A study on sensor position for thigh and lower leg motion sensors during walking (Focusing on the knee sagittal plane angle)

Abstract

This paper describes the use of nine-axis motion sensors to evaluate the motion sensor position on the thigh and lower leg during walking. The motion sensors are mounted on a subject's body using adhesive tape. The muscles constantly relax or contract because of human movement. Therefore, joint angle estimation using motion sensors produces different accuracy depending on the position where the motion sensor is mounted. Evaluating the motion sensor position is important for improving the joint angle estimation accuracy. For this study, the authors used six nine-axis motion sensors and a 3D motion analysis system to assess walking exercise. Three motion sensors were mounted to the thigh; three were mounted to the lower leg. The knee joint angle was estimated using a sensor fusion algorithm that corrected the centrifugal acceleration and the tangential acceleration in the acceleration sensor output. We evaluated the accuracy of knee joint angle estimation by comparing the nine-axis motion sensor results and the 3D motion analysis system results. Results demonstrated the possibility of high-accuracy estimation when the motion sensor is attached to a position 50% or 75% from the upper end of the thigh and another sensor is attached to a position 25% or 50% from the upper end of the lower leg.

Keywords

• sensor position
• motion sensor
• sensor fusion
• joint angle
• walking