Operation with and without PLC

Machine commissioning may also be performed only with partially implemented PLC functionality. For this purpose, the CNC-end driver of the HLI contains mechanisms for internal simulation of interactions between PLC and CNC.

Example:

The axis is to be run in with a rudimentary PLC. For this purpose, the PLC sets only the Axis Enables and other functionalities are not yet implemented in the PLC.

In order, nevertheless, to be able to switch operating modes or perform a Reset, the HLI driver now simulates the required acknowledgements of the PLC so that the required action can be performed nevertheless.

To achieve this behavior and to ensure reliable operation nevertheless, the PLC issues a corresponding information item to the CNC, a so-called present marker for each functionality covered by the PLC. This present means that the PLC wishes to operate the corresponding interface and sends the required acknowledgements.

For this purpose, the PLC must inform the CNC once globally in the HLI that it exists. In addition, all control commands are enabled individually. This means that three scenarios are conceivable:

CNC without PLC
CNC with PLC which does not use all elements of the HLI
CNC with PLC which uses all elements of the HLI

The housekeeping sections of each channel resp. each axis have this present element by which the PLC assumes corresponding responsibility for this interface.

In addition, each housekeeping unit of a control command, the control unit, contains an element with which the PLC informs the CNC that it supports this command. This X_Enable element means, at the same time, that, if the corresponding command can also be issued via the GUI, this is routed via the PLC and reaches the CNC from there. The CNC can thus no longer distinguish whether a command is arriving from the PLC or the GUI.

Operation with and without PLC 1: — Figure 0.6: Interaction, MC control unit and PLC

The connection of the GUI via the CNC is not necessary. Likewise, an interface may communicate directly with the PLC, and the additionally provided communication channel GUI -> CNC -> PLC is not used in such cases.