© 2006 Prentice Hall, Inc.15 – 1 Operations Management Chapter 15 – Short-Term Scheduling © 2006 Prentice Hall, Inc. PowerPoint presentation to accompany Heizer/Render Operations Management, 8e

© 2006 Prentice Hall, Inc.15 – 2 Strategic Importance of Short-Term Scheduling  Effective and efficient scheduling can be a competitive advantage  Faster movement of goods through a facility means better use of assets and lower costs  Additional capacity resulting from faster throughput improves customer service through faster delivery  Good schedules result in more reliable deliveries

© 2006 Prentice Hall, Inc.15 – 3 Scheduling Decisions Organization Managers Must Schedule the Following Arnold Palmer Hospital Operating room use Patient admissions Nursing, security, maintenance staffs Outpatient treatments University of Missouri Classrooms and audiovisual equipment Student and instructor schedules Graduate and undergraduate courses Lockheed-Martin factory Production of goods Purchases of materials Workers Hard Rock Cafe Chef, waiters, bartenders Delivery of fresh foods Entertainers Opening of dining areas Delta Airlines Maintenance of aircraft Departure timetables Flight crews, catering, gate, ticketing personnel Table 15.1

© 2006 Prentice Hall, Inc.15 – 4 Activity in Sequencing  Sequence the following cars into as many work days as needed. Garage can work on two cars simultaneously  Assume first come first serve sequencing; 8 hour workday. Customers arrive in the following order DAY 1  Car 3: Maintenance ; time needed 6 hours  Car 4: Maintenance ; time needed 10 hours  Car 1: Repair ; time needed 2 hours  Car 2: Repair ; time needed 2.5 hours DAY 2  Car 5: Maintenance ; time needed 3.5 hours  Car 6: Repair ; time needed 3.5 hrs  Car 7: Maintenance ; time needed 4 hours

© 2006 Prentice Hall, Inc.15 – 5 Solution: Sequencing Repair Track 2 Car 4: Repair – 2 hours Car 5: Repair – 3.5 hours Car 7:Maintenance 2.5 hours Repair Track 1 Car 3: Repair - 6 hours Car 1: Maintenance 2 hours Repair Track 1 Repair Track 2 Car 4: Repair – 8 hours Repair Track 2 Car 7:Maintenance 1.5 hours Repair Track 1 Car 2: Maintenance 2.5 hours Car 6:Maintenance 3.5 hours Day 1 Day 2 Day 3

© 2006 Prentice Hall, Inc.15 – 6 Activity in Sequencing_2  Schedule the following cars into 2 work days. Garage can work on two cars simultaneously  Method: Garage controlled scheduling (First assigned first serve; or capacity-based scheduling). 8 hours per day work time.  Car 3: Maintenance ; time needed 6 hours  Car 4: Maintenance ; time needed 10 hours  Car 1: Repair ; time needed 2 hours  Car 2: Repair ; time needed 2.5 hours  Car 5: Maintenance ; time needed 3.5 hours  Car 6: Repair ; time needed 3.5 hrs  Car 7: Maintenance ; time needed 4 hours

© 2006 Prentice Hall, Inc.15 – 7 Solution: Sequencing _2  Schedule for days 1 and 2. Notice one track for long duration work and the other for fast jobs! Repair Track 2 Car 4: Repair – 2 hours Car 3: Repair – 6 hours Repair Track 1 Car 1: Repair - 2 hours Car 5: Maintenance 3.5 hours Car 2: Maintenance 2.5 hours Repair Track 1 Car 6: Maintenance 3.5 hours Car 7:Maintenance 4.0 hours Repair Track 2 Car 4: Repair – 8 hours Fast turnaround jobs Long turnaround jobs Day 2 Day 1

© 2006 Prentice Hall, Inc.15 – 8 Definitions  Scheduling is the assignment of due dates to specific work or jobs.  Loading is the assignment of jobs to work centers.  Sequencing: Determining the order in which jobs should be done at each work center so that due dates are met.  Input-Output control: Any technique that enables managers to manage workflows at each work center by comparing work added to work completed.

