Investigation of the Motion of Spring Suspended Pistons

摘要

This report describes the investigation of the modeling and construction of low vibration mechanical compressors, such as used in cryogenic coolers. The classic 'Oxford' cryocooler has a clearance seal between the piston and the cylinder which is maintained by the use of spiral disc springs. In a typical compressor this clearance is about 12 microns, and therefore the spring suspension system must have a linearity of no more than 3 or 4 microns to avoid contact. It has always been assumed that to maintain this linearity, the surfaces between which the springs are clamped must be very flat and very parallel to each other. It has also been assumed that the flatness and parallel- ness of the clamping at the inside of the spring is more important than at the outside. We investigate how the linearity of motion is dependent on the clamping conditions of the springs. Tests were carried out on a typical suspension system which was deliberately assembled between non-parallel clamping surfaces, and the linearity of the resulting motion was measured. A simple theoretical model was developed which gives good agreement with the experimental results.