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1. introduction:
Dust-free paper (also known as puffed core material) is a new type of hygienic product with high added value. It has excellent high moisture absorption, reliable water lock, health and safety, and is widely used in women's sanitary napkins, adult urinary incontinence, baby diapers and other products.
Since the DeviceNet device network is based on the producer/customer network mode, it enables the control data to reach the various site units on the network at the same time, and the network utilization is high; it allows the message of the state switching to be sent, which can achieve a faster response and effectively reduce The amount of network traffic. Periodic message delivery 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 for dust-free paper production lines:
Our company's complete dust-free paper production line is imported from Europe and is the most advanced equipment in the industry. Its control system absorbs the all-round automation concept of Rockwell Company in the United States, running through the network of its Netlinx system.
Figure 1 Rockwell Automation Communication Network Diagram
A seamless connection from the information layer (Ethernet) to the control layer (ControlNet) and the field layer (DeviceNet) is realized. As shown in Figure 1.
Dust-free paper requires stricter production process conditions, and it belongs to a process of Dry Forming. The basic process is: uniformly pulverizing wood pulp, fiber, SAP, PE powder and other raw materials through a molding station in a constant temperature, constant humidity, constant pressure environment, and then spraying, heating/melting, hot pressing, and cooling. , cutting, winding and other processes to produce qualified products.
Our company's production line control layer includes a total of nine Ethernet PLC AB (eight) and AB SLC500 (one) programmable controller. They are controlled separately: Air Air (Main Air condiTIon), Raw material preparaTIon, TIssue Unwinder, Hot Oil System, Main Filter system, Main Line Control System ( Nine process areas, such as Main Line) and Reel.
Six of the PLCs are installed in the PLC control cabinet in the MCC1 room of the motor control center in the middle of the plant. The Ethernet interfaces of each PLC are connected to the hub (HUB) in the PLC cabinet via twisted pair. The other three PLCs are installed in the control cabinet at the equipment site, and their Ethernet interfaces are also connected to the MCC1 hub (HUB) via fiber optics.
Five AB industrial PCs equipped with RSview32 software are installed in the central control room. Their Ethernet interfaces are connected to a HUB in the central control room, and then connected to the HUB in the PLC cabinet through an optical fiber. The network is also connected to the enterprise intranet through the HUB, so that the Ethernet network is formed by the TCP/IP protocol to form an information (management) layer. (As shown in Figure 2 below: Control layer and information layer network diagram)
In addition to the local and remote I/O modules and the Panel View human-machine interface, most programmable controllers are equipped with DeviceNet scanners (1771-SDN or 1747-SDN) and passed the DeviceNet communication module (1336). -GM5, 1203-GK5, 1794-ADN, etc.) On-site intelligent devices, such as inverters, motor soft starters, Flex I/O, 9000 series photoelectric switches, etc., form a DeviceNet device network, which is effective for field-level devices. control.
3. DeviceNet features and features:
DeviceNet is a fieldbus based on CAN-BUS technology. It is an open communication network that conforms to the IEC61158 international fieldbus industry standard.
DeviceNet is used for communication network between field device and PLC. The transmission rate can be set to 125, 250, 500KPBS, the maximum distance is 500 meters, and the maximum number of nodes (sites) is 64, allowing online configuration and hot swapping. .
DeviceNet supports master/slave, multi-master, peer, and other communication methods. The user's PLC can use the control program and the data of the host PC to effectively monitor the field devices through the DeviceNet network.
DeviceNet can be configured and managed using Rockwell's RS Networx for DeviceNet or DeviceNet Manager software.
The DeviceNet network is simple and real-time. It adopts a producer/customer model and provides powerful fault diagnosis and elimination capabilities. It is an ideal device layer fieldbus.
4. The physical structure of the Devicenet network of the dust-free paper production line.
Our company's DeviceNet network is hosted by four AB PLC5-40E and one SLC5/04. The DeviceNet scanner module (AB 1771-SDN or 1747-SDN) is installed on the local rack of the PLC. The 1771 scanner has two channels, each of which can be connected to a maximum of 64 stations (generally 63). Each PLC uses the local network scanner to connect to each fieldbus device in the control area through the DeviceNet communication adapter (1203-GK5, 1336-GM5, 1794-AND, etc.). These stations mainly include: AB inverter (1336F, 1336E, 160SSC series,) A-B motor soft starter (SMC 150 series) FLEX I/O (1794 series); ARMOR Block protection type I/O components, 9000 series photoelectric Switch, etc.
A typical DeviceNet network takes the form of a trunk/spur line physical structure. Our company uses a circular connection of Daisy Chain, which uses Belden's standard circular five-core shielded communication cable to connect the sites. (As shown in Figure 3 below, the daisy chain DeviceNet device communication network; take the inverter network as an example)
Due to the scattered distribution of equipment in our factory, some stations are far apart. Especially on some site sites, the distance is more than 100 meters. Therefore, the transmission rate of all DeviceNet networks is set to 125 KBPS to ensure reliable communication. In addition to distributed I/O, human-machine interface and sensors are located outside the production site, the DeviceNet network system of more than one hundred inverters is distributed in two motor control center (MCC) rooms, which realizes centralized control of the motor. , unified management. (As shown in Figure 4: MCC indoor DeviceNet inverter network corner Note: The yellow cable in the figure is the network communication cable)
Between the various workstations of DeviceNet, we mostly use the open sub-interface (Note: some stations in the field use sealed T-type sub-interface or sealed connection), the power line, communication line and shielded line between the station and the station. Separately and joined together 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 PC interface adapter (1770-KFD) or the device network PC card (1784-PCD) of the device network RS-232-C.
