Cartesian sensor-less force control for industrial robots

In this paper, a Cartesian sensor-less force control method for industrial robots is proposed. The disturbance torques at each joint, generated by external forces at the end-effector of robot, are estimated using a disturbance observer, then they are converted to the force/moment in Cartesian space with the robot Jacobian. The force control algorithm is realized through a powerful position servo of industrial robot controller. Furthermore, the friction's harmful effect on the sensor-less force control is reduced using a high frequency dither signal. The validity of the proposed control algorithm is investigated through the experiments with industrial robots. Real application tests are conducted like a peg-in-hole assembly and a die casting application and contact stability with a stiff environment is also checked by a push task with various push levels.