pi2009
2-198
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Physik
Instrumente
(PI)
GmbH
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Co.
KG
2008.
Subject
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Cat120E
Inspirations2009
08/10.18
Piezo Nano Positioning
follow. Rapid actuation of
nanomechanisms can cause
recoil-generated ringing of the
actuator and any adjacent com-
ponents. The time required for
this ringing to damp out can be
many times longer than the
move itself. In time-critical
industrial nanopositioning
applications, this problem
obviously grows more serious
as motion throughputs
increase and resolution
requirements tighten.
Classical servo-control tech-
niques cannot solve this prob-
lem, especially when reso-
nances occur outside the
servo-loop such as when ring-
ing is excited in a sample on a
fast piezo scanning stage as it
reverses direction. A solution is
often sought in reducing the
scanning rate, thereby sacrific-
ing part of the advantage of a
piezo drive.
A patented real-time feedfor-
ward technology called
InputShaping
®
nullifies reso-
nances both inside and outside
the servo-loop and thus elimi-
nates the settling phase. For
more information see p. 2-201
or visit www.Convolve.com.
Heat Generation in a Piezo
Actuator in Dynamic
Operation
PZT ceramics are (reactive)
capacitive loads and therefore
require charge and discharge
currents that increase with
operating frequency. The ther-
mal active power, P (apparent
power x power factor, cos H9272),
generated in the actuator dur-
ing harmonic excitation can be
estimated with the following
equation:
(Equation 23)
Heat generation in a piezo actu-
ator.
Where:
P = power converted to
heat [W]
tan H9254 = dielectric factor (? power
factor, cos H9272, for small
angles L50883 and H9272)
f = operating frequency
[Hz]
C = actuator capacitance
[F]
U
p-p
= voltage (peak-to-peak)
For the description of the loss
power, we use the loss factor
tan L50883 instead of the power fac-
tor cos H9272, because it is the
more common parameter for
characterizing dielectric materi-
als. For standard actuator
piezoceramics under small-sig-
nal conditions the loss factor is
on the order of 0.01 to 0.02.
Thismeansthatupto2%of
the electrical power flowing
through the actuator is convert-
ed into heat. In large-signal
conditions however, 8 to 12 %
of the electrical power pumped
into the actuator is converted
to heat (varies with frequency,
temperature, amplitude etc.).
Therefore, maximum operating
temperature can limit the piezo
actuator dynamics. For large
amplitudes and high frequen-
cies, cooling measures may be
necessary. A temperature sen-
sor mounted on the ceramics is
suggested for monitoring pur-
poses.
For higher frequency operation
of high-load actuators with
high capacitance (such as
PICA-Power actuators, see p.
1-88), a special amplifiers
employing energy recovery
technology has been devel-
oped. Instead of dissipating the
reactive power at the heat
sinks, only the active power
used by the piezo actuator has
to be delivered.
The energy not used in the
actuator is returned to the
amplifier and reused, as shown
in the block diagram in Fig. 26.
The combination of low-loss,
high-energy piezoceramics and
amplifiers with energy recov-
ery are the key to new high-
level dynamic piezo actuator
applications.
For dynamic applications with
low to medium loads, the
newly developed PICMA
®
actu-
ators are also quite well suited.
With their high Curie tempera-
ture of 320 °C, they can be
operated with internal temper-
atures of up to 150 °C.
Fig. 26. Block diagram of an amplifier with energy recovery for
higher frequency applications
Piezo Actuator Electrical Fundamentals (cont.)
2-199
Piezo Nano Positioning
Piezo Flexure Stages /
High-Speed Scanning Systems
Nanopositioning / Piezoelectrics
Linear Actuators & Motors
Fast Steering Mirrors /
Active Optics
Piezo Drivers /
Servo Controllers
Piezoelectrics in Positioning
Nanometrology
Micropositioning
Linear
Vertical & Tip/Tilt
2- and 3-Axis
6-Axis
Single-Channel
Multi-Channel
Modular
Accessories
Index
Control of Piezo Actuators and Stages
Position Servo-Control
Fig. 28. Block diagram of a typical PI closed-loop piezo positioning system
Fig. 29. Closed-loop position servo-control. For optimum performance, the sensor
is mounted directly on the object to be positioned (direct metrology)
Fig. 27. Variety of digital piezo controllers
Position servo-control elimi-
nates nonlinear behavior of
piezoceramics such as hystere-
sis and creep and is the key to
highly repeatable nanometric
motion.
PI offers the largest selection of
closed-loop piezo mechanisms
and control electronics world-
wide. The advantages of posi-
tion servo-control are:
L52159 High linearity, stability,
repeatability and accuracy
L52159 Automatic compensation for
varying loads or forces
L52159 Virtually infinite stiffness
(within load limits)
L52159 Elimination of hysteresis
and creep effects
PI closed-loop piezo actuators
and systems are equipped with
position measuring systems
providing sub-nanometer reso-
lution, linearity to 0.01 %, and
bandwidths up to 10 kHz. A
servo-controller (digital or ana-
log) determines the output
voltage to the PZT ceramics by
comparing a reference signal
(commanded position) to the
actual sensor position signal
(see Fig. 28).
For maximum accuracy, it is
best if the sensor measures the
motion of the part whose posi-
tion is of interest (direct metrol-
ogy). PI offers a large variety of
piezo actuators with integrated
direct-metrology sensors.
Capacitive sensors provide the
best accuracy (see Nano-
metrology p. 3-1 ff ). Simpler,
less accurate systems measure
things like strain in drive ele-
ments.
www.pionline.it, www.pifrance.fr, www.pi-china.cn, www.goa-tech.co.il, www.alt.nl, www.bfioptilas.es, www.pi.ws, www.piceramic.de, www.pi-usa.us, www.pi-usa.us, www.pi-japan.jp, www.pi-japan.jp, www.physikinstrumente.co.uk, www.dyneos.ch, www.parameter.se, dms@deepms.com, www.deepms.com, www.warsash.com.au, www.parameter.se, www.eliovac.com.ar, www.rsdobrasil.com.br, www.woojoohitech.com, www.cairnhill.com, www.tetmakina.com, Seewww.piceramic.com, Seep.1-94ff.andwww.piceramic.com, Seewww.piceramic.com, Seealsowww.piceramic.com, andoscillatingmotione.g.in, info@pi-usa.us, www.pi-usa.us, info@pi-usa.us, www.pi-usa.us, info@pi-japan.jp, www.pi-japan.jp, info@pi-japan.jp, www.pi-japan.jp, info@pi-china.cn, www.pi-china.cn, info@pifrance.fr, www.pifrance.fr, uk@pi.ws, www.physikinstrumente.co.uk, info@pionline.it, www.pionline.it, info@piceramic.de, www.piceramic.de,
www.publitas.com, www.publitas.nl
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