AUTOMATIC BRAKING SYSTEM

AUTOMATIC BRAKING

SYSTEM

In this project we show the concept of auto braking system. In this system we use one sensor base technology. When vehicle move on the road and in the case of sudden braking sensor sense the obstruction and immediately offer a braking system.

We attach this ABS system with any type of braking system either hydraulic system or induction braking. In this concept we use one photo sensor with infra red light. Infra red light transmit the signal in the air and if there is any obstruction then  this light is reflected from the object to the photo sensor and further circuit is on automatically.

In the transmitter components we use infra red led as a transmitter and photodiode as a receiver. This photodiode is connected to the IC 555.

IC 555 is an 8 pin monostable timer IC. Photodiode is connected to the pin no. 2 directly. When pin no 2 become more negative then IC 555 provides an output to the pin no 3. Pin no 4 and 8 is connected to the positive supply. For this purpose we use 5 Volt regulated power supply for the IC. For the 5 volt regulated power supply we use IC 7805 regulator to provide a 5 volt regulation.  Output of the IC 555 is connected to the H bridge circuit through 2 autocoupler components. Autocoupler is a 4 pin IC with 2 pin on either side. In this autocoupler there is one input led and one photodiode in the other side. Autocoupler provide an isolation between the input and output circuit through the optical isolation circuit.

DC motor is controlled by the ‘H’ Bridge circuit. H Bridge is a combination of four transistors circuit. In the H Bridge two transistors are NPN and two transistors are PNP transistor. With the help of these four transistors we control the direction of the dc motor automatically.

Working of Infra Red transmitter and receiver circuit

Photo Transistor

A phototransistor is in essence nothing more than a normal bipolar transistor that is encased in a transparent case so that light can reach the Base-Collector diode. The phototransistor works like a photodiode, but with a much higher sensitivity for light, because the electrons that tunnel through the Base-Collector diode are amplified by the transistor function.

Phototransistors are specially designed transistors with the base region exposed. These transistors are light sensitive, especially when infrared source of light is used. They have only two leads (collector and emitter). When there is no light the phototransistor is closed and does not allow a collector-emitter current to go through. The phototransistor opens only with the presence of sufficient light

An auto electronic device that conducts current when exposed to light is the PHOTOTRANSISTOR. A phototransistor, however, is much more sensitive to light and produces more output current for a given light intensity that does a photodiode. Figure 3-32 shows one type of phototransistor, which is made by placing a photodiode in the base circuit of an NPN transistor. Light falling on the photodiode changes the base current of the transistor, causing the collector current to be amplified. Phototransistors may also be of the PNP type, with the photodiode placed in the base-collector circuit.

Figure 3-33 illustrates the schematic symbols for the various types of phototransistors. Phototransistors may be of the two-terminal type, in which the light intensity on the photodiode alone determines the amount of conduction. They may also be of the three-terminal type, which have an added base lead that allows an electrical bias to be applied to the base. The bias allows an optimum transistor conduction level, and thus compensates for ambient (normal room) light intensity.

DC GEAR MOTOR.

The two types of motors that you are likely to use in robotic adventure are DC motors and RC servo motors. The most common motor for robotics is the DC gear motor, which works by gearing down a fast Dc motor to make the motor turn at a slower speed and give the motor a higher torque suitable for robot locomotion.

A DC gear motor is basically a regular DC motor with a special gear box attached to the output shaft. Your robot electrical drive circuitry can control the dc gear motor to rotate the wheels of your robot for locomotion.

You can get a DC motor without a gear head, but generally these are too fast (around 15,000 RPM). For a robot to move at a reasonable rate you have to gear down a DC motor to about 30 to 80 RPM . When DC motor is geared down, you get a slower speed and plenty of torque.

‘H’ BRIDGE CIRCUIT

One of the most popular motor controller circuits is an H bridge circuit. An H bridge circuit turns a motor on and off, allows a computer or processor to control a motor’s direction and regulate speed, and may even provide a breaking mechanism. A dc gear motor’s rotation direction is usually controlled with an H bridge circuit.

A processor can not control a motor directly for a several reasons. First, a computer doesn’t output enough power to drive a motor. Second, a computer cannot control direction because it has only outputs. Third, motors are noisy electrically speaking, and would quickly damage a computer. Essentially, the computer sends, signals to the H Bridge to tell it to go forward, reverse, brake or add speed. The H Bridge then steps up the voltage and power for the motor. The H Bridge circuits also isolate the computer or processor from destructive voltage spikes and noise, which arise mainly from motors. In addition to using an H bridge circuit, you might want to have two sets of batteries: one for your electronics and another for your motors.

