english for mechatronics engineering (1)

7/27/2019 English for Mechatronics Engineering (1)

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English for Mechatronics Engineering Page 1

TABLE OF CONTENTS

TABLE OF CONTENTS ....................................................................................... 1PART 1: DIGITAL LOGIC .................................................................................. 3

CHAPTER 1: INTRODUCTION ................................................................................. 3LOGIC GATES .......................... ........................... ........................... ............................ .... 3

CHAPTER 2: APPLICATIONS OF LOGIC GATES ................................................ 8INTEGRATED CIRCUIT .......................................... ........................ .............................. 8APPLICATIONS ........................ ........................... ........................... ............................ .... 8

CHAPTER 3: BASIC ELECTRONIC COMPONENTS .......................................... 10RESISTANCE ............................ ........................... ........................... ........................... ... 10CAPACITOR ................................................................................................................. 11DIODE ........................................................................................................................... 13LIGHT EMITTING DIODE ......................... ........................... ........................... ............ 15BIPOLAR JUNCTION TRANSISTOR (BJT) ................................................ ................ 18

CHAPTER 4: MICROCONTROLLER ..................................................................... 20INTRODUCTION .......................... ........................... ............................ ......................... 20IMPORTANT FEATURES .......................... ........................... ........................... ............ 21POWER SUPPLY CIRCUIT ........................ ........................... ........................... ............ 22HOW TO START WORKING? ....................... ............................ ........................... ....... 23

PART 2: MECHANICAL ACTUATION SYSTEMS ....................................... 26CHAPTER 1: INTRODUCTION ............................................................................... 26

MECHANISMS ............................................................................................................. 26TYPES OF MOTION .......................... ........................... ........................... ..................... 27DEGREE OF FREEDOM............................. ........................... ........................... ............ 27

CHAPTER 2: CAMS .................................................................................................. 29ECCENTRIC CAM ........................ ........................... ............................ ......................... 29


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DROP CAM .......................... ........................... ............................ ........................... ....... 31FLAT CAM ........................... ........................... ............................ ........................... ....... 32

CHAPTER 3: GEARS ................................................................................................. 34SPUR GEAR .............................. ........................... ........................... ........................... ... 35HELICAL GEAR ........................... ........................... ............................ ......................... 36DOUBLE HELICAL GEAR ................................. ........................... ........................... ... 37BEVEL GEAR ........................... ........................... ........................... ............................ .. 38WORM GEAR ........................... ........................... ........................... ............................ .. 39RACK AND PINION .......................... ........................... ........................... ..................... 41GEAR TRAIN ............................ ........................... ........................... ........................... ... 42

CHAPTER 4: BELT AND CHAIN DRIVES ............................................................. 44PROS AND CONS .............................. ........................... ........................... ..................... 44FLAT BELTS ........................ ........................... ............................ ........................... ....... 45ROUND BELTS............................................................................................................. 46VEE BELTS .......................... ........................... ............................ ........................... ....... 47TIMING BELTS ............................................................................................................ 48CHAIN DRIVE .......................... ........................... ........................... ............................ .. 49CHAINS VERSUS BELTS .......................... ........................... ........................... ............ 50

CHAPTER 5: BEARINGS .......................................................................................... 51DEEP-GROOVE ........................ ........................... ........................... ............................ .. 52FILLING - SLOT ........................... ........................... ............................ ......................... 53ANGULAR CONTACT .......................... ............................ ........................... ................ 54DOUBLE-ROW ......................... ........................... ........................... ............................ .. 55SELF-ALIGNING .......................... ........................... ............................ ......................... 56STRAIGHT-ROLLER BEARING ......................... ........................... ........................... ... 58TAPER ROLLER ........................... ........................... ............................ ......................... 59NEEDLE ROLLER ............... ........... ......................... ..................................................... 61


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PART 1: DIGITAL LOGIC

CHAPTER 1: INTRODUCTION

Many control systems are concerned with setting events in motion or stopping them

when certain conditions are met. For example, with domestic washing machine, the heater

is only switched on when there is water in the drum and it is to the prescribed level. Such

control involves digital signals where there are only two possible signal levels. Digital

circuitry is the basis of digital computers and microprocessor controlled systems. There

are two input signals which are either1 or0 signals and an output signal which is 1 or0

signal. The controller is here programmed to only give a 1 output if both the input signals

are 1. Such an operation is said to be controlled by a logic gate .Logic gate is the basic

building blocks for digital electronic circuits. The term combinational logic is used for the

combining of two or more basic logic gates to form a required function.

LOGIC GATES

Logic gates are the basic components in digital electronics. They are used to create

digital circuits and even complex integrated circuits. For example, complex integrated

circuits may bring already a complete circuit ready to be used microprocessors and

microcontrollers are the best example but inside them they were projected using several

logic gates. In this tutorial we will teach you everything you need to know about logic

gates, with several examples.

As you may already know, digital electronics accept only two numbers, 0 and 1.

Zero means a 0 V voltage, while 1 means 5 V or 3.3 V on newer integrated circuits. You

can think 0 and 1 as a light bulb turned off or on or as a switch turned off or on.

a. AND gate: Suppose we have a gate giving a high output only when both input A and

input B are high; for all other conditions it gives a low output. This is an AND logic gate.

We can visualize the AND gate as an electric circuit involving two switches in series.

Only when switch A and B are closed, there is a current.


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(a) Represented by switches (b) Symbols

The relationship between the inputs and the outputs of an AND gate can be expressed

in the form of an equation, called Boolean equation. The Boolean equation for the AND

gate is written as

A . B = Y

An example is a burglar alarm in which it gives an output, the alarm sounding, when

the alarm is switched on and when a door is opened to active a sensor.

The relationships between inputs to a logic gate and the outputs can be tabulated in a

form known as truth table. This specifies the relationships between the inputs and outputs.

We can write the truth table as

A B Output

0 0

0 11 0

1 1

b. OR gate: An OR gate with inputs A and B gives an output of a 1 when A or B is 1. We

can visualize such a gate as an electric circuit involving two switches in parallel. When

switch A or B is closed, then there is a current. OR gates can also have more than inputs.

We can write the Boolean equation for an OR gate as:

A + B = Y


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(a) Represented by switches (b) Symbols

A B Output

0 0

0 1

1 0

1 1

c. NOT gate: a NOT gate has just one input and one output, giving a 1 output when the

input is 0 and a 0 when input is 1. The NOT gate gives an output which is the inversion of

the input and is called an inverter. The 1 representing NOT actually symbolizes logic

identity, i.e. no operation, and the inversion is depicted by the circle on the output. Thus, if

we have a digital input which varies with time, the output variation with time is the

inverse.

