Download - Progect II 070933

By: Fadel H. Ramadan Project II, EEE 450

ID: 07075933 Supervised By: Dr.Osama Al Rawi

BSC in Electrical Engineering

Gulf University

College of Engineering

Electrical and Electronic Engineering Department

Control Stepper Motor Manually A project

Submitted to the Electrical and Electronic Engineering Department/

Gulf University in partial fulfillment of the requirements for the degree of Bachelor of Science in Electrical Engineering

By:

Fadel H. Ramadan

Supervised by:

Dr. Osama Al-Rawi

Submission Date :9/5/2012

Acknowledgment




At the beginning most people told that it will be hard and the effort will be in vain

but our belief in ourselves and our faith that we can make the future of our

University better was and still our motivation. To set an example of the "Source Of

Quality Education'' But we would achieve nothing without the help of those who

has given us the encouragement, time and effort. So we dedicate the project for all

who had helped us and enlighten our way with their vision. So thank you

Dr. Nouaman Nouaman

Dr. Osama Al-Rawi

Dr. Mohammad Majid

Thanks to everyone helped and believed in us

Thank you all




AbstractStepper motors are extremely important to the industry as it is used in many

applications depends on position control like filling and packaging. But this kind of

motors requires special driving technique. Our project aims to build Hybrid

Unipolar Stepper Motor Driver can withstand up to 50 Volt and 1 Ampere with

high accuracy ,simple interface and easy maintenance.

The controlling method is manually using set of 555 IC timer and a 4 bit Universal

shift register DM74LS194A to produce the sequence pattern.

The project targets the students of electrical engineering to get a general picture of

this machine and it's characteristics.




List of Abbreviations:

IC: Integrated Circuit

DC: Direct Current

PM: Permanent Magnet

VR: Variable reluctance

RPM: revolutions per minute

Fadel Hasan Ramadan Project II, EEE 450

07075933 Dr.Osama Al Rawi


Table of Contents

1. Acknowledgment

2.Abstract

2. List of Abbreviations

- CHAPTER ONE: INTRODUCTION

1.1 Introduction

1.2 Motivation

1.3 Aim of the project

- CHAPTER TWO: Theoretical Background and Applications

2.1 Introduction: '' What is Stepper Motor and What are its basic

characteristics? ''

2.2 Early history of stepper motors

2.3 Types Of Stepper Motors

2.3.1 Permanent-magnet (PM) Stepper Motors

2.3.2 Variable-reluctance (VR) Stepper Motors

2.3.3 Hybrid Stepper Motors

2.3.4 Two-phase stepper motors

a. Unipolar motors

b. Bipolar motor

2.4 Applications

- CHAPTER THREE: Practical Experiment

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3.1 Introduction

3.2 The Circuit Driver

3.3 Basic Stepper Motor Driver Operation

3.4 Inputs Vs. Outputs Waveforms

3.5 Integrated Circuit Chips Used

3.6 74194 Stepper Motor Driver Notes

3.7 74194 Stepper Driver Initialization Notes

3.8 Stepper Circuit Board Parts List

- CHAPTER FOUR: Conclusion

3. References

4. Appendices: Data Sheet

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CHAPTER ONEINTRODUCTION

1.1 IntroductionThis report is about one type of many of electrical machines, in particular the one

which converts electrical energy to mechanical energy. DC Motors and Stepper

Motor in particular which I will clarify and the main topic of this report.

Here I give only short review and important at the same time for an electrical

engineer knowledge and to be familiar to deal with such motors that can be found

around us and depend on it daily at home , office, factory, and even a hospital .

The way that I'm going to explain is first to mention the requires information and

background and at last an experiment of sampling a circuit to drive a stepper motor

to put a picture in mind and let the information fit which each other.

1.4 MotivationThis report has done to implement my knowledge and study of Electrical

Engineering major it is presented to My Instructor DR. Osama Al-Rawi

and it is basic since it is requirement as graduation project.

1.5 Aim of the projecta. Explain what is stepper motors and their theory.

b. Show the History of this machine.

c. Some Application.

d. Using simple and available discrete components to drive the motors.

