GSI Helmholtz Centre for Heavy Ion Research
GSI Helmholtz Centre for Heavy Ion Research
Measuring through glass windows with laser tracker under
cold-vacuum conditions: investigations and results
Vasileios Velonas [email protected]
on behalf of the Survey & Alignment Team: I. Pschorn, T. Miertsch, K. Knappmeier, A. Junge
GSI Helmholtz Centre for Heavy Ion Research IWAA Grenoble 2016
Outline
2
Motivation
Measuring through air-glass-air
Measuring through air-glass-vacuum-cold
Building a mathematical model (MM) to gain absolute coordinates in a given reference system
Summary and outlook
GSI Helmholtz Centre for Heavy Ion Research IWAA Grenoble 2016
Motivation
What was the trigger for this investigation...
Measuring through glass window in cold conditions up to 4K Observing targets which are positioned on the cold mass Combination of theodolite and laser tracker Only 2D information gained from this procedure
cryostat fiducials
3
GSI Helmholtz Centre for Heavy Ion Research IWAA Grenoble 2016
Motivation
... and what we aim at, is ...
The high precise monitoring regarding deformations of the
cold mass along with movements vs. cryostat of superconducting components in 3D!!
4
cryostat fiducials
GSI Helmholtz Centre for Heavy Ion Research IWAA Grenoble 2016
Step 1 - Measuring through glass windows in air-glass-air
First phase measurements
5
Coplanar glass window (N-BK7) between laser tracker and points
Trying to track through a glass window
Glass window in an extreme slope position regarding the laser beam
Measuring through other glass windows
Autocollimation of the laser beam
• Measurements were not always possible
• Reproducibility of the position behind the windows was chaotic
• Laser tracker head could not find the target by autocollimation
• No tracking was possible through the window
• The reflection of the glass window was too high
Nothing did really work!
GSI Helmholtz Centre for Heavy Ion Research IWAA Grenoble 2016
Step 2 – Coating of a glass window
The glass window that we released to coat was a 15 mm thickness borosilicate (N-BK7) coplanar glass window
6
Two main parameters are highly important to know before coating a glass window:
1. The max. allowed reflection from both planes of the glass (in
our case 0.5 %)
2. What is the needed wavelength which is allowed to pass through? (in our case for all laser trackers)
GSI Helmholtz Centre for Heavy Ion Research IWAA Grenoble 2016
Wavelengths of the laser trackers
Leica LTD 500 Leica AT402 FARO SI2 FARO Vantage
[nm] [nm] [nm] [nm]
Absolute Distance Measurement (ADM) 780 795 1550 1550
Laser Interferometer (IFM) 633 * 633 *
Automatically Target Recognition (ATR) * 905 * *
Laser-Pointer 633 635 633-635 653-663
Step 3 - What is the wavelength of our instruments?
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FARO SI2 FARO Vantage Leica LTD 500 Leica AT402
Source: Leica and Faro
GSI Helmholtz Centre for Heavy Ion Research IWAA Grenoble 2016
Step 3 - What is the wavelength of our instruments?
Reflection diagram including all our laser trackers
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The ADM wavelength range of Faro
The laser pointer wavelength range of Leica and Faro
The ADM wavelength range of Leica
Source of the diagram: Prinz Optiks GmbH
GSI Helmholtz Centre for Heavy Ion Research IWAA Grenoble 2016
Step 4 - Measuring through coated glass window in air-glass-air
Second phase measurements
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Coated glass window Setup of the instrument-glass window-points (long distance)
Setup of the instrument-glass window-points (short distance)
Autocollimation of the laser beam Extreme position (approx.60°) of the glass window regarding the laser beam
• Different setup of the instruments and the SMRs regarding the glass window
• Measuring the same position of the targets at least five times in two telescope positions
• All laser trackers could find the targets without any problem
• Tracking the laser beam behind the glass window was possible
The position of the points behind the glass window is highly reproducible for all instruments sdXYZ= 5 μm (1σ)
Coating the glass was successful!
