GB2322157A - Security device - Google Patents

Abstract

A security device for revealing code patterns comprises a plurality of elements 6, 15 arranged for movement between a pair of plane polarising sheets 3, 14 and light passing through one sheet and through the elements is viewed through the other sheet. Each element is separated into a plurality of zones 8 and each zone is subdivided into a plurality of sectors 9. Some of the sectors rotate the plane of polarisation of transmitted light by ninety degrees, others have no effect on the polarisation. The sectors of a zone can, therefore, produce a pattern of light and dark when viewed between the sheets - a polarising sector of element 6, as shown in fig. 6a, acts to transmit light, and the polarising sectors of two elements 6 and 15 interact, as shown in fig. 6b, to prevent light transmission. The positions of the elements can allow different zone patterns to be revealed. In one embodiment the elements are arranged as endless belts with detent teeth defining selected belt positions.

Description

SECURITY DEVICE The present invention relates to a security device in which a code is read by polarised light, and to the mechanism of such a device.

Security devices in which a code is read by means of polarised light are known. For example British patent 2 167 484 describes a security code device which comprises a plurality of elements, each of which causes rotation of the plane of polarised light passing through it by an amount that varies from zone to zone of the element. The device has a plurality of elements which are movable relative to one another, and a pair of plane polarisers, one on either side of the plurality of elements. By moving the elements to different relative positions, different colours are seen in different zones. If the position of each element corresponds to a digit of a code number, moving each element to a unique position determined by that code number will produce a unique arrangement of colours in different zones when white light is shone on the device. Thus, input data which are fed in to the security device in the form of instructions as to the position of each element are converted into output data in the form of the colour or combination of colours of light emerging from the exit polariser.

A computer program may be supplied with the security device, to verify to the program that the authentic security device, and hence the authentic program, is being used. This may be achieved by the computer program generating a random number which tells the user where to position each of the elements. The user will see a number of different colours in different zones of the device, and is required to key in to the computer the colours.

The computer compares the colours with stored reference colours corresponding to the number and either allows use of the program, (if the correct colours are input), or denies use of the program, (if incorrect colours are input).

The elements are housed in a guide, and they may be linear or circular. Circular elements, having sector shaped zones, may be rotatable relative to one another within the guide.

One problem we have found with such devices is that the colours which are perceived by one user may be perceived differently by another user, this may be caused by a number of factors including; colour blindness, the similarity of colour hues produced by such devices, and the relative calibration of the input reference colours on the computer operating the program in comparison to another similar computer operating the same program.

Consequently, a user may input incorrect colour combinations even when the authentic security device is being used. This problem may be overcome by using a computer-operated machine reader to determine the colours, and placing the reader in a fixed position relative to the device. The provision of such a reader, however, adds to the expense and complexity of the device.

It is the object of the present invention to reduce the above mentioned problem It is the object of a further aspect of the invention to provide a security device of the type described which is compact and easy to use.

According to the first aspect of the present invention there is provided a security device comprising a plurality of elements, each causing rotation of the plane of polarisation of light passing through it by an amount that varies from zone to zone of the element, the device comprising a pair of plane polarisers mounted one on either side of the plurality of elements which are each movable to any of a plurality of positions relative to the polarisers, such that the colour of light having passed through the polarisers and elements depends on the position of the elements relative to the polarisers, characterised in that all the elements within the device comprise of material that rotates the plane of polarised light passing through it by 900, (the direction of rotation is not important), and that the said zones of the elements are split into a plurality of regularly designated sectors that are manufactured, (by methods known to those skilled in the art, e.g. punching out holes in the element, or by methods presently unknown), in such a way as to either rotate the plane of polarised light passing through them by the same degree as their comprising element or to let polarised light pass through the said sectors unaffected.

By providing the device with these characteristic elements and zones the colour of light passing through the polarisers and elements will now be made up of regular light and dark, (black and white), patterns, with the structure of the pattern being dependent on the position of the elements and the zonal sectors relative to the polarisers.

