New PCL/CNC Uses New Software Technology to Closely Link Motion Control to a PC-based Control System

For years, the term "motion control" has been much-debated in the field of industrial automation. However, in its literal sense, motion control denotes the coordination of multiple drives. At trade shows and exhibitions, truly innovative systems are rare and often stand next to those having more traditional architectures. However, new technologies in software are changing conventional architecture, particularly in the field of drive control. Examination of the recently introduced PC-based control systems from Schleicher, with the ability to coordinate up to 64 NC axes, illustrates the great potential of truly innovative solutions. This new architecture not only reallocates the responsibilities of tasks between the drives and the higher-level control system, but also offers a solution that masters complex and specialized motions. It represents the possibility to fundamentally evolve new concepts in machine control.

Changing responsibilities
In traditional automation systems, the tasks were clearly distributed. A PLC linked inputs and outputs, the CNC coordinated the motion of the axes either by interpolation or, as with robot control, by coordinate transformation. But today, major changes are occurring in the assignment of elementary function blocks to the control units involved. Parts of the drive control are performed by either corresponding PLC functions, or special positioning modules - or they are delegated to a lower level, for instance, within the position controller itself as in the case of servo amplifiers. Today, with the advent of local intelligent power electronics, the entire control circuit along with 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 even assume the power control of the individual drives. In these cases in particular, 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. Having a high-speed connection is, of course, fast becoming a system wide requirement, as drive data must be available to various functional units at the same time for processing.

For example, a resolver simultaneously supplies the current rotor position to the current controller; provides the speed controller with the measured revolutions; and, at the same time, must report the actual position values to the position control unit, the profile generator or to a continuous path control system. In addition, the visual display system requires constant feedback data to enable it to display a path directly in graphic form. With the cycle times commonly encountered today, this is no small matter. Consequently today, efficient and comprehensive facilities for data communication are a critical requirement for any complete Motion Control solution.

Control System Diagram
Control System Diagram
(click image to enlarge)

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