Method of self-adjusting a machine to compensate for part-to-part variations

A method of compensating for dimensional variations in mass-produced workpieces at a workstation which comprises a processing unit having a vision system and a tool for performing an operation on a workpiece which is held in a fixed location on a fixture, the vision system having a three-dimensional scanning camera for scanning workpieces and a processor for developing from scans of workpieces, coordinate data about workpieces within a coordinate system of the vision system, a robot operable by a controller to move one of the fixture and the processing unit relative to the other of the fixture and the processing unit within a three-dimensional orthogonal coordinate system of the robot by translation along X, Y, and Z axes which intersect at an origin of the coordinate system and by turning angularly about each of the X, Y, and Z axes, the method comprising:

• securing a master workpiece in the fixed location on the fixture;
• moving the scanning camera to a scan start position and then from the scan start position along a scan path while the scanning camera scans a region of the master workpiece which contains a feature on which the tool would perform an operation, the feature comprising a surface having a two-dimensional area defined by X-axis and Y-axis coordinate data, and at locations within the two-dimensional area, the surface being further defined by Z-axis coordinate data;
• developing from a scan of the region of the master workpiece, master coordinate data for the feature in the coordinate system of the vision system;
• moving the tool to a master home position for the tool in the robot's coordinate system from which the tool would begin to move along a prescribed operating path for performing a prescribed operation on the feature and recording coordinate data for the master home position in the robot's coordinate system;
• removing the master workpiece from the fixture and securing an unfinished workpiece in the fixed location on the fixture;
• moving the scanning camera to the scan start position and then along the scan path while the scanning camera scans a region of the unfinished workpiece which is expected to contain a feature substantially identical to the feature of the master workpiece;
• developing from the scan of the region of the unfinished workpiece, coordinate data for the feature of the unfinished workpiece in the coordinate system of the vision system;
• in the processor, calculating differences between the coordinate data for the feature from the scan of the region of the unfinished workpiece and the coordinate data for the master home position, and transmitting the calculated differences to the controller;
• and
• in the controller, creating a modified home position for the tool in the robot's coordinate system by modifying the coordinate data for the master home position for the tool by the differences transmitted to the controller, moving the tool to the modified home position and then moving the tool from the modified home position along the prescribed operating path as the tool performs the prescribed operation on the unfinished workpiece.