This installation features four stacker cranes, servicing the freezer high
rise store, and eight shuttles servicing their infeeds and outfeeds.
One of the more interesting features of this installation was that the cabin
onboard the crane needed to move up and down the mast by about a metre or so,
so that the cabin did not interfere with the top rail while the crane was at
the top level and cabin did not interfere with the bottom rail while the crane
was at the top.
The crane rail was somewhat rough, causing the crane to be jolted against
its mast as it travelled along. Often the crane would complete its hoist
travel, prior to completing its long travel, causing the crane to be sitting in
the one position on the mast, causing indents there as the long travel
continued. This would subsequently cause problems with the hoist positioning.
So to compensate for this, the hoist travel was slowed so as to complete as
near as possible to the time that the long travel completes, so that the dents
would be distributed randomly along the mast, rather than collected
at the hoist stop positions. To achieve this, the crane PLC needed to maintain
a table of the times it takes for each long travel distance and each hoist
travel distance, and, by machine learning, adjust its hoist speed, to time the
completion of the hoist travel to coincide with the completion of the long
travel.
Communications between the
“Movement Controller”and the cranes is via an infra-red serial link.
Communications between the
“Movement Controller”and the host computer system is via FTP/TCP-IP/Ethernet.
All PLCs are Allen-Bradley.
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