The Laser Reference Line Method and its Comparison to a
Total Station in an ATLAS like Configuration.
JINR: V. Batusov, J. Budagov, M. Lyablin
CERN: J-Ch. Gayde, B. Di Girolamo, D. Mergelkuhl, M. Nessi
Presented by V. Batusov , M.Lyablin
Formulation of the ATLAS needs
ATLAS Experimental Hall
Beam-pipe Central part
BP1
BP2
Т
Beam-pipe at
cavern end
Base of the ATLAS
Beam-pipe at
cavern end
Tasks that can be solved using the LRL :
 - Metrological measurements in inaccessible conditions for existing methods
 - On-line position control of ATLAS detector and subsistence in date taking period
 - Connection of the on-line coordinate systems of the LHC and detectors in date
taking period
Laser Reference Line: Operation and Design
Position of the measuring
General design
The center of angular
positionerО1
quadrant photoreceiverQPr1
Θ
Φ
О1
Laser beam
β
Laser in the angular positioner
Measured
object-В
О2
О3
A
The end pointО2 of the laser
reference line
- the center of the quadrant
photoreceiver QPr2
Laser reference line includes as a “key points”:
 Starting point O1
 Endpoint O2
 Measuring point O3
Pipe adjustment –
use parts of pipes for combining of the laser and total station measurements
AdapterАwith total station target
Final QPr2 with adapter А2
Collimator
T
BP1
Laser with angular positioner
Z
Y
X
BP2
Laser beam
adapter А1with QPr1
Measuring stations in global
coordinate system
 BP1,BP2-parts of pipes to install the laser and quadrant photodetector
 T-measurement pipe
 XYZ-global coordinate system
LFL adjustment of the pipe
QPr1 with adapter А1
BP2
BP1
Z´
T
Y´
X´
Final QPr2 with adapter А2
Laser beam
Laser with angular
positioner
Part of the beam-pipe mock-up for
the adjusting
 For measurements of the coordinates of the centers of ends of the
measured pipe T one use a local coordinate system X’Y’Z’
Joint LFL and Total Station measurement procedure
Basic scheme
The Total Station target with adapter A1
Laser
2D – linear positioner
Z’
Т1
Т
A
В1 Laser beam
X’
Y’
В2
B
Т2
Z
The quadrant photoreceiver QPr1
O
with adapterA2
X
Y
C
D
The measurement stations– global coordinate system
• we used universal adapters A1 and A2 for the points A, B, B1 and B2
measurements in the LFL
• we aligned the endpoint B of the LFL with 2D – linear positioner
Local coordinate system in the joint measurements of the laser
and Total Station measurement systems
Z’
Y’
A
QPr with adapter
X’ B
1
B2
B
T
T1
16m
T2
49.6m
 measurements were made at 16m distance from the laser
 length of the laser reference line was ~50m
LRL measurement procedure
QPr with adapter А1
D
Laser ray
Measuring tube T
D
D
Base tube BP1 or BP2
Total station target with adapter A
D
 offsets of total station target and of quadrant
photodetector in the adapters has coincided
Laser measurements calibration
displacement of QPrin
QPr steps of 50 ± 3µm
precision positioner in
four directions
U1
U2
U3
U4
Gravity
vector
The laser ray
QPr1
QPr2
QPr3
QPr4
multimeters
U1, U2, U3, U4- signal from photodiodes
Dimensionless values Sup, Sdown, Sleft, Sright,
used in the construction of calibration
curves
U= U1+ U2+ U3+ U4
Quadrant detector was installed in the
same position relative to the gravity
vector
Laser measurements calibration
0.8
0.8
0.7
0.7
0.6
Si
Displacement Right, Left
Displacement Up,Down
0.5
0.6
Si
Up
Down
0.4
0.5
Right
Left
0.4
0.3
0.3
0.2
0.2
0.1
0.1
0.0
0.0
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
1.1
1.2
1.3
1.4
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
(mm)
(mm)
0,9
0,8
Si
Displacement Vert, Hor
0,7
0,6
Hor
Vert
0,5
0,4
0,3
0,2
0,1
0,0
0,0
0,1
0,2
0,3
0,4
0,5
0,6
0,7
0,8
0,9
1,0
1,1
1,2
1,3
1,4
(mm)
 calibration curves were determined in 4 directions- Up, Down, Left, Right
 then they were paired into the Horizontal and Vertical directions
Laser measurements calibration
0.8
0.7
Averaged displacement
0.6
Smean
0.5
0.4
0.3
0.2
0.1
0.0
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
1.1
1.2
1.3
1.4
(mm)
 An averaged calibration curve was used for the measurements of the
positions of the centers of the ends of measured tube T
LFL measurement precision
The following sources influence on the LRL measurement accuracy:
 Inaccurate mechanical setting of the laser beam reference points
with respect to the ends of the reference pipes.
 Fluctuation of refractive index of the air in which the laser beam
propagates.
 Distortion of the laser beam shape by the collimation system.
 Accuracy of the calibration measurement system.
 Perpendicularity of the QPr with respect to the laser beam during the
measurement.
100
Laser Fiducial Line measuring accuracy
80
()
60
40
20
0
0
10
20
30
40
50
L(m)
Determination of the coordinates of the pipe ends using the
averaged calibration curve
2D coordinate system:X´,Z´
QPr
dX´
Z’ dZ´
В
X´
Laser beam spot
 By using of the calibration curve the values dz, dx were determined
 This values are the coordinates of the center B of the end of the pipe
measured in the local coordinate system X’, Z’
Comparison of the Laser and Total Station measurements
Set 1
Total
Station–
Set 3
Set 2
Pipe end centers Pipe end centers
Pipe end centers
LRL difference Δ
Horizontal (mm)
Vertical (mm)
B1
B2
B1
B2
B1
B2
0.06
0.02
−0.07
−0.15
0.12
0.37
−0.13
−0.11
−0.07
−0.15
−0.41
−0.35
 Two series of measurements (Set 1, Set 3) have been available in which the position of
the pipe T relative to the LRL has been chosen to be misaligned by d ≤ 0.5 mm
corresponding to the linear portion of the calibration curve and one series of
measurements (Set 2) with d ≥ 0.5 mm
 In the Set 1 and Set 3 data the average difference is = −0.07 mm with a spread of
individual differences in the interval from −0.15 to 0.06 mm (σ=0.08mm)
 In the Set 2 data the values are = 0.24 mm with a spread of individual differences in
the interval from −0.41 to 0.37 mm (σ=0.38mm)
Conclusion
 An original method for precision measurements when alignment of beam
pipe ends on a reference axis has been proposed and tested. The test
measurements have been performed using jointly the LRL in a 2D local
coordinate system and a Total Station survey instrument in a global 3D
coordinate system. The fiducial marks at the pipe ends have been
measured with both instrumentations. A transformation to a common
coordinate system has been applied to allow the comparison of the
results.
 The results of the measurements coincide to an accuracy of
approximately ±100 µm in the directions perpendicular to a common
reference line close to the middle of a 50m line.
 The test shows that the proposed LRL system is a promising method for
the on-line positioningand monitoring of 2D coordinates of fiducial
marks. It could be used for highly precise alignment of equipments
linearly distributed.
 The tested system could be improved using the innovative laser-based
metrological techniques that employ the phenomena of increased
stability of the laser beam position in the air when it propagates in a pipe
as it works as a three-dimensional acoustic resonator with standing
sound waves could be integrated in the setup. This property is the
physical basis for the development of a measurement technique with a
significant gain in attainable accuracy.