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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

Beam-pipeCentral part

BP1

BP2

Т

Beam-pipeat cavern end

Beam-pipeat cavern end

Base of the ATLAS

Formulation of the ATLAS needsTasks that can be solved using the LRL :

- - Metrologicalmeasurements 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

quadrant photoreceiverQPr1

The center of angular positionerО1

Θ

Φ

О1

Laser beam

О2

β

О3

A

Laser in the angular positioner

The end pointО2 of the laser reference line

- the center of the quadrant photoreceiver QPr2

Measured object-В

Laser ReferenceLine: Operation and DesignGeneral designLaser reference line includes as a “key points”:

- Starting point O1
- Endpoint O2
- Measuring point O3

AdapterАwith total station target

Final QPr2 with adapter А2

Collimator

T

BP2

BP1

Laser beam

Laser with angular positioner

adapter А1with QPr1

Z

Y

Measuring stations in global coordinate system

X

Pipe adjustment –use parts of pipes for combining of the laser and total station measurements- BP1,BP2-parts of pipes to install the laser and quadrant photodetector
- T-measurement pipe
- XYZ-global coordinate system

BP2

BP1

Z´

T

Y´

X´

Final QPr2with adapter А2

Laser beam

Part of the beam-pipe mock-up for the adjusting

Laser with angular positioner

LFL adjustment of the pipe- For measurements of the coordinates of the centers of ends of the measured pipe T one use a local coordinate system X’Y’Z’

The Total Station target with adapter A1

Laser

2D – linear positioner

Z’

Т

Т1

X’

A

B

Т2

Y’

В1

Laser beam

В2

Z

The quadrant photoreceiver QPr1

with adapterA2

O

Y

X

C

D

The measurement stations– global coordinate system

Joint LFL and Total Station measurement procedure Basic scheme- 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

Z’

X’

B2

A

B

B1

Y’

T

T1

T2

16m

49.6m

Local coordinate system in the joint measurements of the laser and Total Stationmeasurement systems- measurements were made at 16m distance from the laser
- length of the laser reference line was ~50m

D

Laser ray

Base tube BP1 or BP2

D

Measuring tube T

D

Total station target with adapter A

D

LRL measurement procedure- offsets of total station target and of quadrant photodetector in the adapters has coincided

displacement of QPrin steps of 50 ± 3µm precision positionerin four directions

QPr

U1

U2

U3

U4

Gravity

vector

The laser ray

multimeters

QPr2

QPr1

QPr4

QPr3

Laser measurements calibrationDimensionless values Sup, Sdown, Sleft, Sright, used in the construction of calibration curves

Quadrant detector was installed in the same position relative to the gravity vector

U1, U2, U3, U4- signal from photodiodes U= U1+ U2+ U3+ U4

Laser measurements calibration

- calibration curves were determined in 4 directions- Up, Down, Left, Right
- then they were paired into the Horizontal and Vertical directions

Laser measurements calibration

- 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.

QPr

В

Z’

dZ´

dX´

X´

Laser beam spot

Determination of the coordinates of the pipe ends using the averaged calibration curve- 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

- 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.

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