The geometric error motions of rotary stages greatly affect the accuracy of constructed\nmachines such as machine tools, measuring instruments, and robots. In this paper, an embedded\nsensor system for real-time measurement of two radial and three angular error motions of a rotary\nstage is proposed, which makes use of a rotary encoder with multiple scanning heads to measure\nthe rotational angle and two radial error motions and a miniature autocollimator to measure two tilt\nangular errors of the axis of rotation. The assembly errors of the grid disc of the encoder and the\nmirror for autocollimator are also evaluated and compensated. The developed measuring device can\nbe fixed inside the rotary stage. In the experiments, radial error motions of two points on the axis\n(h= 5 mm and 60 mm) were measured and calibrated with LVDTs, and the data showed that the\nradial error motions of the axis were less than 20 micro m, and the calibration residual errors were less\nthan 2 micro m. When intermittent external forces were applied to the stage, the change of the stageâ??s\nerror motion could also be monitored accurately.
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