CHAPTER 6: SCHEDULING

TRUE/FALSE

  1. The final step of production scheduling assigns actual jobs to designated facilities with unambiguous stipulations that they be completed at specific times.

ANS:T

  1. Sequencing answers the question: What is the order in which the work will be done?

ANS:T

  1. Loading assigns work at the facilities and specifies the order in which jobs should be done.

ANS:F

  1. FIFO is an appealing sequencing policy because it seems to be the fairest rule to follow. Sometimes—to emphasize the fair treatment sense—it is called “first-come, first-serve” (FCFS).

ANS:T

  1. Gantt layout charts provide work schedule control and they are a great help in determining the best work sequences.

ANS:F

  1. When sequencing models are used, it is assumed thatthe time for an operation includes: 1. job set-up time, 2. work processing or operations times, and 3. waiting times.

ANS:F

  1. Total flow time is the cumulative time required to complete a group of jobs.

ANS:T

  1. The average amount of time it takes to complete each job in the group is the mean flow time.

ANS:T

  1. Shop loading is required to assign specific jobs or teams to specific facilities.

ANS:T

  1. A major objective of loading is to spread the load so that waiting is minimized, flow is smooth and slow, and congestion is avoided.

ANS:F

  1. Shifting of job requirements can lead to an unbalanced load among departments which often happens after decisions have been made which tend to be irreversible.

ANS:T

  1. Variability of the order mix is a factor in planning capacity which requires taking corrective actions during aggregate scheduling.

ANS:T

  1. When there are many jobs and facilities, sequencing rules have diminishing economic importance.

ANS:F

  1. The Gantt layout chart shows the job schedule at each facility and the state of completion of all jobs.

ANS:T

  1. The Gantt layout chart is updated once a week.

ANS:F

  1. Sequencing inflexibility occurs when the updating of charts (redrawing them) is supported by software.

ANS:F

  1. Production scheduling plans are accomplished by the shop loading function and the sequencing function for the job shop.

ANS:T

  1. The assignment of work and its timing need to be orchestrated.

ANS:T

  1. The systems approach is called for so that the total number of assignments that are made by the scheduler is minimized.

ANS:F

  1. The flow shop system is pre-designed to optimize production throughput by using synchronization of the production schedule at all workstations.

ANS:T

  1. The backlog is generally much larger than the work in process which can be seen as work waiting on the shop floor of a facility. Some managers brag about how much work is waiting. It is taken as a sign of success.

ANS:T

  1. Gantt charts deal with the system’s realities of loading for production scheduling.

ANS:T

  1. Good Gantt charting prevents split assignments that improve productivity and quality.

ANS:F

MULTIPLE CHOICE

  1. _____ developed resource plans based on forecasts of orders in generic units such as standard hours.

a. / The master production schedule (MPS)
b. / Linear programming
c. / Aggregate planning
d. / Material requirements planning (MRP)

ANS:C

  1. Shop floor control is part of

a. / loading. / c. / master production scheduling.
b. / loading and sequencing. / d. / Gantt charting.

ANS:B

  1. Gantt charts _____.

a. / deal with the system’s realities of loading for production scheduling
b. / show which jobs have not started that should have started
c. / indicate progress toward completion
d. / all of the above

ANS:D

  1. The chart that reserves specific times at the various facilities for the actual jobs that have been assigned is called a _____ chart.

a. / load layout / c. / sequencing layout chart
b. / Gantt layout / d. / Gantt project chart

ANS:B

  1. Sequencing jobs according to their shortest processing times is called the

a. / LPT rule. / d. / STP rule.
b. / SPT rule. / e. / FIFO rule.
c. / flow sequencing rule.

ANS:B

  1. S.M. Johnson’s algorithm derives the minimum completion times for all “no passing” cases. “No passing” means:

a. / the order of processing jobs through the first facility must be preserved at the last facility.
b. / the order of processing jobs through the first facility must be preserved for the next facility.
c. / the order of processing jobs through the first facility must be preserved for all subsequent facilities.
d. / none of the above

ANS:C

  1. Each facility carries a backlog of work called _____.

a. / the bottleneck / c. / burden
b. / the load / d. / work-in-process (WIP)

ANS:B

  1. The rows in the Gantt load chart represent what kinds of resources?

a. / stations / c. / people
b. / departments / d. / all of the above

ANS:D

  1. When work is going to be late, or it is expected to miss the due date, it is said to be

a. / imperfect. / c. / an opportunity cost.
b. / backlogged. / d. / a loss function.

