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XPS-Q8 Controller
15.0
Analog Encoder Calibration
This section refers only to analog sine encoder inputs. The purpose of the analog
encoder interpolation feature is to improve the stage accuracy by detecting and
correcting analog encoder errors such as offsets, sine to cosine amplitude differences,
and phase shift.
Other kinds of errors can exist in the encoder such as impure sine or cosine signals. This
feature will not compensate for them and will disturb the results of the calibration
process.
Also, this calibration process assumes that the errors are small, i.e., less than a few
percent.
Below are figures and numbers to illustrate the type of errors and their impact on
accuracy.
Offset Error
The offset error generates 0.32% interpolation error per percent offset on the sine or
cosine signals. With a 20 µm scale pitch, 1% sine offset generates 63.5 nm peak to peak
interpolation error.
The real signal is not always symmetrical to 0. The offset error is defined as the
difference between the signal's horizontal axis where it is symmetrical and 0.
Amplitude Mismatch
185
Figure 59: Offset Error.
Note
Figure 60: Amplitude Mismatch.
XPSDocumentation V1.4.x (EDH0301En1060 — 10/17)
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