Reliable force-sensorless contact detection method for ball screw drive cartesian robot

This paper proposes a reliable method for contact detection in ball screw drive industrial robots. Moreover, the proposed method assumes a type of robot has no force sensor for contact detection. Reaction force observer estimates the external force without such a sensor. To succeed, however, the method requires correct modeling of the robot dynamics for obtaining precise estimation of force. A ball screw has a characteristic of complex nonlinear friction, which includes viscous friction, coulomb friction, rolling friction, etc. The friction model therefore includes some error due to variation its parameters. The contact detection must be correct even if the force estimation includes a degree of error. In this method, a jerk signal indicate the impact of contact on sensorless force estimation, even if the robot model has some identification error. In addition, the dynamic threshold is set at a level that facilitates precise contact detection by comparison with the jerk signal from the robot's motion. The validity of the proposed method is confirmed in experimental studies performed on an actual industrial robot, whose operation involves a ball screw.