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The document outlines the key concepts and methods for short-term scheduling. It discusses scheduling issues like forward versus backward scheduling and scheduling criteria. It also covers scheduling processes for process-focused facilities and the use of tools like input-output control, Gantt charts, and the assignment method to schedule jobs and resources in the short term. The learning objectives focus on explaining short-term scheduling relationships, applying scheduling tools and techniques, and using methods like Johnson's rule and finite capacity scheduling.

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Operations Management Chapter 15 – Short-Term Scheduling PowerPoint presentation to accompany Heizer/Render Principles of Operations Management, 7e Operations Management, 9e © 2008 Prentice Hall, Inc. 15 – 1
Outline  Global Company Profile: Delta Air Lines  The Strategic Importance of Short- Term Scheduling  Scheduling Issues  Forward and Backward Scheduling  Scheduling Criteria © 2008 Prentice Hall, Inc. 15 – 2
Outline – Continued  Scheduling Process-Focused Facilities  Loading Jobs  Input-Output Control  Gantt Charts  Assignment Method © 2008 Prentice Hall, Inc. 15 – 3
Outline – Continued  Sequencing Jobs  Priority Rules for Dispatching Jobs  Critical Ratio  Sequencing N Jobs on Two Machines: Johnson’s Rule  Limitations of Rule-Based Dispatching Systems  Finite Capacity Scheduling (FCS) © 2008 Prentice Hall, Inc. 15 – 4
Outline – Continued  Theory of Constraints  Bottlenecks  Drum, Buffer, Rope  Scheduling Repetitive Facilities  Scheduling Services  Scheduling Service Employees with Cyclical Scheduling © 2008 Prentice Hall, Inc. 15 – 5
Learning Objectives When you complete this chapter you should be able to: 1. Explain the relationship between short- term scheduling, capacity planning, aggregate planning, and a master schedule 2. Draw Gantt loading and scheduling charts 3. Apply the assignment method for loading jobs © 2008 Prentice Hall, Inc. 15 – 6
Learning Objectives When you complete this chapter you should be able to: 4. Name and describe each of the priority sequencing rules 5. Use Johnson’s rule 6. Define finite capacity scheduling 7. List the steps in the theory of constraints 8. Use the cyclical scheduling technique © 2008 Prentice Hall, Inc. 15 – 7
Delta Airlines  About 10% of Delta’s flights are disrupted per year, half because of weather  Cost is $440 million in lost revenue, overtime pay, food and lodging vouchers  The $33 million Operations Control Center adjusts to changes and keeps flights flowing  Saves Delta $35 million per year © 2008 Prentice Hall, Inc. 15 – 8
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 dependable deliveries © 2008 Prentice Hall, Inc. 15 – 9
Scheduling Issues  Scheduling deals with the timing of operations  The task is the allocation and prioritization of demand  Significant issues are  The type of scheduling, forward or backward  The criteria for priorities © 2008 Prentice Hall, Inc. 15 – 10
Scheduling Decisions Organization Managers Must Schedule the Following Arnold Palmer Operating room use Hospital Patient admissions Nursing, security, maintenance staffs Outpatient treatments University of Classrooms and audiovisual equipment Missouri Student and instructor schedules Graduate and undergraduate courses Lockheed Martin Production of goods factory Purchases of materials Workers Hard Rock Cafe Chef, waiters, bartenders Delivery of fresh foods Entertainers Opening of dining areas Delta Air Lines Maintenance of aircraft Departure timetables Table 15.1 Flight crews, catering, gate, ticketing personnel © 2008 Prentice Hall, Inc. 15 – 11
Scheduling Flow Figure 15.1 © 2008 Prentice Hall, Inc. 15 – 12
Forward and Backward Scheduling  Forward scheduling starts as soon as the requirements are known  Produces a feasible schedule though it may not meet due dates  Frequently results in buildup of work-in- process inventory Due Now Date © 2008 Prentice Hall, Inc. 15 – 13
Forward and Backward Scheduling  Backward scheduling begins with the due date and schedules the final operation first  Schedule is produced by working backwards though the processes  Resources may not be available to accomplish the Due Now schedule Date © 2008 Prentice Hall, Inc. 15 – 14
Forward and Backward Scheduling  Backward scheduling begins with the due date andhschedules the final e es ar off proac trade- operationefirstlop a p es a e nd Of ten th to dev u le a ed sched s  Scheduleeisible e date by working co mbin a f as produced u tween stomer d backwards though the processes be cu  Resources may not be available to accomplish the Due Now schedule Date © 2008 Prentice Hall, Inc. 15 – 15
Different Processes/ Different Approaches Process-focused Forward-looking schedules facilities MRP due dates Finite capacity scheduling Work cells Forward-looking schedules MRP due dates Detailed schedule done using work cell priority rules Repetitive facilities Forward-looking schedule with a balanced line Pull techniques for scheduling Product-focused Forward-looking schedule with stable facilities demand and fixed capacity Capacity, set-up, and run times known Capacity limited by long-term capital Table 15.2 investment © 2008 Prentice Hall, Inc. 15 – 16
Scheduling Criteria 1. Minimize completion time 2. Maximize utilization of facilities 3. Minimize work-in-process (WIP) inventory 4. Minimize customer waiting time Optimize the use of resources so that production objectives are met © 2008 Prentice Hall, Inc. 15 – 17
Scheduling Process- Focused Facilities 1. Schedule incoming orders without violating capacity constraints 2. Check availability of tools and materials before releasing an order 3. Establish due dates for each job and check progress 4. Check work in progress 5. Provide feedback 6. Provide work efficiency statistics and monitor times © 2008 Prentice Hall, Inc. 15 – 18
