Active tuning of a torsional resonant structure

• US 6,384,406 B1
• Filed: 03/23/2001
• Issued: 05/07/2002
• 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): ALLEN, STEPHONE B
• Application Number:
  US09/816,804
• Publication Number:
  US 20020020810A1
• Time in Patent Office: 410 Days
• Field of Search: 250/234-236, 359/198, 359/199, 359/212, 359/221, 359/223-226, 359/290, 359/872, 316/308, 316/309
• US Class Current: 250/234
• 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 26/10 Scanning systems
• 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: G09G 2300/0469 Details of the physics of pixel operation
• CPC Class Codes: G09G 3/025 with scanning or deflecting the beams in two directions or dimensions
• CPC Class Codes: G09G 3/346 based on modulation of the reflection angle, e.g. micromirrors micromirrors devices per se G02B26/0833
• CPC Class Codes: G09G 5/005 Adapting incoming signals to the display format of the display terminal
• CPC Class Codes: Y10S 359/904 Micromirror

Abstract

A MEMs scanning device has a variable resonant frequency. In one embodiment, the MEMs device includes a flexible arm that extends from a oscillatory body. An electrical field applies a force to the flexible arm, thereby bending the flexible arm to shift the moment of inertia of the oscillatory body and a secondary mass carried by the flexible arm. The shifted moment of inertia 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. 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 movable mass carried by the oscillatory body and offset from the pivot axis, the movable mass being responsive to an electrical signal to move radially relative to the pivot axis;

a sensor oriented to detect motion of the oscillatory body, the sensor being operative to produce a sense signal indicative of the detected motion; and

an electronic control circuit having an input terminal coupled to the sensor and an output terminal coupled to the movable mass, electronic control circuit being responsive to the sense signal to produce the electrical signal.

2. The optical scanner of claim 1 wherein the electronic control circuit includes an error detection circuit having a first input terminal for receiving a reference signal and a second input terminal coupled to receive the sense signal, the error detection circuit being operative to produce the electrical signal as a function of a difference between the sense signal and the reference signal.

3. The optical scanner of claim 1 wherein the movable mass includes a first electrode and the oscillatory body includes a second electrode, the first and second electrodes being oriented to produce an electric field having a component radial to the pivot axis.

4. The optical scanner of claim 1 wherein the oscillatory body and the movable mass are integrally formed from a common material.

5. The optical scanner of claim 4 wherein the common material is a semiconductor.