GB2508927A

GB2508927A - Retroreflective LCD display panel

Info

Publication number: GB2508927A
Application number: GB201222729A
Authority: GB
Inventors: Stephen Andrew Randall
Original assignee: LES HUGH SCOTT
Current assignee: LES HUGH SCOTT
Priority date: 2012-12-17
Filing date: 2012-12-17
Publication date: 2014-06-18
Also published as: GB201222729D0

Abstract

A display comprising a first transmissive liquid crystal display (LCD) panel 102, a second retroreflective panel 104 disposed behind the LCD panel to reflect light transmitted through the front viewing surface of the LCD panel back towards the viewer. The display further has a memory for storing one or more images and a control means to cause the display of said images 124, 126 on the LCD panel. The LCD display panel may comprise two orthogonal light polarising filters 112, 114 and an electrode layer 118 to change the transmissive properties of cells within the liquid crystal layer. The LCD may comprise a twisted nematic liquid crystal layer or a vertical alignment liquid crystal layer and may include colour filters 122. In one embodiment the display panel is part of a road sign and includes a control device for transmitting signals to cause the control means to change the displayed graphic 124, 126.

Description

Display Panel

BACKGROUND

a. Field of the Invention

This invention relates to display panels and in particular to display panels for use in road signs.

b. Related Art Temporary road signs are commonly deployed alongside carriageways to indicate, for example, overnight roadworks, temporary lane closures, temporary reduced speed limits, or other time limited information.

Especially on roads in which there are two or more lanes of traffic travelling in each direction, these signs are often placed on both sides of the carriageway so that they are clearly visible to traffic in all lanes. It is, therefore, necessary for workers to cross the carriageway in order to deploy these signs. Under the UK Highways Agency's Aiming For Zero' initiative, the safety of road workers is now of paramount importance. The UK Highways Agency wish to eliminate all live carriageway crossings by 2016 and it is, therefore, necessary for contractors to change the way they work to find ways to reduce the number of carriageway crossings.

The use of so called smart signs' has become more common in recent years.

These smart signs comprise hinged sections or panels having a single graphic only on one side or a different graphic on each side. In this way, the sign may be masked when not in use or the configuration of the sign may be changed, as illustrated in Figure 1. The road sign illustrated in Figures la and lb indicates a lane closure. The sign includes a hinged panel, bounded by the dashed lines, that allows the displayed status of the in a first configuration The number of states or configurations of these signs is, therefore, limited to the number of separate hinged panels and the number of graphics displayed on each of these panels.

The movement of the hinged section is actuated by motors within the sign which are powered by heavy duty batteries. The operation of the motors may then be controlled by a road worker from a hand held control unit, without needing to cross the carriageway.

There are, however, a number of disadvantages of these systems. A first issue is reliability. A large number of signs have been known to fail so that the configuration of the sign cannot be changed. Much of this is due to the failure of the moving parts within the sign. A second disadvantage is that the signs are very heavy and are, therefore, difficult to handle and deploy, as well as requiring modified frames to hold the extra weight. A further disadvantage is that they typically require heavy duty batteries to power the motors on the sign. These batteries are very easy to steal and are very expensive to replace. Furthermore, each time the sign requires maintenance or battery replacement, there is a risk of injury to those carrying out this work.

It is, therefore, an object of the present invention to provide an improved

SUMMARY OF THE INVENTION

According to a first aspect of the invention there is provided a display comprising: -a first panel comprising a light transmissive liquid crystal layer; -memory means for storing one or more graphics to be displayed by the first panel; -control means for applying signals to said liquid crystal layer, the signals being arranged to activate cells of the liquid crystal layer so as to cause changes in the light transmissive properties of the cells to display one of said graphics; and -a second panel disposed rearward of the first panel relative to a viewer of the display, the second panel comprising a retroreflective surface arranged to reflect light such that said reflected light is transmitted through the liquid crystal layer towards said viewer.

Preferably the first panel further comprises a first light polarising filter and a second light polarising filter, the first and second light polarising filters being oriented at 9Q0 with respect to each other, and the liquid crystal layer being located between the first and second light polarising filters.

The first panel, preferably, further comprises an electrode layer including a plurality of electrodes, each electrode being associated with a cell of the liquid crystal layer, and the control means transmits electrical signals to activate one or more of the electrodes so as to change the light transmissive properties of one or more cells.

