A Study on the Comparative Analysis of Self-Aligned and Alignment-Free Mechanisms for Shoulder Rehabilitation

Abstract This study focuses on the comparative evaluation of self-aligned (S-A) and alignment-free (A-F) mechanisms for upper limb rehabilitation robots, aiming to improve comfort and adaptability in rehabilitation exercises. The manuscript introduces a detailed analysis of the kinematic adaptability and interaction forces and torques associated with the 3Ra3P and 3Ra2R1P configurations, providing critical insights into their respective strengths and limitations. The methods include kinematic modeling and experimental evaluation of interaction forces during rehabilitation tasks, specifically “eating” and “combing” movements. Key findings reveal that the alignment-free design demonstrated superior adaptability to complex movement trajectories, allowing greater joint displacement and enhanced flexibility. However, this increased adaptability was associated with higher interaction forces and torques, indicating increased resistance and reduced compatibility. Conversely, the self-aligned design exhibited lower interaction forces, suggesting a smoother and more controlled rehabilitation experience, but with reduced flexibility. These insights emphasize the importance of selecting the appropriate design based on specific rehabilitation objectives. The implications of this work are significant for the development of personalized rehabilitation systems, as it highlights the trade-offs between adaptability and resistance in robotic assistance, guiding clinicians in optimizing rehabilitation protocols for individual patient needs.