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CHAPTER TWOTheoretical Background

andApplications

2.1 Introduction:

'' What is Stepper Motor and What are its basic characteristics? '' [1]

Figure 1.1[2] Illustrates the cross-sectional structure of a typical stepper motor; this

is so called single stack variable reluctance motor. We shall first study how this

machine works, using this figure. The stator core has six silent poles or teeth, while

the rotor has four poles, both stator and rotor core being of soft steel. Three sets of

windings are arranged as shown in the figure. Each set has tow coils connected in

series . A set of windings called 'phase'. And consequently this machine is a three-

phase motor. Current is supplied from a DC power source to the windings via

switches I, II and III.

In state :

(1)The winding of phase I is supplied with current through switch I or 'phase' I

is excited in technical terms .The magnetic flux which occurs in the air-gap

due to the excitation is indicated by arrows. In state (1), the two stator salient

poles of phase I being excited are in alignment with two of the four rotor

teeth. This is an equilibrium state in terms of dynamics. When switch II is

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closed to excite phase II in addition to phase I, magnetic flux is built up at

the stator poles of phase II in the manner shown in state (2), and a counter-

clockwise torque is create owing to 'tension' in the inclined magnetic field

lines. The rotor will then, eventually, reach state (3).

Thus the rotor rotates through a fixed angle, which is termed the 'step angle',

15ᵒ in this case, as one switching operation is carried out. If switch I is now

opened to de-energize phase I, the rotor will travel another 15ᵒ to reach state

(4). The angular position of the rotor can thus be controlled in units of the

step angle by a switching process. If the switching is carried out in sequence,

the rotor will rotate with a stepped motion; the average speed can also be

controlled by the switching process.

Nowadays, transistors ate used as electronic switches for driving a stepping

motor, and switching signals are generated by digital ICs or a

microprocessor (see Fig. 1.2).[3] As explained above, the stepping motor is

an electrical motor which converts a digital electric input into a mechanical

motion. Compared with other devices that can perform the same or similar

functions, a control system using a stepping motor has several significant

advantages as follows:

(1) No feedback is normally required for either position control or

speed control.

(2) Positional error is non-cumulative.

(3) Stepping motors are compatible with modern digital equipment.

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For these reasons, various types and classes of stepping motor have been used in

computer peripherals and similar systems.

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2.2 Early history of stepper motors.[4]

(1) An issue of JIEE published in 1927 carried an article '' The Application

of Electricity in Warships'', and a part of this article described a three-phase

variable-reluctance stepping motor of the above type which was used to remote-

control the direction indicator of torpedo tubes and guns in British warship.

(2) According to an article in IEEE Transaction on Automatic Control,

stepping motors were later employed in the US Navy for a similar purpose.

Though practical applications of modern stepping motors occurred in the 1920s,

the prototypes of variable-reluctance motors actually existed in earlier days. We

shall here refer to two noteworthy inventions made in 1919 and 1920 in Britain.

a. Tooth structure to minimize step angle. A UK patent was obtained

in 1919 by C.L Walker, a civil engineer in Aberdeen, Scotland, for the invention of

a stepping motor structure which can more in small step angles (see Fig. 1.3.)[5]

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b. Production of a large torque from a sandwich structure. C.B

Chicken and J.H Thain in Newcastle upon Tyne in 1920 obtained a US

patent for the invention of a stepping motor which could produce a large

torque per unit volume of rotor. The longitudinal construction of this

machine is shown in Fig. 1.4[6]

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2.1 Types Of Stepper Motors:[7]

2.1.1 Permanent-magnet (PM) Stepper Motors: The permanent-magnet

stepper motor operates on the reaction between a permanent-magnet

rotor and an electromagnetic field. Figure 1.5 shows a basic two-pole

PM stepper motor. The rotor shown in Figure 1.5 (a) has a permanent

magnet mounted at each end. The stator is illustrated in Figure 1.5

(b). Both the stator and rotor are shown as having teeth. The teeth on

the rotor surface and the stator pole faces are offset so that there will

be only a limited number of rotor teeth aligning themselves with an

energized stator pole. The number of teeth on the rotor and stator

determine the step angle that will occur each time the polarity of the

winding is reversed. The greater the number of teeth, the smaller the

step angle.

