Frequency tunable resonant scanner

• US 20020014579A1
• Filed: 09/06/2001
• Published: 02/07/2002
• Est. Priority Date: 08/05/1999
• Status: Active Grant

• Current Assignee: Microvision, Inc.
• Original Assignee: Microvision, Inc.
• Inventors: Dunfield, John C.
• Granted Patent: US 6,525,310 B2
• Time in Patent Office: Days
• US Class Current: 250/216
• 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 microelectromechanical scanner, comprising:

a sealed body including at least a portion of a substrate;

an oscillatory body within the sealed body and carried by the substrate, the oscillatory body being coupled to the substrate for periodic movement;

a selected gas within the sealed body, the selected gas having a partial pressure responsive to an input signal; and

a coupling arm coupled between the oscillatory body and the substrate, the coupling arm including a first section having physical parameters responsive to gas pressure within the sealed body, the coupling arm being configured to define a resonant frequency of oscillation of the oscillatory body that is a function of the physical parameters;

2. The microelectromechanical scanner of claim 1 wherein the input signal includes an electrical signal.

3. The microelectromechanical scanner of claim 2 wherein the first section includes a polymer.

4. The microelectromechanical scanner of claim 1 further comprising a reflective layer carried by the oscillatory body.

5. 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;

an enclosure surrounding the movable body and at least a portion of the base;

a flexible member extending between the movable body and the base, the flexible member including a gas absorbing material, the gas absorbing material having material properties responsive to a partial pressure of a selected gas within the enclosure; and

an electrically activated pressure controller, coupled to the enclosure and responsive to an electrical signal to increase or decrease the partial pressure of the gas.

6. The microelectromechanical resonant device of claim 5 wherein the pressure controller includes a piezoelectric material incorporated into the package.

7. The microelectromechanical resonant device of claim 5 wherein the movable body and flexible member form an integral body.

8. The microelectromechanical resonant device of claim 5 wherein the base and movable body are both formed from a semiconductor material.

9. The microelectromechanical resonant device of claim 5 wherein the pressure controller includes an input terminal, an output terminal, a resistive material interposed therebetween, and an outgassing nodule thermally coupled to the resistive material, the outgassing nodule being responsive to heat energy to outgas the selected gas.

10. The microelectromechanical resonant device of claim 5 further comprising a frame interposed between the base and the movable body, the frame being coupled to the base and configured for movement about a second axis substantially orthogonal to the pivot axis.

11. 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 container containing the oscillatory body, the body support, and a selected fluid;

a movable mass carried by the oscillatory body and offset from the pivot axis, the movable mass being of a type that absorbs the selected fluid; and

a source of the selected fluid coupled to or within the container, the source of the selected fluid being responsive to an electrical signal to increase or decrease the concentration of the selected fluid within the container.

12. The optical scanner of claim 11 further comprising:

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

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.

13. The optical scanner of claim 12 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.

14. The optical scanner of claim 11 wherein the oscillatory body and the movable mass are integrally formed from a common material.

15. The optical scanner of claim 14 wherein the common material is a semiconductor.

17. The resonant scanning apparatus of claim 16 wherein the second body and the first body are integrally formed from a common material.

18. The resonant scanning apparatus of claim 16 further comprising a torsional arm extending between the first and second bodies.

19. The resonant scanning apparatus of claim 16 wherein the input is a pressure input, further comprising a pressure source configured to apply pressure to the variable mass.

20. The resonant scanning apparatus of claim 16 wherein the input is an electrical input, further comprising:

an electrical signal source electrically coupled to the variable mass in response to a control signal.

21. The resonant scanning apparatus of claim 20 further comprising a motion sensor coupled to detect relative motion of the first and second bodies, the motion sensor being operative to produce the control signal in response to the detected relative motion.

16. A resonant scanning apparatus having a controllable resonant frequency, comprising:

a first body;

a second body coupled to the first body, the first and second bodies being sized and configured for relative motion at a first resonant frequency; and

a variable mass coupled to one of the first and second bodies, the variable mass being positioned to produce a force on the first or second body, wherein the first and second bodies are responsive to the force to move at a second resonant frequency different from the first resonant frequency, the variable mass being responsive to an input to increase or decrease in mass while the first and second bodies are in relative motion.

22. 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.

23. The method of claim 22 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.

24. The method of claim 22 wherein the step of changing the selected distance includes adding mass to or removing mass from the portion of the MEMs device.

25. The method of claim 22 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.

26. The method of claim 22 wherein the step of monitoring the periodic motion of the MEMs device includes optically detecting movement or position of the portion.

27. The method of claim 22 further comprising the steps of:

receiving an input scanning signal; and

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

29. The method of claim 28 wherein the step of detecting the resonant frequency of the MEMs device includes monitoring variation in selected electrical properties of the MEMs device.

30. The method of claim 28 wherein the periodic movement of the MEMs device is about a pivot axis and wherein the step of varying the resonant frequency of the MEMs device includes varying the center of mass of the MEMs device relative to the pivot axis.

31. The method of claim 28 wherein varying the center of mass of the MEMs device relative to the pivot axis includes increasing or decreasing the mass of a portion of the MEMs device.

32. The method of claim 31 wherein the MEMs device includes a mirror body that moves periodically and wherein increasing or decreasing the mass of a portion of the MEMs device includes increasing or decreasing the mass of the mirror body.

33. The method of claim 28 wherein the step of scanning the light beam with the resonant MEMs device includes:

directing the beam of light at a moving portion of the MEMs device; and

reflecting the beam of light with the moving portion.

34. The method of claim 28 wherein the step of detecting the resonant frequency of the MEMs device and the step of synchronizing the MEMs device to the synchronization signal by varying the resonant frequency of the MEMs device are substantially simultaneous.

36. The MEMs device of claim 36 wherein the variable mass is a gas absorptive material.

28. A method of scanning a light beam in response to a synchronization signal, comprising the steps of:

receiving the synchronization signal having a synchronization frequency;

activating a resonant MEMs device for periodic movement at a resonant frequency;

detecting the resonant frequency of the MEMs device;

synchronizing the MEMs device to the synchronization signal by varying the resonant frequency of the MEMs device; and

scanning the light beam with the resonant MEMs device at the varied resonant frequency.

35. A MEMs device having an electrically controllable resonant frequency, comprising an oscillatory body configured for periodic movement relative to a reference point, the oscillatory body including a primary portion and a secondary portion that together define a center of mass of the oscillatory body that follows a movement path relative to the reference point, wherein the secondary portion includes a variable mass, and wherein a change in the variable mass of the secondary portion varies the movement path of the center of mass.