GB2412806A

GB2412806A - Temporarily hidden display images

Info

Publication number: GB2412806A
Application number: GB0407527A
Authority: GB
Inventors: Pascal Guirauton; Maryline Thorailler; Tomonari Ishikawa; Paul Simon Ewers
Original assignee: Visteon Global Technologies Inc
Current assignee: Visteon Global Technologies Inc
Priority date: 2004-04-02
Filing date: 2004-04-02
Publication date: 2005-10-05
Anticipated expiration: 2024-04-02
Also published as: GB2412806B; GB0407527D0

Abstract

The present invention relates to a display for displaying temporary images, for example in a motor vehicle display device or instrument cluster, the temporary images being hidden when not displayed. A display device 101 comprises a display panel 3 having front surface 4 and a rear surface 5, a Moir’ grating 2 formed within the panel, a light scattering layer 14 formed within the panel 3, and an image formation means 32. The Moir’ grating 2 is closer to the front surface 4 of the panel than is the light scattering layer 14. The Moir’ grating 2 and the light scattering layer 14 are arranged so that visible light 10 incident on the front surface 4 of the panel creates a virtual Moir’ image that appears to lie behind the light scattering layer. Incident light passes through the Moir’ grating 2 towards the light scattering layer 14, the light scattering layer then being arranged to scatter back towards the Moir’ grating 2 and out of the front surface of the panel a proportion 11',15 of said incident light 10 in order form a Moir’ image 26 that appears to lie behind the light scattering layer 14. The image formation means 32 is operable to illuminate temporarily from the rear surface 6 of the panel 3 the light scattering layer 14 in order to form a temporary image 42 visible from the front surface 4 of the panel 3 and which is otherwise hidden from view from the front surface of the panel, said image 42 when formed appearing to lie in a plane that lies in front of the Moir’ image 26 formed by the Moir’ grating 2.

Description

1 241 2806 Temporarily Hidden Display Images The present invention relates

to a display for displaying temporary images, for example in a motor vehicle display device or instrument cluster, the temporary images being hidden when not displayed.

There is often a requirement to display temporary images to a user of a device, for example a warning symbol to the driver of a motor vehicle. One way of doing this is to provide a display device with addressable pixels, such as a liquid crystal or plasma display, however such display devices are relatively expensive, and are visually distinct from a display surface that may be used with a mechanical display device, such as a speedometer or temperature gauge having a moving dial or pointer.

Often, it is desirable to hide or at least partially conceal a display feature or element such as a warning symbol, until this is illuminated. Partly this is for aesthetic reasons, so that the display is not unduly cluttered in appearance, and partly this is to make the display element stand out more prominently when this is illuminated. Such completely or partially hidden display features or elements will be referred to hereinafter as "hidden display images".

One way of providing a hidden display image is to provide a darkened screen, for example a dark grey translucent screen, and to form on the back of the screen an image. The image may be back-projected, for example being formed as part of an illuminating source and focussed onto the screen. Another way of forming an image on the back of a screen is to print a 4 303a2 31 March 2004 2 - mask on the back of the screen, and then flood the masked and unmasked areas of the back of the screen with light so that light exits the front of the screen to form an image defined by the contours of the mask. All such light projection techniques will be referred to hereinafter by the term "rear- projection". While all such prior art rear-projection methods of providing a temporarily hidden display image are effective in that the image may be substantially or completely hidden when not in use, a number of practical and aesthetic limitations have been noted in practice.

For example, the screen may need to be darkened in order to conceal a mask printed on the back of the screen. Although this provides the advantage that display features such as display information, scales and units of measure may be printed on the front of the screen, the background is inherently dull and uninteresting. Furthermore, the screen will absorb the rear-projection light associated with the hidden display images, which either makes the image dull or necessitates the use of a brighter light source.

Furthermore, when a bright light source is incident on the front of the display, particularly sunlight, this may illuminate any masks or other components associated with the hidden image behind the screen, which is unsightly and potential distracting to a user of the display device. Such effects can only be ameliorated by further darkening the screen, thereby increasing the previously mentioned disadvantages of conventional rearprojection approaches.

In many cases, the designer of a display device such as a motor vehicle instrument panel would want to use a bright or 4308a2 31 March 2004 - 3 reflective background screen on which to position permanent display elements such as mechanical needle pointers and on which to print permanent display information. Such bright or reflective display background screens are not well suited to conventional rear- projection techniques.

It is an object of the present invention to provide a more convenient apparatus and method for temporarily displaying hidden images.

