RTC
®
5 PC Interface Board
Rev. 1.9 e
8 Advanced Functions for Scan Head and Laser Control
174
8.6.4 Adjustment
SCANLAB calculates 3D correction tables so that the
plane of the focus mid-position (without setting an
offset via set_defocus, set_defocus_list,
set_offset_xyz or set_offset_xyz_list) is achieved
with z = 0. Particularly when the 3-axis scan system
(with its respective 3D correction table) is intended
for maintaining the laser focus in a specific plane, you
must therefore adjust the mechanical distance
between the scan system and the working plane so
that this plane coincides with the z = 0 plane. If the
mechanical distance is different, then the laser focus
(at least at the edges of the working field or volume)
might not be sharp.
For the varioSCAN and varioSCAN
de
, you’ll also need
to maintain a specific distance to the scan system.
The needed mechanical distances can be obtained
from the 3-axis scan system’s or the varioSCAN’s user
manual. Usually, the working distance used for calcu-
lating a correction table can also be queried via
get_table_para.
Once the working distance and any distance to the
scan system are correctly adjusted, then the focus
position should be fine-tuned. For this, scan a test
pattern onto the middle of the z = 0 working plane.
The optimum focus position for processing results
can be achieved:
•with a varioSCAN and a varioSCAN
de
by manually
adjusting the focusing ring,
•with a varioSCAN
FLEX
by adjusting the focusing
optic’s position via the command move_to,
•with a varioSCAN FC (also with an intelliWELD
®
FC) by adjusting coefficient A of the assigned 3D
correction table
(1)
.
Checking the Z-Axis Calibration
The optimum output values for the Z-axis also
depend on various parameters such as beam diver-
gence of the used laser and tolerances of the optical
components. Such data is generally not available to
SCANLAB and therefore not reflected in calculating
3D correction tables.
Therefore, in some cases the pre-calculated
correction table might not fit optimally to the indi-
vidual scan system. To test whether this is the case,
run a laser marking test application that covers the
entire image field. Check if the laser focus meets the
requirements of your application. If you find that the
spot diameter varies considerably, it might be
necessary to re-calibrate the Z-axis correction.
Here, the user can adjust coefficients A, B and C of
the parabolic function (z
out
= A + Bl +Cl
2
) that
determines the relationship between the Z output
value z
out
and the focus length value l. Here, for each
point
(x|y|z)
in the working volume, the (unit-free)
focus length value l corresponds to the focus length
difference between the specified point
(x|y|z)
and
the point
(0|0|0)
. The aim of the Z-axis calibration
procedure is to determine suitable coefficients A, B
and C. These coefficients can be subsequently trans-
mitted to the RTC
®
5 with the command
load_z_table.
(1) Coefficients A, B and C can be queried via get_head_para and
newly defined via load_z_table. Only A should be modified. B
and C should be transmitted unchanged – as queried – via
load_z_table.
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