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18 May 2009 Optical system for the simultaneous measurement of two-dimensional straightness errors and the roll angle
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A three-degree-of-freedom measurement system for the acquisition of the straightness and roll errors of a moving linear stage is described. The horizontal (Δx) and vertical (Δy) straightness errors are obtained by measuring the lateral displacement of a triple prism with a laser beam and position sensitive detectors. From two simultaneously performed vertical straightness measurements the roll angle (Θz) can be calculated. The system consists of a cable-free reflector head and a detector head. The position sensitive detectors have been calibrated using a precision x,y-stage equipped with two plane mirror interferometers. Different position sensitive detectors are compared with regard to position sensitivity, linearity, null-shift stability and sensitivity to the intensity profile of the detected laser beam. In combination with an already known triple-beam plane mirror interferometer, additional information about the linear position (Δz) and the pitch (Θx) and yaw (Θy) angle can be obtained from three parallel linear measurements. Thus all six-degree-of-freedom geometric errors can be measured simultaneously. Systematic errors of the three-degree-of-freedom measurement due to misalignment of the laser beams and geometric errors of the triple reflectors are discussed. An approach for correction of those errors caused by the triple reflectors is shown. The method is based on determination of the reflector geometry and calculation using the additional information (Δz) acquired by the interferometer. Furthermore the metrological properties of the proposed system for the measurement of straightness and roll are compared to other measurement principles. Experimental results demonstrate the measurement capabilities of the system.
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I. Rahneberg, H.-J. Büchner, and G. Jäger "Optical system for the simultaneous measurement of two-dimensional straightness errors and the roll angle", Proc. SPIE 7356, Optical Sensors 2009, 73560S (18 May 2009);

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