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CHAPTER 1
POWER SUPPLY UNIT
1.1 Introduction:
Power supplies of electronics devices can be broadly divided
into line-frequency
and switching power supplies. The line-frequency supply is
usually a relatively simple
design, but it become increasingly bulky and heavy for
high-current equipment due to
the need for large mains frequency transformers and head-slinked
electronic regulator
circuitry.
Our project power supply unit is designed to provide 5V and 12V
dc supply. The
power supply unit consists of step down transformer, bridge
rectifier, filter and voltage
regulator.
1.2 Transformer:
In general, the AC line voltage presenting your house wiring is
not suitable for
electronic circuits. Most circuit required a considerably lower
voltage, while a few
require high voltages. The transformer serves to convert the AC
line voltage to a
voltage level more appropriate to the need of the circuit to be
powered. At the same
time, the transformer provides electrical isolation between the
ac and the circuit being
powered, which is an important safety consideration.
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Figure 1.1 Construction of Transformer
1.2.1 Step down transformer:
Step down transformer is a static machine and it transfer the
electrical power
from one circuit to another circuit without changing the
frequency. In our project we
have used step down transformer to reduce the voltage level from
230V to12V.
Fig .Step down transformer
Step down transformer are designed to reduce electrical voltage.
Their primary
voltage is greater than their secondary voltage. They can
include features for electrical
isolation, power distribution, and control and instrumentation
applications.
Step down transformer are made from two or more coils of
insulated wire wound
around a core made of iron. When voltage is applied to one coil
(called the primary or
input) it magnetizes the iron core, which induces a voltage in
the other coil, (called the
secondary or output). The turns ratio of the two sets of
windings determines the of
voltage transformation.
1.3.1 Bridge rectifier:
The rectifier is an electronic device, which converts an
alternating current wave
to a pulsating direct current wave form. The bridge rectifiers,
developed about 100
years ago, are an essential part of powering our electronic
appliances. They take
household current and change it to a more useful form.
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1.3.2 Working principle:
Here we use bridge rectifier because it is more efficient when
compared to half
wave rectifier. It is the most frequency-used circuit for
electronic dc power supplies.
During the positive half cycle of the input, diodes D1 and D2
are forward biased
and we get output across RL. This was all about only positive
cycle of AC input wave.
During the negative half cycle the diodes D3 and D4 of bridge
rectifier are in
forward biased, and other two diodes are reverse biased. So,
only D3 and D4 conducts
and we get output across the RL.
1.4 Filter:
The pulsating dc from the rectifier is generally still not
suitable to power the
actual load circuit. The pulsations typically vary from 0 volts
to the peak output voltage
of the transformer. Therefore, we insert a circuit to store
energy during each voltage
drops. This circuit is called a filter, and its job is to reduce
the pulse from the rectifier
to much smaller ripple voltage. No filter configuration can be
absolutely perfect, but a
properly designed filter will provided a dc output voltage with
only a small ac ripple.
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1.4.1 Capacitor filter:
If we place a capacitor at the full-wave rectifier as shown to
the left, the capacitor
will charge to the peak voltage each to the peak voltage each
half cycle, and then will
discharge more slowly through the load while the rectifier
voltage drops back to zero
before beginning the next half-cycle. Thus, the capacitor helps
to fill in the gaps
between the packs, as shown in red in the first figure to the
right.
Although we have used straight lines for simplicity, the decay
is actually the normal
exponential decay of any capacitor discharging through a load
resistor. The extent to
which the capacitor voltage drops depends on the capacitance on
the capacitor and the
amount of current drawn by the load; these two factor
effectively from the RC time
constant for voltage decay.
1.4.3 Voltage regulator:
The 78xx (sometimes L78xx, LM78xx, MC78xx...) is a family of
self-contained
fixed linear voltage regulator integrated circuits. The 78xx
family is commonly used
in electronic circuits requiring a regulated power supply due to
their ease-of-use and
low cost. For ICs within the family, the xx is replaced with two
digits, indicating the
output voltage (for example, the 7805 has a 5 volt output, while
the 7812 produces
12 volts). The 78xx line are positive voltage regulators: they
produce a voltage that is
positive relative to a common ground. There is a related line of
79xx devices which are
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complementary negative voltage regulators. 78xx and 79xx ICs can
be used in
combination to provide positive and negative supply voltages in
the same circuit.
78xx ICs have three terminals and are commonly found in the
TO220
form factor, although smaller surface-mount and larger TO3
packages are available.
These devices support an input voltage anywhere from a couple of
volts over the
intended output voltage, up to a maximum of 35 to 40 volts
depending on the make,
and typically provide 1 or 1.5 amperes of current (though
smaller or larger packages
may have a lower or higher current rating). IC regulator is used
to give 6 volt because
the 6 volt sensor is used in the circuit.
