Abstract
Every year, stroke-induced upper limb impairment impacts millions of people worldwide, necessitating intensive rehabilitation to regain motor control. While conventional physical therapy and end-effector-based robots have been utilized, they often face limitations such as high labor costs, therapist fatigue, and an inability to control the redundancy of the human arm, which can lead to nonphysiologic compensatory movements. To address these challenges, this paper presents the development of the hybrid shoulder rehabilitation exoskeleton, an advanced iteration of the previous HYBRID-1 prototype. The hybridshoulder exoskeleton introduces two major design modifications based on performance evaluations and cable tension issues identified in the initial version. First, the shoulder girdle mechanism was redesigned by replacing the inverted slider-crank linkage with a planar crank-rocker four-bar linkage consisting of four revolute joints to better align with human anatomy. Second, a novel pretension mechanism was integrated into the Cable-Driven Parallel Mechanism toprevent cable derailment and maintain consistent tension using a system of rods, rollers, and compression springs.The design was first validated through a 3D-printed miniature model and CAD simulations, which confirmed the accuracy of the forward and inverse kinematic models. Subsequently, a real-scale prototype was manufactured featuring an adjustable shoulder cuff and additional base support to enhance structural stability for clinical applications. Initial assembly and preliminary testing indicate that these modifications provide a robust platform for intensive, task-specific rehabilitation. Future work will focus on performance testingwith healthy subjects to evaluate the system’s adaptability to various body parameters such as height and arm diameter. Keywords:Stroke Rehabilitation, Shoulder Exoskeleton, Shoulder Girdle Mechanism, Passive Pretension Mechanism, Crank-Rocker Four-Bar Linkage.