Page 387 - Sensors and Control Systems in Manufacturing

Industrial Sensors and Contr ol
high-phase fidelity and bandwidth. The selectable bandwidth setting 341
allows the user to adapt the system to different applications. For the
highest accuracy and sub-nanometer resolution, the bandwidth can
be limited to 10 Hz.
For high-dynamics measurements, a bandwidth of up to 6.6 kHz
is possible, with a resolution still in the 1-nm range.
The user can choose a measurement range from 20 to 500 µm,
depending on the nominal measurement range of the selected sensor.
The ten-channel system provides different extended measuring
ranges for each selected sensor.
The capacitive sensor’s measuring capacitance is the metrology
system for most nano-positioning applications. They are absolute-
measuring high-dynamics devices. The capacitive sensors / control
electronics use a high-frequency AC excitation signal for enhanced
bandwidth and drift-free measurement stability (Fig. 7.16).
The electronics of the capacitive position sensor incorporate an
innovative design providing superior linearity, low sensitivity to
cable capacitance, low background noise, and low drift.
The Integrated Linearization System (ILS) compensates for influ-
ences caused by errors, such as non-parallelism of the plates. A com-
parison between a conventional capacitive position sensor system
and the results obtained with the ILS is shown in Fig. 7.17. When
nano-capacitance sensors are used with digital controllers, which add
polynomial linearization techniques, a positioning linearity of up to
0.003 percent is achievable.
The travel range is 15 µm; the gain 1.5 µm/V. Linearity is better
than 0.02 percent; even higher linearity is achievable with digital

FIGURE 7.16 A 15-µm piezo nano-positioning stage with an integrated capacitive
position sensor.