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Mechatronics
If you cannot be a star in the Sky, at least be a lamp in your Home !
By:- Swamy Vivekananda
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Mechatronics
Prepared by:
Dr. N.V.Raghavendra
Dept. of Mechanical Engineering
National Institute of Engineering, Mysore.
MECHATRONICS
UNIT 1
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MECHATRONICS
The integration of electronic engineering, electrical
engineering, computer technology and control engineering with
mechanical engineering is increasingly forming a crucial part in
the design, manufacture and maintenance of a wide range of
engineering products and processes. The term mechatronics
describes this integrated approach.
Why Mechatronics ?
In recent years, the application of micro-electronics and
computers in the design and manufacturing sector has
significantly improved functionality, quality and productivity of
mechanical products
Integrated embedded technology has become integral part of
automation
Automation and control represent a broad area with diverse
applications, such as, manufacturing processes and equipments,
process control, robotics, home automation, office automation,
and so on.
Mechatronics has enabled high level of flexibility and
sophistication in products and processes.
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Multidisciplinary Scenario
Multidisciplinary Scenario
In figure 1, one can distinguish between the traditional and current
curriculumscenario which are separated by an axis
The figure shows how the traditional electrical and mechanical
disciplines have given birth to new disciplines, which further encouraged
many other branches to emerge
The engineering disciplines are now converging rather than diverging,
because of requirements of inter-disciplinaryknowledge
The engineering filed is being radically altered with the advent of
digital technology, low cost VLSI chips, embedded technology, control
networking systems (filedbus technology), microcontrollers, advanced
software tools (CAD/CAM, OO-based, artificial neural networks, fuzzy
logic, etc), and so on.
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Multidisciplinary Scenario
Advanced technological designs are highly complex and of
inter-disciplinary nature involving synergetic integration of
mechatronics, photonics, computronics and communication
Studies have shown that the productivity of an industry can
increase upto 40% by employing engineers with inter-
disciplinary skills
Some typical mechatronics platforms: space shuttles, air
crafts, industrial machines, automobiles, robots, material
transfer equipments, etc
Origin of Mechatronics
The term mechatronics originated in Japan in the late 1970s to
describe design of electro-mechanical products
The field has been driven in recent times by rapid progress in the field
of microelectronics
Major areas where rapid developments are taking place are:
Motion control
Robotics
Automotive systems
Intelligentcontrol
Actuators and sensors
Modeling and design
System integration
Manufacturing
Micro devices and optoelectronics
Vibrations and noise control
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Evolution of Mechatronics
Mechatronics has evolved through four stages during its
development to the present state:
1. Primary level mechatronics
2. Secondary level mechatronics
3. Tertiary level mechatronics
4. Quaternary level mechatronics
Evolution of Mechatronics
Primary level mechatronics
This level encompasses input/output (I/O) devices such as sensors
and actuators that integrate electrical signaling with mechanical
action at the basic control level
Electrically controlled fluid valves and relay switches are two
examples
Secondary level mechatronics
Integrates microelectronics into electrically controlled devices
Sometimes, these products are stand-alone
Example: a cassette tape player
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Evolution of Mechatronics
Tertiary level mechatronics
The mechatronic systems at this level are called smart
systems
The control strategy uses microelectronics, microprocessors,
and other application specific integrated circuits as bits and
pieces for control realisation
A microprocessor based electrical motor used for actuation
purpose in industrial robots is an example of such systems
Evolution of Mechatronics
Quaternary level mechatronics
This level attempts to improve smartness a step ahead by
introducing intelligence and FDI (fault detection and
isolation) capability into the systems
Artificial neural network and fuzzy logic try to capturesome of the intellectual capabilities of the intelligence
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Scope of Mechatronics
Integrated design issuesin Mechatronics
Mechatronics is a design philosophy and an integrated approach to
engineeringdesign
An important characteristic of mechatronic devices and systems is
their built-in intelligence, which results through a combination of
precision mechanical and electrical and real-time programming
integrated with the design process
The integration within a mechatronic system is performed through thecombination of hardware and software.
Hardware integration results from designing the mechatronic system
as an overall system and bringing together the sensors, actuators, and
microcomputers into the mechanical system.
