Demonstration of active vibration control on the Hughes cryocooler testbed

Narrowband control theory is applied experimentally to the Hughes Stirling-cycle cryocooler, which consists of a displacer and a balancer placed in a back-to-back configuration and commanded to move in opposite directions in order to cancel the vibration forces produced by their motions. The existing control design using 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. In this control concept, 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 was 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