Introduction The rapid development of mobile communication technology and handheld computers in recent years, along with their widespread application in other fields, will inevitably have a profound impact on the manufacturing industry, bringing significant opportunities and challenges to digital manufacturing. Digital manufacturing in a network environment depends not only on the digitalization and informatization of upper-level management and design, but also on the digitalization and informatization of the workshop floor. We propose a new human-machine collaborative digital manufacturing model based on mobile communication technology. This model introduces wireless mobile communication technology to create a distributed human-machine collaborative work mode that fully leverages both "human intelligence" and "machine intelligence." Shop Floor Digital Assistants (PDAs) and new CNC systems constitute the two core components of this new manufacturing model. This paper only discusses the latter. A New Open CNC System Using Wireless Communication Technology The new open CNC system using wireless communication technology consists of two parts: one is a portable handheld controller, i.e., a CNC PDA; the other is installed on the machine tool, performing traditional motion control and PLC functions, called an embedded machine tool controller. The two parts communicate via Wi-Fi (802.11) or Bluetooth interfaces, and its structural block diagram is shown in Figure 1. In this model, a significant portion of the functions currently found in CNC systems will be transferred to the CNC PDA. These functions primarily include machining program creation, simulation and downloading (including manual programming and downloading large-scale machining programs from CAD/CAM workstations or desktop computers), machine tool adjustment, acquisition of machining data and machine tool status, and communication with workshop management/scheduling servers. The machine tool controller will then primarily perform real-time motion control and PLC functions. This new type of CNC is a truly embedded system, significantly reducing the size and cost of CNC systems. Simultaneously, the CNC PDA also fundamentally changes the operating mode of CNC machine tools, shifting from a machine-centric to a human-centric approach. Operators are no longer constrained by the machine tool in terms of position or posture. Operation is more convenient, more comfortable, and facilitates multi-machine operation by a single operator. [img=373,241]http://image.mcuol.com/News/080228102628540.jpg[/img] Because this specialized CNC PDA can access the internet via wireless LAN and the internet, it can obtain support from workshop or unit servers and even CAD/CAM technology centers, thus greatly enhancing the functionality of CNC systems. At the same time, because the CNC PDA is a universal CNC device, it can display the operating interface of various machine tools and control different CNC machine tools. Therefore, an operator holding a CNC PDA and several CNC machine tools can form a human-machine collaborative machining unit. This human-centered machining unit supported by digital technology is more flexible and reliable than traditional flexible machining units. Furthermore, the CNC PDA also has local database management capabilities, thus it can be used to build a distributed database for networked manufacturing in the workshop, making it a fundamental node for real-time acquisition of field data in a distributed architecture. 1.1 Hardware Structure of the CNC PDA The hardware architecture of the CNC PDA based on IEEE 802.11 mainly consists of a 32-bit embedded microprocessor, high-speed memory, FLSH electronic disk, wireless communication module, high-efficiency battery, and LCD touch screen (as shown in Figure 2). The hardware design uses the Intel Strong ARM SA-1100 32-bit RISC microprocessor, which uses the ARM SA-1 core as its system core, with a clock frequency of up to 206MHz, providing powerful processing capabilities for the CNC PDA. For communication, the CNC PDA provides a USB interface, a serial interface, and a wireless communication module. These interfaces facilitate data communication with upper-level servers or embedded machine tool controllers. The wireless module uses an Airgo transceiver chipset supporting IEEE 802.11a/b/g wireless LAN standards. This chipset can simultaneously support OFDM (Orthogonal Frequency Division Multiplexing) frequency conversion in the 2.4GHz and 5GHz frequency bands. In addition to IEEE 802.11a/b, it also supports IEEE 802.11g, which was recently adopted as a standard. [img=351,224]http://image.mcuol.com/News/080228102628761.jpg[/img] IEEE 802.11g is a wireless LAN specification that utilizes the 2.4GHz frequency band to achieve a maximum data transmission speed of 54 Mbit/s. This chipset consists of a baseband chip and an RF chip, supporting wireless LAN modes using IEEE 802.11a (5 GHz bandwidth), IEEE 802.11b (2.4 GHz bandwidth), and IEEE 802.11g. The baseband chip incorporates IEEE 802.11 MAC and PHY functions and performs MIMO signal processing. Simultaneously, the chipset embeds an IEEE 802.11 security function accelerator and Quality of Service (QoS) guarantee circuitry. As shown in Figure 2, the main device of the CNC PDA consists of a microprocessor and an IEEE 802.11 chipset. The IEEE 802.11 chipset receives control commands from the host computer, which are then processed by the baseband controller and command the wireless transceiver to emit radio waves with a bandwidth of 2.4-5.0 GHz. The connection between the IEEE 802.11 chipset and the host computer can be achieved via USB, MINI PCI, or CARDBUS, thus eliminating the need for external bridging devices. The upper-layer communication protocol of the HCI (Host Controller Interface) is handled by the host computer, while the lower-layer communication protocol is handled by the baseband layer chip and the wireless transceiver chip within the chipset. The CNC PDA can transmit data and control CNC machine tools with the 802.11 wireless network card of the embedded machine tool controller. Because the main system management functions, human-machine interaction, and CNC programming are transferred to the CNC PDA, the machine tool control part of the new CNC is much simpler than that of traditional CNC equipment, approximating a motion controller and a PLC. Its hardware and software configuration mainly meets the requirements of real-time control of the servo system and machine tool I/O functions, but it must add a wireless communication module. In terms of hardware, an embedded industrial control PC architecture based on the 104 bus is adopted. This architecture not only fully meets the above requirements but also features small size, compact structure, robustness, reliability, and low cost, making it a relatively ideal choice. 