MECHATRONIC - Mechatronics

8/2/2019 MECHATRONIC - Mechatronics

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Mechatronics


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Definition

Mechatronics is the combination of

Mechanical Engineering, Electronics

Engineering, Computer Engineering and

Control Engineering to create useful products


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Mechatronics involves combined work in the

following fields: Mechanical Systems

Electronics

Computer Engineering Control Engineering


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A Mechatronic System

The importance of Mechatronics is best

understood by considering an example.

We will see how the above engineering fieldsfuse in a Mechatronics system.

We will see how a holistic view is better than

modular view in these cases.


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Quad rotor

Quad rotor is a vehicle which is like a

helicopter with four propellers

These four propellers together provide thethrust required to lift the quad rotor

The quad rotor can be made to move forward,

backward, right or left by differentially

controlling the thrusts provided by each

propellers.


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Quad rotor


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More on Quad rotor

Of the four propellers, two rotate clockwise

and two rotate anticlockwise, while they are

shaped such that all four produce downward

thrust.

This is to make sure that the angular

momentum of the propellers is cancelled

among themselves so that the total vehicledoes not rotate.


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Propellers


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Mechanical System

The Mechanical system of the Quad rotor has

a frame and four propellers

As said above, two of the four propellers areclockwise and the other two are anticlockwise


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Electro-mechanical sub-system

The actuators which are generally used for

turning the propellers are DC Motors

We preferably use Brushless DC motors The speed of these motors can be very

precisely controlled.

They are driven by a central voltage source,generally a Lithium Polymer battery


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Brushless motor


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Electronics

Each of the Brushless motor requires an

Electronic speed controller to control the

speed of the motor and to provide enough

current to the motor.

It has an onboard microcontroller called

ATMega88

It has a lot of other control circuitry


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Electronics(Sensor systems)

The above Quad rotor has 3-axis

Accelerometers, 3-axis Gyros and 3-axis

Magnetometers to measure the Inclination

and heading of the Quad rotor

It has on board Analog to Digital Converters to

digitize the sensor readings


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Sensors


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Computation and Algorithms

The digitized outputs from the sensors are

filtered to obtained noise free and

acceleration compensated tilt values. This

requires a lot of computation and filtering

algorithms.

The Microcontroller needs to perform all the

above tasks and this demands forcomputation efficiency.


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The Control System

This is crux of the whole system which adds

life to the whole system.

The quad rotor shown in the above case isinherently in neutral equilibrium.

This means that the Quad rotor need not stay

in the horizontal position even if it starts from

horizontal position.

Even slightest disturbance can change its

orientation without any resistance(feedback)


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Control System

This means, any asymmetry in any of the four

motors/propellers/speed controllers/initial

conditions/circuit wiring can cause the Quad

rotor to change its orientation from

horizontal.

This is a serious problem as perfect symmetry

cannot be achieved.


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So, we need Feedback

To get this feedback, we need a Sensor

Once the sensor senses a difference, we want

to compensate. So we need an Actuator But we need to take in the sensor data,

interpret it sensibly, process it and give

required input to the actuator. So we need a

Processing Unit.


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Interesting Work

It is interesting to note that one of the first

hobby Quad rotor was made by only two

people.

The observation is that if one wants to be

good at Mechatronics, he needs to be good at

both Electronic and Mechanical parts,

because, it is only then that he develops aholistic view about the end product.


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Just being good at electronics will not suffice

as you need to have a very good feel of the

response of the system and need to do a lot of

analysis on the mechanics of the system.

On the other hand, just being good at

Mechanical part will not make him see the

advantages of the use of Electronics in thesystem.


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Holistic view

A person who has a good overview of both thesystems reacts the following way:

He does not go with IC Engines in replacement

for the DC motors because IC engines havemuch slower response as compared to DCmotors.

He will not use an aileron mechanism tocontrol the thrust from each motor as it ismuch less responsive than DC motors.