The light and dark tonal pattern is caused by the well know properties of plane polarisers in combination with material that causes rotation of polarised light passing through it by 900. A plane polariser will only transmit light whose polarisation lies on the polariser's polarisation axis, a maximum amount of light will pass through two parallel polarisers if their polarisation axis are aligned, if their polarising axis are at right angels to each other, (900) , a minimum amount of light, (almost no light), will pass through the polarisers. In this device it is intended that the pair of plane polarisers are set in a position where a minimum amount of light passes through them. As elements within this device are intended to cause rotation of polarised light by 900 then a single element will allow light to pass through a pair of plane polarisers set in the aforementioned, (at right angles), orientation, by rotating the polarisation of light exiting from the first polariser by 900 so that its plane of polarisation is parallel with the axis of polarisation of the second polariser and thus able to pass through it. If two elements from this device are placed between the aforementioned orientation of plane polarisers then no light, (or a minimum amount of light), will pass between the polarisers, this is due to plane of the polarised light passing through the first element being rotated by 900 and then being rotated by another 900, (The direction of rotation is not important to the elements.), by the second element meaning that the light will leave the second element with its plane of polarisation perpendicular, (900), to the axis of polarisation of the second polariser, (or the same plane of polarisation of light exiting the first polariser) . This effect caused by these elements can be extended to form a rule where odd numbers of layers of these elements let light pass through plane polarisers set at right angles to one another and even numbers of layers of these elements and no elements will not let light pass, this rule breaks down with very large numbers of layers of these elements as the opacity of the elements becomes a factor in the equation, (This rule will work in reverse if the plane polarisers are set with their axis of polarisation in parallel.). Thus simple tonal patterns can be generated by a device with the above characteristics allowing a user to correctly recognise the output of such a device without the complications of colour recognition.

The number of pattern combinations is dependent on the number of sectors in a zone, as there are only two possible visual outputs per sector, (dark and light), then the maximum possible number of patterns is dependent on 2x where x is the total number of sectors in the zone of an element. It is preferable that the maximum possible number of patterns in a system is not too large, for ease and speed of recognition, and it is also preferable that the same maximum number is not to small, for security. A sensible number of sectors would be three with eight possible patterns, or four with sixteen possible patterns, however depending on the final intended use of the device the number of sectors may be higher or lower.

It is found that if a system is used that employs a low number of sectors per zone, it may be possible to determine the structure of each individual zone in an element and hence correctly predict the output of a device relative to an input, by moving individual zones from one element over a fixed combination of other elements, noting the tonal changes as one sector of a zone passes into or leaves another sector of the zone relative to the fixed combination of elements and the polarisers, and then comparing these movements with other such movements.

It has been found that this potential problem can be reduced by first disallowing the passage of light in any area within an element that is not within a zone, by 'painting' the non zonal area with an opaque dye or paint.

It has also been found that this potential problem can be reduced by encoding each sector of a zone of an element with a pattern of small sectors which are manufactured and operate in the same manner as the aforementioned sectors, such that the colour pattern of light having passed through such a group of small sectors can either be made up of dark and light tones, (black and white).

This encoded zonal structure is produced by combining two patterns, a higher resolution 'obscuring' pattern and the 'originally intended' pattern for the zone, following a rule where black (dark) areas (of the pattern) and black areas combine to form black areas in the combination pattern, white (light) areas combined with black areas to form white areas, and white areas combined with white areas to form back areas. This combination pattern is manufactured within a single zone of an element by replacing the black areas of the combination pattern with non-light-rotating sectors of a zone and the white areas with plane polarized light rotating sectors of the zone, thus encoding (masking) the originally intended pattern.

This added pattern of small sectors will obscure the original sector pattern within a zone thus making the task of determining zonal structure within an individual element increasingly difficult. The difficulty will depend directly on the number of small sectors per sector of a zone.

Complicating the originally intended zonal pattern with small sectors will increase the maximum number of pattern combinations by the factor described earlier, it will also make individual pattern recognition complicated and time consuming, defeating the object of this aspect of this invention. This potential problem is eradicated by designing the small sector patterns within a zone of an element to combine with the equivalent small sector patterns within the zones of the other elements within the device when viewed between plane polarisers, to form patterns that are of the same level of definition as the patterns solely formed by the sectors of a zone. This combination of small sector patterns will follow the previously described rule for how elements that rotate polarised light by 90 allow or disallow the passage of light through plane polarisers set at right angles to each other on either side of the plurality of elements within the device.

The process for combining the small sector patterns within a zone of an element with the equivalent small sector patterns within the zones of the other elements within the device, to form patterns that are of the same level of definition as the patterns formed solely by the sectors of a zone can be extended with an extra fixed element that can be placed within the device or attached to one of the plane polarisers, where the fixed element has zones within it that are split into the same plurality of sectors and small sectors as the sectors and small sectors within a zone of the movable elements within the device. This small sectors patterns within the sectors of the zones of the fixed element can be designed to combine with correctly aligned small sector patterns within the sectors of zones of the plurality of elements within the device to form patterns when light is passed through all elements of the device between a pair of plane polarisers, that are of the same definition as the patterns formed solely by the sectors of a zone when light is passed through an elements of a device between a pair of plane polarisers.