© 2006 Prentice Hall, Inc.15 – 9 Figure 15.1 Positioning Scheduling

© 2006 Prentice Hall, Inc.15 – 10 Defining Scheduling  Scheduling deals with the assignment of activities (demand) to resources (supply) (or vice-versa) and timing of activities. E.g. supply could be production capacity of a firm )  Types of scheduling situations  Type I: Supply options (M) are fewer than demand options (N)  Type II: Supply options (M) are equal to demand options (N)  Type III: Supply options (M) exceed the number of demand options (N)

© 2006 Prentice Hall, Inc.15 – 11 Objectives of Scheduling  Goals of scheduling  Type I: Supply options (M) are fewer than demand options (N)  Assign scarce supply to demand to minimize cost or maximize benefits  Type II: Supply options (M) are equal to demand options (N)  Assign supply to demand to minimize cost or maximize benefits for total process  Type III: Supply options (M) exceed the number of demand options (N)  Scheduling is done for limited capacity and excess capacity is outsourced.

© 2006 Prentice Hall, Inc.15 – 12 Methods of Scheduling  Forward scheduling concept  Scheduling begins as soon as customer requests and requirements are known  Scheduling begins from the estimated start date of the project and works forward to determine the start and finish dates for each of the activities that make up the order.  Backward scheduling concept  Scheduling begins from the expected delivery date and works backwards to determine the finish and start dates for the activities that make up the order. [Usually this method is available for projects that have long completion times, large number of units or parts, and have the completion of project on or before the delivery deadline as a key objective].

© 2006 Prentice Hall, Inc.15 – 13 Loading_Activity_A  We own a hotel which has a large ballroom. We have to schedule activities for two Saturdays in May. The closing time of the ballroom each Saturday is 10 pm. Which activities would you schedule? We charge per hour for the time a client spend using room. No charges for cleaning and preparation times.  Event A: 9 am - 1 pm, Cleanup needed after event 2 hrs.  Event B: 4 pm – 7 pm, preparation needed before event 0.5 hours. Cleanup needed after event 1 hrs.  Event C: 5 pm - 10 pm, preparation needed before event 1 hours. Cleanup after event 2 hrs.  Event D: 9 am -12 pm, preparation needed before event 1 hours. Cleanup after event 1 hrs.  Event E: 11 am – 8 pm, preparation needed before event 2 hours. Cleanup after event 2 hrs.

© 2006 Prentice Hall, Inc.15 – 14 Activity_A Scheduling Criteria and Options  Option1  Event A: 9 am - 1 pm AND Event B: 4 – 7 pm  Event D: 9 am -12 pm AND Event C: pm.  Option 2  Event A: 9 am - 1 pm AND Event C pm.  Event D: 9 am -12 pm AND Event B: 4 – 7 pm  Option 3  Event A: 9 am - 1 pm AND Event B OR Event C  Event E: 11 am – 8 pm Scheduling Criteria: Why did we schedule the way we did? We are tried to maximize the utilization of the ballroom (maximize utilization)! Other criteria; Min. Cost, Min. waiting time or Work in progress (WIP)

© 2006 Prentice Hall, Inc.15 – 15 Comparing Options_Activity_A  Option1  Event A: 9 am - 1 pm AND Event B: 4 – 7 pm  Event D: 9 am -12 pm AND Event C: pm.  Option 2  Event A: 9 am - 1 pm AND Event C pm.  Event D: 9 am -12 pm AND Event B: 4 – 7 pm  Option 3  Event A: 9 am - 1 pm AND Event B OR Event C  Event E: 11 am – 8 pm OPTION 3: Less switching costs, maximize utilization, minimize waiting times, maximize profits

