Optimizing Processes with RFID and Auto ID, 2009

3 Optical codes
Finder border,
solid border
Fig. 3.2 Data Matrix code structure
ber of rows and columns are to be expected in the data area, and also
determining, therefore, the size of the cells. By default, the code is
depicted in black on a white background. However, an inverse depiction
with white on a black background is also permissible.
The standard requires a quiet zone of one cell’s width minimum
around the code in order to cleanly separate the code and background.
The number of columns and lines ranges from a 10 × 10 matrix
to a maximum of 144 × 144 columns and lines. The largest rectangular
version has 16 lines and 48 columns. The majority of Data Matrix
codes that are used is in the region of up to 48 × 48 cells.
One of the Data Matrix’ special strengths is that the code can be applied
to a part directly using various marking processes, that is to say,
without a label. However, the standard’s requirements here can very
often not be adhered to without incurring very high costs. Therefore,
the actual directly marked codes seldom correspond 100 % to the
standard. Depending on the form of the background, for example
concave or convex, distortions occur. The marking systems are not
set ideally or the backgrounds are not prepared accordingly, in turn
resulting in cells that are too large or small or create scratches and
changes to the background color. Moreover, it is a special challenge to
read 2D codes with an image processing system that must tolerate
additional influences, e.g. material reflections, trapezoid-shaped distortions
due to sloping angles of viewing or shadows that are cast by
uneven surfaces.
3.3.2 Codable data with Data Matrix ECC200
Data Matrix Codes support a wide range of coding schemes that also
determine the codable data quantity.
The coding schemes available are ASCII, Text, C40, ANSI X12, EDIFACT,
and Base 256. The use of special code words enables switching
between the symbol sets or to special coding, such as the EAN Data
42
Data area
Alternating border