Design and experimental evaluation of a multi-winding gas-spring gravity compensation mechanism for high-torque sit-to-stand assistance

Abstract

Conventional gravity compensators capable of handling large loads are often bulky and require hardware modifications for different payload ranges. This study presents a multi-winding gas-spring gravity compensation mechanism (MW-GCM) for high-torque sit-to-stand assistance and evaluates its mechanical feasibility using a sensorized one-axis testbed. The MW–GCM uses four parallel cable paths designed to reduce the nominal load carried by each path while transmitting the gas-spring force and allowing the energy-storage element to be located away from the joint axis. The sit-to-stand assistance target was obtained from a quasi-static two-knee anthropometric model. By adjusting the gas-spring pressure and initial stroke, the mechanism can be retuned for different load conditions without component replacement. Experiments under variable load and speed conditions demonstrated high-torque compensation and showed direction-dependent torque error consistent with losses in the cable–pulley transmission. These results demonstrate mechanism-level feasibility under controlled testbed conditions.