1. Scheduling Operations
Chapter 13

2. Chapter 13 Outline Batch Scheduling Gantt Charting
Finite Capacity Scheduling
Theory of Constraints
Priority Dispatching Rules
Infinite Capacity Loading
Planning and Control Systems

3. Synonyms Shop Floor Control Scheduling Operations
Production Activity Control (PAC)
Detailed Planning and Scheduling (DPS)

4. Batch Scheduling Very complex scheduling environment
Can be thought of as “Network of Queues”
Customers spend most of their time waiting
Closely related to MRP (See chapter 16)

5. Batch Processing Move-queue-work-wait-move
WS 1
WS 2
move
queue
wait
wait
queue
move
move
Work is done according to work order

6. Difficulties Of Batch/Job Shop Scheduling
Variety of jobs processed
Different routing and processing requirements of each job
Number of different orders in the facility at any one time
Competition for common resources

7. Responsibilities of Production Control Department
Loading
Check availability of material, machines & labor
Sequencing
Release work orders to shop & issue dispatch lists for individual machines
Monitoring
Maintain progress reports on each job until it is complete

8. Gantt Charting Developed by Henry Gantt in 1917 Related concepts:
Makespan – total time to complete a set of jobs
Machine utilization – percent of make span time a machine (or person) is used.
Used primarily to monitor progress of jobs

9. Job Data for Scheduling Example

10. In what sequence should the jobs be done?
Scheduling Example
In what sequence should the jobs be done?
Job 2
Job 4
Job 5
Process A
Process C
Job 1 A C
Process B
Job 3 B

11. Where is the bottleneck?
Total Machine times for the five jobs:
Machine A: 15 hours
Machine B: 12 hours
Machine C: 16 hours
C appears to be the bottleneck.
But! A is used for every job; C is not.
Either one could determine makespan.

12. Gantt Chart for Example

13. Finite Capacity Scheduling
Finite capacity scheduling loads jobs onto work stations being careful not to exceed the capacity of any given station.
Done at the detailed planning and scheduling (DPS) level
Part of the loading responsibility.

14. Theory of Constraints (TOC)
Proposed by Goldratt in The Goal (1983)
Goal is to make money.
Key elements of “goals” according to TOC:
Throughput—what is made and sold
Inventory—raw materials
Operating expenses—cost of conversion
Production does not count until it is sold!

15. Theory of Constraints (TOC)
A constraint is anything that is slowing down production—a bottleneck.
A machine or workstation
The market
Procurement system
The bottleneck determines the capacity of the system.
Implication: the operations manager should focus on the bottleneck to increase capacity and throughput (and make more money).

16. Priority Dispatching Rules
What are priority dispatching rules?
If you have more than one job waiting at a work station, how do you select which one to process next? The criterion you use for selecting the next job is your dispatching rule.
In front office services, the most common rule is “first come, first served.”
Part of the sequencing responsibility

17. Priority Dispatching Rules
Commonly used in manufacturing:
MINPRT (Minimum Processing Time or SPT, shortest processing time) This rule minimizes total waiting time.
Critical Ratio (Minimizes average lateness)
Commonly used in services:
FCFS (First Come, First Served)

18. Infinite Capacity Loading
“Infinite capacity loading” loads jobs onto work centers without regard for the total capacity of the work center.
If the capacity for any given work center has been exceeded, the schedule must be changed.
This is generally done at the MRP level before detailed scheduling and planning

19. Infinite capacity loading example: time lines
Time line for job 1
Due date A
(2 hrs)
Move/Wait
(4 hrs) B
(3 hrs)
Move/Wait
(4 hrs) C
(4 hrs)
Day 1
Day 2
Day 3
Time line for job 2
Due date
C (6 hrs)
Move/Wait
(4 hrs)
A (4 hrs)
Day 1
Day 2
Day 3

20. Infinite Capacity Loading example
Work center A
Work center B
Work center C
Hours scheduled 1 2 3
Day 1 2 3
Day 1 2 3
Day

21. Planning and Control Systems
What delivery date do I promise?
How much capacity do I need?
When should I start on each particular activity or task?
How do I make sure that the job is completed on time?
Advanced Planning & Scheduling (APS)

22. Summary Batch Scheduling Gantt Charting Finite Capacity Scheduling
Theory of Constraints
Priority Dispatching Rules
Infinite Capacity Loading
Planning and Control Systems

23. End of Chapter Thirteen