Refrigeration – Gas compression – heat regeneration and expansion – e.g.,...
Reexamination Certificate
1999-11-02
2001-05-22
Wayner, William (Department: 3744)
Refrigeration
Gas compression, heat regeneration and expansion, e.g.,...
C060S520000
Reexamination Certificate
active
06233947
ABSTRACT:
INTRODUCTION
The present invention is direction to a high efficiency fuzzy logic based Stirling cycle cryogenic cooler which is particularly useful for night vision and medical applications.
BACKGROUND OF THE INVENTION
Cryogenic refrigerators have been used since the 1960's for infrared detector cooling (for example, for military use). The compressor portion of the Stirling cryogenic cooler consists of two sets of pistons and springs that are placed 180° out of phase with respect to each other. This is schematically illustrated in
FIG. 2
as will be discussed later. In order to improve a mean time to failure operation, Madni U.S. Pat. No. 5,734,593 discloses a fuzzy logic controller for such a system which provides a control output signal which controls the final cooling power of the cooler-compressor of the Stirling system. Such output signal, as disclosed in the Madni '593 Patent, is a pulse width modulated (PWM) signal of the square wave type.
In driving a compressor, especially of the Stirling type, it is known that a sine wave drive, for example, accomplished by a rotating wheel and crank, is preferable for some modes of operation. However, in a cryogenic system as used in the present applications, that is an infrared detector, or in medical applications, both power requirements and size would effectively eliminate the use of such a sinusoidal drive.
OBJECT AND SUMMARY OF INVENTION
It is therefore a general object of the invention to provide a high efficiency fuzzy logic based Stirling cycle cryogenic cooler.
In accordance with the above object, there is provided a cryogenic cooling system where a Stirling cycle cooler-compressor having opposed pistons is used for circulating a coolant fluid to a cold tip, having an actual temperature, TC, which is in proximity to the object being cooled, the cooler-compressor cooling the fluid to a predetermined set point temperature, TS, and including a fuzzy logic controller responsive to AT, the difference between TS and TC, for providing an output control signal to the cooler-compressor, the system comprises means for generating during a cool down mode an output control signal of a square wave type having maximum cooling power. Means for generating during a demand mode an output control signal of the sinusoidal type are also provided as well as means for switching, in response to a predetermined AT value from the cool down to the demand mode and vice versa.
In another embodiment of the invention, the pistons of the cooler have spring returns in opposition to the ambient pressure of the coolant fluid for placing them in a neutral position and the sine wave generator is effectively turned off every one-quarter cycle after reaching a peak to allow the ambient cooling fluid pressure or the springs to return the pistons to a neutral position.
REFERENCES:
patent: 5734593 (1998-03-01), Madni et al.
patent: 5752385 (1998-05-01), Nelson
patent: 6084320 (2000-07-01), Morita et al.
Madni Asad M.
Vuong Jim B.
Wan Lawrence A.
BEI Sensors & Systems, Inc.
Flehr Hohbach Test Albritton & Herbert LLP
Wayner William
Wright Jerry G.
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