RTC
®
5 PC Interface Board
Rev. 1.9 e
8 Advanced Functions for Scan Head and Laser Control
188
innovators for industry
8.7.7 Synchronization of Processing-
on-the-fly Applications
Execution of command lists can be started by either
a software command or an external start signal (the
latter triggered, for instance, by a light barrier or a
mechanical contact) (see
).
If execution of the scanning process shouldn’t be
started directly after receipt of the light-barrier signal
(e.g. because the transport system first needs to
position the workpiece into the scan system’s real
image field), then some ways to implement an appro-
priate delay are:
• For position-forwarding via the McBSP interface:
command at the
beginning of the command list
• For position-forwarding via encoder/counters:
(to reset
the counter(s)) and a subsequent
command at the
beginning of the command list
• For position-forwarding via encoder counters:
,
or
(to reset the counter(s)) and a subse-
command at the
beginning of the command list.
is useful for 2D
encoder-based Processing-on-the-fly applica-
tions. This function waits until both encoders are
simultaneously within the specified range and
thus doesn’t depend on the actual trajectory used
to reach this range
(1)
.
• Alternative for position-forwarding via
encoder/counters: With external list starts, a track
delay can be configured that postpones
execution of the list start relative to the triggering
input signal or corresponding command (see
). This also allows the execution of
objects in the virtual 24-bit image field (outside
the real 20-bit image field) to be delayed long
enough for their coordinates to be transformed
into the real image field via Processing-on-the-fly
corrections.
External list starts triggered by an external start
signal (or by
immediately because of the track delay setting
are held in a queue that can accommodate up to
8 starts (each start trigger will be automatically
generated when the delay has expired, also see
). This helps avoid dead time between
the execution of multiple (Processing-on-the-fly)
list programs. Moreover, the list command
can be used to trigger further
list starts at defined intervals.
The commands
,
can also be used to interrupt a list for intermediate
motions (of the conveyor belt or XY stage etc., e.g.
when using a virtual image field – see
). If the intermediate motions aren’t for
marking purposes, then you should switch off the
“laser active” laser control signals prior to each
motion (hence before interrupting the list via
etc.). Otherwise, such motions
might result in unintended marking or burn-in. For
encoder-based Processing-on-the-fly applications,
you can also use
to temporarily
(before an interruption) move the laser focus to a safe
park position. After the interruption, use
to move back to the starting position or
some other position.
Galvanometer scanner behavior during intermediate
motions (i.e. during list interruption after
etc.) is dependent on the applied
Processing-on-the-fly correction:
• With McBSP-based Processing-on-the-fly
correction as well as the encoder-based
Processing-on-the-fly corrections
,
, the galvanometer
scanners will be stationary during list inter-
ruption. After interruption, the next marking may
need to be preceded by a jump to the desired
starting position.
• Encoder-based
correction continuously corrects the galva-
nometer scanner positions in accordance with the
current encoder values (e.g. of an XY stage),
whereby the laser focus remains stationary
relative to the XY stage and is therefore always at
the same XY-stage location during the interme-
diate motion). The advantage: when a continuous
line is processed whose length requires fragmen-
(1) If you would use
instead, you would need to call
these commands individually and consecutively for each
encoder. Here, simultaneous fulfilment of both encoder criteria
would depend on the XY stage motion’s explicit trajectory and
you would need to define an appropriate trajectory even
before loading the lists.
