Open CNC System--The Mainstream of New Generation NC

As a basic equipment necessary for manufacturing complex, high-quality, high-precision products, computer numerical control (CNC) systems have become an important part of today's advanced manufacturing technology. However, the hardware modules and software structures that make up the CNC system (represented by FANUC, SIEMENS, etc.) on the market today are mostly proprietary and incompatible with each other. The interaction modes and communication mechanisms between the modules of the system are also different. This results in the relative independence of the control systems of different manufacturers and the closure of each other.

With the advancement of technology and the intensification of market competition, this special-purpose CNC system has increasingly exposed its inherent defects. On the one hand, the poor interconnection capability between the various control systems affects the mutual integration of the systems, the different styles of operation and the extensive use of special parts, which not only increases the user training costs, but also gives the numerical control equipment users (end users of the NC system). ) brings a lot of inconvenience; on the other hand, the closure of the system makes its expansion and modification extremely limited, causing the CNC equipment manufacturer (NC system intermediate users) to rely on the system supplier, and it is difficult to put their own expertise, technology Experience is integrated into the control system and forms its own product features, which will not help to improve the competitiveness of the host products. In addition, the dedicated hard and software structure also limits the continuous development of the system itself, making the system development investment, long cycle, high risk, slow update, and is not conducive to the technological progress of CNC products. In short, this status quo of numerical control system can not adapt to the changes and competition in the manufacturing market today, nor can it meet the needs of modern manufacturing to the development of information technology and agile manufacturing mode.

1 The concept and approach of CNC system opening

concept

The main purpose of the research on open CNC system is to resolve the contradiction between frequent changes and closed control systems, so as to establish a unified reconfigurable system platform and enhance the flexibility of the CNC system. In layman's terms, the purpose of openness is to make the NC controller similar to today's PCs. The system is built on an open platform and has a modular organization structure, allowing users to select and integrate as needed, and to change or expand the system. The function quickly adapts to different application requirements, and the functional modules that make up the system can be sourced from different component suppliers and compatible with each other.

In fact, the open CNC system based on the above guiding principles is also in line with IEEE's definition of open systems: it can run on multiple platforms, interoperate with other systems, and provide users with a unified style of interaction. According to this definition, an open CNC system should have the following basic characteristics:

Interoperability. By providing standardized interfaces, communication and interaction mechanisms, different functional modules can run on the system platform with standard application interfaces, and achieve equal interoperability and coordination.

portability. The functional software of the system has nothing to do with the device, that is, the application of a unified data format, interaction model, and control mechanism, so that the functional modules constituting the system can be derived from different developers, and the functional modules can be operated through a consistent device interface. Above the hardware platform provided by different vendors.

The grades are all suitable. The functions and scale of the CNC system can be flexibly set and easily modified. It can increase the hardware or software to form a more powerful system, and can also reduce its functions to adapt to low-end applications.

Complementarity. It means that the selection of each hardware module and function software that constitutes the system is not controlled by a single supplier, and can be replaced according to its function, reliability and performance requirements without affecting the overall coordinated operation of the system.

Open approach

How to make the traditional dedicated closed system open to the outside, different system developers and research institutions have proposed some solutions. According to the different levels of openness, there are three ways to divide them. Their open levels are different, the difficulty is different, and the open effects obtained are also very different. As shown in Figure 1, the dotted line divides the control system into two layers: the Man-Machine Control (MMC) layer and the control kernel layer. Among them, the control kernel is the core part of the CNC system to complete the scheduling and control of the real-time processing process, which is generally associated with the real-time nature of the system. The three methods are based on different treatments open to these two levels.

Figure 1 Open approach to the control system

a, open the human-machine control interface.

This approach allows developers or users to construct or integrate their own modules into the Man-Machine Interface (MMI). This method provides users with the flexibility to formulate the operation interface and operation steps applicable to their specific requirements, and is generally used in a system based on a PC as a graphical human-machine control interface.

b, open system core interface.