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Sensors, Actuators and Interfacing

Every Mechatronic system consists of Sensors,

Actuators and interfacing

Through the rest of our presentation, we willbe introducing a lot of Sensors, Actuators and

interfacing systems


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Sensors

Sensors measure the value of a particular

physical quantity.

We do not follow any particular order in listingthese sensors as we feel it is best that way!!


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Potentiometer

Potentiometer is one of the simplest sensor.

It can measure amount of angle that the knobhas rotated.

The potentiometer is like a rotary rheostat.

When powered, the output voltage of thepotentiometer varies linearly with the angle

rotated. The rated resistance of a potentiometer is the

sum of the pull up and pull down resistances.


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Potentiometer


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Applications

Potentiometer is widely used in servo motor

applications to provide an angle feedback.

Linear potentiometers also exist which cangive position feedback.


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Limitations

Potentiometers, basically being resistors give

rise to some thermal noise.

Thermal noise is a general problem in anyanalog sensor.

Potentiometer, being a contact measurement,

is affected by backlash.


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Ultrasonic Range Sensor

An Ultrasonic range sensors measures thedistance of an object from it self

It is a non contact distance measurer

The sensor sends out an ultra sonic soundwave.

The wave travels, gets reflected at the object

and is received by the sensor again. The time gap between this is used to

determine the distance.


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Ultrasonic range sensor


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Types of Output

There are different types of output.

The sensors can give an analog output which

is proportional to the distance of the object.It gives a continuous output.

Some sensors process the analog signal

obtained and output a pulsed output, where

the width of the pulse determines the

distance of the object.


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Pulse output


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Applications

Obstacle detection

Ultrasonic range sensors are extensively used

in robotics for non contact measurement anddetection

SONAR in defence applications


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Limitations

The sensor has a finite cone of view and

hence its resolution is not negligible when the

distance of the object increases.

If more than one sensor is being used at a

time then care should be taken that none of

the sensors get any stray echo

The accuracy of the sensor is not very high


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IR Sensor

Well known as the proximity sensor.

If there is an object near the sensor the sensor

will output a logic high. The IR sensor consists of an IR light source,

and an IR detector.

The IR detector detects whether there has

been a reflection of the IR light from an

object


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A simple IR sensor


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Characteristics

Generally used as an On Off sensor

Only presence is known, the exact distance is

difficult to find Even this sensor can be activated by stray IR

light.

Variation : Passive IR


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Passive Infrared Sensors

Used to detect the presence of humans in a

region.

This works on the same principle as the simpleIR sensor.

The IR radiation emitted by our body is

detected and the adequate output is given


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Applications

IR sensors are used as proximity sensors.

PIR sensors are used to detect presence of

humans in a location and then control deviceslike lights and fans

A non contact bump sensor can be easily

devised from a IR sensor


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Other Infrared sensors

IR Camera

IR based Tilt sensing


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Infrared Camera

As we know, all objects emit Infrared rays

depending on their temperature.

These Infrared rays are not visible to eye. An Infrared camera can see it.

This provides very good sight even in pitch

darkness.

The following video demonstrates it.


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Infrared Tilt Sensor

The sky and the ground have distinct IR

signatures, i.e. if you look sky and ground with

an IR camera, you will find them clearly

separated.

At, sufficiently high altitudes and open

environment, this horizon can be used as a

horizontal reference and the tilt can bemeasured.


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The IR tilt sensor uses four IR cameras and the

data from these cameras is used to measure

the tilt.

The following shows a video of this tilt sensor

A commercial product which is used by some

aeromodellers for flight stabilization is called

FMA - FS copilot


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Limitations

The arena of operation should be sufficiently

open.

This can be used only above a height (about 2

meters) from the ground


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GPS

GPS : Global Positioning System

This gives us the position of object of interest

anywhere on earth!

Position is given in terms of Three dimensional

co-ordinates, them being Latitude , Longitude

and the height.

Some systems give an output of even the

velocity of the object of interest


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How does it work

The system gets a fix with 4 or moresatellites when it is initializes.