Figure 1.5

When a PM stepper motor has a steady DC signal applied to one

stator winding, the rotor will overcome the residual torque and line up

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with that stator field. The holding torque is defined as the amount of

torque required to move the rotor one full step with the stator

energized. An important characteristic of the PM stepper motor is that

it can maintain the holding torque indefinitely when the rotor is

stopped. When no power is applied to the windings, a small magnetic

force is developed between the permanent magnet and the stator. This

magnetic force is called a residual, or detent torque. The detent

torque can be noticed by turning a stepper motor by hand and is

generally about one-tenth of the holding torque.

2.1.2 Variable-reluctance (VR) Stepper Motors: The variable-reluctance

(VR) stepper motor differs from the PM stepper in that it has no

permanent-magnet rotor and no residual torque to hold the rotor at

one position when turned off. When the stator coils are energized, the

rotor teeth will align with the energized stator poles. This type of

motor operates on the principle of minimizing the reluctance along

the path of the applied magnetic field. By alternating the windings

that are energized in the stator, the stator field changes, and the rotor

is moved to a new position. The stator of a variable-reluctance

stepper motor has a magnetic core constructed with a stack of steel

laminations. The rotor is made of unmagnetized soft steel with teeth

and slots. The relationship among step angle, rotor teeth, and stator

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teeth is expressed using the following equation:

Figure 1.6 shows a basic variable-reluctance stepper motor. In this

circuit, the rotor is shown with fewer teeth than the stator. This

ensures that only one set of stator and rotor teeth will align at any

given instant. The stator coils are energized in groups referred to as

phases. In Figure 1.6, the stator has six teeth and the rotor has four

teeth. According to the above mentioned Eq. , the rotor will turn 30°

each time a pulse is applied. Figure 1.6 (a) shows the position of the

rotor when phase A is energized. As long as phase A is energized, the

rotor will be held stationary. When phase A is switched off and phase

B is energized, the rotor will turn 30° until two poles of the rotor are

aligned under the north and south poles established by phase B. The

effect of turning off phase B and energizing phase C is shown in

Figure 1.6 (c). In this circuit, the rotor has again moved 30° and is

now aligned under the north and south poles created by phase C. After

the rot or has been displaced by 60° from its starting point, the step

sequence has completed one cycle. Figure l.6 (d) shows the switching

sequence to complete a full 360° of rotation for a variable-reluctance

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motor with six stator poles and four rotor poles. By repeating this

pattern, the motor will rotate in a clockwise direction. The direction of

the motor is changed by reversing the pattern of turning ON and OFF

each phase.

Figure 1.6

The VR stepper motors mentioned up to this point are all single-stack

motors. That is, all the phases are arranged in a single stack, or plane.

The disadvantage of this design for a stepper motor is that the steps

are generally quite large (above 15°). Multistack stepper motors can

produce smaller step sizes because the motor is divided along its axial

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length into magnetically isolated sections, or stacks. Each of these

sections is excited by a separate winding, or phase. In this type of

motor, each stack corresponds to a phase, and the stator and rotor have

the same tooth pitch.

2.1.3 Hybrid Stepper Motors: The hybrid step motor consists of two

pieces of soft iron, as well as an axially magnetized, round

permanent-magnet rotor. The term hybrid is derived from the fact

that the motor is operated under the combined principles of the

permanent magnet and variable-reluctance stepper motors. The stator

core structure of a hybrid motor is essentially the same as its VR

counterpart. The main difference is that in the VR motor, only one of

the two coils of one phase is wound on one pole, while a typical

hybrid motor will have coils of two different phases wound on one

the same pole. The two coils at a pole are wound in a configuration

known as a bifilar connection. Each pole of a hybrid motor is

covered with uniformly spaced teeth made of soft steel. The teeth on

the two sections of each pole are misaligned with each other by a

half-tooth pitch. Torque is created in the hybrid motor by the

interaction of the magnetic field of the permanent magnet and the

magnetic field produced by the stator. Stepper motors are rated in

terms of the number of steps per second, the stepping angle, and load

capacity in ounce-inches and the pound-inches of torque that the

motor can overcome. The number of steps per second is also known

as the stepping rate. The actual speed of a stepper motor is

dependent on the step angle and step rate and is found using the

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following equation:

2.3.4 Two-phase stepper motors:[11]

There are two basic winding arrangements for the electromagnetic coils in a

two phase stepper motor: bipolar and unipolar.

c. Unipolar motors

A unipolar stepper motor has logically two windings per phase, one for each

direction of current. Since in this arrangement a magnetic pole can be

reversed without switching the direction of current, the commutation circuit

can be made very simple (e.g. a single transistor) for each winding.

