Translational tables now form a vital pan in three-dimensional surface topography systems. In some systems typically. one translational table is used to provide measurements in one of the axes and the translational 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 these systems, the stylus is held stationary during the measurement. It is clear from the above, that irrespective of the motion mechanism employed, the measurement depends heavily on the accuracy and repeatability of positioning of the translational tables. There are, as yet, no standards specifically prepared for calibrating translational tables and this can lead to problems with traceability. This paper sets out to define and assess procedures for determining the accuracy and repeatability of positioning translational tables in the x? and y?axes by using as an example, two tables that work on different principles: (1) a lead 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 bared on the standard technique employed for machine tool calibration and provides a basis for assessing and quantifying table errors that arc likely to significantly affect the logging and characterization of surface data in three-dimensions (3D). In this paper the displacement and velocity characteristics of the tables are examined as well as dynamic stability, lead screw error, backlash, and repeatability of positioning. The paper also assesses the suitability of the two systems for use in static and on-the-fly data collection.
Citation: International Journal of Machine Tools and Manufacture
Pub Type: Journals