Active Multi-Axis Vibration Cancellation for Split-Stirling Cryocoolers

Abstract

Many proposed spacecraft-borne instruments rely on miniature Stirling cryocoolers for focal plane cooling; a significant drawback of these coolers is the vibration induced by the reciprocating motion of the cooler’s internal components. This paper describes an active vibration cancellation system for the expander of a Hughes split-Stirling cryocooler. A multi-axis electrodynamic actuator counters the axial force and two lateral torques generated by the cooler. The actuator is driven by a frequency-tracking narrowband controller to null error signals obtained from load cells. The controller is composed of a parallel arrangement of analog modules to handle multiple harmonics. In a single-axis cancellation test, the cross-axis coupling of the actuator is found to be significant compared to the multi-axis content of the cooler vibration. However, this coupling is shown to have little effect on a multi-axis cancellation system.