Handling of Piezo Actuators

Piezo actuators are subject to high mechanical and electrical loads. Moreover, the brittle
ceramic or crystalline materials require carefulhandling.
Avoid mechanical shocks to the actuator,
which can occur if you drop the actuator,
for example.
Do not use metal tools during installation.

Fig. 52: Avoiding lateral forces
and torques

Avoid scratching the ceramic or polymer
coating and the end surfaces during installation and use.

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1

Prevent the ceramic or polymer insulationfrom coming into contact with conductiveliquids (such as sweat) or metal dust.
If the actuator is operated in a vacuum:
Observe the information on the permissible
piezo voltages for specific pressure ranges(p. 150).

Fig. 53: Prevention of torques

If theactuator could come into contact with
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insulating liquids such as silicone or
hydraulic oils: Contact info@piceramic.com.
If the actuator has accidently become dirty,
carefully clean the actuator with isopropanol or ethanol. Next, completely dry it in adrying cabinet. Never use acetone forcleaning. When cleaning in an ultrasonicbath, reduce the energy input to the necessary minimum.

Fig. 54: Avoiding tensilestresses by means of amechanical preload

Recommendation: Wear gloves and protective glasses during installation and startup.
DuraAct patch actuators and encapsulated
PICMA® piezo actuators have a particularlyrobust construction. They are partially exempt
from this general handling information.
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Mechanical Installation (fig. 52, 53, 54)
Avoid torques and lateral forces when
mounting and operating the actuator byusing suitable structures or guides.
When the actuator is operated dynamically:
Install the actuator so that the center ofmass of the moving system coincides withthe actuator axis, and use a guiding forvery large masses.
Establish contact over as large an area as
possible on the end surfaces of a stackactuator.
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Select opposing surfaces with an evennessof only a few micrometers.
GluingIf the mounting surface is not even, use
epoxy resin glue for gluing the actuators.
Cold-hardening, two-component adhesives
are well suited for reducing thermomechanical stresses.
Maintain the operating temperature range
specified for the actuator during hardening
and observe the temperature expansion
coefficients of the involved materials.
Uneven mounting surfaces are found, forexample, with PICMA® Bender and PICMA®
Chip actuators, since these surfaces are notground after sintering (fig. 55).
Applying a Preload (fig. 54)
Create the preload either externally in themechanical structure or internally in a case.
Apply the preload near the axis within thecore cross-section of the actuator.
If the actuator is dynamically operated andthe preload is created with a spring: Use aspring whose total stiffness is approximately one order of magnitude less thanthat of the actuator.

Fig. 55: Mounting of a onesidedly clamped bending
actuator by gluing

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156

P I E Z O D R I V E S | W W W. P I . W SIntroducing the Load Evenly (fig. 56)
The parallelism tolerances of the mechanicalsystem and the actuator result in an irregularload distribution. Here, compressive stresses may cause tensile stresses in the actuator. Regarding the even application of a load,
there are diverse design solutions that differ
from each other in axial stiffness, separabilityof the connection and rotatability in operation,e.g. in the case of lever amplification.

Tensilestresses

Fig. 56: Avoiding an irregular load application

Gluing the actuator (cf. gluing section)

Electrically insulate the actuator against theperipheral mechanics. At the same time,observe the legal regulations for therespective application.

Hardened spherical end piece with point
contact to even opposing surface
Hardened spherical end piece with ring
contact to a spherical cap

Observe the polarity of the actuator forconnection.

Connection via a flexure joint

Only mount the actuator when it is shortcircuited.

If the actuator is coupled in a milling
pocket, make sure that there is full-area
contact on the end surface of the actuator.
For this purpose, select the dimensions of
the milling pocket correspondingly or makefree cuts in the milling pocket (fig. 57).
If a point load is applied to the end pieceof the actuator: Dimension the end pieceso that its thickness corresponds to half
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the cross-sectional dimension
in1order toprevent tensile stresses on the actuator(fig. 58).

When the actuator is charged: Discharge
the actuator in a controlled manner with a10 kΩ resistance. Avoid directly short-circuiting the terminals of the actuator.

Fig. 57: Full-area contact of
the actuator

Do not pull out the connecting cable of theamplifier when voltage is present. The
mechanical impulse triggered by this could
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damageTensilestresses

Safe Operation

Electrical Connection (fig. 59)
From an electrical point of view, piezo actuators are capacitors that can store a greatamount of energy. Their high internal resistances lead to very slow discharges with time
constants in the range of hours. Mechanical orthermal loads electrically charge the actuator.
Connect the case or the surrounding
mechanics to a protective earth conductorin accordance with the standards.

Reduce the DC voltage as far as possible
during actuator operation (p. 151). You candecrease offset voltages with semi-bipolar
operation.

Fig. 58: Proper dimensioningof the end pieces in the caseof point contact

Always power off the actuator when it is
not needed.
Avoid steep rising edges in the piezo voltage, since they can trigger strong dynamic
forces when the actuator does not have apreload. Steep rising edges can occur, forexample, when digital wave generators are
switched on.

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Fig. 59: Mechanical loads
electrically charge the actuator. Mounting only whenshort-circuited

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PIEZO

NANO

POSITIONING