AppendixC_Old Lathe safety device

T.Ndabeni,212125710
iv
Lathe Universal Safety Device
Heavy Duty Portal
Carriage and Wagon
Wheel Lathe
11/28/2014
Transnet Rail Engineering, a Business Unit of Transnet Limited.
Transnet Engineering SLD
By: ThobekileNdabeni
Supervisor : V.S. Malaza
coordinator : Mr. PR Tjale
28 November 2014

T.Ndabeni,212125710
v
ACKNOWLEDGEMENT
I would like to express my great gratitude and appreciation to all those who
gave me the possibility to complete this technical report.
A special thanks to my experiential training coordinator from the Cape
Peninsula University of Technology, Mr PR Tjale who helped me by his suggestions
and encouragement throughout my training.
A special thanks goes to the general station manager of the Wheel business
Mr S Mlungu who gave me the opportunity to implement my engineering skills in
solving the safety problems associated with the business’s old Lathe machine.
I would also like to acknowledge with much appreciation the crucial role of the
staff of Transnet S.O.E Saldanha, who gave the permission to use all required
machinery and the necessary material to complete this design project.
A special thanks goes to my Supervisor Mr V.S Malaza, who help me to
purchase, assemble the parts and gave suggestion about the project.
I would to appreciate the guidance given by other supervisor as well as the
panels especially in our project presentation that has improved our presentation
skills by their comment and tips.

T.Ndabeni,212125710
vi
Plagiarism Document
I understand that plagiarism means academic theft i.e. using someone else’s work
and putting it forth as one’s own. This could comprise: electronic copies e.g. copies
from the internet, including YouTube and printed sources e.g. books, journals,
magazines, etc. Please tick off each point below, PRINT your details and sign below.
I declare that:
□ I have not plagiarised in the attached assignment/ task/ written piece.
□ I have applied in-text referencing on all information that comes from electronic and
printed sources, including pictures, diagrams, charts, graphs and tables.
□ I have used the Harvard system for in-text referencing as well as out-of-text
referencing.
□ I have used the IEEE system for in-text referencing as well as out-of-text
referencing.
□ In the case of group work, each member of the group have signed the plagiarism
document. Each member understands the consequences of plagiarism.
□ As an individual assignment, I declare that I have not copied the work of another
student.
□ I have used my own words in writing the attached assignment/ text, and have not
copy and pasted any materials.
□ I understand that I must still use in-text referencing even though I have written
texts in my own words.
□ I understand that it is unacceptable to copy any tasks/ projects from print or
internet sources even if they appear as ‘free downloads’ and despite the use of in-
text referencing.
Student’s NAME:……..…………………….……. SURNAME:……………..……………
SIGNATURE:………….……………………… DATE:…………………………….
(Date on cover page to be same as date above) Adapted by Aysha

T.Ndabeni,212125710
vii
Abstract
Design and fabricating the Lathe Universal Safety Device is a conceptual
understanding of automotive engineering which is not provided in daily lectures room
due to the fact that it is advance knowledge in this field.
The project gives awareness of what is going on inside the wheel department
workshop and the safety precautions taken in conjunction with the machines used in
the workshop. The purpose of this project is to design, an electronic device which will
enforce these safety precautions and thus saving lives. The design is not new and
the idea is employed by other newly designed machineries in the workshop.
Tests have been done to ensure the device meet the objective stated. The
progress of this project needs documenting, as it can be a good reference for the
next student who involve in this project as well as for a research related to this type
of safety electronic device. This report describes the project development of the first
prototype of Lathe Universal Safety Device.

T.Ndabeni,212125710
viii
Table of Contents
SUPERVISOR’S DECLARATION III
STUDENT’S DECLARATION IV
ACKNOWLEDGEMENTS V
PLAGIARISM DACLARATION VI
ABSTRACT VII
TABLE OF CONTENTS VIII
CHAPTERS IX-X
LIST OF FIGURES XI-XII
LIST OF TABLES XII
LIST OF SYMBOLS XII
DIFINITIONS XII

T.Ndabeni,212125710
ix
CHAPTERS
Chapter 1....................................................................................................................................1
INTRODUCTION........................................................................................................................ 1
1.1 Project Synopsis......................................................................................................1
1.1.1 Specific Project Synopsis .................................................................................... 1
1.2 Objective of Final Year Project................................................................................ 2
1.3 Scope of Work.........................................................................................................2
1.4 Project Planning.......................................................................................................3
1.5 Flow Chart Description ............................................................................................ 4
1.6 Gantt chart ............................................................................................................... 6
Chapter 2....................................................................................................................................7
REVIEW OF RELEVENT LITERATURE................................................................................... 7
2.1 Theory and Analysis....................................................................................................7
2.2 Machine General Operation........................................................................................ 7
2.2.1 Safety Operating Procedure of the Portal machine ............................................ 8
Starting Push Button to the Actuated..................................................................................... 8
2.3 Safety Risk factors ......................................................................................................9
2.4 Projects/Device General Function Description......................................................... 10
Chapter 3.................................................................................................................................. 11
METHODOLOGY..................................................................................................................... 11
3.1 Protecting Device...................................................................................................... 11
3.1.1 Over-currents..................................................................................................... 11
3.1.2 Over Load .......................................................................................................... 11
3.1.3 Ambient temperature ......................................................................................... 11
3.1.4 Operating voltage............................................................................................... 12
3.1.5 Is the circuit AC or DC ....................................................................................... 12
3.1.6 Specifications..................................................................................................... 12
3.2 Power supply............................................................................................................. 13
3.2.1 Introduction ............................................................................................................ 13
3.2.2 Theory of operation...................................................... Error! Bookmark not defined.
3.2.3 Power Circuit Calculations..................................................................................... 14
3.2.3.1 Voltage Transformation.................................................................................. 14
3.2.3.2 Rectification Calculation................................................................................. 14
3.2.3.3 FILTER ........................................................................................................... 15