This method of obscuring the sector structure of an individual zone of an element means that the intended combined sector pattern of zones from the plurality of elements with this device can only be observed if the zones and sector patterns are aligned in exactly the same manner in relation to the pair of plane polarisers, and that if an element from this device is moved relative to the other elements and the pair of plane polarisers, then a different recognizable pattern will only be observed if another zone of the moved element exactly aligns with the aligned plurality of zones and sectors from the other elements. If this aligning is not exact the small sectors within the sectors of the zones will combine to form a pattern with a more complex structure that the intended pattern to be recognized.

This aspect of the invention may be extended; where in place of elements which cause the rotation of the plane of polarised light by 90 , pairs of elements may be included within the device that rotate the plane of polarised light by an angle that is xO, where the first element rotates the plane of polarised light by +xO (clockwise) and the second rotates the plane of polarised light by -xO (anticlockwise). When light is passed through a single element of this form placed between a pair of plane polarisers with their axis of polarisation at right angles to each other then a single colour hue is seen, if a second element of this form is then added to the first which rotates the plane of polarised light by the same degree as the first element but in the opposite direction then no light, (or a minimum amount of light), will pass through the polarisers and the two elements. If a third element is added, (to the system), that rotates the plane of polarised light in the same direction and to the same degree as the first element then the same colour hue will be seen when light passes through the polarisers as when a single element with these properties is placed in this system. A rule can be determined that predicts the outcome colour when light passes through a set number of elements which rotate the plane of polarised light by +x" or -xO placed between plane polarisers with their axis of polarisation at right angles to each other: The elements' rotation of the plane of polarised light can be compounded to determine the final rotation of light, if there is an equal quantity of positive, (clockwise), and negative, (anticlockwise), rotating elements then light passing through the system will be unaffected by the elements, If there is an unequal balance between positive, (clockwise), and negative, (anticlockwise), rotating elements then light passing through the system will be rotated to the same degree as the sum of the rotations of the remaining positive, (clockwise), rotating or negative, (anticlockwise), rotating elements, a colour hue will be seen that is representative of this degree of rotation.

The rule relating to elements rotating the plane of polarised light by +xO or -xO can be used to produce a simple pattern recognition system, (using the same principles as outlined earlier in this aspect of the invention,) that uses a low number of colours as well a dark tone, (black) , to increase the number of possible combinations produced by a device in comparison to a similar device, (same number of sectors within a zone, same number of elements, same number of positions that the elements can be moved to), that uses the dark tonal, (black), and light tonal, (white), system described earlier. This system can also be extended to use the small sector obscuring process, with or without a fixed element.

According to the second aspect of this invention there is provided a security device comprising a plurality of elements, each causing rotation of the plane of polarisation of light passing through it by an amount which varies from zone to zone of the element, the device comprising a pair of plane polarisers mounted one on either side of the plurality of elements which are each movable to any of a plurality of positions relative to the polarisers, such that the colour of light having passed through the polarisers and elements depends on the position of the elements relative to the polarisers, characterised in that the device is provided with a mechanism allowing for a large number of possible positions of the plurality of elements within the device within a physical structure that does not inhibit the user of the device from recognizing the colour patterns generated by the device (depending on the position of the elements relative to the polarisers), and does not inhibit the user from carrying this device in a small pocket or wallet.

It has been found that the mechanism of devices of the form described by British Patent 2 167 484 do not allow for a device to be manufactured that is small and light enough to be carried in a wallet or pocket, in conjunction with having the capacity to generate a large number of possible combinations of outputs, (that can be easily and accurately read by the user), from a low number of inputs. It is the intention of this aspect of the invention to reduce this problem and provide such a mechanism for a device that is capable of producing a large possible number of accurate easy to read combinations of outputs from a low number of inputs within a physical size that is similar in dimensions to a credit card.

The mechanism is based on a system that uses all the advantages of a linea system for moving the plurality of elements within a device in conjunction with the advantages of using a circular system rotating the plurality of elements within the device. The mechanism reducing the disadvantages of a linear system which is the potential length of a device which needs a large potential number of input choices per element in comparison to a low number of overall inputs, and also removes the disadvantages of a circular mechanism which are; the manufacturing problem of aligning the angle of rotation of zones within an element so that the output of the device can be accurately predicted, and the relatively large size that a device has to be to accommodate a flat rotating mechanism that produces accurate outputs that can be easily recognized by a user.

