Microscopic motion control of a parallel visual alignment stage

This paper investigates motion control of a visual alignment stage with four parallel limbs for the planar alignments between mask and panel. The parallel alignment stage has the high load capacity but small moving range. Hence, the control performance much depends on how well the uncertainty at low velocities such as nonlinear friction can be compensated. The perturbation observer based control is so efficient to compensate the frictional uncertainty arising specifically in microscopic movement and as a result enables to achieve fine controlled motion. Experimental results in the visual alignment demonstrate the effectiveness of the suggested control method.