According to the invention, there is provided a display device for temporarily displaying a hidden image, comprising a display panel, the panel having a front surface and a rear surface, a Moire grating formed within the panel, a light scattering layer formed within the panel, and an image formation means, wherein: - the Moire grating is closer to the front surface of the panel than is the light scattering layer; - the Moire grating and the light scattering layer are arranged so that visible light incident on the front surface of the panel creates a virtual Moire image that appears to lie behind the light scattering layer; and the image formation means is operable to illuminate temporarily from the rear surface of the panel the light scattering layer in order to form a temporary image visible from the front surface of the panel and which is otherwise hidden from view from the front surface of the panel, said image when formed appearing to lie in front of the Moire image formed by the Moire grating.

In preferred embodiments of the image the Moire grating creates a Moire image that appears to lie between about 5 and 4 3 0 8a2 31 March 2004 - 4 mm behind the front surface of the panel, which is in total about 1 mm to 3 mm thick. The temporary image formed by the image formation means then appears to lie in the plane of the light scattering layer, i.e. spaced in front of the Moire image, and apparently floating in free space. This is a visually striking effect, and helps to capture the attention of a viewer of the temporary hidden image, which is particularly useful when the hidden image is a visual warning symbol.

To form the temporary hidden image, the light scattering layer must be capable of allowing some visible light to pass from the rear surface of the panel to the front surface of the panel. Therefore, in some configurations, it is possible that some of the image formation means could be visible to some degree from the front surface of the panel. The Moire image, however, will tend to mask any such imperfections, simply because it is not a dark background field, but a visually distinct image. Furthermore, the Moire image will also become brighter when illuminated with brighter visible light, and so any variation in shading or other imperfection in the appearance of the light scattering layer due to the image formation means will not become more noticeable when the panel is illuminated by bright light.

The image formation means includes a light source which may project visible light onto the rear surface of the panel.

Alternatively, the image formation means may include a light source which is in contact with the rear surface of the panel.

In preferred embodiments of the invention, the Moire grating 4308a2 31 March 2004 has a first grating and a second grating. The gratings are then separated by a distance in a direction transverse to the extent of the panel, that is, in the direction of light incident on the front surface of the panel.

The first grating and the second grating may be formed on opposite sides of a common substrate, for example by embossing or by lithographic techniques, the thickness of the substrate serving to provide said separation of the first and second gratings.

The grating may, for example, be formed as concentric gratings having different pitches. The Moire pattern will then be an alternating series of relatively bright and darker concentric bands, having a pitch corresponding to the distance over which the first and second gratings go in and out of phase with each other, depending also on the viewing angle to any point on the Moire grating.

Other Moire grating patterns may be used, for example, oval, spiral, square, star-shaped or parallel gratings, and each of these will produce a corresponding Moire pattern.

To form a distinct Moire image, the substrate is preferably clear and uncoloured.

In one embodiment of the invention, the image formation means includes a mask which defines the contours of the temporary image. The mask may be formed on a rearward side of the light scattering layer.

The image formation means may form either a movable temporary 4308a2 31 March 2004 - 6 - image, or alternatively a static temporary image.

To provide interesting visual effects, the panel may include a coloured layer which serves in use to colour the Moire image formed by the Moire grating. Preferably, such a coloured layer lies between the Moire grating and the light scattering layer.

The light scattering layer may have a white colour, or a silvery colour.

Also according to the invention, there is provided a method for temporarily displaying a hidden image on a display panel, the panel having a front surface and a rear surface and between said surfaces a light scattering layer formed within the panel and a between said light scattering layer and said front surface a Moire grating within the panel, comprising the steps of: illuminating from the front surface the Moire grating to create a virtual Moire image that appears to lie behind the light scattering layer; temporarily introducing from the rear surface of the panel optical radiation into the light scattering layer in order to create a corresponding temporary image visible from the front surface of the panel and which appears to float in front of the Moire image, said temporary image not being visible from the front surface of the panel when said optical radiation is not introduced into the light scattering layer.