The mechanism operateS on the principle that an element of a device can be formed into a long (flat) ribbon, containing the same number of zones along the length of the ribbon as the number of possible inputs intended for that element. Due to the structure of a ribbon it can be looped round an axle saving a considerable amount of space, this looping can take two forms; the first would be when one end of the ribbon is attached to the other end of the same ribbon with the ribbon effectively being mounted on one long flat axle, the second form would be to attach each end of the ribbon to a separate axle so that the ribbon could be used like a scroll, winding the ribbon off one axle as it is would onto the second axle.

The second form, (scroll), of mounting an element in ribbon form does allow for a very large number of possible input combinations per element within a restricted space, however it is complicated to operate accurately, (to allow for small sector aligning in respect of the first aspect of this invention), and to manufacture. As the first form, (looped and joined to itself), of mounting an element as a ribbon allows for a large number of possible input combinations per element along with facilitating a system for very accurately aligning zones and sectors within a element, it is thought unnecessary to use the second form of mounting the ribbon in the preferred embodiment of this invention.

A plurality of elements can be moved independently of one another on the same central axle of a device operating this mechanism, by using element ribbons of different widths, each element being progressively a set amount wider than the first element. If all the elements are looped end to end with themselves, (as described earlier), then mounted on a axle with the element with the greatest width being mounted first, followed by the element with the next greatest width in progression until all the elements are,mounted, making sure that all the lower or upper lengths of the elements are aligned, each element will then be capable of having an attachment made to the exposed area of its surface, allowing it to be moved independently of the other elements. The system for mounting the elements on the central axis leaving an exposed area of surface to allow for an attachment to be made that allows an individual element to be moved independently can be modified to allow for attachments to be made either on an upper exposed edge or a lower exposed edge of an element, by aligning the elements so that an area from every element is either exposed on the upper or lower edge of the element. All the elements have to be mounted so that their zones, (sectors, and small sectors) align on the same horizontals.

To accurately locate zones from an element over zones from other elements within the device, a ratchet mechanism is used to individually align each element, where a spring loaded 'tooth' is attached to an individual element, to allow the element to be independently moved via the 'tooth', in conjunction with a plurality of 'grooves' within the body of the device, allowing the 'tooth' attached to an individual element to be located in a plurality of positions along the device (dependent on the number of groves). The distance between each groove should be exactly the same distance between each zone of an element to allow for exact positioning of sectors and small sectors, (if included) , within a zone.

The 'tooth' is released from a 'groove' by pushing it against a spring that keeps it tight against that 'grove' in the ratchet, allowing it to move freely until the pressure on the spring is released, making the spring force the 'tooth' back into a groove of the ratchet, and thus accurately locating the element in that position. A common use of this form of ratchet mechanism is used to extend, retract and position knife blades on 'Stanley' knives.

The 'Stanley' knife ratchet mechanism has to be extended to allow the element to be fully rotated around the central axle without having to turn the device over to locate the 'tooth' in the desired position. To achieve this two sprung 'teeth' are positioned on each element each in a directly opposite position to the other, (each as far away from each other along the length of the looped ribbon as possible), the grooved part of the ratchet mechanism is only present on the front part of the device restricting movement of any sprung 'tooth' on this side of the device, a smooth slide on the opposite side of the device to the 'grooves', (viewing side), will allow unrestricted movement of a sprung 'tooth' in this position. This ratchet mechanism allows only one sprung 'tooth' to be located at a time in the 'grooves' of the device, allowing an element to be positioned in all its possible plurality of positions by locating only one of the sprung teeth. In the preferred embodiment of this device the two 'teeth' on each element will be labeled with either a character, (like an arrow), pointing up, or a character pointing down, (they may alternatively be colour coded), allowing for two sets of positioning numbers to be displayed either above or below the line of movement of the 'teeth', the two sets of positioning numbers contain all the possible numerical positions that the elements' zones can accurately be located in. When a 'tooth' is positioned the user will be able to determine the elements numerical position by noting which number the device on the tooth' is pointing to.

The spring locating the 'teeth' in the grooves of the device is fabricated in a manner that allows it to be rotated around the end of a flat axle without breaking, sticking, or damaging any part of the device. This is achieved in two ways: the first way is to use a flat spring with its longest length being perpendicular to the direction of movement of the 'tooth', thus only the width of the spring needs to be stressed as it moves over the edge of the axle, if the width of the spring is small in comparison to the thickness of the axle then little or no stress will be incurred by the spring from this manner of movement, this process may destabilize the maneuverability of a 'tooth' depending on the structure of the 'tooth' and the 'groove' system. The second way of allowing a flat spring to be rotated around the edge of the flat axle will be to position the spring with its length parallel to the direction of movement of the 'tooth', using a spring which is stressed in a manner which will cause it to release its stress as the tip of the spring passes over the edge of the flat axle, causing the leading edge of the spring to hook itself around the end of the flat axle, as the 'tooth' is returns to the flat part of the axle the mechanism allows the spring to be re-stressed into its original format.

