Patent ID: 8231355

Claim:
A free piston gas compressor comprising: a cylinder, a piston, said piston reciprocable within said cylinder in alternating compression and expansion strokes, a reciprocating linear electric motor drivably coupled to said piston having at least one excitation winding, and a controller programmed to obtain a measure reflecting one or the other of a duration of the compression stroke and a duration of the expansion stroke and to control or adjust power input to the linear motor on the basis of a relationship including at least one of the present compression stroke duration or expansion stroke duration, the relationship being indicative (directly or indirectly) of the TDC position of the piston including in the absence of an collision, said controller is programmed to obtain a measure reflecting each of the compression stroke duration and the expansion stroke duration and to execute the steps of: obtaining a measure reflecting the difference between the compression stroke duration and the expansion stroke duration, adjusting the power input to said excitation winding in response to the obtained measure.