TECHNICAL FIELD OF THE INVENTION

This invention relates to display panels, particularly, but not exclusively, display panels which are intended to be mounted on a vehicle.

BACKGROUND

Known display panels include an array of light emitting diodes (LEDs) carried on a printed circuit board (PCB). The LEDs form the individual pixels of a display and are each controlled to emit light of a desired colour and brightness, enabling the panel to display a static or moving image. Large display panels are often formed from a number of separate PCBs, referred to herein as tiles, which are mounted adjacent to each other with little or no intervening gaps. This enables display panels of various sizes to be produced economically, and also allows malfunctioning tiles to be replaced without having to scrap the entire display panel.

US 5 867 236 discloses a display panel having a back plate 22, a transparent front cover 20, and an array of LED display tiles 10 supported on the back plate. In Figure 13 a composite seal 44 is constructed between the back plate 22 and the front cover 20. The composite seal consists of a non-permeable material 48 between polymeric seals 50 and 50'.

The construction of such such display panels poses a number of problems, which are particularly pertinent when the panels are required to be used in automotive applications.

Where the display panel is to be mounted on the outside of a vehicle such as a public transport vehicle it is necessary to make the display panel as thin as possible so as not to obscure the driver's vision and to reduce the risk of accidental damage e.g. from collision with tree branches or contact with washing equipment such as rotating brushes. Also, passenger vehicles may have a stipulated maximum width which cannot be exceeded.

It is also important that the panels should be waterproof under a wide range of adverse environmental conditions. Apart from protecting generally against ingress of rain water, high pressure water jets are often used to clean vehicles, typically supplying 100 litres per minute at 100 kPa. The panels must also protect against ingress of dust, corrosive exhaust emissions and other environmental contaminants. The problem is even worse due to the fact that large vehicles tend to vibrate and flex in normal use as they negotiate bends, potholes, uneven road surfaces, hump-back bridges, etc. Such movements may create a bellows effect which, along with changes in operating temperature, can result in a reduced internal pressure which acts to draw water into the panel through any leaks in the seal.

The display panels are therefore, in general, required to be slim, rugged, lightweight, energy efficient, and capable of withstanding a wide temperature range.

SUMMARY OF THE INVENTION

When viewed from one aspect the present invention proposes a display panel:

- a back plate (2);

- a transparent front cover (3);

- an edge gasket (4) interposed between the back plate (2) and the front cover (3);

- an array of LED display tiles (6) supported on the back plate (2);

characterised in that

a frame (5) surrounding the front cover (3) is engaged with the back plate (2) in such a way that the frame acts to clamp the edge gasket (4) between the front cover and the back plate.

In an embodiment the frame (5) has a front limb (30) which overlies the edge of the front cover (3).

When viewed from a second aspect the present invention provides a display panel including an edge gasket (4) which is substantially U-shaped with a pair of spaced legs (33) and (34) connected by a cross piece (35).

When viewed from a third aspect the present invention provides a display panel including the frame (5) is substantially of L-section with a front limb (30) which overlies the edge of a front cover (3) and a side limb (31) which covers an edge gasket (4).

When viewed from a fourth aspect the invention provides a display panel which includes a back plate (2) and an array of LED display tiles (6) supported in rows by mutually spaced elongate tile guides (7a-7d) secured to the back plate, in which the tile guides (7a-7d) locate opposite edges of the tiles (6) in such a way that the tiles can move away from the tile guides whilst still being accurately held in a fixed relationship to the adjacent tiles in a direction parallel to the back plate (2).

When viewed from a fifth aspect the invention provides a display panel which includes a back plate (2) and an array of LED display tiles (6) supported in rows by mutually spaced elongate tile guides (7a-7d) secured to the back plate, in which the tiles (6) include magnets (25) to hold the tiles (6) to the tile guides (7a-7d).

When viewed from a sixth aspect the invention provides a display panel which includes an array of LED display tiles (6), in which each tile (6) has a front face (20) which carries an array of LEDs and a rear surface (21) which carries electronic control and power supply circuitry for the tile. When viewed from a seventh aspect the invention provides an LED display tile (6) having a front face (20) which carries an array of LEDs and a rear surface (21) which carries a DC voltage converter.

When viewed from an eighth aspect the invention provides an LED display tile (6) having a front face (20) which carries an array of LEDs and a rear surface (21) which carries on-board diagnostic circuitry (52).

In an embodiment of the tile the diagnostic circuitry (52) monitors one or more of the tile's input voltage, DC converter output voltages, LED current, and tile operating temperature.

BRIEF DESCRIPTION OF THE DRAWINGS

The following description and the accompanying drawings referred to therein are included by way of non-limiting example in order to illustrate how the invention may be put into practice. In the drawings:

Figure 1 is a general exploded view of a display panel;

Figure 2 is a front view of a back plate which is included in the display panel;

Figure 3 is section A-A through a corner portion of the display panel as indicated in Fig. 1 ;

Figure 4 is section B-B through an edge region of the display panel as indicated in Fig. 3;

Figure 5 is a general rear view of a single tile, located at a corner of the display panel, along with the corresponding area of the back plate;

Figure 6 is section C-C through an edge region of the display panel as indicated in Fig. 1 ;

Figure 7 is a rear view of the display panel, partially truncated, showing the cable entry points; and

Figure 8 is a block circuit diagram of a power delivery system of the display panel.