ANS:B

  1. _____ decisions must often be made with fast data scans that rely on the assistance of graphics such as the Gantt load chart.

a. / Marketing / c. / P/OM
b. / Finance / d. / all of the above

ANS:C

  1. Gantt load charts show what kind of information?

a. / Certain departments have reserved time for preventative maintenance.
b. / Particular jobs cannot be split up.
c. / For resolution of due date problems, cumulative backlog data can be shown for the current week and the prior week.
d. / a, b, and c
e. / the competitive situation.

ANS:D

  1. The reason that the best possible assignments cannot be made for every job is

a. / many job assignments cannot be split.
b. / jobs compete with each other for available time at facilities for which they are best suited.
c. / best assignments are a matter of opinion.
d. / assignments are temporary and conditions change.

ANS:B

  1. _____ and _____ are done over and over again in a typical job shop.

a. / Forecasting; assigning / c. / Loading; sequencing
b. / Loading; assigning / d. / Assigning; loading

ANS:C

  1. On the face of it, the most natural arrangement for doing work is in the order that the jobs are received. This is the same as

a. / random walk selection. / c. / FOFI.
b. / LIFO. / d. / FIFO.

ANS:D

  1. Which of the following do many supermarkets prefer to use for selling their late-dated products?

a. / LIFO
b. / FIFO
c. / random walk—luck of the draw
d. / red carpet—meaning wait in one line for the next available operator
e. / Everything goes except a.

ANS:B

  1. Which is a difference between loading and sequencing?

a. / Loading specifies the precise timing of assignments.
b. / Sequencing specifies the precise timing of assignments.
c. / Loading allows customers to be notified of delivery dates.
d. / Loading charts are revised regularly.

ANS:B

  1. _____ flow time is composed of the sum of the complete-to-ship times for each job in the group.

a. / Mean / c. / Sequencing
b. / Job / d. / Total

ANS:D

  1. Which of the following is TRUE of the mean flow time?

a. / It is the average of the complete-to-ship times for every job in the group.
b. / It is the average of the wait-to-start and processing times for every job in the group.
c. / It is the average of the release times for every job in the group.
d. / It is the average of the start-to-finish times for every job in the group.
e. / both a and b

ANS:E

  1. Production scheduling is always a system’s problem because _____ compete with each other for the best facilities.

a. / jobs and people / c. / jobs and teams
b. / people and teams / d. / jobs, people, and teams

ANS:D

  1. Strategic planning is required to _____ for the expected blend of job shop orders.

a. / design the facilities
b. / staff the departments
c. / select suppliers and design the product mix
d. / all of the above

ANS:D

  1. Loading assumes that the material requirements analysis has been done and that orders have been properly placed for the required _____.

a. / materials / c. / subassemblies
b. / needed parts / d. / all of the above

ANS:D

  1. The objective function of sequencing models can be to _____.

a. / minimize system’s costs
b. / minimize total system’s time
c. / maximize total system’s profit if margin data are available
d. / do all of the above

ANS:D

  1. Proper charts, like Gantt charts, reflect

a. / the interests of customers. / c. / both a and b
b. / the impact of suppliers. / d. / neither a nor b

ANS:C

  1. In general, the time scale on the Gantt load chart is labeled in _____.

a. / dated calendar time
b. / time units of specific intervals ahead
c. / either a or b
d. / neither a nor b

ANS:C

  1. In facility loading, when work that is scheduled is not completed on time, _____.

a. / the scheduler underestimated the time required for completion
b. / there is a process problem to be determined
c. / either a or b
d. / neither a nor b

ANS:C

  1. In facility loading, constant matching of estimated and actual times:

a. / improves the database for estimation.
b. / monitors process productivity.
c. / reflects on the knowledge and skill of the schedulers.
d. / all of the above

ANS:D

SHORT ANSWER

  1. What are heuristics?

ANS:

Heuristics are rules of thumb that are intended to produce the most satisfactory solutions (called satisficing) that can be found in a reasonable time. A typical factory system involves so many options that it is not possible to determine an optimal production schedule. Instead of optimization, heuristic methods are used to “satisfice.” Heuristic methods will be discussed in other chapters. It will also help to have students look up “heuristic” in Wikipedia.

