A Torsion-Bar-Based Variable Gravity Compensation Mechanism for Robotic Joint Systems

Abstract

This letter presents a compact torsion-bar-based variable gravity compensation (TVGC) mechanism for robotic joints. Unlike conventional compensators that employ externally mounted elastic elements with fixed torque characteristics, the proposed TVGC embeds a high-stiffness torsion bar within the link and integrates a reducer and torque limiter inside the joint, eliminating dead space and avoiding workspace interference. Joint rotation is converted into torsional deformation of the embedded bar through the reducer, while torque-limiter engagement and input-angle regulation enable adjustable compensation across payloads and operating conditions. A static model and an optimization strategy are developed to shape the compensation profile and minimize residual gravitational torque under explicit mechanical constraints. A fully internalized single-axis prototype is fabricated and evaluated using a torque-measurement testbench. The experimental results demonstrate stable, tunable, and load-adaptive compensation that substantially reduces peak gravitational torque, validating the proposed TVGC as an embedded solution for compact, high-torque robotic joints.