T.Ndabeni,212125710
x
3.2.3.4 Voltage Regulation......................................................................................... 16
3.2.3.5 Complete power supply.................................................................................. 17
3.3 Sensing Devices........................................................................................................ 18
3.3.1 Copying Slides (CS) Mechanical door switch ................................................... 18
3.3.2 Infra-red Motion Detectors................................................................................. 19
3.3.3 DPST switch....................................................................................................... 21
3.4 LOGIC CIRCUIT DESIGN ........................................................................................ 23
3.4.1 Introduction ........................................................................................................ 23
3.4.2 System layout..................................................................................................... 23
3.4.3 Logic truth-table ................................................................................................. 24
3.4.4 Logic Circuit diagram ......................................................................................... 25
3.5 Output signals ........................................................................................................... 26
3.5.1 Light Emitting Diodes lights ............................................................................... 26
3.5.2 The 555 timer Circuit.......................................................................................... 28
3.5.3 Buzzer/Siren and Flashing Red light ................................................................. 30
Chapter 4.................................................................................................................................. 32
RESULT AND DISCUSSION................................................................................................... 32
4.1 Device diagrams........................................................................................................ 32
4.1.1 Complete Circuit Diagram.................................................................................. 32
4.1.2 Complete Device................................................................................................ 33
4.1.3 PCB design........................................................................................................ 34
4.2 Component List......................................................................................................... 35
4.3 CONCLUSION .......................................................................................................... 36
4.4 RECOMMENDATION............................................................................................... 36
4.5 References................................................................................................................ 36

T.Ndabeni,212125710
xi
LIST OF FIGURES
Figure 1 :Process Flow Diagram...............................................................................................5
Figure 2: Gantt Chat ..................................................................................................................6
Figure 3 : Lathe Safety Operating Procedure ...........................................................................8
Figure 4: Eye Injury....................................................................................................................9
Figure 5: Thumb Injury...............................................................................................................9
Figure 6: Middle Finger Injury....................................................................................................9
Figure 7: Leg Injury ....................................................................................................................9
Figure 8:Old Lathe Machine ....................................................................................................10
Figure 9: Project Flow Diagram ...............................................................................................10
Figure 10: Type Of Fuse Casing .............................................................................................12
Figure 11: Type Of Fuse Used ................................................................................................12
Figure 12: Power Supply Basic Block Diagram....................... Error! Bookmark not defined.
Figure 13: Single Phase Voltage Transformer........................................................................14
Figure 14: Voltage Full-bridge Rectifier Simulation.................................................................14
Figure 15: Actual Voltage Full-bridge Rectifier........................................................................15
Figure 16: Filtering Stage ........................................................................................................15
Figure 17: Voltage Regulation Simulation (curtesy of Livewire simulation software).............16
Figure 18: Complete Power Supply Simulation Diagram........................................................17
Figure 19: Complete Power Supply Breadboard Construction Diagram ................................17
Figure 20: Complete Power Supply Vera board Construction Diagram .................................17
Figure 21: Copying Slide Logic Switch (Specification)............................................................18
Figure 22: Copying Slide Logic Switch (Actual) ......................................................................18
Figure 23: 5 mm IR used in the design ...................................................................................20
Figure 24: 3mm and 5mm range IR Sensors..........................................................................20
Figure 25: breadboard IR sensor installation circuit................................................................20
Figure 26: Interconnection of DPST switches.........................................................................21
Figure 27: DPST main Switch..................................................................................................22
Figure 28: DPST Start Button Switch......................................................................................22
Figure 29: DPST start Switch location.....................................................................................22
Figure 30: DPST main Switch location....................................................................................22
Figure 31: Logic Circuit Simulation Diagram...........................................................................25
Figure 32: Low Voltage LED....................................................................................................26
Figure 33: GREEN LED light Source ......................................................................................27
Figure 34: Yellow/Orange LED light Source ...........................................................................27
Figure 35: RED LED light Source............................................................................................27
Figure 36: 555 Timer Simulation Circuit..................................................................................28
Figure 37: 555 Timer Simulation Output Pulse .......................................................................29
Figure 38: Complete 555 Timer Breadboard Construction Diagram ......................................29
Figure 39: Complete 555 Timer Vera board Construction Diagram .......................................29
Figure 40: Siren Simulation Circuit Diagram ...........................................................................31
Figure 41: Actual Siren Used in the Design ............................................................................31
Figure 42: Complete Simulation Diagram ...............................................................................32
Figure 43 : Power Supply Circuit.............................................................................................33
Figure 44 : Vera Board Power Supply Circuit & 555 timer Circuit ..........................................33
Figure 45: Sensing Circuit Vera Board....................................................................................33

T.Ndabeni,212125710
xii
Figure 46: Power Supply with the Output Current...................................................................33
Figure 47: Power Supply with the Output Voltage ..................................................................33
Figure 48: Logic Circuit on Breadboard...................................................................................33
Figure 49: PCB "B" ..................................................................................................................34
Figure 50:PCB "A" ...................................................................................................................34
LIST OF TABLES
Table 1: Truth Table for logic decision making……………………………………........31
Table 2: technical specification for the type of light source…………………………..34
Table 3: Design’s Component list and Prices ………………………………………….42
CHAPTERS LIST OF SYMBOLS
Ω- ohms LED-Light Emitting Diode
K-Kilo (*1000) Kg-Kilogram
µ-micro (*10−6
) m- Meter
DC-Direct Current AC-Alternating Current D-Duty Cycle
f- Frequency
Definitions
S.O.P- Standard/Safety Operating Procedures
AC- Alternating Current
DC- Direct Current
Power Dissipation fuse - The amount of heat lost or released
P sim – Power Simulation

