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Industrial vision system components:Industrial vision system components:

Feedback

Image analysis

Optics and camera

Digitalisation

Illumination

Object

Data

Industrial Vision: illuminationIndustrial Vision: illumination

2001-04-11 2Industrial Vision: Types of illuminationIndustrial Vision: Types of illumination

Directional illuminationDirectional illumination: : light falls from one direction on the objectlight falls from one direction on the object• Two reflections: specular (like on a mirror) and lambertian (diffuse), depending Two reflections: specular (like on a mirror) and lambertian (diffuse), depending

on the object surface on the object surface • Example: crack detectionExample: crack detection

““Bright field”Bright field”: light seems to come from the camera.: light seems to come from the camera.• The reflected light contains the information.The reflected light contains the information.

““Backlight”:Backlight”: light comes from behind the objectlight comes from behind the object• By preference we use a telecentric light beam.By preference we use a telecentric light beam.• There is no reflection toward the cameraThere is no reflection toward the camera• This illumination produces sharp contoursThis illumination produces sharp contours• The shadow gives information on the dimensionsThe shadow gives information on the dimensions• Backlight is ideal to “binarise” the objectBacklight is ideal to “binarise” the object• Example: bottles passing by on a conveyer belt, in front of a red lightplaneExample: bottles passing by on a conveyer belt, in front of a red lightplane

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BinarisesBacklightBright field

No shadows

Semi-mirror

2001-04-11 4Industrial Vision: Types of illuminationIndustrial Vision: Types of illumination

Diffuse illumination:Diffuse illumination:

““clouded skyclouded sky”: light falls from many directions on the object”: light falls from many directions on the object• All parts of the object are equally illuminatedAll parts of the object are equally illuminated

““dark fielddark field” : light falls from the sides ” : light falls from the sides

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Dark fieldEnhances edges

Clouded sky

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• Try to find the optical properties of the objectTry to find the optical properties of the object• Select the illumination that shows the object the bestSelect the illumination that shows the object the best• Measure the dimensions of the object beforehandMeasure the dimensions of the object beforehand• Define the required resolutionDefine the required resolution• Select the sensor that meets your resolutionSelect the sensor that meets your resolution

A bad image never give good resultsA bad image never give good results

2001-04-11 7Optical crack detectionOptical crack detection

Light polarisation:Light polarisation:

LinearLinear EllipticalElliptical

2001-04-11 8Optical crack detectionOptical crack detection

Polarised light:Polarised light:•Diffuse reflection is not polarisedDiffuse reflection is not polarised•Specular reflection keeps the polarisationSpecular reflection keeps the polarisation

Brewster angle:Brewster angle:

•Plastic has a brewster angle of about 60 degrees: parallel Plastic has a brewster angle of about 60 degrees: parallel polarisation is not reflected.polarisation is not reflected.

•Metal has almost no Brewster angleMetal has almost no Brewster angle

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IlluminationIllumination

• Choices:Choices:• Light distribution Light distribution • Light position(s)Light position(s)• PolarizationPolarization• Flash / ContinuousFlash / Continuous• Color (spectrum)Color (spectrum)

• Artefacts:Artefacts:• ShadowsShadows• ReflectionsReflections• Non-uniform illuminationNon-uniform illumination

Highlight important featuresHighlight important features