Automation based on monitoring computer (PC), programmable controller (PLC), human machine interface (HMI), intelligent instrument, industrial control communication network DCS (distributed control system) and FCS (field bus control system) has become the technical pillar of modern factories and has been widely used in modern production lines at home and abroad. According to the statistics of relevant departments, among the PLCs shipped worldwide in recent years, according to the end users, automobiles account for 23%; Food processing accounted for 16.4%; Chemical industry accounted for 14.6%; Metal mines accounted for 11.5%; Papermaking accounts for 23.1%. It can be seen that the application of PLC system in food processing industry is second only to the automobile industry.
In China’s petrochemical, metallurgy, electrical, chemical fertilizer and other industries, the automation upgrade of the original relay control system has been completed. In contrast, the relatively backward food industry has gradually understood and respected the automatic control and management system with PLC and PC as the core after the introduction of flour processing production lines from abroad in the early 1990s. The rapid development of science and technology has effectively promoted the technological transformation of the food industry. The food processing enterprises are gradually developing towards scale and modernization in the process of restructuring, and the food processing is developing towards fine processing and deep processing. What is particularly noticeable is the wide application of PLC programmable control technology in the technical transformation and new projects of the food industry. PLC control replaces relay control; The dynamic display of the counter terminal of the process flow replaces the analog screen display; PC and distributed control network make the whole production line under the control and management of counting machine, completely changing the backward appearance of traditional food processing and becoming the development trend and direction of the industry.
This topic mainly studies the application of the automatic control system composed of PLC and man-machine interface in an egg yolk pie automatic production line: starting from the control requirements put forward by the user, the comprehensive analysis of the finishing part of the egg yolk pie production line, the basic control requirements are realized through PLC programming, and then the precise timing and positioning of each component are carried out through on-site debugging, and the process parameters are adjusted. A set of humanized, The simplified man-machine interface can finally meet the control requirements and process requirements. This topic is mainly about the application of PLC in the production line.
Production line control requirements
(1) Equipment process: mixing – forming – baking – cooling – sterilization – packaging
(2) The control requirements of the sorting part are as follows:
① After baking the egg yolk pie, toss the oil and cool it before entering the finishing part.
The finishing part includes milk filling and scraping. The egg yolk pie is transferred from the suction cup part to the finishing part through the suction cup device. That is, the egg yolk pie is brought to the milk feeding conveyor belt by the suction cup. There is a material detection and conveying signal x0 at the front end of the conveyor belt. When x0 detects the signal, after the milk feeding delay, the milk feeding servo Y0 operates and starts the conveyor belt.
② The milk filling device can fill the egg yolk pie on the left and right sides respectively. When the left detection milk filling signal X1 detects the signal, the milk feeding will stop. At the same time, the left milk feeding operation solenoid valve will operate. After the operation delay of the milk feeding operation solenoid valve, the left milk feeding opening and closing solenoid valve will open and the feeding will start at the same time. After the time delay, the left milk feeding opening and closing solenoid valve will be closed, At the same time, the left milking and milking solenoid valve operates to start milking. After the left milking and milking delay, the milking ends and the milking and conveying operation. After the material delay, the milking and conveying stops after the delay time. Repeat the second step until the predetermined number of rows is completed. (the milk filling operation solenoid valve, the opening and closing solenoid valve and the extruding solenoid valve shall have operation delay and off delay).
③ When the right side detects the milk filling signal X2, the milk feeding stops, and the right side milk filling operation solenoid valve operates. After the operation delay of the milk filling operation solenoid valve, the right side milk filling switch port solenoid valve opens and starts to pump. After the time delay, the right side milk filling switch port solenoid valve opens and delays. After the time expires, the right side milk filling switch port is closed, and the right side milk filling and milking solenoid valve operates to start milking, After the time delay of milking and milking on the right, the milking will be finished and the milking and conveying will run. After the time delay of materials, the milking and conveying will stop. Repeat step 3 until the predetermined number of rows is completed.
(the milk filling operation solenoid valve, the opening and closing solenoid valve and the extruding solenoid valve shall have operation delay and off delay).
④ The scraping servo performs scraping when the milk feeding is stopped (stop at the end of one cycle).
⑤ There are 3 groups of sorting. Sorting signal 1, sorting signal 2 and sorting signal 3 correspond to X3, X4 and X5 respectively. After detecting the signal, the corresponding sorting solenoid valve acts and resets after a certain delay. The two blanking signals and the detected blanking signals correspond to two blanking servos.
⑥ It is equipped with the servo emergency stop reset of finishing and blanking I, the servo emergency stop reset of finishing and blanking II, the cake conveying emergency stop reset, the scraping emergency stop reset, and the milk filling emergency stop reset. At the same time, there shall be a signal alarm system.
⑦ Manual / manual switching is required. After pressing the start button, automatic control will be executed.