© 2006 Prentice Hall, Inc.15 – 16 Activity_Scheduling If you could change one thing in the operations scheduling of this case, what would you change? We own a hotel which has a large ballroom. We have to schedule activities for two Saturdays in May. The closing time of the ballroom each Saturday is 10 pm. Which activities would you schedule? We charge per hour for time spent in room. No charges for cleaning and preparation times.  Event A: 9 am - 1 pm, Cleanup needed after event 2 hrs.  Event B: 4 pm – 7 pm, preparation needed before event 0.5 hours. Cleanup needed after event 1 hrs.  Event C: 5 pm - 10 pm, preparation needed before event 1 hours. Cleanup after event 2 hrs.  Event D: 9 am -12 pm, preparation needed before event 1 hours. Cleanup after event 1 hrs.  Event E: 11 am – 8 pm, preparation needed before event 2 hours. Cleanup after event 2 hrs.

© 2006 Prentice Hall, Inc.15 – 17 Activity_Scheduling If you could change one thing in the operations scheduling of this case, what would you change? Demand Options:  Charge for cleaning time  Set minimum reservation time Capacity Options:  Build new ballroom  Extend working hours per day

© 2006 Prentice Hall, Inc.15 – 18 Scheduling Criteria  Types of scheduling/sequencing criteria  Goal-based approaches  Minimize cost, waiting times  Minimize work-in-process  Maximize profits  Priorities-based approaches  First-come first serve or Last-in-first-out  Longest processing time  Earliest due date  Shortest processing time

© 2006 Prentice Hall, Inc.15 – 19 Job Loading Methods  Types of scheduling methods  Arbitrary approaches  Useful when there are no constraints of resources (Supply exceeds demand)  Rule-based approaches  Useful when there are constraints of resources  Priorities-based approaches  Useful when there are constraints of resources and there are priorities among suppliers or customers

© 2006 Prentice Hall, Inc.15 – 20 Assignment Method (Type II Scheduling)  A special class of linear programming models that assign tasks or jobs to resources  Objective is to minimize cost or time  Only one job (or worker) is assigned to one machine (or project)

© 2006 Prentice Hall, Inc.15 – 21 Assignment Method 1.Create zero opportunity costs by repeatedly subtracting the lowest costs from each row and column 2.Draw the minimum number of vertical and horizontal lines necessary to cover all the zeros in the table. If the number of lines equals either the number of rows or the number of columns, proceed to step 4. Otherwise proceed to step 3. 3.Subtract the smallest number not covered by a line from all other uncovered numbers. Add the same number to any number at the intersection of two lines. Return to step 2. 4.Optimal assignments are at zero locations in the table. Select one, draw lines through the row and column involved, and continue to the next assignment.

© 2006 Prentice Hall, Inc.15 – 22 Assignment Example ABC Job R-34$11$14$ 6 S-66$ 8$10$11 T-50$ 9$12$ 7 Typesetter ABC Job R-34$ 5$ 8$ 0 S-66$ 0$ 2$ 3 T-50$ 2$ 5$ 0 Typesetter Step 1a - Rows ABC Job R-34$ 5$ 6$ 0 S-66$ 0$ 0$ 3 T-50$ 2$ 3$ 0 Typesetter Step 1b - Columns Least numbers per row Least numbers per column

© 2006 Prentice Hall, Inc.15 – 23 Assignment Example Step 2 - Lines ABC Job R-34$ 5$ 6$ 0 S-66$ 0$ 0$ 3 T-50$ 2$ 3$ 0 Typesetter Because only two lines are needed to cover all the zeros, the solution is not optimal (it is fewer than the number of jobs to assign) Step 3 - Subtraction ABC Job R-34$ 3$ 4$ 0 S-66$ 0$ 0$ 5 T-50$ 0$ 1$ 0 Typesetter The smallest uncovered number is 2 so this is subtracted from all other uncovered numbers and added to numbers at the intersection of lines