GSI Helmholtz Centre for Heavy Ion Research IWAA Grenoble 2016
Step 4 - Measuring through coated glass window in air-glass-air
Results
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-8.00
-7.95
-7.90
-7.85
-7.80
-7.75 0 1000 2000 3000 4000 5000 6000
Dis
plac
emen
t of t
he ta
rget
[m
m]
Distance between laser tracker and SMR [mm]
Pseudo position of the target (X-axis) caused by the glass window regarding the real position (air-glass-air)
Leica AT402
FARO SI2
FARO Vantage
Leica LTD500
SMR
X
Y
glass window
top view
SMR
X
Z
glass window
side view
GSI Helmholtz Centre for Heavy Ion Research IWAA Grenoble 2016
Step 4 - Measuring through coated glass window in air-glass-air
Results
11
SMR
X
Y
glass window
top view
SMR
X
Z
glass window
side view
-0.60
-0.40
-0.20
0.00
0.20
0.40
0.60
0 1000 2000 3000 4000 5000 6000
Dis
plac
emen
t of t
he ta
rget
[m
m]
Distance between laser tracker and SMR [mm]
Pseudo position of the target (Y-axis) caused by the glass window regarding the real position (air-glass-air)
Leica AT402
FARO SI2
FARO Vantage
Leica LTD500
GSI Helmholtz Centre for Heavy Ion Research IWAA Grenoble 2016
Step 4 - Measuring through coated glass window in air-glass-air
Results
12
SMR
X
Y
glass window
top view
SMR
X
Z
glass window
side view
0.00
0.20
0.40
0.60
0.80
1.00
1.20
0 1000 2000 3000 4000 5000 6000
Dis
plac
emen
t of t
he ta
rget
[m
m]
Distance between laser tracker and SMR [mm]
Pseudo position of the target (Z-axis) caused by the glass window regarding the real position (air-glass-air)
Leica AT402
FARO SI2
FARO Vantage
Leica LTD500
GSI Helmholtz Centre for Heavy Ion Research IWAA Grenoble 2016
Step 5 – Measuring through coated glass window in air-glass-vacuum-cold
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Using of break resistant reflector (BRR) Vacuum in the chamber 10-3 mbar Cold conditions up to 90 K using liquid nitrogen The angle of incidence (AOI) is up to 5°
LT SMR 2
window vacuum chamber
laser beam
SMR 1
X
Z side view
Angle of incidence (AOI)
The chamber (front side)
Setup of the instruments and conditions for the measurements
GSI Helmholtz Centre for Heavy Ion Research IWAA Grenoble 2016
Step 5 – Measuring through coated glass window in air-glass-vacuum-cold
Third phase measurements
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The chamber Set up in a long distance
Set up in a short distance
• All laser trackers could find the target without any problem, in vacuum as well as in cold condition
The insight of the chamber
The position of the points behind the glass window is again highly reproducible for all instruments sdXYZ= 5 μm (1σ)
GSI Helmholtz Centre for Heavy Ion Research IWAA Grenoble 2016
Step 6 – Recognizing the problem measuring through different optical media by laser trackers. Definition of the absolute position
• Pointing error (top view)
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• Range error (side view)
GSI Helmholtz Centre for Heavy Ion Research IWAA Grenoble 2016
Step 6 – Recognizing the problem measuring through different optical media by laser trackers. Definition of the absolute position
The problem of the range error caused by different optical media which the laser tracker can not understand
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LT SMR
window vacuum chamber
n1 (Temperature, Pressure, Humidity)
laser beam (LB)
GSI Helmholtz Centre for Heavy Ion Research IWAA Grenoble 2016
Step 6 – Recognizing the problem measuring through different optical media by laser trackers. Definition of the absolute position
The problem of the range error caused by different optical media which the laser tracker can not understand
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LT SMR
window vacuum chamber
laser beam (LB)
LB: n1=f(T, P, H)
LB: n2=f(Glass material, LT wavelength)
LB: n3=1
GSI Helmholtz Centre for Heavy Ion Research IWAA Grenoble 2016
Step 6 – Recognizing the problem measuring through different optical media by laser trackers. Definition of the absolute position
For the correction of the pointing error quaternions (mathematical tool) were used to manipulate the rotation in 3D in combination with Snell’s law
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distance from glass to reflector (medium: vacuum) DLT = Dreal *nvacuum
distance through glass DLT = Dreal *nglass
wave front
distance from LT source to the glass (medium: air) DLT = Dreal *nair
Angle of incidence (AOI)
GSI Helmholtz Centre for Heavy Ion Research IWAA Grenoble 2016
Step 7 – Building a Mathematical Model (MM)
To calculate absolute coordinates to a given reference system a MM is needed to correct the pointing and range errors
The MM is a function of all parameters which are known and measureable:
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Geometry of the window Position of the laser tracker
Angle of incidence Material of the window
Wavelength of the laser tracker Temperature
Pressure Humidity
et al.