T.Ndabeni,212125710
Practical Training2 Technical Report | Transnet Rail Engineering, a Business Unit
Of Transnet Limited. 06/10/2014 Page 1
Chapter 1
INTRODUCTION
As an electrical engineering student of Cape Peninsula University of Technology
(CPUT) the final year project gives student a chance to practice all the knowledge
and skills that they gained along the theory academic session in solving problems
through a project in order to be an efficient and a good technical engineer.
1.1 Project Synopsis
One of the important factors that every working environment should adapt and take
into tremendous consideration is the safety factor. The purpose of this technical
report is to completely and clearly describe the necessity of employing Electrical
Engineering based concepts in improve safety in every workshop.
Through a thorough observation we found that the company loses millions of rands
annually due to employees being injured in the workplace. This consequently leads
to slow rate of production. Each and every machine in the work has its Standard
Operating Procedure which is available to the operator. These procedures were
implemented so to reduce these injuries. The procedures are seen as the safest and
fastest way to operate these machines.
1.1.1 Specific Project Synopsis
One of the most unsafe machines in the workshop is the Heavy Duty Portal Carriage
and Wagon Wheel Lathe machine. This machine was installed in 1976. So it
definitely lacks the installation of basic safety devices which could help to prevent
these injuries as mentioned in the above paragraph (Chapter 1.1: Project Synopsis).
This project will focus on this particular machine as it is the most unsafe in the
workshop.
The main aim of this project is to ensure that the operator (Artisan) operating the
machine follows the proper operating procedures. The other aim is to achieve a
safer working environment not only for the machine operators, but for other general
workers who are sometimes unaware of the dangers associated with the machine.

T.Ndabeni,212125710
1.2 Objective of Final Year Project
After submitting a proposal report to the company which proposed the design
of a device that will enforce these operating procedures, it was very important to
design a device which would be installed in the workshop so to serve as a
surveillance unit.
1.3 Scope of Work
Lathe Safety Device needs special coordinated scope of work. As this is a
new project, special scope of work is yet to be determined so that the main objective
and goal can be achieved
These scopes helps me to be focused and know my job. The scopes are:
a) Literature review on heavy duty Lathe machine.
b) Design logic circuit using Livewire and Psim software.
c) Know the addition or external components to be used.
d) Assemble the design with the Lathe and with the additional components.
e) Test the device and modify if needed.
It is time where the soft skill e.g. punctuality, self-discipline, time management
and problem solving have been practiced because the project highly depend on the
effectiveness of all the skill as much as the knowledge we have learnt.

T.Ndabeni,212125710
1.4 Project Planning
This project begun with a research and literature review made via internet,
books, supervisor and other relevant academic material related to the title, this
literature review takes about two weeks and continues along the way of the project
as there is much to learn.
At the same week, we planned and designed schedule management of this project
which included scheduled management for the project. This is done by using
Microsoft Excel thus using Gantt chart method.
Supervisor gave briefing about the introduction of the project and the function
of the Lathe as well as its workings. The logic planning of the model design took
about 2 weeks to be done. The simulation is done using livewire, KiCad, PCB
wizard3 and P-sim simulation software. The simulation design is deeply discussed
and the best design is selected. The design must be suitable for assembly to the
Lathe machine as it will be used to improve safety around it.
The next task is preparation of progress presentation of the project. In this
particular week, the student receives aids from the supervisor about the
presentation. The preparation of the presentation requires comments and
suggestions from the supervisor.
The next week is project construction week where we started with the actual
construction of the project.
Next come the assembly, testing, correction, and finishing of the model. This task
scheduled to take time about four weeks.
Next task is the final report writing and final presentation preparation. This take about
one week to accomplished. The report is done with the supervisor’s guidance. All the
task is scheduled to take about sixteen weeks overall.

T.Ndabeni,212125710
1.5 Flow Chart Description
The system will have three output signals, which are;
 Green
 Yellow/Orange
 Red ,and
 Flashing Red color ,and
 Buzzer
These colours serve as communication signal between the employers and machines
conditions under live voltage.
 Green: The green colour means, the machine is “On” and the Copying slides
are not closed yet and the machine motors are not running. This also means
there is no danger as far as metal particle are concerned.
 Yellow: The yellow colour means the machine is “On” and the protecting
Copying slides are closed. This also means that the machine is ready to cut
the wheel at hand.
 Red :The red colour means the machine is On, the slide door are closed and
the motors are running, so any person in the vicinity of the machine should be
careful of the dangers associated with the machine.
 Flashing Red: The flashing Red colour means the machine is on and the
doors are not closed or are not closed properly, and the motors are running.
This flashing red light is a great way to indicate any foul play as far as
following the proper Safety operating procedure.
 Buzzer: The flashing Red colour also means the operator is attempting to
remove the chunks formed when the machine is under operation. There are
motions sensors that will detect any movement in the rear of the machine
when it is under operation. A logic decision will be taken ,where the machine
will be disabled and there will be a sound that will notify the personnel
operating the machine that ,there is foul play occurring, which is against the
Safety operating Procedures.

T.Ndabeni,212125710
1.5.1 Process Flowchart
The following diagram serves to demonstrate the logic description above.
Figure 1 : Process FlowDiagram

T.Ndabeni,212125710
1.6 Gantt chart
Figure 2: Gantt Chat

T.Ndabeni,212125710
Chapter 2
REVIEW OF RELEVENT LITERATURE
2.1 Theory and Analysis
In this section of the document we will be looking at technical information regarding
this device and how did we went about constructing this prototype. We will also focus
on giving technical explanations for the selection of the components employed.
2.2 Machine General Operation
When working with the portal machine certain procedures have to be followed, if not
adhered to there might be a loss of limbs, eye sight, life, hearing and even financial
losses. This is the result of injuries occurring in the workshops.
When the machine is under operation small particles that are cut from the wheel find
a way to fly out of proportion. These particles can enter the eye and consequently
damaging it if proper operating procedures are ignored. These particles have the
ability to burn or cut the skin when in contact with it. A gate is provided which will act
as a bearer between the operator and the particles. This door is referred to as
“Copying Slides”. These copying slides are sometimes not closed properly and these
particles can again find a way to the operator.
There is a great deal in investing in safety techniques, which are implemented in
each and every workshop. These include the use of
1. Safety/Standard operating Procedures (SOP).
2. Personal Protecting Equipment (PPE) and
3. Safety Awareness Courses
In this chapter we will briefly explore these techniques placed by the company.
However this design is based on the uses of SOP.

