20 scheduling (1)

7/27/2019 20 Scheduling (1)

1/39

2012 Lew Hofmann

Scheduling

7/27/2019 20 Scheduling (1)

2/39

2012 Lew Hofmann

Air New Zealand Crew Scheduling

Flight and crew scheduling is a complex processthat begins with a five-year market plan.

This general plan is further refined to a three-year

plan, and put into an annual budget that listsspecific departure and arrival times.

Crew availability must be matched to the flightschedule. Pilots and attendants each come with

their own set of preferences and constraints.

Sophisticated optimization models are used todesign generic, minimum-cost schedules.

7/27/2019 20 Scheduling (1)

3/39

2012 Lew Hofmann

Scheduling

Demand scheduling is for customers: Itassigns customers to a definite time for orderfulfillment.

Workforce scheduling is for employees: It

determines when employees work. Operations scheduling focuses on how best to

use existing capacity.

1. Assigning jobs to workstations.

2. Assigning people to workstations.

3. Assigning people to jobs. (Typical with most office work.)

Often, several jobs must be scheduled at one or more workstations. Typically,a variety of tasks can be performed at each workstation. (Especially using One-

Worker, Many Machines)

7/27/2019 20 Scheduling (1)

4/39

2012 Lew Hofmann

Flow Shops and Job Shops

Product-Focused/Line flow (Flow Shops) High volume and low variety, medium- to high-

volume production utilizing line or continuousprocesses

Easier to schedule because the work flowis common.

Process-focused/Flexible flow (Job Shops)

Low-to medium-volume production utilizing job orbatch processes

High variety of products with low volume output

Harder to schedule because work flows are

more varied.

7/27/2019 20 Scheduling (1)

5/39

2012 Lew Hofmann

Problems in Scheduling Job

Shops Having a wide variety of low-volume jobs.

Time to complete a job varies with the job.

Due dates vary.

Demand is less predictable.

Wide variety of equipment and tools needed.

7/27/2019 20 Scheduling (1)

6/39

2012 Lew Hofmann

Scheduling in Job Shops

1. Allocatingjobs to equipment orwork stations.

2. Allocatingpeople to jobs orwork stations

3. Sequencing of jobs (Determining the order in

which jobs are accomplished.)

4. Trackingwork-in-progress

7/27/2019 20 Scheduling (1)

7/39

2012 Lew Hofmann

Gantt Charts

Gantt chart: A tool to monitor the progress of work andto view the loads on workstations.

Gantt charts take two basic forms

The Gantt Prog ress Chartgraphicallydisp lays th e current s tatus of each job o r act iv i ty

relative to its scheduled completion date.

The Gantt Workstat ion Chart/Machine

Chartshows the load/usageon the workstations,

equipment, or other productive assets, and their non-

productive time.

7/27/2019 20 Scheduling (1)

8/39

2012 Lew Hofmann

GANTTPROGRESS CHARTSHOWS THE STATUS (PROGRESS) OF EACH JOB

Colored bars show progress.

Brackets show job duration, start and end times.

Current Date

DECEMBER

JOB 27 28 29 30 1 2 3 4 5 6 7 8 9 10

Group Paper

Article Review

Study for Quiz

Write Resum

Study for Exams

Christmas Cards

7/27/2019 20 Scheduling (1)

9/39

2012 Lew Hofmann

DECEMBER

VEHICLE 27 28 29 30 1 2 3 4 5 6 7 8 9 10

Bus # 1

Bus # 2

Bus # 3

Bus # 4

Bus # 5

Bus # 6

GANTT WORKSTATION CHART

(Mach ine Chart)Shows the utilization of assets

X indicates equipment is unproductive & not available.

Blanks indicate equipment is available to be scheduled.

7/27/2019 20 Scheduling (1)

10/39

2012 Lew Hofmann

Gantt Works tat ion Chart for

Hosp i tal Operat ing Rooms

7/27/2019 20 Scheduling (1)

11/39

2012 Lew Hofmann

Gantt Progress Chart made with

Microsoft Project software

7/27/2019 20 Scheduling (1)

12/39

2012 Lew Hofmann

7/27/2019 20 Scheduling (1)

13/39

2012 Lew Hofmann

7/27/2019 20 Scheduling (1)

14/39

2012 Lew Hofmann

7/27/2019 20 Scheduling (1)

15/39

2012 Lew Hofmann

http://associate.com/gantt/

Emergency Room Work Assignments
http://associate.com/gantt/http://associate.com/gantt/

7/27/2019 20 Scheduling (1)

16/39

2012 Lew Hofmann

SCHEDULING TERMSJob Loading means assigning jobs to people or machines.

