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The operating environment of the Axiom Plus consists of two
separate parts or “threads”. These are the sequential program and
the PLC program. The sequential program executes actual move
commands and is programmed using the Sequential Program editor.
The PLC program is a scanned logic program that operates like a
stand alone Programmable Logic Controller (PLC). The two
programs communicate with each other through internal binary
logic bits, referred to in this document as “bit flags” or simply “flags”.
There are a total of 64 user-definable bit flags in the Axiom Plus for
communication between PLC program scan and Sequential motion
program. There are 32 discrete flags which are “Read/ Write” in the
sequential program and “Read Only” in the PLC, and 32 that are
“Read/Write” in the PLC and “Read Only” in the sequential program.
In addition to these 64, there are a number of special purpose
(designated) flags that are “Read/Write” in the PLC and can be
monitored (read) in the sequential program. These flags control and
monitor the trajectory generator, which, in turn, commands the
drive section, causing motion. By combining the functionality of
these two threads, complex control programs can be written that
would be difficult or impossible with a PLC or sequential motion
controller alone.
As the name implies, the sequential motion program is executed
sequentially. One instruction is executed to completion before the
next is begun. All move commands are set up and executed by the
sequential motion program. In addition, input/output commands,
branch commands and time delay commands can be executed in a
sequential motion program. The sequential program is most useful
for efficiently executing a series of sequential program steps, often a
part of machine control applications. In simple applications, the
sequential motion program can be used to run the entire
application. In more complex applications, it can be used in
conjunction with the PLC functionality to implement a control
program capable of running virtually any single axis application.
The PLC program operates as a traditional “ladder logic” controller.
It allows a scanned I/O and logic program to execute
asynchronously with respect to the sequential motion program.
Because of the 64 communication flags between the PLC and the
sequential motion program, it is possible to effectively address
applications requiring complex I/O and logical operation along with
single axis motion control. The PLC is best suited for handling
12-1
Programming
12