1.5. Discrete Components:
1.5.1 Resistance:
It may be defined as the property of a substance, due to which
it opposes the
flow of electricity through it. Resistance is the opposition
that a substance offers to the
flow of electric current. It is represented by the uppercase
letter R. The standard unit
of resistance is the Ohm (). When an electric current of one
ampere passes through a
component across which a potential difference (voltage) of one
volt exists, then the
resistance of that component is one ohm. In general, when the
applied voltage is held
constant, the current in a direct-current (DC) electrical
circuit is inversely proportional
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to the resistance. If the resistance is doubled, the current is
cut in half; if the resistance
is halved, the current is doubled. This rule also holds true for
most low frequency
alternating-current (AC) systems, such as house hold utility
circuits.
1.6 Light Emitting Diodes:
LED is commonly called LEDs, are real unsung heroes in the
electronics world.
They do dozens of different jobs and are found in all kinds of
devices. Among other
things, they form numbers on digital clocks, transmit
information from remote controls,
light up watches and tell you when your appliances are turned
on. Collected together,
they can form images on a jumbo television screen or illuminate
a traffic light.
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CHAPTER 2
RELAY
2.1 Introduction:
A Relay is an electrically operated switch. Many relays use an
electromagnet to
operate a switching mechanism, but other operating principles
are also used. Relays
find application where it is necessary to control, a circuit by
low power signal, of where
several circuits must be controlled by one signal. The first
relays were used in long
distance telegraph circuits, repeating the signal coming in from
one circuit and re-
transmitting it to indicator. Relays found extensive used in
telephone exchange early
computers to perform logical operations. A type of relay that
can candle the high power
required to directly drive an electrical motor is called a
conductor.
Solid state relays control power circuits with no moving parts,
instead using
semiconductor device triggering by light to perform switching.
Relays with calibrated
operating characteristics and something multiple operating coils
are used to product
electrical circuits from overload or faults in modern electrical
power system these
functions are performed by digital instructions still called
Production Relay.
2.2 Construction:
A simple electromagnetic relay such as the one taken from a car
in the first
picture is an adaptation of an electromagnet. It consist of a
coil of wire surrounding
soft iron core, an iron yoke, which provides a low reluctant
path for magnetic flux, a
movable iron armature, and a sets, of contact. The armature is
hinged to the yoke and
mechanically linked to a moving contact or contacts. It is held
in a place by a spring so
that when the relay is de-energized there is an air gap in the
magnetic circuit. In this
condition, one of the two sets of contact in the relay pictured
is closed, and together set
is open relays other relays may have more or fewer sets of
contacts depending on their
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function. The relay in the picture also has a wire connecting
the armature of the yoke.
This ensures continuity of the circuit between the moving
contacts on the armature,
and the circuit track on the PCB via the yoke which is soldered
to the PCB.
2.3 Operation:
When a current flows through the coil, the resulting magnetic
field attracts an
armature that is mechanically linked to a moving contact. The
movement either makes
or breaks a connection with a fixed contact. When the current to
the coil is switched
off, the armature is returned by a force approximately half as
strong as the magnetic
force to its relaxed position. Usually this is a spring, but the
gravity is also used
commonly in industrial motor starts. Most relays are
manufactured to operate quickly.
In low voltage applications, this is to reduce noise. In a high
voltage application. In a
high voltage or high current application, this is to reduce
arcing.
If the coil is energized with DC, a diode is frequently
installed across the coil, to
dissipate the energy from the collapsing magnetic field at
deactivation, which would
otherwise generate a spike of voltage and might cause damage to
circuit components.
Some automotive relays already include that diode inside the
relay case. If the coil is
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designed to be energized with AC, a small copper ring can be
crimped to the end of the
solenoid. This shading ring creates a small out-of-phase
current, which increases the
minimum pull on the armature during the AC cycle.
2.3.2 NO Contact:
Normally-open (NO) contacts connect the circuit when thee relay
is activated;
the circuit is disconnected when the relay is inactive. It is
also called a Form A contact
or make contact.
2.3.3 NC Contact:
Normally-closed (NC) contacts disconnect the circuit when the
relay is
activated; the circuit is connected when the relay is inactive.
It is also called a Form B
contact or break contact.
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CHAPTER 3
IR SENSOR
3.1 Introduction:
Infrared (IR) light is electromagnetic radiation with longer
wave lengths than
those of visible light, extending from the normal red edge of
the visible spectrum at
0.74 micrometers (m) to 0.3mm. This range of wavelengths
corresponds to a
frequency range of approximately 430 down to 1THz, and includes
most of the thermal
radiation emitted by objects near room temperature. Infrared
light is emitted by
absorbed by molecules when they change their rational-vibration
movements. The
existence of infrared radiation was first discovered in 1800 by
astronomer William
Herschel.
3.2 Infrared rays:
Infrared (IR) light is electromagnetic radiation with longer
wavelengths than
those of visible light, extending from the nominal red edge of
the visible spectrum at
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0.74 micrometers (m) to 0.3 mm. This range of wavelengths
corresponds to a
frequency range of approximately 430 down to 1THz, and includes
most of the thermal
radiation emitted by objects near room temperature. Infrared
light is emitted or
absorbed by molecules when they change their
rotational-vibration movements. The
existence of infrared radiation was first discovered in 1800 by
astronomer William
Herschel.
