Background to the Invention There are known display devices which display a sequence of composite images, each composite image comprising a series of spaced-apart image portions in strip form on an image sheet strategically placed behind, or in front of, a mask sheet, or grid, having a series of transparent windows interposed by a series of opaque strips, either the mask sheet or the image sheet being movable so that, when a series of image portions is aligned with the series of transparent windows on the mask sheet, the corresponding composite image is displayed. Conventionally, each image portion of each image is of substantially the same width measured in the direction of relative movement between the image sheet and mask sheet.

The clarity of each of the displayed images, the changeover time between adjacent displayed images, and the dwell time on each of the displayed images are normally of paramount importance to the user of the display device such as an advertiser.

Known methods of effecting relative movement between the mask sheet and the image sheet have employed a cam/cam follower whereby rotary movement of the cam is converted to reciprocating movement of either the mask sheet or the image sheet. In order to land completely within, and to display for a predetermined time (or"dwell"on), each image, the transparent windows on the mask sheet are

conventionally narrower than the image portion width, typically 50% of the image portion width.

A problem with known display devices of the type described above is that they may only display either a series of individual, or static, images or a series of sequential images, the latter creating an illusion of movement in a"jerky"or non- seamless way. Moreover, if there are several images, say five or more, interposed on the image sheet, then the conventional arrangement described above whereby each transparent window is considerably narrower than the image portion width, usually results in an image portion width and corresponding transparent window width which is so narrow that the brightness of the displayed image is impaired.

In addition, having a relatively narrow image portion width and corresponding transparent window width requires relatively precise mechanics of the drive means for moving the mask sheet, or image sheet, so that the transparent windows land completely within a respective image portion. In the event that the transparent windows do not land fully within the desired image portions of a given series of such image portions, then the adjacent image will also be at least partially exposed to create an undesirable effect known as"ghosting". The problem of"ghosting"is exacerbated in cases where the width of the transparent windows is substantially the same, or similar, to the image portion width and this is why, conventionally, it is preferred to make the windows narrower than the image portions.

Moreover, while individual displayed images, such as advertisements, and the eye catching movement from one displayed image to the next, are attractive to the advertiser, it has been found that advertisers prefer to be sole advertisers on a display device and often do not wish to have more than one advert on each display device. It would be desirable to provide a display device of the general type described above which offers substantially seamless animated movement and which does not appreciably suffer from"ghosting"effects.

Summary of the Invention The present invention provides a display device comprising: an image sheet carrying a plurality of composite images, each composite image being comprised of a respective set of spaced-apart image portions; a mask sheet located adjacent said image sheet and comprising a plurality of spaced-apart windows; and means for effecting relative movement between the mask sheet and the image sheet so that, in use, the sets of image portions are, in turn, in register with the plurality of windows thereby exposing the corresponding composite image in turn, wherein said composite images include at least one major composite image and at least two minor composite images, the image portions of which said at least one major composite image is comprised being of greater width than the image portions of which said at least two minor composite images are comprised.

Preferably, the width of the minor image portions is 20-80%, more preferably 30- 55%, of the width of the major image portions.

Preferably, the image sheet comprises a set of major image portions interposed by a plurality of sets of minor image portions the arrangement being such that adjacent image portions belong to a different respective set of image portions.

Preferably, the display device comprises at least four, and advantageously at least eight, sets of minor image portions.

In the preferred embodiment, the moving means is arranged to cause relative movement of said image sheet and said mask sheet between a first end position and a second end position, wherein in each of said first and second end positions the windows are in register with a set of major image portions.

It is also preferred that the width of the major image portions is greater than the width of said windows. It is particularly preferred that the window width is between 20%-80%, preferably 30%-55% of the width of the major image portions.

Preferably, the minor image portions are of substantially equal width with the windows.

In the preferred embodiment, the at least one major composite image comprises a static image. More preferably, said at least two minor composite images comprise a series of sequential images for creating animated movement.

Preferably, the image portions are provided in substantially parallel strips, each strip comprising a respective image portion, the windows being strip-like in form and being substantially parallel with the image portion strips. More preferably, the moving means is arranged to cause relative reciprocating movement between said image sheet and said mask sheet in a direction substantially perpendicular to said image portion strips.

