A diamond-shaped amplified piezo actuator (APA) fabricated using six multilayered piezo stacks with maximum displacement of 173 μm at 175V and the amplification factor of 4.3. The dynamic characterization of the actuator was carried out at different frequencies (100 Hz–1 kHz) and at different AC voltages (20V–40V). The actuator response over this frequency range was found neat, without attenuation of the signal. Numerical modeling of multilayered stack actuator was carried out using empirical equations, and the electromechanical analysis was carried out using ABAQUS software. The block force of the APA was 81 N, calculated by electromechanical analysis. This is similar to that calculated by dynamic characterization method

Panda, PK

Raja, S

Sahoo, B

Shankar, V

Vijayakumar, MP

English

National Aerospace Laboratories Institutional Repository

Hindawi Publishing CorporationSmart Materials ResearchVolume 2012, Article ID 203625, 8 pagesdoi:10.1155/2012/203625Research ArticleElectromechanical and Dynamic Characterization ofIn-House-Fabricated Amplified Piezo ActuatorP. K. Panda,1 B. Sahoo,1 S. Raja,2 Vijaya Kumar M. P.,2 and V. Shankar21Materials Science Division, National Aerospace Laboratories, Council of Scientific and Industrial Research, Bangalore 560017, India2 Structural Technologies Division, National Aerospace Laboratories, Council of Scientific and Industrial Research,Bangalore 560017, IndiaCorrespondence should be addressed to P. K. Panda, pkpanda@nal.res.inReceived 21 November 2011; Accepted 27 December 2011Academic Editor: Tao LiCopyright © 2012 P. K. Panda et al. This is an open access article distributed under the Creative Commons Attribution License,which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.A diamond-shaped amplified piezo actuator (APA) fabricated using six multilayered piezo stacks with maximum displacementof 173 μm at 175V and the amplification factor of 4.3. The dynamic characterization of the actuator was carried out at differentfrequencies (100Hz–1 kHz) and at different AC voltages (20V–40V). The actuator response over this frequency range was foundneat, without attenuation of the signal. Numerical modeling of multilayered stack actuator was carried out using empiricalequations, and the electromechanical analysis was carried out using ABAQUS software. The block force of the APA was 81N,calculated by electromechanical analysis. This is similar to that calculated by dynamic characterization method.1. IntroductionLead zirconate titanate (PZT) is a well-known piezo materialthat produces electric charges on application of mechanicalstress (as sensor) or undergoes dimensional change whensubjected to an electric field (as actuator) [1–5]. One majordrawback of the piezo materials is the low displacementof the order of 0.1–0.15% of the total length; therefore,thick piezo stacks are required even for the moderate-strainrequirements. For high-strain requirements wherein therequirement of the strain is in few millimeters, simple mul-tilayer stacks are not suitable. This leads to the developmentof the various types of high-strain amplified actuators suchas hydraulic actuator [6–13], Moonie [14] and Cymbal [15],diamond-shaped actuator, and bow-shaped actuator.In this study, the details of the fabrication and charac-terization of a diamond-shaped amplified actuators rare pre-sented. Numerical modeling of multilayered stack actuatorand amplified actuator is carried out using empirical equa-tions and the electromechanical analysis using ABAQUS soft-ware. The values are correlated to the experimental results.2. Experimental Procedure2.1. Preparation of PZT Slurry. PZT stacks were fabricated bytape-casting method using in-house-prepared PZT powders[16]. A well-dispersed PZT slurry was prepared using re-quired amount of PZT powder, organic solvents (methylethyl ketone and ethanol), dispersant (Triton), binder, plas-ticizers, and so forth, by ball milling for 72 hr. An optimizedPZT slurry composition is presented in Table 1. The slurrywas then filtered and cast on a silicon-coated Mylar sheet us-ing a laboratory tape caster. The thickness of the green tapesis varied between 20 μm and 200 μm by changing the para-meters such as the clearance of doctor blade, the castingspeed, and the viscosity of the slurry.2.2. Fabrication of Multilayered (ML) Stack. The green PZTtapes of thickness 80 μmwere dried, cut into required dimen-sions, screen-printed with platinum electrode paste, anddried. The individual layers are then stacked and laminatedone above the other using uniaxial stacking machine. Fol-lowing the above procedure, 6 numbers of