Abstract: To meet the control requirements of a large metallographic specimen cutting machine, a control system combining an OMRON CPM2A PLC and an NS10-V1 touchscreen was designed for this type of machine. The control system uses the PLC as its core and the touchscreen as the human-machine interface. The PLC handles data processing and control tasks, while the touchscreen performs operation and display functions. Variable frequency speed control technology is used to continuously adjust the speed of the motor driving the cutting blade. Microstepping drive technology is used to control the movement of the stepper motors in the X, Y, and Z directions. Keywords: metallographic; cutting machine; PLC; touch panel Abstract: Facing the control requirements for the Metallographic sample cutting machine, the control system of the cutting machine was designed by the method of combining OMRON CPM2A PLC with NS10-V1 touch panel in this paper. As far as the control system is concerned, the core of the control system is PLC, the touch panel is used for the man-machine intercommunication interface, PLC dedicates itself to data processing and control, the functions of operation and display are finished by the touch panel. Frequency conversion timing technology is adopted to control the asynchronism motor of driver cuts to attain stepless timing. By making use of the electrical driver-by step, To control X, Y, and Z to three step motor. Key words: metallographic; cutting machine; PLC; touch panel 0 Introduction Metallographic analysis is an important means to ensure product quality and investigate the cause of accidents in the manufacturing industries such as machinery, metallurgy, automobile, mold, and agricultural machinery[1]. To perform metallographic analysis, metallographic samples must be prepared. With the continuous development of control technology, touch screens and programmable controllers are increasingly widely used in industrial control [2]. Touch screens, also known as PT, are a new generation of high-tech graphical human-machine interface products. They can monitor the equipment on the production site in real time with graphics or numbers, and can also set touch switches and digital input programming keys on the touch screen to control the equipment. In the control system composed of touch screen and PLC, the touch screen completes the operation, display and fault alarm of the equipment, while the PLC compiles the program according to the requirements of the production process and directly controls the equipment. This paper uses OMRON CPM2A PLC and touch screen NS10-V1 to design a control system for a large metallographic sample cutting machine. 1 Overall structure of the control system The main execution components of the control system are three stepper motors and one three-phase asynchronous motor. The three-phase asynchronous motor drives the grinding wheel to rotate at high speed through a two-stage belt drive. Since the rotation speed of the grinding wheel has a great influence on the quality of the cut sample, the grinding wheel should have different rotation speeds when cutting different workpieces. The system control frequency converter can make the speed of the grinding wheel infinitely adjustable from 0 to 3400 r/min. Three stepper motors are driven by dedicated drivers for microstepping. The grinding wheel moves up and down and the worktable moves horizontally and vertically. The core controller of the control system, the PLC, needs to provide logic control signals to make the asynchronous motor and the stepper motor move in coordination to complete the cutting action. The control system is mainly composed of five parts: touch screen, PLC, frequency converter, stepper motor driver, speed detection circuit, and position detection circuit. The block diagram of the control system is shown in Figure 1. The control system is based on the OMRON CPM2A PLC and expands the analog I/O unit CPM1A-MAD01, whose analog output is used as the frequency control signal of the frequency converter. The NS10-V1 touch screen is used as the human-machine interface of the system. The PLC centrally solves the problems of data processing and automatic control, and the touch screen completes the functions of parameter setting and display [5]. When the system is running, the user first sets the control information through the touch screen. The PLC sends control signals to the frequency converter and stepper motor driver according to the cutting mode and cutting parameters selected by the user, based on the position signal detected by the proximity switch and the speed signal collected by the speed sensor, so that the worktable, cantilever and grinding wheel move in coordination to complete the cutting task. During the operation of the system, the touch screen can display control information such as speed and cutting feed in real time, and display fault alarms. [align=center] Fig.1 Block diagram of control system Fig.2 Electric principle diagram of frequency transformer control[/align] 2 Hardware design of control system 2.1 Implementation of frequency converter control 2.1.1 Electric principle diagram of frequency converter control The system uses L100-075HFE type frequency converter. The rated input current is 20A, the rated output current is 16A, the output frequency range is 0.5～60Hz, and it is suitable for asynchronous motors