Push and Pull Production Systems - Comparisons of CONWIP with MRP

6 important questions on Push and Pull Production Systems - Comparisons of CONWIP with MRP

Regarding CONWIP Robustness, encircle the right answer:

 

"A CONWIP system is more/less robust to erros in WIP level than a pure push system is to errors in release rate."

A CONWIP system is MORE robust to erros in WIP level than a pure push system is to errors in release rate.

What is meant by the fact that push systems are less efficient than an equivalent CONWIP system?

It means that a push system will have more WIP or longer CT on average, for a given level of TH, than an equivalent CONWIP system.

Josh states: "A push system has more variability in CT than an equivalent CONWIP system, because the standard deviations of CT are much larger even though the mean cycle time is somewhat smaller."
Is Josh right?

He is not completely right. Actually mean cycle times will be larger for the push system as well.

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What would you expect to happen to figure 10.7 if a higher value of h or lower value of p was used?

 

The picture would 'shrink vertically' using the same values on the axis.
Robustness in terms of actual values would get smaller (a smaller area in the graph), but relative robustness would stay more or less the same (the area under the pure push curve also gets smaller).

Why does the book state the second last sentence on p. 372 as:

''We find the best WIP level for the CONWIP system is ... . In the push system, the best TH turns out to be ..."

instead of:

''We find the best WIP level for the CONWIP system to be ...  and for the push system to be ... ."
or "We find the best TH for the push system to be ... and for the CONWIP system to be ..." ?

Because in a CONWIP line you control WIP and observe TH and in a push system you control TH and observe WIP.

Can the MVA model in 10.4.2 be used for any CONWIP line?

No, it is only reasonably accurate for . Also it only applies to lines where stations behave as M/G/1 queues, so when   and no multi-machine stations.

The question on the page originate from the summary of the following study material:

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