REGENERATIVE

BRAKES

Regenerative brakes

A Regenerative brake is a mechanism that reduces vehicle speed by converting some of its kinetic energy into electrical energy. This electrical energy is then stored for future use or fed back into a power system for use by other vehicles.

Regenerative brakes in electric railway vehicles feed the generated electricity back into the supply system. In battery electric and hybrid electric vehicles, the energy is stored in a battery or bank of capacitors for later use.

Regenerative braking should not be confused with dynamic braking, which dissipates the electrical energy as heat.

Traditional friction-based braking is still used with regenerative braking for the following reasons:

• The regenerative braking effect rapidly reduces at lower speeds.
• The amount of electrical energy capable of dissipation is limited by either the capacity of the supply system to absorb this energy or on the state of charge of the battery or capacitors. No regenerative braking effect can occur if another electric vehicle on the same supply system is not currently drawing power or if the battery or capacitors are already charged. For this reason, it is normal to also incorporate dynamic braking to absorb the excess energy.
• For these reasons there is typically the need to control the Regenerative Braking and to match the friction braking and Regenerative braking to produce the desired total braking output. The GM EV-1 was the first commercial car to do this. Engineers Abraham Farag and Loren Majersik were issued 2 patents for this 'Brake by Wire' technology.

 

 

 

MOTOR AS A BRAKE

Regenerative braking utilizes the fact that an electric motor can also act as a generator. The vehicle's electric traction motor is reconnected as a generator during braking and its output is connected to an electrical load. It is this load on the motor that provides the braking effect.

An early example of this system was the Energy Regeneration Brake, developed in 1967 for the Amitron. This was a completely battery powered urban concept car whose batteries were recharged by regenerative braking, thus increasing the range of the automobile

Electric railway vehicle operation

During braking, the traction motor connections are altered to turn them into electrical generators. The motor fields are connected across the main traction generator (MG) and the motor armatures are connected across the load. The MG now excites the motor fields. The rolling locomotive or multiple unit wheels turn the motor armatures, and the motors act as generators. Either sending the generated current through onboard resistors (dynamic braking) or back into the supply (regenerative braking) provides the braking load.

When rail operator c2c's began using regenerative braking with a fleet of Bombardier Class 357 EMUs, monitoring over the first two weeks showed an immediate energy saving of 15%. Savings of 17% are claimed for Virgin Trains Pendolinos.^[4] There is also less wear on friction braking components.

For a given direction of travel, current flow through the motor armatures during braking will be opposite to that during motoring. Therefore, the motor exerts torque in a direction that is opposite from the rolling direction.
Braking effort is proportional to the product of the magnetic strength of the field windings, times that of the armature windings.

Comparison of dynamic and regenerative brakes

Dynamic brakes ("rheostatic brakes" in the UK), unlike regenerative brakes, dissipate the electric energy as heat by passing the current through large banks of variable resistors. Vehicles that use dynamic brakes include forklifts, Diesel-electric locomotives and streetcars. If designed appropriately, this heat can be used to warm the vehicle interior. If dissipated externally, large radiator-like cowls are employed to house the resistor banks.

The main disadvantage of regenerative brakes when compared with dynamic brakes is the need to closely match the generated current with the supply characteristics. With DC supplies, this requires that the voltage be closely controlled. Only with the development of power electronics has this been possible with AC supplies, where the supply frequency must also be matched (this mainly applies to locomotives where an AC supply is rectified for DC motors).

A small number of mountain railways have used 3-phase power supplies and 3-phase induction motors. This results in a near constant speed for all trains as the motors rotate with the supply frequency both when motoring and braking.

 

 

Friction is the force that opposes the relative motion of two surfaces in contact. It is not a fundamental force, as it is derived from electromagnetic forces between atoms. When contacting surfaces move relative to each other, the friction between the two objects converts kinetic energy into thermal energy, or heat. Friction between solid objects is often referred to as Dry Friction and frictional forces between two fluids (gases or liquids) as Fluid Friction. In addition to these there is also Internal Friction which illustrates a body's ability to recover from external deformantion. Contrary to popular belief, sliding friction is not caused by surface roughness, but by chemical bonding between the surfaces.^[1]

Classical approximation

The classical approximation of the force of friction between two solid surfaces is known as Coulomb friction, named after Charles-Augustin de Coulomb. The equation is:

F= μR

where,

μ is the coefficient of friction, which is an empirical property of the          contacting materials,

N is the normal force exerted between the surfaces, and

F_f is either the force exerted by friction, or, in the case of equality, the maximum possible magnitude of this force.

