Note: Descriptions are shown in the official language in which they were submitted.
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WINDSHIELD FOR HEAD-UP DISPLAY SYSTEM
Back~round of the Invention
1. Field of the Inventio
This invention relates to a combiner for a head-up display system and
in particular to an automotive windshield functioning as the combiner for the
head-up display system and having a wedged configuration to eliminate double
imaging.
2A. Technical Considerations
A head-up display system is a visual di~play arrangement that
displays information to a viewer whlle he simultaneously views the real world
around and through the display. ~ead-up display systems are often
incorporated into aircraft coc~pits for pilots to monitor flight information.
More recently, the systems have been used in land vehicles such as cars,
trucks and the like. ~he display is generally positioned so that the viewer
does not have to glance downward to the vehicle dashboard and away from the
viewing area in front of the vehicle as is normal for a vehicle operator in
viewing the vehicle operating information.
A head-up display system generally includes a display pro~ection
system, a collima~or, and a combiner. The pro~ection system includes a light
source that pro~ects operating information through the collimator which
generally aligns the pro~ected light rays. ThP collimated light is then
reflected off the combiner, which i5 in the vehicle operator's field of view.
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In this manner, important vehicle information such as, for example, fuel
information and vehicle speed is displayed within the operator's field of
vision through the windshield and permits the operator to safely maintain eye
contact with the real world while simultaneously viewing the displayed
information. The reflected images of the display may be focused at a position
anywhere from immediately in front of the vehicle to optical infinity.
Laminated windshields have been used as the combiner in a head-up
display system to reflect a display image as taught in U.S. Patent No.
2,264,044 to Lee. However, it has been observed that a secondary image is
reflected off the outer surface of the windshield. This secondary image is
superimposed over but offset from the first image and reduces the overall
image clarity.
It would be advantageous to have a windshield for a head-up display
which function~ a~ a combiner and provides a clear display image without
incorporating additional components on or within the windshield.
2B. Patents of Interest
~ . S. Patent No. 1,871,877 to Buckman teaches a display sys~em having
a glass sheet mounted on the windshield or dashboard which reflects
instrumentation information to the vehicle operator.
U. S. Patent No. 2,264,044 to Lee teaches a motor vehicle having an
illuminated speedometer display that is reflected off the inboard surface of
the vehicle windshield.
U. S. Patent ~o. 2,641,152 to Mihalakis teaches a vehicle projection
device wherein instrumentation information is reflected off of a reflecting
screen on the inboard surface of the vehicle windshield. The reflecting
surface has a satin finish and can be metal, glass, or plastic.
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U. S. Patent No. 2,750,833 to Gross teaches an optical display system
for eliminating double images which occur in reflector type sights such as
those used in aircraft gun sighting installations. A collimated light beam is
polarized and separated into two ray branches. One of the two ray branches is
then eliminated.
U. S. Patent No. 3)276,813 to Shaw, Jr. teaches a motor vehicle
display system which utilizes a highly reflective coating on the inboard
surface of the vehicle windshield to reflect instrumentation information to
the vehicle operator.
U. S. Patent ~o. 3,446,916 to Abel teaches an image combiner
utilizing a portion of the aircraft window. The inner surface portion of the
window is coated with a partially reflective film.
U. S. Patent Nos. 3,554,722, 3,591,261, and 3,647,285 to Harvey et
al. teaches a double glaæed glass window structure which eliminates
ob~ectionable fringe patterns produced in this structure when float glass of
nonuniform thickness is utilized. The window structure includes a pair of
spaced apart, float glass sheets, one or both of which are tapered from a
thick edge to an opposing thin edge. When both the gla~s sheets are tapered,
the glass sheets are positioned such that a thick edge of one glass sheet is
positioned over a thin edge of the opposlng glass sheet.
U. S. Patent No. 3,899,241 to Malobicky, Jr. et al. teaches a
windshield adapted for use in alrcraft and includes a transparent reflective
coating on the inboard surface in the center portion of the forward vis{on
area to form a vision image receiving area. Vehicle information is reflected
off the reflective coating to the vehicle operator.
U. S. Patent ~o. 3,940,204 to Withrington and 4,218,111 to
Withrington et al. teach an optical display system utllizing holographic
lenses.
