Low-speed motion control of a mechanical system

Position control of a mechanical system at low speed in the presence of dry friction leads to a slip-stick process and steady-state errors when state feedback is used. In this article, the power transfer between servomotors and the system is analyzed using a Hamiltonian formulation. The analysis shows that power dissipation at low speed cannot be achieved efficiently using a proportional derivative error feedback, with constant gains. A sliding mode approach is proposed and evaluated for achieving accurate positioning of a servomotor in the presence of significant dry friction. Simulation results show the performance of a constant-gain sliding mode controller and of a self-adjusting sliding mode controller.