For surfaces in relative motion, μ is the coefficient of kinetic friction (see below), the Coulomb friction is equal to F_f, and the frictional force on each surface is exerted in the direction opposite to its motion relative to the other surface.

For surfaces at rest relative to each other, μ is the coefficient of static friction (generally larger than its kinetic counterpart), the Coulomb friction may take any value from zero up to F_f, and the direction of the frictional force against a surface is opposite to the motion that surface would experience in the absence of friction. Thus, in the static case, the frictional force is exactly what it must be in order to prevent motion between the surfaces; it balances the net force tending to cause such motion. In this case, rather than providing an estimate of the actual frictional force, the Coulomb approximation provides a threshold value for this force, above which sliding would commence.

This approximation mathematically follows from the assumptions that surfaces are in atomically close contact only over a small fraction of their overall area, that this contact area is proportional to the normal force (until saturation, which takes place when all area is in atomic contact), and that frictional force is proportional to the applied normal force, independently of the contact area (you can see the experiments on friction from Leonardo Da Vinci). Such reasoning aside, however, the approximation is fundamentally an empirical construction. It is a rule of thumb describing the approximate outcome of an extremely complicated physical interaction. The strength of the approximation is its simplicity and versatility – though in general the relationship between normal force and frictional force is not exactly linear (and so the frictional force is not entirely independent of the contact area of the surfaces), the Coulomb approximation is an adequate representation of friction for the analysis of many physical systems.

ü    Coefficient of friction

The coefficient of friction (also known as the frictional coefficient) is a dimensionless scalar value which describes the ratio of the force of friction between two bodies and the force pressing them together. The coefficient of friction depends on the materials used – for example, ice on steel has a low coefficient of friction (the two materials slide past each other easily), while rubber on pavement has a high coefficient of friction (the materials do not slide past each other easily). Coefficients of friction range from near zero to greater than one - under good conditions, a tire on concrete may have a coefficient of friction of 1.7.

When the surfaces are adhesive, Coulomb friction becomes a very poor approximation (for example, Scotch tape resists sliding even when there is no normal force, or a negative normal force). In this case, the frictional force may depend strongly on the area of contact. Some drag racing tires are adhesive in this way.

The force of friction is always exerted in a direction that opposes movement (for kinetic friction) or potential movement (for static friction) between the two surfaces. For example, a curling stone sliding along the ice experiences a kinetic force slowing it down. For an example of potential movement, the drive wheels of an accelerating car experience a frictional force pointing forward; if they did not, the wheels would spin, and the rubber would slide backwards along the pavement. Note that it is not the direction of movement of the vehicle they oppose, it is the direction of (potential) sliding between tire and road.

The coefficient of friction is an empirical measurement – it has to be measured experimentally, and cannot be found through calculations. Rougher surfaces tend to have higher values. Most dry materials in combination have friction coefficient values between 0.3 and 0.6. Values outside this range are rarer, but Teflon, for example, can have a coefficient as low as 0.04. A value of zero would mean no friction at all, an elusive property – even Magnetic levitation vehicles have drag. Rubber in contact with other surfaces can yield friction coefficients from 1.0 to 2.

                                                                                                                                                                                           

 

 

 

Types of friction

Ø    Static friction

Static friction occurs when the two objects are not moving relative to each other (like a rock on a table). The coefficient of static friction is typically denoted as μ_s. The initial force to get an object moving is often dominated by static friction. The static friction is in most cases higher than the kinetic friction. Rolling friction occurs when one object "rolls" on another (like a car's wheels on the ground). This is classified under static friction because the patch of the tire in contact with the ground, at any point while the tire spins, is stationary relative to the ground. The coefficient of rolling friction is typically denoted as μ_r.

Limiting friction is the maximum value of static friction, equal to the force applied to a body on the verge of motion across a surface.