DeviceNet's management software RS Networx for DeviceNet is a Windows-based software that allows you to configure the device network and perform project management and network troubleshooting. It supports AB and third party device configuration spreadsheets (EDS).
The DeviceNet protocol defines two types of messages: Explicit Message and I/O Message. Both messages can be transmitted on the bus at the same time.
During the configuration process, the scanner should first be configured to set the I/O address interface between the scanner and the PLC to establish communication between the scanner and each station adapter.
When configuring each station on the network, first define the address (ie station number) of each station. The address of the station may not be continuous, but it is consistent with the DIP switch settings of each station adapter.
For I/O type workstations such as Flex I/O or Armor Block I/O, we assign I/O Messages to the inputs and outputs of each station. I/O messages are transmitted periodically and have a higher priority to ensure its real-time performance.
For equipment sites such as inverters and soft starters, we use the explicit message format to assign the word length sent/received between the PLC and each station; define the communication method and (we define it as polled mode, Each scan cycle); establish a corresponding "soft" I / O relationship with the PLC.
Then use the PLC5 programming software RSlogix5 to compile the block transfer (BTR/BTW) command to realize the I/O information collection and control of the PLC on the device. The PLC control program can issue control commands to each station according to the working status of each station to achieve the process requirements.
Since all the PLCs of our company are connected to the Ethernet, there is a Rsview32 monitoring workstation in the control room on the Internet. Each display can display the monitoring interface of different process areas of the RS view. In the central control room, you can control the equipment of the whole plant, as well as the current working status of each station. The human-machine interface is very friendly.
6. The use of the DeviceNet network.
(1) DeviceNet fieldbus can save a lot of money.
From the installation stage, power supply and communication are provided to all stations on the entire network through a single communication cable. Compared with point-to-point control, a large number of cables and bridges are saved. Not only does it reduce installation time, but it also reduces installation costs.
From the control point of view: the use of network communication and "soft" I / O mode, also saved I / O modules and large sums of money.
For example, the inverter workstation, start/stop, acceleration/deceleration commands, etc.; voltage, current, temperature and other parameters can be realized from 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 the diagnosis is convenient and the elimination is rapid.
Because DeviceNet uses only one communication cable to control the entire device network, the device failure rate is greatly reduced. The communication terminals of each station support hot plugging. If a site has problems and troubleshooting, it will not affect the normal operation of other sites on the network.
The use of data communication to control each station not only greatly reduces the number of cables in the traditional point-to-point mode, but also greatly reduces the number of faults and further improves the system stability.
The centralized control of the MCC is very effective through the equipment network, which greatly facilitates the diagnosis of equipment failure. For example, for the control of the inverter, due to the MCC and network control mode, there are only five typical control circuits for more than one hundred inverters, which are easy to remember and troubleshoot. When a certain inverter fails, not only can the alarm information be seen from the general control room, but also the alarm information can be obtained from the human-machine interface of the network scanner or the inverter, which is convenient and quick.
(3) System monitoring is more convenient and intelligent.
Through RSview monitoring interface mode, the central control room can access and control some sites on the equipment network at any time, adjust the control parameters according to needs; can monitor the working status of the online equipment, such as motor current, temperature and other parameters to ensure the normal operation of each device.
7. DeviceNet network maintenance and troubleshooting:
(1) Communication interference problem
The status display of some stations in the operation and debugging phase of our factory (the RSview man-machine interface of the control room) is sometimes inconsistent with its actual working state or the control command execution is not strict. After diagnosis and analysis, we mainly took the following measures.
1). Check and tighten the resistance of each terminal to prevent signal reflection.
The terminating resistor is used to prevent (reduce) the reflection of the communication signal. To check if the terminating resistor is working properly, you can measure any two CAN-H (blue line) and CAN-L (white line) on the network in case of power failure (only in case of preventive maintenance or system failure). The resistance between the terminals should be around 60Ω-70Ω (because I use a daisy-chain structure).
2). Connect the grounding wire of the DeviceNet network reliably to eliminate external noise interference.
To prevent circulation, the shielded cable of the signal cable can only be grounded at one end. The grounding point is preferably taken from the physical center station closest to the network to achieve the best effect and minimize noise interference. The grounding wire of our factory is taken from the scanner station of the PLC rack.
Grounding method: reliably connect V- with Shield and Drain and PE
Through 1), 2) the above two methods and regular PM inspection can ensure that the network communication system works well and reliable.
In addition, in order to ensure reliable communication, the following conditions should be noted when wiring the network:
1). In order to prevent the communication cable from being disturbed by the power cable, the communication cable should be routed separately. If the communication cable and the power cable share the slot, the communication cable should be routed through the 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 one site fails and the stock does not have the same type of spare parts replaced, it may cause trouble.
If a site fails, the stock has the same type of spare parts, and the station can work normally after replacing the spare parts of the same model. If a different type of spare part is replaced, the physical station (EDS) detected by the network scanner is inconsistent with the scan list. The scanner will have an alarm and the station will not work properly. At this time, you have to reconfigure the scan list and download it to the scanner, so that the station can work normally. This is a problem that should be noted.
8. Conclusion:
The dust-free paper production line greatly improves the reliability and real-time performance of the control system thanks to the DeviceNet fieldbus control technology. The use of fieldbus technology for automated control of the production line is an ideal solution. The significant advantages of fieldbus technology determine that its widespread application is an inevitable trend in the field of control.
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