Frequency tunable resonant scanner with auxiliary arms

• US 6,535,325 B2
• Filed: 04/20/2001
• Issued: 03/18/2003
• Est. Priority Date: 08/05/1999
• Status: Expired due to Fees

• Current Assignee: Microvision, Inc.
• Original Assignee: Microvision, Inc.
• Inventors: Helsel, Mark P., Wine, David W.
• Primary Examiner(s): Epps, Georgia
• Assistant Examiner(s): Spector, David N.
• Application Number:
  US09/839,850
• Publication Number:
  US 20010033410A1
• Time in Patent Office: 697 Days
• Field of Search: 359/290, 359/291, 359/292, 359/223, 359/224
• US Class Current: 359/291
• CPC Class Codes: G02B 26/0833 the reflecting element being a micromechanical device, e.g. a MEMS mirror, DMD G02B26/0825 takes precedence; micromechanical devices in general B81B
• CPC Class Codes: G02B 26/101 with both horizontal and vertical deflecting means, e.g. raster or XY scanners colour television using laser beams scanning a display screen H04N9/3129
• CPC Class Codes: G02B 27/017 Head mounted
• CPC Class Codes: G02B 27/0176 characterised by mechanical features

Abstract

A MEMs scanning device has a variable resonant frequency. In one embodiment, the MEMs device includes a flexible arm that extends from an oscillatory body. An electrical field applies a force to the flexible arm, thereby bending the flexible arm to change the moment of inertia of the oscillatory body and a secondary mass carried by the flexible arm. The shifted combined center of mass changes the resonant frequency of the MEMs device. In another embodiment, an absorptive material forms a portion of a torsional arm that supports the oscillatory body. The mechanical properties of the absorptive material can be varied by varying the concentration of a gas surrounding the absorptive material. The varied mechanical properties change the resonant frequency of the scanning device. A display apparatus includes the scanning device and the scanning device scans about two or more axes, typically in a raster pattern. Various approaches to controlling the frequency responses of the scanning device are described, including active control of MEMs scanners and passive frequency tuning.

Claims

1. A microelectromechanical resonant device having a resonant frequency of oscillation corresponding to a desired application, comprising:

a base;

a movable body coupled to the base for resonant motion relative to the base about a pivot axis, the base having a mass and a geometry;

one or more torsional arms extending between the base and the movable body and aligned with the pivot axis that define the pivot axis; and

a flexible member extending from the movable body, the flexible member being configured to flex in response to movement of the movable body about the pivot axis, the flexible member being coupled to the movable body at a location offset from the pivot axis, wherein the dimensions and material of the one or more torsional arms, flexible member, the mass and the geometry are selected to produce the resonant frequency corresponding to the application.

2. The microelectromechanical resonant device of claim 1 wherein the movable body includes a reflective coating oriented to reflect light incident on the movable body along a path radial to the pivot axis.

3. The microelectromechanical resonant device of claim 1 wherein the movable body includes at least four edges, and wherein the torsional arms are coupled to the movable body at a first two of the edges and the movable arms are coupled to the movable body at a second two of the edges different from the first two edges.

4. The microelectromechanical resonant device of claim 1 wherein the one or more torsional arms include a pair of torsional arms coupled to the movable body.

5. The microelectromechanical resonant device of claim 4 wherein the torsional arms are coupled on opposite sides of the movable body and define the pivot axis.

6. A microelectromechanical resonant device, comprising:

a base;

a movable body coupled to the base for resonant motion relative to the base about a pivot axis; and

a flexible member extending from the movable body, the flexible member being configured to flex in response to movement of the movable body about the pivot axis, the flexible member being coupled to the movable body at a location offset from the pivot axis, wherein the movable body and flexible member form an integral body.

7. A microelectromechanical resonant device, comprising:

a base;

a movable body coupled to the base for resonant motion relative to the base about a pivot axis; and

a flexible member extending from the movable body, the flexible member being configured to flex in response to movement of the movable body about the pivot axis, the flexible member being coupled to the movable body at a location offset from the pivot axis, wherein the base, flexible member, and movable body are all formed from a semiconductor material.

8. An optical scanner comprising:

an oscillatory body;

a body support coupled to the oscillatory body and configured to permit the oscillatory body to move about a pivot axis;

a flexible arm coupled to the oscillatory body at a location offset from the pivot axis, the flexible arm being configured to flex in response to movement of the oscillatory body about the pivot axis, wherein flexing of the flexible arm exerts a force on the movable body that opposes movement of the movable body about the pivot axis; and

a sensor carried by the flexible member and responsive to flexing of the flexible member to produce a sense signal indicative of an angular orientation, velocity or acceleration of the oscillatory body relative to the pivot axis.

9. The optical scanner of claim 8 wherein the body support includes a pair of torsional arms coupled to the oscillatory body and configured to define the pivot axis.

10. The optical scanner of claim 8 wherein the torsional arms are coupled on a first two sides of the oscillatory body and the flexible member is coupled to the oscillatory body on a third side different from the first two sides.

11. The optical scanner of claim 8 wherein the oscillatory body is coupled to a substrate and wherein the oscillatory body includes a first electrode and the substrate includes a second electrode, the first and second electrodes being positioned to produce a force on the oscillatory body having a component oriented to produce pivoting of the oscillatory body about the pivot axis.

12. An optical scanner comprising:

an oscillatory body;

a body support coupled to the oscillatory body and configured to permit the oscillatory body to move about a pivot axis;

a flexible arm coupled to the oscillatory body at a location offset from the pivot axis, the flexible arm being configured to flex in response to movement of the oscillatory body about the pivot axis, wherein flexing of the flexible arm exerts a force on the movable body that opposes movement of the movable body about the pivot axis wherein the oscillatory body and the flexible arm are integrally formed from a common material.

13. The optical scanner of claim 12 wherein the body support includes a pair of torsional arms coupled to the oscillatory body and configured to define the pivot axis.

14. The optical scanner of claim 12 wherein the torsional arms are coupled on a first two sides of the oscillatory body and the flexible member is coupled to the oscillatory body on a third side different from the first two sides.

15. The optical scanner of claim 12 wherein the oscillatory body is coupled to a substrate and wherein the oscillatory body includes a first electrode and the substrate includes a second electrode, the first and second electrodes being positioned to produce a force on the oscillatory body having a component oriented to produce pivoting of the oscillatory body about the pivot axis.