Patent ID: 7075292

Claim:
An apparatus for determining free piston position comprising: an apparatus for determining stroke and average position of reciprocating motion of a free piston in a free piston machine, comprising a pulse train generating means and a free piston position computing means: said free piston machine having a case enclosing said free piston and a free piston driving means; said free piston having no mechanical connection with said driving means; said pulse train generating means having a magnet disposed on said free piston and a magnetic sensor disposed on said case; said magnetic sensor and said magnet aligned perpendicularly to the direction of reciprocating motion of said free piston when said free piston being positioned at a designed center of reciprocating motion of said free piston; said magnetic sensor generating pulses when said magnet being positioned within a predetermined distance from said magnetic sensor in the direction of reciprocating motion of said free piston; said free piston position computing means including measuring means of duration of said pulse, interval between said pulses, and computing velocity of reciprocating motion of said free piston; said free piston position computing means computing stroke of said free piston based on said duration of pulse and said velocity of reciprocating motion of said free piston; and said free piston position computing means computing offset of the average piston position of reciprocating motion of said free piston from a designed average piston position thereof based on said interval between pulses, computed stroke of said free piston, and said velocity of reciprocating motion of said free piston.