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

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Clarence E. Rash
subsystem to another subsystem may not produce the optimal design.
Instead, an integrated approach in which all elements of the HMD are
designed in concert generally will result in the best and most functional
overall design. The IHADSS is the first product of the integrated approach.
However, care must be taken not to assume that an integrated approach is
one which always will produce a single HMD configuration. In fact, the
various missions, and the conditions under which they must be completed,
are so different, that a single HMD design, while optimal for one set of
conditions, may be significantly deficient for other mission scenarios. A
solution to this problem may be a modular approach (Bull, 1990), where the
HMD system consists of a base mounting unit (e.g., helmet platform), and
interchangeable modules are attached, each for a specific set of mission
requirements. This modular approach can be effective as long as an
integrated approach is used which does not compromise the basic
requirements of any subsystem. For example, the helmet, while now being
used as a platform to attach optics, must still serve its primary function of
providing impact, visual, and acoustical protection.
Fielded systems
To date, two HMD systems have been fielded in U.S. Army aviation,
the ANVIS and the IHADSS. These systems are vastly different in design
and implementation. ANVIS is a combined sensor/display optics package
which mounts unto existing aviator helmets by means of a visor assembly
mounting bracket. The ANVIS is binocular (100% overlap) and uses 3 rd
generation I 2 sensors, which being head-mounted do not require an
additional head tracking system. Typical ANVIS optical characteristics
(for procurements prior to December 1996) include: a focus range of 28
cm (11 inches) to infinity, unity (1x) magnification, 27-mm effective focal
length objective (f/1.2), 27-mm effective focal length eyepiece lens,
resolution of greater than 0.82 cycles/milliradian (cy/mr), minimum 2000x
brightness gain ( 3000x for newer versions), -6 to +2 diopter eyepiece focus
adjustment, and a 52-72 mm interpupillary distance (IPD) adjustment. The
ANVIS housing can be flipped up or down and has a 10-G breakaway
feature. A tilt adjustment of approximately 8º is provided. There is a
minimum vertical and fore/aft adjustment range of 16 mm. They operate
off of one lithium or two “AA” batteries. A dual battery pack is Velcro TM
mounted on the rear of the helmet to improve the CM. A summary of
ANVIS optical and electro-optical (EO) specifications is presented in
Table 1.1. Additional summaries of ANVIS performance characteristics
are provided by McLean et al. (1997); Harding et al. (1996) DeVilbiss,