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Unit 1
Introduction to Mechatronics Systems
Mechatronicsis thesynergistic combination ofMechanical engineering,Electronic
engineering,Computer engineering,Control engineering,andSystems Design engineering in orderto design, and manufacture useful products. The term mechatronics is defined as amultidisciplinary
engineering system design, that is to say it rejects splittingengineering into separate disciplines.
A mechatronics engineer unites the principles of mechanics, electronics, and computing to
generate a simpler, more economical and reliable system. Mechatronics is centered onmechanics,
electronics,computing,control engineering,molecular engineering (fromnanochemistry and
biology), andoptical engineering,which, combined, make possible the generation of simpler, more
economical, reliable and versatile systems. The portmanteau "mechatronics" was coined by Tetsuro
Mori, the senior engineer of theJapanese companyYaskawa in 1969. Anindustrial robot is a prime
example of a mechatronics system; it includes aspects of electronics, mechanics, and computing to
do its day-to-day jobs.
The development of mechatronics has gone through three stages: The first stage corresponds
to the years around the introduction of word mechatronics.
During this stage, technologies used in mechatronics systems developed rather independently of
each other and individually.With start of eighties a synergic integration of different technologies
started taking place.A notable example is opto-electronics, an integration of optics and electronics.
The concept of hardware/software co-design also started in this year.
The third stage, which is considered as start of Mechatronics Age, starts with the earlynineties. The most notable aspect of this stage are more and more integration of different engineering
disciplinesand increased use of computational intelligence in the mechatronics products andsystems.Another important development in the third stage is the concept of micromechatronis, i.e.,
start of miniaturization the components such as microactuators and microsensors.Design of such
products and processes, therefore, has to be the outcome of a multi-disciplinary act ivity rather than
an interdisciplinary one.
Hence mechatronics challenges the traditional engineering thinking, because the way it is operating,
is crossing the boundaries between the traditional engineering disciplines.
SENSORS
A sensor is a device which receives and responds to a signal. A sensor's sensitivity indicates
how much the sensor's output changes when the measured quantity changes. For instance, if the
mercury in a thermometer moves 1 cm when the temperature changes by 1 C, the sensitivity is
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1 cm/C (it is basically the slope Dy/Dx assuming a linear characteristic). Sensors that measure very
small changes must have very high sensitivities.
A good sensor obeys the following rules:
Is sensitive to the measured property Is insensitive to any other property likely to be encountered in its application Does not influence the measured propertyCharacteristics of sensor
Thesensitivitymay in practice differ from the value specified. This is called a sensitivityerror, but the sensor is still linear.
Since the range of the output signal is always limited, the output signal will eventually reacha minimum or maximum when the measured property exceeds the limits. The full scale range
defines the maximum and minimum values of the measured property. If the output signal is not zero when the measured property is zero, the sensor has anoffsetor
bias.This is defined as the output of the sensor at zero input.
If the sensitivity is not constant over the range of the sensor, this is callednonlinearity.Usually this is defined by the amount the output differs from ideal behavior over the full
range of the sensor, often noted as a percentage of the full range.
If the deviation is caused by a rapid change of the measured property over time, there is adynamicerror. Often, this behaviour is described with abode plotshowing sensitivity error
and phase shift as function of the frequency of a periodic input signal.
If the output signal slowly changes independent of the measured property, this is defined asdrift (telecommunication).
Long term driftusually indicates a slow degradation of sensor properties over a long periodof time.
Noiseis a random deviation of the signal that varies in time. Hysteresisis an error caused by when the measured property reverses direction, but there is
some finite lag in time for the sensor to respond, creating a different offset error in onedirection than in the other.
If the sensor has a digital output, the output is essentially an approximation of the measuredproperty. The approximation error is also calleddigitizationerror.
If the signal is monitored digitally, limitation of thesampling frequencyalso can cause adynamic error, or if the variable or added noise noise changes periodically at a frequency
near a multiple of the sampling rate may inducealiasingerrors. The sensor may to some extent be sensitive to properties other than the property being
measured. For example, most sensors are influenced by the temperature of their environment.
DISPLACEMENT AND POSITION SENSORS
Displacement Measurement
Measurement of displacement is the basis of measuring:
Position
VelocityAcceleration
StressForce
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Pressure
Proximity
Thickness
Displacement Sensors types
Potentiometers displacement sensors Inductive displacement sensors Capacitive displacement sensors Eddy current displacement sensors Piezoelectric displacement sensors Ultrasonic displacement sensors Magnetostrictive displacement sensors Optical encoder displacement sensors Strain Gages displacement sensors
Resistive displacement sensors: An electrically conductive wiper that slides against a fixed
resistive element. To measure displacement, a potentiometer is typically wired in a voltage divider
configuration.
A known voltage is applied to the resistor ends. The contact is attached to the moving
object of interest The output voltage at the contact is proportional to the displacement.
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Inductive displacement sensorsThe coil acts as a source of magnetomotive force that drives the flux through the magnetic
circuit and the air gap. The presence of the air gap causes a large increase in circuit reluctance and a
corresponding decrease in the flux. Hence, a small variation in the air gap results in a
measurable change in inductance.
