Abstract
This study aims to investigate an appropriate ankle velocity reference (ω <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ref</sub> ), which is the average ankle velocity of a certain healthy subject when walking with a certain walking speed. The goal is to improve a Passive Controllable Ankle Foot Orthosis (PICAFO) by implementing the ankle velocity reference. Firstly, the function to estimate ω <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ref</sub> , based on walking speed and body mass index (BMI), is obtained from 16 able-bodied subjects walking gait data. The effect of controlled stiffness (based on wref) to the user's ankle kinematics and muscle activity was evaluated by comparing it to other settings, such as walking barefooted and various constant damping stiffness (0%, 30%, 60%, and 100% of the maximum damping stiffness). Two able-bodied subjects (normal and overweight) participated in the evaluation, where they had to walk at two different walking speeds (1 and 2 km/h). The result showed that ankle kinematics and muscle activity were improved when w was controlled during walking speed of 1 km/h for both subjects. In terms of ankle kinematics, the toe clearance occurred, and walking stability increased. In terms of muscle activity, the average muscle activity had reduced by ~29% for the normal subject and by ~57% for an overweight subject, which shows that PICAFO provides necessary damping stiffness to replace the muscle works partially. In the future, by using the ω <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ref</sub> based on walking speed and BMI, the therapists can skip the trial and error process of finding an appropriate PICAFO prescription for a post-stroke patient.
Highlights
A recently developed Ankle Foot Orthosis (AFO) by researchers had an articulated ankle joint with the addition of a mechanical actuator or electrical actuator to control the walking gait [1]
These results prove that different walking speed people require unique ankle joint stiffness that needs to be supported by the Passive Controllable Ankle Foot Orthosis (PICAFO) system
This research has focused on improving passive AFO equipped with MR brake, called PICAFO by implementing ankle velocity as the control reference, based on walking speed and body mass index (BMI)
Summary
A recently developed Ankle Foot Orthosis (AFO) by researchers had an articulated ankle joint with the addition of a mechanical actuator or electrical actuator to control the walking gait [1]. An active AFO tracks the predicted motion path, which suits the user’s intention measured by EMG [7] Another example is a passive AFO that maintains the correct walking gait by controlling the joint stiffness. D. Adiputra et al.: Improving Passive AFO System Using Estimated Ankle Velocity Reference and damping stiffness [11], [12] are controlled to maintain the correct walking gait. Using the estimated ankle velocity reference, the passive AFO can adapt to different gait phases and different walking styles, such as the walking speed. There were 1440 sets of walking data that were used for establishing ωref estimation function
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