Planning and Control Files Planning Files 1. An item master file contains information about each component 2. A routing file indicates each component’s flow through the shop 3. A work-center master file contains information about the work center Control Files Track the actual progress made against the plan © 2008 Prentice Hall, Inc. 15 – 19
Loading Jobs  Assign jobs so that costs, idle time, or completion time are minimized  Two forms of loading  Capacity oriented  Assigning specific jobs to work centers © 2008 Prentice Hall, Inc. 15 – 20
Input-Output Control  Identifies overloading and underloading conditions  Prompts managerial action to resolve scheduling problems  Can be maintained using ConWIP cards that control the scheduling of batches © 2008 Prentice Hall, Inc. 15 – 21
Input-Output Control Example Work Center DNC Milling (in standard hours) Week Ending 6/6 6/13 6/20 6/27 7/4 7/11 Planned Input 280 280 280 280 280 Actual Input 270 250 280 285 280 Cumulative Deviation –10 –40 –40 –35 Planned Output 320 320 320 320 Actual Output 270 270 270 270 Cumulative Deviation –50 –100 –150 –200 Cumulative Change 0 –20 –10 +5 in Backlog Figure 15.2 © 2008 Prentice Hall, Inc. 15 – 22
Input-Output Control Example Work Center DNC Milling (in standard hours) Week Ending 6/6 6/13 6/20 6/27 7/4 7/11 Planned Input 280 280 280 280 280 Actual Input 270 250 280 285 280 Cumulative Deviation –10 –40 –40 –35 Planned Output 320 320 320 320 Explanation: Explanation: 250 input, 270 input, Actual Output 270 270 270 270 270 output implies 270 output implies Cumulative Deviation –50 –100 –150 –200 –20 change 0 change Cumulative Change 0 –20 –10 +5 in Backlog Figure 15.2 © 2008 Prentice Hall, Inc. 15 – 23
Input-Output Control Example Options available to operations personnel include: 1. Correcting performances 2. Increasing capacity 3. Increasing or reducing input to the work center © 2008 Prentice Hall, Inc. 15 – 24
Gantt Charts  Load chart shows the loading and idle times of departments, machines, or facilities  Displays relative workloads over time  Schedule chart monitors jobs in process  All Gantt charts need to be updated frequently to account for changes © 2008 Prentice Hall, Inc. 15 – 25
Gantt Load Chart Example Work Day Monday Tuesday Wednesday Thursday Friday Center Metalworks Job 349 Job 350 Mechanical Job 349 Job 408 Electronics Job 408 Job 349 Painting Job 295 Job 408 Job 349 Processing Unscheduled Center not available Figure 15.3 © 2008 Prentice Hall, Inc. 15 – 26
Gantt Schedule Chart Example Start of an Day Day Day Day Day Day Day Day activity Job 1 2 3 4 5 6 7 8 End of an activity A Scheduled activity time allowed Maintenance Actual work B progress Nonproduction time C Point in time when chart is reviewed Now Figure 15.4 © 2008 Prentice Hall, Inc. 15 – 27
Assignment Method  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) © 2008 Prentice Hall, Inc. 15 – 28
Assignment Method  Build a table of costs or time associated with particular assignments Typesetter Job A B C R-34 $11 $14 $ 6 S-66 $ 8 $10 $11 T-50 $ 9 $12 $ 7 © 2008 Prentice Hall, Inc. 15 – 29
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. © 2008 Prentice Hall, Inc. 15 – 30
Assignment Method 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. © 2008 Prentice Hall, Inc. 15 – 31
Assignment Example Typesetter A B C Job R-34 $11 $14 $ 6 S-66 $ 8 $10 $11 T-50 $ 9 $12 $ 7 Step 1a - Rows Step 1b - Columns Typesetter Typesetter A B C A B C Job Job R-34 $ 5 $ 8 $ 0 R-34 $ 5 $ 6 $ 0 S-66 $ 0 $ 2 $ 3 S-66 $ 0 $ 0 $ 3 T-50 $ 2 $ 5 $ 0 T-50 $ 2 $ 3 $ 0 © 2008 Prentice Hall, Inc. 15 – 32
Assignment Example Step 2 - Lines The smallest uncovered number is 2 so this is Typesetter subtracted from all other A B C uncovered numbers and Job added to numbers at the R-34 $ 5 $ 6 $ 0 intersection of lines S-66 $ 0 $ 0 $ 3 T-50 $ 2 $ 3 $ 0 Step 3 - Subtraction Typesetter Because only two lines A B C are needed to cover all Job the zeros, the solution R-34 $ 3 $ 4 $ 0 is not optimal S-66 $ 0 $ 0 $ 5 T-50 $ 0 $ 1 $ 0 © 2008 Prentice Hall, Inc. 15 – 33
Assignment Example Step 2 - Lines Start by assigning R-34 to worker C as this is the only Typesetter possible assignment for A B C worker C. Job T-50 must Job go to worker A as worker C R-34 $ 3 $ 4 $ 0 is already assigned. This S-66 $ 0 $ 0 $ 5 leaves S-66 for worker B. T-50 $ 0 $ 1 $ 0 Step 4 - Assignments Typesetter Because three lines are A B C needed, the solution is Job optimal and R-34 $ 3 $ 4 $ 0 assignments can be S-66 $ 0 $ 0 $ 5 made T-50 $ 0 $ 1 $ 0 © 2008 Prentice Hall, Inc. 15 – 34
Assignment Example Step 4 - Assignments Typesetter Typesetter A B C A B C Job Job R-34 $11 $14 $ 6 R-34 $ 3 $ 4 $ 0 S-66 $ 8 $10 $11 S-66 $ 0 $ 0 $ 5 T-50 $ 9 $12 $ 7 T-50 $ 0 $ 1 $ 0 From the original cost table Minimum cost = $6 + $10 + $9 = $25 © 2008 Prentice Hall, Inc. 15 – 35
Sequencing Jobs  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 © 2008 Prentice Hall, Inc. 15 – 36
Sequencing Example Apply the four popular sequencing rules to these five jobs Job Work Job Due (Processing) Time Date Job (Days) (Days) A 6 8 B 2 6 C 8 18 D 3 15 E 9 23 © 2008 Prentice Hall, Inc. 15 – 37
Sequencing Example FCFS: Sequence A-B-C-D-E Job Work Job (Processing) Flow Job Due Job Sequence Time Time Date Lateness A 6 6 8 0 B 2 8 6 2 C 8 16 18 0 D 3 19 15 4 E 9 28 23 5 28 77 11 © 2008 Prentice Hall, Inc. 15 – 38
Sequencing Example FCFS: Sequence A-B-C-D-E Job Work Job (Processing) of Flow flowJob Due Average completion time = Sum total time Job = 77/5 = 15.4 days Sequence Time Number of jobs Date Time Lateness A 6 6 Total job work time 8 0 Utilization = Sum of total flow time = 28/77 = 36.4% B 2 8 6 2 Average number of 8 Sum of total 16 time 18 C flow 0 jobs in the system = = 77/28 = 2.75 jobs D 3 Total job work time 15 19 4 E 9 Total late days 28 23 5 Average job lateness = Number of jobs = 11/5 = 2.2 days 28 77 11 © 2008 Prentice Hall, Inc. 15 – 39
Sequencing Example SPT: Sequence B-D-A-C-E Job Work Job (Processing) Flow Job Due Job Sequence Time Time Date Lateness B 2 2 6 0 D 3 5 15 0 A 6 11 8 3 C 8 19 18 1 E 9 28 23 5 28 65 9 © 2008 Prentice Hall, Inc. 15 – 40