The Boolean equation describing the NOT gate is

A Y

A bar over a symbol is used to indicate that the inverse, or complement, is being taken;

thus the bar over the A indicates that the output Y is the inverse value of A.

d. NAND gate: The NAND gate can be considered as a combination of an AND gate

followed by a NOT gate. Thus when input A is 1 and input B is 1, there is an output of 0,

all other inputs giving an output of 1.

Input Output

1

0


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The NAND gate is just the AND gate truth table with the outputs inverted. An alternative

way of considering the gate is as an AND gate with a NOT gate applied to invert both the

inputs before they reach the AND gate. The figure below shows the symbols used for the

NAND gate, being the AND symbol followed by the circle to indicate inversion.

The Boolean equation describing the NAND gate is:

A B Y

The following is the truth table:

A B Output

0 0

0 1

1 0

1 1

e. NOR gate: The NOR gate can be considered as a combination of an OR gate followed

by a NOT gate. Thus when input A or input B is 1 there is an output of 0. It is just the ORgate with the outputs inverted. An alternative way of considering the gate is as an OR gate

with a NOT gate applied to invert both the inputs before they reach the OR gate. The

figure below shows the symbols used for the NOR gate; it is the OR symbol followed by

the circle to indicate inversion.

The Boolean equation for NOR gate is:

A B Y


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The following is the truth table for the NOR gate.

A B Output

0 0

0 1

1 0

1 1

f. XOR gate: XOR stands forexclusive OR. XOR gate compares two values and if they

are different its output will be 1. XOR operation is represented by the symbol . So Y

= A B is the Boolean equation for the XOR gate.

The following is the truth table for the XOR gate.

A B Output

0 0

0 1

1 0

1 1

g. XNOR gate: XNOR stands for exclusive NOR and is an XOR gate with its output

inverted. So, its output is at 1 when the inputs have the same value and 0 when they

are different. XNOR operation is represented by the symbol (). The Boolean equation for

XNOR gate is:

A () B = Y


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CHAPTER 2: APPLICATIONS OF LOGIC GATES

INTEGRATED CIRCUIT

Logic gates are available as integrated circuits. The different manufacturers have

standardized their numbering schemes so that the basic part numbers are the same

regardless of the manufacturer. For example, Fig. 1(a) shows the gate systems available in

integrated circuit 7408; it has four two-input AND gates and is supplied in a 14-pin

package. Power supply connections are made to pins 7 and 14, these supplying the

operating voltage for all four AND gates. In order to indicate at which end of the package

pin 1 starts, a notch is cut between pins 1 and 14. Integrated circuit 7411 has three AND

gates which each having three inputs; integrated circuit 7421 has two AND gates with

each having four inputs. Figure 1(b) shows the gate systems available in integrated circuit

7402. This has four two-input NOR gates in a 14-pin package, power connections being to

pins 7 and 14. Integrated circuit 7427 has three gates with each having three inputs.

Figure 1: Integrated circuit (a) 7408, (b) 7402

APPLICATIONS

1. Digital comparator

A digital comparator is used to compare two digital words to determine if they are

exactly equal. The two words are compared bit by bit and a 1 output given if the words are

equal. To compare the equality of two bits, an XOR gate can be used; if the bits are both 0

or both 1 the output is 0, and if they are not equal the output is a 1. To obtain a 1 output

when the bits are the same we need to add a NOT gate, this combination of XOR and

NOT being termed an XNOR gate. To compare each of the pairs of bits in two words we


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need an XNOR gate for each pair. If the pairs are made up of the same bits then the output

from each XNOR gate is a 1. We can then use an AND gate to give a 1 output when all the

XNOR outputs are ones. Figure 2 shows the system.

A3

B3

A2

B2

A1

B1

A0

B0

A = B

Figure 2: Comparator

2. Coder

The Fig. 3 shows a simple system by which a controller can send a coded digital signal

to a set of traffic lights so that the code determines which light, RED, AMBER OR

GREEN, will be turned on. To illuminate the RED light we might use the transmitted

signal A = B = 0, for the AMBER light A = 0, B = 1 and for the GREEN light A = 1, B =

0. We can switch on the lights using these codes by using three AND gates and two NOT

gates.

AMBER

A

RED

B

GREEN

Figure 3: The traffic lights


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CHAPTER 3: BASIC ELECTRONIC COMPONENTS

RESISTANCE

The electrical resistance of an object is a measure of its opposition to the passage of a

steady electric current. An object of uniform cross section will have a resistance

proportional to its length and inversely proportional to its cross-sectional area, and

proportional to the resistivity of the material.

Discovered by Georg Ohm in the late 1820s, electrical resistance shares some

conceptual parallels with the mechanical notion of friction. The SI unit of electrical

resistance is the ohm, symbol . Resistance's reciprocal quantity is electrical conductance

measured in Siemens, symbol S.

The resistance of a resistive object determines the amount of current through the object

for a given potential difference across the object, in accordance with Ohms laws:

VI

R

where

R is the resistance of the object, measured in ohms, equivalent to Js/C2

Vis the potential difference across the object, measured in volts

Iis the current through the object, measured in amperes

We all know that voltmeter and ammeter are used for measuring the voltage and the

current respectively. For the resistance, the meters that use to measure it is the ohmmeter.

But what if we don't have an ohmmeter to use?

Color coding system for resistors consists of three colors to indicate the resistance

value in ohms of a certain resistor, sometimes the fourth color indicate the tolerance value

of the resistor. By reading the color coded in correct order and substituting the correct

value of each corresponding color coded as shown in the table below, you can

immediately tell all you need to know about the resistor. Each color band represents a

number and the order of the color band will represent a number value. The first 2 color

bands indicate a number. The 3rd

color band indicates the multiplier or in other words the

number of zeros. The fourth band indicates the tolerance of the resistor. In most cases,

there are 4 color bands. However, certain precision resistors have 5 bands or have the

values written on them, refining the tolerance value even more.
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Color1

st

Band

2nd

Band

3rd

Band

4th

band

(multiplier)

5th

Band

(Tolerance)

Black 0 0 0 100

Brown 1 1 1 101

Red 2 2 2 102

Orange 3 3 3 103

Yellow 4 4 4 104

Green 5 5 5 105

Blue 6 6 6 106

Violet 7 7 7 107

Gray 8 8 8 108

White 9 9 9 109

CAPACITOR

A capacitor (formerly known as condenser) is a passive two-terminal electrical

component used to store energy in an electric field. The forms ofpractical capacitors vary

widely, but all contain at least two electrical conductors separated by a dielectric

(insulator); for example, one common construction consists of metal foils separated by a

thin layer of insulating film. Capacitors are widely used as parts of electrical circuits in

many common electrical devices.

