HEAD-UP DISPLAYS 1. INTRODUCTION The head-up display (HUD) creates a new form of presenting information by enabling a user to simultaneously view a real scene and superimposed information without large movements of the head or eye scans. HUDs have been used for various applications such as flight manipulation, vehicle driving, machine maintenance, and sports, so that the users improve situational comprehension with the real-time information. Recent downsizing of the display devices will expand the HUD utilization into more new areas. The head-mounted display (HMD) has been used as a head- mounted type of HUDs for wearable computing that gives user situational information by wearing a portable computer like clothes, a bag, and a wristwatch. A computer has come to interact intelligently with people based on the context of the situation with sensing and wireless communication systems. 1.1 HISTORY The first HUDs were derived from static gun sight technology for military fighter aircraft. Rudimentary HUDs projected a "pipper" to aid aircraft gun aiming. As HUDs advanced, more (and more complex) information was added. HUDs soon displayed computed gunnery solutions, using aircraft information such Dept. of IT, Dr. AIT Page 1
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HEAD-UP DISPLAYS
1. INTRODUCTION
The head-up display (HUD) creates a new form of presenting information by enabling
a user to simultaneously view a real scene and superimposed information without large
movements of the head or eye scans. HUDs have been used for various applications such as
flight manipulation, vehicle driving, machine maintenance, and sports, so that the users
improve situational comprehension with the real-time information. Recent downsizing of the
display devices will expand the HUD utilization into more new areas.
The head-mounted display (HMD) has been used as a head-mounted type of HUDs
for wearable computing that gives user situational information by wearing a portable
computer like clothes, a bag, and a wristwatch. A computer has come to interact intelligently
with people based on the context of the situation with sensing and wireless communication
systems.
1.1 HISTORY
The first HUDs were derived from static gun sight technology for military fighter aircraft.
Rudimentary HUDs projected a "pipper" to aid aircraft gun aiming. As HUDs advanced,
more (and more complex) information was added. HUDs soon displayed computed gunnery
solutions, using aircraft information such as airspeed and angle of attack, thus greatly
increasing the accuracy pilots could achieve in air to air battles.
HUD technology was next advanced in the Buccaneer, the prototype of which first flew on
30 April 1958. The aircraft's design called for an attack sight that would provide navigation
and weapon release information for the low level attack mode.
There was fierce competition between supporters of the new HUD design and supporters of
the old electro-mechanical gun sight, with the HUD being described as a radical, even
foolhardy option. The Air Arm branch of the Ministry sponsored the development of a
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Strike Sight. The Royal Aircraft Establishment (RAE) designed the equipment, it was built
by Cintel, and the system was first integrated in 1958. The Cintel HUD business was taken
over by Elliott Flight Automation and the Buccaneer HUD was manufactured and further
developed continuing up to a Mark III version with a total of 375 systems made; it was
given a `fit and forget' title by the Royal Navy and it was still in service nearly 25 years
later. BAE Systems thus has a claim to the world's first Head Up Display in operational
service.[2]
In the United Kingdom, it was soon noted that pilots flying with the new gun-sights were
becoming better at piloting their aircraft.[citation needed] At this point, the HUD expanded
its purpose beyond weapon aiming to general piloting. In the 1960s, French test-pilot
Gilbert Klopfstein created the first modern HUD and a standardized system of HUD
symbols so that pilots would only have to learn one system and could more easily transition
between aircraft. The modern HUD used in instrument flight rules approaches to landing
was developed in 1975.[3] Klopfstein pioneered HUD technology in military fighter jets
and helicopters, aiming to centralize critical flight data within the pilot's field of vision.
This approach sought to increase the pilot's scan efficiency and reduce "task saturation" and
information overload.
Use of HUDs then expanded beyond military aircraft. In the 1970s, the HUD was
introduced to commercial aviation,[4] and in 1988, the Oldsmobile Cutlass Supreme
became the first production car with a head-up display.[5]
Until a few years ago, the Embraer 190 and Boeing 737 New Generation Aircraft (737-
600,700,800, and 900 series) were the only commercial passenger aircraft available with
HUDs. However, the technology is becoming more common with aircraft such as the
Canadair RJ, Airbus A318 and several business jets featuring the displays. HUDs have
become standard equipment on the Boeing 787.[6] Furthermore, the Airbus A320, A330,
A340 and A380 families are currently undergoing the certification process for a HUD.[7]
HUDs are also added to the Space Shuttle orbiter.