T.Ndabeni,212125710
2.2.1 Safety Operating Procedure of the Portal machine
These procedures must be followed according to the descending order. These
procedures are;
1. Wheel set to be rolled into the machine.
2. Drivers to be set to the chucking diameter
3. The suitable profile template to be set.
4. All selector switches to be set to “Automatic sequence”.
5. The keys of the keyboard to be actuated according to the figures of the
measuring sheet for diameter and lateral correction.
Starting Push Button to the Actuated
6. The following steps are represented by the flow diagram below.
a) The wheel set to be chucked.
b) The tool blocks to be positioned – by power rapid traverse motion and
creep rate motion respectively to the diameter specified on the
keyboard(Automated)
c) The tool block to be laterally positioned(Manual)
d) The copying slides to be traversed so that their tracers contact the
templates.
e) The main driving system and the feeder mechanism to be switched on.
The copying control is affected by the tracers.
f) With the profiling operation complete the tool block return to their initial
position.
g) The wheel set to be unchecked to be lowered to rest on the rail and to
be rolled out of the machine.
Figure 3 : Lathe Safety Operating Procedure (Curtesy of Transnet safety office)

T.Ndabeni,212125710
2.3 Safety Risk factors
The SOP’s are sometimes misused due to ignorance or lack of understanding. The
main cause of the problems concerning safety in workshops is the lack of
implementation of these operating procedures mentioned above (see Figure 2.2.1).
On the other hand the risk does not affect the operators alone, but almost half of
these injuries occur to general workers, visitors or contractors. These workers may
be cleaners, plumber, construction workers, pest control etc.
Consequently these additional employees may be contractors which will not be given
sufficient safety awareness and correct PPE. This is when most of the injuries occur.
However this project is to provide instant awareness, to people in the workshops.
Below are pictures of some of these injuries which recently occurred in the
workshop.
Figure 4: Thumb Injury
Figure 6: Eye Injury
Figure 5: Middle Finger Injury
Figure 7: Leg Injury

T.Ndabeni,212125710
2.4 Projects/Device General Function Description
This project will ensure that the operator is given proper visual and audio signal
which will help to avoid such events. The device will also help to indicate the
machine’s ‘electrical’ status at given time, for example it will give off a signal to the
operator and other personnel when the Lathe is under live/On conditions.
NOTE: The flow of this document will be in synchrony with the device’s operational
flow diagram which is shown in figure 9 below.
Figure 8: Old Lathe Machine
Figure 9: Project Flow Diagram
To Motor
controller

T.Ndabeni,212125710
Chapter 3
METHODOLOGY
3.1 Protecting Device
Although care is taken to properly design electrical and electronic circuits; over-
currents in the form of short-circuits and overload can occur. The sole purpose of
fuses and circuit breakers is to protect personnel and/or equipment from serious
harm when an over-current condition arises. This guide is intended to help create a
better understanding of the various parameters concerning over-current protection
and the proper application of circuit protective devices. This guide creates a basic
understanding of over-current principles and applications but is not intended to
supplant sound engineering principles or replace specific application testing.
3.1.1 Over-currents
An over-current is a condition which exists in an electrical circuit when the normal
load current is exceeded. The two basic forms of an over-current are overloads and
short circuits. Fuses and circuits breakers primary role in a circuit is to protect
personnel and equipment when dangerous over-currents do happen.
3.1.2 Over Load
An overload is an over-current condition where the current exceeds the normal full
load-capacity of the circuit but where no fault condition (short-circuit) is present. A
momentary overload condition (also known as “in-rush” currents) may also occur
when a circuit is first initialized due to capacitor charging and/or motor-start-up.
3.1.3 Ambient temperature
It is important to note that if the fuse is intended to be used in an environment with
possibly very high or low ambient temperatures, then the nominal fuse current would
need to be sized significantly higher or lower (see ambient temperature under
Chapter 3.1.6).

T.Ndabeni,212125710
3.1.4 Operating voltage
The basic rule of thumb is that the voltage rating of the fuse must always higher than
the voltage rating of the circuit that it is protecting. For example, if the circuit voltage
is 24 volts, then the fuse voltage rating must be higher than 24 volts (yes...it can be
250 V...just so long as it’s higher than the circuit voltage).
3.1.5 Is the circuit AC or DC
There exist two distinct types of circuits AC (alternating current) and DC (direct
current). AC power is what you will typically find in your home from the electrical
utility. AC power is created primarily by moving machines such as generators and
delivered through the electric grid.
DC power is typically used in electronic and automotive applications. DC power
generally is created via a chemical reaction (as batteries and solar cells) or
converted AC power through the use of AC to DC power conversion methods.
3.1.6 Specifications
 Power(heat)Dissipation fuse
 normal operating Current : 2A
 Break Down Current :2.7 A(135% of 2A)
 operating voltage :220-240Vac,50Hz
 Ambient Temperature: -15°C to 30°C
 PCB Considerations : thru-hole mounted
Figure 10: Type of Fuse Used
Figure 11: Type of Fuse Casing

T.Ndabeni,212125710
3.2 Power supply
3.2.1 Introduction
The workshop we will be installing this device has a 230 AC main voltage port. The
device has components which are manufactures using semiconductor material.
These material requires low ,DC voltages which will be utilised in the sensor ,logic
and timing parts of the circuitry.
As elaborated in the first chapter that the project needs a 12Vdc in order to work
properly. So to get the voltages that we require, a 12V regulators have been utilised
in order to force and step down (regulate) the voltage from the filter stage to the
wanted 12 DC voltage.