Sequencing Example SPT: Sequence B-D-A-C-E Job Work Job (Processing)Sum of total flow time Flow Job Due65/5 = Job Average completion time = = 13 days Sequence Time Time Number of jobs Date Lateness B 2 2 Total job work time 6 0 Utilization = Sum of total flow time = 28/65 = 43.1% D 3 5 15 0 Average number of 6 Sum of total 11 time 8 A flow 3 jobs in the system = = 65/28 = 2.32 jobs C 8 Total job work time 18 19 1 E 9 Total late days 23 28 5 Average job lateness = Number of jobs = 9/5 = 1.8 days 28 65 9 © 2008 Prentice Hall, Inc. 15 – 41
Sequencing Example EDD: Sequence B-A-D-C-E Job Work Job (Processing) Flow Job Due Job Sequence Time Time Date Lateness B 2 2 6 0 A 6 8 8 0 D 3 11 15 0 C 8 19 18 1 E 9 28 23 5 28 68 6 © 2008 Prentice Hall, Inc. 15 – 42
Sequencing Example EDD: Sequence B-A-D-C-E Job Work Job (Processing) of Flow flowJob Due Average completion time = Sum total time Job = 68/5 = 13.6 days Sequence Time Number of jobs Date Time Lateness B 2 2 Total job work time 6 0 Utilization = Sum of total flow time = 28/68 = 41.2% A 6 8 8 0 Average number of 3 Sum of total 11 time 15 D flow 0 jobs in the system = = 68/28 = 2.43 jobs C 8 Total job work time 18 19 1 E 9 Total late days 23 28 5 Average job lateness = Number of jobs = 6/5 = 1.2 days 28 68 6 © 2008 Prentice Hall, Inc. 15 – 43
Sequencing Example LPT: Sequence E-C-A-D-B Job Work Job (Processing) Flow Job Due Job Sequence Time Time Date Lateness E 9 9 23 0 C 8 17 18 0 A 6 23 8 15 D 3 26 15 11 B 2 28 6 22 28 103 48 © 2008 Prentice Hall, Inc. 15 – 44
Sequencing Example LPT: Sequence E-C-A-D-B Job Work Job (Processing) of total flow time Due Average completion time = Sum Flow Job = 103/5 = 20.6 days Job Sequence Time Number of jobs Date Time Lateness E 9 9 Total job work time 23 0 Utilization = Sum of total flow time = 28/103 = 27.2% C 8 17 18 0 Average number of 6Sum of total flow time A 23 8 15 jobs in the system = = 103/28 = 3.68 jobs D 3 Total job work time 26 15 11 B 2 Total late days 28 6 22 Average job lateness = Number of jobs = 48/5 = 9.6 days 28 103 48 © 2008 Prentice Hall, Inc. 15 – 45
Sequencing Example Summary of Rules Average Average Number Average Completion Utilization of Jobs in Lateness Rule Time (Days) (%) System (Days) FCFS 15.4 36.4 2.75 2.2 SPT 13.0 43.1 2.32 1.8 EDD 13.6 41.2 2.43 1.2 LPT 20.6 27.2 3.68 9.6 © 2008 Prentice Hall, Inc. 15 – 46
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 (or poorly) on any criteria but is perceived as fair by customers  EDD minimizes lateness © 2008 Prentice Hall, Inc. 15 – 47
Critical Ratio (CR)  An index number found by dividing the time remaining until the due date by the work time remaining on the job  Jobs with low critical ratios are scheduled ahead of jobs with higher critical ratios  Performs well on average job lateness criteria Time remaining Due date - Today’s date CR = = Workdays remaining Work (lead) time remaining © 2008 Prentice Hall, Inc. 15 – 48
Critical Ratio Example Currently Day 25 Due Workdays Priority Job Date Remaining Critical Ratio Order A 30 4 (30 - 25)/4 = 1.25 3 B 28 5 (28 - 25)/5 = .60 1 C 27 2 (27 - 25)/2 = 1.00 2 With CR < 1, Job B is late. Job C is just on schedule and Job A has some slack time. © 2008 Prentice Hall, Inc. 15 – 49
Critical Ratio Technique 1. Helps determine the status of specific jobs 2. Establishes relative priorities among jobs on a common basis 3. Relates both stock and make-to-order jobs on a common basis 4. Adjusts priorities automatically for changes in both demand and job progress 5. Dynamically tracks job progress © 2008 Prentice Hall, Inc. 15 – 50
Sequencing N Jobs on Two Machines: Johnson’s Rule  Works with two or more jobs that pass through the same two machines or work centers  Minimizes total production time and idle time © 2008 Prentice Hall, Inc. 15 – 51
Johnson’s Rule 1. List all jobs and times for each work center 2. Choose the job with the shortest activity time. If that time is in the first work center, schedule the job first. If it is in the second work center, schedule the job last. 3. Once a job is scheduled, it is eliminated from the list 4. Repeat steps 2 and 3 working toward the center of the sequence © 2008 Prentice Hall, Inc. 15 – 52
Johnson’s Rule Example Work Center 1 Work Center 2 Job (Drill Press) (Lathe) A 5 2 B 3 6 C 8 4 D 10 7 E 7 12 © 2008 Prentice Hall, Inc. 15 – 53
Johnson’s Rule Example Work Center 1 Work Center 2 Job (Drill Press) (Lathe) A 5 2 B 3 6 C 8 4 B E D C A D 10 7 E 7 12 © 2008 Prentice Hall, Inc. 15 – 54
Johnson’s Rule Example Work Center 1 Work Center 2 Job (Drill Press) (Lathe) A 5 2 B 3 6 C 8 4 B E D C A D 10 7 E 7 12 Time 0 3 10 20 28 33 WC 1 B E D C A WC 2 © 2008 Prentice Hall, Inc. 15 – 55
Johnson’s Rule Example Work Center 1 Work Center 2 Job (Drill Press) (Lathe) A 5 2 B 3 6 C 8 4 B E D C A D 10 7 E 7 12 Time 0 3 10 20 28 33 WC 1 B E D C A WC 2 B E D C A Time 0 1 Time 3 5 7 9 10 11 12 13 17 19 21 22 2325 27 29 31 33 35 B E D C A © 2008 Prentice Hall, Inc. 15 – 56
Limitations of Rule-Based Dispatching Systems 1. Scheduling is dynamic and rules need to be revised to adjust to changes 2. Rules do not look upstream or downstream 3. Rules do not look beyond due dates © 2008 Prentice Hall, Inc. 15 – 57
Finite Capacity Scheduling  Overcomes disadvantages of rule-based systems by providing an interactive, computer-based graphical system  May include rules and expert systems or simulation to allow real-time response to system changes  Initial data often from an MRP system  FCS allows the balancing of delivery needs and efficiency © 2008 Prentice Hall, Inc. 15 – 58
Finite Capacity Scheduling Interactive Finite Capacity Scheduling MRP Data • Routing files • Master • Work center schedule information • BOM • Inventory Tooling Priority and other rules resources • Expert systems Setups and run time • Simulation models Figure 15.5 © 2008 Prentice Hall, Inc. 15 – 59
Finite Capacity Scheduling © 2008 Prentice Hall, Inc. 15 – 60
