1 Introduction
Polyethylene plastic in the production process, extrusion granulation process equipment is a class of more complex mechanical equipment, the control system is to ensure normal operation and the product quality. In the past the production line equipment mostly imported supporting DCS control system, its maintenance and improvement are more difficult and high cost. We have recently made new extrusion granulation equipment, the use of the PLC control system, its performance is stable and low cost.
In the transformation of pre-production run, because the feed instability and frequent changes of product brands, making manual operation is not only difficult to achieve the ideal level of product, and often blocking material, explosion-proof membrane as the pressure is too high damage and other mechanical failure, so as the production start rate is not high, reaching less than the nominal output device. PLC control system with control has significantly improved equipment reliability and continuous stability, so that product quality has reached a higher level.
2 device characteristics and process control requirements
2.1 Device Technological Characteristics
Figure 1 The process flow diagram for the plastic production line, which includes mixing machine, feeding machine, melting most of the pump and the granulator 4.
Mixer function is to mix components from different raw materials, and to Make a kind of thick plastic-like fluid - melt plastic; feeding machine is used to absorb out of the melt plastic mixing machine, and its transfer to the melt evenly melt pump to quickly step out of the entrance. After refining the treated plastic melt plastic, pushed through at high pressure into the template section of filamentous; in the granulator was evenly cut, and finally the formation of particulate product standards, through the particles of water and transported to the cooling process after the system .
Automatic control of extrusion process shown in Figure 2:
Map: FT-2425 is expected to flow into the mixing machine, range is 0 ~ 15T / h;
PT-2426 for the feeder outlet pressure range is 0 ~ 10MPa;
PT-2427 for the melt pump outlet pressure range is 0 ~ 50MPa;
2.2 Control requirements
2.2.1 Main loop control
According to equipment and technology requirements, the main extruder requires three control components: feeder control circuit, melt pump control loop and control loop granulator. Fusion pump oil storage tanks in addition to temperature control circuit and melt pump lubricant outlet temperature control loop and so on.
????? feeder control circuit - the entrance in the mixer has an electronic scale, can detect the dynamic flow of feed, the changes in feeding machine is used to control the speed-eating materials.
????? melt pump control loop - the loop cascade control, the melting rate of the feed pump work machine speed and feed machines together to control the outlet pressure. One feeder speed as the secondary control parameters, feeder outlet pressure of PID output as the main control parameters of the melt pump speed through the regulation, control, feeder outlet pressure stabilized at 5mp.
????? granulator control loop - the loop is also used cascade control, that is, the working speed granulator by the melting speed of the pump and the pump outlet pressure melting together to control. Which melting speed of the pump as an auxiliary control parameter, melt pump outlet pressure PID output as the main control parameters, namely, control of speed through the granulator regulation to ensure that the particle size uniformity, appearance qualified.
2.2.2 Interlocking
In the device control also need some alarm interlock control, the main alarm interlock control are:
????? feeder oil pressure alarm interlock
????? melt pump oil pressure alarm interlock
????? feeding machine, the melt pump and motor bearing temperature alarm interlock granulator
????? melt pump network before and after the blast membrane State Interlocking
?????¤ pelletizing granulator room window switch interlock
????? granulator granule low water flow interlock
????? feeder, melt pumps and low speed granulator interlock
2.2.3 Hand / Auto Switching Control
As the device at boot time, running and working parameters of a more complex and usually requires the operator to manually control the system run more stable when the device after a period of time to switch to the automatic control system. Therefore, feeder control circuit, melt pump control loop and granulator control loop must be controlled to achieve a smooth switch without disturbance.
3 System Components
The automatic control system shown in Figure 2, its use, the lower computer architecture. In the control room from industrial control computer as a human interface station operator station, the next bit of the PLC with OMRON s SYSMAC CS1 system; CS1 system is a high-speed, high efficiency, high reliability, compact CPU of the PLC system, the CPU use CS1 -CPU65H model.
Between the computer and the PLC with Controller Link network, the network uses twisted pair communications cable, the maximum communication rate of 2M, the maximum distance of 1km.
