Helmet-Mounted Displays: - USAARL - The - U.S. Army

Introductory Overview 13
1970's. Task and Kocian (1995) cite the U.S. Navy’s Visual Target
Acquisition System (VTAS), developed in the 1960's, as the first fully
operational visually coupled sighting system. [However, the system was
abandoned due to lack of sufficient missile fire control technology.] For
Army aviation, the AN/PVS-5 NVG was the first pilotage imagery HMD
(first tested in 1973), and the IHADSS was the first integrated HMD
(fielded since 1985).
Simply, an HMD projects head-directed sensor imagery and/or fire
control symbology onto the eye, usually superimposed over a see-through
view of the outside world. As such, HMDs offer the potential for enhanced
situation awareness and effectiveness. However, their design and
implementation are not without problems and limitations. Virtually every
HMD, concept or fielded system, suffers from one or more deficiencies,
such as high head-supported weight, center of mass (CM) off-sets,
inadequate exit pupil, limited FOV, low brightness, low contrast, limited
resolution, fitting problems, and low user acceptance (Cameron, 1997;
Naor, Arnon, and Avnur, 1987). Of the potential problems with HMDs,
none are more troublesome than those associated with the interfacing of the
system with the human user. The wide variation in head and facial
anthropometry makes this a formidable task, requiring HMD designs rich
in flexibility and user adjustments.
An HMD designer must develop a system which is capable of
satisfying a large number of widely different and often conflicting
requirements in a single system. Such design goals include but are not
limited to the following (Lewis, 1979):
� Maximum impact protection
� Maximum acoustical protection
� Maximum speech intelligibility
� Minimum head supported weight
� Minimum bulk
� Minimum CM offset
� Optimum head aiming/tracking accuracy
� Maximum comfort and user acceptance
� Maximum freedom of movement
� Wide FOV
� Minimum obstructions in visual field
� Full color imagery
� Maximum resolution
� High brightness and contrast
� No induced sensory illusions