Scanlab RTC 4, Installation And Operation Manual

Page: 49 / 136

RTC
®
4 PC Interface Board
Rev. 1.3 e
5 Advanced Programming
49
innovators for industry
Scanner Control
The RTC
®
4 supports two different modes for
scanning raster image lines. The two modes differ in
the way the galvanometer scanners are controlled
when moving from one pixel position to the next. The
scanner mode is selected with the command
set_pixel_line .
Mode 0
In this mode, the scanners "jump" from one pixel to
the next in one step. Depending on the pixel distance,
some overshooting may occur – see
figure 21 on
page 49 .
In this mode, the pixel step period T must be
relatively long: T
≈
1 ms … 10 ms.
To make sure that each pixel is marked at its exact
position, the LaserOn delay must be longer than
the required settling time.
In Mode 0, each pixel will be marked at its exact
position. The position does not depend on the
dynamic performance of the scan head. However,
the overall marking time will be quite long.
Mode 0 should always be used if one pixel is marked
by more than one laser pulse.
Mode 1
In Mode 1, each image line is treated like a normal
vector. That means the movement is split up into a
number of microsteps. After an initial acceleration
phase, the laser focus will move with an approxi-
mately constant velocity along the entire image line.
The pixels will be marked in passing.
In this mode, the LaserOn delay can be set to a
few microseconds.
The pixel period T can be chosen according to the
suitable laser frequency. It is typically about
50
µ
s.
The entire image will be slightly shifted because
of the lag between the set position and the real
position. This can be compensated by adjusting
the start position of each image line.
To suppress distortions during the acceleration
phase, some idle pixels (with zero pulse width)
can be inserted at the beginning of each image
line.
Scanner P
osition
LASERON Signal
LaserOn
Delay
Time
Time
Real Position
Set Position
Laser pulse should
not start before
the set position is
reached.
Mode 0
21
Timing of laser and scanner control in Pixel Output Mode 0
Scanner P
osition
LASERON Signal
LaserOn
Delay
Time
Time
Real Position
Set Position
(Microvectors)
Mode 1
22
Timing of laser and scanner control in Pixel Output Mode 1
The pixel output period in this example is T = 50
µ
s (= 5 microsteps).