Technologies and Methodologies Enabling Reliable Real-Time Wireless Automation
Mikael Bjrkbom, Lasse M. Eriksson, Joni Silvo · Sciyo eBooks · 2010
Intelligence and Network Systems 86 1.1 Wireless automation Wireless automation and the related field of wireless sensor networks (WSN) are currently attracting researchers and industry world-wide.The progress of development has emerged into two industrial wireless automation standards, namely WirelessHART (2007) and ISA100.11a ( 2009).In the current phase, these standards consider mainly monitoring applications without guarantees of real-time performance.However, in automation systems, it is possible to handle the missing data and variable time-delays induced by the somewhat non-deterministic wireless communications by proper design of the system, especially via appropriate control design.The primary benefit of wireless control technology is the reduced installation cost, as a considerable investment is made in the wiring of factories, both financially and in labor (Brooks, 2001).The use of wireless technology is not only a replacement of cables; the benefits go beyond that.With wireless devices, increased flexibility is gained, as sensors can be placed more freely, even on rotating machines.Robustness is increased, as the communication can be done over several paths in a mesh network and failure of cables is eliminated (TSMP, 2010).Finally, there are the opportunities for new applications that are enabled by wireless control.Some existing or emerging applications are remote control of devices, for example cranes or dexterous and mobile robots, mobile applications, and wireless monitoring of large plants for fault detection, maintenance, production quality monitoring, and compliance to environmental regulations (Gungor & Hancke, 2009).There is a strong aim (Moyne & Tilbury, 2007) to develop and deploy wireless networked control systems (WiNCS), where a control system communicates over a wireless network, in factory and home automation.In a related field, sensor network applications have as well received much attention (Akyildiz et al., 2002;Baronti et al., 2007).Today, wireless automation technologies are mostly used in monitoring applications, because in these applications the operational requirements can be satisfied with the current technology.The industry is cautious in applying wireless to closed-loop control, due to the inherent unreliability of wireless communications.Next we summarize the main research activities on WiNCS to enable wireless automation. Research on wireless networked control systemsA networked control system (NCS) is a distributed real-time control system consisting of the plant, sensors, controllers, actuators, and a shared data network that is used for communication between the components of the system (Antsaklis & Baillieul, 2004).A general NCS layout is depicted in Fig. 1.In WiNCS, wireless networks are used for transferring data.One of the benefits of NCS is reduced cabling cost (Neumann, 2007), which is removed completely by the introduction of wireless devices.Other advantages include ease of adding field devices, introducing two-way communication with field devices for remote configuration and device health monitoring, and more advanced control strategies are possible because of improved availability of field level data (Gungor & Hancke, 2009;Neumann, 2007).Wireless control systems deliver more benefits than NCSs as there are no wires, but also more problems, mainly because of the unreliable shared communication medium.The main concern against deploying wireless networks for control is the uncertainty of communication and inability to guarantee a sufficient quality of service for the control system.The network must provide real-time and continuous operation, as www.intechopen.com