The Turmell-Meter: In Vivo Ankle Kinematics by Using Draw-Wire and
Inertial Sensors
Abstract
Objective: To implement a prototype specific for human ankle kinematics
studies in limited spaces, immobile, or lying down patients. Based on
anatomy and anthropometry, using a screw theory model, draw-wire and
inertial sensors were employed Methods: We included ankle injury studies
to highlight the importance of measuring the in vivo range of motion; we
studied the ankle anatomy, biomechanics, and anthropometry to estimate
the size and movements of the device. We simulated the biaxial
representation of ankle motion through the product of exponential
mapping. Finally, we designed a structure based on trilateration by
projecting tetrahedrons, an acquisition circuit with firmware and
calibration software. Results: The prototype has two main parts: support
and adjustable platform. We proposed a method to find the position by
projecting three apexes on the base using draw-wire sensors, an
acquisition board, a single-board computer, a display, Bluetooth, Wi-Fi,
and two inertial measurement units. The power source had battery backup
with boost and buck converters. Conclusion: We proposed an ankle model
in the screw theory framework, a method for localization, and a novel
device for in vivo measurements specific for lying patients on a bed,
the ground, outdoors, or remote locations without complex setups. The
double-battery management is robust and long lasting. Significance: The
device is an alternative for measuring the range of motion in laying
down patients. We will use it in modeling, diagnosis, and
rehabilitation.