Bollard System for Binding

Design and Fabrication of an Automated Bollard System

DESIGN AND FABRICATION OF AN AUTOMATED BOLLARD SYSTEM

BY

Adegboro Kolawole Samuel ENG0601413Aihie Osayanrhion ENG0603483Arutere Oghenevwoke Abraham ENG0402482Ememerurai Uzuazo Nita ENG0601348Idogho Ohwobete Ichiako ENG0409413Unokhogie Emmanuel Egwakhide ENG0409432Uruemuesiri Aruwa ENG0601331Omoriawo Augusta Renny ENG0409276

MECHANICAL ENGINEERING DEPARTMENTFACULTY OF ENGINEERING

UNIVERSITY OF BENINBENIN CITY

IN PARTIAL FUFILMENT FOR THE AWARD OF A BACHELOR OF ENGINEERING (B.Eng.) AT THE UNIVERSITY OF BENIN,

BENIN CITY

NOVEMBER 2011

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CERTIFICATION

This is to certify that the project “Design and Fabrication of an Automated

Barrier System (Rising Arm Mechanism)” was carried out by the following

students:

Adegboro Kolawole Samuel ENG 0601413

Aihie Osayanrhion ENG 0603483

Arutere Oghenevwoke Abraham ENG 0402482

Ememerurai Uzuazo Nita ENG 0601348

Idogho Ohwobete Ichiako ENG 0409413

Unokhogie Emmanuel Egwakhide ENG 0409432

Uruemuesiri Aruwa ENG 0601331

Omoriawo Augusta Renny ENG 0409276

In partial fulfilment for the award of a Bachelor of Engineering (B.Eng.)

at the University of Benin, Benin City.

__________________ ______________________ P. O. OLAGBEGI DR. D. I. IGBINOMWANHIA PROJECT SUPERVISOR PROJECT CO-ORDINATOR

Date: ____________ Date: ____________

_____________________DR. D. I. IGBINOMWANHIA

HEAD OF DEPARTMENT

Date: __________________

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DEDICATION

This project is dedicated to the Almighty God and to all our friends and

families too numerous to mention who stood by us throughout our stay on

campus.

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ACKNOWLEDGEMENT

We acknowledge the entire staff of the Department of Mechanical

engineering and our Project Supervisor without whose support this then

proposed project would never have become a reality.

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TABLE OF CONTENTS

CERTIFICATION............................................................................................................................ ii

DEDICATION............................................................................................................................... iii

ACKNOWLEDGEMENT................................................................................................................ iv

TABLE OF CONTENTS...................................................................................................................v

LIST OF FIGURES........................................................................................................................ vii

ABSTRACT................................................................................................................................... ix

CHAPTER 1.................................................................................................................................. 1

1.0 INTRODUCTION................................................................................................................1

1.1 BACKGROUND OF STUDY..............................................................................................1

1.2 PROBLEM STATEMENT.................................................................................................2

1.3 AIM...............................................................................................................................3

1.4 OBJECTIVES...................................................................................................................3

CHAPTER 2.................................................................................................................................. 4

2.0 LITERATURE REVIEW........................................................................................................4

2.1 THE RAISING ARM BARRIER..........................................................................................4

2.1.1 BRIEF HISTORY............................................................................................................5

2.1.2 PRESENT DAY APPLICATIONS......................................................................................8

2.2 THE CONTROL SYSTEM.................................................................................................9

2.2.1 SENSORS................................................................................................................9

2.2.2 RELAY SWITCHES.................................................................................................17

CHAPTER 3................................................................................................................................ 30

3.0 CONCEPTUAL DESIGN.................................................................................................... 30

3.1 CONCEPT 1 – HYDRAULIC JACK...................................................................................30

3.2 CONCEPT 2 – BELT AND PULLEY SYSTEM....................................................................32

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3.3 CONCEPT 3 – SCREW JACK..........................................................................................34

3.4 MODE OF OPERATION................................................................................................36

3.4.1 Mechanism..........................................................................................................36

3.4.2 Control................................................................................................................ 37

CHAPTER 4................................................................................................................................ 38

4.0 DETAILED DESIGN...........................................................................................................38

4.1 COMPONENTS OF THE AUTOMATED BARRIER SYSTEM.............................................38

4.1.1 MECHANICAL COMPONENTS (Mechanism).........................................................38

4.1.2 ELECTRICAL COMPONENTS.................................................................................43

4.2 THE RAISING ARM (CROSSBAR)..................................................................................47

4.3 ELBOW JOINT..............................................................................................................51

4.4 SHAFT......................................................................................................................... 52

4.5 BEARING.....................................................................................................................53

4.6 CRANK........................................................................................................................ 54

4.7 SCREW JACK................................................................................................................54

4.8 CONTROL SYSTEM DESIGN.........................................................................................60

4.8.1 The Control Design Process.................................................................................60

4.8.2 The Flow Diagram................................................................................................62

4.8.3 Control Diagram..................................................................................................62

4.8.4 Circuit Diagram....................................................................................................63

CHAPTER 5................................................................................................................................ 64

5.0 CONCLUSION..................................................................................................................64

5.1 RECOMMENDATIONS.................................................................................................65

5.2 FURTHER WORK..........................................................................................................65

5.3 SUMMARY..................................................................................................................65

REFERENCES..............................................................................................................................67

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LIST OF FIGURES

Figure 1 - A “2 x 5m” automatic barriers c/w 4m underskirts & pogo stick end

supports.................................................................................................................4

Figure 2 - Mooring barriers were the first type of barrier; the term has since

expanded usage.....................................................................................................6

Figure 3 - A section from the WWII road barrier erected at Achtercairn, Gairloch

© Rob Scott, and Gairloch Heritage Museum........................................................6

Figure 4 – Latching relay with permanent magnet..............................................20

Figure 5 - Solid state relay with no moving parts.................................................23

Figure 6 - 25A or 40A solid state contactors........................................................24

Figure 7 – Modified Hydraulic Jack......................................................................31

Figure 8 - The Belt and Pulley System..................................................................33

Figure 9 - The Screw Jack.....................................................................................35

Figure 10 - 3D Model of the Project.....................................................................36

Figure 11 - Layout of the Automated Barrier System...........................................38

Figure 12 – The Crank..........................................................................................39

Figure 13 – The Bearing Casing............................................................................40

Figure 14 – The Screw Jack..................................................................................41

Figure 15 – The Shaft (Crankshaft).......................................................................42

Figure 16 – The Crossbar (Barrier Arm)................................................................42

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Figure 17 – The Elbow Joint.................................................................................43

Figure 18 – Schematic of a Step-down Transformer............................................43

Figure 19 - Schematic of a Rectifier.....................................................................44

Figure 20 – Relay Circuit......................................................................................45

Figure 21 – Proximity Card Reader with Access Card...........................................46

Figure 22 - The Crossbar......................................................................................47

Figure 24 - The Shaft Layout................................................................................53

Figure 25 - Steps in Design of a Control System...................................................61

Figure 26 - The Flow Diagram..............................................................................62

Figure 27 - The Systems' Block Diagram..............................................................62

Figure 28 - Circuit Diagram of the Control System...............................................63

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ABSTRACT

This project is the design and installation of an automated bollard system

to solve the problem of vehicle access to a certain route. The route in focus in

this case is the Engineering Access Road. Formerly this road was completely

blocked off and this prevented staff from plying the route to and from their

offices.

Different methods were explored such as: the use of retractable bollards,

an operator controlled bollard. We settled on using a rising arm bollard with

automatic control.

Of the different mechanisms that exist to operate the raising arm

mechanism, we chose the use of a screw jack which when compared to other

mechanisms; like the use of a hydraulic jack or a belt and pulley system was

simpler and yet still effective, more compact and involved the use of easily

procurable components.

An automated bollard system was designed and installed on the

Engineering access road, which comprised the raising mechanism with relays,

sensors and card readers used to control the system as well as speed bumps and

road signs used to inform the road user of the barrier ahead.

