Electroactive polymer (EAP) is a kind of smart material that exhibits a large deformation on the application of a small potential across the electrodes. On the contrary, the materials can also exhibit sensorial behavior by generating a small electrical potential on the application of mechanical force. These characteristics make these materials to be a promising candidate for applications involving actuators with self-sensing ability. In this work, we report on the development of integrated sensing and actuation of ionic polymer–metal composite. Integrated sensing is accomplished by crafting discrete sensing and actuation sections over a single device by patterning the surface of the electrodes. A control scheme and estimation technique are implemented for self-sensing feedback control that uses the electrode resistance change during deformation. The artificial neural network is used to handle the hysteresis during modelling the relation between electrode resistance change and actual tip displacement. While the need for stable control to overcome nonlinearity and inherent back relaxation behavior of the material is accomplished by using a robust sliding mode controller. The developed model and controller are experimentally verified and found to be capable of predicting and controlling the actuators with excellent tracking accuracy without the need for a separate position sensor and makes the device to perform as a self-sensing actuator.
The ionic electroactive polymer (IEAP) actuators are the type of smart material that is capable of generating large deformations on the application of a small potential across the electrodes. In addition, the IEAP actuators with ionic liquid as an electrolyte are capable of operating in an open-air environment. These aspiring characteristics put forward these actuators to be a promising candidate for replacing traditional actuators in micro-actuation applications. The CPC actuators are distinguished from other types of IEAP’s by the presence of porous carbon as an electrode material and an ionic liquid as electrolyte. In this work we propose design and fabrication of a multi-degree freedom motion platform based on four carbon-polymer composite (CPC) actuators. The complete platform is fabricated as a single structure with appropriate masking. This motion system is highly dexterous and is capable of generating three different motion namely tip, tilt and piston motion. The experiment results have demonstrated high levels of manipulability from the CPC actuators that are outstanding in the class of soft ionic actuators while keeping the fabrication method simple, scalable and cost-effective.
Carbide-derived carbon (CDC) based actuators have been typically formulated as trilayer systems and applied in bending displacement. In this work, we want to demonstrate that CDC deposited on glass fiber fabric (CDC-TL) with an additional poly-3.4-ethylenedioxythiophene (PEDOT) layer electropolymerized on top forming a polylayer (expressed as CDC-PEDOT-TL) can be used as a linear actuator. Isotonic and isometric electro-chemo-mechanical deformation (ECMD) measurements in lithium bis(trifluoromethane) sulfonamide propylene carbonate (LiTFSI-PC) were performed, revealing that the CDC expansion at discharging can be found in CDC-PEDOT-TL (main expansion at oxidation of 0.5% strain) in same extent of 0.24 %. The stress found in similar values of 30 kPa for both system. Besides the nearly 5times better conductivity of CDC-PEDOT-TL, the charge density reduce nearly half in comparison to CDC-TL.
The ionic electroactive polymer (IEAP) actuators with carbonaceous electrodes and ionic liquid electrolytes are distinguished by their ability for operation in open air. Nevertheless, their behavior is influenced by at least two parameters of the ambient environment – temperature and humidity. Both parameters affect many factors of the IEAP materials: viscosity and ionic conductivity of the electrolyte, specific capacitance of the electrodes, stiffness of the polymer, etc. This circumstance makes it difficult to comprehend the actual physical and electrochemical processes occurring in the IEAP materials as well as hinders the control of the actuators in the possible applications. This work is focused on characterizing the temperature and humidity-dependence of the electromechanical and electrochemical response of IEAP actuators. An extensive experiment was performed with several types of IEAP actuators in a temperature- and humidity-controlled environment. The characterization of electrical and electromechanical response measurements were carried out at temperatures ranging from 0°C to +60°C and relative humidity ranging from 0% to 90%. The result showing that impact of both parameters on IEAP actuators is easily recognizable.
Ionic electroactive polymer (IEAP) actuators with carbon based porous electrodes and ionic liquid electrolyte are attractive alternatives compared to the actuators composed of noble metal electrodes. Besides of numerous other parameters, the porosity of the electrode matrix has high influence on the electrochemical behavior and mechanical response of these actuators. Porosity has direct influence on the tortuosity, electronic conductivity, ionic conductivity, ion diffusivity, mobility, as well as the specific area and specific capacitance of electrode. It can also influence directly the mechanical properties of the IEAP laminate: durability, stiffness, etc. In this study, a detailed physical model that incorporates porosity of electrodes and its relation to the electrochemical, transport and mechanical behavior of the IEAP actuator is developed. The behavior of the actuator under different porosity values is investigated through finite elements simulation. The outputs of the simulation are cation concentration, current consumed and deformation of the actuator etc. Altering porosity and determining its optimum value help to comprehend the occurring physical and electrochemical processes, as well as to design actuators capable of delivering optimum electrical and mechanical response.
In order to diminish the effect of terminals to the aqueous ionic electroactive polymer (IEAP) actuators, the electrical input terminals should be made of a noble metal – platinum or gold. In any case, they should not be made of copper. As a matter of fact, copper is electrochemically not stable enough, even at very low voltages. As soon as a voltage is applied between the terminals, the ions of copper formed in the process of oxydation migrate very fast into the IEAP. The bending of IEAP actuators is caused by the movement of cations in the applied electric field. In the region of electrical terminals the infiltrated cations of copper will participate in this process and give additional effect. With the help of a showy experiment we compare the bending of a water-swollen ionic polymer membrane using terminals made of copper and made of gold. The experiment demonstrates impressively, that the copper ions originated from the copper contacts cause bending close to the terminals, and alter the composition of the membrane between the terminals.
We present a novel experimental method for qualitative visualization and quantitative characterization of the time-dependent behavior of bending ionic electroactive polymer actuators. The thin fibers, attached to the actuator, represent the surface normal at the given points of the bending actuator. The structure, formed by the skeleton of many adjacent fibers, amplifies the visual overview about the whole actuator. The four coordinates formed by four tips of two fibers enable determining the axial as well as the bending strains of a bending actuator.
This work reports on the modelling and control of ionic electroactive polymer actuators with electrodes based on nanoporous carbon, which are working in ambient environment. The model incorporates the humidity level value as one of the input parameters, and so captures the environment-dependent dynamics of the actuator. The effect of ambient humidity on the actuators is studied through the frequency response analysis and is followed by neural network method of modelling. A closed loop set point tracking control system based on gain scheduled model predictive control is designed and developed for position control of actuator and is verified experimentally. The developed model and controller is capable to predict and control the actuators at under the humidity conditions varying in the range of 3% - 97%.