With the introduction of Germany's Industry 4.0 , intelligent manufacturing has become the main direction of manufacturing technology development. China's Made in China 2025 and the US Industrial Internet initiatives have both clearly defined the core position of intelligent manufacturing from a national strategic perspective, and the exchange of technologies and the integration of standards among them are constantly deepening. In particular, China's transformation from a manufacturing giant to a manufacturing powerhouse is more urgent. Focusing on the development of intelligent equipment and products, and promoting the intelligentization of production processes, has become crucial to achieving the goals of Made in China 2025. Among the ten key areas are high-end CNC machine tools and robots, making CNC technology for intelligent manufacturing a priority issue that needs to be addressed.
The core of achieving intelligent manufacturing lies in the deep integration of information processing and physical processes. Traditional manufacturing processes primarily rely on production equipment to manufacture products in a physical space. The equipment and processes themselves generate little or no data, and even the limited data is fragmented. Improvements in manufacturing efficiency and automation mainly depend on physical equipment. With the development of network information technology, this has gradually evolved into a collaborative and interactive model between people, people and machines, and machines and machines through the Internet of Things (IoT) and the Internet. This further establishes digital models of physical equipment and processes, continuously simulating and optimizing them to improve production efficiency and effectiveness. This is the so-called CPS (Cyber-Physical Systems) fusion system. CNC systems for intelligent manufacturing must be built on the foundation of CPS. They are no longer merely control systems for machine tools, but rather become intelligent nodes in factories and even entire smart cities.
Technical routes to achieve intelligent numerical control
There is no universally accepted definition of intelligent manufacturing; relevant literature primarily describes it from the perspective of its characteristics. In 1988, Japan's Ministry of International Trade and Industry (MITI) proposed the concept of an intelligent manufacturing system (IMS), and in 1989, a formal international cooperation project document was formed. The aim was to jointly develop a new generation of manufacturing systems through international cooperation to meet the challenges of global change in the 21st century, given the trend of globalization. The IMS project's vision of the factory of the future in the 1990s largely encompassed the essence of intelligent manufacturing today.
Intelligent manufacturing is a system; it's not merely a combination of intelligent technologies, nor is it limited to the production and manufacturing business. It integrates the latest technologies across the entire value chain, encompassing R&D, manufacturing, and customer service. Therefore, the intelligentization of CNC systems cannot be considered solely from the perspective of improving process flexibility, quality, and efficiency within the manufacturing process itself; it must be considered from the perspective of the entire system. Especially for Chinese CNC system manufacturers and research institutions, whose traditional manufacturing technologies lag behind those of advanced developed countries, how to surpass them under the guidance of new models and concepts has become a new path for the development of CNC systems. "Internet+" based on internet and computer technologies is precisely a crucial breakthrough point in technological upgrading. How to leverage China's advantages in the integration of the internet and manufacturing will become an important path for the transformation and upgrading of the manufacturing industry.
The China Cyber-Physical Systems (CPS) white paper proposes four core elements: "one hardware" (sensing and automatic control), "one software" (industrial software), "one network" (industrial network), and "one platform" (industrial cloud and intelligent service platform). These elements address the complexity and uncertainty in manufacturing and application services through four processes: state perception, real-time analysis, scientific decision-making, and precise execution, thereby improving resource allocation efficiency and achieving resource optimization (Figure 1). State perception involves sensing the operational state of the physical world through various sensors; real-time analysis involves transforming data, information, and knowledge through industrial software; scientific decision-making involves facilitating the flow of data and knowledge sharing across heterogeneous systems through a big data platform; and precise execution involves providing feedback responses to decisions through mechanical hardware such as controllers and actuators. CPS exhibits a clear hierarchical structure, ranging from a single intelligent component or product to an entire smart factory. The construction of CPS is a process of evolving from small, localized systems—single components, single devices, single links, or single scenarios—to larger and more complex systems. CPS is divided into three levels: unit level, system level, and system-of-systems (SoS) level. Although CNC machine tools can be viewed as composed of multiple units such as spindle units, feed units, and cooling systems at the unit level, these units do not have the function of independently undertaking tasks in the system. Therefore, it is easier to understand the three-layer architecture of manufacturing systems and manufacturing ecosystems by viewing the CNC system as a unit-level CPS.
