Effect of Mobility Devices on Orientation Sensors That Contain MagnetometersBy Kendell, Cynthia; Lemaire, Edward D.; Journal of Rehabilitation Research and Development, Vol. 46, No. 7, pp. 957-962
Publication Date: 2009
Study undertaken to quantify the error caused by assistive mobility devices on commercially available orientation sensors that contain magnetometers, and to examine the viability of using these orientation sensors in rehabilitation research. The investigation was prompted by the observation that, while orientation sensors containing magnetometers use the earth’s magnetic field as a reference, ferromagnetic objects, including components of assistive devices, may distort this magnetic field, leading to inaccurate orientation output. Study data were collected via two MTx orientation sensors connected to an XBus Master data collection unit and attached to a plastic frame such that the relative angle between sensors was constant. A series of mobility devices were then moved in proximity to the plastic frame: one aluminum and one stainless steel knee-ankle-foot orthosis, one ankle-foot orthosis, one exoskeletal and one endoskeletal transtibial prosthesis, two standard walkers, and one manual and one power wheelchair. For each mobility device, the average difference in relative angle between the baseline and peak angles was calculated for each of five trials. Errors ranged from less than 0.10 to 35.29 degrees, depending on the amount of metal present in the mobility device and frame positioning near the device. While strategic orientation sensor placement on some mobility devices can minimize these errors to an acceptable levels, the authors recommend implementing testing protocols to verify orientation sensor accuracy for these applications.
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