T.Ndabeni,212125710
3.2.2 Power Circuit Calculations
3.2.2.1 Voltage Transformation
Here a single-phase step down transformer is utilised. Before we could decide on a
transformers ration we needed to know the required secondary voltage of the transformer,
when the secondary turns N(s)= 1. The primary voltage is Said to be Vrm(P) =163 V and the
secondary voltage Vrms(S)= 16 v;
Vrms(p)
Vrms(s)
=
N(p)
N(s)
N(p)=
𝑁(𝑆)∗𝑉𝑟𝑚𝑠(𝑝)
Vrms(s)
=
(1∗163)
16
=10 turns
3.2.2.2 Rectification Calculation
In this stage we rectify the low AC voltage to a DC voltage. A Full bridge rectifier will
be employed. This type of rectification consists of four diodes connected in a loop, as
shown in figure … below. However two diodes operate simultaneously for the
positive cycle of the sinusoidal voltage. The other two diodes operate simultaneously
for the negative cycle of the sinusoidal voltage.
The magnitude of the DC voltage will be slightly lesser than that of the AC voltage.
This is due to the voltage drop across the diodes when they are under operation.
The good part is that the output DC voltage will only be affected by two diodes at a
time, instead of all four diodes.
The diodes employed are the 1N4148 type. These diodes have an internal
resistance which will generally result is a voltage drop of 1.2Vdc each.
To the Filtering
Capacitor
14 Vdc
d
c
ba
From the secondary
of the transformer
16.3 Vdc
Figure 12: Single Phase Voltage Transformer
Figure 13: Voltage Full-bridge Rectifier Simulation

T.Ndabeni,212125710
The full bridge wave rectification circuit is shown in the diagram below (see figure
15). This shows how we simply constructed this rectifier using for identical rectifier
diodes.
3.2.2.3 FILTER
In this stage we simply try to reduce the spikes caused by the rectifier, as they only
converts the negative part of the sinusoidal voltage to be positive. After this stage
the voltage is still not stable as it switches from a positive voltage to zero.
However a capacitor is employed which will bridge/reduce the spikes formed in the
rectification stage. The value of the capacitor can affect it functional properties. The
bigger the capacitor the lesser the spikes formed. However if we use an excessive
capacitance value we will be compensating the charging period of the capacitor, this
will result to the capacitor failing to filter these spikes.
The value of capacitance we selected was 470µF. This is a reasonable value as it
can easily charge up and slowly discharge at a rate that will be appropriate.
Voltage withspikes Voltage withspikes
Figure 14: Actual Voltage Full-bridge Rectifier
Figure 15: Filtering Stage

T.Ndabeni,212125710
3.2.2.4 Voltage Regulation
This part of the document entitles the importance of regulators in any power
supplying unit. After the filtering stage the 14v output voltage is said to be a DC
voltage but with a fluctuating magnitude. The use of regulator will reduce or eliminate
the ripples formed .in this device we have employed a
 Model RG178L12; 12VDC (100mA max) and a
 Model RG78L05; 5Vdc (100mA max).
The 12Vdc will be used for most parts of the circuit; this includes the LED lights, logic
circuit and switching mechanisms. However the 5Vdc will only be utilised in the
transmitter diode, which is in the Infra-Red sensor part of this device.
Two identical capacitors of a capacitance of 0.001µF are used in the construction of
the regulation stage. The first capacitor is mounted after the filtering stage. This
capacitor is to further filter some ripples which escaped the filtering stage. This
capacitor also serves as a snubber device which reduces the rate of change of this
DC voltage and thus protecting the regulator from drastic voltage change.
On the other hand the second capacitor is mounted after the regulator .like the first
capacitor it acts as a snubber device which reduces the rate of change of this DC
voltage when the load changes.
Figure 16: Voltage Regulation Simulation (courtesy of Livewire simulation software)

T.Ndabeni,212125710
3.2.2.5 Complete power supply
The combination of all these voltage transformation stages results in a fixed 12Vdc
power supply for this device.
Figure 17: Complete Power Supply Simulation Diagram
Figure 18: Complete Power Supply Breadboard Construction Diagram
Figure 19: Complete Power Supply Vera board Construction Diagram

T.Ndabeni,212125710
3.3 Sensing Devices
3.3.1 Copying Slides (CS) Mechanical door switch
3.3.1.1 General operation
It is one of our interests to be able to detect whether or not the copying slides are
transverse correctly and abides the Safety Operating Procedure. The
mechanical/physical position of the copying slides is represented logically. As
mentioned in the previous chapter, when the slides are opened it is seen as logic ‘0’
and when the slides are closed it is electrically seen as logic‘1’.
3.3.1.2 Specific operation
A mechanical switch which will be mounted on both the slides is employed for this
job. This switch has two separate parts, which when joined makes a complete circuit.
When the two slides make contact the two parts (A&B) will automatically result to
logic ‘1’.
Part A is referred to as female and Part B is referred to as male. The male is simply
a copper wire which will complete the circuit when the copying slides are closed. The
two holes on the female are where the legs of the male enters and makes contact
with the metal part inside the female (see Figure 21 above).
The switch makes a clicking sound which indicates that is closed properly. This also
occurs when the operator opens the copying slides. This mechanism will be used as
an input signal of the logic circuit.
3.3.1.3 Technical Data
V = 500 V I = 10 A,Uimp = 4 kV
A
B
Figure 21: Copying Slide Logic Switch (Actual) Figure 20: Copying Slide Logic Switch (Specification)

