H∞ model-based robust control of a manipulator

Mechanical manipulators are modeled by a set of coupled nonlinear second-order differential equations. When a complete model of the manipulator dynamics is obtained, model-based controllers which decouple and linearize the manipulator dynamics can track the desired trajectories uniformly in all configurations of the manipulator. However, there is a degree of uncertainty in the parameters of the manipulator, especially if it is carrying unknown loads. Therefore, model-based control schemes that are robust against modelling errors and disturbances are required. This paper proposes a robust control scheme based on H^∞ control theory. Given a nominal model of the manipulator dynamics, the controller consists of a model-based controller followed by a H^∞ controller. The model-based controller approximately linearizes the manipulator dynamics. The H^∞ controller compensates for disturbances and unmodeled dynamics. Simulations and experiments on a two-link direct drive manipulator exhibits the effectiveness of the proposed H^∞ model-based robust control scheme