This note considers the swinging up of a cart-pendulum system with viscous friction by energy control. An experimental result indicates that a complete swinging up of the pendulum cannot be achieved by the control strategy of Lozano et al. when the effects of the friction are not negligible. It is shown that the performance is improved when a slight modification is introduced to the control algorithm by cancellation of the friction term in the closed-loop equation of the pendulum. The effectiveness of the proposed controller is demonstrated experimentally.