DETAILED DESCRIPTION OF THE DRAWINGS

Referring firstly to Fig. 1, the illustrated display panel 1 is intended to be mounted on the outside of a passenger transport vehicle. The display panel includes a back plate 2, a transparent window or front cover 3, an edge gasket 4 interposed between the back plate 2 and the front cover 3, and a frame 5. An array of LED display tiles 6 are provided to be supported on the back plate 2. In this example the display panel would have sixty LED display tiles 6 which are arranged in three rows of twenty, but the number of tiles may vary depending on the size of the display panel. For clarity only one of the tiles is shown in the drawing.

The front cover 3 may be of any suitable transparent polymer. A high impact resistance, non shatter, fire resistant polycarbonate is a particularly suitable material. A hard scratch-resistant coating can be applied to the outer surface of the polycarbonate front cover as used on eyewear lenses and exterior automotive components. The characteristics of polycarbonate compare to those of polymethyl methacrylate (PMMA, acrylic), but polycarbonate is stronger and will hold up longer to extreme temperature. Polycarbonate is highly transparent to visible light, with better light transmission than many kinds of glass. Unlike many thermoplastics, polycarbonate can undergo large mechanical deformation without cracking or breaking .

Fig. 2 shows the back plate 2 in more detail. The back plate may be formed of a lightweight flexible corrosion-resistant non-ferrous metal such as aluminium, and is of generally rectangular shape. Four epoxy powder coated steel or similar ferrous metal tile guides 7a-7d run along the length of the back plate 2 for mounting the three rows of tiles 6, with the tile guides extending along the upper and lower edges of the tiles. In between each pair of tile guides there is a single power backplane PCB, only one 8 being shown, each running along the length of the back plate parallel to the tile guides 7a-7d. The tile guides and power backplane PCBs may be fixed to the back plate 2 using self-adhesive tape and/or stainless steel bolts, or other suitable means. At one end of the back plate 2 there are three sets of power and data entry apertures 9a-9c to provide for power and data cable entry between the tile guides 7a-7d. These apertures are provided with rear power cable entry gaskets lOa-lOc, as shown in Fig. 1. Additional data entry apertures l la-l lf are provided at spaced positions along the back plate 2 to provide further data cable entry points adjacent to each power backplane PCB. These are again provided with sealing gaskets 12a-12f (Fig. 1) at the rear of the back plate 2.

Referring to Fig. 3, the adjacent tile guides, e.g. 7a and 7b, locate the upper and lower edges of the tiles 6 in such a way that the tiles can move as the display panel flexes whilst still being accurately held in a fixed relationship to the adjacent tiles in a direction parallel to the back plate. It is important to ensure that visible discontinuities do not appear in the display as the human eye is able to detect mis-alignments between the tiles as little as 1mm. A front face 20 of each tile 6 carries a matrix of LEDs while the rear surface 21 carries low-profile control and power supply circuitry for the PCB. The electronic circuitry is covered by a protective rear pan or moulding 22 which, as shown in Fig.s 4 and 5, includes pre-formed bosses 23 that locate in holes 24 in the tile guides 7a and 7b. A single boss 23 is provided centrally of the upper edge of each tile 6 and a second boss is formed centrally in the lower edge so that the tile is accurately located parallel to the back plate 2 whilst being free to flex perpendicular to the back plate. The mouldings 22 also incorporate thin disc magnets 25 along their upper and lower edges to hold the LED display tiles 6 to the ferrous tile guides 7a-7d in a manner which allows the tiles to move away from the tile guides when the display panel flexes whilst automatically re-gripping when the display panel retains its normal flat configuration. The rear moulding 22 may also provide plug-in connections with the power backplane PCB 8 (not shown in Fig. 5).

The gasket 4 and edge frame 5 maintain a flexible seal against water entry within a small volume whilst accommodating the necessary fixings for attaching the panel to the side bodywork of a vehicle or other suitable substrate. The frame 5 may be formed of a single rectangular framing piece, but is preferably comprised of straight and corner sections. Referring to Fig. 6, The frame 5 may be of L-section stainless steel or aluminium with a front limb 30 and a side limb 31. The front limb 30 overlies the edge of the front cover 3 and acts to compress the gasket 4 between the front cover 3 and the back plate 2 maintaining a flexible yet water-tight seal. The side limb 31 provides mechanical protection for the edge gasket 4 and reduces the risk of particulate and moisture contamination. The edge gasket 4 is preferably of rubber or other suitable elastomer and is generally U-shaped with a pair of spaced legs 33 and 34 connected by a cross piece 35. The space between the legs 33 and 34 is able to receive fixings such as bolts 36 (Fig. 3) which can be inserted through the back plate to secure the display panel to a vehicle. In addition, the back plate carries threaded pillars 37 (Fig. 6) which are also located between the legs 33 and 34 of the gasket 4 to receive countersunk head screws 38 or similar fastening elements which are inserted through the front limb 30 of the edge frame, front panel 3, and the cross piece

35 of the gasket, thereby securing the frame 5 to the back plate 2 and clamping the gasket between the front cover 3 and the back plate 2. The gasket is provided with V-shaped ribs 40 which are compressed against the front cover 3 and the back plate 2 to ensure that an effective water seal is maintained and prevent water entry into the panel. (In the drawing the ribs 40 are shown diagrammatically in their un-compressed state.)