In a preferred embodiment of this device the plurality of elements within the device will have plane polarisers enclosing either the front or the back loop, (viewing side loop or non-viewing side loop), of the plurality of looped elements contained within the mechanism previously described in this invention. The perception of the patterns or colours seen by the user of the device when light passed through the plane polarisers and element between them will not be hindered by the elements that do not appear between the plane polarisers as these are generally totally transparent and will not cause any perceivable changes to the state of unpolarised light.

Alternative embodiments of this device can have the plane polarisers placed on either side of both the front and back loops of elements within the device, (increasing the colour complexity of the device), or a combination of all back or front loops of elements within the device with a specified number of the remaining front or back loops of elements, (also increasing the colour complexity of the device).

The invention will now be further described, by way of example, with reference to the following drawings in which: Figure 1 is a diagrammatic representation of non polarised light passing through a linea polariser.

Figure 2 is a diagrammatic representation of plane polarised light passing through material that rotates plane polarised light by 900.

Figure 3 is a view of an element, its zones, and sections.

Figure 4 is a diagrammatic view of plane polarised light passing through the sections of a zone of an element.

Figure 5 is a view of a possible pattern seen within a zone of the device when light is passed through its polarisers, and elements.

Figure 6 is an exploded view of possible polariser and element structure within a device, and its effect on the passage of light through its structure.

Figure 7 is a representation of all the possible pattern combinations produced within a zone of four sectors.

Figure 8 is a view of an element containing zones that are surrounded by an opaque paint.

Figure 9 is a representation of how zonal structure can be obscured by small sectors.

Figure 10 is a representation of how small sector patterns can be combined to produce patterns with the same definition as sector patterns.

Figure 11 is an exploded view of a possible fixed element, movable element, and polariser construction within the device.

Figure 12 is a representation of the possible pattern formed when zones containing small sector structure are not correctly aligned.

Figure 13 is a diagrammatic representation of plane polarised light passing through two elements which rotate plane polarised light by the same amount but in opposite rotations.

Figure 14 is a representation of how two zones of different elements which rotate plane polarised light by the same amount but in opposite rotations can combine to produce a resultant pattern.

Figure 15 is a plan view of linea and circular devices.

Figure 16 is a series of views of ribbon structures within the device.

Figure 17 is a view of how ribbon elements are mounted on a flat axle.

Figure 18 is a series of views of the ratchet mechanism within the device.

Figure 19 is a series of views of how the ratchet mechanism allows an element within the device to be located to all its possible positions.

Figure 20 is a series of views of how the spring on the 'tooth' part of the ratchet mechanism can be rotated over the edge of a flat axle.

Figure 21 is a series of views of how the polarisers within the device can be positioned in relation to the looped elements of the device.

Figure 1 shows the effect on non-polarised white light 2 passing through a linear polariser 3, with its axis of polarisation 5 parallel to the horizontal. The plane polariser 3 only allows light 4 in the same plane as its axis of polarisation 5 to pass through the polariser 3.

Figure 2 shows plane polarised light 4 parallel to the horizontal passing through an element 6 that rotates plane polarised light by 900, and the resulta light. The resultant plane polarised light 7 exiting the top sector 10 will be rotated by 90" producing light polarised in a plane parallel to the vertical 7. The resultant plane polarised light 4 exiting the bottom sector 11 will not be effected by effected by the sector 11.

Figure 5 shows the pattern seen when light is passed through the arrangement in Figure 4 when it is placed between two plane polarisers with their axis of polarisation at right angles to each other. Light will pass through the sector 10 that rotates the light by 900 producing a light (white) sector of the pattern 12, and light will not pass through the sector of the pattern 11 that does not effect the passage of plane polarised light producing a dark (black) sector of the pattern 13.

Figure 6a shows the effect on non-polarised white light 2 as it passes through an arrangement within the device containing one element 6 that rotates the plane of polarised light by 90 , placed between two plane polarisers 3,14, one with its axis of polarisation parallel to the horizontal 3, and the other with its axis of polarisation parallel to the vertical 14. Only plane polarised light 4 with its plane of polarisation parallel to the horizontal is let through the first plane polariser 3, this polarised light is rotated 900 by the element 6 to produce a resultant plane polarised light 7 with its axis of polarisation parallel to the vertical, this polarised light 7 is allowed to pass through the second polariser 14, as its plane of polarisation is the same as the axis of polarisation of the plane polariser 14, producing a light (white) pattern 12 when this arrangement is viewed.

