Force and impact control for robot manipulators using time delay

A new approach to the interaction control of systems with unknown dynamics has been developed by combining natural admittance control (NAC) with time delay control (TDC). The proposed nonlinear controller does not require specific knowledge of the system's dynamics or the environment nor does it necessitate the estimation of system parameters, except inertia, rendering it easy to implement. It rejects unmodeled dynamics, nonlinearities and disturbances without difficult characterization process while preserving the desired dynamics. The simulation results demonstrate not only good external disturbance rejection, robustness to parameter changes and insensitivity to noise, but also demonstrate good trajectory following providing good rejection of internal Coulomb friction. This novel control technique is also used to develop a nonlinear bang-bang impact controller (NBBIC) for stabilization of a robot manipulator upon collision with a stiff environment. It uses the above-mentioned NAC/TDC control algorithm with negative force feedback to absorb impact forces and stabilize the system. This control input alternates with zero when no environment force is sensed due to loss of contact. This alternation of control action repeats until the impact transient subsides and steady state is established. After impact transient, proportional-derivative force control is used. It is shown via simulations that NBBIC provides stable interaction between the robot with severe nonlinear joint friction and a stiff environment and achieves rapid response while minimizing force overshoots.