  1. Define production and operations scheduling.

ANS:

Production scheduling assigns actual jobs to designated facilities with unambiguous stipulations that they be completed at specific times. Operations scheduling which is done by airlines, railroads, banks, etc. carries the same unambiguous conditions.

  1. What questions are answered by “loading” and “sequencing” respectively?

ANS:

Loading answers the question: Which department is going to do what work? Sequencing answer the question: What is the order in which the work will be done?

  1. Define sequencing. How is it used?

ANS:

Sequencing assigns priorities that determine the order with which work will be done. Sequencing rules determine which job should be first in line, which second, etc. SPT is the rule whereinshortest processing time units go first. Those who demand fair treatment when joining a queue usually want first in, first out which is FIFO.

  1. Define loading. What is the importance of loading?

ANS:

Loading is also called shop loading. It assigns specific jobs or teams to specific facilities. Loading is needed for machine shops, hospitals, offices, etc. Although loading assigns work to facilities, it does not specify the order in which jobs should be done at the facility. Sequencing methods determine the order of work at the facility.

  1. What kinds of information do Gantt load charts provide?

ANS:

Gantt load charts use a graphic system to provide job assignments and status. It is easy to follow progress on various jobs by visualizing the degree to which the bars representing the jobs have been completed. Causes of delay are indicated as well as updated estimates for job completions. The charts make it easy to visualize situations but do not allow optimizations.

  1. What problems are caused by using the LIFO sequencing rule?

ANS:

The last-in, first-out rule causes spoiled milk problems. That is because the first-in with the earliest date is waiting until all of the later-date items are shipped. If there is no age-spoilage problem, then, as its advocates point out, LIFO can save warehousing costs. LIFO items are more readily accessible. For a family waiting for hours to enter an attraction at a theme park, LIFO can cause extreme stress

  1. What is a sequencing chart and how is it used?

ANS:

A sequencing chart is a Gantt layout chart that shows sequence assignments. It reserves specific times on the various facilities for the actual jobs that have been assigned.

  1. Differentiate between total flow time and mean flow time.

ANS:

Total flow time is the cumulative time required to complete a group of jobs. It is composed of the sum of the complete-to-ship times (including waiting time) for each job in the group. Mean flow time is the average amount of time required to complete each job in the group. It is the average of the wait-to-start and processing times for every job in the group.

PROBLEMS

  1. What is the order of processing the jobs using Johnson’s rule for the data given in the following table?

PROCESSING TIME (DAYS)
JOB / MACHINE 1 / MACHINE 2
A / 8 / 12
B / 4 / 9
C / 11 / 7
D / 14 / 6
E / 10 / 5

ANS: B-A-C-D-E

  1. Draw a Gantt chart and find the value of make-span (time to complete all jobs) using the sequence A-B-C-D-E for the following problem.

Processing Time (Days)
Job / M1 / M2
A / 3 / 6
B / 8 / 4
C / 2 / 7
D / 4 / 2
E / 6 / 5

ANS: 26 days

  1. TheDoorKnobCompanyhasfourordersonhand,andeachmustbeprocessedinthe sequentialorder:

First:DepartmentA—pressshop

Second:DepartmentB—platingandfinishing

Thefollowingtableliststhenumberofdaysrequiredforeachjobineach department.Forexample, jobIVrequirestwo daysin thepressshopand three daysin the finishingdepartment. Assumethatnootherworkisbeingdonebythe departmentsandthat‘‘nopassing’’ofjobsisallowed. UseJohnson’s rule to find the best-workschedule.(Best-workschedulemeansminimum timeto finishallfourjobs.)

Job I / Job II / Job III / Job IV
Department A / 1 / 8 / 5 / 2
Department B / 7 / 3 / 6 / 3

ANS: Job I – Job IV – Job III – Job II

  1. TheMarketResearchStorehasfourordersonhand,andeach mustbe processedin thesequential order:

First:Department1 —computeranalysis

Second:Department2 —reportwritingandprinting

Thefollowingtableliststhenumberofdaysrequiredbyeach jobin eachdepartment. Forexample,jobDrequires one dayduringcomputeranalysisandtwo days in reportwritingandprinting.