identical ML2 Smart Materials ResearchPZT powderSlurryPZT tapePunchElectrodingStack and laminateCofiringTerminaldrawingFigure 1: Pictorial representation of fabrication procedure of ML stack.10 mmFigure 2: Typical picture of fabricated ML stacks.Table 1: Typical PZT slurry composition.Components Amounts (%)PZT powder 65–70Dispersant 1.25Solvent 25Plasticizer 1.75Binder 2stacks of height 14mm (green stage) are fabricated. All thestacks are then isopressed at 30MPa/5min with preheatingat 60◦C/5min. Binder burnout of the stacks is carried outat 520◦C/2 h with very slow heating rate (15◦C/1 h). Thecofiring of the stacks is done at 1250◦C/1 h. The stacks areleveled to have parallel surfaces, finished, and electrode, andtwo terminals are drawn by soldering the wires. A pictorialrepresentation of fabrication procedure of ML stack is shownin Figure 1. The stacks are then poled at 2 kV/mm in hotsilicone oil bath for 45min, and displacement and block forcewere characterized. Typical picture of the fabricatedML stackis shown in Figure 2.2.3. Fabrication of Al Frame and APA. An aluminium metalframe of length 60mm (internal) and height 24mm (inter-nal) is fabricated. The inside angle of the frame with its mid-Figure 3: A typical picture of fabricated diamond-shaped APA.dle horizontal line is 15◦. All the 6 PZT stacks are then fixedinside the metal frame using a flange in a prestressed con-dition. The photograph of fabricated diamond-shaped PZTactuator is shown in Figure 3. The weight of the APA is 26.5 g.3. Results and Discussions3.1. Displacement and Block Force Measurement. The indi-vidual ML stacks are characterized for displacement andblock force using a block force measuring unit. The actuatoris placed on top of a force sensor (load cell) inside thesample holder, and its positive and negative terminals areproperly connected to the respective terminals of the voltageSmart Materials Research 3Block force (N): 811Free displacement (µm): 120 100 200 300 400 500 600 700 800 900Force (N)Displacement (nm)20004000600080001000012000140000Figure 4: Block force versus free displacement graph of ML stack.Strain gauge10 µmdc source+−+−∼Figure 5: Test setup for displacement measurement of the actuators[16].0204060801001201401601800 20 40 60 80 100 120 140 160 180Displacement (µm)Applied voltage (V)Figure 6: Displacement versus voltage graph of APA.Function generatorOscilloscopeAmplifierAPAAccelerometerFigure 7: Test setup for voltage and frequency characterization ofthe APA.source. Displacement of the actuator is measured by a highlysensitive laser interferometer. For measurement of blockforce, the actuator is prestressed by selecting a suitable spr-ing of specific stiffness. The displacement and the force gene-rated by the actuator for different springs are plotted. Thesoftware calculates a linear fit for these points. The blockforce is determined from the intersection points of the line onX-axis, and the free displacement is measured from its inter-section on Y-axis. The graph of displacement versus force isshown in Figure 4.The displacement characteristics of the APA and assem-bled ML stacks are measured using a strain gauge. The testsetup for displacement measurement of the APA is shownin Figure 5. It is observed that the displacement increaseswith increase in voltage, and a maximum displacement of173 μm and 40 μm is measured for APA and assembledML stacks, respectively, at 175V. On decreasing the voltage,the displacement curve does not follow the same path anda hysteresis loop is obtained (Figure 6). The amplificationfactor for diamond-shaped APA is nearly 4.3 times.3.2. Dynamic Characterization of Amplified Actuator. Thepiezo stack as an electrical load is capacitive in nature. Thecapacitance of the stack assembly is measured and is around2.42 μF. This is a useful parameter in the design of electronicsactuator amplifier for APA.3.3. Characterization of the Actuator at Different AC Signaland Frequency. For vibration control applications, it is nec-essary to characterize the dynamic response of the stack atdifferent amplified sinusoidal AC signal and at different fre-quencies. The dynamic response of APA was carried out at40V (±20V) peak to peak and up to a frequency of 1 KHz.The test setup is shown in Figure 7. A sinusoidal input sig-nal to the stack assembly produces mechanical vibrations onthe stack which is coupled to a unit under test (UUT) eitherto carry out UUT’s resonance search (open loop) or to con-trol UUT’s vibrations (closed loop). For dynamic applica-tions, it is necessary to quantify the acceleration responseon the stack assembly with respect to force input to theAPA stack assembly at different input voltage levels aswell as at different frequencies. A miniature accelerometer4 Smart Materials ResearchAmplitudeTime (ms)(a) 250Hz and 20VAmplitudeTime (ms)(b) 1000Hz and 20VAmplitudeTime (ms)(c) 250Hz and 30VAmplitudeTime (ms)(d) 1000Hz & 30VFigure 8: Typical plots of actuator response at (a) 250Hz and 20V, (b) 1000Hz and 20V, (c) 250Hz and 30V, and (d) 1000Hz & 30V.14 16 18 20 22 24 26 28 30 3211.21.41.61.822.22.42.62.8320304050607080Sinusoidal input voltage (volts)Force (N)Acceleration (g)Figure 9: Variation of “g” and actuator force versus input voltage.