A novel real-time singularity avoidance approach for manual guidance of industrial robots

In this paper, online manual guidance of industrial robots using impedance control with singularity avoidance is studied. In this method, operator enters the robot workspace, physically holds the end-effector equipped with force sensor and manually guides the robot. In doing so, the operator generates the desired trajectory for applications like welding or painting. Robot singular configuration is possible during the process which makes it unsafe due to unexpected high velocity robot joints and the physical human-robot interaction. Therefore, real-time identification of singularity position and orientation must be evaluated during trajectory generation. The use of manipulability ellipsoid is suggested as a simple method for the singularity identification. By combining the manipulability ellipsoid and impedance control, a simple and new approach is proposed to warn operator before reaching singularity. Based on the proposed approach, effect of opposite force is exerted on the human hand in the predefined distance to singularity. Real-time implementation is the main advantage of the proposed approach because it keeps robot away from reaching singularity. Real-time experiments are performed using a SCARA robot. In the first experiment, the operator stops the trajectory generation process when an opposite force is produced. In the second experiment, the operator insists on entering the singular points. Experimental results show the effectiveness of the proposed approach in dealing with singularity problem during the trajectory generation by an operator for industrial robots.