On-line Joint Limit Avoidance for Torque Controlled Robots by Joint Space Parametrization
This addresses joint limit avoidance for torque-controlled robots, which is crucial for safe and efficient robotic manipulation, though it appears incremental as it builds on existing control methods.
The paper tackles the problem of stabilizing time-varying joint trajectories while avoiding joint limits for torque-controlled robots by introducing a joint space parametrization using exogenous states, and demonstrates stability and convergence in experiments on a humanoid robot's two degrees-of-freedom.
This paper proposes control laws ensuring the stabilization of a time-varying desired joint trajectory, as well as joint limit avoidance, in the case of fully-actuated manipulators. The key idea is to perform a parametrization of the feasible joint space in terms of exogenous states. It follows that the control of these states allows for joint limit avoidance. One of the main outcomes of this paper is that position terms in control laws are replaced by parametrized terms, where joint limits must be avoided. Stability and convergence of time-varying reference trajectories obtained with the proposed method are demonstrated to be in the sense of Lyapunov. The introduced control laws are verified by carrying out experiments on two degrees-of-freedom of the humanoid robot iCub.