Theory of Constraints  Throughput is the number of units processed through the facility and sold  TOC deals with the limits an organization faces in achieving its goals 1. Identify the constraints 2. Develop a plan for overcoming the constraints 3. Focus resources on accomplishing the plan 4. Reduce the effects of constraints by off- loading work or increasing capacity 5. Once successful, return to step 1 and identify new constraints © 2008 Prentice Hall, Inc. 15 – 61
Bottlenecks  Bottleneck work centers are constraints that limit output  Common occurrence due to frequent changes  Management techniques include:  Increasing the capacity of the constraint  Cross-trained employees and maintenance  Alternative routings, procedures, or subcontractors  Moving inspection and test  Scheduling throughput to match bottleneck capacity © 2008 Prentice Hall, Inc. 15 – 62
Drum, Buffer, Rope  The drum is the beat of the system and provides the schedule or pace of production  The buffer is the inventory necessary to keep constraints operating at capacity  The rope provides the synchronization necessary to pull units through the system © 2008 Prentice Hall, Inc. 15 – 63
Scheduling Repetitive Facilities  Level material use can help repetitive facilities  Better satisfy customer demand  Lower inventory investment  Reduce batch size  Better utilize equipment and facilities © 2008 Prentice Hall, Inc. 15 – 64
Scheduling Repetitive Facilities  Advantages include: 1. Lower inventory levels 2. Faster product throughput 3. Improved component quality 4. Reduced floor-space requirements 5. Improved communications 6. Smoother production process © 2008 Prentice Hall, Inc. 15 – 65
Scheduling Services Service systems differ from manufacturing Manufacturing Services Schedules machines Schedule staff and materials Inventories used to Seldom maintain smooth demand inventories Machine-intensive and Labor-intensive and demand may be smooth demand may be variable Scheduling may be bound Legal issues may constrain by union contracts flexible scheduling Few social or behavioral Social and behavioral issues issues may be quite important © 2008 Prentice Hall, Inc. 15 – 66
Scheduling Services  Hospitals have complex scheduling system to handle complex processes and material requirements  Banks use a cross-trained and flexible workforce and part-time workers  Retail stores use scheduling optimization systems that track sales, transactions, and customer traffic to create work schedules in less time and with improved customer satisfaction © 2008 Prentice Hall, Inc. 15 – 67
Scheduling Services  Airlines must meet complex FAA and union regulations and often use linear programming to develop optimal schedules  24/7 operations like police/fire departments, emergency hot lines, and mail order businesses use flexible workers and variable schedules, often created using computerized systems © 2008 Prentice Hall, Inc. 15 – 68
Demand Management  Appointment or reservation systems  FCFS sequencing rules  Discounts or other promotional schemes  When demand management is not feasible, managing capacity through staffing flexibility may be used © 2008 Prentice Hall, Inc. 15 – 69
Scheduling Service Employees With Cyclical Scheduling  Objective is to meet staffing requirements with the minimum number of workers  Schedules need to be smooth and keep personnel happy  Many techniques exist from simple algorithms to complex linear programming solutions © 2008 Prentice Hall, Inc. 15 – 70
Cyclical Scheduling Example 1. Determine the staffing requirements 2. Identify two consecutive days with the lowest total requirements and assign these as days off 3. Make a new set of requirements subtracting the days worked by the first employee 4. Apply step 2 to the new row 5. Repeat steps 3 and 4 until all requirements have been met © 2008 Prentice Hall, Inc. 15 – 71
Cyclical Scheduling Example M T W T F S S Employee 1 5 5 6 5 4 3 3 Capacity (Employees) Excess Capacity © 2008 Prentice Hall, Inc. 15 – 72
Cyclical Scheduling Example M T W T F S S Employee 1 5 5 6 5 4 3 3 Employee 2 4 4 5 4 3 3 3 Capacity (Employees) Excess Capacity © 2008 Prentice Hall, Inc. 15 – 73
Cyclical Scheduling Example M T W T F S S Employee 1 5 5 6 5 4 3 3 Employee 2 4 4 5 4 3 3 3 Employee 3 3 3 4 3 2 3 3 Capacity (Employees) Excess Capacity © 2008 Prentice Hall, Inc. 15 – 74
Cyclical Scheduling Example M T W T F S S Employee 1 5 5 6 5 4 3 3 Employee 2 4 4 5 4 3 3 3 Employee 3 3 3 4 3 2 3 3 Employee 4 2 2 3 2 2 3 2 Capacity (Employees) Excess Capacity © 2008 Prentice Hall, Inc. 15 – 75
Cyclical Scheduling Example M T W T F S S Employee 1 5 5 6 5 4 3 3 Employee 2 4 4 5 4 3 3 3 Employee 3 3 3 4 3 2 3 3 Employee 4 2 2 3 2 2 3 2 Employee 5 1 1 2 2 2 2 1 Capacity (Employees) Excess Capacity © 2008 Prentice Hall, Inc. 15 – 76
Cyclical Scheduling Example M T W T F S S Employee 1 5 5 6 5 4 3 3 Employee 2 4 4 5 4 3 3 3 Employee 3 3 3 4 3 2 3 3 Employee 4 2 2 3 2 2 3 2 Employee 5 1 1 2 2 2 2 1 Employee 6 1 1 1 1 1 1 0 Capacity (Employees) Excess Capacity © 2008 Prentice Hall, Inc. 15 – 77
Cyclical Scheduling Example M T W T F S S Employee 1 5 5 6 5 4 3 3 Employee 2 4 4 5 4 3 3 3 Employee 3 3 3 4 3 2 3 3 Employee 4 2 2 3 2 2 3 2 Employee 5 1 1 2 2 2 2 1 Employee 6 1 1 1 1 1 1 0 Employee 7 1 Capacity (Employees) Excess Capacity © 2008 Prentice Hall, Inc. 15 – 78
Cyclical Scheduling Example M T W T F S S Employee 1 5 5 6 5 4 3 3 Employee 2 4 4 5 4 3 3 3 Employee 3 3 3 4 3 2 3 3 Employee 4 2 2 3 2 2 3 2 Employee 5 1 1 2 2 2 2 1 Employee 6 1 1 1 1 1 1 0 Employee 7 1 Capacity (Employees) 5 5 6 5 4 3 3 Excess Capacity 0 0 0 0 0 1 0 © 2008 Prentice Hall, Inc. 15 – 79

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Heizer 15

  • 1.
    Operations Management Chapter 15 – Short-Term Scheduling PowerPoint presentation to accompany Heizer/Render Principles of Operations Management, 7e Operations Management, 9e © 2008 Prentice Hall, Inc. 15 – 1
  • 2.
    Outline  Global Company Profile: Delta Air Lines  The Strategic Importance of Short- Term Scheduling  Scheduling Issues  Forward and Backward Scheduling  Scheduling Criteria © 2008 Prentice Hall, Inc. 15 – 2
  • 3.