Much of the energy from the Sun arrives on Earth in the form of
infrared
radiation. Sunlight at zenith provides an irradiance of just
over q kilowatt per square
meter at sea level. Of this energy, 527 watts is infrared
radiation, 445 watts is visible
light, and 32 watts is ultraviolet radiation. The balance
between absorbed and emitted
infrared radiation has a critical effect on the Earths climate.
Infrared light is used in
industrial, scientific, and medical applications. Night-vision
devices using infrared
illumination allow people or animals to be observed without the
observer being
detected. In astronomy, imaging at dust. Infrared imaging
cameras are used to detect
heat loss in mechanical is insulated systems, to observe
changing blood flow in the
skin, and to detect overheating of electrical apparatus.
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CHAPTER 4
DC GEAR MOTOR
4.1 Introduction:
A gear is a simple device that can change the speed, directions
or torque of a
motor. Visually, a typical gear looks like a wheel with teeth
around its circumference.
A gear box usually refers to a cars transmission, which is full
of gears. A gear motor
is a type of electrical motor. Like all electrical motors, it
uses the magnetism induced
by an electric current to rotate a rotor that is connected to a
shaft. The energy transferred
from the rotor to the shaft is the used to a power of a
connected device. In a gear motor,
the energy output is used to return a series of gears in an
integrated gear train. There
are a number of different types of gear motors, but the most
common are AC
(alternating current) and DC (direct current). A geared DC Motor
has a gear assembly
attached to the motor. The speed of motor is counted in terms of
rotations of the shaft
per minute and is termed as RPM.
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The gear assembly helps in increasing the torque and reducing
the speed.
Using the correct combinations of gears in a gear motion, its
speed can be reduced to
any desirable figure. This concept where gears reduce the speed
of the vehicle but
increasing its torque is knows as gear reduction. This Insight
will explore all the minor
and major details that make the gear head and hence the working
of geared DC motor.
4.2.1 Construction:
The DC Gear motor, consisting of a DC electric motor and a
gearbox, is at the
heart of several electrical and electronic applications.
Precision Micro drives have been
designing and developing such high quality mini DC gear motor in
an easy to mount
package for a range of products and equipment.
Our miniature gear motor work smoothly and efficiently,
supporting these
electrical and electronic applications. These geared motors have
reduction gear trains
capable of providing high torque at relatively low shaft speed
or revolutions per minute
(RPM). Precision Micro drives DC geared motors reduce the
complexity and cost of
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designing and constructing applications such as industrial
equipment, actuators,
machine tools, and robotics.
Precision Micro drives have engineered a range of planetary and
spur gear
motors (also known as mini-geared motors and micro-geared
motors) suitable for many
future and existing applications. The main characteristics of
these gear motors are
miniature form factors, offering significant strength torque,
and other technical
capabilities that these applications require. Their linear
performance characteristics
make term suitable for many applications requiring a controlled
performance.
Whether you are looking for automotive, medical, or domestic
applications, DC
Gear motors from Precision Micro drives not only offer the
variable speed and torque
control required in each of these applications. These also
possess quality characteristics
of reliability, ruggedness, and compactness.
The operations performed by Precision Micro drives geared
motors
appear simple and effortless. However, they are highly
sophisticated devices, and some
units are encapsulated in housings to prevent exposure to
moisture and dust. Precision
Micro drives are the leading supplier of sub 60 mm DC Gear
motors in the industry.
4.3. Working:
The DC motor works over a fair range of voltage. The higher the
input voltage
more is the RPM (rotations per minute) of the motor. For
example, if the motor works
in the range of 6-12V, it will have the least RPM at 6V and
maximum at 12V.
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The working of the gears is very interesting to know. It can be
explained by the
principle of conservation of angular momentum. The gear having
smaller radius will
cover more RPM than the one with large radius. However, the
larger gear will give
more torque to the smaller gear than vice versa. The comparison
of angular velocity
between input gear (the one that transfers energy) to output
gear gives the gear ratio.
When multiple gears are connected together, conversations of
energy is also
followed. The directions in which the other gear rotates is
always the opposite of the
gear adjacent to it. In any DC motor, RPM and torque are
inversely proportional.
Hence the gear having more torque will provide a lesser RPM and
conserves. In a
geared DC motor, the concept of pulse width modulation is
applied. The equations
detailing the working and torque transfer of gears are shown
below.
In a geared DC motor, the gear connecting the motor and the gear
head is quite
small, hence it transfers more speed to the larger teeth part of
the gear head and makes
it rotate. The larger part of the gear further turns the smaller
duplex part receives the
torque but not the speed from its predecessor which it transfers
to larger part of other
gear and so on. The third gears duplex part has more teeth than
others and hence it
transfers more torque to the gear that is connected to the
shaft.
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In a gear motor, the magnetic current (which can be produced by
either
permanent magnets or electromagnets) turns gears that the either
in a gear reduction
unit or in an integrated gear box. A second shaft is connected
to this gears. The result
is that the gears greatly increase the amount of torque the
motor is capable of producing
while simultaneously slowing down the motors output speed. The
motor will not need
to draw as much current to function and will more slowly, but
will provide greater
torque.
4.3.1 Speed:
If a gear driven by a motor (the input gear) has more teeth than
the gear it is
connected gear, or output gear, will move faster than the output
gear. This increases
speed at the output. Reversing the gearing will reduce speed at
the input.
