Most force control algorithms become unstable in case of stiff contact between the end-effector and the environment. To cope with this problem, the authors introduce active damping based on force sensor data. Linear active damping is introduced using the force derivative which is obtained either by means of filtered differentiation or by means of a state-space estimator, and both enable stable stiff contact. Nonlinear active damping through a feedforward method is introduced. The novel algorithm is simple and does not require knowledge of the contact stiffness. It enables satisfactory force response which is fast and without overshoot in the case of a high feedback gain with stiff contact. This algorithm has better potential for rejecting positional disturbances than many current algorithms.
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