INTRODUCTIONLABVIEW is a program development application, much
like C or FORTRAN.LABVIEW is however, different from those
applications in one important respect. Other programming systems
use text based languages to create lines of code, while LABVIEW
uses a graphical programming language, to create programs in block
diagram and its controlling and indicating unit as front panel.
LABVIEW, like C or FORTRAN, is a general-purpose programming system
with extensive libraries of functions for many programming tasks.
LABVIEW includes libraries for data acquisition, data analysis,
data presentation and data storage. A LABVIEW program is called a
virtual instrument (VI) because its appearance and operation can
imitate an actual instrument.
VIRTUAL INSTRUMENTSVirtual instrument (VI) is a program in
graphical programming language. It models the appearance and
function of a physical instrument. The distinction between
traditional and virtual instrument is illustrated in fig.1.
Fig. 2 shows two LabVIEW windows: front panel (containing
controls and indicators) and block diagram (containing terminals,
connections and graphical code). The front panel is the user
interface of the virtual instrument. It consists of controls and
indicators, which are the iterative input and output terminals of
the VI, respectively.
ControlsControls are knobs, push buttons, dial, and output input
devices. Indicators are graphs, LEDs, and other displays.
FIGURE: FRONT PANNEL
FIGURE: BLOCK DIAGRAM.
Controls simulate instrument input devices and supply data to
the block diagram of the VI. Indicators simulate instrument output
devices and display data the block diagram acquires or generates.
The code is built using graphical representations of functions to
control the front panel objects. The block diagram contains this
graphical source code. Front panel objects appear as terminals on
the block diagram. Additionally, the block diagram contains
functions and structures from built-in LabVIEW VI libraries. Wires
connect each of the nodes on the block diagram, including control
and indicator terminals, functions, and structures. From the aspect
of distance learning, the most important issue of virtual
instruments is the fact that they can be used to simulate physical
phenomena to generate signal that appears as it would appear if it
had been acquired by real transducers. The same software is being
used for real and virtual phenomena. That way virtual instrument
becomes the part of virtual laboratory.
FIGURE 3:Virtual instrument
Transducer
Signal conditioning
data acquisition
VirtualPhysical LaboratoryPhenomenon Control
Data Analysis Measurement Results
Fig: Virtual Laboratory
Some Palettes Used In LABVIEW:
Some features of LabVIEW: Graphical programming
Data-flow-controlled execution, as compared to sequential execution
of text-line based languages. Real time visual debugging features
Built in drivers and function libraries for the serial, parallel
and network computer ports. Simple file input-output
operations.
Plug-and-play interface devices for most types of external
equipment.
Direct program portability (binary files) between different
platforms: PCs, Macintosh, Sun, HP-UX and operating systems. A
wealth of visual debugging tools. Add-on software packages for
specific extension of the program features, for instance image
processing. Built-in interactive graphic control and display
Database (SQL) interfacing, libraries for industrial PLCs Ready to
use analysis functions including: Signal generation (sine wave,
triangular wave, square wave, saw tooth, uniform, Gaussian white
and periodic white noise etc.)
Digital signal processing (FFT, power spectrum, Hilbert
transform, convolution, derivative, integral etc.)
Measurement (power spectrum, time domain windowing, transfer
function, harmonic analyzer, pulse parameters, peak detection etc.)
Filtering (Butterworth, IIR, Chebyshev, Bessel filter, median
filter etc.) Windows (Hanning, hamming, triangle, flat top, force
window, exponential window etc.)
Curve fitting (Linear, exp., poly. nonlinear Lev-Mar. fit,
interpolation etc.) Probability and statistics functions (mean,
standard deviation, RMS, histogram, distributions(chi square,F,t,
inverse distributions, erfc(x), erf(x), contingency table etc),
ANOVA(1D,2D,3D) etc)
Array operations (numerical methods, root, etc.) Code interface
function to use DLLs written any other language. This feature gives
the opportunity to use the codes written in conventional languages
(C/C++, Visual Basic, etc.) to be used in a LabVIEW program. Add-on
software packages for specific extension of the program features,
for instance image processing.
ADVANTAGES OF VIRTUAL INSTRUMENTS FlexibilityExcept for the
specialized components and circuitry found in traditional
instruments, the general architecture of stand-alone instruments is
very similar to the PC-based virtual instrument. Both require one
or more microprocessors, communication ports (for example, serial
and GPIB), and display capabilities, as well as data acquisition
modules. What makes one different from other are their flexibility
and the fact that you can modify and adapt the instrument to your
particular needs. A traditional instrument might contain an
integrated circuit to perform a particular set of data processing
functions; in a virtual instrument, these functions would be
performed by software running on the PC processor.
