04 05 06 Scheduling

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Operations Scheduling

Class04, 05, 06

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Scheduling

Work Center Typical Scheduling and Control Functions

Job-shop Scheduling

BatchShop Scheduling

Personnel Scheduling

Examples of Scheduling Rules

Shop-floor Control

Principles of Work Center Scheduling

Issues in Scheduling Service Personnel

SCHEDULING

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SCHEDULING

DETERMINATION OF WHEN LABOUR,

EQUIPMENTS AND FACILITIES ARE

NEEDED TO PRODUCE A PRODUCT OR

PROVIDE A SERVICE.

SCHEDULING IS THE LAST STAGE OF

PLANNING BEFORE PRODUCTION

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Typical Scheduling and Control

Functions

Allocating orders, equipment, and personnel.

Determining the sequence of orderperformance.

Initiating performance of the scheduled work.

Shop-floor control.

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Scheduling

Process-Focused

Manufacturing

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Scheduling and Shop-Floor

Decisions

MaterialRequirementsPlan (MRP)

CapacityRequirementsPlan (CRP)

Order-Processing orRouting Plans

PlannedOrder ReleasesReport

Work CenterLoading andOvertime Plan

Assignment ofOrders toWork Centers

MasterProduction

Schedule (MPS)

Product Designand

Process Plans

Day-to-Day Scheduling and Shop-Floor Decisions

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Work-Center Scheduling

Objectives

Meet due dates

Minimize lead time

Minimize setup time or cost

Minimize work-in-process inventory

Maximize machine utilization

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Pre-production Planning

Design the product in customer order

Plan the operations the product mustpass through ..... this is the routing plan

Work moves between operations on a

move ticket

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Common Shop Floor

Control Activities

The production control departmentcontrols and monitors order progress

through the shop.Assigns priority to orders

Issues dispatching lists

Tracks WIP and keeps systems updated

Controls input-output between work centers

Measures efficiency, utilization, andproductivity of shop

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Shop Floor Planning and Control

Input-Output Control

Gantt Chart Finite and Infinite Loading

Forward and Backward Scheduling

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Input-Output Control

Input-output control identifies problemssuch as insufficient or excessive

capacity or any issues that prevents theorder from being completed on time.

Input-output control report compares

planned and actual input, planned andactual output, and planned and actualWIP in each time period

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Input-Output Control Report

Week: -1 1 2 3 4Planned input: labor-hrs 100 50 40 100

Actual input: labor-hrs 50 40 30 80

Cumulative deviation -50 -60 -70 -90Planned output: labor-hrs 120 70 50 100

Actual output: labor-hrs 110 50 20 70

Cumulative deviation -10 -30 -60 -90Planned ending WIP: l-h 50 30 20 20

Actual ending WIP: l-h 70 10 0 10 20

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Gantt Charts

Gantt charts are useful tools to

coordinate jobs through shop; graphicalsummary of job status and loading ofoperations

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Assigning Jobs to Work Centers:

How Many Jobs/Day/Work Center

Infinite loadingAssigns jobs to work centers without regard to

capacity

Unless excessive capacity exists, long queuesoccur

Finite loading

Uses work center capacity to schedule orders Popular scheduling approach

Integral part of CRP

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Assigning Jobs to Work Centers:

Which Job Gets Built First?

Forward scheduling Jobs are given earliest available time slot in

operation

excessive WIP usually results

Backward scheduling Start with promise date and work backward

through operations reviewing lead times todetermine when a job has to pass througheach operation

Less WIP but must have accurate lead times

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Order-Sequencing Problems

Sequencing Rules

Criteria for Evaluating SequencingRules

Comparison of Sequencing Rules

Controlling Changeover Costs Minimizing Total Production Time

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Job Sequencing

The process of determiningwhich job to start first on which

machine / work center

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Priority Rules for Job Sequencing

(n Jobs on One machine)

1. First-come, first-served (FCFS)

2. Shortest operating time (SOT)

3. Earliest due date first (EDD)

4. Last come, first served (LCFS)

5. Longest Processing Time

6. Least slack time remaining (STR) first

7. Critical Ratio (CR)

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Schedule Performance

Measures

Meeting due dates of customers or

downstream operations.

