Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
HEAD UP DISPLAY SYSTEM AND METHOD
Field
The present disclosure relates to systems and methods for projecting images
onto glass; in particular, the
present disclosure relates to methods and systems for providing head up
displays in vehicles.
Background
In consumer vehicles which provide a head up display, such head up displays
utilize a wedge shape that is
sandwiched into the windshield, so as to align the image reflected from the
inner surface of the windshield
with the image reflected from the outer surface of the windshield (see FIG.
1). When the aligned reflected
images reach the viewer's eye, they appear to be a single image with little or
no "ghosting" effect.
However, such wedge designs require high tolerances for the thickness profile
of the windshield, in the
area of where the head up display wedge is located. To maintain such high
tolerances, the windshields
are manufactured in a mold and press, and thus such windshields are typically
more expensive to produce.
Furthermore, the alignment of the two reflected images, in the wedge design of
head up display
windshields, is dependent on the viewer's eyes being positioned at a
particular height relative to the head
.. up display. Thus, if the viewer's line of sight is located higher or lower
than the specified height for the
head up display, the viewer may perceive two images that are misaligned from
one another, thereby
degrading the quality of the image as perceived by the viewer.
Wedge head up display designs typically use s-polarized light for the image
projected onto the head up
display portion of the windshield. Light reflected from a glass surface
becomes polarized with increasing
angle of incidence. At angles above the Brewster angle for the glass surface,
all light reflected from the
glass surface is s-polarized, whereas the p-polarized light is refracted into
the glass.
Recently, films have been developed which are designed to reflect a limited
portion of polarized light from
the surface of the film. Such films are designed to be incorporated into a
laminated windshield, wherein
the film is sandwiched between two layers of glass. An example of a reflective
polarizer film is described
in the Patent Cooperation Treaty application no. PCT/U52019/051733 by
Vanderlofske et al. These films
exploit the polarization properties of the Brewster angle to reduce or
eliminate ghost images from the
projected image viewed by the viewer. To use such films as specified, the
angle of incidence is required
to fall within a predetermined range. Provided the angle of incidence falls
within the predetermined
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range, depending on the refractive index of the glass layers used in the
windshield, virtually all of the p-
polarized light from a projector will be refracted into the glass of the
windshield. As such, no image is
reflected from the outwardly facing surface of the windshield, which is in
opposed facing relation to the
projector. The next surface interface encountered by the projected image is
the film, which has a larger
Brewster angle than the glass, and therefore the film surface reflects some of
the p-polarized light,
thereby producing an image viewed by the viewer. Thus, such head up display
windshields incorporating
the film, when the image is projected within the predetermined range of
incident angles, produces a
reflected image with little or no ghosting image that is viewed by the viewer
at different heights relative
to the height of the projected image.
Such head up display systems, as described above, may be used in consumer
vehicles, which typically have
a windshield that is oriented at an angle of approximately 45 to 60 to the
horizontal. In such head up
display systems, the projector is typically mounted in the dashboard.
Summary
In one aspect of the present disclosure, a projector display system comprises
a laminate glass panel having
first and second glass layers sandwiching a reflective polarizer layer, or
film, between the two glass layers.
The reflective polarizer layer has a predetermined range of incident angles,
the range defined by an upper
limit and a lower limit, with the reflective polarizer layer having a minimum
reflectance of a first polarized
light component of, for example, approximately 25% when the angle of incidence
of the image projected
onto the laminate glass panel falls within the specified predetermined range.
A projector is positioned so
as to project an image onto the laminate glass panel at an angle of incidence
that is, for example, at least
less than the lower limit of the predetermined range of incident angles. The
resulting image, reflected
on the laminate glass panel, may have a faint ghost image or no perceived
ghost image, depending on the
thickness and refractive index of the first glass layer of the laminate glass
panel that is facing the projector.
Surprisingly, the Applicant found that projecting an image onto the laminate
glass panel, at an angle of
25 incidence well outside the predetermined range specified for the
reflective polarizer layer or film, still
resulted in a clear image with either a faint or no ghost image detected. This
finding enables the use of
the laminate glass panel in a head up display system for use in vehicles
having windshields that are vertical
or nearly vertical, such as are found in buses or recreational vehicles.
Because the reflectance of the p-
polarized light is less at the much smaller angles of incidence, as compared
to the reflectance of the
30 reflective polarizer layer for incident angles that fall within the
predetermined range specified for the
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reflective polarizer layer, in some embodiments the Applicant uses a more
powerful backlight for the
projector. For example, the Applicant may use a backlight between 5,000 and
10,000 lumens, whereas a
typical head up display system may use a projector having a backlight between
1,000 and 2,000 lumens.