Lower CostBy employing virtual instrumentation solutions, you
can lower capital costs, system development costs, and system
maintenance costs, while improving time to market and the quality
of your own products.
Plug-In and Networked HardwareThere is a wide variety of an
available hardware that you can either plug into the computer o
access through a network. These devices offer a wide range of data
acquisition capabilities at a significantly lower cost than that of
dedicated devices. As integrated circuit technology advances, and
off-the self components become cheaper and more powerful, so do the
boards that use them. With these advances in technology comes an
increase in data acquisition rates, measurement accuracy, precision
and better signal isolation. Depending on the particular
application, the hardware you choose might include analog input or
output, digital input or output counters, timers, filters,
simultaneous sampling, and waveform generation capabilities. The
wide gamut of boards and hardware could include any one of thee
features or a combination of them.
Distributed ApplicationsA virtual instrument is not limited or
confined to a stand-alone PC. In fact, with recent developments in
networking technologies and the internet, it is more common for
instruments to use the power of connectivity for the purpose of
task sharing. Typical examples include supercomputers, distributed
monitoring and control devices, as well as data or result
visualization from multiple locations.
Reduces Cost and Preserves InvestmentsBecause you can use a
single computer equipped wit LabVIEW for countless application and
purpose, it is a versatile product. It is not only versatile but
also extremely cost-effective. Virtual instrumentation with LabVIEW
proves to be economical, not only in the reduced development costs
but also in its preservation of capital investment over along the
period of time. As your needs change, you can modify systems easily
without the need to buy new equipment. You can create complete
instrumentation libraries for less than the cost of a single
traditional, commercial instrument.
Flexibility and ScalabilityEngineers and scientists have needs
and requirements that can change rapidly. They also need to have
maintainable, extensible solutions that can used for a long time.
By creating virtual instruments based on powerful development
software such as LabVIEW, you inherently design an open framework
that seamlessly integrates software and hardware. This ensures that
your applications not only work well today but that you can easily
integrate new technologies in the future as they become available,
or extend your solutions beyond the original scope, as new
requirements that require a broad range of solutions.
Other Advantages: The users are able to define instruments
inside the software. Lower costs of instrumentation Portability
between various computer platforms
Easy-to-use graphical user interface. Graphical representation
of program structures Code can be compiled to standalone.EXE or
.DLL file. TCP/IP connectivity (Web server integrated into virtual
instrument) Virtual instruments are easily adaptable to changing
demands. The user interface can be adapted to the needs of
different users.
COMPONENTS IN A VIA VI consists of two panels: one is the front
panel, and other is the block diagram. These are defined below: The
interactive user interface of a VI is called the front panel,
because it simulates the panel of a physical instrument. The front
panel can contain knobs, push buttons, graphs, and other controls
and indicators. You enter data using a mouse and keyboard, and then
view the results on the computer screen. The VI receives
instructions from a block diagram, which you construct in G. the
block diagram a pictorial solution to a programming problem. The
block diagram is also the source code for the VI.
Indicators:Indicators are used to output numeric (integer or
floating point), character, and Boolean data in LabVIEW. On the
block diagram, indicators are represented with a thin border.
Controls:Controls are used to input numeric (integer or floating
point), character, and Boolean data in LabVIEW. On the block
diagram, controls are represented with a thick border.
For Loop Structure:A For Loop executes its sub-diagram N times,
where the count equals the value contained in the terminal.
You set the count explicitly by writing a value from outside the
loop to the left of the count terminal. The iteration terminal, I,
contains the current number of completed iterations; 0 during the
first iteration, 1 during the second, and so on up to N-1. If you
write 0 to the count terminal, the loop does not execute.
While Loop Structure:A While Loop executes its sub- diagram
until a Boolean value you write to the conditional, terminal is
FALSE. LABVIEW checks the conditional terminal value at the end of
each iteration, and if the value is TRUE, iteration occurs, so the
loop always executes at least once. The default value of
conditional terminal is FALSE, so if it s unwired, the loop
iterates only once.
The iteration terminal behaves exactly as it does in the For
Loop. In the LABVIEW, there is also a stop termination for the
while loop; i.e., the loop will continue to execute until the stop
condition is TRUE.
Shift Register:Both loop structures can have terminals called
shift registers that you use for passing data from the current
iteration to the next iteration.
