Electricity: electrical systems and devices – Control circuits for electromagnetic devices – For relays or solenoids
Reexamination Certificate
2000-11-28
2004-09-07
Toatley, Jr., Gregory J. (Department: 2836)
Electricity: electrical systems and devices
Control circuits for electromagnetic devices
For relays or solenoids
Reexamination Certificate
active
06788520
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to microelectromechanical systems (MEMS). More particularly, it relates to sensing a control state of MEMS devices.
BACKGROUND ART
Previous patents and publications have described fiber-optic switches that employ moveable micromirrors that move between two positions. An example is shown in FIG.
1
. Some of the prior art also employs electrostatic clamping of these mirrors at one or more of its two positions. For example, optical crossbar switches consisting of a series of moveable mirrors that are magnetically actuated are known in the art. The mirrors can be electrostatically clamped either in the horizontal position to the substrate or in the vertical position to the sidewalls of a separate chip. In the vertical position, the mirrors deflect light from an input fiber into an output fiber.
Previous work has described optical switches that use mirrors that are actuated between several discrete positions for switching light. These optical switches may rely on electrostatic comb drives to rotate the mirror. An electrostatic comb drive uses electrostatic forces between interdigitated fixed and movable comb members to rotate a device such as a mirror. It is possible to determine the relative angular position of the movable comb drive member with respect to the fixed comb drive member by measuring the capacitance between them. Unfortunately, comb drives have a limited range of angular movement and the capacitance may change only slightly over a desired range of discrete positions of the mirror. If each discrete position represents a different control state of an optical switch, it is difficult to correlate the capacitance measurement from the comb drive to the control state of the switch. Furthermore, not all optical switches use comb drive actuators.
Some of the prior art approaches require electrostatic clamping of a mirror structure to various electrodes in its different positions. For example, Behin et al. describe an optical crossbar switch consisting of a series of moveable mirrors that are magnetically actuated and can be electrostatically clamped either in the horizontal position to the substrate or in the vertical position to the sidewalls of a separate chip. Fujita et al. describe similar micromirrors that are electrostatically clamped against a shallow stop when deflected vertically.
FIG. 1
depicts an optical crossbar switch
100
that contains mirrors
102
that rotate between horizontal and vertical positions in order to switch optical signals
104
between one or more input fibers
106
and one or more output fibers
108
. The mirrors
102
are typically rotated by a combination of magnetic force and mechanical torsion in a hinge member (not shown) at the axis of rotation of the mirror. Optical switches like that shown in
FIG. 1
are described in detail in U.S. Pat. No. 4,580,873, entitled “Optical Matrix Switch,” Issued Apr. 8, 1986 to Frank H. Levinson, which is incorporated herein by reference. Comb drives are generally not used to actuate this type of switch because it is difficult to create a comb drive that could directly move the mirror over the desired angular range without some additional mechanical linkage. One means for fault detection in optical switches involves monitoring of the optical signals received by the output fibers
108
. A splitter incorporated into the switch or fiber taps at the output fibers
108
can be used to monitor the output signals. This prior art method may also require monitoring of the input signal, since the criteria for failure is often a discrepancy between the input and the output signals. Unfortunately, monitoring the input and output optical signals incurs additional optical losses to the switch
100
since it requires tapping optical energy from the signals for monitoring. Furthermore, monitoring the input and output signals does not specifically indicate the cause of the failure, as the mirror position is not directly monitored.
There is a need, therefore, for an improved MEMS device with improved fault detection to directly detect faults in the control state of the mirror positioning mechanism.
OBJECTS AND ADVANTAGES
Accordingly, it is a primary object of the present invention to provide microelectromechanical system (MEMS) device having a fault detection system that directly measures mirror control state.
