Piezoelectric
materials are crystalline solids whose asymmetric structures create
an electric dipole moment in the crystal lattice, which is sensitive
to both elastic strain and applied electrical field (see diagram
right).
In other words, when an electrical field is applied to a piezoelectric
material, a stress is induced and the material changes shape (called
the piezoelectric effect). The motion acheived can be calculated
from the induced stress and the Young's modulus of the material.
It is this motion that is utilised in piezo actuators.
Conversely, an applied stress generates an electrical field through
the inverse piezoelectric effect. This effect is used in piezo
gas lighters and the like.
Introduction to CEDRAT Piezoelectric Actuators, transducers
and motors
Using these new piezo materials, several classes of low voltage
piezo actuators have been developed by CEDRAT TECHNOLOGIES in
order to cover a wide range of needs and applications. These actuators
were initially developed to meet the most rigourous requirements
of the French and European space agencies (CNES, ESA). They are
now available either in standard or in customised products.
Direct Piezo Actuators (DPAs) and Parallel Pre-stressed Actuators
(PPAs)
DPAs
and PPAs are solid-state linear actuators. They use the expansion
of the active material directly to produce a useful displacement.
This displacement is proportional to the voltage over a 170V range.
Typically, the actuator deformation is about 0.1% (1µm/mm), so
their displacements are limited to about 100µm for practical purposes.
However the forces generated are large - easily higher than 1kN.
DPAs use a conventional series prestress, so they are limited
to quasi-static applications such as micro positioning.
Parallel Pre-stressed Actuators (shown right) utilise an external
deformable frame to prestress the ceramics so the level of presstress
can be higher. Therefore PPAs are cheaper and more compact than
DPAs and display better dynamic behaviour.
Amplified Piezo Actuators (APAs)
APAs
(shown right) are solid-state long-stroke linear actuators. They
are based on the expansion of the active material and on a mechanism
for mechanically amplifying the displacement. This amplified displacement
is also proportional to the voltage over a 170V range.
The advantages of APAs are their relatively high displacements
combined with its large forces and compact size along the active
axis. This leads to deformation of 1% (10µm/mm) or more, so their
stroke may achieve more than 500µm.
As APAs are compact they can be stacked in series for reaching
strokes up to 1mm. Their inherent robustness allows them to be
used in dynamic applications, including resonant devices. Under
resonant conditions the required drive voltage for maximum stroke
is very small (about 1 to 10V).
Ultrasonic Piezo Actuators (UPAs)
UPAs are low-voltage compact generators of ultrasonic vibrations.
They are special versions of APA, optimised to place their useful
resonant mode in the ultrasonic range (above 20kHz). Their active
axis is short (typically less than 40mm), but they produce quite
high vibration level (10 to 20µm) using low voltages (about 1
to 10V). They are a miniaturisation of standard longitudinal ultrasonic
transducers, also offered by CEDRAT.
Ultrasonic Piezo Drives (UPDs)
UPDs are low-voltage generators of elliptical ultrasonic vibrations.
They are a special version of UPA, optimised to acheive two complementary
resonant modes in the ultrasonic range (above 20kHz). They produce
vibrations (1-5µm) with controllable elliptical trajectory, using
low voltages (1 to 10V).
Linear & Rotating Piezo Motors (LPMs, RPMs)
Piezo motors are long-stroke actuators with blocking force at
rest without power supply. They offer low-voltage actuation with
unlimited resolution. They exist either in linear or in rotating
versions. Both are based on a combination of electromechanical
elliptical motion and friction forces. The elliptical motion can
be either ultrasonic, generated by UPD, and leading to ultrasonic
piezo motor (USM), or quasistatic, generated by APA and leading
to stepping piezomotor (so called Inchworm). Strokes of LPMs are
typically of 1-20mm but much longer long strokes are possible.
Forces are in the range of 10-50N. RPMs with customised torque
and speed can be easily defined by using standard UPDs or APAs
and choosing the rotor.
Piezoelectric
materials are crystalline solids whose asymmetric structures create
an electric dipole moment in the crystal lattice, which is sensitive
to both elastic strain and applied electrical field (see diagram
right). 
DPAs
and PPAs are solid-state linear actuators. They use the expansion
of the active material directly to produce a useful displacement.
This displacement is proportional to the voltage over a 170V range.
Typically, the actuator deformation is about 0.1% (1µm/mm), so
their displacements are limited to about 100µm for practical purposes.
However the forces generated are large - easily higher than 1kN.
APAs
(shown right) are solid-state long-stroke linear actuators. They
are based on the expansion of the active material and on a mechanism
for mechanically amplifying the displacement. This amplified displacement
is also proportional to the voltage over a 170V range.