Apparatus for calibration of an angular displacement

摘要

A system for calibrating a rotary table (10) includes an indexing table (20) (which is a Hirth coupling table) and an angular interferometer (100), together with a control (200). The indexing table is mechanically coupled to the rotary table (this being the only connection between the rotary table to be calibrated and the calibration system), and the interferometer is set up to measure rotation of the indexing table. During rotation of the rotary table (10) to a target angle, the control (200) monitors the interferometer reading, and when this reading exceeds a predetermined threshold, actuates a drive motor (240) of the table (20) to counter rotate the table, thereby to maintain the optics (106) of the interferometer in alignment with the laser beams (L2, L3) and thus enable continuous measurement of the position of the indexing table.