In this paper, we describe a general control framework for output reference trajectory tracking of compliantly actuated robots in the presence of time-varying disturbances. In order to obtain strong robustness and attenuate chattering, a continuous sliding mode control (CSMC) design is employed. However, this CSMC structure can not guarantee the high tracking performance of the closed loop system since exiting mismatched time-varying disturbances in compliantly actuated robots. Due to the significance of dealing with the mismatched problem, a new sliding surface with the assistance of generalized proportional integral observers (GPIOs), which only use the position measurement of the motor and link, is designed such that system states can be driven to equilibrium point. Meanwhile, under this proposed general control framework, called the CSMC+GPIO scheme, the robustness of compliant robot systems is further enhanced since matched disturbance estimation is used to controller. Also, a detailed stability analysis of the closed loop system under the proposed approach is presented. Experimental results are provided to illustrate the promised position tracking performance of the proposed control strategy under the different test conditions.
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