Superimposed force/torque-control of cooperating robots

Cooperating robots are used in industrial environments for handling large and/or heavy workpieces. The robots get calibrated to each other, so every involved robot knows the exact position of the other robots. The robots are controlled by pure position control. Inevitable position errors come up and lead to massive forces and torques, which stress the workpiece internally. We show a method how those forces and torques can be minimized by using active force/torque-control. Hereby we enable effective load sharing in any orientation because a free-wheeling bearing is not necessary any more. The position controlled trajectory is still calculated by the standard robot controller, the force control is superimposed to that trajectory. Hence the path velocity in cooperating mode with force control can be set to the same level as without force control. Initially the studies were of simulative nature. After that the controller was parameterized and verified with two real industrial robots. We developed a framework, which is vendor-independent and can be used for any system of industrial cooperating robots.