Angle measurements during 2D and 3D movements of a rigid body model of lower limb: Comparison between integral-based and quaternion-based methods

Angle measurement system using inertial sensors was developed by our research group, in which lower limb angles were calculated based on the integral of angular velocity using Kalman filter. The angle calculation method was shown to be practical in measurement of angles in the sagittal plane during gait of healthy subjects. In this paper, in order to realize practical measurements of 3 dimensional (3D) movements with inertial sensors, the integral-based and the quaternion-based methods were tested in measurement of 2D movements in the sagittal plane and 3D movements of rigid body models of lower limb. The tested three calculation methods, extended integral-based method, quaternion-based method proposed in this study and simplified previous quaternion-based method, were suggested to measure the 2D movements with high measurement accuracy. It was also suggested that there were no large difference in measurement of 2D and 3D movements between 3 methods. Visualization by stick figure animation of circumduction gait simulated by a healthy subject also suggested that the angle calculation methods can be useful. It is expected to improve measurement accuracies of 3D movements to those of 2D movements.