MAKERERE UNIVERSITY

COLLEGE OF ENGINEERING, DESIGN, ART AND TECHNOLOGY

SCHOOL OF ENGINEERING

PROJECT TITLE

DESIGN,SIMULATION ANDCONTROL OF AN ARTICULAR

DRILLING ARM

ELECTRONICS AND CONTROLS

NAME:KATENDE ALLANREG NO:08/U/519

STUDENT NO:208001106

Project Proposal@2012

DESIGN,SIMULATION ANDCONTROL OF AN ARTICULAR

DRILLING ARM

ELECTRONICS AND CONTROLS

NAME:KATENDE ALLANREG NO:08/U/519

STUDENT NO:208001106

Project Proposal@2012

Project TitleDesign,Simulation& Control of an Articular Drilling Arm

Electronics&Controls.

Supervisors

Supervisor:Dr.Okodi Samuel.MCo-supervisor:Dr.Nabuuma Betty

Release date: February 8, 2012Category: 1 (online)

Edition: First

Comments: Submitted as Partial Fulfillment for the aquisition ofa Bachelors Degree in Mechanical Engineering

Rights: c©Katende Allan @ 2012

Makerere UniversityCollege of Engineering, Design, Art and Technology

School of EngineeringDepartment of Mechanical Engineering

BSc Mechanical Engineering

Ugandawww.tech.mak.ac.ug

Tel: (+256) 784 015 478Alternatively: (+256) 702 129 090E-mail: akatende@tech.mak.ac.ug