1.2 Software Structure of the CNC PDA Currently, there are many embedded operating systems used in handheld computers, such as Windows CE, Pocket OS, Palm OS, Hopen, and embedded Linux. Windows CE.NET is currently an operating system based on the Win32 application programming interface (API) for handheld computers. We use Windows CE.NET and Visual Studio.Net as the operating system platform and application development platform for the CNC PDA, respectively. The entire software system is designed according to functional modules. The system implementation is divided into three layers: the human-machine interface and system management layer, the data organization and management layer, and the communication layer for communication with the upper-level server and the lower-level embedded machine tool controller. The communication layer includes the establishment of communication links, the implementation of data link communication protocols, and the specific implementation of the presentation layer. Database management completes the creation, sorting, retrieval, and maintenance of data, enabling true mobile transmission. The system's control and management layer is the core of the entire software system. For CNC PDAs, the differences in functionality and intelligence are reflected in this layer, and the addition or removal of system functions also occurs at this layer. This includes user-operation-related functional submodules such as program compilation and interpretation, adjustment, automation, diagnostics, parameter setting, and simulation. Each functional module exchanges information with the underlying layer through wireless communication programs. Its software functional module structure is shown in Figure 3. The communication layer uses three communication methods: serial port, USB, and wireless communication port. The serial port communication method uses RS232 serial bus technology, full-duplex, with a transmission baud rate of 57600bps; the USB communication method uses USB 2.0 high-speed universal serial bus, with a transmission rate up to 480Mbps; the wireless communication method follows the IEEE 802.11 communication protocol, supporting a maximum transmission rate of 54Mbps. The application software of the entire system has functions such as control, data processing, human-computer interaction, and network communication. [img=371,288]http://image.mcuol.com/News/080228102628852.jpg[/img] 2. Wireless Communication Technology in New CNC Machines 2.1 802.11 Communication Mechanism Currently, commonly used wireless networking methods for handheld computers include GPRS, IEEE 802.11 (Wi-Fi), Bluetooth technology, and HOMERF (Home Radio Frequency). Each of these methods has its advantages and disadvantages. IEEE 802.11 is the latest version of the Wireless Local Area Network (WLAN) standard released in 1999. Compared with the Bluetooth protocol and the HOMERF standard, the IEEE 802.11 protocol has advantages such as longer transmission distance and faster transmission speed, and is the mainstream of wireless communication technology development. Like other IEEE 802.x standards, the 802.11 standard focuses on defining the Physical Layer (PHY) and Media Access Control (MAC) sublayers. The MAC layer of IEEE 802.11 provides access control for the wireless shared medium. In addition, it provides network connectivity, authentication, security, and power management functions necessary for supporting wireless transmission and site mobility. In recent years, the 802.11 standard has been expanded into the 802.11b, 802.11a, and 802.11g series, which use different physical layer standards, increasing communication rates to 11 Mbit/s, 22 Mbit/s, and even 54 Mbit/s, but without significant changes to the MAC layer protocol. 2.2 Specific Implementation Schemes for Wireless Communication in New CNC Systems In the new CNC architecture, the CNC PDA communicates with the workshop server and machine tool controller via the IEEE 802.11x communication protocol. The implementation scheme for wireless communication varies depending on the configuration of the machine tool control system. The main types are as follows: (1) Wireless communication interface circuit connecting the wireless module of the CNC PDA to the microcontroller CNC system; (2) The wireless module of the CNC PDA is connected to the RS232/802.11 converter of the traditional CNC system; (3) Communication between the wireless module of the CNC PDA and the 802.11x wireless network card of the embedded machine tool controller is achieved through the wireless communication interface circuit based on the microcontroller. In the microcontroller CNC system, wireless communication between the CNC PDA and the microcontroller is realized through a microcontroller-based wireless communication interface circuit. This microcontroller wireless communication interface circuit is composed of a single-chip transmitter chip (MICRF102) and a single-chip receiver chip (MICRF007) launched by Micrel. It operates in the internationally common ISM band 300-400MHz, has ASK modulation and demodulation capabilities, strong anti-interference capabilities, and is very suitable for industrial control. At the same time, it also has the advantages of good frequency stability, high receiving sensitivity, and low power consumption. It can facilitate serial data wireless communication between the CNC PDA and the microcontroller. The working principle of its interface circuit is shown in Figure 4. [img=231,183]http://image.mcuol.com/News/080228102628963.jpg[/img] For traditional CNC machine tools, the communication interface provided by these devices is usually a common RS-232 serial interface. How can these devices communicate with CNC PDAs? An economical and fast solution is to connect an external