UNSPECIFIED. (1995) DETERMINATION OF SQUEEZE FILM DAMPING IN CAPACITANCE-BASED CANTILEVER FORCE PROBES. PRECISION ENGINEERING-JOURNAL OF THE AMERICAN SOCIETY FOR PRECISION ENGINEERING, 17 (2). pp. 94-100. ISSN 0141-6359

Abstract

Capacitance-based techniques are increasingly being used as the sensing method for low-force probes.(1,2) Because the gap between electrodes is generally very small, relative motion between two electrode surfaces results in squeeze film forces that can provide an effective damping action. Recent investigations of the effect of damping on the fidelity of stylus measurement indicates that optimal dynamic conditions correspond to a system critical damping ratio between 0.4 and 0.8.(3,4) This paper presents a theoretical analysis of the squeeze film forces between a cantilever beam and adjacent solid surface during lateral vibration based on an assumed mode of deflection. Two mode shapes were computed one using the static beam deflection curve and the other the fundamental mode shape of a continuous prismatic beam. Experiments were carried out on 11 samples, of which 3 were too heavily damped for a realistic estimate of damping ratio. Comparison with calculated results revealed an absolute worst-case error of 0.063 in the damping ratio, with a standard deviation of 0.0175, which is considered to be within experimental error.

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