Re: Shop Order Days Mystery -- BPCS-L



Stephen, I will try and help a little with the confusion that you have with
SFC720

To quote
------------------

We have stepped through the scheduling engine (SFC739) - arduous task - and
are very confused about something.  It would seem that as the program loops
from one operation to the next, regardless of work center correlation, the
hours of capacity remaining from the previous operation's work center serves
as the basis for the next operation's hours remaining of capacity.  Maybe I
am completely missing something, but to my simple mind this makes no sense
at all.  The previous operation's work center capacity remaining is
irrelevant to the next work center's capacity.  Can anyone shed some light
on this for me?  Each of our work centers has a variable amount of standard
capacity and these remainder hour quantities leave us with partial days
which are apparently rounded up to whole days.  I think that is why we end
up with 5 days of operation queue.

At the big picture level, we really don't want a work center's capacity to
impact the start and end dates of any operations on a shop order.  Whether
forward or backward scheduling, we want the days between operations to
consistently be the sum of the queue and move days defined in the routing.
We want to see we are overloaded on the capacity reports etc, but do not
want the operation start and end dates to be affected.


---------


A major source of difficulty for the poor author of SFC739 is that he does not
have any shift start and end times kept in BPCS. So he has to play games to
approximate clock time from capacity used.

Now for the vast majority of customers the time spent at an operation is
extremely important. Make the ideal assumption that move and que are zero. If
operation 1 takes a half day and operation 2 takes a full day, and you do not
overlap operations (an option in BPCS) you will not finish the order in one day
if both shifts start and end at the same time. SFC739 assumes that you start
both shifts use the same amount of clock time, and assumes the transfer of the
entire lot (when it is finished) between operations.  It tries to consume
available time on the second operation because of the half day consumed on the
first operation. Your move and que times may be large enough to cover for your
entire run time, but many  BPCS users are not so fortunate. So while I agree
that the 'BPCS way' is clumsy and could use a lot of improvement (and may not
fit your environment as well as it could) if they did not use run times in
scheduling they would have lost an incredible amount of sales.

In most shops an order for 80,000 takes longer to complete than an order for
10,000. If run times never become part of the calculation, than size of the
order never becomes a consideration in scheduling.

hope this helps

Harmon Zieske
Nexgen


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