Linear Variable Differential Transformer (LVDT)Motion of a magnetic core changes the mutual inductance of two secondary coils relative to a
primary coil Primary coil voltage: VSsin(wt)
Secondary coil induced emf:
V1=k1sin(wt) and V2=k2sin(wt)
k1 and k2 depend on the amount of coupling between the primary and the secondary coils,which is proportional to the position of the coil.When the coil is in the central position,
k1=k2; VOUT=V1-V2=0When the coil is is displaced x units,
k1 not equal to k2 ;
VOUT=(k1-k2)sin(wt)
Positive or negative displacements are determined from the phase
of VOUT.
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The linear variable differential transformer(LVDT) is a type of electricaltransformerused for
measuring linear displacement. The transformer has threesolenoidalcoils placed end-to-end around
a tube. The center coil is the primary, and the two outer coils are the secondaries. A cylindrical
ferromagnetic core, attached to the object whose position is to be measured, slides along the axis of
the tube.
Analternating currentis driven through the primary, causing avoltageto be induced in each
secondary proportional to its mutualinductancewith the primary. Thefrequencyis usually in the
range 1 to 10kHz.
As the core moves, these mutual inductances change, causing the voltages induced in the secondaries
to change. The coils are connected in reverse series, so that the output voltage is the difference(hence "differential") between the two secondary voltages. When the core is in its central position,
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equidistant between the two secondaries, equal but opposite voltages are induced in these two coils,
so the output voltage is zero.
When the core is displaced in one direction, the voltage in one coil increases as the other decreases,
causing the output voltage to increase from zero to a maximum. This voltage is inphasewith the
primary voltage. When the core moves in the other direction, the output voltage also increases fromzero to a maximum, but its phase is opposite to that of the primary. The magnitude of the output
voltage is proportional to the distance moved by the core (up to its limit of travel), which is why the
device is described as "linear". The phase of the voltage indicates the direction of the displacement.
Because the sliding core does not touch the inside of the tube, it can move without friction, makingthe LVDT a highly reliable device. The absence of any sliding or rotating contacts allows the LVDT
to be completely sealed against the environment.
LVDTs are commonly used for position feedback inservomechanisms,and for automated
measurement in machine tools and many ot her industrial and scientific applications.
A proximity sensoris asensorable to detect the presence of nearby objects without any physical
contact. A proximity sensor often emits anelectromagneticorelectrostaticfield, or a beam of
electromagnetic radiation(infrared,for instance), and looks for changes in thefieldor return signal.
The object being sensed is often referred to as the proximity sensor's target. Different proximity
sensor targets demand different sensors. For example, acapacitiveorphotoelectric sensormight be
suitable for a plastic target; aninductiveproximity sensor requires a metal target.
The maximum distance that this sensor can detect is defined "nominal range". Some sensors haveadjustments of the nominal range or means to report a graduated detection distance.
Proximity sensors can have a high reliability and long functional life because of the absence of
mechanical parts and lack of physical contact between sensor and the sensed object.
Proximity sensors are also used in machine vibration monitoring to measure the variation in distance
between a shaft and its support bearing. This is common in large steam turbines, compressors, andmotors that use sleeve-type bearings.
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A thermocoupleis a junction between two different metals that produces avoltagerelated to a
temperaturedifference. Thermocouples are a widely used type oftemperature sensorfor
measurement and control[1]and can also be used to convert heat into electric power. They are
inexpensive[2]
and interchangeable, are supplied fitted with standard connectors, and can measure a
wide range of temperatures. The main limitation is accuracy: system errors of less than one degree
Celsius(C) can be difficult to achieve.[3]
Any junction of dissimilar metals will produce an electric potential related to temperature.
Thermocouples for practical measurement of temperature are junctions of specificalloyswhich have
a predictable and repeatable relationship between temperature and voltage. Different alloys are used
for different temperature ranges. Properties such as resistance to corrosion may also be importantwhen choosing a type of thermocouple. Where the measurement point is far from the measuring
instrument, the intermediate connection can be made by extension wires which are less costly than
the materials used to make the sensor. Thermocouples are usually standardized against a reference
temperature of 0 degrees Celsius; practical instruments use electronic methods of cold-junction
compensation to adjust for varying temperature at the instrument terminals. Electronic instruments
can also compensate for the varying characteristics of the thermocouple, and so improve theprecision and accuracy of measurements.
Thermocouples are widely used in science and industry; applications include temperature
measurement forkilns,gas turbineexhaust,dieselengines, and other industrial processes.
Resistance thermometers, also called resistance temperature detectorsor resistive thermal
devices(RTDs), aretemperaturesensorsthat exploit the predictable change inelectrical resistance
of some materials with changing temperature. As they are almost invariably made ofplatinum,they
are often called platinum resistance thermometers(PRTs). They are slowly replacing the use of
thermocouplesin many industrial applications below 600 C,due to higher accuracy and
repeatability.[1]
There are many categories; carbon resistors, film, and wire-wound types are the most widely used.
Carbon resistorsare widely available and are very inexpensive. They have very reproducibleresults at low temperatures. They are the most reliable form at extremely low temperatures.
They generally do not suffer from significanthysteresisor strain gauge effects. Carbon
resistors have been used for many years because of their advantages.
Film thermometershave a layer of platinum on asubstrate;the layer may be extremely thin,perhaps onemicrometer.Advantages of this type are relatively low cost (the high cost ofplatinum being offset by the tiny amount required) and fast response. Such devices haveimproved performance although the different expansion rates of the substrate and platinum
give "strain gauge"effects and stability problems.