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Integrated design issuesin Mechatronics
Software integration is primarily based on advanced control
functions
Figure below illustrates how the hardware and software
integration takes place
Mechatronics Design Process
Product design has inherent complexity due to the multi-
disciplinary nature of the design process
The Mechatronic design approach applies concurrent
engineering concepts instead of the traditional sequential
approach
The mechatronic design process consists of three phases: a)
modeling and simulation, b) prototyping and c) deployment
Because of their modularity, mechatronic systems are well suited
for applications that require reconfiguration
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Mechatronics Design Process
Mechatronics Design Process
Hardware-in-the-loop simulation
In the prototyping step, many of the noncomputer subsystems of
the model are replaced with actual hardware
Sensors and actuators are also put in their respective places
The resulting model is part mathematical and part real
This process of fusing and synchronising model, sensor, and
actuator information is called real-time interfacing or hardware-
in-the-loop simulation
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Advanced Approaches in Mechatronics
Recent developments in Mechatronics are creating opportunitiesin intelligent manufacturing
Sensor-based manufacturing systems are becoming order of the
day
The new approach is towards the design of intelligent
autonomous inspection systems as well as intelligent decision
making systems that perform tasks automatically, without human
intervantion
Mechatronic technology used in manufacturing will impact new
equipment as well as some retrofit applications
Advanced Approaches in Mechatronics
Intelligent Supervisory Control Structure
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Advanced Approaches in Mechatronics
Model based Monitoring System
Mechatronic System with OpenArchitecture Platform
Advanced Approaches in Mechatronics
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Advanced Approachesin Mechatronics
Major advanced mechatronic application:
Autonomous production cells with image-based object recognition
Integrated supervisory systems with multi-process control capability
and shared databases from CAD drawings
FMS with off and on-line programming
Bio-robotics
Endoscopic and orthopedic surgery
Magnetically levitated vehicles
Robotics in nuclear and space applications
Sensors and Transducers
The term sensor is used for an element which produces a signal
relating to the quantity being measured. For example, in an electrical
resistance temperature element, the quantity being measured is
temperature and the sensor transforms an input of temperature into a
change in resistance.
The term transducer is often used in place of the term sensor.
Transducers are defined as elements that when subject to some physical
change experience a related change. Transducers also convert signals in
one form into another.
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Performance Terminology
1. Range and span
2. Error
3. Accuracy
4. Sensitivity
5. Hysteresis error
6. Non-linearity error
7. Repeatability
8. Stability
9. Dead band time
10.Resolution
11.Output impedance
Performance Terminology
1. Range and span:
The range of a transducer defines the limits between which the
inputs can vary
The span is the maximum value of the input minus the
minimum value
A load cell for the measurement of forces might have a range of
0 to 50 KN and a span of 50 KN
2. Error:
Error = measured value true value
3. Accuracy
It is the extent to which the value indicated by a measurement
system might be wrong
It is thus the summation of all the possible errors that are likely
to occur, as well as the accuracy to which the transducer has
been calibrated
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Performance Terminology
4. Sensitivity:
It is the relationship indicating how much output you get perunit input
For example, a resistance thermometer may have a sensitivity
of 0.5 ohms/0 C
This term is also frequently used to indicate the sensitivity to
inputs other than that being measured, i.e., environmental
changes, such as temperature changes in the environment
5. Hysteresis error:
Transducers can give different outputs from
the same value of quantity being measured
according to whether that value has beenreached by a continuously increasing
change or continuously decreasing change.
This effect is called hysteresis.
Performance Terminology
6. Non-linearity error:
For many transducers a linear relationship between the input and
output is assumed over the working range, i.e., a graph of output
plotted against input is assumed to give a straight line.
Few transducers however, have a truly linear relationship and
therefore, errors occur as a result of the assumption of linearity.
The error is defined as the maximum difference from the straight
line.
Various methods are used for the numerical expression of the non-
linearity error.