Advantageously, the moving means comprises a cam and a cam follower, the cam follower being arranged to impart reciprocating movement either to said image sheet or said mask sheet. Preferably, the cam is shaped to provide an increased dwell time in said first, and preferably also, said second end positions.

The present invention is not limited in overall display dimensions. Typically display dimensions include typical advertising sizes such as A3, A1, A2, A0,"6 Sheet", Banner and larger. The present invention can be used with the major/minor image portions and corresponding windows arranged, in use, either vertically or horizontally. It will be appreciated that, irrespective of whether the image portions/transparent windows are arranged vertically or horizontally, the term"width"is to be construed as the dimension in the direction of reciprocating movement of the image sheet or the mask sheet, as appropriate.

The preferred embodiment of the invention provides substantially seamless animated movement without suffering from"ghosting effects". The preferred embodiment further enables the desired features of both animated movement (from the set of minor image portions) and a static main display image (from the major image portions) to be provided by a single display device.

Other advantageous aspects of the invention will become apparent to those ordinarily skilled in the art upon review of the following description of a specific embodiment and with reference to the accompanying drawings.

Brief Description of the Drawings An embodiment of the invention is now described by way of example and with reference to the accompanying drawings in which: Figure 1 schematically illustrates, in plan view, a portion of conventional display device having a plurality of image portions in strip form on an image sheet placed behind a mask sheet having a plurality of transparent windows interposed by a plurality of opaque strips; Figure 2 illustrates, in plan view, a first embodiment of a display device according to the present invention, in which the image sheet carries one set of major image portions and eight sets of minor image portions; Figure 3 is a schematic side view of a cam and cam follower suitable for use with the display device of Figure 2 ; Figure 4a is a schematic side view of the cam and part of the cam follower of Figure 3 in a first position;

Figure 4b is a first view of a second embodiment of the display device of the present invention, in which the image sheet has one set of major image portions and twelve sets of minor image portions, the relative position of the image sheet and mask sheet corresponding to the first position of cam and cam follower shown in Figure 4a; Figure 5a is a schematic side view of the cam and part of the cam follower of Figure 3 in a second position; Figure 5b is a second view of the display device of Figure 4b in which the relative position of the image sheet and mask sheet corresponds to the second position of cam and cam follower shown in Figure 5a.

Detailed Description of the Drawings In the drawings, similar reference numerals have been used to indicate like parts.

Referring now to Figure 1 of the accompanying drawings, there is shown a conventional image sheet A carrying a plurality of composite images (not shown), each composite image being comprised of a plurality of, or a set of, spaced-apart image portions B, each image portion B being of substantially equal width. The image portions B are provided in substantially parallel strips, each image portion B comprising a strip which carries a portion of one of the composite images carried by the image sheet A. The respective series of image portions B for each composite image are interposed on the image sheet A such that adjacent image portions B belong to different respective composite images. Thus, from a notional staring point, the first image portion B carries the first portion of a first composite image, the second, or next, image portion B carries the first portion of a second composite image and so on. In Figure 1, it is assumed for illustrative purposes

only that image sheet A carries five composite images. The first image portion B 11 represents the first portion of the first image. The second image portion B21 represents the first portion of the second image and so on until the sixth image portion B12 represents the second portion of the first image and the seventh image portion B22 represents the second portion of the second image, and so on. This sequence continues over the full length of the image sheet A, so that the first and sixth image portions form part of one series of image portions and the second and seventh image portions form part of another series of image portions, and so on.

The width of the image portions B depends on the length of the image sheet and on the number of composite images to be displayed. Typically, image portions B have a width of between 0.2 mm to 1.5 mm Also shown in Figure 1 is a mask sheet C comprising a plurality of spaced-apart windows D interposed by a plurality of spaced-apart opaque strips E such that the windows D and the opaque strips E alternate on the mask sheet C. The windows D, which are normally formed form transparent material such as glass or transparent plastics, are usually evenly spaced apart and substantially parallely disposed with respect to one another. The spacing between windows D is substantially equal to the spacing between successive image portions B in a series corresponding to a given composite image. The windows D are strip-like in form and are usually of substantially equal width. In use, the mask sheet C is placed against, or adjacent, the image sheet A such that the mask sheet C and image sheet A are disposed in respective substantially parallel planes and so that the windows D and the image portions B are substantially parallel with one another. When each window D coincides with a respective image portion B, each image portion B belonging to the same set, or series, of image portions B thereby exposing the respective image portions B. As a result, the composite image corresponding to the exposed image portions B is displayed. In Figure 1, windows D are shown coinciding with the image portions Blx corresponding to the first composite image, where x is an index the value of which denotes the position of the image

