Transcript Microsoft PowerPoint document

STAMP : Saclay Telescope for the Alignment of Many Points
CCD (long arm)
lens
screen + grid
y
z
x
glass plates
at 45°
laser beam
CCD (short arm)
STAMP characteristics (Freiburg/Saclay DATCHA version) :
•2 arms (long & short) for the measurement of the laser beam position ( y, z) and
direction (qy, qz)
•Absolute positioning (using fiducial grids)
•Precision on laser position in the STAMP local coordinate system:
y,z ~ 10 mm ; qy,qz ~ 50 mrad
•Dynamical range (mm) : 30*38 with peripheral grids (screen size: 40*45)
• Transparency ~ 92%
•  laser = 685 nm ( 0.2 mW)
•Dimensions (mm) : 290 * 100 * 50
Freiburg 7/07/2000
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40 mm
STAMP PRINCIPLE:
290 mm
reference laser beam
(TEM00 from pigtail)
x
LEDs for
calibration with
the grid
screen +
fiducial grid
reconstructed
spot position
lens
CCD
laser spot on CCD
(demagnification: g ~ 1/10)
laser spot on screen
100 mm
STAMP top view
pixel unit
reconstruction precision on the screen,  = 10 mm
 on the CCD (.g): 1 mm ( 13 % of a pixel).
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STAMP CALIBRATION (1)
Goal: Correct for the unprecise mechanical positioning of the
glass plates and the fiducial grids.
Principle:
•Build a reference STAMP out of 2 precisely known positions
of a reference grid (using CMM + optical control)
•With the same camera, compare the STAMP grid seen by
reflection on the glass plate with the reference grid.
external camera looking at the grid of
the 2nd arm (long arm) or at the reference
support cube of the reference
grid
grid at the mirrored position of the 2nd grid
(with respect to the reflecting face of the 2nd
glass plate)
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2nd grid (from
the long arm)
(mechanical reference,
spheres - -, not shown )
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STAMP CALIBRATION (2)
•The positions of the reference grids w.r.t. the STAMP support balls of the calibration
bench (measured with a CMM and an optical bench) define the reference STAMP
(calistamp) with its transfer matrix T:
Spot coordinates on the 2 screens
(short and long arms)
xs
ys
xl
yl
T
y
z
qy
qz Laser coordinates
T is calculated with a software simulation program. The calibration constants are used for
the corrections of the measured spot coordinates.
2 set of calibration constants (for each arm):
Long term calibration constants, derived from the ‘ CALISTAMP ’ calibration (done
only once).
• Calistamp grid to STAMP grid : dx, dy, qz, scale(x), scale(y)
+ 5 parameters to account for STAMP
screen distortions (photo paper)
• 4 deviation constants: dx, dy, qx, qy
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Reconstructed grids:
Stamp/calistamp grid fit quality:
c2
x
Stamp grid
(peripheral)
y
Calistamp grid
(full)
Arm nb
mm
STAMP deviations
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Stability of ‘ CALISTAMP’ calibration constants:
Comparison of calibration constants from two calibration runs taken at 2 monthes interval (25/01/2000
and 22/03/2000):
•The vertical scale shows the maximum effect of the difference (i.e. at the grid edges).
•The horizontal scale refers to the 12 short arms and the 12 long arms for the 12 DATCHA STAMPs
mm
Stamp/calistamp
grid position dx, dy
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mm
mm
Stamp/calistamp
grid rotation and
x-y scales
Stamp deviations
Dy, Dz
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STAMP CALIBRATION (3)
Short term calibration constants, derived from illuminated screen images
• STAMP grid to CCD pixels : Dx, Dy, Q, demagnifications (x, y)
+ 5 parameters to account for lens aberrations (identical for all arms)
Stamp grid fit quality:
c2
x
Present difficulties:
• Permanent illumination system (red LEDs) not yet installed
• Calibration done after removal of STAMP from their supports and
after removal of a light protection cover made out of scotch tapes:
CCDs may have moved during this operation (stability < 1 mm
required).
