Relative orientation estimation between the hand and its fingers is important in many applications, such as virtual reality (VR), augmented reality (AR) and rehabilitation. It is still quite a big challenge to do the estimation by only exploiting inertial measurement units (IMUs) because of the integration drift that occurs in most approaches. When the hand is functionally used, there are many instances in which hand and finger tips move together, experiencing almost the same angular velocities, and in some of these cases, almost the same accelerations are measured in different 3D coordinate systems. Therefore, we hypothesize that relative orientations between the hand and the finger tips can be adequately estimated using 3D IMUs during such designated events (DEs) and in between these events. We fused this extra information from the DEs and IMU data with an extended Kalman filter (EKF). Our results show that errors in relative orientation can be smaller than five degrees if DEs are constantly present and the linear and angular movements of the whole hand are adequately rich. When the DEs are partially available in a functional water-drinking task, the orientation error is smaller than 10 degrees.

No abstract

No abstract

Optical tracking systems (OTS) can provide high position accuracy over a large workspace. However, the orientation from the OTS is related to the distance between markers, which contains large errors when the distance is small or line-ofsight problems occur. The orientation estimation with a gyroscope is complementary to the OTS-based orientation. In this article, an error-state Kalman filter (ESKF) is proposed to fuse them. Two experiments were performed to verify the performance: first, a unit including markers and a gyroscope was placed statically and rotated dynamically in 3-D space. Secondly, two units were used to estimate the relative orientation between the hand and fingers. The static and dynamic orientation errors reduced from 0.39 • ± 0.16 • and 2.75 • ± 1.56 • to 0.23 • ± 0.02 • and 1.50 • ± 0.62 • , respectively, when the distance between markers was 13 mm. The second experimental results show that the fused method improved the OTS performance by smoothing the estimate, filling the relative orientation during the line of sight period, and correcting the estimation when there were identification problems of markers.