Operating Instructions
Chapter
3
CLV 490 Bar Code Scanner
8 009 993/O824/20-12-2004
©
SICK AG · Division Auto Ident · Germany · All rights reserved
3-7
Product description
System and error messages help you to configure the device and to locate the source of
errors during startup and reading mode.
3.2.1
Autofocus function
The autofocus function enables the CLV to detect the distance of an object during the read-
ing process, without the need for external sensors, and then adjusts the focus position au-
tomatically to the reading plane of the bar code. In order to do so, the CLV measures the
object distance each time in its reading field in front of the reading window and internally cre-
ates a distance profile. Following this, it positions the focus on the object.
3 operating modes are provided for various applications:
•
Minimum distance:
the CLV focuses on the minimum distance in the distance profile
and ignores the background in the reading field. Application: with unobstructed view of
the object without any surrounding objects protruding into the reading plane.
One object with bar code(s) only is inside the reading field during one reading pulse.
•
Differential background:
the distance profile of the reading field background is pro-
grammed (teach-in) in the CLV without any objects present. During the reading process,
the CLV then focuses on the object which it recognizes by comparing the actual dis-
tance profile to the distance profile of the background. Application: with unobstructed
view of the object restricted by other objects that protrude constantly into the reading
plane.
One object with barcode(s) only is inside the reading field during one reading pulse.
•
Differential background and tracking:
if several objects with different distances to the
CLV are positioned in the reading field at the same time (distance conflict), the CLV fo-
cuses on the object that is nearest to but has not exceed its internal focus switchover
point. Application: in OTS operation (applications with internal tracking or tracking by the
OTC 400 Omni Tracking Controller).
The distance profile of the background can also be displayed in the "CLV-Setup" program.
The autofocus range is defined by the aperture angle, the autofocus space, and (in the case
of line scanners with oscillating mirror) also by the angle of deflection. The park setting of
the focus position, from which the device focuses for each read, can be specified in addition
to a time and/or position-related delay (timeout or hysteresis). If necessary, an offset can
be defined for the focus position to be set by the measurement. The depth of field, which
radiates in the direction of the scan lines and is caused by the V-principle of the beam de-
flection, is optimized as a result (
).
Fig. 3-3:
Optimization of the depth of field for the object
Optimum focus position:
measured distance plus offset for maximum
Measured distance
Depth of field (DOF)
