PLC

PLC

Function

The PLC on the SINUMERIK is programmed using the user-friendly SIMATIC STEP 7 software. The STEP 7 programming software is based on the Windows operating system and makes it convenient and easy for the user to utilize the full capacity of the PLC.

The statement list STL, function block diagram FBD and ladder diagram LAD programming languages are available. In addition, system function blocks SFB and system functions SFC integrated in the operating system can also be called. The PLC can also be programmed in other SIMATIC S7 high-level languages, such as S7-Graph or Structured Control Language SCL.

Benefits

A large number of functions can be executed via the NCK and PLC interface, ensuring excellent machining flexibility. Some of these are:

• Controlling positioning axes
• Executing synchronized actions (auxiliary functions)
• Reading and writing NCK system/NCK user variables by the PLC

The PLC basic program, which is part of the toolbox, organizes the exchange of signals and data between the PLC user program and the NCK, PCU/IPC and machine control panel areas.

In the case of signals and data, a distinction is made between the following groups:

• Cyclic signal exchange:
  Commands from the PLC to the NCK (such as start, stop) and NCK status information, e.g. program running. The cyclic exchange of data is performed by the basic program at the start of the PLC cycle (OB1). This ensures, for example, that the signals from the NCK remain constant throughout a PLC cycle.
• Event-driven signal transfer NCK → PLC
  PLC functions executed depending on the workpiece program are initiated via auxiliary functions in the workpiece program. If a block with auxiliary functions is executed, the type of auxiliary function determines whether the NCK has to wait for this function to execute (e.g. tool change) or whether the function will be executed together with the workpiece machining process (e.g. tool loading on milling machines with chain magazine). In order for CNC machining to be affected as little as possible, data transfer must be as fast as possible, yet reliable. Data transfer is, therefore, interrupt-driven and acknowledgement-driven. The basic program evaluates the signals and data, sends an acknowledgment to the NCK, transfers some of the data to OB40 and the rest to the user interface at the beginning of the cycle. CNC machining is not affected if the data do not require an acknowledgment from the user.
• Event-driven signal exchange PLC → NCK
  Whenever the PLC sends a request to the NCK (such as a request to traverse an auxiliary axis), a PLC → NCK event-driven signal exchange takes place. In this case, data transfer is also acknowledgment-driven. When performed from the user program, this type of signal exchange is triggered using a function block (FB) or function call (FC). The associated FBs and FCs are provided together with the basic program.
• Messages
  The acquisition and editing of user messages is handled by the basic program. The message signals are transferred to the basic program via a specified bit array. Here, the signals are evaluated, then transferred to the PLC diagnostic buffer when one of the message events occurs. If an OP is available, the messages are transferred to the OP and displayed on it.