Position control of robot manipulators manipulating a flexible payload

Robotic manipulation of a flexible payload is a complex and challenging control problem. This paper demonstrates from both theoretical and experimental perspectives that through proper design of the control gains, the simple scheme of PD plus gravity compensation can control a flexible payload manipulated by multiple robots to a desired position/orientation while damping the vibrations of the payload at each contact. The suppression of the vibration at each contact is helpful to suppress all vibrations of the flexible body. If the payload has a large stiffness or small mass, the proposed scheme can regulate the deformations at the contacts to zero, and also, the offsets of all static deformations of the payload with reference to the original positions decay to zero. A "clamped-free" model is used to decompose the dynamics of the payload into two distinct dynamic subsystems. This allows us to treat these dynamic subsystems separately and prove that desired motion trajectories can be achieved with the proposed scheme. As an example, the experiment of manipulating a flexible sheet using two CRS A460 robots is further described.