codesure tm printed code verification and inspection ... codesure white paper 4-17-08.pdf ·...

Machine Vision Consulting

CodeSureTM Printed Code Verification

and Inspection Technology

Written by:

April 15, 2008


7 Old Towne Way Sturbridge, MA 01518

Contact: Joe Gugliotti Cell: 978-551-4160

Fax: 508-347-1355

[email protected] www.machinevc.com


Machine Vision Consulting Overview

Machine Vision Consulting, Inc. is based in Sturbridge, MA and has a lab building in

Westborough, MA and an assembly building in Troy, NY. MVC is focused on the

integration of machine vision technology to provide automated inspection and

process control during the manufacturing and packaging processes in a wide variety

of industries.

• End users come to MVC for complete machine vision solutions.

• Machine builders and automation integrators work with MVC to develop

the machine vision portion of their overall assembly, processing, handling, or

packaging solution.

• OEM’s of packaging systems, code printers, robotics, and other process

systems work with MVC as an extension of their engineering organizations to

design, install, and support vision system options.

As the vision industry has matured with easier-to-use products, one thing remains

the same - vision projects are inherently complex. The development and deployment

of a vision system requires a team of experienced vision engineers that can avoid

potential problems that arise when combining high technology from multiple domains

(PLC communications, robotics, vision architecture, real world lighting and optics,

motion, human intervention).

MVC works with its clients to provide a thorough evaluation of the application, a

detailed proposal with images, and a complete vision solution per the specifications

and system acceptance criteria. Machine Vision Consulting works with the client as a

partner and provides sound guidance to assure the application is done correctly the

first time.

MVC has developed turn-key solutions based on its machine vision experience and

expertise. One of these solutions is verifying the correctness and legibility of codes

that are printed onto the ends of cans, the bottoms of aerosol containers and bottles,

packages, labels, or lids. The CodeSureTM solution is discussed in this paper.

Introduction to Code Verification

The focus of this white paper is on using machine vision for the verification and

quality inspection of alphanumeric codes that have been printed onto a can end, the

bottom of an aerosol container, a bottle bottom, a flat container, or a jar lid. By

verification, the focus is that the vision system will automatically confirm that the

expected code has been applied to the container and is legible. The code may

contain a lot code identifier, an expiration date, a plant code, or some other

important production information. Any container that does not contain the expected

code information or that is determined to contain illegible print will be kicked off the

production line.

The printing method often used to create the code is a Continuous Inkjet Printer.

While this method generally produces an acceptable code visually, the printing

process has some inherent variations that make the application of automated code

verification more challenging.


Why Is Code Verification Important?

Code verification facilitates the execution of a product recall. If the printed code is

incorrect, missing, or illegible, the producer has no way to verify the pedigree of the

product, nor does the consumer. All traceability to a lot code and expiration date is

lost once that product leaves the printer with an illegible, incorrect, or missing code.

The lack of codes has caused some producers to be forced to recall everything made

because un-coded product has made it to the consumer.

Code verification is critical for bright-stocking. Unlabeled, but coded, generic product

is sent to a warehouse for storage until a customer requests that particular product.

The product is then brought into a labeler and code verification is required to assure

the consumer that the appropriate product container receives the appropriate label.

This is especially important for contract packagers. Cans are blind items and the

printed code provides the only way to know what is supposed to be inside. Vials may

contain a clear liquid that cannot be identified by looking at it. Bottles with tamper

seals all look the same in their unlabeled form except for the printed codes that may

be on the bottom.

Code verification is important to consumer safety. In that cans are blind items,

mixing up a soy product with a milk product or mixing clam chowder with chicken

soup can lead to serious consequences to the consumer and to the packager. If

drugs are involved, correct product identification becomes critical and contributes to

E-Pedigree conformance and patient safety.

In addition to characters that are acceptably distorted, incorrect characters may be

present. If an incorrect code is being printed and the printing error is not detected

quickly, the loss can be substantial, perhaps an hour or two of production that must

be destroyed because its history cannot be verified. Once a product is marked

incorrectly, it generally has to be destroyed, as its pedigree can no longer be

guaranteed.

Given these issues, the machine vision software that is used to verify these codes

becomes the critical component of a code verification solution. If a character is so

distorted that it is unreadable, the code needs to be rejected. However, an

acceptable level of character distortion must be tolerated by an automated

verification system to minimize false rejects and maintain the yield of the line.

How And Why Do Printed Codes Vary In Quality?

