Differential Inverse Kinematics of a Redundant 4R Exoskeleton Shoulder Joint

A.Q.L. Keemink (Corresponding Author), G. van Oort, M. Wessels, A. Stienen

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    Most active upper-extremity rehabilitation exoskeleton designs incorporate a 3R rotational shoulder joint with orthogonal axes. This kind of joint has poor conditioning close to singular configurations when all joint axes become coplanar, which reduces its effective range of motion. We investigate an alternative approach of using a redundant non-orthogonal 4R rotational shoulder joint. By inspecting the behavior of the possible nullspace motions, a new method is devised to resolve the redundancy in the differential inverse kinematics (IK) problem. A 1D nullspace global attraction method is used, instead of naive nullspace projection, to guarantee proper convergence. The design of the exoskeleton and the proposed IK method ensure good conditioning, avoid collisions with the human head, arm and trunk, can reach the entire human workspace, and outperforms conventional 3R orthogonal exoskeleton designs in terms of lower joint velocities and no body collisions.
    Original languageEnglish
    Pages (from-to)817-829
    Number of pages13
    JournalIEEE transactions on neural systems and rehabilitation engineering
    Issue number4
    Publication statusPublished - 1 Apr 2018


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