CALIBRATION OF TRANSLATIONAL TABLES FOR USE IN 3-DIMENSIONAL SURFACE-TOPOGRAPHY MEASUREMENT SYSTEMS

Translational tables now form a vital part in three-dimensional surfac e topography systems. In some systems typically, one translational tab le is used to provide measurements in one of the axes and the translat ional motion provided by the gearbox of the system is used to provide the other axis. In other systems, two translational tables are used to provide all the movement for data acquisition from the surface. In th ese systems, the stylus is held stationary during the measurement. It is clear from the above, that irrespective of the motion mechanism emp loyed, the measurement depends heavily on the accuracy and repeatabili ty of positioning of the translational tables. There are, as yet, no s tandards specifically prepared for calibrating translational tables an d this can lead to problems with traceability. This paper sets out to define and assess procedures for determining the accuracy and repeatab ility of positioning translational tables in the x- and y-axes by usin g as an example, two tables that work on different principles: (1) a l ead screw stepper motor driven table; and (2) a brushless linear motor driven table. Each of these systems has its particular problems. The system proposed, is based on the standard techniques employed for mach ine tool calibration and provides a basis for assessing and quantifyin g table errors that are likely to significantly affect the logging and characterization of surface data in three-dimensions (3D). In this pa per the displacement and velocity characteristics of the tables are ex amined as well as dynamic stability, lead screw error, backlash, and r epeatability of positioning. The paper also assesses the suitability o f the two systems for use in static and on-the-fly data collection.