Brief Description of the Drawings
FIG. 1 is a photograph of an image projected on a laminated glass panel of an
embodiment of the head up
display system of the present disclosure.
FIG. 2A is a photograph of the projector and laminated glass panel of an
embodiment of the head up
display system of the present disclosure.
FIG. 2B is a closeup of a portion of the system shown in FIG. 3A, including
approximate measurements of
the angle of incidence.
FIG. 3 is a photograph of a projector of an embodiment of a head up display
system of the present
disclosure.
FIG. 4 is a schematic diagram of a prior art head up display system.
FIG. 5 is a schematic diagram of an embodiment of head up display system of
the present disclosure.
Detailed Description
In one aspect of the present disclosure, it is desirable to incorporate a head
up display in a larger vehicle,
such as a recreational vehicle, a transport bus, agricultural equipment and
heavy industrial equipment.
However, these types of vehicles typically have windshields that are
substantially vertically oriented, such
that the windshield may tilt inwardly towards the driver's cabin at an angle
of approximately 00 to 15
.. from the vertical. As discussed in the background section of this patent
application, the wedge style of
head up display windshields are difficult and therefore expensive to
manufacture, and do not produce the
same quality of projected images for users of the vehicle who are of different
heights.
The advancement of polarizer reflector films, which may be incorporated into
laminated windshields,
reduce the expense and difficulty of manufacturing windshields for head up
display systems. However,
.. such films are specifically designed to be used within the predetermined,
specified range of angles of
incidence, so as to maximize the reflection of the polarized light from the
film and to reduce any ghost
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images that are the result of the light reflecting from the surface of the
first and second layers of glass
that comprise the laminate windshield. Due to the cabin and dashboard
configuration of the large vehicles
that typically use vertical or near-vertical windshields, the Applicant has
found it difficult to position the
projector within the vehicle so as to bring the angle of incidence within the
predetermined range specified
for the polarizer reflector films, as specified by the film's manufacturer.
The Applicant has discovered that, surprisingly, using much smaller angles of
incidence that are below the
lower limit of the range of incident angles, specified by the film's
manufacturer, results in the clear
projection of an image onto the laminate windshield that is visible and clear.
Due to the relatively smaller
angle of incidence, a ghost image may also be visible, depending on the
configuration; however, the
Applicant has found that the ghost image sufficiently overlaps the primary
image, so as to not significantly
degrade or distract from the overall projected image.
In some embodiments, the Applicant has substantially increased the brightness
of the projector's
backlight, as compared to projectors used in prior art head up displays. For
example, without intending
to be limiting, the Applicant may use a backlight ranging between 5,000 and
10,000 lumens, as compared
to the 1,000 to 2,000 lumens that may be found in a typical prior art head up
display. The Applicant has
found that using a brighter projector backlight may be necessary to compensate
for the reduced amount
of light that is reflected by the laminate windshield when using the smaller
angle of incidence.
Example
In one example, as shown in FIGS. 2A, 2B and 5, the Applicant constructed a
laminate glass panel 10,
comprising a first glass layer 10a, a second glass layer 10b and an assembly
of interlayers 10c sandwiched
between the first and second glass layers. The assembly of interlayers 10c, in
this example, included a
reflective polarizer layer, comprising a film as will be further described
below. As will be appreciated by
a person skilled in the art, the assembly of interlayers in a typical laminate
windshield for a vehicle may
also include one or more protective interlayers, which may include for example
one or more polyvinyl
butyral ("PVB") layers, for constructing a laminated glass panel that will
hold together after breaking, also
commonly referred to as "safety glass" in vehicle windshields. The assembly of
interlayers may
additionally include adhesive layers for bonding together the sandwiched
assembly of layers.
In this example, the first and second glass layers each had a thickness X of
1.6 mm, and the film thickness
Y of 1.1 mm. The assembly of interlayers 10c, which includes the PVB
protective interlayers and the
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adhesive for binding the film to each glass panel, was a Windshield Combiner
PVB Film manufactured by
3M' (technical data sheet located at:
https://multimedia.3m.com/mws/media/20651530/3m-
windshield-combiner-film-with-pvb-3m-wcf-pvb-technical-data-sheet.pdf last
accessed on December 7,
2021). According to the technical data sheet, the film's manufacturer, 3M',
specifies the film is to be
used at a target angle of incidence in the range of 55 to 65 , and that the
visible p-polarized light reflection
at an angle of incidence of 60 has a minimum threshold amount of reflectance
in the range of 25% to
33%. It will be appreciated that the above example is provided for
illustration purposes only, and that
other reflective polarizer films and different thicknesses of the glass layers
may be used in the construction
of a laminate glass panel and are intended to be included in the scope of the
present disclosure.
