Design of a Pneumatic Actuated Ankle-Foot Orthosis which has Talocrural and Subtalar Joint

As aging progresses, risk of falls in elderly people increases due to the decreasing the range of motion (RoM) of eversion and the weakening of the plantar flexor. Balance training is performed to reduce the risk of falls and powered ankle-foot orthosis (PAFO) can be utilized in this process. The elderly can conduct training on the narrow roads or on the rugged ground with assistance on rotation of eversion and propulsion by PAFO. However, existing PAFOs were developed just by considering the talocrural joint which make the rotation of sagittal plane of ankle which is called by plantar flexion and dorsiflexion. So, we developed the 2 Degree of Freedom (DoF) PAFO which has the Talocrural and Subtalar joints for frontal plane rotation which is called inversion and eversion. We established the coordinate system and calculated the spatial formulas for talocrural and subtalar joint based on anatomical data. Developed PAFO has the pneumatic artificial muscle (PAM) as an actuator which is controlled by solenoid valve with PWM methods, light-weight 3D printed body and knee orthosis for interfacing with wearer in three area which are thigh, shank and foot. The total weight of developed PAFO is 2. 14kg and it can be 1. 44kg without the weight of knee orthosis (0.7kg). Measurement sensors for PAFO were the absolute encoders to measure the angle of talocrural and subtalar joint, tensile loadcell to measure the magnitude of force from PAM, pressure sensor to measure the pressure of PAM and FSR sensor to judge the phase of the gait cycle. The results of the paper show the validation of design, kinematics and functional capacity for human subject experiments with proportional myoelectric control (PMc) of developed PAFO.