Figure 6b shows the effect on non-polarised white light 2 as it passes through an arrangement within the device containing two elements 6 and 15 (that both rotate the plane of polarised light by 900), placed between two plane polarisers 3,14, one with its axis of polarisation parallel to the horizontal 3, and the other with its axis of polarisation parallel to the vertical 14. Only light 4 with its plane of polarisation parallel to the horizontal is let through the first plane polariser 3, this polarised light is rotated 900 by the first element 6 to produce a resultant plane polarised light 7 with its axis of polarisation parallel to the vertical, which is then further rotated by another 900 by the second element 15 to produce a resultant plane polarised light 4 with its axis of polarisation parallel to the horizontal, this polarised light 4 is not allowed to pass through the second polariser 14, as its plane of polarisation is at right angles to the axis of polarisation of the plane polariser 14, producing a dark (black) pattern 13 when this arrangement is viewed.

Figure 7 shows all the possible light and dark (black and white) pattern combinations form a zone 8 containing four sectors 9, when viewed through crossed polarisers. There are 24, (16) possible combinations.

Figure 8 shows zones 8 within an element 6 surrounded by an opaque paint 15.

Figure 9a shows how a zone 8 can be split into sectors 9 of rotating 10 and non-rotating sectors 11, and further split into small sectors 16, of rotating 10 and nonrotating 11 small sectors.

Figure 9b shows how a simple zonal structure pattern 17 can be encoded with a more complex small sector pattern 18. If a simple zonal pattern of sectors 17 (as viewed through crossed polarisers) is combined with a more complex zonal pattern of small sectors 18, a resultant masked pattern 19 can be produced if a combination rule is followed where black (dark) areas (of the patterns) and black areas combine to form black areas of the masking pattern, whit (light) areas combined with black areas to form white areas, and white areas combined with white areas to form black areas. The resultant encoded (masking) pattern 19 can be manufactured within one element by replacing every black area (dark) 13, with a non-light-rotating sector 11, and every white area (light) 12 with a plane of polarised light rotating sector 10.

Figure 10a shows how the original zonal structure 17 from Figure 9b, can be seen when the encoded pattern 19 from Figure 9b is combined with a decoding pattern 20 (contained within another element) and viewed through crossed polarisers.

Figure 10b shows how complex encoding patterns of the type described in Figure 9b, (e.g. pattern 18) can be combined to form simple zonal patterns when viewed through crossed polarisers. In this example four encoding patterns; 21,22,23,24, are used that can be combined with themselves in any way to produce predictable simple zonal patterns (e.g. 21+22+23+24 = 25, a simple zonal pattern) allowing any of the encoding patterns; 21,22,23,24, to be combined with any simple zonal structure, e.g. 26, within an element to produce an encoded zonal structure 27, which when examined in conjunction with three other encoded zonal structures (similar in structure to pattern 27), between crossed polarisers will produce a simple zonal pattern 28 (e.g. (21+26)+(22+26)+(23+26)+(24+17) = 28) of the desired complexity for user friendly pattern recognition. These patterns are formed from the sum of all the encoding patterns, 21,22,23,24 and all the simple zonal patterns like 25, within the zones. An alternative embodiment of the combining of encoded zonal structures like 27 would be to have one specific encoding pattern for every zone of an individual element, making the sum of all the encoding patterns of zones of each individual element equal in complexity to a simple zonal structure of the desired complexity needed for user recognition.

Figure 11 shows a fixed element 29 in conjunction with a plurality of movable elements 6 between crossed polarisers 3,14.

Figure 12 shows two encoding zonal structures 21,22, their sum 30, and the pattern formed 31 when the encoded structures 21,22 are misaligned by one small sector width to the left.

Figure 13 shows the path of plane polarised light parallel to the horizontal 4 passing through an element 32 that rotates plane polarised light by +xO, the resultant plane polarised light 34 exiting the element 32 with its plane of polarisation at +xO to the horizontal passing through a second element 33 that rotates plane polarised light by -xO, and the resultant plane polarised light exiting the system with its plane of polarisation parallel to the horizontal 4.

Figure 14 shows how two zones 35 and 36 from two separate elements that rotate plane polarised light respectively +xo and -xO, are combined to form a zone 37 showing its effect on plane polarised light within each of its sectors 38. For a further example four (+to) sectors will combined with three (-xO) sectors to produce a sector that rotates plane polarised light by +xO.

Figure 15a shows a plan view of a linea device mechanism of the form described by British patent 2 167 484. The mechanism contains an element 39, split up into a plurality of zones 40, it also contains a window of crossed polarisers 41 on either side of the element 39.