Distance of the sensor from each of the

satellite is estimated. Now this information is transmitted using a

certain protocol called NMEA protocol

A protocol standardizes the different kinds ofoutputs that are possible when one uses aGlobal Positioning system


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NMEAPROTOCOL

Begins with a $ term

Different kinds of data are separated by ,

symbols

The end of a single sentence is denoted by a

* symbol

There is a checksum which follows each of this

sentence. This helps us check the data

obtained.


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Limitations

Very unreliable indoors and other closed

places like subways etc.

The satellite fix must be present always

The velocity reading sometimes is very

inaccurate

A typical GPS receiver has an accuracy over a

range of a circle of 3 meters

The output of a GPS is not direct.


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GPS Augmentation in weak signal

environments

A company called Locatacorp has recently

developed a technology which can directly

augment any GPS in the vicinity of the

module.

The following animation shows it clearly

This system is called Locatalite


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Locatalite


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Camera

A camera can be used as a sensor

It ca be used to detect any sort of change in

the configuration of the system

As long as something visible is changing, the

camera can be used to detect the changes in

the environment.

Changes are measured by going to each pixel

and checking each pixel


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The difficulty

Each pixel is characterized by the RGB values.

So, we have to explain all the concepts like

straight line, round box, bright light, big nose,

blue eyes, beautiful face or anything that we

want only in terms of an array of RGB values.

This is what makes Image processing a difficult

and intensive process.


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The Camera is different

The camera is a different kind of sensor

The output of a camera is very simple .Only

raw data is given by simple cameras.

To get useful information out of the system

some amount of processing needs to be done.

Detection through image processing has a

wide range of application


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Some image processing examples

Line detection

Light detection

Contour detection Mono SLAM


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Limitations

The image processing is highly computationintensive

There is no defined right path to take

The setup should be very robust. Even slightunwanted movements of the camera cangreatly spoil the results .

The image processing cannot be done onsmaller processing units, more often than nota computer needs to be connected


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Hall Effect sensor

This is another non contact position sensor

This works based on hall effect

The sensor detects the strength of themagnetic field and gives a corresponding

voltage output.

The Hall effect sensor works at a lower range.

While the out put is continuous, the sensor is

normally used for ON OFF applications


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Applications

They are widely used in brushless motors todetect when the rotor crosses a particular point

A cars fuel tank uses a hall effect sensor to detect

if tank is full or empty. Non contact position sensor with a continuous

output

Hall effect sensors can be used to detect strain in

the object

Master follower robots


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Usage ofHall effect sensor


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Inductive position sensors

When presence of a metal object needs to be

detected, we can use inductive sensors.

These sensors work on the basis of induction

These are widely used in two stroke engines

for timing the spark.


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Pressure Sensors

Pressure sensors detect the pressure at any pointof time.

These are used in may applications

There are different kinds of pressure sensorso Peizo resistive

o Potentiometric

o Peizoelectric

o Capacitive

o Inductive

o And many other types


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Applications

Pressure Sensor

Altitude sensing

Flow speed sensing Leak sensing

Level/Depth sensing


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Z Cam

Z Cam is a very recent technology which can

measure the Z of each pixel along with RGB

values

This allows us to take and build 3D images

It has not been released as a product yet.

It will have wide applications in gaming and

mobile robot positioning


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Encoders

Encoders are used to measure the rotation

angle.

They have a shaft which is to be connected to

the part of the system which rotates.

The output of the encoder gives the angle by

which the shaft rotates.


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Encoders


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Types of Encoders

There are two main types of encoders

Absolute Encoders: These Encoders give the

absolute angle rotated by the shaft. Their

output is, at a very basic level, a binary code.

Relative encoders: These Encoders give the

incremental angle rotated by the shaft. They

do not convey the absolute angle rotated bythe shaft.


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Absolute encoders

These encoders need as many bits as the logarithm ofthe number of levels that you want i.e. Nb = ceil(log2N)where N is the number of levels that we want.