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Performance Terminology
a) Using end-range values b) Best straight line for all values
Performance Terminology
c) Best straight line through Zero point
The error is generally quoted as a
percentageof the full range output
For example, a transducer for the
measurement of pressure might be
quoted as having a non-linearity error
of 0.5% of the full range
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Performance Terminology
7. Repeatability / reproducibility:
Ability of a transducer to give the same output for repeated
applications of the same input value
Repeatability = (max.min. values given) X 100
full range
For example, a transducer measuring angular velocity can be
said to have a repeatability of 0.1% of the full range at a
particular angular velocity
Performance Terminology
8. Stability:
It is the ability to give the same output when used to measure a
constant input over a period of time
The term drift is often used to describe the change in output
that occurs over time
The drift may be expressed as a percentage of the full range
output
9. Dead band time: It is the range of input values for which there is no output
The dead band time is the length of time from the application
of an input until the output begins to respond and change
For example, bearing friction in a flow meter using a rotor
might mean that there is no output till input has reached a
particular velocity threshold
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Performance Terminology
10.Resolution: The resolution is the smallest change in the input value that will
produce an observable change in the output
For a wire-wound potentiometer the resolution might be specified
as, say, 0.50
11 Output impedence:
When a sensor giving an electrical output is interfaced with an
electronic circuit it is necessary to know the output impedence
since this impedence is being connected either in series or parallel
with that circuit
The inclusion of the sensor can thus significantly modify the
behaviour of the system to which it is connected
Static and Dynamic Characteristics
Static characteristics are the values given when steady-state
conditions occur, i.e., when the transducer has settled down after
having received some input
Dynamic characteristics refer to the behaviour between the time
that the input value changes and the time that the value given by
the transducer settles down to the steady-state value
Dynamic characteristics are stated in terms of the response of the
transducer to inputs in particular forms, such as step input, ramp
input or sinusoidal input
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Static and Dynamic Characteristics
1. Response time:
This is the time which elapses aftera constant input, is applied to the
transducer up to the point at which
the transducer gives an output
corresponding to some specified
percentage, e.g., 95% of the value of
input.
2. Time constant:
This is the 63.2 % response time.
The time constant is a measure of the
inertia of the sensor and so how fastit will react to changes in its input;
the bigger the time constant slower
will be its reaction to a changing
inputsignal.
Static and Dynamic Characteristics
3. Rise time:
This is the time taken for the output to rise to some specified
percentage of the steady-state output. Often the rise time refers to
the time taken for the output to rise from 10% of the steady-state
value to 90 or 95% of the steady-state value
4. Settling time:
This is the time taken for the output to settle to within somepercentage, e.g., 2% of the steady-state value
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Static and Dynamic Characteristics
4. Settling time: Consider the following data which indicates how a
thermometer readingchangedwith time.
The steady-state value is 550 C and
therefore, 95% of 55 is 52.250 C, the 95%
response time is about 228 secs.
Displacement, Position and Proximity
1. Displacement sensors are concerned with the measurement of
the amount by which some object has been moved
2. Position sensors are concerned with the determination of the
position of some object with reference to some reference point
3. Proximity sensors are a form of position sensor and are used to
determine when an object has moved to within some distanceof the sensor. They are essentially devices which give on-off
outputs
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Displacement, Position and Proximity Sensors
Considerations for selection:
The size of the displacement, or how close the object is before it
is detected
Whether the displacement is linear or angular
The resolution required
The accuracy required
What material the measured object is made up of
Contact or non-contact type
The cost
Potentiometer Sensor
It consists of a resistance element with
a sliding contact which can be moved
over the length of the element
Such elements can be used for linear or
rotary displacements, the displacement
being converted into a potential
difference
The rotary potentiometer consists of a
circular wire-wound track or a film of
conductive plastic over which a
rotatable sliding contact can be rotated
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Potentiometer Sensor
With a constant input voltage Vs between
terminals 1 and 3, the output voltage V0between terminals 2 and 3 is a fraction of the
input voltage
This fraction depends on the ratio of the
resistance R23 between terminals 2 and 3
compared with the total resistance R13
between terminals 1 and 3
V0/Vs = R23/R13
If the track has a constant resistance per unit
length, i.e., per unit angle, then the output isproportional to the angle through which the
slider has rotated. Hence, angular
displacement can be converted into a potential
difference
Potentiometer Sensor
An important effect to be considered with a potentiometer is the effect
of a load RL connected across the output. The resistance RL is in
parallel with the fraction x of the potentiometer resistance Rp.
