Hybrid position and force control of two industrial robots manipulating a flexible sheet: Theory and experiment

It is verified in this paper that the widely used scheme of PD plus a force control is also suitable for controlling a flexible system of two industrial robots manipulating a flexible sheet. It is proven by LaSalle's theorem that under the proposed control law, the desired rigid body motion can be achieved and simultaneously the vibrations of the sheet at each contact are suppressed. The offsets of all static deformations of the sheet with reference to the original positions decay to zero. The internal forces between the payload and the robots are well controlled to avoid any damage to the system. The investigation is based on the decomposition of the payload dynamics into two distinct dynamic subsystems, using a "clamped-free" model. Experiments of two CRS A460 robots manipulating a flexible aluminum sheet confirm these theoretical predictions.