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Frontiers of Information Technology & Electronic Engineering >> 2020, Volume 21, Issue 5 doi: 10.1631/FITEE.1900455

An untethered cable-driven ankle exoskeleton with plantarflexion-dorsiflexion bidirectional movement assistance

Affiliation(s): School of Mechanical Engineering and Automation, Beihang University, Beijing 100083, China; Shenyuan Honors College, Beihang University, Beijing 100083, China; School of Biological Science and Medical Engineering, Beihang University, Beijing 100083, China; MIT Media Lab, Massachusetts Institute of Technology, Cambridge, MA 02139-4307, USA; Beijing Advanced Innovation Center for Biomedical Engineering, Beihang University, Beijing 100083, China; less

Received: 2019-08-30 Accepted: 2020-05-18 Available online: 2020-05-18

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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 prototypes have been developed, but most of these can assist only unidirectional movement. In this paper we present an untethered 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 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 exoskeleton on human motion augmentation or rehabilitation.

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