
B-63983EN/02 10.STEP SEQUENCE FUNCTION
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(2) Easy debugging and maintenance
· Graphical display enables the operator to easily understand
the execution state of a program visually.
· Erroneous steps in a program can be found easily.
· A part of a program can be easily modified.
(3) High-speed program
· Since only the subprograms required for a certain process
are executed, the cycle time is reduced.
(4) Transition from ladder programs
· Since steps and transitions consist of conventional ladder
programs, conventional ladder programs can be converted
to new step sequence programs, without discarding ladder-
program resources.
In step sequence programming, a sequence control program is divided
into two types of subprograms, steps and transitions. Steps describe
processes. Transitions connect steps and determine whether the
transition conditions from one step to another evaluate true. As shown
in Fig. 10.1.1(d), a step sequence program is described using
graphical symbols.
Fig. 10.1.1(d) Example of machining the workpiece
As shown in this example, the program flow from process 1 through
process 5 is expressed visually. Detailed programs related to the
movements performed as part of each process, and the signals used
for determining whether transition conditions for proceeding to the
next step are satisfied, are not described here. To program
complicated control flows, many other functions are supported, such
as divergence, jump, and nesting functions. The details of these
functions are described later.
Step sequence programming is suitable for creating programs which
control processes sequentially. Programs used for controlling a unit
which operates according to a certain sequence, such as a loader,
[ ]
Step A
Transition B
Starts execution. Waits for machining request.
(Process 1)
Machining request?
®
When machining is requested
Holds a workpiece on the pallet. (Process 2)
Step C
Transition D
Loading completed?
®
Once loading has been completed
Machines the workpiece. (Process 3)
Step E
Transition F
Machining completed?
®
Once machining has been completed
Unloads the workpiece to the pallet. (Process 4)
Step G
Transition H
Unloading completed?
®
Once unloading has been completed
Moves the pallet. (Process 5)
Step I