1. VELO Metrology CERN Metrology Lab (EST/MF)
Olivetti CNC (600x900x1600 mm3) on air-cushion with granite base, ± 3um precision over full volume
Optical and touching head
Measure first downstream sides of all modules, then turn head and measure upstream sides.
Detector half will be laid down in same position as in the VELO
~ 750
~ 1100

2. Metrology Overview
VELO will be surveyed as two completely mounted halves
Designed to fit inside CNC without changing mechanics, or frame. Only repeater crates will be dismounted
Measurement head enters through holes in the frame, designed to protect modules
5 fiducials per sensor, plus 4 reference chamfers on base plate
Base plate support must be identical to final experiment
No control over temperature or humidity
Survey is risky (and expensive) – strong motivation to fully mount one half in case of late module delivery

3. chamfers

4. Metrology: procedure protection frame
Measurement head enters through holes in frame cover between modules, with approx 5 mm clearance
Always two people working on detector, one from metrology, one physicist (watching)
modules
protection
collar

5. Metrology: Top view VELO half laid down by crane
open question: transport from Assembly lab to metrology (200 m) done with final transport as an exercise? Overkill?

6. Metrology: Optical head
200x objective with 12 mm focal distance
Microscope with reticules adapted to our fiducial marks, field of view ~0.5 mm, maximum diameter 25 mm
CCD camera
(supplier: AUBERT)
Delivery date: end September

7. Metrology: Schedule standard magnification (x50)
February 2005 – test measurements with VELO telescope
standard magnification (x50)
high magnification (x 160)
Analysis by Tomas Lastovicka showed that we achieved a precision of 1.4 micron (2x better than quoted precision)
Resulted in improved analysis

8. Metrology: Schedule
May 2005, first check of new optics. Plan to measure sensor fiducials together with strips and deduce measurement precision
Used 7 mechanical sensors supplied by Liverpool
25µm (measured 22µm)
50µm
overetched
Used as preparation for final metrology by taking detailed photos of sensor
21 reference points identified for R and Phi sensors
(NB unfortunately we only had mechanicals so some info missing)

9. Vue generale du silicium (strip droit) Didier Glaude
Circonference interieure
Circonference exterieure P3 P2 P4 Y+
P1/P1A P5 X+
ATTENTION LES VUES QUI SUIVENT SONT INVERSEES PAR RAPPORT A LA REALITE

10. Centre des 4 trous repere 2040 (strip droit)
P1/P1A

11. Centre des 4 trous repere 1540 (strip droit)

12. FAILURE! Metrology: schedule Result of survey:
proposed x50 magnification not sufficient to make reliable measurement of our fiducials. Increased to x200 for final order

13. Metrology: Schedule (cont)
End September: delivery of final optics, verification with sensor measurements
End October: mockup of baseplate and cover to hold three mechanical modules with the correct spacing, with the holes in the cover, to practice the measurement and verify the allocated time (nb relies on delivery of mechanicals from L’pool)
Mid April – 2.5 weeks for survey of R half then L half (TBC after October test)