© 2006 Prentice Hall, Inc.15 – 24 Assignment Example Because three lines are needed to cover all the numbers, the solution is optimal and job assignments can now be made Step 2 - Lines ABC Job R-34$ 3$ 4$ 0 S-66$ 0$ 0$ 5 T-50$ 0$ 1$ 0 Typesetter Start by assigning S-66 for worker B. Job T-50 must go to worker A. This leaves R-34 to worker C as this is the least cost assignment for worker C. Step 4 - Assignments ABC Job $ 3$ 4 R-34$ 3$ 4$ 0 $ 0$ 5 S-66$ 0$ 0$ 5 $ 1$ 0 T-50$ 0$ 1$ 0 Typesetter

© 2006 Prentice Hall, Inc.15 – 25 Assignment Example Step 4 - Assignments ABC Job $ 3$ 4 R-34$ 3$ 4$ 0 $ 0$ 5 S-66$ 0$ 0$ 5 $ 1$ 0 T-50$ 0$ 1$ 0Typesetter From the original cost table Minimum cost = $6 + $10 + $9 = $25 ABC Job R-34$11$14$ 6 S-66$ 8$10$11 T-50$ 9$12$ 7 Typesetter Costs Table

© 2006 Prentice Hall, Inc.15 – 26 Opportunity Loss: Example 2 (Deriving Opportunity Loss Table) ABC Job R-34$11$14$ 6 S-66$ 8$10$11 T-50$ 9$12$ 7 Typesetter ABC Job R-34$15-$11$15-$14$15-$6 S-66$15-$8$15-$10$15-$11 T-50$14-$9$14-$12$14-$7 Typesetter (Sales – Costs) Table ABC Job R-34$ 4$ 1$ 9 S-66$ 7$ 5$ 4 T-50$ 5$ 2$ 7 Typesetter Assume that the fixed sale price for each job is as follows : R-34 = $ 15 /unit; S-66 = $ 15 /unit; T-50 = $ 14 /unit; Opportunity Loss Table Assignment Costs Table

© 2006 Prentice Hall, Inc.15 – 27 Assignment: Example 2 (Deriving Opportunity Loss Table) The table has profit margins that are earned for each unit made. To find the optimal assignment, use the method but subtract the highest score of each row not the least one. ABC Job R-34$ 4$ 1$ 9 S-66$ 7$ 5$ 4 T-50$ 5$ 2$ 7 Typesetter Opportunity Loss Table ABC Job R-34-$ 5-$ 8$ 0 S-66$ 0-$ 2-$ 3 T-50-$ 2-$ 5$ 0 Typesetter ABC Job R-34-$ 5-$ 6$ 0 S-66$ 0$ 0-$ 3 T-50-$ 2-$ 3$ 0 Typesetter Take highest number from each column and subtract from all the numbers in the column. Note -2 is the highest number in column B! 1 2 3

© 2006 Prentice Hall, Inc.15 – 28 Assignment: Example 2 (Deriving Opportunity Loss Table) Draw lines across the zeros. As only two lines cross all the zeros, solution is not yet optimal. Opportunity Loss Table ABC Job R-34-$ 5-$ 6$ 0 S-66$ 0$ 0-$ 3 T-50-$ 2-$ 3$ 0 Typesetter Take highest number from uncrossed cells and subtract it from all other uncrossed numbers in each column. Add the number to number on the intersection Intersection to get table 5. This is not an optimal solution – 2 lines through all zeros 4

© 2006 Prentice Hall, Inc.15 – 29 Opportunity Loss: Example 2 Assign C to R-34; assign A to T-50; assign B to S-66; The profit margin of the assignment is taken from first table: = $5 + $ 5 + $ 9 = $ 19 ABC Job R-34$ 4$ 1$ 9 S-66$ 7$ 5$ 4 T-50$ 5$ 2$ 7 Typesetter Gross Margin - Opportunity Loss Table 1 ABC Job R-34-$ 3-$ 4$ 0 S-66$ 0$ 0-$ 5 T-50$ 0-$ 1$ 0 Typesetter5 ABC Job R-34-$ 5-$ 6$ 0 S-66$ 0$ 0-$ 3 T-50-$ 2-$ 3$ 0 Typesetter4 Largestuncrossednumber Table 5 now has three lines going through all the zeros. An optimal assignment can now be Made for our problem!

