Prototyping Force-Controlled 3-DOF Hydraulic Arms for Humanoid Robots

Abstract

This paper reports on a hydraulic dual arm robot developed as a rapid prototype for our hydraulic humanoid robot. The lightweight arms (4 kg each) have three joints driven by hydraulic linear servo actuators that can achieve higher torque and speed than human arms. A double four-bar linkage provides a wide range of motion (210°) to the shoulder joint. Each joint has torque controllability that is fully utilized for compliant whole-body motion control tasks. Based on singular perturbation analysis, we discuss how damping on the joints is actively modulated by hydraulic force feedback control, which is then utilized in our passivity-based task-space force control scheme. The effectiveness of the proposed system is experimentally evaluated through zero-force tracking gravity compensation with a 10 kg payload and object manipulation tasks.