cs.RO · 2607.18940 Copy arXiv ID · Jul 21, 2026 Save The Twist Decomposition of Serial Robots Under Lower-Mobility Tasks Authors: Luc Baron , Damien Chablat
Organizations: IICiMed · Polytechnique Montréal, box 6079, sta. CV, QC, H3C 3A7 Canada · box 6079, sta. CV, QC, H3C 3A7 Canada · LS2N - équipe RoMas, LS2N · Université de Nantes, Ecole Centrale de Nantes, LS2N, UMR CNRS 6004, 1 rue de la Noë, 44321 Nantes, France
Abstract This paper introduces a twist decomposition framework for serial manipulators performing lower mobility tasks. Rather than relying on Jacobian null-space projections, the method separates the end-effector twist into task and redundant components using geometrically defined twist projectors. This formulation provides a direct and intuitive distinction between task-relevant and task-irrelevant motions in operational space, enabling a compact inverse kinematics scheme that naturally handles both manipulator and task redundancy.
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May 29, 2026 · cs.RO J/K move · Enter open · S save
Mohammad Dastranj, Mahdi Hejrati, Jouni Mattila
Unit of Automation Technology and Mechanical Engineering, Faculty of Engineering and Natural Sciences Tampere University, 33720 Tampere, Finland
This paper proposes actuator-aware inverse kinematics for torque-controlled redundant robots under joint-limit constraints. In the considered architecture, the inverse-kinematic output is not merely a purely kinematic joint-velocity command; it is the required joint velocity supplied to a downstream torque-level controller. Therefore, a small commanded task residual may not necessarily improve realized motion. The proposed method formulates a convex quadratic programming problem whose decision variable is the joint-level required velocity. Control barrier function style bounds impose reference-level joint-limit admissibility, while the task equation is handled through a penalized slack variable. Redundancy is resolved using a controller-compatibility objective that accounts for previous-command consistency and actuator torque-capacity weighting. The method is independent of the particular torque-level controller and can serve as an intermediate IK layer between an endpoint trajectory and a redundant robot controller. Experiments on a virtual-decomposition-controlled seven-degree-of-freedom upper-limb exoskeleton compare the method with standard inverse-kinematic baselines and a constrained task-preserving quadratic programming baseline. The results indicate lower limit-pushing commands, bounded admissible required velocities, and improved realized task behavior in the tested trajectory, without modifying the downstream controller.