Alternative E-mail:akatende@hotmail.com

Contents

List of Figures vi

1 Introduction 1

1.1 Background . . . . . . . . . . . . . . . . . . . . . . . . . . 1

1.2 Problem Statement . . . . . . . . . . . . . . . . . . . . . . 2

1.3 Objectives . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

1.3.1 Main Objective . . . . . . . . . . . . . . . . . . . . 2

1.3.2 Specific Objectives . . . . . . . . . . . . . . . . . . 3

1.4 Justification . . . . . . . . . . . . . . . . . . . . . . . . . . 3

1.5 Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

1.6 Methodology . . . . . . . . . . . . . . . . . . . . . . . . . . 4

1.6.1 Introduction . . . . . . . . . . . . . . . . . . . . . . 4

1.6.2 Literature Review . . . . . . . . . . . . . . . . . . . 4

1.6.3 Design Analysis . . . . . . . . . . . . . . . . . . . . 4

1.6.4 Construction . . . . . . . . . . . . . . . . . . . . . . 4

1.6.5 Software Development . . . . . . . . . . . . . . . . 4

1.6.6 Testing . . . . . . . . . . . . . . . . . . . . . . . . . 4

1.7 Experimental Setup . . . . . . . . . . . . . . . . . . . . . . 5

1.7.1 Introduction . . . . . . . . . . . . . . . . . . . . . . 5

1.7.2 Arduino Duemilanove . . . . . . . . . . . . . . . . 5

1.7.3 Arduino Mega . . . . . . . . . . . . . . . . . . . . . 6

1.7.4 Power supply . . . . . . . . . . . . . . . . . . . . . . 7

1.7.5 L297 Motor driver IC . . . . . . . . . . . . . . . . . 7

1.7.6 Diodes . . . . . . . . . . . . . . . . . . . . . . . . . 7

1.7.7 Resistors . . . . . . . . . . . . . . . . . . . . . . . . 9

1.7.8 Breadboards . . . . . . . . . . . . . . . . . . . . . . 9

1.8 Progress . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

1.8.1 Introduction . . . . . . . . . . . . . . . . . . . . . . 10

2 Literature Review 13

2.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . 13

2.2 Microcontrollers . . . . . . . . . . . . . . . . . . . . . . . . 13

2.2.1 Types of microcontrollers . . . . . . . . . . . . . . . 14

2.2.2 Why we need a Microcontroller . . . . . . . . . . . 14

2.2.3 Arduino . . . . . . . . . . . . . . . . . . . . . . . . . 14

2.2.4 Why Arduino was chosen among all microcon-

trollers . . . . . . . . . . . . . . . . . . . . . . . . . 14

2.2.5 Advantages of microcontrollers . . . . . . . . . . . 16

2.3 Types of Motors . . . . . . . . . . . . . . . . . . . . . . . . 16

2.4 DC Motors . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

2.4.1 Advantages of DC Motors . . . . . . . . . . . . . . 17

2.4.2 Disadvantages of DC Motors . . . . . . . . . . . . 18

2.5 Servo Motors . . . . . . . . . . . . . . . . . . . . . . . . . . 18

2.5.1 Advantages of Servo Motors . . . . . . . . . . . . . 18

2.5.2 Disadvantages of Servo Motors . . . . . . . . . . . 19

2.6 Stepper Motors . . . . . . . . . . . . . . . . . . . . . . . . 20

iii

2.6.1 Characteristics . . . . . . . . . . . . . . . . . . . . 20

2.6.2 Types of Stepper Motors. . . . . . . . . . . . . . . 20

2.6.3 Advantages of Stepper Motors . . . . . . . . . . . . 21

2.6.4 Disadvantages of Stepper Motors . . . . . . . . . . 22

2.6.5 Stepping Modes . . . . . . . . . . . . . . . . . . . . 22

2.7 Motor Controllers . . . . . . . . . . . . . . . . . . . . . . . 23

2.7.1 Types of Motor controllers . . . . . . . . . . . . . . 24

2.8 Proposed Work Plan . . . . . . . . . . . . . . . . . . . . . . 26

2.9 Estimated Budget . . . . . . . . . . . . . . . . . . . . . . . 27

Bibliography 28

List of Figures

1.1 Arduino Duemilanove [16] . . . . . . . . . . . . . . . . . . 5

1.2 Arduino Mega [9] . . . . . . . . . . . . . . . . . . . . . . . 6

1.3 Power Supply [9] . . . . . . . . . . . . . . . . . . . . . . . 7

1.4 L297 Pin configuration [11] . . . . . . . . . . . . . . . . . 7

1.5 Diode [14] . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

1.6 Schematic of the diode [14] . . . . . . . . . . . . . . . . . 8

1.7 Prototyping board [15] . . . . . . . . . . . . . . . . . . . 8

1.8 Resistors [14] . . . . . . . . . . . . . . . . . . . . . . . . . 8

1.9 Experimental Setup . . . . . . . . . . . . . . . . . . . . . . 9

1.10 The L297 and L298 Schematic . . . . . . . . . . . . . . . . 10

1.11 The Prototype of the schematic . . . . . . . . . . . . . . . 11

1.12 The L293 Circuit . . . . . . . . . . . . . . . . . . . . . . . 11

2.1 Arduino Uno [13] . . . . . . . . . . . . . . . . . . . . . . . 15

2.2 DC motor [2] . . . . . . . . . . . . . . . . . . . . . . . . . . 17

2.3 Servo Motor [15] . . . . . . . . . . . . . . . . . . . . . . . 19

2.4 Typical servo motor system [14] . . . . . . . . . . . . . . 19

2.5 Servo motor control [3] . . . . . . . . . . . . . . . . . . . . 19

vi LIST OF FIGURES

2.6 Unipolar stepper motor Windings [18] . . . . . . . . . . . 21

2.7 Unipolar stepper motor [18] . . . . . . . . . . . . . . . . . 21

2.8 Bipolar stepper motor [18] . . . . . . . . . . . . . . . . . . 22

2.9 Proposed Budget . . . . . . . . . . . . . . . . . . . . . . . . 27

CHAPTER 1

Introduction

1.1 Background

This proposal mainly considers the development of motor control cir-

cuits that will be used for precise positioning control of a robot arm.

Robots are general purpose programmable machines that can be used

as substitutes for humans in carrying out some operations such as

machining, spraying, loading, welding, manipulating machine tools,

fastening, parts inspection, sorting, radiation monitoring, and assem-

bling. Their ability to perform such operations makes them suitable

for use in industries such as manufacturing, health care, military and

transportation. However, the potential benefits offered by robots can

only be realized through proper design, construction and integration

of all robot system components. This includes design of suitable me-

chanical manipulators as well as electronics hardware and software to

control them. The inability of the mechanical component of the robot

system to perform tasks without instructions makes control one of the

technological foundations of industrial automation. A robot is able to

carry out the right tasks only when it is given the right instruction. Al-

though this is part of a bigger project, the main focus of this project will

be robot motion control and specifically the design and construction of

motion controllers for an articulated robot arm to enable it carry out

drilling operations.

