CHAPTER 19 Scheduling Operations Management, Eighth Edition, by William J. Stevenson Copyright © 2005 by The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill/Irwin

Work Center 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 3

Scheduling Scheduling: Establishing the timing of the use of equipment, facilities and human activities in an organization Effective scheduling can yield Cost savings Increases in productivity

Typical Scheduling and Control Functions Allocating orders, equipment, and personnel Determining the sequence of order performance Initiating performance of the scheduled work Shop-floor control 5

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

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

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

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.

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

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

Johnson’s Rule Optimum Sequence List the jobs and their times at each work center Select the job with the shortest time If the shortest time is on the first center, Do the job First; If it is on the 2nd center, Do the job Last. In case of tie, do the job on the first machine. Eliminate the job from further consideration Repeat steps 2 and 3 until all jobs have been scheduled

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

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

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

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

Example 2 Average Tardiness (days) Average Flow Time (days) 3.2 8.60 43.00 STR 2.4 7.80 39.00 EDD 7.20 36.00 SOT 4.6 10.00 50.00 FCFS Average Tardiness (days) Average Flow Time (days) Total Flow Time (days) Rule

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

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

Scheduling Service Operations Appointment systems Controls customer arrivals for service Reservation systems Estimates demand for service Scheduling the workforce Manages capacity for service Scheduling multiple resources Coordinates use of more than one resource

Cyclical Scheduling Hospitals, police/fire departments, restaurants, supermarkets Rotating schedules Set a scheduling horizon Identify the work pattern Develop a basic employee schedule Assign employees to the schedule

Service Operation Problems Cannot store or inventory services Customer service requests are random Scheduling service involves Customers Workforce Equipment