Shift Registers are local variables that feed forward or
transfer values from the completion of one iteration to the
beginning of the next. A shift Register has a pair of terminals
directly opposite each other on the vertical sides of the loop
border. The right terminal, the rectangle with the up arrow, stores
the data at the completion of the iteration. LABVIEW shifts that
data at the end of the iteration, and it appears in the left
terminal, the rectangle with the down arrow, in time for the next
iteration. You can use shift registers for any type of data, but
the data you write to each register terminals must be of the same
type.
Case Structure:
The Case Structure has two or more sub-diagrams, or cases, of
which only one will execute when the structure executes. This
depends in the value of the Boolean or numeric scalar you wire to
the external side of the selection terminal. If a Boolean is wired
to the selector, the case structure must have two cases, FALSE and
TRUE. If a numeric is wired to the selector, the structure can have
from 0 to N cases.
Arrays And Graphs in LABVIEW: Initialize Array:
Returns an N-dimensional array in which every element is
initialized to the specified value. This function is resizable, so
we typically define an array of one element. The element cannot be
an array.
Build Array:
Concatenate inputs in a top to bottom order. Pop-up on an input
node and select change to Array to change it in to an array input.
For an Ndimensional array, element inputs must have N-1 dimension
and array inputs must have N dimensions.
Index Array:
Returns an element of the array at the index input. If the array
is multi-dimensional you must add additional index by resizing or
popping up and adding terminals. You can also slice out sub- arrays
(e.g. rows or coloums) by disabling the index terminals from the
popup.
XY GRAPHA graph indicator is a two dimensional display of one or
more plots. The graph receives and plots data as a block. The XY
graph is a general-purpose, Cartesian graphing object that you can
use to plot multi-valued functions.
Use this arrangement to bundle two 1D arrays into a cluster, to
be plotted. The input into an XY graph indicator for a single plot
is a cluster a X array and a Y array. You can also display multiple
plots on a XY graph.
Sample Simulation Of Few Programs Using LABVIEW. 1: Square Wave
Generation:
Figure: Block Diagram Of Square Wave Generation.
Output Waveforms Obtained After Simulation.
2: Amplitude Modulation:
Figure: Block Diagram Of Amplitude Modulation.
Output Waveform After Simulation
INTRODUCTION TO PROJECT
HARDWARE REQUIREMNTThe following hardware is required to
implement PC Based Automatic Car Parking System: Personal Computer
with Pentium Processor PCI CB68LP DAQ Card & I/O Connector
Proximity Sensors & Signal Conditioners Wooden Base DC Stepper
Motor
AUTOMATIC CAR PARKING SYSTEM
The diagram shows the layout of a simple car park. It has an
entry barrier and an exit barrier. The car park itself has six
spaces and series of displays to indicate whether it is full, has
spaces or is empty, with a numerical indicator to determine the
exact amount. Designing need to be done that will allow cars into
the parking zone when it is empty or has spaces and to exit the car
park through the correct barrier. Designing must also do to control
the display boxes in the center of the screen.
1 System Planning:The system planning begins with the
understanding of what to do and what we are going to develop is
feasible or not from the users perspective. Here we mainly thinks
about to provide the user better facilities then the earlier one so
that his efficiency and performance is improved. So first of all we
perform the feasibility study to understand the projects
feasibility under mainy areas then we think about the main
characteristics that are must for the projecty. All the description
is as below.
Feasibility Study: a) Technical Feasibility There is work going
on electrical components with the help of assembly language. The
proposed equipment has the technical capability to make a decision
required to use the system. This system will be upgraded later.
Using this technology there are technical guarantees of accuracy,
reliability ease of access and security.
b) Economical Feasibility: This system that can be developed
technically and that will be used must still be profitable for the
users. Its financial benefits must exceed then costs when we
investigate the full system.
c) Operational Feasibility: This system is beneficial because
that will meet the operating requirements of the organization if it
is developed and installed.
There is sufficient for the project from the user. The people
are involved and give suggestion time to time when the project is
planned and developed. This proposed system has no harm. It
increase the performance of the user.
2 FUNCTIONAL REQUIREMENTS OF THE SYSTEMThe performance
requirements of the system mainly encompass processing and response
time requirements. The system developed must follow certain
performance criteria namely.
a)FunctionalThe system should satisfy stated needs. It should be
suitable, accurate, interoperable, compliant and
secure.b)Reliable
The system should be mature, fault tolerant and
recoverable.c)Usable
The system should be easy to use i.e. it should be
understandable, learnable and operable.d)Efficient
The system should make optimal use of system
resources.f)Maintainable
Repairing of the system should be easy, it should be analyzable,
changeable, stable and testable.g)Portable
The system should be easy to transpose from one environment to
other. It should be adaptable, installable and replaceable.