As illustrated in FIG. 5, a projector 20 was positioned at a distance D of
approximately 0.4 to 0.5 m
between the projector and the surface of the glass panel 10, so as to project
an image at an angle of
incidence 0 of approximately 15 . The glass panel 10 was oriented at an angle
a of approximately 10
from the vertical. The primary reflected image, represented as line 22, is
reflected by the reflective
polarizer layer 10c and viewed by the viewer A. Ghost image 24, reflected from
the surface 12 of the first
glass layer 10a, is faint as compared to the primary image. A second ghost
image 26, reflected from the
surface 14 of the second glass layer 10b, may sometimes also be visible.
However, the Applicant found
that the first and second ghost images 24, 26 were relatively faint and well
aligned with the primary image
22, given the type and thickness of glass used and the small angle of
incidence. As shown in FIG. 1, which
is a photograph of the projected image of the head up display system
photographed in FIG. 2A, one ghost
image 26 is visible and a second ghost image 24 is much less visible in the
photograph so as to be barely
detectable. As compared to the primary image 22, the ghost image 26 is
relatively faint, and furthermore
the ghost image 26 substantially overlaps the primary image 22. Therefore, the
ghost image 26 minimally
impacts the visibility and legibility of the primary image 22.
To produce the results shown in FIG. 1, the Applicant used a projector 20
having a backlight of
approximately 10,000 lumens. The Applicant estimates that the reflectance of
the film, when used at the
selected angle of incidence of approximately 15 , may be in the range of
approximately 10%, which is
dimmer than the manufacturer's estimated reflectance of 25% to 33% when the
angle of incidence is in
the predetermined range of 55 to 65 for this film. As such, the Applicant
finds it may be desirable to use
a brighter projector backlight, in the range of 5,000 to 10,000 lumens, as
compared to a typical backlight
for head up display projectors, which may range from 1,000 to 2,000 lumens.
The brighter backlight in
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the projector therefore compensates for the reduced reflectance of the p-
polarized light at the reduced
angle of incidence 0 utilized by the Applicant.
FIG. 4 illustrates a typical head up projector system configuration utilizing
a laminate glass panel 10
constructed using first and second glass panels 10a, 10b and the assembly of
interlayers 10c is the same
Windshield Combiner PVB Film manufactured by 3M' described above. In this
configuration, the angle
of incidence 0 is in the range of 55 to 65 , which is the predetermined range
of angles of incidence
determined by the film's manufacturer 3M', and the windshield or glass panel
10 is oriented at an angle
a of approximately 45 , as is more typical of a consumer vehicle where head up
displays may be found.
As mentioned above, the reflectance of the film, when used in the
predetermined range of angles of
incidence, is estimated to be between 25% to 33%.
The Applicant notes that adjustments to the head up display system may be
required for different
configurations of laminate glass shields. For example, some windshields may
comprise first and second
glass layers that each have a thickness X of approximately 3 mm, producing a
windshield with an overall
thickness of 7.1 mm. Because of the thicker glass panels, the first and second
ghost images reflected by
the respective surfaces of the first and second glass panels may be positioned
further apart from the
primary image reflected by the film. Adjustments to the system, therefore, may
include repositioning the
projector 20 at an angle of incidence of less than 15 . Other adjustments may
include different
configurations of the glass panel, such as having a first glass layer 10a,
which is proximate the projector,
having a smaller thickness X as compared to the second glass layer 10b. As an
example, the first glass
panel may have a thickness of 1.6 mm or less, and the second glass panel may
have a thickness of 4 mm
or greater. In other configurations, the laminate panel may be constructed so
as to apply a reflective
polarizer film directly to the outer surface of the 12 of the first glass
layer 10a, so that the light from the
projector does not pass through any glass before it is reflected from the
film. Such configurations may
optionally include a thin plastic protective layer that covers the exposed
surface of the reflective polarizer
film or layer, which may include for example, the plastic material that is
typically used as a screen
protector for a digital device. Other configurations may include incorporating
an optically absorbing
material in the first or second glass layers, or in both the first and second
glass layers, so as to absorb
more of the light and therefore reduce the amount of light that is reflected
by the first and/or second
glass layers 10a, 10b.
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