A Control Method to Reduce the Oscillation of a Robot Manipulator with Elastic Joints and Non-Backdrivable Gear Trains.

Abstract

A control method to reduce the oscillations of a robot manipulator with elastic joints and non-backdrivable gear trains is proposed. The examined robot manipulator will be used as an arm for robots which work in the human living fields. Such a manipulator should be carefully designed from the safety point of view. Focusing on the interaction force between a human and a manipulator, there are two important aspects to gain the safety. When the manipulator contacts slowly with a human, the elasticity of the joints and the body will play an important role to prevent any injury. On the other hand, if the manipulator collides against a human with rather high speed, the kinetic energy will be the main index to measure the expected damage. The authors will point out that the effective manipulator mechanisms used where a human is in the robot's working space is one with high-gear-ratio gear trains (as a result of non-Backdrivable) and elastic joints. However, the elastic joints cause oscillations. The main purpose of this paper to propose a new method to reduce such an oscillation. This method is discussed based on the stability analysis with Lyapunov's theorem. The simulation and experimental results are also given to show the effectiveness of the method.