RESEARCH ON THE COMPLIANT CONTROL OF ELECTROHYDRAULIC SERVO DRIVE FORCE/POSITION SWITCHING FOR A LOWER LIMB EXOSKELETON ROBOT

In order to improve the flexibility of the foot landing of a lower limb exoskeleton robot based on an electro-hydraulic servo drive and to reduce its impact with the ground, an active compliance control method for force/position switching based on fuzzy control is proposed. According to the mathematical model of each component of the electro-hydraulic servo system of the core drive unit of the lower limb exoskeleton robot, the transfer functions of the position control system and the force control system are obtained respectively, and then its specific working characteristics are studied. Before the feet hit the ground, the position servo control system under the action of a fuzzy controller is used to achieve the movement of legs in free and unconstrained space, and the moment the foot touches the ground, the system is switched to a force servo control system to precisely control the output force, thereby reducing the rigid impact between the feet. In the meantime, the validity of the designed switching method and controller is verified by the joint simulation of MATLAB and AMESIM. The simulation results show that the electro-hydraulic servo force/position switching method based on a fuzzy algorithm is able not only to guarantee the movement accuracy of the foot end of the lower limb exoskeleton robot, but can also effectively reduce the impact force between the foot end and the ground.