Form error compensation of on-machine noncontact measurement of precision grinding for large and middle-diameter aspheric elements

Based on the cross grind ing mode for large-diameter aspheric, a high-precision profile error compensation method by using an on-machine noncontact measuring sensor is presented to improve the manufacturing accuracy and efficiency of large and middle-diameter aspheric elements. Profile errors arising from machine motion errors and tool offset errors are obtained through the measured data from on-machine noncontact measurement. By measuring a standard flat ruler, the motion errors of the measurement sensor from the machine positioning errors is calibrated, the grinding tool setting error could be calculated according to the on-machine coordinate to achieve the grinding tool offset quick eccentricity calibration. By comparing the measured profile and the ideal profile, the normal residual error of each grinding program point was calculated, and the new compensation path was generated thereafter. The 300-mm-diameter K9 mirror was ground to verify the proposed compensation grinding method. Results indicate that the profile error was reduced from 35μm to 10μm through the tool setting error elimination during semi-finish grinding stage. Using the compensation grinding path according to the normal residual error, the profile accuracy was improved from 10μm to 4μm in fine grinding stage. It could be concluded that the proposed compensation grinding method is effective to improve profile accuracy and manufacturing efficiency for the large and middle-diameter aspheric elements.