© 2006 Prentice Hall, Inc.15 – 30 Gantt Load Chart Method (Type III Scheduling) Day MondayTuesdayWednesdayThursdayFriday Work Center Metalworks Mechanical Electronics Painting Job 349 Job 408 ProcessingUnscheduled Center not available Job 350 Job 349 Job 295 Figure 15.3

© 2006 Prentice Hall, Inc.15 – 31 Plan 1: Gantt Staffing Chart (Type III Scheduling) Mon TueWedThu Fri SatSun Bill Off Off MaryOffOff Sue Off Off Will Off Off Bob Off Off MonOffOff Josh Off Off 1. Required Capacity Max available staff Max off duty limits Scheduled off-duty Extra staff needed Scheduled off duty minus Max. off duty limit ( row 4. Minus row 3.) Schedule What would you advise the manager to do?

© 2006 Prentice Hall, Inc.15 – 32 Plan 2: Gantt Staffing Chart (Type III Scheduling) Mon TueWedThu Fri SatSun BillOffOff MaryOffOff Sue OffOff WillOff Off BobOff Off MonOffOff Josh Off Off 1. Required Capacity Max available staff Max off duty staff Scheduled off-duty Extra staff needed Minus 3 Schedule This solution shifts all temp staff requirement to weekends What could be the benefit/problem with this plan?

© 2006 Prentice Hall, Inc.15 – 33 Gantt Schedule Chart Example Figure 15.4 Job Day 1 Day 2 Day 3 Day 4 Day 5 Day 6 Day 7 Day 8 A B C Now Maintenance Start of an activity End of an activity Scheduled activity time allowed Actual work progress Nonproduction time Point in time when chart is reviewed

© 2006 Prentice Hall, Inc.15 – 34 Sequencing  Specifies the order in which jobs should be performed at work centers  Priority rules are used to dispatch or sequence jobs  FCFS: First come, first served  SPT: Shortest processing time  EDD: Earliest due date  LPT: Longest processing time

© 2006 Prentice Hall, Inc.15 – 35 Sequencing Example Job Job Work (Processing) Time (Days) Job Due Date (Days) A68 B26 C818 D315 E923 Apply the four popular sequencing rules to these five jobs

© 2006 Prentice Hall, Inc.15 – 36 Sequencing: FCFS Example Job Sequ- ence Job Work (Proce ssing) Time Wait Times Flow Time Job Due Date Job Lateness A60680 B26862 C D E FCFS: Sequence A-B-C-D-E (assume that all jobs arrived on same day in the sequence given). arrived on same day in the sequence given).

© 2006 Prentice Hall, Inc.15 – 37 Sequencing Example FCFS: Sequence A-B-C-D-E Average completion time = = 77/5 = 15.4 days Total flow time Number of jobs Utilization = = 28/77 = 36.4% Total job work time Total flow time Average number of jobs in the system = = 77/28 = 2.75 jobs/month Total flow time Total job work time Average job lateness = = 11/5 = 2.2 days Total late days Number of jobs

© 2006 Prentice Hall, Inc.15 – 38 Sequencing Example Job Sequence Job Work (Processing) Time Flow Time Job Due Date Job Lateness B2260 D35150 A61183 C E SPT (Shortest processing time): Sequence B-D-A-C-E The sequence changes with the priority rule

© 2006 Prentice Hall, Inc.15 – 39 Sequencing Example SPT: Sequence B-D-A-C-E Average completion time = = 65/5 = 13 days Total flow time Number of jobs Utilization = = 28/65 = 43.1% Total job work time Total flow time Average number of jobs in the system = = 65/28 = 2.32 jobs/months Total flow time Total job work time Average job lateness = = 9/5 = 1.8 days Total late days Number of jobs

