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Measurement of the actuation transmitting mechanism of the segment prototype of the LAMOST telescope

The segment prototype of the active Schmidt plate segment of the Large sky Area Multi-Object Spectroscopic Telescope (LAMOST) was setup and measured. Nanometer displacement actuator with resolution of 50 nm was used for displacement inputting and both normal capacitive displacement sensors with resolution of 4.2 nm, and differential capacitive displacement sensors with resolution of 5 nm, for displacement reading. For the output displacements of the segment demands for finer displacement increment, three independent groups of lever reducing mechanism with reduction ratio of 1/4 were introduced in the prototype, and the measurement was to test the actuation transmitting performance of the lever systems. Theoretical actuation transfer formula were given and compared with measured data at three typical pointing angles of the segment prototype. The raw data were well corrected with extrapolation technique by monitoring temporal environmental influence on measurement system. The results confirmed that the actuation transmitting performance was as good as required. Its ultimate reducing transmitting ratio is very linear and stable, close to theoretical 3.047 within relative error of 6%, which is easy to be corrected by close-loop control for each segment of the active optics in LAMOST. Also, the measurement process proved itself that the differential capacitive displacement sensor be capable for the application to the active optics in the LAMOST.