
Open access
Author
Date
2020-12Type
- Doctoral Thesis
ETH Bibliography
yes
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Abstract
Geometric accuracy tests are an integral part of machine tool acceptance
procedures. With an increasing demand for higher machine tool accuracy
at lower costs and the requirement to test under shop floor conditions, the
measuring task becomes more and more challenging. The field of spindle
metrology is particularly affected. As permissible maximum errors decrease,
a corresponding decrease in measurement uncertainty is required. A feasible
strategy to cope with this is to increase the accuracy of the measurement
instrumentation. However, in shop floor environments disturbances are likely
to degrade the measuring performance. Not only sensors and transducers are
affected, but also the mechanical setup is prone to disturbing influences. As a
consequence, a gap between the measuring performance which is determined
under controlled inspection room conditions and the performance under real
shop floor application conditions emerges.
The objective is therefore to enable the utilization of existing and nominally
capable spindle measurement instrumentation in shop floor environments
and on machine tools without the abatement of measurement accuracy.
The chosen approach to achieve the objective incorporates on-machine
and in-process error identifications of the spindle measurement setup. The
gained information are used to develop target-oriented countermeasures,
improvements of the measurement setup, and correction procedures. Electromagnetic
interference as well as environmental temperature variations
are identified as main disturbance sources. Due to the characteristics of the
related error systems, cap tests are utilized for the experimental error analysis.
Electromagnetic interference markedly degrades the performance of
capacitive displacement transducers which are commonly utilized for spindle
measurements. However, it is shown that an electromagnetic compatible
measurement setup is accomplished by the electrical insulation of the measuring
circuit against structural components of the machine tool and thus
the electrical machine tool system. A testing procedure and a corresponding
testing device are proposed which enable the on-machine performance testing of capacitive displacement transducers and the performance verification of
the setup recommendation for test setups.
In order to identify the thermal distortion of a fixture, an on-machine
analysis method is proposed. The achieved measurement uncertainty is
almost independent of the fixture dimensions. An experimental thermal
analysis of the specific fixture indicates uniformly distributed fixture material
temperatures and the admissibility of a lumped capacity assumption, which
results in the expectation of thermal expansion leading to dimensional
scaling without distortion. This expectation is confirmed by the experimental
identification procedure. The experimental data can directly be used for the
compensation of thermally induced fixture distortion.
The cap test approach is also applied for the analysis of thermally
induced errors of axial displacement transducers. Clamping positions of the
transducers are considered as boundary conditions in the error identification
procedures. In particular, the thermal behaviors of inductive displacement
transducers are analyzed. Steady state error coefficients are evaluated
which allow a comparison of different transducer models and an appropriate
selection of transducers. In addition, a static error correction approach
directly makes use of these coefficients. For the correction of dynamic errors
an observer-based correction approach is developed. In the tested cases of
two inductive displacement transducer models relative error reductions in the
range of 85-95% are achieved. Show more
Permanent link
https://doi.org/10.3929/ethz-b-000473479Publication status
publishedExternal links
Search print copy at ETH Library
Publisher
ETH ZurichSubject
error identification; measurement uncertainty; error analysis; machine tool measurement; measurement error; displacement measurement; compensation; observer; thermally induced error; error correction; capacitive displacement measurement; axial displacement transducerOrganisational unit
03641 - Wegener, Konrad / Wegener, Konrad
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ETH Bibliography
yes
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