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CHAPTER 1

1.0 INTRODUCTION

Bollards originally referred to short vertical posts used on a quay for

mooring. Now it describes a variety of structures to control or direct road traffic,

such as posts arranged in a line to obstruct the passage of motor vehicles. In

addition, barriers are used in the lighting industry to describe short, post-like

light fixtures. The bollard referred to in this context, is a barrier used for guiding

traffic.

1.1 BACKGROUND OF STUDY

Although we live in a civilized world, it has been a well-known fact that

humans cannot always be counted on to instinctively act in accordance with

rules or in ways beneficial to their fellow men. As such there is the need to

control human behaviour.

In this modern age, many different methods for controlling human

behaviour in a vast number of scenarios have been employed. One of such

scenarios is in the area of access to certain restricted areas. If such places are

left open, without any form of control, anyone may access such areas. An

extreme solution would be to completely block off this area, but this would also

prevent authorized personnel from gaining access. Other methods such as

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‘STOP’, ‘NO ENTRY BEYOND HERE’ and ‘AUTHORISED PERSONNEL ONLY’ signs

have been employed with varying degrees of success. One solution that showed

an efficient level of control in the area of access by motor vehicle is the barrier

system.

1.2 PROBLEM STATEMENT

Vehicle movement through the Faculty of Engineering was restricted with a

static barrier. This was because of disturbances caused by vehicles plying the

route. And this blocked off every vehicle passing through Engineering including

lecturers of the Faculty, especially those of Civil and Chemical Engineering from

getting to their various offices through the normal route and also lecturers going

to staff school to pick their kids.

The current barrier system employed throughout most of Nigeria and in the

University of Benin in particular is the manually operated counter-weight type.

And this type possesses a number of draw backs. For one, it relies on the

use of manual labour, the operator must be present at all times and in all

weather conditions for the system to function – which is not practical or even

humane not to mention the amount of strain suffered by the individual required

to push down the counter-weight. Another problem lies in human sentiment,

the operator has to a large extent autonomous control over who has access

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through his gate so he may decide to abandon his duty and allow unauthorised

access to the area for his own selfish gain.

We propose an automated barrier system as a solution. This system would

employ the use of proximity card readers, infrared motion sensors and a

mechanized barrier as part of the automated barrier system. This system, void of

human emotion and undeterred by rain or sunshine, would serve as a barrier to

unauthorized vehicles and would at the same time allow only authorized

personnel through.

This automated barrier installation would serve the intent of the former

barrier – blocking off non-staff, and still allowing staff to easily drive to their

offices and staff school through Faculty of Engineering without the added

disadvantages of the barrier system currently employed on the campus.

1.3 AIM

The design, fabrication and full installation of an automated barrier system

(rising arm mechanism) that would consist of a mechanized barrier, proximity

card readers, infrared motion sensors and a backup power source.

1.4 OBJECTIVES

To design and install a mechanized barrier.

To design and install a barrier control system.

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To devise a means to reduce the speed vehicles passing through the

barrier and to ensure that each passing vehicle is accessed individually.

To connect to a backup power supply.

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CHAPTER 2

2.0 LITERATURE REVIEW

The automated barrier system

is an automatically controlled

road barrier system. It is

designed to restrict unwanted

traffic and discourage vehicle

movement through the area

as well as allow authorized personnel through without the involvement of an

operator.

2.1 THE RAISING ARM BARRIER

The rising arm barrier is a road barrier designed to control traffic by the

lifting and lowering of the arm. This type falls under non-crash-resistant barriers

and are distinct from crash- and attack-resistant barriers that are hardened

barrier systems used to protect military, government, and other compounds and

buildings of higher security levels. Non-crash-resistant barriers are "perceived

impediments to access" and address the actions of two groups:

1. Persons who are law-abiding and comply with implied civil prescriptions of

behaviour as defined by the manner in which barriers are put to use; and

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Figure 1 - A “2 x 5m” automatic barriers c/w 4m underskirts & pogo stick end supports


2. Others who are potentially threatening and disrupting for whom barrier

applications are proscriptive by notifying intruders their behaviour is

suspect and additional levels of security wait to identify them.

It is used in locations where it is needed to restrict access to particular

classes of traffic or just as a check point. When used with an operator, it may be

used as a toll gate point. It comprises a raising arm, the lifting mechanism, the

housing and road signs and symbols designed to inform the driver of the barrier

ahead (Charles G. Oakes, 2011).

2.1.1 BRIEF HISTORY

A barrier, a name inherited from the Norman-French name ‘Boulard’ still

often found in Normandy, is a short wooden, iron or stone post used on a

quayside for mooring ships. Mooring barriers are seldom exactly cylindrical, but

typically have a larger diameter near the top to discourage mooring warps (dock

lines) from coming loose. Single barriers sometimes include a cross rod to allow

the mooring to be bent into a figure eight. The word now also describes a

variety of structures to control or direct road traffic, such as posts arranged in a

line to obstruct the passage of motor vehicles (Wikipedia, 2010).

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Figure 2 - Mooring barriers were the first type of barrier; the term has since expanded usage

In addition, barriers are used in the lighting industry to describe short,

post-like light fixtures. The term may be related to bole, meaning a tree trunk.

Our interest is in the variety of structures to control or direct road traffic.

Barriers, as functional street furniture, began with the Romans who

constructed milestone markers, horse troughs, and tethering posts made of

wood or stone. They later were used to protect pedestrians and buildings from

horse-drawn vehicles (Charles G. Oakes, 2011).

Figure 3 - A section from the WWII road barrier erected at Achtercairn, Gairloch © Rob Scott, and Gairloch Heritage Museum.

Barriers enjoy considerable variety as to their construction (cast iron,

stainless steel, steel/cast iron composite, recycled plastic, plastic covers) and

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functional design (fixed, telescoping, removable, collapsible, and

collapsible/concealable). Surpassing in variety the diverse construction and

design functions of barriers are the many settings in which barriers are used

(Charles G. Oakes, 2011).

Traffic barriers constitute hazards themselves and should only be used

when the obstacle poses a greater threat than the barrier itself. In all cases,

roadside hazards must be assessed for the danger they pose to traveling

motorists based on size, rigidity and distance from the edge of travel-way. For

instance, small roadside signs and some large signs (ground-mounted

breakaway post) often do not merit roadside protection as the barrier itself may

pose a greater threat to general health and well-being of the public than the

obstacle it intends to protect. In many regions of the world, the concept of

clear-zone is taken into account when examining the distance of an obstacle or

hazard from the edge of travel-way.

Clear-zone also known as clear recovery area or horizontal clearance is

defined as a lateral distance in which a motorist on a recoverable slope may

travel outside of the travel-way and return their vehicle safely to the roadway.

This distance is commonly determined as the 85th percentile in a study

comparable to the method of determining speed limits on roadways through

speed studies and varies based on the classification of a roadway. In order to

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provide for adequate safety in roadside conditions, hazardous elements,

whether they be obstacles or steep slopes can be placed outside of the clear-

zone in order to reduce or eliminate the need for roadside protection.

When barrier is needed, careful calculations are completed to determine

length of need which takes into account the aforementioned factors.

Specifically, the traffic volumes and therefore, the classification of the roadway

in addition to the distance of the hazard from the edge of travel-way and the

distance or offset of the barrier to be placed or installed from the edge of travel-

way. It is the case in current times, that barrier or rail that is to be used in

construction and maintenance operations has undergone extensive testing in

both government and private research facilities in order to determine proper

'crash-worthiness' and effectiveness in conditions which are prescribed for its

use. In particular, most roadside protection, whether it be a concrete barrier or

rail, or a metal beam fence will perform properly only when placed in adequate

proximity to the travel-way so as to prevent vehicle impacts at large (obtuse)

angles. The method in which a barrier protects motorists from roadside hazards

is in how it dissipates the energy of an impact (Department Of Infrastructure,

Energy And Resources (USA), 2008).

2.1.2 PRESENT DAY APPLICATIONS

Barriers are used extensively in our society for many varying applications.

