Presentation Automate BARCODE AND SYMBOLOGY BASICS FOR MACHINE VISION
2017-04-24
: 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
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
•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
•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
•
Limited content
•
Unidirectional
•
Readers can not read 2D codes
•
Requires high contrast marking
•
Not suitable for Direct Part Marking
•
Analog reading can produce error
2D
Codes
•
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:
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
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
•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
•Speed (read per second)
•Connectivity
Scan Width
Depth of Field
Focal Point
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
•1D / 2D
•Black on White
•White on Black
•Mirrored
•Low Contrast
•GS1 Check
•DPM
•Multi-code
Marking Methods
Common Direct Part Marking Methods
Direct Part Marking
Laser*
Ink Jet*
Dot Peen*
Label Printing
Flexographic (Offset Printing)
Ink Jet (Thermal or Drop on Demand)*
Thermal Transfer (Print and Apply)*
Laser*
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:
http://www.gs1.org/barcodes-epcrfid-id-
keys/gs1-general-specifications
441 Pages of good information………..
The Quality Question –What Is The Answer?
Incorrect Text Format or
Content
Regulatory
Issues
Loss of Identity
or Traceability
Pain and Problems
Upset or
Confused
Customers
Unreadable Codes…
Process Downtime
Vendor
Compliance
Penalties
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?
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
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.
•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
scan
profiles
1D Code Grading Process
Grading Process
•Calculate number grades for 9 different measurement
on each reflectance profile (9 numbers on 10 scans)
•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
Handheld
Verification System
Portable
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
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 structured
Correctly
Data is not structured properly to the
selected GS1 Application standards.
New Things (the TLAs)
•What is a TLA? –
•CIA, NSA,NRO,DHS….?
•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
Email: helpdesk@Microscan.com
www.microscan.com