⑧ All general parameters shall be displayed and set on the touch screen. It is also provided with factory value setting and factory value recovery, and parameter record and last record recovery are required.
⑨ There should be a monitoring picture of the whole assembly line to reflect various control states.
⑩ Set a service time. The service time can be changed to control the effective running time of the machine, and all outputs are prohibited after the time expires.
Control system analysis
For control system analysis, I / O points shall be allocated according to control requirements, PLC model shall be selected according to I / O points and control requirements, frequency converter, touch screen and servo model shall be selected, and then program flow function block diagram shall be drawn according to control requirements.
Model selection
PLC model selection: select a 60 point PLC according to the distribution of input and output points, and add an expansion module. Because the pulse output is required to select transistor type, the PLC model is xc3-60t-e, plus an expansion module xc-e8x8yr.tp model selection: 256 color TFT true color of 10.4 inch large screen, which should support RS-232 / RS485 / RS422 communication, Therefore, tpa61-t frequency converter is selected: eds1000-4t0022g / b. servo selection: vec-vb-r40h21b-m-b.4 control system design
(1) Communication between PLC and frequency converter
This system uses four frequency converters, that is, the communication between four frequency converters and one PLC. Since its PLC is the XC series of Xinjie and the frequency converter is the eds1000 series of Yineng, they cannot communicate with each other through modbus, but require free format communication.
Free format communication means that its communication format can be defined according to user needs.
Start character (1 byte) data block (maximum 128 bytes) Terminator (1 byte)
The communication is transmitted in the form of data blocks. Each block can transmit 128 bytes at most. At the same time, a start / stop symbol can be set for each block according to the actual application, or it can not be set. After setting, PLC will automatically add the start / stop character when sending data, and will remove the start / stop character when receiving data.
Therefore, when PLC adopts free format communication protocol to realize the data exchange between PLC and intelligent instruments, it has great flexibility and avoids the limitation of the internal special protocol of PLC.
The PLC communicates with three frequency converters. The addresses of the three frequency converters should be set as 01, 02 and 03 respectively, and the corresponding ASCII is 31, 32 and 33. If the frequency of the frequency converter is required to be given, the host command, auxiliary index and command index can be found in the Manual of the frequency converter, and then converted into ASCII format. The main work is to convert the input decimal frequency into ASCII code values and write them into four registers respectively, and then accumulate the previous numbers, that is, the ASCII code values of all bytes from “slave address” to “operation data” are accumulated and put into four registers, and the frame end is 0d Add the ASCII code value of the constant number, and then perform ASCII conversion on the frequency. Conduct and operation on 00ffh and ff00h, and then carry out logical shift, and then put each number into the register. When writing the station number of the frequency converter, D400 is accumulated by a timer, and then the number of D400 is decoded and sent to M50. The station number and frequency of the three frequency converters are given by M50.
(2) Signal detection
In the signal detection system, the main one is the material detection and feeding signal, which corresponds to the milk filling and feeding process, the finishing and feeding first servo operation process and the finishing and feeding second servo operation process respectively.
(3) Milk feeding
The corresponding flow of milk filling and conveying is S0. S0 is started by the previous milk filling and conveying detection signal. After the milk filling and conveying delay, the conveying servo sends pulses to carry out milk filling and conveying. D8170 is pulse_ 1 accumulated number of pulses. When m8170 (milk feeding and conveying servo operation flag) gets a falling edge, it enters the scraping and milking detection process. The reason why the milking detection process is opened here instead of in the above signal detection process is to prevent the milking process from being opened by mistake due to the detection of wrong signals.
(4) Scraping
The servo operation of the scraping process is similar to the servo operation of the milk filling and conveying, and will not be described here.
(5) Milking detection process
When the left milking detection photoelectric switch detects a signal, open the left milking process. (similar to the one on the right).
(6) Milking process
When the milking process is opened, the left milking operation solenoid valve will be opened to set Y12. After the operation delay T200 of the left milking operation solenoid valve, the left milking switch port solenoid valve will be opened to set Y200. After the t201 delay, the left milking solenoid valve will be opened to set y201. After the T202 delay, the switch port solenoid valve will be closed. After the t203 delay, the left milking solenoid valve will be closed. After the t204 delay, Close the operation solenoid valve and exit the left milking process after time delay. (similar to the one on the right).
(7) Sorting
The sorting is simply to set the sorting solenoid valve through the sorting signal and reset it through the operation delay.
(8) Finishing and blanking servo operation
There are two stages of finishing and blanking servo, which need to go through the falling delay. So there should be a segment flag bit.
summary
The application of PLC programmable control technology in the food industry has played a positive role in ensuring the stability of product quality and production rate, ensuring the stability of equipment efficiency and process effect, improving the safety and reliability of production operation, reducing the labor intensity of operation and management personnel, reducing the production personnel and improving the labor value, and realizing the modernization of production management.