DISPLAY DEVICE

Abstract: A display device (2) comprises first image providing means (9) and second image providing means and a prism (6). The first image providing means is disposed in a region adjacent a first face (26) of the prism (6) and the said second image providing means is disposed in a region adjacent a second face (24) of the prism (6). The device (2) is adapted to display an image provided by the said first image providing means (9) in a third face (28) of the prism (6); and adapted to display an image provided by the said second image providing means in the said third face (28) of the prism (6). The arrangement is such that an observer may view the said first image providing means (9) and the said second image providing means through substantially the same part of the said third prism face (28) by viewing the said third prism face (28) from two different angles.

Description: Display Device The present information relates to a display device. More particularly, but not exclusively, the invention relates to a display device for displaying a plurality of images. For the purposes of this document, the word 'image' is used very broadly and includes anything that an observer might wish to view, for whatever reason. Hence the expression covers aspects of real articles, such as clock faces, as well as representations, such as photographs or pictures. For the avoidance of doubt, an image within the context of this document may have it's appeal in it ' s aesthetic qualities, it's informational content or a combination of the two. What is more, such an image may be static or moving. If a display device is to display an image effectively, the image must be clearly visible from the intended observer's viewpoint. Hence, the image must appear suitably large at that viewpoint. If two or more images are to be observed from substantially the same viewpoint, then each must fulfil the same requirement. In certain circumstances this has caused problems - generally where space is limited and the respective sizes of a plurality of images should not be reduced to the extent necessary for each to be accommodated. In certain conventional arrangements, this has inevitably led to compromises which have resulted in either the clarity of the images being compromised as a consequence of size reduction, or the omission of one or more images. Solutions to this problem have been provided in the form of displays which mechanically replace one image in a viewing area with a subsequent image. However, these are generally complex and, therefore, expensive and often bulky. Alternative arrangements have included projection devices, but these suffer from similar drawbacks and are only suitable in a limited number of environments, in any case. Alternative solutions include electrical or electronic displays (such as television screens and the like), but these are also relatively expensive and are limited in terms of the type and quality of image that can be presented. The present invention sets out to provide a display device for displaying a plurality of images, to an observer located at a viewpoint, which has a relatively simple structure , is inexpensive to manufacture and which can display a wide variety of different types of images. Accordingly, the invention provides a display device comprising first image providing means and second image providing means and a prism; wherein the said first image providing means is disposed in a region adjacent a first face of the prism and the said second image providing means is disposed in a region adjacent a second face of the prism; the device being adapted to display an image provided by the said first image providing means in a third face of the prism; and adapted to display an image provided by the said second image providing means in the said third face of the prism; the arrangement being such that an observer may view the said first image providing means and the said second image providing means through substantially the same part of the said third prism face by viewing the said third prism face from two different .angles. Such an arrangement enables a display device according to the invention to display a plurality of images which an observer may view with only a slight shift in viewing angle (and no change in viewpoint). The observer can view either of the images at full size, at will, and without having to operate any controls. Preferably the prism is a right angle prism, and the said first face of the prism is adjacent the right angle and the said second face of the prism is the hypotenuse face. The display device may further comprise a base, the said base supporting the said prism by a portion thereof situated adjacent the said first face of the prism or by the said first face of the prism itself. The base may accommodate an instrument for providing a reading; the said instrument defining the said first image providing means. The instrument may be a clock, thermometer, barometer, or calculator. The base may be provided with control means for controlling the instrument without removing it from the base. The control means may take the form of a keypad situated on an outer surface of the base. The base may comprise a recess for receiving a portion of the said prism. The device may further comprise support means for supporting the said prism by a portion thereof situated adjacent the said second face of the prism or by the said second face of the prism itself. In a particularly preferred embodiment, the said support means is in the form of a plate. Preferably, the plate comprises a recess for accommodating the said second image providing means. The plate may be slid relative to the prism, so as to allow access to the said recess. In a particularly preferred embodiment, the movement of the plate is restricted, so as to ensure that the plate maintains its support for the prism during the course thereof. The device may include other types of prism, rather than a right-angle prism. In such a case, the prism may be a porro prism, a dove prism, an Amici prism, a pentaprism or a rhomboid prism. These and other preferred features of the invention are set out in the appended claims. Embodiments of the invention will now be described by way of example and with reference to the accompanying drawings in which:- Figure 1 is a wire-frame view of a back-plate and base of a display device according to a first embodiment of the invention; Figure 2 is a perspective view of the complete display device of Figure 1 ; Figure 3 is a view of a back-plate of the display device of Figures 1 and 2; Figure 4 is a cross-sectional view of the display device of Figures 1 to 3; and Figures 5 to 7 are perspective views of three further embodiments of the invention. Referring to Figures 1 and 2, it will be seen that a first embodiment of a display device 2 according to the invention comprises a base 4, a right-angle prism 6 and a back-plate 8. The base 4 has a front face 16, a seat face 18 and a bottom face 20. It also comprises two substantially parallel side faces 22. The seat face 18 of the base 4 is provided with a