In this paper Ionic Polymer-Metal Composites (IPMC) actuators motion control is addressed by using a new approach based on the modified fractional super twisting control strategy. We present the theoretical aspect of the proposed control strategy and then the performances of the controlling strategy are validated for an IPMC actuator by using an ad hoc developed experimental setup. The reported results show that the standard fractional super twisting control and the proposed modified fractional super twisting control over perform standard PI controllers.
Ionic polymer-metal composites (IPMCs) are electroactive polymers which transform the mechanical forces into electric signals and vice versa. The paper proposes an enhanced fractional order transfer function (FOTF) model for IPMC membrane working as actuator. In particular the IPMC model has been characterized through experimentation, and a more detailed structure of its FOTF has been determined via optimization routines. The minimization error was attained comparing the simple genetic algorithms with the simplex method and considering the error between the experimental and model derived frequency responses as cost functions.
Abstract:The paper presents a fractional order model of a heating process and a comparison of fractional and standard PI controllers in its closed loop system. Preliminarily, an enhanced fractional order model for the heating process on non-continuous materials has been identified through a fitting algorithm on experimental data. Experimentation has been carried out on a finite length beam filled with three non-continuous materials (air, styrofoam, metal buckshots) in order to identify a model in the frequency domain and to obtain a relationship between the fractional order of the heating process and the different materials' properties. A comparison between the experimental model and the theoretical one has been performed, proving a significant enhancement of the fitting performances. Moreover the obtained modelling results confirm the fractional nature of the heating processes when diffusion occurs in non-continuous composite materials, and they show how the model's fractional order can be used as a characteristic parameter for non-continuous materials with different composition and structure. Finally, three different kinds of controllers have been applied and compared in order to keep constant the beam temperature constant at a fixed length.
Digital realization of non-integer-order controllers is important to exploit the benefits provided by these controllers, in terms of flexibility, dynamic performance and robust stability, for applications in mechatronics, industrial and automotive systems. To realize infinite-dimensional fractional-order operators and controllers in the digital domain, a discrete-time approximation is necessary that must be characterized by stable and minimum-phase properties for control purposes. This paper provides a design method useful for a wide class of plants and applies a consolidated approximation technique. Moreover, the practical implementation problems of digital non-integer control algorithms are deeply analyzed by considering the effects of the sampling period, of the conversion between analog and digital domain (and vice versa) and the associated quantization. Results show benefits and limitations of the approach.
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