IPMC actuators

Since an IPMC functions as a pathway for hydrated cations, its properties will be expected to affect the performance of an IPMC actuator. The membrane materials used in IPMCs have so far been limited to a few commercially available perfluorinated ionic polymers, such as Nafion, and the thickness of the IPMC has also been restricted to the available thickness of the commercial membrane [67]. However, IPMC actuators employing new ionic membranes have now been reported [68]. The membranes are prepared from fluoropolymers grafted with polystyrene sulfonic acid (PSSA). IPMCs assembled with these membranes have been shown to exhibit at least several times larger displacements than the Nafion-based IPMC with similar thickness. 

Fig. 1.1 Schematic representation of the actuation mechanism for an IPMC actuator. Application of a bias voltage causes mobile ions to migrate to one of the electrodes. The concomitant migration of solvent causes the ion rich region to swell, generating a bending motion. Over time the actuator relaxes due to the built-up pressure gradient [2]. IEEE 2004, reprinted with permission...

Keywords Artificial muscle IPMC Actuator Sensor Endovascular surgery ... 

High flexibility, low drive voltage, and large bending deflection are definite advantages of IPMCs over other rigid piezoelectric ceramic materials. These characteristics make IPMC actuators and sensors very popular in various biomedical applications. 

Fig. 2.2 Actuation and sensing mechanism of IPMC actuators and sensors...

Modeling the actuation response of IPMC for robust control of IPMC actuators is described in references 12 and 13. [12—13] Step response of actuators can be used for identification of actuator dynamics to derive a second order transfer... 

However, the electrical conductivity of the carbon nanomaterials is vulnerable to degradation due to the inefficient dispersion in a large-scale actuator. To this end, some metallic additives have been incorporated into the carbon-based electrode to enhance the electrical conductivity and actuation stability For instance, for the IPMC actuator where the reduced graphene oxide was used as electrode, the electrical conductivity of the electrodes could be efficiently improved after introduction of Ag nanoparticles (Fig. 8.2E) (Lu et al., 2013). As a result, both the actuation frequency and stability could be improved. Upon application of a low voltage of 1V, the actuator could be driven at a wide frequency range (0.01-10 Hz), and no obvious decrease in displacement was observed over 500 cycles of actuation. 

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. 

To facilitate the real applications of IPMCs in devices and robots, a unique systems approach is taken in Chapter 4 to look at the modeling of IPMC actuators and sensors. The presented actuation model is derived based on dynamics-governing partial differential equations and incorporates the effect of surface electrode resistance. The model, with nice scalabil-... 

Fig. 2.1 IPMC actuation under a 1.22 V voltage (a) and the illustration of the hydrated cation migration and the corresponding actuation (b). Reprinted from [Park et al. (2008)] with permission from Elsevier, Copyright 2008, and from [Paquette et al. (2005a)] with permission from Cambridge University Press.

As discussed in the previous sections, there is a rather good understanding of the mechanisms and underlying processes of IPMC actuation. Furthermore, different models have been developed to precisely predict the deformation due to an applied voltage. The models can be categorized as physical models, black-box models, and gray-box models [Shahinpoor and Kim... 

In the following, an equivalent beam and equivalent bimorph beam model for simple IPMC actuation is first presented. Thereafter more complex actuation configurations and corresponding modeling considerations are provided. 

Fig. 2.36 Measured force-displacement relationship of an IPMC actuator for small displacement. Reprinted from [Lee et al. (2005)].

The developed bimorph beam model of IPMC was validated using the finite element method (FEM) and the used software was MSC/NASTRAN. As the software does not directly support the electromechanical coupling, the thermal analogy technique as described in [Lim et al. (2005) Taleghani and Campbell (1999)] was used. The simulated versus measured force-displacement relationship of an IPMC actuator is shown in Fig. 2.39. The relative errors for A = 0 between the calculated values and the measured data for 2V and 3V are 2.8% and 3.7%, respectively. The equivalent Young s moduli estimated from the equivalent beam model and the equivalent bimorph beam model are 1.01 GPa and 1.133-1.158 GPa, respectively, which are very close. However, the values from the equivalent beam model... 

By coupling Eq. (3.11) to the previously described equations, a basic model for IPMC actuation was obtained. The damping equation turned out to... 

A Physics-based, Control-oriented Model for IPMC Actuators... 

Current modeling work on IPMC actuators typically falls into three categories, with progressively increased level of complexity and fidelity blackbox models, gray-box models, and white-box models. Black-box models... 

Fig. 4.1 Illustration of IPMC actuation mechanism. Reprinted from [Chen and Tan...

For the beam dynamics G(s), it suffices to use the first vibration mode of the beam since the actuation bandwidth of an IPMC actuator is relatively low, typically under 10 Hz ... 

The full actuation model is represented by G s)H s). Since H s) involves non-rational functions, such as sinh(-), cosh(-), and a/, it is infinitedimensional. For practical implementation of feedback control design, however, finite-dimensional models are desirable. Simple model reduction steps can be taken to obtain finite-dimensional models for IPMC actuators, by exploiting the knowledge of physical parameters and specific properties of hyperboiic functions. In particular, based on the physical parameters of IPMCs (see Section 4.2.3), 7(s) 10, and K 10 , and we can make... 

Fig. 4.11 Experimental and simula on results on tracking of IPMC actuator under PI control. Reprinted from [Chen and fan (.2UU8j with - -...

In this section we present a nonlinear circuit model for IPMC actuators. A key component of the circuit is the nonlinear capacitance, derived based on the original PDEs governing the ion dynamics. In addition, the circuit includes ion diffusion resistance [Bonomo et al. (2007) Porfiri (2008)], pseu-... 

While the nonlinear capacitance captmes ion transport djmamics, a good model needs to accommodate other relevant djmamics. Fig. 4.21 shows a nonlinear circuit model for IPMC actuators, which incorporates the nonhn-ear capacitance Ci, the pseudocapacitance due to the electrochemical adsorption process at the polymer-metal interface, ion diffusion resistance i c) electrode resistance and nonhnear DC resistance of polymer R c-The pseudocapacitance Cg, and nonlinear DC resistance R c are further elaborated below. 

Fig. 4.21 Nonlinear circuit model for IPMC actuators. Reprinted from [Chen et al.

With an apphed DC voltage, the current Idc of IPMC actuator does not vanish at the steady state, which indicates the existence of polymer resistance. Such resistance, however, is not linear [Bonomo et al. (2007)]. In this work, we use a third-order polynomial function Y(V) to empirically approximate Idc-... 

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