Piezo Engineering Tutorial
QNP3 Hardware Manual
reason, the maximum temperature that Aerotech’s piezo actuators can be used is approximately 80°C. In
precision positioning applications, temperatures approaching this can cause serious detrimental effects to
the accuracy and performance of the piezo stage.
Piezo actuators are well-suited for operation at extremely low temperatures, as well. The crystals in
piezoelectric material remain in their piezoelectric configuration no matter how low the temperature drops.
Standard commercially available stack actuators can operate down to -40ºC with no problems. The biggest
issue in cold environments is not the piezo itself, but induced stress from thermally contracting
mechanisms. For extremely cold environments, special design considerations are required for the actuator
to survive the cooling process. Carefully chosen electrodes and extremely homogeneous ceramic must be
used to prevent cracking because of unmatched thermal expansion coefficients.
Piezo ceramics do operate differently at low temperatures. At these low temperatures, the ceramic stiffens,
which causes a decrease in the amount of strain generated per volt. This is offset by increased electrical
stability in the crystal structure, allowing fully bi-polar operation. Other advantages of low temperature
operation include lower hysteresis, better linearity, lower capacitance and smaller dielectric loss.
For the highest accuracy, Aerotech recommends operation at or near 20°C because that is the temperature
in which the nanopositioning stages are built and calibrated. Contact an Aerotech Applications Engineer if
extreme temperature environments are expected in your operation as we will assist you in selecting or
customizing the proper piezo positioning stage for the highest level of performance in any environment.
C.3.7.3 Vacuum
Low-voltage (<200 V) piezo acutators are particularly well-suited for vacuum operation. Piezo actuators do
not require lubrication that typically requires great care when selecting for ultra-high vacuum applications.
Vacuum pressures from 10 to 10
-2
Torr need to be avoided because the insulation resistance of air
dramatically decreases in this range (known as the corona area), thus allowing easier dielectric breakdown.
Aerotech’s piezo nanopositioning stages can be prepared for ultra-high vacuum operation.
C.4 Piezo Stage Properties and Nomenclature
Aerotech’s piezo nanopositioning stage series are designed with the end-user in mind. As a result, it is
important that our customers have a thorough understanding of our specifications so that they can best be
matched to the application or end-process. The following is a description of the specifications and
nomenclature used in our data sheets.
C.4.1 Accuracy/Linearity
As discussed in Section 3.2, piezo actuators exhibit hysteresis and non-linearity when operated on open-
loop mode. When operating in closed-loop mode, the non-repeatabilities due to piezo actuator hysteresis are
eliminated. However, the piezo stage may still exhibit non-linearities and hysteresis that affect the overall
positioning accuracy of the device. The magnitude of these non-linearities are a function of the quality of the
closed-loop feedback sensor and electronics used in the design, as well as the quality of the mechanical
stage design. With our high-resolution capacitance sensors, advanced electronics and optimized flexure
designs, linearity errors below 0.02% are achievable. Accuracy and linearity are measured with precise laser
interferometers at a distance of ~15 mm above the moving carriage of the piezo nanopositioner (unless
otherwise noted).
The terms accuracy and linearity are sometimes used synonymously when describing the positioning
capability of piezoelectric nanopositioners. However, they can have subtle differences in meaning.
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Appendix C
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