Fluid handling – Processes
Reexamination Certificate
1999-09-23
2001-06-05
Hepperle, Stephen M. (Department: 3753)
Fluid handling
Processes
C137S599070, C251S129010
Reexamination Certificate
active
06240944
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the control of proportional flow and pressure control of valves. More particularly the invention relates to the use of valve arrays and specifically microvalve arrays to permit partial closing or opening of the effective flow path in valves.
BACKGROUND OF THE INVENTION
In prior art devices, proportional flow or pressure control has been performed by partially closing or opening a valve to control the restriction of the valve, and thus the flow through the valve and the pressure drop across the valve. In the case of a microvalve, which is electrostatically actuated, it is not possible to perform proportional control in this manner due to the electrostatic pull-in effect when the critical field is reached in the valve structure.
In certain designs for microvalves and arrays, proportional control of flow and pressure has been attempted using a pulse-width modulation technique at a frequency ranging from approximately 20Hz to several hundred Hz, to control the amount of time the valve is open and closed. This pulse-width modulation technique requires constant operation of the valve arrays, resulting in a lifetime operating requirement for the number of actuations for the valves to be in the two to twenty billion range. Such a requirement for a proportional control valve is extremely difficult to achieve, if it is indeed possible with today's technology.
One example of a miniature gas valve is shown in commonly owned U.S. Pat. No. 5,082,242, divisional U.S. Pat. No. 5,180,623, and further divisional U.S. Pat. No. 5,244,537. These patents, incorporated by reference herein, describe an electronic microvalve in which the operative voltage is minimized. The microvalve is an integral structure made on a single piece of silicon and is a flow through valve with inlet and outlet on opposite sides of the silicon wafer.
Examples of microstructure gas valve control are shown in U.S. Pat. No. 5,176,358, divisional U.S. Pat. No. 5,323,999 and further divisional U.S. Pat. No. 5,441,597. These patents, also incorporated by reference herein, describe a flow control device in which there are separate main flow and flow control (servo) passages between an inlet port and an exit port. The valves are formed on a monolithic semiconductor and are electrostatically controlled. U.S. Pat. No. 5,822,170, also incorporated by reference herein, describes in greater detail a touch mode electrostatic actuator which is useful in the above described valves, and which would be subject to a lifetime operating requirement for the number of actuations for the valves to be in the two to twenty billion range.
Accordingly, it would be of great advantage in the art if the usable lifetime of a valve array for a proportional flow or pressure control application would be greatly increased.
It would be another great advance in the art if more precise control of electrostatic arrays could be achieved, particularly in the manner in which separate valves in an array are actuated.
Other advantages will appear hereinafter.
SUMMARY OF THE INVENTION
It has now been discovered that the above and other objects of the present invention may be accomplished in the following manner. Specifically, the present invention provides for a design in which some, rather than all, of the valve array is actuated once for a flow or pressure control situation, instead of constant modulation of all of the valves.
The array is formed so that actuation actuates a number of valves ranging from one valve to all the valves in the array. The device and method of its use may be used to control flow between a source pressure and an exit pressure chamber. In another embodiment, the device also includes a proportional exit port in communication for discharging a controlling pressure therefrom, the exit port being positioned to receive the proportion of fluid not discharged through the addressable array.
The device of this invention includes an addressable array interposed between a source pressure and an exit pressure chamber, the array comprising a plurality of valves, the total open area of which define the opening between the source pressure and the exit pressure. It also includes an actuator for separately actuating each valve of the array between an open and a closed condition, whereby the total number of open valves determines the flow between the source pressure and the exit pressure.
The valves are preferably electrostatically actuated valves that are fabricated monolithically on a single substrate. The electrostatically actuated valves include upper and lower electrodes addressable by a conductor. Other actuation means are also contemplated.
In the preferred embodiment, one of the upper and lower electrodes is common to all the valves and the other of the upper and lower electrodes are connected in groups, whereby actuation of a specific group or groups actuates a number of valves ranging from one valve to all the valves in the array.
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Article “Development of a MEMS Microvalve array for Fluid Flow Control”, Nelsimar Vandelli, Donald Wroblewski, Margo Velonis and Thomas Bifano, Journal of Microelectromechanical Systems, vol. 7, No. Dec. 4, 1998.
Article Micromachined Silicon Microvalve, T.Ohnstein, T.Fukiura, J.Ridley and U.Bonne, Sensor and System Development Center, Honeywell Inc., Bloomington, MN, Proceedings of MEMS, 1990, IEEE Microelectro Mechanical Systems, Napa Valley, CA, Feb. 11-14, 1990, pp. 95-98.
Cabuz Eugen I.
Ohnstein Thomas R.
Hepperle Stephen M.
Honeywell International , Inc.
Shudy, Jr. John G.
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