Active Gravity compensation using Tendon Antagonism for Earth-based testing of Space Soft Continuum Robotics

Abstract

Continuum soft manipulators (CSMs) offer key advantages over rigid robots for on-orbit servicing (OOS), but their deployment requires realistic ground-based testing environments. To emulate microgravity conditions for CSMs, this paper proposes tendon antagonism as a model based gravity compensation method. It is shown that a tendon layout design consisting of one linear tendon and two tendons shaped as five-segment piecewise-linear approximations of sinusoids is sufficient to counteract planar bending moment by gravitational loading. Dynamic simulations compare a gravity-loaded plant model, a gravity free reference model, and an uncompensated baseline using a geometric variable strain formulation. Results show accurate tracking on bending DOFs with negligible (10−5 rad/m) tracking errors in steady-state conditions and remain small during motion (10−2 rad/m), increasing moderately at higher actuation levels. Small errors in task space (18 mm) stem from uncontrolled elongation DOF, as tendon actuation is limited to tension only. The design is further validated experimentally, using machine vision for pose estimation. Results show high accuracy of the simulation, and demonstrate that tendon antagonism reduces gravitational sagging and enables tracking of the reference configuration across actuation values. Average positional error reduces by 80%, from 103 mm to 18 mm when using the compensation mechanism. At high actuation values, results show overcompensation for the gravity load, hinting to possible improvements in the tendon control scheme. Future research could implement real-time control or control of the remaining free DOFs.