Coordination control of a 3 DOF distributed human assistive load lifting system with force amplification

This paper deals with coordination control of a 3 DOF lifting system with human power amplification, taking passivity control into account to ensure safety interactions between human and object. A scissor mechanism based lifting system is designed to achieve compactness while an accumulator-pump/motor-cylinder architecture is employed to save electric energy from DC motor and recover potential energy during load descending. Dynamics of mechanical systems as well as electrohydraulic drive unit is modeled mathematically. Control system is designed with equivalent master/slave coordination control strategy to address the issue existing in human assistive operation and the controller for the DC motor is designed with back-stepping algorithm. By applying the idea of the shape and locked systems, the control objective is achieved successfully and the system passivity condition is satisfied consequently by introducing a fictitious flywheel virtually connected with the controller to perform energy storage. Simulation results show that the proposed coordination control strategy for multi-objects is applicable to implement the position and attitude control of the lifting system and the coordination control issue can be dealt with successfully even in the presence of sudden load disturbance.