1. 2001-04-11 1 Industrial vision system components: Feedback Image analysis Optics and camera Digitalisation Illumination Object Data Industrial Vision: illumination

2. 2001-04-11 2 Industrial Vision: Types of illumination Directional illumination: light falls from one direction on the object Two reflections: specular (like on a mirror) and lambertian (diffuse), depending on the object surface Two reflections: specular (like on a mirror) and lambertian (diffuse), depending on the object surface Example: crack detection Example: crack detection “Bright field”: light seems to come from the camera. The reflected light contains the information. The reflected light contains the information. “Backlight”: light 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 camera There is no reflection toward the camera This illumination produces sharp contours This illumination produces sharp contours The shadow gives information on the dimensions The shadow gives information on the dimensions Backlight is ideal to “binarise” the object Backlight is ideal to “binarise” the object Example: bottles passing by on a conveyer belt, in front of a red lightplane Example: bottles passing by on a conveyer belt, in front of a red lightplane

3. 2001-04-11 3 Binarises BacklightBright field No shadows Semi-mirror

4. 2001-04-11 4 Industrial Vision: Types of illumination Diffuse illumination: “clouded sky”: light falls from many directions on the object All parts of the object are equally illuminated All parts of the object are equally illuminated “dark field” : light falls from the sides

5. 2001-04-11 5 Dark field Enhances edges Clouded sky

6. 2001-04-11 6 Try to find the optical properties of the object Try to find the optical properties of the object Select the illumination that shows the object the best Select the illumination that shows the object the best Measure the dimensions of the object beforehand Measure the dimensions of the object beforehand Define the required resolution Define the required resolution Select the sensor that meets your resolution Select the sensor that meets your resolution A bad image never give good results

7. 2001-04-11 7 Optical crack detection Light polarisation: Linear Elliptical

8. 2001-04-11 8 Optical crack detection Polarised light: Diffuse reflection is not polarisedDiffuse reflection is not polarised Specular reflection keeps the polarisationSpecular reflection keeps the polarisation Brewster angle: Plastic has a brewster angle of about 60 degrees: parallel polarisation is not reflected.Plastic has a brewster angle of about 60 degrees: parallel polarisation is not reflected. Metal has almost no Brewster angleMetal has almost no Brewster angle

9. 2001-04-11 9 Illumination Choices: Choices: Light distribution Light distribution Light position(s) Light position(s) Polarization Polarization Flash / Continuous Flash / Continuous Color (spectrum) Color (spectrum) Artefacts: Artefacts: Shadows Shadows Reflections Reflections Non-uniform illumination Non-uniform illumination Highlight important features