Development and validation of an absolute Frequency Scanning Interferometry (FSI) network 1 st PACMAN workshop, CERN, Geneva, Switzerland 3 rd February.
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Development and validation of an absolute Frequency Scanning Interferometry (FSI)
network
1st PACMAN workshop, CERN, Geneva, Switzerland
3rd February 2015
Solomon William KAMUGASA
solomon.william.kamugasa@cern.ch 1st PACMAN workshop, CERN, Geneva
PACMAN metrology1. Fiducialisation of components2. Alignment of components on a common support
Integrate these 2 steps
CMM preferred (0.3µm + 1ppm)
However…
• Measurement volume is limited
• It’s immobile
Goal:
• Develop portable alternatives
• Cable of comparable accuracies
• Able to cope with larger measurement volumes
One such alternative is FSI multilateration
Pre-alignment in tunnel11-14 µm over 200m
solomon.william.kamugasa@cern.ch 1st PACMAN workshop, CERN, Geneva
• Coordinate determination using distances only
Multilateration
𝑙𝑖𝑗+𝑣 𝑖𝑗=√ (𝑥𝐹 −𝑥𝑅)2+ (𝑦𝐹− 𝑦𝑅)2+ (𝑧𝐹−𝑧𝑅 )2
• Requires distances from at least 3 known points
• Distance-coordinate relationship is well known
• Self-calibration possible by increasing stations and targets
• Coordinate uncertainty dependent on distance uncertainty
Z
Y
X
𝑙𝑖𝑗 𝑣 𝑖𝑗
𝑅𝐹
solomon.william.kamugasa@cern.ch 1st PACMAN workshop, CERN, Geneva
Distance measurement system
Absolute Multiline by Etalon• Absolute distance (FSI)• Uncertainty 0.5µm/metre • Traceable to SI metre• Up to 100 distance measurements
simultaneously
1st PACMAN workshop, CERN, Genevasolomon.william.kamugasa@cern.ch
System adaptation
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++
HardwareModification of fibre end to enable absolute distance measurement between two points.1. Design of suitable housing2. Development of calibration strategy to determine any offsets
solomon.william.kamugasa@cern.ch 1st PACMAN workshop, CERN, Geneva
N=2 glass sphere• Unlimited viewing angle• Lower return intensity
SMR• Limited viewing angle• Greater return intensity
Advantages of wide viewing angle• Better geometry hence
better precision• Provides more options for
system configuration
Retroreflector options
300
Requirements• High precision machining
of 0.5” and 1.5” spheres• Potentially compatible with
Micro-triangulation
solomon.william.kamugasa@cern.ch 1st PACMAN workshop, CERN, Geneva
±1mm(3cm sphere)
Lateral tolerance test
Why important?• Greater tolerance = easier
channel alignment• Ability to continue measuring
even with slight misalignment
solomon.william.kamugasa@cern.ch 1st PACMAN workshop, CERN, Geneva
Impact of misalignment on distance
Do we measure the same distance if slightly misaligned?
We conducted simulations in MATLAB to find out.Assumptions: uniform refractive index of air = 1
uniform refractive index of glass = 2
1mm
1mm
solomon.william.kamugasa@cern.ch 1st PACMAN workshop, CERN, Geneva
Impact of misalignment on distance
Effect of lateral misalignment on distance measured using a 0.5 inch sphere
solomon.william.kamugasa@cern.ch 1st PACMAN workshop, CERN, Geneva
Impact of misalignment on distance
Effect of lateral misalignment on distance measured using a 1.5 inch sphere
solomon.william.kamugasa@cern.ch 1st PACMAN workshop, CERN, Geneva
Multilateration strategyNeed to measure distances to several points from a single point
Divergent beam
Motorised rotating head
Several channels on one mount
solomon.william.kamugasa@cern.ch 1st PACMAN workshop, CERN, Geneva
Several distances from one pointDivergent beam
Motorised mount
Several channels one mount
Single beam to several targets• Limited measurement volume (diverging
lens)• Limited measurement range (laser power)• Technical know-how (software and
hardware)Single beam to several targets• Careful calibration strategy• Method to ‘teach’ instrument position of
targets• Maximum measurement range (20m) and
volume 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
solomon.william.kamugasa@cern.ch 1st PACMAN workshop, CERN, Geneva
Stretched wire measurementAttempt 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 wire2. Include reflector in wire tensioning system(Both options likely to have an impact on other measurements)3. Detect wire using WPS
solomon.william.kamugasa@cern.ch 1st PACMAN workshop, CERN, Geneva
Network simulationsCERN’s LGC++ will be used to conduct simulations & to solve the 3D network
Simulations will:1. Compare various network configurations to help choose the
best2. Take into account existing constraints3. Determine the optimum number of channels4. Provide post adjustment statistics and outlier detection.
solomon.william.kamugasa@cern.ch 1st PACMAN workshop, CERN, Geneva
Inter-comparison and validation
FSI multilateration
AccuracyReliability Robustness
Micro-triangulationInter-
comparison
Leitz CMM
Validation
1st PACMAN workshop, CERN, Geneva
Extrapolation & summaryUltimate 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
solomon.william.kamugasa@cern.ch
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