Optimizing The Application; Dynamic Positioning With Galvanometer Scanners - Scanlab hurrySCAN 10 Installation & Operation Manual

6

Optimizing the Application

6.1 Dynamic Positioning with
Galvanometer Scanners
SCANLAB's galvanometer scanners and amplifier
boards allow precise dynamic control of the two
deflection mirrors. This enables exact positioning of
the laser beam with high speed.
Most laser applications require the laser focus to
trace contours within the working plane at a constant
processing speed. To achieve this, the control subdi-
vides the contours into microsteps. Microstep length
is determined by the output period and desired
speed. Galvo dynamics are usually optimized for such
microvector control. For ensuring optimum opera-
tion, the following properties of galvanometer scan-
ners must be considered:
Positioning Speed
As galvo dynamics are usually optimized for
microvector control, it is advisable to also use vectors
when positioning with the laser switched off.
Compared to hard jumps, a defined positioning
speed will prevent excessive oscillation and usually
produce shorter positioning times. Positioning
speeds can generally be significantly higher than
processing speeds.
A typical and a maximum positioning speed (in
[rad/s]) each is listed in "Technical Specifications" on
page 34. There, the typical positioning speed is also
specified (for a selected F-Theta objective) as posi-
tioning speed within the image field (in [m/s]).
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With the SCANLAB RTC PC interface board or the
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RTC SCANalone standalone board, the positioning
speed (jump speed) can be set via the
set_jump_speed software command. The RTC
jump speed (in [bit/s]) is derived by multiplying the
positioning speed (in [mm/s]) by the correction file's
calibration factor (in [bit/mm]). With vector tuning,
the jumps themselves should be executed via the
commands jump_abs or jump_rel.
Processing Speed
The processing speed must be adjusted according to
the particular application. As an example, a typical
marking speed for marking small characters (marking
speed in the image field in [m/s] for a selected F-Theta
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hurrySCAN 10, digital, 1064 nm, f = 254 mm
Rev. 2.6 e
6 Optimizing the Application
objective) is specified in "Technical Specifications" on
page 34. For other applications or optical configura-
tions, the appropriate processing speed can differ
considerably from the specified value.
An appropriate initial value for optimizing the posi-
tioning speed is the marking speed listed in "Technical
Specifications" on
mark speed) that can be set via an RTC
specified by multiplying by the correction file's cali-
bration factor (in [bit/mm]).
Tracking Error (Time Lag)
Galvanometer scanner movements do not occur
instantaneously with respect to vector control, but
rather after a certain time lag, the tracking error. The
tracking error characterizes the reaction properties of
the galvanometer scanners and is specified as
another key dynamic parameter (see "Technical Spec-
ifications" on page
period must be significantly shorter than the tracking
error. Otherwise, instead of moving the galvos with
constant speed, the servos would attempt to follow
the individual microsteps. This, in turn, would
increase power consumption and thermally stress the
galvos. SCANLAB therefore recommends as short an
output period as possible, no more than 20% of the
tracking error. SCANLAB's RTC
achieve very good results with an output period of
10 µs.
Oscillation behavior and tracking error must be taken
into account by the application software, which
synchronizes the scan head and the laser control. If
the scan head is controlled via a SCANLAB RTC
interface board or via an RTC
lone board, then synchronization is easily realized by
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appropriately setting the scanner and laser delay
parameters. SCANLAB recommends the following as
initial values for delays:
• Laser-On Delay: 60% of the tracking error
• Laser-Off Delay: 120% of the tracking error
• Jump Delay: 200% of the tracking error
• Mark Delay: 100% of the tracking error
• Polygon Delay: 50% of the tracking error
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The RTC user manual describes how delays can be
optimized for an application's quality requirements.
page 34. The process speed (RTC
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board is
34). The vector control output
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boards consistently
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SCANalone standa-
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PC
29