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Algorithms
Graphical Presentation
This installation features a single overhead crane, with a grab mechanism,
which picks up 23 metre long "baumers" of foam (up to 1.2 metres high
and 2.4 metres wide) from an infeeding conveyor,
and stores these, while curing on three trestles (on three levels, with
accommodation for five baumers each).
Once cured, the baumers are relocated to stacks on the floor, until required
by production. When called for from production the baumers are picked up and
taken to the appropriate outfeeding conveyor.
There are several interesting features of this installation: complex
algorithms, graphical representation of the foam stacks, the handling of
non-precise loads, and the need to "excavate" to reach the required baumer.
Algorithms
The baumers are of varying lengths, widths, heights, densities, and
hardnesses.
The variations in length are relatively small, however these restrict the
longest baumers to curing on the top trestle level, those not so long to
curing on the middle trestle level, those shorter still to curing on the
lowest trestle level, whilst only the shortest can be placed on the floor
space beneath the trestles for curing.
Certain areas of the warehouse floor can accomodate wider baumers than other
areas, so when placing baumers, care is taken not to waste the wider floor space
on narrower baumers. Also, as stacks are built, there is a limit on placing
wider baumers on top of narrower baumers. For most baumer grades a baumer is
allowed to be upto ten per cent wider than any baumer beneath it, while for
other grades a baumer is allowed to be no wider than any baumer beneath it.
Baumer product details state a nominal height for the baumer. As the baumer
is manufactured, its actual height is measured, and recorded and tracked for
the baumer as it makes its way to the warehouse infeed. When it is picked up
by the crane and placed in the warehouse, the crane reports the height of the
top of the baumer above the floor level. As it cures, its height will reduce,
however if it was allowed to cure in the curing area, its height will not be
required until it is relocated to the main warehouse blocking stacking area,
when its height will again be measured.
This height is needed to establish the
total height of the stack so that we don't build stacks which will interfere
with the crane's travel. The height is used, along with the density and width
to determine the amount of pressure it is adding to the baumers beneath it.
The height is also used to determine to where it can be relocated when needing
to move it to access the baumers beneath it. And, finally, the height is used
to provide the crane with the data needed to pick it up.
The density and hardness are used to establish the pressure the foam can
tolerate, and so determine what can be placed above it. This calculation has
varying coefficients depending on the type of foam.
Certain foam grades possess a higher degree of springiness, causing them
to form less stable stacks, thereby limiting the height to which their stacks
can rise.
In addition, some baumers may have manufacturing defects which, although they
contain quality foam, cause them to be unable to be stacked. Such defects
include varying heights or humps. These baumers must not be stacked on top
of.
The quantity of baumers, the warehouse size, and the variety of foam grades
make it impossible to store like baumers together.
There are two outfeeds from the warehouse. The baumer product details
specify which outfeed it is most likely be needed to be delivered to. This is
also taken into account in determining where in the warehouse to place it.
Baumers to be retrieved are entered onto a schedule. The products on the
schedule are noted when placing baumers, so that wanted baumers are not
buried deeper than necessary.
Baumers delivered to production are occasionally returned with their height
halved to be stored again.
All the above considerations must be taken into account, when storing,
relocating, and retieving baumers so as to maximise the capacity of the
warehouse and the access to the baumers.
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Graphical Presentation
The warehouse details are presented as an end-on look at the stacks of
baumers. The baumers are shown to scale (though the horizontal scale is a
quater of the vertical scale), with a target representing the data associated
with each baumer placed on the lowest point of the grid covered by the
baumer's physical representation.
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The above screen dump shows the crane lowering a baumer onto the middle
trestle level. The top and bottom trestles are shown in the east position,
while the middle trestle is in the west position. The tall black towers
are the infeeding and first outfeeding conveyors, while the short black box
represents the second outfeeding conveyor. The cured baumers are those sporting
a "C" in their target. You will notice that some baumers on the top of stacks
in the block stacked area are not cured; at the time they were manufactured
there was insufficient space in the curing area (the trestles and beneath them)
to accommodate them. The baumers in the curing locations have since mostly
cured and are now sporting the "C".
The columns of "X"s indicate areas which have been disabled. The three
locations at the east end of the warehouse have been reserved for use by the
fork trucks, while floor position 19 is disabled because the operator at the
block-off saw had to return a part baumer (length shortened rather than height
shortened) to the warehouse, preventing the location from being used in
automatic.
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Other Details
The “Movement Controller”
communicates to one PLC which controls the trestles and the conveyor system and
a second which controls the crane.
Communication between the “Movement Controller”
and the crane is via an infra-red serial link.
PLCs are Omron and Mitsubishi.
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