Metrological characterisation of polymeric bearings at the nanometre level

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Abstract
The performance of polymeric bearings for metrological applications requiring nanometre-level precision is examined. An initial assessment of lubricated and dry polyacetal and PTFE/Pb composite bearings using a modified stylus measuring instrument is presented. Results of these tests indicate that smooth and repeatable motion of this precision is possible. Reducing the thickness of PTFE in the latter stick - slip behaviour and a change in the friction coefficient from approximately 0.31 to 0.09. To further investigate these and other bearings, a dedicated test rig based on capacitance gauging has been produced. Being constructed almost entirely from the low-expansivity glass ceramic `Zerodur', it has a low thermal susceptibility of 300-600 nm K-1 enabling the monitoring of long-term effects such as creep and wear. The precision gauging has subnanometre precision over a bandwidth of 1 kHz introducing the possibility of measuring transient effects such as film delamination and stick - slip. Initial results, indicating nanometre-level performance with PTFE thin film bearings, are presented.
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