1986-09-23
1989-05-02
Arnold, Bruce Y.
350400, G02B 530, G02B 2728
Patent
active
048262986
DESCRIPTION:
BRIEF SUMMARY
In a conventional key-operated lock, the key is shaped to move a plurality of tumblers to a selected combination of positions which uniquely allows the lock to turn. In a combination lock, the tumblers are moved to different combinations of positions by means other than a key, but only one combination of tumbler positions will allow the lock to open. In a conventional combination lock, the lock must be virtually dismantled and reassembled if the selected combination which allows the lock to turn is to be changed. When a security device which has a plurality of variable elements is used in combination with a computer, it is a relatively easy matter to adjust the selected combination of states which allows the lock to open, for example by feeding into the computer new instructions to allow the lock to open in response to a new combination of element states.
According to one aspect of the invention, there is provided a method of controlling access to apparatus comprising generating a random number, feeding input data into a security device in response to said random number, feeding output data from said security device, generated in response to said input data, to a control device, generating reference information in response to said random number generated and allowing access to said apparatus when the output data corresponds to said reference data.
In one arrangement, the security device comprises a plurality of relatively movable elements which can be moved to any of a plurality of combinations of positions, said input data comprising instructions to move respective elements to respective positions, each said element varying the plane of polarization of light passing through it according to its position, said output data being dependent on the colour of light emerging through all of said variable elements and a pair of polarizing screens.
According to another aspect of the invention there is provided a security device comprising a plurality of elements, each movable to any of a plurality of positions and each causing rotation of the plane of polarization of light passing through it by an amount depending on its position, the device comprising a pair of plane polarizing screens mounted one on either side of the plurality of elements, such that the colour of light having passed through the screens and elements depends on the positions of the elements relative to the screens. By moving the elements to a different combination of positions, different colours can be generated. If the elements have different thicknesses at different zones across the width of the screen, then the colours of the light emerging from different zones will also be different. By feeding input data into the security device in the form of instructions as to the position of each element, output data can be derived in the form of the colour or a combination of colours of the light emerging from the screen when white light is shone upon the device.
An example of the invention will now be described with reference to the accompanying drawings, in which:
FIG. 1 is a perspective view of an element of an encoding device, and
FIG. 2 is a perspective view of an encoding device with four such elements.
The element of FIG. 1 comprises a backing strip 11 of uniform cross section formed of toughened polyvinyl chloride (pvc) with a handle 12 at one end bearing a label 13 identifying the element. A plurality of equal sized zones 14 are located along the strip. Each zone may be provided with a covering layer which rotates the plane of polarization of light passing through it by an angle depending upon its thickness. Some coatings have a preferred plane of polarization so that the light passing through it is affected not only by the thickness of the coating but also by its preferred plane of polarization. The Figure shows eight zones 14, each with a coating of polyethylene whose thickness has a selected constant value between nil and a maximum value.
FIG. 2 shows four such elements mounted in a linear guide 21 formed between two polarized screens 22 whose
REFERENCES:
patent: 3793565 (1974-02-01), Smith
patent: 4369481 (1983-01-01), Early
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