CA3141256A1 - Head up display system and method - Google Patents

Abstract

A projector display system comprises a projector and a laminate glass panel comprising first and second glass layers and an assembly of interlayers sandwiched therebetween. The first glass layer is substantially parallel to the second glass layer and the assembly of interlayers includes a reflective polarizer film. The reflective polarizer film of the laminate glass panel has a predetermined range of incident angles defined by an upper limit and a lower limit, wherein when the image is projected onto the laminate glass panel at an incident angle within the predetermined range of incident angles, the reflective polarizer film is adapted to reflect a minimum threshold amount of a first polarized light component of the said image.
The projector projects an image onto the laminate glass panel at a selected incident angle that is at least 300 less than the lower limit of the said predetermined range of incident angles.

Description

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 Date recue / Date received 2021-12-08 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

2 Date recue / Date received 2021-12-08 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

3 Date recue / Date received 2021-12-08 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

4 Date recue / Date received 2021-12-08 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

5 Date recue / Date received 2021-12-08 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.

6 Date recue / Date received 2021-12-08

Claims (24)

WHAT IS CLAIMED IS:

1. A projector display system, comprising:
a laminate glass panel comprising first and second glass layers and an assembly of interlayers sandwiched between the first and second glass layers, wherein the first glass layer is substantially parallel to the second glass layer, the assembly of interlayers comprising a reflective polarizer film;
a projector for projecting an image onto the laminate glass panel, wherein the projector and the first glass layer of the laminate glass panel are in opposed facing relation to one another;
the reflective polarizer film of the laminate glass panel having a predetermined range of incident angles defined by an upper limit and a lower limit, wherein when the said image is projected onto the laminate glass panel at an incident angle within the predetermined range of incident angles, the reflective polarizer film is adapted to reflect at least 25% of a first polarized light component of the said image; and wherein a selected incident angle of the image projected onto the laminate glass panel is at least 300 less than the lower limit of the said predetermined range of incident angles.

2. The system of claim 1, wherein the projector comprises a backlight of at least 5,000 lumens.

3.
The system of claim 1, wherein the first glass layer has a thickness of less than or equal to 1.6 mm.

4. The system of claim 3, wherein the second glass layer has a thickness of less than or equal to 1.6 mm.

5. The system of claim 1, wherein the laminate glass panel is oriented at a tilt angle selected in a tilt range between 00 and 15 from the vertical.

6. The system of claim 1, wherein the first polarized light component is a p-polarized light component of the said image.

7. The system of claim 6, wherein the image projected by the projector is composed of p-polarized light.

8. The system of claim 3, wherein the second glass layer has a thickness that is at least 2.0 times the thickness of the first glass layer.

9. The system of claim 1, wherein the selected incident angle of the image projected onto the laminate glass panel is at least 40 less than the lower limit of the said predetermined range of incident angles.

10. A method of projecting an image onto a nearly vertical laminate glass panel, comprising:

orienting a laminate glass panel at a tilt angle selected between 00 and 15 from the vertical, the laminate glass panel comprising first and second glass layers and an assembly of interlayers sandwiched between the first and second glass layers, wherein the first glass layer is substantially parallel to the second glass layer, and wherein the assembly of interlayers includes a reflective polarizer film, and wherein the reflective polarizer film has a predetermined range of incident angles defined by an upper limit and a lower limit, wherein when the said image is projected onto the laminate glass panel at an incident angle within the predetermined range of incident angles, the reflective polarizer film is adapted to reflect at least 25% of a first polarized light component of the said image;
positioning a projector for projecting an image onto the laminate glass panel, wherein the projector and the first glass layer of the laminate glass panel are in opposed facing relation to one another, and wherein a selected incident angle of the image projected onto the laminate glass panel is at least 30 less than the lower limit of the said predetermined range of incident angles.

11. The method of claim 10, wherein the projector is positioned at a distance less than 1 meter from the first glass layer of the laminate glass panel.

12. The method of claim 10, wherein the projector comprises a backlight of at least 5,000 lumens.

13. The method of claim 10, wherein the first glass layer has a thickness of less than or equal to 1.6 mm.

14. The method of claim 10, wherein the second glass layer has a thickness of less than or equal to 1.6 mm.

15. The method of claim 10, wherein the first polarized light component is a p-polarized light component of the said image.

16. The method of claim 15, wherein the image projected by the projector is composed of p-polarized light.

17. The method of claim 13, wherein the second glass layer has a thickness that is at least 2.0 times the thickness of the first glass layer.

18. A projector display system, comprising:
a laminate glass panel comprising first and second glass layers and an assembly of interlayers sandwiched between the first and second glass layers, wherein the first glass layer is substantially parallel to the second glass layer, and a reflective polarizer layer applied to an outer surface of the first glass panel;

a projector for projecting an image onto the laminate glass panel, wherein the projector and the reflective polarizer layer of the laminate glass panel are in opposed facing relation to one another;
the reflective polarizer layer of the laminate glass panel having a predetermined range of incident angles defined by an upper limit and a lower limit, wherein when the said image is projected onto the laminate glass panel at an incident angle within the predetermined range of incident angles, the reflective polarizer film is adapted to reflect a minimum threshold amount of a first polarized light component of the said image; and wherein a selected incident angle of the image projected onto the laminate glass panel is at least 300 less than the lower limit of the said predetermined range of incident angles.

19. The system of claim 18, wherein the first and second glass layers each have a thickness of at least 3.0 mm.

20. The system of claim 18, wherein the laminate glass panel is oriented at a tilt angle selected in a tilt range between 00 and 15 from the vertical.

21. The system of claim 18, wherein the first polarized light component is a p-polarized light component of the said image.

22. The system of claim 21, wherein the image projected by the projector is composed of p-polarized light.

23. The system of claim 18, wherein the selected incident angle of the image projected onto the laminate glass panel is at least 40 less than the lower limit of the said predetermined range of incident angles.

24. The system of claim 18, wherein the laminate glass panel further comprises a protective layer, wherein the reflective polarizer layer is sandwiched between the protective layer and the first glass layer of the laminate glass panel.