Uses include community services, diverse building types, parks, trails and

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trailheads, traffic ways, and restricted roadways. In addition are other open

spaces for which barriers are specified: Playgrounds, Sports Fields, Landscapes,

Bus stops, Traffic Medians, Fire Lanes, Mall Entrances, Store Fronts, Pathways,

Toll Booths, Site Perimeters, Building Setbacks, Utilities Islands, Utilities Shelters,

Bicycle Lanes, Intersections, Highway Access Lanes, Building Shell Hardening,

etc. (Wikipedia, 2011).

2.2 THE CONTROL SYSTEM

The automatic control system of the barrier comprises of the relay

switches and the sensors (the proximity card reader and the infrared sensors).

Together these components form the controlling system of the barrier. When a

user places an access card in close proximity to the card reader, it reads it,

verifies it and sends signal to the relay switches which in turn activate the

barrier to open. The reverse occurs when the vehicle crosses the beams of the

infra-red sensors. When the infra-red sensors detect the break in the infra-red

beam, they then signal the relay switches which in turn activate the barrier to

close.

2.2.1 SENSORS

A sensor is a device that measures a physical quantity and converts it into

a signal which can be read by an observer or by an instrument (Wikipedia,

2011). For example, a mercury-in-glass thermometer converts the measured

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temperature into expansion and contraction of a liquid which can be read on a

calibrated glass tube. A thermocouple converts temperature to an output

voltage which can be read by a voltmeter. For accuracy, most sensors are

calibrated against known standards. A sensor's sensitivity indicates how much

the sensor's output changes when the measured quantity changes. For instance,

if the mercury in a thermometer moves 1cm when the temperature changes by

1⁰C, the sensitivity is 1cm/⁰C (it is basically the slope dy /dx assuming a linear

characteristic). Sensors that measure very small changes must have very high

sensitivities. Sensors also have an impact on what they measure; for instance, a

room temperature thermometer inserted into a hot cup of liquid cools the liquid

while the liquid heats the thermometer. Sensors need to be designed to have a

small effect on what is measured; making the sensor smaller often improves this

and may introduce other advantages. Technological progress allows more and

more sensors to be manufactured on a microscopic scale as micro-sensors using

MEMS technology. In most cases, a micro-sensor reaches a significantly higher

speed and sensitivity compared with macroscopic approaches.

A proximity sensor is a sensor able to detect the presence of nearby

objects without any physical contact. A proximity sensor often emits a beam of

electromagnetic radiation (infrared, for instance), and looks for changes in the

field or return signal. The object being sensed is often referred to as the

proximity sensor's target. Different proximity sensor targets demand different

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sensors. For example, a capacitive or photoelectric sensor might be suitable for

a plastic target; an inductive proximity sensor requires a metal target.

The maximum distance that this sensor can detect is defined as the

"nominal range". Some sensors have adjustments of the nominal range or

means to report a graduated detection distance.

Proximity sensors can have a high reliability and long functional life

because of the absence of mechanical parts and lack of physical contact

between sensor and the sensed object.

Proximity sensors are also used in machine vibration monitoring to

measure the variation in distance between a shaft and its support bearing. This

is common in large steam turbines, compressors, and motors that use sleeve-

type bearings.

A proximity sensor adjusted to a very short range is often used as a touch

switch.

A proximity sensor is divided in two halves and if the two halves move

away from each other, then a signal is activated.

A. Brief History

Long before man created sensors, sensors have existed in nature. All living

organisms contain biological sensors with functions similar to those of the

mechanical devices. Most of these are specialized cells that are sensitive to:

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Light, motion, temperature, magnetic fields, gravity, humidity, vibration,

pressure, electrical fields, sound, and other physical aspects of the

external environment

Physical aspects of the internal environment, such as stretch, motion of

the organism, and position of appendages (proprioception)

Environmental molecules, including toxins, nutrients, and pheromones

Estimation of biomolecules interaction and some kinetics parameters

Internal metabolic milieu, such as glucose level, oxygen level, or

osmolality

Internal signal molecules, such as hormones, neurotransmitters, and

cytokines

Differences between proteins of the organism itself and of the

environment or alien creatures.

Organisms use these specialized cells to ‘perceive’ their environments and

make decisions, instinctive or otherwise, on how to react (Wolfbeis, 2000).

B. Present Day Uses

Sensors are used in everyday objects such as touch-sensitive elevator

buttons (tactile sensor) and lamps which dim or brighten by touching the base.

There are also innumerable applications for sensors of which most people are

never aware. Applications include cars, machines, aerospace, medicine,

manufacturing and robotics.

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A proximity sensor can be used in windows, and when the window

opens an alarm is activated.

C. Classification of Measurement Errors

A good sensor obeys the following rules:

Is sensitive to the measured property

Is insensitive to any other property likely to be encountered in its

application

Does not influence the measured property.

Ideal sensors are designed to be linear or linear to some simple

mathematical function of the measurement, typically logarithmic. The output

signal of such a sensor is linearly proportional to the value or simple function of

the measured property. The sensitivity is then defined as the ratio between

output signal and measured property. For example, if a sensor measures

temperature and has a voltage output, the sensitivity is a constant with the unit

[V/K]; this sensor is linear because the ratio is constant at all points of

measurement.

D. Sensor deviations

If the sensor is not ideal, several types of deviations can be observed:

The sensitivity may in practice differ from the value specified. This is

called a sensitivity error, but the sensor is still linear.

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Since the range of the output signal is always limited, the output signal

will eventually reach a minimum or maximum when the measured

property exceeds the limits. The full scale range defines the maximum and

minimum values of the measured property.

If the output signal is not zero when the measured property is zero, the

sensor has an offset or bias. This is defined as the output of the sensor at

zero input.

If the sensitivity is not constant over the range of the sensor, this is called

nonlinearity. Usually this is defined by the amount the output differs from

ideal behaviour over the full range of the sensor, often noted as a

percentage of the full range.

If the deviation is caused by a rapid change of the measured property

over time, there is a dynamic error. Often, this behaviour is described

with a Bode plot showing sensitivity error and phase shift as function of

the frequency of a periodic input signal.

If the output signal slowly changes independent of the measured

property, this is defined as drift (telecommunication).

Long term drift usually indicates a slow degradation of sensor properties

over a long period of time.

Noise is a random deviation of the signal that varies in time.

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Hysteresis is an error caused by when the measured property reverses

direction, but there is some finite lag in time for the sensor to respond,

creating a different offset error in one direction than in the other.

If the sensor has a digital output, the output is essentially an

approximation of the measured property. The approximation error is also

called digitization error.

If the signal is monitored digitally, limitation of the sampling frequency

also can cause a dynamic error, or if the variable or added noise changes

periodically at a frequency near a multiple of the sampling rate may

induce aliasing errors.

The sensor may to some extent be sensitive to properties other than the

property being measured. For example, most sensors are influenced by

the temperature of their environment.

All these deviations can be classified as systematic errors or random

errors. Systematic errors can sometimes be compensated for by means of some

kind of calibration strategy. Noise is a random error that can be reduced by

signal processing, such as filtering, usually at the expense of the dynamic

behaviour of the sensor.

E. Sensor Resolution

The resolution of a sensor is the smallest change it can detect in the

quantity that it is measuring. Often in a digital display, the least significant digit

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will fluctuate, indicating that changes of that magnitude are only just resolved.

The resolution is related to the precision with which the measurement is made.

For example, a scanning tunnelling probe (a fine tip near a surface collects an

electron tunnelling current) can resolve atoms and molecules.

F. Motion Sensor: Infra-Red Sensors

There are many different ways to create a motion sensor. For example:

It is common for stores to have a beam of light crossing the room near the

door, and a photo-sensor on the other side of the room. When a

customer breaks the beam, the photo-sensor detects the change in the

amount of light and rings a bell.

Many grocery stores have automatic door openers that use a very simple

form of radar to detect when someone passes near the door. The box

above the door sends out a burst of microwave radio energy and waits for

the reflected energy to bounce back. When a person moves into the field

of microwave energy, it changes the amount of reflected energy or the

time it takes for the reflection to arrive, and the box opens the door.

