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Ch 15 - Short-Term Scheduling

  1. Scheduling Processed-focused Facilities (Job Shops)
    1. Primary Activities (p606)
      1. Establishing due dates for each job
      2. Checking availability of tools and materials before releasing a job
      3. Loading - assigning jobs to work centers (MRP/CRP can be helpful)
      4. Sequencing - specifying the order in which jobs should be done at each work center
      5. Checking work in progress and determining corrective action when necessary.
  2. Sequencing Jobs      (p612)
    1. Priority rules - do not give optimal solution. For examples, see pages 612-616.
      1. FCFS - First Come, First Served
      2. *SPT - Shortest Processing Time
      3. *EDD - Earliest Due Date
      4. *LPT - Longest Processing Time
      5. *Critical ratio = (Due date - Today's date) / Work time remaining
                     If CR > 1, then job has slack.        If CR < 1, then job should be expedited.
    2. *Johnson’s Rule     (p616)
      1. Optimization method to minimize total processing time for sequencing n jobs thru 2 work centers.
      2. Procedure
        1. Select job with shortest time
        2. If shortest time corresponds to work center 1
          then place corresponding job as early as possible
          else place corresponding job as  late as possible.
        3. Eliminate that job and repeat steps a and b with remaining jobs.
      3. Example 7 - Tool and die shop - p616
                   Processing Time for Jobs (in hours)           
          Job 

        Work Center 1

        Work Center 2

        A
        B
        C
        D
        E

        5
         3
         8
        10
          7

        2
        6
        4
        7
        12
      4. Solution
                        Job Sequence                                             
          First    Second    Third    Fourth    Fifth  
        -
        B
        B
        B
        B        		 -
        -
        -
        E
        E        		 -
        -
        -
        -
        D        		 -
        -
        C
        C
        C        		 A
        A
        A
        A
        A

Optimal sequence is B, E, D, C, A.  (See page 617 for graph of job flow.)
        Do assigned HW         (This page was last edited on October 22, 2009 .)