Vibration reduction in balanced linear compressors

Dadd MW (1), Bailey PB (1), Davey G (1), Davis T (2), Thomlinson BJ (2)

  1. Department of Engineering Science, University of Oxford, Parks Road, Oxford, OX1 3PJ, UK.
  2. AFRL, Albuquerque, NM, USA

CRYOCOOLERS 11, Ross RG, 175-182, 2001

Coolers for Space applications are often powered by reciprocating compressors that use a linear compressor technology. These can deliver the requirements for long life and high reliability but have not yet produced acceptable uncompensated vibration levels at a reasonable cost. If two nominally identical compressors are mounted back to back the vibration level is reduced, but may still be too high for many applications.

Further reduction of vibration is achieved through the use of Adaptive Control systems, which are expensive and reduce the reliability of the system. If the residual vibration can be reduced by better matching of the two compressors, then cheaper, more reliable electronics can be used to achieve the desired vibration level.

Under a research and development effort with the Air Force Research Laboratory, all sources of vibration were considered but effort was concentrated on improving the matching of a compressor pair to limit the main causes of vibration. The dynamics of a compressor were modelled. The force generated by the coil was calculated from flux densities determined by a finite element analysis of the magnetic circuit. The rest of the system was modelled as a damped harmonic oscillator.

An attempt was made to reduce the residual vibration in an opposed pair of compressors by duplicating the model to simulate a compressor pair and investigating the effect of small variations of a number of parameters. These results were used to estimate the accuracy with which various parameters must be matched to achieve a certain residual vibration and this information was then used to improve the assembly of a compressor pair.
Most of the components for this compressor were already available so it was not possible to make major changes. Detailed measurements were made on all components and assemblies so that the vibration spectrum could be related to a compressor with documented manufacturing and building standards.