Multiple degrees-of-freedom arm with passive joints for on-the-machine measurement system by calibrating with geometric solids

To fabricate three-dimensional profiles with high accuracy, on-the-machine measurement is useful. Methods for the on-the-machine measurement by calibr ation with geometric solids used for references have been developed. In thi s paper, an arm with passive joints for on-the-machine measurement is propo sed. As a prototype, the arm has 4 degrees of freedom (DOF) including two p assive joints. The probing system has 7 DOF, including the DOF of the machi ne tool, in total. Angles of the passive joints are changed by driving the numerically controlled (NC) table and the main spindle of the machine tool, where the arm is mounted. To calculate the optimal posture of the arm for the shape to be measured, a numerical method of the inverse kinematics is a lso proposed. The arm has enough positioning accuracy to calibrate its post ure. Shapes can be automatically measured with the accuracy of micrometer o rder by the on-the-machine measurement method as well as a commercial three -dimensional (3-D) coordinate measuring machine and a profilometer. (C) 199 9 Elsevier Science Inc. All rights reserved.