3.Cost Benefit Analysis Cost incurred:1.Personnel CostThese
include staff salaries and benefits as well as pay for those who
are involved in developing the system. These cost are one time
costs and are labeled as developmental costs. In time was consumed.
Hence, it can be said that a there was a little personnel cost
involved.
2.Supply CostsThese costs are variable and basically include
cost of components used ( resisters, capacitors, transistors,
transformer, relays etc.), cost of tools which are used ( electric
iron, punching device, programmer, screw drivers etc.) and thee
like. These costs are high and generally dominate other cost.
3.Operational and Maintenance Cost:These costs are associated
with the running cost of the project. These include replacement of
component as the component become faulty, cost of personnel
involved in running the project or the other cost that are
necessary for the maintenance of the maintenance of the project.
Generally these costs are very low and are variable. These are not
the regular periodic cost but occur very occasionally.
Benefits Achieved 1.Cost-Savings BenefitsThis system leads to
reduction in administrative and required than earlier method. Also
now the same work requires less time. So this project reduces the
running cost by a large factor, this is a beneficial one.
2. Improved- Service-Level BenefitsThis system improves the
performance of handling the power supply and also controlling the
generator functioning. It reduces time gap between different stages
of work, earlier the user go to the generator and manually start or
stop the generator. This communication took time. With earlier
systems the user faces the difficulty when one of the phases is
gone then only one phase output is provided but by this we get the
two phase output at the time. This is a major enhancement in the
performance of the system. So by using this new system there are
some more development cost then earlier one but the running cost
and the maintenance cost are reduces by this. So by this project
there are always an overall benefit achieved.
SENSORS:A sensor is a type of transducer. Direct-indicating
sensors, for example, a mercury thermometer, are human-readable.
Other sensors must be paired with an indicator or display, for
instance a thermocouple. Most sensors are electrical or electronic,
although other types exist. Sensors are used in everyday life.
Applications include automobiles, machines, aerospace, medicine,
industry and robotics. Technological progress allows more and more
sensors to be manufactured on the microscopic scale as microsensors
using MEMS technology. In most cases a microsensor reaches a
significantly higher speed and sensitivity compared with
macroscopic approachesTypes Since a significant change involves an
exchange of energy, sensors can be classified according to the type
of energy transfer that they detect.
Thermal:
temperature sensors: thermometers, thermocouples, temperature
sensitive resistors (thermistors and resistance temperature
detectors), bi-metal thermometers and thermostats heat sensors:
bolometer, calorimeter
Electromagnetic:
electrical resistance sensors: ohmmeter, multimeter electrical
current sensors: galvanometer, ammeter electrical voltage sensors:
leaf electroscope, voltmeter electrical power sensors: watt-hour
meters magnetism sensors: magnetic compass, fluxgate compass,
magnetometer, Hall effect device metal detectors RADAR
Mechanical:
pressure sensors: altimeter, barometer, barograph, pressure
gauge, air speed indicator, rate of climb indicator, variometer gas
and liquid flow sensors: flow sensor, anemometer, flow meter, gas
meter, water meter, mass flow sensor mechanical sensors:
acceleration sensor, position sensor, selsyn, switch, strain
gauge
Chemical:Chemical sensors detect the presence of specific
chemicals or classes of chemicals. Examples include oxygen sensors,
also known as lambda sensors, ion-selective electrodes, pH glass
electrodes, and redox electrodes. A carbon monoxide detector is a
chemical sensor often used in the home. These detectors continually
sample air and will sound an alarm if the amount of invisible,
odorless, and potentially deadly carbon monoxide levels in our home
and/or workplace rises above 400 PPM. In manufacturing, chemical
sensors are used to manage process controls, quality assurance, and
safety. The engine management systems of automobiles take
information from sensors and adjust engine parameters to achieve
the best mix of fuel economy, performance and emissions. Oxygen
sensors have been used in automobiles since the late 70s. Many
areas require automobiles to pass an emissions test annually. The
test equipment also uses chemical sensors to check the exhaust
emissions. Chemical sensors have been developed to detect threats
from explosives and biological weapons. Monitoring for these
threats includes border crossings, major transportation systems,
and large public spaces.[1] For example, airport security utilizes
chemical sensors used to sniff out explosives and even drugs.