It is normal for many on-the-fly code printers to suffer random variations in the

appearance of their printed characters; there are many process setup variables, such

as line speed variations, marking head misalignment, package shape, nozzle

distance, and other factors. Thus, the yield of the vision system used to verify the

accuracy of these critical printed codes is a key contributor to the yield of the line –

how often you get the correct answer, whether it’s Pass or Fail, even when the

individual characters or the entire string varies in appearance because of processes

one cannot always control.


Appearance variations are based on the moment-to-moment fluctuations in the

quality of the ink jet-printed codes. This quality fluctuation is often a result of the

human interaction with the print head set-up, especially after cleaning or servicing.

The print head must be installed straight or slanted print may result. The distance

between the print head and the object must be consistent between runs or the size

of the characters can change. If the container is rotating during printing, the printed

code will reflect that in its appearance, creating bowing. In the worst case, the print

head is clogged or is out of ink, creating a situation of “no code” or illegible codes.

Skew Bow Perspective

As character formation variations are brought into the application, the challenge is to

interpret what characters have been printed despite acceptable variations such as

bowing, skewing, stretching, compressing, or flexing. Truly defective codes must be

rejected, while an automated code verification system must accept codes that may

not look perfect, but are acceptable when the code content is correct and legible.

Dealing With Character Distortion And Rotation

An advanced vision software tool from CognexTM, called OCVMaxTM, forms the

foundation for an Optical Character Verification solution from MVC called CodeSureTM.

CodeSureTM imports the appropriate electronic font file to eliminate the need to have

the operator train the system as to what characters look like. The vision system is

verifying that the expected characters are present, so it understands what the

characters should look like in the image based on the importation of the font file

used by the CIJ to create the printed code.

CodeSureTM can tolerate random character quality and appearance variations that

must be tolerated on the production line in order to keep the line efficiency high.

CodeSureTM can also verify rotated codes, critical when round containers are being

verified. In this case, the codes can often be presented in any theta orientation.


Font and Character Training

With lesser solutions, the characters of the font being used are trained by taking

images of every character under varying conditions and building up a statistical

model of what each character looks like. In an instance where the characters exhibit

moment-to-moment variations in appearance, this image-based font training would

be a never-ending process.

With CodeSureTM, the same electronic font file that the code printer uses is imported

into the CodeSureTM solution. A TrueTypeTM font is an example of an electronic font

file. Most ink-jet printing systems are utilizing an electronic font description file and

CodeSureTM uses the same file to train the shapes of the character models.

Font training involves selecting a font file to import into the vision system, making

the trained characters in the vision system look the same as what the characters

printed should look like. At run time, the CodeSureTM algorithms compensate

automatically for any acceptable variations in the appearance of the characters in the

printed code.

The font file import function contributes to robustness, ease of use by the operator,

and the maintenance of system validation.

CodeSureTM automatically loads the following font file types:

Xymark – Simplex, Simplex A, and Simplex Roman using .vf or .vb files.

Domino – Arial, OCR-A, OCR-B, and Roman using .cst files.

Videojet – 5X7, 7X9, 10X16 using .xcl files.

Markem – 5X5, 5X7, and 10X16 using .ffm files.

MVC will work with the client to allow CodeSureTM to work with other font files as

needed.

Entering The Code String To Be Verified

For safety purposes, MVC recommends that the character string to be verified is

entered manually into CodeSureTM via the included Operator Interface. While it is

sometimes required that the character string be sent automatically by a line

controller to both the printer and to the code verification system at the same time,

this could potentially lead to the wrong code being printed and the wrong code being

deemed acceptably verified by a machine vision solution.

Some double-check needs to be instituted in this case to prevent an incorrect code

from being printed and accepted. For example, this automatic data entry from the

line controller should at least be done in two separate steps, one for the code printer

and one for the CodeSureTM verifier. The codes should then be checked by a

supervisor to be sure each is correct.


Good Character String Candidates

Character strings that can be successfully analyzed with CodeSureTM typically share

most of the following characteristics:

Characteristic Description

Clear Image The image contains sharp character edges.

Good Contrast The image contains a minimum contrast level of 30 grey

levels between the characters and the background.

Print Quality The characters appear with little distortion from their

expected shapes.

Included Font

The characters in the string are composed of a font

installed as part of the CodeSureTM installation and used by

the CIJ printer.

Good Surface

The string appears on a clean flat surface with little or no

qualities that could alter the desired appearance of a

particular character.

