The measurement
involves taking images for every stage of the drilling process. The object beam
coming from the sample interferes with the reference beam inside the video
head. The reference beam is phase-shifted (0°, 90°, 180° and 270°) so that four
different images can be taken for the same sample condition. This allows
calculating surface displacements as a phase shift. At least one of these image
sets is required for each sample condition so that one set from before drilling
and one after each drilling increment can be compared. Displacements are
measured in one specific direction, the sensitivity direction (Figure 5.8),
which depends on illumination and observation directions. The user can choose
these freely to accommodate a variety of measurement conditions. The angles
have to be known for the stress calculation.

The stress calculation
uses information from all pixels in a ring-shaped area around the hole,
bordered by inner and outer integration radius. The area immediately next to
the hole edge does not provide useful information because the drilling process
always disturbs it. The analysis area can be modified in the software. An inner
radius of twice the hole radius and an outer radius four times the hole radius
(ri=2, ro=4) have been found useful for most situations.

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To analyze the images,
the exact hole position and hole size (magnification) need to be identified.
This is achieved with a Define hole image that is acquired during or after the
measurement process

For running the
measurement follow the instruction below:

1. Select the Part
level on the project tree by clicking correct part to open the Info tab (Figure
5.9).

2. Fill the Project
info and Part information text boxes.

3. Select the correct
material from the Material selection box.

4. Select the correct
measurement from the Project tree by clicking.

5. Press the Settings
button and select the Drill tab (Figure 5.10).

6. Set the Backout
distance so that no part of the drill remains visible in the image.

7. Set the wanted
Drilling steps. Drilling steps are material and rotation speed dependent, for
more information see chapter

8. Select the Camera
tab (Figure 5.11).

9. Select the number of
image sets taken at every depth increment (automatic measurement) to the
Exposure count selection box and set delays for the Automating images and
Between exposures.

10. Press the Ok
button.

11. Press the …
button to open the Depths tab (Figure 5.12).

12. Set the Number of
depths and Final depth mm manually or select ready made values from the
Library.

13. Press the Ok
button.

14. Select the
Automatic measurement and press the Start button to start the automatic
measurement or continue with the manual measurement with following
instructions:

a) Press the Start
button

b) Press the Start
drilling button and wait until the drilling is done.

c) Press the Save image
button.

d) Repeat the steps a-c
for reaching the desired final depth.

16. Press the Stop
button.

17. Place the external
light as shown in figure 5.2.

18. Press the Save hole
image.

19. Press the New
analysis button to open the Calculation tab.

20. Adjust the red
analysis area to fit the hole (Figure 5.13).

21. Press the Calculate
button.

22. Press the Save
analysis button.

23. Press the Exit
button.

The measurement is now
ready.

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