Minimizing the flow time (the time a jobspends in the process).

Minimizing work-in-process inventory.

Minimizing idle time of machines or workers.

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Example of Job Sequencing:

First-Come First-ServedSuppose you have the four

jobs to the right arrive for

processing on one

machine.

What is the FCFS schedule?

Do all the jobs get done on

time?

No, Jobs B, C,

and D are

going to be

late.

JOB (In order of

arrival)

Processing

Time(Days)Due date(Days)

A 3 4

B 5 7

C 4 6

D 2 5

Answer: FCFS Schedule

JOB (In order ofarrival)

ProcessingTime(Days)

Due date(Days) Flow Time Delay

A 3 4 0+3=3 0

B 5 7 3+5=8 1

C 4 6 8+4=12 6

D 2 5 12+2=14 9

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Shortest Operating TimeSuppose you have the four

jobs to the right arrive forprocessing on one machine.

What is the SOT schedule?


time?

No, Jobs A,Cand B are goingto be late.

Answer: Shortest Operating Time Schedule

JOB (In order of

arrival)

Processing


A 3 4

B 5 7

C 4 6

D 2 5




D 2 5 0+2=2 0

A 3 4 2+3=5 1

C 4 6 5+4=9 3

B 5 7 9+5=14 7

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Earliest Due Date FirstSuppose you have the four

jobs to the right arrive forprocessing on one machine.

What is the earliest due date

first schedule?


time?

No, Jobs Cand B are

going to be

late.

JOB (In order of

arrival)

Processing


A 3 4

B 5 7

C 4 6

D 2 5

Answer: Earliest Due Date First




A 3 4 0+3=3 0

D 2 5 3+2=5 0

C 4 6 5+4=9 3

B 5 7 9+5=14 7

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Last-Come First-Served

No, Jobs B andA are going tobe late.

Suppose you have the fourjobs to the right arrive forprocessing on one machine.

What is the LCFS schedule?


time?

JOB (In order of

arrival)

Processing


A 3 4

B 5 7

C 4 6

D 2 5

Answer: Last-Come First-Served Schedule

JOB (In order of

arrival)

Processing

Time(Days) Due date(Days) Flow Time Delay

D 2 5 0+2=2 0

C 4 6 2+4=6 0

B 5 7 6+5=11 4

A 3 4 11+3=14 11

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Longest Processing Time

No, Jobs C, Aand D aregoing to belate.


What is the LPT schedule?


time?

JOB (In order of

arrival)

Processing


A 3 4

B 5 7

C 4 6

D 2 5

Answer: Longest Processing Time

JOB (In order of

arrival)

Processing


B 5 7 0+5=5 0

C 4 6 5+4=9 3

A 3 4 9+3=12 8

D 2 5 12+2=14 9

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Slack Time Remaining

No, Jobs C, Band D aregoing to belate.


What is the STR schedule?

Do all the jobs get done ontime?

JOB (In order of

arrival)

Processing


A 3 4

B 5 7

C 4 6

D 2 5

Answer: Slack Time Remaining

JOB (In order of

arrival)

Processing


A 3 4 0+3=3 0

C 4 6 3+4=7 1

B 5 7 7+5=12 5

D 2 5 12+2=14 9

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Critical Ratio

No, Jobs A, B Cand D aregoing to belate.


What is the CR schedule?

Do all the jobs get done ontime?

JOB (In order

of arrival)

Processing


A 3 4

B 5 7

C 4 6

D 2 5

Answer: Critical Ratio (CR)

Critical ratio

1.333333

1.4

0.75

2.5

JOB (In

order ofarrival)

Critical ratio

Processing

Time(Days)

Due

date(Days)

Flow

Time Delay

C 0.75 4 3 0+4=4 1

A 1.33 3 4 4+3=7 3

B 1.4 5 7 7+5=12 5

D 2.5 2 5 12+2=14 9

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Sequencing Rules

For comparison between various ruleuse

Average flow time:

37/4 = 9.25 days

Average number of jobs in the system:

37/14 = 2.643 jobs Average job lateness:

18/4 = 4.5 days

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Scheduling on n jobs on Two Machines

Johnsons rule:Objective: To minimize the flow time from beginning of

the first job until the finish of the last.

