Chapter
6
Operating Instructions
CLV 490 Bar Code Scanner
6-16
©
SICK AG · Division Auto Ident · Germany · All rights reserved
8 009 993/O824/20-12-2004
Operation
Event-controlled focus position switchover (alternative)
Event-controlled focus position switchover can be used if the autofocus function does not
provide the expected accuracy for the application. Event-controlled focus position
switchover is required in the following cases, for example:
•
Conveyed material with a black surface (e.g. vehicle tires)
The laser light emitted by the CLV is absorbed by the surface of the material, which
means that the distance measurement may no longer be sufficiently accurate.
•
Conveyed material with highly reflective surfaces (e.g. anti-static bags)
•
Conveyed material with bar codes on the front edge in the conveying direction. At high
conveyor speeds, the CLV can no longer adjust the focus in time.
Explanation
Distance measurement
The distance measurement carried out by the CLV is independent of the focus control type.
It is used for automatic focus adjustment in autofocus mode and for determining the code
distance. For the distance measurement, the CLV determines a distance value for each
scan angle between –30
°
and +30
°
(line scanner) or between –25
°
and +25
°
(line scanner
with oscillating mirror). These distance values are used to create an up-to-date distance
profile between the min. and max. scan angle. Once mean value calculation has been
carried out, the distance profile is available after every 10th scan (e.g. every 10 ms at a
scanning frequency of 1,000 Hz). The distance measurement is carried out inside the limits
of 400 to 2,200 mm (15.8 to 86.7 in). If an object is being conveyed, the CLV determines
(with reading from above) an average object profile according to the conveyor speed. At
1,000 Hz and a speed of 2 m/s (6.6 ft/s), this occurs over a path of 20 mm (0.79 in) for
each object.
The angular resolution of the periodic distance measurement is 1.5
°
in the scanning
direction without an active median filter, and the typical distance measurement uncertainty
Action
Settings in CLV-Setup
1. Set up distance
configurations
Ö
R
EADING
C
ONFIGURATION
tab
Ö
R
EADING
A
REA
section
Ö
D
ISTANCE
CONFIGURATION
button
Ö
D
ISTANCE
CONFIGURATION
tab
– Focus position
Oscillating mirror:
– additionally: Oscillating mirror amplitude CW
Ö
A
SSIGNEMENT
T
ABLE
tab
– Index
– Valid configurations
To restrict the reading area for all valid distance configurations
proceed as described in
, CP limits
2. Select focus position
switchover (refered to the
start of the reading interval)
Ö
R
EADING
C
ONFIGURATION
tab
Ö
F
OCUS
C
ONTROL
sections
Ö
I
NPUTS
/S
ERIAL
/A
UTOFOCUS
– immediate or synchronous (default setting)
or
– latched (special application)
3. I
NPUTS
/S
ERIAL
trigger source:
select function for "IN 3"
and "IN 4" switching inputs
Ö
D
EVICE
C
ONFIGURATION
tab
Ö
A
SSIGNMENT
OF
I
NPUTS
section
Ö
IN 3
– Focus control
Ö
IN 4
– Focus control
Table 6-8: Guide: Configuring focus position switchover