rectangular recess 19 that is essentially defined by an upstanding lip 21. The recess 19 is configured to accommodate one of the right-angle faces 26 of the prism 6, which is provided with a slightly rebated edge 7, in order to allow it to fit comfortably within the recess 19. The base 4 is also provided with a clock recess 30. An access bore 31 opens into the rear of the clock recess 30 and extends from the bottom face 20 of the base 4. A clock 9 is housed within the clock recess 30 and, therefore, sits underneath the right angle face 26 of the prism 6 that is seated within the prism recess 19. Conventional means (not shown) for adjusting the clock 9 are provided on its rear surface and these can be accessed from the bottom face 20 of the base 4, via the access bore 31, in order to adjust the clock 9 as necessary. The clock 9 is a reverse-readout clock, that is to say one in which the hands move anti-clockwise and in which the face is a mirror-image of a traditional clock-face. It will be noted that the overall shape of the base 4 is such as to carry-through the configuration of the prism 6 and, when the base 4, prism 6 and back-plate 8 are assembled together, as shown in Figure 2, the overall shape of the display device 2 is essentially prismatic in total. Of course, providing that the base 4 provides support for the prism 6 and can accommodate the clock 9 (or some other instrument or image) the base 4 may have any other shape that is desired. The back-plate 8 is secured to the base 4 by means of a pair of sprung countersunk pins 14. These pins 14 engage with slots 10 provided at the lower end of the back-plate 8. The back-plate 8 is also provided with an overhanging lip 1 1, which extends along its top-edge. The back-plate 8, by virtue of being secured to the base 4 in this manner, effectively holds the prism 6 in place within the display device 2. The overhanging lip 11 provides extra security in this respect. The back-plate 8 also provides protection for the prism 6. As can be seen more clearly in Figures 3 and 4, the back-plate 8 is provided with a picture recess 32 on its side which faces the prism 6 in the assembled structure. By virtue of the relationship between the slots 10 and the pins 14, the back-plate 8 can be slid to one side, so that a picture, photograph or some other basically laminar object can be fitted into the picture recess 32, so that when the back-plate 8 is returned to the position shown in Figure 2, it is sandwiched between the back-plate 8 and the hypotenuse face 24 of the prism 6. Of course, other mechanisms may be provided for inserting a picture or the like between the back-plate 8 and the prism 6, but the described arrangement has the advantage of keeping the prism 6 securely in place throughout the whole operation. The thus assembled display device 2 operates as follows. The clock face is internally reflected by the hypotenuse face 24 of the prism and can be viewed if the line of sight of the observer is at greater than an angle θ c to the normal to the hypotenuse face 24. θ c is the critical angle for light incident from the clock face to undergo total internal reflection at the glass/air boundary (see Fig. 4). The critical angle θ c is determined as follows: θ c -.sin " ' (n 2 /nj) where n is the refractive index of air (for most purposes this can be taken as equal to 1) and ni is the refractive index of the glass from which the prism is made. Hence θ c will vary for different types of glass, although in most cases it will be around 40°. This internal reflection has the effect of reversing the image of the clock face, which therefore appears as a normal clock face to the observer. If the line of sight is altered, such that it is along a path having an angle less than θ c relative to the normal, the reflection of the clock face is initially combined with that of the object behind the hypotenuse face 24 and, as the angle is reduced still further (to about 20°), the reflection of the clock face becomes secondary to the object behind the hypotenuse face 24 and the image of that object effectively becomes primary. Eventually, as the angle is reduced still further, the image behind the hypotenuse face 24 becomes visible instead of the clock face at a normal angle of incidence. Hence, with only a slight shift in viewing angle (and no change in viewpoint), the observer can view either of the two images at full size, at will, and without having to operate any controls. The above embodiment merely serves to show the principle behind the invention. Many other static or moving images could be substituted for that of the clock face. Naturally, pictures or photographs could be used. However, suitable images could also be provided by a calendar, a thermometer, a barometer, a calculator display or some other instrument read-out. The same can be said of the images located adjacent the hypotenuse face 24. Additionally, the back-plate could be omitted and the hypotenuse face 24 of the prism 6 could be printed with an image, or some larger object could be positioned adjacent the hypotenuse face 24. The base may be made of a wide variety of suitable materials. It may also include other features on its front face 16, or its side face 22. For example, it might include a calculator key pad; in such a case, the calculator display could be located in the clock recess 30 in place of the clock. The display would then be read through the prism 6. Alternatively, the base 4 might include a pen holder or other desk accessory. A company name or personal logo could be printed on the base 4 or be situated in either the clock recess or the picture recess. The prism may be formed from glass, Perspex, acrylic or other transparent or translucent materials. It may be plain or have a clock face located on its front right angle surface 28. Figure 5 shows an embodiment similar to the embodiment of Figures 1 to 4, but in this case, the back-plate is omitted. Due to the omission of the back-plate 8, the prism 6 is affixed to the base 4 by an adhesive. Figure 6 shows a display device generally similar to that shown in Figure 5, but in this case the overall design is curved and the prism has an elliptical hypotenuse face 24 and a circular right-angle face 26 adjacent the base 4. Figure 7 shows an arrangement in which the right-angled prism is replaced by an elongate prism 6 which is effectively squared off at one end, and has the form of a rhomboid prism at the other. In this case, one of the images (once again, a clock in this example) is situated adjacent the squared end, and reflects off the inclined face, which corresponds with the hypotenuse face 24 of the previous examples. Any further image to be used in conjunction with the image of the clock will be positioned upon the rear of the inclined face. Many further modifications and variations will be suggest themselves to those versed in the art upon making reference to the foregoing illustrative embodiments of the invention, which are given by way of example only, and which are not intended to limit the scope of the invention, that being determined by the appended claims.

