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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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