Talking about how to get a good job in PLC control technology course
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In recent years, we can clearly see in the printing industry exhibitions held all over the country that the technical level of China's printing machinery industry has now developed to the level of the international 1990s. The remarkable sign of the progress of China's printing machinery is that the control part and automation level of printing machinery have been significantly improved. Among them, programmable controller PLC is a new type of automatic control device integrating computer technology, automatic control technology and communication technology. As an industrial controller, it is small in size, powerful in function, convenient to use, low in price and high in reliability. Features, widely used in a variety of mechanical equipment and production processes. For the printing industry, the various processes of the printing process can also rely on the unique advantages of PLC to achieve precise control of the printing machinery.
In order to adapt to the increasingly widespread application of PLC, in recent years, many technical schools have opened the PLC course. For the printing and publishing schools that specialize in the transportation of professional and technical talents for the printing industry, in the face of the popularization of PLC technology, it is naturally no exception to open a relevant course for the precise control of printing machinery. How to teach this course? As a high-tech course, it is more difficult for Chinese students who are only junior high school. Therefore, how to stimulate interest in learning and explore new teaching ideas is especially important. In the following, combined with teaching practice, talk about some views on PLC teaching in printing machinery control technology.
1, introduce the theme from the things in daily life
At the beginning of the printing machinery control course, students did not understand the course. Some students would understand the various instruction codes appearing in the textbooks as computer programming courses, plus their own basic problems, resulting in fear. In response to this common situation, teachers must change the traditional teaching ideas in the past, and carry out targeted improvement on theoretical textbooks, experimental textbooks and teaching methods to improve the effectiveness of teaching. In this information age, information is the power, mastering as much information as possible, can walk in the front end of the times. Teachers who work in the front line of teaching should acquire more professional knowledge, learn more, enrich their experience, and improve their own quality. This way, you can only say something in class. ,
For the introduction part, the examples of PLC widely used in daily life can be listed first, such as: mobile phone production line, food production control, robot control, elevator control, and even robot control, etc., all have PLC credit. After the introduction of the theme, the printing process is a complicated process, including a series of processes, such as the supply of paper, the supply of ink and its accessories, the wetting of the printing plate during offset printing, and the printing itself (from the printing plate to the printing plate). Repeated overprinting of paper to obtain multi-color graphics; processing of printed sheets after printing, acceptance and packaging of printed products, power supply of printing presses, and inspection and control processes of printing processes. The end result of the printing process is to obtain quality prints. The acquisition of quality products depends on many external and internal factors, which are related to the nature of the original printed materials, the condition and adjustment of the main components of the printing press, the working state of the printing press, and the external environmental conditions. In order for students to understand these problems, and to control these contents through the PLC in the future, we must start with the relationship between the control principle and the printing process.
2, the example comparison is very important
The example method is widely used in teaching. The printing machinery control is no exception. The printing machine is a high-precision machine. The quality of the printed matter depends on the machining and installation accuracy. The balance of waterways and ink paths (referred to as ink and water balance) and the accuracy of the combined pressure. It is not easy to explain these things for students to understand. Therefore, it is necessary to simulate the effects before and after the control on the PLC controller. If there is no PLC control, it will be understood why the printing accuracy cannot be improved. After using PLC control, the proportion of ink is adjusted. Why the precise control, the content of these principles can directly show the effect through the operation, this comparison method of the example effect is conducive to strengthen the students' memory.
3, the principle introduction should be more practical
Since the students of the technical school are not college students, the basic theory level is low. Therefore, in the process of theoretical explanation, the method of college students' education cannot be used, but the part with strong practicality is to be introduced, and the explanation should be simplified as much as possible during class. As a result, students are too deep in theoretical knowledge, and they are unable to understand in depth, resulting in feelings of learning. Taking the water roller and ink roller motion control of the printing press as an example, since each color group of the printing press has a water path and an ink path device. In order to adjust the speed of the water roller, the water roller is controlled by the inverter. At the same time, the speed of the main motor also needs to be adjusted by the inverter. In order to realize multi-channel speed regulation, a digital-to-analog converter is installed on the inverter to convert the digital quantity sent by the PLC into a 0~10V DC voltage output, thereby realizing the requirement of multi-channel speed regulation. In addition, during the operation of the motor, the sensor sends the operating condition to the analog/digital converter to convert it into a digital quantity, and uploads it to the monitoring part to realize real-time communication between the human and the machine. This theory involves a wide range of knowledge, which cannot be fully understood by the students. Therefore, explaining this part can simplify the process, as long as the students master the movement of the water roller and the ink roller are analog quantities, which are converted into digital quantities and then input. PLC and PLC compare the actual detected operating parameters with the theoretical values, then calculate the error, and then feed back to the control device of the motor through the digital-to-analog conversion device to control the number of revolutions. This explanation makes it easier to clarify the basic principles that need to be known.
4, explain according to the operation flow chart
In the class, lead the students to draw the corresponding diagrams with the teacher's ideas, which is of great benefit to the understanding and memory of the knowledge points, to draw the PLC ladder diagram of the start, hold and stop of the printing machine motor system as an example:
The stop-stop circuit only uses the commands related to the contacts and the coils, and does not require the programming components to do the intermediate links. The command systems of various types of PLCs have related instructions, and the circuit utilizes self-holding, thereby having a memory function, and the conventional The relay control circuit is basically similar, so it becomes a common case in the basic teaching of PLC. The ladder diagram is shown in Figure 1. The corresponding program:
PLC ladder diagram of motor system start-stop control Runntable program written according to the ladder diagram of Figure 1.
