I. Research Background Current research and demonstration applications of open control systems, both domestically and internationally, focus on PC hardware and software development. Essentially, this is a specialized application of PCs in I/O interfaces and human-machine interfaces (see Figure 1), which has significant limitations in structure and performance. First, no independent open structure suitable for CNC machining control has been defined. The openness possessed is inherent to the computer itself, not specifically defined for the characteristics of CNC machining. The cost of this borrowing approach is complete reliance on the computer's structural framework. As a general-purpose platform, the PC computer, in both its underlying hardware design and operating system environment, does not consider the specificities of CNC machining, thus failing to fundamentally build a CNC platform. Second, open CNC systems based on industrial PCs cannot guarantee real-time performance and reliability. During operation, PCs, using general-purpose operating systems, consume significant system resources. Tasks unrelated to CNC machining may consume a larger share of the system's workload, interfering with the system's timely response to on-site machining, reducing the system's processing speed for critical control events, and increasing system overhead, all of which contribute to system instability. Third, the cost of industrial PC-based CNC systems is too high. A computer capable of meeting the speed requirements of CNC machining requires an investment of at least several thousand yuan, plus a motion control card, making cost reduction difficult. In contrast, an embedded microprocessor costs only a little over one hundred yuan, and the programmable chip used costs only around one hundred yuan. Furthermore, the real-time operating system used is free and open-source, eliminating additional costs associated with software copyright usage. All of these factors significantly reduce costs, ensuring a good performance-price ratio for patent applications. Fourthly, the network functionality of current open CNC systems in the industrial PC model is based on computer networks. Because these networks do not consider the high-volume signal data flow requirements of CNC machining and status monitoring, their speed limits restrict the system's remote network application capabilities, essentially limiting its application to inter-system program transfer. Additionally, NC+PC CNC systems generally do not provide a secondary development environment, offering only interface and parameter reconfiguration and definition functions. Some systems provide PLC programming functions and corresponding programming tools, but these are merely simple configurations of switching quantities. PC-based open CNC products, on the one hand, change the number of control axes and channels by adding or removing interfaces on the board; on the other hand, they provide users with their own system software function libraries in a packaged form, allowing users to configure the system control themselves. However, this form of openness undoubtedly increases the requirements for users' secondary development capabilities, lacks specificity, is not user-friendly, and has poor operability. This paper, based on the above problems, focuses on three aspects: the hierarchical construction of the open structure architecture, the network activation mechanism for status monitoring, and the intelligentization of the secondary development platform to conduct research on a novel open CNC system architecture. II. Hierarchical Open Structure The design goal of the hierarchical approach is to facilitate the realization of system scalability and configurability, which are two important indicators for judging the openness of a system. Scalability refers to the ability of the system to flexibly add hardware control interfaces to expand functions and improve performance; configurability refers to the ability to customize the system by configuring and compiling control software using existing underlying structural modules without increasing the hardware structure. The hierarchical architecture is based on the modular concept, but it differs from general modular structure methods. Hierarchical design not only considers the functional characteristics of each component in the system, but also the role and position of each component in the overall structural system's control links. It clarifies the inheritance and derivation relationships between components and, in fact, uses this inheritance and derivation as a standard for dividing system component elements, rather than simply relying on functional standards to plan the various elements of the system and their relationships. Hierarchical design is not only a system framework design concept, but it can be applied to all levels of the system's internal and external structures. When components are subdivided layer by layer according to required functions and performance requirements, the same inheritance and derivation relationships and hierarchical standards are applied to each substructure within the component. As shown in Figure 2, a hierarchical CNC system has a basic layer 0, which includes all components required for the system's basic control functions and the necessary hardware and software interfaces to meet general functional expansion needs. As the core structure of the system, layer 0 must have good internal and external interfaces. Internally, it must ensure smooth communication and access between components while also shielding the details of the internal structure to maintain the stability and security of the entire system. Additional layers above layer 0 are built on the extension interfaces of layer 0, expanding the system's functionality and improving control performance by supplementing hardware and opening software interfaces. Additional layers are divided into two types: supplementary extensions and parallel extensions. Supplementary expansion expands the system's functionality by opening new interfaces and configuring different control software forms on the basis of existing components. Parallel expansion adds a functional component with the same structure to fulfill a specific control requirement or open a new control channel. The significance of distinguishing between these two expansion methods lies in fully utilizing two different inheritance forms: structural inheritance and interface inheritance. Supplementary expansion follows interface inheritance, embedding itself into the interface level of system components as functional points. This feature facilitates the standardization of the implementation of individual functional expansion requirements, meeting users' custom needs at any time. Parallel expansion follows structural inheritance, replicating a completely new functional channel as a whole functional group, forming a parallel control scheme with the original hierarchy. This feature allows for the overall expansion of the open structure. The motion control module is the core component of the CNC system. Motion control components based on an open structure must possess both parallel expansion and supplementary expansion interface forms (see Figure 3). Parallel expansion is used to expand the number of control axes, deriving four-axis and five-axis components with the same functional characteristics based on basic three-axis control. Supplementary expansion is used for adding special functions, providing users with custom function implementation interfaces. Both basic components and components derived from parallel expansion possess equivalent supplementary expansion interfaces. Figure 3 illustrates the parallel expansion of a basic three-axis motion control component into four-axis and five-axis motion control components. Each motion component is further extended with three special functions: complex curve interpolation, position error compensation, and vibration state monitoring. The intelligent guidance mechanism of the secondary development platform : As shown in Figure 5, the secondary development platform model employs a guided development mode. Utilizing predefined information libraries, user functional requirements described in a special language are converted into combinations of specific strategies from these libraries. Then, a code compiler matching the CNC system's microcontroller core translates the strategy descriptions and transmits them via the computer's parallel port and download cable to the CNC system's simulation development interface. The CNC system internally has a corresponding dedicated simulation development storage area for online verification of user-customized function code. This storage area is shielded from the normal CNC program storage area to ensure the security of secondary development. Performance indicators of the secondary development are returned through verification strategies and evaluation mechanisms. The secondary development environment includes two development methods: language description and guided settings. The language description method uses a structured functional mechanism, predefining the algorithm structure for system extensions. Users only need to add their own functional requirement descriptions based on the algorithm's prompts. The secondary development platform provides an independent structured description language (syntax structure shown in Figure 6), employing object-oriented programming principles to fully describe the specific working states of CNC component objects through functional object groups. The language description scheme allows for flexible algorithmic specifications to delve into the details of the system's internal software structure, suitable for custom configuration of the system's underlying strategy. The guided setup uses a development wizard (development interface shown in Figure 7) to customize user extension needs through a graphical user interface, generally used for simpler extension development. The combination of these two mechanisms constitutes a hierarchical structure for secondary development. IV. Conclusion The open CNC system built using a hierarchical structure and microcontroller core represents a significant breakthrough in system architecture. The hierarchical concept permeates every component element of the entire system, along with the guided intelligent secondary development strategy. The hierarchical framework simplifies the development, use, and maintenance of the CNC system, truly achieving openness throughout the entire lifecycle of the CNC equipment.