Accurate Control Of Printing Machine By Mitsubishi Plc

1. Introduction
     In recent years, with the improvement of automation technology in China, factory automation has also reached a new level.Mitsubishi PLC As a new industrial controller, PLC has unique advantages in small size, complete functions, low price and high reliability, and has been widely used in various fields.Mitsubishi PLC

      作为国内最大的印刷机生产厂家---北人集团公司，为了使产品性能稳定，易于维护，我们采用了以PLC为主控器的控制方案印刷机 由于双色印刷机要求易于操作，精度高，故其输入，输出点较多，因此采用了双机通讯印刷机 上位机采用三菱FX2N-80MR+32EX+4D/A，主要负责主传动的控制，各机组离合压的控制，以及气泵，气阀的控制等印刷机 下位机采用三菱 FX2N-64MR+4A/D,主要负责水辊电机的控制，主传动的调速输出，调版电机数据采集等控制 同时选用了一台三菱5.7寸触摸屏，主要负责水辊电机速度显示，调版显示，以及整机故障显示等控制 本系统运行可靠，维护方便，操作简便直观，大大提高了胶印机的档次，受到用户好评控制     

2. System Structure

     The structure of the system is as follows:

       Among them, RS485 communication is used between the upper computer and the lower computer, which is convenient and reliable. Safety is very important for multicolor machines. In the design, each unit should consider not only safety control, including emergency stop and safety button of its own unit, but also convenient operation, including that each unit should have a punctual and counter-point button. Therefore, on the one hand, the input points increase a lot; on the other hand, the routing is also inconvenient. This problem can be well solved by using two-computer communication. The routing of each unit can enter the control cabinet nearer to it according to the principle of proximity, which not only saves routing, but also facilitates control.      

      Because the printing press is a machine with high precision, the quality of printed matter depends on the accuracy of machining and installation, on the other hand, it also depends on the balance of waterway, ink path and the accuracy of pressure combination. Each color group of the two-color machine has waterway and ink circuit devices. In order to adjust the speed of the water roll, each water roll is controlled by a frequency converter. At the same time, the speed of the main motor also needs to be adjusted by the frequency converter. Therefore, in order to achieve multi-channel speed regulation, we adopt Mitsubishi 4D/A digital-to-analog converter, which converts the digital quantity given by the PLC side into 0-10V DC voltage output according to the corresponding algorithm, and realizes the multi-channel speed regulation requirements well.

      在印刷过程中，调版是一个比较繁琐的过程。尤其对多色机来说，各组版对正的精度会对印品产生很大的影响。如果套印不准，印刷品就会出现字面重叠或影像不清。一般来说，印版轴向调节范围为-2mm~+2mm ,周向调节范围为-1mm~+1mm。如果使用手动调版，会浪费很多时间，而且精度不高。为了实现自动打版，我们在版辊上安装了电位器，通过电位器将模拟量传送给4A/D，经过PLC处理，可将版辊的转动精度很好地控制在打版范围内。

      Touch screen, as a new type of human-machine interface, has attracted much attention since its emergence. Its simple and easy to use, powerful function and excellent stability make it very suitable for industrial environment. Users can freely combine text, buttons, graphics, numbers, etc. to process or monitor information that may change at any time. With the rapid development of mechanical equipment, the past operation interface needs skilled operators to operate, which can not improve efficiency. However, the use of human-machine interface can clearly indicate and inform operators of the current status of machinery and equipment, making the operation simple and vivid. The use of touch screen can also standardize and simplify the machine wiring, reduce the number of I/O points required for PLC control, reduce production costs, and relatively improve the added value of the whole set of equipment. Mitsubishi Touch Screen and Mitsubishi PLC have good versatility. They can monitor and modify programs online without having to repeat the plug-and-play interface.    

3. Software Design    

      3.1 Paper Feeding Design

      The overall electrical design of the printing press is relatively complex, and the time requirement is also very strict. Proximity switches are installed in many parts of the machine to detect different time points. In the printing process, the quality of paper is an important link that affects the quality of the machine. The so-called paper walking quality refers to the phenomenon of no distortions, double sheets and so on. If there are distortions and double sheets, in high-speed conditions, the worn paper will be rolled into the machine, thus destroying the rubber and bringing great losses to users. The process flow is as follows:   

      In the experiment, we found that the program compiled according to the above process has no problem at low speed, but when the speed increases to 7000r/h, the phenomenon of distorted locking will occur. The main reason is that the reaction time of the bald head and the lag of the action time of the magnet. In order to advance the output of the electromagnet, I used the input and output refresh instructions of interrupt and Mitsubishi programming instructions to make the output of the electromagnet execute immediately and advance the action time of the electromagnet. Even at the speed of 12 000 r/h, it can lock the fault well. The paper has solved a big problem of feeding paper.         

      3.2 Clutch Pressure Design 

      Separation pressure and combination pressure play an important role in printing. The accuracy of clutch pressure has a direct impact on the quality of printing. Pressing too early will dirty the embossing roller, which will bring a lot of inconvenience to the operation. Pressing too early will make the last sheet of paper can not print the complete pattern, resulting in waste of paper.      In the design, the procedure flow of pressure separation and pressure combination is shown as follows:    

      In printing, the plate roller and the rubber roller are pressed together first, and the rubber roller and the press roller are pressed together afterwards. In our machine, all the pressure-closing devices are pneumatic, each cylinder has a time to move. Because the printing speed is multi-stage, between 3000 and 12000 r/h, different speeds can be selected according to user's needs. However, the action time of the cylinder is certain, and the rotation angle of the gear is certain. Therefore, when the speed of the machine is different, the closing time is also different. In order to solve this problem, we find out the delay time for different machine speeds according to the theoretical calculation value. When the speed of the machine section is equal to the theoretical value, the corresponding time is delayed, so that the press rollers and rubber rollers can be accurately combined. After many tests, there is no problem with the separation pressure and the combination pressure.    

      3.3 Design of Human-Machine Interface

      In the man-machine interface, seven pictures are designed, including the overall graphics, fault display, machine speed and counting display, water roller speed display, adjustment monitoring and so on. Fault display uses indicator and gives position element to realize flicker effect, which makes operator know the fault location conveniently and has a good overall sense. In the display of water roller speed, a bar chart is designed to show the increase of water volume. Just press the bar chart, the water volume can be increased. At the same time, it can be easily monitored. As shown in the figure: 

4. Concluding remarks

      A set of electrical design of printing press belongs to system design, including hardware and software design, covering a wide range. Here, I only briefly introduce some of the more important parts, there are many other details, here are no longer listed one by one. Using Mitsubishi's control system, it feels reliable and convenient, and no major problems are found in the process of batch production of machines. Compared with other products, Mitsubishi's overall software system interface is more friendly, which brings great convenience to user programming and maintenance. Its touch screen and PLC have good versatility. It can monitor and modify the program through touch screen, which is beyond the reach of other products. In short, Mitsubishi's industrial control components bring a lot of convenience to designers and users.