Ø    Kinetic friction

Kinetic (or dynamic) friction occurs when two objects are moving relative to each other and rub together (like a sled on the ground). The coefficient of kinetic friction is typically denoted as μ_k, and is usually less than the coefficient of static friction. From the mathematical point of view, however, the difference between static and kinetic friction is of minor importance: Let us have a coefficient of friction which depends on the sliding velocity and is such that its value at 0 (the static friction μ_s ) is the limit of the kinetic friction μ_k for the velocity tending to zero. Then a solution of the contact problem with such Coulomb friction solves also the problem with the original μ_k and any static friction greater than that limit.

Since friction is exerted in a direction that opposes movement, kinetic friction usually does negative work, typically slowing something down. There are exceptions however, if the surface itself is under acceleration. One can see this by placing a heavy box on a rug, then pulling on the rug quickly. In this case, the box slides backwards relative to the rug, but moves forward relative to the floor. Thus, the kinetic friction between the box and rug accelerates the box in the same direction that the box moves, doing positive work.

Examples of kinetic friction:

• Sliding friction is when two objects are rubbing against each other. Putting a book flat on a desk and moving it around is an example of sliding friction

Ø       Fluid friction is the friction between a solid object as it moves through a liquid or a gas. The drag of air on an airplane or of water on a swimmer are two examples of fluid friction.

Ø       Rolling friction

Rolling friction is the frictional force associated with the rotational movement of a disc or other circular objects along a surface. Generally the frictional force of rolling friction is less than that associated with kinetic friction.^[2] Typical values for the coefficient of rolling friction are .001. ^[3] One of the most common examples of rolling friction is the movement of motor vehicle tires on a roadway, a process which generates heat and sound as bi-products.

                                                                                    

REDUCING FRICTION

·       Devices

Devices such as tires, ball bearings or roller bearing can change sliding friction into a much smaller type of rolling friction. Many thermoplastic materials such as nylon, HDPE and PTFE are commonly used for low friction bearings. They are especially useful because the coefficient of friction falls with increasing imposed load.

·         Techniques

One technique used by railroad engineers is to back up the train to create slack in the linkages between cars. This allows the train engine to pull forward and only take on the static friction of one car at a time, instead of all cars at once, thus spreading the static frictional force out over time.

·         Lubricants

A common way to reduce friction is by using a lubricant, such as oil, water, or grease, which is placed between the two surfaces, often dramatically lessening the coefficient of friction. The science of friction and lubrication is called tribology. Lubricant technology is when lubricants are mixed with the application of science, especially to industrial or commercial objectives.

Superlubricity, a recently-discovered effect, has been observed in graphite: it is the substantial decrease of friction between two sliding objects, approaching zero levels (a very small amount of frictional energy would still be dissipated).

Lubricants to overcome friction need not always be thin, turbulent fluids or powdery solids such as graphite and talc; acoustic lubrication actually uses sound as a lubricant.

ENERGY OF FRICTION

According to the law of conservation of energy, no energy is destroyed due to friction, though it may be lost to the system of concern. Energy is transformed from other forms into heat. A sliding hockey puck comes to rest due to friction as its kinetic energy changes into heat. Since heat quickly dissipates, many early philosophers, including Aristotle, wrongly concluded that moving objects lose energy without a driving force.

Physical deformation is associated with friction. While this can be beneficial, as in polishing, it is often a problem, as the materials are worn away, and may no longer hold the specified tolerances.

The work done by friction can translate into deformation and heat that in the long run may affect the surface's specification and the coefficient of friction itself. Friction can in some cases cause solid materials to melt.

STEPPER

MOTORS

WHERE WE FIND STEPPER MOTORS??

Stepper motors can be found in almost any piece of electro-mechanical equipment. From my personal experiences, good sources for stepper motors include:

·        Surplus dot-matrix printers
If you find one of these at a swap meet, surplus store, or garage sale for a good price, buy it! They usually contain at least 2 motors, sometimes with optical shaft encoders attached to the motors! Also a good source for matching gears and toothed belts. As a general rule, larger printers will have larger, more powerful stepper motors in them.

·        Old floppy disk drives
These usually contain at least 1 stepper motor, and if you're fortunate, possibly a driver IC that can be salvaged and re-used in your own projects. Along with the motor you will get some optical interrupter units used by the drive to sense the state of the write-protect tabs and to index the disk.

·        Surplus stores
These places buy surplus from others and sell it to the public, often at great prices. The average price for a small to medium stepper motor is usually around $5.00.

