Contribution to the performance evaluation of decentralized material flow controls on the example of a control prototype

Abstract

The new control paradigm Internet of Things (IoT) in intralogistics propagates highly modular and flexible decentralized control systems based on agent technology and radio-frequency identification (RFID). The productive application of such systems demands the fulfillment of several requirements, which exist in the industrial reality of the facility logistics. The real-time requirements in decentralized control systems are examined within the scope of the Collaborative Research Center (CRC 696) "Logistics on Demand" (sub-project C5 -"Real-Time Logistics"). The systematic performance analysis of legacy and new controls is an important aspect of this research work. In this paper an approach for the evaluation of the performance of decentralized control is proposed. The collection and analysis of performance data is facilitated by self-developed measuring instruments. IntroductionRecently applied research in the field automated material handling shows a strong inclination to developing decentralized control concepts (see [Win08], [HLS06] and [Wil06]). Improved scalability and adaptability as well as the reusability of system components (see [Lor03], [BSc01]) are often mentioned as the system advantages to be expected. Here increased profitability is to be guaranteed by shorter start-up periods and low effort expandability (see [GCK08]). However there is a gap between the vision of a desired decentralized material flow control and the realization of this vision in industrial practice. The use for performance evaluation instruments, proposed in this paper, helps to close this gap. Internet of Things in IntralogisticsThe control paradigm Internet of Things in intralogistics (see [GtH10]) propagates a decentralized approach to control material handling systems. The transported goods themselves take over the control and use the transport capability as well as other capabilities of the material handling plant. Modern technologies like radio-frequency identification (RFID) are used, having relevant information for transportation on the RFID-tag of the corresponding transportation good. A possibility to realize such distributed control systems is the usage of software-agents. The control system examined in this work is a multi-agent-system, where unit load agents are negotiating with each other and with conveyor agents to get access to plant resources. The concept provides for the distribution of control hardware and software along the mechanical components of a conveyor plant. This distribution is meant to produce a high modularity of the control. However, this makes additional demands to real-time capability and the performance of responsible control components. Real-Time Problems and Control Performance as a Research TopicThe real-time capability of material flow control is an important requirement which is in contrast to the decentralized control principle (see [HLL07],[Ste03]). The reason for this confrontation lies in the nature of distributed systems with decentralized data management and processing. In these system...