Lateral x-ray: 4 marks vs 2 marks

1
Lateral x-ray 4 marks vs 2 marks

• Test perfomed using the plate 57 of one
  brickwith 4 x-ray frontal marks and 4 x-ray
  lateral marks
• The distances between maps in micron are shown in
  the following slides (as depend on plate
  position).
• Legend- MAPFXR4 map evaluated using 4 x-rays
  frontal marks- MAPLXR4 map evaluated using 4
  x-rays lateral marks- MAPLXR2 min/max X side
  map evaluated using 2 out of 4 x-rays lateral
  marks located on the plate side where x is
  minimum/maximum. ()
• () A map is a transformation between stage
  coordinates and nominal (or detector or
  what.ever.you.want) coordinates
• () The same mark positions of the case with 4
  marks are used to not introduce effects due to
  the mark position accuracy. The map is obtained
  by simply setting the other marks as NOT FOUND.

2
MAPFXR4 MAPLXR4
Distance between maps (micron)
The rough positions of the marks used are shown
in black (1 map) and in white (2 map)
3
MAPFXR4 MAPLXR2 minX side
Distance between maps (micron)
The rough positions of the marks used are shown
in black (1 map) and in white (2 map)
4
MAPFXR4 MAPLXR2 maxX side
Distance between maps (micron)
The rough positions of the marks used are shown
in black (1 map) and in white (2 map)
5
Comments

• The distance between MAPFXR4 MAPLXR4 is below
  10 micron over the whole emulsion plate
• The map evaluated with only 2 lateral marks get
  worse and the distance can increase up to 50
  micron on the opposite side of lateral marks .
• Let compare the 4-marks frontal x-ray map
  with a 2-marks frontal x-ray map obtained by
  simply setting as NOT FOUND the 2 marks with
  higher x positions
• And what happen if we evaluate the distance
  between this map and the 2 marks lateral x-rays
  map?

6
MAPFXR4 MAPFXR2 minX side
Distance between maps (micron)
The rough positions of the marks used are shown
in black (1 map) and in white (2 map)
7
MAPFXR2 minX side MAPLXR2 minX side
Distance between maps (micron)
The rough positions of the marks used are shown
in black (1 map) and in white (2 map)
8
Final comments

• Changing from a 4 marks map to a 2 marks map
  introduces errors in the position estimation.
  This is also true if you have 4 marks map but you
  didnt find 2 marks.
• This is not expected if you dont change the map.
  For examples if you use only a 2 marks map for
  the entire brick (i.e. in the scan-back).
• This is due the different number of free
  parameters available for the transformation (6 in
  the case of 3 and more marks, 4 in the case of 2
  marks). The scaling of Y coordinates cannot be
  well estimated by measuting only 2 marks (with
  quite the same Y).
• 4-marks lateral marks are necessary if you dont
  want to manage these large errors (at the
  beginning of scanback and at the end of the
  scanforth or every time you change the map).