For example, a if we want to have 210 = 1024 levelsfrom 00 to 3600, we need to have 10 wires from theEncoder.

This makes it slightly cumbersome to use it directlywith a microcontroller without additional circuitry.

Also, these are slightly intricate in design which makesthem costly.


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Relative & Absolute Encoders


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Relative encoders

Relative encoders, as the name suggests, give

the incremental angle rotated by the shaft.

The precision of these encoders is given in ppr

(pulses per revolution).

There exist as high as 4000 5000 ppr

encoders.


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Applications

Encoders are widely used in computer mice.

There are three encoders in a normal ballmouse, two for X and Y and one for scroll.

These are relative encoders, as it is only theincrement in motion that is needed and notthe absolute position of the mouse.

They are also used in industrial robots andautomation of manufacturing lines.

They are used in some photographic lenses


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LIDAR

LIDAR stands for Light Detection and Ranging

LIDAR is used to measure distances.

It uses a LASER beam which is directed to thetarget whose distance is to be measured.


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LIDAR

LIDAR sends out a LASER pulse ,which gets

reflected from the target and comes back.

The time of flight of the pulse is measured.

This gives the distance.


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Scanning Laser Range Finder

Scanning Laser Range Finder is an advanced

version of the single beam LIDAR.

It uses a rotating mirror which directs the

Laser beam in all the directions and measures

the distance of the obstacle in that direction

The output of this is a 2D Range scan.


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Scanning Laser Range Finder


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Pic of LIDAR


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Applications of LIDAR

Used widely in autonomous robotics for

obstacle detection, positioning, path planning

etc.

Terrain mapping

Precise non contact distance measurement for

surveying


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Limitations

Does not work for extremely shiny surfaces

Cannot detect the presence of glass

Gives a precisely 2D

scan which is difficult toapply in a 3D environment


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Inertial Measuring Unit

Inertial Measurement Unit is the modulewhich gives the orientation, acceleration in allthree direction using a set of accelerometers

and gyros It consists of accelerometers along all three

directions and rate gyros about all threedirections.

Some of the IMUs also have Magnetometersalong all three directions


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IMU, an old one


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MEMS accelerometers and gyros


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MEMS Accelerometers

An accelerometer measures acceleration

Many of the commercially available and used

accelerometers are MEMS accelerometers

MEMS stands for Micro Electro Mechanical

Systems.

The following slide shows the internal

structure of an accelerometer


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Working of accelerometer

Accelerometer can be considered as a springmass system

MEMS accelerometer has a precisely known mass

called proof mass. The pseudo force experienced by the proof mass

results in a strain in a piezoelectric sensor.

This produces a voltage which is amplified and

given out. Damping is also present


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Analogy of a MEMS accelerometer


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Working of an accelerometer

There are other ways of measuring the stress

produced by proof mass some of them being

Change in resistance

Change in capacitance


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MEMS Rate Gyros

Rate gyros measure the angular velocity

A basic rate gyro will give a voltage

proportional to the angular velocity as the

output.

They are generally rated in terms of the

maximum and minimum speeds that they can

measure


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MEMS gyros analogy


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Working of a rate gyro

A rate gyro has an oscillating piezo-electric

crystal.

When the gyro rotates along a direction

perpendicular to the direction of oscillation,

the crystal experiences a coriolis force.

This force is measured by another piezo-

electric crystal which gives a voltage output.


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Magnetometers

Magnetometers measure the Magnetic field

passing through it.

This is used to find the orientation of the

sensor along the horizontal plane.

Applications of accelerometers and


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Applications of accelerometers and

rate gyros

Robotics

Positioning

Tilt sensing

and many more


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Merits of MEMS devices

They are small and light weight

They are relatively easy to manufacture

They are relatively cheap


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Limitations of MEMS devices

They have relatively larger noise and bias and

are less accurate as compared to other gyros


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Opto Sensors


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Optical Sensors

Advantages :-

o Simple, no loading effect, can have a very longrange

o Does not get affected by stray magnetic fields andinterferences.