portion in the series (x = 1 to 8 in Figure 1). Relative movement between the mask sheet C and image sheet A causes the transparent windows D to coincide with the second series of image portions B so that the second image is displayed over the entire display, and so on. It will be understood that Figure 1 shows only part of the mask sheet C and image sheet A, the overall size and shape of the mask sheet C and image sheet A depending on the application. Further, in Figure 1, the mask sheet C is shown partially cut-away so that a potion of the image sheet A may be viewed.

It will also be understood that the mask sheet C and image sheet A together form part of a display device which typically also includes means (not shown in Figure 1) for effecting relative movement between the mask sheet C and image sheet A.

In Figure 1, it will be seen that the direction of relative movement, as indicated by arrow M, is generally perpendicular to the longitudinal axes of image portions B and windows D. The display device may also include a light source (not shown) for illuminating a displayed composite image. Typically, the light source, when present, is located behind the image sheet. Assuming that the image portions B are carried on the front face of the image sheet A, the mask sheet C may be located either behind or in front of the image sheet A, the former option being particularly suitable when the image sheet A is illuminated from behind by a light source.

A conventional display device having the mask sheet C and image sheet A of Figure 1 suffers from the problems outlined above. In particular, for typical cases where the image portion width is approximately twice the window width, there is a"dwell"time of, typically, two or three seconds on each series of image portions B. If the image portions B of a series carry sequential image portions, the dwell is discernible to an observer (not shown) such that non-seamless, or jerky, animated movement is observed. Further, the arrangement of Figure 1 does not allow the

conventional display device to display a"static"composite image, followed by an illusion of animated movement (formed by a series of sequential image portions).

Figure 2 illustrates a display device, generally indicated as 10, arranged in accordance with a first embodiment the present invention. The display device 10 is generally similar to the display device of Figure 1 and includes an image sheet 12 and a mask sheet 18. However, in contrast to the display device of Figure 1, the image portions on image sheet 12 are not each of substantially equal width.

Rather, the image sheet 12 carries a set, or series, of major image portions 14 and a plurality of sets, or series, of minor image portions 16. Preferably, each major image portion 14 is of substantially equal width and each minor image portion is of substantially equal width, but the major image portion width is greater than the minor image portion width. The set of major image portions 14 together comprise a major composite image, while each set of minor image portions 16 together comprises a respective minor composite image. The image portions 14,16 are substantially parallel with one another and advantageously provided in strip form, each strip carrying a respective portion of a respective composite image.

The mask sheet 18 comprises spaced-apart, substantially parallel, windows 22 interposed by opaque strips 24 such that the windows 22 and opaque strips 24 alternate on the mask sheet 18. The windows 22 are preferably transparent and may be formed from transparent material, such as glass or plastics, or may be provided by gaps defined between the opaque strips 24. The spacing between adjacent windows 22 is substantially equal to the spacing between successive image portions 14,16 of a given series of image portions 14,16. Thus, as the mask sheet 18 and image sheet 12 move relative to one another, the windows 22 will, in turn, coincide with a respective image portion of a given set, or series, of image portions 14,16, thereby exposing the corresponding composite image in turn. In Figure 2, it will be seen that each window 22 coincides with a respective major image portion 14 and that relative movement between the mask sheet 18

and image sheet 12 in the direction of arrow M will cause the windows to coincide with each series of minor image portions 16 in turn, thereby exposing the respective composite images in turn In the preferred embodiment, the windows 22 are each of substantially equal width, the width of the windows 22 being substantially equal to the width of the minor image portions 16, and therefore narrower than the width of the major image portions 14. As a result, there will be a discernible"dwell"time as a window 22 passes across a major image portion 14. Thus, the major image portions 14 are particularly suitable for providing a"static"composite image such as, for example, a brand name, logo or other static advertisement. Because the window width is the same, or substantially the same, as the width of the minor image portions 16, there will be no, or substantially no"dwell"time as a window 22 passes across a minor image portion 16. Thus, the minor image portions 16 are particularly suitable for providing composite images that form part of a sequence of images for creating animated movement.