Figure 1. The essence of CPS
Driven by internet technology, an increasing number of new business models are emerging. The most representative of these is the "sharing economy," which has brought us new business formats based on the sharing model, such as ride-hailing apps and apartment rental apps in the automotive and real estate sectors. How can the internet and new economic models be implemented in the manufacturing industry? How to adapt to the "sharing economy" will become an important research topic.
The advent of smartphones has triggered explosive growth in internet-related industries, with new business models constantly emerging. Technological breakthroughs in smart terminals have played a crucial role in this growth, as all internet-related applications and technologies rely on the connections established between people and smart terminals. In the machine tool industry, the smart terminal connecting people and equipment is precisely the CNC system, the brain of the CNC machine tool. Therefore, developing CNC systems for intelligent manufacturing based on a CPS (Computer-Side Platform) architecture and building a manufacturing ecosystem around it is a feasible path to achieving intelligent manufacturing.
Open interconnection of CNC systems
From the emergence of the first numerical control system in the 1850s to modern open numerical control systems, there have been many major changes, but these changes have been limited to the innovation and upgrading of single-machine functions and unit technologies. Progress in networking technologies for equipment has been slow.
In recent years, CNC system products with different structural levels have emerged, including complete systems, semi-finished products, and core software, as shown in Table 1. For example, the German company ISG only provides the intellectual property rights for the CNC software, allowing users to configure or further develop their own branded CNC products. The US National Institute of Standards and Technology (NIST) and other open-source organizations provide open-source Linux CNC software, whose source code is freely available to users and can be developed under the GNU shared license. German companies PA (PowerAutomation) and Beckhoff provide modular CNC system platforms, allowing users to configure them to create their own branded CNC products. The US company DeltaTau provides PMAC motion control cards and related software, allowing users to develop their own CNC systems, etc.
Table 2 describes the changes in CNC system interconnection methods: CNC system interconnection methods have gradually upgraded from the earliest serial communication to Ethernet communication. The communication ports and protocols of different types (brands) of CNC systems vary greatly. Table 1 also shows that at different times and stages, CNC system manufacturers have designed and provided communication methods and protocols for different application goals. For example, the earliest I/O method was used for handshaking and collaborative work with other devices. In the second stage, during the serial communication period (in fact, many domestic and foreign manufacturers are still using this technology), mainly due to the limited memory of CNC systems, online NC file downloads were used when encountering large programs, i.e., the most basic DNC function. This method was widely used by domestic CNC manufacturers due to its low technical threshold, simplicity, ease of implementation, and low cost. However, this also limited the application of network technology in domestic CNC systems, resulting in extremely limited functionality. In the third stage, mid-to-high-end CNC systems such as Fanuc and Siemens were equipped with Ethernet interfaces. For example, Siemens CNC systems provided standardized LAN communication protocols based on OPC, and data acquisition and file transfer moved towards standardization. However, the system design and network protocol design at this stage were still limited to LAN applications and were more based on the traditional DNC design concept. The network transmission functions of CNC systems at this time were mainly aimed at data uploading and downloading (such as backup/restore, NC program download and upload, parameter setting, etc.) to meet the goal of point-to-point or LAN interconnection applications. However, with the advent of the Internet era, the above functions and their protocol forms seemed somewhat inadequate.
Table 2. Changes in CNC System Interconnection Methods
Taking the OPC protocol released in 1996 as an example, its original purpose was to abstract PLC-specific protocols (such as Modbus, Profibus, etc.) into standardized interfaces and provide standardized connection and communication support to systems such as HMI/MES via Ethernet. This communication for local area networks has the following disadvantages: platform limitations, difficulty in firewall penetration, OPC cannot support the Internet, weak security functions, and data integrity cannot be guaranteed.
