Surface Profile Measurement During Turning Using Fringe-Field Capacitive Profilometry

The use of fringe-field capacitive sensing for surface profile measurement during the turning process is described. Measurements of the local surface height are inferred from variations in a fringe electric field induced between the sensing element and the workpiece. The surface profile is determined from high-speed scanning of the sensing element across the surface. The technique is particularly well-suited to the relatively harsh environment of in-process measurement. We have implemented a system in which profile measurements are made continuously, in real-time, and immediately adjacent to the cutting tool. The results of tests conducted to determine the accuracy and sensitivity of this capacitive profilometer are presented. In-process measurements of surfaces generated by turning with roughness in the range of 0.3 to 4.0 μm were made. Comparisons with static profile measurements made using standard stylus instrumentation are presented, and show quantitative agreement.