MM
GSI Helmholtz Centre for Heavy Ion Research IWAA Grenoble 2016
Step 8 – Applying the Mathematical Model (MM)
Results in air-glass-air (FARO Vantage)
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-9.00
-8.00
-7.00
-6.00
-5.00
-4.00
-3.00
-2.00
-1.00
0.00 0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000
Dis
plac
emen
t of t
he ta
rget
[m
m]
Distance between the laser tracker (Vantage) and the SMR [mm]
Pseudo position of the target (X-axis) caused by the glass and its actual position by applying the MM (air-glass-air)
Without the MM
With the MM
SMR
X
Y
glass window
top view
SMR
X
Z
glass window
side view
GSI Helmholtz Centre for Heavy Ion Research IWAA Grenoble 2016
Step 8 – Applying the Mathematical Model (MM)
Results in air-glass-air (FARO Vantage)
21
SMR
X
Y
glass window
top view
SMR
X
Z
glass window
side view
-0.30
-0.20
-0.10
0.00
0.10
0.20
0.30
0.40
0.50
0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000
Dis
plac
emen
t of t
he ta
rget
[m
m]
Distance between the laser tracker (Vantage) and the SMR [mm]
Pseudo position of the target (Y-axis) caused by the glass and its actual position by applying the MM (air-glass-air)
Without the MM
With the MM
GSI Helmholtz Centre for Heavy Ion Research IWAA Grenoble 2016
Step 8 – Applying the Mathematical Model (MM)
Results in air-glass-air (FARO Vantage)
22
SMR
X
Y
glass window
top view
SMR
X
Z
glass window
side view
-0.20
0.00
0.20
0.40
0.60
0.80
1.00
1.20
0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000 Dis
plac
emen
t of t
he ta
rget
[m
m]
Distance between the laser tracker (Vantage) and the SMR [mm]
Pseudo position of the target (Z-axis) caused by the glass and its actual position by applying the MM (air-glass-air)
Without the MM
With the MM The geometrical reconstruction of the points behind the glass window is precise for all instruments sdXYZ= 15 μm (1σ) (absolute accuracy)
GSI Helmholtz Centre for Heavy Ion Research IWAA Grenoble 2016
Step 8 – Applying the Mathematical Model (MM)
Results in air-glass-vacuum-cold (all instruments)
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0
1
2
3
4
5
6
7
8
9
10
0 5 10 15 20 25 30
Dis
plac
emen
t of t
he ta
rget
[m
m]
Epoch (Timeline)
Pseudo position of the target (X-axis) caused by the glass-vacuum-cold conditions and its actual position by applying the MM (air-air-conditions)
Leica AT402 without the MM Leica AT402 wih the MM FARO SI2 without the MM FARO SI2 with the MM FARO Vantage without the MM FARO Vantage with the MM Leica LTD500 without the MM Leica LTD500 with the MM
W V
C
WW WW
W
WW: Without Window W: Warm V:Vacuum C:Cold
GSI Helmholtz Centre for Heavy Ion Research IWAA Grenoble 2016
Conclusion and outlook
The reproducibility of the points behind the glass window is highly accurate in air-glass-air as well as in air-glass-vacuum-cold condition (sdXZY= 5 μm).
Comparing relative coordinates behind the glass window requires a position of the instrument more than 3 m in order to avoid disturbance. Combining the instruments in this case is fatal, do not do this!
Using the mathematical model absolute coordinates can be calculated. The pointing and range errors can be eliminated which are caused by the glass window (sdXZY= 15 μm).
The material of the glass window in combination with the wavelength of the instrument defines the refractive index of the glass window, thus the material of the glass window has to be chosen wisely.
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GSI Helmholtz Centre for Heavy Ion Research IWAA Grenoble 2016
Conclusion and outlook
The mechanical properties of the window (size of the glass surface,
thickness) has to be taken in account in order to reduce or eliminate the bulge of the window, caused by the vacuum in the chamber, which can produce an error in the mathematical model. Also, as smaller the angle of incidence is, as more negligible this error can be.
Cross checking and optimization of the mathematical model by a practical approach is in progress.
The movement of the SMR center point because of the contraction in cold environment has to be taken in account in order to distinguish it from the displacement of the cold mass.
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GSI Helmholtz Centre for Heavy Ion Research IWAA Grenoble 2016
Thank you for your
attention!
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