When there is a potential difference (voltage) across the conductors, a static electric

field develops across the dielectric, causing positive charge to collect on one plate and

negative charge on the other plate. Energy is stored in the electrostatic field. An ideal

capacitor is characterized by a single constant value, capacitance, measured in farads. This

is the ratio of the electric charge on each conductor to the potential difference between

them.
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The capacitance is greatest when there is a narrow separation between large areas of

conductor; hence capacitor conductors are often called "plates," referring to an early

means of construction. In practice, the dielectric between the plates passes a small amount

of leakage current and also has an electric field strength limit, resulting in a breakdown

voltage, while the conductors and leads introduce an undesired inductance and resistance.

Capacitors are widely used in electronic circuits for blocking direct current while

allowing alternating current to pass, in filter networks, for smoothing the output of power

supplies, in the resonant circuits that tune radios to particular frequencies and for many

other purposes.

A capacitor consists of two conductors separated by a non-conductive region. The non-

conductive region is called the dielectric. In simpler terms, the dielectric is just an

electrical insulator. Examples of dielectric mediums are glass, air, paper, vacuum, and

even a semiconductor depletion region chemically identical to the conductors. A capacitor

is assumed to be self-contained and isolated, with no net electric charge and no influence

from any external electric field. The conductors thus hold equal and opposite charges on

their facing surfaces, and the dielectric develops an electric field. In SI units, a capacitance

of one farad means that one coulomb of charge on each conductor causes a voltage of one

volt across the device.

The capacitor is a reasonably general model for electric fields within electric circuits.

An ideal capacitor is wholly characterized by a constant capacitance C, defined as the ratio

of charge Q on each conductor to the voltage Vbetween them:

QC

V
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example, a diode with a Zener breakdown voltage of 3.2 V will exhibit a voltage drop of

very nearly 3.2 V across a wide range of reverse currents. The Zener diode is therefore

ideal for applications such as the generation of a reference voltage (e.g. for an amplifier

stage), or as a voltage stabilizer for low-current applications.

A diode bridge is an arrangement of four (or more) diodes in a bridge circuit

configuration that provides the same polarity of output for either polarity ofinput. When

used in its most common application, for conversion of an alternating current (AC) input

into direct current a (DC) output, it is known as a bridge rectifier. A bridge rectifier

provides full-wave rectification from a two-wire AC input, resulting in lower cost and

weight as compared to a rectifier with a 3-wire input from a transformer with a center-

tapped secondary winding.

The essential feature of a diode bridge is that the polarity of the output is the same

regardless of the polarity at the input. The diode bridge circuit is also known as the Graetz

circuitafter its inventor, physicist Leo Graetz.

HW: Describing the basic operation of Diode Bridge?
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LIGHT EMITTING DIODE

A light-emitting diode (LED) is a semiconductor light source. LEDs are used as

indicator lamps in many devices and are increasingly used for otherlighting. Introduced as

a practical electronic component in 1962, early LEDs emitted low-intensity red light, but

modern versions are available across the visible, ultraviolet, and infrared wavelengths,with very high brightness.

When a light-emitting diode is forward-biased (switched on), electrons are able to

recombine with electron holes within the device, releasing energy in the form of photons.

This effect is called electroluminescence and the color of the light (corresponding to the

energy of the photon) is determined by the energy gap of the semiconductor. LEDs are

often small in area (less than 1 mm2), and integrated optical components may be used to

shape its radiation pattern. LEDs present many advantages over incandescent light sourcesincluding lower energy consumption, longer lifetime, improved robustness, smaller size,

and faster switching. LEDs powerful enough for room lighting are relatively expensive

and require more precise current and heat management than compact fluorescent lamp

sources of comparable output.

Light-emitting diodes are used in applications as diverse as replacements for aviation

lighting, automotive lighting (in particular brake lamps, turn signals, and indicators) as

well as in traffic signals. LEDs have allowed new text, video displays, and sensors to bedeveloped, while their high switching rates are also useful in advanced communications

technology. Infrared LEDs are also used in the remote control units of many commercial

products including televisions, DVD players, and other domestic appliances.
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A seven-segment display (SSD), orseven-segment indicator, is a form of electronic

display device for displaying decimal numerals that is an alternative to the more complex

dot-matrix displays. Seven-segment displays are widely used in digital clocks, electronic

meters, and other electronic devices for displaying numerical information.

A seven segment display, as its name indicates, is composed of seven elements.

Individually on or off, they can be combined to produce simplified representations of the

Arabic numerals. Often the seven segments are arranged in an oblique (slanted)

arrangement, which aids readability. In most applications, the seven segments are of

nearly uniform shape and size (usually elongated hexagons, though trapezoids and

rectangles can also be used), though in the case of adding machines, the vertical segments

are longer and more oddly shaped at the ends in an effort to furtherenhance readability.

In a simple LED package, typically all of the cathodes (negative terminals) or all of the

anodes (positive terminals) of the segment LEDs are connected and brought out to a

common pin; this is referred to as a "common cathode" or "common anode" device. Hence

a 7-segment plus decimal point package will only require nine pins (though commercial

products typically contain more pins, and/or spaces where pins would go, in order to

match industry standard pinouts).

Integrated displays also exist, with single or multiple digits. Some of these integrated

displays incorporate their own internal decoder, though most do not each individual

LED is brought out to a connecting pin as described. Multiple-digit LED displays as used

in pocket calculators and similar devices used multiplexed displays to reduce the number

of IC pins required to control the display. For example, all the anodes of the A segments

of each digit position would be connected together and to a driverpin, while the cathodes

of all segments for each digit would be connected. To operate any particular segment of
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any digit, the controlling integrated circuit would turn on the cathode driver for the

selected digit, and the anode drivers for the desired segments; then after a short blanking

interval the next digit would be selected and new segments lit, in a sequential fashion.

Often in pocket calculators the digit drive lines would be used to scan the keyboard as

well, providing further savings; however, pressing multiple keys at once would produce

odd results on the multiplexed display.

An LED matrixor LED display is a large, low-resolution form of dot matrix display,

useful both for industrial and commercial information displays as well as for hobbyist

humanmachine interfaces. It consists of a 2-D matrix of LEDs with their cathodes joined

in rows and their anodes joined in columns (or vice versa). By controlling the flow of

electricity through each row and column pair it is possible to control each LED

individually. By scanning across rows, quickly flashing the LEDs on and off, it is possible

to create characters or pictures to display information to the user. By varying the pulse rate

per LED, the display can approximate levels of brightness. Multi-colored LEDs or RGB-

colored LEDs permit use as a full-color image display. The refresh rate is typically fast

enough to prevent the human eye from detecting the flicker.