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y
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FREIBURG 4m TEST:
~ 1.7 m
~ 1.7 m
laser
x
fixed Stamp
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x
x
Stamp on a
movable
platform
Run conditions:
•No shielding tubes
•All fans on
•All light off
fixed Stamp
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Measured quantities in the 4m test:
The local support coordinate systems are defined from the 3 balls (cone/slot/flat) positions.
qy1
sagy
slot
qy3
flat
yo3
cone
yo1
Support 1
Support 2
Support 3
Quantities measured by the STAMP and the CMM:
• Sagittas : sagy, sagz
• Coordinates of the external frames in the local coordinate frame of the central support:
yo1, zo1, yo3, zo3 , qy1, qz1, qy3, qz3 ( For the STAMP: assume that the axis o1y1 and o3y3 are
parallel to the x2o2y2 plane)
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Results of the 4m test:
9 data sets: 7 different positions of support 2, 2 runs per data set
•pos 0_1 : Reference positions
•pos 0_2 : STAMP 2 removed and remounted
•pos 1 : 12 mm shift in z (laser moved)
•pos 2 : add a 10 mrad tilt around y axis (images mixed up > missing)
•pos 3 : remove the 12 mm z shift
•pos 4 : add a 10 mm shift in y (laser moved)
•pos 5 : remove the tilt around y
•pos 6_1 : back to the reference position
•pos 6_2 : laser moved
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Measured quantities in the 14m test:
4260 mm
3390 mm
x
STAMP 1
x
mirrors
STAMP 2
5630 mm
x
x
mirrors
STAMP 3
STAMP 4
Quantities measured by the STAMP :
• Coordinates of the external frames in the local coordinate frame of the STAMP 2 support:
yo1, zo1, yo3, zo3 , yo4, zo4 , qy1, qz1, qy3, qz3 , qy4, qz4 ( assuming that the axis o1y1, o3y3 and o4y4 are parallel to
the x2o2y2 plane)
Quantities measured by the CMM :
• Coordinates of the balls which defines the local
coordinate frame of the STAMP 2 support.
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Spot at 14 m
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Nices features:
• Use commercial products (CCD, glass plates, lenses).
• No precision mechanics required.
• Can easily be improved with new CCDs ( larger CCD => shorter device).
• Large range (from 30x38 mm to 40x40mm with the LED scheme shown below).
• Can work with visible laser light.
• Fast and simple calibration (1 week for 180 STAMPs).
• Radiation hardness (same technology as the TC255 tested at Prospero).
• High transparency : 56% of intensity left after 7 STAMPs (intermediate h ray with 4 MDT and 3 TGC layers).
Present problems:
• The DATCHA/Freiburg STAMP has been built with a too soft aluminium alloy with ball inprints larger than 10 mm.
• When working with visible laser, some light protection (short tubes ) may be needed to protect from parasitic light.
May be solved by using a pulsed laser and background image subtraction (not done in the Freiburg test).
• Bad laser optics used for the Freiburg test (problem at 14 m).
and potential improvements:
• Size (length = 290mm). With a twice as large CCD (presently 4 x
3.5 mm for the TC237), the demagnification can be reduced to 1/5
and the length decreased down to 200 mm.
• The thick glass plate (5mm) can possibly be replaced by a thin
mylar foil (10mm) canceling the secondary reflection and the beam
deviation.
• The LED system for illumination of the grid during the runs for the
control of the lens-CCD positions w.r.t. the screen has not yet been
tested). Simulation shows that the grid can be replaced by 4 LEDs at
the screen corners (see figure).
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Integration inside the ATLAS spectrometer :
The principle of the STAMP implementation in the End
Cap spectrometer is shown on the sketch on the right. The
laser can be placed either at the EI or at the EO layer.
No STAMP size problem is expected st the EM and EO
layers. At EI, it is possible to replace the STAMP by the
laser itself. This may even simplify the system
implementation with the intermediate polar beam (large
distance between the bar and the beam, which requires a
periscope system when optical sensors are used.
platform
EI bar
Laser head
Piezo aiming system (+- 0.1 mm, remote control)
Laser fiber
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STAMP cost table :
•Mechanics
•glass plates
•CCD TC 237
•lenses
TOTAL
Freiburg 7/07/2000
300 x 2
300 x 2
50 x 2
2000 FF
600 FF
600 FF
100 FF
3300 FF (500 Euros)
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