Wire-wound thermometerscan have greater accuracy, especially for wide temperature ranges. The
coil diameter provides a compromise between mechanical stability and allowing expansion of the
wire to minimize strain and consequential drift.
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ME1402 MECHATRONICS
(Common to Mechanical and Production- VI Semester)
OBJECTIVE
To understand the interdisciplinary applications of Electronics, Electrical, Mechanical and
Computer Systems for the Control of Mechanical and Electronic Systems.
1.MECHATRONICS, SENSORS AND TRANSDUCERS 9
Introduction to Mechatronics SystemsMeasurement SystemsControl SystemsMicroprocessorbased Controllers. Sensors and TransducersPerformance TerminologySensors for
Displacement, Position and Proximity; Velocity, Motion, Force, Fluid Pressure, Liquid Flow, Liquid
Level, Temperature, Light SensorsSelection of Sensors
2.ACTUATION SYSTEMS 9
Pneumatic and Hydraulic SystemsDirectional Control ValvesRotary Actuators. Mechanical
Actuation SystemsCamsGear TrainsRatchet and pawlBelt and Chain DrivesBearings.
Electrical Actuation SystemsMechanical SwitchesSolid State SwitchesSolenoidsD.CMotorsA.C MotorsStepper Motors.
3.SYSTEM MODELS AND CONTROLLERS 9
Building blocks of Mechanical, Electrical, Fluid and Thermal Systems, RotationalTransnationalSystems, Electromechanical SystemsHydraulicMechanical Systems. Continuous and discrete
process ControllersControl ModeTwoStep modeProportional ModeDerivative Mode
Integral ModePID ControllersDigital ControllersVelocity ControlAdaptive Control
Digital Logic ControlMicro Processors Control.
4. PROGRAMMING LOGIC CONTROLLERS 9
Programmable Logic ControllersBasic StructureInput / Output ProcessingProgramming
MnemonicsTimers, Internal relays and countersShift RegistersMaster and Jump ControlsData HandlingAnalogs Input / OutputSelection of a PLC Problem.
5.DESIGN OF MECHATRONICS SYSTEM 9
Stages in designing Mechatronics SystemsTraditional and Mechatronic Design - Possible Design
Solutions Case Studies of Mechatronics Systems, Pick and place robotautomatic Car Park
SystemsEngine Management Systems.
TOTAL : 45
TEXT BOOKSW. Bolton, Mechatronics, Pearson Education, Second Edition, 1999.
REFERENCES
Michael B. Histand and David G. Alciatore, Introduction to Mechatronics and Measurement
Systems, McGraw-Hill International Editions, 2000.
Bradley D. A., Dawson D., Buru N.C. and. Loader A.J, Mechatronics, Chapman and Hall, 1993.
Dan Necsulesu, Mechatronics, Pearson Education Asia, 2002 (Indian Reprint).
Lawrence J. Kamm, Understanding Electro Mechanical Engineering, An Introduction to
Mechatronics, PrenticeHall of India Pvt., Ltd., 2000.
Nitaigour Premchand Mahadik, Mechatronics, Tata McGraw-Hill publishing Company Ltd, 2003
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Unit 1
Unit 2 ACTUATION SYSTEMS
Pneumatic and Hydraulic SystemsDirectional Control ValvesRotary Actuators. Mechanical
Actuation SystemsCamsGear TrainsRatchet and pawlBelt and Chain DrivesBearings.Electrical Actuation SystemsMechanical SwitchesSolid State SwitchesSolenoidsD.C
MotorsA.C MotorsStepper Motors.
Pneumatic systems
Pneumaticsis a branch of technology, which deals with the study and application of use ofpressurized gas to affect mechanical motion.
Pneumatic systems are extensively used inindustry,wherefactories are commonly plumbed with
compressed air or other compressedinert gases.This is because a centrally-located and electrically-
poweredcompressor that powerscylinders and other pneumatic devices throughsolenoid valves is
often able to provide motive power in a cheaper, safer, more flexible, and more reliable way than a
large number ofelectric motors andactuators.
Pneumatics also has applications indentistry,construction,mining,and other areas.
Gases used in pneumatic systems
Pneumatic systems in fixed installations such as factories use compressed air because a sustainable
supply can be made by compressing atmospheric air. The air usually has moisture removed and a
small quantity of oil added at the compressor, to avoid corrosion of mechanical components and to
lubricate them.
Factory-plumbed, pneumatic-power users need not worry about poisonous leakages as the gas is
commonly just air. Smaller or stand-alone systems can use other compressed gases which are an
asphyxiationhazard, such asnitrogen- often referred to asOFN (oxygen-free nitrogen),when
supplied in cylinders.
Any compressed gas other than air is an asphyxiation hazard - including nitrogen, which makes up
approximately 80% of air. Compressedoxygen(approx. 20% of air) would not asphyxiate, but itwould be an extreme fire hazard, so is never used in pneumatically powered devices.
Portable pneumatic tools and small vehicles such asRobot Warsmachines and other hobbyistapplications are often powered by compressedcarbon dioxidebecause containers designed to hold it
such assoda streamcanisters and fire extinguishers are readily available, and thephase changebetween liquid and gas makes it possible to obtain a larger volume of compressed gas from a lighter
container than compressed air would allow. Carbon dioxide is an asphyxiant and can also be afreezing hazard when vented inappropriately.
