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

Open the PDF directly: View PDF PDF.
Page Count: 40

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
Many Machine Readable Codes for AutoID
1D Bar Codes
“2D Bar Codes”
Best code for Direct Part Marking
Types of Barcodes Typology of Symbologies
Stacked 1D codes
and true 2D codes
GS1 DataBar
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
How Typical Barcodes Work
Variable shapes that encode information
Typical codes have
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
Create a scan reflectance
Detect threshold crossings
Create a space/bar List
Pass to a decoder
Essentially an analog process
2D Code Construction - Data Matrix
4 Physical Components
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
Reed-Solomon algorithm for error
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
1D Codes
Simple readers (low cost)
Large infrastructure in commerce
Well understood marking methods
High read rates
Limited content
Readers can not read 2D codes
Requires high contrast marking
Not suitable for Direct Part Marking
Analog reading can produce error
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
Key Code Properties
Narrow Element Width
The nominal width of the narrowest bars in the code
Other terms commonly used for narrow bar width:
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
Specified in “Mil. = 0.001” (primarily in the US) or millimeters
Essential for code specification overall size by itself does not mean much
Typical Laser Code Readers
Hand held
Tunnel Scanners
Laser Reader Basics
How it works
Drags a laser dot across
the code
Digitizes reflectance
Creates a scan
reflectance profile
Passes to decoder
Laser Bar Code Reading - Critical Parameters
Depth of Field vs X size vs Scan Width
Speed (read per second)
Scan Width
Depth of Field
Focal Point
Typical Imaging Reader
• Mini’s
Smart Cameras
Discrete Cameras
Image stretching
optics for 1D codes
Imager Code Reading - Critical Parameters
Resolution and FOV Calculations
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
1D / 2D
Black on White
White on Black
Low Contrast
GS1 Check
Marking Methods
Common Direct Part Marking Methods
Direct Part Marking
Ink Jet*
Dot Peen*
Label Printing
Flexographic (Offset Printing)
Ink Jet (Thermal or Drop on Demand)*
Thermal Transfer (Print and Apply)*
Good Practice
*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
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:
441 Pages of good information………..
The Quality Question What Is The Answer?
Incorrect Text Format or
Loss of Identity
or Traceability
Pain and Problems
Upset or
Unreadable Codes…
Process Downtime
Verification Of 1D And 2D Codes
Verification (also called Grading) is a Measurement
its purpose is to:
Predict Readability Trading partners, etc.
Monitor Marking System Simple SPC
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?
Without verification, some “bad”
parts escape into the process
With verification, we prevent bad codes
from ever being made
Trust but Verify!
Just checking that the code can be read is not good
enough. It must be read with an adequate margin
A -Because all marking/printing systems degrade over time and the code never gets better
Without Standards There Is Chaos
ISO 15416
1D codes
ISO 15415
Printed 2D codes
-1-2006/ISO 29158
Direct Part Marks
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.
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
1D Verification - Imaging and Scanning
Result is 10
1D Code Grading Process
Grading Process
Calculate number grades for 9 different measurement
on each reflectance profile (9 numbers on 10 scans)
Reference Decode
Minimum Reflectance
Minimum Edge Contrast
• …….
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
Mark or part surface
Very low or inconsistent
mark contrast
Quiet Zone Violation
Off Line Verification Systems for 1D codes
Off Line Systems
Verification System
Verification System
Verification System
Provide Grade and Diagnostic Information
In-Line Verification Systems
Verification Systems for 2D codes
Off Line Systems
On Line Systems
Desktop Verification System Handheld Verification System
Portable 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
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 structured
Data is not structured properly to the
selected GS1 Application standards.
New Things (the TLAs)
What is a TLA?
Market Wide Initiatives
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

Navigation menu