Modellierung, Entwurf und automatisierte Herstellung von Multilayer-Polymeraktoren

Transcription

1 Modellierung, Entwurf und automatisierte Herstellung von Multilayer-Polymeraktoren Modeling, design and automated fabrication of polymer-based multilayer actuators Thorben Hoffstadt, Dominik Tepel und Jürgen Maas VDI GMA-FA 4.6 Unkonventionelle Aktorik. Situng am Oktober 4 in Saarbrücken Vortrag im Rahmen des Workshop der Nachwuchswissenschaftler

2 Outline. Introduction. Modelling of DEAP-based multilayer actuators 3. DEAP stack-actuator design 4. Automated manufacturing process 5. Conclusion l l l l v p

3 . Electroactive Polymers Introduction Considered will be electronic EAPs and in particular dielectric electroactive polymer transducers denoted as DEAP transducers. Fundamental design of a DEAP transducer compliant electrodes polymer (e.g. silicone, polyurethane, acrylic) Functional principle is based on the electrostatic pressure that results when the DEAP is charged: vp el r E r t vp V E vp V 3

4 . Properties of DEAP-based transducers Polymer acts as a dielectric i DE Re i capacitance C p Parasitics of polymer and electrode loss resistances R p and R e v DE Rp C p v p Electrical Parameters depend on the mechanical state Due to the electromechanical coupling DEAP transducer can be used as actuators, sensors and generators mechanical behavior actuation electrical stimuli Electrical Energy Mechanical Energy electrical behavior sensing mechanical stimuli 4

5 . DEAPs as sensors and generators DEAP as sensor Electrical parameters depend on mechanical state λ Identification of at least one electrical parameter Sensor-based concepts DEAP exclusively used as sensor i DE v DE i DE Re Sensor-less concepts i DE Rp DEAP transducer is simultaneously used as sensor i C p v p DEAP as (electrostatic) generator 3 minimum strain relax DEG Discharge DEG 4 initial system stretch DEG v Sens ~ i DE v DE v Act v Act v Sens ~ i DE v DE maximum field strength Charge DEG maximum strain 5

6 . DEAP Multilayer Actuators for pulling and pushing Actuation in direction of the electric field Compression of the polymer in -direction Pulling force in -direction x v p DEAP stack-actuator Multilayer increasing the absolute deformation l l Actuation perpendicular to the electric field Elongation of the polymer in - direction Pushing force in -direction DEAP roll-actuator Multilayer increasing the pushing force vde V l v p vde V Tepel, D.; Graf, C.; Maas, J.: Modeling of mechanical properties of stack actuators based on Electroactive polymers. Proceedings of SPIE Smart Structures/NDE, San Diego, USA, Vol. 8687, S , 3. Hoffstadt, T.; Graf, C.; Maas, J.: Modeling of Roll-Actuators based on Electroactive Polymers. Proceedings of SPIE Smart Structures/NDE, San Diego, USA, Vol. 8687, S , 3. 6

7 . Applications of DEAP multilayer actuators DEAP actuators are predestined for position applications in small devices Promising technology e.g. for automation applications, haptic feedback v v DE DE electrical contactors pneumatic valves & gripper [M.Giousouf: Dielectric Elastomer Actuators Potential Use in Automation Technology, ACTUATOR, pp , ] force feedback glove [R. Zhang, P. Lochmatterg, A. Kun and G. Kovacs: Spring Roll Dielectric Elastomer Actuators for a Portable Force Feedback Glove, Proc. of SPIE Vol. 668, 668T-, 6] 7

8 . DEAP Roll-actuator with polymer core New roll-actuator design Bi-axially prestretched active material is winded up around compressed polymer core. Prestretched polymer core must support the force in the operating point of the actuator caused by the prestretched DEAP material. polymer core prestretch λ γ,eap, prestretch λ,core, prestretch λ,eap, DEAP material t polymer r electrode prestretch λ,core, prestretch λ,eap, w prestretch λ γ,eap, polymer core Hoffstadt, T.; Graf, C.; Maas, J.: Modeling of Roll-Actuators based on Electroactive Polymers. Proceedings of SPIE Smart Structures/NDE, San Diego, USA, Vol. 8687, S , 3. l 8

9 F,load =. DEAP Roll-actuator with polymer core No-load-strain behavior of the realied prototype:.6.5 simulation measurement l l no-load strain,nl inactive area polymer core electrode contact voltage v DE in kv Parameters of the prototype: l 3mm; t 4μm; N ; r 5mm on,,, EAP, 7;, EAP, ; YEAP 4,5MPa; Ycore MPa 9

10 Pulling force F,load in N Modelling of DEAP-based multilayer actuators Stack-actuator: actuator films are mechanically connected in series electrically connected in parallel F load Y = 3MPa; ε r = 7; A = 64mm² Electrode Polymer t t E = V / µm E = V / µm E = 3 V / µm E = 4 V / µm E = 5 V / µm E = 6 V / µm Current limit under consideration of the lifetime Stretch y x v p A A one actuator film describes the stretch-force-behavior of the whole actuator el E elast electromechanical coupling: F A A E Y λ act el elast r λ 3 λ hyperelastic material behavior: (using Neo-Hookean approach, equibiaxial deformation in x- and y-direction) el r E i i i W p Hoffstadt, T.; Tepel, D.; Maas, J.: Model-based Design Optimiation Rules of DEAP Actuators. 4th International Conference on New Actuators - ACTUATOR 4, Bremen, June 4.

