Assessment of hand kinematics using inertial and magnetic sensors

Background: Assessment of hand kinematics is important when evaluating hand functioning. Major drawbacks ofcurrent sensing glove systems are lack of rotational observability in particular directions, labourintensive calibration methods which are sensitive to wear and lack of an absolute hand orientationestimate.

Methods: We propose an ambulatory system using inertial sensors that can be placed on the hand, fingers andthumb. It allows a full 3D reconstruction of all finger and thumb joints as well as the absoluteorientation of the hand. The system was experimentally evaluated for the static accuracy, dynamicrange and repeatability.

Results: The RMS position norm difference of the fingertip compared to an optical system was 5±0.5 mm(mean ± standard deviation) for flexion-extension and 12.4±3.0 mm for combined flexion-extensionabduction-adduction movements of the index finger. The difference between index and thumb tipsduring a pinching movement was 6.5±2.1 mm. The dynamic range of the sensing system and filterwas adequate to reconstruct full 80 degrees movements of the index finger performed at 116 timesper minute, which was limited by the range of the gyroscope. Finally, the reliability study showed amean range difference over five subjects of 1.1±0.4 degrees for a flat hand test and1.8±0.6 degrees for a plastic mold clenching test, which is smaller than other reported data gloves.

Conclusion: Compared to existing data gloves, this research showed that inertial and magnetic sensors are of interest for ambulatory analysis of the human hand and finger kinematics in terms of static accuracy, dynamic range and repeatability. It allows for estimation of multi-degree of freedom joint movements using low-cost sensors.