4.3.2 Torque:
Basically, when gears reduce speed, they increase torque, or
force that can be
used to turn wheels or other gears. In geared motor, the gear
system consists a set of
gear small pulley.
In a gear motor, the magnetic current (which can be produced by
either
permanent magnets or electromagnets) turns gears that the gear
either in a gear
reduction unit or in an integrated gear box. A second shaft is
connected to these gears.
The result is that the gears greatly increase the amount or
torque the motor is capable
of producing while simultaneously slowing down the motors output
speed.
The motor will not need to draw as much current to function and
will move more
slowly, but will provide greater torque. Its having the function
of torque reducing
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characteristics. When the torque is provided the torque will be
splitting (or) reduce by
gear pulleys.
In performance curve, the speed is initially increase from when
power is get to
the device, then its reducing by a gear system.
In base curve,
The torque is directly proportional to the applying a current of
the motor.
The torque is indirectly proportional to the speed of the
motor.
T I
T P/V
T I/S
Where,
T-torque represents new
S-Speed in RPM
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4.5. Specifications:
DC supply 4 to 12 V
RPM: 30 at 12 V
Total length: 46mm
Motor diameter: 36mm
Motor length: 25mm
Brush type: Precious metal
Gear head diameter: 37mm
Gear head length: 21mm
Output shaft: Centered
Shaft diameter: 6mm
Shaft length: 22mm
Gear assembly: Spur
Motor weight: 100gms
4.6. Applications:
Garage door openers, Stair lifts, Timer cycle knobs on washing
machine, Power drills,
Cake mixers, Jacks, Cranes, Lifts, Clamping, Robotics,
Conveyance and Mixing are
too numerous to count.
CHAPTER 5
STEPPER MOTOR
5.1 Introduction:
A stepper motor is an electro mechanical device, which converts
electrical pulses
into discrete mechanical movements. The shaft or spindle of a
stepper motor rotates in
discrete step increments when electrical command pulses are
applied to it in the proper
sequence. The sequence of the applied pulses is directly related
to the direction of
motor shafts rotation. The speed of the motor shafts rotation is
directly related to the
frequency of the input pulses and the length of rotation of
input pulses applied.
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5.2 Advantages:
The rotation angle of the motor is proportional to the input
pulse.
The motor has full torque at stand still (if the winding are
energized)
Precise positioning and repeatability of movement since good
stepper motors
have an accuracy of 3 5% of a step and this error is
non-cumulative from one
step to the next.
Excellent response to starting stopping reversing.
Very reliable since there are no contact brushes in the motor.
Therefore the
life to the motor is simply dependent on the life of the
bearing.
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The motors response to digital input pulses provides open-loop
control, making
the motor simpler and less costly to control.
It is possible to achieve very low speed synchronous rotation
with a load that is
directly coupled to the shaft.
A wide range of rotational speed is proportional to the
frequency of the input
Pulses.
5.2.2 Disadvantages:
Resonance can occur if not properly controlled.
Not easy to operate at extremely high speeds.
5.3 Open Loop Operation:
One of the most significant advantages of a stepper motor is its
ability to be
accurately controlled in an open loop system. Open loop control
means no feedback
information about position is needed. This type of control
eliminates the need for
expensive sensing and feedback devices such as optical encoders.
Your position is
known simply by keeping track of the input step pulses.
5.4 Types:
Variable-reluctance
Permanent-magnet
Hybrid
5.4.1 Variable-reluctance (VR):
This type of stepper motor has been around for a long time. It
is probably
the easiest to Understand from a structural point of view.
Figure 1 shows a cross section
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of a typical V.R. stepper motor. This type of motor consists of
a soft iron multi-toothed
rotor and wound stator. When the stator windings are energized
with DC current the
poles become magnetized. Rotation occurs when the rotor teeth
are attracted to
energized stator poles.
Figure 1. Cross-section of a VR Motor
5.4.2 Permanent Magnet (PM):
Often referred as a tin can or can stack motor the permanent
magnet step
motor is a low cost and low-resolution type motor with typical
step angles of 7.50 to
150. PM motors as the name implies have permanent magnets added
to the motor
structure. Then rotor no longer has teeth as with the VR motor.
Instead the rotor is
magnetized with alternating north and south poles situated in a
straight line parallel to
the rotor shaft. These magnetized motor poles provide increased
magnetic flux
intensity and because of this the PM motor exhibits improved
torque characteristics
when compared with the VR type.
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5.4.3 Hybrid (HB):
The hybrid stepper motor is more expensive then the PM stepper
motor but
provides better performance with respect to step resolution,
torque and speed. Typical
step angles for the HB stepper motor range from 3.60 to 0.90.
The hybrid stepper motor
combines the best features of both the PM and VR type stepper
motor. The rotor is
multi-toothed like the VR motor and contains an axially
magnetized concentric magnet
around its shaft. The teeth on the rotor provide and even
magnetic flux to preferred
locations in the air gap. This further increases the detent,
holding and dynamic torque
characteristics of the motor when compared with both the VR and
PM types. The two
most commonly used types of stepper motors are the permanent
magnet and the hybrid
types. If a designer is not sure which type will best fit his
applications requirements he
should first evaluate the PM type as it normally several times
less expensive. If not
then the hybrid motor may be the right choice. There also exist
some special stepper
motor designs. One is the disc magnet motor. Here the motor is
designed as a disc with
rare earth magnets. This motor type has some advantages such as
low inertia and a
optimized magnetic flow path with no coupling between the two
stator windings. These
qualities are essential in some applications.