with a capacity of 7.5KW (3000r/min)[3]. The frequency converter controls the motor through a main circuit connection and a control circuit connection, as shown in Figure 2. Main circuit connection: L1, L2, and L3 of the frequency converter are input terminals, connected to a 50Hz, 380V three-phase AC power supply via a leakage current protector. Output terminals U, V, and W are connected to the AC motor. Changes in the frequency converter's output frequency control changes in the motor speed; the relationship between the two is approximately linear, achieving stepless speed regulation. Input control signal connection: The PLC's output terminals 01100 to 01103 are connected to the frequency converter's intelligent input terminals. The CPM1A-MAD01 analog output module is connected to the frequency converter's O and L terminals. The 0-10V voltage signal output from the analog I/O unit controls the frequency converter's output frequency, which is proportional to the set voltage. Output signal connection: An LED is connected to output terminals 11 and 12 and the common output terminal respectively, serving as an indicator of frequency converter operation and motor overload. A buzzer is connected between alarm terminals AL0 and AL2 as the fault alarm output of the frequency converter. 2.1.2 Implementation of speed detection and PID control The rotation speed of the grinding wheel has a great influence on the quality of the cut sample. Therefore, the rotation speed of the grinding wheel should be controlled by PID closed loop to improve the speed control accuracy. First, a motor speed is set through the touch screen operation menu. The motor rotates at this speed to drive the grinding wheel to cut the workpiece. During the rotation, the photoelectric sensor samples the rotation speed of the grinding wheel in real time. After the speed signal is processed, it is sent to the high-speed counter of the PLC. After processing, the PID instruction is used to control the output of the analog I/O. The frequency converter receives the analog signal output by the PLC and controls its output frequency, thereby adjusting the rotation speed of the grinding wheel and realizing the PID closed loop regulation of the grinding wheel speed [4]. 2.2 Implementation of stepper motor control 2.2.1 Pulse output function of CPM2A The transistor output type CPM2A has a high-speed pulse output function, using two output points, 01000 and 01001. There are three cases: (1) Two-point single-phase pulse output without acceleration/deceleration: the output frequency is 10Hz～10kHz, and the duty cycle is 50%. (2) Two-point pulse output with different duty cycles: the frequency range is 0.1Hz～999.9Hz, and the duty cycle is 0～100%. (3) One-point single-phase pulse output with trapezoidal acceleration/deceleration: it is divided into two cases: pulse + direction output and acceleration/deceleration (CW/CCW) pulse output, with a duty cycle of 50%[6]. The pulse output control instructions of CPM2A, the PLUS command can control the number of output pulses, and the value range is -16777215～16777215. The SPED command can set the frequency of the output pulse, and the output frequency range is 10Hz～10kHz. The PWM command can output a variable duty cycle pulse at the specified output port. The ACC command can output a trapezoidal acceleration/deceleration pulse, which can be used for acceleration/deceleration control. The pulse output function of CPM2A can be conveniently used for stepper motor control. The cutting machine control system has three stepper motor drivers that require pulse signals. Point 01000 outputs a specified number of pulses at a specified frequency to control the feed speed and depth of the grinding wheel; point 01001 outputs a specified number of pulses to control the forward and backward displacement of the worktable; the general output terminal 01004 outputs pulses at a specified frequency (range 0-500Hz), which are amplified by a frequency multiplier (100 times) circuit before being input to the stepper motor drivers to control the left and right movement of the worktable. 2.2.2 Stepper Motor Driver Interface Circuit The stepper motor and driver are selected from 85BYG450A and SH-2H090M. The driver amplifies the signals provided by the PLC into signals that the stepper motor can accept. The PLC provides two main signals to the driver: one is the stepper pulse signal CP. Controlling the frequency of CP allows for precise speed adjustment of the motor, thereby effectively regulating the feed speed of the worktable and grinding wheel; controlling the number of CP signals allows for precise positioning of the motor, achieving control over the cutting amount of the workpiece. The other path is the direction level signal DIR. When DIR is high, the motor rotates forward; when DIR is low, the motor rotates in reverse. Figure 3 shows the wiring diagram of the stepper motor driver. [align=center] Figure 3 Connection diagram of driver Figure 4 The main program flow chart of system[/align] 3 Control System Software Design The control system software design mainly includes the design of the main control program and the automatic control program. The automatic control program mainly includes the straight cutting program, the three-step forward-one-step backward cutting program, the layer-by-layer cutting program, and the continuous cutting program. After power-on reset and system initialization, the main control program communicates with the touchscreen, receives control information transmitted from the touchscreen, and, according to the user-selected cutting mode, performs a cyclic scan of the input signals during the cutting process. After processing the input information, it outputs different signals to control the various execution components of the system, enabling them to work in coordination and complete the workpiece cutting. The functions of the main control program include power-on reset and automatic control of each cutting mode. The flowchart of the main control program is shown in Figure 4. 