SUMMARY
The objects and advantages are attained by an apparatus and method that allow for detection of whether a rotatable MEMS element is in a first or second position, , e.g., horizontal or vertical, and whether it is properly clamped in either of these two positions. This sensing capability is useful for fault detection. By sensing the mirror position, mirror failure can be immediately detected, and traffic through the switch can be appropriately re-routed. Embodiments of the invention provide apparatus and methods for detecting whether mirrors used in a certain type of optical switch are in the “on” or “off” position. Specifically, this invention applies to switches that employ mirrors that move between an “on” or “off” position, wherein they reflect light from an input fiber into an output fiber in the “on” position, and allow the light to pass in the “off” position. Electrodes are positioned in this system such that the mirrors are close to, and therefor capacitively coupled to, a different electrode depending on whether they are in the “on” or “off” position. This invention is especially useful for switches that already employ electrodes for electrostatic clamping of mirrors in one or more positions, since those same electrodes can be used both to electrostatically clamp the mirrors and to sense their position. The method described in this invention comprises sensing of the capacitance between the mirrors and the one or more electrodes used to clamp the mirrors in its one or more positions in order to detect which of the positions the mirrors are clamped in. Furthermore, the magnitude of the capacitances can be monitored to detect improper clamping. The apparatus may be incorporated into a MEMS mirror optical switch controlled by a computer processor.
REFERENCES:
patent: 4580873 (1986-04-01), Levinson
patent: 4935700 (1990-06-01), Garbini et al.
patent: 5043043 (1991-08-01), Howe et al.
patent: 5302886 (1994-04-01), Jacobsen et al.
patent: 5638946 (1997-06-01), Zavracky
patent: 5646464 (1997-07-01), Sickafus
patent: 5648618 (1997-07-01), Neukermans et al.
patent: 5717631 (1998-02-01), Carley et al.
patent: 5867302 (1999-02-01), Fleming
patent: 5881598 (1999-03-01), Sapuppo et al.
patent: 5914507 (1999-06-01), Polla et al.
patent: 5960132 (1999-09-01), Lin
patent: 5963788 (1999-10-01), Barron et al.
patent: 5969848 (1999-10-01), Lee et al.
patent: 5971355 (1999-10-01), Biegelsen et al.
patent: 5998906 (1999-12-01), Jerman et al.
patent: 6025951 (2000-02-01), Swart et al.
patent: 6094293 (2000-07-01), Yokoyama et al.
patent: 6396975 (2002-05-01), Wood et al.
patent: 6396976 (2002-05-01), Little et al.
patent: 0683414 (1995-11-01), None
patent: 0057233 (2000-09-01), None
E. K. Chan et al, “Characterization of Contact Electromechanics Through Capacitance-Voltage Measurements and Simulations” Journal of Microelectromechanical Systems, vol. 8, No. 2, Jun. 1999.
E. K. Chan et al, “Electrostatic Micromechanical Actuator with Extended Range of Travel” Journal of Microelectromechanical Systems Dec. 2000.
P. Cheung et al. Design, Fabrication, Position Sensing, and Control of an Electrostatically-driven Polysilicon Microactuator, IEEE Transactions on Magnetics, vol. 32, No. 1, Jan. 1996.
A. Selvakumar, “A High-Sensitivity Z-Axis Capacitive Silicon Microaccelerometer with a Torsional Suspension”, Journal of Microelectromechanical Systems, vol. 7, No. 2, Jun. 1998.
H. Toshioshi et al. “Electrostatic Micro Torsion Mirrors for an Optical Switch Matrix” Journal of Microelectromechanical Systems, vol. 5 No. 4, 231-7 Dec. 1996.
L.Y. Lin et al. “Free-Space Micromachined Optical Switches with Sub-Millisecond Switching Time for Large-Scale Optical Cross Connects” OFC '9
Beerling Timothy E.
Behin Behrang
Daneman Michael J.
Kiang Meng-Hsiung
Lau Kam-Yin
Isenberg Joshua D.
JDI Patent
Kitov Z
Toatley , Jr. Gregory J.
LandOfFree
Capacitive sensing scheme for digital control state... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Capacitive sensing scheme for digital control state..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Capacitive sensing scheme for digital control state... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3232265