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U. S. Patent No. 4,261,635 to Freeman teaches a head-up display
system including a holographic combiner positioned inboard of the vehicle
wlndshield. The hologram i9 disposed substantially orthogonal to and midway
along an axis between the observer's eye position and the pro~ection optics so
as to deviate light from an image produced by the pro~ection optics to the
observer eye with minimal field aberration.
U. S. Patent No. 4,398,799 to Swift teaches a head-up display system
which simultaneously records the pilot's view of the outside scene and the
projected display by reflecting the outside scene and superimposed display off
a mirror mounted on the pilot's helmet and recording the reflected view with a
camera mounted on the pilot's helmet.
U. S. Patent No. 4,613,200 to Hartman teaches a head-up display
system which uses two parallel holographic optical elements to reflect
instrumentation in~ormation to the vehlcle operator. One of the elements is
made part of or attached to the vehicle windshield.
U. S. Patent No. 4,711,544 to Iino et al. teaches a display system
for a vehicle wherein instrumentation information is reflected off the front
glass of the vehicle so that the image display can be formed in a desired
position, aligned with the line of sight of the driver without obstructing the
front sight of the driver.
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Summary of the Invention
The present invention provides a windshield for a head-up display
system that reduces the amount of double imaging that occurs when a laminated
windshield is used as the combiner in the display sy3tem. The windshield
functions as a combiner for the head-up display system wi~hout requiring any
additlonal elements or components to be incorporated onto or into the
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windshield assembly. The windshield in the present invention is constructed
such that the opposing, outer ma~or surfaces of the windshield are
non-parallel and oriented relative to each other so that an lmage projected
from a display source and reflected off a first ma~or surface of the
windshield is substantially superimposed over the same image from the display
source reflected off the opposing ma~or surface of the windshield.
In one particular embodiment of the invention, the windshield
includes a pair of glass plies secured to each other by a sheet of
thermoplastic interlayer material tapered in thickness from one edge to its
opposing edge. The tapered configuration of the interlayer may be achieved by
casting the interlayer to the desired configuration or differentially
stretching the interlayer to the desired shapedO When the glass plies and
tapered interlayer are assembled and lamlnated to form a unitary structure,
the opposing ma~or surfaces of the laminate are non-parallel and offset at a
predetermined angle sl~ch that images from the display source that are
reflected off the opposing ma~or surfaces of the laminate are substantially
superimposed over each other.
Brief Descri~tion of the Drawln~s
Figure 1 is a schematic of head-up display ystem for a vehicle.
Figure 2 is an enlarged, partial cross-sectional view of Figure 1
illustrating a head-up display using a prior art windshield.
Figure 3 is an enlarged, partial cross-sectional Vi2W of Figure 1
illustrating a head-up display usin~ a windshield incorporating features of
the present invention.
Figure 4 ls an exploded cross-sectional view of an alternate
embodiment of the invention.
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Detailed Descri~tion of the Invention'
The present invention relates to the elimination of double imaging in
a head-up display system that uses an automotive windshield as the combiner
but it should be appreciated that the present invention may be used in any
type of combiner having a laminate construction where double imaging is to be
eliminated.
With reference to Figure 1, head-up display 10 system includes a
motor vehicle windshield 12, an image source 14 and a pro~ection assembly 16,
preferably mounted immediately beneath the upper surface of the vehicle
dashboard 18 and positioned between the image source 14 and windshield 12.
Light rays emanate from the image source 14 and are pro~ected onto the
windshield 12, which operates as a comblner as will be discussed later, and
reflected into the field of vision of the vehicle operator 20. The light rays
pro~ected onto the windshield 12 are collimated so as to create a virtual
image in front of the car, preferably at about 10 to 50 feet ~3 to 15 meters)
in front of the windshield 12.
Although not limiting in the present invention, the image source 14
preferably is a transmissive liguid crystal d~splay ~LED) that i~ adequately
illuminated to project information carrying light rays through the pro~ection
assembly 16 onto the windshield 12 at a location within the vehicle operator's
direct line of sight while permitting peripheral viewing of the outside real
world as the operator 20 monitors the display. It is contemplated that
alternative viewing locations will also provided an effective head-up display
for vehicle windshield. The displayed image (not shown) may include numerical
or graphical symbols including for example, vehicle speed, fuel level, engine
RPMs, temperature, and warning symbols.