Advantages of pneumatics
Simplicity of Design And Control
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o Machines are easily designed using standard cylinders & other components. Controlis as easy as it is simple ON - OFF type control.
Reliabilityo Pneumatic systems tend to have long operating lives and require very little
maintenance.
o Because gas is compressible, the equipment is less likely to be damaged by shock.The gas in pneumatics absorbs excessive force, whereas the fluid of hydraulics
directly transfers force.
Storageo Compressed Gas can be stored, allowing the use of machines when electrical power is
lost.
Safetyo Very low chance of fire (compared to hydraulic oil).o Machines can be designed to be overload safe.
Hydraulic systems
Hydraulic machineryare machines and tools which usefluid powerto do simple work.Heavy
equipmentis a common example.
In this type of machine, high-pressureliquidcalledhydraulic fluidis transmitted throughoutthe machine to varioushydraulic motorsandhydraulic cylinders.The fluid is controlled directly or
automatically bycontrol valvesand distributed throughhosesandtubes.
The popularity of hydraulic machinery is due to the very large amount of power that can be
transferred through small tubes and flexible hoses, and the high power density and wide array of
actuatorsthat can make use of this power.
Hydraulic machinery is operated by the use of hydraulics, where a liquid is the powering medium
Advantages of hydraulics
Liquid (as a gas is also a 'fluid') does not absorb any of the supplied energy. Capable of moving much higher loads and providing much higher forces due to the
incompressibility.
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The hydraulic working fluid is basically incompressible, leading to a minimum ofspringaction. When hydraulic fluid flow is stopped, the slightest motion of the load releases the
pressure on the load; there is no need to "bleed off" pressurized air to release the pressure on
the load.
Directional control valvesare one of the most fundamental parts inhydraulic machinery.Theyallow fluid flow into different paths from one or more sources. They usually consist of apiston
inside a cylinder which is electrically controlled. The movement of the cylinder restricts or permits
the flow, thus it controls the fluid flow.
Directional control valves are mainly two types:
Hydraulic and Pneumatic.
Hydraulic directional control valves are for a liquid working fluid (e.g. water,hydraulic oil)and
pneumatic directional control valves are for a gaseous (usually air) working fluid.
Control valves
Directional control valvesroute the fluid to the desired actuator. They usually consist of a spool
inside acast ironorsteelhousing. The spool slides to different positions in the housing, intersectinggrooves and channels route the fluid based on the spool's position.
The spool has a central (neutral) position maintained with springs; in this position the supply fluid is
blocked, or returned to tank. Sliding the spool to one side routes the hydraulic fluid to an actuator
and provides a return path from the actuator to tank. When the spool is moved to the oppositedirection the supply and return paths are switched. When the spool is allowed to return to neutral
(center) position the actuator fluid paths are blocked, locking it in position.
Directional control valves are usually designed to be stackable, with one valve for each hydrauliccylinder, and one fluid input supplying all the valves in the stack.
Tolerances are very tight in order to handle the high pressure and avoid leaking, spools typically
have aclearancewith the housing of less than a thousandth of an inch (25 m). The valve block will
be mounted to the machine's frame with a three pointpattern to avoid distorting the valve block and
jamming the valve's sensitive components.
The spool position may be actuated by mechanical levers, hydraulicpilotpressure, orsolenoids
which push the spool left or right. Asealallows part of the spool to protrude outside the housing,
where it is accessible to the actuator.
The main valve block is usually a stack of off the shelfdirectional control valves chosen by flow
capacity and performance. Some valves are designed to be proportional (flow rate proportional to
valve position), while others may be simply on-off. The control valve is one of the most expensive
and sensitive parts of a hydraulic circuit.
Pressure relief valvesare used in several places in hydraulic machinery; on the return circuitto maintain a small amount of pressure for brakes, pilot lines, etc... On hydraulic cylinders, to
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prevent overloading and hydraulic line/seal rupture. On the hydraulic reservoir, to maintain a
small positive pressure which excludes moisture and contamination.
Pressure regulatorsreduce the supply pressure of hydraulic fluids as needed for variouscircuits.
Sequence valvescontrol the sequence of hydraulic circuits; to ensure that one hydrauliccylinder is fully extended before another starts its stroke, for example.
Shuttle valvesprovide a logicalorfunction. Check valvesare one-way valves, allowing an accumulator to charge and maintain its
pressure after the machine is turned off, for example.
Pilot controlled Check valvesare one-way valve that can be opened (for both directions) bya foreign pressure signal. For instance if the load should not be hold by the check valve
anymore. Often the foreign pressure comes from the other pipe that is connected to the motor
or cylinder.
Counterbalance valvesare in fact a special type of pilot controlled check valve. Whereasthe check valve is open or closed, the counterbalance valve acts a bit like a pilot controlled
flow control.
Cartridge valvesare in fact the inner part of a check valve; they are off the shelfcomponentswith a standardized envelope, making them easy to populate a proprietary valve block. They
are available in many configurations; on/off, proportional, pressure relief, etc. They generallyscrew into a valve block and are electrically controlled to provide logic and automated
functions.
Hydraulic fusesare in-line safety devices designed to automatically seal off a hydraulic lineif pressure becomes too low, or safely vent fluid if pressure becomes too high.
