APPARATUS FOR CONTROLLED LAPPING OF OPTICAL SURFACES TO CORRECT DEVIATIONS FROM DESIRED CONTOURS

Apparatus for scanning an aspheric optical surface in a spiral pattern and lapping with short strokes is provided by rotating a table supporting the workpiece at a controlled rate, radially moving an arm carriage, and cyclically driving the arm on the carriage with a crank to produce short lapping strokes along the spiral scanning path. A program prepared from contour deviation plots along several diameters of the workpiece (made by knife-edge measurement techniques) control the rate of rotation of the workpiece inversely proportional to deviations from the desired surface contour. After repeated use of one program has reduced deviations by at least half, measurements are again made and a new program is prepared. Each iteration of a given program is run at a rate which assures completion of the entire program in an interval of time during which the rate of material removal will not vary by more than 10 percent.