Typically, given a phase, one end of each winding is made common: giving

three leads per phase and six leads for a typical two phase motor. Often,

these two phase commons are internally joined, so the motor has only five

leads. A microcontroller or stepper motor controller can be used to activate

the drive transistors in the right order, and this ease of operation makes

unipolar motors popular with hobbyists; they are probably the cheapest way

to get precise angular movements. (For the experimenter, one way to

distinguish common wire from a coil-end wire is by measuring the

resistance. Resistance between common wire and coil-end wire is always

half of what it is between coil-end and coil-end wires. This is due to the fact

that there is actually twice the length of coil between the ends and only half

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from center (common wire) to the end. Unipolar stepper motors with six or

eight wires may be driven using bipolar drivers by leaving the phase

commons disconnected, and driving the two windings of each phase

together. It is also possible to use a bipolar driver to drive only one winding

of each phase, leaving half of the windings unused.

Figure2.2.5

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d. Bipolar motor

Bipolar motors have logically a single winding per phase. The current a

needs to be reversed in order to reverse a magnetic pole, so the driving

circuit must be more complicated, typically with an H-bridge arrangement.

There are two leads per phase, none are common. Because windings are

better utilized, they are more powerful than a unipolar motor of the same

weight.

Fig 2.2.6

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2.2 Applications:As the sizes of Stepper Motor Varies, the uses and it's applications varies in

different ways. Specially in motion control position systems, Which follows the

open-loop theory (no feedback required). Briefly, Here is some areas where it is

used:

1- Office Equipments: Printers, Scanners and Optical disk drive.

2- Medical Equipments: digital dental photography, fluid pumps,

respirators, blood analysis machinery, chemically mixing machine.

Milling Machine[8]

Serial

Printer[9]

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CHAPTER THREE

Practical Experiment

3.1 Introduction:

This chapter is mainly about our stepper motor driver using discrete component

simple and expensive which is available in any electronic shop. The experiment is

to connect theoretical part with practical part in order to make it more

understandable by my colleague.

In the next section you will find the circuitboard schematic with component's lists

and the driver operation, which implies the basic control function for the stepper

motor; such as: Forward, Reverse, Stop, Slower and Faster step rate are possible.

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3.2 The Driver Circuit:

* [10]

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3.3 Basic Stepper Motor Driver Operation:

1. The LM555 (IC 1) a stable oscillator produces CLOCK pulses that are fed to

PIN 11 of the 74194 (IC 2) shift register.

2. Each time the output of the LM555 timer goes HIGH (positive) the HIGH

state at the 74194's OUTPUT terminals, (PIN's 12, 13, 14, 15), is shifted

either UP or DOWN by one place.

The direction of the output shifting is controlled by switch S1. When S1 is in

the OFF position (centre) the HIGH output state will remain at its last

position and the motor will be stopped.

Switch S1 controls the direction indirectly through transistors Q2 and Q3.

When the base of Q2 is LOW the output shifting of IC 2 will be pins 15 - 14

- 13 - 12 - 15; .etc.

When the base of Q3 is LOW the output shifting of IC 2 will be pins 12 - 13

- 14 - 15 - 12; .etc.

The direction of the output's shifting determines the direction of the motor's

rotation.

3. The outputs of the 74194 are fed to four sets of paralleled segments of a

ULN2803 Darlington driver (IC 3).

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When an input of a ULN2803 segment is HIGH, its darlington transistor will

turn ON and that OUTPUT will conduct current through one of the motors

coils.

4. As the coils of the motor are turned ON in sequence the motor's armature

rotates to follow these changes. Refer to following diagram.

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3.4 Inputs Vs. Outputs Waveforms:

The following diagram shows the stepping order for the outputs of the ULN2803

(IC 3) as compared to the input and output of the 74194 (IC 2). The output is

shown stepping in one direction only.

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3.5 Integrated Circuit Chips Used IC 1 - LM555 - Timer, normally configured as an stable oscillator but can be

used a monostable timer for 1 step at a time operation or can be used as a

buffer between external inputs and IC2. (See later Diagrams.)