Auxiliary valvesin complex hydraulic systems may have auxiliary valve blocks to handlevarious duties unseen to the operator, such as accumulator charging, cooling fan operation,
air conditioning power, etc. They are usually custom valves designed for the particular
machine, and may consist of a metal block with ports and channels drilled. Cartridge valves
are threaded into the ports and may be electrically controlled by switches or a microprocessor
to route fluid power as needed.
Hydraulic rotary actuators
The hydraulic rotary actuator is a device which transform hydraulic power (pressure and flow) in
rotational mechanical power (torque and speed).
It is used for alternative movements with a limited rotation angle (max 280).The simplicity of
construction allows to obtain very high mechanical efficiency values, close to 95%.
Mechanical actuation systems
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Mechanical linear actuators operate by conversion of rotary motion into linear motion. Conversion is
commonly made via a few simple types of mechanism:
Screw:Screw jack,ball screw androller screw actuators all operate on the principle of thesimple machine known as the screw. By rotating the actuator's nut, the screw shaft moves in
a line. Wheel and axle:Hoist,winch,rack and pinion,chain drive,belt drive,rigid chain andrigid
belt actuators operate on the principle of the wheel and axle. By rotating a wheel/axle (e.g.
drum,gear,pulley orshaft)a linear member (e.g.cable,rack,chain orbelt)moves.[1]
Cam:Cam actuators function on a principle similar to that of thewedge,but providerelatively limited travel. As a wheel-like cam rotates, its eccentric shape provides thrust at the
base of a shaft.
Some mechanical linear actuators only pull (e.g. hoist, chain drive and belt drive) and others only
push (e.g. cam actuator).
CamsA linear actuatoris anactuatorthat, when driven by a non-linear motion, createslinearmotion (asopposed to rotary motion, e.g. of anelectric motor). Mechanical and hydraulic actuation are the most
common methods of achieving the linear motion.
A camis a rotating or sliding piece in a mechanicallinkageused especially in transforming rotarymotion into linear motion or vice-versa.[1][2]It is often a part of a rotatingwheel(e.g. an eccentric
wheel) or shaft (e.g. a cylinder with an irregular shape) that strikes aleverat one or more points on
its circular path. The cam can be a simple tooth, as is used to deliver pulses of power to asteam
hammer,for example, or aneccentricdisc or other shape that produces a smooth reciprocating (back
and forth) motion in thefollower,which is a lever making contact with the cam.
Gear train
A gear trainis a set or system ofgears arranged to transfer rotationaltorque from one part of amechanical system to another.
Gear trains may consist of:
Driving gears - attached to the input shaft Driven gears/Motor gears - attached to the output shaft Idler gears - interposed between the driving and driven gear in order to maintain the direction
of the output shaft the same as the input shaft or to increase the distance between the drive
and driven gears. A compound gear train refers to two or more gears used to transmit motion.
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Types of gear trains include:
Simple gear train Compound gear train Epicyclic gear train Reverted gear train
A gear train is two or more gear working together by meshing their teeth and turning each other in a
system to generate power and speed. It reduces speed and increases torque. To create large gear
ratio, gears are connected together to form gear trains. They often consist of multiple gears in the
train. The smaller gears are one-fifth of the size of the larger gear. Electric motors are used with the
gear systems to reduce the speed and increase the torque. Electric motor is connected to the driving
end of each train and is mounted on the test platform. The output end output end of the gear train is
connected to a large magnetic particle brake that is used to measure the output torque.
Types of Gear Trains
Simple Gear Train- The most common of the gear train is the gear pair connecting parallelshafts. The teeth of this type can be spur, helical or herringbone. The angular velocity is
simply the reverse of the tooth ratio. The main limitation of a simple gear train is that the
maximum speed change ratio is 10:1. For larger ratio, large size of gear trains are required.
The sprockets and chain in the bicycle is an example of simple gear train. When the paddle is
pushed, the front gear is turned and that meshes with the links in the chain. The chain moves
and meshes with the links in the rear gear that is attached to the rear wheel. This enables the
bicycle to move.
Compound Gear Train- For large velocities, compound arrangement is preferred. Twokeys are keyed to a single shaft. A double reduction train can be arranged to have its input
and output shafts in a line, by choosing equal center distance for gears and pinions.
Epicyclic Gear Train- It is the system of epicyclic gears in which at least one wheel axisitself revolves around another fixed axis.
Planetary Gear Train- It is made of few components, a small gear at the center called thesun, several medium sized gears called the planets and a large external gear called the ring
gear. The planet gear rolls and revolves about the sun gear and the ring gear rolls on the
planet gear. Planetary gear trains have several advantages. They have higher gear ratios.
They are popular for automatic transmissions in automobiles. They are also used in bicycles
for controlling power of pedaling automatically or manually. They are also used for power
train between internal combustion engine and an electric motor.
ApplicationsGear trains are used in representing the phases of moon on a watch or clock dial. It is also
used for driving a conventional two-disk lunar phase display off the day-of-the-week shaft of
the calendar.
Ratchet & pawl
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A ratchetis a device that allows continuous linear or rotary motion in only one direction while
preventing motion in the opposite direction. Because most socket wrenchestoday use ratcheting
handles, the term "ratchet" alone is often used to refer to a ratcheting wrench, and the terms "ratchet"
and "socket" are closely associated in many users' minds.
