Mechanics Unloading Analysis and Experimentation of a New Type of Parallel Biomimetic Shoulder Complex

The structure design for high ratio of carrying capacity to deadweight is one of the challenges for the bionic mechanism,while the problem concerning high carrying capacity has not yet be solved for the existing shoulder complex.A new type biomimetic shoulder complex,which adopts 3-PSS/S（P for prismatic pair,S for spherical pair） spherical parallel mechanism（SPM）,is proposed.The static equilibrium equations of each component are established by using the vector method and the equations for constrain forces with certain load are solved.Then the constrain force on the middle limb and that on the side limbs are compared in order to verify the unloading performance of the mechanism.In addition,the prototype mechanism of the shoulder complex is developed,and the force feedback experiment is conducted to verify the static analysis,which indicates that the middle limb suffers most of the external force and the effect of mechanics unloading is achieved.The 3-PSS/S spherical parallel mechanism is presented for the shoulder complex,and the realization of mechanics unloading is benefit for the improvement of the carrying capacity of the shoulder complex.

Designing Unpowered Shoulder Complex Exoskeleton via Contralateral Drive for Self-rehabilitation of Post-stroke Hemiparesis

Rehabilitation using exoskeleton robots can effectively remediate dysfunction and restore post-stroke survivors’ physical ability. However, low kinematic compatibility and poor self-participation of post-stroke patients in rehabilitation restrict the outcomes of exoskeleton-based therapy. The study presents an Unpowered Shoulder Complex Exoskeleton (USCE), consisting of Shoulder Girdle Mechanism (SGM), Ball-and-Socket Joint Mechanism (BSM), Gravity Compensating Mechanism (GCM) and Adjustable Alignment Design (AAD), to achieve self-rehabilitation of shoulder via energy transfer from the healthy upper limb to the affected counterpart of post-stroke hemiplegic patients. The SGM and AAD are designed to improve the kinematic compatibility by compensating for displacements of the glenohumeral joint with the adaptable size of USCE for different wearers. The BSM and GCM can transfer the body movement and energy from the healthy half of the body to the affected side without external energy input and enhance the self-participation with sick posture correction. The experimental results show that the USCE can provide high kinematic compatibility with 90.9% movement similarity between human and exoskeleton. Meanwhile, the motion ability of a post-stroke patient’s affected limb can be increased through energy transfer. It is expected that USCE can improve outcomes of home-based self-rehabilitation.

Adaptive Multi-Objective Optimization of Bionic Shoulder Joint Based on Particle Swarm Optimization

To get the movement mode and driving mechanism similar to human shoulder joint,a six degrees of freedom(DOF) serial-parallel bionic shoulder joint mechanism driven by pneumatic muscle actuators(PMAs)was designed.However,the structural parameters of the shoulder joint will affect various performances of the mechanism.To obtain the optimal structure parameters,the particle swarm optimization(PSO) was used.Besides,the mathematical expressions of indexes of rotation ranges,maximum bearing torque,discrete dexterity and muscle shrinkage of the bionic shoulder joint were established respectively to represent its many-sided characteristics.And the multi-objective optimization problem was transformed into a single-objective optimization problem by using the weighted-sum method.The normalization method and adaptive-weight method were used to determine each optimization index's weight coefficient;then the particle swarm optimization was used to optimize the integrated objective function of the bionic shoulder joint and the optimal solution was obtained.Compared with the average optimization generations and the optimal target values of many experiments,using adaptive-weight method to adjust weights of integrated objective function is better than using normalization method,which validates superiority of the adaptive-weight method.