Referring now to Fig. 7, data and power connections to the tiles 6 are made via connectors which are accessible through in the apertures 9a-9c and l la-l lf. Power is supplied via a power connector 50a-50c which is mounted directly on each power backplane PCB 8-8c and accessed through the power and data entry apertures 9a-9c. The rear mouldings 22 of the LED tiles may be connected to the power backplane via direct plug-in connectors or flexible leads. Data connections are made via data connectors 52 mounted on the rear mouldings 22 of the tiles 6. Data interconnections between the panels may be made via additional connectors on the rear mouldings 22 and ribbon cables which are received in a space between the rear mouldings and the back plate 2. When the display panel is attached to a vehicle using the bolts

36 the power and data cable entry gaskets lOa-lOc and the sealing gaskets 12a-12f for the data cable entry apertures l la-l lf are compressed between the back plate 2 and the surface of the vehicle to seal the cable entry apertures against water ingress, power and data being supplied to the display panel via cables which pass through a small number of corresponding holes in the side of the vehicle.

Existing LED display screens have many additional mains power supplies to power the LED tiles which operate at 5V and require up to 7A each. Public transport vehicles typically have batteries which nominally supply 24V. Such display panels therefore require 24V to 5V DC converters along with the associated power distribution wiring to each LED tile. This presents a space-v-current design conflict. On the one hand it is possible to have one or two DC power supplies for the entire screen, but this requires thick distribution wiring, which takes up valuable space, and extremely high currents, which is a major safety hazard. Increasing the number of power supplies lowers the distribution currents, but there is a trade off in the additional space required for the extra power supplies. Referring to Fig. 8, the present display panel does not require any power supplies since a physically small 24V-5V DC power supply 50 is incorporated on the rear surface of each LED tile 6. This arrangement has the following advantages:

1. Reduced thickness of cables reduces the weight of the display panel.

2. Since the DC converter only supplies a single tile it need only supply a relatively small current, avoiding the need for heavy conductors.

3. There is lower heat dissipation with less risk of over-heating and less risk of potential fire hazard. Each LED tile has additional on-board protection, which is particularly useful in the electrically noisy automotive environment. Each on-board DC converter 50 is rated up to 60V, is protected by a surface-mount supply fuse 51, and incorporates voltage spike suppression circuitry to prevent any voltage spikes exceeding the 60V maximum. If the 60V is exceeded, the voltage suppression circuitry will absorb it, and if the current then rises too high the fuse will blow, thus protecting the LED tile from damage and protecting the vehicle against potential fire risk.

The LED tiles 6 also have on-board diagnostic circuitry 52 which monitors and reports diagnostic information back to a server via an interlock controller 53 in a control box 54 which is mounted external to the display panel in any convenient position within the vehicle. This diagnostic circuitry 52 monitors various parameters such as the LED tile's input voltage, DC converter output voltages, LED current, and board temperature. All this information is received by the interlock controller 53 which can make a decision to reboot the display panel if there is a problem or ultimately to shut it down if the panel does not recover.

The display panel power delivery system receives the vehicle's 24V DC supply 55 via a main supply fuse 56 (e.g. 30A). Each row of tiles - top, middle and bottom - is supplied via a separate second-stage fuse 57-59 (typically 15A) to keep the electrical currents within normal automotive range. In addition to rebooting the display panel when an error is detected the interlock controller 53 switches the panel off and on when the vehicle's engine is switched off and on. The controller is able to isolate the entire supply to the display panel by means of a power relay 60 having circuit breaker contacts interposed between the main supply fuse 56 and the second-stage fuses 57-59.

From the foregoing description it will be appreciated that the display panel is particularly adapted for the automotive environment, providing a rugged, lightweight, energy efficient, wide temperature range, dust proof, waterproof and ultra thin LED screen for mounting on the outside (or inside) of vehicles. While traditional LED display panel enclosures are typically greater than 300 mm the present enclosure may be as little as 22mm thick. The enclosure may be IP66 rated and will not only withstand high pressure water jets when the vehicle is washed, it will also withstand the daily road, dust, grime and contaminates.

Whilst the above description places emphasis on the areas which are believed to be new and addresses specific problems which have been identified, it is intended that the features disclosed herein may be used in any combination which is capable of providing a new and useful advance in the art.