Abstract: Robotics and enterprise information technology are two key technologies for improving manufacturing efficiency and process levels. This paper, based on an analysis of fieldbus network control technology, introduces a scheme for networking robots in an industrial field using the Lonworks bus. This scheme enables multi-robot collaboration and remote operation control, while also creating conditions for enterprise information technology implementation.
Keywords: Fieldbus; Lonworks; Remote operation; Enterprise information technology
Abstract: Robot technology and enterprise information technology are two key means to improve the manufacture efficiency and technical level. In this paper, a robot network system by means of Lonworks fieldbus technology is formulated on the basis of introducing its conception and structure. The solution makes it possible for both robots cooperation and telerobotics. It also provides fundamentals for the application of enterprise information technology.
Key words: Robot, Field bus, Lonworks, Telerobotics, Enterprise information technology.
1 Introduction
Robotics and enterprise information technology are two key technologies for improving production efficiency and process level in China's manufacturing industry. The former addresses technical issues, while the latter addresses management issues. They are important ways for the manufacturing industry to carry out technological innovation and increase efficiency and profits, and have considerable economic benefits and application value.
In modern manufacturing, intelligent robot technology integrates sensing, control, information processing, artificial intelligence, and network communication. Its functions are becoming increasingly powerful, its structure more complex and sophisticated, and the number of sensors and actuators it equips is constantly increasing. Fieldbus, as the underlying network of industrial control, serves two purposes: firstly, it connects individual, dispersed field robots into a networked control system capable of communication and collaboration, while secondly, it enables plant-wide transmission and sharing of production data through the enterprise's internal LAN. Currently, network control systems based on fieldbus technology are becoming a major solution for large and medium-sized enterprises in China to achieve industrialization driven by informatization.
2 Lonworks Fieldbus Technology
2.1 Fieldbus
Fieldbus is a system built on networked control, applied in production sites to achieve bidirectional serial multi-byte digital communication between microcomputer-based measurement and control equipment. It is an open, digital, multi-point communication low-level control network. Designed for production control equipment, it typically uses short frames to transmit data, with network speeds usually reaching several kilobytes per second to 10 Mbps, offering excellent real-time performance. Fieldbus technology provides an effective way to construct network-integrated fully distributed control systems.
Compared to distributed control, fieldbus technology offers advantages such as openness, networked information sharing, intelligence, high decentralization, functional autonomy, and high reliability. It can significantly reduce the number of hardware components and investment, and is easier to install, expand, and maintain. Current fieldbus technologies mainly include Foundation Fieldbus, PROFIBUS (DP, PA, FMS), CAN, Lonworks, and Industrial Ethernet, each with different characteristics in terms of network protocols, transmission rates and distances, application scenarios, and limitations on the number of stations.
2.2 Lonworks Technology
Lonworks (Local Operating Networks) fieldbus technology is an advanced open networked control technology introduced by Echelon. It features a simple structure, easy wiring, and is easily expandable and can accommodate new functionalities. For various user functional requirements, simply select different control nodes, use the development platform, write the corresponding programs, and connect them to the control network to complete the task; no physical modifications to the network structure are required. Lonworks is currently the most widely used fieldbus technology in distributed monitoring systems such as production sites and intelligent buildings.
Lonworks supports various transmission media and network topologies. When using a transformer-coupled interface FTT-10 transceiver and a twisted-pair bus architecture, it can achieve speeds of 78kbps/2700m, and the transmission distance can be extended via repeater routers. A Lonworks network can have up to 64 nodes, expandable through bridging routers. Data transmission between intelligent nodes is supported by hardware such as neural network chips and the network itself, using network variables. Each node can have up to 62 network variables configured. The data structure defined according to Lonworks' standard network variables resolves interoperability issues with products from different manufacturers. Currently, thousands of companies have launched Lonworks products.
The intelligent nodes and their neuron chips are the foundation of the Lonworks bus. They are directly installed in the production field to collect industrial field signals and output control quantities. At the same time, they upload and receive various network data through the network. Their structure is shown in Figure 1.
