Real-time stiffness compensation and force control of cooperating robots in robot-based double sided incremental sheet forming

In robot-based incremental sheet forming, the forming robot is displaced due to the forming forces and the comparable low stiffness. As the forming forces can not be predicted precisely, the stiffness needs to be compensated based on the measurement of a force torque sensor. While previous approaches used precalculated lookup tables, this publication presents a multi body system robot model that can calculate the displacement of the tool center point in real-time. In incremental sheet forming, the supporting robot is typically force controlled to bring superimposed stress into the forming zone. Unfortunately, this could lead to oscillations in the stiffness compensation. The presented force control approach takes the stiffness compensation into account to ensure a smooth movement of the forming robot. In a series of 30 forming experiments the effectiveness of the developed stiffness compensation and force control is validated.