Passivity-constrained variable impedance control based on hierarchical decoupling controller for hydraulic manipulators

Abstract

Impedance control makes the manipulator compliant by regulating the dynamic behavior between the environment and itself. As contact-based applications become more complex, variable impedance control has attracted more attention. However, variable impedance control can cause instability when directly switching impedance parameters, which is a conflict between maintaining the passivity and varying impedance parameters. To solve this conflict, a novel passivity-constrained variable impedance controller for hydraulic manipulators is proposed within the framework of model predictive control. With the impedance relationship and the manipulator dynamics integrated into a prediction model, the proposed strategy utilizes the passivity constraint and the impedance error cost to achieve an optimized tradeoff between passivity guarantee and impedance variation. Furthermore, the inner-loop motion of the hydraulic manipulator is controlled by the hierarchical decoupling controller with the manipulator dynamics and the nonlinearity of the valve-controlled cylinder system considered. The effectiveness of this method was verified by experiments on a heavy-duty hydraulic manipulator. Compared with the traditional method, the proposed method can improve the passivity while ensuring the timely modulation of impedance parameters.