english for mechatronics engineering 1

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 pro

TABLE OF CONTENTS

TABLE OF CONTENTS 1

PART 1: DIGITAL LOGIC 3

CHAPTER 1: INTRODUCTION 3

LOGIC GATES 3

CHAPTER 2: APPLICATIONS OF LOGIC GATES 8

INTEGRATED CIRCUIT 8

APPLICATIONS 8

CHAPTER 3: BASIC ELECTRONIC COMPONENTS 10

RESISTANCE 10

CAPACITOR 11

DIODE 13

LIGHT EMITTING DIODE 15

BIPOLAR JUNCTION TRANSISTOR (BJT) 18

CHAPTER 4: MICROCONTROLLER 20

INTRODUCTION 20

IMPORTANT FEATURES 21

POWER SUPPLY CIRCUIT 22

HOW TO START WORKING? 23

PART 2: MECHANICAL ACTUATION SYSTEMS 26

CHAPTER 1: INTRODUCTION 26

MECHANISMS 26

TYPES OF MOTION 27

DEGREE OF FREEDOM 27

CHAPTER 2: CAMS 29

DROP CAM 31

FLAT CAM 32

CHAPTER 3: GEARS 34

SPUR GEAR 35

HELICAL GEAR 36

DOUBLE HELICAL GEAR 37

BEVEL GEAR 38

WORM GEAR 39

RACK AND PINION 41

GEAR TRAIN 42

CHAPTER 4: BELT AND CHAIN DRIVES 44

PROS AND CONS 44

FLAT BELTS 45

ROUND BELTS 46

VEE BELTS 47

TIMING BELTS 48

CHAIN DRIVE 49

CHAINS VERSUS BELTS 50

CHAPTER 5: BEARINGS 51

DEEP-GROOVE 52

FILLING - SLOT 53

ANGULAR CONTACT 54

DOUBLE-ROW 55

SELF-ALIGNING 56

STRAIGHT-ROLLER BEARING 58

TAPER ROLLER 59

NEEDLE ROLLER 61

PART 1: DIGITAL LOGIC

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

(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

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

A + B = Y

(a) Represented by switches (b) Symbols

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

Input Output

1

0

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:

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 OR gate 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  

The following is the truth table for the NOR gate

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

The following is the truth table for the XOR gate

A (·) B = Y

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

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

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

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 Ω 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 Ohm’s laws:

V I R

where

R is the resistance of the object, measured in ohms, equivalent to J·s/C2

V is the potential difference across the object, measured in volts

I is 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

3rdBand

4th band (multiplier)

5th Band (Tolerance)

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

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 conductive region The 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

non-is assumed to be self-contained and non-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 V between them:

Q C V



DIODE

A diode is a type of two-terminal electronic component with nonlinear resistance and

conductance (i.e., a nonlinear current–voltage characteristic), distinguishing it from components such as two-terminal linear resistors which obey Ohm's law A semiconductor diode, the most common type today, is a crystalline piece of semiconductor material connected to two electrical terminals A vacuum tube diode (now rarely used except in some high-power technologies) is a vacuum tube with two electrodes: a plate and a cathode

The most common function of a diode is to allow an electric current to pass in one

direction (called the diode's forward direction), while blocking current in the opposite direction (the reverse direction) Thus, the diode can be thought of as an electronic version

of a check valve This unidirectional behavior is called rectification, and is used to convert alternating current to direct current, and to extract modulation from radio signals in radio receivers—these diodes are forms of rectifiers

A Zener diode is a special kind of diode which allows current to flow in the forward direction in the same manner as an ideal diode, but will also permit it to flow in the reverse direction when the voltage is above a certain value known as the breakdown voltage, "Zener knee voltage" or "Zener voltage." The device was named after Clarence Zener, who discovered this electrical property A Zener diode exhibits almost the same properties, except the device is specially designed so as to have a greatly reduced breakdown voltage, the so-called Zener voltage By contrast with the conventional device,

a reverse-biased Zener diode will exhibit a controlled breakdown and allow the current to

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 of input 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

circuit after its inventor, physicist Leo Graetz

HW: Describing the basic operation of Diode Bridge?

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 other lighting 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 sources including 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 be developed, 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

A seven-segment display (SSD), or seven-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 further enhance 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 driver pin, while the cathodes

of all segments for each digit would be connected To operate any particular segment of

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 matrix or 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 human–machine 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

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

Bipolar transistors 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-carrier devices

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 not pointing 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"

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 is pointing 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

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 (µC) 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

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 data bus – 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

 Power saving 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 are 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-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 it’s 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

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 to the chip itself Even though the whole process is quite logical, there are often some queries, not because it is complicated, but for numerous variations Let’s 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 That’s 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 is necessary 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

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 microcontroller’s 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

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

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

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

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

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

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 of segments 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

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