Application of touch screen and PLC in low sealing furnace control system
1 Introduction
The low-sealing furnace is one of the important links in the CRT production process, and is mainly used to seal the screen cone by baking. It generally includes several parts such as a furnace body, a driving device, a displacement device, and a railing on the furnace. The furnace body includes a furnace body, a mesh belt guide, an RC fan, and a heater. The furnace body is composed of high-quality carbon steel and stainless steel, filled with thermal insulation cotton, and the circulation air passage is composed of stainless steel inner cavity plate. The RC fan acts as a stirring to make the temperature uniformity in the furnace. The heater consists of a high-quality heating wire and a stainless steel frame for constant temperature. The driving part is provided with an automatic tensioning device and a mesh belt deviation adjustment mechanism, which mainly realizes the continuous adjustment of the mesh belt speed through the frequency converter, so that the workpiece moves at a uniform speed in the furnace body.
The following is an example of the extension of the BMCC5L low-sealing furnace to illustrate the realization of its control system. It mainly includes low-voltage power receiving cabinets, three heating cabinets and temperature control cabinets. The working principle is as follows: the low-voltage power receiving cabinet provides the power supply such as the fan on the furnace, the hot wire, etc., the temperature is set by the temperature controller in the temperature control cabinet, and the output of the temperature controller is used to control the power regulator in the heating cabinet, the regulator The output controls the heater to adjust the temperature of the furnace to the required temperature. There is a PLC system and touch screen in the temperature control cabinet, which realizes the function of real-time monitoring by automatically turning on the whole system, automatically shutting down, and alarming at any time. The system is mainly to complete the control of the heating wire, RC fan, exhaust fan, chiller and the rear 8 zone cooling valves of 14 heating zones.
2, control system hardware configuration
Figure 1 system hardware configuration block diagram
The system has 260 points: 162 points for digital input and 98 points for digital output. The control system adopts OMRON's C200HG-CPU43, which belongs to the medium-sized PLC and has RS232 communication port, which can meet the requirements of higher performance. The substrate has a maximum of 10 slots, so that each slot has 26 points, and a 32-point module is required. Therefore, the input uses a high-density C200H-ID216, and the output selects a group 2 high-density transistor output unit C200H-OD215, thereby knowing 6 inputs. Module, 4 output modules. In addition, a string communication board C200HW-COM06 is added to the system, and the RS232 port is used to communicate with the touch screen to achieve human-machine exchange. In the monitoring aspect, digital company's GP577R-TC41-24VP is used to realize manual control and monitoring alarms. Its system hardware configuration is as follows:
The temperature control device on the panel of the temperature control cabinet controls the temperature of the low sealing furnace, has a PID adjustment function, and is used together with the SCR power regulator in the heating cabinet, so that the voltage of the heater can be adjusted within the range of 0 to 100%, according to the setting The difference between the fixed temperature and the current temperature automatically adjusts the value of the voltage output to the heater, so that the temperature in the furnace is accurately controlled.
The heating cabinet supplies power to the heater of the low-sealing furnace, and is equipped with a power regulator, and the temperature control in the temperature control cabinet automatically adjusts its output power to achieve the purpose of temperature control. The department controls the addition of 1 to 14 zones of heating. In the cabinet, an air switch is installed to supply power to the newly added 1~14 area power regulator SCR. The SCR adjuster is provided with a display panel capable of displaying the voltage of each phase, the magnitude of the current, the magnitude of the output power, and the like. This panel also shows the abnormal status of the SCR regulator.
The power part of the fan is the RC fan of the low-sealing furnace, and the power supply of the exhaust fan and the air cooler. The power-on and off is also controlled by the air switch. It is output to each fan in a given current range through an AC contactor, and its operation and stop are controlled.
3. Control system software design
Figure 2 temperature control cabinet control buttons
When the low-closed furnace total busbar is powered, the power indicator on the panel of the power receiving cabinet is lit, and then the heating cabinet and the temperature control cabinet are powered on in turn, and the corresponding indicator lights. The system is mainly based on the buttons of the temperature control cabinet as shown in Fig. 2, through the manual or automatic mode to complete the automatic start and close of the hot wire, fan and cooling valve in each zone of the furnace, and real-time monitoring of its state, whether there is an abnormal situation. The system control flow is shown in Figure 3.
