Signal fidelity and tracking force in stylus profilometry

Abstract

This paper presents an experimental study of the influence of tracking force the signal fidelity in stylus profilometry. To do this, a simple, retrofit variable force actuator has been designed, built and assessed. This consists of a permanent magnet attached to the stylus arm about which is a noncontacting solenoid actuating coil. This simple device readily provides a continuously variable stylus force over the range 0.01 to 15 mN. Using this, surface finish values on specimens of steel, aluminium, brass and copper have been measured over a range of stylus loads and traverse speeds. Analysis of these traces has been carried out both by evaluation of the surface finish parameters, Rq, Ra, RMS slope and RMS peak curvature and a qualitative analysis using scanning electron microscopy. As might be expected, results indicate that stylus techniques give consistently reproducible values over a wide range of loads and speeds. However, limits are identified outside which erroneous values of surface finish parameters may be obtained or damage incurred if excessive loads or improper tracking speeds are used.