Claims: CLAIMS: 1. A display device comprising first image providing means and second image providing means and a prism; wherein the said first image providing means is disposed in a region adjacent a first face of the prism and the said second image providing means is disposed in a region adjacent a second face of the prism; the device being adapted to display an image provided by the said first image providing means in a third face of the prism; and adapted to display an image provided by the said second image providing means in the said third face of the prism; the arrangement being such that an observer may view the said first image providing means and the said second image providing means through substantially the same part of the said third prism face by viewing the said third prism face from two different angles. 2. A display device according to Claim 1, wherein the prism is a right angle prism, and the said first face of the prism is adjacent the right angle and the said second face of the prism is the hypotenuse face. 3. A display device according to Claim 1 or 2, further comprising a base, the said base supporting the said prism by a portion thereof situated adjacent the said first face of the prism or by the said first face of the prism itself. 4. A display device according to Claim 3, wherein the base accommodates an instrument for providing a reading; the said instrument defining the said first image providing means. 5. A display device according to Claim 4, wherein the said instrument is a clock. 6. A display device according to Claim 4, wherein the said instrument is a thermometer. 7. A display device according to Claim 4, wherein the said instrument is a barometer. 8. A display device according to Claim 4, wherein the said instrument is a calculator. 9. A display device according to any one of Claims 4 to 8, wherein the base is provided with control means for controlling the instrument without removing it from the said base. 10. A display device according to Claim 9, wherein the control means is a keypad situated on an outer surface of the said base. 11. A display device according to Claim 9, wherein the control means are provided on the body of the instrument and the base contains a bore or aperture, via which the control means can be accessed. 12. A device according to Claim 3, or any claim dependent upon Claim 3, wherein the said base comprises a recess for receiving a portion of the said prism. 13. A device according to Claim 3, or any claim dependent upon Claim 3, further comprising support means for supporting the said prism by a portion thereof situated adjacent the said second face of the prism or by the said second face of the prism itself. 14. A display device according to Claim 13, wherein the said support means is in the form of a plate. 15. A display device according to Claim 14, wherein the said plate comprises a recess for accommodating the said second image providing means. 16. A display device according to Claim 15 wherein the said plate may be slid relative to the prism, so as to allow access to the said recess. 17. A display device according to Claim 16, wherein the movement of the said plate is restricted, so as to ensure that the said plate maintains its support for the prism during the course thereof. 18. A display device according to Claim 16 or 17, wherein one of the base and the plate is provided with a slot and the other of the base and the plate is provided with a projection for location within the slot in a sliding relationship so as to enable the sliding of the plate to take place, whilst securing the connection between the two. 19. A display device according to Claim 1, wherein the said prism is a porro prism. 20. A display device according to Claim 1 , wherein the said prism is a dove prism. 21. A display device according to Claim 1 , wherein the said prism is an Amici prism. 22. A display device according to Claim 1, wherein the said prism is a pentaprism. 23. A display device according to Claim 1 , wherein the said prism is a rhomboid prism.

Inventors: WHITCOMB ELLIS FITZROY PETERSE, WHITCOMB, ELLIS, FITZROY, PETERSEN
Applicants: DESIGNAWARE TRADING LTD, WHITCOMB ELLIS FITZROY PETERSE, DESIGNAWARE TRADING LIMITED, WHITCOMB, ELLIS, FITZROY, PETERSEN
Application year: 2000
Main classification: G09F19
IPC codes: G09F19