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Figure 3. Cross-section of a hybrid
Stepper motor
5.4.4 Size and Power:
In addition to being classified by their step angle stepper
motors are also
classified according to frame sizes which corresponding to the
diameter of the body of
the motor. For instance a size 11-stepper motor has a body
diameter of approximately
1.1 inches. Likewise a size 23 stepper motor has a body diameter
of 2.3 inches. The
body length may however, vary from motor to motor within the
same frame size
classification. As a general rule the available torque output
from a motor of particular
frame size will increase with increased body length.
Power levels for IC-driven stepper motors typically range from
below a watt for
very small motors up to 10-20 watts for larger motors. The
maximum power dissipation
level. Or thermal limits for the motor are seldom clearly stated
in the motor
manufactures data. To determine this we must apply the
relationship P = V X I. For
example, a size 23 step motor may be rated at 6V and 1A per
phase.
Therefore, with two phases energized the motor has a rated power
dissipation of
12 watts. It is normal practice to rate a stepper motor at the
power dissipation level
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where the motor case raises 650C above the ambient in still air.
Therefore, if the motor
can be mounted to a heat sink it is often possible to increase
the allowable power
dissipation level. This is important as the motor is designed to
be and should be used
at this maximum power dissipation, to be efficient from a
size/output power/cost point
of view.
5.7 The Rotating Magnetic Field:
When a phase winding of a stepper motor is energized with
current a magnetic
flux is developed in the stator. The direction of this flux is
determined by the Right
Hand Rule which states: If the coil is grasped in the right hand
with the fingers
pointing in the direction of the current in the winding (the
thumb is extended at a 900
angle to the fingers), then the thumb will point in the
direction of the magnetic field.
The rotor then aligns itself so that the flux opposition is
minimized. In this case
the motor would rotate clockwise so that its south pole aligns
with the north pole of
stator B at position 2 and its north pole aligns with the south
pole of stator B at position
6. To get the motor to rotate we can now see that we must
provide a sequence of
energized the stator windings in such a fashion that provides a
rotating magnetic flux
field with the rotor follows due to magnetic attraction.
5.10 Stepper motor driver circuit:
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Stepper motor performance is strongly dependent on the driver
circuit. Torque
curves may be extended to greater speeds if the stator poles can
be reversed more
quickly, the limiting factor being the winding inductance. To
overcome the inductance
and switch the windings quickly, one must increase the drive
voltage. This leads further
to the necessity of limiting the current that these high
voltages may otherwise induce.
5.10.1 L/R driver circuits:
L/R driver circuits are also referred to as constant voltage
drives because a
constant positive or negative voltage is applied to each winding
to set the step positions.
However, it is winding current, not voltage that applies torque
to the stepper motor
shaft. The current I in each winding is related to the applied
voltage V by the winding
inductance L and the winding resistance R. The resistance R
determines the maximum
current according to Ohm's law I=V/R. The inductance L
determines the maximum rate
of change of the current in the winding according to the formula
for an inductor di/dt
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= V/L. Thus when controlled by an L/R drive, the maximum speed
of a stepper motor
is limited by its inductance since at some speed, the voltage U
will be changing faster
than the current I can keep up. In simple terms the rate of
change of current is L / R
(e.g. a 10 mH inductance with 2 ohms resistance will take 5 ms
to reach approx. 2/3 of
maximum torque or around 24 ms to reach 99% of max torque). To
obtain high torque
at high speeds requires a large drive voltage with a low
resistance and low inductance.
With an L/R drive it is possible to control a low voltage
resistive motor with a
higher voltage drive simply by adding an external resistor in
series with each winding.
This will waste power in the resistors, and generate heat. It is
therefore considered a
low performing option, albeit simple and cheap.
5.10.3 Full step drive (one phase on):
In this drive method only a single phase is activated at a time.
It has the same
number of steps as the full step drive, but the motor will have
significantly less than
rated torque. It is rarely used. The animated figure shown above
is a wave drive motor.
In the animation, rotor has 25 teeth and it takes 4 steps to
rotate by one teeth position.
So there will be 25*4 = 100 steps per full rotation and each
step will be 360/100 = 3.6
degrees.
5.10.4 Full step drive (two phases on):
This is the usual method for full step driving the motor. Two
phases are always
on so the motor will provide its maximum rated torque. As soon
as one phase is turned
off, another one is turned on. Wave drive and single phase full
step are both one and
the same, with same number of steps but difference in
torque.
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5.12 Half stepping:
Its angle per step is half of the full step.