11 . Stretch-force-behavior of a DEAP stack-actuator Optimiing the actuator based on a dimensionless, normalied stretch-forcebehavior energy density stored in the (constant) DEAP capacitance: u c C v el V Uc p p r E V substitution of the electrostatic pressure: F A u Y act c 3 normaliing the force and the energy density a dimensionless charateristic results: F act uc A Y Y 3 T. Hoffstadt and J. Maas: Model-based Optimiation and Characteriation of DEAP Stack-Actuators, SMASIS 4-769, SMASIS 4.

12 . Stretch-force-behavior of a DEAP stack-actuator Operation with constant energy density equals operation with constant electric field u v c p const. E const. vp E t Y t.4 normalied force F act / (A Y) / Y =.5 / Y =. / Y =.5 / Y = pushing force pulling force stretch

13 . Design Optimiation Blocking-Force F act l l, const. y x v p normalied force F act / (A Y) / Y =.5 / Y =. / Y =.5 / Y = stretch Stretch-force-behavior has two characteristics No-Load-Stretch Blocking-force (obtained if the actuator cannot deform) No-load-stretch (obtained if the actuator generates no force free stroke) l v p l l l 3

14 . Design Optimiation Blocking-Force Operating the actuator at a constant stretch λ, the resulting force is linearly increased with the electrical energy density: Fact u c, A Y, Y 3, If a pre-stretch (load) λ, is applied the blocking-force results to: Fact A Y, u Y c Blocking-Force is scalable by cross-sectional area A but is independent from the Young s modulus Y Slope is adjustable by applied pre-load λ, normalied Blocking-Force F act / (A Y) , =, =.9, =.8 Blocking-Force v p F act l, l, const energy ratio / Y 4

15 . Design Optimiation No-Load-Stretch The no-load-stretch is obtained if no force is exerted: uc, Y Fact uc elast 3 8u with = 3 c 3 Y 4 Using a linear-elastic approach a comparable equation results: Y Y u uc Y elast c No-Load-Stretch is independent from the geometry but decreases with increasing Young s modulus Y: F act = l No-Load-Stretch v p l l l hyper-elastic model linear-elastic model energy ratio / Y 5

16 . Design Optimiation Coupling Coefficient d w Y d Optimiation of mechanical work density with respect to the applied electrical energy Instantaneous mechanical work: W Fact l Fact w V V A This also yields to a normalied mechanical energy density: w Y uc Y 3 Operating point with maximum electromechanical coupling: 3 4 u Y!, 6 c 3 3 opt normalied energy w / Y coupling coeffecient w u.95 c.9.9 uc.85.8 stretch uc.85.8 stretch Y Y / Y =.5 / Y =. / Y =.5 / Y =

17 . Performance Limitations Operating the stack-actuator with a constant voltage a corresponding initial energy density results: vp, vp uc, uc t t Effect of electromechanical instability occurs if: u c, elast Fload Y Y A Y.9 stable region Instability limits the maximum stretch depending on the generated force Zhao, X., and Suo, Z., 7. Method to analye electromechanical initial energy ratio u stability of dielectric elastomers. Applied Physics Letters, 9, p. 69. c, / Y stretch F act /(A Y) = -. load F act /(A Y) = -.5 load F act /(A Y) = load F act /(A Y) =.5 load F act /(A Y) =. load limit of electromechanical instability F load A Y instable region 7

18 . Performance Limitations Depending on the exerted force the critical stretch and corresponding energy vary Electromechanical instability limits the Maximum No-Load-Stretch 3, crit Fact.63 3 uc,, crit Fact.79 Y 6 Maximum Blocking-Force F u act, crit A Y 3 c,, crit, crit Y 6 cirtical stretch,crit cirtical initial energy ratio,,crit /Y stable region pushing force F act /(A Y) instable region pulling force instable region stable region F act /(A Y) 8