IC 2 - 74194 - 4-Bit Bidirectional Universal Shift Register. The shift register

provides the logic that controls the direction of the drivers output steps.

IC 3 - ULN2803 - 8 Segment, Darlington, High Current, High Voltage

Peripheral Driver. Each segment can handle currents of up to 500 milliamps

and voltages up to 50 volts. In this circuit 2 output segments are connected

in parallel, this allows a maximum output current of 1 amp per phase.

IC 4 - LM7805 - Positive 5 Volt Regulator. Provides low voltage power to

the driving circuitry and can also power external control circuits.

23




3.6 74194 Stepper Motor Driver Notes: Due to the lack of error detection and limited step power, this circuit should

not be used for applications that require accurate positioning. (The driver is

designed for hobby and learning uses.)

There are links to other stepper motor related web pages further down the

page. These may be helpful in understanding stepper motor operation and

control.

For the parts values shown on the schematic, if the external potentiometer

(RT) is set to "ZERO" ohms, the calculated CLOCK frequency will be

approximately 145 Hz and a motor will make 145 steps per second. This

step rate should be slow enough for most motors to operate properly.

The maximum RPM at which stepper motors will operate properly is low

when compared to other motor types and the torque the motor produces

drops rapidly as its speed increases. Testing may be needed to determine the

minimum values for RT and C1 to produce the maximum CLOCK

frequency for any given motor. Data sheets, if available, will also help

determine this frequency.

If RT is set to 1 Mega Ω, the calculated step rate will be 0.73 Hz and the

motor would make 1 step every 1.39 seconds.

There is no minimum step speed at which stepper motors cannot operate.

Therefore, in theory, the values for RT and C1 can be as large as desired but

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there are practical limitations to these values. The main limitation is the

'leakage' current of electrolytic capacitors.

External CLOCK pulses can also be used to control the driver by passing

them through IC 1 via the "T2" terminal of the circuitboard. Using IC 1 as

an input buffer should eliminate "noise" that could cause the 74194's output

to go into a state where more than one output is HIGH.

If stepping rates greater than 145 per second are needed, capacitor C1 can be

replaced with one of lower value.

A 0.47uF capacitor would give a calculated range of 1.5 to 310 steps per

second.

A 0.33uF capacitor would give a calculated range of 2.2 to 441 steps per

second.

Alternately, capacitor C1 can be removed from the circuitboard and an

external clock source connected at terminal 'T2'. With C1 removed, the

practical limit on the step rate is the motor itself.

In the above items the "calculated" minimum and maximum CLOCK

frequencies are valid for the nominal part values shown. Given the

tolerances of actual components and the leakage currents of electrolytic

capacitors the actual CLOCK rates may be lower or higher.

The direction of the motor can be controlled by another circuit or the parallel

output port of a PC. This will work as long as the voltage at the bases of Q2

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and Q3 can be made lower than 0.7 volts. Additional NPN transistors may

be required to achieve this result, depending on the method used.

If the bases of both Q2 and Q3 are made LOW at the same time the

SN74194 will go into a RESET mode. This will cause the step sequence to

stop and on the next clock pulse pins 15 and 14 will go to a HIGH state.

Making the bases of both Q2 and Q3 LOW at the same time can be used to

reset the SN74194 to its starting position without having to remove the

circuit power.

Each stepper motor will have its own power requirements and as there is a

great variety of motors available. This page cannot give information in this

area. Users of this circuit will have to determine motor phasing and power

requirements for themselves.

Power for the motors can be regulated or filtered and may range from 12 to

24 volts with currents up to 1,000 milliamps depending on the particular

motor.

Motors that operate at voltages lower than 12 volts can also be used with this

driver but a separate supply of 9 to 12 volts will be needed for the control

portion of the circuit in addition to the low voltage supply for the motor.

A LED connected to the output of the LM555 timer (IC 1) flashes at the

CLOCK frequency. If a direction has been selected, The motor will move

one step every time the led turns ON.

26




There is no CLOCK output terminal on the circuitboard but there is a pad to

the right of the LED that can be used if a clock output signal is required.

This pad is connected to pin 3 of the LM555 IC.

