light beam on the display screen scanning a light beam on a screen in displays other than projection devices G09G3/02; scanning systems in general G02B26/10; projectors using laser light sources in general H04N9/3161
• CPC Class Codes: H10N 30/802 Drive or control circuitry or methods for piezoelectric or electrostrictive devices not otherwise provided for

Abstract

A piezoelectric transducer is driven to mechanically oscillate a mirror at a mechanical resonant frequency with high precision despite frequency variations introduced by temperature, tolerances and ageing of components.

Claims

1. An arrangement for electrically driving a piezoelectric transducer to mechanically oscillate a mirror at a mechanical resonant frequency, comprising:

a) an inductor electrically connected to the transducer to form a resonant circuit having an electrical resonant frequency which is greater than the mechanical resonant frequency throughout variations in temperature, ageing and tolerances of the transducer and the inductor;

b) means for driving the resonant circuit with an electrical drive signal having a drive frequency which differs from the electrical resonant frequency by a parameter; and

c) means for adjusting the parameter to make the drive frequency correspond to the mechanical resonant frequency to compensate for said variations in the electrical resonant frequency.

2. The arrangement of claim 1, wherein the transducer has an inherent capacitance, and wherein the inductor has inductance and is electrically connected in series with the transducer to form a series resonant circuit.

3. The arrangement of claim 1, wherein the electrical resonant frequency is more than two times greater than the mechanical resonant frequency.

4. The arrangement of claim 2, wherein the driving means includes a bridge circuit having two arms connected across a supply of DC voltage, each arm having a pair of actuatable switches and a junction therebetween;

and wherein the series resonant circuit is connected between each junction of the arms.

5. The arrangement of claim 4, wherein each switch is a transistor, and wherein the bridge circuit includes a diode connected between one of the switches of each arm and the junction of the respective arm.

6. The arrangement of claim 4, wherein the driving means includes a controller for cyclically controlling actuation of the switches to convert the DC voltage to the drive voltage having an alternating current waveform having cycles.

7. The arrangement of claim 6, wherein the controller closes at least one of the switches in each arm and opens at least another of the switches in each arm for a switching time period which determines said parameter to be adjusted.

8. The arrangement of claim 7, wherein the capacitance is charged during each half cycle of the drive voltage.

9. The arrangement of claim 6, wherein the controller closes at least one of the switches for a time interval that determines an amplitude of the drive signal.

10. A method of electrically driving a piezoelectric transducer to mechanically oscillate a mirror at a mechanical resonant frequency, comprising the steps of:

a) electrically connecting an inductor to the transducer to form a resonant circuit having an electrical resonant frequency which is greater than the mechanical resonant frequency throughout variations in temperature, ageing and tolerances of the transducer and the inductor;

b) driving the resonant circuit with an electrical drive signal having a drive frequency which differs from the electrical resonant frequency by a parameter; and

c) adjusting the parameter to make the drive frequency correspond to the mechanical resonant frequency to compensate for said variations in the electrical resonant frequency.

11. The method of claim 10, wherein the transducer has an inherent capacitance, and wherein the inductor has inductance and is electrically connected in series with the transducer to form a series resonant circuit.

12. The method of claim 10, wherein the electrical resonant frequency is more than two times greater than the mechanical resonant frequency.

13. The method of claim 11, wherein the driving step includes forming a bridge circuit having two arms connected across a supply of DC voltage, each arm having a pair of actuatable switches and a junction therebetween;

and connecting the series resonant circuit between each junction of the arms.

14. The method of claim 13, wherein each switch is a transistor, and wherein the bridge circuit includes a diode connected between one of the switches of each arm and the junction of the respective arm.

15. The method of claim 13, wherein the driving step includes a controller for cyclically controlling actuation of the switches to convert the DC voltage to the drive voltage having an alternating current waveform with cycles.

16. The method of claim 15, wherein the controlling step closes at least one of the switches in each arm and opens at least another of the switches in each arm for a switching time period which determines said parameter to be adjusted.

17. The method of claim 16, wherein the capacitance is charged during each half cycle of the drive voltage.

18. The method of claim 15, wherein the controlling step includes controlling an amplitude of the drive voltage by controlling a time interval during which one of the switches is closed.