Active temperature control of Stirling-cycle cryocoolers

Cryogenic coolers capable of continuously maintaining the required cryogenic temperature (on the order of 65 K) are essential for space-borne infrared (IR) surveillance sensors. To optimize their IR signature sensitivity performance, the temperature at the IR focal planes needs to be precisely controlled. A temperature control algorithm is developed to actively control the Stirling-cycle cryocooler cold finger tip temperature by adjusting the cooler compressor stroke amplitudes. Since the compressor stroke amplitudes are also used to control the fundamental frequency vibration force, included in the temperature control algorithm is a distribution law that distributes the desired stroke amplitude change to each compressor so that the force balance at the fundamental frequency is maintained. Proceeding to the distribution law is a control law that uses proportional, derivative, and integrated temperature error information to generate the required total stroke amplitude change for achieving the precision temperature control. The developed temperature control algorithm is implemented on a 68000-based processor board, and integrated and tested on the Air Force´s Standard Spacecraft Cryocooler built by Hughes