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  Mems scanner with dual magnetic and capacitive driveUSPTO Application #: 20060152106Title: Mems scanner with dual magnetic and capacitive drive Abstract: A MEMS scanning device includes more than one type of actuation. In one approach capacitive and magnetic drives combine to move a portion of the device along a common path. In one such structure, the capacitive drive comes from interleaved combs. In another approach, a comb drive combines with a pair of planar electrodes to produce rotation of a central body relative to a substrate. In an optical scanning application, the central body is a mirror. In a biaxial structure, a gimbal ring carries the central body. The gimbal ring may be driven by more than one type of actuation to produce motion about an axis orthogonal to that of the central body. In another aspect, a MEMS scanning device is constructed with a reduced footprint. (end of abstract)
Agent: Microvision, Inc. - Bothell, WA, US Inventors: Jun Yan, Vincenzo Casasanta, Selso H. Luanava, Hakan Urey, Frank A. DeWitt, Clarence T. Tegreene, Christopher A. Wiklof USPTO Applicaton #: 20060152106 - Class: 310309000 (USPTO) The Patent Description & Claims data below is from USPTO Patent Application 20060152106. Brief Patent Description - Full Patent Description - Patent Application Claims
CROSS REFERENCES TO RELATED APPLICATIONS [0001] The present application depends from Provisional Patent Application No. 60/423,584 entitled MEMS DRIVE STRUCTURES, by Yan et al., filed Nov. 4, 2002. TECHNICAL FIELD [0002] The present invention relates to microelectromechanical system (MEMS) devices and, more particularly, to MEMS devices with motive forces. BACKGROUND OF THE INVENTION [0003] A variety of approaches to actuating MEMS devices have been described. Some approaches use magnetic fields to pivot a moving member relative to a substrate. One such approach is described in U.S. Pat. No. 5,912,608 to Asada, entitled PLANAR TYPE ELECTROMAGNETIC ACTUATOR and U.S. Pat. No. 5,767,666 to Asada et al., entitled PLANAR TYPE ELECTROMAGNETIC ACTUATOR INCORPORATING A DISPLACEMENT DETECTION FUNCTION, each of which is incorporated herein by reference. Other approaches use electrostatic forces to pivot a moving member or to drive a sliding piece relative to a substrate. Examples of such devices can be found in U.S. Pat. No. 5,629,790 to Neukermans et al., entitled MICROMACHINED TORSIONAL SCANNER and U.S. Pat. No. 5,867,297 to Kiang et al., entitled APPARATUS AND METHOD FOR OPTICAL SCANNING WITH AN OSCILLATORY MICROELECTROMECHANICAL SYSTEM, each of which is incorporated herein by reference. [0004] Among the applications for such MEMS devices are scanning beam imaging, including image acquisition and display. In image acquisition, such MEMS devices typically include a mirror that pivots to sweep a beam through a prescribed scanning field. A detector in the imaging device collects reflected light and produces an electrical signal in response. A processor then identifies image information from the electrical signal. Equipment incorporating such devices can be found in barcode readers, image capture systems, confocal imagers, and other applications. [0005] Scanning beam displays, such as that described in U.S. Pat. No. 5,467,104 of Furness et al., entitled VIRTUAL RETINAL DISPLAY, which is incorporated herein by reference, are one approach to overcoming many limitations of conventional displays. As shown diagrammatically in FIG. 1, in one embodiment of a scanned beam display 40, a scanning source 42 outputs a scanned beam of light that is coupled to a viewer's eye 44 by a beam combiner 46. In some scanned displays, the scanning source 42 includes a scanner, such as scanning mirror or acousto-optic scanner, that scans a modulated light beam onto a viewer's retina. In other embodiments, the scanning source may include one or more light emitters that are rotated through an angular sweep. [0006] The scanned light enters the eye 44 through the viewer's pupil 48 and is imaged onto the retina 59 by the cornea. In response to the scanned light the viewer perceives an image. In another embodiment, the scanned source 42 scans the modulated light beam onto a screen that the viewer observes. One example of such a scanner suitable for either type of display is described in U.S. Pat. No. 5,557,444 to Melville et al., entitled MINIATURE OPTICAL SCANNER FOR A TWO-AXIS SCANNING SYSTEM, which is incorporated herein by reference. [0007] Sometimes such displays are used for partial or augmented view applications. In such applications, a portion of the display is positioned in the user's field of view and presents an image that occupies a region 43 of the user's field of view 45, as shown in FIG. 2A. The user can thus see both a displayed virtual image 47 and background information 49. If the background light is occluded, the viewer perceives only the virtual image 47, as shown in FIG. 2B. [0008] As shown diagrammatically in FIG. 3, the scanning source 42 includes an optical source 50 that emits a beam 52 of modulated light. In this embodiment, the optical source 50 is an optical fiber that is driven by one or more light emitters, such as laser diodes (not shown). A lens 53 gathers and focuses the beam 52 so that the beam 52 strikes a turning mirror 54 and is directed toward a horizontal scanner 56. The horizontal scanner 56 scans the beam 52 periodically in a sinusoidal fashion. The horizontally scanned beam then travels to a vertical scanner 58 that scans periodically to sweep the horizontally scanned beam vertically. For each angle of the beam 52 from the scanners 56 and 58, an exit pupil expander 62 converts the beam 52 into a set of beams 63. Eye coupling optics 60 collect the beams 63 and form a set of exit pupils 65. The exit pupils 65 together act as an expanded exit pupil for viewing by a viewer's eye 44. One such expander is described in U.S. Pat. No. 5,701,132 of Kollin et al., entitled VIRTUAL RETINAL DISPLAY WITH EXPANDED EXIT PUPIL, which is incorporated herein by reference. [0009] Returning to the description of scanning, as the beam scans through each successive location in the beam expander 62, the beam color and intensity is modulated in a fashion to be described below to form a respective pixel of an image. By properly controlling the color and intensity of the beam for each pixel location, the display 40 can produce the desired