Unfortunately we can not have a sergeant major to shout every now and then. But ... there is a solution. Let's connect the soldiers by mean of a rope. On the floor we can translate this to a certain quantity of work in process between two operations. The rope is of a certain length. Like the work in process can be of a certain quantity.
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Just to make sure everybody gets a signal if he's going too slow or too fast, the work in process, should be controlled in such a way, it gives a signal either to slow down or to
move a little bit faster. The Japanese call this KANBAN. However is there not a better method?
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The answer is in the following picture. In stead of many ropes (= much work in process)
Dr. Eli Goldratt (author of the Goal) found a solution with one rope (= less work in process). He
implemented his solution by connecting the first operation with the slowest operation.
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As you can see in this picture the soldiers between the
first and the slowest soldier can more or less set their own pace. They
are so fast (have so many over-capacity), that they can adapt their
pace. As long as they stay in front of the slowest soldier and they do
not pass the first soldier, everybody is happy. |
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The soldiers behind the slowest soldier can adapt their pace in
case of an incident, they will pick up again. As long as they do not pass the
slowest soldier, their pace is right. Each time the 'drum' needs raw material,
it should be there. The material issue operation and the schedule of the
constraint (= DRUM) must be connected to each other. This to guarantee the
material arrives in the right sequence and the right quantity and at the right
time, when needed at the constraint. The linking of both elements (= Drum and
Material issue) we call 'pulling a rope'. As a proper definition of the rope we
could say:
'It is a mechanism that forces all parts of the system to work up to the pace dictated by the drum'.
This is the basis for a new approach of issuing the raw materials in pace with the drum. The implementation is known by Drum-Buffer-Rope.
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