Research on position/force hybrid control of an FFHD robot with EHS-actuators

Abstract

An Electro-Hydraulic Servo (EHS) Four-Footed Heavy-Duty (FFHD) robot is designed and developed in this work. An integration layout cylinder design scheme for the non-lightweight EHS four-footed robot with high loads and hip joint torques is proposed, and a mathematical element analysis model for a parallel EHS cylinder system is derived. Multiple inherent characteristics of the parallel-executed cylinder integration system model are then further explored. Based on the controllable functional requirements of interconnected joints and the influence reduction in internal force coupling, a force/position hybrid control scheme for the parallel-executed cylinder is determined, and the force/position signal module design unit is used to solve the force/position hybrid control in reverse. The implementation process of magnetic flux compensation and speed compensation is discussed in detail, considering the inherent requirements of the EHS-executed cylinder force control unit module. A compliant controller is then applied to the EHS-executed cylinder force unit module, and the proportional integral derivative (PID) controller is determined in the EHS-executed cylinder position control unit module. The compound control strategy proposed in this paper is verified on a parallel EHS platform. The experimental verification results reveal that the values of position/force attenuation amplitude and lag phase are no greater than 10.0% and 20°, respectively. The feasibility of the interconnected implementation of the proposed hybrid control scheme is then analyzed. The conclusions obtained in this research provide relevant insights for the application of FFHD robot control systems.