A smart controller, along with its sensors and actuators, constitutes a node, which can connect to various I/O devices, such as limit switches, force sensors, and articulated motors in industrial robot systems. LonWorks' masterless site-to-site network architecture ensures that the failure or shutdown of any node does not affect the normal operation of other user nodes, thus improving system stability. Furthermore, the logical connections between network nodes make adding and modifying nodes easy, facilitating system adjustment, expansion, and upgrades. The core of each node is a neuron chip, a general-purpose processor for communication processing, data acquisition, and control. It performs data acquisition, control, and network operations by running on-chip Neuron C applications.
3 Robot monitoring system based on Lonworks technology
3.1 Control Network Design
In manufacturing processes, close coordination and collaboration between industrial robots are essential. Therefore, communication and sensor data sharing between robots are indispensable, particularly for intelligent handling of anomalies such as material shortages, malfunctions, and jamming. Traditional centralized communication methods suffer from drawbacks such as complex hardware structures, difficult on-site wiring, limited scalability, and poor real-time performance, making them unsuitable for the high-speed, precision, and coordinated processing needs of industrial robots. To address this, fieldbus technology connects numerous dispersed low-level sensors and actuators. Each low-level controller and monitoring computer acts as a network node connected to the bus, forming a control network with high-speed data communication and information sharing capabilities. Within this control network, intelligent nodes at each control level send relevant production data as network variables to the fieldbus network. The monitoring host and other intelligent nodes at the control level can access and analyze this data according to program settings, achieving ideal global monitoring and ensuring good coordination among the low-level industrial robots during processing. This is especially crucial in handling anomalies on the production line. For robots and computers with advanced intelligent information processing capabilities, all this real-time data creates conditions for further sensor fusion and information fusion.
Figure 2 shows a solution for networked robot monitoring using LonWorks fieldbus technology in manufacturing. The system's backbone network adopts a bus structure, connecting each workshop within the factory to the core monitoring host in the office building. Subnets are distributed within the workshops, all using a ring structure to effectively overcome the impact of network outages. Each subnet is connected to the backbone network via a corresponding router, enabling communication with the control network host. Different monitored objects use different types of sensors and actuators, which are scattered throughout the factory. Using a typical distributed control approach would be difficult to connect them to a single system, but the openness of LonWorks technology easily solves this problem. Various monitoring signals during production are divided into two paths. One set of signals is connected to the robot controller in the field, enabling relatively independent local control. The other set of monitoring signals, along with the control signals from each robot on the production line, is connected to the I/O ports of intelligent modules distributed in each workshop. Data is transmitted over the network via the fieldbus, achieving a monitoring system that combines on-site robot control with network remote operation. In this way, when an abnormal situation occurs in the production line, the control network can coordinate the work of multiple robots and handle the emergency; while when the fieldbus network fails, the relatively independent robot system can still work normally.
3.2 System Monitoring and Management
After calculation and conversion by the intelligent modules, various on-site production data are sent to the monitoring center computer via the Lonworks network. Through FIX or other configuration software, data is received via DDE (Dynamic Data Exchange) or ODBC (Open Database Connectivity), generating data files and displaying them in real time. This enables online monitoring of all robots on the entire factory production line and provides multimedia audible and visual alarms for abnormal signals. Programs written in the FIX configuration software can also diagnose and trigger alarms for the disassembly, power failure, and malfunctions of each intelligent module.
To meet the needs of enterprise information management, an additional TCP/IP enterprise intranet network card can be inserted inside the control network monitoring host with a Lonworks network card. FIX or other configuration software can then be used to achieve production data sharing in enterprise management. Authorized departments can remotely monitor the production process through the enterprise intranet according to their respective access permissions. Furthermore, the configuration software has an automatic report generation function, capable of generating various reports for the entire plant and individual workshops. All types of information and data can be directly provided to enterprise management personnel. Based on this, an enterprise information management system in the form of CIMS or ERP can be built to support plant-wide and workshop-level management and decision-making. The data flow is shown in Figure 3.
