Network control of dust-free paper production line using DeviceNet fieldbus control technology

1. Introduction:

Dust-free paper (also known as expanded core material) is a new type of high value-added sanitary product. It has the advantages of excellent high hygroscopicity, reliable water lock, hygienic safety, etc., and is widely used in women's sanitary napkins, adult urinary incontinence, baby diapers and other product fields.

Since the DeviceNet device network is based on the producer/client network model, it enables control data to reach each site unit on the network at the same time, and the network utilization rate is high; it allows the state switching message to be sent, which can achieve faster response and effectively reduce the network communication volume. Periodic message sending provides better certainty; peer-to-peer communication allows data and status information to be exchanged between devices; these advantages provide a strong guarantee for higher productivity.

2. Open network control structure of dust-free paper production line:

Our company's dust-free paper production line is fully imported from Europe and is currently the most advanced equipment in the industry. Its control system absorbs the concept of all-round automation of Rockwell Corporation of the United States and runs through all levels of the network of its Netlinx system.

Figure 1 Rockwell Automation communication network diagram

A seamless connection is achieved from the information layer (Ethernet) to the control layer (ControlNet) and the field layer (DeviceNet). As shown in Figure 1.

Dust-free paper requires relatively strict production process conditions. It belongs to a dry papermaking process (Dry Forming). Its basic process is: in a constant temperature, constant humidity, constant air pressure environment, the crushed wood pulp, fiber, SAP, PE powder and other raw materials are uniformly formed through the forming station, and then through the processes of spraying, heating/melting, hot pressing, cooling, slitting, rolling, etc., to produce qualified products.

The production line control layer of our company includes a total of nine AB PLC5 (eight units) and AB SLC500 (one unit) programmable controllers with Ethernet function. They control nine process areas: air conditioning (Main Air condition), raw material preparation (Raw material preparation), unwinder (Tissue Unwinder), hot oil heating system (Hot oil System), filter packaging system (Main Filter system), main line control system (Main Line), and reel system (Reel).

Six of the PLCs are installed in the PLC control cabinet in the motor control center MCC1 room in the middle of the plant. The Ethernet interface of each PLC is connected to the hub in the PLC cabinet via twisted pair cables. The other three PLCs are installed in the control cabinet at the equipment site, and their Ethernet interfaces are also connected to the hub of MCC1 via optical fiber.

Five AB industrial PCs with RSview32 software are installed in the central control room, and their Ethernet interfaces are connected to a hub in the central control room, and then connected to the hub in the PLC cabinet via an optical fiber. The network is also connected to the enterprise Intranet through the HUB, so that an Ethernet network is formed through the TCP/IP protocol to form the information (management) layer. (As shown in Figure 2 below: Schematic diagram of control layer and information layer network)

In addition to connecting local and remote I/O modules, Panel View human-machine interface and other devices, most of the programmable controllers are equipped with DeviceNet scanners (1771-SDN or 1747-SDN), and through DeviceNet communication modules (1336-GM5, 1203-GK5, 1794-ADN, etc.), field intelligent devices such as inverters, motor soft starters, Flex I/O, 9000 series photoelectric switches, etc. are connected to form a DeviceNet device network, which realizes effective control of field-level devices.

3. Functions and features of DeviceNet:

DeviceNet is a field bus based on CAN-BUS technology. It is an open communication network that complies with the IEC61158 international field bus industry standard.

DeviceNet is a communication network used between field devices and PLCs. The transmission rate can be set to 125, 250, 500KPBS, the maximum transmission distance is 500 meters, the maximum number of nodes (stations) is 64, and online configuration and hot plugging are allowed.

DeviceNet supports master/slave, multi-master, peer, and other communication modes. The user's PLC can use the control program and the data of the upper PC to effectively monitor the field equipment through the DeviceNet network.

DeviceNet can be configured and managed by Rockwell's RS Networx for DeviceNet or DeviceNet Manager software.