(with 10.5mV/g sensitivity and 0.2 g weight) was mountedon the stack followed by its signal conditioning amplifier.The weight of the APA stack assembly is 26.5 grams. Thetotal weight of the APA stack assembly and accelerometertogether is 26.7 grams. Experiments were carried out andmeasurements were recorded on digital storage oscilloscopeat three different sinusoidal input drive voltage levels (20Vp-p, 30V p-p and 40V p-p) to the stack actuator and in thefrequency range of 125Hz to 1KHz. Typical plots of responseof stack at 250Hz and at 1000Hz are presented in Figures8(a)–8(d). From the sensitivity of the accelerometer and themill volt output produced by the actuator, the acceleration(g) and the force produced by the actuator were calculated.The “g” was 2.7 g/cm2, and the force was 81N at 40 volts, andthe variation at different voltage is presented in Figure 9.3.4. Numerical Modeling of Multilayered Stack Actuator. Thestack actuators are made up of thin layers of PZT patches,laminated one over the other. Modeling all the thin layersof PZT stack using the piezoelectric solid finite element,available in commercial software is cumbersome. Hence,Smart Materials Research 5−+Figure 10: Finite-element model of the stack actuator.Table 2: Actuator material properties.Properties Data unitsYoung’s modulus 45 GPaPiezoelectric constant 390× 10−12 m/vDensity 7500 kg/m3Poisons ratio 0.22 —an equivalent model is built from the following empirical re-lations:Dx = n′d′33EV,E33 = F′blocktd′33A′EV,t = length of the stack actuatornumber of layers in the actuator,φfem = voltagecal × thicknessfemthicknesscal ,(1)where E33 is Young’s modulus, d33 represents piezoelectricstrain constant, n indicates the number of layers, EV refersto the electric potential across each layer, A is cross-sectionalarea of the stack actuator, t is thickness of each layer,φfem denotes equivalent electric potential in finite-elementmethod.3.5. Finite-Element Modeling of the Stack Actuator. Assuming10 piezo layers, each of piezoelectric strain constant (390 ×10−12 C/N), a finite-element model was created using squarecross-section elements to avoid any discrepancy (Figure 10).The two consecutive layers of the finite-element model willhave opposite polarity to each other, so as to obtain theextension/compression from all the layers simultaneouslyTable 3: Characteristics of the actuator (actuator APA).Description Data UnitsDisplacement 41 μmBlocked force 1450 NVoltage range 175 VHeight 61.9 mmArea 8× 6 mm2Table 4: Free deflection and block force of the stack actuator.Analysis Displacement (μm) Blocked force (N)APA 41 1450FEA (ABAQUS) 40.9 1452(i.e., parallel capacitor configuration). The actuator materialproperties used for modeling are presented in Table 2.Similarly, the characteristics of the actuator are presented inTable 3.The actuator is characterized using the stress-strain rela-tion of a coupled electromechanical system{s} = [C]{ε} − [C][d]{Ek}, (2)where C is the material stiffness matrices (N/m2), d is thepiezoelectric strain constant (m/v), Ek is the electric field(v/m), and ε is the material strain.3.6. Electromechanical Analysis Using ABAQUS. The freedeflection and the block force are measured from theelectromechanical analysis using ABAQUS. While the freedeflection is the actuator deformation when maintained inan unconstrained state with the maximum applied voltage,the block force is the reaction developed by the actuatorwhen maintained in a completely constrained state. Theresults of the analysis compared with themeasured results arepresented in Table 4, and the block force and free displace-ment profile are presented in Figures 11(a) and 11(b).Figure 12 represents the CAD model of APA, in whichthe casing is made of aluminum material, and the actuatoris placed in between the casing. The aluminum materialproperties used are Young’s modulus E = 70GPa, density =2720 kg/m3, and Poisson’s ratio 0.3.The weight of the APA is approximately 26.5 grams.Finite-element model of APA is made in Hypermesh