On-machine methods for identifying and compensating force-ripple and side-forces produced by actuators on a multiple-axis stage

Abstract

Methods, apparatus, and systems are disclosed for identifying force-ripple and/or side-forces in actuators used for moving a multiple-axis stage. The identified force-ripple and/or side-forces can be mapped, and maps of corresponding position-dependent compensation ratios useful for correcting same are obtained. The methods are especially useful for stages providing motion in at least one degree of freedom using multiple (redundant) actuators. In an exemplary method a stage member is displaced, using at least one selected actuator, multiple times over a set distance in the range of motion of the subject actuator(s). Each displacement has a predetermined trajectory and respective starting point in the range. For each displacement, respective section force-command(s) are extracted and normalized to a reference section force-command to define a section compensation-ratio. Multiple section compensation-ratios are assembled, as functions of displacement in the range, to provide a map of compensation ratios for the actuator(s) throughout the range.