In addition to providing the open capabilities of the above methods, this method also allows users to add their own special modules to the control core module. Through the core interface of the open system, users can add their own unique control software modules to the kernel interface pre-released by the system according to certain specifications.

c, open architecture

The open architecture solution is a more thorough open plan. It attempts to provide a full range of openness from software to hardware, from the human-machine interface to the underlying control kernel. Under the guidance of open architecture standards and a series of specifications, people can configure on-demand assembly systems that are versatile, high-performance, price-controllable, and independent of a single vendor.

From the implementation method, PC-NC (Personal Computer Numerical Control) is a relatively realistic approach to NC openness. That is, on the basis of the PC hardware platform and operating system, the commercially available software and hardware cards are used to construct the numerical control system function. However, the operating system of the existing PC lacks real-time performance, and reliability still needs to be improved. The PC-NC can be mainly classified into three types: the NC board is inserted into the PC, the PC board is inserted into the NC device, and the software NC. The form in which the NC board is inserted into the PC is to insert the motion control board or the entire CNC unit (including the integrated PLC) into the expansion slot of the personal computer. The PC is not real-time processed, and the real-time control is undertaken by the CNC unit or the motion control board. This method can easily realize the openness and personalization of the human-machine interface, that is, the opening of the first level; on this basis, The programmability of the inserted NC board can partially realize the opening of the system core interface, that is, the opening of the second level mentioned above. This form of PC board insertion into the NC is mainly used by some large CNC controller manufacturers. There are two reasons for this: First, many users are familiar with their products and are used to it; on the other hand, controller manufacturers cannot give up their traditional proprietary CNC technology in a short period of time. Therefore, this compromise has emerged by providing a PC front-end interface in a traditional CNC that is flexible to PC processing. Obviously, the NC core of this system maintains the original closedness, so it can only achieve the opening of the above first level. The so-called software NC refers to the functions of the NC system, such as compiling, interpreting, interpolating, and PLC, all of which are implemented by software modules. With the support of application software (such as Visual C++, Visual Basic, etc.), such systems can be properly organized, divided, standardized, and developed by using existing operating system platforms (such as DOS, Windows, etc.). Realize the opening of each of the above levels.

It should be pointed out that the introduction of the concept of open systems into the development needs of the CNC system indicates that the conditions for the system to become open are becoming more mature. However, the open architecture CNC system with open system features is still in the growth stage. The scientific, clear definition and corresponding normative standards of the open architecture CNC system are still in the process of further development and improvement.

2 Research trends

The emergence of an open architecture of control systems will lead to the creation of a new generation of controllers and will be a major pillar of future manufacturing. Therefore, Europe, the United States and Japan have carried out a lot of research work and introduced their own open architecture specifications.

In 1989, the US government-sponsored NGC (Next Generation Controller) research program, which was widely adopted as a standard proposal for open structure controllers, received widespread attention. The significant difference between NGC and traditional CNC is that it is based on "open architecture", whose primary goal is to develop the "Specification for an Open System Architecture Standard" (SOSAS), which is used to manage workstations and machine tools. Controller design and structural organization. NGC plans to complete prototype research in 1994 and transfer it to industrial development applications. For example, companies such as Ford, GM and Chrylser of the United States jointly proposed the development plan of OMAC (Open Modular Architecture Controller) under the guidance of the NGC program. The program defines a specification for an open, modular architecture controller for the automotive industry that inherits the VMS of the VME series. Although it is not perfect at present, due to the standardization of the "API interface layer", users can fully utilize their own initiative, so that they can load the unique functions they need; even they can load Windows OS, and existing CAM, etc. The PC resources are transplanted into the controller; at the same time, the real-time database can realize the high efficiency and portability of the data, and has extremely high practical value. The benefits of implementing OMAC are that it reduces the cost of investment and production cycles, and it is easy to integrate market-based general-purpose technology with the user's own proprietary technology, so that controllers for new programs can be efficiently reconstructed. New technologies can be implanted in time.

