Joint Stiffness Measurements of Multi-joint Type Robot Manipulators with Serial Mechanisms

When a force is applied at the endpoint of a manipulator arm, the endpoint will deflect by an amount which depends on the stiffness of the arm and the force applied. There are several sources, for example, arm links, transmissions, reducers, and servo drive systems that produce deflections or vibrations of the industrial manipulator arm. We've investigated the measuring methods of the equivalent joint stiffness of a industrial robots with serial mechanisms. In this paper, two measuring methods are proposed. One is simultaneous measurement method, and the other individual method. According to the experimental conditions, the former is devided into two methods further, servoing state measurement, and mechanically fixed state measurement. The experimental results for the typical industrial robot, PUMA560, show that we can regard the equivalent stiffness of each joint to be linear.