CCD_Rasnik straightness monitoring system
CCD_Rasnik: Principle of the coding of the mask.
(patent pending)
A mask is generated by stacking position coded basic building blocks.
We will call such a block a B3. The horizontal and vertical codes
give the position of the basic building block in the total mask.
The size of one spot (field in the chessboard) is
in the order of 100 microns, which covers roughly
10 times 10 CCD camera pixels.
When you are a registered user you can
jump here
to get more detailed information.
You can
apply for access when you meet the
conditions.
Example of a coded mask.
Glass mask
The actual mask is a metal on glass mask, as used for integrated
circuit production (or a contact copy of such a mask). The
anti-reflective coated side should be pointing to the projecting lens.
These masks are produced by commercial firms, taking Gerber files
as input. Postscript files, plotted on high resolution machines,
turned out to be disappointing. Since postscript interpreters
work with floats, rather then integers, it is very hard to define
the data in such way that rounding off is done in the proper way.
Also tests were performed with gray code locations instead of inverting them.
In practice gray has to be defined as fine lines of black and white
and the results are unpredictable.
Actual cameraview
You can have a look at an actual
cameraview as grabbed
with a demokit (17 kbyte jpg).
How to decode
the pattern again (password needed).
go to
CCD_Rasnik home page.
You can mail
suggestions for this page to:
Henk Groenstege.
july 1996