Torsional hinged device with improved coupling between a magnet mounted to said device and an electrical coil

A pivoting device such as a MEMS mirror provides improved coupling between a permanent magnet on the device and an adjacent electrical coil that may provide a drive force or position sensing. The improved coupling is obtained by forming a cavity in the coil structure. The cavity receives the permanent magnet such that the spacing between the magnet and the electrical windings or coil is at a minimum.

TECHNICAL FIELD

The present invention relates generally to the field of torsional hinged Micro Electro Mechanical Systems (MEMS) oscillating devices. More particularly, the invention relates to an arrangement to improve the coupling between a permanent magnet attached to the pivoting device and an electrical coil. The magnet and coil arrangement can be used to accurately sense the rotational position of the pivoting device, or alternately the arrangement can provide the drive power to pivot or oscillate the device.

BACKGROUND

Torsional hinged mirrors are now being used as scanning mirrors in laser printers to provide a beam sweep or scan of the image of a modulated light source across a photoresist medium, and as pointing mirrors for redirecting a light beam to one or more specific locations. Devices supported by torsional hinges, other than mirrors may also benefit from this invention. Torsional hinged devices that use silicon for the hinges provide excellent performance at a very advantageous cost and with a very long life, since material fatigue is almost non-existent in torsional hinge devices made of silicon. Magnetic coupling between a permanent magnet on a torsional hinged structure and an electrical coil positioned close to the permanent magnet may be used to provide a drive force to pivot or oscillate the device, or the electrical coil may generate an output signal as the magnet moves with respect to the coil. The output signal will be indicative of the rotational position of the torsional hinged device.

However, as will be appreciated by those skilled in the art, the drive force resulting from electrical signals applied to the electrical coil, or the sensed electrical signals generated as the permanent magnet moves with respect to the electrical coil diminishes as a function of the square of the distance between the magnet and the electrical coil.

Therefore, methods and structures that reduce this distance without a corresponding decrease in structural strength or an increase in complexity or cost would be advantageous.

SUMMARY OF THE INVENTION

The problem of reducing the distance between the permanent magnet and the associated electrical coil is generally solved or circumvented, and technical advantages are generally achieved, by the embodiments of the present invention which provide a pivoting device or assembly with improved coupling between a permanent magnet attached to the device and an electrical coil.

The assembly comprises an elongated hinge layer having a front side and a back side and a first end and a second end. The elongated hinge layer defines a pivoting structure comprising a pair of torsional hinges extending along a pivot axis, a magnet support area at a first location on the back side of the pivoting structure, and a functional support area at a second location of the pivoting structure. According to one embodiment of the invention, the magnet support area and the functional support area are spaced apart such that a functional surface such as a mirror may be on the front side, the back side, or even on both the front and back side, whereas according to another embodiment, the magnet and functional surface are back to back.

The pivoting structure is supported by the torsional hinges so that the structure pivots about the pivot axis. A permanent magnet is attached to the hinge layer at the magnet support area on the back side of the hinge layer and an electrical coil is positioned proximate to the permanent magnet such that a magnetic coupling exists between the two. The electrical coil structure comprises a coil support having a top surface that defines a cavity extending to a selected depth level. The coil support further defines a windings area having a multiplicity of electrical windings with the topmost winding at a level at about the selected depth of the cavity. A support structure supports the pivoting structure so that the permanent magnet attached to the hinge layer is located at least partially within the cavity.

The foregoing has broadly outlined the features of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages 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 embodiments disclosed may be readily utilized as a basis for modifying or designing other structures or processes for carrying out the same purpose of the present invention. It should also be realized by those skilled in the art that such constructions do not depart from the spirit or scope of the invention as set forth in the appended claims.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The making and using of the described 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 illustrative of specific ways to make and use the invention, and should not limit the scope of the invention.

Referring now toFIGS. 1A and 1Bthere is illustrated a pivoting device incorporating the teachings of the present invention. As shown, the device comprises an elongated hinge layer10defining a pivoting structure having first and second torsional hinge members14aand14bthat extend along a pivot axis shown as dotted line16. Torsional hinges14aand14bare attached to and support a functional oscillating device or area12such as, for example a mirror which may be located on the front side, or the back side or even both the front and back side. According to the embodiment ofFIG. 1torsional hinges14aand14balso support a connecting member18and a permanent magnet area20. An end portion22aof the hinge layer is supported by a coil support structure24. The elongated hinge layer includes a front side visible inFIGS. 1,2and3and a back side that is hidden in these figures. A permanent magnet26illustrated inFIGS. 2,3,4A,5A and5B is attached to the back side of the permanent magnet area20of the hinge layer10. An optional counterweight28may be attached to the front side of the permanent magnet area20to keep the moment center of the device on the pivot axis16. The end portion of22bof hinge layer10opposite coil support structure24may be supported by mechanical support, such as a pair of support structures30aand30b.Alternately, a single support structure could be used rather than the two structures indicated. Support structures30aand30bmay simply provide mechanical support, or alternately support structures30aand30bmay be piezoelectric elements that provide the energy to pivot the torsional hinge supported structure by expanding and shrinking out of phase as indicated by arrows32aand32b.

