Fundamentals of Machine Vision- Lighting

FUNDAMENTALS OF MACHINE VISION- LIGHTING

Part 3 in a Series: Illumination Terms and Techniques

© 2014, Pete Kepf, All Rights Reserved

Pete Kepf, CVPwww.kepf.me


Introduction

Overview: Lighting is critical variable Applications and their lighting schemes

Lighting Lenses Sensors

What do you want your image to look like? Software Part Attributes


What is Machine Vision?

Machine Vision is the use of a computer to acquire visual information and/or extract image information for purposes of data storage or automatic decision making.

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What are some Typical Industrial Applications?

Motion/ Robot Guidance Defect/ Flaw Detection Inspection/ Grading/ Sorting Identification/ Verification Data Acquisition Measurement/ Gauging


What makes a Vision System?

Vision Components

Lens Camera Processor Input/ Output

Peripherals

Lighting Frame/ Enclosure Controls/ Software Part Handling/

Reject/ Sorter


Application Examples

Motion:Front LightingNear IR

Flaw:Front LightingBlue Filter

MeasurementBack LightingVisible

Sort:Front DiffuseVisible

MeasurementStructuredPattern Projector

CountFront LineVisible


Goals

• High S/N• High Contrast• Even Distribution• Repeatable

• Product Variability• Ambient

Conditions


Lighting Effects

Light Source Frequency Brightness Angle “Shape” Duration

Object Surface

Reflectivity Geometry

What do you need the image to look like?


How Light Works

Reflection: Angle of Incidence = Angle of Reflection

Absorption: Frequency Specific

Refraction: Affects angle and Frequency

Scattering: Multi-angle Reflection


How Optics are Affected

Reflectivity: Polish/ CoatingScattering: Dirt/ Scratch

Absorption: Lens MaterialRefraction: Lens Material


How Sensor is Affected

Reflectivity: Polish/ CoatingScattering: Dirt/ Scratch

Absorption: Sensor Material/FilterRefraction: Sensor Material


Lighting for Machine Vision

Back Light Pattern Projector

Line Light

Ring Light

Axial Light

Dome Light


Lighting Characteristics

Frequency/ Wavelength (Color) Polarization Intensity (Brightness) Direction (Soft/ Spectral/

Polarized) Duration (Constant/ Pulse)


Polarization

Filter Source and Camera

Source: www.thermalcamerarentals.com

https://www.google.com/url?sa=i&rct=j&q=&esrc=s&source=images&cd=&cad=rja&uact=8&ved=0CAYQjB0&url=http://www.thermalcamerarentals.com/how-do-infrared-thermal-imaging-cameras-work.html&ei=XZRCVMKKI5GAygTfhIGABA&bvm=bv.77648437,d.aWw&psig=AFQjCNHglS1whv65BoQQh8gIVOcE97y7nQ&ust=1413735615111561


Lighting Source Frequency (Color/ Spectrum)

(Previous: Halogen- Fluorescent- Xenon; Now: LED)

Source: www.thermalcamerarentals.com

Wavelength (nanometers) = 3,000,000 / Color temp (Kelvin).

https://www.google.com/url?sa=i&rct=j&q=&esrc=s&source=images&cd=&cad=rja&uact=8&ved=0CAYQjB0&url=http://www.thermalcamerarentals.com/how-do-infrared-thermal-imaging-cameras-work.html&ei=XZRCVMKKI5GAygTfhIGABA&bvm=bv.77648437,d.aWw&psig=AFQjCNHglS1whv65BoQQh8gIVOcE97y7nQ&ust=1413735615111561


IntensityLumens vs. Lux: 1 lx = 1 lm/m2

Lumen = Light Emitted Total "amount" of visible light in a defined beam or

angle, or emitted from a source. Also depends on its spectrum, via the nominal response of the human eye.

Lux = Area Accounts for the area over which the lumens are

dispersed. 1000 lumens, concentrated into an area of one square meter provides an illuminance of 1000 lux. The same 1000 lumens, spread out over ten square meters, produces a dimmer illuminance of only 100 lux.

Source: Wikipedia

http://en.wikipedia.org/wiki/Lumen_%28unit%29


DirectionSeite: 17

Top (or Front)

Light source and image sensor are on the same side of the part. Diffuse On-axis Dark/ Bright

Field

Back

Light source and image sensor are on opposite sides of the part.• Diffuse• Collimated

Structured

Light source has a known geometry.

• Line• Grid


Front (Spot) LightUses:

• Small Parts• Structured Light


Direction: Top Lighting

Diffuse On-axis Bright/ Dark Field


Bright Field/ Dark Field


Ring Light

Shadow-less illumination

Applications:• specular surface• diffused surface

General-purpose


Line LightApplications• imaging • web• line scanFeatures• adjustable lens• enhanced cooling • low current

consumptionUses• Road surface

inspection• Bottle inspection• Carpet Inspection• Print Inspection


Diffuse Work Envelope Light

Useful for:

• Robot Work Cells

• Top Light Assembly

• Reflective Parts


Diffuse Dome Light (“Cloudy Day Illuminator”)

Uses:• Metal and chromed bearing

surface inspection • CD / DVD assembly

inspection• Package inspection of glossy

plastics and finishes• Inspection of metal stampings

and parts with electrical contacts

• Automotive applications• Medical device packaging and

tray packs• Pharmaceuticals blister form

fill and trim• Cosmetics and makeup

packaging equipment and lines

• Diffused Tube Lights are meant for inspecting elongated parts

• Metal and chromed bearing surface inspection

Image of Sphere


Dual On-Axis Light (DOAL)

Uses:• Sphere inspection for

surface flaws• Ball bearing inspection• CD/DVD label inspection• LCD display inspection• Automotive part

inspection


Off Axis Ring LightUses• Illumination of scratches on reflective surfaces• Ball grid array (BGA) inspection• Water contamination inspection• Bottle Cap inspection• Microscopic stage illumination• Inspect molded epoxy parts to uncover

imperfections such as cracks, bubbles, and structural damage


Direction: Back Lighting

Diffuse CollimatedUses:• Absence/presence of objects• Defect detection in glass/plastic

containers• Object tracking (Fish in

aquarium)• PCB (printed circuit board)

board assembly through-hole lead detection

• Web inspection (pin-holes in web)

• Bottle cap detection• Bolt/Bolt thread inspection• Glass Sheet defect detection• Sub-pixel dimensional

inspection


Back Light

Useful for:

• Gauging• Measureme

nt


Direction: StructuredSeite: 29

Line Grid


Pattern Projector

Useful for:

• Structured Light

• Height Derivation


Duration Constant

Non-Moving Parts Use Care with Ambient Typically large area No Controller

> 10 microseconds Line Speeds up to 1200 parts/ minute LED with Controller Configurable Form Factor

> 100 nanoseconds Part speeds up to 3500 feet/ second LED with Controller Configurable Form Factor


Summary Goals:

High S/N High Contrast Even Distribution Repeatable

Variables Frequency Brightness Angle “Shape” Duration

Other Components Lens Camera Sensor

Some Lighting Terms Top/ Front Back Structured On-axis Diffuse

Lighting “W”

Fundamentals of Machine Vision- Lighting

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