Robust Adaptive Tracking Control Based on State Feedback Controller With Integrator Terms for Elastic Joint Robots With Uncertain Parameters

This brief addresses a robust adaptive control scheme based on a cascaded structure with a full state feedback controller with integrator terms as inner control loop and computed torque as outer control loop for flexible joint robots. Together with integrator effect, the adaptive control law can enhance position accuracy under uncertainties of the robot model, especially, the high friction caused by harmonic drive with high gear ratio. In this brief, the adaptive friction compensation is designed based on the LuGre friction model, which exhibits some advantages compared with the static friction model (e.g., no chattering effect at zero motor velocity). Furthermore, structural oscillations of the link side can be effectively damped by using joint torque feedback in the state feedback controller. Therefore, the proposed adaptive control approach can simultaneously provide high control performance both in terms of the dynamic behavior and the position accuracy. Global asymptotic tracking is achieved for the complete controlled system. The system stability is derived using Lyapunov approaches and Barbalat's lemma. Experimental results validate the practical efficiency of the approach.