5.12.1 Micro stepping:
What is commonly referred to as micro stepping is often "sine
cosine micro
stepping" in which the winding current approximates a sinusoidal
AC waveform. Sine
cosine micro stepping is the most common form, but other
waveforms can be used.[4]
Regardless of the waveform used, as the micro steps become
smaller, motor operation
becomes more smooth, thereby greatly reducing resonance in any
parts the motor may
be connected to, as well as the motor itself. Resolution will be
limited by the
mechanical station, backlash, and other sources of error between
the motor and the end
device. Gear reducers may be used to increase resolution of
positioning. Step size
repeatability is an important step motor feature and a
fundamental reason for their use
in positioning.
Example: many modern hybrid step motors are rated such that the
travel of
every full step (example 1.8 degrees per full step or 200 full
steps per revolution) will
be within 3% or 5% of the travel of every other full step, as
long as the motor is operated
within its specified operating ranges. Several manufacturers
show that their motors can
easily maintain the 3% or 5% equality of step travel size as
step size is reduced from
full stepping down to 1/10 stepping. Then, as the micro stepping
divisor number grows,
step size repeatability degrades. At large step size reductions
it is possible to issue
many micro step commands before any motion occurs at all and
then the motion can
be a "jump" to a new position.
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CHAPTER 6
STARTER MOTOR
6.1 Introduction:
The starter motor converts electrical energy to mechanical
energy and is
mounted on the cylinder block in a position to engage a ring
gear on the engine
flywheel. Starting is usually accomplished by the operator
activating a starter switch
as part of ignition key operation. This allows a relatively
small current to flow to a
starter solenoid relay and operate a plunger attached to a drive
pinion engagement
lever. The plunger movement engages the drive pinion with the
ring gear and closes a
set of heavy duty contacts, allowing a large current to flow
from the battery to the
starter motor, rotating the armature and drive pinion, and
causing the crankshaft to spin.
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When the engine starts and is able to run on its own, the
operator usually releases
the key and this withdraws the pinion from the ring gear and
brings the armature to a
halt.
6.2 Starting Systems:
The electric starter motor or starting motor is the most common
type used on
gasoline engines and small Diesel engines. The modern starter
motor is either a
permanent-magnet or a series-parallel wound direct current
electric motor with a starter
solenoid (similar to a relay) mounted on it. When current from
the starting battery is
applied to the solenoid, usually through a key-operated switch,
the solenoid engages a
lever that pushes out the drive pinion on the starter driveshaft
and meshes the pinion
with the starter ring gear on the flywheel of the engine.
The solenoid also closes high-current contacts for the starter
motor, which
begins to turn. Once the engine starts, the key-operated switch
is opened, a spring in
the solenoid assembly pulls the pinion gear away from the ring
gear, and the starter
motor stops.
6.3 Parts:
Armature
Commutator
Brushes
Pole Shoe
Field Coil
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6.5 Application:
Industry
Automobile
HVAC Device
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CHAPTER 7
STARTER SOLENOID SWITCH
7.1 Introduction:
The quality solenoid switches catered by us are at par with
international
standards. Our solenoid switches are specially designed for high
current applications.
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7.2 Working of Solenoid Switch:
A solenoid switch works by having an electromagnet which is used
to convert
electrical energy into mechanical energy. The magnetic field
within the solenoid helps
create a linear motion.
The solenoid receives a large electric current from the car
battery and a small
electric current from the ignition switch. As the ignition
switch is turned, a small
electric current is sent to the starter solenoid. The pair of
heavy contacts closes, relaying
the large electric current to the starter motor, which in turn
sets the engine in motion.
Once the engine starts, the key-operated switch is turned, a
spring in the solenoid
assembly pulls the pinion gear away from the mesh, and the
starter motor stops. The
starter's pinion is clutched to its driveshaft through an over
running sprog clutch which
allows the pinion to transmit drive in only single direction. In
this manner, drive is
transmitted through the pinion to the flywheel ring gear.
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7.4 Maintenance:
If the power supply to the solenoid is insufficient, it will
fail to start the motor
and may produce a rapid clicking or clacking sound. The lack of
the power may be
caused by a low or dead battery, by corroded or loose
connections in the battery cable,
or by a damaged positive (red) cable from the battery. Any of
such problem may create
resistance for the current resulting in proper transmission of
the power. To reduce the
chances for such as failure, the battery connections should be
cleaned and tightened at
every oil change. Starting fault of the solenoid can detected at
service center by a test
of the car's starting, charging and battery systems.
7.5 Applications of Solenoid Switch:
Besides wide scale engine starting applications, solenoid
switches are used to
switch on many other types of motors while mechanically engaging
or disengaging
their shafts. This allows latching and opening mechanisms for
windows, doors and
hatches to derive two functions from the same piece of
coordinated equipment.
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CHAPTER 8
PROGRAMMABLE LOGIC CONTROLLER
8.1 Introduction:
Its always good to get an over view of where designs have been
and where they
are going. To do this its essential to get a birds eye view of
the concepts and processes
that make the PLC so valuable in industrial control. Pitting
PLCs against other control
types will also serve to show the pros and cons for different
applications.
8.2 Construction:
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A programmable logic controller is a specialized computer used
to control
machines and processes. It therefore shares common terms with
typical PCs like central
processing unit, memory, software and communications. Unlike a
personal computer
through the PLC is designed to survive in a rugged industrial
atmosphere and to be
very flexible in how it interfaces with inputs and outputs to
the real world.