1- List the operation time for each job on both machines.

2- Select the shortest operation time.

3- If shortest time is for the first machine, do the job first,

If it is for the second machine, do the job last

4- Repeat step-2 and 3 for remaining job until the

schedule is complete. Dont consider the job already

allotted.

Assumption: Processing of the jobs in Two machine in the order ofAB(First A and then B).

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Johnsons Rule (Part 1)Suppose you have the following six jobs with timerequirements in two stages of production. What is the

job sequence using Johnsons Rule?

Time in HoursJobs M/C-1 M/C-21 30 702 100 953 50 90

4 20 605 90 306 100 15

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Johnsons Rule (Part 1)

61

4 62

4 1 5 63

4 1 3 2 5 64

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Scheduling on n jobs on Three Machines

Johnsons rule:

The rule is applicable under the following condition.

Cond. 1- The smallest processing time of Machine-A

should be greater than or equal to largest processing

time on Machine-B.

OR

Cond. 2- The smallest processing time on Machine-C

should be greater than or equal to the largest processing

time on Machine-B

Rule: Assume Two fictitious machine X and Y

X= A+B and Y= B+C and Order XY

Assumption: Processing of the jobs in Three machine in the order ofABC(First A and then B and then C).

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Johnsons Rule (Part 2)Suppose you have the following Five jobs with timerequirements in Three stages of production. What is

the job sequence using Johnsons Rule?

Time in HoursJobs M/C-1 M/C-2 M/C-31 18 10 82 19 12 183 12 5 16

4 16 6 145 21 9 10

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The smallest processing time on machine-A is 12 which is

greater than or equal to largest processing time on machine-B.

A B C X=A+B Y=B+C1 18 10 8 28 18

2 19 12 18 31 303 12 5 16 17 21

4 16 6 14 22 205 21 9 10 30 19

JOB

Processing Time

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Time In Pro. Time Time Out Time In Pro. Time Time Out Time In Pro. Time Time Out

3 0 12 12 12 5 17 17 16 33

2 12 19 31 31 12 43 43 18 61

4 31 16 47 47 6 53 61 14 75

5 47 21 68 68 9 77 77 10 87

1 68 18 86 86 10 96 96 8 104

JOB

Machine-A Machine-B Machine-C

Idle Time for MachineC = 38 Hrs.

Total Operation Time = 104 Hours

Idle Time for MachineA = 18 Hrs.

Idle Time for MachineB = 62 Hrs.

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Scheduling on n jobs on m Machines

Johnsons rule:

The rule is applicable under the following condition.

Cond. 1- The smallest processing time of Machine-A1 should

be greater than or equal to largest processing time on

Machine-A2Am-1.

OR

Cond. 2- The smallest processing time on Machine-Am should

be greater than or equal to the largest processing time on

Machine-A2.Am-1Rule: Assume Two fictitious machine X and Y

X= A1+A2++Am-1 and Y= A2+A3++Am and Order

A1,A2Am

Assumption: Processing of the jobs in m machine in the order of A1,A2,.Am(First A1 and then A2 and then .Am).

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Johnsons Rule (Part 3)Suppose you have the following Five jobs with timerequirements in Four stages of production. What is the

job sequence using Johnsons Rule?

Time in HoursJobs M/C-1 M/C-2 M/C-3 M/C-41 18 10 8 82 19 12 10 183 12 5 11 16

4 16 6 9 145 21 9 7 10

Class Assignment Time10 Minutes

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ASSIGNMENT METHOD

(SPECIALISED LINEAR PROGRAMMING)

Application

1. n -Jobs to n -Machines2. Each job is assigned to one and only

one destination.

3. Only one criterion to be used ( MinimumCost or Maximum profit or Minimum

time etc.)