In preferred embodiments of the display, the light reflected from the retrorefiective surface is white light.

In some embodiments the liquid crystal layer comprises a twisted nematic liquid crystal. In other embodiments the liquid crystal layer is a vertical alignment liquid crystal layer.

To aid viewing of the display, the display preferably further comprises an anti-reflection layer disposed forward of the first panel relative to a viewer of the display.

In embodiments in which the first panel comprises a first light polarising filter and a second light polarising filter, the first panel preferably further comprises a colour filter layer located between the liquid crystal layer and the first light polarising filter, the colour filter layer and the first light polarising filter being located forward of the liquid crystal layer relative to a viewer of the display, and wherein the colour filter layer is arranged to enable polychromatic graphics to be displayed by the first layer.

The control means may further comprise a clock and programmable timing means, the timing means being arranged to generate a first timing signal to activate the first panel to display one of said graphics stored in the memory and a second timing signal to end display of said graphic.

According to a second aspect of the invention there is provided a road sign comprising a display according to the first aspect of the invention.

According to a third aspect of the invention there is provided a display assembly comprising a display according to the first aspect of the present invention and a control device, the control device comprising means for transmitting signals to be received by the control means of the display, wherein the signals transmitted by the control device comprise a signal to activate the first panel to display one of said graphics stored in the memory.

In preferred embodiments, the signals transmitted by the control device comprise a signal representing a bespoke graphic to be displayed by the first panel.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be further described, by way of example only, and with reference to the accompanying drawings, in which: Figure 1 a shows a first configuration of a prior art road sign used to indicate lane closures; Figure lb shows a second configuration of the prior art road sign of Figure la; Figure 2 is an exploded view of a road sign incorporating a first embodiment of a display panel of the present invention; and Figure 3 is an exploded view of a road sign incorporating a further embodiment of a display panel of the present invention.

DETAILED DESCRIPTION

A first embodiment of a display panel 1 of the present invention is illustrated in Figure 2 and comprises a liquid crystal panel 2 and a retroreflective panel 4. The liquid crystal panel 2 is located forward of the retroreflective panel 4 relative to a viewer of the display 1.

In a first, non-activated state the liquid crystal panel 2 is light transmissive, and is preferably transparent. In this way, light incident on a front surface 6 of the display panel 1 is able to pass through the liquid crystal panel 2 in a first direction to impinge on a front surface 8 of the retroreflective panel 4. Light reflected by the retroreflective panel 4 is then able to pass back through the liquid crystal panel 2 in a second, opposite direction towards a viewer of the display 1. In this way the reflected light acts as a backlight for the liquid crystal panel 2.

The liquid crystal panel 2 comprises a plurality of segments or cells (not shown).

Each of these cells may be switched between the first, non-activated state and a second, activated state. In the activated state, the light transmissive properties of the liquid crystal panel 2 are changed so that the light is no longer able to pass through the liquid crystal panel.

In use, therefore, a graphic may be displayed on the liquid crystal panel 2 by selectively activating some of the cells to alter their light transmissive properties.

Light, and in particular light reflected by the retroreflective layer 4, is transmitted through the non-activated segments, but is no longer able to pass through the activated segments, such that the graphic is seen as a dark image against a bright

background.

This invention has particular application in the display of road signs and, in particular, may be used to display temporary road signs to indicate, for example, overnight roadworks, temporary lane closures, temporary reduced speed limits, or other time limited information. The following description, therefore, is directed to the use of a display panel 1 as a road sign. It will be appreciated, however, that the display panel 1 may be used in numerous other applications which will become apparent from an understanding of the operation of the display 1.

The retroreflective panel 4 comprises a substrate 10 having a retroreflective surface 8. The substrate 10 may be made of any suitable material such as aluminium, which provides a substantially rigid support for the display panel 1.

The retroreflective surface 8 may be formed using any known materials and methods, and may, for example, be formed by a plurality of corner prisms or glass beads, as is known in the art. The retroreflective surface 8 may comprise a retroreflective coating applied to a surface 8 of the substrate 10.

In a preferred embodiment, the retroreflective surface 8 is designed such that the reflected light is white light. In other embodiments, however, it may be beneficial if the reflected light is yellow light or blue light.

