19-1 Scheduling

CHAPTER19

Scheduling

McGraw-Hill/IrwinOperations Management, Eighth Edition, by William J. StevensonCopyright © 2005 by The McGraw-Hill Companies, Inc. All rights

reserved.

19-2 Scheduling

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

· Can be a single machine, a group of machines, or an area where a particular type of work is done

Work Center

19-3 Scheduling

· Scheduling: Establishing the timing of the use of equipment, facilities and human activities in an organization

· Effective scheduling can yieldCost savings

Increases in productivity

Scheduling

19-4 Scheduling

· Allocating orders, equipment, and personnel

· Determining the sequence of order performance

· Initiating performance of the scheduled work

· Shop-floor control

Typical Scheduling and Control Functions

19-5 Scheduling

High-Volume Systems

· Flow system: High-volume system with Standardized equipment and activities

· Flow-shop scheduling: Scheduling for high-volume flow system

Work Center #1 Work Center #2 Output

19-6 Scheduling

High-Volume Success Factors

· Process and product design

· Preventive maintenance

· Rapid repair when breakdown occurs

· Optimal product mixes

· Minimization of quality problems

· Reliability and timing of supplies

19-7 Scheduling

Scheduling Low-Volume Systems

· Loading - assignment of jobs to process centers

· Sequencing - determining the order in which jobs will be processed

· Job-shop schedulingScheduling for low-volume systems with

many variations in requirements

19-8 Scheduling

Sequencing

· Sequencing: Determine the order in which jobs at a work center will be processed.

· Workstation: An area where one person works, usually with special equipment, on a specialized job.

19-9 Scheduling

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 in a common sequence.

· Minimizes Total Idle Time and Flow Time.

· Several Conditions Must Be Satisfied

19-10 Scheduling

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

19-11 Scheduling

Johnson’s Rule Optimum Sequence1. List the jobs and their times at each work center

2. Select the job with the shortest time1. If the shortest time is on the first center, Do the

job First;

2. If it is on the 2nd center, Do the job Last.

3. In case of tie, do the job on the first machine.

3. Eliminate the job from further consideration

4. Repeat steps 2 and 3 until all jobs have been scheduled

19-12 Scheduling

Johnson’s Rule (n Jobs on 2 Centers)Processing Time (Hours)

Jobs Work Center 1 Work Center 2

A 1.50 0.50

B 4.00 1.00

C 0.75 2.25

D 1.00 3.00

E 2.00 4.00

F 1.80 2.20

19-13 Scheduling

Sequencing

· 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.

Everything is#1 Priority

19-14 Scheduling

Priority Rules

· FCFS - first come, first served

· SOT - shortest processing time

· EDD - earliest due date

· LCFS - Last come, first served

· STR - slack time remaining

· Rush - emergency

Top Priority

19-15 Scheduling

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 breakdownsAccidentsWorker illness

19-16 Scheduling

3.28.6043.00STR

2.47.8039.00EDD

2.47.2036.00SOT

4.610.0050.00FCFS

AverageTardiness

(days)

AverageFlow Time

(days)

TotalFlow Time

(days)Rule

Example 2

19-17 Scheduling

Scheduling Difficulties· Variability inSetup timesProcessing timesInterruptionsChanges in the set of jobs

· No method for identifying optimal schedule· Scheduling is not an exact science· Ongoing task for a manager

19-18 Scheduling

Minimizing Scheduling Difficulties· Set realistic due dates

· Focus on bottleneck operations

· Consider lot splitting of large jobs

19-19 Scheduling

Scheduling Service Operations

· Appointment systemsControls customer arrivals for service

· Reservation systemsEstimates demand for service

· Scheduling the workforceManages capacity for service

· Scheduling multiple resourcesCoordinates use of more than one

resource

19-20 Scheduling

Cyclical Scheduling· Hospitals, police/fire departments, restaurants, supermarkets

· Rotating schedulesSet a scheduling horizonIdentify the work patternDevelop a basic employee scheduleAssign employees to the schedule

19-21 Scheduling

Service Operation Problems

· Cannot store or inventory services· Customer service requests are random· Scheduling service involves

CustomersWorkforceEquipment