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Supplement
J Operations Scheduling
1. Performance Measures for Scheduling Processes
• Front-office process:
• Back-office process:
• Performance measures (a “job” is defined as the object receiving service or being
manufactured)
o Flow time
o Past due (tardiness)
o Makespan
Makespan
=
Time of completion
of last job
−
Starting time
of first job
o Total inventory
Total
inventory
=
Scheduled receipts for
all items
+
On-hand inventories
of all items
o Utilization
o These performances are interrelated
▪ Minimizing the average flow time tends to increase ______________.
▪ Minimizing makespan for a group of jobs tends to increase ______________.
2. Job Shop Scheduling
• In this section, the focus is on scheduling approaches that can be used for environments that
have either: (1) divergent flow processes or (2) line flow processes.
• A manufacturer’s operation with divergent flows is often called a _______________.
o
o
o
• A manufacturer’s operation with line flow is often called a _________________.
o
o
o
1. Priority sequencing rules
a. Additional priority sequencing rules.
• Critical ratio (CR)
remaining timeshop Total
date) s(Today' - date) (Due
=CR
• Shortest processing time (SPT)
• Slack per remaining operations (S/RO)
remaining operations ofNumber
remaining) timeshop (Total - date)] s(Today' - date) [(Due
/=ROS
2. Scheduling jobs for one workstation
a. Single-dimension rules
• Example J.1 Comparing the EDD and SPT
• Scheduling at One Operation Using SPT. Use Application J.1:
Given the following information, devise an SPT schedule for the automatic routing
machine.
Order
Sequence
Hours
Since
Order
Arrived
Begin
Work
Finish
Time
(hr)
Flow
Time
(hr)
Scheduled
Customer
Pickup
Time
Actual
Pickup
Time
Hours
Early
Hours
Past
Due
1.
2.
3.
4.
Total
Average
b. Multiple-dimension rules
• Scheduling at One Operation Using CR and S/RO. Use Application J.2:
The following four jobs have just arrived at an idle drill press and must be scheduled.
Job
Processing Time
at Drill Press
(wk)
Time Remaining
to Due Date
(wks)
Number of
Operations
Remaining*
Shop Time
Remaining*
(wks)
AA
4
5
3
4
BB
8
11
4
6
CC
13
16
10
9
DD
6
18
3
12
EE
2
7
5
3
* Including drill press
Order
Standard time,
Including
Setup (hr)
Due Date
(hrs from now)
AZ135
14
14
DM246
8
20
SX435
10
6
PC088
3
18
Create the sequences for two schedules, one using the Critical Ratio rule and one using the
S/RO rule. (Students complete highlighted sections)
Critical Ratio
Slack/Remaining Operation
Job
Priority Index
Sequence on
Drill Press
Job
Priority Index
Sequence on
Drill Press
3. Scheduling jobs for multiple workstations
3. Flow Shop Scheduling
• Makespan implications
• Determining a production sequence for a group of jobs to minimize the makespan has two
advantages.
o
o
• Johnson’s rule is a procedure that _____________________________________
o Step 1:
o Step 2:
o Step 3:
o Sequencing Jobs at a Two-Station Flow Shop. Use Application J.3:
Use the following data to schedule two workstations arranged as a flow shop.
Time (hr)
Job
Workstation 1
Workstation 2
A
4
3
B
10
20
C
2
15
D
8
7
E
14
13
Workstation 1
Workstation 2
Start
Finish
Start
Finish
Makespan = ______
4. Labor-Limited Environments
• The resource constraint is the amount of labor available, not the number of machines or
workstations.
• The scheduler must also assign workers to their next workstations.
• Advanced planning and scheduling (APS):
