Salvatore Graziani

A nonlinear model for ionic polymer metal composites as actuators

This paper introduces a comprehensive nonlinear dynamic model of motion actuators based on ionic polymer metal composites (IPMCs) working in air. Significant quantities ruling the acting properties of IPMC-based actuators are taken into account. The model is organized as follows. As a first step, the dependence of the IPMC absorbed current on the voltage applied across its thickness is taken into account; a nonlinear circuit model is proposed to describe this relationship. In a second step the transduction of the absorbed current into the IPMC mechanical reaction is modelled. The model resulting from the cascade of both the electrical and the electromechanical stages represents a novel contribution in the field of IPMCs, capable of describing the electromechanical behaviour of these materials and predicting relevant quantities in a large range of applied signals. The effect of actuator scaling is also investigated, giving interesting support to the activities involved in the design of actuating devices based on these novel materials. Evidence of the excellent agreement between the estimations obtained by using the proposed model and experimental signals is given.

A Tactile Sensor for Biomedical Applications Based on IPMCs

In this paper, a first prototype of a multifunctional tactile sensor using ionic polymer metal composites (IPMCs) is proposed, designed, and tested. Two IPMC strips are used, one as an actuator and one as a sensor, both positioned in a cantilever configuration; working together they enable the system to detect the presence of a material in contact with it and to measure its stiffness. These sensing capabilities can be exploited in various biomedical applications, such as catheterism, laparoscopy and the surgical resection of tumors. Moreover, the simple structure of the proposed tactile sensor can easily be extended to devices in which a sensing tip for exploration of the surrounding environment is required. Compared with other similar tools, the one proposed works with a very low-power supply (the order of magnitude being a few volts), it needs very simple electronics, it is very lightweight and has a low cost.

A model for ionic polymer metal composites as sensors

This paper introduces a comprehensive model of sensors based on ionic polymer metal composites (IPMCs) working in air. Significant quantities ruling the sensing properties of IPMC-based sensors are taken into account and the dynamics of the sensors are modelled. A large amount of experimental evidence is given for the excellent agreement between estimations obtained using the proposed model and the observed signals. Furthermore, the effect of sensor scaling is investigated, giving interesting support to the activities involved in the design of sensing devices based on these novel materials. We observed that the need for a wet environment is not a key issue for IPMC-based sensors to work well. This fact allows us to put IPMC-based sensors in a totally different light to the corresponding actuators, showing that sensors do not suffer from the same drawbacks.

A model of ionic polymer-metal composite actuators in underwater operations

Ionic polymer metal composites (IPMCs) are active materials that exhibit a bi-directional electromechanical coupling: a voltage produces membrane bending, while by bending an IPMC membrane a voltage output is obtained. IPMCs are of increasing interest in a number of application fields. More specifically, IPMCs can work in wet environments, even in water, and this represents a valuable capability in a number of applications fields such as underwater robotics, surveillance, and biomedical applications. In this work a totally new model of an active IPMC beam, solicited by a voltage signal and immersed in water, is introduced. The model estimates the moment produced by the applied voltage. Therefore, the classical Euler–Bernoulli cantilever beam theory and the concept of hydrodynamic function are used to describe the interaction between the beam and the water. Knowledge of this interaction allows estimation of the IPMC active beam motion in water.

Characterization of the harvesting capabilities of an ionic polymer metal composite device

Harvesting systems capable of transforming dusty environmental energy into electrical energy have aroused considerable interest in the last two decades. Several research works have focused on the transformation of mechanical environmental vibrations into electrical energy. Most of the research activity refers to classic piezoelectric ceramic materials, but more recently piezoelectric polymer materials have been considered. In this paper, a novel point of view regarding harvesting systems is proposed: using ionic polymer metal composites (IPMCs) as generating materials. The goal of this paper is the development of a model able to predict the energy harvesting capabilities of an IPMC material working in air. The model is developed by using the vibration transmission theory of an Euler?Bernoulli cantilever IPMC beam. The IPMC is considered to work in its linear elastic region with a viscous damping contribution ranging from 0.1 to 100?Hz. An identification process based on experimental measurements performed on a Nafion? 117 membrane is used to estimate the material parameters. The model validation shows a good agreement between simulated and experimental results. The model is used to predict the optimal working region and the optimal geometrical parameters for the maximum power generation capacity of a specific membrane. The model takes into account two restrictions. The first is due to the beam theory, which imposes a maximum ratio of 0.5 between the cantilever width and length. The second restriction is to force the cantilever to oscillate with a specific strain; in this paper a 0.3% strain is considered. By considering these two assumptions as constraints on the model, it is seen that IPMC materials could be used as low-power generators in a low-frequency region. The optimal dimensions for the Nafion? 117 membrane are length = ?12?cm and width = ?6.2?cm, and the electric power generation is 3?nW at a vibrating frequency of 7.09?rad?s?1. IPMC materials can sustain big yield strains, so by increasing the strain allowed on the material the power will increase dramatically, the expected values being up to a few microwatts.

