Integral Sliding-Mode Observer-Based Disturbance Estimation for Euler-Lagrangian Systems

In this article, a novel integral sliding-mode observer is proposed to estimate the external disturbance and velocity of Euler-Lagrangian systems. This method provides high bandwidth and precise estimation with only commanded input and position measurement. A system velocity measurement is not required to construct the sliding-mode manifold. The convergence of the estimation error to zero is theoretically in finite time, which is proven by a direct Lyapunov method utilizing the passivity property of Euler-Lagrangian systems. An integral sliding manifold is designed to reduce the reaching phase, such that the robustness of the estimation is enhanced. The method has been applied to a robot manipulator to estimate the joint velocity and external contact forces in a physical human-robot task. Simulations and experiments reveal that this novel method provides fast, precise, and robust estimation results and can be used to replace the measurement of an external force sensor. The successful application of this observer to a force-sensor-less admittance controller for a manipulator contributes to the implementation of a sensor-free safety framework for human-robot collaboration (HRC).