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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

How to start

How to specify the task

How to get a good image


How to specify the inspection task
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


Too high expectations
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


How to set the requirements
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


Tolerance and accuracy
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


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 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



The real life
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


Yield problems
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


How to get a good image
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


The optical system

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


Impact of the lens
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


Very high precision gauging
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


Field of view fow
Field of View (FOW)

Pixels in Y direction

Piksels in X direction

How to start


Grey scale pictures

Pixel grid

Greyscale

Original

Grey scale pictures

How to start


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

Pixel resolution

How to start


How to select camera
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


To big object

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


Multi camera example
Multi camera example

How to start


Camera in perspective

Camera

Camera in perspective

  • Advanced four point calibration for correction of perspective

How to start


The purpose of lighting
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


Moving object during inspection

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


Front light
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


Special front light
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


Back light
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


Protection from external light
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


Final comments
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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