Simulation of the stopping behavior of industrial robots using a complementarity-based approach

The braking behavior of industrial robots is an important aspect for the hazard assessment of human-robot interaction involving high robot speeds. This paper proposes an adaptation of a complementarity-based treatment of friction forces [1] to the simulation of the stopping behavior of robots. A time-stepping scheme is used for integration. The system matrices are computed using an auto-coding scheme to allow rapid adaptation to arbitrary serial kinematic robots. The model is capable of handling the set-valuedness of the friction curve. Comparison of the model results with the measured braking behavior of an industrial robot shows that the general behavior of the model is correct. However, the agreement of model and measurement is still not satisfying. Better mass parameter values and functions for the brake moment are required. Simulations performed with the model suggest a strong and possibly hazardous decay of the stopping behavior for specific robot motions that is hard to predict without an appropriate model.