MBA 8452 Systems and Operations ManagementMBA 8452 Systems and Operations Management

Operations Operations SchedulingScheduling

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Objectives

Explain work center capacity

Describe infinite and finite loading, forward and backward scheduling

Solve scheduling problems

Explain scheduling in service operations

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Scheduling

Allocates resources over time (short-run) to accomplish specific tasks

Examples Hospital: operating room, staff University: course, classroom, instructor Airline: flight departure, arrival, and crew Factory: product production, worker

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Operations Scheduling Work Center

An area in a business in which productive resources are organized and work is completed

Capacity and Scheduling Infinite loading Finite loading Forward scheduling Backward scheduling

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Typical Scheduling and Control Functions

Allocating orders, equipment, and personnel to work centers

Determining the sequence of job orders

Initiating performance of the scheduled work

Shop-floor control

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Work-Center Scheduling Objectives

Meet due dates

Minimize lead time

Minimize setup time or cost

Minimize work-in-process inventory

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Some Priority Rules for Job Sequencing

First-come, first-served (FCFS) Shortest operating/processing time

(SOT)

Earliest due date (DDate)

Least slack time remaining (STR)(due date - current date) - (remaining processing time)

Smallest critical ratio(due date-current date)/(remaining processing time)

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Job Sequencing

Performance Measures Average Lateness - meet due

dates of customers or downstream operations

Mean Flow Time - minimize the time a job spends in the process

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Job Sequencing on One Machine ExampleSix jobs are lined up for processing on one machine. Their processing times (in order of arrival) and due dates are listed below

JobProcessing Time (days) Due Date

A 9 22B 7 17C 3 16D 4 13E 8 16F 6 9

What is the sequencing schedule using FCFS, SOT, STR, or DDate rule?

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Job Sequencing on One Machine Example--FCFS Rule

Average lateness = 9.3 days

Mean flow time = 22.5 days

JobProcessing Time (days)

Due Date (days hence)

Flow Time (days)

Days Late

A 9 22 9 0B 7 17 16 0C 3 16 19 3D 4 13 23 10E 8 16 31 15F 6 9 37 28

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Job Sequencing on One Machine Example--SOT Rule

Average lateness = 5.67 days

Mean flow time = 18 days

JobProcessing Time (days)

Due Date (days hence)

Flow Time (days)

Days Late

C 3 16 3 0D 4 13 7 0F 6 9 13 4B 7 17 20 3E 8 16 28 12A 9 22 37 15

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Job Sequencing on One Machine Example--STR Rule

Average lateness = 7.67 days

Mean flow time = 22.33 days

JobProcessing Time (days)

Due Date (days hence)

Slack (days)

A 9 22 13B 7 17 10C 3 16 13D 4 13 9E 8 16 8F 6 9 3

JobProcessing Time (days)

Due Date (days hence)

Flow Time (days)

Days Late

F 6 9 6 0E 8 16 14 0D 4 13 18 5B 7 17 25 8A 9 22 34 12C 3 16 37 21

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Job Sequencing on One Machine Example--DDate Rule

JobProcessing Time (days)

Due Date (days hence)

Flow Time (days)

Days Late

F 6 9 6 0D 4 13 10 0C 3 16 13 0E 8 16 21 5B 7 17 28 11A 9 22 37 15

Average lateness = 5.17 days

Mean flow time = 19.17 days

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Job Sequencing on One Machine Example--Schedule Chart

0 9 16 19 23 31 37

FCFS

SOT 0 3 7 13 20 28 37

0 6 14 18 25 34 37

STR

DDate 0 6 10 13 21 28 37

A B C D E F

C D F B E A

F E D B A C

F D C E B A

Time (in days)

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Job Sequencing on One Machine Some General Results

For job sequencing on one machine/work center, schedule completion time (makespan) is always the same regardless of the job order

SOT minimizes average flow time and average waiting time

Earliest DDate rule minimizes the worst (maximum) lateness

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Job Sequencing on Two Machines Johnson’s Rule

Minimizes the time to complete all jobs in both work centers/machines (makespan)

Procedure of Applying Johnson’s Rule List the operation times for all jobs Select the shortest operating time overall If the SOT is for the:

1st machine - schedule that job first2nd machine - schedule that job last

Repeat steps and , until all jobs are scheduled

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Job Sequencing on Two Machines Example--Johnson’s Rule

Five jobs need to be processed at two workstations with the following processing time requirement

J ob Workstation 1 Workstation 2A 12 22B 4 5C 5 3D 15 16E 10 8

Processing Time (hour)

What is the best sequence of jobs that minimizes the flow time of all jobs? Answer: B-A-D-E-C

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Job Sequencing on Two Machines Example--Schedule Chart

Work Station

0 5 10 15 20 25 30 35 40 45 50 55 60 65

Hour

B A D E C1

2 B A D E CIdle Idle

Idle--available for further work

Makespan = 65 hours

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Shop-Floor (Production Activity) Control

Major Functions

1. Assign priority to each shop order

2. Maintain work-in-process quantity information

3. Convey shop-order status information

4. Provide actual output data for capacity control purposes

5. Provide quantity by location by shop order for WIP inventory and accounting purposes

6. Provide measurement of efficiency, utilization, and productivity of manpower and machines

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Input/Output Control

Input OutputWorkCenter

Planned input should never exceed planned output (in the long run)

Focuses attention on bottleneck work centers

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Personnel Scheduling in Services

Scheduling consecutive days off

Scheduling daily work times

Scheduling hourly work times