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Strain-gauged Element
The electrical resistance strain gauge is a metal wire,or a metal foil strip of semiconductor material which
is wafer like and can be stuck onto surfaces like a
postage stamp
When subject to strain, its resistance R changes, the
fractional change in resistance dR/R being
proportional to the strain
i.e., dR/R= G. Where G is a constant of
proportionalityand termed the gauge factor
The gauge factor is normally supplied by the
manufacturer of the strain gauges from a calibration
made of sample straingauges taken from a batch
Strain-gauged Element
One from of displacement sensor has strain
gauges attached to flexible elements in the form of
cantilevers, rings or U-shapes.
The change in resistance is a measure of the
displacement or deformation of the flexible
element
Such gauges have linear displacement of the order
of 1 mm to 30 mm and have a non-linear error of
about 1% of full range
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Capacitive Element
The capacitance C of a parallel plate capacitor
is given by C = r0A/d where r is the
relative permittivity of the dielectric between
the plates, 0 a constant called the permittivity
of free space, A is the area of overlap between
the two plates and d the plate separation
Capacitive sensors for the monitoring of linear
displacements might thus take the forms shown
in the adjoining figure
In case (a), if separation d is increased by a
displacement x, then the capacitance becomes:
Differential Transformers
Linear Voltage Differential Transformers, generally abbreviated as LVDT
Consists of 3 coils symmetrically spaced along an insulated tube.
The central coil is the primary coil and the other two are identical
secondary coils which are connected in series in such a way that their
outputs oppose each other
A magnetic core is moved through the central tube as a result of the
displacement being monitored
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Differential Transformers
When there is an ac input to
the primary coil, alternating emfs areinduced in the secondary coils
With the magnetic core in
central position, emf induced in each
coil is same. They are so connected that
their outputs oppose each other, the net
result being zero output
When the core is displaced from the central position, there is a
greater amount of magnetic core in one coil than the other. The result is that a
greater emf is induced in one coil than the other.
Therefore, there is a net output from the two coils. Greater the displacement,
more is the net output voltage.
Differential Transformers
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Differential Transformers
eqn(1)
Differential Transformers
With this form of output, the same amplitude output voltage is
produced for two different displacements. To give an output voltage which is
unique to each value of displacement we need to distinguish between where
the amplitudes are same but there is a phase difference of 1800.
A phase sensitive demodulator, with a low pass filter, is used to
convert the output into a d.c. voltage which gives a unique value for each
displacement.
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Differential Transformers
A rotary variable differential
transformer (RVDT) can be used for the
measurement of rotation, and it operates on the
same principle as the LVDT
The core is a cardioid shaped piece of
magnetic material and rotation causes more of it
to pass into one secondary coil than the other
The range of operation is typically
40% with a linearity error of about 0.5% ofthe range
Eddy Current Proximity Sensors
If there is a metal object in close
proximity to an alternating magnetic
field, then eddy currents are induced in
it, and the eddy currents themselves
produce a magnetic field
As a result impedence of the coil
changes and so the amplitude of the ac
current
The figure shows the basic form of such a sensor which can be used for non-
magnetic but conductive materials
These sensors are small in size, relatively inexpensive, highly sensitive and
high in reliability
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Optical Encoders
An encoder is a device that provides a digitaloutput as a result of a linear or angulardisplacement
Two types of position encoders: incrementaland absolute
In incremental type shown in adjoiningfigure, a beam of light passes through slotsin a disc and is detected by a suitable lightsensor
When the disc is rotated, a pulsed output isproduced by the sensor with the number ofpulses being proportional to the anglethrough which the disc rotates
Optical Encoders
The angular position of the disc, and hence the shaft
rotating it, can be determined by the number of pulses
produced since some datum position
The inner track is used to locate the home position
The other two tracks enable the determination of
direction of rotation
The resolution is determined by the number of slots
on the disc
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Optical Encoder: Absolute type
This gives an output in the form of a binary number of several digits,
each such number representing a particular angular position
The rotating disc has many concentric circles of slots and sensors to
detect the light pulses
The slots are arranged in such a way that the sequential output from
the sensors is a number in the binary code
Optical Encoder: Absolute type
Typical encoders tend to have up to 10 or 12 tracks
The number of bits in the binary number will be equal to the number of
tracks
With 10 tracks there will be 10 bits and so the number of positions that can
be detected is 210, i.e., 1024, and a resolution of 360/1024 = 0.350.