1. Platform limitations: Cross-platform compatibility is virtually impossible. OPC is developed based on Microsoft's COM/DCOM technology and can only run on Windows systems. It is not supported on embedded platforms such as Linux, which are popular in today's industrial control field. Furthermore, in early 2002, Microsoft announced the cessation of COM technology development, and the technological foundation of OPC faced obsolescence.
2. Firewall penetration is difficult. OPC communication is difficult to complete when crossing computer boundaries. Users need to open many ports in the firewall to allow DCOM communication to pass through, which seriously affects the security and reliability of the entire network.
3. Lack of support for Internet applications such as the Web; OPC cannot support the Internet.
4. Weak data structure support: OPC cannot support complex data specifications such as structured data.
5. Weak security features: Security features that are very important in network applications, such as device authentication and data encryption, were not designed in the old OPC protocol.
6. Data integrity cannot be guaranteed. In the event of communication interruption or abnormality, the OPC protocol cannot guarantee the accurate delivery of transmitted data, and data communication is often damaged and cannot be recovered.
To address the aforementioned shortcomings, the fourth stage of communication design saw the emergence of protocols such as OPCUA and MTConnect, designed for Internet applications.
OPCUA is an extension and upgrade of the original OPC protocol by the OPC Foundation. It first addresses the dependency issue on operating system platforms and provides greater support for applications in the internet environment. OPCUA solves network security and firewall penetration problems through tunneling technology and supports emerging communication technologies for internet applications, such as publish/subscribe. Its technical framework is shown in Figure 2.
Figure 2 OPCUA Architecture
MTConnect is an open-source, free machine tool communication standard initiated by the American Machine Tool Technician (AMT) and developed in conjunction with world-leading manufacturing companies such as General Electric. It aims to improve interoperability between manufacturing equipment, devices, and software applications from different manufacturers and software vendors. Its technical framework is shown in Figure 3. However, the system architectures of major CNC manufacturers differ, and their parameters, file naming conventions, and even operating systems vary. Standardizing a vast number of CNC devices and enabling a large number of client-side applications such as ERP and MES to work collaboratively remains a long and arduous journey.
The MTConnect protocol only specifies communication between the client and the device, but it does not address internet applications and their interoperability interfaces. Like OPCUA, its fundamental problem is that it still relies on point-to-point communication, but internet applications require more than that. Therefore, the MTConnect protocol needs a set of cloud application specifications to supplement it, enabling truly smooth internet applications for CNC machine tools.
Figure 3 MTConnect Architecture
Development of intelligent numerical control systems
Against the backdrop of Industry 4.0 and "Internet Plus," the future development and competition of CNC systems have undergone new changes. In China, more competition will focus on how to leverage the advantages of the Internet to infinitely expand the computing power of CNC systems. Furthermore, understanding emerging business models such as the sharing economy and rationally creating functions that are compatible with them will become an important trend for the future.
1. Requirements for Intelligent CNC Systems
Figure 4. The demand for intelligent CNC machine tools
From the perspective of manufacturing technology itself, the intelligence of CNC systems is carried out in four aspects as shown in Figure 4: intelligent operation, intelligent machining, intelligent maintenance, and intelligent management.
Machine tools employ various sensors during machining, leveraging real-time monitoring and compensation technologies to further enhance performance. Companies like Mazak and Okuma in Japan offer many advanced technologies in intelligent manufacturing, such as spindle vibration damping and intelligent collision avoidance. Shenyang Machine Tool's i5 CNC system provides feature-based programming and graphical diagnostics.
2. Cloud-based CNC system
Building upon cloud computing, the University of Stuttgart in Germany proposed a "glocalized" cloud-based CNC system, as shown in Figure 5. As can be seen, the human-machine interface, CNC core, and PLC of the traditional CNC system are all moved to the cloud. Only the machine tool's servo drive and safety control are retained locally. Communication modules, middleware, and Ethernet interfaces are added to the cloud, communicating with the local CNC system via a router. This creates a "digital twin" of each machine tool in the cloud, allowing for configuration, optimization, and maintenance, greatly facilitating machine tool use. This achieves what is known as Controller as a Service (CaaS).
