- 學位論文
在無線網狀網路上的Modbus通訊架構
A Modbus Communication Framework Over Wireless Mesh Networks
摘要
自1979年Schneider Automation Inc.發展Modbus用於PLC(Programmable Logic Device)設備的工業控制協定後，因其協定開放且易於應用在系統資源不高的PLC設備，已被廣泛應用在各種工業自動化控制領域，尤其對民眾生活直接影響的基礎設施，如電力工程、水利工程、機電設施等。而後隨著乙太網路的快速發展，也促使Modbus導入網路概念而發展出Modbus/TCP協定，原本工業控制的範圍也得以延伸到其他異質網路，突破了的傳統工業控制網路的限制。 在802.11無線網路基礎架構上的Wireless Mesh Network(WMN)無線網狀網路，可讓所有的節點可互相通訊並轉送來自其他節點的封包，讓整個網路形成一個網狀架構，彼此互相備援並可延伸訊號涵蓋範圍，此概念也被應用於無線感測網路(Wireless sensor network)技術中，成為近期被廣泛討論研究的重要議題。 嚴峻的工業環境中，電纜需要安置在管道間內，重要的控制線路還必須要有雙重備援，除此之外還必須面對溫差極大、高濕度甚至化學藥劑的侵蝕以及馬達所產生的電磁訊號干擾。就目前複雜的工業應用，工業佈線將需要難以想像的成本以及複雜的施工和維護費用，施工時也可能使得工廠運作停擺。因此本論文提出將工業控制協定結合網狀網路的架構Wireless Modbus Mesh Network (WMMN)，利用網狀網路拓樸為基礎的控制環境，並可直接與現有設備結合，儘管斷電或其他因素導致其中某個節點停止運作，但整個網路還是能透過鄰近的節點傳輸資料，進而避免無法預期的損失。藉由WMMN 能加快系統建置速度及可靠性和降低建置的成本，並且結合建構在802.11上網路安全技術，能有效避免控制訊號被惡意竄改或重製而造成系統出現安全漏洞。
並列摘要
In 1979, Schneider Automation Inc. developed an industrial control protocol called Modbus, which can be used in Programmable Logic devices (PLC). It has been widely adopted in industrial automatic control applications, especially the ones that directly impact the public, e.g. electrical engineering, hydraulic engineering, electrical and mechanical facilities, because of it’s openness and simple use in low-end PLC devices. On the other hand, the fast development of Ethernets inspires the introduction of networking capability in Modbus. Thus, the Modbus/TCP protocol emerges. It facilitates the industrial control through networks, which extends the scope of traditional industrial control applications. Wireless Mesh Networks (WMNs), based on the 802.11 wireless framework, enable that all nodes can communicate with each other and transmit packets through other nodes. In a WMN, the network is formed as a mesh structure. Nodes can be backups of other nodes in supporting reliable communications, and can be used to extend the signal coverage of other nodes. The mesh concept has been applied in sensor networks and has received much attention in the recent years. In a harsh industrial environment, cables need to be installed in the pipe room. Important control lines must also be redundant. The change of temperature, high humidity, erosion by chemicals, and signal interference produced by electromagnetic motor will endanger the cables. In practice, industrial wiring incurs incredible cost and complexity of installation and maintenance, and may require the factory shutdown during cable installation. Therefore, this paper proposes the integration of the Modbus industrial control protocol and wireless mesh networks, called Wireless Modbus Mesh Network (WMMN), for the use a wireless industrial control environment The proposed WMMN can integrate directly with existing devices, and supports robustness. That is, even when there are power outages or failures of nodes, the whole control network is able to transmit data through the remaining nodes. Thus, unexpected losses can be avoided. On the other hand, the proposed WMMN can accelerate the system deployment, increase the reliability, and reduce the deployment cost for industrial control. The security feature of 802.11 technology can also effectively protect the signals from being tampered and reproduced.