mba.782.operations.schedulingcaj9.15.1 operations management operations scheduling manufacturing...

MBA.782.Operations.Scheduling CAJ9.15.1

Operations Management

Operations Scheduling

• Manufacturing Execution Systems

• Equipment Scheduling

– Work Centers

– Priority rules

– Johnson’s rule

– Backward / Forward scheduling

• Workforce Scheduling


• Work flow = Cash flow

• Work flow is driven by a schedule

• ____ % of time actually working; ____ % of time waiting in queues

• Schedule equipment and workforce

Oper. Sched.

Manufacturing Execution Systems


• Becomes exceedingly complex because....

– Unpredictability of demand for all resources

– Variability of throughput times

– Tradeoffs among:

Utilization of people and equipment vs. Work in Process vs. ability to meet promised delivery dates

Oper. Sched.

Equipment Scheduling


• A work center is an area in a business in which productive resources are organized and work is completed.

– where a particular type of work is done.

– Finite / infinite ____________

– backward / forward _____________

– machine and/or labor ___________

Equip. Sched..

Work Centers


• Queue time

– ___________ for the resource of interest

• Flow time = operation time + queue time

– time for a job to _______________ the process

• Lateness = ( Flow time - Due date ) +

• Completion time (aka, ______________ )

– finish time of last job - start time of first job

Equip. Sched.

Definitions


• Meeting ____ ______ of customers or downstream operations.

• Minimizing the flow time

– the time a job _________ in the process

• Minimizing work-in-process inventory.

• Minimizing _____ ______ of machines or workers.

• Maximize machine utilization

Equip. Sched.

Schedule Performance Measures


• Allocating orders, equipment, and personnel.

• Determining the ____________ of order performance.

• Schedule jobs as a _________ with process stagesback to back.

• Re-schedule every day.

Equip. Sched.

Scheduling Activities


• Used for n-Jobs on One Machine

• Local Priority Rules

– schedule jobs according to their effect on the _____________________ workstation

• Global Priority Rules

– sequence jobs according to their effect on ____________ work requirements

Equip. Sched.

Priority Rules and Techniques


• Suppose these four jobs arrive for processing on one machine:

Local Priority Rules

First Come, First Serve (FCFS)

Job Processing Due Date Flow(in order time (in hours Time Lateness Slackof arrival) (in hours) from now)

A 2 8 2 0.0 6B 4 9 6 0.0 5C 7 29 13 0.0 22D 1 1.5 14 12.5 0.5E 5 22 19 0.0 17F 3 10 22 12.0 7

Total: 76 24.5Average: 12.67 4.08


• The job with the shortest processing time is processed

first


Shortest Operation Time (SOT)

Job Processing Due FlowSequence time Date Time Lateness Slack

D 1 1.5 1 0.0 0.5A 2 8 3 0.0 6F 3 10 6 0.0 7B 4 9 10 1.0 5E 5 22 15 0.0 17C 7 29 22 0.0 22

Total: 57 1Average: 9.5 0.17


• Schedule job with smallest slack first


Slack Time Remaining (STR)

Job Processing Due FlowSequence time Date Time Lateness Slack

D 1 1.5 1 0.0 0.5B 4 9 5 0.0 5A 2 8 7 0.0 6F 3 10 10 0.0 7E 5 22 15 0.0 17C 7 29 22 0.0 22

Total: 60 0Average: 10 0.00


Global Priority Rules.

Critical Ratio (CR)

remainingtimeShop

dateduetoremainingTimeCR

• Sequence: ____ , ____ , ____ , ____

Operation TimeTime at Remaining Number of Shop TimeLathe to Due Date Operations Remaining

Job (hours) (days) Remaining (days) CR

AA 2.3 15 10 6.1 2.46BB 10.5 10 2 7.8 1.28CC 6.2 20 12 14.5 1.38DD 15.6 8 5 10.2 0.78


Global Priority Rules.

