Dynamic magnetic information storage or retrieval – General processing of a digital signal – In specific code or form
Patent
1991-10-17
1993-10-19
Nelms, David C.
Dynamic magnetic information storage or retrieval
General processing of a digital signal
In specific code or form
235449, G11B 509
Patent
active
052551296
DESCRIPTION:
BRIEF SUMMARY
This invention relates generally to a machine which is preferably used in conjunction with a document sorting machine, and is intended to read and verify coded information contained within a magnetic strip or stripe, herein called `thread` on a bank note or other security document.
There are many difficulties in providing a machine which can with great reliability read and verify coded information with in practical terms absolute accuracy. Some of the difficulties arise from the nature of the document and its usage. The document is normally in paper form and is often folded or crumpled by a user. Although it is desirable to incorporate a hidden form of coding, such as a code embodied in a so-called security thread, if the coding is to be any more than trivial, that is to say is to have some relationship to a serial number of the bank note or some other coded significance, the physical embodiment of the coding must be robust and not readily susceptible to damage or error.
For these and a variety of other reasons, magnetically coded threads are generally considered to be preferable. Although the present invention is not limited to use with any particular form of magnetic coding, the preferred form of the invention is intended for use with bank notes or other security documents including magnetically coded threads as described in the International Patent Application published under No. WO90/08367 having a priority date of the 20th January 1989. Important characteristics of such a thread are that binary digits are represented by bit cells of substantially constant length and that a sequence of bits of the same binary value are represented by a continuous portion of the magnetic material, the length of the portion corresponding to the number of bits in the sequence. The thread is preferably discontinuous, bits of the other binary value being denoted by the absence of the said magnetic material. If there are several contiguous bits the material will be absent for a corresponding number of bit lengths. However, the bits of the other binary value may be represented by lengths (which may be contiguous) of different magnetic material instead of the absence of material.
A problem in the design and organisation of a reader of a security thread is that in practice it is difficult to ensure that a security document will be presented to a reading machine in a uniform manner, that is to say always with its edges properly aligned parallel to some given axis of presentation. Furthermore, the position of a security thread or coding on it may vary. A versatile reader intended for use with a multiplicity of differently coded threads or having the same general format and capable of validating a variety of different documents, such as bank notes of different denominations or currencies, must be able to detect the coding of the security thread presented, in general, anywhere on the bank note. It is customary to provide a security thread which runs entirely across a bank note but even so it is necessary to be able to detect a thread which may be positioned, possibly askew, anywhere across the a bank note. Since there are practical limitations on the track width of a magnetic transducer, in order to be able to detect a security thread reliably it is desirable in practice to provide an array of magnetic heads in order to sense along a respective one of a multiplicity of parallel tracks extending approximately parallel to the direction in which the document is moved, by any suitable transport mechanism, through the reader.
A difficulty in the scanning of a security document for the presence of a correctly coded magnetic security thread is the existence of other regions of the document containing magnetised or magnetisable matter, for example magnetic ink. Signals from such regions will inevitably be picked up by an array of heads which are intended to ensure that signals are picked up from a security thread which might appear anywhere within the bank note. In order to distinguish between magnetic portions forming part of the security
REFERENCES:
patent: 3593334 (1971-07-01), Bickel
patent: 3735372 (1973-05-01), Coccagna
patent: 4219152 (1980-08-01), Couch et al.
patent: 4612653 (1986-09-01), Livingston et al.
patent: 4837642 (1989-06-01), Smidth
Nelms David C.
Shami K.
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