Exploiting kinematic constraints to compensate magnetic disturbances when calculating joint angles of approximate hinge joints from orientation estimates of inertial sensors

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Original languageEnglish
Title of host publication2017 International Conference on Rehabilitation Robotics (ICORR)
Pages971-976
Number of pages6
ISBN (electronic)9781538622964
Publication statusPublished - 2017

Publication series

NameIEEE International Conference on Rehabilitation Robotics
ISSN (Print)1945-7898
ISSN (electronic)1945-7901

Abstract

Inertial Measurement Units (IMUs) have become a widely used tool for rehabilitation and other application domains in which human motion is analyzed using an ambulatory or wearable setup. Since the magnetic field is inhomogeneous in indoor environments and in the proximity of ferromagnetic material, standard orientation estimation and joint angle calculation algorithms often lead to inaccurate or even completely wrong results. One approach to circumvent this is to exploit the kinematic constraint that is induced by mechanical hinge joints and also by approximate hinge joints such as the knee joint and the finger (interphalangeal) joints of the human body. We propose a quaternion-based method for joint angle measurement for approximate hinge joints moving through inhomogeneous magnetic fields. The method exploits the kinematic constraint to compensate the error that the magnetic disturbances induce in the IMU orientation estimates. This is achieved by realtime estimation and correction of the relative heading (azimuth) error that is caused by the disturbance. Since the kinematic constraint does not allow heading correction when the joint axis is vertical, we extend the proposed method such that it improves accuracy and robustness when the joint is close to that singularity. We evaluate the method by simulations of a quick hand motion and study the effect of inaccurate sensor-to-segment (anatomical) calibration and joint constraint relaxations. As a main result, the proposed method is found to reduce the root-mean-square error of the joint angle from 25.8° to 2.6° in the presence of large magnetic disturbances.

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Exploiting kinematic constraints to compensate magnetic disturbances when calculating joint angles of approximate hinge joints from orientation estimates of inertial sensors. / Laidig, Daniel; Schauer, Thomas; Seel, Thomas.
2017 International Conference on Rehabilitation Robotics (ICORR). 2017. p. 971-976 8009375 (IEEE International Conference on Rehabilitation Robotics).

Research output: Chapter in book/report/conference proceedingConference contributionResearchpeer review

Laidig, D, Schauer, T & Seel, T 2017, Exploiting kinematic constraints to compensate magnetic disturbances when calculating joint angles of approximate hinge joints from orientation estimates of inertial sensors. in 2017 International Conference on Rehabilitation Robotics (ICORR)., 8009375, IEEE International Conference on Rehabilitation Robotics, pp. 971-976. https://doi.org/10.1109/icorr.2017.8009375
Laidig, D., Schauer, T., & Seel, T. (2017). Exploiting kinematic constraints to compensate magnetic disturbances when calculating joint angles of approximate hinge joints from orientation estimates of inertial sensors. In 2017 International Conference on Rehabilitation Robotics (ICORR) (pp. 971-976). Article 8009375 (IEEE International Conference on Rehabilitation Robotics). https://doi.org/10.1109/icorr.2017.8009375
Laidig D, Schauer T, Seel T. Exploiting kinematic constraints to compensate magnetic disturbances when calculating joint angles of approximate hinge joints from orientation estimates of inertial sensors. In 2017 International Conference on Rehabilitation Robotics (ICORR). 2017. p. 971-976. 8009375. (IEEE International Conference on Rehabilitation Robotics). doi: 10.1109/icorr.2017.8009375
Laidig, Daniel ; Schauer, Thomas ; Seel, Thomas. / Exploiting kinematic constraints to compensate magnetic disturbances when calculating joint angles of approximate hinge joints from orientation estimates of inertial sensors. 2017 International Conference on Rehabilitation Robotics (ICORR). 2017. pp. 971-976 (IEEE International Conference on Rehabilitation Robotics).
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abstract = "Inertial Measurement Units (IMUs) have become a widely used tool for rehabilitation and other application domains in which human motion is analyzed using an ambulatory or wearable setup. Since the magnetic field is inhomogeneous in indoor environments and in the proximity of ferromagnetic material, standard orientation estimation and joint angle calculation algorithms often lead to inaccurate or even completely wrong results. One approach to circumvent this is to exploit the kinematic constraint that is induced by mechanical hinge joints and also by approximate hinge joints such as the knee joint and the finger (interphalangeal) joints of the human body. We propose a quaternion-based method for joint angle measurement for approximate hinge joints moving through inhomogeneous magnetic fields. The method exploits the kinematic constraint to compensate the error that the magnetic disturbances induce in the IMU orientation estimates. This is achieved by realtime estimation and correction of the relative heading (azimuth) error that is caused by the disturbance. Since the kinematic constraint does not allow heading correction when the joint axis is vertical, we extend the proposed method such that it improves accuracy and robustness when the joint is close to that singularity. We evaluate the method by simulations of a quick hand motion and study the effect of inaccurate sensor-to-segment (anatomical) calibration and joint constraint relaxations. As a main result, the proposed method is found to reduce the root-mean-square error of the joint angle from 25.8° to 2.6° in the presence of large magnetic disturbances.",
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