Procedure

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ProcedureHungarian Assignment Method

1. PERFORM ROW REDUCTIONS BYSUBTRACTING THE MINIMUM VALUE IN EACHROW FROM OTHER ROW VALUES

2. PERFORM COLUMN REDUCTIONS BYSUBTRACTING THE MINIMUM VALUE IN EACHCOLUMN FROM ALL OTHER COLUMN VALUES

3. THE RESULTING TABLE IS ANOPPORTUNITY COST MATRIX. CROSS OUT ALLZEROS IN THE MATRIX USING THE MINIMUMNUMBER OF HORIZONTAL OR VERTICAL LINES.

Procedure

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4. IF THE NUMBER OF LINES EQUALS THE

NUMBER OF ROWS / COLUMN THE MATRIX, AN

OPTIMUM SOLUTION HAS BEEN REACHED

AND ASSIGNMENTS CAN BE MADE WHERETHE ZEROS APPEAR.

OTHERWISE, MODIFY THE MATRIX BY

SUBTRACTING THE MINIMUM UNCROSSED

VALUE FROM ALL OTHER UNCROSSEDVALUES AND ADDING THIS SAME AMOUNT TO

ALL CELLS WHERE TWO LINES INTERSECT.

ALL OTHER VALUES IN THE MATRIX REMAIN

UNCHANGED


Procedure

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5. REPEATSTEPS3 AND 4 UNTIL AN OPTIMUMSOLUTION IS REACHED

6. ASSIGNMENT

a. Locate a row /column contains only one zeroelement. Assign the job to that and cross out the

zeros if any in the column corresponding to the

assigned cell.

b. Repeat for each row, which contains only one

zero.

c. If no row/column with single zero, then select

arbitrarily any cell and complete the assignment.

d. Determine the total cost with reference to the

original cost table.


Example of Assignment

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Example of Assignment

Problem

A B C D

1 45 40 51 67

2 57 42 63 553 49 52 48 64

4 41 45 60 55

JobWorker

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A B C D1 5 0 11 27

2 15 0 21 13 Step-1

3 1 4 0 16

4 0 4 19 14

Worker Job

Example of Assignment Problem

1- PERFORM ROW REDUCTIONS BY SUBTRACTING THE

MINIMUM VALUE IN EACH ROW FROM OTHER ROW

VALUES

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A B C D

1 5 0 11 14

2 15 0 21 0 Step-2

3 1 4 0 3

4 0 4 19 1

Worker Job


2- PERFORM COLUMN REDUCTIONS BYSUBTRACTING THE MINIMUM VALUE IN EACH

COLUMN FROM ALL OTHER COLUMN VALUES

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3- THE RESULTING TABLE IS AN OPPORTUNITY COST MATRIX.CROSS OUT ALL ZEROS IN THE MATRIX USING THE MINIMUMNUMBER OF HORIZONTAL OR VERTICAL LINES.

4- IF THE NUMBER OF LINES EQUALS THE NUMBER OF ROWS /COLUMN THE MATRIX, AN OPTIMUM SOLUTION HAS BEEN

REACHED AND ASSIGNMENTS CAN BE MADE WHERE THE ZEROSAPPEAR

A B C D

1 5 0 11 14

2 15 0 21 0 Step-33 1 4 0 3

4 0 4 19 1

WorkerJob

& 4

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A B C D

1 5 0 11 142 15 0 21 0 Step-4

3 1 4 0 3

4 0 4 19 1

Worker Job


5- Assignment

Step-5&6

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1 2 3 4 5

A 10 3 3 2 8

B 9 7 8 2 7

C 7 5 6 2 4

D 3 5 8 2 4

E 9 10 9 6 10

JOBMACHINIST

Assignment Problem

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Scheduling

Product-Focused

Manufacturing

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Product-Focused

Scheduling

Two general types of product-focused

production: Batch - large batches of several

standardized products produced

Continuous - few products producedcontinuously.... minimal changeovers

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Scheduling Decisions

If products are produced in batches on thesame production lines: How large should production lot size be for

each product?

When should machine change overs bescheduled?

If products are produced to a delivery

schedule:At any point in time, how many productsshould have passed each operation if timedeliveries are to be on schedule?

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Batch Scheduling

EOQ for Production Lot Size How many units of a single product should be

included in each production lot to minimizeannual inventory carrying cost and annual

machine changeover cost?