Chemical sensors are also being developed to sniff out illnesses in
people.
In supramolecular analytical chemistry novel molecular sensors
are developed for a wide range of such applications.
Optical radiation:
light time-of-flight. Used in modern surveying equipment, a
short pulse of light is emitted and returned by a retroreflector.
The return time of the pulse is proportional to the distance and is
related to atmospheric density in a predictable way. LIGHT SENSORS:
OR (PHOTODETECTORS), including semiconductor devices such as
photocells, photodiodes, phototransistors, CCDs, and Image sensors;
vacuum tube devices like photo-electric tubes, photomultiplier
tubes; and mechanical instruments such as the Nichols radiometer.
INFRA-RED SENSOR: especially used as occupancy sensor for lighting
and environmental controls.SCANNING LASER:- A narrow beam of laser
light is scanned
over the scene by a mirror. A photocell sensor located at an
offset responds when the beam is reflected from an object to the
sensor, whence the distance is calculated by triangulation.
Ionizing Radiation:
radiation sensors: Geiger counter, dosimeter, Scintillation
counter, Neutron detection subatomic particle sensors: Particle
detector, scintillator, Wire chamber, cloud chamber, bubble
chamber. See Category:Particle detectors
Acoustic:
Acoustic : uses ultrasound time-of-flight echo return. Used in
mid 20th century polaroid cameras and applied also to robotics.
Even older systems like Fathometers (and fish finders) and other
'Tactical Active' Sonar (Sound Navigation And Ranging) systems in
naval applications which mostly use audible sound frequencies.
Sound sensors : microphones, hydrophones, seismometers.
Other Types:
MOTION SENSORS: radar gun, speedometer, tachometer,
odometer, occupancy sensor, turn coordinator. ORIENTATION
SENSORS: gyroscope, artificial horizon, ring laser gyroscope
DISTANCE SENSOR (NONCONTACTING): Several technologies can be
applied to sense distance: magnetostriction
Non Initialized Systems:
Gray code strip or wheel- a number of photodetectors can sense a
pattern, creating a binary number. The gray code is a mutated
pattern that ensures that only one bit of information changes with
each measured step, thus avoiding ambiguities.
Initialized Systems:These require starting from a known distance
and accumulate incremental changes in measurements.
Quadrature Wheel- A disk-shaped optical mask is driven by a gear
train. Two photocells detecting light passing through the mask can
determine a partial revolution of the mask and the direction of
that rotation. Whisker Sensor- A type of touch sensor and proximity
sensor
Biological sensors:All living organisms contain biological
sensors with functions similar to those of the mechanical devices
described. Most of these are specialized cells that are sensitive
to:
Light, motion, temperature, magnetic fields, gravity, humidity,
vibration, pressure, electrical fields, sound, and other physical
aspects of the external environment;
Physical aspects of the internal environment, such as stretch,
motion of the organism, and position of appendages
(proprioception); An enormous array of environmental molecules,
including toxins, nutrients, and pheromones; Many aspects of the
internal metabolic milieu, such as glucose level, oxygen level, or
osmolality; An equally varied range of internal signal molecules,
such as hormones, neurotransmitters, and cytokines; And even the
differences between proteins of the organism itself and of the
environment or alien creatures.
Artificial sensors that mimic biological sensors by using a
biological sensitive component, are called biosensors. The human
senses are examples of specialized neuronal sensors. See Sense.
INTRODUCTION TO PROXIMITY SENSORS
PROXIMITY SENSOR:The Inductive Proximity Sensor (IPS) is a solid
state device that generates an output signal when metal objects are
either inside or entering into its sensing area from any direction.
No physical contact is required nor desired. IPS's work best with
ferrous metals, however, they also work well with non-ferrous
metals (aluminum, brass, copper etc.) at reduced sensing distances.
First introduced in the mid 60's, Inductive Proximity Sensors were
designed as an alternative to mechanical limit switches for many
applications. Initially, IPS's were made with housing similar in
size and dimension to the limit switch, but had short sensing
distances. Following very good results with these new devices,
market pressure led to the development of larger sensors with
increased sensing distances. Inductive Proximity Sensors have no
moving parts, operate very fast, are extremely reliable, require no
maintenance, and operate under extreme environmental conditions.
They typically interface with Programmable Logic Controllers (PLC),
process and personal computers with appropriate hardware and
software. They also can control relays, solenoids, valves, etc., up
to their maximum output current.