RS-232/802.11 converter to the serial interface of the traditional CNC system to convert the serial port RS-232 signal of the CNC device to the wireless communication signal, making it conform to the IEEE 802.11x communication protocol. This enables the CNC device to connect to a wireless local area network, effectively expanding the networking communication capability of the CNC device, and ultimately enabling stationary CNC devices to achieve wireless communication with freely movable CNC PDAs. In summary, a wireless serial port based on the IEEE 802.11 protocol is an important trend in digital manufacturing in a network environment. Its wireless communication structure is shown in Figure 5. The implementation of wireless communication between the two can actually be regarded as replacing the wired serial port connection with a wireless module, that is, treating the wireless channel composed of two wireless modules as a two-port device. For the two devices, the terminal correspondence between the wired connection and the wireless connection is the same during serial communication. The communication program for replacing the wired connection with a wireless channel is also basically the same. However, the following points need to be noted: [img=374,265]http://image.mcuol.com/News/080228102629034.jpg[/img] (1) In the communication program of the wired connection, the serial port frame format and serial port rate can be set arbitrarily. The connection cable itself has no restrictions on the above two parameters. However, in the wireless module, these two parameters are fixed values, so these two parameters must be consistent with the settings of the wireless module. (2) In the wired connection, there is no time interval between the time when the transmitting end sends data and the time when the receiving end receives data. However, the wireless module needs to perform transmit-receive conversion and clock synchronization when sending data, so there is a time interval between the time when the master device sends data and the time when the slave device receives data during wireless communication. (3) Serial communication is full-duplex when connected by wire. Communication of the wireless module is bidirectional half-duplex. Therefore, the sending and receiving times should be staggered during communication programming. For modern open CNC systems, standard and powerful wireless communication can be achieved with the support of a general operating system. Currently, the operating systems used in open CNC systems at home and abroad are either based on DOS or Windows 98/NT. DOS is a single-task operating system running in 16-bit real mode with good real-time performance, but it is limited by 16-bit real mode and it is difficult to achieve the requirements of efficient and reliable network, especially wireless network communication; Windows 98/NT is powerful, but its architecture is large and its real-time performance is poor, which cannot meet the requirements of CNC. Windows CE.NET is a new generation of embedded operating system launched by Microsoft. It has strong real-time performance, combines the advantages of DOS and Windows, is "small and exquisite", has a completely open modular architecture, supports Bluetooth and 802.11x wireless communication protocols and a user-friendly graphical interface. Considering the greater technical support and available resources of Microsoft products, combined with our years of research and application experience, we chose Microsoft as the operating system platform for the embedded machine tool controller of the new CNC system. The hardware uses an industrial control motherboard with a 104 bus and an 802.11x wireless network card to achieve wireless communication with the CNC PDA wireless module. 2.3 Introduction to the STR-6 Wireless Data Transmission Module We selected the STR-6 wireless transceiver module manufactured by Shanghai Sanbo Technology Co., Ltd. to realize wireless communication between the CNC PDA and the traditional CNC machine tool's RS-232 serial port. It features low-power transmission, high anti-interference capability and low bit error rate, long transmission distance, multiple channels, and a large buffer. It provides three interface methods: standard RS-232, RS-485, and UART/TTL levels, and can be directly connected to computers, user's RS-485 devices, microcontrollers, or other UART devices. Two computers connected to the STR-6 wireless transceiver module can achieve wireless transmission within a distance of up to 500 meters. The working principle diagram of the wireless module is shown in Figure 6. [img=287,104]http://image.mcuol.com/News/080228102629095.jpg[/img] STR-6 Wireless Transceiver Module Communication Implementation Method: Before sending data, wireless module A first sends a handshake signal to the other party, wireless module B. After receiving the handshake signal, wireless module B sends back an acknowledgment signal. If wireless module A does not receive a correct acknowledgment signal, it indicates that the two parties have not established a normal wireless communication connection. Wireless module A then continues to send handshake signals until it receives a acknowledgment signal. After receiving the acknowledgment signal, wireless module A begins to send data. Based on the received information, wireless module B stores the data in the path specified by the user, completing the entire wireless communication process. Conclusion Workshop digitization is a crucial foundation for enterprise manufacturing digitization and informatization, and it is also a challenge we face. It is unrealistic to expect to eliminate human involvement and rely entirely on computer and automation technologies to achieve manufacturing digitization and informatization. Only by introducing current wireless and mobile communication technologies into the manufacturing industry, enabling anytime, anywhere information access and human-machine communication, and seamlessly combining human and machine intelligence to form a human-centered, collaborative manufacturing model, can this goal be truly achieved. The development of a new type of CNC system with CNC PDA functionality, employing wireless communication technology, will lay a solid foundation for realizing this innovative manufacturing model.