An evaluation platform is being developed that consists of a circular treadmill and a gait emulator mechanism. The platform allows for repeatable experiments on the prototype steerable prosthesis with different gait speeds and loads to define a performance criterion for the steerable prostheses, and enable iterative improvements to the design of the prosthesis.
The platform will be used for developing the control methods for the prototype prosthesis to accommodate different surface profiles and different radiuses of turn. It will be used to explore how a steerable ankle-foot prosthesis may enhance maneuverability for traversing slopes.
The objective of this research is to develop a practical, low-weight, tendon-driven, ankle-foot prosthetic robot capable of steering to enhance agility during turnings and accommodating for the changes in the profile and slope of the ground.
This prototype is aimed to mimic the mechanical impedance of the human ankle in both dorsiflexion-plantarflexion and inversion-eversion DOFs.
Ankle Rotations During Stance Period of Step Turn
This study compares the three-dimentional rotations of the ankle during straight walk and step turn. Infrared camera system (Qualisys Oqus ®) is used to track the trajectories and angles of the foot and leg at different stages of the gait. The range of motion in inversion-eversion (IE) increased during turning while rotation in lateral-medial (ML) direction decreased and dorsiflexion-plantarflexion (DP) changed the least. The results suggest the addition of an extra controllable degree of freedom in the inversion-eversion direction to prosthetic ankle-foot robots may enhance their maneuverability.
The results show an increasing inversion for leaning the body toward the inside of the turn. DP starts with similar angles to straight walk and progressively shows less plantarflexion. ML rotation initiates with an increased medial rotation transitioning to lateral rotation at toe off.
Estimation of Human Ankle Mechanical Impedance
Mechanical impedance of human ankle plays a major role in lower extremity functions and locomotion. Mechanical impedance of the ankle defines the evoked torques in the ankle to the motion perturbations.
The aim of this study is to estimate the mechanical impedance of human ankle in different periods of gait. The results will be used for the design of the lower extremity assistive robots, including ankle-foot prosthetic robots, that mimic the time-varying mechanical impedance of human ankle during different scenarios of gait, such as steering and traversing a slope that require an ankle joint with controllable degrees of freedom in both sagittal and frontal planes.
Anklebot (Interactive Motion Technologies, Inc.) is the main device used in this study to apply torque perturbations to the human ankle, measure the movement of the foot, and identify the mechanical impedance of the ankle.
Anklebot is a backdrivable therapeutic robot with low friction that allows human subjects to move their foot freely in three DOFs relative to the shank. Of those, two DOF are actuated by two nearly-parallel linear actuators attached to the leg (through a shoe and knee-brace) and aligned approximately between the knee and the ball of the foot. Subjects wear a modified shoe and a knee brace, to which the Anklebot is connected.