231575 Piezo-Mechanics GB

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1.4. Energy/Power balancePiezo actuators are “motors” converting electricalenergy P into a piezomechanical response.The (non resonant) electrical energy content P of anelectrically charged piezostack isP = 1 /2 CU 2The piezomechanical response areStroke: ∆lForce generation: ∆FMechanical energy E = ∆l x ∆F1.4.1. (Nano)Positioning philosophy:C = actuator’s capacitanceU = applied voltageHere the user of an actuator is mainly interested in thedisplacement/stroke ∆l of the actuator and (maybe) theultrafine positioning capability down to the subnanometerrange. A variation of force or generation ofmechanical energy during piezo actuator’s action is nota priority.In terms of energy efficiency, piezoactuators are thennot well matched for most positioning applications,because only a small part of actuator’s energy content isneeded to be transferred to the coupled mechanics.Optimizing piezo actuators for dynamic positioningpurposes means that the electrical energy input shall beas low as possible to get a certain displacement. Orwith other words, actuator’s capacitance (in relation tothe driving voltage) shall be as low as possible to minimizethe electrical current/power requirements for adistinct dynamic response (e.g. for oscillating arrangements): A PZT material with low dielectric constant εtogether with a high piezoelectric constant d 33is required.For dynamic positioning purposes PIEZOMECHANIKprovides excellently adapted PZT materials like thestandard ceramic and the HS/HT ceramic, showinghigh strain together with low dielectric constant.Low ε materials have other interesting propertiestoo: high operating temperatures and high stabilityagainst depoling. So energy aspects are not theonly one criterion for selecting this type of PZTceramic.Notice:Low dielectric ultrasound PZT materials show rathersmall strain rates under non resonant conditions andare not optimized for actuation.Examples for positioning strategyThe “mother of piezo actuation” were optics, whereactuators are used frequently to shift a distinct optomechanicalcomponent with ultrahigh accuracy to getan optimum adjust e.g. of a laser resonator.Optomechanical components like stages or mirrormounts are usually systems using soft reset springs andshow therefore low stiffnesses.Adjusting of optomechanics by piezo actuators doesnot require a production of high mechanical energies orforces.An example for high dynamic positioning is fast valvecontrol, where the actuator is shifting a mechanical partlike a small ball or a needle to open or to close thevalve.1.4.2. Power optimisation“Positioning” according 1.4.1. ruled piezo actuationnow for nearly 30 years, but new applications areemerging, where a piezo actuator must be adapted toother strategies:In these cases a piezoactuator shall provide high displacementstogether with high force generation toachieve high mechanical energy transfer.Examples are adaptronic/smart structures of high stiffness,which shall be highly deformed by integratedactuators. This is a requirement to ensure large mechanicalenergy transfer.Examples e.g. adaptive frame structures of machines,car bodies, wings of air planes for active vibration excitationand cancellation or shape optimization.⇒ High mechanical energy shall be transferred intoa mechanical structure.⇒ To provide this large mechanical energy output,an increased electrical energy input is required viaa reasonable large electrical capacitance of theactuator to get a high mechanical energy densitywithin the ceramics.⇒ A PZT material is requested showing an elevateddielectric constant ε combined with a very highstrain and force generation rate.Notice: Large ε materials are widely offered,but often do not show the wanted large piezomechanicalresponse. Piezomechanik is offering the high powerPZT material HP, which shows the highestmechanical energy density available for PZTceramics. The energy density is roughlydouble that of standard materials (like PZT 5A)or the HS/HT material. To get the same powerout from “positioning actuators”, the actuatorvolume must be simply doubled with consequencesfor weight, space and price comparedto the energy optimized HP material.With a HP based actuator PSt 1000/25/100 mechanicalpulse powers of more than 100 kWatts have beengenerated.8
2. Piezoelectric andelectrostrictive ceramicsPZT ceramics will be the heart of solid state actuation for the near and mid future.New electroactive materials like highest strain/single crystalline formulations cannot compete for technical and costreasons for broad applications at the moment.Piezomechanik provides a set of piezoelectric PZT ceramic materials for stack manufacturing, which covers a verywide range of applications.This is true both for co-fired low voltage as well as discretely stacked high voltage materials.The standard program has been defined by compromising technical performance and pricing.Nevertheless, special materials are available on request.2.1. Low voltage actuators (cofired monolithic stacks)Operating voltage range: (–)30 V thru (+)150 VOperating temperature: –50 °C thru +100 °CAxial coefficient of thermal expansion (CTE): approx. –3 ppm/°CVacuum compatibleLow voltage actuators for cryogenic applications on request.Low voltage actuators based on HP, HS/HT materials on request (see below)Low voltage actuators for other voltage ranges (e.g. 200 V) on request2.2. High voltage actuatorsFig. 8:Normalized stroke/voltage diagram of low voltage stacks(relative stroke 1 for voltage step 0 V/U max )A. For bipolar operation in the range(–)0.2 U max thru (+)U maxB. For unipolar operation in the range0 V thru (+)U max2.2.1 Standard PZTOperating voltage range: (–)100 V thru (+)1500 V for PSt 1500 … stacks(–)200 V thru (+)1000 V for PSt 1000 … stacksOperating temperature: –60 °C thru +120 °CAxial coefficient of thermal expansion (CTE): approx. +1 ppm/°CVacuum compatibleActuators for cryogenic (–273 °C) applications on request (e.g. tuning of superconducting accelerator resonators)Fig. 9:Normalized stroke/voltage diagram of standard highvoltage stacks PSt 500 and PSt 1000A. For bipolar operation in the range(–)0.2 U max thru (+)U maxB. For unipolar operation in the range 0 V thru (+)U max9
Page 1 and 2: Piezomechanik GmbHPiezo-Mechanics:A
Page 3 and 4: Table of content5. Comparison of lo
Page 5 and 6: 1.2. Actuator design: Piezostacks a
Page 7: 1.3.3. Intermediate states (0 < Sme
Page 11 and 12: 2.3. Electrostrictive PMN ceramicsT
Page 13 and 14: 3.3. Electrical capacitancesPiezo-s
Page 15 and 16: 3.6. StiffnessesLike any other soli
Page 17 and 18: 3.10. Lifetime, reliabilityLifetime
Page 19 and 20: 4.4. Internal force detectionEspeci
Page 21 and 22: 4.8. Custom designed actuatorsOn re
Page 23 and 24: 5.4. Vacuum compatibilityThe operat
Page 25: 6. Mounting proceduresBare stacksMo
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231575 Piezo-Mechanics GB

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