These devices use radar.

The same thing can be done with ultrasonic sound waves, bouncing them

off a target and waiting for the echo.

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All of these are active sensors. They inject energy (light, microwaves or

sound) into the environment in order to detect a change of some sort.

The "motion sensing" feature on most lights (and security systems) is a

passive system that detects infrared energy. These sensors are therefore known

as PIR (passive infrared) detectors or pyro-electric sensors. In order to make a

sensor that can detect say a human being, one needs to make the sensor

sensitive to the temperature of a human body. Humans, having a skin

temperature of about 93⁰F, radiate infrared energy with a wavelength between

9 and 10 micrometres.

2.2.2 RELAY SWITCHES

A relay is an electrically operated switch. Many relays use an

electromagnet to operate a switching mechanism mechanically, but other

operating principles are also used. Relays are used where it is necessary to

control a circuit by a low-power signal (with complete electrical isolation

between control and controlled circuits), or where several circuits must be

controlled by one signal. The first relays were used in long distance telegraph

circuits, repeating the signal coming in from one circuit and re-transmitting it to

another. Relays were used extensively in telephone exchanges and early

computers to perform logical operations.

A type of relay that can handle the high power required to directly control

an electric motor is called a contactor. Solid-state relays control power circuits

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with no moving parts, instead using a semiconductor device to perform

switching. Relays with calibrated operating characteristics and sometimes

multiple operating coils are used to protect electrical circuits from overload or

faults; in modern electric power systems these functions are performed by

digital instruments still called "protective relays" (Wikipedia, 2011).

A. Mechanism

A simple electromagnetic relay consists of a coil of wire surrounding a soft

iron core, an iron yoke which provides a low reluctance path for magnetic flux, a

movable iron armature, and one or more sets of contacts. The armature is

hinged to the yoke and mechanically linked to one or more sets of moving

contacts. It is held in place by a spring so that when the relay is de-energized

there is an air gap in the magnetic circuit. In this condition, one of the two sets

of contacts in the relay is closed, and the other set is open. Relays may have

more or fewer sets of contacts depending on their function. A relay also has a

wire connecting the armature to the yoke. This ensures continuity of the circuit

between the moving contacts on the armature, and the circuit track on the

printed circuit board (PCB) via the yoke, which is soldered to the PCB.

When an electric current is passed through the coil it generates a

magnetic field that attracts the armature and the consequent movement of the

movable contact(s) either makes or breaks (depending upon construction) a

connection with a fixed contact. If the set of contacts was closed when the relay

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was de-energized, then the movement opens the contacts and breaks the

connection, and vice versa if the contacts were open. When the current to the

coil is switched off, the armature is returned by a force, approximately half as

strong as the magnetic force, to its relaxed position. Usually this force is

provided by a spring, but gravity is also used commonly in industrial motor

starters. Most relays are manufactured to operate quickly. In a low-voltage

application this reduces noise; in a high voltage or current application it reduces

arcing.

When the coil is energized with direct current, a diode is often placed

across the coil to dissipate the energy from the collapsing magnetic field at

deactivation, which would otherwise generate a voltage spike dangerous to

semiconductor circuit components. Some automotive relays include a diode

inside the relay case. Alternatively, a contact protection network consisting of a

capacitor and resistor in series (snubber circuit) may absorb the surge. If the coil

is designed to be energized with alternating current (AC), a small copper

"shading ring" can be crimped to the end of the solenoid, creating a small out-

of-phase current which increases the minimum pull on the armature during the

AC cycle.

A solid-state relay uses a thyristor or other solid-state switching device,

activated by the control signal, to switch the controlled load, instead of a

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solenoid. An optocoupler (a light-emitting diode (LED) coupled with a photo

transistor) can be used to isolate control and controlled circuits.

B. Types

I. Latching Relay

Figure 4 – Latching relay with permanent magnet

A latching relay has two relaxed states (bi-stable). These are also called

"impulse", "keep", or "stay" relays. When the current is switched off, the relay

remains in its last state. This is achieved with a solenoid operating a ratchet and

cam mechanism, or by having two opposing coils with an over-centre spring or

permanent magnet to hold the armature and contacts in position while the coil

is relaxed, or with a remanent core. In the ratchet and cam example, the first

pulse to the coil turns the relay on and the second pulse turns it off. In the two

coil example, a pulse to one coil turns the relay on and a pulse to the opposite

coil turns the relay off. This type of relay has the advantage that one coil

consumes power only for an instant, while it is being switched, and the relay

contacts retain this setting across a power outage. A remanent core latching

relay requires a current pulse of opposite polarity to make it change state.

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http://en.wikipedia.org/wiki/File:Latching_relay_bistable_permanent_magnet.jpg


II. Reed RelayA reed relay is a reed switch enclosed in a solenoid. The switch has a set

of contacts inside an evacuated or inert gas-filled glass tube which protects the

contacts against atmospheric corrosion; the contacts are made of magnetic

material that makes them move under the influence of the field of the enclosing

solenoid. Reed relays can switch faster than larger relays, require only little

power from the control circuit, but have low switching current and voltage

ratings. In addition, the reeds can become magnetized over time, which makes

them stick 'on' even when no current is present; changing the orientation of the

reeds with respect to the solenoid's magnetic field will fix the problem.

III. Mercury-Wetted RelayA mercury-wetted reed relay is a form of reed relay in which the contacts

are wetted with mercury. Such relays are used to switch low-voltage signals (one

volt or less) where the mercury reduces the contact resistance and associated

voltage drop, for low-current signals where surface contamination may make for

a poor contact or for high-speed applications where the mercury eliminates

contact bounce. Mercury wetted relays are position-sensitive and must be

mounted vertically to work properly. Because of the toxicity and expense of

liquid mercury, these relays are now rarely used.

IV. Polarized RelayA polarized relay placed the armature between the poles of a permanent

magnet to increase sensitivity. Polarized relays were used in middle 20th

Page | 22


Century telephone exchanges to detect faint pulses and correct the telegraphic

distortion. The poles were on screws, so a technician could first adjust them for

maximum sensitivity and then apply a bias spring to set the critical current that

would operate the relay.

V. Machine Tool RelayA machine tool relay is a type standardized for industrial control of

machine tools, transfer machines, and other sequential control. They are

characterized by a large number of contacts (sometimes extendable in the field)

which are easily converted from normally-open to normally-closed status, easily

replaceable coils, and a form factor that allows compactly installing many relays

in a control panel. Although such relays once were the backbone of automation

in such industries as automobile assembly, the programmable logic controller

(PLC) mostly displaced the machine tool relay from sequential control

applications.

VI. Ratchet RelayThis is again a clapper type relay which does not need continuous current

through its coil to retain its operation.

VII. Contactor RelayA contactor is a very heavy-duty relay used for switching electric motors

and lighting loads, although contactors are not generally called relays.

Continuous current ratings for common contactors range from 10 amps to

several hundred amps. High-current contacts are made with alloys containing

Page | 23


silver. The unavoidable arcing causes the contacts to oxidize; however, silver

oxide is still a good conductor. Such devices are often used for motor starters. A

motor starter is a contactor with overload protection devices attached. The

overload sensing devices are a form of heat operated relay where a coil heats a

bi-metal strip, or where a solder pot melts, releasing a spring to operate

auxiliary contacts. These auxiliary contacts are in series with the coil. If the

overload senses excess current in the load, the coil is de-energized. Contactor

relays can be extremely loud to operate, making them unfit for use where noise

is a chief concern.

VIII. Solid-State RelayA solid state relay (SSR) is a solid state electronic component that provides

a similar function to an electromechanical relay but does not have any moving

components, increasing long-term reliability.

