Design of A Novel Statically Balanced Mechanism for End-effector-type Upper Limb Assistance

Partial loss of upper limb motor function is a typical sequela of stroke. To help such patients actively cope with daily challenges and improve their quality of life, limb functional assistances play important roles. To this end, this paper proposes a three-degree-of-freedom parallel mechanism, which can be used for human upper limb assistance. The base of the proposed mechanism is a circular track that can be attached to the waist of the human body. The mechanism consists of two chains containing parallelogram linkage, which presents good constraints for the mobile platform and facilitates the static balance design by adding springs, thereby providing reliable assistive functions and lightweight portability. The mobility of the proposed mechanism is analyzed via the screw theory, and it is verified that the mechanism generates the aimed movements. Then, the kinematic analysis of the mechanism is presented. Finally, the static balance design is carried out in detail, and the spring constants of the three added springs are calculated. The result shows that the mechanism can achieve perfect static balance. The proposed mechanism is expected to provide a potential candidate for assistive devices and be developed into a prototype providing upper limb assistance.