The liquid crystal panel 2 comprises a plurality of layers including a first, rear polarising light filter 12, a second, front polarising light filter 14 and, between the two filters 12, 14, a liquid crystal layer 16. The two polarising filters 12, 14 are oriented at 900 to each other such that they form crossed-polarisers. In this embodiment, the liquid crystal layer 16 comprises twisted nematic liquid crystals.

In the non-activated state, the liquid crystal molecules are arranged to twist light that is transmitted through the layer by 900. As such, light polarised in a first direction by the rear polarising filter 12 is twisted through 90° by the liquid crystal layer 16, and is then able to pass through the second polarising filter 14. The same is also true of light passing in the opposite direction through the liquid crystal panel 2.

When a current is applied to the liquid crystal layer 16, the liquid crystal molecules align themselves, and the liquid crystal is said to be in an activated state. In this activated state light is not longer transmitted through the liquid crystal panel 2. In use, light is polarised in a first direction by the rear polarising filter 12, passes straight through the liquid crystal layer 16 and is then blocked by the second polarising filter 14 which is at 900 to the first filter 12.

To enable selected areas of the liquid crystal panel 2 to be switched to the activated state the liquid crystal layer 2 is divided into an array of cells (not shown). An electrode panel 18, located between the rear polarising filter 12 and the liquid crystal layer 16, comprises a plurality of electrodes (not shown), each electrode corresponding to one of the cells of the liquid crystal layer 16. The electrodes allow current to be supplied selectively to each cell individually to switch the liquid crystal layer 16 within that cell between the non-activated and activated states.

The display panel 1 further comprises control means (not shown), to supply control signals to the electrodes, and memory means to store data corresponding to one or more graphics to be displayed by the liquid crystal panel 2. The one or more graphics may include, for example, images, pictograms and/or text.

In use, a user selects from the memory one of the graphics to be displayed. The control means then transmits a plurality of control signals, based on the stored data, to activate the required electrodes such that the cells of the liquid crystal layer 16 are switched from the non-activated to the activated state, such that the graphic is displayed in the liquid crystal panel.

In this example, the liquid crystal panel 2 blocks the transmission of light in areas corresponding to the graphic to be displayed so that the graphic appears as a dark

image against a bright background.

In some situations it is desirable to prevent any transmission of light through the liquid crystal panel 2 so that no light is reflected by the retroreflective panel 4 back towards a viewer of the display 1. This has advantages, for example, when the display 1 is being used as a temporary road sign and it is desired to not display any sign for a period of time. If the liquid crystal layer 2 were maintained in a non-activated state, then light would be able to pass through the liquid crystal layer 2 and be reflected by the retroreflective layer 4. This would mean that the display 1 would appear bright, even though no sign was being displayed, which could potentially distract motorists.

It is, therefore, desirable if the control means is arranged such that when the display panel 1 is in an OFF state, i.e. no sign is being displayed, all of the cells of the liquid crystal layer 16 are held in an activated state so as to prevent light transmission through the liquid crystal panel 2.

The display panel 1 further comprises a transparent plate 20, preferably made from a glass or plastics material, located at the front of the display panel 1, closest to a viewer of the sign. The transparent plate 20 provides a protective layer in front of the liquid crystal panel 2.

To prevent glare from the display panel 1, it is desirable to include an anti-reflection coating on a front surface 6 of the panel 20. This is especially desirable when the display panel 1 is used to display road signs and it is advantageous to minimise the amount of reflection from the front surface 6 of the display 1.

In a second preferred embodiment of the invention the liquid crystal panel 2 comprises a vertical alignment liquid crystal layer. When this layer is in a non-activated state, the liquid crystal molecules are oriented such that no light is able to be transmitted through the liquid crystal panel. When the layer is switched to an activated state the molecules rotate so that light is able to be transmitted through the panel. In this embodiment, therefore, the OFF state of the display panel corresponds to the cells of the liquid crystal layer being in a non-activated state.

As described in relation to the previous embodiment of the display panel, a memory stores data corresponding to one or more graphics to be displayed. In use, a user selects one of the graphics to be displayed, and the control means transmits a plurality of control signals that activate the required electrodes within the electrode panel. In this embodiment the control signals are transmitted to cells in the liquid crystal layer corresponding to an inverse of the graphic to be displayed, to switch these cells from the non-activated to the activated state. As such, cells corresponding to the graphic to be dsiplayed remain in a non-activated state.

