A Novel Parallel Exoskeleton for Wrist Rehabilitation: Conceptual Design, Kinematics, and Singularity Analysis
TL;DR
The design and kinematic validation of a novel 3-DOF spherical parallel exoskeleton featuring base-fixed actuators featuring base-fixed actuators featuring exponential rotational matrices is presented, providing systematic derivations of equations in compact form.
Abstract
Wrist rehabilitation requires high precision, haptic transparency, and accurate alignment with the human joint’s physiological center of rotation. Conventional robotic systems often suffer from high moving inertia or joint misalignment. This paper presents the design and kinematic validation of a novel 3-DOF spherical parallel exoskeleton featuring base-fixed actuators. By mounting all actuators to a fixed base, the proposed architecture significantly reduces moving mass, achieving a low-inertia response critical for safe patient–robot interaction. The “virtual center” concept eliminates physical central joints, enabling a compact design completed by the user’s anatomy. To perform the kinematic and singularity analyses of the manipulator, two distinct models were used: Rotated Frame Based (RFB) and Initial Frame Based (IFB). Performance metrics, namely the manipulability index and condition number, are evaluated to assess dexterity and isotropy. Comparative kinematic analysis of Rotated (RFB) and Initial Frame Based (IFB) models confirm ideal central isotropy (κ=1.0). While RFB yields 94.14% high-dexterity (κ<5.0) and 99.78% usable (κ<10.0) workspace coverage, IFB achieves 78.80% high-dexterity (κ<5.0) and 92.18% usable (κ<10.0) workspace coverage. Analytical manipulability metrics validate singularity-free motion throughout the anatomical range. Additionally, the use of exponential rotational matrices in this paper provides systematic derivations of equations in compact form.