A dot matrix display is a display device used to display information on machines,

clocks, railway departure indicators and many other devices requiring a simple display

device of limited resolution. The display consists of a matrix of lights or mechanical

indicators arranged in a rectangular configuration (other shapes are also possible, although

not common) such that by switching on or off selected lights, text or graphics can be

displayed. A dot matrix controller converts instructions from a processor into signals

which turns on or off lights in the matrix so that the required display is produced.
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BIPOLAR JUNCTION TRANSISTOR (BJT)

A bipolar junction transistor (BJT) is a three-terminal electronic device constructed of

doped semiconductor material and may be used in amplifying or switching applications.

Bipolartransistors are so named because their operation involves both electrons and holes.

Charge flow in a BJT is due to bidirectional diffusion of charge carriers across a junction

between two regions of different charge concentrations. This mode of operation is

contrasted with unipolar transistors, such as field-effect transistors, in which only one

carrier type is involved in charge flow due to drift. By design, most of the BJT collector

current is due to the flow of charges injected from a high-concentration emitter into the

base where they are minority carriers that diffuse toward the collector, and so BJTs are

classified as minority-carrierdevices.

NPN TYPE

NPN is one of the two types of bipolar transistors, consisting of a layer of P-doped

semiconductor (the "base") between two N-doped layers. A small current entering the base

is amplified to produce a large collector and emitter current. That is, an NPN transistor is

"on" when its base is pulled high relative to the emitter.

Most of the NPN current is carried by electrons, moving from emitter to collector as

minority carriers in the P-type base region. Most bipolar transistors used today are NPN,

because electron mobility is higher than hole mobility in semiconductors, allowing greater

currents and faster operation. A mnemonic device for the remembering the symbol for an

NPN transistor is notpointing in, based on the arrows in the symbol and the letters in the

name. That is, the NPN transistor is the BJT transistor that is "not pointing in".
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PNP TYPE

The other type of BJT is the PNP, consisting of a layer of N-doped semiconductor

between two layers of P-doped material. A small current leaving the base is amplified in

the collector output. That is, a PNP transistor is "on" when its base is pulled low relative to

the emitter.

The arrows in the NPN and PNP transistor symbols are on the emitter legs and point in

the direction of the conventional current flow when the device is in forward active mode.

A mnemonic device for the remembering the symbol for a PNP transistor ispointing in

(proudly), based on the arrows in the symbol and the letters in the name. That is, the PNP

transistor is the BJT transistor that is "pointing in".

P-N-P Transistor
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CHAPTER 4: MICROCONTROLLER

INTRODUCTION

When we have to learn about a new computer we have to familiarize about the

machine capability we are using, and we can do it by studying the internal hardware

design (devices architecture), and also to know about the size, number and the size of the

registers.

A microcontroller is a single chip that contains the processor (the CPU), non-volatile

memory for the program (ROM or flash), volatile memory for input and output (RAM), a

clock and an I/O control unit. Also called a "computer on a chip," billions of

microcontroller units (MCUs) are embedded each year in a myriad of products from toys

to appliances to automobiles. For example, a single vehicle can use 70 or more

microcontrollers.

The Intel MCS-51 (commonly referred to as 8051) is a Harvard architecture, single

chip microcontroller (C) series which was developed by Intel in 1980 for use in

embedded systems. Intel's original versions were popular in the 1980s and early 1990s.

While Intel no longer manufactures the MCS-51, binary compatible derivatives remain

popular today. In addition to these physical devices, several companies also offer MCS-51

derivatives as IP cores for use in FPGAs or ASICs designs.

Intel's original MCS-51 family was developed using NMOS technology, but later

versions, identified by a letter C in their name (e.g., 80C51) used CMOS technology and

consumed less power than their NMOS predecessors. This made them more suitable for

battery-powered devices.
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IMPORTANT FEATURES

The 8051 architecture provides many functions (CPU, RAM, ROM, I/O, interrupt logic,

timer, etc.) in a single package

8-bit ALU, Accumulator and 8-bit Registers; hence it is an 8-bit microcontroller 8-bit databus It can access 8 bits of data in one operation 16-bit address bus It can access 216 memory locations 64 KB (65536 locations)

each of RAM and ROM

On-chip RAM 128 bytes (data memory) On-chip ROM 4 kByte (program memory) Four byte bi-directional input/output port UART (serial port) Two 16-bit Counter/timers Two-level interrupt priority Powersaving mode (on some derivatives)For any electronics project the power supply plays a very important role in its proper

functioning. In this project we are using external A.C supply (220 v) as input, this high

voltage is converted into 12 Volts A.C by step down transformer, then we use voltage

regulators and filters with bridge rectifier to convert the A.C into D.C voltage. For voltage

regulation we are using LM 7805 and 7812 to produce ripple free 5 and 12 volts D.C

constant supply.

MCS-51 based microcontrollers typically include one or two UARTs, two or three

timers, 128 or 256 bytes of internal data RAM (16 bytes of which a re bit-addressable), up

to 128 bytes of I/O, 512 bytes to 64 kB of internal program memory, and sometimes a

quantity of extended data RAM (ERAM) located in the external data space. The original

8051 core ran at 12 clock cycles per machine cycle, with most instructions executing in

one or two machine cycles. With a 12 MHz clock frequency, the 8051 could thus execute

1 million one-cycle instructions per second or 500,000 two-cycle instructions per second.

Enhanced 8051 cores are now commonly used which run at six, four, two, or even one

clock per machine cycle, and have clock frequencies of up to 100 MHz, and are thus

capable of an even greater number of instructions per second

Features of the modern 8051 include built-in reset timers with brown-out detection, on-

chip oscillators, self-programmable Flash ROM program memory, built-in external RAM,
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extra internal program storage, SPI, and USB host interfaces, CAN or LIN bus, PWM

generators, analog comparators, A/D and D/A converters, RTCs, extra counters and

timers, more interrupt sources, and extra power saving modes.

POWER SUPPLY CIRCUIT

There are two things worth attention concerning the microcontroller power supply circuit:

Brown out is a potentially dangerous state which occurs at the moment the

microcontroller is being turned off or when power supply voltage drops to the lowest level

due to electric noise. As the microcontroller consists of several circuits which have

different operating voltage levels, this can because its out of control performance. In

order to prevent it, the microcontroller usually has a circuit for brown out reset built-in.

