Operations Management: An Integrated Approach, 5th Edition

SEQUENCING JOBS THROUGH TWO WORK CENTERS

At times, all jobs must be processed through the same two work centers sequentially. For example, when you do laundry, clothes go through the washer before the dryer. Different kinds of clothing need different wash cycles and different drying times, but the sequence is the same. To shorten the time it takes to do your laundry, you can use Johnson's rule. Johnson's rule is a scheduling technique for developing a sequence when jobs are processed through two successive operations. The operations can be at machine centers, departments, or different geographical locations. The job flow must be unidirectional: the first activity for every job is the same, and you must finish it before you can begin the second activity (wash the clothes before you dry the clothes). Johnson's rule is an optimizing technique and always minimizes makespan. To use Johnson's rule, follow this procedure.

Johnson's rule

A technique for minimizing makespan in a two-stage, unidirectional process.

Step 1 List the jobs and the processing time for each activity.

Step 2 Find the shortest activity processing time among all the jobs not yet scheduled. If the shortest activity processing time is a first activity, put the job needing that activity in the earliest available position in the job sequence. If the shortest activity processing time is a second activity, put the job needing ...