Variable Display Device This invention relates to a display device, and more particularly to one in which displayed indicia can be changed. There is a growing need for such devices. For example, in petrol stations it is required to have a large display advertising the price of the petrol, perhaps showing the price of several different grades of petrol and/or showing both the price per litre of petrol and its equivalent per gallon. Furthermore, it frequently occurs that the prices displayed must be changed. Traditionally, the display used has been a simple poster, and a new poster is pasted up when the price changes. With the frequent price changes in recent years, this has become impractical. More recently, therefore, electronic displays have been used, which have the advantage that the display can be changed instantaneously, from a remote location such as the pay kiosk or the Manager's office if desired. However, there is a certain amount of reaction against the aesthetic appeal and legibility of purely electronic displays, and there is therefore a need for a mechanically changeable system in which the various letters, numerals and other indicia can be printed in a bold, contrasting and clearly legible manner. Furthermore, it is clearly desirable that such a system should be relatively simple, both from

the point of view of cost and of reliability.

The uses of such a system are of course not restricted to displaying the price of petrol. Another example is in the field of changeable road traffic signs, for example where an indication needs to be given to motorists of different types of hazard or differing route diversions, etc. Currently, one such road traffic display system uses a number of parallel, rotatable prisms, each face of which bears a part of a composite display. Rotating all the prisms in parallel enables the composite display to be changed, but in practice only three possible displays can be provided and there is no provision for changing individual characters of the display. Another known system is in use in railway stations, airport lounges, etc. At each display position there is a quite large number of display plates bearing different indicia, which are pivotable about a horizontal axis, and a drive means to flip the required plate into the display position. Such systems can be made very versatile, but require complicated mechanical arrangements to enable them to pivot the required display plate into the display position, and complex control systems to set up the composite display. Such systems would therefore be much too complex to be practical in a situation such as a petrol price display, where the information to be

displayed might be, say, a three or four digit number. The present invention provides a variable display device, comprising a pack of display cards bearing respective indicia, a transport -carriage for moving the cards between a display position and non-display position, the cards in the pack having a plurality of holes there¬ through, t _h ere being a plurality of selector pins arranged to engage in respective holes in the pack of cards and each pin being individually movable between and^ engaged and a non-engaged position, each card having an open-ended slot at one or some of the positions where there is a hole through the pack, arranged so that the corresponding selector pin does not engage that card, so that when that selector pin is moved into the engaging position it retains the or each card having a hole but permits relative displacement of the or each card having a slot at that location so that a card is movable to the display position by the transport carriage.

Preferably it is the non-retained card which is moved, the selector pin assembly being fixed. However the alternative arrangement is also possible.

In a preferred form, the transport carriage is vertically movable and the display position is beneath the non-display position. The pack of cards can then simply rest on the transport carriage under gravity, so that when the selector pins engage in the holes in the pack, the non-engaged card can slide downwards to the display position, resting on the transport carriage as it moves

downwards .

Preferably the range of travel of the card between the display position and the non-display position is less than the length of the card in that direction. This means that the upper portion of the card will still engage between adjacent cards in the pack when it moves down into the display position, reducing the risk of it snagging when the transport carriage is again moved upwards when the display is to be changed. A preferred display device according to the invention will now be described by way of example, with reference to the accompanying drawings, in which:

Fig. 1 is a schematic perspective view of the device, Fig. 2A is a schematic front elevation of parts of the device.

Fig. 2B is a section on the line X-X in Fig. 2A, Fig. 3 is a vertical section through a part of • the device, Fig. 4A and Fig. 4B show two examples of display cards for use in the device.

Fig. 5 is a block diagram showing the connection of solenoid modules used in the device, and

Fig. 6 is a block diagram of a control circuit ^: or the device.

