School of Mechatronics Engineering, Harbin Institute of Technology, Harbin 150001, China.
School of Computer Science and Technology, Harbin Institute of Technology, Harbin 150001, China.
Sensors (Basel). 2021 Mar 5;21(5):1813. doi: 10.3390/s21051813.
Inertial measurement unit (IMU)-based joint angle estimation is an increasingly mature technique that has a broad range of applications in clinics, biomechanics and robotics. However, the deviations of different IMUs' reference frames, referring to IMUs' individual orientations estimating errors, is still a challenge for improving the angle estimation accuracy due to conceptual confusion, relatively simple metrics and the lack of systematical investigation. In this paper, we clarify the determination of reference frame unification, experimentally study the time-varying characteristics of reference frames' deviations and accordingly propose a novel method with a comprehensive metric to unify reference frames. To be specific, we firstly define the reference frame unification (RFU) and distinguish it with drift correction that has always been confused with the term RFU. Secondly, we design a mechanical gimbal-based experiment to study the deviations, where sensor-to-body alignment and rotation-caused differences of orientations are excluded. Thirdly, based on the findings of the experiment, we propose a novel method to utilize the consistency of the joint axis under the hinge-joint constraint, gravity acceleration and local magnetic field to comprehensively unify reference frames, which meets the nonlinear time-varying characteristics of the deviations. The results on ten human subjects reveal the feasibility of our proposed method and the improvement from previous methods. This work contributes to a relatively new perspective of considering and improving the accuracy of IMU-based joint angle estimation.
基于惯性测量单元 (IMU) 的关节角度估计是一项日益成熟的技术，在临床、生物力学和机器人领域有广泛的应用。然而，由于概念上的混淆、相对简单的指标以及缺乏系统的研究，不同 IMU 的参考系偏差（即 IMU 个体方向估计误差）仍然是提高角度估计精度的挑战。在本文中，我们澄清了参考系统一的确定，实验研究了参考系偏差的时变特性，并相应地提出了一种具有综合指标的新方法来统一参考系。具体来说，我们首先定义了参考系统一（RFU），并将其与一直与 RFU 混淆的漂移校正区分开来。其次，我们设计了一个基于机械万向节的实验来研究偏差，其中排除了传感器与身体的对准和旋转引起的方向差异。第三，基于实验的结果，我们提出了一种新的方法，利用铰链关节约束下关节轴的一致性、重力加速度和局部磁场来全面统一参考系，这符合偏差的非线性时变特性。对 10 名人体受试者的研究结果表明了我们提出的方法的可行性和优于先前方法的改进。这项工作为考虑和提高基于 IMU 的关节角度估计的精度提供了一个相对较新的视角。
