chap013.ppt scheduling operations

7/30/2019 Chap013.ppt Scheduling Operations

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McGraw-Hill/Irwin The McGraw-Hill Companies, Inc. 2007, All Rights Reserved

Scheduling Operations

Chapter 13


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Chapter 13 Outline

Batch Scheduling

Gantt Charting

Finite Capacity SchedulingTheory of Constraints

Priority Dispatching Rules

Infinite Capacity LoadingPlanning and Control Systems


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Synonyms

Shop Floor Control

Scheduling OperationsProduction Activity Control (PAC)

Detailed Planning and Scheduling(DPS)


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Batch Scheduling

Very complex scheduling environment

Can be thought of as Network of Queues

Customers spend most of their time waitingClosely related to MRP (See chapter 16)


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Batch Processing

Move-queue-work-wait-move

WS 1 WS 2

Work is done according to work order

waitmove

queue

move

movewaitqueue

move

movemove


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Difficulties Of Batch/Job Shop

Scheduling

Variety of jobs processed

Different routing and processingrequirements of each job

Number of different orders in the

facility at any one time

Competition for common resources


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Responsibilities of Production

Control Department

Loading

Check availability of material, machines& labor

Sequencing

Release work orders to shop & issuedispatch lists for individual machines

Monitoring

Maintain progress reports on each jobuntil it is complete


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Gantt Charting

Developed by Henry Gantt in 1917

Related concepts:

Makespantotal time to complete a set of jobsMachine utilizationpercent of make span time a

machine (or person) is used.

Used primarily to monitor progress of jobs


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Job Data for Scheduling Example

Job

Work center/

Machine Hours

Due

Date

1 A/2, B/3, C/4 3

2 C/6, A/4 2

3 B/3, C/2, A/1 4

4 C/4, B/3, A/3 4

5 A/5, B/3 2


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Scheduling Example

Process A Process C

Job 1 AC

B

Process B

Job 3

In what sequence should the jobs be done?Job 5 Job 2 Job 4


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Where is the bottleneck?

Total Machine times for the five jobs:

Machine A: 15 hours

Machine B: 12 hours

Machine C: 16 hours

C appears to be the bottleneck.

But! A is used for every job; C is not.

Either one could determine makespan.


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Gantt Chart for Example


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Finite Capacity Scheduling

Finite capacity scheduling loads jobs ontowork stations being careful not to exceedthe capacity of any given station.

Done at the detailed planning andscheduling (DPS) level

Part of the loading responsibility.


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Theory of Constraints (TOC)

Proposed by Goldratt in The Goal (1983)

Goal is to make money.

Key elements of goals according to TOC:

Throughputwhat is made and sold

Inventoryraw materials

Operating expensescost of conversion

Production does not count until it is sold!


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Theory of Constraints (TOC)

A constraint is anything that is slowingdown productiona bottleneck.

A machine or workstation

The market

Procurement system

The bottleneck determines the capacity ofthe system.

Implication: the operations manager shouldfocus on the bottleneck to increase capacityand throughput (and make more money).


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What are priority dispatching rules?If you have more than one job waiting at a

work station, how do you select which one to

process next? The criterion you use forselecting the next job is your dispatching rule.

In front officeservices, the most common

rule is first come, first served.

Part of the sequencing responsibility


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Commonly used in manufacturing: MINPRT (Minimum Processing Time orSPT, shortest

processing time) This rule minimizes total waiting time.

Critical Ratio(Minimizes average lateness)

Commonly used in services: FCFS (First Come, First Served)


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Infinite Capacity Loading

Infinite capacity loading loads jobs onto

work centers without regard for the total

capacity of the work center.

If the capacity for any given work center has

been exceeded, the schedule must be changed.

This is generally done at the MRP level before

detailed scheduling and planning


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Infinite capacity loading example: time lines

A

(2 hrs)

Move/Wait

(4 hrs)

B

(3 hrs)

Move/Wait

(4 hrs)

C

(4 hrs)

Day 1 Day 2 Day 3

Due date

Move/Wait

(4 hrs) A (4 hrs)

Day 1 Day 2 Day 3

Due date

C (6 hrs)

Time line for job 1

Time line for job 2


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Infinite Capacity Loading example

6

5

4

3 Job 2

2

1

Job 1 Job 1Hoursschedule

d

Work center A

6

5

4

3

2

1 Job 1

Work center B

6

5

4

3

2

1 Job 1

Job 2

Work center C

1 2 3Day

1 2 3Day

1 2 3Day


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Planning and Control Systems

What delivery date do I promise?

How much capacity do I need?

When should I start on each particular activityor task?

How do I make sure that the job is completed

on time?Advanced Planning & Scheduling (APS)


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Summary

Batch Scheduling

Gantt Charting

Finite Capacity SchedulingTheory of Constraints


Infinite Capacity LoadingPlanning and Control Systems


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End of Chapter Thirteen

chap013.ppt scheduling operations

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