RTC
®
5 PC Interface Board
Rev. 1.9 e
7 Basic Functions for Scan Head and Laser Control
99
innovators for industry
7.2 Delay Settings for Synchro-
nizing Scan Head and Laser
Control
The timing of the scan head and laser control signals
must be compatible with the dynamic behavior of the
system components, i.e. the response of the scanners
and the laser, and the specific interaction between
the workpiece and laser radiation.
To accomplish this, the user can set the following
delays
(1)
:
• Laser delays:
– LaserOn delay
– LaserOff delay
• Scanner delays:
– Jump delay (optional variable)
– Mark delay
– Polygon delay (optional variable).
All delays are described in detail in this chapter.
7.2.1 Laser Delays
There are two different laser delays:
LaserOn delay and LaserOff delay.
The laser delays affect when the “laser active” laser
control signals (i.e. the laser) are turned on or off
before or after a mark or arc command or a series of
mark and arc commands (if applicable, the RTC
®
5
will thereby switch from “laser standby” to
“laser active” signals or vice versa). Laser delays do
not affect the total marking time, except when they
are negative.
The LaserOn delay and the LaserOff delay are set by
the list command
The time resolution for the laser delays is
0.5
µ
s
.
The delays must be appropriate for the defined jump
speed and marking speed (also see
).
LaserOn Delay
The LaserOn delay defines the moment when the
RTC
®
5 turns on the laser. LaserOn delay is automati-
cally inserted at the start of a mark or arc command
(first microstep). Thus, the laser is switched on only
after execution of the first few microsteps. This delay
can be used for several purposes:
• Many applications require laser marking without
variations of intensity, especially without burn-in
effects at the start or end of a vector. To achieve
homogenous marking results, it is essential to
scan the vectors with a constant velocity.
At the beginning of a mark or arc vector, however,
the mirrors first have to be accelerated up to the
defined marking speed.
shows that the laser focus initially moves only
very slowly. A burn-in effect may occur.
To avoid this, the LaserOn delay must be set to a
suitable,
positive
value. Thus the mirrors will have
already reached a certain angular velocity when
the laser eventually turns on. However, if the
LaserOn delay is too long, the first part of
the vector will be cut off.
• Some materials take some time until they react to
the exposure to laser radiation. In this case, it can
be useful to “preheat“ the starting point of a
mark or arc vector before marking. This can be
done by setting the LaserOn delay to a
negative
value. A negative LaserOn delay extends the total
marking time, because it is inserted
before
the
actual mark or arc command. Additionally, the
scanner delay is automatically extended if a
preceding LaserOff delay has not yet finished (see
"Automatic Delay Adjustments", page 107
LaserOff Delay
• Due to the acceleration phase at the beginning
of the movement, a difference (a lag called
tracking error) occurs between the set position
and the real position of each mirror – see
After execution of a mark or arc command, the
laser should not be turned off immediately
because the scanners have not yet reached the
final set position. Therefore a LaserOff delay is
inserted automatically before the laser is turned
off (also see notes
). For short marking
vectors, if a preceding LaserOn delay has not yet
finished then the LaserOff delay will automati-
(1) Furthermore, for high-precision optimization needs, an auto-
matic readjustment of “laser active” laser control signals – and
thus of the laser power – even during execution of vector and
arc commands can be realized via the automatic laser control
commands (see
).