The components that make a PLC work can be divided in to three
core areas.
The power supply and rack.
The central processing unit(CPU)
The input/output(I/O) section
PLCs come in many shapes and sizes. They can be so small as to
fit in your shirt
pocket while more involved control systems and large PLC racks.
Smaller PLCs (a.k.a.
Bricks) are typically designed with fixed (I/O) points. For our
construction, well
look at the more modular rack based systems. Its called modular
because the rack
can accept many different types of I/O modules that simply slide
into the rack and plug
in.
The rack is the component that holds everything together.
Depending on the
needs of the control system it can be ordered in different sizes
to hold more modules.
Like a human spine the rack has a backplane at the rear which
allows the cards to
communicate with the CPU. The power supply plugs into the rack
as well and supplies
a regulated DC power to other modules that plug into the rack.
The most popular power
supplies work with 120v DC sources.
The Central Processing Unit (CPU) Module is the brain of the
PLC. The Primary
functions are to read inputs, execute the control program, and
update outputs. CPU
architecture may differ from one manufacturer to another, but in
general, most CPUs
follow this typical three-component organization.
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The CPU consists of following three components:
i) Processor ii) Memory system iii) Power supply
i) Processor:
The processor executes the user program stored in the memory
system in the
form of ladder diagrams. It makes all the decisions necessary to
carry out the user
program based on the status of inputs and outputs for control of
a machine or
process. It can also perform arithmetic functions, data
manipulation and
communication between the local I/O, remotely located I/O and
other networked
PLC.
ii) Memory system:
The memory system is the area in the CPU where all the programs,
are stored
and executed by the processor to provide the desired control of
field devices.
iii) Power supply:
Power supply is necessary to convert 120V or 240V a.c into the
low voltage d.c
(+5V & -5V) required for processor and internal power
required for the I/O
modules. This power supply unit does not supply power for the
actual input or
output devices. This can be built into the PLC or be an external
unit. Common
voltage levels required by the PLC are 24Vdc, 120Vac,
220Vac.
8.3 PLC Operation:
The CPU accepts input signal from sensors like push buttons,
limit switches,
analog sensors, selector switches, and thumbwheel switches.
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Stores the status of input in the memory area called input image
table.
Execute the stored user program from memory and sends
appropriate output
commands to control devices like motor starters, solenoid
valves, pilot lights,
and position valves through output image table.
Update the content of output image table.
The system power supply provides all the voltages required for
the proper
operation of the various central processing unit sections.
8.5. I/O Modules:
The input/output (I/O) system is the section of a PLC to which
all of the field
devices are connected. If the CPU can be thought of as the
brains of a PLC, then the
I/O system can be thought of as the arms and legs. It creates
the physical connection
between the field equipment and the PLC. I/O modules are
available as either input
only, output only or a combination of inputs and outputs.
8.5.2 Discrete Input Module :
A discrete input also referred to as a digital input. Discrete
input module is the
most common input interface used with PLC. Discrete input
signals from field devices
can be either AC or DC.
The discrete input module communicates the status of the various
real world
input devices connected to the module to the CPU. Hence it
provides the physical
connection between the CPU and field devices. Digital or
discrete signals are non-
continuous signals that have only two statesON and OFF. In the
ON condition a
discrete input may be referred to as logic 1 or logic high. In
the OFF condition a discrete
input may be referred to as logic 0 or a logic low.
8.5.3 Typical INPUT Modules:
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o DC voltage (110, 220, 14, 24, 48, 15-30V) or current (4-20
mA).
o AC voltage (110, 240, 24, 48V) or current (4-20 mA).
o TTL (transistor-transistor logic) input (3-15VDC).
o Analogue input (12-bit).
o Word input (16-bit/parallel).
o Thermocouple input.
o Resistance temperature detector.
o High current relay.
o Low current relay.
o Latching input (24VDC/110VAC.
o Isolated input (24VDC/85-132VAC).
o Intelligent input (contains a microprocessor).
o Positioning input.
o PID (proportional, integral, differentiation) input.
o High-speed pulse.
8.5.5 Typical Output Modules:
DC voltage (24, 48,110v) or current (4-20mA).
AC voltage (110,240v) or current (4-20mA).
Isolated (24VDC).
Analog output (12-bit).
Intelligent output.
ASCII output.
Dual communication port PLC.
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8.6 Memory Section:
This section stores (electronically) retrievable digital
information in three
dedicated locations of the memory. These memory locations are
routinely scanned by
the processor. The memory will receive (write mode) digital
information or have
digital information accessed (read mode) by the processor. This
read/write (R/W)
capability provides an easy way to make program changes.
The memory contains data for several types of information.
Usually, the data
tables, or image registers, and the software program RLL are in
the CPU modules
memory. The program messages may or may not be resident with the
other memory
data.
A battery backup is used by some manufacturers to protect the
memory contents
from being lost should there be a power or memory module
failure. Still other use
various integrated circuit (IC) memory technologies and design
schemes that will
protect the memory contents without the use of a battery
backup.
