RTC
®
4 PC Interface Board
Rev. 1.3 e
5 Advanced Programming
51
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Notes
• After a timed jump (mark) command, a
jump delay
, a
mark delay
or a
polygon delay
is inserted, just like after a normal jump (mark)
command. That means the total time for the
command is the
sum
of the specified time and the
corresponding delay.
(Also see the section
• The timed jump and mark commands can be used
for 2D vectors only.
5.9 Automatic Self-Calibration
What It Achieves
Environmental fluctuations, especially temperature
changes, can cause galvanometer scanner drift, i.e. a
shift (offset drift) and an increase or decrease in size
(gain drift) of the working image field. Therefore,
high-precision applications should only be started up
when the scanners have reached their operating
temperature. In addition, the magnitudes of environ-
mental fluctuations, e.g. operating temperature
changes, to which the scan head is exposed should be
kept as small as possible. For applications that are
subjected to unavoidable environmental fluctua-
tions, but nevertheless require high long-term
repeatability, SCANLAB provides scan heads with
automatic self-calibration (optional for apertures
≥
14 mm). Scan heads delivered with this option have
an internal reference sensor system. This reference
system provides the RTC
®
4 software with the ability
to automatically calibrate the galvanometer scanner
position detectors any time the user deems it appro-
priate. Thus, drift effects can be reliably compensated
and positioning accuracy is maintained over long
periods of time. Remaining long-term drift effects are
the same order of magnitude as short-term repeat-
ability.
How It Works
Automatic self calibration of the scan head is started
via the command
auto_cal(...,1)
.
During calibration, the scan head automatically seeks
several reference positions within the scannable area
that are defined by the internal sensor system. The
seek values are determined and compared with fixed
reference values. From the resulting deviations, offset
and gain compensation factors are calculated.
These compensation factors are immediately made
available for use in all future positioning tasks until
the
auto_cal(...,1)
is called again or until compen-
sation is shut off via
auto_cal(...,2)
. The entire cali-
bration procedure takes place in about 5 seconds.
The
auto_cal(...,0)
command is available for deter-
mining the reference values. The resulting output
coordinates for the various sensor positions are
stored in non-volatile memory on the RTC
®
4 board.
This way, the values are not lost when the system is
shut down.
The laser must be switched off during the calibration
procedure and no other commands are transferred to
the scan head until the calibration is completed.
For further information, see