In this way, the liquid crystal layer continues to block the transmission of light in areas corresponding to the graphic to be displayed such that, as in the previous embodiment, the graphic appears dark against a bright background.

The above described embodiments have been limited to monochrome displays, for example the display of black and white or greyscale graphics when the retroreflective panel reflects white light. In many situations, however, it is desirable to display a polychrome or coloured graphic. For example, road signs in the United Kingdom include a red border to denote a warning or prohibitive sign, or a red bar denoting a lane closure, while the remainder of the pictogram or text is predominantly black.

A further embodiment of a display panel 101 permitting the display of polychrome graphics is shown in Figure 3. Many of the features of this embodiment are the same as or similar to features of earlier embodiments and these features have, therefore, been indicated with reference numerals incremented by 100. In this embodiment the liquid crystal panel 102 further comprises a colour filter layer 122 located between the liquid crystal layer 116 and the front polarising filter 114. The colour filter layer 122 comprises an array of coloured regions (not shown), each of the coloured regions corresponding to and aligned with one cell of the liquid crystal layer 116. The coloured regions are arranged in repeating groups of three, comprising red, green and blue. Each group of three cells (red, green and blue) makes up a single segment (not shown) of the liquid crystal layer 116. By altering the degree of light transmission through each of the cells, the resultant colour of the segment is thereby altered. By allowing complete light transmission through all three cells, the segment appears white; while preventing transmission of light through all three cells creates a dark or black segment.

In use, light reflected by the retroreflective panel 104 passes through the first polarising filter 112 and then through the liquid crystal layer 116. Any light that is transmitted through the liquid crystal layer 116 then passes through the coloured filter layer 122, before passing through the second polarising filter 114 and being emitted from a front 106 of the display 101.

In this embodiment, the memory (not shown) of the display panel 101 stores data corresponding to one or more graphics to be displayed. The data includes data related to the shape of the graphic and data related to the colour or colours of different parts of the graphic. The control means (not shown) transmits a plurality of control signals, based on the stored data, to activate the required electrodes such that each of the cells of the liquid crystal layer 116 transmits the required amount of light to create a dark (black), white or coloured segment of the liquid crystal panel 2.

For example, considering the graphic illustrated in Figure 3, control signals are sent to a first set of segments 124, corresponding to the text 50', so that none of the cells transmit light and the numbers appear black. A second group of control signals are sent to a second set of segments 126, corresponding to the ring or annular border of the sign, so that the cells aligned with the red colour filter transmit light and the cells aligned with the green and blue filters do not transmit light. In this way the ring appears red. A third group of control signals is sent to the remaining segments so that light is transmitted through all of the cells and

these background' segments appear white.

In some embodiments, a display panel 1, 101 of the present invention further comprises a wide view film (not shown) located in front of the liquid crystal panel 2 with respect to a viewer of the display 1. This film increases the viewing angle of the display 1 as is known in the art. When the display 1 is being used as a road sign at the side of the carriageway it will generally not be necessary to include the wide view film because the signs will be viewed within a relatively limited horizontal angular range, governed by the width of the carriageway. Additionally the signs will typically be viewed at a relatively large distance from the display 1, for example between 40m and 120m. However, in other applications it may be beneficial to increase the viewing angle of the display panel 1 by applying a wide view film.

One advantage of the display panel 1, 101 of the present invention is that a large number of different graphics may be displayed using a single display panel 1, 101.

When used as a temporary road sign, for example, it is not, therefore, necessary to store a large number of different signs, with only a small fraction of these being deployed at any one time. Instead, a smaller number of display panels 1, 101 according to the present invention could be used, and the appropriate sign selected for display from a database of signs stored in the memory.

In addition, the sign displayed by the display panel 1, 101 can be changed or removed very quickly, rather than requiring mechanical means to cover all or part of the sign as described above. The power consumption of the display panel 1, 101 is very low as power is only required to switch the liquid crystal panel 2, 102, and no power is required to light the display 1, 101. Furthermore, the power consumption ot the panel 1, 101 is less than that required by conventional smart signs that use motors to move hinged sections of the signs, as described above.