Wiring Diagram:
Connection:
Operation:An Inductive Proximity Sensor consists of an
oscillator, a ferrite core with coil, a detector circuit, and
output circuit, housing, and a cable or connector. The oscillator
generates a sine wave of a fixed frequency. This signal is used to
drive the coil. The coil in conjunction with ferrite core induces a
electromagnetic field. When the field lines are interrupted by a
metal object, the oscillator voltage from the coil. The reduction
in the oscillator voltage is caused by eddy currents induced in the
oscillator voltage is caused by eddy currents induced in the metal
interrupting the field lines. This reduction in voltage of the
oscillator is detected by the detecting circuit. In standard
sensors, when the ouptput signal is generated. In an Analog
Proximity Sensor, a pre-set level is not used. The Analog sensor
circuitry utilizes the change of the oscillator output voltage to
generate a DC output
voltage proportional to the distance the metal object is from
the sensing head.
Sensor Configuration:
Operation configuration:Output may be Normally Open (NO) or
Normally Closed (NC). Some models feature both a normally open (NO)
and normally closed (NC) output which is called a complementary
output. Fig: Electronic Output Circuits
DC Inductive Proximity Sensor may be 2-wire, or 4-wire, A3wire
or 4-wire DC sensor can be an NPN or PNP output transistor. If the
output load is connected to the negative power source than a sensor
with a PNP output transistor is required. A PNP sensor is also
known as a source sensor. If the output load is connected to the
positive power source, then a sensor with an NPN output transistor
is required. An NPN sensor is also known as a sink sensor. Flush
Mount sensors are sometimes called Shielded or Embeddable. A metal
band surrounds the sensing head which contains a coil wound around
a ferrite core.
Fig. Sensor Electromagnetic Field
The resulting electromagnetic field is directed in front of the
sensor face. Flush sensors have a narrow sensing field which may be
desirable in certain applications. In a Non-Flush (Non-shielded or
Non-embeddable) sensor, (Figure 4), there is no metal band and the
resulting electromagnetic field lines larger sensing distance than
Flush sensor. Sensing Distance: There are several sensing distance
definitions used in industry. The nominal sensing distance (Sn), is
the conventional quantity to designate the operational distance, it
is specified in the ordering pages, and does not include variations
in production tolerances, supply voltage tolerances, and ambient
temperature tolerances. A standard target used to specify sensing
distance is a square piece of mild steel having a thickness of 1mm
(0.04 in.) The sides of the square are equal to the diameter of the
circle inscribed on the sensor face or three times the rated
operating distance Sn, whichever is greater. The assured operation
distance (Sa) is the smallest useful sesing distance which
guarantees operation under variations in temperature, voltage and
manufacture. It is given as 81 % of Sn. See Figure % 0.81 Sn. The
effective sensing distance (Sr), is measured at nominal supply
voltage and nominal ambient temperature and takes into account
manufacturing tolerances: 0.9 SnSu1.21 Sn
FIG. 5 SENSING DISTANCE DEFINITIONS Sr.-MNFG. TOLERANCES
Hysteresis:Hysteresis is the switch-on point when the object
approaches the sensors active surface, and switch off point, when
the object is moving away from the sensors active surface. Without
sufficient Hysteresis, an Inductive Proximity Sensor would chatter
(continuously switching on and off), so it is designed into the
sensor circuitry. The differential travel (Hysteresis) is given as
a percent of the expected rated operating distance sr. Fig 6:
Hysteresis
Maximum switching frequency:The switching frequency indicates
the maximum number of switching operations of a sensor per second.
The value listed in the product specifications is achieved with the
conditions shown in Figure7. the value is always dependent on
target size, distance from sensing face and speed of target. Using
a smaller target or space may result in a reduction of a specific
sensor maximum switching frequency. Fig: Switching Frequency
LINEAR STEPPER MOTORS
Overview:The linear stepper motor has been made flat instead of
round so its motion will be along a straight line instead of
rotary. A picture of a linear motor and its amplifier is shown in
Fig. 11-69, and the basic parts of the linear motor are shown in
Fig. 11-70. In this diagram you can see the motor consists of a
platen and aforcer. The platen is the fixed part of the motor and
its length will determine the distance the motor will travel. It
has a number of teeth that are like the rotor in a traditional
stepper motor except it is passive and is not a permanent magnet.
The forcer consists of four pole pieces that each have three teeth.
