A novel magnetic suspension cum linear actuator system for satellite cryo coolers

Stirling cycle cryogenic coolers have been widely used for device cooling in satellites. Various types of magnetic bearings and linear actuators find application in such systems. The most widely used configurations have two-axis-radially-active suspension stations placed at either end of a reciprocating shaft in the compression and expansion sections. Separate or integral linear motors are provided in each section for axial shaft movement. It may be noted that such configurations are rather complicated and less reliable because of the presence of numerous electro-mechanical components, sensors and electronic servo channels. In this paper, a simple and reliable scheme is suggested which axially stabilizes and linearly perturbs the piston so that the need of a separate motor for axial actuation can be totally dispensed with. The piston is radially supported by passive repulsive bearings. In the axial direction, a servo actuator `balances´ the piston and also actuates it bi-directionally. Implementation of this `bearing cum motor theme´, reduces the number of electromechanical and electronic components required to operate the system and hence minimizes the chances of system failure. Apart from this, the system´s power consumption is reduced and efficiency is improved as electrical heating losses caused by quiescent-operating currents are removed and electromagnetic losses on the moving parts are minimized. The necessary system parameters have been derived using finite element analysis techniques. Finally, the proposed design is validated by computer-aided system simulation