In the case of teaching this example, when the student just touches the ladder diagram and is not familiar with the ladder diagram, the teacher can draw the main work flow chart structure and the main part during the teaching, such as X400, X401 and T450 in Figure 1. The Y430 and Y431 parts can be given, so that the students can fill in the simple part of the auxiliary, such as the X401 and X402 normally closed contacts in Figure 1. As the number of exercises increases, the ladder diagram given by the teacher can be Gradually reduce, so that the part of the student fills gradually, and finally the ladder is drawn completely by the students themselves. The advantage of teaching in this way is that the new knowledge points are gradually mastered in the repeated practice, that is, the proficiency is increased and the teaching tasks can be completed step by step. Every time an exercise is completed, the teacher will comment, and the common mistakes of the students are pointed out. The X401 normally closed contact and the X402 normally closed contact in Figure 1 above are easily overlooked. These teachers should summarize and summarize them. Stressed many times in the classroom.
In this way, after repeated iterations and repeated recollections, the students not only have a deeper understanding of the principles, but also have a certain understanding of the drawing methods and common mistakes, and then through the supporting training, Get a good grasp of the ladder drawing method.
5. Let students learn how to learn from their mistakes.
Students who master a technology will certainly make mistakes in one way or another. Usually, the teacher will point out where the mistake is and how to do it correctly. This kind of effect is often not very ideal, because the characteristics of people: compared to the easy to get things, people tend to cherish what they have hard to get, that is to say, the problem that teachers directly break through is easy to forget, but through the students' own thinking The correct solution is often memorable.
In the classroom to check out the student design or operation errors, you can determine the scope of the error through specific phenomena, but do not disclose the specific error, let them have the purpose and direction to check and think, if necessary, the teacher gives tips and principles, Even telling students what books and materials should be consulted, but the answer to the question is still to be considered by the students themselves. Taking the fault control of the printing press as an example, the overall electrical design of the printing press has strict time requirements. In many places of the machine, a travel switch and a proximity switch are provided to detect paper feed at different points in time. In the printing process, whether the paper is smooth or not is an important indicator of the quality of the printing machine. The so-called smooth paper condition refers to the phenomenon of arbitrage, double sheeting, etc. If there is such a phenomenon, in the case of high speed operation of the printing machine, the damaged paper will be caught in the machine, thereby destroying the rubber and damaging. machine. In the paper feeding process, the common fault is the front paper failure. In order to detect such a fault, two photodetectors are used in the printing press to send the signal on the left side of the paper to the monitoring system through the input point, and the other two photodetectors send the signal on the right side of the paper to the monitoring system, and one photoelectric The detecting head is used to measure the over-heading signal of the paper. According to the requirements, when any one of the three kinds of signals is abnormal, the I color group is turned into the stop working state, and no signal is transmitted to the back, and the II color, the III color, and the IV color group are transmitted. It also stops accordingly, and the main motor starts to slow down.
Due to the continuous increase of the running speed of the printing press, in the case of high-speed paper feeding of 7000 rph or more, the reaction time of the proximity switch laser head and the operating time of the electromagnet may be delayed, and the phenomenon that the paper cannot be locked may occur. In order to solve this problem, the high-speed counter sets the group high-speed scan mode, and the interrupt command is used in the scan program in the PLC programming, so that the electromagnet action signal can be output in advance when the fault occurs, so that the electromagnet can act in time, even in the At a speed of 12000 rph, it can also lock the faulty paper well, solving a big problem of high-speed paper feeding.
When students do this test, the most common mistake is the valve opening and closing and the speed of the paper roll. The closing time of the valve is calculated by the PLC based on the feedback result of the paper roll speed, and the valve closing time. It will also affect the paper transport. If there is a double problem when it is opened early, there will be no paper feed idling when it is late. These will also affect the rotation speed of the paper roll, which is a closed loop control structure. The usual response of students is to slow down when the opening and closing time is fast, and to adjust it faster when it is slower. Otherwise, it is unilateral to adjust the paper roller speed, which can not solve the problem fundamentally. To solve this problem, we must add the appropriate standard amount. In order to draw this conclusion, let the students try according to their own ideas. Skills education can be found or close to the correct answer, so skills education is not a unilateral educational process, but a multi-faceted educational process that includes students' self-education.
6, the use of multimedia computer-assisted instruction
Multimedia technology is now widely used in teaching. Animation is the best and most economical simulation method. It uses vivid and rich picture effects to attract students' attention, emphasizes the operation of various parts of the control process, and deepens students' key knowledge. Intuitive impressions that motivate students to learn. For example, when introducing the workflow of a four-color printing press, you can simulate multiple internal rollers, where the paper is sent during the running process, and which ink roller starts to be stamped. These can be marked with eye-catching colors for students. They have a clear understanding of their internal workflow.
7, summary
The design and manufacturing level of the printing press is constantly improving, especially the development of high-tech such as automation control, which has greatly changed the control system of the printing machine. The programmable controller, frequency conversion technology and computer control technology are in the printing machinery. The application is becoming more and more extensive, and the performance of the printing press is becoming more and more advanced. The part that needs manual operation is gradually reduced, and the machine's own control ability for the entire printing process is continuously enhanced. All in all, modern presses are moving toward high speed, high automation and high reliability. As a talent delivery unit in the publishing and printing industry, we must use a variety of means and methods to teach the teaching process, focusing on effectiveness and operability, so as to cultivate qualified printing technology talents.