Demonstration of active vibration control of the Hughes cryocooler testbed

Narrowband control theory is applied experimentally to the Hughes Stirling-cycle cryocooler expander. The existing control design employing position loop servos failed to provide adequate attenuation for the high-order harmonic vibration forces. A vibration control algorithm based on narrowband control theory is developed to actively control the high-order vibrations. A load cell measuring the high-order vibration forces is used as a feedback element and a servo compensator is designed to produce an infinite open-loop gain at each harmonic frequency. The algorithm is implemented with a digital signal processor and integrated and tested on the cryocooler expander. Peak vibration at the second harmonic frequency was reduced by more than a factor of 25 in the test. The effect of sampled-data parameters such as sampling rate and quantization on the vibration control performance was evaluated. The test data indicate the technical feasibility of applying the proposed active vibration control to meet the next-generation cryocooler vibration specifications