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Optical Encoder: Absolute type
Binary and Gray codes
In the normal form of binary code,
change from one binary code to the
next can result in more than one bit
changing
Due to misalignment, one of the bits
may change fractionally before the
others, which leads to false counting
In gray code, only one bit changes in
moving from one number to the next
Proximity Switches
Lever operated Roller operated
Cam operated
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Proximity Switches
Reed Switch
It is a non-contact proximity switch
It consists of two magnetic switch
contacts sealed in a glass tube
When a magnet is brought close to the
switch, the magnetic reeds are attracted to
each other and close the switch contacts
The reed switch is commonly used for checking closure of automatic
doors
It is also used in tachometers which involve the rotation of a toothed
wheel past the reed switch. If one of the teeth has a magnet attached to it,
every time it passes the switch it momentarily closes the contacts and
produces an electrical pulse in the associated circuit
Proximity Switches
Photo-electric sensor
Photo-sensitive devices can be
used to detect the presence of an opaque
object by it breaking a beam of light, or
infrared radiation falling on such adevice or by detecting light reflected
back by the object
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Hall Effect Sensor
A current flowing in a conductor is like a beam of
moving charges and will be deflected from its straightline path when a magnetic field is applied on it
This effect was discovered by E.R.Hall in 1879 and is
called the hall effect
Consider electrons moving in a conductive plate with a
magnetic field applied at right angles to the plane of
the plate as shown in the adjoining figure
As a consequence, electrons are deflected to
one side of the plate and that side becomes negatively
charged while the opposite side becomes positivelycharged
This charge separation produces an electric
field in the material
Hall Effect Sensor
Where V is the transverse potential difference,
B is the magnetic flux density at right angles to the
plate, I is the current through it,
t the plate thickness and
KH a constant called the hall coefficient
Thus, if a constant current source is used with a
particular sensor, the hall voltage is a measure of the
magnetic flux density
Hall effect sensors are generally supplied in an
integrated circuit with the necessary signal processing
capability
Hall effect sensors are immune to environmental
contaminants and can be used under severe service
conditions
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Hall Effect Sensor
There are two basic forms of hall effect sensors, linear where the output varies
in a reasonably linear manner with the magnetic flux density, and threshold
where the output shows a sharp drop at a particular magnetic flux density
Hall effect sensor has the advantage of being able to operate as a switch thatcan operate up to 100 KHz repetition rate, cost less than electro-mechanical
switches
Hall Effect Sensor
Hall effect sensors can be used to sense
position, displacement and proximity if the
object being sensed is fitted with a small
permanent magnet
It can be used to sense the level of fuel in an
automobile fuel tank, as shown in adjoining
figure
A magnet is attached to a float and as the level
of fuel changes, the float distance from from the
hall sensor also changes
The result is a hall voltage output which is a measure of the
distance of the float from the sensor and hence the level of fuel in the tank
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Tactile Sensor
A tactile sensor is a particular form of pressure
sensor
It is used on the finger tips of robotic hands to
determine which hand has come into contact
with an object
They are also used for touch display screens
where a physical contact has to be sensed
One form of tactile sensor uses piezoelectric polyvinylidene fluoride (PVDF)
film. Two layers of the film are used and are separated by a soft film which
transmits vibrations
The lower PVDF film has an alternating voltage applied to it and this results
in mechanical oscillations of the film (the piezoelectric effect in reverse)
Tactile Sensor
The intermediate film transmits these vibrations to the upper PVDF film
As a consequence of the piezoelectric effect, these vibrations cause an
alternatingvoltage to be produced across the upper film
When pressure is applied to the upper PVDF film its vibrations are
affected and the output alternatingvoltage is changed
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