Precision Test Equipment for Nano Gauging Probes
Abstract
Due to the increasing demands on the processing tolerance in manufacturing
technology and on the miniaturization of industrial components, nanometrology is
increasingly more important in manufacturing processes. Therefore, precise
measuring instruments and sensors play a decisive role for the accurate
characterization and inspection of products.
For linear length inspection, highly accurate gauging probes, i.e. nano gauging
probes, are of great importance. They possess a resolution within the nanometer
range and have an accuracy of less than 100 nm. This group of precision gauging
probes includes probes based on electronic as well as optical principles, e.g.
inductive, incremental-optical or interference optical. To guarantee the
accuracy and the traceability to the definition of the meter, calibration and
test of nano gauging probes are necessary. Existing test methods and machines
suffer from various disadvantages. Some permit only manual test procedures which
are time-consuming, e.g. with high accurate gauge blocks as material measures.
Other tests exhibit higher accuracy but are capable of measuring only in the
micrometer range or result in uncertainties of more than 100 nm in the large
measuring ranges.
In order to make the test possible with a high resolution as well as a large
measuring range, a precision test equipment for nano gauging probes was
constructed, that with a resolution of 1.24 nm, a measuring range up to 20 mm
(60 mm) and a measuring uncertainty of approx. ±10 nm can fulfill the
requirements of high resolution within the nanometer range while simultaneously
covering a large measuring range in the order of millimeters. This work is based
on a calibration equipment for length sensors developed at the Institute of
Process Measurement and Sensor Technology at the Ilmenau Technical University.
The precision test equipment is equipped with a plane mirror interferometer. As
a new approach for the avoidance of the Abbe error, a continuous angular control
of the measuring body is realized with the help of piezo translators. Thus,
during the test procedure, the measuring body reaches a tilt of less than 0.2"
is reached and the Abbe error is minimized.
A drive system consisting of ball guides, a fine thread spindle and a DC motor
positions the measuring body. For the automation of the test procedure a
measuring program adhering to the measurement principle outlined in VDI/VDE 2617
guideline was designed. With this program a gauging probe can be tested in less
than thirty minutes with eleven measuring points and five repetitions.
Theoretical and experimental investigations show that the precision test
equipment has a test uncertainty of approx. ±10 nm at the measuring range of 18
mm, that corresponds to a relative uncertainty of approx. ±5·10-7. With small
uncertainty, the minimization of the Abbe error and short test times this device
can be regarded as an universal and efficient precision test equipment, which is
available for the accurate test of arbitrary precision gauging probes and other
linear length sensors
