Mechnical Design Systems Laboratory, Hiroshima University

Measurement accuracy of articulated arm coordinate measuring machines (AACMMs) is often significantly lower than that of conventional CMMs with three linear axes. To improve their measurement accuracy, the accuracy of its forward kinematic model, to calculate the end effector position from the angular positions of rotary axes, is a key. This paper proposes a new scheme to experimentally identify the forward kinematic model. To accurately measure the displacement of the stylus sphere, attached as the end effector, a device with three displacement sensors (the R-Test device) is used. The measured sphere profiles are used to identify not only the Denavit-Hartenberg (D-H) errors, but also the angular position measurement error profiles of rotary encoders. The experimental results show that using the R-test device can improve the measurement accuracy of the AACMM.

Keywords: Coordinate measuring machines, Measurement accuracy, R-test