Figure 5 - Solid state relay with no moving parts

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http://en.wikipedia.org/wiki/File:Solid_state_relay.jpg


Figure 6 - 25A or 40A solid state contactors

With early SSR's, the trade-off came from the fact that every transistor

has a small voltage drop across it. This voltage drop limited the amount of

current a given SSR could handle. The minimum voltage drop for such a relay is

equal to the voltage drop across one transistor (~0.6 – 2.0Volts), and is a

function of the material used to make the transistor (typically silicon). As

transistors improved, higher current SSR's, able to handle 100 to 1200Amperes,

have become commercially available. Compared to electromagnetic relays, they

may be falsely triggered by transients.

IX. Solid State Contactor RelayA solid state contactor is a heavy-duty solid state relay, including the

necessary heat sink, used for switching electric heaters, small electric motors

and lighting loads; where frequent on/off cycles are required. There are no

moving parts to wear out and there is no contact bounce due to vibration. They

are activated by AC control signals or DC control signals from Programmable

logic controller (PLCs), PCs, Transistor-transistor logic (TTL) sources, or other

microprocessor and microcontroller controls.

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http://en.wikipedia.org/wiki/File:Solid-state-contactor.jpg


X. Buchholz RelayA Buchholz relay is a safety device sensing the accumulation of gas in

large oil-filled transformers, which will alarm on slow accumulation of gas or

shut down the transformer if gas is produced rapidly in the transformer oil.

XI. Forced-Guided Contacts RelayA forced-guided contacts relay has relay contacts that are mechanically

linked together, so that when the relay coil is energized or de-energized, all of

the linked contacts move together. If one set of contacts in the relay becomes

immobilized, no other contact of the same relay will be able to move. The

function of forced-guided contacts is to enable the safety circuit to check the

status of the relay. Forced-guided contacts are also known as "positive-guided

contacts", "captive contacts", "locked contacts", or "safety relays".

XII. Overload Protection RelayElectric motors need overcurrent protection to prevent damage from

over-loading the motor, or to protect against short circuits in connecting cables

or internal faults in the motor windings. One type of electric motor overload

protection relay is operated by a heating element in series with the electric

motor. The heat generated by the motor current heats a bimetallic strip or melts

solder, releasing a spring to operate contacts. Where the overload relay is

exposed to the same environment as the motor, a useful though crude

compensation for motor ambient temperature is provided (Wikipedia, 2011).

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C. Present Day uses

Relays are used for the following purposes:

Control a high-voltage circuit with a low-voltage signal, as in some types

of modems or audio amplifiers.

Control a high-current circuit with a low-current signal, as in the starter

solenoid of an automobile.

Detect and isolate faults on transmission and distribution lines by opening

and closing circuit breakers (protection relays).

A DPDT AC coil relay with "ice cube" packaging Isolate the controlling

circuit from the controlled circuit when the two are at different potentials,

for example when controlling a mains-powered device from a low-voltage

switch. The latter is often applied to control office lighting as the low

voltage wires are easily installed in partitions, which may be often moved

as needs change. They may also be controlled by room occupancy

detectors in an effort to conserve energy.

Logic functions. For example, the Boolean AND function is realised by

connecting normally open relay contacts in series, the OR function by

connecting normally open contacts in parallel. The change-over or Form C

contacts perform the XOR (exclusive or) function. Similar functions for

NAND and NOR are accomplished using normally closed contacts. The

Page | 27


Ladder programming language is often used for designing relay logic

networks.

Early computing. Before vacuum tubes and transistors, relays were used

as logical elements in digital computers. See ARRA (computer), Harvard

Mark II, Zuse Z2, and Zuse Z3.

Safety-critical logic. Because relays are much more resistant than

semiconductors to nuclear radiation, they are widely used in safety-

critical logic, such as the control panels of radioactive waste-handling

machinery.

Time delay functions. Relays can be modified to delay opening or delay

closing a set of contacts. A very short delay (a fraction of a second) would

use a copper disk between the armature and moving blade assembly.

Current flowing in the disk maintains magnetic field for a short time,

lengthening release time. For a slightly longer (up to a minute) delay, a

dashpot is used. A dashpot is a piston filled with fluid that is allowed to

escape slowly. The time period can be varied by increasing or decreasing

the flow rate. For longer time periods, a mechanical clockwork timer is

installed.

D. Relay Application Considerations

Selection of an appropriate relay for a particular application requires

evaluation of many different factors:

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Number and type of contacts – normally open, normally closed, (double-

throw)

Contact sequence – "Make before Break" or "Break before Make". For

example, the old style telephone exchanges required Make-before-break

so that the connection didn't get dropped while dialling the number.

Rating of contacts – small relays switch a few amperes, large contactors

are rated for up to 3000 amperes, alternating or direct current

Voltage rating of contacts – typical control relays rated 300V~AC or

600V~AC, automotive types to 50V-DC, special high-voltage relays to

about 15000V

Coil voltage – machine-tool relays usually 24V~AC, 120 or 250V~AC, relays

for switchgear may have 125V or 250V-DC coils, "sensitive" relays operate

on a few Milli-Amperes

Coil current

Package/Enclosure – open, touch-safe, double-voltage for isolation

between circuits, explosion proof, outdoor, oil and splash resistant,

washable for printed circuit board assembly

Assembly – Some relays feature a sticker that keeps the enclosure sealed

to allow PCB post soldering cleaning, which is removed once assembly is

complete.

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Mounting – sockets, plug board, rail mount, panel mount, through-panel

mount, enclosure for mounting on walls or equipment

Switching time – where high speed is required

"Dry" contacts – when switching very low level signals, special contact

materials may be needed such as gold-plated contacts

Contact protection – suppress arcing in very inductive circuits

Coil protection – suppress the surge voltage produced when switching the

coil current

Isolation between coil circuit and contacts

Aerospace or radiation-resistant testing, special quality assurance

Expected mechanical loads due to acceleration – some relays used in

aerospace applications are designed to function in shock loads of 50g or

more

Accessories such as timers, auxiliary contacts, pilot lamps, test buttons

Regulatory approvals

Stray magnetic linkage between coils of adjacent relays on a printed

circuit board.

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CHAPTER 3

3.0 CONCEPTUAL DESIGN

There are various ways or concepts in which a barrier (rising arm

mechanism) can be designed and here we are going to consider different ways

in which the automated barrier can be designed.

The ways or concepts considered are:

The use of a hydraulic jack

The use of a simple pulley system with a belt drive

The use of screw jack driven by an electric motor

3.1 CONCEPT 1 – HYDRAULIC JACK

This is based on the principle of fluid statics and fluid kinematics and it is

used for either storing the hydraulic energy then transmitting when needed or

magnifying the hydraulic energy and transmitting when needed.

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Figure 7 – Modified Hydraulic Jack

A hydraulic jack is an incredibly simple device, considering its usefulness.

It comprises a cylinder or reservoir, which can hold hydraulic fluid, and a

pumping system to move the fluid. Generally, oil is used as a hydraulic fluid,

because it relieves the necessity of lubricating the components of the jack. The

pumping system generally comprises some sort of pump; hand-powered or

more likely, mechanically powered, that serves to apply pressure to the fluid.

The pumping system pushes hydraulic fluid through a one-way valve that allows

the fluid to pass into the jack cylinder, but does not allow the fluid to pass back.

Obviously, the jack has some sort of footing and a plate that is moved by the

cylinder when the jack is activated.

A hydraulic jack's functioning is described very accurately by Pascal's

principle, which states that a force applied to an enclosed fluid is transferred

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equally throughout the entire fluid. This means that the fluid must not be able

to be compressed. When the jack's pump is activated, it applies pressure on the

hydraulic fluid, which fills the cylinder. Because the cylinder is completely filled

while the pump is active, and the one-way valve completely encloses the fluid,

pressure builds within the cylinder. The pressure escapes via the easiest way

possible: it pushes up on the plate of the jack, hence putting out force. The

pump basically exerts a small force on the fluid continuously until the fluid has

enough pressure to push up the jack, which lifts whatever is being lifted at the

time. This means that the hydraulic jack can exert massive forces with a simple

pump.

Due to the complexity of this design of the hydraulic system and the cost

of producing it another design was considered and that was the use of a pulley

system driven by a dc motor.

