New PCL/CNC Uses New Software Technology to Closely Link Motion Control to a PC-based Control System
Nothing works without blocks
There are numerous different types of drive applications. The spectrum ranges from individual axes moving towards a single destination, to complex groups of axes in which the synchronous operation or inline processing involves coordinating multiple axes with one external motion. Coordinating multiple axes can place high demands on the control system's performance. If it is just a matter of traveling a single path, programming by hand is perhaps still a conceivable option. However, even cam plates can, in many cases, cause the quantity of data and commands to grow significantly. So much so that a library made up of function blocks becomes essential for programming.
The strength of a motion control system stands and falls with the performance, flexibility and scope of functions offered. In particular, the convenient simplified handling of the software blocks that control the drive technology is a key advantage. Sophisticated, specialized motions, whose direct programming would be highly intricate in the DIN language of CNC, can be easily realized by using function blocks. In such cases, operator control is simplified and more understandable especially if the necessary communication between function blocks takes place in the background, without involving the user.
Everything on one processor
This innovative and convenient form of drive programming is made possible by the new Schleicher control system's hardware and software architecture. In this complete solution, a single-processor system takes charge of all the controller tasks, from motion and sequence control through visual display and connectivity with the enterprise. The obvious advantages are both operational and economic. For instance, implementing the system on a single processor saves on both interfaces and hardware costs. The challenge posed by this approach is clear. In spite of the broad range of tasks performed, the performance must not be allowed to suffer in any one area. Neither should the advantage of a convenient, familiar interface be lost. On the one hand, Windows®-based solutions have become the established means for designing operator interfaces, but the real-time performance that is required in industrial scenarios, such as response times in the microsecond range, cannot be provided by a PC running Windows®XP alone. In the case of hardware interrupts, for example, a network interface card, the latency during which no process change can take place, is not bounded as required by a real-time task. Thus, despite the fact that standard Windows solutions can offer a priority control facility, multitasking functionality and interprocess communication - in practice they do not meet deterministic real-time demands.
Dual operating system
In order to be able to offer both user-friendly controls and real-time performance on a single PC, Schleicher deploys a special combination of operating systems that are tuned to work together. ProNumeric uses the VxWin® package from KUKA Controls, which combines the Wind River VxWorks® real-time operating system with Microsoft Windows XP. This integrated solution combines the advantages of both types of operating systems. The time-critical tasks are performed in hard real-time by VxWorks and the high-end graphic HMI functions and connectivity take advantage of the convenient Windows XP user interface.
The memory areas of the operating systems remain strictly separated and protected by the x86 MMU (Memory Management Unit). The KUKA VxWin real-time driver ensures that VxWorks has priority for processing all the time-critical tasks. A changeover from VxWorks to Windows only takes place if the task management facility of the real-time operating system reports it is running with no load. Windows and the real-time operating system communicate with each other via a TCP/IP network.
This control system architecture offers a strictly deterministic time response and ensures the hard real-time capability of the PLC runtime and the CNC functions. At the same, time the Windows environment can be used via OPC for tasks such as the visual display and processing of operator dialogs. In addition to which, it is possible to use Windows-based project planning tools with access to online manuals and standard Windows programs.
Dual Operating Systems Diagram
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