Material Transport Systems

Chapter 10

Objectiveso By end of the class,

students should be able to:o Describe the five transport

system that are commonly used in manufacturing

o Explain characteristics of AGV (Guidance and traffic controls)

o Explain characteristics of conveyors

o Perform engineering analysis on material transport system

Material Transport systemo Needed to transport

materials (raw material, finished goods, WIP..etc) within manufacturing facilities and to/from warehouse or storage areas.

Common Material Handling Equipment

Equipment Features Typical Application

Industrial truck (manual or powered)

Low to medium cost, low rate of deliveries/hr

Moving light loads and palletized containers

Automated guided vehicles system

High cost, flexible routing

Moving pallet loads and WIP

Monorails and other rail guided vehicles

High cost, flexible routing

Moving single assemblies or large qty

Conveyors Various types Moving product in manufacturing lines

Cranes and hoist High lift capacity Moving large, heavy items in factories

Industrial Trucks

(a) Two-wheel hand truck, (b) four-wheel dolly, (c) hand-operated low-lift pallet truck

Automated Guided Vehicleso AGVS is a material handling

system that uses independently operated, self-propelled vehicles guided along a defined pathways.

o Appropriate where different materials are moved from various load points to various unload points.

Application of AGVs

Unit load carrier and pallet trucks: Used in storage and distribution and Flexible manufacturing system

Driver-less train: Used in moving large quantity of materials over large distances

Vehicle Guidance Technology

Self Guided Vehicles: Operated without defined pathways but with beacons located throughout the facilities. Pathway can be changed by changing the navigation data.

Imbedded guide wires : Guided by equal intensity of electromagnetic field on two sensors.

Paint strips: Guided by optical sensors

Vehicle Management & Safetyo Traffic Controls:

o Onboard sensors o Vehicle will stop upon detecting

obstacleo Sensors can be optical or ultrasonic

o Zone controlso Operating rules that no vehicle will

enter the zone if there is already occupied by another vehicles

o Safetyo Speeds normally slower than walking

paceo vehicle automatic stop if it strays more

than a short distance from specified path

o Emergency bumper-the vehicle automatically stop if the bumper is activated.

Conveyor Types

Roller and skate wheel conveyor Belt conveyor

Chain conveyor

(a) Single direction conveyor

(b) Continuous loop conveyor

Conveyor Types

Conveyor Operation & Features

o Powered conveyor can be divided into two:o Continuous conveyor moving

at constant velocityo Asynchronous conveyor

operating with a stop and go motion. Used :oAs buffersoTo allow differences in

production rate between adjacent process

oTo accommodate different conveyor speed

Monorails/Other railed guided vehicles

Crane and Hoists

Analysis of Material Transport System

o Based on MHI assumptions.o Focuses on 3 areas:

o Charting techniqueso Analysis of vehicle based

systemo Conveyor Analysis

Charting Techniqueso Purpose is to display the

material flowso Two techniques:

o From-To Chart

From-To-Chart

To 1 2 3 4 5

From

1 0 9/50* 5/120 6/205 0

2 0 0 0 0 9/80

3 0 0 0 2/85 3/170

4 0 0 0 0 8/85

5 0 0 0 0 0

Note: loads/hr /Travel Distance

Flow Diagram

1

4

3

2

5

9/50

9/806/205

8/852/85

3/170

5/120

Analysis of Vehicle Based Systems

o Assumption:o Vehicle operates at constant

velocity ignoring acceleration and deceleration,

o The time for typical delivery:o Loading at pick up station, o Traveling time to drop off

stationo unloading at drop off station,o empty traveling time of the

vehicleo Therefore:

LT

LT

UT

d ec L U

c e

L LT T T

v v

o can be used to calculate: o Hourly rate of deliver per

vehicle, o AT depends on

o Availability of the vehicles, Ao Traffic congestion, Tf

o Efficiency of manual driver, Eo Therefore

Analysis of Vehicle Based Systems

cT60

dvc c

ATR

T T

60 fAT AT E

Analysis of Vehicle Based Systems

o Number of vehicles required to satisfy specified delivery requirement,Rf

o Total workload

o Number of required vehiclesf cWL R T

fc

dv

RWLn

AT R

Example 1An automated guided vehicle system has an average travel distance per delivery = 200 m and an average empty travel distance = 150 m. Load and unload times are each 24 s and the speed of the AGV = 1 m/s. Traffic factor = 0.9. How many vehicles are needed to satisfy a delivery requirement of 30 deliveries/hour? Assume that availability = 0.95 and worker efficiency = 1.0.

Example 2Four forklift trucks are used to deliver pallet loads of parts between work cells in a factory. Average travel distance loaded is 350 ft and the travel distance empty is estimated to be the same. The trucks are driven at an average speed of 3 miles/hr when loaded and 4 miles/hr when empty Terminal time per delivery averages 1.0 minute (load = 0.5 minute and unload = 0.5 minute). If the traffic factor is assumed to be 0.90, availability = 100%, and worker efficiency = 0.95, what is the maximum hourly delivery rate of the four trucks? (1mile=5280 ft)

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