pi2009
2-178
©
Physik
Instrumente
(PI)
GmbH
&
Co.
KG
2008.
Subject
to
change
without
notice.
Cat120E
Inspirations2009
08/10.18
Piezo Nano Positioning
Quick Facts
Note
This section gives a brief summary
of the properties of piezoelectric
drives and their applications. For
detailed information, see Funda-
mentals of Piezoelectricity begin-
ning on p. 2-181.
Stack actuators are the most com-
mon and can generate the highest
forces. Units with travel ranges up
to 500 µm are available. To protect
the piezoceramic against destruc-
tive external conditions, they are
often provided with a metal casing
and an integrated preload spring to
absorb tensile forces.
Piezo tube actuators exploit the
radial contraction direction, and
are often used in scanning micro-
scopes and micropumps.
Bender and bimorph actuators
achieve travel ranges in the mil-
limeter range (despite their com-
pact size) but with relatively low
force generation (a few newtons).
Shear elements use the inverse-
piezo-effect shear component and
achieve long travel and high force.
For more information, see p.
2-207 ff.
Guided piezo actuators (1 to 6
axes) are complex nanopositioners
with integrated piezo drives and
solid-state, friction-free linkages
(flexures). They are used when
requirements like the following
need be met:
L52159 Extremely straight and flat
motion, or multi-axis motion
with accuracy requirements in
the sub-nanometer or sub-micro-
radian range
L52159 Isolation of the actuator from
external forces and torques, pro-
tection from humidity and for-
eign particles
Such systems often also include
lever amplification of up to 20
times the displacement of the piezo
element, resulting in a travel range
of several hundred µm.
Piezomotors are used where even
longer travel ranges are required.
Piezomotors can be divided into
two main categories:
L52159 Ultrasonic Motors (Fig. 2a)
L52159 Piezo-Walk
®
Motors (Fig. 2b)
The motion of ultrasonic piezomo-
tors is based on the friction
between parts oscillating with
microscopic amplitudes. Linear
ultrasonic motors are very compact
and can attain high speeds com-
bined with resolutions of 0.1 µm or
better. Rotary motors feature high
torques even at low rpm.
Piezo-Walk
®
linear drives (see
p. 1-3 ff ) offer high positioning and
holding forces (up to hundreds of
newtons) with moderate speeds
and resolutions in the subnanome-
ter range.
All implementations are self-lock-
ing when powered down.
Actuator Designs
Fig. 1b. Selection of monolithic PICMA
®
technology actuators
Fig. 1a. Selection of classical piezo stack actuators, with adhesive used to join the layers
2-179
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
Piezo Nano Positioning
Operating Voltage
Two types of piezo actuators have
become established. Monolithic-
sintered, low-voltage actuators
(LVPZT) operate with potential dif-
ferences up to about 100 V and are
made from ceramic layers from 20
to 100 µm in thickness. Classical
high-voltage actuators (HVPZT),
on the other hand, are made from
ceramic layers of 0.5 to 1 mm
thickness and operate with poten-
tial differences of up to 1000 V.
High-voltage actuators can be
made with larger cross-sections,
making them suitable for larger
loads than the more-compact,
monolithic actuators.
Stiffness, Load Capacity, Force
Generation
To a first approximation, a piezo
actuator is a spring-and-mass sys-
tem. The stiffness of the actuator
depends on the Young's modulus
of the ceramic (approx. 25 % that
of steel), the cross-section and
length of the active material and a
number of other non-linear
parameters (see p. 2-189). Typical
actuators have stiffnesses
between 1 and 2,000 N/µm and
compressive limits between 10
and 100,000 N. If the unit will be
exposed to pulling (tensile) forces,
a casing with integrated preload
or an external preload spring is
required. Adequate measures
must be taken to protect the piezo-
ceramic from shear and bending
forces and from torque.
Travel Range
Travel ranges of Piezo Actuators
are typically between a few tens
and a few hundreds of µm (linear
actuators). Bender actuators and
lever amplified systems can
achieve a few mm. Ultrasonic
piezomotors and Piezo-Walk
®
drives can be used for longer trav-
el ranges.
Resolution
Piezoceramics are not subject to
the stick slip effect and there-
fore offer theoretically unlimited
resolution. In practice, the resolu-
tion actually attainable is limited
by electronic and mechanical fac-
tors:
a) Sensor and servo-control elec-
tronics (amplifier): amplifier noise
and sensitivity to electromagnetic
interference (EMI) affect the posi-
tion stability.
b) Mechanical parameters: design
and mounting precision issues
concerning the sensor, actuator
and preload can induce micro-fric-
tion which limits resolution and
accuracy.
PI offers piezo actuators and posi-
tioning systems that provide sub-
nanometer resolution and stabili-
ty. For more information, see
p. 2-183 ff.
Operating Characteristics of Piezoelectric Actuators
Fig. 2b. Custom linear drive
with integrated
NEXLINE
®
Piezo-Walk
®
piezomotor
Fig. 3. Example of a compact piezo
nanopositioning and scanning system
with integrated flexure guidance,
sensor and motion amplifierFig. 2a. Ultrasonic piezo linear motors
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
pi2009 main