In the embodiment of Figure 2, it is assumed by way of example that the image sheet 12 carries one series of major image portions 14 and eight series of minor image portions 14, although it will be understood that the number of series of major image portions or minor image portions is not limiting. The composite image provided collectively by the series of major image portions 14 is assumed to be a static image while each series of minor image portions 16 is assumed to provide a respective composite image which forms part of a sequence of images for creating animated movement. Assuming that the relative starting position of the mask sheet 18 and image sheet 12 is as shown in Figure 2, then, as the mask sheet 18 and image sheet 12 move relative to one another in the direction of arrow M, there is displayed a"major"static composite image followed by eight"minor" sequential composite images, the latter providing an animated sequence of movement.

By way of example only, the major image portion width may be approximately 0.4 mm, the width of the subsequent eight minor image portions 16 may be approximately 0.2 mm each, so that the total configuration is completed in 2.0 mm and repeated in sequence across the image sheet 12. The transparent window 22 width may be approximately 0.2 mm and the opaque strip 24 width may be approximately 1.8 mm. As a result, the"major"composite image provided by the major image portions 14 appears static as the transparent windows 22 of 0.2 mm width traverses the 0.4 mm wide major image portions 14. The following eight minor image portions 16 are equal in dimension to the transparent window width at 0.2mm and, in general, where the image portion width is substantially equal to the window width, no"dwell"time is discernible by the observer, thereby giving an illusion of seamless, or substantially seamless, animated movement as the respective"minor"composite images are displayed in sequence.

In an alternative example, for an image sheet 12 of AO size, a suggested major image portion 14 width would be approximately 0.8 mm, with a minor image portion 16 width of approximately 0.4 mm. A suggested transparent window 22 width would be approximately 0. 45 mm, with an opaque strip 24 width of approximately 3.55 mm Referring now to Figure 4b, there is illustrated a second embodiment of the display device of the present invention, generally indicated as 110. The display device 110 is generally similar to the display device 10 although the image sheet 112 comprises one series of major image portions 114 interposed by 12 series of minor image portions 116. By way of example only, if the image sheet 112 was intended for use in a"6 sheet"sized display device, then the major image portion 114 width may be approximately 1.2 mm, while the following twelve minor image 116 portions could each be approximately 0.4 mm wide, making a total of thirteen images in the configuration. For such a"6 sheet"display, a transparent window

122 width of approximately 0.4 mm and an opaque strip 124 width of approximately 5.6 mm are preferred.

Using the present technology, minor image portion 16,116 widths of 0. 2-0. 5 mm; major image portion 14,114 widths of 0.4-1. 0 mm; and transparent window 22, 122 widths of 0.25-0. 75 mm are envisaged.

The display device 10,110 further includes means (not shown in Figures 2 or 4b) for effecting relative movement between the image sheet 12,112 and the mask sheet 18,118. Preferably, the relative movement is reciprocating movement in the direction indicated by arrow M. In the embodiments of Figures 2 and 4b, reciprocating movement is effected between a first end position and a second end position, the relative movement effected between the first and second end positions being substantially equal to the spacing, or pitch, between successive image portions from the same series, e. g. the pitch between corresponding points of successive major image portions 14,114. It is further preferred that in both the first and second end positions the arrangement is such that the windows 22,122 coincide with the series of major image portions 14,114.

Figure 3 shows, in schematic side view, preferred means for effecting relative movement between the mask sheet 18,118 and image sheet 12,112 in the form of a cam 30 and a cam follower 32. The cam follower 32 comprises a pair of cam rollers 34,35 rotatably mounted on a respective arm 36,37 and arranged for engagement with the cam 30. The arms 36,37 are connected to a common pivot point 38. The cam 30 may be driven by any suitable drive means, for example an electric rotary motor (not shown). Rotation of the cam 30 causes the cam follower 32 to pivot about pivot point 38. As is conventional, the pivotal movement of the cam follower 32 is determined by the profile of the cam 30. It will be apparent that, by coupling either the mask sheet 18, 118 or the image sheet 12,112 to an arm 36, 37 of the cam follower 32, rotational movement of the cam

30 may be converted into reciprocating movement of the mask sheet or image sheet coupled to the cam follower 32. In either the Figure 2 or Figure 3 embodiment, the velocity of movement of the image sheet 12,112, or the mask sheet 18,118, is determined by the speed of revolution of the drive motor (not shown) and/or the profile of the cam 30.

