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9
Technical Principles to Aid Usage of MINISCALE PLUS
9.8
Referencing
9.9
Periodic Deviations
9.10 Interpolation Errors
9.11 Comparator Errors
30
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Incremental measuring systems cannot determine the exact position after being
switched on. For this reason, another track is added alongside the incremental
track; the reference track. One or multiple reference points can be marked on the
reference track.
A reference run of the carriage is required to reference the system. The axis usually
travels in one direction until a mechanical stop. From there, the axis travels
backwards until the reference mark is covered. Usually, the equidistant reference
mark is always approached from the same direction.
The controller can then modify the internal counter to a specified value using the
reference signal. For the analog interface module, the controller recognizes a
predefined position for the incremental signals (this is usually SIN = COS and both
greater than zero), as well as REF = ‚high' as the reference position.
All incremental distance measuring systems are influenced by the effects of
periodic deviation, whose wavelength corresponds exactly to the graduation
spacing or a fraction of it. This periodic deviation, also called short-wave deviation,
occurs due to small deviations in the sensor system or electrical signal processing.
This means that the sine and cosine signals deviate from the mathematically exact
form. Deviations can be classified depending on the arrangement (harmonics).
SWD period
Deviation occurs due to
1 signal period
Sine/cosine offset
1/2 signal period
Sine and cosine amplitude are different
1/3 – 1/8 signal period
Sensors deliver a signal which is fundamentally different
from the sine wave shape
If periodic deviations only occur during digitization and calculation of position, then
we talk about an interpolation error. This can occur in some circumstances if the
transmitter and receiver circuitry are not precisely matched to one another.
The comparator error, also referred to as the Abbe error, is a systematic deviation
which occurs when the axis of the length standards do not coincide with the axis
of the distance standards. The causes for the deviation are minute rotary
movements in the axis design, which influence the measuring result.
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