As shown in the Figures, the coil support24is preferably a molded or machined plastic spool shaped structure having a top member34with a top surface34aand a bottom surface34b. As is clearly seen inFIGS. 2 and 3, the top member34is connected to a bottom member36that also includes a top surface36aby a core member38. A cavity40is formed in the top surface34aof the top member34to provide space for the permanent magnet26. Coil support24also defines a windings area42between the bottom surface34aof top member34and the top surface36aof bottom member36. A multiplicity of electrically conductive windings44are located in the windings area42by repeatedly winding a wire or electrical conductor around the core member38. The two endings44aand44bof the wire are shown inFIGS. 1 and 4B, and as will be appreciated by those skilled in the art, the coil may function as a drive coil by connecting an alternating electrical voltage across the two endings44aand44bto create a magnetic field that will interact with the permanent magnet26. This interaction will cause pivoting movement of the magnet and the other portions of the torsional hinge supported pivoting device defined in hinge layer10. Alternatively the windings or coil may function as a sensing coil that provides an electrical output signal that indicates the rotational position of the magnet as it pivots about the torsional hinge. Permanent magnet26of the preferred embodiment illustrated byFIGS. 1,2and3is rectangular shaped with a North-pole/South-pole orientation that is orthogonal to the pivot axis16and in a plane parallel to the hinge layer. It will however, be appreciated that the permanent magnet may also have a North-pole/South-pole orientation that is perpendicular to the plane of the hinge layer as illustrated by the square and disk shaped permanent magnets26aand26bofFIG. 2.

As will be appreciated by those skilled in the art, the magnetic coupling between a permanent magnet and an electrical coil varies as the square of the distance between the two. Therefore, for the best magnetic coupling, it is important to locate the permanent magnet26close to coil or conductive windings44. A first technique to decrease the distance, according to the invention, is to form cavity40in the top member34as discussed above and as is clearly shown inFIGS. 2,3and7. However, it has been found that although the distance can be decreased and the magnetic coupling improved by forming a cavity to receive the permanent magnet, such as shown inFIG. 7, for some applications further improvement is needed. Therefore, referring toFIGS. 3,4A and4B there is shown an arrangement that further improves the magnetic coupling. Referring to4B, there is shown a coil support24and conductive windings44according to the preferred embodiment of the invention. As shown in theFIGS. 2,3,4A and4B a cavity40that is formed in spool shaped coil support24is rectangular and has a first dimension as represented by double headed arrow46inFIGS. 3 and 4Bthat can be selected to be either parallel to or perpendicular to the pivoting axis16.FIG. 4Bshows an embodiment wherein the first dimension46of cavity40is perpendicular to the pivoting axis16, and is equal to the thickness of the core member38of coil support structure24. Consequently, the top most windings44do not have any core material between the magnet and the windings in the cavity dimension46. Note especially areas48ofFIGS. 3,4A (right side) and4B. Alternately, the first dimension46of cavity40may be only slightly less than the core thickness such that the remaining material is reduced, but not completely removed. Thus, the pole ends of the permanent magnet20are still located much closer to the windings. The difference is clearly illustrated inFIG. 4Awhich shows on the left side a cavity with a first dimension that is slightly less than the core material thickness such that the cavity does not extend completely through the core material. Consequently, the remaining material is reduced. The right side ofFIG. 4Ashows that forming the cavity with a first dimension that is equal to the core thickness, removes such that the top most windings are exposed as shown at area48.FIG. 4Aalso illustrates that the distance d2(i.e. when the first cavity dimension is equal to the core) between the windings and the end of the magnet end is smaller than the distance d1, (where the core material is either thinned or not changed).

FIGS. 5A and 5Billustrate the rotations of the permanent magnet26and counterweight28around pivot axis16of the embodiment ofFIG. 1. In a preferred embodiment the maximum angle of rotation is about 8° as shown inFIG. 5B.

Referring toFIGS. 6,6A and7there is shown another embodiment of the invention that incorporates a cavity40that does not remove sufficient core member material to expose the top most core windings. Elements of the embodiment ofFIGS. 6,6A and7that are the same as discussed above with respect to the embodiment ofFIG. 1carry the same reference number. As shown, there is a pivoting device that includes improved coupling between a permanent magnet26(FIGS. 6A and 7), and an electrical coil44wound on a coil support structure24. The device includes an elongated hinge layer having a front side and a back side and first and second torsional hinge members14aand14bthat extend along a pivot axis16. Each of the torsional hinges, such as hinge14bformed in said hinge layer include a first end attached to a function support area or member and a second end attached to a support structure. The support structure may simply provide mechanical support, or may comprise two pairs of piezoelectric elements30aand30bfor providing a drive force to pivot the device. The function support member typically will include a mirror52attached to the front side of the functional support member50. The permanent magnet26is attached to the back side of the functional support area or member50. The spool shaped coil support structure24includes a top member34having a top surface34aand a bottom surface34b. Also included is a bottom member36with a top surface36a. A core member38connects the top member34and the bottom member36. A cavity40of a selected depth is defined in the top surface34aof a top member34, and a wire or conductor is continuously wrapped around the core member38to form windings44between the bottom surface34bof top member34and the top surface36aof bottom member36. The selected depth of cavity40extends into the top member36and core member38to a level that is preferably below the top most windings.