1. Introduction

With the development of PLC technology and the emergence of a large number of intelligent devices, the rack type centralized control system and the bus mode discrete control system have become two major modes of real-time field control system. The bus mode discrete control system has been widely used because of its flexible configuration, stable operation and simple circuit. NetLinx is a low-cost, high-efficiency and low-cost industrial field control network.

2. Application advantages

Compared with the traditional control system, DeviceNet Fieldbus has the following advantages: using information technology and digital signal communication technology, effectively improving the measurement and control accuracy of the system; applying network technology, data transmission is reliable, information response is fast, anti-interference ability is enhanced; it has the functions of automatic diagnosis and fault display; it can better meet the requirements of information integration of control system The bus node has a good protection level and can be directly installed in the industrial field; the system design and debugging is more flexible and convenient, the control performance is greatly improved; the comprehensive cost of the system is greatly reduced.

3. Introduction of application scheme

This paper introduces the network configuration and debugging process of DeviceNet Bus Based on the improvement example of Omron’s automation products based on DeviceNet Bus in our company’s production line welding fixture.

3.1 reasons for improvement and objectives to be achieved

The production line is a BIW manual welding mainline with double rod as the main transmission tool in the past. It is a design product several years ago. It adopts the traditional PLC centralized control (one main frame and two expansion racks), and realizes manual and automatic operation of all clamps on the main line. All the digital I / O points are connected from the PLC cabinet. The large amount of wire, complex wiring and high failure rate bring a lot of inconvenience to the field maintenance and seriously affect the production. Especially on the left and right side walls of station 2, there are many clamping cylinders, and the I / O circuit is relatively large, which not only brings great load to the repeatedly moving tank chain, but also a large number of lines because of such frequent reciprocating movement, it is easy to cause damage to the line, bring inconvenience to the troubleshooting, and even affect the production.

After analyzing and comparing various control schemes, we decide to adopt fieldbus control system with DeviceNet as the underlying network to solve this problem fundamentally.

After the transformation and upgrading, the automatic control performance of the system will be greatly improved, and the system is reliable, with low failure rate and convenient maintenance, which can effectively reduce the shutdown time and improve the production efficiency.

3.2 scheme planning

On the premise of ensuring the normal operation of the original system, only improve the control mode of the left and right side clamps of position 2, build a distributed control system, and add the state network communication card for real-time data exchange with the monitoring system of the upper computer. The upper computer uses Kingview software to simulate the screen configuration and monitor the production status. For the controlled components on position 2, the input devices connected to the bus are buttons and proximity switches, and the output devices are solenoid valves. The working status and fault information of No.2 position fixture are transmitted to upper computer and controller through DeviceNet Network.

3.3 system construction and debugging

(1) Overall planning, according to the actual situation of the site to carry out a reasonable layout of the line. For the left and right side wall clamps of position 2, the cylinders on both sides are symmetrically distributed, and the output solenoid valves are basically symmetrical. The bus comes out from the main PLC and is connected to the discrete control box adjacent to the main control cabinet on the left, and then to the control box on the right through the tank. Figure 1 is the topology of the bus part.

Application of DeviceNet Bus Technology in industrial field bottom control system

Figure 1 DeviceNet Bus Architecture

(2) The discrete modules in the field (input and output modules of protection grade IP20 and input module of protection grade IP67 in small control box) are connected to the nodes of DeviceNet Bus. Omron bus module is divided into terminal block connection and standard connector connection. DeviceNet Bus standard cable is a 4-core coaxial cable with shielding layer. The color of the core wire is red (24V +), black (24V zero line), blue (signal positive) and white (signal negative). Four colors are marked on the module connected with the terminal block, and one should be ensured during wiring To: the plug connection of the standard plug connector shall be connected according to the requirements on the specific module drawing. No matter the terminal block connection or plug-in connection, the final test standard is that the wires of any color should be connected to the end, so after connecting the bus, the resistance of the multimeter must be used to detect whether all links are smooth. Both ends of the network bus should be installed with correct terminal resistance (120 ω, standard terminal resistance provided by OMRON company is optional). When the system is not powered on, the resistance value between can-h and can-l should be between 50 ω and 70 ω.

