Scanlab RTC6 PCIe Board - Sky Writing Mode 3; Synchronization

RTC6 boards
Doc. Rev. 1.0.21 en-US
7 Basic Functions for Scan Head Control and Laser Control
162
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Sky Writing Mode 3
The time cost of Sky Writing motions for vectors and
arcs having only small directional changes within a
Polyline is probably disproportionately high for the
gained accuracy.
Therefore, set_sky_writing_mode or
set_sky_writing_mode_list can be used to switch to
Sky Writing Mode 3. A switching limit angle can be
defined for this by set_sky_writing_limit or
set_sky_writing_limit_list.
Then only for larger angle deviations (cos() < Limit )
between successive Mark Commands of a Polyline a
Sky Writing motions is executed as in
Sky Writing Mode 2.
In contrast, smaller angular changes (cos()  Limit )
result in a (variable) polygonal delay, see Section
”Variable Polygon Delays”, page 151. See also
Figure 45.
Notes
• In case a Polyline ends with a short mark vector
(shorter than mark speed × Timelag ) - and a
Polygon Delay has been executed but not a
Sky Writing motion - then the length of the short
vector (caused by the Tracking Error) may possibly
not achieve the precision expected with
Sky Writing.
• At the beginning and end of a Polyline, as well as
when interrupted with “non-
Sky Writing Mode 2-capable“ list commands, a
Sky Writing Mode 1 movement always occurs in
Sky Writing Mode 3, see Section
”Sky Writing Mode 2”, page 161.
Synchronization
The timing diagram for scan-head and laser control in
Sky Writing Mode 1 is shown in Figure 46. The timing
diagram for Sky Writing Mode 2 and
Sky Writing Mode 3 is similar, but here the
galvanometer scanners perform no reverse motion in
the run-in and run-out phases.
The Timelag , Nprev , Npost and LaserOnShift
parameters are specifiable for set_sky_writing_para
and set_sky_writing and the corresponding
list commands:
• The Nprev parameter is a whole number in units of
10 µs and defines the duration of the run-in:
• The Npost parameter is a whole number in units of
10 µs and defines the duration of the run-out:
• The parameters Timelag (64-bit IEEE floating
point value rounded to integer multiple of
1/64 µs) and LaserOnShift (whole number in units
of 1/64 µs) define the delay of the Signals for
“Laser Active” Operation switch-on and switch-
off time points relative to the set starting position
and set ending position:
– Delay of switch-on time point relative to the set
starting position / µs
= Timelag + 1/64 µs × LaserOnShift
– Delay of switch-off time point relative to the set
ending position / µs
= Timelag
Mode Duration
1 20 × Nprev [µs]
2, 3 10 × Nprev [µs]
Mode Duration
1 20 × Npost [µs]
2, 3 10 × Npost [µs]