andsubsequently analyzed for static loading. Further the freevibration analysis is performed using ABAQUS. The staticanalysis has shown that the casing is safe with a factor ofsafety 4.7.3.7. Piezo Static and Electromechanical Analysis of the APA.Piezoelectric analysis is carried out with upper and lowerpads completely constrained (u, v,w = 0) (Figure 13).By applying an equivalent voltage (175V), the von Misesstress (92MPa) and the block force are computed (81N),respectively. Further analysis is done for finding the induceddisplacement of the APA actuator under unconstrained6 Smart Materials ResearchStep 1 inc1, t = 1.000000e + 000DisplacementsMax = 4.09e − 05Min = 0e + 00>3.64e − 05<3.64e − 05<3.18e − 05<2.73e − 05<2.27e − 05<1.82e − 05<1.36e − 05<9.1e − 06<4.55e − 06<0e + 00xz(a)Step 1 inc1, t = 1.000000e + 000Reaction forcesMax = 3.24e + 02Min = 0e + 00>2.88e + 02<2.88e + 02<2.52e + 02<2.16e + 02<1.8e + 02<1.44e + 02<1.08e + 02<7.19e + 01<3.6e + 01<0e + 00(b)Figure 11: (a) Free displacement and (b) block force measurement using FEA.Casing ActuatorFigure 12: CAD model of the APA.Figure 13: Pzeio static analysis APA actuator.state (148 μm). The result is presented in Figure 14. Similarlyfor different actuator voltages, the free deflections are com-puted, at actuator level as well as for the APA. The resultsare presented in Table 5 for different voltage configura-tions.4. ConclusionsA diamond-shaped APA was successfully fabricated by de-signing suitable metal frame and using 6 multilayered PZTstacks. The APA produces displacement of 173 μm withSmart Materials Research 7Step 1 inc1, t = 1.000000e + 000DisplacementsMax = 1.48e − 04Min = 8.19e − 37>1.32e − 04<1.32e − 04<1.15e − 04<9.87e − 05<8.22e − 05<6.58e − 05<4.93e − 05<3.29e − 05<1.64e − 05<8.19e − 37xzyFigure 14: Electromechanical analysis of APA.Table 5: Displacement values of APA.ActuatorVoltage (V)Equivalentnumericalvoltage (V)ABAQUS-freeDisplacement ofactuator(Δx) μmABAQUS-APADisplacement(μm)175 5250 40.9 148160 4800 37.4 135140 4200 32.8 118120 3600 28.1 102100 3000 23.4 84.680 2400 18.7 67.760 1800 14 50.840 1200 9.38 33.820 600 4.68 16.90 0 0 0displacement amplification of 4.3 times. The actuator wassubjected to different frequencies and different AC voltages.The performance was found very well over the frequencyrange without attenuation of the signal. Both the waveforms,namely, input to the stack actuator and accelerometeroutput, is showing no distortion thereby indicating thestack actuator assembly is behaving linearly. The equivalentnumerical modeling of APAwas built, and electromechanicalanalysis was carried out. The induced displacement obtainedwas 148 μm for the maximum operational voltage. The actu-ator free displacement and block force were also computedto be 40.9 μm and 1450N, respectively. The maximum von-Mises stress estimated is 92MPa, which gives a factor of safetyof 4.7, and block force generated is 81N. The block force ofthe APA was 81N, calculated by electromechanical analysis.This is similar to that calculated by dynamic characterizationmethod.AcknowledgmentsThe authors gratefully acknowledgeMr. M. K. Sridhar, Head,Materials Science Division, and Dr. A. R. Upadhya, Director,NAL, for their encouragement and the support during thecourse of this study. The authors also thank Mr. Chandraiah,project assistant, for his help in preparation of PZT tapes.References[1] R. E. Newnham and G. R. Ruschau, “Smart electroceramics,”American Ceramic Society Bulletin, vol. 75, no. 10, pp. 51–61,1996.[2] G. H. Haertling, “Rainbow ceramics-a new type of ultra-high-displacement actuator,” American Ceramic Society Bulletin,vol. 73, no. 1, pp. 93–98, 1994.[3] R. E. Newnham and G. R. Ruschau, “Smart electroceramics,”Journal of the American Ceramic Society, vol. 74, no. 3, pp. 463–480, 1991.[4] E. F. Crawley and J. De Luis, “Use of piezoelectric actuators aselements of intelligent structures,” AIAA Journal, vol. 25, no.10, pp. 1373–1385, 1987.[5] K. Uchino, “Advances in ceramic actuatormaterials,”MaterialsLetters, vol. 22, no. 1-2, pp. 1–4, 1995.[6] J. Juuti, K. Korda´s, R. Lonnakko, V. P. Moilanen, and S.Leppa¨vuori, “Mechanically amplified large displacement pie-zoelectric actuators,” Sensors and Actuators A, vol. 120, no. 1,pp. 225–231, 2005.[7] C. 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Electromechanical and Dynamic Characterization of

In-House-Fabricated Amplified Piezo Actuator

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Electromechanical and Dynamic Characterization of In-House-Fabricated Amplified Piezo Actuator

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