Requirements :-

o A Light Source

o A photodetector

o Light guidance devices


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Optical Gyro Sensor


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SagNac Effect

Sagnac Effect :- The optial

path light difference is

experienced by two light

beams travelling in

opposite directions in a

rotating frame.


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Actuators

Actuators are those elements in a mechatronic

system that give a mechanical output for a

control signal from a computer .

Again the list of actuators are not in a

particular order !


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DC Motor

One of the most commonly seen and used

actuator.

Converts electric energy into mechanical

(rotation) energy.

DC Motors are used in a wide range of

applications


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DC Motor


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Controlling a DC motor

The Voltage given to a DC motor controls the

speed of the DC motor

APulse Width Modulated (PWM) digital signal

can also be used for controlling a DC motor

The following slide shows a PWM signal

Many of the microcontrollers have internal

circuitry for producing PWM


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PWM

Speed-torque characteristics of a DC


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Speed torque characteristics of a DC

motor


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Servo Motors

These are DC motors coupled with a

potentiometer.

These motors allow us to precisely specify the

position to which the motor must rotate to

This itself is control system!

There are both digital and analog servos


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Digital Servos

The control signal to these servos is given by

sending a pulse.

The width of the high pulse determines the

position of the servo.

Commercially available digital servos do not

rotate the whole of 360 degrees.


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Servo motor


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Stepper Motors

As the name suggests, stepper motors rotate

in steps.

Strictly speaking, stepper motor is just an

array of electromagnets.

It has a common ground and generally four

wires.

Each of these is connected to an alternatearray of electromagnets as shown in the figure

S ki


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Stepper motor working

S


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Stepper motor

A li i


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Applications

Stepper motor is mainly used in industrial

robots where, precise movement is needed.

It can also be used where precise control over

the speed is needed.

B hl DC M


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Brushless DC Motors

Brushless motors are different from normal

motors in that they have separate circuitry for

changing the polarity of motor.

So they do not have carbon brushes which arepresent in normal motors.

M it d D it


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Merits and Demerits

Merits

Low power losses

Precise speed control

Lesser moment of inertia Lesser maintenence required

Demerits

Need control circuitry More expensive

Difficult to repair

Li A t t


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Linear Actuators

Linear actuators convert the rotational motion

to linear motion

Strictly speaking these are not wholly separate

class of actuators but some extensions ofDCmotor

These are widely used in industrial robotics

I t f


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Interfaces

The controllers , the sensors, the actuators all

these need to be interfaced with each other

Only if there is a continuous communication

possible is there a way to get the system to aworking condition.

There are two basic interfaces that must be

done to complete a control system

Th T I t f


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The Two Interfaces

Sensors to the controller

o The different sensors in a system must be

connected to the controller of the system. Thecontroller must be able to access the output of

the sensors at anytime to be able give the right

control signals to the actuators.

Th T I t f


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The Two Interfaces

Controller to Actuators

o The actuators need to be controlled based on the

sensor outputs. The controller needs to send the

right control signals for this to happen. Theseinterfaces must be secure and should not allow

any noise to be transmitted.

A l t Di it l C t


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Analog to Digital Convertors

Many of the sensors produce a Voltage output

These voltages need to be digitized for using it

in computers

Hence we need Analog to Digital

convertors(ADCs)

ADCs


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ADCs

ADCs are characterized mainly by the

resolution that they have.

An 8 bit ADC means that there are 28 = 256

distinct levels possible in between 0 and Vcc

i.e a 10 bit ADC working with a voltage of

5Volt can distinguish between 5/210 which is

nearly 5mV

DACs


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DACs

Digital to Analog converters convert a digital

signal to analog signal

This is required to drive any real actuators

APulse Width Modulator with a capacitor at

the output is a very crude DAC


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Communication to computer


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Communication to computer

In robotics, communication to computer is

usually done by serial or parallel ports


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SELF BALANCING CYCLE


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THANK YOU

MECHATRONIC - Mechatronics

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