Job Flow Time: Time that a job is in the system. It starts when ajob becomes available to be worked on. (Wait time + work time)

Wait Time is that portion of Job Flow Time that ajob is availablebut not being worked on. (In the Queue)

Past Due is a measure ofjob lateness. (Days late, or % of jobslate. Often expressed as the average number of days late.)

Makespan time is thejob flow time required to complete a

group or batch of jobs. For example, completing multiple jobs forone customer.

Utilization = (Time spent working on a job) / (Job Flow Time)

How long it took you to do it how long you had it

7/27/2019 20 Scheduling (1)

17/39

2012 Lew Hofmann

Example

I gave you an assignment last Tuesday. (Job Loading) and it isdue next Tuesday.

Job Flow Time is seven days.

If you did it the same day I assigned it

Wait time was zero

If you do it just before class on Tuesday

Wait time will be 7 days

If it takes you 30 minutes to do it, regardless of when you do it.

Utilization is 0.5 hrs / 56 or 0.89%

(Seven 8-hour work days = 56 hours.)

Utilization is what % of the flow time (time you had the job) didyou spend working on it.

7/27/2019 20 Scheduling (1)

18/39

2012 Lew Hofmann

SCHEDULING STRATEGIES

1) Forward Scheduling: Starts at the current timeand works forward to schedule in the future

2) Backward Scheduling: The focus is on the job due date.You back up from the due date to determine the start date.

Typical in a repetitive type production environment (line flow)

Assembly line situation where jobs are customer specific

Some high variety, low volume situations such as construction.

Typical in a job shop environment

EG: Dentist office or Car repair facility

They look forward in time to see when you (or job) canbe scheduled.

Tends to cause higher inventory costs in manufacturing.

7/27/2019 20 Scheduling (1)

19/39

2012 Lew Hofmann

Job Shop Dispatching

Single-Workstation SchedulingSingle-Dimension Rules

First Come, First Served (FCFS)

Earliest Due Date (EDD)

Shortest Processing Time (SPT) Longest Processing Time (LPT)

Multiple-Dimension Rules (we are not covering these)

Critical Ratio (CR)

Slack Remaining per operation (S/RO)

Multiple-Workstation Scheduling

Johnsons Rule

7/27/2019 20 Scheduling (1)

20/39

2012 Lew Hofmann

JOB SEQUENCING

Job Sequence Work Time Flow Time Due Date Lateness

PROCESSING

JOB TIME DUE DATE

A 4 34

B 10 25

C 2 18

D 14 30

E 12 14

F 6 22

First Come, First Served

Earliest Due Date

Shortest Processing Time

Longest Processing Time

7/27/2019 20 Scheduling (1)

21/39

2012 Lew Hofmann

FIRST-COME, FIRST SERVED

PROCESSING

JOB TIME DUE DATE

A 4 34

B 10 25

C 2 18

D 14 30

E 12 14

F 6 22

4

14

16

30

42

48

154

0

0

0

0

28

26

54

AVERAGE DAYS LATE = (Total days late / # Jobs) = (54 / 6) = 9 days

AVERAGE COMPLETION TIME = (Total Flow Time / # Jobs) = (154 / 6) = 25.7 days

AVERAGE # JOBS IN SYSTEM = (Total Flow Time / Total Work Time) = 154 /48 = 3.2 jobs

FLOW TIME = The time a job spends in the system = 154 days

LATENESS: The time (hours, days or weeks) that jobs are late getting back to customers.

Jobs are scheduled

as they come in.

7/27/2019 20 Scheduling (1)

22/39

2012 Lew Hofmann

Earliest Due Date

12

14

20

30

44

48

168

0

0

0

5

14

14

33

AVERAGE DAYS LATE = (Total days late / # Jobs) = (33 / 6) = 5.5 days

AVERAGE COMPLETION TIME = (Total Flow Time / # Jobs) = (168 / 6) = 28 days

AVERAGE # JOBS IN SYSTEM = (Total Flow Time / Total Work Time) = 168 /48 = 3.5 jobs

Jobs are sequenced

according to when

they are due.