3.2 CONCEPT 2 – BELT AND PULLEY SYSTEM

Pulley is a simple machine used to lift objects. A pulley consists of a

grooved wheel or disk within housing, and a rope or cable threaded around the

disk. The disk of the pulley rotates as the rope or cable moves over it. Pulleys are

used for lifting by attaching one end of the rope to the object, threading the

rope through the pulley (or system of pulleys), and pulling on the other end of

the rope.

Page | 33


Belt or flexible-connector drives are simple devices used to transmit

torques and rotational motions from one to another or to several other shafts,

which would usually be parallel. Power is transmitted by a flexible element

(flexible connector) placed on pulleys, which are mounted on these shafts to

reduce peripheral forces.

A belt and pulley system is characterized by two or more pulleys in

common to a belt. This allows for mechanical power, torque, and speed to be

transmitted across axles. If the pulleys are of differing diameters, a mechanical

advantage is realized.

Figure 8 - The Belt and Pulley System

This is a block and tackle pulley system. In this design the prime mover is

the motor which is connected through a shaft to the pulley, and the pulley to

another shaft connected to the barrier arm or barrier. The pulley transmits the

Page | 34


rotary motion generated from the motor to the shaft which in turn raises and

lower the barrier arm or barrier.

This design is simple but has a low mechanical advantage. If a pulley

system was perfect and achieving 100% efficiency, then the pulleys and their

ropes would be weightless, frictionless and not stretch or warp at all. Living in

the real world, we know that this is not the case. Some of your effort is lost in

overcoming this friction between the pulley wheels and the ropes. It has limited

power transmission and wear can occur regularly of belt due to friction, which

will lead to constant maintenance.

This now led to us choose the next design which is the use of a power

screw, also driven by a motor.

3.3 CONCEPT 3 – SCREW JACK

A screw is one of the six classical simple machines. It can convert a

rotational motion to a linear motion, and a torque (rotational force) to a linear

force. The most common form consists of a cylindrical shaft with helical grooves

or ridges called threads around the outside. The screw passes through a hole in

another object or medium, with stationary threads on the inside of the hole.

When the screw is rotated relative to the stationary threads it moves along its

axis relative to the medium surrounding it; for example rotating a woodscrew

Page | 35


forces it into wood. Geometrically, a screw can be viewed as a narrow inclined

plane wrapped around a shaft.

Power screws convert the input rotation of an applied torque to the

output translation of an axial force. The screw jack is an example of power

screw.

MOTOR

Screw thread

Figure 9 - The Screw Jack

Here same as the previous design the power screw is driven by a dc

motor. As the motor rotates, the power screw converts the rotary motion of the

motor in to translational motion. The crank which is connected to the shaft (or

crankshaft in this case) then converts this translational motion from the screw in

to rotary motion which is used to raise and lower the barrier arm that

undergoes a rotational motion.

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This design was selected because it’s is compact, simple to design, easy to

manufacture; no specialized machinery is required, large mechanical advantage,

precise and accurate linear motion, smooth, quiet, and low maintenance,

minimal number of parts, and most are self-locking.

Figure 10 - 3D Model of the Project

3.4 MODE OF OPERATION

3.4.1 Mechanism

The mechanism employed is the crank mechanism which changes

reciprocating motion to circular motion and vice versa. The end of the crank is

attached to a pivot rod called the connecting rod. The end of the rod attached to

the crank moves in circular motion, while the other end is usually constrained to

move in a linear sliding motion in and out.

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In this project the jack serves as the connecting rod; one end of the crank

is attached to the jack while the other end is to a steel shaft.

The linear (upward and downward) motion of the jack turns the crank

thereby creating a circular motion of the shaft, and in turn an angular

displacement of the beam.

3.4.2 Control

The card reader and infrared sensors are connected to the two switches in

the relay. Both switches are on when the relay coil is on and off respectively.

On swiping the RF signal card on the card reader, signal is transmitted to

the relays. The first relay is activated, which causes the motor in the screw jack

to rotate. The linear motion of the jack is converted to circular motion with the

use of crank.

Breaking the infrared signal of the sensors activates the second relay. The

circuit changes polarity causing the motor to rotate in the opposite direction.

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CHAPTER 4

4.0 DETAILED DESIGN

4.1 COMPONENTS OF THE AUTOMATED BARRIER SYSTEM

The automated barrier system consists of mechanical and electrical (for

controls) components.

Figure 11 - Layout of the Automated Barrier System

4.1.1 MECHANICAL COMPONENTS (Mechanism)

1. Crossbar

2. Elbow joint

3. Shaft

4. Bearings (Two)

5. Crank

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6. Screw – Jack

A mechanism is a device designed to transform input forces and

movement into a desired set of output forces and movement. Mechanisms

generally consist of moving components such as gears and gear trains, belt and

chain drives, cam and follower mechanisms, and linkages as well as friction

devices such as brakes and clutches, and structural components such as the

frame, fasteners, bearings, springs, lubricants and seals, as well as a variety of

specialized machine elements such as splines, pins and keys. The mechanism

designed consists of the following parts:

A. Crank

A crank is an arm attached at right angles to a rotating shaft by which

reciprocating motion is imparted to or received from the shaft. It is used to

change circular into reciprocating motion, or reciprocating into circular motion.

Figure 12 – The Crank

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The arm may be a bent portion of the shaft, or a separate arm attached to

it. Attached to the end of the crank by a pivot is a rod, usually called a

connecting rod. The end of the rod attached to the crank moves in a circular

motion, while the other end is usually constrained to move in a linear sliding

motion, in and out.

B. Bearing (Plain Bearing)

A bearing is a device that allows constrained relative motion between two

or more parts, typically rotation or linear movement. Bearings may be classified

broadly according to the motions they allow and according to their principle of

operation as well as by the directions of applied loads they can handle.

Figure 13 – The Bearing Casing

Plain bearings use surfaces in rubbing contact, often with a lubricant such

as oil or graphite. A plain bearing may or may not be a discrete device. It may be

nothing more than the bearing surface of a hole with a shaft passing through it,

Page | 41


or of a planar surface that bears another (in these cases, not a discrete device);

or it may be a layer of bearing metal either fused to the substrate (semi-

discrete) or in the form of a separable sleeve (discrete). With suitable

lubrication, plain bearings often give entirely acceptable accuracy, life, and

friction at minimal cost. Therefore, they are very widely used.

However, there are many applications where a more suitable bearing can

improve efficiency, accuracy, service intervals, reliability, and speed of

operation, size, weight, and costs of purchasing and operating machinery.

C. Screw Jack

A screw is a device that changes angular motion into linear motion, and

usually, to transmits power. This is the prime mover of the mechanism and it

transmits the force use to raise and lower the crossbar (barrier arm).

Figure 14 – The Screw Jack

Page | 42


D. Shaft (Crankshaft)

This is a rotating member usually of circular cross-section used to transmit

power or motion. This is the rotating rod in the mechanism that provides the

power to raise the crossbar (barrier arm). It receives its torque from the crank.

Figure 15 – The Shaft (Crankshaft)

E. Crossbar (Barrier Arm)

The crossbar or barrier arm is the beam that is used to obstruct the traffic.

Figure 16 – The Crossbar (Barrier Arm)

F. Elbow Joint

This is used to connect the crossbar (Barrier arm) to the crank mechanism

(the crank and crankshaft) at 90⁰.

Page | 43


Figure 17 – The Elbow Joint

G. Fasteners

These are devices that are used to connect or join on or more components

of an article or structure. There are thousands of fastener types and variations

available. The ones we used majorly are bolts, nuts, washers, screws, bushings.

4.1.2 ELECTRICAL COMPONENTS

These are the components used to power, automate and control the

mechanism. It is made up of the following components:

A. Transformers

A transformer is a static (or stationary) piece of apparatus by means of

which electric power in one circuit is transformed into electric power of the

same frequency in another circuit.

Figure 18 – Schematic of a Step-down Transformer

Page | 44


It can raise or lower the voltage in a circuit but with a corresponding

decrease or increase in current. The physical basis of a transformer is mutual

induction between two circuits linked by a common magnetic flux. In its simplest

form, it consists of two inductive coils which are electrically separated but

magnetically linked through a path of low reluctance.

