Abstract: This paper designs a CNC milling machine teaching platform based on a machine controller (MP2310) and presents a specific implementation method, providing a new approach for the development of CNC teaching equipment. Using this platform, not only can traditional CNC machining training operations be performed, but also a more comprehensive understanding of the electrical control principles and motion programming of CNC machine tools can be achieved.
0 Introduction
Currently, most courses offered by universities are closely linked to practical applications. Combining theoretical knowledge with corresponding experimental courses helps students solidify their theoretical understanding and improve their independent thinking and practical skills. However, the reality is less than ideal. Laboratory equipment is often purchased too late and lags behind actual production applications. Frequent purchases of experimental equipment undoubtedly increase the university's teaching costs.
In addition, most of the experimental teaching equipment on the market is modularly produced, which is difficult to combine with the course. At the same time, students cannot understand the working principle of the equipment in depth, and the price is high. Therefore, designing experimental equipment that is consistent with the course content and closely related to actual production will greatly motivate students to learn, cultivate students' practical hands-on ability, and realize the classroom teaching model of "autonomous learning and cooperative interaction". The construction of the machine tool platform can take the actual situation of the students of this school as the point of fit, and take the course content and market technology development direction as the guide, so as to better expand students' thinking and cultivate high-quality talents with certain competitive ability [1]. Given the flexibility and innovation of this processing platform, students can design processing schemes independently according to their own ideas and innovations. In addition, under the guidance of the experimental instructors, students can deepen their understanding of each module in the CNC machining platform, which can better help students understand and master the corresponding knowledge points in the theoretical courses. It can truly promote the practical application of the knowledge learned by contemporary undergraduates, cultivate new century talents with strong hands-on ability, and become an effective aid to solve the employment problem of college students and promote the development of the national economy.
The CNC machine tools used in our school's CNC machining skills training courses are mostly produced by well-known domestic and foreign CNC manufacturers, such as the SINUMERIK series from German company SIEMENS, FANOC from Japan, Dalian CNC and Guangzhou CNC, etc. The following problems exist in the CNC machine tool processing equipment currently in use [2]:
(1) The CNC system is relatively complex, and the operators need to have certain mechanical processing knowledge and undergo a long period of professional training;
(2) The source code and module interfaces of the CNC system are not very open, making it difficult to carry out secondary development of the system;
(3) CNC systems are expensive;
To address the above issues and in accordance with the teaching requirements of undergraduate practical training at Shenzhen University, a CNC machining platform suitable for both mechanical and electrical engineering students and non-mechanical and electrical engineering students was designed.
1. Hardware Platform Design
Unlike the CNC systems developed by well-known large-scale CNC manufacturers abroad, this self-made three-axis CNC machining platform is based on a human-machine interface (HMI) and an MP2310 machine controller. The aim is to build a low-cost, easy-to-operate CNC machining system capable of processing common mechanical parts. The system's working principle is shown in Figure 1 below.
The machining platform control system employs a semi-closed-loop feed servo system. The position detection points of the machine tool's X, Y, and Z axes and the spindle are achieved through servo motor encoders. The movement of the milling platform is indirectly detected by sensing the rotation angle of the servo motors, rather than directly detecting the actual position of the milling platform using sensors such as linear scales. The designed platform system does not include mechanical transmission components, thus possessing relatively stable control performance. Although its stability is not as high as that of an open-loop system controlled by stepper motors, it is superior to a fully closed-loop system.
Figure 1. Block diagram of CNC system hardware structure
Furthermore, the errors of each component within the position loop of the semi-closed-loop system can be compensated to a certain extent through relevant algorithms. The designed semi-closed-loop CNC system for the milling machine platform has a simple structure, is easy to debug, and has relatively high precision, meeting the practical training and scientific research processing requirements of the engineering training center.
The core component of the milling machine teaching platform studied in this project is the MP2310 machine controller. The machine controller controls the precise operation of the servo motors of each motion axis by sending relevant instructions to the servo driver. The machine controller has position control functions: positioning, external positioning, origin return, multi-axis interpolation, constant speed feed and constant quantity feed, etc. At the same time, the machine controller can realize control command programming such as loop, jump, conditional branch, parallel execution, selection execution and branch through its dedicated motion language [3]. In addition, the machine controller has powerful PLC ladder diagram programming function. It can process signals such as operation panel, machine tool limit, alarm and solenoid valve using its I/O module. In addition, the machine controller can transmit relevant information with the human-machine interface.
