The R-test is a new instrument to measure three-dimensional displacement of a precision sphere attached to a spindle relative to a work table by using three displacement sensors. Its application to error calibration for five-axis machine tools has been studied in both academia and industry. For the simplicity in calculating the sphere center displacement, all conventional R-test devices use contact-type displacement sensors with a flat-ended probe. Conventional contact-type R-test may be potentially subject to the influence of the friction or the dynamics of supporting spring in displacement sensors particularly in dynamic measurement. This paper proposes a non-contact R-test with laser displacement sensors. A new algorithm was proposed to estimate the three-dimensional displacement of sphere center by using laser displacement sensors, It compensates the measurement uncertainty caused by the inclination of the target surface. Experimental case studies are presented to evaluate its measurement performance by comparing with the conventional contact-type R-test device.

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