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Biomechanical design analysis and experiments evaluation of a passive knee-assisting exoskeleton for weight-climbing

Bo Li (Army Logistics University of PLA, Chongqing, China and Chongqing University of Technology, Chongqing, China)
Bo Yuan (Army Logistics University of PLA, Chongqing, China and Niudi Tech. Co. Ltd., Chongqing, China)
Shuai Tang (Army Logistics University of PLA, Chongqing, China)
Yuwen Mao (Engineering Research Center for Disaster and Emergency Rescue Equipment of China, Chongqing, China)
Dongmei Zhang (Engineering Research Center for Disaster and Emergency Rescue Equipment of China, Chongqing, China)
Changyun Huang (Army Logistics University of PLA, Chongqing, China)
Bilian Tan (College of Art and Science, New York University, New York, USA)

Industrial Robot

ISSN: 0143-991x

Article publication date: 21 August 2018

Issue publication date: 29 August 2018




This paper aims to investigate weight-climbing assistance strategy for the biomechanical design of passive knee-assisting exoskeleton (PKAExo) and evaluate a designed PKAExo which stores energy when the knee joint flexes and releases the energy to assist ascending when the knee joint extends.


The authors constructed theoretic modeling of human weight-climbing to analyze characteristics of knee angle and moment. They then conducted camera-based movement analysis, muscle strength and endurance tests and surface electromyography (sEMG) measures to verify the relationship of knee angle and moment with both stair height and load weight. Afterwards, the authors proposed an assistant strategy for passive knee assistance, then gave out designed PKAExo and conducted mechanical experiment to test the knee-assisting torque. Finally, the authors conducted comparison experiment based on measuring the sEMG signals of knee extensor to verify the assistance effect of the PKAExo for weight-climbing.


The knee extensor produces the maximum force during weight-climbing, and the muscle force provided by knee extensor has significant increasing rate along with the stair height. Thus, the assistance torque of PKAExo is designed to increase nonlinearly along with increasing knee angle. It stores energy when knee flexes and assists when knee extends. Both the mechanical experiment and comparison experiment have demonstrated that the PKAExo is able to provide nonlinear assistance torque for weight-climbing, thus decreasing the average maximum load of knee extensor by about 21 per cent, reducing muscle fatigue and enhancing wearer’s weight-climbing ability.


The authors construct theoretic maximum force model produced by knee extensor for weight-climbing in static situation and conduct a series of experiments to verify and revise the model, which is the fundamental reference for knee-assisting mechanism designed for weight-climbing. The authors have also provided and validated an assistant strategy and the mechanism based on the biomechanical analysis, which aims to translate wearer’s energy-providing mode form high load to mid-low load by storing energy when knee flexes and assisting when knee extends. The PKAExo decreases the maximum load of knee extensor, reduces muscle fatigue and helps people to easily climb with load.



The authors thank the College of Mechanical Engineering in Chongqing Industrial and Commercial University for lending BioPac equipment to our team. Funding for this research was provided by National Natural Science Foundations of China (Grant Nos. 51505494 and 11504427), China Postdoctoral Science Foundation (Grant No. 2015M582836), and Chongqing Science & Technology Funding (Grant No. cstc2018jscx-msyb1110).


Li, B., Yuan, B., Tang, S., Mao, Y., Zhang, D., Huang, C. and Tan, B. (2019), "Biomechanical design analysis and experiments evaluation of a passive knee-assisting exoskeleton for weight-climbing", Industrial Robot, Vol. 45 No. 4, pp. 436-445.



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