1. Capacity Planning, Aggregate Scheduling, Master Schedule, and Short-Term Scheduling
1. Facility size
2. Equipment procurement
Long-term
Aggregate Scheduling
1. Facility utilization
2. Personnel needs
3. Subcontracting
Intermediate-term
Master Schedule
1. MRP
2. Dis-aggregation of master plan
Intermediate-term
Students should be asked to identify three decisions at each level.
Short-term Scheduling
1. Work center loading
2. Job sequencing
Short-term

2. Scheduling Low-Volume Systems
Loading - assignment of jobs to process centers
Sequencing - determining the order in which jobs will be processed
Job-shop scheduling
Scheduling for low-volume systems with many variations in requirements

3. Loading Jobs in Work Centers
Assigning jobs to work centers
Considerations
Job priority (e.g., due date)
Capacity
Work center hours available
Hours needed for job
Approaches
Gantt charts (load & scheduling) - capacity
Assignment method - job to specific work center

4. Loading Two Approaches to loading:
- Finite Loading – limit the amount of work that is released to a given work center on the basis of capacity consideration.
Input/output control is a method for keeping track of assigned resource (input) and the work completed by a resources (output). This helps identify a backlog (input rate in greater that output rate). The remove a backlog to slow down the input.

5. Loading
- Infinite loading – assign job to center regardless of available capacity. This requires that proper planning has been done to make sure enough capacity is available to take care of all work to be done.

6. Scheduling
Definition: Determination of when something is to be done and the tasks and activities required to do it. Establishing the timing of the use of equipment, facilities and human activities in an organization
Scheduling aids in on-time completion
Direct link to value perceived by customers
Scheduling improves the utilization of the firm’s resources
Direct link to productivity

7. Strategic Implications of Short-Term Scheduling
By scheduling effectively, companies use assets more effectively and create greater capacity per dollar invested, which, in turn, lowers cost
This added capacity and related flexibility provides faster delivery and therefore better customer service
Good scheduling is a competitive advantage which contributes to dependable delivery
You might stress to students that scheduling is what the end-customer actually sees.

8. The Goals of Short-Term Scheduling
Minimize completion time
Maximize utilization (make effective use of personnel and equipment)
Minimize WIP inventory (keep inventory levels low)
Minimize customer wait time
While we would like to minimize customer wait time, an alternate goal might be to make customer wait time consistent - we could always ask them to come later.

9. Scheduling Services Considerations
Scheduling services different from manufacturing
Inability to store or inventory services
Random nature of customer requests for service
Point of customer contact
Back-office operations
Front-office operations 9

10. Choosing a Scheduling Method
Qualitative factors
Number and variety of jobs
Complexity of jobs
Nature of operations
Quantitative criteria
Average completion time
Utilization (% of time facility is used)
WIP inventory (average # jobs in system)
Customer waiting time (average lateness)

11. Forward and Backward Scheduling
Forward scheduling: begins the schedule as soon as the requirements are known
jobs performed to customer order
schedule can be accomplished even if due date is missed
often causes buildup of WIP
Backward scheduling: begins with the due date of the final operation; schedules jobs in reverse order
used in many manufacturing environments, catering, scheduling surgery
Students should be asked to consider how, using either process, they would modify the schedule when (a) an order is cancelled, (b) a priority, rush order is accepted, or (c) a delay is encountered.

12. Scheduling Difficulties
Variability in
Setup times
Processing times
Interruptions
Changes in the set of jobs
No method for identifying optimal schedule
Scheduling is not an exact science
Ongoing task for a manager 12

13. Minimizing Scheduling Difficulties
Set realistic due dates
Focus on bottleneck operations
Consider lot splitting of large jobs 13

14. Sequencing
Sequencing: Determine the order in which jobs at a work center will be processed.
Priority rules: Simple heuristics used to select the order in which jobs will be processed.
Job time: Time needed for setup and processing of a job.

15. Priority Rules for Dispatching Jobs
FCFS
EDD
SPT
LPT CR
First come, first served
The first job to arrive at a work center is processed first
Earliest due date
The job with the earliest due date is processed first
Shortest processing time
The job with the shortest processing time is processed first
Longest processing time
The job with the longest processing time is processed first
Critical ratio
The ratio of time remaining to required work time remaining is calculated, and jobs are scheduled in order of increasing ratio.

16. Assumptions of Priority Rules
The setup of jobs is known
Setup time is independent of processing sequence
Setup time is deterministic
There will be no interruptions in processing such as:
Machine breakdowns
Accidents
Worker illness

17. First Come, First Served Rule
Process first job to arrive at a work center first
Average performance on most scheduling criteria
Appears ‘fair’ & reasonable to customers
Important for service organizations
Example: Restaurants

18. SPT and LPT Rule
SPT – Schedule a job with shortest processing time first
LPT – Schedule a job with longest processing time first

19. Earliest Due Date Rule Process job with earliest due date first
Widely used by many companies
If due dates important
If MRP used
Due dates updated by each MRP run
Performs poorly on many scheduling criteria

