Precise tracking of underwater electric manipulator via model-based adaptive robust control with joint-friction compensation

The underwater electric manipulator is potentially complemented to perform high-accuracy underwater operations, owing to the high accuracy and rapid response of motor-driven mechanisms. However, some special designs for sealing and pressure resistance in underwater environments result in increased joint-friction, model nonlinearity, and parameter uncertainty. Therefore, this paper proposes a model-based adaptive robust control design of underwater electric manipulators, with joint-friction compensation for precise tracking performance. Specifically, an adaptive robust controller with the basic dynamics model is designed firstly to ensure essential tracking performance. Additionally, joint-friction characteristics are meticulously considered to construct an improved LuGre model. This is followed by the parameter identification and the formulation of an additional joint-friction desired compensation control law. In comparative underwater experiments, it is verified that the proposed controller can effectively address model nonlinearity and parameter uncertainty with joint-friction compensation, thereby achieving precise tracking performance.