Neck Torque Study Induced by Head-Borne Visual Augmentation Systems (VAS) in Ground-Based Applications

http://www.dtic.mil/cgi-bin/GetTRDoc?AD=ADA519127&Location=U2&doc=GetTRDoc.pdf


The Johns Hopkins University
Applied Physics Laboratory

NSTD-09-1057
Final Report
Contributors:
Emily Ward
Quang Luong

Neck Torque Study Induced by Head-Borne Visual Augmentation Systems (VAS)
in Ground-Based Applications

While providing a critical capability to conduct missions under the cover of darkness, Night
Vision Goggles (NVG) are a recognized source of acute and chronic neck injuries. US Army
Night Vision & Electronic Sensors Directorate and the Naval Surface Warfare Center needed to
characterize the mass, Center of Gravity (CG) and neck torque generated by existing NVG and
Visual Augmentation Systems (VAS) in order to understand the potential for neck pain and
injury created by existing systems, and provide insight on the mass and CG properties needed for future systems. NVG use light intensifier tubes to amplify existing light while VAS incorporate both light intensifiers and infra-red thermal imagers. (For the purposes of this report, NVG systems are a sub-set of VAS.) This project had three tasks:
1. Develop a method to measure the mass and CG of VAS.
2. Measure the mass and CG of seven (7) VAS and their associated mounts: AN/PVS-7D,
AN/PVS-14, AN/PVS-15A, AN/PVS-23, Fusion Goggles, AN/PEQ-20, Advanced
Digital Multispectral (ADM)-NVG. Calculate the neck torque generated by these
systems.
3. Develop computational models of the VAS, mounts and helmets with appropriate mass
properties to allow virtual measurement of mass, CG and neck torque. Additionally, a
virtual model was built of the FGS-PI system.
Each VAS and mount was tested on three (3) sizes of Advanced Combat Helmets (ACHs):
Medium, Large and Extra-Large. Additionally, the AMD-NVG was tested on the SOCOM
Lightweight Helmet. Each helmet system combination was tested in 4 positions:
 Lowered – Maximum distance
 Lowered – Minimum distance
 Stowed – Maximum distance
 Stowed – Minimum distance
Using the mass and CG measurements collected for the VAS, the neck torques about the atlantooccipital joint of the neck were calculated. The atlanto-occipital joint is located at the top of the neck where the skull rests. The neck torques for the different systems and configurations ranged from 0.44 N-m to 1.51 N-m (which excluded the effects of the helmet). The helmet imposes a negative torque on the neck ranging from -0.43 N-m (medium ACH) to -0.52 N-m (extra-large ACH). This negative torque of the helmet reduces the neck torque effects of the VAS and mount.
When the US Army Aeromedical Research Laboratory’s (USAARL’s) neck torque criteria for
rotary-wing aviators is applied to the data collected, there were only 3 test conditions which
exceeded their criteria1F1F1F
2. These were with the AN/PVS-15 and Wilcox mounts in the stowed
position on the large and extra-large ACHs