In order to save space, the ladder diagram is not given here, and the flow chart will be explained below. After the PLC is powered on, first determine whether the fans are fully open. Only when the fans are fully open can the heaters work. Mode selection, mainly automatic and manual two states. In the automatic mode, press the auto start button on the panel, the auto light is on, so that the fan automatically opens the shift register, and the fans in each zone are automatically opened one by one. When all the fans are working, the heating block 1 is automatically started, so that the heating shift register of the 1 to 5 zone is operated, so that the heating wires of the 1 to 5 zones start to work. Then the heating block 2 is automatically started, and the 6 to 14 zone heating shift register is operated, so that the 6 to 14 zone heating wires start to work. Therefore, the PID is automatically adjusted according to the process setting temperature in each zone until the requirements are met. When it is necessary to stop production, the hot wire and the fan are stopped. In this way, the automatic stop button on the control cabinet is pressed, so that the hot wires in each zone stop working one by one. At this time, automatic stop timing is performed, and the time is automatically stopped to stop the fans in each zone.
In the manual mode, first press the fan start button on the panel to make the fans in each zone open sequentially. When all the fans are working normally, press the heating block 1 start button on the panel, and the hot wires in Zones 1 to 5 start working. Similarly, press the start button of the heating block 2, and the hot wire in the 6-14 area also starts to work. After the system is stable, the workpiece can be burned. When it is necessary to stop, press the stop button of the heating block 1 and the hot wire in the 1 to 5 zone starts to stop. Pressing the stop button of the heating block 2, the hot wire in the 6-14 area also starts to stop heating. When the hot wire is all stopped, press the fan stop button, then the fans in each zone will stop running. Until the next start.
If an abnormality occurs in the workpiece during the production process, press the very stop button and the mesh belt stops rotating for emergency treatment. And any area hot wire or fan abnormal situation, there is a corresponding display on the control cabinet or touch screen, and its corresponding sound and light alarm, notify the operator.
4, monitoring system description
This system uses DIGITAL company GP577R-TC41-24VP type touch screen as the upper level monitoring, which can display the live signal, real-time alarm and control point in real time. The monitoring system consists of five windows: the system main screen window, the heating zone RC fan operation screen, the heating zone hot wire operation screen, the cooling valve operation screen, and the equipment failure history screen. A link is established between the five windows, the button is switched through the window, and a connection is established between the variable and the PLC, and the corresponding status information is displayed in real time through the touch screen to form an overall monitoring of the system.
Now take the system main screen as an example to illustrate the function of the monitor screen. The main screen of the system is divided into two areas: the light component area and the switch component area. The lamp part area is on the left side of the screen, and the I/O point of the PLC is used as the monitor display. When these monitor points are ON, green is displayed, and when it is OFF, white is displayed. This indicates whether the current state of the original cabinet and the new cabinet and the network belt is in the automatic state or the receiving state, whether it is running or stopped, whether it is normal or abnormal. The switch component area is mainly used as a selection button, and when these buttons are touched, it switches to the relevant page. The abnormality occurrence button is mainly to monitor whether the system has an abnormal condition. If there is a red display, the touch can be adjusted to the fault screen to show which device has any fault. When the cooling valve button is touched, it will jump to the cooling valve operation screen, showing the opening and closing status of each cooling valve, and whether it is malfunctioning. Touch the fan manual button to switch to the heating zone RC fan operation screen to display whether the fan in each zone is in the running state, whether there is any abnormality, and whether the fan in the corresponding zone is on or off. Touch the heating manual button to switch to the hot wire running screen of the heating zone. This screen mainly displays whether the hot wire in each zone is in the running state, whether there is any abnormality, and whether the hot wire in the corresponding zone is heated or stopped. Touch the device fault history button to display when an alarm occurs, when it is resumed, and whether it is confirmed. And in five windows can be switched to each other for easy monitoring.
Figure 4 touch screen main menu screen
5 Conclusion
The system has been put into practical operation, and the performance is stable and reliable, which better meets the process requirements. PLC as the main controller of the system has its unique advantages in terms of safety and reliability and network interconnection. The touch screen human-machine interface system has excellent performance in flexibility and friendliness, so that the degree of automation is further improved. However, the system has limitations in communication with other control systems. The signal exchange between the original cabinet and the new cabinet through the cable signal line is limited, and it cannot be implemented with the inlet control system, the exit control system, and the replacement control system. Full communication makes it difficult for operators to get sufficient information. One of the solutions can be to add LINK units in the respective PLC modules to achieve communication between the PLCs, and better control of the entire system.
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