Dynamic Slack / Operation Remaining

remainingoperationsofNumber

remainingtimeShopdateduetoremainingTimeRODS

/

• Sequence: ____ , ____ , ____ , ____

Operation TimeTime at Remaining Number of Shop TimeLathe to Due Date Operations Remaining

Job (hours) (days) Remaining (days) STR / RO

AA 2.3 15 10 6.1 0.89BB 10.5 10 2 7.8 1.10CC 6.2 20 12 14.5 0.46DD 15.6 8 5 10.2 -0.44


• Used to schedule n-jobs through 2 sequential machines

© 1995 Corel Corp.

© 1995 Corel Corp.

Saw Drill

Job AJob A

Job BJob B

Job CJob C

Jobs (N = 3)

Oper. Sched.

Johnson’s Rule


All jobs are to be listed, and the time required on each

machine is shown.

Select the job with the shortest activity time. If the shortest

time lies with the first machine, the job is scheduled first; if

with the second machine, the job is scheduled last.

Once a job is scheduled, eliminate it.

Apply steps 2-3 to the remaining jobs,

working toward the center of the sequence.

Oper. Sched.

Johnson’s Rule


Jobs to be sent through a 2-machine sequence...

Job Saw Time Drill TimeA 5 2B 3 6C 8 4D 10 7E 7 12

Oper. Sched.

Johnson’s Rule


Oper. Sched.

Forward and Backward Scheduling

• Forward Scheduling

– schedule the ____________ possible starting time

– due dates determined by internal scheduler

• Backward Scheduling

– determine the _____________ possible starting time

– for externally set due dates


Oper. Sched.


Forward

Hour: 1 2 3 4 5 6 7 8 9 10Facility

IIIIII

Job Hour Due Facility Number and (hours required) in Sequence

A 8 III (1), II (3), I (2)B 6 II (2), III (1), I (1)C 4 I (2), III (1)


Oper. Sched.


Job Hour Due Facility Number and (hours required) in Sequence

A 8 III (1), II (3), I (2)B 6 II (2), III (1), I (1)C 4 I (2), III (1)

Backward

Hour: 1 2 3 4 5 6 7 8 9 10Facility

IIIIII


Oper. Sched.

Workforce Scheduling in Services

• Need to know

– forecasted staffing levels

– specific skills needed during the time-frame

– work-hour constraints

• Consecutive days-off requirements

– methods exist to provide the _____ schedule

• Complex scheduling situations

– computer programs used to find ______________

schedules, given many constraints


Oper. Sched.

Scheduling Consecutive Days Off

• Objective

– find the schedule that minimizes the number of five-

day workers with two consecutive days off, subject to

the demands of the daily staffing schedule

• Procedure

– given the total number of workers needed each day,

create a schedule by adding one worker at a time


Oper. Sched.

Scheduling Consecutive Days Off

Monday Tuesday Wednesday Thursday Friday Saturday SundayWorker 6 3 5 3 7 2 3


• Read Chapter 15

• Concepts / Terminology

• Review Lecture notes

• Recommended Problems

Topic Title

Chapter Wrap-Up


Principles of Work Center Scheduling

1. There is a direct equivalence between work flow and cash flow.

2. The effectiveness of any job shop should be measured by speed of flow through the shop.

3. Schedule jobs as a string, with process steps back-to-back.

4. A job once started should not be interrupted.


Principles of Job Shop Scheduling (Continued)

5. Speed of flow is most efficiently achieved by focusing on bottleneck work centers and jobs.

6. Reschedule every day.

7. Obtain feedback each day on jobs that are not completed at each work center.

8. Match work center input information to what the worker can actually do.


Principles of Job Shop Scheduling (Continued)

9. When seeking improvement in output, look for incompatibility between engineeringdesign and process execution.

10. Certainty of standards, routings, and so forth is not possible in a job shop, but always work towards achieving it.

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