The control function of programmable controller is very powerful, and it is easy to use. It has been widely used in industrial control and electrical automation. Based on this, taking Mitsubishi FX2N programmable controller as an example, this paper briefly analyses the connection sequence control and storage program control system of the programmable controller, and concretely analyses several common programming methods of the storage program control system for your reference. In the process of industrial development in China, programmable logic controller has been widely used, which effectively promotes the development of electrical automation in China.
In the process of application, the programmable controller has many advantages, such as long service life, small volume, strong versatility, high reliability, easy operation, easy to understand and so on. In recent years, the development of electronic products in our country is very rapid, and the price has also been reduced, which reduces the price of programmable controller, and is conducive to the positive application of programmable controller in a larger range. Connection sequence control system mainly connects electronic components, contactors and relays by different wire connections, so that the logical part of the control task can be realized. At present, programmable logic controller (PLC) is widely used.
Its essence is a micro-computer. The requirement of electrical control is mainly realized by stored program control system. In this way, the purpose of the control program can be achieved without changing the connection mode of the hardware wires. Compared with the traditional hard logic control, the programmable logic controller has greater advantages, and also subverts the original programming habits. For operators, the original hardware wiring mode and programming thinking mode are no longer applicable, which requires operators to re-learn the programming of programmable controller, thermostatic element understand the storage program control system, and break the original thinking mode. According to the author’s practical experience, programmable controllers are usually programmed by sequential control design method, empirical design method, relay circuit conversion design method, etc. As an advanced design method, the sequential control design method is more suitable for beginners. For engineers who have some experience in using programmable logic controllers, this method can also improve the efficiency of programming effectively, thus facilitating the reading, modification and debugging of programs [1].
Throughout the current industrial field, many production processes are based on time sequence and internal state by presupposing the sequence and then inputting different signals. In the process of production, the executing agencies can achieve automatic production and maintain a certain order of operation. Therefore, the design method of sequential control is very simple.
It only needs to set up the sequential function diagram based on the production process, and draw the trapezoidal diagram on this basis.
At present, there are three main methods to transform sequential function diagrams into ladder diagrams. Programming with step-by-step sequence control instructions.
Programmable Controller (PLC) is a sequential function diagram. There are two instructions designed, namely step return instruction RET and step sequence control instruction STL. Based on these two instructions, the sequential function diagram can be transformed into a ladder diagram. Only the next step needs to be driven, and the state relay of the previous step will automatically end without reset instructions. Take Figure 1 as an example, suppose a truck is to transport material from place A to place B, and then return to place B. Fig. 1 is a sequential functional diagram of the single-cycle working mode. The sequence function diagram is transformed by “start-protect-stop” circuit. This transformation method is close to the idea of traditional empirical design method, that is, the self-locking contacts, stop conditions and start conditions of each step are defined first, then the auxiliary relay M of each step is driven, so that the auxiliary relay M of this step and the action content of this step can be output in parallel. Method. Based on the “start-protect-stop” circuit, two programmable controller instructions, RST and SET, are used for conversion. SET has self-protection function, so it does not show self-protection contacts.
The experience design method and circuit transformation design method of relay are based on logical relay, and the suitable ladder diagram program of programmable logic controller is compiled. That is to say, the electrical contactor control circuit is transplanted on the programmable controller. But the scanning mode of relay contactor circuit and programmable controller is different. If the relay contactor circuit and programmable controller are transplanted forcibly regardless of their differences, some problems may arise, such as contact competition, one-off output competition, etc. Therefore, the programming method based on docking program is mainly applicable to the transformation of old control circuits, which can not be adopted in many programmable controllers. At the same time, empirical design method has greater randomness and exploratory, and has not formed a complete and fixed programming steps. For the more complex programmable controller program, in order to complete its interlocking, interlocking and memory functions, it often needs to use a large number of intermediate units, involving many factors, which are often more complex. Once a part of the system is modified, other parts of the system will also be greatly affected, the design workload is large, and the design effect is not ideal. At the same time, it takes a lot of time to use the programming method based on docking program, and other engineers are difficult to improve and maintain it, which may cause some difficulties in practical application [3]. Three conversion methods of programmable logic controller are introduced in the paper. They are programmed with step-by-step sequence control instructions, transformed with “start-protect-stop” circuit and programmed with conversion as the center. The three methods have their own advantages and disadvantages, and their application ranges are different. For example, sequential function diagrams can be obtained by any conversion method. If the engineers are familiar with the traditional relay contactor circuit, then the “start-protect-stop” circuit can be used.
On the basis of the former conversion method, the programming method of conversion center makes full use of the two instructions of the programmable controller. Compared with the former conversion method, it has the advantages of convenient operation and conciseness. However, when using the programming method that has been transformed into a center, we should also pay attention to the fact that the auxiliary relay M and the output action of the “start-protect-stop” circuit can not output in parallel to drive the action of each part, mainly using the parallel circuit of the representative step or the common contacts of the auxiliary relay at the end of the ladder diagram to drive [4].
According to the three conversion methods, we can find that the most concise and convenient method is to use step-by-step sequence control instructions to program. In contrast, this method has the fastest response speed and shorter scanning time, because it has the least program steps. It is worth noting that this method requires engineers to master certain state relay knowledge and theory. Generally speaking, the above three conversion methods are more practical, and can also achieve the purpose of transforming sequential function diagram into trapezoidal diagram, and refer to the actual situation in the specific selection. The programmable logic controller (PLC) develops very rapidly in our country, and its application scope is more and more extensive, so it has very broad application prospects. In all kinds of programmable controllers, the programming ideas and methods of the article can be applied, and each mode has a certain logical and relatively solidified corresponding relationship. Programmers should have a certain understanding of each programming mode and master its key points and key factors, constantly improve their ability to write sequential control programs, and promote the healthy development of programmable controllers in China.