Control system and method for preventing destructive collisions in free piston machines

A method for preventing destructive collisions in a free piston machine having a piston reciprocating in linear oscillation within a cylinder, the cylinder having at least one cylinder end structure, the machine also having a negative feedback control system controlling a piston force, the control system summing a feedback signal and a reference input signal and deriving an error difference signal, the method comprising:

• (a) summing a perturbation signal with the feedback signal and the reference input signal;
• (b) detecting a collision of the piston against the cylinder end structure and generating a signal at an output in response to a detected collision;
• and
• (c) varying the magnitude of the perturbation signal in a direction which reduces piston amplitude in response to each detection of a collision.

An apparatus for preventing destructive collisions in a free piston machine having a piston reciprocating in linear oscillation within a cylinder, the cylinder having at least one cylinder end structure, the machine also having a negative feedback control system controlling a piston force, the control system summing a feedback signal and a reference input signal and deriving an error difference signal, the apparatus comprising:

• (a) means for summing a perturbation signal with the feedback signal and the reference input signal;
• (b) means for detecting a collision of the piston against the cylinder end structure and generating a signal at an output in response to a detected collision;
• and
• (c) means for varying the magnitude of the perturbation signal in a direction which reduces the piston amplitude in response to each detection of a collision.

An apparatus for detecting collisions in a free piston machine, the collisions generating mechanical vibrations in a characteristic frequency range, the apparatus comprising:

• (a) a mechanical vibration detector having an output for an electrical signal representing a detected mechanical vibration;
• (b) a filter connected to the output of the vibration detector and having a passband at the characteristic frequency range;
• and
• (c) means for comparing the magnitude of the output from the filter to a reference representing the output of the filter in the absence of collisions and having an output for changing in response to the filter output exceeding the reference and thereby signaling the detection of a collision.

A method for detecting collisions in a free piston machine, the collisions generating mechanical vibrations in a characteristic frequency range, the method comprising:

• (a) detecting mechanical vibrations of the machine by generating an electrical signal representing the detected vibrations;
• (b) filtering the detected mechanical vibration signal by passing the characteristic frequency range;
• and
• (c) comparing the magnitude of the filtered signal to a reference representing the filtered signal in the absence of collisions and signaling the detection of a collision in response to a filtered signal exceeding the reference.