A ratchet consists of a roundgear(see Figure 1) or linearrackwith teeth, and a pivoting,springloaded finger called apawl(or click[1])that engages the teeth. The teeth are uniform but
asymmetrical, with each tooth having a moderate slope on one edge and a much steeper slope on the
other edge.
When the teeth are moving in the unrestricted (i.e., forward) direction (see Figure 2), the pawl easilyslides up and over the gently sloped edges of the teeth, with a spring forcing it (often with an audible
'click') into the depression between the teeth as it passes the tip of each tooth. When the teeth movein the opposite (backward) direction, however, the pawl will catch against the steeply sloped edge of
the first tooth it encounters, thereby locking it against the tooth and preventing any further motion inthat direction.
Backlash
Because the ratchet can only stop backward motion at discrete points (i.e., at tooth boundaries), aratchet does allow a limited amount of backward motion. This backward motionwhich is limited
to a maximum distance equal to the spacing between the teethis calledbacklash.In cases where
backlash must be minimized, a smooth, toothless ratchet with a high friction surface such asrubber
is sometimes used. The pawl bears against the surface at an angle so that any backward motion will
cause the pawl to jam against the surface and thus prevent any further backward motion. Since the
backward travel distance is primarily a function of the compressibility of the high friction surface,
this mechanism can result in significantly reduced backlash.
Belt drives
A beltis a loop of flexible material used to link two or more rotatingshaftsmechanically. Belts may
be used as a source of motion, totransmit powerefficiently, or to track relative movement. Belts are
looped overpulleys.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, aconveyor beltis one application where the belt is adapted to continually carry a loadbetween two points.
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Belts are the cheapest utility for power transmission between shafts that may not be axially aligned.
Power transmission is achieved by specially designed belts and pulleys. The demands on a belt drive
transmission system are large and this has led to many variations on the theme. They run smoothly
and with little noise, and cushion motor and bearings against load changes, albeit with less strength
than gears or chains. However, improvements in belt engineering allow use of belts in systems that
only formerly allowed chains or gears.
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. Loadfluctuations 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.
The angular-velocity ratio may not be constant or equal to that of the pulley diameters, due to slipand stretch. However, this problem has been largely solved by the use of toothed belts. Temperatures
ranges from 31F (35C) to 185 F (85 C). Adjustment of center distance or addition of an idler
pulley is crucial to compensate for wear and stretch.
Flat belts
The drive belt: used to transfer power from the engine's flywheel. Here shown driving athreshing
machine.
Flat belts were used early inline shaftingto transmit power in factories.[1]
It is a simple system of
power transmission that was well suited for its day. It delivered high power for high speeds (500 hp
for 10,000 ft/min), in cases of wide belts and large pulleys. These drives are bulky, requiring high
tension leading to high loads, so vee belts have mainly replaced the flat-belts except when highspeed is needed over power. TheIndustrial Revolutionsoon demanded more from the system, and
flat belt pulleys needed to be carefully aligned to prevent the belt from slipping off. Because flat
belts tend to climb towards the higher side of the pulley, pulleys were made with a slightly convex or
"crowned" surface (rather than flat) to keep the belts centered. Flat belts also tend to slip on the
pulley face when heavy loads are applied and many proprietary dressings were available that could
be applied to the belts to increase friction, and so power transmission. Grip was better if the belt was
assembled with the hair (i.e. outer) side of the leather against the pulley although belts were also
often given a half-twist before joining the ends (forming aMbius strip), so that wear was evenly
distributed on both sides of the belt (DB). Belts were joined by lacing the ends together with leatherthonging,[2][3]or later by steel comb fasteners.[4]A good modern use for a flat belt is with smaller
pulleys and large central distances. They can connect inside and outside pulleys, and can come in
both endless and jointed construction.
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Round belts
Round belts are a circular cross section belt designed to run in a pulley with a circular (or near
circular) groove. They are for use in lowtorquesituations and may be purchased in various lengthsor cut to length and joined, either by a staple, gluing or welding (in the case ofpolyurethane). Early
sewing machinesutilized a leather belt, joined either by a metal staple or glued, to a great effect.
Vee belts
Belts on aYanmar 2GM20marinediesel engine.
A multiple-V-belt drive on anair compressor.
Vee belts (also known as V-belt or wedge rope) solved the slippage and alignment problem. It is
now the basic belt for power transmission. They provide the best combination of traction, speed of
movement, load of the bearings, and long service life. The V-belt was developed in 1917 byJohn
Gatesof theGates Rubber Company.They are generally endless, and their general cross-sectionshape istrapezoidal.The "V" shape of the belt tracks in a mating groove in thepulley(or sheave),
with the result that the belt cannot slip off. The belt also tends to wedge into the groove as the load
increasesthe greater the load, the greater the wedging actionimprovingtorquetransmission
and making the V-belt an effective solution, needing less width and tension than flat belts. V-belts
trump flat belts with their small center distances and high reduction ratios. The preferred centerdistance is larger than the largest pulley diameter, but less than three times the sum of both pulleys.
