Rockwell Automation 2755 Atomscan Bar Code Scanner - Manual (Page 17)

Chapter 3
Designing the System
3–6
The AtomScan scanner can read a symbol correctly even if the symbol or
package is not correctly oriented. Figure 3.4 shows several possible
positions.
Figure 3.4
Positioning Terminology
Correctly positioned
symbol and package
Tilted symbol
Pitched package
and symbol
Skewed package
and symbol
•
Tilt: A symbol is tilted when the symbol’s bars are not 90
°
to the scan
line. The symbol can be read with any tilt, provided the scan line passes
through all bars and quiet zones on each sweep for the required minimum
number of scans. Tilt may reduce the number of scans in a given
application. Scanners 2755-L6SB and -L6RB have elliptical spots, which
may limit their tolerance for tilted symbols.
•
Pitch: A symbol is pitched when the symbol’s bars are at different
distances from the scanner. From the scanner’s perspective, a pitched
symbol will appear to have a smaller Narrow Element width than it
actually has. This may reduce both the read rate and the Read Range.
However the symbol can still be read if the apparent Narrow Element
width is within the scanner’s specifications. See the section at the end of
this chapter, Compensating for Pitched symbols.
Note: Like skew, pitch may be used deliberately to reduce specular
reflection, as long as the application still has the number of scans per
symbol it needs.
•
Skew: A symbol is skewed when the ends of the symbol’s bars are not at
the same distance from the scanner. The symbol can be read if the
distance of both ends of the bar are within the scanner’s Read Range, and
the skew is less than
40 degrees from the centerline. Unlike pitch, skew
does not affect the read range.
Note: Some skew is necessary to prevent strong reflected light
(specular reflection) from interfering with a successful read. A skew
between 20
°
-30
°
is ideal. Or skew may be combined with pitch to give
this angle.
Tilt, Pitch, and Skew