The Wireless Sensor Networks for Factory Automation: Issues and Challenges L. Q. Zhuang, K. M. Goh and J. B. Zhang Singapore Institute of Manufacturing Technology 71 Nanyang Drive Singapore 638075 lqzhuang@simtech.a-star.edu.sg Abstract The emerging technology of wireless sensor network (WSN) has changed the way people interact with the physical world. WSN produces myriad interdisciplinary research issues on information processing, control, communication and computation. It has also provided new paradigm for factory automation that has remarkable impacts on control, tracking, monitoring, and diagnostics of the manufacturing processes and equipments. This paper will provide a short survey on the research issues and implementation challenges coming with wireless networked control, distributed signal processing, condition-based maintenance and industrial efforts for standardization of communications, protocols and smart transducers. 1. Introduction Wireless technologies for telecommunication such as GSM, CDMA, GPRS, CDMA2000, TD-SCDMA, HSDPA and WiMAX etc. have revolutionary impacts on the personal communication. Wi-Fi, based on IEEE 802.11 standard, has provided pervasive Internet access infrastructure at home, at office, at school and at public place for many kinds of information exchanges and Web application services. For factory automation, the wireless telecommunication and wireless Internet services have also enabled e-manufacturing that providing more operation efficiency at enterprise level. However, at the shop floor level, the fundamental networking technologies are still based on Fieldbus that providing wired link between program logical controllers (PLC) and other devices such as transducers, actuators, motors and switches to form the control chain. The radio- frequency identification (RFID) technology serves for electronic labels for asset tracking and object identification in the factory yet lacks support for sensing, information processing and actuation by its transponders. To simplify the machinery access and monitoring in hash environments as well as to reduce the cost of cabling and maintenance by using mobile or ad-hoc device, wireless personal area network (WPAN) based on IEEE 802.15 standards have become new fundamental technologies in factory automations, including Bluetooth (802.15.1), UWB (802.15.3) and ZigBee (802.15.4). Such sensors and actuators that are based on wireless interface and protocols provide new paradigm for factory automation as they have integrated sensing, control, computation and communication capabilities into a single tiny node (Figure 1) and will form a mesh network called wireless sensor network (WSN) [1]. Control over the WSN with the characteristics of packet delay, packet loss and packet disorder has posed new challenges in the areas of traditional robust control, performance analysis and signal processing. Classical communication theory and control theory have not shown much common ground for these new research challenges as it is difficult to provide the unified mathematical model for issues in both research areas. Hence new approaches are needed to address these challenges. As WSN is the low power pervasive computation platform for factory monitoring, process control and supervisory control, optimization for power becomes one of the key issues that have implied the tradeoff between the control and communication performance. Such tradeoff requires new design methods for the traditional layered OSI model and new optimization framework for information exchanges and iteration between different OSI sub-layers [2]. This new approach is referred as cross-layer design and layering as optimization decomposition. Standardization of WSN is one of the most important industrial drives to its commercial success for factory automation applications. The standardization processes are focused in two areas: network protocol and sensor interface. The prior is described in the ZigBee specification (2006) [3] which are defined on top of IEEE 802.15.4. The later is referred as transducer electronic data sheet (TEDS) containing interface information connected to any kinds of sensors and the standard is defined in the IEEE 1451. Power Unit Wireless Communication Unit Computation Unit Control Unit Sensor Actuator Figure 1. Node of WSN. 1-4244-0826-1/07/$20.00 © 2007 IEEE 141