This circuit immediately resets the whole electronics when the voltage level drops below

the lower limit.

Reset pin is usually referred to as Master Clear Reset (MCLR) and serves for external

reset of the microcontroller by applying logic zero (0) or one (1) depending on the type of

the microcontroller. In case the brown out is not built in the microcontroller, a simple

external circuit for brown out reset can be connected to this pin.
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HOW TO START WORKING?

A microcontroller is a good-natured genie in the bottle and no extra knowledge is

required to use it.

In order to create a device controlled by the microcontroller, it is necessary to provide

the simplest PC, program for compiling and simple device to transfer the code from PC tothe chip itself. Even though the whole process is quite logical, there are often some

queries, not because it is complicated, but for numerous variations. Lets take a look.

Writing program in assembly language

In order to write a program for the microcontroller, a specialized program in the

Windows environment may be used. It may, but it does not have to... When using such a

software, there are numerous tools which facilitate the operation (simulator tool comes

first), which is an obvious advantage. But there is also another ways to write a program.Basically, text is the only thing that matters. Any program for text processing can be used

for this purpose. The point is to write all instructions in such an order they should be

executed by the microcontroller, observe the rules of assembly language and write

instructions exactly as they are defined. In other words, you just have to follow the

program idea. Thats all!

To enable the compiler to operate successfully, it is necessary that a document

containing this program has the extension, .asm in its name, for example: Program asm.When a specialized program (mplab) is used, this extension will be automatically added. If

any other program for text processing (Notepad) is used then the document should be

saved and renamed. For example: Program.txt -> Program.asm. This procedure is not

necessarily performed. The document may be saved in original format while its text may

be copied to the programmer for further use.

Compiling a program

The microcontroller cannot understand the assembly language. That is why it isnecessary to compile the program into machine language. It is more than simple when a

specialized program (mplab) is used because a compiler is a part of the software. Just one

click on the appropriate icon solves the problem and a new document with .hex extension

appears. It is actually the same program, only compiled into machine language which the

microcontroller perfectly understands. Such documentation is commonly named hex


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code and seemingly represents a meaningless sequence of numbers in hexadecimal

number system.

In the event that other software for program writing in assembly language is used,

special software for compiling the program must be installed and used as follows - set up

the compiler, open the document with .asm extension and compile. The result is the same-

a new document with extension .hex. The only problem now is that it is stored in your PC.

Programming a microcontroller

In order to transfer a hex code to the microcontroller, it is necessary to provide a

cable for serial communication and a special device, called programmer, with software.

There are several ways to do it.

A large number of programs and electronic circuits having this purpose can be found

on the Internet. Do as follows: open hex code document, set a few parameters and click

the icon for compiling. After a while, a sequence of zeros and ones will be programmed

into the microcontroller through the serial connection cable and programmer hardware.

What's left is to place the programmed chip into the target device. In the event that it is

necessary to make some changes in the program, the previous procedure may be repeated

an unlimited number of times.

Development systems

A device which in the testing program phase can simulate any environment is called a

development system. Apart from the programmer, the power supply unit and the

microcontrollers socket, the development system contains elements for input pin

activation and output pin monitoring. The simplest version has every pin connected to one

push button and one LED as well. A high quality version has LED displays, LCD

displays, temperature sensors and all other elements which can be supplied with the target


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device. These peripherals can be connected to the MCU via miniature jumpers. In this

way, the whole program may be tested in practice during its development stage, because

the microcontroller doesn't know or care whether its input is activated by a push button or

a sensor built in a real device.


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PART 2: MECHANICAL ACTUATION SYSTEMS

CHAPTER 1: INTRODUCTION

MECHANISMS

Mechanisms are devices which can be considered to be motion converters in that they

transform motion from one form to some other required form. They might, for example,

transform linear motion into rotational motion, or motion in one direction into a motion in

a direction at right angles, or perhaps a linear reciprocating motion into rotary motion, as

in the internal combustion engine where the reciprocating motion of the pistons is

converted into rotation of the crank and hence the drive shaft.

Mechanical elements can include the use of linkages, cams, gears, rack-and-pinion,

chains drives, belt drives, etc. For example, the rack-and-pinion can be used to convert

rotational motion to linear motion. Parallel shaft gears might be used to reduce a shaft

speed. Bevel gears might be used for the transmission of rotary motion through 900. A

toothed belt or chain drive might be used to transform rotary motion about one axis to

motion about another. Cams and linkages can be used to obtain motions which are

prescribed to vary in a particular manner.

Many of actions which previously were obtained by the use of mechanisms are,

however, often nowadays being obtained, as a result of a mechatronics approach, by the

use of microprocessor systems. For example, cams on a rotating shaft were previously

used for domestic washing machines in order to give a timed sequence of actions such as


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opening a valve to let water into the drum, switching the water off, switching a heater on,

etc. Modern washing machines use a microprocessor-based system with the

microprocessor programmed to switch on outputs in the required sequence.

While electronics might now be used often for many functions that previously were

fulfilled by mechanisms, mechanisms might still be used to provide such functions as:

1. Force amplification, e.g. that given by levers.2. Change of speed, e.g. that given by gears.3. Transfer of rotation about one axis to rotation about another, e.g. a timing belt.4. Particular types of motion, e.g. that given by a quick-return mechanisms.

TYPES OF MOTION

The motion of any rigid body can be considered to be a combination of translational

and rotational motions. By considering the three dimensions of space, a translation

motion can be considered to be a movement which can be resolved into components along

one or more of the three axes. A rotational motion can be considered as a rotation which

has components rotating about one or more of the axes. A complex motion may be a

combination of translational and rotational motions. For example, think of the motion

which is required for you to pick up a pencil from a table. This might involve your hand

moving at a particular angle towards the table, rotation of the hand, and then all the

movement associated with opening your fingers and moving them to complex motions.

DEGREE OF FREEDOM


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An important aspect in the design of mechanical elements is the orientation and

arrangement of the elements and parts. A body that is free in space can move in three,

independent, mutually perpendicular directions and rotate in three ways about those

directions. It is said to have six degrees of freedom (DOF). The number of degrees of

freedom is the number of components of motion that are required in order to generate the

motion.

The problem is design is often to reduce the number of degrees of freedom and this

then requires an appropriate number and orientation of constraints. Without any

constraints a body would have six degrees of freedom. A constraint is needed for each

degree of freedom that is to be prevented from occurring. Provided we have no redundant

constraints then the number of degrees of freedom would be 6 minus the number of

constraints. However, redundant constraints often occur and so for constraints on a single

rigid body we have the basic rule.

