Three-dimensional motion capture protocol for seated operator in whole body vibration

A new methodology to measure the response of seated people to whole body vibration (WBV) is presented in this work. The proposed methodology is based on using motion capture systems with reflective markers to detect the position versus time motion of selective landmarks on the human body during vibration while taking into consideration the seatback. The methodology also circumvented the problem of tracking the motion of the physical markers on the lower thoracic and lumbar areas of the spine, which cannot be seen by the cameras due to the existence of the seatback, by introducing virtual (calculated) markers that substitute for the physical markers. Additional (redundant) markers were attached to the segments of interest to generate local coordinate systems that can be used to obtain the trajectories of the virtual markers. Simulated ride files containing both complex vibration and mild impact signals were played back through a man-rated 6 d.f. motion platform. The methodology was tested on three seated subjects; there was considerable agreement between the trajectories of the physical and virtual markers. Error assessments also showed insignificant discrepancy between the physical and virtual markers. The proposed methodology showed encouraging results in WBV testing and may be useful for other applications where people perform tasks in a seated position.Relevance to industryPeople who operate heavy construction machinery can be at increased risk for low back pain and other musculoskeletal problems. WBV in combination with postural constraints is one potential underlying cause for these complaints. However, WBV is difficult to study without altering the typical operator environment as the seatback and armrests often limit the ability to monitor human motion, particularly the lumbar spine. The development of an efficient and effective technique for measuring three-dimensional (3D) displacement data of the lower back region of seated operators in realistic environments exposed to WBV, could advance the development and validation process of computer human modeling in this field. Preventing these problems can save people significant suffering and industry significant cost due to compensation, medical care, lost productivity, and retraining.