    Outline – Continued  Scheduling Process-Focused Facilities  Loading Jobs  Input-Output Control  Gantt Charts  Assignment Method © 2008 Prentice Hall, Inc. 15 – 3
  • 4.
    Outline – Continued  Sequencing Jobs  Priority Rules for Dispatching Jobs  Critical Ratio  Sequencing N Jobs on Two Machines: Johnson’s Rule  Limitations of Rule-Based Dispatching Systems  Finite Capacity Scheduling (FCS) © 2008 Prentice Hall, Inc. 15 – 4
  • 5.
    Outline – Continued  Theory of Constraints  Bottlenecks  Drum, Buffer, Rope  Scheduling Repetitive Facilities  Scheduling Services  Scheduling Service Employees with Cyclical Scheduling © 2008 Prentice Hall, Inc. 15 – 5
  • 6.
    Learning Objectives When you complete this chapter you should be able to: 1. Explain the relationship between short- term scheduling, capacity planning, aggregate planning, and a master schedule 2. Draw Gantt loading and scheduling charts 3. Apply the assignment method for loading jobs © 2008 Prentice Hall, Inc. 15 – 6
  • 7.
    Learning Objectives When you complete this chapter you should be able to: 4. Name and describe each of the priority sequencing rules 5. Use Johnson’s rule 6. Define finite capacity scheduling 7. List the steps in the theory of constraints 8. Use the cyclical scheduling technique © 2008 Prentice Hall, Inc. 15 – 7
  • 8.
    Delta Airlines  About 10% of Delta’s flights are disrupted per year, half because of weather  Cost is $440 million in lost revenue, overtime pay, food and lodging vouchers  The $33 million Operations Control Center adjusts to changes and keeps flights flowing  Saves Delta $35 million per year © 2008 Prentice Hall, Inc. 15 – 8
  • 9.
    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 dependable deliveries © 2008 Prentice Hall, Inc. 15 – 9
  • 10.
    Scheduling Issues  Scheduling deals with the timing of operations  The task is the allocation and prioritization of demand  Significant issues are  The type of scheduling, forward or backward  The criteria for priorities © 2008 Prentice Hall, Inc. 15 – 10
  • 11.
    Scheduling Decisions Organization Managers Must Schedule the Following Arnold Palmer Operating room use Hospital Patient admissions Nursing, security, maintenance staffs Outpatient treatments University of Classrooms and audiovisual equipment Missouri Student and instructor schedules Graduate and undergraduate courses Lockheed Martin Production of goods factory Purchases of materials Workers Hard Rock Cafe Chef, waiters, bartenders Delivery of fresh foods Entertainers Opening of dining areas Delta Air Lines Maintenance of aircraft Departure timetables Table 15.1 Flight crews, catering, gate, ticketing personnel © 2008 Prentice Hall, Inc. 15 – 11
  • 12.
    Scheduling Flow Figure 15.1 © 2008 Prentice Hall, Inc. 15 – 12
  • 13.
    Forward and Backward Scheduling  Forward scheduling starts as soon as the requirements are known  Produces a feasible schedule though it may not meet due dates  Frequently results in buildup of work-in- process inventory Due Now Date © 2008 Prentice Hall, Inc. 15 – 13
  • 14.
    Forward and Backward Scheduling  Backward scheduling begins with the due date and schedules the final operation first  Schedule is produced by working backwards though the processes  Resources may not be available to accomplish the Due Now schedule Date © 2008 Prentice Hall, Inc. 15 – 14
  • 15.
    Forward and Backward Scheduling  Backward scheduling begins with the due date andhschedules the final e es ar off proac trade- operationefirstlop a p es a e nd Of ten th to dev u le a ed sched s  Scheduleeisible e date by working co mbin a f as produced u tween stomer d backwards though the processes be cu  Resources may not be available to accomplish the Due Now schedule Date © 2008 Prentice Hall, Inc. 15 – 15
  • 16.
    Different Processes/ Different Approaches Process-focused Forward-looking schedules facilities MRP due dates Finite capacity scheduling Work cells Forward-looking schedules MRP due dates Detailed schedule done using work cell priority rules Repetitive facilities Forward-looking schedule with a balanced line Pull techniques for scheduling Product-focused Forward-looking schedule with stable facilities demand and fixed capacity Capacity, set-up, and run times known Capacity limited by long-term capital Table 15.2 investment © 2008 Prentice Hall, Inc. 15 – 16
  • 17.
    Scheduling Criteria 1. Minimize completion time 2. Maximize utilization of facilities 3. Minimize work-in-process (WIP) inventory 4. Minimize customer waiting time Optimize the use of resources so that production objectives are met © 2008 Prentice Hall, Inc. 15 – 17
  • 18.
    Scheduling Process- Focused Facilities 1. Schedule incoming orders without violating capacity constraints 2. Check availability of tools and materials before releasing an order 3. Establish due dates for each job and check progress 4. Check work in progress 5. Provide feedback 6. Provide work efficiency statistics and monitor times © 2008 Prentice Hall, Inc. 15 – 18
  • 19.
    Planning and ControlFiles Planning Files 1. An item master file contains information about each component 2. A routing file indicates each component’s flow through the shop 3. A work-center master file contains information about the work center Control Files Track the actual progress made against the plan © 2008 Prentice Hall, Inc. 15 – 19
  • 20.
    Loading Jobs  Assign jobs so that costs, idle time, or completion time are minimized  Two forms of loading  Capacity oriented  Assigning specific jobs to work centers © 2008 Prentice Hall, Inc. 15 – 20
  • 21.
    Input-Output Control  Identifies overloading and underloading conditions  Prompts managerial action to resolve scheduling problems  Can be maintained using ConWIP cards that control the scheduling of batches © 2008 Prentice Hall, Inc. 15 – 21
  • 22.
    Input-Output Control Example Work Center DNC Milling (in standard hours) Week Ending 6/6 6/13 6/20 6/27 7/4 7/11 Planned Input 280 280 280 280 280 Actual Input 270 250 280 285 280 Cumulative Deviation –10 –40 –40 –35 Planned Output 320 320 320 320 Actual Output 270 270 270 270 Cumulative Deviation –50 –100 –150 –200 Cumulative Change 0 –20 –10 +5 in Backlog Figure 15.2 © 2008 Prentice Hall, Inc. 15 – 22
  • 23.
    Input-Output Control Example Work Center DNC Milling (in standard hours) Week Ending 6/6 6/13 6/20 6/27 7/4 7/11 Planned Input 280 280 280 280 280 Actual Input 270 250 280 285 280 Cumulative Deviation –10 –40 –40 –35 Planned Output 320 320 320 320 Explanation: Explanation: 250 input, 270 input, Actual Output 270 270 270 270 270 output implies 270 output implies Cumulative Deviation –50 –100 –150 –200 –20 change 0 change Cumulative Change 0 –20 –10 +5 in Backlog Figure 15.2 © 2008 Prentice Hall, Inc. 15 – 23
  • 24.
