Scanlab RTC6 PCIe Board - Automatic Self-Calibration; Use for Drift Compensation; How It Works

RTC6 boards
Doc. Rev. 1.0.21 en-US
8 Advanced Functions for Scan Head Control and Laser Control
275
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8.10 Automatic Self-Calibration
8.10.1 Use for Drift Compensation
Long-term repeatability is very important in many
applications, for example, for rapid prototyping in
which the processing operation can span several
hours. For such laser applications, the
galvanometer scanner’s long-term drift and
temperature drift, which manifest as a shift (offset
drift) and increase or decrease in the size (gain drift)
of the working Image Field, can exceed the allowed
tolerances.
In such applications, it is helpful to start up the
application only after the galvanometer scanners
have reached their operating temperature. In
addition, the magnitudes of environmental
fluctuations (for example, operating temperature
changes to which the scan system is exposed) should
be kept as small as possible and the scan system
preferably operated with a constant load.
For higher long-term repeatability requirements,
SCANLAB scan systems can be equipped with an
additional internal sensor system for automatic self-
calibration (ASC sensor system, Home-In sensors).
This allows the position detectors of the
galvanometer scanners to be calibrated and gain
drift and offset drifts to be reliably compensated. The
positioning accuracy is thus maintained over long
periods of time. Remaining long-term drift effects are
of the same order of magnitude as short-term
repeatability accuracies.
8.10.2 How it Works
By auto_cal, a measurement routine can be started
for determining the exact control values for reference
positions (Home-In positions) defined by the internal
sensor system.
For drift measurement, the routine should be
executed:
• When setting up the equipment – to determine
reference values for the Home-In positions,
see Chapter 8.10.3 ”Determining Reference
Values”, page 277
• During the application at appropriate time
intervals – to determine if and how the Home-In
positions have changed, see Chapter 8.10.4
”Calibration During the Application”, page 277
For drift compensation, appropriate gain values and
offset values can be calculated and set separately for
each galvanometer scanner based on the determined
deviations between the current Home-In position and
the reference value. See also Chapter 7.3.6 ”Output
Values to the Scan System”, page 181, #9.
The setting can also be made manually with set_hi, if
customer-specific measuring procedures are to be
used, see Section ”Customer-Specific Calibration”,
page 278.
Notes
• Prior to performing a measurement routine,
auto_cal( Command = 4 ) can be used to check if:
– the attached scan system in fact has an internal
sensor system for automatic self-calibration
(Home-In sensors)
– the sensor system is functioning properly