Referring to the drawings, there is shown a variable display device intended for displaying the price of petrol at petrol stations, and which can be

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displayed in a prominent position on the station forecourt, for example at the top of a sign pole. It comprises a weather-proof, double-sided generally box¬ like frame 1, e.g. of extruded aluminium, within which are provided fluorescent tubes 3 for illumination of the sign. Behind the display face on each side of the frame 1, there is a translucent plastics panel 13, arranged to be illuminated by the fluorescent tubes 3 without shadows (see Fig. 3). A short distance in front of the translucent panel 13 is a clear plastics front panel 2, which can be slidably removed as desired. Immediately behind the front panel 2, there are two opaque panels 12 (Fig. 3) on which may be printed various fixed information such as the words "price per gallon" or "price per litre", for display through the front panel 2. The two panels 12 are spaced vertically from each other, so that below each there is a display window 16 extending horizontally across the sign. As can be seen from Fig. 1, each of these display windows 16 is four characters wide but it will be appreciated that the number of such character positions provided can be adapted to suit the particular requirements for which the sign is produced. Furthermore, in different applications there may be a need for only one display window 16, or more than two; and the sign may be single-sided or double-sided as required, or two identical single-sided signs may be

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provided back-to-back .

In the space between the translucent panel 13 and the front panel 2, between each character position and at the sides of the frame, there are respective vertical extruded H-section frame members 11 (see Figs. 2A and 2B). At each character position, the mutually facing channels of two adjacent H-section members 11 act as guide channels in which a pack of cards 4 is vertically slidable. The cards 4 are made from transparent plastics material, and have printed thereon respective desired indicia. For example, the pack of cards at each character position may have a set of digits from 0 to 9, or a set of alphabetic characters, or more specialist characters, as desired. It will be appreciated that the characters printed on these cards 4 can easily be made bold, large and easily legible, and can be in a dark colour such as black so as to contrast well with the illuminated background provided by the translucent screen 13. A transport carriage 7 comprises four horizontal extruded H-section members 18, in the horizontal webs 22 of which are cut apertures 20 to receive the vertical H-section frame members 11, so that the transport carriage 7 is vertically slidable guided by these vertical frame members 11. It is not essential that the horizontal member 18 should actually be of H-section; an upwardly opening ϋ-section channel coul

be used instead. The four horizontal members 18 correspond one to each display window 16, and thus there is an upper member 18 and a lower member 18 on each side of the sign. On each side of the sign, the upper and lower members 18 are joined together by two vertical rods 24 which are attached by rear brackets 26 on the members 18. The rods 24 are aligned with two of the vertical members 11, so that they do not cast obtrusive shadows through the display cards 4. At the top of the transport carriage 7, the corresponding rods 24 at the front and rear are joined by horizontal links 28. The horizontal links 28 are supported on respective wires 30, which pass over pulleys 8 at the top of the frame 1 and wrap around the spindle 32 of a motor and gear box arrangement 9. Thus, by operating the motor 9 the transport carriage 7*comprising the four horizontal H-section members 18 can be raised and lowered bodily, from a lower position in which each horizontal member 18 is at the bottom of its display window 16 (the position seen in Fig. 3) to an upper position which is generally level with the bottom edge of the panel 12 above the window 16.

Behind the opaque panel 12, at each character position, there is a solenoid module 34. Each solenoid module 34 has five selector pins 6 which project forwardly into the space between the translucent panel

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13 and the front panel 2, behind the opaque panel 12 so that they are not visible, and generally at the top edge of the opaque panel 12. Each selector pin 6 is individually controlled by a respective solenoid within the solenoid module 34. Thus, by energising the required solenoids, any desired combination of the selector pins 6 can be pushed forward into the space between the panels 13, 2, with the remaining pins 6 being retracted. As seen particularly in Fig. 4A and 4B, each transparent display card 4 has a row of holes 5 at its top edge. These holes are aligned with the positions of the selector pins 6. Thus, if all the selector pins 6 are moved into the projecting position, the pack of cards 4 at each character position will hang on the pins 6, one behind another, in a non- display position behind the opaque panel 12.