The pitch of each tooth is staggered with respect to the teeth of
the platen. It uses mechanical roller bearings or air bearings to
ride above the platen on an air gap so that the two never
physically come into contact with each other. The magnetic field in
the forcer is changed by passing current through its coils. This
action causes the next set of teeth to align with the teeth on the
platen and causes the forcer to move from tooth to tooth over the
platen in linear travel. When the current pattern is reversed, the
forcer will reverse its direction of travel. A complete switching
cycle consists of four full steps, which moves the forcer the
distance of one tooth pitch over the platen. The typical resolution
of a linear motor is 12,500 steps per inch, which provides a high
degree of resolution. The typical load for a linear motor is low
mass that requires high-speed movements.
Fig: A linear motor and its amplifier.(Courtesy of Parker
Compumotor Division).
Fig: The forcer is shown on top of the platen of a linear motor.
The electromagnets are identified on the forcer. (Courtesy of
Parker Compumotor Division.)
Theory of Operation:
The forcer consists of two electromagnets that are identified in
Fig. 11-70 as magnet A and magnet B and one permanent magnet. The
permanent magnet is a strong rare-earth permanent magnet. The
electromagnets are formed in the shape of teeth so that their
magnetic flux can be concentrated. In the diagram you can see that
the forcer has four sets of teeth and these teeth are spaced in
quadrature so that only one set of teeth is aligned with the teeth
on the platen at any time. When current is applied to the coil
(field winding) of the electromagnets, their magnetic flux passes
through the air gap between the forcer and the platen, causing a
strong attraction between the two. The magnetic flux from the
electromagnets also tends to reinforce the flux lines of one of the
permanent magnets and cancels the flux lines of the other permanent
magnet. The attraction of the forces at the time when peak current
is flowing is up to ten times the holding force. When a pattern of
energizing one coil and then another is established, the resulting
magnetic field will pull the motor in one direction from one tooth
to the next. When current flow to the coil is stopped, the forcer
will align itself to the appropriate tooth set and create a holding
force that tends to keep the forcer from moving left or right to
another tooth. The linear stepper motor controller sets the pattern
for energizing and de-energizing the field coils so that the motor
moves smoothly in either direction. By reversing the pattern, the
direction the motor travels is reversed.
Figure shows a block diagram of the linear stepper motor
controller. From this diagram you can see that it has a
microprocessor that interfaces with a digital-to-analog converter,
a force angle modifier, and a power amplifier. It also has a power
supply for the amplifiers and it may have an accelerometer
amplifier as an option. The microprocessor has ROM and EPROM memory
to store programs.
Fig: A block diagram of a linear motor controller. (Courtesy of
Parker Compumotor Division.)
Applications:
The applications for a linear motor tend to be straight-line
motion. These types of applications are slightly different from
traditional stepper motor applications where the rotary motion is
converted to linear motion with a ball and screw, rack and pinion,
or other method. Figure 11-72 shows the linear motor used in a coil
winding positioner application. The linear motor in this
application is teamed with a servomotor that controls the speed of
the coil winding mechanism. The linear motor determines the exact
location of the next coil that is added to the spool. The speed of
the linear motor can be increased or decreased when the machine is
spooling larger-diameter or smaller-diameter wire. The ability of
the linear motor to provide small incremental steps makes it a good
match for this application. Figure 11-73 shows a second application
where the linear motor is used to transport a semiconductor wafer
through a precision laser inspection station. The linear motor
provides excellent locating ability for this application. A
Compumotor L-L20-P96 system acts as the traverse element to guide
the wire, while a Z Series servo motor rotates the spindle. Both
axes are coordinated by a Compumotor 4000 indexer preprogrammed to
produce a number of different coil types. Precise position control
and mechanical simplicity over a long length of travel are provided
by the linear motor.
Fig: A linear stepper motor used in a coil winding application.
The linear motor is used to control the position of the coil
winder. (Courtesy of Parker Compumotor Division.)
In this application, the linear motor acts as a transport for
semiconductor wafers. The L20 linear motor system offers increased
throughput and gentle handling of the wafer.
Fig: A linear stepper motor used to transport a silicon
semiconductor wafer through a laser inspection station.
(Courtesy of Parker Compumotor Division.)
Motor Fundamentals:Overview: Motors come in many different
types, shapes, and sizes. Most of the motors used in motion control
can be divided into two categories: stepper motors and servo
motors. This document describes these two types of motors.
Table of Contents:1. Stepper Motors 2. Advantages of Stepper
Motors 3. Disadvantages of Stepper Motors 4. Servo Motors 5.
