Inertial Motion Capture Lab, Department of Mechanical Engineering, Hankyong National University, Anseong 17579, Korea.
Sensors (Basel). 2018 Nov 16;18(11):4003. doi: 10.3390/s18114003.
Local frame alignment between an inertial measurement unit (IMU) system and an optical motion capture system (MCS) is necessary to combine the two systems for motion analysis and to validate the accuracy of IMU-based motion data by using references obtained through the MCS. In this study, we propose a new quaternion-based local frame alignment method where equations of angular velocity transformation are used to determine the frame alignment orientation in the form of quaternion. The performance of the proposed method was compared with those of three other methods by using data with different angular velocities, noises, and alignment orientations. Furthermore, the effects of the following three factors on the estimation performance were investigated for the first time: (i) transformation concept, i.e., angular velocity transformation vs. angle transformation; (ii) orientation representations, i.e., quaternion vs. direction cosine matrix (DCM); and (iii) applied solvers, i.e., nonlinear least squares method vs. least squares method through pseudoinverse. Within our limited test data, we obtained the following results: (i) the methods using angular velocity transformation were better than the method using angle transformation; (ii) the quaternion is more suitable than the DCM; and (iii) the applied solvers were not critical in general. The proposed method performed the best among the four methods. We surmise that the fewer number of components and constraints of the quaternion in the proposed method compared to the number of components and constraints of the DCM-based methods may result in better accuracy. Owing to the high accuracy and easy setup, the proposed method can be effectively used for local frame alignment between an IMU and a motion capture system.
惯性测量单元 (IMU) 系统和光学运动捕捉系统 (MCS) 之间需要进行局部框架对准，以便将这两个系统结合起来进行运动分析，并通过 MCS 获得的参考来验证基于 IMU 的运动数据的准确性。在这项研究中，我们提出了一种新的基于四元数的局部框架对准方法，其中角速度变换方程用于以四元数的形式确定框架对准方向。通过使用具有不同角速度、噪声和对准方向的数据，比较了所提出的方法与其他三种方法的性能。此外，首次研究了以下三个因素对估计性能的影响：(i) 变换概念，即角速度变换与角度变换；(ii) 方向表示，即四元数与方向余弦矩阵 (DCM)；(iii) 应用求解器，即非线性最小二乘法与通过伪逆的最小二乘法。在我们有限的测试数据中，我们得到了以下结果：(i) 使用角速度变换的方法优于使用角度变换的方法；(ii) 四元数比 DCM 更适合；(iii) 应用的求解器通常并不关键。在所提出的四种方法中，该方法表现最佳。我们推测，与基于 DCM 的方法相比，所提出的方法中的四元数的组件和约束数量较少，这可能导致更高的准确性。由于具有高精度和易于设置的特点，所提出的方法可有效地用于 IMU 和运动捕捉系统之间的局部框架对准。