It will be understood that the specific cam/cam follower mechanism shown in Figure 3 is given by way of example only and that other cam/cam follower arrangements are equally suitable for use with display device 10,110.

To achieve an illusion of seamless animated movement of the respective series of minor composite images, the cam 30 is preferably of the constant-rise-and-fall type which effects substantially continual movement of the mask sheet 18,118, or image sheet 12,112, as appropriate. If a prolonged display dwell time is desired for a particular composite image, the cam 30 profile may be provided with a portion of substantially constant radius with which the cam follower 32 is arranged to engage when the windows 22,122 are coincident with, or in register with, the corresponding series of image portions 14,114, 16,116. For example, in the embodiment of Figure 4b it is assumed that it is desired to display the major composite image for a prolonged period. The major composite is arranged to be displayed when the mask sheet 118 and image sheet 112 adopt the first or second end positions of the reciprocating movement and this corresponds with the"top" and"bottom"of the lift provided by the cam 30. Thus, by providing a portion of substantially constant radius at the top of the cam lift, and preferably also at the bottom of the cam lift, (as is illustrated in Figure 4a), the windows 122 dwell on the major image portions 116 for a relatively long period. In the preferred embodiment, the remainder of the cam 30 profile is shaped to provide a substantially constant rise and fall rate as the windows 122 traverse the minor image portions 116.

It will be understood that the cam 30 could be replaced with a stepped cam (not shown). Stepped cams provide a fast image changeover time while constant rate rise and fall cams facilitate variation of the"dwell"and changeover times between respective displayed images.

Figure 4a shows the cam 30 with the cam follower 32 (only one roller 35 shown) at, or substantially at, the top of the cam lift. Figure 4b shows the corresponding position of the mask sheet 118 relative to the image sheet 112. It will be observed that the windows 122 are coincident with a respective major image portion 114 and, in particular, that windows 122'and 122"are in register with major image portions 114'and 114"respectively. Hence, in the positions shown in Figure 4a and 4b, the major composite image is displayed. In use, as the cam 30 rotates about its axis 31, the cam follower 32 is displaced in the direction indicated by arrow M1 by an amount, and at a rate, that is determined by the profile of the cam 30. The movement of the cam follower 32 causes a corresponding relative movement between the image sheet 112 and the mask sheet 118. As a result, windows 122 traverse the minor image portions 116 thereby exposing the minor image portions 116 (and therefore the corresponding minor composite images) in sequence. Movement in the direction MI continues until the cam follower 32 reaches the bottom of the cam lift.

Figure 5a shows the cam 30 with the cam follower 32 (only one roller 35 shown) at, or substantially at, the bottom of the cam lift. Figure 5b shows the corresponding position of the mask sheet 118 relative to the image sheet 112. It will be observed that the windows 122 are coincident with a respective major image portion 114 and, in particular, that windows 122'and 122"are now in register with major image portions 114"and 114"'respectively. Hence, in the positions shown in Figure 5a and Sb, the major image is again displayed. As the cam 30 continues to rotate about its axis 31, the cam follower 32 is now displaced in the direction indicated by arrow M2 (opposite M1) by an amount, and at a rate,

that is determined by the profile of the other side of the cam 30. The movement of the cam follower 32 causes a corresponding relative movement between the image sheet 112 and the mask sheet 118. As a result, windows 122 again traverse the minor image portions 116 thereby exposing the minor image portions 116 in sequence. Movement in the direction M2 continues until the cam follower 32 reaches the top of the cam lift. Thus, in the preferred embodiment, the major composite image is displayed when the cam follower 32 is at the top and at the bottom of the cam lift, and the minor composite images are displayed in sequence during each half revolution of the cam 30.