T.Ndabeni,212125710
3.3.2 Infra-red Motion Detectors
3.3.2.1 Introduction
In this design we have employed the IR LED sensor which is part of the Infra-
Red sensor family. We have employed this sensor as it is economical reasonable,
easy to maintain and is effective for this type of function. Below is the specific
operation of this type of sensor.
3.3.2.2 Specific system operation
This is the stage which acts as an interrupt detector; here the sensor detects the
presence of a person or any object in the rear of the Lathe machine. Once the object
or person has been detected the sensor will quickly send a signal to the inputs of the
logic circuit. , then the logic circuit will trigger the siren/buzzer, this signal will disable
the machine. There are many types of sensors that can be used in this project.
Before choosing the one to be used and well economical sensor, I would like to
discuss about the various types of sensors as follows.
This stage is there to sense any unauthorised movement concerning the safety
precautions of the machine and the sensor to be used is an infra Red sensor
(IR).Below is the technical operation of these infra-Red sensors;
3.3.2.3 Technical IR operation
IR LED emits infrared radiation. This radiation illuminates the surface in front of LED.
The surface reflects the infrared light. The amount of light reflected, depends on the
reflectivity of the surface. This reflected light is made incident on reverse biased IR
sensor. When photons are incident on reverse biased junction of this diode, electron-
hole pairs are generated, which results in reverse leakage current. Amount of
electron-hole pairs generated depends on intensity of incident IR radiation. More
intense radiation results in more reverse leakage current. This current can be passed
through a resistor so as to get proportional voltage. Thus as intensity of incident rays
varies, voltage across resistor will vary accordingly.
IR LED is used as a source of infrared rays. It comes in two packages 3mm or 5mm.
3mm is better as it is requires less space. IR sensor is nothing but a diode, which is

T.Ndabeni,212125710
sensitive for infrared radiation. This infrared transmitter and receiver are called as IR
TX-RX pair. It can be obtained from any decent electronics component shop and
costs less than R10.
The colour of IR transmitter and receiver is different. However you may come across
pairs which appear exactly same or even has opposite colours than shown in Figure
24 and it is not possible to distinguish between TX and RX visually.
Figure 22: 3mm and 5mm range IR Sensors Figure 23: 5 mm IR used in the design
Figure 24: breadboard IR sensor installation circuit

T.Ndabeni,212125710
3.3.3 DPST switch
As mentioned in the chapter above this design should be connected in a way that it
doesn’t interfere with the normal operating procedures of the machine. The reason
for this is to avoid extra or additional responsibilities for the operator, as it will
become complex to operate the machine.
3.3.3.2 General system layout
The entire device is designed so to be synchronously operated with the machine. We
had to design this device so that it doesn’t add additional work for the operator. To
power or switch on the device we used a Single-throw-Double-Pole switch. This
switch is to enable the operator to switch on both the machine and the device with a
single button.
The device is designed in a way that it doesn’t interfere with machines operating
procedure. We had to keep the procedures the way there are. The device is
connected to the machine so that it allows synchronism between the two, so for the
input signal DPST start of the device we also employed a DPST switch so to have a
logic signal when the operator pushes the start button of the machine (see number
6.e of the Safety Operating Procedures).
The diagram below (see Figure 26) represents the interconnection between the
Lathe machine and the design.
Figure 25: Interconnection of DPST switches

T.Ndabeni,212125710
3.3.3.3 DPST main switch
The device is to be externally mounted on the machine. However when the machine
is to be switched on/off it should automatically switch on the device. The device and
the machine are to be interconnected through a Double Pole Singe Throw switch. As
mentioned above this switch is regarded as an input signal to the logic circuit.
3.3.3.4 DPST start button switch
According to the Safety Operating Procedures the operator is required to push a
Start button so to start with the wheel cutting process. The machines start button will
be replaced with a Double Pole Singe Throw switch so to achieve a simultaneous
reaction between the machine and the device. The DPST is also regarded as an
input signal of the devices logic circuit.
3.3.3.5 Actual Device pictures
Figure 33 below shows the actual positioning of the main ON/OFF button. However
the push to start button is mounted on the PLC control panel which is shown in
Figure 34 below.
Figure 26: DPST main Switch
Figure 27: DPST Start Button Switch
Figure 29: DPST main Switch location Figure 28: DPST start Switch location

T.Ndabeni,212125710
3.4 LOGIC CIRCUIT DESIGN
3.4.1 Introduction
The logic circuit diagram serves are the brains of this design. It consists of three
input signal and three output signal ports. The input signals can be a basic switch or
any other advice switching devices, such as motion sensors etc. On the other hand
the output signals are LED lights and a siren/buzzer.
3.4.2 System layout
As mentioned in the chapter above (see Chapter 3.3: Sensor devices) the logic
circuit needs the input signals/sensing devices so that it produce the necessary logic
decisions which will be represented by output devices as mentioned below(see
chapter 3.4: output Devices
The following is the list of input signals;
1. DPST switch ,Main switch /Push-to-Start Button(DPST)
2. Motion Sensor (MS)
3. Copying slides switch(CS)
The following is the list of output signals;
1. RED LED Light
2. GREEN LED Light
3. Yellow LED Light
4. Siren/Buzzer
KEYS: INPUTS
Copying slides (CS): Closed =‘1’
: Opened=‘0’
STDP switch, main switch /Push-to-Start Button
: Closed=‘1’
: Opened =‘0’
Motion Sensor (MS) : Person present =‘1’
: No person present = ‘0’
NOTE: Logic ‘1’ = 5 volts
Logic ‘0’ = 0 volts

T.Ndabeni,212125710
G-green light signal
R-Red light signal
O-Orange light signal
FR-Flashing Red light signal
3.4.3 Logic truth-table
This table provides the logic level of the output signal with respect to the logic level
of the input signal. It shows the output behavior towards all possible logic
combinations that can occur during the machine operation.
Table 1: Truth Table for logic decisionmaking
Input Output
MS CS STDP main STDP start G R O FR/Buzzer
0 0 0 0 0 0 0 0
0 0 0 1 0 0 0 0
0 0 1 0 1 0 0 0
0 0 1 1 0 0 0 1
0 1 0 0 0 0 0 0
0 1 0 1 0 0 0 0
0 1 1 0 0 0 1 0
0 1 1 1 0 1 0 0
1 0 0 0 0 0 0 0
1 0 0 1 0 0 0 0
1 0 1 0 1 0 0 0
1 0 1 1 0 0 0 1
1 1 0 0 0 0 0 0
1 1 0 1 0 0 0 0
1 1 1 0 1 0 0 0
1 1 1 1 0 0 0 1

T.Ndabeni,212125710
3.4.4 Logic Circuit diagram
This is an electronic representation of the logic table above (see Table 1). It simply
provides ease in constructing this circuit.
Gree
n
RED
Orange
Figure 30: Logic Circuit Simulation Diagram
Siren

