english for mechatronics engineering (1)
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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.
http://en.wikipedia.org/wiki/Semiconductorhttp://en.wikipedia.org/wiki/Lightinghttp://en.wikipedia.org/wiki/Visible_spectrumhttp://en.wikipedia.org/wiki/Ultraviolethttp://en.wikipedia.org/wiki/Infraredhttp://en.wikipedia.org/wiki/Semiconductor_diodehttp://en.wikipedia.org/wiki/Voltage_biashttp://en.wikipedia.org/wiki/Electronshttp://en.wikipedia.org/wiki/Carrier_generation_and_recombinationhttp://en.wikipedia.org/wiki/Electron_holehttp://en.wikipedia.org/wiki/Photonhttp://en.wikipedia.org/wiki/Electroluminescencehttp://en.wikipedia.org/wiki/Colorhttp://en.wikipedia.org/wiki/Energy_gaphttp://en.wikipedia.org/wiki/Light-emitting_diodehttp://en.wikipedia.org/wiki/Energy_conservationhttp://en.wikipedia.org/wiki/Service_lifehttp://en.wikipedia.org/wiki/Navigation_lighthttp://en.wikipedia.org/wiki/Navigation_lighthttp://en.wikipedia.org/wiki/Automotive_lightinghttp://en.wikipedia.org/wiki/Light-emitting_diodehttp://en.wikipedia.org/wiki/Traffic_signalhttp://en.wikipedia.org/wiki/Infraredhttp://en.wikipedia.org/wiki/Remote_controlhttp://en.wikipedia.org/wiki/Remote_controlhttp://en.wikipedia.org/wiki/Infraredhttp://en.wikipedia.org/wiki/Traffic_signalhttp://en.wikipedia.org/wiki/Light-emitting_diodehttp://en.wikipedia.org/wiki/Automotive_lightinghttp://en.wikipedia.org/wiki/Navigation_lighthttp://en.wikipedia.org/wiki/Navigation_lighthttp://en.wikipedia.org/wiki/Fluorescent_lamphttp://en.wikipedia.org/wiki/Thermal_management_of_high-power_LEDshttp://en.wikipedia.org/wiki/Service_lifehttp://en.wikipedia.org/wiki/Energy_conservationhttp://en.wikipedia.org/wiki/Light-emitting_diodehttp://en.wikipedia.org/wiki/Energy_gaphttp://en.wikipedia.org/wiki/Colorhttp://en.wikipedia.org/wiki/Electroluminescencehttp://en.wikipedia.org/wiki/Photonhttp://en.wikipedia.org/wiki/Electron_holehttp://en.wikipedia.org/wiki/Carrier_generation_and_recombinationhttp://en.wikipedia.org/wiki/Electronshttp://en.wikipedia.org/wiki/Voltage_biashttp://en.wikipedia.org/wiki/Semiconductor_diodehttp://en.wikipedia.org/wiki/Infraredhttp://en.wikipedia.org/wiki/Ultraviolethttp://en.wikipedia.org/wiki/Visible_spectrumhttp://en.wikipedia.org/wiki/Lightinghttp://en.wikipedia.org/wiki/Semiconductor -
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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
http://en.wikipedia.org/wiki/Display_devicehttp://en.wikipedia.org/wiki/Decimalhttp://en.wikipedia.org/wiki/Numeral_systemhttp://en.wikipedia.org/wiki/Dot-matrixhttp://en.wikipedia.org/wiki/Digital_clockhttp://en.wikipedia.org/wiki/Arabic_numeralshttp://en.wikipedia.org/wiki/Oblique_typehttp://en.wikipedia.org/wiki/Hexagonhttp://en.wikipedia.org/wiki/Trapezoidhttp://en.wikipedia.org/wiki/Rectanglehttp://en.wikipedia.org/wiki/Adding_machinehttp://en.wikipedia.org/wiki/Cathodehttp://en.wikipedia.org/wiki/Anodehttp://en.wikipedia.org/wiki/Multiplexed_displayhttp://en.wikipedia.org/wiki/Multiplexed_displayhttp://en.wikipedia.org/wiki/Anodehttp://en.wikipedia.org/wiki/Cathodehttp://en.wikipedia.org/wiki/Adding_machinehttp://en.wikipedia.org/wiki/Rectanglehttp://en.wikipedia.org/wiki/Trapezoidhttp://en.wikipedia.org/wiki/Hexagonhttp://en.wikipedia.org/wiki/Oblique_typehttp://en.wikipedia.org/wiki/Arabic_numeralshttp://en.wikipedia.org/wiki/Digital_clockhttp://en.wikipedia.org/wiki/Dot-matrixhttp://en.wikipedia.org/wiki/Numeral_systemhttp://en.wikipedia.org/wiki/Decimalhttp://en.wikipedia.org/wiki/Display_device -
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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.
