Scan Head And Laser Control; Vector Commands; Arc Commands; Microsteps - Scanlab RTC 4 Installation And Operation Manual

4.2 Scan Head And Laser Control

Vector Commands

The basic commands for scan head control are the
jump commands and the mark commands. These
commands require as parameters the X and Y coordi-
nates of the end point of the corresponding vector
Each vector starts at the current output position,
which is usually the end point of the preceding
vector. The initial output position at start-up
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(or after a reset of the RTC
the image field, i.e. the point (0|0).
Please refer to chapter 4.4 "Image Field Size", page 29
for a description of the image field coordinate
system.
Jump Commands
A jump command (jump_abs
(usually) fast movement of the scanner mirrors. The
laser focus "jumps" to the new position. In general,
the laser is switched off during the jump. The jump
speed can be defined with the list command
set_jump_speed (see page
If the laser system does not allow fast switching, the
jump speed must be set high enough to prevent a
visible marking effect on the workpiece. Also see the
command home_position (page
Mark Commands
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The RTC 4 automatically turns on the laser at the
beginning of a mark command. During a mark
command (mark_abs or mark_rel), the laser focus
moves along the specified vector with a constant
marking speed, producing a straight mark on the
workpiece.
If another mark (or arc) command follows immedi-
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ately afterward, the RTC 4 leaves the laser on.
Therefore, a sequence of individual mark (and arc)
commands creates a polyline mark. The laser is
turned off after the last mark (or arc) command in a
series of mark (or arc) commands, or if the end of the
current list is reached.
The list command set_mark_speed (see page 109)
defines the marking speed. The marking speed
can be changed anywhere in a list.
(1) The coordinates must be specified as digital control values
(without units). To avoid confusion with coordinates in [mm],
SCANLAB uses the expression "coordinate values [in Bits]".
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RTC 4 PC Interface Board
Rev. 1.3 e
4 Principle Of Operation
(1)
.
4) is the center of
or jump_rel) causes a
107).
89).

Arc Commands

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The RTC 4 software driver provides arc commands
for marking circular arcs. These commands require
parameters for the X and Y coordinates of the arc
center and the arc angle. The arc starts at the current
output position.
At the beginning of an arc command, the RTC
automatically turns on the laser. During an arc
command (arc_abs or arc_rel), the laser focus moves
with the defined marking speed along the specified
arc. The laser is turned off after the last arc (or mark)
command in a series of arc (or mark) commands, or
if the end of the current list is reached.

Microsteps

Each vector defined by a jump, mark or arc command
is divided into a number of small steps by the RTC
These microsteps are transferred to the scan head at
a constant time rate (output period ∆t) In controlling
its galvanometer scanners, the scan head implements
the steps via an analog servo loop.
Figure 4 shows how the X component of a vector is
divided into microsteps. The Y component is split up
in the same way.
x
Dx
(t | x )
Dt
0 0
x x coordinate of the current output
0
position before scanning the vector
x x coordinate of the end position
1
of the vector
Dt step period
The X component of a vector is split up into microsteps.
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4 also
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4.
(t | x )
1 1
(t +i·Dt | x +i·Dx)
0 0
Time
4
15