Collision detection and reaction for a collaborative robot with sensorless admittance control

Abstract

This paper presents a method of sensorless admittance control for a robot manipulator with multiple degrees of freedom in the event of a collision. A particular attention is given to a low-cost collaborative robot controlled by a typical PID (Proportional-Integral-Derivative) controller. The paper proposes a new approach for model-based detection and reaction for a sudden collision. First, a collision detection method that can handle modeling errors and measurement noise simultaneously is proposed. The proposed collision observer is based on the principle of forced response of a mechanical system. The low-pass filter and the high-pass filter are combined in a unified fashion to identify a true collision more robustly compared with conventional methods. Unlike a band-pass filter, the method does not distort the residual signals. In addition, an online method that can instantly compute the inertial parameter for admittance control is proposed such that the joint torques generated by the modified trajectory do not exceed the maximum limits. A simulation and a real-world experiment based on a three degrees-of-freedom robot manipulator are carried out to validate our theoretical results.