Production Scheduling Nahmias, Chapter 8 ( D t lj l i ) (sv ...

High Customer Service - Meeting Due dates
• Service Level 1: • Lateness:
– Particularly common in – Difference between order due date
make to order systems. y
and completion p date ( (can be
– Fraction of orders which are positive).
filled on or before their due – Average lateness has little meaning
dates .
by itself. Need also to consider the
lateness variance.
• Tardiness:
• Service level 2:
– Is equal to the lateness of a job if it is
– Common in make to stock late and zero, otherwise.
systems.
– Average tardiness is meaningful but
– Fraction of demands met
from stock.
unintuitive.
Scheduling Approaches & Assumptions
• Scheduling as practice dates back to Scientiffic Management
– Serious analysis contingent on computer power - started in 1950’s
• MRP/ERP:
– Benefits: Simple paradigm, paradigm hierarchical approach. approach
– Problems
• MRP assumes that lead times are a constant attribute of the part,
independent of the status of the shop (assumes infinite capacity).
• Strong incentive to use pessimistic lead time estimates to hedge
• Classic Scheduling: (only classic in academia)
– Benefits: “Optimal” schedules (large integer programming problems)
– Problems: Bad assumptions.
• All jobs available at the start of the problem.
• Deterministic processing times.
• No setups.
• No machine breakdowns.
• No cancellation.
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