(3) Install DeviceNet Network configuration tool software configurator V2.2, which is used to assign network nodes and configure I / O addresses of discrete modules for devices on the bus. After installing the software, it is necessary to update and upgrade the EDS configuration file, otherwise the module may not be recognized during bus scanning.

(4) Assign the node address to each device to be added to the DeviceNet Network and set the correct communication baud rate. The communication baud rate of all nodes in each network segment of DeviceNet Network must be consistent, and no device with duplicate node address is allowed. Right click the node device icon on the bus in the network configuration interface to change the address of each node. After the node devices are configured, the I / O channel address of the device with node number can be assigned on the I / O tab of the bus distributor. Of course, you can also easily cancel or add the default I / O address of the module. By clicking the “register / unregistered” button on the global tab, it is very convenient to shield the wrong or temporarily unnecessary modules from the bus, which brings very flexible processing to the debugging work.

(5) The rack slot module configuration of PLC is downloaded to PLC by programming equipment. Before connecting the bus distributor, we need to connect the PLC module to the programming device through the RS232 interface on the PLC module. Through the on-line function, the function module and I / O module on the main frame and the I / O module on the expansion rack are configured one by one into the PLC I / O configuration according to the actual slot number, and then downloaded to the PLC. PLC will scan the modules on the rack through the configuration If it is found that the configuration information is inconsistent with the actual situation, the specific error prompt will be given in the diagnosis information, and the problem point can be found intuitively through the prompt. The slot number in C200H is fixed, but the slot number in cs1h-h processor is allocated continuously. If we want to skip a slot and do not configure it, we need to configure the slot as “16 point virtual”. In this way, it only occupies the slot number but does not assign the actual address. Click the right mouse button in the Ethernet slot to set the relevant communication settings of Ethernet, such as IP address, and download it to PLC after setting, so as to connect with PLC through network cable.

(6) Through the programming device, all the node device parameters configured by DeviceNet Network are downloaded to the bus distributor. This process is divided into two steps: first, download the configured node device configuration data to the bus distributor module through the download option in the file options; then double-click to open the bus distributor, download the configured I / O channel configuration to the bus distributor, and then click the download button to download. This process must be carried out when the programming equipment and PLC are online (RS232 interface or Ethernet card interface), and it should be noted that once the data is downloaded to the bus distributor, it will be stored in the bus distributor, even if power is off, it will not be lost. Therefore, sometimes when the old module is used to scan the bus, there will be conflict information prompt It indicates that the current scanned bus device does not match the storage content in the bus distributor (including node address mismatch, model mismatch, I / O address inconsistency, etc.), and the LED display screen of the bus distributor will also give the node number of the corresponding conflicting device. When this happens, you need to manually edit the actual bus configuration and I / O configuration and download it to the bus allocator to scan again.

(7) Modification of the original program. Before modifying the program, first replace the old rack and PLC with the upgraded mainframe and PLC, the other modules remain unchanged, and then upgrade the CPU in the offline program. The internal variable address of the program will also change accordingly (because the addressing method of internal address for different PLC modules may be different), and the external I / O will remain unchanged. The program after automatic conversion is downloaded to PLC through RS232 interface for on-line trial operation to see if it is different from the original module. The final conclusion is that the automatic conversion of internal points will not affect the normal operation of the original program. After running correctly, the I / O address of bit 2 can be modified according to the I / O configuration in the bus distributor, and then saved to the new PLC.

(8) Backup all programs and bus node configuration files for future data recovery and maintenance.

4. Conclusion

The operation practice of the system shows that the system is powerful, safe and reliable, and flexible in operation. It creates obvious economic benefits for the production of BIW on the production line, and greatly improves the production efficiency, automatic production level and management level.

Editor in charge: GT

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