Position Monitoring - Scanlab RTC 5 PC Interface Board Installation And Operation Manual

8.1.3 Position Monitoring

For some applications, it's important to monitor scan
system positioning even when processing, and, if
necessary, with documentability.
For this purpose, the actual positions of the scan axes
(hence the galvanometer scanners and/or the scan
system's Z axis) must be selected to be returned from
the scan system via the command
control_command. The returned actual position
values can be queried via get_values
(1)
set_trigger/set_trigger4
If returned actual positions of the scan axes need to
be compared with cartesian coordinate values (X, Y,
Z) (which are the call parameters for RTC
commands), then it must be additionally taken into
account that these coordinate values generally –
depending on the selected settings – undergo various
corrections and transformations (e.g. an image field
correction, a coordinate transformation and/or a
Processing-on-the-fly correction) before they are
outputted as control values to the scan system (also
see page 126). To facilitate such comparability of the
scan system's returned actual position values with
original cartesian coordinate values (X, Y, Z), the
®
RTC 5 command set provides commands for
backward transformation of position values.
For runtime reasons, the backward transformation
needs to subsequently be performed by the PC rather
®
than on the RTC 5 board itself. For this, all correction
and transformation settings currently assigned to the
scan system can be transferred from the RTC
to the PC via the upload_transform
Afterwards, an individual XY value pair or an indi-
vidual Z value can be backward transformed via
transform. With get_transform
get_waveform), you can backward transform an
entire series of XY value pairs or Z values previously
recorded via set_trigger/set_trigger4.
(1) However, transfer times to/from the scan head will cause the
most recently returned actual position to lag the most recently
outputted control signal by a few clock cycles.
®
RTC 5 PC Interface Board
Rev. 1.9 e
8 Advanced Functions for Scan Head and Laser Control
or recorded via
.
®
5
®
5 board
command.
(also see
Notes
• Wobbel transformations, Processing-on-the-fly
corrections and eventual clipping during forward
transformation can never be backward trans-
formed (see following table).
Forward
transformation
Wobbel motion
Processing-on-the-fly correction
Coordinate transformations
(total matrix and offset) to the X
and Y coordinates
Offset to the Z coordinate
Clipping to the edge of the
positionable (20-bit real)
image field range
Image field correction
Gain and offset correction of
automatic self-calibration
Clipping to the edge of the
maximum possible range of
control values.
Likewise, backward transformation isn't possible
if a noninvertable transformation matrix was
defined during forward transformation (note:
clipping to ±50 for each individual matrix coeffi-
cient while taking into account a factor defined
via set_scale; see page 161). The noninvertability
will already be reported by the
upload_transform command.
If forward transformation included a clipping to
the edges of the positionable image field or to the
edges of the maximum possible range of control
values, then backward transformation will
(ideally) calculate the cartesian coordinates of
these edge values instead of the original values.
• Via get_values, four freely specifiable signals can
be queried simultaneously (example: galva-
nometer 2's actual position via StatusAX, galva-
nometer 1's actual position via StatusAY, the
actual Z-axis position via StatusBX, plus an
additional desired signal such as LaserOn). In
contrast, the get_value
's' in the command name) isn't useful for
Backward
trans-
formation
possible
no
no
yes
yes
no
yes
yes
no
command (without the
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