Ideally the display panel 1, 101 should be able to be operated remotely using, for example, a hand-held control device (not shown). In these embodiments the display panel 1, 101 comprises suitable receiving means connected to the control means for receiving signals transmitted by the control device. A user may use the control device to select a graphic to be displayed from the memory and activate the display panel 1, 101 to display the selected graphic.

In some embodiments the display panel 1, 101 additionally comprises means for receiving a bespoke graphic to be displayed. In these embodiments, rather than a graphic being retrieved from memory, a user transmits a bespoke graphic or message to be displayed. The control means in the display panel 1, 101 receives this bespoke graphic and then transmits the necessary control signals to the electrode panel 18, 118 and liquid crystal layer 16, 116 to display the required image, pictogram or text. This could be used, for example, to display a temporary sign or message to road users warning of likely congestion due to a large sporting or music event.

In further embodiments of the display panel 1, 101 of the present invention the control means may additionally comprise a clock and programmable timing means (not shown). The timing means may be programmed by a user with a start time and an end time, corresponding to times of day at which the display of a graphic should start and stop. This has particular advantages when it desired to have a restricted speed limit on a section of road only at certain times of the day, for example between 0730 and 0900 hours, and 1630 and 1800 hours.

The display panel of the present invention, therefore, can be readily used to display road signs at the side of a carriageway and overcomes many of the disadvantages of prior art road signs and display boards. In particular, the display panel of the present invention is relatively lightweight and has minimal power consumption, but is able to display a large number of different images, pictograms and text. Furthermore, the display panel is able to be operated remotely and can provide the user with the ability to display a bespoke graphic quickly and easily.

Claims

CLAIMS1. A display comprising: -a first panel comprising a light transmissive liquid crystal layer; -memory means for storing one or more graphics to be displayed by the first panel; -control means for applying signals to said liquid crystal layer, the signals being arranged to activate cells of the liquid crystal layer so as to cause changes in the light transmissive properties of the cells to display one of said graphics; and -a second panel disposed rearward of the first panel relative to a viewer of the display, the second panel comprising a retroreflective surface arranged to reflect light such that said reflected light is transmitted through the liquid crystal layer towards said viewer.
2. A display as claimed in Claim 1, wherein the first panel further comprises a first light polarising filter and a second light polarising filter, the first and second light polarising filters being oriented at 900 with respect to each other, and the liquid crystal layer being located between the first and second light polarising filters.
3. A display as claimed in Claim 1 or Claim 2, wherein the first panel further comprises an electrode layer including a plurality of electrodes, each electrode being associated with a cell of the liquid crystal layer, and the control means transmits electrical signals to activate one or more of the electrodes so as to change the light transmissive properties of one or more cells.
4. A display as claimed in any preceding claim, wherein the light reflected from the retroreflective surface is white light.
5. A display as claimed in any preceding claim, wherein the liquid crystal layer comprises a twisted nematic liquid crystal.
6. A display as claimed in any of Claims ito 4, wherein the liquid crystal layer is a vertical alignment liquid crystal layer.
7. A display as claimed in any preceding claim, wherein the display further comprises an anti-reflection layer disposed forward of the first panel relative to a viewer of the display.
8. A display as claimed in any preceding claim, when dependent on Claim 2, in which the first panel further comprises a colour filter layer located between the liquid crystal layer and the first light polarising filter, the colour filter layer and the first light polarising filter being located forward of the liquid crystal layer relative to a viewer of the display, and wherein the colour filter layer is arranged to enable polychromatic graphics to be displayed by the first layer.is
9. A display as claimed in any preceding claim, wherein the control means further comprises a clock and programmable timing means, the timing means being arranged to generate a first timing signal to activate the first panel to display one of said graphics stored in the memory and a second timing signal to end display of said graphic.
10. A road sign comprising a display as claimed in any preceding claim.
11. A display assembly comprising a display as claimed in any of Claims 1 to 9 and a control device, the control device comprising means for transmitting signals to be received by the control means of the display, wherein the signals transmitted by the control device comprise a signal to activate the first panel to display one of said graphics stored in the memory.
12. A display assembly as claimed in Claim ii, wherein the signals transmitted by the control device comprise a signal representing a bespoke graphic to be displayed by the first panel.
13. A display substantially as herein described, with reference to or as shown in Figure 2 or Figure 3.
14. A display assembly substantially as herein described with reference to Figure 2 and Figure 3.