OCR / OCV
The decision to adopt OCR or OCV inspection is often determined by three key factors, namely
- The requirement for data integrity and accuracy 2) the coding technology 3) the industry requirement
- The coding technology
- The industry requirement
Optical Character Recognition, the marked character is isolated and is identified by a method of comparing it to every character in a font database. The character is identified as being the one which best matches the character being inspected.
OCR the returned score is the confidence level that a character identified as an ‘x’ is indeed an ‘x’. It is not an indication of the character’s quality.
Optical Character Verification to be useful the system must know the characters being presented. The process verifies the quality of this character against the model held in its database. OCV the returned score can be taken as a quality score for the character.
Wherever possible maintain a single layout Template.
Many products have a date marked on them in some form or other – be it a use by, best before or Date Of manufacture.
Ensure that the characteristics of the printed mark is not in any way effected by the print speed/ linear speed of the product passing by the printer.
Clarity and crispness – avoid saw tooth edges
Fully formed – no breaks in characters or missing dots
No additional or misplaced dots
No Ink Bleed
Separation between characters
It is essential that a gap is maintained between each character. The Gap should be at least 1/5th of the character width.
Select and maintain a single Font Type on all products.
Ideally a producer will use the same font type for all products. Each font used must be setup on the vision system.
The physical mark will often be printed whilst the product is being transported past the marking head. The speed of the transportation past the marking head can vary. It is essential that the marking system is implemented in such a way that allows for accuracy of the characters.
The size of the characters is unimportant so long as the size is consistent. Define the optimal size for your product and maintain this in all cases if at all possible.
As with any vision inspection system, the key to a successful OCR system is the repeatability of the contrast levels between foreground (characters) and background not necessarily the actual level of contrast.
Wherever possible control as much of the processes as possible, particularly the marking and printing technology. Similarly mechanical variations need to be engineered out of the process so the product is presented repeatably and reliably in the same location, with the same controlled lighting. If properly controlled and the image contrast and print quality is maintained to a specification then a high performing, high throughput OCR system can be achieved.
A successfully deployed System will be one which identifies the characters marked on a product successfully and repeatably.
The correct identification allows the system to determine whether or not the characters are correct. If the quality of the code is poor the characters will not be identified and the product will be rejected, the OCR system – judged in isolation- is functioning correctly.
The system will be adjudged to comprise of the marking device and the inspection equipment .
Together they will constitute the Controlled Mark & Verify system. The system must perform two tasks well.
1. to maintain a high yield
2. to identify incorrect & poorly marked product.
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