image. [0010] Simplified versions of respective electrical waveforms for vertical and horizontal scanning are shown in FIGS. 4A and 4B. Responsive to the electrical waveforms, the beam traces the pattern 68 shown in FIG. 5 in an image plane, such as the plane of beam expander 62 of FIG. 3. Though FIG. 5 shows only eleven lines of image, one skilled in the art will recognize that the number of lines in an actual display will typically be much larger than eleven. [0011] As can be seen by comparing the actual scan pattern 68 to a desired raster scan pattern 70, the actual scanned beam 68 can be "pinched" at the outer edges of the beam expander 62. That is, in successive forward and reverse sweeps of the beam, the pixels near the edge of the scan pattern are unevenly spaced. This uneven spacing can cause the pixels to overlap or can leave a gap between adjacent rows of pixels. Moreover, because the image information is typically provided as an array of data, where each location in the array corresponds to a respective position in the ideal raster pattern 70, the displaced pixel locations can cause image distortion. Some approaches to treating such distortions or image imperfections are described in U.S. Pat. No. 6,140,979 to Gerhard, et al. entitled SCANNED DISPLAY WITH PINCH TIMING AND DISTORTION CORRECTION, which is incorporated herein by reference. [0012] For a given refresh rate and a given wavelength, the number of pixels per line is determined in the structure of FIG. 3 by the mirror scan angle .theta. and mirror dimension D perpendicular to the axis of rotation. For high resolution, it is therefor desirable to have a large scan angle .theta. and a large mirror. However, larger mirrors and scan angles typically correspond to lower resonant frequencies. A lower resonant frequency provides fewer lines of display for a given period. Consequently, a large mirror and larger scan angle may produce unacceptable refresh rates for many MEMS scanners. OVERVIEW OF THE INVENTION [0013] In one embodiment, a MEMS device includes a moving portion, a first electromagnetic field based actuator coupled to drive the moving portion along a first path, and second electromagnetic field based actuator coupled to drive the moving portion along the first path, wherein the first and second electromagnetic actuators to utilize different types of electromagnetic interaction to drive the moving portion along the first path. In one embodiment, the first electromagnetic actuator is an electrostatic actuator and the second electromagnetic actuator is a magnetic actuator. In another embodiment, the first electromagnetic actuator is electrostatic actuator and the second electromagnetic actuator is a comb-drive actuator. [0014] In one embodiment, a MEMS device includes a coil carried by a moving member that interacts with a static magnetic field to provide a drive force along a selected path. The MEMS device also includes a capacitor plate aligned to provide a drive force along the selected path. A drive circuit actuates both the coil and the capacitor plate to produce a joint drive force that is a combination of the drive force from the coil and the drive force from the capacitor plate. [0015] In one embodiment, the scanning mechanism includes a biaxial scanner that uses a single mirror to provide both horizontal and vertical movement of one or more beams. The biaxial scanner is formed from a gimbal structure having a central mirror portion and a surrounding portion that carries the central mirror portion. A substrate carries the surrounding portion. The central mirror portion is driven by one or more of electrostatic and magnetic forces. The surrounding portion is driven by electrostatic and magnetic forces. [0016] In another approach, a biaxial MEMS scanner utilizes magnetically and capacitively generated forces to drive the central mirror portion. In still other approaches, a single axis scanner includes magnetic and capacitive actuators that jointly drive a central body about an axis. [0017] In other embodiments, other types of MEMS devices, such as gyroscopes include magnetic and capacitive actuators that jointly drive a central body about an axis. In another embodiment, a MEMS device includes a capacitive plate type of actuator and a comb drive actuator that jointly drive a central body. The comb drive may be a push-pull type as described in WO025170A1: MICROMECHANICAL COMPONENT COMPRISING AN OSCILLATING BODY of Schenk et al or may be an offset comb drive such as that described in Conant, Nee, Lau and Muller; "A Fast Flat Scanning Micromirror", 2000 Solid-State Sensor and Actuator Workshop, Hilton Head, S.C., June 2000, pp. 6-9; and R. Conant, J. Nee, K. Lau, R. Muller, "Dynamic Deformation of Scanning Micromirrors," presented at IEEE/LEOS Optical MEMS 2000, Kauai, Hi., August 2000. [0018] In one embodiment, a display incorporates a MEMS device that includes a plurality of actuators of different types. [0019] In one embodiment, the MEMS scanner is a resonant scanner that has a characteristic resonant frequency. Where the resonant frequency does not match the rate at which image data is supplied, data may be clocked into and out of the a buffer at different rates. [0020] Alternatively, the MEMS scanner may have a tunable resonant frequency that can be adjusted to conform to the rate at which image data is provided. In one embodiment of such a MEMS scanner, described in U.S. Pat. No. 6,245,590 to Wine, et al., entitled FREQUENCY TUNABLE RESONANT SCANNER AND METHOD OF MAKING, which is incorporated herein by reference, a primary oscillatory body carries a secondary mass that can move relative to the primary oscillatory body, thereby changing the rotational inertia. The changed rotational inertia changes the resonant frequency and can be controlled by an applied control signal. By monitoring movement of the oscillatory body and comparing the monitored movement to the desired scanning frequency, a control circuit generates the appropriate control signal to synchronize the scanning frequency to the input data rate. Continue reading... Full patent description for Mems scanner with dual magnetic and capacitive drive Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Mems scanner with dual magnetic and capacitive drive patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. Each week you receive an email with patent applications related to your keywords. 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