PERT 08 Penjadwalan Jangka Pendek (1)

� Pentingnya Penjadwalan jangka pendek

� Forward & Backward Scheduling

� Input Output Control

� Gantt Charts

Strategic Implications of Short-TermScheduling

� By scheduling effectively, companies use

assets more effectively and create greater

capacity per dollar invested, which, in turn,

lowers cost

� This added capacity and related flexibility

provides faster delivery and therefore better

customer service

� Good scheduling is a competitive advantage

which contributes to dependable delivery

�Deals with timing of operations

� Short run focus: Hourly, daily, weekly

�Types

TodayToday Due Date

BB EE

Forward SchedulingForward Scheduling

TodayToday Due Date

BB EE

Backward SchedulingBackward Scheduling

Short-Term Scheduling

� Hospital– Outpatient treatments

– Operating rooms

� University– Instructors

– Classrooms

� Factory– Production

– Purchases

© 1984-1994 T/Maker Co.

Short-Term Scheduling Examples

Organization Managers Must ScheduleOperating room use

Patient admission

Nursing, security, maintenance staffs

Outpatient treatments

Classrooms and audiovisual equipment

Student and instructor schedules

Graduate and undergraduate courses

Production of goods

Purchase of materials

Workers

Scheduling Decisions

� Mount Sinai Hospital

� Indiana University

� Lockheed-MartinFactory

Organization Managers Must Schedule

Chefs, waiters,bartenders

Delivery of fresh foods

Entertainers

Opening of dining areas

Maintenance of aircraftDeparture timetables

Flight crews, catering, gate, and ticketing personnel

Scheduling Decisions

� Hard Rock Cafe

� Delta Airlines

Capacity Planning, Aggregate Scheduling, Master

Schedule, and Short-Term Scheduling

Capacity Planning

1. Facility size

2. Equipment procurement

Aggregate Scheduling

1. Facility utilization

2. Personnel needs

3. Subcontracting

Master Schedule

1. MRP

2. Disaggregation of master plan

Long-term

Intermediate-term

Short-term

Intermediate-term

Short-term Scheduling

1. Work center loading

2. Job sequencing

Forward and Backward Scheduling

� Forward scheduling: begins the schedule as soon as the

requirements are known

– jobs performed to customer order

– schedule can be accomplished even if due date is

missed

– often causes buildup of WIP

� Backward scheduling: begins with the due date of the

final operation; schedules jobs in reverse order

– used in many manufacturing environments, catering,

scheduling surgery

The Goals of Short-Term Scheduling

� Minimize completion time

� Maximize utilization (make effective

use of personnel and equipment)

� Minimize WIP inventory (keep

inventory levels low)

� Minimize customer wait time

�Qualitative factors– Number and variety of jobs

– Complexity of jobs

– Nature of operations

�Quantitative criteria– Average completion time

– Utilization (% of time facility is used)

– WIP inventory (average # jobs in system)

– Customer waiting time (average lateness)

Choosing a Scheduling Method

Level Use

Methods

Repetitive-

Focused

Product-

Focused

Process-

Focused

Variety of

Methods

Scheduling Methods Differ by Process

� High variety, low volume systems

� Products made to order

� Products need different materials and

processing

� Complex production planning and control

� Production planning aspects

– Shop loading

– Job sequencing

Process-Focused Work Centers

Requirements for Scheduling Process-Focused Work Centers

� Schedule incoming orders without violating capacity

constraints of individual work centers

� Check availability of tools and materials before releasing

an order to a department

� Establish due dates for each job and check progress against

need dates and order lead times

� Check work-in-progress as jobs move through the shop

� Provide feedback on plant and production activities

� Provide work-efficiency statistics and monitor operator

times for payroll and labor distribution analyses

Types of Planning Files

� Item master file - contains information

about each component the firm

produces or purchases

� Routing file - indicates each

component’s flow through the shop

� Work-center master file - contains

information about the work center such

as capacity and efficiency

� Assigning jobs to work centers

� Considerations

– Job priority (e.g., due date)

– Capacity

• Work center hours available

• Hours needed for job

� Approaches

– Gantt charts (load & scheduling) - capacity

– Assignment method - job to specific work center

Loading Jobs in Work Centers

-+5-10-200Cumulative

Change in Backlog

-200-150-100-50Cumulative

Deviation

270270270270Actual Output

320320320320Planned Output

-35-40-40-10Cumulative

Deviation

280285280250270Actual input

280280280280280Planned input

7/117/46/276/206/136/6Week Ending

Input-Output Control

Explanation: 270 input, 270

output, implies 0 change

Explanation: 250 input,

270 output implies –20

change (20 standard

hours less in the work

center)

Order Release Begins Shop Loading

No

Release

Order

Hold

Release

Priority & Capacity

OK?

Gross Requirements

Scheduled Receipts

Available

Net Requirements

Planned Order Receipt

Planned Order Release

Yes

1 2

100

100

3

Options for Managing Facility Work Flow

� Correcting performance

� Increasing capacity

� Increasing or reducing input to the work

center by:

– routing work to or from other work centers

– increasing or decreasing subcontracting

– producing less (or more)

� Shows relative workload in facility

� Disadvantages

– Does not account for unexpected events

– Must be updated regularly

Work Center M T W Th F

Metal Works Job 349 Job 350

Mechanical Job D Job G

Electronics Job B Job H

Painting Job C Job E Job I

Gantt Load Chart

Gantt Load Chart for Week of March 6

� Shows relative workload in facility

� Disadvantages– Does not account for unexpected events– Must be updated regularly

Job 349Job 408Job 295Painting

Job 349Job 408Electronics

Job 406Job 349Mechanical

Job 350Job 349Metalworks

FridayThursdayWednesdayTuesdayMondayDay

Work

Center

Processing UnscheduledCenter not available (for

example, maintenance time,

repairs, shortages)

Gantt Scheduling ChartStart of an activity

Scheduled activity time allowed

Point in time when chart is reviewed

S T W T F S

DayJob

Job A

Job B

Job C

Maintenance

Now

End of an activity

Actual work progress

Non-production time

Day

1

Day

2

Day

3

Day

4

Day

5

Day

6

Day

7