Design and Validation of a Two-Degree-of-Freedom Powered Ankle-Foot Orthosis with Two Pneumatic Artificial Muscles

• Published in: Mechatronics (Oxford) Vol. 72; p. 102469
• Main Authors: Choi, Ho Seon, Lee, Chang Hee, Baek, Yoon Su
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.12.2020
• Subjects: Balance training; Pneumatic artificial muscle (PAM); Powered ankle-foot orthosis (PAFO); Sliding mode control; Subtalar joint; ADC; FTS; Subtalar joint; PVM; Pneumatic artificial muscle (PAM); P-btnc; RoM; COMCoP; FFT; PJMc; EMG; PAFO; CC; FSR; Pavg; θavg; 2-D; 3-D; RMSE; Balance training; Sliding mode control; SEA; Powered ankle-foot orthosis (PAFO); dof; P-bc; PAM
• ISSN: 0957-4158; 1873-4006
• DOI: 10.1016/j.mechatronics.2020.102469

•The subtalar joint is an important part of balance training.•System design and validation were proposed for a 2-df PAFO.•Spatial formulas for the talocrural and subtalar joints were calculated and added.•For precise control, a sliding mode control for a nonlinear system of PAM was used.•Kinematics, workspace, frequency response, and clinical experiments were analyzed. Powered ankle-foot orthosis (PAFO) is a field of wearable robotics that improves the lives of people of old age or with physical impairments by aiding in the wearer's ankle joint movements. Most of the PAFOs developed thus far offer only one degree-of-freedom (dof), which uses the talocrural joint alone as the axis of rotation, where the emphasis is on moving forward. However, because this type of wearable robotics has evolved, developing PAFOs for functional rehabilitation has become necessary. This enhances the quality of walking rather than providing simple rehabilitation. The subtalar joint is responsible for the rotation of the inversion and eversion of the ankle, enabling balanced walking in humans, and is an important part of balance training for elderly people or stroke patient rehabilitation. Therefore, we developed a 2-dof PAFO that uses a calculated spatial formula of the subtalar joint based on anatomical data. In recognition of the fact that the pneumatic artificial muscle (PAM) can be used within the contracting range alone because of the instinct of the PAM, we analyzed the workspace of the fabricated PAFO through kinematic analysis and verified the possibility of using the PAFO during the gait cycle. Experiments were also conducted on the closed-loop force frequency response using a sliding mode control of the solenoid valve to validate the control characteristics. Lastly, clinical experiments with healthy subjects were conducted for validation in wearing conditions.