In traditional automation systems, the tasks are clearly distributed. A programmable logic controller (PLC) links inputs and outputs, and the CNC coordinates the motion of the axes. Today, parts of the drive control are performed by either corresponding PLC functions or special positioning mpdules, or they are delegated to a lower level within the position controller itself as in the case of servo amplifiers. With the advent of local intelligent power electronics, the entire control circuit and the integral profile generator are often embedded in the drive. Units such as these are now only parameterized by the higher-level control system, and usually receive their jobs via a field bus.

In contrast, other systems feature central control systems that assume the power control of the individual drives. In these cases, it is essential to have a fast bus connection between the power and monitoring sections and the control system, which is connected to a high-performance computer.

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.

This form of drive programming is made possible by the control system hardware and software architecture in a PCbased control system from Schleicher Electronic, which makes integrated CNC/PLC automation equipment. 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.

Windows®-based solutions have become the established means for designing operator interfaces, but the real-time performance required in industrial scenarios cannot be provided by a PC running Windows XP alone. Schleicher deploys a combination of operating systems tuned to work together. ProNumeric uses the VxWin® package from KUKA Controls that combines the Wind River VxWorks® real-time operating system with Microsoft Windows XP. Time-critical tasks are performed in hard real-time by VxWorks, and the graphic HMI functions and connectivity use the Windows XP interface.

The memory areas of the operating systems remain 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 realtime 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.

The ProNumeric PC-based control unit offers integration of the PLC with the motion functions controlled by the CNC. As with separate hardware, the CNC is responsible for the motion control, while the PLC, running in parallel, controls and monitors the peripherals. The PLC is programmed according to IEC 61131-3 with STL, FBD, LAD, ST, and sequential function charts. ProNumeric allows the user to select the programming environments in accordance with IEC 611313, commissioning tools for servo axes, network tools, and other functions.

PC-based systems can also be configured as communication centers. In addition to providing the fieldbus interface connection for actuators and sensors, PC-based systems offer an ideal platform for interaction with various drives, even those from different manufacturers. A further advantage of this interface is that the CNC is relieved of its position control tasks, freeing up its computing capacity.