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Part Three
Planning and control
Table 15.1 Inventories of materials, information or customers have similar characteristics
Inventory
Of material
(queue of material)
Of information
(queue of information)
Less current information
and so worth less
Needs memory capacity
Defects hidden, possible
data corruption
Makes stages
independent
Of customers
(queue of people)
Wastes customers’ time
Cost
Ties up working capital
Space
Needs storage space
Defects hidden, possible
damage
Makes stages independent
Needs waiting area
Gives negative
perception
Promotes job
specialization /
fragmentation
Servers kept busy by
waiting customers
Avoids having to match
supply and demand
Quality
De-coupling
Utilization
Stages kept busy by
work-in-progress
Stages kept busy by
work in data queues
Avoids need for
straight-through
processing
Coordination
Avoids need for
synchronization
Source: Adapted from Fitzsimmons, J.A. (1990) Making continual improvement: a competitive strategy for service
firms, in Bowen, D.E., Chase, R.B., Cummings, T.G. and Associates (eds) Service Management Effectiveness,
Jossey-Bass.
Here items are processed and then passed directly to the next stage ‘just-in-time’ for them to
be processed further. Problems at any stage have a very different effect in such a system. Now
if stage A stops processing, stage B will notice immediately and stage C very soon after. Stage
A’s problem is now quickly exposed to the whole process, which is immediately affected by
the problem. This means that the responsibility for solving the problem is no longer confined
to the staff at stage A. It is now shared by everyone, considerably improving the chances
of the problem being solved, if only because it is now too important to be ignored. In other
words, by preventing items accumulating between stages, the operation has increased the
chances of the intrinsic efficiency of the plant being improved.
Non-synchronized approaches seek to encourage efficiency by protecting each part of the
process from disruption. The lean synchronized approach takes the opposite view. Exposure
of the system (although not suddenly, as in our simplified example) to problems can both
make them more evident and change the ‘motivation structure’ of the whole system towards
solving the problems. Lean synchronization sees accumulations of inventory as a ‘blanket
of obscurity’ that lies over the production system and prevents problems being noticed.
This same argument can be applied when, instead of queues of material, or information
(inventory), an operation has to deal with queues of customers. Table 15.1 shows how certain
aspects of inventory are analogous to certain aspects of queues.
The river and rocks analogy
The idea of obscuring effects of inventory is often illustrated diagrammatically, as in
Figure 15.3. The many problems of the operation are shown as rocks in a river bed that
cannot be seen because of the depth of the water. The water in this analogy represents the
inventory in the operation. Yet, even though the rocks cannot be seen, they slow the progress
of the river’s flow and cause turbulence. Gradually reducing the depth of the water
(inventory) exposes the worst of the problems which can be resolved, after which the water
is lowered further, exposing more problems, and so on. The same argument will also apply
for the flow between whole processes, or whole operations. For example, stages A, B and C
in Figure 15.2 could be a supplier operation, a manufacturer and a customer’s operation,
respectively.