Figure 5. Concept of cloud-based CNC system
A digital twin is a digital mirror image of a specific physical object, including design specifications and engineering models describing its geometry, materials, components, and behavior, as well as production and operational data specific to the entity it represents. It becomes an inseparable "companion," representing the latest and most accurate real-time mirror image of the physical object's attributes and state, including shape, position, state, and motion. A machine tool's digital twin can exist simultaneously in multiple information domains, possessing multiple "avatars." During the product design phase, it plays a role in scheme demonstration, structural and functional verification, and performance parameter optimization; during the factory planning phase, it participates in layout planning, system optimization simulation, and other tasks; during the operation phase, it performs processing status judgment and prediction, enabling intelligent control and preventative maintenance of the machine tool until the product is scrapped, and even continues to exist afterward.
3. Internet-based numerical control systems and their ecosystem
In the context of the internet, CNC systems must become transparent intelligent terminals capable of generating data, making the manufacturing process and its entire lifecycle "data transparent." This "transparency" of the intelligent terminal enables transparency in the manufacturing process, not only facilitating parts processing but also generating real-time data for management, finance, production, and sales. This facilitates resource integration and information interconnection across a range of production and management aspects, including equipment, production planning, design, manufacturing, supply chain, human resources, finance, sales, and inventory.
Shenyang Machine Tool Group has established a world-leading machine tool ecosystem around the i5 intelligent machine tool. Figure 6 is a schematic diagram of data generation and application of the i5 intelligent machine tool. Through the "transparent" i5 intelligent system, the i5 intelligent machine tool can be online in real time, providing accurate data for the above management process and becoming the foundation of the new manufacturing industry.
Figure 6 shows the data generation and application of the i5 intelligent machine tool.
Figure 7. Intelligent machine tool Internet application framework based on iSESOL
iSESOL (i-Smart Engineering & Services Online) is a cloud manufacturing platform developed by a subsidiary of Shenyang Machine Tool. For example, as a cloud-based capacity sharing platform, users can list their idle capacity on the iSESOL platform. Users with capacity needs can quickly obtain manufacturing capabilities without purchasing equipment. In this way, capacity providers can generate revenue from their idle capacity, while capacity demanders can obtain manufacturing capabilities at a lower cost. Both parties maximize their benefits through this sharing. Undoubtedly, this model will become an important form of "Internet + in manufacturing."
Figure 7 illustrates the intelligent machine tool internet application framework based on the iSESOL platform. All i5 intelligent devices connect to the iSESOL network via the iPort protocol, while non-i5 devices (such as OPCUA terminals or MTConnect terminals) can connect through the iPort gateway. Cloud-based applications such as ERP, MES, and remote dashboards achieve unified access to remote devices through iSESOL's aggregated real-time data and access interfaces. iSESOL provides data dictionary mapping for different devices, unifying access methods. Cloud-based applications can subscribe to various events and data information using standard service or parameter naming, achieving unified device access. End users can install applications on different terminals to access various internet applications on the devices. The production capacity collaboration ecosystem built on this platform currently connects to several thousand machine tools, with approximately 2,500 connected daily.
4. Conclusions and Outlook
The intelligentization and networking of CNC machine tool systems is an inevitable trend. The development of intelligent CNC systems is guided by the concept of CPS, and the intelligence of CNC machine tools is realized from the perspective of the whole system through networks and platforms.
The development of intelligent manufacturing is a gradual process. Currently, there are different understandings of intelligent manufacturing, and no universally applicable solution exists. The innovation and successful implementation of CNC machine tool business models inevitably depend on the intelligence and networking of CNC systems. Future CNC systems will increasingly integrate the internet into the manufacturing process. Through the accumulation, transmission, and mining of data, more and more intelligent manufacturing capabilities will emerge, and transparency and sharing will bring about revolutionary changes to the manufacturing industry.
