Abstract
This study proposes a new coordinate measuring machine (CMM) based on a three-degree-of-freedom parallel kinematics. This paper presents a kinematic calibration method using three-dimensional ball plate calibrated beforehand by accurate conventional CMMs. The least square method using Jacobian matrix estimates the kinematic parameters so that the ball position errors obtained by measuring the ball plate are minimized. The above calculation has been repeated in both numerical simulations and experiments. An increase of the number of estimating parameters has decreased the position error of the ball plate from 180 μm to 6μm in the experiments. Furthermore, accuracies of both length measurement with block gauges and profile measurement with an optical flat have been improved significantly after the calibration. The measurement accuracy most improves when the repetitive operation is discontinued after three calculations. The balls of the ball plate must be extensively located in a three dimensional space.