In parallel with NGC, a long-term research project for the 21st century manufacturing industry in Japan, the Intelligent Manufacturing System (IMS), is also under discussion. The project is led by the Japanese industry and also works with other countries. In 1990, the Japanese IMS Center was established. In 1994, the 10-year IMS program calendar was published and started. Most of the plans are related to advanced manufacturing systems and automation, such as multi-functional machine systems, agile manufacturing systems, knowledge-based artificial intelligence expression systems and intelligent monitoring systems. Wait. These plans will have a profound impact on the future development of control system technology. At the same time, Japan has launched another open system plan, the Open System Environment for Controller (OSEC) program. Its main content is an open system based on the PC platform, the purpose is to determine the structure of "open controllers that do not depend on specific vendors." This program was initiated by three machine tool companies (Toshiba Machine, Toyota Machine, Yamazaki) and three information system development companies (IBM, Mitsubishi Electric, SML), and proposed a layered model of the controller, which clarified the modules of each level. Features, service content and interface specifications. In addition, a new NC language, the FADL language, is defined. At present, the organization has developed into an association dedicated to promoting the openness of the CNC system, involving 18 companies and a community.

In the face of the situation in the international market and the development trend of the manufacturing industry, the countermeasures adopted by Europe are: unite to take advantage of each other's strengths, actively absorb various new technologies in the world, and develop products that satisfy the world market, especially the Asian market. To achieve this goal, we must first have a new type of controller that can accommodate or combine technologies. As early as November 1987, with the support of the German Machine Tool Plant Federation (VDW), the Institute of Manufacturing Control Technology (ISW) of the University of Stuttgart studied the "future control technology" and proposed a new controller solution. The principles are: configurable, modular and open. In October 1991, an Open System Architecture for Control within Automation System (OSACA) was launched. It is a cooperative project of European countries and is based on improving the machine tool and control system manufacturers in the world market. Competitiveness. The project duration was from May 1992 to May 1996 and lasted for 48 months. Its main task is to develop an open control system structure that is independent of the manufacturer. The success of the OSACA program will reduce time-to-market for new products, provide greater customization and flexibility, and reduce development, maintenance, training and documentation costs.

3 Conclusion

The use of an open control system structure is beneficial to both the manufacturer and the user of the CNC system. For control system manufacturers, they can establish extensive cooperation on a common standard platform to achieve collaborative development, greatly shortening the system development cycle, reducing costs and enhancing product competitiveness; for machine tool manufacturers, not only can Need to configure the most suitable control system, you can also integrate your own unique software into the system controller to form your own product features; end users can be said to be the biggest beneficiaries of the open control system, they can maximize their own needs Select the product, equip with the appropriate features to achieve system integration and expansion, while opening up makes the system easier to operate and maintain. In addition, the openness of the controller also creates conditions for CNC technology to continuously absorb the latest achievements in computer hardware and software, which is conducive to the upgrading of CNC products, improve performance and enhance competitiveness. This is also an important reason why open NC controllers are regarded as important strategic technologies by various developed countries and have been invested in research.

China is a big country in the production and application of machine tools, but the application level of numerical control technology is still not high, which seriously restricts the improvement of China's manufacturing industry. The relevant international development plan poses a severe challenge to the development of China's numerical control technology, and it also brings opportunities. First, the implementation of the Open Systems initiative has pushed all system developers in the world to the same starting line. At this starting line, we can establish a system integration development road with international procurement as the way to create conditions for China to manufacture high-performance, high-reliability CNC systems. Secondly, through a consistent programming application interface, it is easy to form its own integration solution. Further reduce the dependence on the seller's market. In addition, with the implementation of the open system plan and the establishment of a unified development platform, the high-tech added value of the CNC system will be mainly embodied in the software, which has created a good opportunity for the development of the national software industry in China. We should fully grasp the opportunities, foster strengths and avoid weaknesses, catch up and develop a new generation of domestic high-performance CNC controllers suitable for China's national conditions.