DAnnual Demand

SOrdering or Set up cost

CCarrying / Holding cost

drate at which units are used out of inventoryDemand rate

prate at which units are supplied to inventoryProduction rate

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Example: EOQ for Production

LotsCPC, Inc. produces four standard electronicassemblies on a produce-to-stock basis. Theannual demand, setup cost, carrying cost, demand

rate, and production rate for each assembly areshown on the next slide.

a) What is the economic production lot size foreach assembly?

b) What percentage of the production lot of powerunits is being used during its production run?

c) For the power unit, how much time will passbetween production setups?

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LotsAnnual Setup Carry Demand Prod.Demand Cost Cost Rate Rate

Power Unit 5,000 $1,200 $6 20 200

Converter 10,000 600 4 40 300

Equalizer 12,000 1,500 10 48 100Transformer 6,000 400 2 24 50

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Lots Economic Production Lot SizesEOQ = (2DS/C[p/(p-d)]

1EOQ = (2(5,000)(1,200)/6[200/(200-20)] 1,490.7

2EOQ = (2(10,000)(600)/4[300/(300-40)] 1,860.5

3EOQ = (2(12,000)(1,500)/10[100/(100-48)] 2,631.2

4EOQ = (2(6,000)(400)/2[50/(50-24)] 2,148.3

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Lots

% of Power Units Used During

Production

d/p = 20/200 = .10 or 10%

Time Between Setups for Power UnitsEOQ/d = 1,490.7/20 = 74.535

days

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Batch Scheduling

Limitations of EOQ Production Lot Size

Uses annual ballpark estimates ofdemand and production rates, not the mostcurrent estimates

Not a comprehensive scheduling techniqueonly considers a single product at a time

Multiple products usually share the samescarce production capacity

Sh Fl C t l

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Shop-Floor Control

Major Functions

1. Assigning priority of each shop order.

2. Maintaining work-in-process quantityinformation.

3. Conveying shop-order status information tothe office.

Shop-Floor Control:

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Shop Floor Control:

Major Functions (Continued)

4. Providing actual output data for capacitycontrol purposes.

5. Providing quantity by location by shop orderfor WIP inventory and accounting purposes.

6. Providing measurement of efficiency,utilization, and productivity of manpower andmachines.

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Input/Output Control

Input Output

Planned input should never exceedplanned output.

Focuses attention on bottleneck workcenters.

WorkCenter

Principles of Work Center

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Principles of Work Center

Scheduling

1. There is a direct equivalence between workflow and cash flow.

2. The effectiveness of any job shop should be

measured by speed of flow through the shop.

3. Schedule jobs as a string, with process stepsback-to-back.

4. A job once started should not be interrupted.

Principles of Job Shop

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Scheduling (Continued)

5. Speed of flow is most efficientlyachieved by focusing on bottleneck workcenters and jobs.

6. Reschedule every day.

7. Obtain feedback each day on jobs that

are not completed at each work center.

8. Match work center input information towhat the worker can actually do.


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Scheduling (Continued)

9. When seeking improvement in output,

lookfor incompatibility between engineeringdesign and process execution.

10. Certainty of standards, routings, and soforth is not possible in a job shop, butalways work towards achieving it.

At the end of each month a research and development team writes status

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At the end of each month, a research and development team writes statusreports for the projects worked on during the month. The team leaders, Andrewand Julie, submit the reports to the R&D director on the first Monday of eachmonth. It is late Friday evening and to their surprise, they have discovered that

the month ends on Sunday and the reports are due on Monday morning. Theyhave decided to come to work early Saturday morning, so they can finish thereports before Monday morning. They split the work as follows: Andrew willwrite and edit the reports while Julie collates data and draws all the necessarygraphs. Assume that Julie starts her work on a report as soon as Andrew is

finished with it and that Andrew works continuously. Times for the reports (inhours) are as follows:

Projects Andrew Julie

A 4 2B 3 5

C 5 1D 7 3E 8 6

What is the order of the projects using Johnson's rule?

How many hours will it take them to finish all the reports?

How many hours is Andrew & Julie idle?

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Thank You

Documents

04 05 06 Scheduling