CA2031264A1 - Windshield for head-up display system - Google Patents

Abstract

ABSTRACT

A windshield for a head-up display system is provided such that the opposing outer major surfaces of the windshield are non-parallel. As a result, an image from a display source and reflected off one outer major surface of the windshield is superimposed over the image reflected off the opposing outer major surface of the windshield.

Description

, 3 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.

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.

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 s f v ~ ~

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.

s~ r. ~, ~ ~ n 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 h~

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.

h ~, '3 r ~ ~ i7 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 ~ ~I r~ ~f ~ ,~ ,S
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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) fJ '~

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.

Claims (20)

1. A laminated transparency comprising:
a first rigid ply;
a second rigid ply ; and means to secure said first ply to said second ply such that opposing outer major surfaces of said transparency are non-parallel and oriented relative to each other so that an image projected from a display source and reflected off an outer surface of said transparency is substantially superimposed over an image projected from said display source and reflected off an opposing outer major surface of said transparency.

2. A laminated transparency comprising:
a first ply having inner and outer opposing major surfaces;
a second ply having inner and outer opposing major surfaces; and means to secure said inner major surface of said first ply to said inner major surface of said second ply such that said outer major surfaces of said plies are non-parallel relative to each other and oriented so that an image projected from a display source and reflected off said outer surface of said first ply is substantially superimposed over an image projected from said display source and reflected off said outer major surface of said second ply.

3. The transparency as in claim 2 wherein said major surfaces of said first and second plies are non-planar.

4. The transparency as in claim 2 wherein said outer surface of each of said plies is parallel to said inner surface of said corresponding ply.

5. The transparency as in claim 4 wherein said plies are glass plies and said securing means is a tapered sheet of thermoplastic material.

6. The transparency as in claim 5 wherein said major surfaces of said first and second plies are non-planar.

7. The transparency as in claim 2 wherein at least one of said plies is tapered in thickness.

8. The transparency as in claim 7 wherein said plies are glass and said securing means is a sheet of thermoplastic material.

9. The transparency as in claim 8 wherein said major surfaces of said first and second plies are non-planar.

10. The transparency as in claim 8 wherein said thermoplastic material sheet is tapered in thickness.

11. A head-up display system for a vehicle including:
means to project a desired display; and a windshield having non-parallel opposing first and second outer major surfaces oriented relative to each other such that an image projected from said display means, when reflected off said first major surface of said windshield is substantially superimposed over said image when reflected off said second major surface of said windshield.

12. The system as in claim 11 wherein said opposing major surfaces of said windshield are non-planar.

13. The system as in claim 11 wherein said windshield includes first and second rigid transparent plies and means to bond said first and second plies together to form a unitary structure.

14. The system as in claim 13 wherein opposing major surfaces of each of said plies are substantially parallel to each other.

15. The system as in claim 14 wherein said transparent plies are glass plies and said bonding means include a tapered sheet of thermoplastic material.

16. The system as in claim 15 wherein said major surfaces of said first and second plies are non-planar.

17. The system as in claim 13 wherein at least one of said plies is tapered in thickness.

18. The system as in claim 17 wherein said transparent plies are glass plies said bonding means includes a sheet of thermoplastic material.

19. The system as in claim 18 wherein said major surfaces of said first and second plies are non-planar.

20. The system as in claim 18 wherein said sheet of thermoplastic material is tapered in thickness.