Torsional actuation

We have fabricated the torsional actuator by depositing PPy on a tube substrate with helically wound platinum fibers. While the fabrication process follows closely the work of Ding et al. [Ding et al. (2003)], they adopted the approach for a different purpose and did not examine torsional actuation of such devices. We have conducted experiments on actuators with different dimensions and fiber winding angles, which have not only confirmed torsion and other deformation modes of these actuators but also validated the nonlinear mechanical model. 

Fig. 5.18 Fabrication of fiber-reinforced torsional actuator (a) Schematic of fabrication setup (b) a fabricated sample. Reprinted from [Fang et al. (2011)] with permission from IEEE, Copyright 2010.

Secondly, conjugated polymers were studied as biomimetic artificial muscles. A scalable physics based electro-chemo-mechanical model was developed to connect an input voltage to bending of the material. The reduced version of the model was used to design a robust adaptive controller. Also, a nonlinear mechanical model was investigated. Furthermore, a torsional actuator was developed by depositing PPy on a tube substrate with helically wound platinum fibers. A set of experiments were conducted to confirm the torsional and other actuation modes as well as the model. 

Fang, Y., Pence, T. J. and Tan, X. (2011). Fiber-directed conjugated-polymer torsional actuator Nonlinear elasticity modeling and experimental validation, lEEE/ASME Transactions on Mechatronics 16, pp. 656-664. 

The tensile actuation in polymer coil muscles is directly linked to torsional actuation derived from the twisted polymer fibre. To illustrate the link between fibre torsional actuation and coil tensile actuation, coils were fabricated as either homochiral or heterochiral , depending on whether the... 

Figure 13.8 Torsional actuation of twisted carbon nanotube yarns, (a) Twisted carbon nanotube yarn operating in 0.2 M tetrabutylam-monium hexafluorophosphate/acetonitrile electrolyte, (b) Paraffin impregnated carbon nanotube yarn operating in air. (c) Two-ply carbon nanotube yarn coated with a poly(vinylidene fluoride-co-hexafluoropropylene) based tetraethylammonium tetrafluoroborate (TEA.BF4) solid polyelectrolyte. (Panel (a) is from ref. 16 Foroughi et al. Torsional Carbon Nanotube Artificial Muscles , Science, 2011, 334, 494-497. Reprinted with permission from AAAS. Panel (b) is from ref. 17 Lima et al. Electrically, Chemically, and Photonically Powered Torsional and Tensile Actuation of Hybrid Carbon Nanotube Yarn Muscles , Science, 2012, 338, 928-932. Reprinted with permission from AAAS. Panel (c) is reprinted with permission from ref. 18 Lee et al. All-Solid-State Carbon Nanotube Torsional and Tensile Artificial Muscles , Nano Lett, 2014, 14, 2664-2669. Copyright 2014 American Chemical Society.)...

The twisting nanotube yam actuators based on first principle mentioned above enable fully dry torsional actuation as the main driving mechanisms are based on electrothermal and/or photothermal effects. These actuators do not require electrolyte, counter electrode, or extra package as it is needed for electrochemically driven actuators (Chun et al. 2014). Indeed, the electroactivity of nanotube yams were firstly described in setup where bundled fibers were immersed in electrolyte the overall capability of twisting of actuators was demonstrated later without ion... 

Fig. 3 Muscle configurations and yam structures for tensile and torsional actuation. Tensile load and paddle positions for (a) a two-end-tethered, fully infiltrated homochiral yam (b) a two-end-tethered, bottom-half-infiltrated homochiral yam (c) a one-end-tethered, fully infiltrated homochiral yam and (d) a two-end-tethered, firlly infiltrated heteioehiral yam. The depicted yams are coiled, noncoiled, four ply, and two ply, respectively. Arrows indicate the observed direction of paddle rotation during thermal actuation. Red and green yam-end attachments are tethers, meaning they prohibit end rotation red attachments also prohibit translational displacement SEM micrographs of (e) a fiilly infiltrated homochiral coiled yam, (f) a neat two-ply yam, and (g) a neat four-ply yam. Illustration of ideal cross sections for (h) Fermat, (i) dual-Archimedean, and (j) infiltrated four-ply Fermat yams (Reproduced from Lima et al. 2012)...

Fig. 2 The structures of MWNT yams used for tensile and torsional actuation. SEM micrographs of (a) a fully infiltrated coiled yam, (b) a neat two-ply yam, and (c) a neat four-ply yam. Illustration of ideal cross sections for (d) Fermat, (e) dual-Archimedean, and (f) infiltrated four-ply Fermat yams (From Lima et al. (2012). Reprinted with permission from AAAS)...

The development of novel electromechanically active materials also demands suitable methods for characterization of their actuation performance. Actuators can be constructed in a variety of configurations - bending, linear length change (Torop et al. 2009 Ghaffari et al. 2013), and torsional actuation (Foroughi et al. 2011) being... 

Fuda Y, Yoshida T (1994) PiezDelectric torsional actuator. Ferroelectrics 160 323-330 Fukada E (2000) History and recent progress in piezoelectric polymers. IEEE Trans Ultrason Ferroelectr Freq Contr 47 1277 1290... 

Z. Xiao, W. Peng, X.-T. Wu, and K.R. Farmer, Pull-in study for round double-gimbaled electrostatic torsion actuators, J. Micromechanics Microengineering 12, 77-81 (2002). 

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