Furthermore, manufacturing production management has a dual nature: vertical management based on the product processing flow, or horizontal management based on production process type and personnel allocation. Modern production line systems, exemplified by robotic processing technology, exhibit high continuity. From initial components or blanks, through multiple production stages of processing and assembly, the final product is formed. The entire process is coherent, and its management model is vertical. On the other hand, in different workshops within the same factory, each production line has robotic equipment and operation/maintenance personnel at the same production stage. For example, each production line has stages such as feeding, assembly, and packaging. If the same product is being produced, then each stage in each production line is parallel and identical. To maximize the efficiency of human resources and facilitate equipment maintenance and production, similar production and technical personnel should be able to divide the management of the same type of production processes and equipment distributed across different workshops. This also reduces the number of spare parts required for production line maintenance. This minimizes the number of standby workers, streamlining from one set of standby personnel per workshop to a smaller number of standby personnel shared across multiple workshops throughout the factory—a horizontal management model.
However, this complex, interconnected model increases management difficulty to some extent. Applying fieldbus-based network control technology can effectively solve this problem. The monitoring interface created using FIX configuration software can monitor the actual processing of each workshop's production line, and also place the processing of similar robots distributed across different workshops within the same computer monitoring window, forming a unified "virtual workshop." This allows for the simultaneous display of field data from similar robots in different workshops within this "workshop," enabling flexible allocation of personnel needed for production, technology, and maintenance, and facilitating efficient production logistics control, thereby improving overall management efficiency.
4 System Software
4.1 Fieldbus Network System Software
Lonworks bus features a comprehensive software platform, including the LNS network communication management system and the Lonbuilder field debugging tool. Its communication protocol, Lontalk, adopts the full seven-layer structure of the ISO/OSI model and is a direct object-oriented network protocol. With the support of the network system software, users only need to input the network topology model and the parameters of each intelligent module and its network variables into the configuration file of the monitoring host, and the entire control network can be automatically configured and run.
4.2 Intelligent Module Programming Software
The application CPU, on-chip memory, and I/O interfaces within the neural network chips of each intelligent module constitute the underlying control system of the fieldbus. Using the network development language Neuron C, the internal programs of each intelligent module can be written on the network monitoring host, and these programs can be downloaded or modified via the bus network.
4.3 Monitoring and Configuration Software
Based on fieldbus technology, and utilizing DDE (Dynamic Data Exchange) or ODBC (Open Database Connectivity) technology, system monitoring software tailored to specific production applications can be developed using configuration software such as FIX and KingSCADA. This enables online monitoring of all robots across the entire factory production site. Simultaneously, the configuration software can also achieve functions such as remote data transmission and sharing, historical data display, automatic report generation, and alarms for abnormal situations.
4.4 Enterprise Information Management Software
Modern manufacturing enterprises should, on the one hand, engage in high-precision, high-efficiency, and high-quality automated production characterized by the application of robots; and on the other hand, they should engage in information-based production using advanced management models such as Computer Integrated Manufacturing Systems (CIMS) and Enterprise Resource Planning (ERP). Fieldbus technology provides the conditions for networked transmission, storage, and sharing of production-level data. Through advanced database software, CAD/CAM software, CIMS, or ERP system software, information management can penetrate into every link from the highest management decision-making level to the lowest production level.
5. Conclusion
Fieldbus technology, as an advanced and intelligent networked control technology, is of significant research value and practical importance for improving the overall coordination and human-machine interaction capabilities of intelligent robot systems based on distributed intelligent robot perception systems constructed from control networks. The advantages of Lonworks fieldbus in terms of high real-time performance, reliability, scalability, and fault tolerance provide an effective way to construct advanced network-integrated fully distributed control systems for intelligent robots. It is a crucial foundation for realizing advanced enterprise management systems such as CIMS and ERP, and is becoming a major solution for large and medium-sized enterprises in my country to achieve industrialization driven by informatization.
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