Bang-bang impact control using hybrid impedance/time-delay control

Abstract

For stabilization of a robot manipulator upon collision with a stiff environment, a nonlinear bang-bang impact controller is developed. Under this control, a robot can successfully achieve contact tasks without changing the control algorithm or controller gains throughout all three modes: free space, transition and constrained motion. It uses a robust hybrid impedance/time-delay control algorithm to first 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 attained. After impact transient, the hybrid impedance/time-delay control algorithm is again utilized. This bang-bang control method provides stable interaction between a robot with severe nonlinear joint friction and a stiff environment, and achieves rapid response while minimizing force overshoots. During contact transition, we employ one simple control algorithm that switches only to zero and maintains the same gains, while other controllers use more than one control algorithm or different control gains. It is shown via experiments that overall performance is superior or comparable to more complicated existing impact force control techniques.