GB1575607A

GB1575607A - Quality control

Info

Publication number: GB1575607A
Application number: GB8511/76A
Authority: GB
Original assignee: GV Planer Ltd
Current assignee: GV Planer Ltd
Priority date: 1977-03-02
Filing date: 1977-03-02
Publication date: 1980-09-24

Description

(54) IMPROVEMENTS IN OR RELATING TO QUALITY CONTROL (71) We, G. V. PLANER LIMITED, of Windmill Road, Sunbury-on-Thames, Middlesex, a British Company, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to quality control, and is particularly concerned with the validating of, or the detection of discrepancy in, printed patterns that have been reproduced from a master orignal.

One known method of such discrepancy or error detection involves a point-by-point comparison of the print with the master, using a scanning mechanism. Whilst good resolution can be obtained with this technique, it is essential to obtain accurate alignment of the pattern and scanning unit.

Another known method, and one which overcomes to a large extent the inherent alignment problem of the scanning technique involves an integral transform (e.g. Fourier transform) system whereby the entire pattern of the print is compared with the master orignal. However, this technique has comparatively poor sensitivity, and thus presents difficulties in verifying complicated patterns.

This latter point is borne out by the fact that the major application of transform techniques is in character recognition, wherein a character can be correctly recognised even in the presence of quite severe errorinducing distortion.

According to one aspect of the present invention, there is provided a method of validating a reproduced pattern with respect to a desired pattern, comprising the steps of obtaining and storing integral transforms of one or more predetermined discrepancies between the reproduced and desired patterns, effecting integral transformation of at least part of the reproduced pattern, comparing the integral transformation with said stored integral transforms and thereby detecting the presence of any of said one or more predetermined discrepancies for determining the validity of the reproduced pattern.

In accordance with another aspect of the present invention, there is provided apparatus for validating a reproduced pattern with respect to a desired pattern, comprising means for effecting integral transformation of at least part of the reproduced pattern; means for providing integral transforms of one or more predetermined discrepancies between the reproduced and desired patterns; said predetermined discrepancies comprising one or more of: a blob or a smudge on, or a gap in, the reproduced pattern that is not present in the desired pattern, and ghosting and/or misalignment between the desired and reproduced patterns; storage means having said predetermined discrepancies stored therein; means for comparing said integral transformation with said stored integral transforms: and means for providing an indication whenever the existence of said one or more predetermined discrepancies is detected by the comparison means or the existence of one of said predetermined discrepancies is detected by the comparison means, thereby to determine the validity of the reproduced pattern.

It has been found that, at least in certain applications, most of the errors, or at least the important errors, fall into convenient classification, so that instead of having to compare the entirety of the reproduction with the original, it is necessary only to single out a relatively small number of predetermined errors. Clearly, a large improvement in efficiency of the complete quality control system results from this.

In using this application the integral transform technique, master transforms of typical errors can be generated and stored, so that only corresponding transforms from the re produced print are of any relevance to the system, resulting in an appreciable reduction in the storage capacity required for verification of a given pattern. The above-mentioned poor sensitivity of the integral transform technique caii thus be greatly improved.

It will be noted that the invention is-independent of the actual printed patterns being compared, and is substantially inde pendent of the printing method used. Furthermore, both sides of a document, which for example may be a currency note, can be checked at the same time.

It has been found that many common errors can be associated with the following categories: (a) Discrete errors, which may occur anywhere in the pattern. Unintentional blobs and gaps are example of this type of error.

(b Generally errors, which effect the whole pattern. Ghosting and misalignment are examples of this type of error.

(c) local errors, which are large ill-defined discrete errors. A smudge is an example of such an error.

-It is envisaged that the discrete errors could: be detected directly, and that four transforms corresponding respectively to substantially 'circular blobs, substantially linear blobs, substantially circular gaps, and substantially linear gaps, would be sufficient.

The general errors are detectable by employing transforms of special subsidiary patterns dependent on the pattern actually employed and being compared.

The local errors, which are the least welldefined, may be detected by a separate method, for example a contrast measurement or comparison, in addition to use of predetermined transforms.

Any suitable technique analogue or digital, may be employed to generate the transforms. For example they mav be computer-gentrated transforms or optically-generated transforms or they may be generated using computer image processing. Furthermore, it is envisaged that a combination of these techniques could be employed to provide maximum efficiency of the method.

The invention will now be described, by way of example, with reference to the acaccompanying drawing.

A copy 10 of the original pattern of a bank note is scanned by a scanner 12, which may provide integral transforms of at least parts of the pattern on the copy 10. The integral transforms are supplied as one of two inputs of a comparator unit 14.

A storage unit 16 has stored therein information relating to the predetermined errors whose existence is sought on copy 10.

This' information is stored in a form compatible with the form of output produced by the scanner 12, and upon passage of the copy bank note 10 past the scanner 12, the information, as inteeral transforms, is suppiled to the other input of the comparator 14 If the comparator 14 does not note a corresDondence between any of the integral transforms at its two inputs, then none of the predetermined errors have been introduced into the copy bank note 10 during reproduction from the master original.