METHOD AVERAGE

LATENESS

AVG. # JOBS IN

SYSTEM

AVG. TIME TO

COMPLETE A JOB

FCFS 9 3.2 25.7

EDD 5.5 3.5 28

SPT

LPT

7/27/2019 20 Scheduling (1)

23/39

2012 Lew Hofmann

Shortest Processing Time


C 2 18

A 4 34

F 6 22

B 10 25

E 12 14

D 14 30TOTALS 48

2

6

12

22

34

48124

0

0

0

0

20

1838



AVERAGE # JOBS IN SYSTEM = (Total Flow Time / Total Work Time) = 124 / 48 = 2.58 jobs

Shortest job is

done first, and

the longest job

is done last.METHOD AVERAGE

LATENESS

AVG. # JOBS IN

SYSTEM

AVG. TIME TO

COMPLETE A JOB

FCFS 9 3.2 25.7

EDD 5.5 3.5 28

SPT 6.3 2.58 20.6

LPT

7/27/2019 20 Scheduling (1)

24/39

2012 Lew Hofmann

Longest Processing Time


D 14 30

E 12 14

B 10 25

F 6 22

A 4 34

C 2 18TOTALS 48

14

26

36

42

46

48212

0

12

11

20

12

3085



AVERAGE # JOBS IN SYSTEM = (Total Flow Time / Total Work Time) = 212/ 48 = 4.42 jobs

Longest job is done

first.

METHOD AVERAGE

LATENESS

AVG. # JOBS IN

SYSTEM

AVG. TIME TO

COMPLETE A JOB

FCFS 9 3.2 25.7

EDD 5.5 3.5 28

SPT 6.3 2.58 20.6

LPT 14.1 4.42 35.3

7/27/2019 20 Scheduling (1)

25/39

2012 Lew Hofmann

A Comparison of four Methods

Earliest Due Date has the least lateness and thus has the best

customer service. It also results in the lowest total inventory

because it goes back to the customer the quickest.

Shortest Processing Time has the lowest average job completiontime and the least # of jobs in the system. Thus it also has the

lowest work-in-process inventory.

First Come, First Serve is considered the most fairby customers,

but it has no other advantage.

METHOD AVERAGE

LATENESS

AVG. # JOBS IN

SYSTEM

AVG. TIME TO

COMPLETE A JOB

FCFS 9 3.2 25.7

EDD 5.5 3.5 28

SPT 6.3 2.58 20.6

LPT 14.1 4.42 35.3

7/27/2019 20 Scheduling (1)

26/39

2012 Lew Hofmann

Which Method To Use?

Shortest Processing Time may have the best measures,but it discriminates against the longest jobs.

Longest jobs may be the most important or bring the biggest

revenues.

If longest jobs are the most important, then consider using theLPT method.

First-Come, First Served is perceived by most

customers to be the fairest method.

The method used should be based on customer

situation, risk, revenues, job importance, etc.

7/27/2019 20 Scheduling (1)

27/39

2012 Lew Hofmann

Multiple-Phase Situations

Multiple Phase (same as in queuing theory)

There are multiple work stations (processing stops)

Johnsons Rule

Easily used for two-phase work flows.

With three or more phases the schedulingtechniques become complex.

Job Shop Dispatching

Used by most job shop companies with three or more

job phases.

The decision about which job to process next at a

workstation is made applying simple priority rules at

each workstation whenever it becomes available.

7/27/2019 20 Scheduling (1)

28/39

2012 Lew Hofmann

Johnsons Rule for 2-phase

SchedulingJOB Phase 1 Phase 2

A 10 5B 7 4

C 5 7

D 3 8

E 2 6

F 4 3

1. Select the job with the

shortest phase time.

RESULTS

2. If the shortest phase time is in phase one, schedule that

job first. If it is in phase two, schedule that job last. In

case of a tie (equal phase times) the decision is arbitrary.

3. Eliminate the job just scheduled and repeat steps 1 & 2

until all jobs are scheduled.

E D C A FB

7/27/2019 20 Scheduling (1)

29/39

2012 Lew Hofmann

M1 12 22

M2 4 5

M3 5 3

M4 15 16

M5 10 8

Eliminate M3 from consideration. The next shortest time

is M2 at Workstation 1, so schedule M2 first.Eliminate M5 from consideration. The next shortest time is

M1 at workstation #1, so schedule M5 next.Eliminate M1 and the only job remaining to be scheduled

is M4.

SequencingwithJohnsons RuleAt the Morris Machine Co.

Time (hr)

Motor Workstation 1 Workstation 2

Sequence = M1M2 M3M4 M5

Shortest time is 3 hours at workstation 2, so

schedule job M3 last.Eliminate M2 from consideration. The next shortest time is

M5 at workstation #2, so schedule M5 next to last.

