Presentation Automate BARCODE AND SYMBOLOGY BASICS FOR MACHINE VISION

: Microscan Automate Barcode And Symbology Basics For Machine Vision Automate_BARCODE AND SYMBOLOGY BASICS FOR MACHINE VISION

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Barcodes and Symbology
Basics for Machine Vision
Jonathan Ludlow
Machine Vision Promoter
Barbie LaBine
Training Coordinator
Microscan Systems Inc.

Introduction, Topics, and Goals
• Who I am
• Introduce myself

• Who are you?
• Show of hands in audience – MV people, Integrators, Bar Code users

• Topics we will cover
• Definition, Reading, Marking/Coding, System Design, and Quality Control

• What we will achieve
• Awareness of issues and constraints for bar code marking, reading and
system design
• Understand that code reading is a machine vision topic.

What are Barcodes?
• Optical, machine readable, representation
of data.
• It all started with rail cars – then moved on
to chewing gum and everything else.
• Typically contain a number
• Index to a look-up
• Identification number

• Can contain text
• There are many types…
• Called symbologies

Types of Barcodes – Typology of Symbologies
Many Machine Readable Codes for AutoID

1D Bar Codes

“2D Bar Codes”
GS1 DataBar

Stacked 1D codes
and true 2D codes

Best code for Direct Part Marking

Who Uses Barcodes?

Why Barcodes Are Important
• Provide an efficient method of product or item identification
• Revolutionized retail since 1974

• Checkout, stock management, asset tracking

• Essential for logistics

• Package tracking, baggage handling….

• Allow item level track and trace and identification

• ID documents, medical samples, industrial WIP tracking, life cycle management

• Powerful marketing tool
• All those QR codes

• Support showrooming
• You have all done this

• Reliable Coding and Reading Systems are Mission Critical to Most
Enterprises

How Typical Barcodes Work
• Variable shapes that encode information
• Typical codes have
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•
•
•

Bars
Spaces
Quiet Zones
A few symbologies encode with height

• Varying widths of bars and spaces encode information
• Example: UPC Code bars and spaces can be 1 to 4 units wide
• UPC Code encodes each character in 7 units of bars and spaces

Encoding Examples
Examples of encoding data

GS1-Code 128

ITF

1D Code Reading
• Scan with a laser and
measure reflected signal
• Or image with a imaging
sensor
• Create a scan reflectance
profile
• Detect threshold crossings
• Create a space/bar List
• Pass to a decoder
• Essentially an analog process

2D Code Construction - Data Matrix
• 4 Physical Components
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•
•
•

Solid border
Broken border/clock pattern
Data storage
Quiet zone

• Consists of evenly spaced “cells” (squares or dots)
• Each “cell” represents either a “0” or a “1”
• Binary – therefore “Digital” in the common tongue.

Data Matrix has Error Correction
•

Built in error correction allows the code to
be read with ~20% damage making it
the ideal symbology for DPM
applications.

• Reed-Solomon algorithm for error
correction
• Origins in NASA Deep Space Network

• Voyager 1 still phoning home from >
2.1 x 1010 km (138 AU) – at 160 bps

Pros and Cons of Different Codes
• Making Good Choices
Pros

Cons

1D Codes

•
•
•
•

Simple readers (low cost)
Large infrastructure in commerce
Well understood marking methods
High read rates

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2D Codes

•
•
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•
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Compact codes
High potential code content
Includes error correction
Omni directional reading
Imaging readers can decode 1D codes
High end readers can do OCR etc.
Read at low contrast
Potential for Direct Part Marking

• Requires imaging reader
• Require task specific lighting
• Requires slightly higher resolution
printing and imaging
• Marking/printing requires more care

Limited content
Unidirectional
Readers can not read 2D codes
Requires high contrast marking
Not suitable for Direct Part Marking
Analog reading can produce error

Key Code Properties

Narrow Element Width

The nominal width of the narrowest bars in the code
Other terms commonly used for narrow bar width:
X-dimension
Mil size
Module width

Cell Size

The nominal width of the individual black or white cell
Other terms commonly used for cell size:
Mil size
Module size
Z-Dimension

Essential for code specification – overall size by itself does not mean much
Specified in “Mil. = 0.001” (primarily in the US) or millimeters

Typical Laser Code Readers
• Hand held

• Embedded

• Tunnel Scanners

Laser Reader Basics
• How it works
• Drags a laser dot across
the code
• Digitizes reflectance
signal
• Creates a scan
reflectance profile
• Passes to decoder

Laser Bar Code Reading - Critical Parameters
• Depth of Field vs X size vs Scan Width
Depth of Field

Scan Width

Focal Point

• Speed (read per second)
• Connectivity

Typical Imaging Reader
• Embedded
• Handheld

• Mini’s
• Smart Cameras
• Discrete Cameras

Image stretching
optics for 1D codes

Imager Code Reading - Critical Parameters
• Resolution and FOV Calculations
• Inputs
• Required Pixels/Element (Module Size)
• Overall Code Size
• Camera Resolution

• Suggested Minimums
• 2D codes - 4 pixels per element
• 1D codes – 2 pixels per element

• Sample calculation 2D code
•
•
•
•

Element size = 0.020”, Code Size = 0.40” (20 by 20 code)
Therefore maximum pixel size = 0.005” (0.020/4)
Code size in pixels is 80 by 80
Now you can work out how well the part needs to be fixtured at a given resolution

Decoding Multiple Codes With An Imager
•
•
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1D / 2D
Black on White
White on Black
Mirrored
Low Contrast
GS1 Check
DPM
Multi-code

Marking Methods
Label Printing

Direct Part Marking

Flexographic (Offset Printing)

Laser*

Common Direct Part Marking Methods

Ink Jet (Thermal or Drop on Demand)*
Thermal Transfer (Print and Apply)*

Ink Jet*

Laser*
Good Practice
•
•
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*Methods than can produce serialized labels
Do not print red bar codes!
Match the DPI to the desired X dimension
Allow for ink bleed
Use ladder orientation on curved surfaces
Use rectangular Data Matrix codes when required

Dot Peen*

How To Encode Data So It Makes Sense
• It you know the code is a UPC then OK

• But what if you read a label and see this?