The invention will now be further described, by way of example only, and with reference to the accompanying drawings, in which: 4 3 0 8a2 31 March 2004 - 7 Figure 1 is a schematic cross-section view of a display panel having a Moire grating of the type used in the display device of the present invention, together with an over-printed graphic element) Figure 2 is a schematic cross-section illustrating the visual effect of the Moire grating and over-printed graphic element of Figure 1, showing how the Moire grating creates a virtual image which appears to lie a distance behind the Moire grating and behind a rear surface of the panel; Figure 3 is a schematic cross-section of a display device for temporarily displaying a hidden image according to a first embodiment of the invention, having a display panel with a Moire grating and an overprinted graphic element similar to those of Figure 1, and behind a rear surface of the panel an image formation means that illuminates temporarily a light scattering layer in the panel which lies behind the Moire grating; Figure 4 is a schematic cross-section illustrating the visual effect of the display device of Figure 3; Figure 5 is a schematic cross-section of a display device for temporarily displaying a hidden image according to a second embodiment of the invention, having a display panel with a Moire grating and an over printed graphic element similar to those of Figure 1, and behind a rear surface of the panel an image formation means that illuminates temporarily a light q 308a2 31 March 2004 - 8 scattering layer in the panel which lies behind the Moire grating; Figure 6 is a schematic cross-section illustrating the visual effect of the display device of Figure 5i Figure 7 is a drawing illustrating the visual effects when using a display panel according to the first embodiment of the invention to display temporarily in a motor vehicle instrument cluster a moving speed indicator pointer, and static warning and status indicators, all of which are formed from relatively brighter areas; and Figure 8 is a drawing illustrating the visual effects when using a display panel according to the second embodiment of the invention to display temporarily in a motor vehicle instrument cluster a moving speed indicator pointer, the indicator pointer being formed from a relatively darker area.

Figure 1 illustrates schematically a cross-section view of a display device 1 with a panel 3 having a Moire grating 2 of the type used in the present invention. The panel 3 extends in a plane which is perpendicular to the plane of the drawings. The Moire grating 2 has a first, or front, grating 4 and a second, or rear grating 5 which are separated by a distance "d" in a direction perpendicular to a front surface 6 of the panel 3. Each grating has alternating areas 8,9 one of which 8 when illuminated by an external light source 7, for example ambient sunlight, is relatively more reflecting to incident visible light 10 than the adjacent areas 9. The 4308a2 31 March 2004 9 - gratings 4,5 each have a slightly different pitch so that the grating areas 8,9 vary from being in phase to out of phase over a distance of the order of lOO's of cycles of the grating period. The Moire grating 2 may be formed in a number of different ways, for example by printing or by surface embossing on opposite sides of a clear polymeric substrate 12, which then also serves to provide the separation distance "d" between the front and rear gratings 4,5.

When the Moire grating 2 is illuminated, most of the incident light 10 enters the panel 3 rather than being reflected by the front surface 6 of the panel 3. Some light will, however, be returned or reflected 15 by the Moire grating. Light which is not reflected 15 by the Moire grating 2 passes through the grating towards a light scattering layer 14. The light scattering layer 14 is separated from the rear grating 5 by a clear transparent spacer layer 16. The light scattering layer 14 is white in colour and is at least partially translucent to visible light.

The light scattering layer 14 scatters back towards the Moire grating 2 a proportion 13 of the light incident on the light scattering layer 14. Depending on the opacity of the light scattering layer 14, some visible light will escape 22 from a rear surface 20 of the panel 3.

Reference is now made also to Figures 4 and 7. Scattered light 13 from the light scattering layer 14 passes through the grating 2 and back out of the front surface 6 of the panel 3 at all angles. When the total returned light 13,15 is viewed 18 in binocular vision, the viewer will see a Moire pattern or image 26 which consists of alternating bands 24,25 43oaa2 31 March 2004 - 10 of relatively darker and lighter regions.

Figure 4 shows schematically the visual effect created by the Moire grating 2. The cyclic phase shift in the registration between the front 4 and rear gratings 5, creates a visible Moire pattern 26. With binocular vision each eye 18 captures retuned light 13,15 at a different angle from the other eye relative to the plane of the panel 3. The position of the bands 24,25 in the Moire pattern 26 is shifted depending on this viewing angle, with the result that each eye 18 sees a slightly different position to the bands 24,25. The result is that the eyes 18 see the Moire pattern 26 as a virtual image lying apparently at a distance "D" behind the front surface 6 of the panel 3. The panel may only be between 1 mm to 2 mm thick, yet the Moire pattern 26 may appear to lie between mm and 50 mm behind the panel front surface 6. The pattern 26 appears to be superimposed on a background colour 28, which may be white if the spacer layer 16 is similarly coloured and the scattering layer 14 is white, or a white or silvery colour if either of the transmissive spacer layer 16 or scattering layer 14 are so coloured.

In a first embodiment of the invention 101, illustrated in Figures 3, 4 and 7, the spacer layer 16 is coloured a medium blue so that the Moire pattern 26 is a blue pattern as shown in Figure 7. In a second embodiment of the invention 101', illustrated in Figures 5, 6 and 8, the spacer layer 16' is translucent and uncoloured, in which case the Moire pattern 26' is a white or silvery pattern.

