1. Development and validation of an absolute Frequency Scanning Interferometry (FSI) network
Solomon William KAMUGASA
1st PACMAN workshop, CERN, Geneva, Switzerland
3rd February 2015

2. PACMAN metrology 1. Fiducialisation of components
25/01/2015
1. Fiducialisation of components
Integrate these 2 steps
2. Alignment of components on a common support
CMM preferred (0.3µm + 1ppm)
However…
Measurement volume is limited
It’s immobile
Pre-alignment in tunnel
11-14 µm over 200m
Goal:
Develop portable alternatives
Cable of comparable accuracies
Able to cope with larger measurement volumes
One such alternative is FSI multilateration

3. Multilateration 𝑅 𝐹 𝑣 𝑖𝑗 𝑙 𝑖𝑗
25/01/2015
Coordinate determination using distances only Z Y X
Distance-coordinate relationship is well known
Requires distances from at least 3 known points
Self-calibration possible by increasing stations and targets
Coordinate uncertainty dependent on distance uncertainty
𝑙 𝑖𝑗
𝑣 𝑖𝑗 𝑅 𝐹
𝑙 𝑖𝑗 + 𝑣 𝑖𝑗 = 𝑥 𝐹 − 𝑥 𝑅 𝑦 𝐹 − 𝑦 𝑅 𝑧 𝐹 − 𝑧 𝑅 2

4. Distance measurement system
25/01/2015
Absolute Multiline by Etalon
Absolute distance (FSI)
Uncertainty 0.5µm/metre
Traceable to SI metre
Up to 100 distance measurements simultaneously

5. System adaptation Hardware
Modification of fibre end to enable absolute distance measurement between two points.
Design of suitable housing
Development of calibration strategy to determine any offsets
Software
Current software provides distance information
Some upgrades have been done linking approximate coordinates with distances
Prototype MATLAB application to convert AML output file to form readable by LGC++

6. Retroreflector options
25/01/2015
SMR
Limited viewing angle
Greater return intensity
N=2 glass sphere
Unlimited viewing angle
Lower return intensity
30 0
Advantages of wide viewing angle
Better geometry hence better precision
Provides more options for system configuration
Requirements
High precision machining of 0.5” and 1.5” spheres
Potentially compatible with Micro-triangulation

7. Lateral tolerance test
Why important?
Greater tolerance = easier channel alignment
Ability to continue measuring even with slight misalignment
±1mm
(3cm sphere)

8. Impact of misalignment on distance
Do we measure the same distance if slightly misaligned?
1mm
1mm
We conducted simulations in MATLAB to find out.
Assumptions: uniform refractive index of air = 1
uniform refractive index of glass = 2

9. Impact of misalignment on distance
Effect of lateral misalignment on distance measured using a 0.5 inch sphere

10. Impact of misalignment on distance
25/01/2015
Effect of lateral misalignment on distance measured using a 1.5 inch sphere

11. Multilateration strategy
Motorised rotating head
Need to measure distances to several points from a single point
Several channels on one mount
Divergent beam

12. Several channels one mount
Several distances from one point
Divergent beam
Single beam to several targets
Limited measurement volume (diverging lens)
Limited measurement range (laser power)
Technical know-how (software and hardware)
Motorised mount
Single beam to several targets
Careful calibration strategy
Method to ‘teach’ instrument position of targets
Maximum measurement range (20m) and volume
Several channels one mount
Several beams in one mount to several targets
Strategy used in ATLAS
Design of suitable mount and support frame
Careful calibration strategy
Divergent beam for easy alignment

13. Stretched wire measurement
Attempt to measure 0.1mm Cu-Be wire directly with FSI
Noticeable increase in intensity
Insufficient for measurement
Maybe possible with thicker wire
Or different lens
Alternatives:
1. Mount tiny reflectors on wire
2. Include reflector in wire tensioning system
(Both options likely to have an impact on other measurements)
3. Detect wire using WPS

14. Network simulations
CERN’s LGC++ will be used to conduct simulations & to solve the 3D network
Simulations will:
Compare various network configurations to help choose the best
Take into account existing constraints
Determine the optimum number of channels
Provide post adjustment statistics and outlier detection.

15. Inter-comparison and validation
FSI multilateration
Accuracy
Reliability
Robustness
Micro-triangulation
Inter-comparison
Leitz CMM
Validation

16. Integration on FPAB

17. Extrapolation & summary
Ultimate aim:
To develop a portable coordinate measuring system based on FSI multilateration for CLIC that can be extrapolated to other projects
Summary:
System modification
Stretched wire measurement
Multilateration strategy
Tests, validation & extrapolation

18. Thank you for your attention!