The procedure for displaying a required card 4 in each character position of each display window 16 is as follows. Firstly, the transport carriage 7 is raised by means of the motor 9 so that each member 18 is generally at the level of the bottom of the corresponding panel 12. In this position, all the cards 4 simply rest on the horizontal web 22 of the horizontal member 18, with their bottom edges in the upwardly directed channel provided by the member 18. All the cards are in the non-display position at this

stage. Next, at each character position the required solenoids are operated to extend some of the selector pins 6 so as to engage the pack of cards, and to retract others. As will be seen in Figs. 4A and 4B, at some of the pin positions, the cards have upwardly open slots 10 in place of simple holes 5, and each card in the pack is given a unique combination of one, two or more slots 10. To select a particular card, all the selector pins 6 are retracted except those which correspond with the slots 10 on that particular card. The selector pin or pins 6 which remain projecting in this condition will engage one or more of the simple holes 5 on each card, except on the desired card where all the projecting pins will coincide with slots 10. Thus, when the transport carriage 7 is again lowered, all the cards in the pack except one will remain hanging on the selected pins 6. The selected card, however, will be free to drop down, guided by the channels provided by the vertical members li and resting on the web 22 of the horizontal member 18 of the carriage, until it is visible in the display window 16.

The vertical travel of the transport carriage 7 is limited at the upper and lower positions by limit switches (not shown) so that the carriage always comes to rest at a fixed upper and lower position. The distance which it travels between these upper and

lower positions is obviously the same as the required distance between the non-display position for the cards 4 behind the panel 12, and the display position in the window 16. The height of the cards 4 is made slightly more than this distance of travel, so that as seen in Fig. 3 the upper edge of the displayed card 4 still engages within the pack of remaining cards in the non-displayed position, while the bottom edge of the displayed card 4 rests on the web 22. This prevents the selected card 4 jamming against the rest of the pack when the transport carriage is lifted again.

The exact number of selector pins 6 on the solenoid module 34 at each character position can of course be changed depending on the number of different cards to be displayed. In a simple system, the cards may be in the form shown in Fig. 4B, ^"' each with only one slot 10. With a card as shown in Fig. 4B which has provision for five selector pins 6, this gives a maximum number of cards in the pack at each character position of five. However, the number of cards which can each be uniquely selected is greatly increased by having more than one slot 10 on each card. For example, if there are two such slots 10 per card as shown in Fig. 4A, an appropriate card can be uniquely selected by setting the required combination of two

out of five selector pins 6. A greater number of combinations can of course be produced by having more than five selector pins 6 at each character position, and/or by having more than two slots 10 per card. Referring to Fig. 5, for a double-sided sign it is obviously required that the same message should be displayed on both sides of the sign. For this reason, on one side of the sign the solenoid modules 34 are directly controlled by a control circuit which energises the solenoids to cause them to retract and project in the desired combination for a particular character selected by the operator. On the other side of the sign, there are slave solenoid modules 34a which are directly coupled to the master solenoid modules 34 on the first side of the sign. Thus, the cards selected by the slave solenoid modules on the second side of the. sign will be exactly the same as those selected by the master modules 34 on the first side. Fig. 6 shows a simplified block diagram of the control circuit for the device. With the transport carriage 7 raised, all or just some of the characters to be displayed can be altered, and this is done one character position at a time by selecting the character position on a binary coded decimal (BCD) thumbwheel switch 36. The output of this switch is decoded by a decoder 38, and acts on the required

of the solenoid modules 34 (and the corresponding slave module 34a) through a respective power switch 40. After selecting the character position, the operator selects the desired digit or other character to be displayed on a second BCD thumbwheel switch 42. The output of this ismultiplexed by a multiplexer 44 so that the signal is provided to all character positions (though only the character position selected on switch 36 will be affected). The multiplexed BCD output is decoded by a decoder 46, and a solenoid select unit 48 sets which of the solenoids of the selected module 34 will be retracted and which extended in order to select the required card 4. Finally, the operator presses an operate button 50, and power is applied by the power switch 40 to the solenoid module 34 selected in order to select the desire^ card. The power is applied for a time period fixed by a timer 52, so that the solenoids can centralise. The above procedure is repeated for each character position to be changed, and then the transport carriage is lowered to display the selected cards 4.

The controls 36, 42, 50 may be accessible at the side of the box sign, or they (or the entire control circuit) may be plugged into a socket at the side of the sign, either when required, or permanently so that they can be located remotely, e.g. in the petrol

station pay kiosk or the Manager's office,