Optimal speed range is 10007000 ft/min. V-belts need larger pulleys for their larger thickness thanflat belts. They can be supplied at various fixed lengths or as a segmented section, where the
segments are linked (spliced) to form a belt of the required length. For high-power requirements, two
or more vee belts can be joined side-by-side in an arrangement called a multi-V, running on
matching multi-groove sheaves. The strength of these belts is obtained by reinforcements with fiberslike steel,polyesteroraramid(e.g.TwaronorKevlar). This is known as a multiple-V-belt drive (or
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sometimes a "classical V-belt drive"). When an endless belt does not fit the need, jointed and link V-
belts may be employed. However they are weaker and only usable at speeds up to 4000 ft/min. A
link v-belt is a number of rubberized fabric links held together by metal fasteners. They are length
adjustable by disassembling and removing links when needed.
Multi-groove belts
A multi-groove or polygroove belt[5]is made up of usually 5 or 6 "V" shapes along side each other.
This gives a thinner belt for the same drive surface, thus is more flexible, although often wider. Theadded flexibility offers an improved efficiency, as less energy is wasted in the internal friction of
continually bending the belt. In practice this gain of efficiency is overshadowed by the reducedheating effect on the belt, as a cooler-running belt lasts longer in service.
A further advantage of the polygroove belt, and the reason they have become so popular, stems from
the ability to be run over pulleys on the ungrooved back of the belt. Although this is sometimes done
with vee belts and a single idler pulley for tensioning, a polygroove belt may be wrapped around a
pulley on its back tightly enough to change its direction, or even to provide a light driving force. [6]
Any vee belt's ability to drive pulleys depends on wrapping the belt around a sufficient angle of the
pulley to provide grip. Where a single-vee belt is limited to a simple convex shape, it can adequately
wrap at most three or possibly four pulleys, so can drive at most three accessories. Where more must
be driven, such as for modern cars with power steering and air conditioning, multiple belts are
required. As the polygroove belt can be bent into concave paths by external idlers, it can wrap anynumber of driven pulleys, limited only by the power capacity of the belt.[6]
This ability to bend the belt at the designer's whim allows it to take a complex or "serpentine" path.
This can assist the design of a compact engine layout, where the accessories are mounted moreclosely to the engine block and without the need to provide movable tensioning adjustments. The
entire belt may be tensioned by a single idler pulley.
Ribbed belt
A ribbed belt is a power transmission belt featuring lengthwise grooves. It operates from contact
between the ribs of the belt and the grooves in the pulley. Its single-piece structure it reported to
offer an even distribution of tension across the width of the pulley where the belt is in contact, a
power range up to 600 kW, a high speed ratio, serpentine drives (possibility to drive off the back of
the belt), long life, stability and homogeneity of the drive tension, and reduced vibration. The ribbed
belt may be fitted on various applications : compressors, fitness bikes, agricultural machinery, foodmixers, washing machines, lawn mowers, etc.[7]
Film belts
Though often grouped with flat belts, they are actually a different kind. They consist of a very thin
belt (0.5-15 millimeters or 100-4000 micrometres) strip of plastic and occasionally rubber. They aregenerally intended for low-power (10 hp or 7 kW), high-speed uses, allowing high efficiency (up to
98%) and long life. These are seen in business machines, printers, tape recorders, and other light-
duty operations.
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Timing belts
Timing belt
Belt-drive cog on abelt-driven bicycle
Timing belts,(also known as Toothed, Notch, Cog, or Synchronousbelts) are apositivetransfer
belt and can track relative movement. These belts have teeth that fit into a matching toothed pulley.
When correctly tensioned, they have no slippage, run at constant speed, and are often used totransfer direct motion for indexing or timing purposes (hence their name). They are often used in
lieu of chains or gears, so there is less noise and a lubrication bath is not necessary.Camshaftsof
automobiles, miniature timing systems, andstepper motorsoften utilize these belts. Timing belts
need the least tension of all belts, and are among the most efficient. They can bear up to 200 hp
(150 kW) at speeds of 16,000 ft/min.
Timing belts with a helical offset tooth design are available. The helical offset tooth design forms a
chevron pattern and causes the teeth to engage progressively. The chevron pattern design is self-
aligning. The chevron pattern design does not make the noise that some timing belts make at
idiosyncraticspeeds, and is more efficient at transferring power (up to 98%).
Disadvantages include a relatively high purchase cost, the need for specially fabricated toothed
pulleys, less protection from overloading and jamming, and the lack of clutch action.
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Specialty belts
Belts normally transmit power on the tension side of the loop. However, designs forcontinuously
variable transmissionsexist that use belts that are a series of solid metal blocks, linked together as ina chain, transmitting power on the compression side of the loop.
Rolling roads
Belts used for rolling roads for wind tunnels can be capable of 250 km/h.[8]
Flying rope
For transmission of mechanical power over distance without electrical energy, a flying rope can be
used[9].Awireormanila ropecan be used to transmit mechanical energy from asteam engineor
water wheelto a factory or pump which is located a considerable distance (10 to 100s of meters or
more) from the power source. A flying rope way could be supported on poles and pulleys similar tothe cable on achair liftoraerial tramway.Transmission efficiency is generally high.
Chain drives
Chain driveis a way of transmitting mechanical power from one place to another. It is often used to
convey power to the wheels of a vehicle, particularlybicyclesandmotorcycles.It is also used in a
wide variety of machines besides vehicles.
Most often, the power is conveyed by aroller chain,known as the drive chainor transmissionchain,[1]passing over asprocketgear, with the teeth of the gear meshing with the holes in the links
of the chain. The gear is turned, and this pulls the chain putting mechanical force into the system.
