Development of an Embedded Myokinetic Prosthetic Hand Controller

Abstract

The quest for an intuitive and physiologically appropriate human machine interface for the control of dexterous prostheses is far from being completed. In the last decade, much effort has been dedicated to explore innovative control strategies based on the electrical signals generated by the muscles during contraction. In contrast, a novel approach, dubbed myokinetic interface, derives the control signals from the localization of multiple magnetic markers (MMs) directly implanted into the residual muscles of the amputee. Building on this idea, here we present an embedded system based on 32 magnetic field sensors and a real time computation platform. We demonstrate that the platform can simultaneously localize in real-time up to five MMs in an anatomically relevant workspace. The system proved highly linear (R2 = 0.99) and precise (1% repeatability), yet exhibiting short computation times (4 ms) and limited cross talk errors (10% the mean stroke of the magnets). Compared to a previous PC implementation, the system exhibited similar precision and accuracy, while being ~75% faster. These results proved for the first time the viability of using an embedded system for magnet localization. They also suggest that, by using an adequate number of sensors, it is possible to increase the number of simultaneously tracked MMs while introducing delays that are not perceivable by the human operator. This could allow to control more degrees of freedom than those controllable with current technologies.

Localization accuracy of multiple magnets in a myokinetic control interface

“…For instance, having a magnet implanted in each target muscle would provide highly selective control signals compared to surface measurements, like those available in Force Myography 22 . The relatively small dimensions of the external sensor boards and control electronics, envisioned to be fully integrated into the socket 16 , would make the system convenient and easy-to-wear when compared, for example, with ultrasound probes used in sonography 23 . Future clinical trials will allow to quantitatively and qualitatively assess such advantages and to make a more thorough comparison with state-of-the-art solutions.…”

“…Several applications, including the one proposed by our group, would highly benefit from an increase in the number of simultaneously trackable MMs 8 , 12 , 15 . In our first work, we proved the viability of a system able to localize the position of four MMs 8 virtually implanted in an anatomically relevant forearm mockup; in a more recent study 16 , we demonstrated an embedded system capable of localizing up to five MMs, in real-time. Besides the practical implementation of the system, we investigated how the accuracy, the precision and the computation time of the localizer are affected by the number and distribution of both the MMs and the sensors 14 .…”

“…We used the point dipole model approximation in order to simplify the solution of the localization problem (inverse problem of magnetostatics) akin to our previous studies 8 , 14 , 16 . This model approximates each MM as a point magnetic dipole located at its centre.…”

Control Methods for Transradial Prostheses Based on Remnant Muscle Activity and Its Relationship with Proprioceptive Feedback

“…In the following works [ 150 , 151 ], researchers assessed the accuracy of the position tracking of multiple magnetic markers with a set of magnetic field sensors. It was found that increasing number of magnets (and decreasing available space between them) causes localization errors and false predictions to occur more often.…”

The Myokinetic Control Interface: How Many Magnets Can be Implanted in an Amputated Forearm? Evidence From a Simulated Environment

“…where accounts for inaccuracies in tracking the displacement of the moving magnet (i.e., model error), while accounts for false predictions of simultaneous displacement affecting the non-moving magnets (i.e., crosstalk effect). and were defined as the Euclidean distance between the actual and the estimated displacement for the moving and non-moving MMs, respectively, akin to our previous works [10], [14], [15], [26].…”