Error calibration of five-axis machine tools by on-machine measurement system using a laser displacement sensor

Abstract

An on-machine measurement system to measure the workpiece's geometry or dimension plays an important role in manufacturing processes. A laser displacement sensor recently attracts more attention which enables on-machine high-speed continuous scanning measurement. We developed an on-machine measurement system using a triangulation-based laser displacement sensor for five-axis machine tools. By driving the machine's rotary axes to tilt or rotate the workpiece, the object's geometry can be measured from all the directions in the three-dimensional space without being detached from a machine table. In such a measurement, location errors and error motions of the machine's rotary axes clearly become major contributors for the measurement uncertainty. To identify location errors of rotary axes by using the on-machine laser measurement system itself, this paper presents its application to the R-test, where the three-dimensional displacement of a precision sphere, attached to a rotary table, is measured in the machine tool coordinate system. In the present laser measurement system, the position and the orientation of the laser displacement sensor must be calibrated in advance by using the motion of the machine's rotary axes. The location errors of rotary axes cause their identification error. Unlike the conventional R-test, where the sphere's displacement is measured by three contact-type displacement sensors, the formulation to identify location errors must consider the influence of this calibration error. Experimental demonstration is presented.

Keywords

• five-axis machine tool
• on-machine measurement
• laser displacement sensor
• triangulation
• location errors
• r-test