Lifetime of PI Ceramic Piezoelectric Actuators
The lifetime of a piezoelectric
actuator is typically not reduced by wear
and tear. All PI Ceramic piezo
actuators are specifically
designed for high-duty-cycle
applications. All materials used
are matched for robustness
and lifetime. Endurance tests
on PI Ceramic actuators prove
consistent performance, even
after billions (1,000,000,000) of
External piezo lifetime tests, such as the ones conducted at NASA's Jet Propulsion Lab, show that even after 100 Billion cycles (100,000,000,000) the tested PI Ceramic PICMA® multilayer piezo actuators provided more than 97% of their initial performance.
PICMA®-type actuators have advantages over other piezo actuators, especially in humid environments. Their monolithic, ceramic-insulated design blocks the diffusion of water molecules into the insulation layer, the major cause of dielectric breakdown.
PI Ceramic invests considerable energy in investigating and continually improving actuator lifetime. The design of the piezoelectric actuators in this catalog reflect several decades of experience in with thousands of industrial piezo actuator applications. Another result of this experience are the “Handling Precautions” in the following section.
Please contact your PI sales & application engineer for further information on lifetime and handling issues.
Piezoelectric actuators must be handled with care because the internal ceramic materials as well as ceramic end-plates are fragile. Do not use metal tools for actuator handling. Do not scratch the coating on the side surfaces.
Besides these general instructions the following precautions have to be considered during handling of PI Ceramic piezoelectric actuators:
- Piezoelectric stack actuators without axial preload are sensitive to pulling forces. A preload of half of the blocking force is generally recommended (see PI main catalog data tables p. 13 to p. 27). This recommendation is also valid for PICATM-Shear actuators in axial direction, perpendicular to the shear diplacement directions.
- Piezoelectric stack actuators may be stressed in the axial direction only. The applied force must be centered very well. Tilting and shearing forces, which can also be induced by parallelism errors of the endplates, have to be avoided because they will damage the actuator. This can be ensured by the use of ball tips, flexible tips, adequate guiding mechanisms etc. An exception to this requirement is made for the PICA™-Shear actuators, because they operate in the shear direction. Do not exceed the maximum shear force specifications for these actuators.
- Piezoelectric stack actuators have to be mounted by gluing them between even metal or ceramic surfaces by a cold or hot curing epoxy, respectively. Ground surfaces are preferred. Please, do not exceed the specified working temperature range of the actuator during curing.
- The environment of all actuators
should be as dry as
possible. While PICMA® actuators
are guarded against
humidity by their ceramic
coating, other actuators
must be protected by other
measures (hermetic sealing,
dry air flow, etc).
The combination of longterm high electric DC fields and high relative humidity values should be avoided with all piezoelectric actuators. The electric field attracts the water molecules or hydroxy ions from the environment to the surface of the stack and leads to a permanent increase in its leakage current. This can finally result in damage to the actuator. There is no polymer coating which can avoid the forced penetration of these molecules.
- It is important to short-circuit
the piezoelectric stack
actuators during any handling
operation. The resulting
loads will induce
charges on the stack electrodes
which might result in
high electric fields if the
leads are not shorted:
- a) changing temperatures, for example during curing or soldering processes, induces charges due to the pyroelectric effect
- b) changing mechanical loads, for example during preload application, induces charges due to the direct piezoelectric effect
- The lateral (side) surfaces of PICMA® and PICA™-Stack actuators are not, or not fully, electrically insulated to allow a more compact design and integration of the stack in the final assembly by the customer. Therefore, the customer is responsible for designing in the required separation or suitable insulating materials, like polyimide foil or PTFE tape, to insulate the stack from its surrounding.
- Prevent any contamination of the stack surfaces with conductive or corrosive substances. Cleaning of the stacks should be done with isopropanol only. Do not use acetone. Avoid excessive ultrasonic cleaning at higher temperatures.
PICMA® piezo actuators (bottom curve) compared with conventional multilayer actuators with polymer insulation (top curve). PICMA® Actuators are not affected by the high-humidity test conditions. Conventional piezo actuators exhibit increased leakage current after only a few hours. Leakage current is an indication of insulation quality and expected lifetime. Test conditions: U = 100 VDC ; T = 25 °C; Relative Humidity = 70%
No pulling force without preload
No lateral force or torque
Bolting between plates is not recommended
Ball tips or flexures to decouple lateral forces or bending forces
Ball tips or flexures to decouple bending forces