Advantages of Servo Motors 6. Disadvantages of Servo Motors
Stepper Motors:Stepper motors are less expensive and typically
easier to use than a servo motor of a similar size. They are called
stepper motors because they move in discrete steps. Controlling a
stepper motor requires a stepper drive and a controller (For more
information about stepper drives, see the related link, Stepper
Motor Drives below). You control a stepper motor by providing the
drive with a step and direction
signal. The drive then interprets these signals and drives the
motor. Stepper motors can be run in an open loop configuration (no
feedback) and are good for low-cost applications. In general, a
stepper motor will have high torque at low speeds, but low torque
at high speeds. Movement at low speeds is also choppy unless the
drive has microstepping capability (for more information on
microstepping see the microstep section of the Stepper Motor
Switching Sequence link below). At higher speeds, the stepper motor
is not as choppy, but it does not have as much torque. When idle, a
stepper motor has a higher holding torque than a servo motor of
similar size, since current is continuously flowing in the stepper
motor windings. Advantages of Stepper Motors: Some of the
advantages of stepper motors over servo motors are as follows:
Low cost Can work in an open loop (no feedback required)
Excellent holding torque (eliminated brakes/clutches) Excellent
torque at low speeds Low maintenance (brushless) Very rugged - any
environment Excellent for precise positioning control No tuning
required
Disadvantages of Stepper Motors:Some of the disadvantages of
stepper motors in comparison with servo motors are as follows:
Rough performance at low speeds unless you use microstepping
Consume current regardless of load. Limited sizes available . Noisy
. Torque decreases with speed (you need an oversized motor for
higher torque at higher speeds) . Stepper motors can stall or lose
position running without a control loop .
COCLUSIONS:Development of PC based automated systems is very
popular for its easy monitoring and controlling from remote place
or near the plant itself. There are various ways to develop these
automated systems. A PC based automatic car parking is a typical
system based on the National Instruments DAQ product and Lab View
Software. Using NI DAQ and Lab View, it is very easy to develop any
automated system. It faced a problem in receiving to and sending
signals fro DAQ Card when the system was in operation. This was
because of loading effect on DAQ Card when all lines of DAQ Card
are activated, which caused voltage drop. However, this problem
overcomes by isolating all inputs and outputs by Optoisolator and
also designing all external circuits to give low output impedance
and high input impedance. This automatic car parking system may be
further improved by introducing the latest image sensors for
identifying the car and also payment of car parking charge.
FUTURE PROSPECT:The system can also be used to make car parking
completely automatic. Pressure sensors have been installed at the
entry and exit gate to sense the car waiting for entry or exit and
give input signals to the computer to count the number of vehicles
entering and leaving the park respectively. The number of cars
available in the park will be the difference of the number of
vehicles entering and the number of vehicles leaving. When a car
approaches top entry gate, the computer will decide whether any
space available or not. If no space is available, the computer will
then send signal to entry gate to keep the gate closed and also to
the monitor to display the message Car Park Full. If there is space
in the park, the user will enter his car number in the keyboard
located at entry gate and the entry gate will open to allow the
care to enter the park. The computer will then store the number of
the car and the time of entering in to the park in the data base.
Similarly, at the time of exit, as soon as the car approaches the
exit gate, the user has to enter his car number. The computer will
then calculate the parking charge multiplying the rate fixed by the
authority and the total period spent in the park and this amount
will be displayed to draw attention opf the car owner to pay. As
soon as the amount paid, the computer will send signal to the exit
gate to open and allow the car to leave the park.
BLOCK DIAGRAM FOR AUTOMATIC CAR PARKING:
1 Personal Computer:The PC must be compatible with Pentium
processor of minimum 800 MHz, speed and minimum 64 MB RAM and PCI
slot.
2DAQ Card And Other Accessories:PCI card of the National
Instruments Inc. has been used for data acquisition. PCI has 40
channels out of which 32 I/O (4 ports of 8 lines), 4 dedicated
output and control & 4 dedicated input and status.
3Keypads With LCD Display:Standard alphanumeric keypad with LCD
display have been used for keying in car number at the time of
entry or exit.
4 Visual Display Unit(VDU):In order to display the status of the
car park before entering in to car park, either CRT or LCD can be
used.
5Cash Counter (Coin Separator) With Display:At the time of
leaving the car park, the parking charge is required to display. A
cash counter is required to place in the convenient place to pay
the parking charge by the users. LCD with coin separator has been
placed at the exit gate to count number of coins of different
denominations.
6 Linear Stepper Motor:12V DC, 0.6 A motor with an arm mounted
on the shaft of the motor has been chosen for closing and opening
the gate.