Electrical generator or motor structure – Non-dynamoelectric – Charge accumulating
Reexamination Certificate
1998-12-29
2001-02-06
Dougherty, Thomas M. (Department: 2834)
Electrical generator or motor structure
Non-dynamoelectric
Charge accumulating
Reexamination Certificate
active
06184607
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an electrostatic actuator array in which the individual cells share a common electrode and wherein an alternate polarity field is generated from a single DC power supply. More particularly the invention relates to a driving means for such an array, wherein an alternate polarity field is derived from a DC current having time allocation of signals to present alternating fields to each actuator.
BACKGROUND OF THE INVENTION
Electrostatic actuators have become selected and are the solution of choice for actuators that employ low power, operate at high speed, require low cost to produce, and are of small size. These devices present significant advantages: over thermal devices by requiring much less power; over electromagnetic devices by using less power and having smaller size; over piezoelectric actuators that have a higher cost and have a much smaller amplitude of motion.
To date, however, there are no commercially available electrostatic actuators. Of particular concern are electrostatic actuation in the presence of dielectrically isolated electrodes, where specific problems are incurred.
In electrostatic actuators, the desired displacement is the result of the attractive electrostatic force generated by the interaction between a distribution of opposite sign charges placed on two bodies, at least one of which is moveable. For the purposes of this invention, these two bodies are known as actuator plates. The actuator plates are placed apart by a predetermined distance. The charge distribution is then generated by applying a potential difference between two conductive electrodes that are part of the actuator plates. The actuator will be in the ON state or mode when a potential difference is applied between the electrodes and the two plates move toward each other. The actuator will be in the OFF state when the electrodes are at the same potential (shorted).
A DC voltage is theoretically capable of inducing the “ON” state of the actuation cycle. Practical problems, however, limit the application of a DC voltage for the actuation of some electrostatic actuators. In real devices, DC driving shows memory effects, such that the behavior of the actuators depends strongly on the history of the actuation process. DC driving also induces stiction (1) through charges injected in the dielectric at the dielectric/metal electrode interface, and (2) through charges trapped at the dielectric/air interface.
In our commonly owned copending application entitled DRIVING DEVICE AND METHOD FOR ELECTROSTATIC ACTUATORS, and having Ser. No. 08/948,337, a method and apparatus was proposed for use with an AC signal. The AC signal method of driving an electrostatic actuator was designed for actuators having a pair of actuator plates having electrodes for conducting a voltage potential thereto. At least one of the pair of actuator plates was movable with respect to the other, so that the actuator plates were positioned to move upon application of an AC voltage potential thereto by electrodes attached thereto. The driving device in this application produced a compounded AC signal with a rise section at least 10 to 100 times mechanical response time of the actuator and a fall time at least 10 to 100 times the mechanical response time of the actuator. Advantages of this invention are spelled out in the above referenced copending application. However, the invention worked best in driving arrays of actuators working in parallel.
Descriptions of various prior art patents are also contained therein and are incorporated herein by reference.
There are, however, possible array configurations where the individual cells have one common electrode but have to operate out of phase. If the common electrode is grounded, in order to generate alternate fields between the electrodes of the electrostatic actuator, a dual power supply is needed, providing positive and negative potentials. The relatively high voltages needed for use in electrostatic activators would expectedly involve the use of DC/DC converters to scale up the voltage supplied by a battery or another available voltage. These DC/DC converters are bulky and expensive.
Because of this, use of a single power supply would be of great advantage in designing electrostatic actuators, in part because favorable system size, weight and cost parameters would result. It would be of great advantage to the art to resolve the conflict for operating requirements for electrostatic actuators having different cells using a common electrode with an electrically floating potential.
It would be another great advance in the art if an improved driving method for electrostatic actuators could be provided with a desired alternate polarity fields to all the actuator cells based on a single DC power supply and a single DC/DC converter.
Other advantages will appear hereinafter.
SUMMARY OF THE INVENTION
It has now been discovered that the above and other advantages of the present invention may be realized in the following manner. Specifically, the present invention comprises an actuator drive for electrostatic actuators driven with alternate polarity fields, in which the cells have one shared electrode, and the power supply is a single DC power supply. The invention reverses the field polarity without using a second power supply, thereby substantially saving size and cost factors, such as in mesopumps where the membranes employ a single conductive layer.
The device is used in electrostatic actuators that have at least one pair of actuator plates and electrodes for conducting a voltage potential thereto. At least one of the pair is movable with respect to the other. The plates are positioned to move upon application of a voltage potential through the electrodes. A driving means provides a voltage potential to the electrodes to cause the movement of the at least one plate. In a typical cell configuration, an upper electrode and a lower electrode have a moveable diaphragm between them. DC voltage is selectively applied to the upper and lower electrodes and to the diaphragm, which is shared with both upper and lower electrodes. By the use of a properly selected time allocation, each electrode is driven from the same DC power supply for part of the cycle to produce alternate polarity fields at all times on each actuator.
The use of a alternate driving voltage, with zero continue component, provides a much improved driving scheme with reduction of charge injection and minimizes the power dissipation in touch-mode electrostatic actuators. The voltage may be derived from a square wave signal, but may also be of other wave forms such as arcuate, triangular, truncated triangular, and the like. The invention herein allows the driving of arrays of electrostatic actuators working out of phase with alternate fields using a single high voltage DC supply. This is distinguished over prior systems in which DC driving induces charging and premature failure of actuators, or when real AC driving is used based on dual power supplies. Increased reliability, reduced cost and size or volume is achieved.
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C. Cabuz, et al., “High Reliability Touch-Mode Electrostatic Actuators”, Technical Digest of the Solid State Sensor and Actuator Workshop, Hilton Head, S.C., Jun. 8-11, 1998, pp. 296-299.
C. Cabuz, “Tradeoffs in MOEMS Materials” Proceedings of the SPIE, vol. 2881, pp. 160-170, Austin, TX.
Minami K et al: “Fabrication of Distributed Electrostatic Micro Actuator (DEMA)” Journal of Microelectromechanical Systems, US, IEEE Inc. New York, vol. 2, No. 3, Sep. 1, 1993 (1993-09-01), pp. 121-127, XP000426532, ISSN: 1057-7157.
Cabuz Cleopatra
Cabuz Eugen I.
Dougherty Thomas M.
Honeywell International , Inc.
Shudy, Jr. John G.
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