6 number of constraints = number of degrees of freedom number of redundancies

Thus if a body is required to be fixed, i.e. have zero degrees of freedom, then if no

redundant constraints are introduced the number of constraints required is 6.

A concept that is used in design is that of the principle of least constraint. This states

that in fixing a body or guiding it to a particular type of motion, the minimum number of

constraints should be used, i.e. there should be no redundancies. This is often referred to

as kinematic design.


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CHAPTER 2: CAMS

A cam is a body which rotates or oscillates and in doing so impacts a reciprocating or

oscillatory motion to a second body, called the follower, with which it is in contact.

As the cam rotates so the follower is made to rise, dwell and fall, the lengths of times

spent at each of these positions depending on the shape of the cam. The rise section of the

cam is the part that drives the follower upwards, its profile determining how quickly the

cam follower will be lifted. The fall section of the cam is the part that lowers the follower,

its profile determining how quickly the cam follower will fall. The dwell section of thecam is the part that allows the followers to remain at the same level for a significant period

of time. The dwell section of the cam is where it is circular with a radius that does not

change.

The cam shape required to produce a particular motion of the follower will depend on

the shape of the cam and the type of follower used. The radial distance from the axis of

rotation of the cam to the point of contact of the cam with the follower gives the

displacement of the follower with reference to the axis of rotation of the cam.

ECCENTRIC CAM

The eccentric cam is a circular cam with an offset centre of rotation. It produces an

oscillation of the follower which is simple harmonic motion and is often used with pumps.

The diagrams (1 to 7) which are seen below show the cam rotating in an anticlockwise


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direction. As it rotates it pushes the flat follower upwards and then allows it to drop

downwards. The movement is smooth and at a constant speed.

A mechanical toy based on a series of eccentric cams is seen below. As the handle is

turned, the shaft and the cams fixed to it rotate. Placed above the cams are a number ofsegments representing a snake. As the cams rotate some of the flat followers are pushed

upwards whilst others drop down. This gives the impression that the snake is moving.


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DROP CAM

Eccentric cams generally allow for a slow rise and fall of the follower. However, a

snail drop cam is used where the drop or fall of the follower must be sudden.

The example snail/drop cam shown opposite rotates in an anticlockwise direction.

Rotating in a clockwise direction would probably lead to the entire mechanism jamming.This highlights one possible disadvantage of using this type of cam profile. Also, to ensure

the rotation is smooth, the vertical centre line of the snail/drop cam is positioned slightly

to the left of the slide (see diagram).

The diagrams below show the rotation of the snail/drop cam. When rotating for one

complete revolution the follower stays level for approximately the first 120 degrees

(diagrams 1 to 4). The follower then rises slowly (diagrams 5 to 6) and then suddenly

drops when it reaches and passes the peak (diagram 7).

The mechanical toy seen below has a snail/drop cam as its main part. The follower is

connected to the characters arm by a wire link. As the cam rotates, the follower rises and

the wire link lifts the characters arm. This gives the appearance of the character lifting a


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fork full of food towards his mouth. As the cam continues to rotate the follower suddenly

falls and also the characters arm and fork.

FLAT CAM

The diagram below shows a basic example of a flat plate cam / linear cam. As the flat

plate cam profile moves to the left the follower moves up and down, matching the shape

of the profile. The flat plate cam then reverses in the opposite direction and the follower

drops and rises again.

A more sophisticated example of a flat plate / linear cam is shown below. The

follower is unusual because it has a roller / wheel to help the smooth movement of the flat

profile cam and follower. It also has a return spring that pushes the follower against the

profile, ensuring that it always runs against it and follows the shape precisely.


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The machine seen below is a mechanical paper punch. As the lever is pushed down a

gear system (called a rack and pinion) moves the flat plate profile to the left. In turn this

pushes down the followers which punch two holes in a piece of paper / card.

The edge of the flat plate cam can be shaped to give different vertical movements of

the cam follower. Flat plate / linear cams are used frequently in machines that carry out

the same repetitive movements.


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CHAPTER 3: GEARS

Gear chains are mechanisms which are very widely used to transfer and transform

rotational motion. They are used when a change in speed or torque of a rotating device is

needed. For example, the car gearbox enables the driver to match the speed and torque

requirements of the terrain with engine power available.

When two gears are in mesh, the larger gear wheel is often called the spur or crown

wheel and the smaller one is the pinion.

Consider two meshed gear wheels A and B.

If there are 20 teeth on wheel A and 40 teeth on wheel B, then wheel A must rotate

through two revolutions in the same time as wheel B rotates through one. Thus the angular

velocity A of the wheel A must be twice that B of wheel B, i.e.

402

20

A

B

number of teeth on B

number of teeth on A

Since the number of teeth on a wheel is proportional to its diameter, we can write


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A B

B A

dnumber of teeth on B

number of teeth on A d

Thus for the data we have been considering, wheel B must have twice the diameter of

wheel A. The term gear ratio is used for the ratio of the angular speeds of a pair of

intermeshed gear wheels. Thus the gear ratio for this example is 2.

SPUR GEAR

Spur gears or straight-cut gears are the simplest type of gear. They consist of a cylinder

or disk with the teeth projecting radically, and although they are not straight-sided in form,

the edge of each tooth is straight and aligned parallel to the axis of rotation. These gears

can be meshed together correctly only if they are fitted to parallel shafts.

Spur gears are used in many devices such as the electric screwdriver, dancing monster,

oscillating sprinkler, windup alarm clock, washing machine and clothes dryer. But you

won't find many in your car.

This is because the spur gear can be really loud. Each time a gear tooth engages a tooth

on the other gear, the teeth collide, and this impact makes a noise. It also increases the

stress on the gear teeth.

To reduce the noise and stress in the gears, most of the gears in your car are helical.
http://science.howstuffworks.com/transport/engines-equipment/inside-sd.htmhttp://science.howstuffworks.com/transport/engines-equipment/dancing-monster.htmhttp://science.howstuffworks.com/transport/engines-equipment/sprinkler.htmhttp://science.howstuffworks.com/transport/engines-equipment/inside-clock.htmhttp://science.howstuffworks.com/transport/engines-equipment/dryer.htmhttp://science.howstuffworks.com/transport/engines-equipment/washer.htmhttp://science.howstuffworks.com/transport/engines-equipment/inside-clock.htmhttp://science.howstuffworks.com/transport/engines-equipment/sprinkler.htmhttp://science.howstuffworks.com/transport/engines-equipment/dancing-monster.htmhttp://science.howstuffworks.com/transport/engines-equipment/inside-sd.htm


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HELICAL GEAR

Helical or "dry fixed" gears offer a refinement over spur gears. The leading edges of

the teeth are not parallel to the axis of rotation, but are set at an angle. Since the gear is

curved, this angling causes the tooth shape to be a segment of a helix. Helical gears can be

meshed in a parallel or crossed orientations. The former refers to when the shafts are

parallel to each other; this is the most common orientation. In the latter, the shafts are non-

parallel, and in this configuration are sometimes known as "skew gears".

