Design of a 2-Degree-of-Freedom Powered Ankle-Foot Prosthesis for Rock Climbing

Emily Rogers

Lower extremity amputation leads to limitations of biological function of individuals, which leads to challenges remaining physically active and participating in athletic activities. Physical activity is very important for cardiovascular health, weight management, and mental health. Designing devices aimed at increasing accessibility to sports will encourage individuals with amputations to continue or begin participating in athletic pursuits such as rock climbing. 

After an initial design in 2015, the group is revisiting this design problem, aiming to create a less massive, more robust and versatile design. The major design changes include a lightweight 2-degree-of-freedom actuator, modular feet for the approach of the climb, as well as slot, edge, and ice climbing, and changing the control to a less invasive system. The position control is predicted to be determined by the user via the Tongue-Computer Interface being designed in parallel.

The initial research presents the design and evaluation of a 2-degree-of-freedom powered ankle-foot prosthesis for rock climbing. The aim of this device is to restore function of the ankle and subtalar joints for trans-tibial amputees during rock climbing, providing the user with myoelectric position control of the foot. Precise positional control of the foot is especially important while climbing, as the climber’s ability to successfully scale a route requires them to reliably reorient the foot to various shapes and orientations of holds. Passive prostheses do not allow the user to reposition the foot, and current powered prostheses are too bulky and heavy to provide benefit during rock climbing. 

The design requirements for this device are that it must be lightweight (< 1.5 kg), low profile, robust, with 2 degrees of freedom of electromyographically controlled movement. The custom designed device consists of 2 non-backdrivable linear actuators in a differential pair, allowing for powered motion in plantarflexion/dorsiflexion and inversion/eversion. Load cells aligned axially with each actuator are used to provide force feedback to the device, allowing for position control during free-space motion, and powering off the actuators when the device is loaded, relying on the non-backdrivable transmission to maintain ankle and foot position while loaded. This control scheme reduces the power requirements of the device, allowing for lighter batteries as well as smaller motors and transmission.