Mechatronics Introduction

7/30/2019 Mechatronics Introduction

1/35N.V. Raghavendra

Mechatronics

If you cannot be a star in the Sky, at least be a lamp in your Home !

By:- Swamy Vivekananda



Mechatronics

Prepared by:

Dr. N.V.Raghavendra

Dept. of Mechanical Engineering

National Institute of Engineering, Mysore.

MECHATRONICS

UNIT 1



Mechatronics

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.



Mechatronics

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.



Mechatronics


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



Mechatronics

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


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



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


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



Mechatronics

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.



Mechatronics

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



Mechatronics



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



Mechatronics

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


Intelligent Supervisory Control Structure



Mechatronics


Model based Monitoring System

Mechatronic System with OpenArchitecture Platform




Mechatronics

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.



Mechatronics

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


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



Mechatronics


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.


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.



Mechatronics


a) Using end-range values b) Best straight line for all values


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



Mechatronics


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


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



Mechatronics


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



Mechatronics


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.


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



Mechatronics


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



Mechatronics

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



Mechatronics


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


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.



Mechatronics

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



Mechatronics

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



Mechatronics


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.




Mechatronics


eqn(1)


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.



Mechatronics


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



Mechatronics

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



Mechatronics

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


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.



Mechatronics


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



Mechatronics

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



Mechatronics

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



Mechatronics

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



Mechatronics

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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Mechatronics Introduction