T.Ndabeni,212125710
3.5 Output signals
3.5.1 Light Emitting Diodes lights
As mentioned above (see chapter 3.4: logic Circuit Design) the design requires
three LED light which will serve as output signals. These LED light have different
colours for different logic conditions, these colours are Red, Yellow/Orange and
Green. Regardless of what colour the LED is they all have the same physical and
electronic properties.
3.5.1.2 General Operation
A light-emitting diode (LED) is a two-lead semiconductor light source. It is a
basic pn-junction diode, which emits light when activated. When a fitting voltage is
applied to the leads, electrons are able to recombine with electron holes within the
device release energy in the form of protons. This effect is
called electroluminescence, and the colour of the light is determined by the
energy band gap of the semiconductor.
3.5.1.3 Device selection
This section of the document entails the use of LED lights as output signal devices.
Advances in light emitting diode (LED) technology, including super-bright white
diodes which are employed in this device. Other performance improvements are
creating new applications and increased acceptability of LEDs in mainstream use.
Additionally, challenging customer requirements in industrial or harsh and hazardous
locations including long life, high brightness, and reliability can be achieved with
currently available LED technology. Once considered only for indication or
decorative purposes, LEDs are now gaining acceptability in signalling, down lights,
floodlights, street lights, and other mainstream uses.
Figure 31: Low Voltage LED

T.Ndabeni,212125710
When compared to other conventional light sources such as incandescent,
fluorescent or metal halide, a LED light source can offer longer life, energy savings,
and equal or better light characteristics, providing years of maintenance free
operation with a quantifiable return on investment.
3.5.1.4 Device selection
The company has a basic type of light source (see Figure 37, 38, 39 below) it uses
for safety awareness reasons. This type of light source consists of 10 LED. The
circuitry and protection of this light source is built internally so it doesn’t require any
external components. This type of light source is available in multi-colours which
include the type of colours we require.
Three LED light sources will be needed for the signalling step; these are RED,
YELLOW/ORAGE and GREEN.
3.5.1.5 Device specifications
As mentioned in the chapter above (Chapter 3.5.1.3) the selected LED light source
operates at low voltages DC power. This type of light source is ideal for switching
uses. It can withstand the fluctuation of DC voltage and its function will not
deteriorate because of this.
Table 2: technical specification for the type of light source
Figure 34: RED LED light Source Figure 32: Yellow/Orange LED light Source Figure 33: GREEN LED light Source

T.Ndabeni,212125710
Note: The weight is measured in “lbs” and the physical dimensions are in
“inches”. Therefore;
 1 lbs = 0.454 Kg
 1 in = 0.0254 m
3.5.2 The 555 timer Circuit
The 555 timer integrated circuit(IC) has become a mainstay in the design of this
electronic device. The 555 can be used to debounce switches,modulate
signals,create accurate clock signals etc. It plays a vital role, which is to produce a
pulse width modulated (PWM) output voltage signal. In this device the voltage will be
used to power the siren/buzzer. The 555 timer pulse length will be set so to produce
a beeping sound instead of a single pulse sound. The pulse length is determined by
charging then discharging a capacitor to a 555 timer.
3.5.2.2 General observation
In order to have an effective output signal, we need to design a pulse which will stay
high longer than it will stay low. This means the time HIGH (𝑡 𝐻 ) must be grater than
time low (𝑡 𝐿).
So we decided on a Duty cycle of 75%.
Even though the 𝑡 𝐻 >𝑡 𝐿 the period (T) should be not too long as it will result in a
longer 𝑡 𝐿.a longer 𝑡 𝐿 would be mistakenly confuse with a no signal condition. We
decided on a Period of 1.33second, thus a frequency of 0.7Hz. .
3.5.2.3 Components Calculations
Selected values: D=0.75, f= 0.7 Hz, and C1=C2= 1µC.
t=T=1/ f = 1/0.75 = 1.33 s
 𝑡 𝐻 = D*T
= 0.75*1.33=1s
 𝑡 𝐿 = T- 𝑡 𝐻
= 1.33- 1
= 0.33s
 𝑅2 = 𝑡 𝐿 (0.693∗ 𝐶1)⁄
= 0.33 (0.693∗ 1 ∗ 10−6
)⁄
= 476 KΩ
 𝑅1 = ( 𝑡 𝐻/(0.693*𝐶1))- 𝑅2
Output–to-siren
Figure 35: 555 Timer Simulation Circuit

T.Ndabeni,212125710
= (1/ (0.693*1*10−6
))-476*103
= 967 KΩ
3.5.2.4 Actual design
The 555 timer output voltage is generally 2/3of𝑉𝑐𝑐. 𝑉𝑐𝑐. =16Vdc, so the total output
voltage is 2/3*16 = 44=10.66Vdc
Figure 36: 555 Timer Simulation Output Pulse
Figure 37: Complete 555 Timer Breadboard Construction Diagram
Figure 38: Complete 555 Timer Vera board Construction Diagram

T.Ndabeni,212125710
3.5.3 Buzzer/Siren and Flashing Red light
3.5.3.1 General System Observation
As explained in chapter 3.5.2 the siren will be sounded when there is foul play during
the operation of the machine. There are three logic possibilities which will result in
the siren being set on. The logic possibilities are as follows
1. When the operator pushes the start button, while the copying slides are no
traversed.
2. Whenever there are too much waste/junk remains in the machine, the
operator or the additional employer has the responsibility to remove that
waste. The dangers arise when the operator attempts to remove these
remains while the motors are still running. The buzzer will alert the person or
the operator behind the machine who can be injured.
3. The third possibility is the combination of possibility (1) and (2).
These possibilities are clearly shown in the Truth Table for logic decision making
(Table 1: Chapter 3.4). The siren system has a flashing Red light which is
activated through the same logic possibilities.
3.5.3.3 Device specification
The siren/buzzer will be powered through the 555 timer output (pin 3).the level of
555 output voltage will not be sufficient ,so a pull up resistor will be employed which
will pull up the voltage to a bigger value, and thus be able to support the siren/buzzer
device.
 Voltage 5-to-16Vdc
 Duty Cycle Continuously rated
 Sound Output 112 dB(A) at 1m
 Sound Frequency 400 - 2900Hz
 App. Range 800m in still air on open field
 Sound Select 32 Sounds - dipswitch selectable with volume control
 Current Consumption 0.24mA - 2.5mA
The internal resistance of the buzzer is measured to be 100 ohms, so as calculated
on the above chapter (The 555 timer circuit) the 555 output voltage is 10.66Vdc and
the maximum operating current of the buzzer is 20mA

