Adaptive feedforward control system and method for reducing vibrations generated by pistons

摘要

An adaptive feedforward vibration control system reduces vibrations at fundamental and harmonic frequencies of matched reciprocating pistons, such as the back-to-back compressor pistons 2, 4 in a Stirling cycle cryocooler 14. The pistons are driven by motor drives 32, 34 connected to servos 28, 30 and signal generators 24, 26. A vibration sensor 22 senses vibrations caused by the pistons. A processor 20 converts the sensed signals from the time domain to the frequency domain, preferably by Fourier analysis, and calculates the fundamental and harmonic frequencies of the vibrations. At least one of the pistons 2, 4 is then driven with correction signals from the processor 20. The correction signals are computed iteratively to increase their accuracy and need only to be updated relatively infrequently to adjust the pistons' motions, thereby enabling the use of a relatively slow microprocessor. The system is also applicable to reducing the vibrations generated by a pair of opposite expander and balancer pistons 8, 10 in a cryocooler.