Abstract: PLC stage programming technology is an advanced regular design for PLC ladder diagram design. It is proved by experiments that the stage programming method makes the PLC control software have a good corresponding relationship with the working sequences of hydraulic-pressure and landscape orientation machinability, and makes the programming and debugging work more efficient. Compared with the ladder programming method, the software edited by this method has fewer sentences, less scanning time and higher effective performance in real-time control. Key words: PLC; stage programming technology; control system In machine tool control systems, multi-process machining systems have many actions. When using traditional relay control, a large number of relays are required, the wiring is complex, and fault diagnosis and equipment maintenance are relatively troublesome. Therefore, the traditional relay control method has been largely eliminated in machine tool control systems, and replaced by digital control systems with PLC and microcontroller as the core. Among them, PLC is widely used in machine tool control systems due to its advantages such as simple programming, convenient use, short design, construction and debugging cycle, strong anti-interference ability, high reliability, and easy realization of mechatronics[1]. However, many control software still follow the logic control idea of ​​low-voltage electrical appliances, and transplant the original relay control principle diagram into ladder diagram software, resulting in a large program, complex logical relationship between control variables, which is very difficult to analyze, and it is easy to overlook some issues that should be considered; when modifying a certain local circuit, it may have unexpected effects on other parts of the system. Therefore, the modification of the ladder diagram is also troublesome, and it is difficult to get a satisfactory result[3]. Level 1 Language Principle In sequential logic control, the working process of the equipment is usually decomposed into several action procedures according to the process flow. Then, according to the requirements of process control, the transition conditions between each action are set in advance, and the action is transferred from one action to the next action, and so on, to complete the entire process flow[2]. In a hierarchical program, the program unit that determines the action status and transition of each process is called a level, which corresponds one-to-one with the process. The transition conditions between processes are called level transition conditions. A level is a program block, consisting of three parts: process processing, transition conditions, and transition direction (Figure 1). Process processing includes the work to be completed within the level; transition conditions determine whether the action of this process has ended; and the transition direction specifies the next process number (level number) to be entered. When the level in the action is ON, the action content is processed, and the output in that level may be valid; otherwise, no output will be output. The entire control program consists of level modules. A level module is a sub-process in the process flow, containing all the levels that implement that process. In the program, each level is given a unique number, i.e., a level number, which can be regarded as a label for the program execution order. [align=center]Figure 1. Structure and Representation of Levels[/align] Level-based language is a process-oriented programmable controller language. It decomposes the control process into several action steps (levels) according to the process flow, compiles the processing program (level program) for each step, and connects these processing programs according to the end conditions and transfer direction of the step, which is the level-based program. It is designed based on action units. 2 Control of the Hydraulic Longitudinal and Transverse Feed Machining System The action requirements of the hydraulic longitudinal and transverse cylinder feed machining system are as follows: 1) Start the hydraulic oil pump, issue the "forward" command to the longitudinal cylinder, the longitudinal cylinder drives the tool to fast advance and feed, and after the feed is completed, it stops at the end position and issues a signal to make the transverse cylinder perform the corresponding action. 2) Immediately afterwards, the transverse cylinder drives the tool to fast advance and feed, after the feed is completed, it quickly returns to the original position and issues a signal to make the longitudinal cylinder quickly return to the original position, and the whole cycle ends. According to the control requirements and the hydraulic system diagram of the hydraulic longitudinal and transverse cylinder feed machining system (Figure 2), draw the working cycle diagram of the hydraulic longitudinal and transverse cylinder feed machining system (Figure 3). Based on the action requirements and working cycle diagram of the hydraulic longitudinal and transverse cylinder feed machining system, the actuator cycle table and the detection element status table are obtained (Table 1). [align=center] Figure 2 Hydraulic system diagram of the hydraulic longitudinal and transverse cylinder feed machining system Figure 3 Working cycle diagram of the hydraulic longitudinal and transverse cylinder feed machining system[/align] Table 1 Actuator cycle table and detection element status table The actuator cycle table is the on/off table of hydraulic solenoid valves YV1～YV2. The detection element status table is obtained by referring to the working cycle diagram and according to the changes in the status of the detection elements in each program. The writing rules are as follows: In a certain program, if the detection element is in the original state, it is recorded as "0" state; if the element is in the excited state, it is recorded as "1" state; if the element changes from 0 to 1 or 1 to 0, it is recorded as 0/1 or 1/0 respectively. In this system, limit switches SQ1～SQ2 are used as detection elements. Their status in each program is shown in the detection element status column of Table 1. 3. Design of Control System Using Ladder Language This equipment uses a SE-11 PLC from Guangyang Electronics (Wuxi) Co., Ltd., which supports ladder language, to control the hydraulic longitudinal and transverse cylinder feed machining system. The design steps are as follows: 1) Draw a flowchart of the machining process based on the action requirements and work cycle of the hydraulic longitudinal and transverse cylinder feed machining system. The control flow of the PLC for this machining process is shown in Figure 4. 2) Determine the input and output signals using Table 1 and Figure 4. First, connect the external input signals (from buttons, limit switches, and other control signals from the field) to the terminals of the PLC's input interface, i.e., connect them to the PLC's input relays; then connect the PLC's output signals (signals controlling external contactors, solenoid valves, etc.) to the external actuators, resulting in the external wiring diagram controlled by the PLC, as shown in Figure 5. 3) According to the machining flowchart and combined with the actuator cycle table and the detection element status table, following the ladder programming rules, design the ladder diagram of the hydraulic longitudinal and transverse cylinder feed machining system using the PLC's internal relays, counters/timers, etc., as shown in Figure 6. Each input/output coil, internal relay coil and contact, special function unit, timer/counter, etc. of the PLC has a specified number and address. [align=center] Figure 4 Control Flowchart of the Hydraulic Longitudinal and Transverse Cylinder Feed Machining System Figure 5 PLC External Wiring Diagram Figure 6 Ladder Diagram of the Hydraulic Longitudinal and Transverse Cylinder Feed Machining System[/align] 4 Conclusion Ladder programming language design is simple, standardized, and universal, making it easy for beginners to accept. For experienced engineers, ladder programming language design can also improve design efficiency, and the debugging, modification, and reading of programs are also very convenient. Therefore, it has strong promotional value in some complex control systems. Author's innovative viewpoint: Applying PLC ladder programming technology to mechanical hydraulic control systems enables a better correspondence between control software and process actions, resulting in high programming and debugging efficiency, and improving the reliability of the control system and the flexibility of the machining system. Economic benefits: From the perspective of improving production efficiency, the direct economic benefit is 210,000 yuan. References: [1] Hu Xuelin. Programmable Controller Application Technology [M]. Beijing: Higher Education Press, 2000. [2] Wan Jiaju, Zhao Zhiying, Luo Liangling. Application of Sequential Control Design Method in Combination Machine Tools [J]. Microcomputer Information, 2005, 12-1: 30-32. [3] Liao Changchu. PLC Programming and Application [M]. Beijing: Machinery Industry Press, 2004.