Colour and or patterns may be seen when light is passed through the polariser window 41, the colours and or patterns depend on the position of the element relative to the polariser window. The size of this mechanism and thus the device is dependent on the size of the element 39 and the maximum number of zones 40 along its length that need to be capable of being viewed through the polariser window 41. When the farthest left hand zone is viewed the right hand edge of the element will be in position 42, when the farthest right hand zone is viewed the left hand edge of the element will be in position 43.

Thus the minimum length of this mechanism is the distance difference between point 42 and 43.

Figure 15b shows a plan view of a circular device mechanism. The mechanism contains a wheel element 44, split into a plurality of zones 45, mounted on a central axle 46. In this mechanism the wheel element 44 is rotated round the central axle 46, with the zones 45 being aligned between the polarisers 47 for viewing. In this device vital space is lost in the mechanism by the relative size of the axle 46 to the element wheel 44 (a larger axle will allow the element to be aligned more accurately than a smaller axle and is therefore mechanically advantageous), and restricted areas 48 on the element wheel where zones 45 cannot be placed if they are to align with the polariser arrangement 47 if arranged linearly.

Figure 16 shows an element in a ribbon form 49. The ends 50 of this element can be joined together to form a looped ribbon 51. The ends 50 of the ribbon can also be arrange in a scroll mechanism 52, this scroll mechanism can be arrange to allow independent movement of separate scrolled elements 52 within a device 53, however the mechanism for allowing this is complicated and involves independent belts 54 attached to the axle 55 of each scroll, which are located by independent winders 56 attached to each belt system.

Figure 17 shows a flat axle 57 in conjunction with a number of looped ribbon elements 51, each looped ribbon element is of a different height to the other elements differing by a set proportion 58. When these are mounted on the flat axle 51, with the 'highest' looped ribbon element being mounted first and then the next highest looped ribbon element being mounted next and so on in order of next highest, then areas of each element will be exposed 59 if all the elements mounted on the axle are aligned in such a manner to allow this. This allows the elements to be independently moved, without obstructing the other elements within the device.

Figure 18a shows a cross sectional view of a sprung tooth ratchet mechanism. Where the sprung tooth 60 can be located in the ratchet groove 62, by means of a spring 61, forcing the tooth into position against the flat axle 51, locating the tooth accurately.

Figure 18b shows how the tooth 60 is not located in a groove 62, when the tooth is pressed down and moved out of position.

Figure l9a is a sectional view of an element 51 mounted on a flat axle 57 with its possible form of rotation 65.

The element has two tooth attachments 64, attached in opposite positions to one another, allowing the element to be fully rotated in all its possible positions from one side, rather than from two sides. The ratchet mechanism 63 is only on one side (the operating side) of the mechanism, meaning that only the tooth that is on the 'operating' side of the mechanism locates the element 51, and not both teeth.

Figure l9b shows a view of the operating face of a device containing two elements. Each element is located via its teeth, each tooth has,a location character on it designed to show the elements position within the device in relation to a set of numerical figures 68. For every element there are two teeth one with a character 'pointing up' 66 and the second with a character 'pointing down' 67, these teeth can respectively denote the position that the element is in by 'pointing to' the positional reference number either above or below it. As the teeth respectively 'operate' all the possible positions of the element then all the possible positions of the element can be denoted numerically using this system, and all the elements can be located in all their possible positions from only one side of the device.

Figure 20a is a view of a tooth 69 with a spring 70 attached at right angles to its direction of movement, and how this device is rotated around the edge of a flat axle 57.

Figure 20b is a view of a tooth 69 with a spring 71 attached parallel to its direction of movement, and how this device is rotated over the edge of a flat axle 57.

Figure 21 is a series of views of how the polarisers 75 in the device can be placed in relation to the elements 51. They can be placed enclosing the 'front part of a looped element 72, the whole looped element 73, or a combination of the 'front part' and a number of 'back parts of looped elements 74.

Claims (20)

1. A security device comprising a plurality of elements, each causing rotation of the plane of polarisation of light passing through it by an amount which varies from zone to zone of the element, the device comprising a pair of plain polarisers mounted one on either side of the plurality of elements which are each movable to any of a plurality of positions relative to the polarisers, such that the colour of light having passed through the polarisers and elements depends on the position of the elements relative to the polarisers, characterised in that all the elements within the device comprise of material that rotates the plane of polarised light passing through it by 900, (the direction of rotation is not important), and that the said zones of the elements are split into a plurality of regularly designated sectors that are manufactured, in such a way as to either rotate the plane of polarised light passing through them by the same degree as their comprising element or to let polarised light pass through the said sectors unaffected so as to produce easily recognizable dark and light patterns (including alphanumeric characters), when white light is shone on the device.

