Transient temperature control system and method for preventing destructive collisions in free piston machines

A method for preventing collisions during a transient cool-down temperature range of a free piston cooler from a first operating temperature of a cold head to a set point operating temperature, the cooler having a piston reciprocating in linear oscillation within a cylinder at a variable stroke, the method comprising:

• (a) sensing the temperature of the cold head and generating a temperature signal;
• (b) generating a transient range maximum allowable stroke signal in response to the temperature signal and a predetermined relationship between the cold head temperature and a maximum piston stroke during the transient cool-down temperature range;
• and
• (c) limiting the stroke of the piston during the transient cool-down temperature range, to prevent collisions within the cooler, in response to the transient range maximum allowable stroke signal.

An apparatus for preventing collisions during a transient cool-down temperature range of a free piston cooler from a first operating temperature of a cold head to a set point operating temperature, the cooler having a piston reciprocating in linear oscillation within a cylinder at a variable stroke, the apparatus comprising:

• (a) a means for sensing the temperature of the cold head and generating a temperature signal;
• (b) a means for generating a transient range maximum allowable stroke signal from the temperature signal and a predetermined relationship between the cold head temperature and a maximum piston stroke during the transient cool-down temperature range;
• and
• (c) a means for controlling the stroke of the piston during the transient cool-down temperature range, to prevent collisions within the cooler, from the transient range maximum allowable stroke signal, and controlling the stroke of the piston during approximately steady state cold head temperature conditions to prevent collisions within the cooler.