    Input-Output Control Example Options available to operations personnel include: 1. Correcting performances 2. Increasing capacity 3. Increasing or reducing input to the work center © 2008 Prentice Hall, Inc. 15 – 24
  • 25.
    Gantt Charts  Load chart shows the loading and idle times of departments, machines, or facilities  Displays relative workloads over time  Schedule chart monitors jobs in process  All Gantt charts need to be updated frequently to account for changes © 2008 Prentice Hall, Inc. 15 – 25
  • 26.
    Gantt Load ChartExample Work Day Monday Tuesday Wednesday Thursday Friday Center Metalworks Job 349 Job 350 Mechanical Job 349 Job 408 Electronics Job 408 Job 349 Painting Job 295 Job 408 Job 349 Processing Unscheduled Center not available Figure 15.3 © 2008 Prentice Hall, Inc. 15 – 26
  • 27.
    Gantt Schedule Chart Example Start of an Day Day Day Day Day Day Day Day activity Job 1 2 3 4 5 6 7 8 End of an activity A Scheduled activity time allowed Maintenance Actual work B progress Nonproduction time C Point in time when chart is reviewed Now Figure 15.4 © 2008 Prentice Hall, Inc. 15 – 27
  • 28.
    Assignment Method  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) © 2008 Prentice Hall, Inc. 15 – 28
  • 29.
    Assignment Method  Build a table of costs or time associated with particular assignments Typesetter Job A B C R-34 $11 $14 $ 6 S-66 $ 8 $10 $11 T-50 $ 9 $12 $ 7 © 2008 Prentice Hall, Inc. 15 – 29
  • 30.
    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. © 2008 Prentice Hall, Inc. 15 – 30
  • 31.
    Assignment Method 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. © 2008 Prentice Hall, Inc. 15 – 31
  • 32.
    Assignment Example Typesetter A B C Job R-34 $11 $14 $ 6 S-66 $ 8 $10 $11 T-50 $ 9 $12 $ 7 Step 1a - Rows Step 1b - Columns Typesetter Typesetter A B C A B C Job Job R-34 $ 5 $ 8 $ 0 R-34 $ 5 $ 6 $ 0 S-66 $ 0 $ 2 $ 3 S-66 $ 0 $ 0 $ 3 T-50 $ 2 $ 5 $ 0 T-50 $ 2 $ 3 $ 0 © 2008 Prentice Hall, Inc. 15 – 32
  • 33.
    Assignment Example Step 2 - Lines The smallest uncovered number is 2 so this is Typesetter subtracted from all other A B C uncovered numbers and Job added to numbers at the R-34 $ 5 $ 6 $ 0 intersection of lines S-66 $ 0 $ 0 $ 3 T-50 $ 2 $ 3 $ 0 Step 3 - Subtraction Typesetter Because only two lines A B C are needed to cover all Job the zeros, the solution R-34 $ 3 $ 4 $ 0 is not optimal S-66 $ 0 $ 0 $ 5 T-50 $ 0 $ 1 $ 0 © 2008 Prentice Hall, Inc. 15 – 33
  • 34.
    Assignment Example Step 2 - Lines Start by assigning R-34 to worker C as this is the only Typesetter possible assignment for A B C worker C. Job T-50 must Job go to worker A as worker C R-34 $ 3 $ 4 $ 0 is already assigned. This S-66 $ 0 $ 0 $ 5 leaves S-66 for worker B. T-50 $ 0 $ 1 $ 0 Step 4 - Assignments Typesetter Because three lines are A B C needed, the solution is Job optimal and R-34 $ 3 $ 4 $ 0 assignments can be S-66 $ 0 $ 0 $ 5 made T-50 $ 0 $ 1 $ 0 © 2008 Prentice Hall, Inc. 15 – 34
  • 35.
    Assignment Example Step 4 - Assignments Typesetter Typesetter A B C A B C Job Job R-34 $11 $14 $ 6 R-34 $ 3 $ 4 $ 0 S-66 $ 8 $10 $11 S-66 $ 0 $ 0 $ 5 T-50 $ 9 $12 $ 7 T-50 $ 0 $ 1 $ 0 From the original cost table Minimum cost = $6 + $10 + $9 = $25 © 2008 Prentice Hall, Inc. 15 – 35
  • 36.
    Sequencing Jobs  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 © 2008 Prentice Hall, Inc. 15 – 36
  • 37.
    Sequencing Example Apply the four popular sequencing rules to these five jobs Job Work Job Due (Processing) Time Date Job (Days) (Days) A 6 8 B 2 6 C 8 18 D 3 15 E 9 23 © 2008 Prentice Hall, Inc. 15 – 37
  • 38.
    Sequencing Example FCFS: Sequence A-B-C-D-E Job Work Job (Processing) Flow Job Due Job Sequence Time Time Date Lateness A 6 6 8 0 B 2 8 6 2 C 8 16 18 0 D 3 19 15 4 E 9 28 23 5 28 77 11 © 2008 Prentice Hall, Inc. 15 – 38
  • 39.
    Sequencing Example FCFS: Sequence A-B-C-D-E Job Work Job (Processing) of Flow flowJob Due Average completion time = Sum total time Job = 77/5 = 15.4 days Sequence Time Number of jobs Date Time Lateness A 6 6 Total job work time 8 0 Utilization = Sum of total flow time = 28/77 = 36.4% B 2 8 6 2 Average number of 8 Sum of total 16 time 18 C flow 0 jobs in the system = = 77/28 = 2.75 jobs D 3 Total job work time 15 19 4 E 9 Total late days 28 23 5 Average job lateness = Number of jobs = 11/5 = 2.2 days 28 77 11 © 2008 Prentice Hall, Inc. 15 – 39
  • 40.
    Sequencing Example SPT: Sequence B-D-A-C-E Job Work Job (Processing) Flow Job Due Job Sequence Time Time Date Lateness B 2 2 6 0 D 3 5 15 0 A 6 11 8 3 C 8 19 18 1 E 9 28 23 5 28 65 9 © 2008 Prentice Hall, Inc. 15 – 40
  • 41.
    Sequencing Example SPT: Sequence B-D-A-C-E Job Work Job (Processing)Sum of total flow time Flow Job Due65/5 = Job Average completion time = = 13 days Sequence Time Time Number of jobs Date Lateness B 2 2 Total job work time 6 0 Utilization = Sum of total flow time = 28/65 = 43.1% D 3 5 15 0 Average number of 6 Sum of total 11 time 8 A flow 3 jobs in the system = = 65/28 = 2.32 jobs C 8 Total job work time 18 19 1 E 9 Total late days 23 28 5 Average job lateness = Number of jobs = 9/5 = 1.8 days 28 65 9 © 2008 Prentice Hall, Inc. 15 – 41
  • 42.
