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, 55 (9), 2134-42

Modeling of Prosthetic Limb Rotation Control by Sensing Rotation of Residual Arm Bone

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Modeling of Prosthetic Limb Rotation Control by Sensing Rotation of Residual Arm Bone

Guanglin Li et al. IEEE Trans Biomed Eng.

Abstract

We proposed a new approach to improve the control of prosthetic arm rotation in amputees. Arm rotation is sensed by implanting a small permanent magnet into the distal end of the residual bone, which produces a magnetic field. The position of the bone rotation can be derived from magnetic field distribution detected with magnetic sensors on the arm surface, and then conveyed to the prosthesis controller to manipulate the rotation of the prosthesis. Proprioception remains intact for residual limb skeletal structures; thus, this control system should be natural and easy-to-use. In this study, simulations have been conducted in an upper arm model to assess the feasibility and performance of sensing the voluntary rotation of residual humerus with an implanted magnet. A sensitivity analysis of the magnet size and arm size was presented. The influence of relative position of the magnet to the magnetic sensors, orientation of the magnet relative to the limb axis, and displacement of the magnetic sensors on the magnetic field was evaluated. The performance of shielding external magnetostatic interference was also investigated. The simulation results suggest that the direction and angle of rotation of residual humerus could be obtained by decoding the magnetic field signals with magnetic sensors built into a prosthetic socket. This pilot study provides important guidelines for developing a practical interface between the residual bone rotation and the prosthesis for control of prosthetic rotation.

Figures

Fig. 1
Fig. 1
Schematic diagram of control system of prosthesis rotation by using a magnet to sense the rotation of residual arm.
Fig. 2
Fig. 2
(a) FE model of upper arm with an implanted permanent magnet. The 3-D FE model (top) and its 2-D view (bottom). The distance from the magnet to the distal end of the arm model is 30 mm. (b) FE model of upper arm with a magnetic shield cap. The shield cap covers the part of the arm model at distal side. The permanent magnet outside the shield cap was used to simulate the magnetostatic interference source. d is the distance between the magnet and the shield cap.
Fig. 3
Fig. 3
Simulated magnetic flux density (B) of the magnet in the basic model shown in Fig. 2(a). (a) Color map of distribution of the B⃑ magnitude on the arm model surface. (b) Thirty-six observation nodes on the circumference of a transverse cross section of the FE model. The transverse cross section was located at x = 30 mm.
Fig. 4
Fig. 4
Magnitudes of simulated magnetic flux density and its three components (Bx, By, and Bz) over 36 observation nodes shown in Fig. 3(b). The jagged results over the nodes (31–36) in the magnitude values of magnetic field might be produced by the modeling errors. (a) B magnitude. (b) Component By. (c) Component Bz. (d) Component Bx.
Fig. 5
Fig. 5
Effects of arm size and magnet size on the peak-to-peak strength of the y-direction component of magnetic flux density on arm surface. (a) Peak-to-peak values of the y-direction component from five different arm models. (b) Peak-to-peak values of the y-direction component from five different magnet models.
Fig. 6
Fig. 6
Sensitivity of the magnetic field to the off-center of the magnet. (a) Schematic diagram of the y- and z-direction shifts of the magnet in the simulation model. (b) Distributions of the y-direction component of the magnetic field over the surface observation nodes when the magnet model shifted 5, 10, and 15 mm along the y-direction, respectively. (c) Same as (b) along the z-direction.
Fig. 7
Fig. 7
Sensitivity of the magnetic field to the displacement of the magnetic sensors. (a) Schematic diagram of the shifted observation nodes along the x-direction in the simulation model. (b) Peak-to-peak values of the y-direction component of the magnetic field on arm surface. The horizontal axis is the displacement of the observation nodes relative to the observation nodes at x = 30 mm [black dots in (a)].
Fig. 8
Fig. 8
Attenuation of magnetostatic interference with shielding. Magnetic flux density magnitudes induced by the permanent magnet outside the shield cap are plotted over the 36 surface observation nodes. The distance (d) between the magnet and shield cap was 10, 20, 30, 40, and 50 mm, respectively.

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