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

Development and validation of an absolute Frequency Scanning Interferometry (FSI)

network

1st PACMAN workshop, CERN, Geneva, Switzerland

3rd February 2015

Solomon William KAMUGASA

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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

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• 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

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Distance measurement system

Absolute Multiline by Etalon• Absolute distance (FSI)• Uncertainty 0.5µm/metre • Traceable to SI metre• Up to 100 distance measurements

simultaneously

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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

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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

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±1mm(3cm sphere)

Lateral tolerance test

Why important?• Greater tolerance = easier

channel alignment• Ability to continue measuring

even with slight misalignment

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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

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Impact of misalignment on distance

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

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Impact of misalignment on distance

Effect of lateral misalignment on distance measured using a 1.5 inch sphere

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Multilateration strategyNeed to measure distances to several points from a single point

Divergent beam

Motorised rotating head

Several channels on one mount

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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

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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

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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.

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Inter-comparison and validation

FSI multilateration

AccuracyReliability Robustness

Micro-triangulationInter-

comparison

Leitz CMM

Validation

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Integration on FPAB

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

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Thank you for your attention!