2 Introduction

1.2 Problem Statement

Many industries today often incur financial obligations as a result of

occupancy of workers in hazardous working environments. This is re-

alized in form of high employee compensation costs, sick leave, and

high insurance premiums. Therefore, where possible there is need to

protect human beings from working in such environments. Addition-

ally, a high need for precision, reliability, consistence in quality and

speed in some industries necessitates adoption of technologies capa-

ble of overcoming human limitations that make it difficult and costly

to achieve the above mentioned goals. For example, human beings of-

ten get bored and tired when they engage in long production runs and

repetitive work cycles. The result is usually poor quality products. In

other cases, tool handling for some machinery is difficult for humans.

Where humans are able to do the job, they are sometimes inconsis-

tent. The effectiveness of these operations and safety of human beings

could be improved through automation. However, while robotics is a

well-developed field and therefore robot systems can be imported into

the country for use in several industries, this approach to technology

transfer would lead to steep learning curves that might lead to un-

wanted outcomes. For example, a general lack of robot troubleshooting

and repair skills among operators would mean long downtimes in case

of failure and consequently poor perception about further adoption of

the technology. One way of solving this problem and therefore support

the technology transfer process is to engage in developing robotics sys-

tems. The skills acquired in thedprocess and the final products will

provide a foundation for interesting industries into considering robot

use in their operations.

1.3 Objectives

1.3.1 Main Objective

The main objective of this project is to design and construct a system

capable of controlling the motion of an articulated drilling arm.

Justification 3

1.3.2 Specific Objectives

1) To design a motor control circuit.

2) To construct the circuit.

3) To develop software that can control the motors.

4) To test the circuit.

1.4 Justification

With the countrys desire to improve on value addition and therefore

the countrys ability to compete globally, there is need to improve the

methods of manufacturing and the value of products. This necessitates

improvement in the level of technology used. Engaging in automation

education projects is one way of building capacity for technology de-

velopment and enhancement. The development of working prototypes

that are capable of solving actual problems will be evidence of improved

capabilities in Ugandas population and will have the potential of acting

as an incentive for further development, and adoption. Documented

procedures will also act as a source of knowledge for subsequent au-

tomation work in Uganda.

1.5 Scope

The project will cover; ectronics design and construction, soft-

ware development which will involve using the Arduino IDE to con-

trol several motors to create an articulating arm. The Arduino IDE is

a like C programming language that makes prototyping easy and ef-

fective,testing,this will involve testing the Hardwafre and software to

make sure that the circuit meets the requirments, we expect also that

the software performs effectively and efficiently.

4 Introduction

1.6 Methodology

1.6.1 Introduction

This section presents the procedures that will be followed in the design

and construction of a system that will be used for precise positioning of

the articulated drilling arm.

1.6.2 Literature Review

This will involve reviewing literature on existing systems and under-

standing how they operate in order to get a broader understanding of

the project.

1.6.3 Design Analysis

This will involve coming up with different simulated concepts of the

circuit in Multism software developed by National Instruments.

1.6.4 Construction

This is the final stage of the design process; it will involve putting to-

gether all the components to make a physical prototype of the circuit.

1.6.5 Software Development

This will involve writing the software that will control the kinematics

of the articulated robot arm.

1.6.6 Testing

This will involve testing the functionality of the constructed circuit,

carrying out performance evaluation and critical adjustments basing

on the kinematics of the robot arm.

Experimental Setup 5

1.7 Experimental Setup

1.7.1 Introduction

This section describes the differents sets of apparatus that are cur-

rently being used during the experimentation process.