7/27/2019 20 Scheduling (1)

30/39

2012 Lew Hofmann

Sequencing

Workstations

M2(4)

M1(12)

M4(15)

M5(10)

M3(5)

Idleavailablefor further work

0 5 10 15 20 25 30Day

35 40 45 50 55 60 65

Idle2 M2(5)M1(22)

M4(16)

M5(8)

M3(3)Idle

1

Gantt Chart for the Morris Machine Co. Repair Schedule

Johnsons Rule minim izes the idle t imeat station 2andgives the fastest repair t imefor all five jobs.

No other sequence will produce a lower make-span time.

M f t i P

7/27/2019 20 Scheduling (1)

31/39

2012 Lew Hofmann

ShippingDepartme

nt

Manu factu r ing ProcessFlexib le Flow / Job Shop

Raw

Materials

Legend:

Batch of parts

Workstation

Job-shop scheduling

can be complex. Thisis only six work

stations.

SCHEDULING JOBS FOR

7/27/2019 20 Scheduling (1)

32/39

2012 Lew Hofmann

SCHEDULING JOBS FOR

MULTIPLE WORKSTATIONS

Each workstation is treated independently using priority

sequencing rules.

When a workstation becomes idle, an appropriate priority rule is

applied to the jobs waiting for that operation, and the job with the

highest priority is selected.

When that operation is finished, the job is moved to the next workstation in its routing, where it waits until it again has the highest priority

at that station.

Identifying the best priority rule to use at a particular work station

(phase) in a process is a complex problem.

Computer simulation models are effective tools to determine

which priority rules work best in a given situation.

Computer simulation is rarely used in smaller-volume operations

S h d li i M lti l W k t ti

7/27/2019 20 Scheduling (1)

33/39

2012 Lew Hofmann

Scheduling in Multiple Workstation

(flexible flow) situations

When a job arrives at a given workstation, it joins that queue and is given

a priority according to the rule being used at that station.

Each workstation istreated independently.

Different jobs traveldifferent routes.

7/27/2019 20 Scheduling (1)

34/39

2012 Lew Hofmann

Scheduling and the Supply Chain

Your Production scheduling should be integrated withyour supply chains.

Demand Forecasts affect the entire supply chain andthus are shared with your suppliers.

Location of inventory (inventory placement) isstrategic and long-term, affecting the supply chain.

Available-To-Promise decisions can be checked withsuppliers for availability of materials and components.

Scheduling should be a part of, rather than reactive to, thesupply chain.

7/27/2019 20 Scheduling (1)

35/39

2012 Lew Hofmann

Scheduling Customers for Service

Backlogs

Customers are in a queue for services and are given a

due date for the fulfillment of an order.

Orallow a backlog to develop as customers arrive.

Customers may never know exactly when their orders

will be fulfilled.

Appointments

Specific times for service

Reservations

Specific times for customers to occupy oruse service facilities

7/27/2019 20 Scheduling (1)

36/39

2012 Lew Hofmann

Scheduling Employees

Fixed Schedule

Workers on shift work or fixed hours.

Rotating Schedule Individual schedules vary from week to week.

Problems:

Holidays / consecutive days off / personal days /vacation days / sick days / labor unionagreements

7/27/2019 20 Scheduling (1)

37/39

2012 Lew Hofmann

Unique Situation Scheduling

EG: Scheduling faculty, courses & rooms.

Faculty have personal preferences & needs

Morning vs. Evening classes

Four-day, Three-day and Two-day schedules

Classroom preferences

Course constraints

Need for labs or tiered rooms or tables

Required courses at conflicting times

Facility constraints

Limited rooms and limited lab availability

Insufficient facilities for high-demand times.

7/27/2019 20 Scheduling (1)

38/39

2012 Lew Hofmann

LABOR-LIMITED ENVIRONMENTS

The limiting resource thus far has been the number ofmachines or workstations available. A more typical

constraint is the amount of labor available.

Labor-limited environmentis an environment in which the

constraint is the amount of human labor available, ratherthan the number of machines or workstations.

Four possible approaches:

1. Assign people to thejob that has been in the system longest.

2. Assign people to the workstation with the most jobs.3. Assign people to the workstation having jobs that require the most work.

4. Assign people to the workstation with the job that has the earliest due

date.

7/27/2019 20 Scheduling (1)

39/39

2012 L H f

Sophisticated Scheduling

Techniques

Expert Systems are now a popular way toschedule complex work flows.

Artificial-Intelligent software that emulates the

decision-making of human experts.

Optimized Production Technology(OPT) and Q-Control are two very sophisticated computerprograms for production scheduling in job shopenvironments.

They combine simulation and heuristics

20 scheduling (1)

Documents