Actuation performance

The central computer is called the master terminal unit, or MTU. The MTU has two main functions to periodically obtain data from RTUs/PLCs and to control remote devices through the operator station. The operator interfaces with the MTU using software called human machine interface (HMI). The remote computer is called the program logic controller (PLC) or remote terminal unit (RTU). The RTU activates a relay (or switch) that turns mechanical equipment on and off. The RTU also collects data from sensors. Sensors perform measurement, and actuators perform control. 

It has been found that prestrain can significantly improve the actuation performance of dielectric elastomer devices [143, 165]. The observed improvements have been largely attributed to an increase in the breakdown strength [168-169], which has been explained via a thermodynamic stability criterion [170]. Prestrain has the additional benefits of improving the mechanical efficiency [171] and response speed of most dielectric elastomers while causing a marginal decrease in the dielectric... 

Kofod used advanced materials models in an attempt to elucidate the effects that prestrain have on the actuation performance of a simple cuboid DE actuator [183]. The results are purely phenomenological however, they indicate that in the special case of a purely isotropic amorphous material, prestrain does not affect the electromechanical coupling directly. The enhancement in actuation strain due to prestrain occurs through the alteration of the geometrical dimensions of the acmator. Kofod also determined that the presence of an optimum load is related to the plateau region in the force-stretch curve and that prestrain is not able to affect the location of this region. 

Carpi F, De Rossi D (2005) Improvement of electromechanical actuating performances of a silicone dielectric elastomer by dispersion of titanium dioxide powder. IEEE Trans Dielectr Electr Insul 12 835... 

Nguyen HC, Doan VT, Park J, Koo JC, Lee Y, Nam J, Choi HR (2009) The effects of additives on the actuating performances of a dielectric elastomer actuator. Smart Mater Stract 18 015006... 

Gallone G, Galantini F, Carpi F (2010) Perspectives for new dielectric elastomers with improved electromechanical actuation performance composites versus blends. Polym Int 59 400-406. doi 10.1002/pi.2765... 

Relating chemical and material properties to actuation behavior has proven to be a major challenge, and remains an important area of investigation for several research groups, as efforts are made to systematically improve actuator performance in proposed devices. Properties at the nanoscale are being seen as increasingly important in this regard, as will be discussed in subsequent sections. 

The role of the electrodes in electrostatic actuators is of critical importance for the actuation performances. The ideal electrode materials should process both high electrical conductivity and mechanical stretchability in compliance with the large deformation of the laminated dielectric elastomer during actuation. In addition, the electrodes should also provide a uniform and stable charge distribution on both of the surfaces. 

Cyclic voltammetry (CV) was carried out on PANi-CNTs composite fibers as part of the mechanical actuator testing (Figure 8). The resolved CV ensure ion and charge transfer required for actuation performance. To improve the conductivity of fibers, very thin Pt layer coated around the fibers. Much improved CVs were obtained with the Pt covered libers. The influence of CNTs on the electroactivity of Pt covered PAni fibers in IM HCl aqueous solution is illustrated in. It can be clearly seen that the addition of CNTs enhanced the amplitude of the redox peaks, indicating a higher electro-activity compared to neat PANi fibers. Peak potentials also shifted with the addition of CNTs which can be attributed to interaction between PAni and CNTs. Three oxidation... 

FIGURE 9 The influence of CNT loading on the electromechanical actuation performance of composite fieres. (A) PANi-CNTs (2% wt) ( )Neat PANi. 

The incorporation of CNT into PANi greatly improves the actuation performance both in terms of the higher strain attainable and better performance tmder load. 

Chapter 2 is focused on physical principles of IPMCs. It starts with an introduction to the fundamentals of IPMCs, including the fabrication techniques, and then takes a careful look at the effect of electrodes on material behavior and actuation performance. Several novel approaches, including a fluorescence spectroscopic visualization method, are then used to yield unique insight into IPMC actuation behaviors, such as the back-relaxation phenomenon. More sophisticated configurations than a singlelayer bender are also discussed in this chapter. 

Chapter 6 is focused on dielectric elastomer materials. In particular, a synthetic elastomer is proposed to enhance the actuation performance and energy density. Methods for preparing the materials are discussed, and various material properties as relevant to the actuation performance are characterized and compared with commercially available dielectric materials. In addition, by incorporating suitable additives, the synthetic elastomer has shown favorable behavior for actuation purposes. 

To study the actuation properties of Ni-doped MFR IPMCs, first the current and displacement in response to an applied voltage were measured in range from —3V to 3V. Due to the oxidation of Ni, the charging process starts at 0.8 V and electric breakdown takes place at 1.8 V. However, after the first cycle of operation, the cmrent density and the displacement remained rather imchanged (see Fig. 3.5). The actuation performance is shown in Fig. 3.6. The displacement of Ni-doped MFR IPMCs was mea-smed when a square pulse was applied using chrono-potentiometry with 2 s pulse dmation and controlled current. The results indicate that the actua-... 

DE actuators have broad applications in areas such as robots, mi-cro/milli devices as presented in [Bar-Cohen (2004) Carpi et al. (2007a) Kim and Tadokoro (2007)]. So far, many configurations of actuators have been proposed such as planar devices, tubes, rolls, folds, and stacks etc. Accordingly, a quick widening of the affordable range of robotic applications is expected to occur in the near future. However, the actuator performance... 

In addition to the qualitative studies on the performance metrics of the elastomeric materials, actuation performances of the proposed material are evaluated with experiments in this subsection. Deformation, time responses, hysteresis and elastic energy efficiency are tested for each specimen. Most of the experiments are performed without prestrain since the prestrain on dielectric elastomer actuator has several negative effects on actuation performance [Choi et al. (2005b)]. Non-prestrained test is desirable for clarif3dng the actuation features of material itself. In the present study, only the experiment for elastic energy efficiency is conducted with prestrain condition, which is for the purpose of comparison with previous results [Pelrine et al. (2000)]. 

Effects of Additives on Actuating Performance of Synthetic Elastomer... 

At the same electric field, the actuation performance of the sjmthetic elastomer filled with the Ti02 and DOP is better than the one filled with only the DOP, as is shown in Fig. 6.18. The main reason for this performance is that the filler Ti02 helps to increase the permittivity of the synthetic elastomer. Finally, we can only get the same actuation performance at a lower electric field if we use both fillers Ti02 and DOP. 

Fig. 6.18 The effect of (a) DOP and (b) Ti02 on the actuation performance. Reprinted from [Nguyen et al. (2009)].

As mentioned earlier, the performance of the actuator depends considerably on the geometry of the actuator. In this section, we analyze typical geometries such as circular, rectangular and trapezoidal ones, and compare the actuator performance among these geometries. 

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