Operations optimisation in a batch job shop

"OShea, Laurence"
Junior Member
Posts: 14
Joined: Fri Mar 29, 2002 3:39 am

Operations optimisation in a batch job shop

Post by "OShea, Laurence" » Thu Aug 29, 2002 1:28 am

"Ray on EV1"
Junior Member
Posts: 14
Joined: Fri Mar 29, 2002 3:39 am

Operations optimisation in a batch job shop

Post by "Ray on EV1" » Sat Aug 31, 2002 6:02 pm

It looks like a key in understanding comes from the statement:
" processing methods, i.e. batch job-shop, planners and supervisors have
great autonomy".

A particular perspective would be to address the issue of local vs. global
optimization. Great autonomy might suggest each cell addresses an
objective function with a local optimum view. The problem space could then
be defined as the span from this collection of local views to an overall,
global optimization.

This could be addressed as combinatorial optimization problem - which cells
should share objective functions and to what degree of overlap. For
example, cells in adjacent work-piece sequence slots may share objectives to
assure some degree of cooperation. Similarly, cells sharing common
resources may benefit from such cooperation.

One of the concerns here is the optimization computational costs increasing
geometrically as the number of cells share objectives - the dimensions of
the optimization space increases. Not only do the computational cost go up,
but the modelers comprehension of the complexity of the local minima
placements become taxed.

This type of issue has been studied for decades under the subjects of
centralized / distributed control. There are many systems where it can be
shown that the original optimization can be achieved equally well with
either centralized or distributed control. But the political environment
will drive the choice to one or the other.

My favorite example is vehicular traffic control in a city. Centralized
control can help coordinate the use of information from different parts of
the city to optimize each vehicles trajectory from a centralized
controller. The same results can be obtained by providing that information
to each vehicle and letting the vehicle make all the control decisions.

Raymond T. Joseph, PE
Aarden Control Engineering and Science