Genetic algorithms and applications in system engineering: a survey

In this paper an overview on Genetic Algorithms (GAs) is reported. GAs are described from a theoretical point of view, important implementation problems are dealt with and a wide variety of GA applications reported in system engineering literature are described. The survey also includes some studies at present in progress in our laboratories, regarding the use of GAs in solving optimisation problems in the fields of neural networks and control theory.

Static and Dynamic Characterization of the Temperature and Humidity Influence on IPMC Actuators

Several models that describe the behavior of ionic polymer-metal composite (IPMC)-based actuators can be found in the literature. The response of IPMC transducers as a function of modifying quantities is a matter of interest; however, it has not been investigated. It is reasonable to argue that environmental humidity and temperature represent the main modifying parameters. In fact, humidity changes the behavior of IPMC transducers, working as both sensors and actuators, because it changes the Young modulus of the devices and, hence, their mechanical response. The influence of temperature is suspected, because polymer characteristics are often influenced by this quantity. In a previous paper, the authors proposed a dynamic model and investigated the scaling effect of geometrical parameters, giving evidence of the excellent agreement between estimations that were obtained using the proposed model and corresponding observations. In this paper, the response of IPMC actuators to both temperature and relative humidity is analyzed, giving interesting information that both integrates IPMC models and allows for a better exploitation of IPMCs.

A resonant force sensor based on ionic polymer metal composites

In this paper a novel force sensor, based on ionic polymer metal composites (IPMCs), is presented. The system has DC sensing capabilities and is able to work in the range of a few millinewtons. IPMCs are emerging materials used to realize motion actuators and sensors. An IPMC strip is activated in a beam fixed/simply-supported configuration. The beam is tightened at the simply-supported end by a force. This influences the natural resonant frequency of the beam; the value of the resonant frequency is used in the proposed system to estimate the force applied in the axial direction. The performance of the system based on the IPMC material has proved to be comparable with that of sensors based on other sensing mechanisms. This suggests the possibility of using this class of polymeric devices to realize PMEMS (plastic micro electrical mechanical systems) sensors.

A circuit to model the electrical behavior of an ionic polymer-metal composite

The electrical behavior of an ionic polymer-metal composite (IPMC), when a voltage is applied across its thickness, is investigated. IPMCs are new materials of increasing interest, to implement artificial muscles in robotic applications, and to implement displacement sensors in measurement fields. They are particularly light and they deform if electrically stimulated with a very low voltage; on the other hand they produce a voltage if mechanically bent. An understanding of the phenomena involved in electromechanical energy conversion may address research activity toward the building of innovative devices where both sensing and actuating functions could be integrated in the same material. The paper illustrates a model that describes the electrical behavior of an IPMC as an actuator using an equivalent circuit. It is a totally new nonlinear lumped parameter model which is able to describe all the phenomena observed in the flow of electrical current through the material, including nonlinear phenomena. The model has been validated by a large set of comparisons between simulations and experimental data. In all the cases analyzed the simulations agree with the experimental data.

Multisensor Strategies to Assist Blind People: A Clear-Path Indicator

The development of electronic sensing devices for the visually impaired requires knowledge of the needs and abilities of this class of people. This paper presents a rough analysis that can be used to properly define the criteria to be adopted for the design of such devices. In particular, attention will be focused on clear-path indicators, highlighting their role in orientation and mobility tasks. A new device belonging to this class is presented. The detector is based on a multisensor strategy and adopts smart signal processing to provide the user with suitable information about the position of objects hindering his or her path. Experimental trials demonstrate the efficiency of the device developed.