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

Beam-pipe at cavern end

Beam-pipe Central part

ATLAS Experimental Hall

Base of the ATLAS

Beam-pipe at cavern end

ТBP1 BP2

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 DesignGeneral design

Laser beam

The center of angular positionerО1

The end pointО2 of the laser reference line

- the center of the quadrant photoreceiver QPr2

Laser in the angular positioner

β

A

Measured object-В

Position of the measuring

quadrant photoreceiverQPr1

О1

О2

Φ

Θ

О3

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

BP1,BP2-parts of pipes to install the laser and quadrant photodetector

T-measurement pipeXYZ-global coordinate system

Laser with angular positioner

TLaser beam

Collimator

Final QPr2 with adapter А2

adapter А1with QPr1

AdapterАwith total station target

BP1 BP2

Measuring stations in global coordinate system

Y

Z

X

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’

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

QPr1 with adapter А1 BP2

Laser beamFinal QPr2 with adapter А2

Laser with angular positioner

Z´

X´

Y´T

BP1

Joint LFL and Total Station measurement procedure Basic scheme

The measurement stations– global coordinate system

BALaser beam

Y

Z

X

Laser

The quadrant photoreceiver QPr1

with adapterA2

The Total Station target with adapter A1

DC

В2В1

Т

2D – linear positioner

Т1 Т2

O

X’

Z’

Y’

• 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

measurements were made at 16m distance from the laser

length of the laser reference line was ~50m

T

QPr with adapter

Y’ A B1 B2 B

Z’X’

T1

16m49.6m

T2

LRL measurement procedure

offsets of total station target and of quadrant photodetector in the adapters has coincided

D

QPr with adapter А1

D Measuring tube TBase tube BP1 or BP2D

Laser ray

D

Total station target with adapter A

Dimensionless 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

The laser raymultimeters

QPrdisplacement of QPrin

steps of 50 ± 3µm precision positioner in

four directionsU1 U2

U3 U4

QPr1

Gravity

vector

QPr3

QPr2

QPr4

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

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

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

Up Down

(mm)

Si

Displacement Up,Down

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

Right Left

Si

(mm)

Displacement Right, Left

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

0,1

0,2

0,3

0,4

0,5

0,6

0,7

0,8

0,9

(mm)

Hor Vert

Displacement Vert, HorS

i

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

Laser measurements calibration

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

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

(mm)

Averaged displacement

Smean

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.

LFL measurement precision

0 10 20 30 40 500

20

40

60

80

100

Laser Fiducial Line measuring accuracy

()

L(m)

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’

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

В

X´

Z’

dX´

dZ´

QPr

Laser beam spot

2D coordinate system:X´,Z´

Total Station–

LRL difference Δ

Set 1 Set 3 Set 2

Pipe end centers Pipe end centers Pipe end centers

B1 B2 B1 B2 B1 B2

Horizontal (mm) 0.06 0.02 −0.07 −0.15 0.12 0.37

Vertical (mm) −0.13 −0.11 −0.07 −0.15 −0.41 −0.35

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)

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.

Conclusion