© 2006 Prentice Hall, Inc.15 – 40 Sequencing Example Job Sequence Job Work (Processing) Time Flow Time Job Due Date Job Lateness B2260 A6880 D C E EDD (Earliest due date) : Sequence B-A-D-C-E

© 2006 Prentice Hall, Inc.15 – 41 Sequencing Example EDD: Sequence B-A-D-C-E Average completion time = = 68/5 = 13.6 days Total flow time Number of jobs Utilization = = 28/68 = 41.2% Total job work time Total flow time Average number of jobs in the system = = 68/28 = 2.43 jobs/ month Total flow time Total job work time Average job lateness = = 6/5 = 1.2 days Total late days Number of jobs

© 2006 Prentice Hall, Inc.15 – 42 Sequencing Example Job Sequence Job Work (Processing) Time Flow Time Job Due Date Job Lateness E99230 C A D B LPT (Longest processing time): Sequence E-C-A-D-B

© 2006 Prentice Hall, Inc.15 – 43 Sequencing Example LPT: Sequence E-C-A-D-B Average completion time = = 103/5 = 20.6 days Total flow time Number of jobs Utilization = = 28/103 = 27.2% Total job work time Total flow time Average number of jobs in the system = = 103/28 = 3.68 jobs Total flow time Total job work time Average job lateness = = 48/5 = 9.6 days Total late days Number of jobs

© 2006 Prentice Hall, Inc.15 – 44 Summary Sequencing Examples Rule Average Completion Time (Days) Utilization (%) Average Number of Jobs in System per month Average Lateness (Days) FCFS SPT EDD LPT Summary of Rules

© 2006 Prentice Hall, Inc.15 – 45 Comparison of Sequencing Rules  No one sequencing rule excels on all criteria  SPT does well on minimizing flow time and number of jobs in the system  But SPT moves long jobs to the end which may result in dissatisfied customers  FCFS does not do especially well on any criteria (or does poorly on most criteria) but it is perceived as fair by customers  EDD minimizes lateness

© 2006 Prentice Hall, Inc.15 – 46 Improving Performance of System  Changing setting of due dates  Changing process serial to parallel form BA C E D BA C E D

© 2006 Prentice Hall, Inc.15 – 47 Example from Service Industry Patie nt Health Issue (Treatment time) First priority appointment Second priority appointment A Pain in head (1 hr) 8-9 am am F Skin disease (1 hr) 9-10 am am G Sun burns (1 hr) am pm B Brain tumor (2 hrs) 8-10 am 10-12pm C Depression (1 hr) 2-3 pm 1-2 pm I Pollen issues (2 hrs) 2-4 pm pm D Migraine pains (2 hrs) 2-4 pm 8-10 am H Skin cancer (2 hrs) 8-10 am 2-4 pm E Skin exam (1 hr) am 2-3 pm There are two doctors in a specialist clinic, one is a dermatologist the other is a neurologist. The patients call-in the order shown. Create a schedule for the clinic assuming that each specialist works 8-12 pm and 1-4pm daily. Assign slots to patients using First come First serve priority rule. Assume that the appointments slots are one hour each.

© 2006 Prentice Hall, Inc.15 – 48 Resolution from Service Industry There are two doctors in a specialist clinic, one is a dermatologist the other is a neurologist. The patients call-in the order shown. Create a schedule for the clinic assuming that each specialist works 8-12 pm and 1-4pm daily. Assign slots to patients using First come First serve priority rule. Assume that the appointments slots are one hour each. Day 1 Day Nurlo gist ABBCDDE Aller gist FGHHII

© 2006 Prentice Hall, Inc.15 – 49 Resolution from Service Industry There are two doctors in a specialist clinic, one is a dermatologist the other is a neurologist. The patients call-in the order shown. Create a schedule for the clinic assuming that each specialist works 8-12 pm and 1-4pm daily. Assign slots to patients using First come First serve priority rule combined with SPT and LPT time slots Day 1 Day Nurlo gist BAECD Aller gist HFGI