The measurementinvolves taking images for every stage of the drilling process.
The object beamcoming from the sample interferes with the reference beam inside the videohead. The reference beam is phase-shifted (0°, 90°, 180° and 270°) so that fourdifferent images can be taken for the same sample condition. This allowscalculating surface displacements as a phase shift. At least one of these imagesets is required for each sample condition so that one set from before drillingand one after each drilling increment can be compared. Displacements aremeasured in one specific direction, the sensitivity direction (Figure 5.
8),which depends on illumination and observation directions. The user can choosethese freely to accommodate a variety of measurement conditions. The angleshave to be known for the stress calculation.The stress calculationuses information from all pixels in a ring-shaped area around the hole,bordered by inner and outer integration radius. The area immediately next tothe hole edge does not provide useful information because the drilling processalways disturbs it. The analysis area can be modified in the software. An innerradius 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.
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 themeasurement processFor running themeasurement follow the instruction below:1. Select the Partlevel on the project tree by clicking correct part to open the Info tab (Figure5.9).2. Fill the Projectinfo and Part information text boxes.
3. Select the correctmaterial from the Material selection box.4.
Select the correctmeasurement from the Project tree by clicking.5. Press the Settingsbutton and select the Drill tab (Figure 5.10).6. Set the Backoutdistance so that no part of the drill remains visible in the image.7. Set the wantedDrilling steps.
Drilling steps are material and rotation speed dependent, formore information see chapter 8. Select the Cameratab (Figure 5.11).9. Select the number ofimage sets taken at every depth increment (automatic measurement) to theExposure count selection box and set delays for the Automating images andBetween exposures.
10. Press the Okbutton.11. Press the .
..button to open the Depths tab (Figure 5.12).12.
Set the Number ofdepths and Final depth mm manually or select ready made values from theLibrary.13. Press the Okbutton.14. Select theAutomatic measurement and press the Start button to start the automaticmeasurement or continue with the manual measurement with followinginstructions:a) Press the Startbuttonb) Press the Startdrilling button and wait until the drilling is done.
c) Press the Save imagebutton.d) Repeat the steps a-cfor reaching the desired final depth.16. Press the Stopbutton.17.
Place the externallight as shown in figure 5.2.18. Press the Save holeimage.19.
Press the Newanalysis button to open the Calculation tab.20. Adjust the redanalysis area to fit the hole (Figure 5.
13).21. Press the Calculatebutton.22. Press the Saveanalysis button.
23. Press the Exitbutton.The measurement is nowready.