Optionally, the panel 3 may be used together with an over-printed graphic element 30, such as a label or text. The 4308a2 31 March 2004 - 11 appearance of such an element is not affected by the Moire pattern 26, and appears to lie on the front surface 6 of the panel 3.

If the only use of the display device 101 were to produce a visible Moire pattern 26, then it would be desirable to minimize or eliminate the light 22 lost through the back surface 20 in order to make the pattern 26 brighter. In such a case, the light scattering layer 14 would be light scattering but opaque.

The first embodiment of the invention 101 is illustrated in schematic cross-sections shown in Figures 3 and 4. A display device 101 according to the invention is similar to the display device 1 of Figures 1 and 2. The difference with Figures 1 and 2 is that the display device of the invention 101 includes behind the rear surface 20 of the panel 3 an image formation means 32 for forming a temporary hidden image.

The image formation means 32 includes a controllable light source 34, such as a light emitting diode or a miniature gas discharge lamp, that lies a convenient distance behind the rear surface 20 of the display 101, for example between 5 mm to 25 mm, or which may optionally be in contact with the rear surface 20 of the display panel. The light source 34 directs optical radiation 36 towards the rear surface 20 of the panel 3.

The image formation means 32 includes a mask 38 to block unwanted optical radiation 37 from reaching the panel 3.

Optical radiation 36 which does reach the panel 3, enters the 4308a2 31 March 2009 - 12 light scattering layer 14. Some of the optical radiation is back-scattered from the light scattering layer 14 and is lost. However, because the light scattering layer is non-opaque, a proportion of this incident optical radiation 36 passes through the light scattering layer 14. Scattered and transmitted optical radiation 40 passes through the Moire grating 2 and towards the eyes 18 of the viewer. The pattern of this optical radiation 40 is defined by the mask 38.

Figure 4 illustrates the optical effect created by this arrangement. As described above, the Moire image 26 appears to lie well behind the front surface 6 of the panel 3. The optical radiation 40 from the light source 34 received by the viewer's eyes 18 makes only one pass through the Moire grating, and ignoring any back-reflections at interfaces in the panel, includes essentially no rays which have been reflected by the areas 8,9 of the front and rear gratings 4,5. There is therefore very little or no apparent difference in the position of the shadow cast by the mask 38 as perceived in binocular vision 18. The result is that in binocular vision this optical radiation 40 appears to originate from an area 42 of the light scattering layer 14 illuminated by the projected optical radiation 36 from the light source 34. The temporarily illuminated area 42 therefore appears to "float" in front of the background Moire pattern 26.

When the light source 34 is extinguished, the area 42 darkens and becomes part of the background Moire pattern 26. The masks 38 may be made invisible from the front surface side of the display device 101, for example, by coating the masks 38 on the side towards the panel rear surface 20 with a dark 43oaa2 31 March 2004 - 13 coating 41 that does not reflect transmitted light 22 back towards the light scattering layer 14.

Optionally, the image formation means 32 may include an actuator 43 by which the image formation means 32 may be made to move 52 transversely across the rear surface 20 of the screen 3, in order to make the illuminated area 42 appear to move.

Figures 5 and 6 show a second embodiment 101' of a display device according to the invention. The second embodiment differs from the first embodiment 101 in that the spacer layer 16' is clear and uncoloured. The Moire pattern 26' therefore has alternating bands 24',25' of relatively dark and bright areas on a white or silvery background 28'. In addition, the image formation means 32' has a plurality of light sources 34, which are fixed in position and which flood the rear surface 20 of the panel 3'. There is one mask 38', which is movable 52' in a direction parallel with the rear surface 20 of the panel 3'. The mask casts a shadow 42' which therefore appears to move 52' in front of the background Moire pattern 26'.

Figure 7 shows the first embodiment of a display device 101, here a motor vehicle speedometer instrument cluster 48. The speed scale 48 is formed from overprinted graphic elements 30. The display device 101 may have several masks 38 and independently operable light sources 34 that are used to project onto the light scattering layer 14 a number of bright areas 60,61,62. In this case, it is desirable if the Moire pattern 26 is darker than that 26' of the second embodiment 101' shown in Figure 8, and therefore the spacer layer 16 is 4308a2 31 March 2004 darkened with a colour, for example a medium blue. This also gives an attractive background colour to the Moire pattern 26.

One area 60 is a movable bright speedometer pointer, which may be formed by making both a light source 34 and mask 38 movable 52 as shown in Figure 3. The pointer is hidden when the vehicle is not operating. Other areas 61,62 are static warning or indication lights, illuminated as required, and hidden when not required.