B. Rectifier

This is used for rectification of electric current during the process of

converting an alternating current (AC), which flows back and forth in a circuit, to

direct current (DC), which flows only in one direction. A device known as a

rectifier, which permits current to pass in only one direction, effectively blocking

its flow in the other direction is inserted into the circuit for the purpose.

Figure 19 - Schematic of a Rectifier

C. The Relays

A relay is an electrically operated switch. Many relays use an electromagnet

to operate a switching mechanism mechanically, but other operating principles

are also used. Relays are used where it is necessary to control a circuit by a low-

Page | 45


power signal (with complete electrical isolation between control and controlled

circuits), or where several circuits must be controlled by one signal. Relays are

used extensively to perform logical operations or switching.

Figure 20 – Relay Circuit

D. Sensors

A sensor is a device that measures a physical quantity and converts it into a

signal which can be read by an observer or by an instrument. The sensor is

responsive to changes in the quantity to be measured, for example,

temperature, position, or motion. The transducer converts such measurements

into electrical signals, which, usually amplified, can be fed to instruments for the

readout, recording, or control of the measured quantities. Sensors and

transducers can operate at locations remote from the observer and in

environments unsuitable or impractical for humans.

Some devices act as both sensor and transducer. A thermocouple has two

junctions of wires of different metals; these generate a small electric voltage

Page | 46


that depends on the temperature difference between the two junctions. A

thermistor is a special resistor, the resistance of which varies with temperature.

A variable resistor can convert mechanical movement into an electrical signal.

Specially designed capacitors are used to measure distance, and photocells are

used to detect light. Other devices are used to measure velocity, acceleration, or

fluid flow. In most instances, the electric signal is weak and must be amplified by

an electronic circuit.

E. Card Reader (Proximity Card Reader)

This is a device that reads signals from cards that has been programmed

and then sends the signals to the relays. Proximity cards are powered by

resonant inductive coupling via an LC circuit including an IC, capacitor and coil

are connected in parallel. The card reader produces an electromagnetic field

that excites the coil and resonant current charges the capacitor, which in turn

energizes and power the IC.

Figure 21 – Proximity Card Reader with Access Card

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4.2 THE RAISING ARM (CROSSBAR)

Figure 22 - The Crossbar

The raising arm forms the crossbar that bars the road when closed and

allows passage when it is raised. It is essential that the arm is sufficiently rigid

throughout its length. This is to avoid unwanted flexing and wobbling of the

arm when it is at rest or being raised.

4.2.1 Material Selection

Deflection is not affected by strength but rather by stiffness as

represented by the modulus of elasticity. Aluminium alloy is suitable for this

purpose because of both its weight to strength ratio and its corrosion resistance.

Page | 48


4.2.2 Deflection of the Crossbar

For a full road, dual carriage, of length of 22’,

A crossbar length of 11’ would adequately cover; for each side of the road.

Specifications:

Length = 3.3528m

Material: aluminium pipe, with square hollow cross section (to minimize

material and weight).

Mass = Density × Volume

Density of aluminum=2700 kg /m3

Volume=Length×cross sectional area

Note that for the same mass and thickness, the ratio of length to breath may be

varied to yield different values of I (area moment of inertia), without affecting

the total cross sectional area or full length and consequently – volume remains

the same.

Volume=3.3528×¿

Volume=4.191×10−3m3

Mass=2700×4.191×10−3×10−3

Mass=11.3157 kg

Page | 49


Weight=Mass× Accelerationdue ¿gravity

Weight=110.969N

Deflection, for fully closed position, the beam is simply supported

y= w l3

48EI

Where: w = weight; l = length; E = modulus of elasticity and I = area moment of

inertia.

For y to be zero,

w l3=0

w=0∨l=0

Of which on known material of the sort exists.

To minimize y for a known length, material and weight, I must be as large as can

be accommodated.

Deflection is maximum when the cross-bar is in opening position – when it is

positioned as a cantilever

ycritical, Minimum Tolerable y=0.010m

For a cantilever,

y= wl3

24 EI

Page | 50


w=110.969N

E –Modulus of elasticity=70GPa; for aluminiumalloy

l – Lengthof the arm=3.3528m

I – Moment of inertiaof cross sectionof the arm

y= wl3

24 EI

I= wl3

48 Ey

I=(110.969×3.3533 )24×70×109×0.001

I=0.248951×10−6m

From Tabulated Moments of Inertia and Section Moduli for Rectangles and

Round Shafts: Moments of Inertia and Section Moduli for Rectangles (Metric

Units),

ForI=0.248951×10−6m,

I ≅ 0.262440×10−6m

For a 54×20 solid beam

Putting I ≅ 0.262440×10−6m intoy= wl3

24 EI to ensure y’ is less than y=0.010m,

y '=(110.969×3.3533 )

24×70×109×0.262440×10−6

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y '=9.486×10−3m

y '< y

Cross-Section area specifications

D = 54mm

B = 20mm

Note that, since y∝ 1I andI∝bd3, increasing values of b and d, especially d,

would yield lower values of y (deflection).

4.3 ELBOW JOINT

An elbow joint is a mechanical member intended to connect two

components at right angle to each other.


We selected a steel elbow joint that would fit both the crossbar and the

shaft.

Diameter: 60

Angle: 90 degrees

Page | 52


4.4 SHAFT

The shaft is a rotating member, usually of circular cross-section used to

transmit power or motion. It provides the angle of rotation of the crank and also

controls the geometry of its motion.

There is really no unique thing about the shaft that requires any special

treatment. However because of the ubiquity of the shaft in so many machine

design applications, there are some advantages of giving the shaft design a

closer inspection.

The shaft to be designed for is a solid shaft and the design consists

primarily; the determination of the correct shaft diameter to ensure satisfactory

strength and rigidity when the shaft is transmitting power under varying

operational conditions.


For a shaft diameter of 60 mm,

Length: 282 mm

Cold drawn steel was used.

Page | 53


4.4.2 Shaft Layout

Figure 23 - The Shaft Layout

The shaft is designed to run through both bearings and to be connected to

its ends by the elbow joint and the crank.

4.5 BEARING

The shaft is to be held in a bearing, about which the arm and the crank

would rotate.

To reduce friction as much as possible, we selected a pair of ball bearings.

A light bearing series used for moderated load and shaft sizes with the following

parameters was selected:

Bearing Number: 212

Bore: 60mm

Outer Diameter: 110mm

Page | 54


Width: 22mm.

4.6 CRANK

This member connects the jack rigidly to the shaft and converts the

translational motion from the jack to rotational motion.

4.7 SCREW JACK

Load on the Jack

Summation of forces about the shaft (O),

ΣFx=0

ΣFy=−f 1−f 2+R=0

f 1+ f 2=R

Summation of moments about the shaft,

ΣM=f 1( l12 )−f 2 ( l2)=0

f 1( l12 )=f 2 (l2 )

f 1=110.969N (weight of the ¯actingat the center )

l1=3.3528¿

l2=0.1015m(Crank length:centre¿centre)

f 2=f 1l2 (

l12 )

Page | 55


f 2=110.969×3.3530.1015×2

f 2=1832.9N

Load at the endof the crank=1832.9N

Force required in raising a load

F=W × tan(α+φ)

F=W × tan α+ tanφ1−tan α× tanφ

φ=frictionangle

tan φ=μ

tan α= lπd

l=no .of starts× pitch

Substituting for tan α , tanφ

F=W×( Pπd

+μ)(1− P

πd×μ)

F=W × (P+πdμ )(πd−Pμ )

Screw Specifications

From the ANSI B1.1 – 1974 and B18.3.1-1978 tables,

Pitch(P):5mm=0.005m

Major Diameter (d) :48mm=0.048m

Coefficient of friction for steel screw and steel nut

μ=0.25(upper limit )

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(H.A Rothbart, Mechanical Design and Systems Handbook, 2nd edition. McGraw-

