Development of a Kinematic Measurement Method for Knee Exoskeleton Fit to a User

Abstract

Proper exoskeleton fit to user impacts the safety of the human robot interaction. Exoskeletons are now being marketed by several manufacturers and yet there are currently no defined methods to measure the exoskeleton fit to the user. This research aims to develop a quantifiable test and measurement framework for evaluating exoskeleton performance, beginning with the tracking of knee kinematics. Key challenges in knee kinematic measurements include the complexity of human biomechanics, the variability of human anthropometry as well as the uncertainty of marker position, relative to underlying skeletal features, as computed by an optical tracking system (OTS). A measurement methodology to assess exoskeleton-to-leg fit based on comparison of knee kinematics between the human and the exoskeleton is proposed. The methodology is based on the use of rigid artifacts to minimize marker motion, and therefore measurement error. Separate artifacts for the exoskeleton and the human limbs enable independent tracking of exoskeleton and knee joint kinematics in order to assess exoskeleton fit to user. A prosthetic test apparatus and a 3D printed human knee model apparatus were also designed and developed to simulate the biomechanics of the human knee. The experimental data from the prosthetic leg test apparatus showed agreement with both the simulated analytical model and the ground truth skeletal structure relative to the artifacts placed on the simulated leg. The reconfigurable artifact was also tested by the researchers to demonstrate how the novel design can be used to track knee kinematics between the human leg and the exoskeleton leg.