If a correspondence is noted by the comparator 14 between the integral transforms received from the scanner 12 and one or more of the integral transforms received from the storage unit 16 the particular copy bank note 10 being scanned is rejected, and this fact is indicated on an indicator 18. Alternatively, or in addition, the indicator 18 may indicate the lack of discrepancy between the reproduced pattern and the original pattern.

WHAT WE CLAIM IS:- 1. A method of validating a reproduced pattern with respect to a desired pattern, comprising the steps of obtaining and storing integral transforms of one or more predetermined discrepancies between the reproduced and desired patterns, effecting integral transformation or at least part of the reproduced pattern, comparing the integral transformation with said stored integral transforms and thereby detecting the presence of any of said one or more predetermined discrepancies for determing the validity of the reproduced pattern.

2. A method according to claim 1, wherein the discrepancy, or at least one of the discrepancies, is a light density discrepancy, and the comparison is made of light densities at at least one position of said reproduced pattern with said at least one discrepancy for detection of discrepancy.

3. A method according to claim 1 or 2 of detecting one or more predetermined discrepancies between the reproduced pattern and the desired pattern of a currency note.

4. A method of validating a reproduced pattern with respect to a desired pattern, substantially as hereinbefore described with reference to the accompanying drawing.

5. Apparatus for validating a reproduced pattern with respect to a desired pattern, comprising means for effecting integral transformation of at least part of the reproduced pattern; means for providing integral transforms of one or more predetermined discrepancies between the produced and desired patterns; said predetermined discrepancies comprising one or more of: a blob or a smudge on, or a gap in, the reproduced pattern that is not present in the desired pattern, and ghosting andlor misalignment between the desired and reproduced patterns; storage means having said predetermined discrepancies stored therein; means for comparing said integral transformation with said stored integral transforms; and means for providing an indication whenever the existence of said one or more predetermined discrepancies is detected by the compraison means of the existence of none of said predetermined discrepancies is detected by the comparison means, thereby to determine the validity of the reproduced pattern.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. pendent of the printing method used. Furthermore, both sides of a document, which for example may be a currency note, can be checked at the same time. It has been found that many common errors can be associated with the following categories: (a) Discrete errors, which may occur anywhere in the pattern. Unintentional blobs and gaps are example of this type of error. (b Generally errors, which effect the whole pattern. Ghosting and misalignment are examples of this type of error. (c) local errors, which are large ill-defined discrete errors. A smudge is an example of such an error. -It is envisaged that the discrete errors could: be detected directly, and that four transforms corresponding respectively to substantially 'circular blobs, substantially linear blobs, substantially circular gaps, and substantially linear gaps, would be sufficient. The general errors are detectable by employing transforms of special subsidiary patterns dependent on the pattern actually employed and being compared. The local errors, which are the least welldefined, may be detected by a separate method, for example a contrast measurement or comparison, in addition to use of predetermined transforms. Any suitable technique analogue or digital, may be employed to generate the transforms. For example they mav be computer-gentrated transforms or optically-generated transforms or they may be generated using computer image processing. Furthermore, it is envisaged that a combination of these techniques could be employed to provide maximum efficiency of the method. The invention will now be described, by way of example, with reference to the acaccompanying drawing. A copy 10 of the original pattern of a bank note is scanned by a scanner 12, which may provide integral transforms of at least parts of the pattern on the copy 10. The integral transforms are supplied as one of two inputs of a comparator unit 14. A storage unit 16 has stored therein information relating to the predetermined errors whose existence is sought on copy 10. This' information is stored in a form compatible with the form of output produced by the scanner 12, and upon passage of the copy bank note 10 past the scanner 12, the information, as inteeral transforms, is suppiled to the other input of the comparator 14 If the comparator 14 does not note a corresDondence between any of the integral transforms at its two inputs, then none of the predetermined errors have been introduced into the copy bank note 10 during reproduction from the master original. If a correspondence is noted by the comparator 14 between the integral transforms received from the scanner 12 and one or more of the integral transforms received from the storage unit 16 the particular copy bank note 10 being scanned is rejected, and this fact is indicated on an indicator 18. Alternatively, or in addition, the indicator 18 may indicate the lack of discrepancy between the reproduced pattern and the original pattern. WHAT WE CLAIM IS:-

1. A method of validating a reproduced pattern with respect to a desired pattern, comprising the steps of obtaining and storing integral transforms of one or more predetermined discrepancies between the reproduced and desired patterns, effecting integral transformation or at least part of the reproduced pattern, comparing the integral transformation with said stored integral transforms and thereby detecting the presence of any of said one or more predetermined discrepancies for determing the validity of the reproduced pattern.

6. Apparatus according to claim 5, com

prising means for measuring the light density of the reproduced pattern, and wherein said comparison means is arranged to compare said density at least at one position of said reproduced pattern with the light density of at least one. of said predetermined discrepancies to effect said validation.

7. Apparatus according to claim 5 or 6, arranged to detect discrepancy between the desired pattern and a reproduced pattern of a currency note.

8. Apparatus for detecting discrepancy between a reproduced pattern and a desired pattern, substantially as hereinbefore described with reference to the accompanying drawing.