1.7.2 Arduino Duemilanove

The Arduino Duemilanove which was released in "2009" is a microcon-

troller board based on the ATmega328 (datasheet). See Fig. 1.1.It has

14 digital input/output pins of which 6 can be used as PWM outputs, 6

analog inputs, a 16 MHz crystal oscillator, a USB connection, a power

jack, an ICSP header, and a reset button. It contains everything needed

to support the microcontroller and you simply connect it to a computer

with a USB cable or power it with a AC-to-DC adapter or battery to get

started. [17]

Figure 1.1: Arduino Duemilanove [16]

6 Introduction

1.7.3 Arduino Mega

The Arduino Mega Fig. 1.2, is a microcontroller board based on the

ATmega1280 (datasheet). It has 54 digital input/output pins (of which

14 can be used as PWM outputs), 16 analog inputs, 4 UARTs (hardware

serial ports), a 16 MHz crystal oscillator, a USB connection, a power

jack, an ICSP header, and a reset button.

Figure 1.2: Arduino Mega [9]

The Arduino Mega can be powered via the USB connection or with an

external power supply. The power source is selected automatically.See

Fig. 1.2. External (non-USB) power can come either from an AC-to-DC

adapter (wall-wart) or battery. The adapter can be connected by plug-

ging a 2.1mm center-positive plug into the board’s power jack. Leads

from a battery can be inserted in the Gnd and Vin pin headers of the

POWER connector. The board can operate on an external supply of 6 to

20 volts. If supplied with less than 7V, however, the 5V pin may supply

less than five volts and the board may be unstable. If using more than

12V, the voltage regulator may overheat and damage the board. The

recommended range is 7 to 12 volts. [9]

The Arduino has a Servo Library that supports up to 48 on servo

motors on the Arduino Mega and 12 servo motors on the Arduino Uno.

Experimental Setup 7

Figure 1.3: Power Supply [9]

Figure 1.4: L297 Pin configura-

tion [11]

1.7.4 Power supply

A power supply unit (PSU) converts mains AC to low-voltage regulated

DC power

1.7.5 L297 Motor driver IC

The L297 Stepper Motor Controller IC generates four phase drive sig-

nals for two phase bipolar and four phase unipolar step motors in

microcomputer-controlled applications. [12]

1.7.6 Diodes

In electronics, a diode is a type of two-terminal electronic component

with nonlinear resistance and conductance.The function of a diode is to

allow an electric current to pass in one direction, while blocking current

in the opposite direction.The figure 1.5 shows the diode and figure 1.6

shows the schematic of the diode.

8 Introduction

Figure 1.5: Diode [14]Figure 1.6: Schematic of the diode [14]

Figure 1.7: Prototyping board [15]Figure 1.8: Resistors [14]

Experimental Setup 9

1.7.7 Resistors

A resistor is a passive two-terminal electrical component that imple-

ments electrical resistance as a circuit element.

1.7.8 Breadboards

A breadboard (protoboard) is a construction base for prototyping of

electronics.

Figure 1.9: Experimental Setup

10 Introduction

1.8 Progress

1.8.1 Introduction

As far as the project is concerned, some work has been done as far

as electronics an controls is conserned,the concepts and circuits built

from the different designs are as illustrated in the literature review.

Though they are still being modified, they can still be briefly discussed

as shown below:

1.8.1.1 The L297 Circuit

Designing the of bipolar stepper motor control circuit driver was done

using national instrument circuit design suite program (Multisim11.1

Education Edition) the components used on an ATmega 328 microcon-

troller, optocoupiers, the L298,L297, capacitors, diodes, and light emit-

ting diodes. The Fig. 1.10 is the designed circuit.The Fig. 1.11 shows

the prototype of the designed circuit in multisim,that is currently being

experimented on.

Figure 1.10: The L297 and L298 Schematic

Progress 11

Figure 1.11: The Prototype of the schematic

Figure 1.12: The L293 Circuit

CHAPTER 2

Literature Review

2.1 Introduction

In this chapter, the literature reviewed includes the, different types of

motors, motor controllers and microcontrollers.

2.2 Microcontrollers

A microcontroller can be considered a self-contained system with a pro-

cessor, memory and peripherals and can be used as an embedded sys-

tem. The majority of microcontrollers in use today are embedded in

other machinery, such as automobiles, telephones, appliances, and pe-

ripherals for computer systems. These are called embedded systems.