20. Advantages of the Critical Ratio Scheduling Rule
Use of the critical ratio can help to:
determine the status of a specific job
establish a relative priority among jobs on a common basis
relate both stock and make-to-order jobs on a common basis
adjust priorities and revise schedules automatically for changes in both demand and job progress
dynamically track job progress and location

21. Two Work Center Sequencing
Johnson’s Rule: technique for minimizing completion time for a group of jobs to be processed on two machines or at two work centers.
Minimizes total idle time
Several conditions must be satisfied

22. Johnson’s Rule Conditions
Job time must be known and constant
Job times must be independent of sequence
Jobs must follow same two-step sequence
Job priorities cannot be used
All units must be completed at the first work center before moving to second

23. Johnson's Rule - Scheduling N Jobs on Two Machines
1. List all jobs and their processing times each machine.
2. Select first the job with the shortest processing time. If the shortest processing time lies with the first machine, the job is scheduled first; if with the second machine, the job is scheduled last.
3. Once a job is scheduled, eliminate it.
Apply steps 2-3 to the remaining jobs until all jobs are assigned. The process will move toward the center of the sequence.

24. Limitations of Rule-Based Dispatching Systems
Scheduling is dynamic; therefore, rules need to be revised to adjust to changes in process, equipment, product mix, etc.
Rules do not look upstream or downstream; idle resources and bottleneck resources in other departments may not be recognized
Rules do not look beyond due dates
You might point out to students that this is another case of models which are insufficiently robust to handle all factors.
Ask students to consider how these limitations might be overcome. (Finite scheduling?) What is the role of information technology?

25. Number of Servers Single Server Multiple Servers Examples:
Multiple Single Servers
Examples:

26. Queue Discipline First come -- first served (FCFS):
Multiple Priorities:
Examples:

27. Project Management
A project is a set of activities aimed at meeting a goal, with a defined beginning and end.

28. Project Management with Certain Time Estimates
Summary of steps:
Determine activities that need to be accomplished
Determine precedence relationships and completion times
Construct network diagram
Determine the critical path
Determine early start and late start schedules

29. Project Scheduling When the Times of Activities are Uncertain
Summary of steps:
Determine the activities that need to be accomplished
Determine the precedence relationships and completion times
Construct the network diagram
Determine the critical path
Determine the early start and late start schedules
Calculate the variances for the activity times
Calculate the probability of completing by the desired due date

30. Project Scheduling with Time Uncertainty
The “Heuristic” approach to dealing with timing uncertainty
Based on understanding of individual activities as conforming to a “beta” distribution
Take three time estimates
Optimistic - What is the (realistic) fastest we can get an activity done?
Pessimistic - What is the (realistic) worst case scenario for delay?
Most likely - What is our “most likely” estimate?

31. Earliest Due Date Rule Process job with earliest due date first
Widely used by many companies
If due dates important
If MRP used
Due dates updated by each MRP run
Performs poorly on many scheduling criteria

32. Best Methods among Priority Rule
SPT and EDD are superior in all measure. SPT is generally the best for minimizing flow and average number of jobs.

33. Critical Ratio (CR) Ratio of time remaining to work time remaining=
Work days
remaining
Due date -
Today'
s date =
Work (lead
) time remaining
Process job with smallest CR first
Performs well on average lateness

34. Advantages of the Critical Ratio Scheduling Rule
Use of the critical ratio can help to:
determine the status of a specific job
establish a relative priority among jobs on a common basis
relate both stock and make-to-order jobs on a common basis
adjust priorities and revise schedules automatically for changes in both demand and job progress
dynamically track job progress and location

35. Two Work Center Sequencing
Johnson’s Rule: technique for minimizing completion time for a group of jobs to be processed on two machines or at two work centers.
Minimizes total idle time
Several conditions must be satisfied

36. Johnson’s Rule Conditions
Job time must be known and constant
Job times must be independent of sequence
Jobs must follow same two-step sequence
Job priorities cannot be used
All units must be completed at the first work center before moving to second

37. Limitations of Rule-Based Dispatching Systems
Scheduling is dynamic; therefore, rules need to be revised to adjust to changes in process, equipment, product mix, etc.
Rules do not look upstream or downstream; idle resources and bottleneck resources in other departments may not be recognized
Rules do not look beyond due dates
You might point out to students that this is another case of models which are insufficiently robust to handle all factors.
Ask students to consider how these limitations might be overcome. (Finite scheduling?) What is the role of information technology?

38. Queuing Theory Where is waiting? Service facility
Fast-food restaurants
post office
grocery store
bank
Manufacturing
Equipment awaiting repair
Phone or computer network
Product orders 38

39. Measures of System Performance
Average number of customers waiting
Average time customers wait
System utilization 39

40. Application of Queuing Theory
We can use the results from queuing theory to make the following types of decisions:
How many servers to employ
Whether to use a single fast server or a number of slower servers
Whether to have general purpose or faster specific servers
Goal:
Minimize total cost = cost of servers + cost of waiting 40

41. System Characteristics
Number of servers
Arrival and service pattern
Infinite Population – The arrival is not affected by waiting line (public places, e.g. gas station)
Finite Population – The arrival is affect by waiting line.
Queue discipline 41