2. A security device as claimed in claim 1, wherein the areas of the elements not within a zone are manufactured in such a manner as to totally prevent the passage of light passing through these non zonal areas.

3. A security device as claimed in claim 1 or claim 2, wherein the zonal areas of the elements of the device are split into a larger plurality of regularly designated sectors than the number of sectors intended to produce a user recognizable pattern, so as to allow for a 'combination' pattern of a higher resolution to the originally intended pattern to be manufactured into each individual zone. This combination (masking) pattern displays the same structure as if two patterns, a higher resolution 'obscuring' pattern and the 'originally intended' pattern are combined following a rule where black (dark) areas (of the pattern) and black areas combine to form black areas in the combination pattern, white (light) areas combined with black areas to form white areas, and white areas combined with white areas to form back areas. This combination pattern is manufactured within a single zone of an element by replacing the black areas of the combination pattern with non-light-rotating sectors of a zone and the white areas with plane polarized light rotating sectors of the zone, thus masking the originally intended pattern.

4. A security device as claimed in claim 3, wherein the higher resolution obscuring' patterns used to 'mask' the 'originally intended' zonal patterns are designed to combine with other zonal obscuring patterns to produce a resultant pattern that is of the same resolution as a user recognizable pattern when 'masked' zones of different elements are aligned and viewed between the polarisers of the device.

5. A security device as claimed in any one of the preceding claims, wherein there is an element that is fixed in position in relation to the polarisers.

6. A security device as claimed in claims 1 to 4, wherein there is an element bonded directly to a polariser.

7. A security device as claimed in any one of the preceding claims, wherein the elements (which rotate the plane of polarised light by 900), are replaced by elements that rotate the plane of polarised light by +xo and -xO.

8. A security device as claimed in any one of the preceding claims, wherein the plurality of movable elements within the device are arranged as looped ribbons (joined to themselves) mounted on a flat axle.

9. A security device as claimed in any one of claims 1 to 7, wherein the plurality of movable elements within the device are arranged as ribbons with each end of the ribbon being attached to a separate axle. Allowing the element to be maneuvered in the manner of a scroll.

10. A security device as claimed in claim 8, wherein each individual element is mounted on a flat axle so as to leave an area of the element exposed when all the elements within the device have been mounted on the same axle, thus allowing each element to be maneuvered independently of any other element within the device.

11. A security device as claimed in claim 10, wherein each element is attached to a spring loaded tooth device that can be located along a slide in a plurality of positional grooves in the body of the device.

12. A security device as claimed in claim 11, wherein each element is attached to a second spring loaded tooth device located in a position opposite on the looped element to the first spring loaded tooth. Both teeth can be located in the same plurality of positional grooves in the body of the device.

13. A security device as claimed in claim 12, wherein spring loaded teeth can only be located in positional grooves on the 'operational' (users') side of the device, so as to stop the tooth on the 'non operational' side of the device from restricting the sole movement of the tooth on the 'operational' side of the device. The 'non operational' side slide for the tooth will be smooth allowing unrestricted movement of a spring loaded tooth.

14. A security device as claimed in claims 11 to 13, wherein the spring of the spring loaded device is stressed in manner to allow it to be rotated over the edge of a flat axle without breaking or damaging any other part of the device.

15. A security device as claimed in claims 11 to 14, wherein the spring of the spring loaded device is attached perpendicular to the direction of movement of the spring loaded tooth to allow it to be rotated over the edge of a flat axle without breaking or damaging any other part of the device.

16. A security device as claimed in claims 11 to 15, wherein the spring loaded tooth is marked with a character allowing it to be located accurately next to a numerical value on the 'operational' side of the device that denotes the exact position of the element, so as to allow one of the pair of teeth per element to represent half of the possible position of that element and the other tooth on that element to represent the remaining possible positions of the element, thus allowing the element to be accurately located in all its possible positions from the 'operational' side of the device.

17. A security device as claimed in claims 8,10,11,12,13,14,15,16, wherein the polarisers within the device can be positioned enclosing both the front and back parts of the looped plurality of elements.

18. A security device as claimed in claims 8,10,11,12,13,14,15,16, wherein the polarisers within the device can be positioned enclosing either the front or back parts of the looped plurality of elements.

19. A security device as claimed in claims 8,10,11,12,13,14,15,16, wherein the polarisers within the device can be positioned enclosing either the front or back parts of the looped plurality of elements and a proportion of the remaining parts of the loops.

20. A security device substantially as herein described with reference to the drawings.