RTC
®
5 PC Interface Board
Rev. 1.9 e
7 Basic Functions for Scan Head and Laser Control
117
Notes
•Via set_sky_writing and
set_sky_writing_mode_list, you can switch back
and forth between Sky Writing modes 1 and 2 or
3. Temporarily switching off is also possible, as
long as
Timelag
>0.
• When searching for appropriate Sky Writing
parameters, initially the set_sky_writing
command and Sky Writing mode 1 should be
used: initially parameter
Timelag
should be
adjusted (with
LaserOnShift
= 0) such, that the
marking vectors’ ends will be exactly marked and
only afterwards the parameter
LaserOnShift
should be adjusted (keeping constant the
parameter
Timelag
), so that the marking vectors’
beginnings are exactly marked, too.
In a second step (if necessary)
set_sky_writing_para can be used to optimize
the parameters
Nprev
and
Npost
:
Nprev
and
Npost
may be decreased (relating to the default
settings of set_sky_writing, see below) to mini-
mize marking times. Alternatively,
Nprev
may be
increased to enable a correspondingly large nega-
tive
LaserOnShift
.
• The parameter
Timelag
should be set to the
tracking error of the galvanometer scanners.
• For the set_sky_writing and
set_sky_writing_list commands,
Nprev
and
Npost
are predefined. Here, the following
applies:
–
Nprev
= approx. 0.15 ·
Timelag
–
Npost
= approx. 0.1 ·
Timelag
This results in the following run-in and run-out
durations:
– Run-in duration / µs
= approx. 3 ·
Timelag
(mode 1)
– Run-in duration / µs
= approx. 1,5 ·
Timelag
(mode 2, 3)
– Run-out duration / µs
= approx. 2 ·
Timelag
(mode 1)
– Run-out duration / µs
= approx. 1 ·
Timelag
(mode 2, 3)
These are safe values for a suitable
Timelag
parameter.
•With set_sky_writing_para or
set_sky_writing_para_list, you can also specify
shorter run-in and run-out phases to reduce
marking times. Shorter run-in and run-out phases
are particularly beneficial when lines are marked
in only one direction without interruption and
jump and marking speeds are set equally.
Take note, though, that in Sky Writing mode no
automatic adjustment of laser and scanner delays
(as described on page 107) is performed:
– If the next marking command’s run-in phase
begins when the preceding command’s
LaserOn delay hasn’t yet expired, then the laser
won’t switch on for the preceding command
(see figure 39, page 109).
– If the next marking command’s run-out phase
begins when the preceding command’s
LaserOff delay hasn’t yet expired, then the laser
won’t switch off for the preceding command
(see figure 40, page 109).
– In Sky Writing mode 1, a positive
LaserOnShift
time (in µs) should exceed the smallest occur-
ring marking time by no more than
(20 ·
Npost
–
Timelag
) – and in Sky Writing
mode 2 and 3 by no more than (10 ·
Npost
–
Timelag
). Otherwise, the laser won’t be
switched on for this marking (this applies as of
Version OUT 535; with older versions, a very
short marking command might result in the
laser switching on only after the command has
been executed and then remaining switched on
until explicitly switched off by one of the fol-
lowing commands).
• Pulse lengths and frequencies (in YAG modes
additionally the Q-Switch delay and the
FirstPulseKiller signal parameters) previously
defined for the “laser active” laser control signals
are kept unchanged in the Sky Writing mode. On
the other hand, previously defined LaserOn,
LaserOff, mark, polygon or variable polygon
delays will not be taken into account in the Sky
Writing mode. They will be fully functional again
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