Robust control for robot manipulators by using only joint position measurements

In this work, we propose an output feedback sliding mode control (SMC) method for trajectory tracking of robotic manipulators. The design process has two steps. First, we design a stable SMC approach by assuming that all state variables are available for feedback. Then, an output feedback version of this SMC design is presented which incorporates a model-free linear observer to estimate unknown velocity signals. We then show that the tracking performance under output feedback design can asymptotically recover the performance achieved under state feedback based SMC design. A detailed stability analysis is given which shows semi-global uniform ultimately boundedness property of all the closed loop signals. The proposed method is implemented and evaluated on a 2-DOF robotic system to illustrate the effectiveness of the theoretical development.