How to startpage 1

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

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

How to startpage 8 The ideal inspection system

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

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

How to startpage 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 for minimise lens distortion and perspective

How to startpage 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 centric Lens

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

How to startpage 16 Grey scale pictures Original Greyscale Pixel grid

How to startpage 17 Pixel resolution 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

How to startpage 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 lines in stead of two points

How to startpage 19 To big object Select a camera with higher resolution Use two cameras calibrated together Use an array of cameras or Use Robot Vision –The robot moves the object in different positions 50 cm Camera 1 Camera 2 Camera Array

How to startpage 20 Multi camera example

How to startpage 21 Camera in perspective Advanced four point calibration for correction of perspective Camera

How to startpage 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 startpage 23 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 Camera Moving object Speed: 6 m/min 100 mm/sec 0,1 mm/ms Required pixel resolution: 0,1 mm

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

How to startpage 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 startpage 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 startpage 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 startpage 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