Measurement method for compliance of vertical-multi-articulated robot application to 7-DOF robot PA-10

This paper presents a measurement method and its results for a compliance of a vertical-multi-articulated robot. In order to calculate the compliance of a robot, a stiffness of each joint of the robot is required. In this paper, a stiffness of each joint of the robot is measured by using a force/torque sensor and a 3-D motion and position measurement system OPTOTRAK 3020. The proposed measurement method is applied for a 7-DOF robot PA-10 made by MITSUBISHI heavy industries. At first, an 11-DOF link model with 4-virtual joints, i.e., the link model includes virtual 4-DOF, is proposed. Then, a compliance matrix is obtained using a measured joint stiffness matrix of the PA-10 and a Jacobian matrix of a proposed 11-DOF link model. In order to investigate accuracy of the measured joint stiffness, and to confirm effectiveness of the measurement method for the joint stiffness and the proposed link model, experiments measuring the compliance of the PA-10 are conducted. In the experiments, the proposed 11-DOF link model is compared with a 7-DOF link model. Experimental results illustrate that the measured joint stiffness are accurate, and the measurement method and the proposed link model are effective for calculating the compliance of the PA-10.