Abstract
Lower-limb assisted exoskeletons are widely researched for movement assistance or rehabilitation training. Due to advantages of compliance with human body and lightweight, some cable-driven prototypes have been developed, but most of these can assist only unidirectional movement. In this paper we present an untethered cable-driven ankle exoskeleton that can achieve plantarflexion-dorsiflexion bidirectional motion bilaterally using a pair of single motors. The main weights of the exoskeleton, i.e., the motors, power supplement units, and control units, were placed close to the proximity of the human body, i.e., the waist, to reduce the redundant rotation inertia which would apply on the wearer’s leg. A cable force transmission system based on gear-pulley assemblies was designed to transfer the power from the motor to the end-effector effectively. A cable self-tension device on the power output unit was designed to tension the cable during walking. The gait detection system based on a foot pressure sensor and an inertial measurement unit (IMU) could identify the gait cycle and gait states efficiently. To validate the power output performance of the exoskeleton, a torque tracking experiment was conducted. When the subject was wearing the exoskeleton with power on, the muscle activity of the soleus was reduced by 5.2% compared to the state without wearing the exoskeleton. This preliminarily verifies the positive assistance effect of our exoskeleton. The study in this paper demonstrates the promising application of a lightweight cable-driven exoskeleton on human motion augmentation or rehabilitation.
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Acknowledgements
We appreciate Shan-yuan SONG, Qi-kai LI, and Zhen SUN from School of Mechanical Engineering and Automation of Beihang University for help in tuning the motor driver. We thank He WANG, Bu-hui JIANG, Hao-hong SU, and Si-yang ZHANG for providing comments and constructive suggestions on the controller design. We also thank Chao LIANG and Li WANG for giving some advice on data processing.
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Tian-miao WANG and Xing-bang YANG conceived the project. Xuan PEI and Tao-gang HOU conducted the experiments and processed the data. Xuan YANG designed the mechanical model. Xuan PEI designed the control system and drafted the manuscript. Xing-bang YANG and Tao-gang HOU helped organize and enhance the structure and contents of the manuscript. Yu-bo FAN, Hugh M. HERR, and Xing-bang YANG helped organize the development or design of research methods. All authors provided feedback during the revision and finalization.
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Tian-miao WANG, Xuan PEI, Tao-gang HOU, Yu-bo FAN, Xuan YANG, Hugh M. HERR, and Xing-bang YANG declare that they have no conflict of interest.
Informed consent was obtained from all individual participants included in the experiment.
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Project supported by the National Natural Science Foundation of China (No. 61703023), Beijing Municipal Natural Science Foundation, China (No. 3184054), China Scholarship Council (No. 201706025021), and National Undergraduate Training Programs for Innovation and Entrepreneurship (No. 201910006118)
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Wang, Tm., Pei, X., Hou, Tg. et al. An untethered cable-driven ankle exoskeleton with plantarflexion-dorsiflexion bidirectional movement assistance. Front Inform Technol Electron Eng 21, 723–739 (2020). https://doi.org/10.1631/FITEE.1900455
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DOI: https://doi.org/10.1631/FITEE.1900455
Key words
- Ankle exoskeleton
- Plantarflexion-dorsiflexion bidirectional assistance
- Biological gait torque
- Cable-driven
- Gait detection