Profile error compensation in cross-grinding mode for large-diameter aspheric mirrors

Abstract

This study proposes a high-precision compensation system using an on-machine noncontact measuring system to improve the manufacturing accuracy and efficiency of largediameter aspheric mirrors by reducing profile errors arising from tool setting errors and machine positioning errors. By measuring a standard hemisphere, the assembly tilt angle of the measurement sensor can be calibrated. The grinding wheel setting offset can be calculated by comparing the measured profile and the ideal profile, and the profile error caused by wheel offset can be reduced by adjusting the grinding origin coordinate. According to the normal unit vector and residual error in the Z direction of the measuring points, the normal residual errors corresponding to the grinding points could be generated as well as the compensation grinding numerical control (NC) program. An 800-mm-diameter K9 mirror was ground to verify the proposed compensation grinding method. The profile error was reduced from 65 to 35 μm during the semi-finish grinding stage. By using the compensation grinding path, the profile accuracy was improved from 35 to 8 μm in the fine grinding stage. The proposed compensation method effectively improves the profile accuracy and manufacturing efficiency for grinding large-diameter aspheric mirrors.

Reviews on the machining and measurement of large components

“…Additionally, Xi et al 59 calculated the grinding wheel setting offset and compensated the normal residual errors by numerical control. An 800-mm-diameter mirror was ground to verify the proposed compensation grinding method.…”

Measurement of Aspheric Surfaces Using an Arcuate Region Scanning Method by 2D Laser Displacement Sensor

“…The high-precision in-situ measurement and compensation of large-diameter aspheric surface are realized by contact measurement method. After four times of compensation, the contour error of 900 mm diameter aspheric surface can be reduced from 40 to 5μm [8][9][10], as shown in the figure 1. In this paper, an effective measurement of aspheric surfaces using arcuate region scanning method by 2D laser displacement sensor is presented.…”

On-machine and in-process surface metrology for precision manufacturing

“…The uncertainty is estimated from the measurement of a sphere with a known radius, and from a comparison with a, hopefully calibrated, form measuring instrument. Xi [244] has developed a correction method for the grinding wheel position, for grinding a 800 mm diameter aspheric mirror, reducing the profile error from 65 µm to 8 µm. Also here, a sphere is used to confirm the obtained improvement.…”