While some embedded systems are very sophisticated, many have min-

imal requirements for memory and program length, with no operating

system, and low software complexity. Typical input and output de-

vices include switches, relays, solenoids, LEDs, small or custom LCD

displays, radio frequency devices, and sensors for data such as tem-

perature, humidity, light level etc. Embedded systems usually have no

keyboard, screen, disks, printers, or other recognizable I/O devices of

a personal computer, and may lack human interaction devices of any

kind. [5]

2.2.1 Types of microcontrollers

1) PIC by microchip

2) ATMEGA 328 by Atmel

3) Basic stamp by parallax

4) Propellor Microcontroller from parallax

2.2.2 Why we need a Microcontroller

Micro-controllers have a number of I/O (input/output) pins which can

be set to ’high’ (+5v) or cleared to ’low’ (0v) under software control. The

purpose of a motor controller is to convert the small powered signals

from your micro-controller into more powerful signals that can drive

motors.

2.2.3 Arduino

Arduino is an open-source single-board microcontroller, descendant of

the open-source Wiring platform, designed to make the process of us-

ing electronics in multidisciplinary projects more accessible. The hard-

ware consists of a simple open hardware design for the Arduino board

with an Atmel AVR processor and on-board I/O support.The software

consists of a standard programming language compiler and the boot

loader that runs on the board. The Arduino Uno (Fig. 2.1)is a micro-

controller board based on the ATmega328 (datasheet). It has 14 digital

input/output pins (of which 6 can be used as PWM outputs), 6 analog

inputs, a 16 MHz crystal oscillator, a USB connection, a power jack, an

ICSP header, and a reset button. It contains everything needed to sup-

port the microcontroller; simply connect it to a computer with a USB

cable or power it with an AC-to-DC adapter or battery to get started.

[8]

2.2.4 Why Arduino was chosen among all microcon-

trollers

There are many other microcontrollers and microcontroller platforms

available for physical computing such as Parallax Basic Stamp, Net-

Microcontrollers 15

Figure 2.1: Arduino Uno [13]

media’s BX-24, Phidgets, MIT’s Handyboard, and many others offer

similar functionality. All of these tools take the messy details of micro-

controller programming and wrap it up in an easy-to-use package.[6].

Arduino also simplifies the process of working with microcontrollers,

but it offers some advantage for teachers, students, and interested am-

ateurs over other systems and these include: [7]

1) Inexpensive.Arduino boards are relatively inexpensive compared

to other microcontroller platforms. The least expensive version of

the Arduino module can be assembled by hand, and even the pre-

assembled Arduino modules cost less than 50 dollars.

2) Cross-Platform.The Arduino software runs on Windows, Mac-

intosh OSX, and Linux operating systems. Most microcontroller

systems are limited to Windows

3) Simple,clear programming environment The Arduino pro-

gramming environment is easy-to-use for beginners, yet flexible

enough for advanced users to take advantage of as well. For

teachers, it’s conveniently based on the Processing programming

environment, so students learning to program in that environ-

ment will be familiar with the look and feel of Arduino

4) Open Source and extensible hardwareThe Arduino is based

on Atmel’s ATMEGA8 and ATMEGA168 microcontrollers. The

plans for the modules are published under a Creative Commons

license, so experienced circuit designers can make their own ver-

sion of the module, extending it and improving it. Even relatively

inexperienced users can build the breadboard version of the mod-

ule in order to understand how it works and save money.

5) Open Source and extensible softwareThe Arduino software

and is published as open source tools, available for extension by

experienced programmers. The language can be expanded through

C++ libraries, and people wanting to understand the technical de-

tails can make the leap from Arduino to the AVR C programming

language on which it’s based. Similarly, you can add AVR-C code

directly into your Arduino programs if you want to .

2.2.5 Advantages of microcontrollers

(a) Faster implementation of changes and corrections

(b) Easy visualisation of the process running.

(c) Increased speed.

(d) Increased security.

