Switching control for tracking of a hybrid position-force trajectory
This addresses the challenge of precise hybrid control in robotics for tasks like assembly or manipulation, but it is incremental as it builds on existing switching control methods by adding a hardware redesign.
This work tackles the problem of tracking time-varying motion-force profiles for a manipulator interacting with a stiff environment by proposing a switching position-force controller, but finds that stability requires unrealistic damping, leading to inferior performance, so it redesigns the manipulator with a compliant wrist to achieve stable tracking and avoid bouncing, as validated by numerical simulations.
This work proposes a control law for a manipulator with the aim of realizing desired time-varying motion-force profiles in the presence of a stiff environment. In many cases, the interaction with the environment affects only one degree of freedom of the end-effector of the manipulator. Therefore, the focus is on this contact degree of freedom, and a switching position-force controller is proposed to perform the hybrid position-force tracking task. Sufficient conditions are presented to guarantee input-to-state stability of the switching closed-loop system with respect to perturbations related to the time-varying desired motion-force profile. The switching occurs when the manipulator makes or breaks contact with the environment. The analysis shows that to guarantee closed-loop stability while tracking arbitrary time-varying motion-force profiles, the controller should implement a considerable (and often unrealistic) amount of damping, resulting in inferior tracking performance. Therefore, we propose to redesign the manipulator with a compliant wrist. Guidelines are provided for the design of the compliant wrist while employing the designed switching control strategy, such that stable tracking of a motion-force reference trajectory can be achieved and bouncing of the manipulator while making contact with the stiff environment can be avoided. Finally, numerical simulations are presented to illustrate the effectiveness of the approach.