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2. PRINCIPLE
Head-up display have now become so compact and lightweight that an emerging
use is for displaying information to workers on site locations such as power stations,
airports and events. A new breed monocular head up displays (HUD) cater for this
application. These displays are discreet and easy to use and are being used in the field by
engineers, security and police forces. Head-up display utilizes a low powered laser device
to literally project a laser image onto the viewer's retina. We are aware of the harmful
effects of the laser and may be wondering about the safety of aiming laser light directly
into the eye. To ensure that its device is safe, Micro vision applied rigorous safety
standards from the American National Standards Institute, Washington, D.C., and the
International Electro technical Commission, Geneva, derived from years of studying the
effects of light on the eye. Laser light can be harmful because its beam is intense, capable
of concentrating its power in a tiny area of incidence. This could be a problem if a fixed
beam-as opposed to a scanned beam-were allowed to dwell on just one spot. We ensure
that the retina is never overwhelmed by limiting the power of the laser light entering the
eye to about a thousandth of a watt and using a high-reliability interlock circuit that turns
on the laser only when the beam is scanning. Furthermore, because this very low-power
light is continuously scanned onto the retina, its energy is dispersed over an area hundreds
of thousands, of times larger than a single spot of an incident beam. Head-Up Display,
also known as a Heads-Up Display or simply HUD, is any type of display that presents data
without blocking the user's view. In civil aviation the HUD is known as a Head-Up
Guidance System (HGS).
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2.1 TYPES
• Fixed- In which the user looks through a display element attached to the
airframe or vehicle chassis. Commercial aircraft and motor vehicle HUDs are of this
type. The system determines the image to be presented depending on the orientation of
the vehicle. The size and weight of the display system can be much greater than in the
other type which is:
• Helmet-mounted, or head-mounted-In which the display element moves
with the user's head. This requires a system to precisely monitor the user's direction of
gaze and determine the appropriate image to be presented. The user must wear a helmet
or other headgear which is securely fixed to the user's head so that the display element
does not move with respect to the user's eye. Such systems are often monocular. One
use of this type of HUD is in the AH-64 Apache and in the Norwegian F-16 Fighting
Falcons.
2.2 CHARACTERISTICS
• The display element is largely transparent, meaning the information is
displayed in contrasting superposition over the user's normal environment
• The information is projected with its focus at infinity. Doing this means
that a user does not need to refocus his eyes (which takes several tenths of a second)
when changing his attention between the instrument and the outside world.
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The company uses microelectromechanical system (MEMS) devices to scan the
beams back and forth and, where appropriate, to mix different colors to produce white
light. Because the beam sweeps over the retina instead of dotting it, lines need not be
serrated and images need not be grainy. Bright as the picture will seem to the naked eye,
it will consume barely a microwatt, potentially saving hugely on battery power. And, by
sending light only where it's needed, the system can keep nosy neighbors in adjacent
airline seats from snooping on your work (or play). With a sufficiently inconspicuous
eyepiece, one might even feign attention to a speech or lecture while, in fact, watching
television.
2.3 RESOLUTION, COLOUR DEPTH AND BRIGHTNESS
The overriding design factor for these type of Head-up display is their
compactness which means that the resolution of these models is not yet as high as some
of the virtual reality Head-up display. Older HUD's offers resolutions starting from
320x240 (qVGA) up to 640 x 480 (VGA) and includes true color models. They are also
available in binocular configurations to give twice the display area. Micro vision’s
Nomad has a resolution of 800 x 600 and is red monochrome. Color is not important for
many applications where content is mainly technical data and text. Micro vision’s
displays use red laser light. One of their strong points is that they are very bright and
can easily be viewed in strong sunlight Field of view (FOV) Average human vision
covers an area of about 200 degrees horizontally by 150 degrees vertically. FWD FOV
figures are typically given as diagonal FOV. That is the perceived angle from one corner
of the screen to the opposite corner.
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(a)Approx. human horizontal field-of-view (b) Approx. human vertical field-of-
view
One of the most important factors for head-up information display is that any text
or technical diagrams are clearly legible. These Head-up display are currently not
designed to immerse the user with wrap-around images but instead to provide the
equivalent of a 'floating monitor' taking up part of the user's field of view
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3. DESIGN FACTORS
There are several factors that engineers must consider when designing a HUD:
Field of vision—because the human eyes are separated, each eye receives a different
image. To prevent pilots' eyes from having to change focus between the outside world
and the display of the HUD, the display is collimated (focused at infinity). In automobiles
the display is generally focused near the distance to the bumper.
Eye box—displays can only be viewed while the viewers' eyes are within a three-
dimensional area called the head motion box or eye box. Modern HUD eye boxes are
usually about 5 by 3 by 6 inches. This allows viewers some freedom of head movement.
It also allows pilots the ability to view the entire display as long as one of their eyes is
inside the eye box.
Luminance/contrast—displays must be adjustable in luminance and contrast to account
for ambient lighting, which can vary widely (e.g., from the glare of bright clouds to
moonless night approaches to minimally lit fields).
Display accuracy—aircraft HUD components must be very accurately aligned with the
aircraft's three axes – a process called bore sighting – so that displayed data conforms to
reality typically with an accuracy of ±7.0 mill radians. In this case the word "conform"
means, "When an object is projected on the combiner and the actual object is visible, they
will be aligned". This allows the display to show the pilot exactly where the
artificial horizon is, as well as the aircraft's projected path with great accuracy. When
Enhanced Vision is used, for example, the display of runway lights must be aligned with
the actual runway lights when the real lights become visible. Bore sighting is done during
the aircraft's building process and can also be performed in the field on many aircraft.[3]
Compatibility—HUD components must be compatible with other avionics, displays, etc.