Specular Reflection - Symbol MK2000 MicroKiosk Product Reference Manual

MK2000 MicroKiosk Product Reference Guide

Specular Reflection

When laser beams reflect directly back into the scanner from the bar code, they can "blind"
the scanner and make decoding difficult. This phenomenon is called specular reflection.
To avoid this, scan the bar code so that the beam does not bounce directly back. But don't
scan at too oblique an angle; the scanner needs to collect scattered reflections from the
scan to make a successful decode. Practice quickly shows what tolerances to work within.
Specular reflection.
Reflected beam is
within specular dead
zone and prevents
decode.
When scanning a 1D bar code, there is only a small specular dead zone to avoid (+ 2
the direct laser beam). The specular dead zone is larger for scanning PDF417 (+ 9
the direct laser beam). However, the scanner is not effective if its beams hit the bar code's
surface at an angle greater than 30
1-14
Side Views
Figure 1-9. Avoiding Specular Reflection
o
from the normal to that surface.
Tilt Bar Code At Slight Angle (Up to 30°)
No specular
reflection.
Decode can occur.
o
from
o
from