4. Touchscreen User Interface Design The system uses the NS10-V1 touchscreen from the NS series. The touchscreen has built-in information processing and communication capabilities, meeting the visualization needs of machine operation and monitoring. The NS10-V1 is a resistive pressure-sensitive touchscreen with up to 20MB of internal screen data memory. Its 10-inch TFT LCD display features 256 colors, high brightness, and a wide viewing angle. Fonts are stored in Unicode, enabling fast multilingual operation and displaying various fonts on a single screen. Image animation, automatic data transmission, and other processes can be controlled using macro programs. User programs and operation data can be transferred to a PC via network or memory card. The NS10-V1 touchscreen has two serial communication ports: A and B. Both conform to the EIA RS-232C communication standard and use a 9-pin D-sub connector. The CPM2A PLC has a built-in RS-232C communication port, allowing the NS10-V1 to be directly connected to the PLC via the RS-232C port. In the cutting machine control system, the NS10-V1 and CPM2A communicate via a 1:1 NT link through an RS-232C port. The NS10-V1 touchscreen uses NS-Designer software for human-machine interface development, and the completed interface can be downloaded to the touchscreen via the computer's RS-232C serial communication port. NS-Designer has a large graphics library and interface editing functions. The intelligent controls in NS-Designer can directly access the relay area inside the PLC. Users can customize the operation interface for the control system simply by dragging and dropping intelligent controls from the device library. Based on the system control and operation requirements, four human-machine interfaces were designed: the main system interface, the automatic operation interface, the cutting parameter setting interface, and the cutting parameter display interface, along with system operation instructions. The automatic operation interface is shown in Figure 5, and the parameter setting operation interface is shown in Figure 6. After the system is powered on, the touchscreen displays the startup interface. After successful password verification, the system enters the main interface, which displays the current date and time. The operation instructions can be viewed using the operation instruction buttons on the main interface. The main interface requires the user to select the cutting mode: straight cut, three-step forward, one-step backward, layer by layer, or continuous. After selecting the cutting mode, the system automatically jumps to the cutting parameter setting interface to set the cutting parameters. After setting, press the start button to start automatic cutting. During the cutting process, the touch screen automatically enters the cutting parameter display interface. The operating parameters and the working status of related components can be dynamically displayed on the touch screen. In case of abnormality, an alarm will be automatically triggered and the system fault information will be displayed on the alarm interface. [align=center] Figure 5 Main operation interface Fig.5 The interface of host operation Figure 6 Cutting parameter operation interface Fig.6 The interface of cutting parameters[/align] 5 Conclusion The innovations of this paper are: 1. In the control system of a large metallographic sample cutting machine with PLC as the core, the application of the touch screen eliminates the switches, buttons, indicator lights, and instruments in the traditional control method, saving space and improving the reliability of the control system. The human-machine interface, monitoring function, and protection measures not only facilitate operation, but also make the system performance safer and more reliable. 2. A variable frequency speed controller is used to steplessly regulate the asynchronous motor. The rotation speed of the grinding wheel is sampled in real time by photoelectric sensor. The high-speed counting function and analog PID control function of PLC are used to realize the PID closed-loop regulation of the grinding wheel speed, which improves the speed control accuracy and ensures that the grinding wheel is not damaged during the sample cutting process. 3. By controlling the coordinated movement of three stepper motors through PLC centralized logic control, four cutting modes are realized: straight cutting, three-step forward and one-step backward cutting, layer-by-layer cutting, and continuous cutting. This not only expands the cutting range, but also enables the cutting machine to cut workpieces of different sizes and hardnesses with high efficiency. 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