Workpiece inspection and handling

Abstract

A workpiece alignment and shifting system for moving circular workpieces from a first inspection station to a second machining station, comprises workpiece holding means for attachment to the face of a disc workpiece to move the latter from one position to another. Robotic means controls the position of the workpiece holding means and is adapted to move in a least two orthogonal directions, both of which are parallel to the plane of the disc when it occupies the first station. The disc is rotated in the inspection station and in the machining station and inspection means determines the position of the geometric center of the disc as it is rotated. Computing means calculates from data delivered by the inspection means the two shifts required along the orthogonal directions of movement of the robotic means, to move the geometric center of the disc to a second desired position whose coordinates are known. The computing means includes memory means for storing the said coordinates. The coordinates are those of the center of rotation of the workpiece holder or chuck in the said second station. The workpiece holding means is vacuum operated. A three axis robot is employed to pick and place disc-like wafers of semi-conductor material for edge grinding, and movement along two of the robot axes, X and Z, is used to control the centering of the wafer on a vacuum chuck in the second grinding station.