Abstract
The ankle joint of a powered ankle–foot orthosis (PAFO) is a prominent component, as it must withstand the dynamic loading conditions during its service time, while delivering all the functional requirements such as reducing the metabolic effort during walking, minimizing the stress on the user’s joint, and improving the gait stability of the impaired subjects. More often, the life of an AFO is limited by the performance of its joint; hence, a careful design consideration and material selection are required to increase the AFO’s service life. In the present work, a compact AFO joint was designed based on a worm gear mechanism with steel and brass counterparts due to the fact of its large torque transfer capability in a single stage, enabling a compact joint. Further, it provided an added advantage of self-locking due to the large friction that prevents backdrive, which is beneficial for drop-foot recovery. The design was verified using nonlinear finite element analysis for maximum torque situations at the ankle joint during normal walking. The results indicate stress levels within its design performance; however, it is recommended to select high-grade structural steel for the ankle shaft as the highest stresses in AFO were located on it.
Highlights
A great deal of work is in progress on wearable orthotics, yet lightweight, portable, and efficiently designed products are not available on the commercial market
Components a possible design modification. For both for cases, it was observed that the maximum stress region was confined within the ankle orthosis and,that due considerations will be made during the. For joint both shaft cases,init an was observed the maximum stress region was confined within prototype to minimize the stress about the ankle shaft and toduring consider the ankle design joint shaft in an orthosis and,concentration due considerations will be made the optimizing the shaft diameter based on the ankle jointabout kinetics
The proposed design for powering the plantar flexion was based on a worm gear mechanism, which is advantageous due to the fact of its large torque transmission capability with self-locking capability
Summary
A great deal of work is in progress on wearable orthotics, yet lightweight, portable, and efficiently designed products are not available on the commercial market. Lightweight wearable orthotics for assistive motor functions have gained considerable popularity and research interest in recent years, which is quite evident from the numerous literature [1,2,3]. The range of these angles varies from person to person, it must be precisely measured during an individual’s gait, as the same values will be controlled by an externally powered flexion mechanism during assisted walking [4]. Ankle flexion assist is usually sought for (a) extending the active years of motor functionality in the elderly population [5], (b) reducing the metabolic cost of walking by providing assisted walking in the case of a healthy individual [6], and (c) improving the motor functions of persons suffering from impaired gait capabilities [7,8,9]
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