    Sequencing Example EDD: Sequence B-A-D-C-E Job Work Job (Processing) Flow Job Due Job Sequence Time Time Date Lateness B 2 2 6 0 A 6 8 8 0 D 3 11 15 0 C 8 19 18 1 E 9 28 23 5 28 68 6 © 2008 Prentice Hall, Inc. 15 – 42
  • 43.
    Sequencing Example EDD: Sequence B-A-D-C-E Job Work Job (Processing) of Flow flowJob Due Average completion time = Sum total time Job = 68/5 = 13.6 days Sequence Time Number of jobs Date Time Lateness B 2 2 Total job work time 6 0 Utilization = Sum of total flow time = 28/68 = 41.2% A 6 8 8 0 Average number of 3 Sum of total 11 time 15 D flow 0 jobs in the system = = 68/28 = 2.43 jobs C 8 Total job work time 18 19 1 E 9 Total late days 23 28 5 Average job lateness = Number of jobs = 6/5 = 1.2 days 28 68 6 © 2008 Prentice Hall, Inc. 15 – 43
  • 44.
    Sequencing Example LPT: Sequence E-C-A-D-B Job Work Job (Processing) Flow Job Due Job Sequence Time Time Date Lateness E 9 9 23 0 C 8 17 18 0 A 6 23 8 15 D 3 26 15 11 B 2 28 6 22 28 103 48 © 2008 Prentice Hall, Inc. 15 – 44
  • 45.
    Sequencing Example LPT: Sequence E-C-A-D-B Job Work Job (Processing) of total flow time Due Average completion time = Sum Flow Job = 103/5 = 20.6 days Job Sequence Time Number of jobs Date Time Lateness E 9 9 Total job work time 23 0 Utilization = Sum of total flow time = 28/103 = 27.2% C 8 17 18 0 Average number of 6Sum of total flow time A 23 8 15 jobs in the system = = 103/28 = 3.68 jobs D 3 Total job work time 26 15 11 B 2 Total late days 28 6 22 Average job lateness = Number of jobs = 48/5 = 9.6 days 28 103 48 © 2008 Prentice Hall, Inc. 15 – 45
  • 46.
    Sequencing Example Summary of Rules Average Average Number Average Completion Utilization of Jobs in Lateness Rule Time (Days) (%) System (Days) FCFS 15.4 36.4 2.75 2.2 SPT 13.0 43.1 2.32 1.8 EDD 13.6 41.2 2.43 1.2 LPT 20.6 27.2 3.68 9.6 © 2008 Prentice Hall, Inc. 15 – 46
  • 47.
    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 (or poorly) on any criteria but is perceived as fair by customers  EDD minimizes lateness © 2008 Prentice Hall, Inc. 15 – 47
  • 48.
    Critical Ratio (CR)  An index number found by dividing the time remaining until the due date by the work time remaining on the job  Jobs with low critical ratios are scheduled ahead of jobs with higher critical ratios  Performs well on average job lateness criteria Time remaining Due date - Today’s date CR = = Workdays remaining Work (lead) time remaining © 2008 Prentice Hall, Inc. 15 – 48
  • 49.
    Critical Ratio Example Currently Day 25 Due Workdays Priority Job Date Remaining Critical Ratio Order A 30 4 (30 - 25)/4 = 1.25 3 B 28 5 (28 - 25)/5 = .60 1 C 27 2 (27 - 25)/2 = 1.00 2 With CR < 1, Job B is late. Job C is just on schedule and Job A has some slack time. © 2008 Prentice Hall, Inc. 15 – 49
  • 50.
    Critical Ratio Technique 1. Helps determine the status of specific jobs 2. Establishes relative priorities among jobs on a common basis 3. Relates both stock and make-to-order jobs on a common basis 4. Adjusts priorities automatically for changes in both demand and job progress 5. Dynamically tracks job progress © 2008 Prentice Hall, Inc. 15 – 50
  • 51.
    Sequencing N Jobson Two Machines: Johnson’s Rule  Works with two or more jobs that pass through the same two machines or work centers  Minimizes total production time and idle time © 2008 Prentice Hall, Inc. 15 – 51
  • 52.
    Johnson’s Rule 1. List all jobs and times for each work center 2. Choose the job with the shortest activity time. If that time is in the first work center, schedule the job first. If it is in the second work center, schedule the job last. 3. Once a job is scheduled, it is eliminated from the list 4. Repeat steps 2 and 3 working toward the center of the sequence © 2008 Prentice Hall, Inc. 15 – 52
  • 53.
    Johnson’s Rule Example Work Center 1 Work Center 2 Job (Drill Press) (Lathe) A 5 2 B 3 6 C 8 4 D 10 7 E 7 12 © 2008 Prentice Hall, Inc. 15 – 53
  • 54.
    Johnson’s Rule Example Work Center 1 Work Center 2 Job (Drill Press) (Lathe) A 5 2 B 3 6 C 8 4 B E D C A D 10 7 E 7 12 © 2008 Prentice Hall, Inc. 15 – 54
  • 55.
    Johnson’s Rule Example Work Center 1 Work Center 2 Job (Drill Press) (Lathe) A 5 2 B 3 6 C 8 4 B E D C A D 10 7 E 7 12 Time 0 3 10 20 28 33 WC 1 B E D C A WC 2 © 2008 Prentice Hall, Inc. 15 – 55
  • 56.
    Johnson’s Rule Example Work Center 1 Work Center 2 Job (Drill Press) (Lathe) A 5 2 B 3 6 C 8 4 B E D C A D 10 7 E 7 12 Time 0 3 10 20 28 33 WC 1 B E D C A WC 2 B E D C A Time 0 1 Time 3 5 7 9 10 11 12 13 17 19 21 22 2325 27 29 31 33 35 B E D C A © 2008 Prentice Hall, Inc. 15 – 56
  • 57.
    Limitations of Rule-Based Dispatching Systems 1. Scheduling is dynamic and rules need to be revised to adjust to changes 2. Rules do not look upstream or downstream 3. Rules do not look beyond due dates © 2008 Prentice Hall, Inc. 15 – 57
  • 58.
    Finite Capacity Scheduling  Overcomes disadvantages of rule-based systems by providing an interactive, computer-based graphical system  May include rules and expert systems or simulation to allow real-time response to system changes  Initial data often from an MRP system  FCS allows the balancing of delivery needs and efficiency © 2008 Prentice Hall, Inc. 15 – 58
  • 59.
    Finite Capacity Scheduling Interactive Finite Capacity Scheduling MRP Data • Routing files • Master • Work center schedule information • BOM • Inventory Tooling Priority and other rules resources • Expert systems Setups and run time • Simulation models Figure 15.5 © 2008 Prentice Hall, Inc. 15 – 59
  • 60.
