Question

What is nervousness in material requirement planning (mrp) system?

Answer 1

Answer:

In practice, material planning is usually conducted using MRP systems. Up to

now, the use of alternative concepts such as LRP or FiRST is not widespread.

Consequently, the analysis of nervousness in MRP systems is the main focus

in literature and in the subsequent analysis.

In literature, MRP nervousness is defined in several ways. In an early work,

Steele [124] defines a "nervous MRP" system as one that causes excessive

changes to low-level requirements when the master schedule is not changed

significantly. He identifies the following reasons for nervousness in MRP systems.

• Master schedule changes/Unplanned demand:

Rescheduling the MPS, in general, leads to replanning activities on lowlevel items. Because of lot-sizing, even minor time-phasing changes on the

MPS level may lead to major rescheduling actions on lower stages. In particular, changes in lot sizes on the MPS level may cause rescheduling of

released orders at lower levels (see also Mather [86]).

• Allocation not issued in expected quantity: (or contrary to the plan, Type

I)

The difference between the actual demand and expected (planned) demand

of a component may lead to changes in the due date of the replenishment

requirement. An allocation gives the planned issue for a shop requirement,

and if it is not available in the expected quantity, then the forecasted runout date will shift. Similar problems occur if a machine break down, or

a supplier cannot deliver the material for a component in time1 . Then,

assemblies on which these components are used must be delayed (see, e.g.,

Mather [86]).

• Order released in unplanned quantity: (or contrary to the plan, Type II)

The impact of this is the same as for type I, i.e. subordinate requirements

will again jump forward, but in this case, all components are influenced.

The same holds for unexpected scrap which causes planned orders to be

needed earlier (see, e.g., Mather [86]).