In Figure 5, the hidden image is a dark speed indicator pointer 50 on a bright Moire pattern background 26'. The speed scale 48' is similar to that of Figure 7. In this case, the mask 38' is the same shape as the dark pointer, and the rear surface 20 of the panel 3' is flooded with bright light from the plurality of light sources 34' to illuminate the light scattering layer 14 outside the area of the mask 38'.

The dark pointer 50 is therefore an image which is otherwise hidden on the display device 101 until the light sources 34' are energised. In this embodiment, the pointer mask 38' moves 52' behind the panel 3', while the light sources 34' are fixed in position.

Therefore, in both embodiments 101,101', one or more light sources 34,34' may be energised from time to time to illuminate temporarily the light scattering layer 14 in the panel 3,3' and so reveal an otherwise hidden image 50,60,61,62, which appears to float freely above a background Moire image 26,26'.

Most commonly, the optical radiation 36,36' from the light 4308a2 31 March 2004 - 15 source 34,34' will be visible light. Optionally, however, the optical radiation may include ultraviolet light in which case the light scattering layer 14 may include a fluorescent compound that glows in response to the incident ultraviolet light. When the light source 34,34' is energised, the otherwise hidden image 50,60,61,62 becomes visible and appears to float freely in front of the background Moire pattern 26,26'.

The display devices described above provide a convenient apparatus and method for temporarily displaying hidden images.

4308a2 31 March 2004 - 16

Claims

Claims: 1. A display device for temporarily displaying a hidden image,

comprising a display panel, the panel having a front surface and a rear surface, a Moire grating formed within the panel, a light scattering layer formed within the panel, and an image formation means, wherein: - the Moire grating is closer to the front surface of the panel than is the light scattering layer; - the Moire grating and the light scattering layer are arranged so that visible light incident on the front surface of the panel creates a virtual Moire image that appears to lie behind the light scattering layer; and the image formation means is operable to illuminate temporarily from the rear surface of the panel the light scattering layer in order to form a temporary image visible from the front surface of the panel and which is otherwise hidden from view from the front surface of the panel, said image when formed appearing to lie in front of the Moire image formed by the Moire grating.
2. A display device as claimed in Claim 1, in which the image formation means includes a light source which projects visible light onto the rear surface of the panel.
3. A display device as claimed in Claim 1, in which the image formation means includes a light source which is in contact with the rear surface of the panel.
4. A display device as claimed in any preceding claim, in which the Moire grating has a first grating and a second grating, said gratings being separated by a distance in a 43oea2 31 March 2004 - 17 direction transverse to the extent of the panel.
5. A display device as claimed in Claim 4, in which the first grating and the second grating are formed on opposite sides of a common substrate, the thickness of the substrate serving to provide said separation of the first and second gratings.
6. A display device as claimed in Claim 5, in which said substrate is clear.
7. A display device as claimed in any preceding claim, in which the image formation means includes a mask which defines the contours of the temporary image.
8. A display device as claimed in Claim 7, in which the mask is formed on a rearward side of the light scattering layer.
9. A display device as claimed in any preceding claim, in which the image formation means forms a movable temporary Image.
10. A display device as claimed in any of Claims 1 to 8, in which the image formation means forms a static temporary image.
11. A display device as claimed in any preceding claim, in which the panel includes a coloured layer which serves in use to colour the Moire image formed by the Moire grating.
12. A display device as claimed in Claim 11, in which said 4308a2 31 March 2004 - 18 coloured layer lies between the Moire grating and the light scattering layer.
13. A display device as claimed in any preceding claim, in which the light scattering layer has a white colour.
14. A display device as claimed in any of Claims 1 to 12, in which the light scattering layer has a silvery colour.
15. A display device as claimed in any preceding layer, in which the light scattering layer is translucent to visible light.
16. A method for temporarily displaying a hidden image on a display panel, the panel having a front surface and a rear surface and between said surfaces a light scattering layer formed within the panel and a between said light scattering layer and said front surface a Moire grating within the panel, comprising the steps of: illuminating from the front surface the Moire grating to create a virtual Moire image that appears to lie behind the light scattering layer; temporarily introducing from the rear surface of the panel optical radiation into the light scattering layer in order to create a corresponding temporary image visible from the front surface of the panel and which appears to float in front of the Moire image, said temporary image not being visible from the front surface of the panel when said optical radiation is not introduced into the light scattering layer.
17. A display device substantially as herein described, with reference to or as shown in the accompanying drawings.

43oea2 31 March 2004

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18. A method for temporarily displaying a hidden image on a display panel, substantially as herein described, with reference to or as shown in the accompanying drawings.

4308a2 31 March 2004