http://en.wikipedia.org/wiki/LEDhttp://en.wikipedia.org/wiki/LEDhttp://en.wikipedia.org/wiki/LED_displayhttp://en.wikipedia.org/wiki/LEDhttp://en.wikipedia.org/wiki/LED_displayhttp://en.wikipedia.org/wiki/Human_eyehttp://en.wikipedia.org/wiki/Human_eyehttp://en.wikipedia.org/wiki/Display_devicehttp://en.wikipedia.org/wiki/Display_devicehttp://en.wikipedia.org/wiki/Dot-matrixhttp://en.wikipedia.org/wiki/Dot-matrixhttp://en.wikipedia.org/wiki/Display_devicehttp://en.wikipedia.org/wiki/Human_eyehttp://en.wikipedia.org/wiki/LED_displayhttp://en.wikipedia.org/wiki/LED -
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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".
http://en.wikipedia.org/wiki/Transistorhttp://en.wikipedia.org/wiki/Doping_%28Semiconductors%29http://en.wikipedia.org/wiki/Semiconductorhttp://en.wikipedia.org/wiki/Semiconductorhttp://en.wikipedia.org/wiki/Electronic_amplifierhttp://en.wikipedia.org/wiki/Electronhttp://en.wikipedia.org/wiki/Electron_holehttp://en.wikipedia.org/wiki/Diffusionhttp://en.wikipedia.org/wiki/Charge_carriers_in_semiconductorshttp://en.wikipedia.org/wiki/Field-effect_transistorhttp://en.wikipedia.org/wiki/Drift_velocityhttp://en.wikipedia.org/wiki/Minority_carrierhttp://en.wikipedia.org/wiki/Minority_carrierhttp://en.wikipedia.org/wiki/Dopedhttp://en.wikipedia.org/wiki/Minority_carrierhttp://en.wikipedia.org/wiki/Electron_mobilityhttp://en.wikipedia.org/wiki/Electron_mobilityhttp://en.wikipedia.org/wiki/Hole_mobilityhttp://en.wikipedia.org/wiki/Mnemonichttp://en.wikipedia.org/wiki/Mnemonichttp://en.wikipedia.org/wiki/Hole_mobilityhttp://en.wikipedia.org/wiki/Electron_mobilityhttp://en.wikipedia.org/wiki/Minority_carrierhttp://en.wikipedia.org/wiki/Dopedhttp://en.wikipedia.org/wiki/Minority_carrierhttp://en.wikipedia.org/wiki/Drift_velocityhttp://en.wikipedia.org/wiki/Field-effect_transistorhttp://en.wikipedia.org/wiki/Charge_carriers_in_semiconductorshttp://en.wikipedia.org/wiki/Diffusionhttp://en.wikipedia.org/wiki/Electron_holehttp://en.wikipedia.org/wiki/Electronhttp://en.wikipedia.org/wiki/Electronic_amplifierhttp://en.wikipedia.org/wiki/Semiconductorhttp://en.wikipedia.org/wiki/Doping_%28Semiconductors%29http://en.wikipedia.org/wiki/Transistor -
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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.
