RTC
®
5 PC Interface Board
Rev. 1.9 e
7 Basic Functions for Scan Head and Laser Control
95
• As with mark and arc commands, during an
ellipse command, the laser focus moves with the
defined marking speed along the specified arc.
The “laser active” laser control signals are
automatically turned on at the beginning of an
ellipse command and turned off at the beginning
of the subsequent jump (or generally: non-mark,
non-arc or non-ellipse) command, provided no
further ellipse commands (or a series of arc, mark
or ellipse commands) follow. Because set_ellipse
is a short list command, it can be called between
a mark command and a subsequent ellipse arc
command without thereby interrupting
polygonal traversal (the laser remains on) (also
see page 217).
• In contrast to mark and arc commands (which
automatically begin marking at the current
output position), elliptical arc commands always
begin marking at the starting point determined
via the above-mentioned parameters. If the arc
starting point doesn’t equal the current position,
then a hard jump to the starting point will be
executed at the beginning of marking (and jump
delays will be ignored).
• Elliptical arcs can also be marked via circular arc
commands (e.g. arc_abs) if an appropriate
coordinate transformation (e.g. scaling that
differs in the x/y directions) was specified with
set_matrix. Here, though, the speed will vary
along the arc (also see note on page 163).
This contrasts with mark_ellipse_abs and
mark_ellipse_rel, where in 10 µs intervals the
step length gets adjusted for the ellipse’s shape at
the current position such that the arc is marked
with a (largely) constant speed (the currently set
marking speed).
For very large eccentricities and also at high
marking speeds, however, such stepwise ellipse
approximation via a 10 µs clock can produce
numerical inaccuracies in the end point regions of
the large half-axis. Consequently, the speed there
might not be precisely constant (e.g. an eccen-
tricity of
a
/
b
= 2 and 100 microvectors per
circumference would produce a speed deviation
of approx. 3.7%).
Moreover, as closed equations don’t exist for
calculating an ellipse arc length, the step length
of the finally-marked microvector is generally
shorter and the marking speed correspondingly
lower than specified. Nevertheless, end positions
will always be exact.
Likewise, the Sky writing option might produce
run-in/run-out irregularities at the large half-axis.
Users should therefore check if their chosen
parameters are compatible with their precision
requirements.
Para Commands
If the vector-defined laser control is activated, also
the para-mark and para-jump commands
(para_jump_abs, para_jump_rel, para_mark_abs,
para_mark_rel) can be used. These commands
simultaneously vary a signal parameter linearly along
the mark or jump vector (see page 147)
(1)
.
(1) Additionally, the RTC
®
5 provides timed para vector commands
(see page 147 and page 198).
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