Bionic Design to Reduce Driving Power for a Portable Elbow Exoskeleton Based on Gravity-balancing Coupled Model

Portability is an important performance to the design of exoskeleton for rehabilitation and assistance.However,the structure of traditional exoskeletons will decrease the portability because of their heavy weight and large volume.This paper proposes a novel bionic portable elbow exoskeleton based on a human-exoskeleton gravity-balancing coupled model.The variable stiffness characteristics of the coupled model is analyzed based on the static analysis.In addition,the optimization of human-exoskeleton joint points is analysis to improve the bionic motor characteristics of the exoskeleton.Theoretical prototype is designed and its driving power and dynamic performance are analyzed.Then,a prototype is designed and manufactured with a total weight of 375 g.The merits of driving power reducing is verified by simulation and the isokinetic experiments.The simulation and isokinetic results show that the driving torque and the driving power of the subject were significantly decreased with wearing the proposed exoskeleton.The driving torques are reduced 79.28%and 57.38%from the simulation results and isokinetic experiment results,respectively.The driving work of experiment was reduced by 56.5%.The development of the novel elbow exoskeleton with gravity-balancing mechanism can expand the application of exoskeleton in home-based rehabilitation.

Hybrid Active–Passive Prosthetic Knee:A Gait Kinematics and Muscle Activity Comparison with Mechanical and Microprocessor-Controlled Passive Prostheses

Existing microprocessor-controlled passive prosthetic knees(PaPKs)and active prosthetic knees(AcPKs)cannot truly simulate the muscle activity characteristics of the active–passive hybrid action of the knee during the normal gait.Differences in EMG between normal and different prosthetic gait for different phases were never separately analyzed.In this study,a novel hybrid active–passive prosthetic knee(HAPK)is proposed and if and how muscle activity and kinematics changes in different prosthetic gait are analyzed.The hybrid hydraulic-motor actuator is adopted to fully integrate the advantages of hydraulic compliance damping and motor efficiency,and the hierarchical control strategy is adopted to realize the adaptive predictive control of the HAPK.The kinematic data and EMG data of normal gait and different prosthetic gait were compared by experiments,so as to analyze the changes in the muscle activity and spatio-temporal data per phase compared to normal walking and the adaptations of amputees when walking with a different kind of prosthesis(the mechanical prosthesis(MePK),the PaPK and the HAPK).The results show that changes in prosthetic gait mainly consisted of decreased self-selected walking speed,gait symmetry and maximum knee flexion,increased first double support phase duration,muscle activation in both opposed and prosthetic limb and inter-subject variability.The differences between controls and MePK,PaPK and HAPK decreases sequentially.These results indicate that the hybrid active–passive actuating mode can have positive effects on improving the approximation of healthy gait characteristics.

Intelligent Knee Prostheses: A Systematic Review of Control Strategies

The intelligent knee prosthesis is capable of human-like bionic lower limb control through advanced control systems and artificial intelligence algorithms that will potentially minimize gait limitations for above-knee amputees and facilitate their reintegration into society.In this paper,we sum up the control strategies corresponding to the prevailing control objectives(position and impedance)of the current intelligent knee prosthesis.Although these control strategies have been successfully implemented and validated in relevant experiments,the existing deficiencies still fail to achieve optimal performance of the controllers,which complicates the definition of a standard control method.Before a mature control system can be developed,it is more important to realize the full potential for the control strategy,which requires upgrading and refining the relevant key technologies based on the existing control methods.For this reason,we discuss potential areas for improvement of the prosthetic control system based on the summarized control strategies,including intent recognition,sensor system,prosthetic evaluation,and parameter optimization algorithms,providing future directions toward optimizing control strategies for the next generation of intelligent knee prostheses.

Design of a Minimally Actuated Lower Limb Exoskeleton with Mechanical Joint Coupling

Powered lower limb exoskeletons have traditionally used four or more powered joints to provide ambulation assistance for individuals with spinal cord injury.Exoskeletons with numerous powered joints commonly lost some excellent features of passive orthoses and further decreased utility due to added weight and increased control complexity.This work adopts joints coupling mechanism to design a powered exoskeleton to minimize the number of actuated joints and control complexity.Unlike conventional powered exoskeletons,the joint-coupled-powered exoskeleton only has a single motor-actuated joint for each exoskeleton leg in conjunction with a unique knee coupled system to enable their users to walk,sit,and stand.And two types of joint coupled systems are designed,respectively,hip-knee coupled and knee-ankle coupled.The joint-coupled-powered exoskeleton system allows a single actuator to power the hip motion,and allows activate knee motion through the coupled motions of the hip or ankle.More specifically,when the mechanical coupled system is activated,the knee joint is unlocked,resulting in synchronized hip-knee or ankle-knee flexion and extension.The coupling mechanism is switched on and off at specific phases of the gait(the stance phase and the swing phase)to generate the desired motions.The research work proves that minimal actuated robotic systems with joint coupled could achieve safe and natural walking.