Sometimes the power is output by simply rotating the chain, which can be used to lift or drag
objects. In other situations, a second gear is placed and the power is recovered by attaching shafts or
hubs to this gear. Though drive chains are often simple oval loops, they can also go around corners
by placing more than two gears along the chain; gears that do not put power into the system or
transmit it out are generally known asidler-wheels.By varying the diameter of the input and output
gears with respect to each other, thegear ratiocan be altered, so that, for example, the pedals of a
bicycle can spin all the way around more than once for every rotation of the gear that drives the
wheels.
Chains versus belts
Drive chains are most often made of metal, while belts are often rubber, plastic, or other substances.
Although well-made chains may prove stronger than belts, their greater mass increases drive train
inertia.
Drive belts can often slip (unless they haveteeth)which means that the output side may not rotate at
a precise speed, and some work gets lost to thefrictionof the belt against its rollers. Teeth on
toothed drive belts generally wear faster than links on chains, but wear on rubber or plastic belts and
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their teeth is often easier to observe; you can often tell a belt is wearing out and about to break more
easily than a chain.
Chains are often narrower than belts, and this can make it easier to shift them to larger or smaller
gears in order to vary the gear ratio. Multi-speed bicycles withderailleursmake use of this. Also, the
more positive meshing of a chain can make it easier to build gears that can increase or shrink indiameter, again altering the gear ratio.
Both can be used to move objects by attaching pockets, buckets, or frames to them; chains are often
used to move things vertically by holding them in frames, as in industrial toasters, while belts are
good at moving things horizontally in the form ofconveyor belts.It is not unusual for the systems tobe used in combination; for example the rollers that drive conveyor belts are themselves often driven
by drive chains.
Drive shaftsare another common method used to move mechanical power around that is sometimes
evaluated in comparison to chain drive; in particular shaft drive versus chain drive is a key design
decision for most motorcycles. Drive shafts te
Bearing
A bearingis a device to allow constrained relative motion between two or moreparts,typically
rotation or linear movement. Bearings may be classified broadly according to the motions they allow
and according to their principle of operation as well as by the directions of applied loads they canhandle.
Plain bearings use surfaces in rubbing contact, often with alubricant such as oil or graphite. A plain
bearing may or may not be adiscrete device. It may be nothing more than thebearing surface of a
hole with a shaft passing through it, or of a planar surface thatbears another (in these cases, not a
discrete device); or it may be a layer ofbearing metal either fused to the substrate (semi-discrete) or
in the form of a separable sleeve (discrete). With suitable lubrication, plain bearings often give
entirely acceptable accuracy, life, and friction at minimal cost. Therefore, they are very widely used.
However, there are many applications where a more suitable bearing can improve efficiency,
accuracy, service intervals, reliability, speed of operation, size, weight, and costs of purchasing and
operating machinery.
http://en.wikipedia.org/wiki/Derailleur_gearshttp://en.wikipedia.org/wiki/Derailleur_gearshttp://en.wikipedia.org/wiki/Derailleur_gearshttp://en.wikipedia.org/wiki/Conveyor_belthttp://en.wikipedia.org/wiki/Conveyor_belthttp://en.wikipedia.org/wiki/Conveyor_belthttp://en.wikipedia.org/wiki/Drive_shafthttp://en.wikipedia.org/wiki/Drive_shafthttp://en.wikipedia.org/wiki/Moving_partshttp://en.wikipedia.org/wiki/Moving_partshttp://en.wikipedia.org/wiki/Moving_partshttp://en.wikipedia.org/wiki/Plain_bearinghttp://en.wikipedia.org/wiki/Lubricanthttp://en.wiktionary.org/wiki/discrete#Adjectivehttp://en.wikipedia.org/wiki/Bearing_surfacehttp://en.wiktionary.org/wiki/bear#Verbhttp://en.wikipedia.org/wiki/Babbitt_%28metal%29http://en.wikipedia.org/wiki/Babbitt_%28metal%29http://en.wiktionary.org/wiki/bear#Verbhttp://en.wikipedia.org/wiki/Bearing_surfacehttp://en.wiktionary.org/wiki/discrete#Adjectivehttp://en.wikipedia.org/wiki/Lubricanthttp://en.wikipedia.org/wiki/Plain_bearinghttp://en.wikipedia.org/wiki/Moving_partshttp://en.wikipedia.org/wiki/Drive_shafthttp://en.wikipedia.org/wiki/Conveyor_belthttp://en.wikipedia.org/wiki/Derailleur_gears7/22/2019 ME2402 Mechatronics Lecture Notes
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Einstein College of Engineering
Thus, there are many types of bearings, with varying shape, material, lubrication, principal of
operation, and so on. For example,rolling-element bearings use spheres or drums rolling between
the parts to reduce friction; reduced friction allows tighter tolerances and thus higher precision than a
plain bearing, and reduced wear extends the time over which the machine stays accurate. Plain
bearings are commonly made of varying types of metal or plastic depending on the load, how
corrosive or dirty the environment is, and so on. In addition, bearing friction and life may be altereddramatically by the type and application of lubricants. For example, a lubricant may improve bearing
friction and life, but for food processing a bearing may be lubricated by an inferior food-safe
lubricant to avoid food contamination; in other situations a bearing may be run without lubricantbecause continuous lubrication is not feasible, and lubricants attract dirt that damages the bearings.
Principles of