Environ m ental Con d itions an d Infl u ences

Temperature Effects

Two effects must be considered:
Note Closed-loop piezo positioningsystems are less sensitive to temperature changes thanopen-loop systems. Optimumaccuracy is achieved if the operating temperature is iden- tical to the calibration tempera- ture. If not otherwise specified, PI piezomechanics are calibrat- ed at 22 °C. Temperature Dependency ofthe Piezo Effect Linear Thermal Expansion Temperature Dependency of the Piezo Effect Linear Thermal Expansion Thermal stability of piezoce-ramics is better than that of most other materials. Fig. 38a shows the behavior of several types of piezoceramics used by PI. The curves only describethe behavior of the piezoce-ramics. Actuators and position- ing systems consist of a combi- nation of piezoceramics and other materials and their over- all behavior differs accordingly. Piezo translators work in awide temperature range. Thepiezo effect in PZT ceramics isknown to function down to almost zero kelvin, but the magnitude of the piezo coeffi- cients is temperature depend- ent.At liquid industrial helium temperaturepiezo gain drops to approxi- mately 10–20% of its room- temperature value.Piezoceramics must be poledto exhibit the piezo effect. A poled PZT ceramic may depole when heated above the maxi-mum allowable operating tem-perature. The “rate” of depol- ing is related to the Curie tem- perature of the material. PI HVPZT actuators have a Curie temperature of 350°C and can be operated at up to 150°C.LVPZT actuators have a Curietemperature of 150 °C and can be operated at up to 80 °C. The new monolithic PICMA Piezo Operation in High Humidity The polymer insulation materi-als used in piezoceramic actua- tors are sensitive to humidity. Water molecules diffuse through the polymer layer and can cause short circuiting ofthe piezoelectric layers. The insulation materials used in piezo actuators are sensitive to humidity. For higher humidity environments, PI offers special systems with waterproofed enclosed stacks, or integrated dry-air flushing mechanisms. A better solution are PICMA
® actuators (see Fig. 39a), which have ceramic-only insulation without any polymer covering and are thus less sensitive to water diffusion (see Fig. 39c).
Fig. 38 a. Linear thermal expansion of different PZT ceramics. Fig. 38 b. The expansion of PICMA ® ceram-ics with their high Curie tem- perature of 320 °C allow oper- ating at temperatures of up to 150 °C.
® piezoceramics is only slightly tem-perature dependent. This, and their low heat generation, makes themideal for dynamic applications. © PI 1998-2005. Subject to change w/o notice. Cat 118 05/09.17 4-36