    Finite Capacity Scheduling ©2008 Prentice Hall, Inc. 15 – 60
  • 61.
    Theory of Constraints  Throughput is the number of units processed through the facility and sold  TOC deals with the limits an organization faces in achieving its goals 1. Identify the constraints 2. Develop a plan for overcoming the constraints 3. Focus resources on accomplishing the plan 4. Reduce the effects of constraints by off- loading work or increasing capacity 5. Once successful, return to step 1 and identify new constraints © 2008 Prentice Hall, Inc. 15 – 61
  • 62.
    Bottlenecks  Bottleneck work centers are constraints that limit output  Common occurrence due to frequent changes  Management techniques include:  Increasing the capacity of the constraint  Cross-trained employees and maintenance  Alternative routings, procedures, or subcontractors  Moving inspection and test  Scheduling throughput to match bottleneck capacity © 2008 Prentice Hall, Inc. 15 – 62
  • 63.
    Drum, Buffer, Rope  The drum is the beat of the system and provides the schedule or pace of production  The buffer is the inventory necessary to keep constraints operating at capacity  The rope provides the synchronization necessary to pull units through the system © 2008 Prentice Hall, Inc. 15 – 63
  • 64.
    Scheduling Repetitive Facilities  Level material use can help repetitive facilities  Better satisfy customer demand  Lower inventory investment  Reduce batch size  Better utilize equipment and facilities © 2008 Prentice Hall, Inc. 15 – 64
  • 65.
    Scheduling Repetitive Facilities  Advantages include: 1. Lower inventory levels 2. Faster product throughput 3. Improved component quality 4. Reduced floor-space requirements 5. Improved communications 6. Smoother production process © 2008 Prentice Hall, Inc. 15 – 65
  • 66.
    Scheduling Services Service systems differ from manufacturing Manufacturing Services Schedules machines Schedule staff and materials Inventories used to Seldom maintain smooth demand inventories Machine-intensive and Labor-intensive and demand may be smooth demand may be variable Scheduling may be bound Legal issues may constrain by union contracts flexible scheduling Few social or behavioral Social and behavioral issues issues may be quite important © 2008 Prentice Hall, Inc. 15 – 66
  • 67.
    Scheduling Services  Hospitals have complex scheduling system to handle complex processes and material requirements  Banks use a cross-trained and flexible workforce and part-time workers  Retail stores use scheduling optimization systems that track sales, transactions, and customer traffic to create work schedules in less time and with improved customer satisfaction © 2008 Prentice Hall, Inc. 15 – 67
  • 68.
    Scheduling Services  Airlines must meet complex FAA and union regulations and often use linear programming to develop optimal schedules  24/7 operations like police/fire departments, emergency hot lines, and mail order businesses use flexible workers and variable schedules, often created using computerized systems © 2008 Prentice Hall, Inc. 15 – 68
  • 69.
    Demand Management  Appointment or reservation systems  FCFS sequencing rules  Discounts or other promotional schemes  When demand management is not feasible, managing capacity through staffing flexibility may be used © 2008 Prentice Hall, Inc. 15 – 69
  • 70.
    Scheduling Service Employees With Cyclical Scheduling  Objective is to meet staffing requirements with the minimum number of workers  Schedules need to be smooth and keep personnel happy  Many techniques exist from simple algorithms to complex linear programming solutions © 2008 Prentice Hall, Inc. 15 – 70
  • 71.
    Cyclical Scheduling Example 1. Determine the staffing requirements 2. Identify two consecutive days with the lowest total requirements and assign these as days off 3. Make a new set of requirements subtracting the days worked by the first employee 4. Apply step 2 to the new row 5. Repeat steps 3 and 4 until all requirements have been met © 2008 Prentice Hall, Inc. 15 – 71
  • 72.
    Cyclical Scheduling Example M T W T F S S Employee 1 5 5 6 5 4 3 3 Capacity (Employees) Excess Capacity © 2008 Prentice Hall, Inc. 15 – 72
  • 73.
    Cyclical Scheduling Example M T W T F S S Employee 1 5 5 6 5 4 3 3 Employee 2 4 4 5 4 3 3 3 Capacity (Employees) Excess Capacity © 2008 Prentice Hall, Inc. 15 – 73
  • 74.
    Cyclical Scheduling Example M T W T F S S Employee 1 5 5 6 5 4 3 3 Employee 2 4 4 5 4 3 3 3 Employee 3 3 3 4 3 2 3 3 Capacity (Employees) Excess Capacity © 2008 Prentice Hall, Inc. 15 – 74
  • 75.
    Cyclical Scheduling Example M T W T F S S Employee 1 5 5 6 5 4 3 3 Employee 2 4 4 5 4 3 3 3 Employee 3 3 3 4 3 2 3 3 Employee 4 2 2 3 2 2 3 2 Capacity (Employees) Excess Capacity © 2008 Prentice Hall, Inc. 15 – 75
  • 76.
    Cyclical Scheduling Example M T W T F S S Employee 1 5 5 6 5 4 3 3 Employee 2 4 4 5 4 3 3 3 Employee 3 3 3 4 3 2 3 3 Employee 4 2 2 3 2 2 3 2 Employee 5 1 1 2 2 2 2 1 Capacity (Employees) Excess Capacity © 2008 Prentice Hall, Inc. 15 – 76
  • 77.
    Cyclical Scheduling Example M T W T F S S Employee 1 5 5 6 5 4 3 3 Employee 2 4 4 5 4 3 3 3 Employee 3 3 3 4 3 2 3 3 Employee 4 2 2 3 2 2 3 2 Employee 5 1 1 2 2 2 2 1 Employee 6 1 1 1 1 1 1 0 Capacity (Employees) Excess Capacity © 2008 Prentice Hall, Inc. 15 – 77
  • 78.
    Cyclical Scheduling Example M T W T F S S Employee 1 5 5 6 5 4 3 3 Employee 2 4 4 5 4 3 3 3 Employee 3 3 3 4 3 2 3 3 Employee 4 2 2 3 2 2 3 2 Employee 5 1 1 2 2 2 2 1 Employee 6 1 1 1 1 1 1 0 Employee 7 1 Capacity (Employees) Excess Capacity © 2008 Prentice Hall, Inc. 15 – 78
  • 79.
    Cyclical Scheduling Example M T W T F S S Employee 1 5 5 6 5 4 3 3 Employee 2 4 4 5 4 3 3 3 Employee 3 3 3 4 3 2 3 3 Employee 4 2 2 3 2 2 3 2 Employee 5 1 1 2 2 2 2 1 Employee 6 1 1 1 1 1 1 0 Employee 7 1 Capacity (Employees) 5 5 6 5 4 3 3 Excess Capacity 0 0 0 0 0 1 0 © 2008 Prentice Hall, Inc. 15 – 79

Editor's Notes