The cam lift may be chosen to cause the transparent windows 22,122 to traverse (or be traversed by) one or more sets of major and minor image portions 14,114 ; 16,116 during one half revolution of the cam 30. In the example of Figures 4 and 5, the cam lift causes two traverses (a respective one during each half revolution of the cam 30) of the transparent windows 122 over the major and minor image portions 114; 116 such that the major composite image is first displayed at the top of each lift of the cam 30 and is displayed again during each half revolution of the cam 30, interspersed by twenty-four displayed minor composite images in two sequences of animated movement in a substantially seamless manner, each sequence of animated movement being provided by a series of twelve minor composite images in sequence. It will be appreciated that the number of sequences of animated movement is only limited by the lift dimension of the cam 30 and the width of major and minor image portions 14,114 ; 16,116. By way of example, in the embodiment of Figures 4 and 5 the cam 30 may be arranged to provide travel of approximately 6 mm in each direction (M1 and M2) to provide one traverse of the minor image portions 116 during each half cycle of the cam 30, or alternatively a travel of approximately 12 mm in each direction to provide a traverse of two sets of minor image portions 116 interrupted by a major image portion 114 during each half cycle. In the preferred embodiment, the major composite image is displayed for a prolonged dwell time and this may be achieved

by providing wider major image portions 14,114 and/or providing the cam 30 with a substantially constant radius in the region corresponding to the windows 22,122 being in register with the major image portions 14,114.

The preferred embodiments of the display apparatus 10,110 provide substantially seamless animated movement without suffering from"ghosting effects".

Seamless animated movement is provided by arranging the window 22,122 width to be substantially the same as the width of the minor image portions 16,116.

Since the windows 22,122 traverse, or are traversed by, the minor image portions 16,116 continuously, i. e. without stopping, "ghosting"does not occur. Moreover, ghosting is avoided at each end of the relative travel between the image sheet 12, 112 and mask sheet 18,118 (i. e. corresponding to the top and bottom of the cam lift) because the width of the major image portions 14, 114 is greater than the width of the windows 22,122.

In an alternative embodiment, the transparent window 22,122 width may be related to the minor image portion 16, 116 width, to create an alternative type of displayed movement. For certain types of advertising, it has been found advantageous to provide a slightly"non-seamless"display, best described as a "fluttering"movement. This can be achieved by making the windows 22,122 narrower than the minor image portions 16, 116. For example, using eight minor image portion 16, 116 widths of approximately 0.4 mm, the transparent window 22,122 width on the mask sheet 18,118 could be approximately 0.3 mm (a width ratio of the minor image portions 16,116 to the transparent window 22,122 of 1.33 : 1), giving an illusion of"fluttering"movement to the observer. In a still further embodiment, it is found that the illusion of seamless movement can be aided by allowing a limited amount of ghosting to take place. This can be achieved by making the windows 22,122, wider than the narrow image portions 1 l, 116. For example, a transparent window 22,122 width of approximately 0.5 mm and a minor image portion 16, 116 width of approximately 0.4 mm would

give a width ratio of 0.8 : 1, giving, with the eight minor image portions 16,116, an illusion of seamless movement to the observer. In cases where the drive motor actuates the mask/image sheet relatively quickly, the same effect can be achieved by having the windows 22,122 up to 50% larger than the minor image portions 16,116. Being able to choose the transparent window minor image portion width ratios further enhances the opportunity for creative display for the advertiser.

As already mentioned, the speed of revolution of the drive motor also influences the speed of movement of the image sheet 12,112 or the mask sheet 18,118 (as appropriate). For example, a suitable motor may be rated at 1-6 rpm. In order to achieve an illusion of movement over the sequence of minor composite images, the moving means (motor/cam/cam follower mechanism) should preferably cause reciprocating movement over at least the minor image portions at a velocity of 15- 100 mm/min, more preferably 50-95 mm/min.

It will be understood that the invention is not limited to any particular size of image sheet or any particular number of images (major or minor) on an image sheet. It is preferred that the mask sheet 18,118 and image sheet 12,112 are in engagement with one another, or at least sufficiently close to one another to avoid significant parallax error. Optionally, an additional sheet, e. g. a sheet of transparent glass or plastics (not shown), or substance, e. g. lubricant, talcum powder etc. , may be introduced between the image sheet 12,112 and mask sheet 18,118 to reduce friction and/or to protect the images from wear.

The present invention is not limited to the embodiments described herein which may be amended or modified without departing from the scope of the invention.