2. CNC Milling Machine Teaching Platform
Figure 2. Schematic diagram of system operation
As shown in Figure 2, for students majoring in electromechanical engineering, the designed CNC milling machine teaching platform not only allows for traditional CNC machining training but also provides a comprehensive understanding of the electrical control principles of CNC machine tools. Since the source code of the machine controller used in this CNC machining platform is completely open, students can program PLC ladder diagrams and motion languages under the guidance of instructors. Furthermore, various parts can be machined through toolpath manipulation. Because each motion instruction written by the student is displayed on the toolpath of the machined part, the course not only demonstrates the effectiveness of experimental training but also allows for clear identification of problems, the development of corresponding improvement methods, and greater innovation. For students majoring in non-electromechanical engineering, due to limitations in training time and professional foundational knowledge, the focus is on explaining how to operate the equipment to machine parts, including workpiece clamping, tool setting, operation panel functions, and accessing part machining. Compared to traditional CNC machining centers, this self-made three-axis CNC machining platform is small in size, simple to operate, and easy for beginners to learn.
3. Design and Implementation of the Teaching Platform
The main mechanical component of the CNC machining platform primarily relies on existing, obsolete, and faulty equipment—a simple CNC milling machine—in the engineering training center. Due to the need to replace the servo system, the mechanical components connecting the servo motors of each axis require design and installation based on the servo motor specifications. Correct design and proper installation of the servo motor connecting parts can effectively extend the motor's lifespan and reduce machining errors caused by the machine tool motor's mechanical vibration. The research and technical roadmap for the teaching platform is shown in Figure 3.
Figure 3 Design Technical Route
A single motion command can be displayed on the toolpath of the machined part, demonstrating the effectiveness of the course experiment (training) while clearly identifying problems, proposing corresponding improvement methods, and achieving greater innovation. For non-mechanical engineering students, due to limitations in training time and professional foundation knowledge, the focus is on explaining how to operate the equipment to machine parts, including workpiece clamping, tool setting, operation panel functions, and selecting parts for machining. Compared to traditional CNC machining centers, this self-made three-axis CNC machining platform is small in size, simple to operate, and easy for beginners to learn.
The main mechanical component of the CNC machining platform primarily relies on existing, obsolete, and faulty equipment—a simple CNC milling machine—in the engineering training center. Due to the need to replace the servo system, the mechanical components connecting the servo motors of each axis require design and installation based on the servo motor specifications. Correct design and proper installation of the servo motor connecting parts can effectively extend the motor's lifespan and reduce machining errors caused by the machine tool motor's mechanical vibration. The research and technical roadmap for the teaching platform is shown in Figure 3.
The human-machine interface (HMI) serves as the primary device for inputting switch signals, parameters, and information. It requires the design and configuration of real-time position display and execution information for the X, Y, and Z axis servo motors of the machine tool. The configuration includes push-button switches for various functions such as mode selection, constant speed and constant quantity operation switches for each axis, automatic program operation, manual operation, machine tool auxiliary switches, and speed control knobs. It also stores machining information for various common parts and tool information for easy retrieval.
The electrical system wiring of a CNC milling machine needs to be designed holistically based on the equipment's functional requirements, including protection circuit design, fault alarm circuit design, servo fault display, cooling system, and lighting. The wire diameter design for the main circuit and control circuit should be calculated based on the actual equipment power and implemented according to relevant electrical standards. Frequently used AC high-frequency power lines and signal lines should be routed separately to avoid interference. Residual current devices (RCDs), thermal protectors, fuses, and other active electrical components should be designed and installed.
Ladder diagram programming. Ladder diagram programs perform sequential control (sequential operation) based on input signals, and start, pause, and stop operations on output signals and motion programs. Ladder diagram programs are written to perform jogging (JOG) and stepping (STEP) operations on the X, Y, Z axes and the spindle, enabling rapid movement or stepping operations on each axis during centering and tool setting.
Motion language programming. Utilizing machine controller programming languages such as axis movement commands (e.g., MOV, MVS, MCW, ZNR, etc.), axis control commands (MSEE, TIM, END, RET, IFELSEIEND, WHILEWEND, etc.), basic control commands (e.g., ABS, INC, POS, PLN, MVM, PLD, etc.), and operation and sequence control commands (+, -, *, /, SIN, COS, TAN, etc.), various common planes, curved surfaces, threads, etc., can be quantitatively machined.
4. Conclusion
In accordance with the research and practical training requirements of the Engineering Training Center of Shenzhen University, a CNC system based on Yaskawa MP2310 technology was developed. This system has the following advantages:
(1) By calling the part graphic on the human-machine interface and setting the machining parameters, the blank to be machined can be centered and tool set, and the target part can be automatically machined. This solves the bottleneck problem of those who have not undergone rigorous CNC professional training and do not have the ability to process graphics such as Pro/E, UG, and Mastercam using CNC equipment.
(2) Jog and Step buttons are set on the human-machine interface to realize rapid movement and centering tool setting operation control of each axis. Compared with the traditional CNC machine tool using handwheel to move the axis for tool setting, this design method saves equipment cost.
(3) The source code is completely open, and the ladder diagram and motion language programming are simple and easy to understand, which facilitates the secondary development of the equipment. At the same time, the machine controller can execute multiple tasks in parallel and control the movement of multiple axes (16 axes) simultaneously, providing a rich platform for students to carry out their projects (graduation) in the later stage.