The angled teeth engage more gradually than do spur gear teeth causing them to run

more smoothly and quietly. With parallel helical gears, each pair of teeth first make

contact at a single point at one side of the gear wheel; a moving curve of contact then

grows gradually across the tooth face to a maximum then recedes until the teeth break

contact at a single point on the opposite side. In spur gears teeth suddenly meet at a line

contact across their entire width causing stress and noise. Whereas spur gears are used for

low speed applications and those situations where noise control is not a problem, the use

of helical gears is indicated when the application involves high speeds, large power

transmission, or where noise abatement is important. The speed is considered to be high

when the pitch line velocity exceeds 25 m/s.

A disadvantage of helical gears is a resultant thrust along the axis of the gear, which

needs to be accommodated by appropriate thrust bearings, and a greater degree of sliding

friction between the meshing teeth, often addressed with additives in the lubricant.
http://en.wikipedia.org/wiki/Helixhttp://en.wikipedia.org/wiki/Noise_abatementhttp://en.wikipedia.org/wiki/Thrusthttp://en.wikipedia.org/wiki/Thrust_bearinghttp://en.wikipedia.org/wiki/Sliding_frictionhttp://en.wikipedia.org/wiki/Sliding_frictionhttp://en.wikipedia.org/wiki/Sliding_frictionhttp://en.wikipedia.org/wiki/Thrust_bearinghttp://en.wikipedia.org/wiki/Thrusthttp://en.wikipedia.org/wiki/Noise_abatementhttp://en.wikipedia.org/wiki/Helix


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DOUBLE HELICAL GEAR

Double helical gears, or herringbone gear, overcome the problem of axial thrust

presented by "single" helical gears by having two sets of teeth that are set in a V shape.

Each gear in a double helical gear can be thought of as two standard mirror image helical

gears stacked. This cancels out the thrust since each half of the gear thrusts in the opposite

direction. Double helical gears are more difficult to manufacture due to their more

complicated shape.

For each possible direction of rotation, there are two possible arrangements of two

oppositely-oriented helical gears or gear faces. In one possible orientation, the helical gear

faces are oriented so that the axial force generated by each is in the axial direction away

from the center of the gear; this arrangement is unstable. In the second possible

orientation, which is stable, the helical gear faces are oriented so that each axial force is

toward the mid-line of the gear. In both arrangements, when the gears are aligned

correctly, the total (or net) axial force on each gear is zero. If the gears become misaligned

in the axial direction, the unstable arrangement generates a net force for disassembly of

the gear train, while the stable arrangement generates a net corrective force. If the

direction of rotation is reversed, the direction of the axial thrusts is reversed, a stable

configuration becomes unstable, and vice versa.

Stable double helical gears can be directly interchanged with spur gears without any

need for different bearings.
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BEVEL GEAR

A bevel gear is shaped like a right circular cone with most of its tip cut off. When two

bevel gears mesh, their imaginary vertices must occupy the same point. Their shaft axes

also intersect at this point, forming an arbitrary non-straight angle between the shafts. The

angle between the shafts can be anything except zero or 180 degrees. Bevel gears with

equal numbers of teeth and shaft axes at 90 degrees are called miter gears.

The teeth of a bevel gear may be straight-cut as with spur gears, or they may be cut in a

variety of other shapes. Spiral bevel gear teeth are curved along the tooth's length and set

at an angle, analogously to the way helical gear teeth are set at an angle compared to spur

gear teeth. Zerol bevel gears have teeth which are curved along their length, but not

angled. Spiral bevel gears have the same advantages and disadvantages relative to their

straight-cut cousins as helical gears do to spur gears. Straight bevel gears are generally

used only at speeds below 5 m/s (1000 ft/min), or, for small gears, 1000 r.p.m.
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WORM GEAR

Worm gears resemble screws. A worm gear is usually meshed with a spur gearor a

helical gear, which is called the gear, wheel, or worm wheel.

Worm-and-gear sets are a simple and compact way to achieve a high torque, large gear

ratio. For example, helical gears are normally limited to gear ratios of less than 10:1 while

worm-and-gear sets vary from 10:1 to 500:1. A disadvantage is the potential for

considerable sliding action, leading to low efficiency.

Worm gears can be considered a species of helical gear, but its helix angle is usually

somewhat large (close to 90 degrees) and its body is usually fairly long in the axial

direction; and it is these attributes which give it screw like qualities. The distinction

between a worm and a helical gear is made when at least one tooth persists for a full

rotation around the helix. If this occurs, it is a 'worm'; if not, it is a 'helical gear'. A worm

may have as few as one tooth. If that tooth persists for several turns around the helix, the

worm will appear, superficially, to have more than one tooth, but what one in fact sees is

the same tooth reappearing at intervals along the length of the worm. The usual screw

nomenclature applies: a one-toothed worm is called single thread or single start; a worm

with more than one tooth is called multiple threads or multiple starts. The helix angle of a

worm is not usually specified. Instead, the lead angle, which is equal to 90 degrees minus

the helix angle, is given.
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In a worm-and-gear set, the worm can always drive the gear. However, if the gear

attempts to drive the worm, it may or may not succeed. Particularly if the lead angle is

small, the gear's teeth may simply lock against the worm's teeth, because the force

component circumferential to the worm is not sufficient to overcome friction. Worm-and-

gear sets that do lock are called self locking, which can be used to advantage, as for

instance when it is desired to set the position of a mechanism by turning the worm and

then have the mechanism hold that position. An example is the machine head found on

some types of stringed instruments.

If the gear in a worm-and-gear set is an ordinary helical gear only a single point of

contact will be achieved. If medium to high power transmission is desired, the tooth shape

of the gear is modified to achieve more intimate contact by making both gears partially

envelop each other. This is done by making both concave and joining them at a saddle

point; this is called a cone-drive.