A typical memory section of the CPU module has a memory size of
98,304
(96K) bytes. This size tells us how many locations are available
in the memory for
storage. Additional memory modules can be added to your PLC
system as the need
arises for greater memory size. These expansion modules are
added to the quantity of
I/O modules are added or the software program becomes larger.
When this is done, the
memory size can be as high as, 1,048,576 (1024K) bytes.
Manufacturers will state memory size in either bytes or words. A
byte is
eight bits, and a bit is the smallest digit in the binary code.
Its either logic 1 or logic
0. A word is equal in length to two bytes or 16 bits. Not all
manufacturers use 16-bit
words, so be aware of your PLC manufacturers has defined as its
memory word bit
size.
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8.4 Ladder Logic:
In these modern times a PC with especially dedicated software
from the PLC
manufacturer is used to program a PLC. The most widely used from
of programming
is called ladder logic. Ladder logic uses symbols, instead of
words, to emulate the real
world relay logic control, which is a relic from the PLCs
history. These symbol are
interconnected by lines to indicate the flow of current trough
relay like contacts and
coils. Over the years the number of symbols has increased to
provide a high level of
functionality.
The completed programmer looks like a ladder but in actuality I
represents an
electrical circuit. The left and right rails indicate the
positive and round of a power
supply. The rungs represent the wiring between the different so
if you can understand
how basic electrical circuits work then you can understand
ladder logic.
In this simplest of examples a digital input (like a button
connected to the first
position on the card) when it is pressed turns on an output
which energizes an indicator
light. The competed program is downloaded from the PC to the PLC
using a special
cable thats connected to the front of the CPU. The CPU is then
put into run mode so
that it can start scanning the logic and controlling the
outputs.
In the world of automation these types of TRUE or FALSE
conditions come
down to a device being ON or OFF, CLOSED or OPEN, PRESENT or
ABSENT,
24nVOLTS or 0 VOLTS. In the PLC it all boils down to our now
familiar binary
system of a 1 or 0. Typically having a bit ON presents a TRUE
condition while OFF
in FALSE. This is arbitrary though as it may make more sense to
use what is called
failsafe logic and have an ON bit an a FALSE condition.
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CHAPTER 9
LIMIT SWITCH
9.1 Introduction:
In electrical engineering a limit switch is a switch operated by
the motion of a
machine part or presence of an object. They are used for control
of a machine, as safety
interlocks, or to count objects passing a point. A limit switch
is an electromechanical
device that consists of an actuator mechanically linked to a set
of contacts. When an
object comes into contact with the actuator, the device operates
the contacts to make
or break an electrical connection. Limit switches are used in a
variety of applications
and environments because of their ruggedness, ease of
installation, and reliability of
operation. They can determine the presence or absence, passing,
positioning, and end
of travel of an object. They were first used to define the limit
of travel of an object;
hence the name Limit Switch.
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A limit switch with a roller-lever operator; this is installed
on a gate on a canal
lock, and indicates the position of a gate to a control system.
Standardized limit
switches are industrial control components manufactured with a
variety of operator
types, including lever, roller plunger, and whisker type. Limit
switches may be directly
mechanically operated by the motion of the operating lever. A
reed switch may be used
to indicate proximity of a magnet mounted on some moving part.
Proximity switches
operate by the disturbance of an electromagnetic field, by
capacitance, or by sensing a
magnetic field.
Rarely, a final operating device such as a lamp or solenoid
valve will be directly
controlled by the contacts of an industrial limit switch, but
more typically the limit
switch will be wired through a control relay, a motor contactor
control circuit, or as an
input to a programmable logic controller.
Miniature snap-action switch may be used for example as
components of such
devices as photocopiers or computer printers, to ensure internal
components are in the
correct position for operation and to prevent operation when
access doors are opened.
A set of adjustable limit switches are installed on a garage
door opener to shut off the
motor when the door has reached the fully raised or fully
lowered position. A numerical
control machine such as a lathe will have limit switches to
identify maximum limits
for machine parts or to provide a known reference point for
incremental motions
Function of limit switch:
Limit switches provide the function of making and breaking
electrical contacts
and consequently electrical circuits.
A limit switch is configured to detect when a system's element
has moved to a
certain position. A system operation is triggered when a limit
switch is tripped.
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Application of limit switch:
Limit switches are widely used in various industrial
applications, and they can
detect a limit of movement of an article and passage of an
article by displacement
of an actuating part such as a pivotally supported arm or a
linear plunger.
The limit switches are designed to control the movement of a
mechanical part.
Limit switches are typically utilized in industrial control
applications to
automatically monitor and indicate whether the travel limits of
a particular
device have been exceeded. Limit switches are used in a variety
of applications
and environments because of their ruggedness, simple visible
operation, ease of
installation and reliability of operation.
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CHAPTER 11
BIBLIOGRAPHY
Reference Books:
[1]. Beginning Arduino Programming by Brian Evans - Technology
in action.
[2]. Arduino Robotics by John-David Warren, Josh Adams
Apree.
[3]. Practical Arduino Engineering by Harold Timmis - Technology
in action.
URL Reference:
[1]. www.arduino.cc
[2]. www.efymag.com
[3]. www.simplelab.co.in