1 Introduction
With the continuous and rapid development of China's textile industry, modern textile technology will be dominated by electronic information technology, with intelligent production as the main feature [1]. At present, the development of the domestic textile machinery equipment control system focuses on realizing the automation of the textile process performance of a single device, and the advanced functions of the machine are enclosed in the single machine system, and the network composition of the system is ignored. The structure (especially its control system) is becoming more and more complicated, making the machine an "island" in the textile enterprise's automation system. Since the 1990s, fieldbus technology and control systems based on this technology have attracted great attention at home and abroad and become a hotspot in the development of automation technology worldwide. It comprehensively uses microprocessor technology, network technology, communication technology and automatic In the control technology, the microprocessor is built into the on-site automatic control equipment, so that the equipment has the ability of digital calculation and digital communication, which not only improves the accuracy of signal measurement, control and transmission, but also creates conditions for its remote transmission.
In the process of the textile industry changing from traditional industry to modern industry, the control technology based on field bus provides opportunities for the development of the decentralized, networked and intelligent control system of the textile industry. This paper introduces the basic principles of fieldbus, compares the characteristics and application occasions of several commonly used fieldbuses today, and builds a frame model of digital textile production system based on fieldbus control technology.
2 Basic principles of fieldbus
Fieldbus is the integration point of the current 3C (Computer, Communication, Control) technology development, and also the meeting point of the development of process control technology, automation instrumentation technology and computer network technology. It is the concentrated reflection of the development of information technology and network technology in the field of control. It is the inevitable result of the extension of information technology and network technology to the scene.
According to the International Electrotechnical Commission (IEC, InternaTIonal Electrotechnical Commission) standard and the definition of the Fieldbus Foundation (FF, Fieldbus FoundaTIon), the fieldbus is a digital, bidirectional transmission, multi-branch communication network that connects intelligent field devices and automation systems [ 2]. Fieldbus technology puts special microprocessors into traditional measurement and control instruments, so that they all have digital computing and digital communication capabilities, and become a network node that can independently undertake certain detection, control and communication tasks. A network system that connects multiple measurement and control instruments, computers, etc. as nodes through ordinary twisted pairs; uses open and standardized communication protocols between multiple computerized measurement and control equipment located at the production control site, as well as on-site instruments and Between the remote computers for monitoring and management, data transmission and information sharing are realized, and various automatic control systems adapted to actual needs are formed.
The field bus is mainly oriented to process control. In addition to transmitting direct information of digital and analog signals, it can also transmit control information. The data unit exchanged by the network is a frame. Compared with Distributed Control System (DCS), Fieldbus Control System (FCS) has high reliability and better security, interchangeability and interoperability, openness, decentralization, etc. advantage.
In summary, the field bus is a real-time control communication network that interconnects the lowest-level field controller and the field intelligent instrumentation of the automation. It follows all or part of the communication protocol of the ISO / OSI open system interconnection reference model.
3 Several common fieldbus technologies
Since the 1980s, well-known international companies have launched several industrial fieldbuses and field communication protocols. The current popular ones are FF (Fieldbus FoundaTIon Foundation Fieldbus), Profibus (Process Fieldbus), CAN (Controller Area Network Controller Local Area Network), LonWorks (Local Operation Network), WorldFIP (Factory Instrumentation Protocol), etc. The main technical differences and applicable occasions are as follows:
3.1 FF fieldbus
FOUNDATION fieldbus is based on the ISO / OSI open system interconnection model, and its physical layer, data link layer, and application layer are the corresponding layers of the FF communication model, and a user layer is added to the application layer. FF has two communication rates: low-speed H1 and high-speed H2. The transmission rate of H1 is 1.25kbit / s, the communication distance can be up to 1900m (can be extended by repeaters), it can support bus power supply and support intrinsically safe anti-riot environment. The transmission rate of H2 is 1M and 2.5kbit / s, and the communication distance is 750m and 500m respectively. The physical transmission medium can support twisted pair, optical cable and wireless transmission. The protocol conforms to the IEC11582 standard. The transmission signal of the physical medium adopts Manchester encoding. Mainly used in the field of process automation, such as: chemical industry, power, oil field and wastewater treatment.
3.2 Profibus fieldbus
The Profibus series is composed of 3 compatible parts such as Profibus-DP, Profibus-FMS and Profibus-PA. Profibus uses the physical layer and data link layer of the OSI model, and these two parts form a subset of the first part of the standard. The transmission rate of Profibus is 9.6kbit / s ～ 12Mbit / s. The maximum transmission distance is 100m at 12Mbit / s and 400m at 1.5Mbit / s. It can be extended to 10km with repeaters. The transmission medium can be twisted pair and optical cable. The main application areas are: DP type is suitable for applications in the field of processing automation, such as pharmaceuticals, cement, food, power, power generation, transmission and distribution; FMS is suitable for general automation manufacturing industries such as textiles, building automation, programmable controllers, low-voltage switches Automation; PA type is the bus type used for process automation.
3.3 CAN fieldbus
The CAN network design uses a three-layer structure model that conforms to the ISO / OSI network standard model: the physical layer, the data link layer, and the application layer. The functions of the physical layer and link layer of the network are completed by the CAN interface device, while the application layer The functions are performed by the processor. Communication has outstanding reliability, real-time and flexibility; adopts short frame structure, short transmission time, anti-interference; nodes have different priorities, which can meet different real-time requirements. The transmission medium can use twisted pair, coaxial cable or optical fiber, etc., the communication speed can reach up to 1Mbit / s (40m), and the direct transmission distance can reach up to 10km (5kbit / s). The main application areas are: automobile manufacturing, robots, hydraulic systems, decentralized I / O, tool machine tools, medical equipment.
3.4 Lonworks fieldbus
LonWorks uses a 7-layer protocol structure similar to the OSI reference model. The core of LonWorks technology is the Neuron chip with communication and control functions. The Neuron chip implements the complete LonWorks LonTalk communication protocol, which allows peer-to-peer communication between nodes. LonWorks communication rate is 78K bit / s ~ 1.25M bit / s, supports a variety of physical media, including twisted pair, optical fiber, coaxial cable, power line carrier and wireless communication, etc .; and supports multiple topologies, flexible networking. The main application areas are: industrial control, building automation, data acquisition, SCADA system, etc., which has superior performance in the establishment of distributed monitoring networks.
3.5 WorldFIP fieldbus
WorldFIP field bus architecture is divided into three levels: process level, control level and monitoring level. Its protocol consists of physical layer, data link layer and application layer. The communication rate is 31.25K bit / s, 1M bit / s, 2.5M bit / s, 25M bit / s. The transmission medium uses shielded twisted pair and optical fiber. It can meet the various needs of users and is suitable for various types of application structures such as centralized, decentralized, and master / slave types. A single WorldFIP bus can meet the needs of process control, factory manufacturing and processing and various drive systems. The main application areas are: power industry, railway, transportation, industrial control, buildings.
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