3.1 Hardware configuration
3.1.1 Operator Station
In the control room equipped with two industrial computersAs a human-machine interface operating station, one of which can be used as system program manager station. IPC key is configured to: P ????? 1.3 CPU, 256MB RAM, 40G hard drive and 19 "flat screen CRT, inserted in the IPC has a Controller Link network card - 3G8F5-CLK21, used, and PLC communications. Printer for the main process Timing parameters of the report to print.
3.1.2PLC module configuration
In the PLC, with the I / O modules are as follows:
Analog input modules - C200H-AD003 (8-channel, 4 ~ 20mA input)
RTD input module - C200H-TS102 (4-channel, thermal resistance signal input)
Thermocouple Input Module - C200H-TS002 (4-channel, thermocouple input) ???
Analog input modules - C200H-DA004 (8-channel, 4 ~ 20mA input) ???
Digital input module - C200H-ID212 (16 points, DC input) ???
Switch output unit - C200H-OC225 (16 points, relay output) ???
??? Converter 3.1.3
Mixing machine, feeding machine, the melt pump and pelletizer by four inverter, which melt pump for the high voltage inverter inverter.
3.2 software composition
System software form shown in Figure 3. In the WindowsNT operating system, equipped with the following description of the various software. ???
??? 3.2.1 operating system
windows NT4 ??? 0 Chinese Edition operating system. Windows NT system with both Windows-friendly and easy to use interface, but also with system reliability and data security.
3.2.2 Monitoring Software
System monitoring software is developed by Rockwell Software RSView 32 (English Version) industrial configuration software, is an integrated type, component-based human-machine interface software, which runs on Windows95/98/2000/NT other operating system, enabling monitoring and control of automation equipment and processes. The complete process can easily monitor the formation of the screen, real-time data acquisition, recording and analyzing trends, alarm report printing and other tasks. The configuration software also has a strong web browser integration, embedded in a standard programming language (VB), online help, support real-time video images and embedded word processing, spreadsheets and text features such as ActiveX.
Complete system monitoring software is the main process equipment parameters and operating status of each process in the form of images and tables to monitor, screen settings and watch the main loop of the regulator parameters Kong Zhi and processes in the main Yibiaoshuju record of trends, alarm recording and setting the value chain.
3.2.3OPC Software
OPC (for process control OLE) is an industry standard, based on Microsoft s OLE (now Active X), COM (component object model) and DCOM (Distributed Component Object Model) technology. OPC, including a set of interfaces, properties, and that the standard set for the process control and manufacturing automation systems. Active X / COM technologies define how the various software components interact with the use and sharing of data. Used in the course regardless of what software or equipment, OPC is a wide variety of process control equipment to provide communications between a public interface.
SYSMAC OPC Server is dedicated to OMRON series PLC and other devices OPC software used in the system configuration software RSView32 data interface to achieve data exchange with the PLC.
3.2.4 Communication Tools
FinsGateWay OMRON series PLC is the communication interface software tools, mainly used in computer and PLC communication network between the various management and provides the data interface to establish communications. In this system, the main computer and the PLC ControllerLink for network communication between the control and data management, in its software can ControllerLink card - 3G8F5-CLK21 to set up and service start-stop control.
3.2.5 Programming Software
OMRON CX-Programmer is a software company PLC programming, debugging tools program, which runs on Windows98 NT operating system, with rich, simple and convenient operating environment and strong programming and debugging functions. OMRON s SYSMAC CS1 series PLC has a more extensive instruction, which includes relays instructions, timer and counter instructions, instruction computing (including trigonometric, exponential, power operation, etc.), data conversion, diagnosis, shift registers, comparison, data transfer, process control and PID control instructions. Use these instructions to complete the extrusion equipment data acquisition and processing parameters; order and logic interlocking control equipment start and stop the motor; each of the major loop PID regulator control.
4 Conclusion
The system was in June 2002Put into operation, after several months of observation and control parameters of the trial and error, the device is stable and reliable, and up facilities in the highest yield, they can meet the quality requirements of a variety of brands products, greatly improved production efficiency, has been good effect.