The LM7805, positive 5 volt regulator used on the circuitboard can also be

used to provide power for external control circuits. With its tab trimmed off,

the regulator can easily dissipate up to 1 watt.

For a 12 volt supply, external circuits can draw up to 100 milliamps.

For a 24 volt supply, external circuits can draw up to 25 milliamps.

The photo of the circuitboard shows the tab of the 7805 regulator cut off,

this is an option that is available on request.

3.7 74194 Stepper Driver Initialization Notes:

When power is applied to the 74194 Stepper Driver circuit there is a very

short delay before stepping of the outputs can begin. The delay is controlled

by Capacitor C2, resistor R4 and transistor Q1.

The function of the delay is to allow the outputs of IC 2 to be set with pin 12

in a HIGH state and pins 13, 14 and 15 in a LOW state before direction

control becomes active. The delay also prevents IC 1 from oscillating until

IC 2 has been set.

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If the power to the circuit is turned off, there should be a pause of at least 10

seconds before it is reapplied. The pause is to allow capacitor C2 to

discharge through R4 and D2.

If the initialization delay were not used, IC 3 could have: none, any or all of

its outputs in a high state when stepping is started. This would cause the

motor to move incorrectly or not at all during normal operation.

The stepper motor driver is ready to start operation as soon as the initialization

delay is complete.

3.8 Stepper Circuit Board Parts List:

Qty. Part # DigiKey Part # DigiKey Description

1 - IC 1 - LM555CNFS-ND - IC TIMER SINGLE 0-70DEG C 8-DIP

1 - IC 2* - 296-9183-5-ND - IC BI-DIR SHIFT REGISTER 16-DIP

1 - IC 3 - 497-2356-5-ND - IC ARRAY EIGHT DARLINGTON 18 DIP

1 - IC 4 - LM7805ACT-ND - IC REG POS 1A 5V +/-2% TOL TO-220

- - -

3 - Q1, 2, 3 - 2N3904FS-ND - IC TRANS NPN SS GP 200MA TO-92

1 - D1 - 160-1712-ND - LED 3MM GREEN DIFFUSED

1 - D2 - 1N4148FS-ND - DIODE SGL JUNC 100V 4.0NS DO-35

1 - D3 - 1N4001FSCT-ND - DIODE GEN PURPOSE 50V 1A DO41

- - -

4 - R1, 2, 8, 9 - 3.3KQBK-ND - RES 3.3K OHM 1/4W 5% CARBON FILM

3 - R4, 6, 7 - 10KQBK-ND - RES 10K OHM 1/4W 5% CARBON FILM

1 - R3, 5 - 470QBK-ND - RES 470 OHM 1/4W 5% CARBON FILM

- - -

1 - C1 - P5174-ND - CAP 1.0UF 50V ALUM LYTIC RADIAL

2 - C2, 3 - P5177-ND - CAP 4.7UF 50V ALUM LYTIC RADIAL

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1 - C4 - P5168-ND - CAP 470UF 35V ALUM LYTIC RADIAL

- - -

4 - - ED1602-ND - TERMINAL BLOCK 5MM VERT 3POS

CHAPTER FOURConclusions

Stepper motors has played major part in the world of technology, it was and still a

huge invention for science of machine control system, as it was mention it was

used since 1919 at British Army and how it was improved until now days. This

report indicates the very basic of stepper motor and its theory, types and

application. It was a success in terms of getting control of the stepper motor. There

is a lot of room for improvement but the main goal was reached. The stepper motor

moved as seen in the experiment in both direction at different speeds and step pace

like the notes said it should.

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References:[1] [2] [3] [4] [5] [6] [8] [9] Stepping Motors and their Microprocessor

controls, Takashi Kenjo Ed:1, Published 1984.

[7] Industrial Electronics, Colin D. Simpson, Published 2006.

[10] http://home.cogeco.ca/~rpaisley4/Stepper1200Proto.html

[11] WEB: Wikipedia

[12] Stepping Motors Fundamentals, Reston C. etal.

[13] Practical Electric Motor Handbook, Irving G., Ed: 1st 1997.

[14] Rotating Machinery: Practical Solutions to Unbalance and Misalignment,

Robert B. McMillan, 2004.

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http://home.cogeco.ca/~rpaisley4/Stepper1200Proto.html




Appendices: Data Sheet

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[1]

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[2]

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