http://en.wikipedia.org/wiki/Harvard_architecturehttp://en.wikipedia.org/wiki/Microcontrollerhttp://en.wikipedia.org/wiki/Intelhttp://en.wikipedia.org/wiki/Embedded_systemhttp://en.wikipedia.org/wiki/Binary_compatiblehttp://en.wikipedia.org/wiki/IP_corehttp://en.wikipedia.org/wiki/FPGAshttp://en.wikipedia.org/wiki/ASICshttp://en.wikipedia.org/wiki/NMOS_logichttp://en.wikipedia.org/wiki/CMOShttp://en.wikipedia.org/wiki/CMOShttp://en.wikipedia.org/wiki/NMOS_logichttp://en.wikipedia.org/wiki/ASICshttp://en.wikipedia.org/wiki/FPGAshttp://en.wikipedia.org/wiki/IP_corehttp://en.wikipedia.org/wiki/Binary_compatiblehttp://en.wikipedia.org/wiki/Embedded_systemhttp://en.wikipedia.org/wiki/Intelhttp://en.wikipedia.org/wiki/Microcontrollerhttp://en.wikipedia.org/wiki/Harvard_architecture -
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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,
http://en.wikipedia.org/wiki/Flash_ROMhttp://en.wikipedia.org/wiki/Central_processing_unithttp://en.wikipedia.org/wiki/Random_access_memoryhttp://en.wikipedia.org/wiki/Read-only_memoryhttp://en.wikipedia.org/wiki/Input/outputhttp://en.wikipedia.org/wiki/Interrupthttp://en.wikipedia.org/wiki/Timerhttp://en.wikipedia.org/wiki/Integrated_circuit_packaginghttp://en.wikipedia.org/wiki/Arithmetic_logic_unithttp://en.wikipedia.org/wiki/8-bithttp://en.wikipedia.org/wiki/Microcontrollerhttp://en.wikipedia.org/wiki/Data_bushttp://en.wikipedia.org/wiki/Address_bushttp://en.wikipedia.org/wiki/Kilobytehttp://en.wikipedia.org/wiki/Bytehttp://en.wikipedia.org/wiki/Bytehttp://en.wikipedia.org/wiki/Serial_porthttp://en.wikipedia.org/wiki/Timerhttp://en.wikipedia.org/wiki/Interrupthttp://en.wikipedia.org/wiki/Power_managementhttp://en.wikipedia.org/wiki/UARThttp://en.wikipedia.org/wiki/Input/Outputhttp://en.wikipedia.org/wiki/Clock_frequencyhttp://en.wikipedia.org/wiki/Flash_ROMhttp://en.wikipedia.org/wiki/Clock_frequencyhttp://en.wikipedia.org/wiki/Input/Outputhttp://en.wikipedia.org/wiki/RAMhttp://en.wikipedia.org/wiki/UARThttp://en.wikipedia.org/wiki/Power_managementhttp://en.wikipedia.org/wiki/Interrupthttp://en.wikipedia.org/wiki/Timerhttp://en.wikipedia.org/wiki/Serial_porthttp://en.wikipedia.org/wiki/Input/outputhttp://en.wikipedia.org/wiki/Bytehttp://en.wikipedia.org/wiki/Bytehttp://en.wikipedia.org/wiki/Kilobytehttp://en.wikipedia.org/wiki/Address_bushttp://en.wikipedia.org/wiki/Data_bushttp://en.wikipedia.org/wiki/Microcontrollerhttp://en.wikipedia.org/wiki/8-bithttp://en.wikipedia.org/wiki/Arithmetic_logic_unithttp://en.wikipedia.org/wiki/Integrated_circuit_packaginghttp://en.wikipedia.org/wiki/Timerhttp://en.wikipedia.org/wiki/Interrupthttp://en.wikipedia.org/wiki/Input/outputhttp://en.wikipedia.org/wiki/Read-only_memoryhttp://en.wikipedia.org/wiki/Random_access_memoryhttp://en.wikipedia.org/wiki/Central_processing_unit -
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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.
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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.
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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.
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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.
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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,