T.Ndabeni,212125710
3.5.3.4 Calculation
The resistance is R = 𝑉 𝐼⁄ = 10.66/20*10−3
= 533 ohms.
So the value of the pull up resistor will be 400 ohms.
3.5.3.5 Technical Information
Below (see Figure 40) is the simulation circuit diagram for the siren circuit. This
includes the power flow that occurs between the circuits which builds up the siren
part of the design.
𝑉𝑐𝑐 : From
logiccircuit
Figure 39: Siren Simulation Circuit Diagram
Figure 40: Actual Siren Used in the Design

T.Ndabeni,212125710
Chapter 4
RESULT AND DISCUSSION
4.1 Device diagrams
4.1.1 Complete Circuit Diagram
Figure 41: Complete Simulation Diagram

T.Ndabeni,212125710
4.1.2 Complete Device
Figure 47: Logic Circuit on Breadboard
Figure 42 : Power Supply Circuit
Figure 43 : Vera Board Power Supply Circuit & 555 timer Circuit
Figure 46: Power Supply with the Output Voltage
Figure 44: Sensing Circuit Vera Board
Figure 45: Power Supply with the Output Current

T.Ndabeni,212125710
4.1.3 PCB design
After the completion of the design project we have found ways to make our project
prototype to be as professional as possible. One of the ways which we did this was
the design of a PCB board for this device.
4.1.3.2 Description
The PCB is separated into two parts which will be coupled together during fitting.
The first PCB (A) will have the power supply circuit which consist of Protecting
device, voltage rectification circuit and voltage regulation. However the second part
PCB B consist of logic circuit, sensing device and output devices.
4.1.3.3 PCB Specifications
The simulation software used in this design is KiCad and PCB wizard3. The design
settings and specifications are listed below
• Physical dimensions: 80x80 mm
• Grid : 0.100 mm grid with 0.060 mm track
• Minimum spacing: 3 mm
• Isolation Gap : 2 mm
Figure 49: PCB "A"(Courtesy of KiCad Simulation) Figure 48: PCB "B"(Courtesy of KiCad Simulation)

T.Ndabeni,212125710
4.2 Component List
Table 3: Design’s Componentlist and Prices
Component
name
# of
units
Price/unit
in rands
Maintenance
schedule
Life
span
in
years
Part number Total
cost
price
LED lights 3 37 20 yrs 15-25 RTLSF 111
4-pin AND
gates
2 4 When
damaged
8-10 74HC21
Voltage
regulator
1 2.60 When
damaged
6-10 78L12 2.60
Electrolytic
capacitor
2 1.20 When
damaged
3-8 1µF 2.40
Door
contact
HZS
1 25 When
damaged
20-25 G232(TUV),EN81 25
switch 1 6 When
damaged
8-10 DPST 6
switch 1 3 When
damaged
10-18 DPST 3
Inverter IC 1 4 When
damaged
8-10 74LS04 4
Electronic
siren/buzzer
1 20 When
damaged
8-10 12Vdc,80Db 20
Single
phase Tx
1 105 When
damaged
10-20 220Vac-
16Vac,2A
105
Rectifier
diodes
4 2.50 When
damaged
5-8 1N4148 2
Electrolytic
capacitor
2 1.20 When
damaged
3-8 0.01 µF 2.40
Electrolytic
capacitor
2 1.20 When
damaged
3-8 470 µF 2.40
OR-gate IC 1 4 When
damaged
8-10 74LS32 4
Pulse
generator
1 4.70 When
damaged
8-10 NE555bipolar
timer
4.70
Current
limiting
Resistors
4 0.40 When
damaged
50-
more
128 Ω resistors 1.60

T.Ndabeni,212125710
4.3 CONCLUSION
Much research has been done considering books, students, component values have
been calculated and circuits have been built with much success. Many problems did
occur especially on the sensing stage when testing however these problems were
successfully solved. The big problem was the imbalance of currents to the switching
relays which caused the relay to switch by the leakage current; this is the stage in
the design that gave a problem. The prototype has been sent to Maintenance Plant
Department (MPD) for testing and approval. If the device is approved it will be
implemented to every Lathe machine requiring this sort of safety unit.
4.4 RECOMMENDATION
This device can be used as an alarm system or automatic light system. It is easily
manipulated so to function as you require it to do. I recommend that the device to be
employed to every workshop as it will save the company millions of rands.
4.5 References
(1) Malindi P., 2005, “Conditioning and interface, Transducers, power
suppliers”[online].Available from: [15 September 2009]
(2) Fred Philpot,2006 “The Pt100 Sensor”[online].available
from:http://www.iqinstruments.com/iqshop/technical/pt100.html
[10 August 2009]
(3) Wikipedia,2007,’Thermocouple’[online], available
from:http://en.wikipedia.org/wiki/Thermocouple [09 November
2009]
(4) PC Oscilloscope and Data Acquisition Products, PT100 Platinum
Resistance Thermometers[online] available
fromhttp://www.picotech.com/applications/pt100.html [30September
2009].

AppendixC_Old Lathe safety device

Recommended

Recommended

More Related Content

Viewers also liked

Viewers also liked (13)

Similar to AppendixC_Old Lathe safety device

Similar to AppendixC_Old Lathe safety device (20)

AppendixC_Old Lathe safety device