Patent Application
20070064293
The present invention relates to resonant torsional hinged mirrors and more particularly to the adjusting of the mirror resonant frequency after assembly of the mirror.
In recent years, MEMS (Micro Electro Mechanical Systems) torsional hinged mirror structures have made significant strides as replacements for spinning polygon mirrors used as the engine for high speed printers and some types of display systems. Such torsional hinged mirror structures have certain advantages over the spinning polygon mirrors including lower cost and weight. However, every new technology has its own set of problems and using torsional hinged mirrors in precision applications is no exception.
One problem area is the manufacturing of such torsional hinged mirrors with a specific resonant frequency. The silicon components used to fabricate such torsional hinged mirrors may be manufactured from silicon wafers using semiconductor manufacturing process steps and methods. These silicon components are then combined with magnets to complete the assembly of many mirrors. Further, the resonant frequency of each mirror of the group of mirrors will likely be within a specified range of frequencies. Unfortunately, each of the assembled mirrors will not have the same resonant frequency because of variations in the silicon processing, silicon wafer thickness, and the exact mass distribution of the composite structure including the magnet size and density as well as variations in adhesive bond lines.
Therefore, it will be appreciated that a method of adjusting the resonant frequency of an assembled torsional hinged mirror could be advantageous.
These and other problems are generally solved or circumvented and technical advantages are generally achieved by embodiments of the present invention, which provides a method of adjusting the resonant frequency of an assembled torsional hinged structure (such as a mirror). The method comprises the step of mounting the torsional hinged device to a support structure, and providing a drive mechanism proximate the mounted torsional hinged device to oscillate the torsional hinged device at its resonant frequency. The resonant frequency is monitored, and is then lowered to within a selected band of frequencies by selectively adding a material to a surface (preferably a back surface) of the device or mirror. According to one embodiment, the material is a material selected from the group consisting of printers ink, epoxy adhesive, solder balls, or any other material that will adhere the back side or edge of the mirror.
The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter, which form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures or processes for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims.
For a more complete understanding of the present invention, and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawing, in which:
The making and using of the presently preferred embodiments are discussed in detail below. It should be appreciated, however, that the present invention provides many applicable inventive concepts that can be embodied in a wide variety of specific contexts. The specific embodiments discussed are merely illustrative of specific ways to make and use the invention, and do not limit the scope of the invention.
Referring now to
Referring now to
As has been briefly discussed, device 10 preferably operates at resonance, and represents one of a multiplicity of torsional hinged devices (especially mirrors) preferably formed from a single crystal silicon wafer using semiconductor processing methods and steps. However, although the devices can be formed so that the resonant frequency falls within a range or band of frequencies, individual devices formed in the wafer will likely still have different resonant frequencies because of variations in fabrication steps and in assembling the device or mirror structure. For example, the thickness of the hinge plate or layer may vary as well as the width of the torsional hinge. Likewise, the thickness of the mirror or front layer and/or the truss layer may also vary in thickness because of variations in the etching process. If the device is a mirror, a reflective coating may be added to the front surface. The thickness of the deposited reflective coating may also slightly vary at different locations on the surface of the mirror and from mirror to mirror. The geometry and density of the permanent magnet may include variations that cause the mass moment of the assembled structure to vary. Also, if the device elements are bonded together, the thickness of the adhesive may vary over the bonded surface.
Studies indicate that these variations can produce frequency variations of ±3% or greater. Unfortunately, systems which use resonant scanning mirrors, such as laser printers or laser projection displays, have constraints on the operating frequency range of the resonant device that are more stringent than ±3%.
Furthermore, because these resonant devices are high-Q devices, the frequency of the drive signal must be very close to the resonant frequency of the device, or the sweep amplitude of the device may be significantly reduced. Consequently, since only a narrow range of resonant frequencies will be acceptable, the yield of the usable resonant devices will be low. If the yield is too low, there is little or no chance of using a resonant device in a commercial application.
The present invention provides a simple but elegant solution to this problem. More specifically referring to
Alternately, a fine coating can be applied by an atomizer or spray. Suitable materials include printer ink, epoxy, adhesive, solder balls, etc.
Although the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims.
Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, composition of matter, methods and steps described in the specification. As one of ordinary skill in the art will readily appreciate from the disclosure of the present invention, processes, compositions of matter, methods, or steps, presently existing or later to be developed, that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized according to the present invention. Accordingly, the appended claims are intended to include within their scope such processes, compositions of matter, methods, or steps.
