IEEE International Workshop on Intelligent Data Acquisition and Advanced Computing Systems: Technology and Applications 21-23 September 2009, Rende (Cosenza), Italy 978-1-4244-4881-4/09/$25.00 ©2009 IEEE 67 Experimental Analysis Towards the Application of RFID Technologies in Industrial Marble Machines Sergio Saponara, Fabrizio Iacopetti, Andrea Carrafiello, Luca Fanucci, Bruno Neri, Riccardo Massini Dip. di Ingegneria dell’Informazione: Elettronica, Informatica, Telecomunicazioni, Università di Pisa, via Caruso 16, I-56122, Pisa, Italy, www.iet.unipi.it {sergio.saponara, fabrizio.iacopetti, andrea.carrafiello, luca.fanucci, b.neri, riccardo.massini}@iet.unipi.it Abstract - The paper presents an experimental characterization of RFID technologies applied to process control in the marble industry. The final aim is the automatic detection of the presence of a marble slab under the abrasive or cutting heads inside an industrial machine. Four RFID systems at 125 kHz, 13.56 MHz, 868 MHz and 2.45 GHz have been implemented starting from commercially available tags and readers and customizing the set up of the acquisition hardware and of the relevant software. The experimental tests and measures also include dirty and wet working environments representative of those found in real applications. Keywords - RFID (Radio Frequency IDentification), Industrial measurements, Wireless systems, Marble industry, Process control, Measurements in dirty/wet environments I. INTRODUCTION Marble machines are made up of consecutive working heads (up to a few dozens) under which the marble slab is transported by a conveyer belt [1]. A marble slab is typically sized 2 m x 3 m and has a thickness up to 10 cm. Currently, the process control for marble slab working is based on the following scheme: mechanical or optical sensors detect the presence of the marble slab on the conveyer belt at the entrance of the industrial machine; such information is used by the PLC controlling the entire machine as the reference time to drive down each cutting/abrasive head when the marble slab is under it, and, when the slab is passing the working head, to drive up the head in the initial position. The above mentioned feed-forward control rule is based on the assumptions that the speed of the conveyer belt, the position of the marble slab on the belt and the relative positions of the heads are constantly known. If one of such assumptions is not verified then the marble slab is not present when the head is driven down; the latter falls on the conveyer belt which is damaged and has to be replaced or repaired causing a long stop of the machine and of the industrial process. Hence a feedback should be provided about the real presence of the marble slab under the head inside the machine. Another problem at the state of the art is that, outside the machine, mechanical sensors suffer of rapid deterioration due to the continuous contact with the slab while optical sensors [2] have to be frequently cleaned and/or re-calibrated due to the dirty working environment. Due to the wet and dirty working conditions, also other sensors proposed for marble machines, based on LASER or vision systems, did not result in successful industrial applications. Capacitive sensors for marble [3] and more complex ultra sound- or georadar-based systems [4, 5] have been studied in literature. However their target is the fine-grain analysis of the porosity and defects of stone materials (e.g. based on dielectric permittivity variations) in a controlled working environment (dry, clean, with stone samples still) rather than the run-time detection of a marble slab in an industrial machine. To address the above issues this paper presents the experimental characterization of 4 different RFID systems used to detect the presence of the marble slab outside and/or inside the marble machine. At the state of the art the application of RFID technologies has been analyzed for logistics (for which commercial solutions are available, see [6] as an example in the marble industry), but less for process control. The target of this work is highlighting the advantages and limits of RFID systems applied to detection tasks, mainly in the marble industry process control, and suggesting which technologies are most suited and how they can be used. II. RFID FOR PROCESS CONTROL IN MARBLE MACHINES RFID is a means of identifying, but also tracking and detecting, an item based on radio frequency communication, which takes place between a transmitter called “reader” and a transponder (silicon chip connected to an antenna), usually called “tag”. The physical coupling is based on magnetic or electromagnetic fields. Tags can either be passive, i.e. powered by the reader field, semi- passive or active, i.e. powered by a battery. For marble machines the effects of the interaction between the radiation emitted by the reader antenna and the stone samples depend on various parameters: the type and shape of the stone slab, the frequency and power levels of the RFID system, the polarization of the antenna,