To increase the flexibility of application of continuous conveyor systems, a completely decentralized control system for a modular conveyor system is introduced in the paper. This system is able to carry conveyor units without any centralized infrastructure. Based on existing methods of decentralized data transfer in IT networks, single modules operate autonomously and, after being positioned into the required topology, independently connect together to become a functioning conveyor system. Parallel to the development of the decentralized control system, identical square modules were developed, which in a compact unit contain all of the features necessary to function as a switch, junction or linear conveyor section. To fulfill this task, every module is equipped with an RFID identification system, sensors, a multi-directional drive, and a microcontroller-based control unit that executes the control algorithm.
The following functions can be performed by these modules with the help of the innovative control algorithm:
• Independent generation of the topological map in the form of routing tables
• Recognition of an incoming conveyor unit and identification of the destination address
• Planning of the path to the destination taking into consideration conveyor units already located in the system
• Protection against collisions and deadlocks, and transportation of the conveyor unit to the next module
• Autonomous regulation of the injection rate to ensure the highest possible throughput
The throughput performance of the control algorithm developed here was analyzed by simulating representative topologies. Furthermore, it was proven that under certain conditions, despite the conveyor routes being used in multiple directions, a situation can never arise where conveyor units block each other and the flow of material comes to a halt in the form of a deadlock.
Contents
1. Introduction
1.1 Motivation
1.2 Aim of the dissertation
1.3 Structure of the dissertation
2. Centralized material flow controls
2.1 Classification of material flow controls
2.1.1 Control concepts
2.1.2 Structure of the control systems
2.1.3 Signal processing
2.2 Tasks of the control levels in the material flow automation
2.3 Operating method of conventional PLC controls
2.3.1 Field of application of a PLC
2.3.2 Structure of a PLC
2.3.3 Programming languages
2.3.4 Operating concepts
2.3.5 PLC networks
2.3.6 Limits of and alternatives to centralized controls for material flow systems
3. Decentralized control systems
3.1 Definition of the term ”decentralized” in material flow
3.2 Research projects in decentralized material flow controls
3.2.1 The Internet of Things
3.2.2 MATVAR
3.2.3 Transport system in analogy to routing in data networks
3.2.4 Need for research to achieve complete decentralization
3.3 Decentralized control of IT networks
3.3.1 The OSI reference model
3.3.2 LAN technology
3.3.3 Transport protocol
3.3.4 Routing in networks
3.3.5 Decentrally controlled information vs. material flows
4. Completely decentralized autonomic continuous conveyor system
4.1 Overview and general assumptions
4.1.1 Requirements for a completely decentralized system
4.1.2 Determination of the physical features
4.1.3 Application example
4.2 Control concept
4.2.1 Decentralized generation of topological information
4.2.2 Identification of the conveyor unit
4.2.3 Routing and route reservation
4.2.4 Transportation of conveyor units
4.2.5 Deadlock avoidance
4.3 Throughput analysis
4.3.1 Simulation environment
4.3.2 Throughput calculation
4.3.3 Topology analysis
4.4 Throughput regulation
4.5 Interfaces to the environment
5. Technical implementation
5.1 Introduction of the ”Flexconveyor”
5.2 Construction
5.2.1 Base plate with lifting mechanism
5.2.2 Diverter with integrated RFID antenna
5.2.3 Roller arrangement and sensor system
5.3 Control of the Flexconveyor
5.3.1 Electrical connection
5.3.2 Control procedure
5.4 Connection of several modules to the topology
6. Summary
Research Objectives and Themes
The dissertation aims to establish a foundation for highly flexible material flow systems by developing a completely decentralized control system that allows modules to operate autonomously without central infrastructure. The work focuses on increasing layout flexibility and system adaptability through modular, intelligent conveyor components.
- Decentralized control architectures in material flow systems.
- Technical implementation of modular, autonomous conveyor components.
- Throughput analysis and deadlock prevention in distributed systems.
- Application of IT-inspired routing mechanisms to physical conveyor systems.
