The research and demonstration applications of open control systems at home and abroad are now focused on the development of hardware and software of PCs. The essence of these applications is a dedicated application of the PC on the I/O interface and human-machine interface (see Figure 1). Both the structure and the performance are very limited: First, no independent open structure suitable for CNC machining control is defined. The openness of the open structure is inherent in the computer itself. It is not defined for the characteristics of numerical control processing. The cost of this method of reference is to completely rely on the structural system framework of the computer. The PC computer as a general platform does not consider the specificity of the numerical control processing from the underlying hardware design and operating system environment, and therefore cannot be fundamentally good. Build a CNC platform. Secondly, the open CNC system of industrial computer mode can not guarantee the real-time and reliability. Because the PC uses a common operating system during operation, it occupies a large amount of system resources. Tasks that are not related to NC machining may take up more of the system's work share. They interfere with the timely response of the system to on-site processing and reduce the The speed with which the system handles important control events increases the overhead of system operation, which can lead to system instability. The third point is that the cost of IPC mode CNC systems is too high. A computer that can meet the requirements of CNC machining speed needs at least a few thousand dollars to invest in a motion control card, making it difficult to reduce costs. But an embedded microprocessor is only a hundred yuan, the programmable device chip is only about a hundred dollars, plus the real-time operating system is free open source code, there will be no use of software copyright The extra costs, which have led to a significant reduction in costs. Ensure that the patent application has a good performance and price ratio. Fourthly, the network function of the open CNC system of the current IPC model is based on the computer network. Since this network does not take into account the requirements for the transmission of large-signal signal data streams due to numerical control processing and condition monitoring, the speed is limited. The system's remote network application capabilities are basically only applicable to program transfers between systems.
In addition, NC+PC mode CNC system basically does not provide any secondary development environment. It only provides some reconfiguration and definition functions of interfaces and parameters. There are also PLC programming functions and corresponding programming tools. Just a simple configuration of the switch. PC-based open CNC products, on the one hand, increase or decrease the number of interfaces to achieve changes in the number of control axes and channels, on the one hand, and on the other hand to provide users with their own system software library to provide the package to the user to achieve The user configures the system control by himself. However, this form of openness has undoubtedly increased the requirements for the user's secondary development capabilities. The opening is not targeted, the open form is unfriendly, and the operability is poor.
This article is based on the above problems, and focuses on the hierarchical structure of the open structure system, the network activation mechanism of condition monitoring and the intelligentization of the secondary development platform.
2 The hierarchical structure of open architecture
The design goal of hierarchical thinking is to facilitate system scalability and configurability, which are two important indicators for judging the openness of a system. Scalability means that the system can flexibly add hardware control interfaces to achieve the expansion of functions and the improvement of performance; configurability refers to the use of existing low-level structural modules through configuration and compilation control without increasing the hardware structure. Software to achieve system customization. The hierarchical architecture takes modularization as the core, but it is different from the general modular structure approach. Hierarchy not only considers the functional features among the various components of the system, but also considers the role and status of the control links between the components in the entire structural system, and clarifies the inherited and derivative relationships between components, and in fact, through definition This kind of inheritance and derivative is used as a standard to divide the elements of the system components, rather than simply relying on functional standards to plan the various elements of the system and the relationships between them. Hierarchy not only serves as a system framework design idea, it can be used at all levels of the system's internal structure and external structure. When the components are subdivided layer by layer according to the required functional and performance requirements, the same derived inheritance relationship and hierarchical standard application Each substructure in the component.
As shown in Figure 2, the hierarchical CNC system has a basic layer 0, which includes all the components required for the basic control functions of the system and the necessary hardware and software interfaces to satisfy the general function expansion. The layer 0 as the core structure of the system must have good The internal and external interfaces of an internal network must ensure the smooth communication between components and access to each other, as well as the details of the internal structure, so as to maintain the stability and security of the entire system. The additional layer above layer 0 is built on the layer 0 expansion interface, extending the functionality of the system and improving the performance of the control by adding hardware and open software interfaces.
There are two additional layers: supplementary expansion and parallel expansion. Supplementary expansion is based on the original components on the basis of opening a new interface to configure the different control software form to achieve the function expansion of the system; parallel expansion is to add a functional component of an equivalent structure to achieve a special control requirements of the system or open up A new control channel. The significance of distinguishing between these two extensions is to make full use of two different forms of inheritance: structural inheritance and interface inheritance. The additional extensions follow the interface inheritance and are embedded into the interface level of the system components in the form of function points. This feature can easily standardize the implementation of the extension requirements for individual functions and meet the user's custom requirements at any time. Parallel expansion follows structural inheritance, and a new functional channel is replicated in the form of a functional group as a whole, and a parallel control scheme is formed with the original hierarchy. This feature can expand the integrity of the open structure. The motion control module is the core component of the numerical control system. The open-structured motion control components must have both parallel and additional extensions (see Figure 3). Parallel expansion is used to control the expansion of the number of axes. Based on the basic three-axis control, four-axis and five-axis components with the same kind of functional characteristics are derived. Additional extensions are used for the addition of special functions. They are user-defined. The function implements the interface, and the basic components and the components derived from the parallel expansion have the same additional extended interfaces. Figure 3 shows a basic three-axis motion control assembly expanded in parallel into four-axis and five-axis motion control components. Each motion component additionally expands the three special functions of complex curve interpolation, position error compensation, and vibration condition monitoring.
3 intelligent development mechanism of secondary development platform
As shown in Figure 5, the secondary development platform model, we adopt a guided development model, with the help of a variety of pre-defined information bases, the use of special language descriptions of the user's functional requirements are converted into a combination of specific strategies in the database, Then through the code compiler that matches the micro control core of the numerical control system, the strategy description is translated and sent to the simulation development interface of the numerical control system via the download cable through the parallel port of the computer. There is a simulation development dedicated storage area corresponding to the CNC system for on-line verification of user-customized function codes. The storage area is shielded from the normal NC program storage area to ensure the safety of secondary development and pass. The verification strategy and evaluation mechanism return the performance indicators of the secondary development.
The secondary development environment includes two methods of language description and guidance setting: language description method uses a structured functional mechanism, pre-defines the algorithm structure of the system extension, users only need to add their own description of the functional requirements according to the algorithm's prompt. The secondary development platform provides an independent structured description language (grammar structure as shown in Figure 6). It adopts an object-oriented programming concept to fully describe the specific working state of a numerical control component object in the form of a functional object group. The language description scheme can deepen the internal software configuration details of the system through the flexible definition of the algorithm specification, and is applicable to the custom configuration of the system's underlying policy scheme. The boot setting adopts the form of a development wizard (the development interface shown in FIG. 7 ) to customize the user's expansion request by a graphical query interface, which is generally used for relatively simple extension development. The combination of these two mechanisms also constitutes a hierarchical structure of secondary development.
4 Conclusion
   The open CNC system constructed by using the hierarchical structure scheme and the micro-control core is a brand-new breakthrough in system architecture. The hierarchical thinking penetrates into every component element of the entire system, and a guided intelligent secondary development strategy. . The hierarchical structure framework will link the development, use and maintenance of the CNC system and make it truly open throughout the entire life cycle of the CNC equipment.
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