19 . Design Optimiations Conclusion Based on the static model of a DEAP stack-actuator the Blocking-Force and No-Load-Stretch were investigated Blocking-Force Fact with uc Fact with A (A : free design parameter) No-Load-Stretch with l with Y, l (Y: material parameter l : free design parameter) Electromechanical Instability A Y Fact, crit, crit Fact.63 3 Fact, crit with A, Y l with l optimal operation point f uc maximum electromechanical coupling l uc, opt normalied force F act / (A Y) l.95.9 l l F act A A.85.8 stretch.75.7 / Y =.5 / Y =. / Y =.5 / Y =..65 l l l l v p 9

20 x 3. DEAP stack-actuator design y Increase of absolute deformation and force multilayer actuator By stacking the actuator films to the designated height and alternating the direction of the contact tab, the DEAP stack-actuator is obtained. contacting electrode DEAP contacting film contact tabs polymer contact electrode end caps (optional) DEAP contacting film DEAP actuator film Tepel, D., Hoffstadt, T., Graf, C., Cording, D., Krause, J., Wagner, J., and Maas, J., 3. Development of an automated manufacturing process for DEAP stack-actuators. EuroEAP3. el - + v r t p voltage thickness permittivity electrost. pressure

21 4. Manufacturing of DEAP Stack-Actuators Dry deposition process: divided into several processing steps fabricate stack-actuators with reproducible and homogeneous properties Tepel, D.; Hoffstadt, T.; Maas, J.: Actuator Design and Automated Manufacturing Process for DEAP Multilayer Stack-Actuators. ACTUATOR 4

22 4. Manufacturing of DEAP Stack-Actuators Sub-process : applying electrodes and folding DEAP film is fixed on the vacuum folding table a mask is positioned over the elastomer a nole is positioned over several sectors and electrodes are applied DEAP film with the applied structured electrodes is folded after 4 spraying and 3 folding processes an actuator module is created whose thickness is 8 times higher than the single film due to the very thin DEAP films, the films are folded to facilitate the handling

23 4. Manufacturing of DEAP Stack-Actuators Sub-process 3: stacking of DEAP sub-modules to designated height folded DEAP film module is lifted by the vacuum gripper folded DEAP film module is transported to the film carrier of the rotary index table folded DEAP film module is stacked and laminated on top of each other 3

24 4. Manufacturing of DEAP Stack-Actuators Sub-process 4: cutting by a ultrasonic knife to separate DEAP stackactuators stacked DEAP film module is fixed and transported by the film carrier of the rotary index table individual actuator modules are cutted out individual actuator modules are seperated 4

25 4. Contacting of the DEAP stack-actuator module To realie a transition from the elastic DEAP to the stiff wiring of the power electronics, a DEAP contacting film is used, which does not harm the actuation. To protect the DEAP stack-actuator against environmental influences, the actuator is encapsulated by winding a polymer film around the stack-actuator. b) winded around the c) end cap with d) a polymer film actuator module in a grooves is applied to is winded around pre-stretched condition fix the contacting pins the stack-actuator contacting end cap electrode a) contacting pins are rolled into the contacting film DEAP contacting film polymer contacting pins stacked DEAP actuator module DEAP contacting film end cap encapsulation material polymer Hoffstadt, T.; Tepel, D.; Maas, J.: Structured electrode design for DEAP transducer with integrated safety mechanisms. EuroEAP 4, Linköping, Sweden, Juni 4. 5

26 4. Experimental validation of the actuator design DEAP stack-actuator No-Load-Stretch behavior of the produced DEAP stack-actuator:.99 calculation measurement. stacked DEAP actuator module encapsulation material end cap No-Load-Stretch electrical field in V/µm compression in mm contacting pin DEAP contacting film Parameters of the stack-actuator: t = 5μm; Y = 3MPa; ε r = 7: N = 6 6

27 Blocking-Force 5. Conclusion DEAP transducer can be used as actuators, sensors and generators Based on an analytical model of a DEAP stack-actuator design rules can be obtaiend.4 l l l l normalied force F act / (A Y) / Y =.5 / Y =. / Y =.5 / Y =. v p stretch No-Load-Stretch DEAP technology is an energy efficient alternative for conventional actuators with further excellent properties. However, concerning the material and the manufacturing a lot of R&D has to be done. 7

28 Acknowledgement This contribution is accomplished within the project "Dielastar - Dielektrische Elastomere für Stellaktoren (Dielectric Elastomer Actuators), funded by the Federal Ministry of Education and Research (BMBF) of Germany under grant number 3X4, see 8

29 Thanks for your kind attention! Thorben Hoffstadt Ostwestfalen-Lippe University of Applied Sciences Department of Electrical Engineering and Computer Science Control Engineering and Mechatronic Systems Phone: +49 () Dominik Tepel Ostwestfalen-Lippe University of Applied Sciences Department of Electrical Engineering and Computer Science Control Engineering and Mechatronic Systems Phone: +49 () Jürgen Maas Ostwestfalen-Lippe University of Applied Sciences Department of Electrical Engineering and Computer Science Control Engineering and Mechatronic Systems Phone: +49 ()