Development of a Wearable IMU System for Automatically Assessing Lifting Risk Factors

Abstract

The objective of this study was to develop a five inertial measurement unit (IMU) sensor system attached to the human body for automatically identifying the duration of the lifting task (LD) performed symmetrically with two hands at various hand locations relative to the body, and three other lifting risk variables including the trunk flexion angle (T), the vertical distance (V) and horizontal distance (H) of the lifting task defined by the revised National Institute for Occupational Safety and Health lifting equation (RNLE). The algorithm that processed the IMU data consisted of two modules: the synchronization module that extracted the synchronization feature of wrists’ motion data to identify the lifting event; and the lifting variable calculations module that employed a body segment length ratio model for calculating the risk variables. The variable calculation module was further modified to include subjects’ body segment length information for improved accuracy. The wearable system was validated by motion data collected by a laboratory grade motion capture system on 10 human subjects performing 360 lifting trials. Results showed that the model performed well for determining the LD (~1 s error) and T (~2° error). However, the mean errors for V and H were large (33 and 6.5 cm, respectively). Inclusion of subjects’ five body segment length measurements improved the mean errors of V and H to 14 and 2.2 cm, respectively.