Worm gears can be right or left-handed following the long established practice for

screw threads.
http://en.wikipedia.org/wiki/Stringed_instrumenthttp://en.wikipedia.org/wiki/Saddle_pointhttp://en.wikipedia.org/wiki/Saddle_pointhttp://en.wikipedia.org/wiki/Stringed_instrumenthttp://en.wikipedia.org/wiki/Machine_head


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RACK AND PINION

A rack is a toothed bar or rod that can be thought of as a sector gear with an infinitely

large radius of curvature. Torque can be converted to linear force by meshing a rack with a

pinion: the pinion turns; the rack moves in a straight line. Such a mechanism is used in

automobiles to convert the rotation of the steering wheel into the left-to-right motion of

the tie rod(s). Racks also feature in the theory of gear geometry, where, for instance, the

tooth shape of an interchangeable set of gears may be specified for the rack (infinite

radius), and the tooth shapes for gears of particular actual radii then derived from that. The

rack and pinion gear type is employed in a rack railway.

The rack and pinion arrangement is commonly found in the steering mechanism of carsor other wheeled, steered vehicles. This arrangement provides a lesser mechanical

advantage than other mechanisms such as recalculating ball, but much less backlash and

greater feedback, or steering "feel". A generating rack is a rack outline used to indicate

tooth details and dimensions for the design of a generating tool, such as a hob or a gear

shaper cutter.

Many machines, such as milling machines and grinders, have movable tables. How

these work is that a pinion is attached to a crank handle, and the rack is attached to theunderside of the machine table. When the operator turns the handle, the pinion moves the

rack in a linear motion, thus moving the table in a linear (back and forth) motion. This is

particularly useful in grinders and milling machines, where the cutting head is stationary,

and the workpiece that is attached to the table is moved back and forth.
http://en.wikipedia.org/wiki/Rack_and_pinionhttp://en.wikipedia.org/wiki/Steeringhttp://en.wikipedia.org/wiki/Automobilehttp://en.wikipedia.org/wiki/Wheelhttp://en.wikipedia.org/wiki/Recirculating_ballhttp://en.wikipedia.org/wiki/Backlash_%28gear%29http://en.wikipedia.org/wiki/Mechanical_advantagehttp://en.wikipedia.org/wiki/Mechanical_advantagehttp://en.wikipedia.org/wiki/Feedbackhttp://en.wikipedia.org/wiki/Feedbackhttp://en.wikipedia.org/wiki/Backlash_%28gear%29http://en.wikipedia.org/wiki/Recirculating_ballhttp://en.wikipedia.org/wiki/Mechanical_advantagehttp://en.wikipedia.org/wiki/Mechanical_advantagehttp://en.wikipedia.org/wiki/Mechanical_advantagehttp://en.wikipedia.org/wiki/Wheelhttp://en.wikipedia.org/wiki/Automobilehttp://en.wikipedia.org/wiki/Steeringhttp://en.wikipedia.org/wiki/Rack_railwayhttp://en.wikipedia.org/wiki/Steeringhttp://en.wikipedia.org/wiki/Rack_and_pinion


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GEAR TRAIN

The term gear train is used to describe a series of intermeshed gear wheels. The term

simple gear train is used for a system where each shaft carries only one gear wheel.

For the such a gear train, the overall gear ratio is the ratio of angular velocities at the

input and output shafts and is thus /A C , i.e.

A

C

G

Consider a simple gear train consisting of wheels A, B and C, as in the upper figure,

with A having 9 teeth and C having 90 teeth. Then, as the angular velocity of a wheel is

inversely proportional to the number of teeth on the wheel, the gear ration is 90/9 = 10.

The effect of wheel B is purely to change the direction of rotation of the output wheel

compared with what it would have been with just the two wheels A and C intermeshed.

The intermediate wheel, B, is termed the idler wheel.

We can rewrite this equation for the overall gear ratio G as

A A B

C B C

G

A simple gear of spur, helical or bevel gears is usually limited to an overall gear ratio

of about 10. This is because of the need to keep the gear train down to a manageable size

if the number of teeth on the pinion is to be kept above a minimum number which is

usually about 10 to 20. Higher gear ratio can, however, be obtained with compound gear


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trains. This is because the gear ratio is the product of the individual gear ratios of parallel

gear sets.

The term compound gear train is used to describe a gear train when two wheels are

mounted on a common shaft. When two gear wheels are mounted on the same shaft they

have the same angular velocity. Thus, for both of the compound gear train in the below

figure, B C . The overall gear ratio G is thus

C CA A B A

D B C D B D

G

Consider a compound gear train with A, the first driver, having 40 teeth, B 20 teeth, C

30 teeth and D, the final driven wheel, 10 teeth. Since the angular velocity of a wheel is

inversely proportional to the number of teeth on the wheel, the overall gear ratio is

20 10 1

40 30 6G

Thus, if the input to wheel A is an angular velocity of 40 rpm, then the output angular

velocity of wheel is 40:(1/6) = 160 rpm.

For the arrangement shown in below figure, for the input and output shafts to be in line

we must also have for the radius of the gears

rA + rB = rC + rD


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CHAPTER 4: BELT AND CHAIN DRIVES

A belt is a loop of flexible material used to link two or more rotating shafts

mechanically. Belts may be used as a source of motion, to transmit powerefficiently, or to

track relative movement. Belts are looped over pulleys. In a two pulley system, the belt

can either drive the pulleys in the same direction, or the belt may be crossed, so that the

direction of the shafts is opposite. As a source of motion, a conveyor belt is one

application where the belt is adapted to continuously carry a load between two points.

PROS AND CONS

Belt drive, moreover, is simple, inexpensive, and does not require axially aligned

shafts. It helps protect the machinery from overload and jam, and damps and isolates noise

and vibration. Load fluctuations are shock-absorbed (cushioned). They need no lubrication

and minimal maintenance. They have high efficiency (90-98%, usually 95%), high

tolerance for misalignment, and are inexpensive if the shafts are far apart. Clutch action is

activated by releasing belt tension. Different speeds can be obtained by step or tapered

pulleys.
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The angular-velocity ratio may not be constant or equal to that of the pulley diameters,

due to slip and stretch. However, this problem has been largely solved by the use of

toothed belts. Temperatures range from 31 F (35 C) to 185 F (85 C). Adjustment of

center distance or addition of an idler pulley is crucial to compensate for wear and stretch.

As a method of transmitting power between two shafts, belt drives have the advantage

that the length of the belt can easily be adjusted to suit a wide range of shaft-to-shaft

distances and the system is automatically protected against overload because slipping

occurs if the loading exceeds the maximum tension that can be sustained by the friction

forces. If the distances between shafts are large, a belt drive is more suitable than gears,

but over small distances gears are to be preferred. Different-size pulleys can be used to

give a gearing effect. However,

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