Hill, New York)

W=1832.9N

F=1832.9× 0.005+(π ×0.048×0.025)¿¿

F=106.68 N

Torque Required in Raising the Load

T=F× d2;d=0.048m

T=106.68× 0.0482

T=2.56Nm

Angular Speed

TimeDesigned for=9.00 s

Angle¿ raise=85 °

Distancemoved by the screw

b2=c2+a2

c2=b2−a2

c= 2√b2−a2

b ' 2=c2+a2−2(ca)cos 5°

a=Crank length (centre¿centre)=0.1015m

b=Totalextended heigthof screw=0.9m

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c= 2√0.92−0.10152

c=0.894m

b ' 2=0.8942+0.10152−2(0.894×0.1015)×cos 5°

b '=0.793m

Distancemade by the screw=b−b '

Distancemade by the screw=0.9−0.793

Distancemade by the screw=0.1068m

Speedof Nut=0.1068/9.00=0.011867ms−1

In Revolution per Minute (rpm)

N= Speed ofnutPitch of Screw

N=0.0118670.005

N=2.3735rpm

In Radian (Rad)

ω=2π N60

ω=2×π ×2.373560

ω=0.2485 rad / s

Power Required by the Jack

Power=T ×ω

Power=2.56×0.2485

Power=0.6364W

Motor Specification:

From International Electro-technical Commission: IEC 60034 Rotating Electrical

Machines,

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TG-05L-SG (12V)

Speed: 3 rpm

Torque: 588mN-m

Speed Reduction of Motor.

Gear Parameters

np=3 rpm

d p=1∈¿25.4mm

From above calculated the speed required to drive the screw is 2.375rpm. We

now designed for a slightly higher speed of 2.5rpm.

nG=2.5 rpm

DG=(np×D p )

nG

D g=(3×25.4 )2.5

=30.48mm

For a motor operating at 12 volts, with power consumption of 0.6364 watts

running for 18 seconds (both opening and closing),

W=IV

I=WV

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I=0.636412

=0.053 Amps per second

For 18 seconds, current consumed

¿18×0.053amps

¿0.9546amps

Which means that 0.9546 amps are consumed each time the barrier

opens and closes.

Taking an inverter efficiency of 80% DC – AC (manufacturer’s

specification), a 200A battery would yield

200 (0.8 )÷0.9546=167.609

≅ 168uses

4.8 CONTROL SYSTEM DESIGN

A control system is a device or set of devices to manage, command, direct

or regulate the behaviour of other devices or systems. The automated barrier

system will have two outputs (to raise and lower the barrier arm) and two

inputs; one from the card reader and the other from the infra-red sensors.

In order to design and implement the control system the knowledge of

the following generic elements were vital:

Controlled Variable which is the barrier arm or crossbar

The Controller which are the relays

The actuating device which is power screw and motor

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The plant or system which is the automated barrier.

4.8.1 The Control Design Process

The following standard methodology was applied to design the control

system and it is represented on a flow chart.

Figure 24 - Steps in Design of a Control System

The devices used in this control system are:

Relays

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Proximity Card Reader

Infrared Motion Sensor

4.8.2 The Flow Diagram

Figure 25 - The Flow Diagram

The power requirement for the motor is 50volts, so we used two step-

down transformers to step the 240V to 55v which is enough for the motor to

run; and a rectifier to convert the Alternating Current (AC) to Direct Current (DC)

and from the rectifier the power is connected to the relays and motor.

4.8.3 Control Diagram

The control system design is an open loop control system that has two

inputs and two outputs. The input devices are the Proximity Card Readers and

the output devices are the Infrared Motion Sensors.

Figure 26 - The Systems' Block Diagram

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The proximity card reader and infrared sensors are connected to the

positive and negative terminals. Each terminal is connected through a relay,

transformer and rectifier to the motor of the power screw jack.

The Proximity card reader is connected to one of the relays and the sensor

is connected to the other relay. The relay then performs the intelligent switching

between the two inputs. The sensors’ relay is connected to the motor in the

reverse direction of the connection of the card reader to make the motor rotate

in the counter direction of the card reader and thus bringing down the crossbar.

As the barrier arm or crossbar rises caused by the rotation of the motor

the limit switch determines the maximum and minimum heights of crossbar. The

limit switch in the motor is a mechanical device that open or close the circuit

when the motor reaches its limit of travel. In other words, when the barrier arm

reaches its maximum or minimum displacement, the limit switch breaks the

circuit and the motor stops to rotate.

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4.8.4 Circuit Diagram

Figure 27 - Circuit Diagram of the Control System

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CHAPTER 5

5.0 CONCLUSION

The automated barrier system was designed for use on the faculty of

engineering access road. It has currently been installed and has been

operational for over three months.

The major achievement in the course of this project is gaining of

knowledge of the realisation of a digital control system via a systematic

approach, and this basic knowledge would help improve one’s capacity to design

in mechanical/digital electronics.

One of the basic problems we encountered during the project

implementation was getting the right material for the barrier for the best weight

to rigidity ratio for the required length. We needed a material that was very light

so as to minimise power requirement and obtain maximum speed with also

minimal deflection across a length of 11inches. To this effect we attempted to

use a PVC pipe which deflected excessively. We also used a steel pipe. The steel

pipe was a lot more suitable than the PVC but it had the drawback of having a

higher mass and consequently a lower speed than required. We finally settled

on an aluminium pipe with a square cross-section. Due to aluminium’s

characteristic light weight and high strength and the improved geometry, it

proved to have the best weight to rigidity ratio for the required length.

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5.1 RECOMMENDATIONS

We suggest that this system be employed throughout the campus, in all

locations that require restricted access.

5.2 FURTHER WORK

As simple as our mechanism is, we in hindsight have discovered that even

simpler mechanisms or mechanisms that require less number of parts exist. We

suggest that other means for raising the crossbar be explored.

The housing for the control panel could be improved on to further shield it

from harsh weather conditions.

Also as seen from above, the power requirements are sufficiently low

enough that a relatively cheap alternate source of power could be used to run

the system. This would also have the added advantage of being

environmentally friendly, as the current source of power is from the power grid,

backed up by an inverter - battery system.

A switch that could act as an auxiliary switch could be placed in a nearby

secure location, like the department; to be used in times of emergency or

unforeseen circumstances that prevent normal operation of the system.

5.3 SUMMARY

The design and construction of an automatic car barrier (raising arm

mechanism) with proximity card reader has been achieved. Tenable, a project of

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this nature is reasonable enough to be carried out, as this will improve

indigenous technology applied in Nigeria.

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REFERENCES

Budynas-Nisbett. (2006). Shigley's Mechanical Engineering Design (8th ed.).

United States of America: McGraw-Hill.

Burns, R. S. (2001). Advanced Control Engineering. London: Butterworth

Heinmann.

Charles G. Oakes, P. (2011, February 16). The Bollard. Retrieved April 10, 2011,

from WBDG Whole Building Drsign Guide:

http://www.wbdg.org/bollard.php

Ellis, G. (2004). Control System Design Guide: A Practical Guide. San Diego,

California: Elsevier Academic Press.

Kuo, B. C. (1995). Automatic Control System (6th ed.). New Delhi: PHI Learning.

Kurmi, R. S. (2008). Strength of Materials (Mechanics of Solid) (26th ed.). New

Delhi: S. Chand.

Ogata, K. (2002). Modern Control Engineering (4th ed.). New Jersey, Upper

Saddle River, United States of America: Prentice Hall.

Rajput, R. K. (2008). Fluid Mechanics and Hydraulics Machine (3rd ed.). New

Delhi: S. Chand.

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Shigley, J. E., & Mischke, C. R. (1996). Standard Handbook of Machine Design

(6th ed.). U.S.A: McGraw-Hill.

Theraja, B. L. (2005). A Textbook of Electrical Technology (23rd ed.). New Delhi:

S. Chand.

Wolfbeis, O. S. (2000). "Fibre-optic chemical sensors and biosensors.". USA: Anal

Chem.

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