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

CNC and PLC closely linked
The ProNumeric, the most advanced PC-based control unit offered by Schleicher, is notable for the very close 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, takes charge of controlling and monitoring the peripherals. The PLC is programmed according to IEC 61131-3 with STL, FBD, LAD, ST and sequential function charts. The program features of the ProNumeric CNC include the extended range of functions according to DIN 66025.

The tight integration of CNC and PLC functions is achieved by the ProNumeric, thanks to a solution that is unique to the market; both the CNC and PLC use a common communications buffer and are completely synchronized. The PLC task is firmly linked to the interpolation. In other words, the PLC cycle time follows the IPO cycle of the CNC precisely. Unlike separated or only loosely integrated hardware, the system does not encounter limiting factors.e.g., valves are to be switched, depending on the position, in direct relationship to a path motion. With conventional control architectures, disparate cycles and communication-related delays between the CNC and PLC restrict the response speed.

ProNumeric PC-based CNC Control Diagram
ProNumeric PC-based CNC Control Diagram
(click image to enlarge)

Integration depth - a key criterion
To achieve optimized machine performance with complex functional sequences, it is essential to ensure the permanent and precise synchronization of the CNC with the PLC. In a fully synchronized system, it is possible to process sensor signals within a single clock cycle of the CNC, which allows corresponding adjustments to be made on the axis without incurring a delay. In the field, this continuous path control is used to instantly compensate for any heat-related drifting incurred by the machine. Temperature sensors supply data to the PLC, which in turn uses this information to calculate and transfer compensation values to the CNC within the same clock cycle.

Conveniently, the open design of the ProNumeric operator interface allows the user to select the programming environments in accordance with IEC 61131-3, commissioning tools for servo axes, network tools and other such functions. Software solutions such as remote maintenance and remote diagnosis facilities, service, document and program management tools from different system houses can be integrated with ease. For shop floor programming, it is also possible to install CAD/CAM packages directly on the controller.

NERTHUS optimizes NC programs
Following the calculation of CNC data and the simulation of the tool path, Schleicher control systems reduce the intermediate points required to define free-form contours with freely selectable contour tolerances by means of the NERTHUS technique. This technique reduces the number of NC blocks and generates an optimized NC part program. Using the Online Curve Interpolator (OCI), the CNC control system reproduces the free form contour, using the information contained in the NC blocks to achieve a constant and smooth path with optimized axis velocities. Simultaneously, it is possible to couple multiple axes by forcing them to one "line shaft" using the field bus to read the master value encoder within the interpolation cycle. The axes are synchronized with each other depending on the clock speed and position of the tool. It is also possible to operate multiple tools together in a group and, if useful, the entire group can be coupled to a higher-level virtual master sensor in order to achieve an optimized overall production speed.

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