A / B / C / D
Department 1 / 8 / 6 / 5 / 1
Department 2 / 3 / 9 / 7 / 2

Assumethatnootherworkisbeingdonebythe departmentsandthat‘‘nopassing’’ofjobsisallowed. UseaGanttsequencingchartto showthe best-workschedule.(Best-workschedulemeansminimumtimeto finishall fourjobs.)

ANS: Best sequence using Johnson’s rule is: D-C-B-A

Minimum Time: 25 days


DATA FOR QUESTIONS 5to 8

(NOTE: Additional problems can be generated by changing the data. Answers can be found by plugging in the data in the Excel file for scheduling.)

Days
Job / Processing Time / Due Date
A / 20 / 35
B / 16 / 54
C / 19 / 44
D / 22 / 27
E / 24 / 47
  1. What is the average completion time using First Come First Served (FCFS) rule?

ANS: 57.8 = 289/5

  1. What is the average tardiness using the First Come First Served (FCFS) rule?

ANS: 23 = 115/5

First Come First Served
Job / Processing Time / Due Date / Completion Time / Tardiness
A / 20 / 35 / 20 / 0
B / 16 / 54 / 36 / 0
C / 19 / 44 / 55 / 11
D / 22 / 27 / 77 / 50
E / 24 / 47 / 101 / 54
Total / 289 / 115
Average Completion Time / 57.8
Average Number of Jobs in System / 2.86
Average Tardiness / 23
Maximum Tardiness / 54
Number of Tardy Jobs / 3
  1. What is the number of tardy jobs using Shortest Processing Time rule?

ANS: 3

Shortest Processing Time
Job / Processing Time / Due Date / Completion Time / Tardiness
B / 16 / 54 / 16 / 0
C / 19 / 44 / 35 / 0
A / 20 / 35 / 55 / 20
D / 22 / 27 / 77 / 50
E / 24 / 47 / 101 / 54
Total / 284 / 124
Average Completion Time / 56.8
Average Number of Jobs in System / 2.81
Average Tardiness / 24.8
Maximum Tardiness / 54
Number of Tardy Jobs / 3
  1. What is the average number of jobs in the system using the Earliest Due Date (EDD) rule? ANS: 3.08 = 311/101

Earliest Due Date
Job / Processing Time / Due Date / Completion Time / Tardiness
D / 22 / 27 / 22 / 0
A / 20 / 35 / 42 / 7
C / 19 / 44 / 61 / 17
E / 24 / 47 / 85 / 38
B / 16 / 54 / 101 / 47
Total / 311 / 109
Average Completion Time / 62.2
Average Number of Jobs in System / 3.08
Average Tardiness / 21.8
Maximum Tardiness / 47
Number of Tardy Jobs / 4
  1. Suppose the SPT rule is being used in a “dynamic” scheduling problem. There are four jobs A, B, C, and D ready to be processed at the present time (time 0).. The processing times for the five jobs are 2, 9, 6 and 3 days respectively. A new job E will arrive on the 7thday. The processing time for job E is 4 days. On which day (from present time) job E will be completed?

Answer: 15

The sequencing order using SPT is A-D-C-B (A = 2 days, D = 3 days, C = 6 days and B = 9 days). When job E comes on 7th day, job C is being processed and will be completed at time 11. After job C is completed, there are two jobs waiting to be processed B (9 days) and E (4 days). Using SPT, job E will be picked up for processing. Job E will then be completed at time 15.

  1. The due date for a job is day 25. It is finished on day 21. What is the lateness of the job? What is the tardiness of the job?

Answer: -4 (Lateness)

Answer: 0 (Tardiness)

Lateness is defined as completion time – due date = 21-25 = -4. The lateness can be positive (job is delayed), or 0 (on time job), or negative (job is completed early).

The tardiness refers only to the positive lateness. For this problem, the tardiness is 0 (zero) because the job is not late. Mathematically, tardiness = maximum (0, lateness). For this problem, tardiness = maximum (0, -2) = 0.

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