Mitsubishi Electric FX Series - Application Program; Example: Carousel Indexer

4.2 Application Program
4.2.1 Example: Carousel Indexer
The following application program will be used to illustrate the creation of a simple program
using the tools of GX IEC Developer.
Operational Sequence
햲
Momentarily operate foot switch to index carousel.
햳
Carousel rotates – ‘In-Position’ sensor turns OFF as carousel begins rotating.
햴
‘In-Position’ sensor turns ON when carousel reaches index position.
햵
Assemble product
햶
Repeat process (Go back to 햲.)
There are a number of issues that must be addressed when designing a PLC program for the
above application. Using a standard Start / Stop circuit is not possible without modification due
to the following difficulties:
쎲
The foot switch may be operated at random. Once activated, it may be possible for the
operator to forget to release the switch which may cause the table to continue to rotate past
its index position.
쎲
Once “In-Position” X1 operates, it remains on, thus the table is prevented from re-indexing.
The design must therefore contain interlocks to prevent miss-operation as described above. An
alternative approach to the design would suggest the use of ‘Pulse Transition Logic’ by means of
the IEC or MELSEC “Edge Triggered” configurations.
Application Program Building a Project
4-4 MITSUBISHI ELECTRIC
M
Proximity Switch
“In Position”
X1
Foot Switch
“Index
Carousel”
X0
Product
Assembly
Station
Drive Motor
Y10
MELSEC PLC I/O List:
MELSEC PLC I/O List:
X0: Foot Switch
X1: In Position
Y0: Motor Drive
Drive Motor
Y0
Proximity Switch
"In Position"
X1
Foot Switch
"Index Carousel"
X0
Product
Assembly
Station