Operation Systems Monitoring and Control

What is an Operation System?

Give some examples

Key characteristics

• Continuous, Repetitive Operation
• Consume Materials and create Products in discrete amounts
• May consume other ancillary resources (e.g. energy)

Black Box view

Measuring Operations Performance

• Yield
• Throughput
• Sojourn/Lead-Time
• Work In Progress
• Cost
• Utilization

Queueing Model of Operations

• Arrival
• Start
• Complete
• Departure*

Little’s Law

Throughput/Lead Time Relationship

Resource Consumption

Yield

The Control Problem

• Goal: Keep the system operating in the design window w.r.t.:
  • Throughput, Lead-time, Yield
• Levers

Additional Notes

Characteristics/Concepts

• Discrete unit of output: Job
• Jobs are produced by performing Processes
• Processes are partially ordered sets of Tasks
• Tasks are:
  • Discrete (start-end)
  • Parametric
  • Variable/Stochastic

• Tasks are performed by Stations which
  • Consume Materials and other resources
  • Have finite Capacity
  • Station’s behavior has a stochastic component

Interactions

• Jobs can be successful or fail
• Processes prescribe the (partial) order in which Tasks can be executed.
• A Task execution is possible only when:
  1. Any preceding Task in the process has been completed
  2. A Station that can perform the task is available.
  3. The materials required are available at the station
  4. Other Required Resources are available
• Otherwise, the Task must wait to be performed.

System “Design Point”

• Some simplifications:
  • Fixed Capacity
  • Yield Independence/constant
  • Linear Costs

• Possible Objectives:
  • Minimize Cost s.t. min Throughput max Lead-time
  • Minimize Lead-Time s.t. min Throughput max Cost
  • Maximize Throughput s.t. max Cost max Lead-Time