1. Introduction As the largest printing press manufacturer in China, Beiren Group Co., Ltd. adopted a PLC-based control scheme to ensure stable product performance and ease of maintenance. Due to the high precision and ease of operation required for two-color printing presses, which have numerous input and output points, a dual-machine communication system was implemented. The upper-level computer, a Mitsubishi FX2N-80MR+32EX+4D/A, is primarily responsible for controlling the main drive, the clutch pressure of each unit, and the air pump and valves. The lower-level computer, a Mitsubishi FX2N-64MR+4A/D, is primarily responsible for controlling the water roller motor, speed control output of the main drive, and data acquisition of the plate adjustment motor. A Mitsubishi 5.7-inch touchscreen was also selected, primarily for displaying the water roller motor speed, plate adjustment, and overall machine faults. This system is reliable, easy to maintain, and simple and intuitive to operate, greatly improving the quality of offset printing presses and receiving positive feedback from users. 2. System Structure The system structure diagram is as follows: The upper-level computer and the lower-level computer use RS485 communication, which is convenient and reliable. For multicolor printing presses, safety is paramount. The design of each unit must consider both safety controls (including emergency stop and safety buttons) and ease of operation (including positive and negative buttons for each unit). This results in a significant increase in input points and inconvenient wiring. Dual-machine communication effectively solves this problem, allowing wiring for each unit to be routed to the nearest control cabinet, saving on cabling and simplifying control. Since printing presses are high-precision machines, the quality of printed products depends on the precision of machining and installation, as well as the balance and accuracy of the water and ink systems. Each color group in a two-color press has its own water and ink system. To facilitate the adjustment of the water roller speed, each water roller is controlled by a frequency converter, and the main motor speed also requires frequency converter adjustment. Therefore, to achieve multi-channel speed adjustment, we adopted a Mitsubishi 4D/A digital-to-analog converter (DAC). This converter converts the digital signals from the PLC into a 0-10V DC voltage output according to a corresponding algorithm, effectively fulfilling the requirements for multi-channel speed adjustment. In the printing process, plate adjustment is a relatively tedious process. Especially for multi-color presses, the alignment accuracy of each plate group has a significant impact on the printed product. If the registration is inaccurate, overlapping text or unclear images will appear on the printed product. Generally, the axial adjustment range of the printing plate is -2mm to +2mm, and the circumferential adjustment range is -1mm to +1mm. Manual plate adjustment is time-consuming and lacks precision. To achieve automatic plate making, we installed potentiometers on the plate rollers. These potentiometers transmit analog signals to the 4A/D converter, which, after processing by the PLC, allows for precise control of the plate roller rotation accuracy within the plate making range. Touchscreens, as a new type of human-machine interface, have attracted attention since their inception. Their ease of use, powerful functions, and excellent stability make them very suitable for industrial environments. Users can freely combine text, buttons, graphics, numbers, etc. to process or monitor and manage information that may change at any time. With the rapid development of mechanical equipment, the previous operating interface required skilled operators to operate, which could not improve efficiency. However, using a human-machine interface can clearly indicate and inform the operator of the current status of the machine equipment, making operation simple and intuitive. Using a touch screen can also standardize and simplify machine wiring, while reducing the number of I/O points required for PLC control, lowering production costs, and relatively increasing the added value of the entire set of equipment. Mitsubishi touch screens and Mitsubishi PLCs have good versatility, allowing for online monitoring and program modification without the need for cumbersome repeated plugging and unplugging of interfaces. 3 Software Design 3.1 Paper Feeding Design The overall electrical design of the printing press is relatively complex, and the timing requirements are also very strict. Proximity switches are installed in many places on the machine to detect different time points. During the printing process, the quality of paper feeding is a crucial factor affecting the machine's quality. The quality of paper feeding refers to the absence of skewed or double-sheeted paper. If skewed or double-sheeted paper is present, at high speeds, the faulty paper will be pulled into the machine, damaging the rubber and causing significant losses for the user. The process flow is as follows: In experiments, we found that the program written according to the above process worked without problems at low speeds, but when the speed increased to 7000 r/h, skewed paper could not be locked. The main reason for this was the lag in the laser head's reaction time and the magnet's action time. During program execution, a cyclic scanning method was used. To advance the electromagnet's output, interrupts and Mitsubishi programming instructions' input/output refresh instructions were used in the design, making the electromagnet's output immediate and advancing its action time. Even at a speed of 12000 r/h, it could effectively lock faulty paper, solving a major paper feeding problem. 3.2 Clutch Pressure Design Clutch pressure plays a crucial role in printing. The accuracy of clutch pressure directly affects the quality of the printed product. Premature pressure application will soil the impression roller, causing operational inconvenience; premature pressure release will prevent the last sheet from printing a complete image, resulting in paper waste. The pressure application and release process is shown in the diagram: During printing, the plate roller and rubber roller first apply pressure, followed by the rubber roller and impression roller. In our machine, pressure application is entirely pneumatic, with each cylinder having a specific actuation time. Since the printing speed is multi-speed, ranging from 3000 to 12000 rpm, different speeds can be selected according to user needs. However, the cylinder actuation time and gear rotation angle are constant; therefore, the pressure application time varies with machine speed. To address this issue, we calculated the machine's delay time for different machine speeds based on theoretical values. Using a comparison command, when the machine's speed matches the theoretical value, a corresponding delay is applied to ensure accurate pressure application between the impression roller and rubber roller. After numerous tests, both pressure application and release have proven successful. 3.3 Human-Machine Interface Design The human-machine interface (HMI) features seven screens, including an overall graphic, fault display, machine speed and count display, water roller speed display, and plate adjustment monitoring. The fault display uses indicators; simply pointing to the positioning element creates a flashing effect, allowing the operator to easily identify the fault location with a good overall feel. The water roller speed display includes a bar chart showing the increase in water volume. Simply pressing the bar increases the water volume, facilitating monitoring as well. (See figure). 4. Conclusion The electrical design of a printing press is a system design, encompassing hardware and software design, covering a wide range. Here, I have only briefly introduced some of the more important parts; many other details exist but will not be listed here. Using a Mitsubishi control system, I found it reliable and convenient, and no major problems were found during mass production. Its PLC is feature-rich, reliable, durable, and has concise instructions. Compared to other products, Mitsubishi's overall software system interface is more user-friendly, greatly facilitating programming and maintenance. Its touchscreen and PLC have excellent compatibility, allowing users to monitor and modify programs via the touchscreen, a feature unmatched by other products. In short, Mitsubishi's industrial control components bring great convenience to designers and users alike.