100% Print Quality Inspection Is It Important For E-Pedigree
Many print quality inspection systems claim to inspect the printed area 100%, but what do they really mean? Are they doing 100% inspection? How is that important for E-pedigree?
In order to obtain 100% inspection, the entire label or package needs to be inspected. This means mechanically traversing the inspection area or using an area scan camera will not accomplish the task. A line scan camera needs to be used that enables inspection across the entire width of the area. The use of high resolution line scan technology enables harvesting the entire area to be inspected in a single pass.
Narrow web printers, like blister pack lines now have available a wide variety of print technologies used to meet their customers demands. It is not just static printed any more. Variable demand printing is becoming a requirement with increasing frequency, like E-Pedigree requirements for linear (1D) and matrix codes (2D) as well as human readable. Most vision inspection systems cannot meet the demand of inspecting variable data so they cannot be classified as doing 100% inspection.
What is meant by variable data printing? Some examples are:
- Bar codes that have a sequence number either ascending or descending.
- Human readable numbers that have a sequence number either ascending or descending.
- Numbers that are derived from a base number sequence like Base 36 therefore using a combination of numbers and letters.
- A mix of bar codes (1D codes) or Matrix codes (2D codes) that have number sequences.
- Number sequences that are random and generated via a database extraction.
The technologies used in most cases are ink jet or toner based systems. This gives a lot of ability to the printer but also introduces potential problems with the printed image. Ink and toner can run out, spatter, or jets can clog causing print quality issues. Inspecting this type of print is essential.
When it comes to inspection of bar codes and matrix codes, they can be inspected at two levels. There is the inspection to determine if the code is readable, meaning it was printed and then read. This assumes that any other bar codes or matrix reading device can read the code as printed notwithstanding the fact that the quality may be less than perfect. A more important inspection of bar codes and matrix codes is to verify the quality of codes to the relevant ISO symbology standards for each bar code and matrix code type. This will assure the code can be read by other reading devices at subsequent stages.
The ISO standards are very rigid in the method of verifying the print quality of the code. The position of the read head including the lights and the camera are very strictly regulated by ISO 15415 (for 2D symbologies) and ISO 15416 (for 1D symbologies). Furthermore, ISO 15426-1 and ISO 15426-2 are verifier conformance standards which must be adhered to. It is also a requirement of ISO to calibrate the vision system on a periodic basis. If a vendor states a system is ISO compliant, make sure they can calibrate the system. If they cannot, it is not an ISO compliant system. You may also want to see if you can calibrate the system or if it requires factory calibration only. It is these strict requirements that assure the code meets ISO standards and can be read further down the stream from the time it is printed. Verification is a quality measurement process in which a code is allocated a grade based on the quality of print as well as the adherence to published standards. Of course codes can still be mechanically damaged at a later stage.
If a vision system cannot read and or verify bar codes or matrix codes it cannot be considered a 100% inspection system in today’s web and blister printing world.
It is also important to have the ability to inspect some areas of the printed image with more exact criteria than others. Inspecting sectors of the label allows the inspection to be tailored since inspection criteria may be different from one customer to another or even from one job to another, or even within the same label. For instance to inspect a bar code in one sector and a logo in another sector is useful if their inspection criteria is different. If a bar code is to fail on a grade less then a B grade (ISO grade 2.5), that can be accomplished while the logo may have a less stringent requirement. When a failing condition is determined it can be communicated to the printer or rewind inspection system to take the agreed appropriate action such as stop and rewind to the splice table or some other action.
E-Pedigree requires 100% inspection because the next step in the process depends on a high quality bar or matrix code or human readable data to be as perfect as possible. Since E-pedigree data is variable, the inspection system needs to validate that the required numbers are indeed printed and they are not duplicated. This is all part of a 100% inspection system.
A true 100% print inspection system can perform all of the above functions. However there is one requirement that is critically important to a vision inspection system. It needs to be simple and easy for the operator to use or he simply will not use it. The best inspection system in the world is useless unless the operators find it easy to use.
When looking for 100% inspection of your printed media, be sure to ask if all of the above functions can be accomplished. Look beyond what you do today to what you could be doing tomorrow. It is always good to look at 100% print quality inspection from a strategic direction.
|
