Frequency tunable resonant scanner

• US 6,803,561 B2
• Filed: 12/13/2002
• Issued: 10/12/2004
• Est. Priority Date: 08/05/1999
• Status: Expired due to Term

• Current Assignee: Microvision, Inc.
• Original Assignee: Microvision, Inc.
• Inventors: Dunfield, John C.
• Primary Examiner(s): LE, QUE TAN
• Application Number:
  US10/318,457
• Publication Number:
  US 20030122066A1
• Time in Patent Office: 669 Days
• Field of Search: 250/234, 250/235, 250/216, 250/221, 359/197-203, 359/207, 359/213
• US Class Current: 250/235
• CPC Class Codes: B81C 1/00293 maintaining a controlled atmosphere with processes not provided for in B81C1/00285
• 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 26/0841 the reflecting element being moved or deformed by electrostatic means
• CPC Class Codes: G02B 26/085 the reflecting means being moved or deformed by electromagnetic means
• CPC Class Codes: G02B 26/0858 the reflecting means being moved or deformed by piezoelectric means
• 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 26/105 with one or more pivoting mirrors or galvano-mirrors G02B26/101 takes precedence
• CPC Class Codes: G02B 27/017 Head mounted
• CPC Class Codes: G02B 27/0176 characterised by mechanical features
• 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

Abstract

A display apparatus includes a scanning assembly that scans about two or more axes, typically in a raster pattern. A plurality of light sources emit light from spaced apart locations toward the scanning assembly such that the scanning assembly simultaneously scans more than one of the beams. The scanning assembly is a resonant scanning assembly with a variable resonant frequency. The resonant frequency of the scanning assembly can be actively controlled by controlling partial pressure of fluids in a package containing the scanning assembly. In one embodiment, the increased partial pressure increases the mass of a scanning mirror, thereby changing the resonant frequency. In another embodiment, a gas absorbing material is coupled to a support arm that carries a scanning mirror. As the gas absorbing material absorbs gas, its physical properties change, thereby shifting the resonant frequency of the scanning assembly. Monitoring the resonant frequency relative to a desired frequency provides in error signal that can be used to frequency lock the resonant scanning assembly to an input signal.

Claims

1. A method of controlling a scanning motion of a MEMs device, comprising the steps of:

activating the MEMs device for periodic motion of a portion of the MEMs device relative to a reference point, the portion having a center of mass offset from the reference point by a selected distance;

monitoring the periodic motion of the MEMs device;

responsive to the monitored periodic motion of the MEMs device, identifying a deviation of the periodic motion from a desired periodic motion;

generating an error signal in response to the identified deviation; and

responsive to the error signal, changing the selected distance.

2. The method of claim 1 wherein the step of activating the MEMs device for periodic motion of a portion of the MEMs device includes applying an electrical driving signal to the MEMs device.

3. The method of claim 1 wherein the step of changing the selected distance includes adding mass to or removing mass from the portion of the MEMs device.

4. The method of claim 1 wherein the MEMs device includes a torsional member that supports the portion of the MEMs device and wherein the step of monitoring the periodic motion of the MEMs device includes monitoring torsional stress in the torsional member.

5. The method of claim 1 wherein the step of monitoring the periodic motion of the MEMs device includes optically detecting movement or position of the portion.

6. The method of claim 1 further comprising the steps of:

receiving an input scanning signal; and

determining from the received input scanning signal the desired periodic motion.