• In this case it is GS1 syntax. The embedded “tags” identify the data
fields. Use them to extract meaningful data
• (01) = Product ID
• (17) = Expiration Date
• (10) = Lot Number

GS1 Symbol and Format Definition
 GS1 = Global Standard 1. Formerly UPC and EAN
 GS1 symbols contain data fields with defined applications identifiers (AI) that identify the
purpose of the data field and define the content format.
 Commonly used AIs:

http://www.gs1.org/barcodes-epcrfid-idkeys/gs1-general-specifications
441 Pages of good information………..

The Quality Question – What Is The Answer?
Loss of Identity
or Traceability

Pain and Problems

Process Downtime

Unreadable Codes…
Upset or
Confused
Customers

Vendor
Compliance
Penalties
Incorrect Text Format or
Content

Regulatory
Issues

Verification Of 1D And 2D Codes
• Verification (also called Grading) is a Measurement
its purpose is to:
• Predict Readability – Trading partners, etc.
• and/or

• Monitor Marking System – Simple SPC
• and/or

• Confirm Conformance – Government, or Customer Specifications etc.
Confirming that a code reads at point of marking is not verification.
Verification is the process of Grading your symbol to a defined specification.

Q - Why Verify 1D And 2D Codes?
A - Because all marking/printing systems degrade over time and the code never gets better
Trust but Verify!

Just checking that the code can be read is not good
enough. It must be read with an adequate margin
Without verification, some “bad”
parts escape into the process

With verification, we prevent bad codes
from ever being made

Without Standards There Is Chaos
ISO 15416
1D codes

ISO 15415
Printed 2D codes

AIM DPM -1-2006/ISO 29158
Direct Part Marks

Standards specify =
•Lighting wavelength and geometry
•Camera geometry
•Reflectance calibration
•Image processing
•Scan profile(1D) or grid (2D) determination
•Profile or grid analysis steps
•Overall grade determination
•Reporting scale and report content

Reflectance Calibration Standard

GS1 Resources
GS1 General Specification
•441 pages of compelling reading

•Essentially incorporated by reference in GS1 rules
•Basis of many Application Standards
•A lot of good information all in one place
•Marking methods, symbol size, symbol location,
quality standards etc.

1D Verification - Imaging and Scanning
•Image generation
•Image at 90 to the code
•Light at 45 degrees
•Prefer red (monochrome) light
•At least 8 pixels per thin line
•Scan profile generation
•Create reflectance (brightness) profiles with a synthetic aperture of
(for instance) 50% of line width
•Scan repeats and pattern
•10 scans evenly spaced
Result is 10
scan
profiles

1D Code Grading Process

Grading Process

• Calculate number grades for 9 different measurement
on each reflectance profile (9 numbers on 10 scans)
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•
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Reference Decode
Contrast
Minimum Reflectance
Minimum Edge Contrast
Modulation
Decodability
…….

Score each scan with the worst score (10 numbers)
Average the worst score numbers (1 number)
This is the symbol grade (4 – good, 0 = really bad/fail)
Standard uses number grades
Translate to letter grades

1D Code Defects

Consistency of light and dark bars

2D Mark Quality Problems
 Improper or
inconsistent mark
dot/cell size
 Improper or
inconsistent mark
dot/cell location

 Improper overall mark
geometry
 Mark or part surface
damage
 Very low or inconsistent
mark contrast
 Quiet Zone Violation

Offset
cell

Off Line Verification Systems for 1D codes
• Off Line Systems

Desktop
Verification System

Portable
Verification System

Provide Grade and Diagnostic Information

Handheld
Verification System

In-Line Verification Systems

Verification Systems for 2D codes
• Off Line Systems

Desktop Verification System

• On Line Systems

Portable Verification System

Handheld Verification System

Print Quality Verification
• Defects in the print quality of the symbol

Scan Refelectance profile
for Linear symbols

2D Analysis for 2D symbols

Verification ≠ Validation
• Verification = Measuring the quality of the code to predict
readability
• Validation = Checking the format and content of a code
• Verification = how neat and legible was the writing

• Validation = check on grammar and/or content

Data Structure Analysis – Format Validation
Checks the data structure based on the specified Application Standard.
The example below is the GS1 data syntax.
Error flagged on right: SSCC is required to contain 18 characters.

Data is not structured properly to the
selected GS1 Application standards.
Data is structured
Correctly

New Things (the TLAs)
• What is a TLA? –
• CIA, NSA,NRO,DHS….?
• Market Wide Initiatives
•
•
•
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GS1 – Global Standard 1
UDI - Unique Device Identifier (Medical Devices)
UID - Unique ID (Military Equipment)
SNI - Standard Numerical Identifiers (Drugs)
PTI - Produce Traceability Initiative (Farm Produce)
……..

Summary And Take Aways
• Code reading is mission critical to many enterprises

• Code reading is a machine vision application
• You have to think about lighting, imaging, resolution and signal
• Code quality is a key factor in successful system design

• Check quality at the point of marking
• Reading is not verifying

That’s All Folks
Jonathan Ludlow
Machine Vision Promoter

Microscan Systems
700 SW 39th St
Renton WA 98057
Telephone: 425-226-5700
Email: helpdesk@Microscan.com
www.microscan.com



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