The following images contain the characteristics that make them acceptable

candidates for analysis with CodeSureTM:

Flat Package


Can End

Concave Aerosol Can Bottom


Flat Label Printed With UV Ink and Imaged With UV Light

(Printed by Videojet)

Poor Character String Candidates

Character strings that cannot be successfully analyzed with CodeSureTM, or any

automated verification system, typically suffer from one or more of the following

characteristics:

Characteristic Description

Poor Image The acquired image does not appear in

focus or properly illuminated.

Font Quality

The characters appear distorted, either

throughout the entire string or in relation

to each other.

Font Size

Characters must have a minimum area of

20 x 15 pixels and a maximum area of

100 x 80 pixels. Characters in a string

must be of the same size.

Low Contrast

Images must have a minimum contrast

of 30 grey levels between the characters

and the background.

Poor Surface

Qualities of the surface where the string

appears prevent the string from reliably

appearing with sufficient quality.


Insufficient Contrast

The characters in the following image do not show enough contrast:

Label

Unpredictable Surface Area

In the following image, the surface material underneath the character string rotates

randomly during the print application, causing unpredictable character defects:

Plastic Bottle Bottom


Poor Font Quality

In the following images, the characters are too distorted to be verified reliably:


Overview of the Image Formation Process

An image formation module will be placed either over or under the conveyor

depending on the location of the printer. The imaging module contains the video

camera, optics, and lighting needed to create an image of the code. The containers

will be on the conveyor and will be passed through the imaging module. No container

handling or specific orientation of a round container is required. The containers can

touch during code verification.

An example of a top-side imaging module follows. The type of lighting shown is used

to image jar lids and is designed to minimize the appearance of lid geometry and

color background graphics printed on the lid, while making the code visible. The

camera on the top of the light is verifying the codes on the lid. The lower side-

mounted cameras and reflectors are providing label verification, which is discussed in

another MVC document.

Imaging Module Over the Conveyor, Shown Without Covers.

Example Only. Each Application is Different and May Require a

Different Imaging Module and Lighting Design.

Camera

Light

Conveyor


The lighting system is designed to provide a clear image of the jar, can, bottle, or

aerosol container top or bottom and is custom-designed for each application. The

goal of the lighting system is to minimize the appearance of any can ridges,

background graphics, or surface concavity.

A sensor will detect that the container is in position and will trigger the CodeSureTM

system for each container.

The resolution of the camera used will be dependent upon the container speed

required on the conveyor line, the size of the container, the resolution required to

confirm each character, and the variation in code placement on the surface. Cameras

are available from 640 X 480 pixel resolution up to 2448 X 2048 pixel resolution.

A reject mechanism can be mounted on the conveyor after the code is verified, such

that any non-conforming coded containers would be ejected from the line.

Conclusions

The cost of verifying that the correct code has been applied to a container can be

easily outweighed by the cost of a lawsuit or a recall. Safety and allergen prevention

are at the top of the priorities list for many manufacturers. Whether it’s a matter of

life and death or a consumer’s inconvenience, today’s manufacturers are making

sure that their product is accurately coded.

Every application is different and may require a different camera resolution, a

different lighting design, may differ in line speed, may require wash-down capability,

and can vary in many ways.

Additional information on Machine Vision Consulting, Inc. can be found on its web

site, www.machinevc.com. Call Joe Gugliotti at 978-551-4160 or e-mail

[email protected] to initiate a conversation on CodeSureTM.

Some images and descriptions contained herein are from the Cognex Corporation document entitled: “OCVMax Application Guide” and dated June 2007.

About the Author:

Joe Gugliotti is responsible for Sales & Marketing at Machine Vision Consulting and

has been a part of the machine vision industry for 22 years. He spent 10 years with

a leading distributor of cameras, optics, and lighting systems for use in machine

vision applications, working closely with Vision OEM’s, Systems Integrators, and End

Users across the U.S. to evaluate their image formation needs and provide the

appropriate solution. Joe spent the next 10 years as an OEM Account Manager and

Senior Sales Engineer for a leading Machine Vision OEM, gaining exposure to

hundreds of applications across a wide range of industries and using vision

technology ranging from simple sensors to advanced PC-based systems and custom

cutting-edge solutions. In his position at MVC, Joe applies all of this experience to

providing full machine vision solutions and consulting services.

codesure tm printed code verification and inspection ... codesure white paper 4-17-08.pdf ·...

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