2.3 Types of Motors

1) Servo Motors

2) Stepper Motors

3) DC Motors

2.4 DC Motors

A direct current (DC) motor is a fairly simple electric motor that uses

electricity and a magnetic field to produce torque, which turns the mo-

tor.Fig. 2.2 At its most simple, a DC motor requires two magnets of

opposite polarity and an electric coil, which acts as an electromagnet.

The repellent and attractive electromagnetic forces of the magnets pro-

vide the torque that causes the DC motor to turn. [1]

DC Motors 17

Figure 2.2: DC motor [2]

2.4.1 Advantages of DC Motors

1) High output power relative to motor size and weight.

2) Encoder determines accuracy and resolution.

3) High efficiency. Can approach 90 percent at light loads.

4) High torque to inertia ratio. Can rapidly accelerate loads.

5) Has reserve power. 2-3 times continuous power for short periods.

6) Has reserve torque. 5-10 times rated torque for short periods.

7) Motor stays cool. Current draw proportional to load.

8) Resonance and vibration free operation.

2.4.2 Disadvantages of DC Motors

1) Higher cost.

2) Complex. Requires encoder.

3) Peak torque is limited to a 1 percent duty cycle.

4) Motor can be damaged by sustained overload.

5) Requires tuning to stabilize feedback loop.

6) Motor develops peak power at higher speeds. Gearing often re-

quired.

2.5 Servo Motors

A Servo is a small device that incorporates a three wire DC motor, a

gear train, a potentiometer, an integrated circuit, and an output shaft

bearing. Of the three wires that stick out from the motor casing, one is

for power, one is for ground, and one is a control input line. The shaft

of the servo can be positioned to specific angular positions by sending

a coded signal. As long as the coded signal exists on the input line,

the servo will maintain the angular position of the shaft. If the coded

signal changes, then the angular position of the shaft changes.From

Fig. 2.5,the work will begin with PLC Sending Position command, the

signal plus or analog to the Position controller in the servo Dive power

of the Position controller will add to the Amplifier power to the motor

to the motor rotation. [6]

2.5.1 Advantages of Servo Motors

1) They work well for velocity control.

2) Servo motors also require low power usage, Repeatability and ac-

curacy are very easy to achieve with servos.

3) High and precise speed operation and control. As speed increases,

the torque of the servo remains constant, making it better than

the stepper at high speeds. They run 3-4 times faster than a step-

per.

4) They have a control loop to check what state the motor is in. The

control loop in a servo motor is constantly checking to see if the

motor is on the right path and, if it is not, it makes the necessary

Servo Motors 19

Figure 2.3: Servo Motor [15]

Figure 2.4: Typical servo motor sys-

tem [14]

Figure 2.5: Servo motor control [3]

adjustments. For example if a heavy load is placed on the motor,

the driver will increase the current to the motor coil as it attempts

to rotate the motor. Basically, there is no out-of-step condition

however too heavy a load may cause an error. [4]

2.5.2 Disadvantages of Servo Motors

1) Higher cost relatively more expensive than stepper motors.

2) Require tuning of control loop parameters

3) More maintenance due to brushes on brushed DC motors

4) Feedback is required

2.6 Stepper Motors

A stepper motor is basically an electromechanical device which con-

verts electrical pulses into discrete mechanical movements. The shaft

or spindle of a stepper motor rotates in discrete step increments when

electrical command pulses are applied to it in the proper sequence. The

motors rotation has several direct relationships to these applied input

pulses. The sequence of the applied pulses is directly related to the di-

rection of motor shafts rotation. The speed of the motor shafts rotation

is directly related to the frequency of the input pulses and the length of

rotation is directly related to the number of input pulses applied. [7]

2.6.1 Characteristics

1) Holding Torque. Steppers have very good low speed and holding

torque. Steppers are usually rated in terms of their holding force

and can even hold a position (to a lesser degree) without power

applied, using magnetic detent torque. [7]

2) Open loop positioning. Perhaps the most valuable and inter-

esting feature of a stepper is the ability to position the shaft in

fine predictable increments, without need to query the motor as

to its position. Steppers can run open-loop without the need for

any kind of encoder to determine the shaft position. [7]