The DeviceNet network has a simple structure and strong real-time performance. It adopts the producer/client mode and provides powerful fault diagnosis and troubleshooting capabilities. It is an ideal device-level fieldbus.

4. The physical structure of the Devicenet network of the dust-free paper production line.

Our company's DeviceNet network uses four AB PLC5-40E and one SLC5/04 as hosts. The local rack of the PLC machine is equipped with a DeviceNet scanner module (AB 1771-SDN or 1747-SDN). The 1771 scanner has two channels, each of which can connect up to 64 stations (generally 63). Each PLC uses the local network scanner to connect to the fieldbus devices in the control area through the DeviceNet communication adapter (1203-GK5, 1336-GM5, 1794-AND, etc.). These stations mainly include: AB inverters (1336F, 1336E, 160SSC series), A-B motor soft starters (SMC 150 series), FLEX I/O (1794 series); ARMOR Block protective I/O components, 9000 series photoelectric switches, etc.

The typical DeviceNet network adopts the trunk/branch line physical structure. Our company uses a daisy chain ring connection, using Belden standard round five-core shielded communication cable to connect each site. (As shown in Figure 3 below, the daisy chain DeviceNet equipment communication network; taking the inverter network as an example)

Since the equipment in our factory is relatively scattered, some sites are far apart. Especially some on-site sites are more than 100 meters apart. Therefore, the transmission rate of all DeviceNet networks is set to 125KBPS to ensure reliable communication. In addition to the distributed I/O, human-machine interface and sensor sites located in the production site, the DeviceNet network system of more than 100 inverters is distributed in two motor control center (MCC) rooms, which realizes the centralized control and unified management of motors. (As shown in Figure 4: A corner of the DeviceNet inverter network in the MCC room Note: The yellow cable in the figure is the network communication cable)

Between the DeviceNet workstations, we mostly use open taps (Note: some stations on site use sealed T-type taps or sealed connectors), and connect the power lines, communication lines, and shielded lines between stations in parallel to form a physical topology in the form of a daisy chain. Terminal resistors are installed at the first and last terminals. (121Ω, 1%, 1/4W)

5 DeviceNet configuration software and control implementation. The communication between

the PC and the PLC device network scanner can be realized by using the device network RS-232-C PC interface adapter (1770-KFD) or the device network PC card (1784-PCD).
DeviceNet management software RS Networx for DeviceNet is a Windows-based software that can be used to configure the device network and perform project management and network fault diagnosis. It supports AB and third-party device configuration electronic data sheets (EDS).

The DeviceNet protocol defines two different types of messages: explicit messages and I/O messages. Both messages can be transmitted on the bus at the same time.
During the configuration process, the scanner should be configured first, the I/O address interface between the scanner and the PLC should be set, and the communication between the scanner and the adapters of each station should be established.

When configuring each station on the network, the address of each station (i.e., station number) must be defined first. The address of the station can be discontinuous, but it must be consistent with the DIP switch setting of each station adapter.

For I/O type workstations such as Flex I/O or Armor Block I/O, we use I/O messages to allocate the input and output of each station. I/O messages are transmitted periodically and have a higher priority, thereby ensuring its real-time performance.

For equipment stations such as frequency converters and soft starters, we use explicit messages to allocate the word lengths for sending/receiving between PLC and each station; define the communication mode (we define it as polled mode, each scan cycle); and establish the corresponding "soft" I/O relationship with PLC.

Then use PLC5 programming software RSlogix5 to compile block transfer (BTR/BTW) commands to realize PLC's collection and control of I/O information of equipment network workstations. PLC control program can send control commands to each station according to the working status of each station to meet the process requirements.

Since all PLCs in our company are connected to Ethernet, there is an RSview32 monitoring workstation in the control room on the network. Each display can show the monitoring interface of different process areas of RS view. In the control room, you can control the equipment of the whole plant and view the current working status of each station. The human-machine interface is very friendly.

6. Experience of using DeviceNet network.

(1) DeviceNet fieldbus can save a lot of costs.

