ORIGINAL ARTICLE RFID-based location-sensing system for safety management Kwangsoo Kim • Myungsik Kim Received: 15 October 2010 / Accepted: 4 April 2011 / Published online: 31 May 2011 Ó Springer-Verlag London Limited 2011 Abstract This paper focuses on an active radio frequency identification (RFID)-based location-sensing system for enhancing the worker’s safety under a cargo crane in a steel industry. For the purpose, the time of flight (TOF)-based distance sensing RFID system with location trilateration algorithm is developed to monitor workers’ position. However, RF signal is easily affected by the surrounding environmental conditions, it is difficult to obtain reliable positional information under the restricted environmental conditions of the crane. For the problem, this paper intro- duces two new improvements. Firstly, circular polarization antennas are developed, which is highly effective for reducing an error in the distance estimation by transceiving RF signals with less dependance on its orientation. Sec- ondly, a three-dimensional location-sensing algorithm that facilitates a distance and position filter is developed for enhancing accuracy by reducing a large error in the esti- mated distance. The field experimental results performed in the POSCO steel company demonstrate that the developed system is capable of finding target positions with signifi- cantly improved accuracy and effectiveness. Keywords Location sensing  Active RFID  Worker safety management 1 Introduction The developments of IT have significantly increased effi- ciency of the industrial domains by introducing more automation in manufacturing and distribution processes. However, some processes such as product inspection, loading and unloading, and so on are still highly dependent upon the physical endeavors of workers, who encounter dangers under automated systems. The steel industry is one industrial domain where the workers’ safety management is significantly demanding; specifically, we focuses on the cargo crane workplace, which is used for loading and unloading products from and to a freighter. Since the steel products are very heavy over several tons, workers who fasten and unfasten the products to the crane encounter danger under the products. Thus, the workers’ position should be thoroughly monitored to ensure the safety of the workers. Also, the monitoring system is highly required to automate the crane process. For such a safety issue, vision-based object identifica- tion techniques can be used [1, 2, 3]. However, such sys- tems require maintenance of the optical line of sight for the visual images. Also, the performances are often signifi- cantly affected by the environmental conditions such as the change of the illumination. Thus, the system offers limited effectiveness for the outdoor crane system that is most common in practice. In this paper, we propose an RF communication-based location-sensing and tracking system for the safety man- agement. The system is composed of active RFID tags, receivers, and a location-sensing server. Tags are attached inside workers’ safety helmets, which is monitored by receivers installed to the cargo crane. The distances to tags from the receivers are estimated using the TOF of the RF signal and transmitted to the location-sensing server. The K. Kim  M. Kim (&) Sogang Institute of Advanced Technology (SIAT), Sogang University, 1 Shinsu-dong, Mapo-gu, Seoul 121-742, Republic of Korea e-mail: reoreo93@gmail.com K. Kim e-mail: kimks@sogang.ac.kr 123 Pers Ubiquit Comput (2012) 16:235–243 DOI 10.1007/s00779-011-0394-0