The following discusslon will be directed towards the use of a prior
art windshield as the combiner in a head-up display system which projects an
image a finite distance in front of the windshield. In particular, referring
to Figure 2, windshield 30 represents a windshield assembly with the opposing
inner and outer major surfaces of the windshield being parallel to each
other. In particular, the windshield 30 includes outer glass ply 32 bonded to
inner gla~s ply 34 by an interlayer material 36. Because the thickness of the
interlayer 36 i3 fairly uniform and the opposing ma~or surfaces of each glass
ply are substantially parallsl to each other, i.e. inner surface 37 of the
ply 32 is parallel to its outer surface 38 and inner surface 39 of the ply 34
is parallel to its outer surface 40, the outer major surfa~e 38 of the glass
ply 32 is parallel to the outer ma~or surface 40 of the glass ply 34 after the
glass plies 32 and 34 and interlayer 36 are laminated together to form a
unitary structure. Although not limiting in the present invention, for the
purposes of illustration, surfaces 38 and 40 are assumed to be planar in the
following di3cus~ion. ~owever, the surfaces may be non-planar, a~ will be
discussed later.
With continued reference to Figure 2, a llght ray A from image source
14 is directed along line 42 and a portion of the light is reflected off
surface 40 of the ply 34 along line 44 to eye 46 of ~he vehicle operator 20.
Additional light rays from the source 14 are directed along additional lines.
For example ray B is directed along line 48 and reflected off the surface 40
along line 50. However, the ray B along line S0 ls not directed to the eye 46
so it will not be detected by the observer 20. A portion of the light ray B
which is directed along line 48 will enter the windshield assembly 30 and be
refracted along line 52. The angular difference between the lines 48 and 52
depends on ~he angle of refractlon as the light ray passes through the air and
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into the glass ply 34. The angle of iefraction in turn depends, in part, on
the angle at which ray B ls incident on surface ~0 and the relative densities
of the air and the glass. The ray B passes through the windshield assembly 30
and a portion of the light ray B is reflected off surface 38 of the ply 32
along line 54. It is assumed that the refractive index of interlayer 36 is
the same as that of the glass plies 32 and 34 so that the light rays are not
distorted as they pass through the windshield assembly 30 along lines 52 and
54O A portion of the light ray B leaves the windshield assembly 30 at the
surface 40 of the glass ply 34 where the direction of the light is again
changed due to the difference in the refraction index between the windshield
assembly 30 and the air, as discussed earlier, and directed along line 56 to
eye 46. Because the light rays A and B received by the eye 46 from the image
source 14 are along two different lines, i.e. lines 44 and 567 the observer 20
will perceive two offset images where in fact there is only one image source
14. The first image 58, or virtual image, is the image seen by the observer
20 from the light directed along line 4~. The second image 60 i3 the image
seen by the observer 20 from the light directed along line 56. When viewing
both images, the virtual image 58 will appear brighter than the second image
60 because a grea~er portion of the light from the lmage source 14 which was
initially directed along line 42 will be directed along line 44 as compared to
the amount of light ~n$tially dir~cted along line 48 and which is finally
directed along line 56 to the observer 20~ This condition of seeing ~wo
offset images is commonly referred to as double imaging, or ghost imaging, and
results when the outer surfaces of the windshield assembly, i.e. surfaces 38
and 40 of windshield assembly 30, are parallel to each other.
In order to reduce the amolmt of double imaging in windshield
assembly 30, the present invention modifies the windshield structure.
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Although not limiting in the present invention, referring to Figure 3 which
illustrates a preferred embodiment of the present invention, windshield 130
includes outer glass ply 132 bonded to inner glass ply 134 by an interlayer
material 136 along inner ma~or surfaces 137 and 139 of plies 132 and 134,
respectively. The interlayer 136 is fabricated such that there is a gradual
tapering of its ~hickness, i.e. the interlayer material gradually decreases in
thickness Prom one edge to its opposing edge. As a result of this "wedged"
shape of the interlayer, when the windshield components are assembled and
laminated, outer ma~or surface 138 of glas~ ply 132 and outer ma~or surface
140 of glass ply 134 will be non-parallel. It has been found that by
controlling the amount by which the glass plies 132 and 134 of the windshield
130 are offset from each other, the double imaging encountered when using a
windshield as shown in Figure 2 as a combiner can be reduced. The actual
wedge angle X required to reduce the double imaglng depends, in part, upon the
thickness of the windshield, the windshield materials, and the relative
positions and orientations of the image source 14, the windshield 130 and the
vehicle operator 20. Although not limiting in the present invention, the
interlayer 136 can be cast in place to provide the desired wedge angle X. As
an alternative, the interlayer 136 can be differentially stretched in any
convenient manner known in the art, such as that disclosed in U.S. Patent No.
