Patent ID: 7266947
Filing Date: 2007-09-11
Classification: F04B,F25B

Abstract:
1. A method for controlling the temperature of a mass cooled by a free piston cryocooler, the method comprising: (a) for output cooling power demands requiring a piston stroke exceeding a selected minimum piston stroke, controlling the output cooling power of the cryocooler by modulating piston stroke as an increasing function of the difference between sensed mass temperature and a command reference input temperature, wherein the selected minimum piston stroke is the minimum piston stroke necessary to maintain gas bearing lubrication of the cryocooler; and (b) for output cooling power demands requiring a piston stroke less than the selected minimum piston stroke, maintaining the piston stroke at substantially the selected minimum piston stroke and applying thermal energy to the mass wherein the thermal energy is applied as an increasing function of the difference between the cooling power applied to the mass by the cryocooler at the selected minimum piston stroke and the cooling power demand wherein, for nominal design operation, the output cooling power demand is greater than the output cooling power at the selected minimum piston stroke and is nearer the output cooling power at the selected minimum piston stroke than the output cooling power demand is to the cooling power at a maximum permissible piston stroke.