2.6.2 Types of Stepper Motors.

Stepper Motors come in a variety of sizes, and strengths, from tiny

floppy disk motors, to huge machinery steppers. Three basic types of

stepper motors include the permanent magnet motor, the variable re-

luctance motor, and the hybrid motor, which is a combination of the

previous two. [7]

1) Unipolar motors.A Unipolar stepper motor has one winding with

center tap per phase. Each section of windings is switched on

for each direction of magnetic field. 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, the

Stepper Motors 21

Figure 2.6: Unipolar stepper motor

Windings [18] Figure 2.7: Unipolar stepper mo-

tor [18]

center tap 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. [7]

2) Bipolar motors.Bipolar permanent magnet and hybrid motors

are constructed with exactly the same mechanism as is used on

unipolar motors, but the two windings are wired more simply,

with no center taps. Thus, the motor itself is simpler but the drive

circuitry needed to reverse the polarity of each pair of motor poles

is more complex .Fig. 2.8 [7]

2.6.3 Advantages of Stepper Motors

1) Inexpensive relative to other motion control systems.

2) Needs no feedback. The motor is also the position transducer.

3) Stable. Can drive a wide range of frictional and inertial loads.

4) Plug and play. Easy to setup and use.

5) Safe. If anything breaks, the motor stops.

6) Excellent low speed torque. Can drive many loads without gear-

ing.

7) Excellent repeatability. Returns to the same location accurately.

8) Overload safe. Motor cannot be damaged by mechanical overload.

Figure 2.8: Bipolar stepper motor [18]

2.6.4 Disadvantages of Stepper Motors

1) Low efficiency. Motor draws substantial power regardless of load.

2) Torque drops rapidly with speed (torque is the inverse of speed).

3) Prone to resonance. Requires micro-stepping to move smoothly.

4) No feedback to indicate missed steps.

5) Low torque to inertia ratio. Cannot accelerate loads very rapidly.

6) Motor gets very hot in high performance configurations.

7) Motor will not pick up after momentary overload.

8) Motor is audibly very noisy at moderate to high speeds.

2.6.5 Stepping Modes

1) WaveDrive This method of stepping the motor energizes one phase

at a time. This method is rarely used and most likely will not be

on modern drivers. This method is very inefficient and produces

less torque than other methods. [7]

Motor Controllers 23

2) Full step This method of stepping the motor energizes both phases

constantly to achieve full rated torque at all positions of the mo-

tor. If a stepper motor has 200 steps, one pulse equals one step.

So, 200 pulses from the NC computer results in 360 degrees of mo-

tor shaft rotation. A uni-polar stepper motor driver operating in

full step mode energizes a single phase. A bipolar stepper motor

driver energizes both coils to make a full step. [7]

3) Half step The Half step mode energizes a single coil then two

coils then one again. Alternating between energizing a single

phase and both phases together gives the motor its higher res-

olution. A 200 step stepper motor operating in half step mode

would have 400 positions, twice the normal resolution. However,

the torque will vary depending on the step position because at

times a single phase will be energizes while at other times both

phases will be energized. Higher end drivers compensate by in-

creasing the current through the single coil when a single coil is

energized. This makes up for the loss in torque, making the half

step mode very stable. [7]

4) Microstepping The micro-stepping mode is the most complex of

all the stepping modes. That is why some stepper drivers only

offer full and half step modes. Micro-stepping is when the cur-

rent applied to each winding is proportional to a mathematical

function, providing a fraction of a full step. The most common

divisions are 1/4th, 1/8th, 1/10th, etc. However, there are some

drivers that provide up to 1/256th of a full step. Micro-stepping

provides greater resolution and smoother motor operation. This is

very advantageous as it reduces the need for mechanical gearing

when trying to achieve high resolution. However, micro-stepping

can affect the repeatability of the motor.

2.7 Motor Controllers

A motor controller is a device or group of devices that serves to govern

in some predetermined manner the performance of an electric motor.

