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How to start

How to start. How to specify the task How to get a good image. How to specify the inspection task. Expectations How to specify the requirements Control and absolute measurements High yield and/or zero faults. Too high expectations?. Focus on key issues – the basis for the investment

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How to start

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  1. How to start

  2. How to start How to specify the task How to get a good image

  3. How to specify the inspection task • Expectations • How to specify the requirements • Control and absolute measurements • High yield and/or zero faults How to start

  4. Too high expectations? • Focus on key issues – the basis for the investment • Don’t include all “nice to have” inspections in the beginning • It is easy to make a system so complex that it never will work according to your expectations • “Keep it simple” • Implement “nice to have” issues over time and after acceptance of the initial system How to start

  5. How to set the requirements • A vision system perform measurements • Dimensions, form, area, angles • Requirements must be a figure or a set of figures with tolerances • Define the measurement procedures How to start

  6. Tolerance and Accuracy • Tolerances: • The specified max and min limits for the measurement • Used as inspection criteria (Pass, Fault) • Accuracy: • The uncertainty of the measurement performed by the inspection system How to start

  7. Absolute measurements The result is absolute correct within the measurement accuracy Must be verified by alternative methods Require complex calibration Measurement accuracy1/10 of tolerance Time consuming Control Relative measurements (compare with one or a set of master objects) Standard deviation (Repeatability) within measurement accuracy Measurement accuracy1/3 – 1/5 of tolerances Most vision systems and the subject for this lecture Control or Absolute Measurements How to start

  8. The ideal inspection system How to start

  9. The real life At Customers Site Operation Operation Finished Products No. 1 No. N Station Station No. 1 No. N Y ppm X(N) ppm X(1) ppm Defect Parts Defect Parts Defect Parts + + + Z(N) ppm Z(1) ppm + A(1) ppm OK Parts OK Parts A(1) ppm Parts due to Parts due to Inspection Inspection Failed Failed Inspection Conditions: Defect,OK , Inspection Failed How to start

  10. Yield problems • Yield often drop due to: • Larger variation in the products than expected • Varying contrast due uncontrolled light • Production working close to the limits How to start

  11. How to get a good image • Camera – sufficient resolution and quality • Lens – according to distance to and size of object • Light – sufficient contrast to see the details • External light protection – secure constant light and contrast How to start

  12. Field of View (FOW)for an area camera Y mm A Line scanning overthe area - Field of View (FOW) X mm The optical system • Camera • Technology:Digital using CCD chips • Lens • Adapted to the individual applications • Camera types • Area • Line scan(high speedapplications) How to start

  13. Impact of the lens • Gives the FOW with a given distance between object and camera • Lens distortion and perspective Camera Lens Distance Grid used forminimiselens distortionand perspective How to start

  14. Very high precision gauging • With a normal lens perspective and shadows may cause it impossible to measure with required accuracy • With a Tele centric lens this problem is minimised • High cost lens, must be bigger than the object Camera Tele centricLens How to start

  15. Field of View (FOW) Pixels in Y direction Piksels in X direction How to start

  16. Pixel grid Greyscale Original Grey scale pictures How to start

  17. VGA Camera 640 x 480 pixels FOV: 5mm x 5mm Resolution ca. 0,01mm FOV: 50mm x 50 mm Resolution ca. 0,1mm FOV: 500mm x 500mm Resolution ca. 1 mm XGA Res. Camera 1024 x 768 pixels FOW: 5mm x 5mm Resolution ca. 0,005mm FOW: 50mm x 50 mm Resolution ca. 0,05mm FOW: 500mm x 500mm Resolution ca. 0,5 mm Pixel resolution How to start

  18. How to select camera • Pixel resolution • Requirement are set by the size of object and measurement tolerances • In many situation we can measure in the sub pixel range • Quality • Normally means the ability to separate greyscale values between individual pixels Measure distance between two linesin stead of two points How to start

  19. Camera 1 Camera 2 50 cm CameraArray To big object • Select a camera with higher resolution • Use two cameras calibrated together • Use an array of camerasor • Use Robot Vision • The robot moves the object in different positions How to start

  20. Multi camera example How to start

  21. Camera Camera in perspective • Advanced four point calibration for correction of perspective How to start

  22. The purpose of lighting • To illuminate the object and highlight contrasts of details • To secure constant light environment, 24 hour a day, 360 days a year How to start

  23. Camera Required pixelresolution: 0,1 mm Moving object Speed: 6 m/min 100 mm/sec 0,1 mm/ms Moving object during inspection • Shutter time must be adjusted to match speed and resolution requirements • In the example a shutter time of max 0,1 ms is required • Shorter shutter time require more light intensity How to start

  24. Front light Camera Light source Light source • Direct light • Experiment with number of lamps and light angle • Diffuse light • Must be used when reflections is a problem • Gives no shadow Lightangle Camera Light source Light source How to start

  25. Special front light • Ring light • For circular object • Cloudy day • On Axis • To avoid shadows in holes • Fibre optics • For small objects and very light intensive applications How to start

  26. Back light • Create a silhouette of the object • Ideal for inspecting holes, edges, measuring areas • May be difficult to implement in a production line Camera Light source How to start

  27. Protection from external light • External light is not suitable as illumination for optical inspection system • All system should be protected against sunlight and external light How to start

  28. Final comments • The key to get a good image is the combination of camera(s) and light • Spend time to find the best solution • The final solution is often different from your starting point • Sometimes an optical inspections can not be done according to your initial requirements • Revise requirements • Or better find it out early than after weeks of efforts after system implementation How to start

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