Abstract
A compact linear and angular displacement measurement device was developed by combining a Michelson interferometer in Twyman-Green configuration and an autocollimator to characterize the movement of a precision stage. A precision stage usually has 6 degrees of freedom of motion (3 linear and 3 angular displacements) due to the parasitic motions, thus linear and angular displacement should be measured simultaneously for the complete evaluation of precision stage. A Michelson interferometer and an autocollimator are typical devices for measuring linear and angular displacement respectively. By controlling the polarization of reflected beam from the moving mirror of the interferometer, some parts of light are retro-reflected to the light source and the reflected beam can be used for angle measurement. Because the interferometer and the autocollimator have the same optic axis, the linear and angular displacements are measured at the same position of the moving mirror, and the moving mirror can be easily and precisely aligned to be orthogonal to the optic axis by monitoring the autocollimator's signal. A single mode polarization maintaining optical fiber is used to deliver the laser beam to the device, and all components except the moving mirror are fixed with bonding to achieve high thermal and mechanical stability. The autocollimator part was designed to have the angular resolution of 0.1" and the measurement range of 60". The nonlinearity error of interferometer was minimized by trimming the gain and offset of the photodiode signals.
Published Version
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