Excerpt from the Book
4.2.5 Deadlock avoidance
(Tanenbaum 2002) describes the existence of a deadlock in information technology as follows:
”A set of processes is deadlocked when every process in the set is waiting for a resource that must be released by another process in the set”
A deadlocked system must have at least two processes. Figure 4.17 shows such an example. Process 1 occupies the screen while it is waiting for the printer. At the same time, process 2 occupies the printer while it is waiting for the screen.
A more common example is found in road traffic when four cars arrive at an intersection at the same time with no rule for the right of way. In the case of ”right before left”, all cars are waiting for the right car to go first and nobody will move (Peterson and Silberschatz 1983).
The phenomenon of deadlock has been studied extensively in the context of computer operating systems (Panson 1985), (Deitel 1983). It is well known that the following four conditions are necessary for a deadlock to occur among concurrent processes (Coffman, Elphick, and Shoshani 1971), (Coffman and Denning 1973):
Summary of Chapters
1. Introduction: Outlines the motivation for flexible material flow systems driven by e-commerce and globalization, defining the dissertation's aim to develop a decentralized control architecture.
2. Centralized material flow controls: Reviews conventional centralized control methods like PLC controls and identifies their limitations in terms of flexibility and adaptability.
3. Decentralized control systems: Analyzes existing research on decentralization, including the "Internet of Things" and IT networking principles applied to logistics.
4. Completely decentralized autonomic continuous conveyor system: Describes the development of an autonomous, decentralized conveyor system, including control concepts, deadlock avoidance, and throughput analysis.
5. Technical implementation: Details the mechanical and electrical construction of the "Flexconveyor" prototype, focusing on modules with integrated control and sensing capabilities.
6. Summary: Concludes with an assessment of the achieved flexibility and discusses future steps toward the industrial application of the decentralized system.
Keywords
Material flow systems, Decentralized control, Autonomous conveyor modules, Intralogistics, Throughput analysis, Deadlock avoidance, RFID, Routing protocols, Modular automation, Flexconveyor, Distributed systems, Industrial Ethernet, Network topology, PLC, Supply chain flexibility.
Frequently Asked Questions
What is the core focus of this research?
This work focuses on designing a completely decentralized control system for modular continuous conveyor systems to increase flexibility and reduce the need for central infrastructure.
What are the primary challenges in material flow systems today?
Challenges include shorter project durations, smaller batch sizes, and the need for higher flexibility to adapt to rapidly changing production environments.
What is the main objective of the proposed control system?
The primary goal is to enable conveyor modules to act autonomously, managing their own routing, identification, and collision avoidance without relying on a central computer.
What methodology is used to develop the control system?
The research uses simulation techniques to test control algorithms and draws inspiration from IT network routing protocols to achieve decentralized material flow management.
What topics are covered in the main section of the dissertation?
The main part covers the requirements for decentralized systems, the control concept, routing algorithms, deadlock avoidance strategies, and a throughput analysis for different topologies.
What defines the proposed control system?
It is characterized by high autonomy, distributed decision-making, and the capability of modules to automatically generate topological information and perform routing tasks.
How are deadlocks handled in this decentralized architecture?
Deadlocks are managed through a "deadlock token" process, where modules verify the route reservation for a conveyor unit across the entire path to ensure circular waiting conditions are prevented.
What is a "cross deadlock" and how is it addressed?
A cross deadlock occurs when multiple circular layouts are interconnected. It is mitigated by self-diagnostic tokens that allow modules to recognize their role as links between circles and apply specific safety checks.
What is the role of the "Flexconveyor" module?
The Flexconveyor is the physical prototype developed in this work; it integrates motors, sensors, and RFID technology to demonstrate the practical viability of the decentralized control logic.
- Quote paper
- Dr.-Ing. Stephan Mayer (Author), 2009, Development of a completely decentralized control system for modular continuous conveyors, Munich, GRIN Verlag, https://www.grin.com/document/132541
