Machining, Measurement, and Control Laboratory

Non-contact R-test for error calibaration of five-axis machine tools
Soichi Ibaraki, Cefu Hong

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 ma- chine 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 al- gorithm was proposed to estimate the three-dimensional dis- placement of sphere center by using laser displacement sen- sors, It compensates the measurement uncertainty caused by the inclination of the target surface. Experimental case stud- ies are presented to evaluate its measurement performance by comparing with the conventional contact-type R-test device.
Key words: R-test, error calibration, dynamic measurement, five-axis machine tool, laser displacement sensor.