From the installation stage, only one communication cable is used to realize power supply and communication for all stations on the entire network. Compared with the point-to-point control method, a large amount of cables, bridges, etc. are saved. Not only the installation time is shortened, but also the installation cost is reduced.

From the control point of view: the use of network communication and "soft" I/O method also saves I/O modules and a large amount of funds.

For example, for the inverter workstation, start/stop, acceleration/deceleration and other commands; voltage, current, temperature and other parameters can all be realized through DeviceNet network communication, saving I/O modules, especially analog I/O modules, which are quite expensive.

(2) The equipment failure rate is greatly reduced, and diagnosis is convenient and elimination is rapid.

DeviceNet uses only one communication cable to control the entire device network, which greatly reduces the equipment failure rate; the communication terminals of each station support hot plugging under power, if a station has a problem and troubleshooting, it will not affect the normal operation of other stations on the network.

Using data communication to control each station not only greatly reduces the number of cables in the traditional point-to-point method, but also greatly reduces the failure links and further improves the stability of the system.

The centralized control of MCC is very effective through the device network, which greatly facilitates the diagnosis of equipment failures. For example, for the control of frequency converters, due to the use of MCC and network control, there are only five typical control circuits for more than 100 frequency converters, which is easy to remember and find faults. When a frequency converter fails, not only can the alarm information be seen from the main control room, but also from the network scanner or the human-machine interface of the frequency converter, which is convenient and fast.

(3) System monitoring is more convenient and intelligent.

Through the RSview monitoring interface, the central control room can access and control some sites on the device network at any time, adjust the control parameters as needed; and monitor the working status of the devices on the network, such as motor current, temperature and other parameters, to ensure the normal operation of each device.

7. Experience in maintenance and troubleshooting of DeviceNet network:

(1) Communication interference problem

During the operation and debugging stage of our factory, the status display of some sites (RSview human-machine interface in the control room) was sometimes inconsistent with its actual working status or the control command was not strictly executed. After diagnosis and analysis, we mainly took the following measures.

1). Check and tighten each terminal resistor to prevent signal reflection.

The terminal resistor is used to prevent (reduce) communication signal reflection. To check whether the terminal resistor is working properly, you can measure the resistance between any two CAN-H (blue wire) and CAN-L (white wire) terminals on the network when the power is off (only possible during preventive maintenance or system failure). The resistance should be around 60Ω-70Ω (because our factory uses a daisy chain structure).

2). Reliably connect the grounding wire of the DeviceNet network to eliminate external noise interference.

To prevent loop current, the shield wire of the signal cable can only be grounded at one end. The grounding point is best drawn from the physical center site closest to the network to achieve the best effect and eliminate noise interference to the maximum extent. The grounding wire of our factory is drawn from the scanner site of the PLC rack.

The grounding method is: reliably connect V- to Shield and Drain to PE.

Through 1), 2) and the above two methods and regular PM inspections, the network communication system can be ensured to work well and reliably.

In addition, to ensure reliable communication, the following situations should be noted when wiring the network:

1). In order to avoid interference from power cables to communication cables, communication cables should be wired separately. If the communication cable and the power cable share the same cable duct, the communication cable should be routed through a metal shielded tube.
2). When the sites are far apart or the total network distance is large, a thick-core communication cable should be used.

(2) If the equipment at a site fails and there is no spare part of the same model in stock, it may cause trouble. If the equipment at a site fails

and there is a spare part of the same model in stock, the site can work normally after replacing it with the spare part of the same model. If a different model of spare parts is replaced, the physical site (EDS) detected by the network scanner is inconsistent with the scan list. The scanner will have an alarm and the site will not work properly. At this time, you have to reconfigure the scan list and download it to the scanner before this site can work normally. This is a problem that should be paid attention to.

8. Conclusion:

The dust-free paper production line uses DeviceNet fieldbus control technology, which greatly improves the reliability and real-time performance of the control system. Using fieldbus technology for automatic control of production lines is an ideal solution. The significant advantages of fieldbus technology determine that its widespread application is an inevitable trend in the control field.