Algebraic estimation and control of single-link flexible joint robots

Abstract

This paper presents an algebraic approach for the estimation and control of single-link flexible joint robots. Typically, a sensory set to directly measure all robot states is hardly available. Especially in cost-efficient robotic systems as widely used in the industry, robots do not profit from ‘link-sided’ position measurements for end-effector control tasks but instead rely on easily accessible ‘motor-sided’ measurements in combination with model-based control strategies. In this paper, we are interested in obtaining online estimates of the unmeasured link position and speed for use in control. To that end, we introduce an algebraic estimation approach which relies only on motor position sensing and an accelerometer mounted near the end-effector. The estimation is based on an algebraic reformulation of the equations of motion which are linear in the unknown variables allowing an estimation process which is of non-asymptotic fashion. The proposed solution is illustrated by simulation and experimentally with an industrial robot. The robot is controlled by a common 2-DOF structure consisting of feed-forward and feedback control loops. Our experimental results show good tracking performance, especially in terms of suppressing residual vibrations.