4,201,351 to Tolli~er and U.S. Patent No. 4,554,713 to Chabel~-which tcachin~a
_
With continued reference to Figure 3, light ray Al from image source
14 is directed along line 142 and reflected off surface 140 along line 144 to
the observer's eye 46. Additional light ray Bl is directed along line 148
and, as discussed earlier, a portion of the light ray is reflected from the
surface 140 along line 150 such that it is not seen by the observer 20. The
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remainine portion of the ray Bl i9 refracted through the glass plies 132 and
134 and the interlayer 136 along line 152, in a manner similar to that
discussed earlier, reflected off the surface 138 of the glass ply 132 along
line 154, and refracted as it leaves the assembly 130 to the observer's eye
46. However, unlike the windshield assembly 30 in Figure 2 wherein the line
56 from ray B is along a different orientation than line 44 from ray A, in
Figure 3 the wedge angle X is such that the refracted light from light ray
exits the assf~mbly 130 along the line 144, i.e. superimposed over the light
from ray Alreflected off the surface 140 of the glass ply 134. As a result,
the image viewed by the observer 20 resulting from light rays Al and Bl are
superimposed over each other so that there is only a single image 158.
It should be appreciated that in a windshield assembly, the surfaces
138 and 140 of the glass plies 132 and 134, respectively, are often not planar
but rather have a curved configuration. However, the amount of relative
curvature in the windshield assembly i30 within the small area used as the
combiner is relatively small so that the area within the combiner portion of
the windshield 130 is nearly planar. Furthermore, if required due to
excessive curvature of the windshield within the combiner area, the image from
the image source 18 can be distorted, for example by incorporating additional
lens arrangements ~not shown) into the pro~ection assembly 16 (shown only in
Figure 1) to account for the curvature of the windshield surfaces.
In one particular embodiment of the invention, the windshield 130
includes 0.090 inch (2.3mm) thick glass plies and two polyvinylbutryl
interlayer plies. Each interlayer ply is originally 0.020 inches (0.05mm)
thick and is differentially stretched so that ~ach interlayer ply has a taper
of approximately 0.003 inches (0.076mm) over a 36 inch (9lcm) interlayer width
for a combined thickne~s differential of approximately 0.006 inches (0.152mm)
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from top to bottom when incorporated i~nto windshield 130. Referring to Figure
1, it has been ob~erved that a windshield of this construction, mounted in a
vehicle at an installation angle Y of approximately 30 with an angle of
incidence Z between the windshield 12 and the light rays from the image source
14 of approximately 65 significantly reduces the amount of double imaging in
a head-up display system as compared to a conventional windshield having a
non-wedged configuration.
Although the windshield configuration 130 of the present invention as
shown in Figure 3 includes two glas~ sheets each having generally parallel
opposing ma~or surfaces and a tapered interlayer ply, based on the teachings
of this disclosure, it is obvious to one skilled in the art that other
windshield configurations can be used to provide a wedged windshield
configuration similar to that shown in Figure 3. In particular9 referring to
Figure 4, one or both of the glass plies ~.32 and 234 may be provided with a
taper such that when the assembly 230 is laminated to form a unitary structure
using a non-stretched interlayer 236, opposing surfaces 238 and 240 of the
windshield 230 are non-parallel and are oriented relative to each other so as
to eliminate the double imaging. I~ is further contemplated that one or more
tapered interlayer may ke used in combination with one or more tapered glass
plies so that the final laminated assembly provides the windshield
construction having the configuration required to reduce double imaging.
The forms of this invention shown and described in ~his disclosure
represent illustrative preferred embodiments and various modifications
thereof. It is understood that various changes may be made without departing
from the scope of the invention as defined by the claimed sub~ect matter which
follows.
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