Friction compensation for a double inverted pendulum

The inverted pendulum system exhibits nonnegligible nonlinearities due to its dynamic structure and friction forces, which cause large limit cycles. The limit cycles are well predicted by the nonlinear simulation model with Coulomb and viscous friction. To compensate the cart-on-rail friction, a friction compensator based on modified first-order Dahl model is implemented. The experiment results show that the amplitudes of the limit cycles are substantially reduced by friction compensation. In particular, the friction compensator works quite well without accurate velocity signals. The study will thus be of value to a variety of systems for compensating friction without extra velocity sensors.