2.7.1 Types of Motor controllers

1) Motor starters A small motor can be started by simply plug-

ging it into an electrical receptacle or by using a switch or cir-

cuit breaker. A larger motor requires a specialized switching unit

called a motor starter or motor contactor. When energized, a di-

rect on line (DOL) starter immediately connects the motor termi-

nals directly to the power supply.

Reduced-voltage, star-delta or soft starters connects the motor

to the power supply through a voltage reduction device and in-

creases the applied voltage gradually or in steps. In smaller sizes

a motor starter is a manually-operated switch; larger motors, or

those requiring remote or automatic control, use magnetic con-

tactors. Very large motors running on medium voltage power

supplies (thousdands of volts) may use power circuit breakers as

switching elements.

A direct on line (DOL) or across the line starter applies the full

line voltage to the motor terminals. This is the simplest type of

motor starter. A DOL motor starter also contain protection de-

vices, and in some cases, condition monitoring. Smaller sizes of

direct on-line starters are manually operated; larger sizes use an

electromechanical contactor (relay) to switch the motor circuit.

Solid-state direct on line starters also exist.

A direct on line starter can be used if the high inrush current of

the motor does not cause excessive voltage drop in the supply cir-

cuit. The maximum size of a motor allowed on a direct on line

starter may be limited by the supply utility for this reason. For

example, a utility may require rural customers to use reduced-

voltage starters for motors larger than 10 kW.

DOL starting is sometimes used to start small water pumps, com-

pressors, fans and conveyor belts. In the case of an asynchronous

motor, such as the 3-phase squirrel-cage motor, the motor will

draw a high starting current until it has run up to full speed.

This starting current is typically 6-7 times greater than the full

load current. To reduce the inrush current, larger motors will

have reduced-voltage starters or variable speed drives in order to

minimise voltage dips to the power supply.

A reversing starter can connect the motor for rotation in either

direction. Such a starter contains two DOL circuits,one for clock-

wise operation and the other for counter-clockwise operation, with

mechanical and electrical interlocks to prevent simultaneous clo-

Motor Controllers 25

sure.[6] For three phase motors, this is achieved by transposing

any two phases. Single phase AC motors and direct-current mo-

tors require additional devices for reversing rotation.

2) Intelligent controllers An Intelligent Motor Controls (IMC) uses

a microprocessor to control power electronic devices used for mo-

tor control. IMCs monitor the load on a motor and accordingly

match motortorque to motor load. This is accomplished by reduc-

ing the voltage to the AC terminals and at the same time lowering

current and voltage ampere reactive This can provide a measure

of energy efficiency improvement for motors that run under light

load for a large part of the time, resulting in less heat, noise, and

vibrations generated by the motor. [10]

2.8 Proposed Work Plan

Estimated Budget 27

2.9 Estimated Budget

Figure 2.9: Proposed Budget

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[3] Servo motor. December 2011.

[4] Super Tech & Associates. Computer controlled 3 axis wood router.

September 2009.

[5] Servo City. What is a microcontroller? January 2012.

[6] Servo City. What is a sevo? January 2012.

[7] Servo City. What is a stepper motor? January 2012.

[8] M. Uchiyama D. Sato. Dexterous motion design for dd parallel

robot. Journal of Robotics Research, pages 26–35, 2005.

[9] Josh Adams & Harold Molle John David Warren. Arduino

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[10] Thyge Knüppel. Structural analysis for fault detection and isola-

tion in electrical distribution systems. April 2008.

[11] Sgs Thomson Micro-Electronics. L297 stepper motor controller.

Application Note, pages 17–18, 2011.

[12] Sgs Thomson Micro-Electronics. L297 stepper motor controller.

Application Note, pages 1–5, 2011.

[13] Manuel Odendahl. Arduino physical computing for

bastler,designers and geeks. pages 15–16, 2011.

[14] Cathleen Shamieh. Electronics for dummies. pages 5–7, 2011.

[15] Cathleen Shamieh. Electronics for dummies. pages 2–3, 2011.

[16] Dale Wheat. Arduino internals. pages 1–10, 2011.

[17] Carl E. Wieman and Leo Hollberg. Using diode lasers for atomic

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[18] Padmaraje Yedamale. Stepper motor microstepping with

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www.tech.mak.ac.ug

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