·        Mail Order Companies
You can find surplus motors or even new, packaged units. Naturally the new units are going to cost more, but this may save time and money if you're building equipment with the motors that will be used at more than a "hobby" level. For general tinkering and small scale robotics, used motors will work just fine.

HOW STEPPER MOTORS WORK??
We experimented with free-spinning DC motors. DC motors have a very gradual acceleration and deceleration curves; stabilization is slow. Adding gearing to the motor will help to reduce this problem, but overshoot is still present and will throw off the anticipated stop position. The only way to effectively use a DC motor for precise positioning is to use a servo. Servos usually implement a small DC motor, a feedback mechanism (usually a potentiometer with attached to the shaft by gearing or other means), and a control circuit which compares the position of the motor with the desired position, and moves the motor accordingly. This can get fairly complex and expensive for most hobby applications.

Stepper motors, however, behave differently than standard DC motors. First of all, they cannot run freely by themselves. Stepper motors do as their name suggests -- they "step" a little bit at a time. Stepper motors also differ from DC motors in their torque-speed relationship. DC motors generally are not very good at producing high torque at low speeds, without the aid of a gearing mechanism. Stepper motors, on the other hand, work in the opposite manner. They produce the highest torque at low speeds. Stepper motors also have another characteristic, holding torque, which is not present in DC motors. Holding torque allows a stepper motor to hold its position firmly when not turning. This can be useful for applications where the motor may be starting and stopping, while the force acting against the motor remains present. This eliminates the need for a mechanical brake mechanism. Steppers don't simply respond to a clock signal, they have several windings which need to be energized in the correct sequence before the motor's shaft will rotate. Reversing the order of the sequence will cause the motor to rotate the other way. If the control signals are not sent in the correct order, the motor will not turn properly. It may simply buzz and not move, or it may actually turn, but in a rough or jerky manner. A circuit which is responsible for converting step and direction signals into winding energy patterns is called a translator. Most stepper motor control systems include a driver in addition to the translator, to handle the current drawn by the motor's windings.

Figure 1.1 - A typical translator / driver connection

A basic example of the "translator + driver" type of configuration. Notice the separate voltages for logic and for the stepper motor. Usually the motor will require a different voltage than the logic portion of the system. Typically logic voltage is +5 Vdc and the stepper motor voltage can range from +5 Vdc

COMMON CHARACTERISTICS OF STEPPER MOTORS

Stepper Motor Characteristics

A stepper motor generates excellent torque at low speed, and falls rapidly as it speeds up. The torque curve may be extended by using current limiting drivers and increasing the driving voltage -- the best performing drive systems use line voltages.

Steppers exhibit more vibration than other motor types, as the discrete step tends to snap the rotor from one position to another. This vibration can become very bad at some speeds, and can cause the motor to lose torque. The effect can be mitigated by accelerating quickly through the problem speed range, physically dampening the system, or using a micro-stepping driver. Motors with greater number of phases also exhibit smoother operation than those with fewer phases.

Fundamentals of Operation

Stepper motors operate much differently from normal DC motors, which simply spin when voltage is applied to their terminals. Stepper motors, on the other hand, effectively have multiple "toothed" electromagnets arranged around a central metal gear, as shown at right. The electromagnets are energized by an external control circuit, such as a microcontroller. To make the motor shaft turn, first one electromagnet is given power, which makes the gear's teeth magnetically attracted to the electromagnet's teeth. When the gear's teeth are thus aligned to the first electromagnet, they are slightly offset from the next electromagnet. So when the next electromagnet is turned on and the first is turned off, the gear rotates slightly to align with the next one, and from there the process is repeated.Each of those slight rotations is called a "step." In that way, the motor can be turned a precise angle. There are two basic arrangements for the electromagnetic coils: bipolar and unipolar.

Open Loop vs. Closed Loop Commutation

Steppers are generally commutated open loop, ie. the driver has no feedback on where the rotor actually is. Stepper motor systems must thus generally be over engineered, especially if the load inertia is high, or there is widely varying load, so that there is no possibility that the motor will lose steps. This has often caused the system designer to consider the trade-offs between a closely sized but expensive servo system and an oversized but relatively cheap stepper.

A new development in stepper control is to incorporate a rotor position feedback (eg. an encoder or resolver), so that the commutation can be made optimal for torque generation according to actual rotor position. This turns the stepper motor into a high pole count brushless servo motor, with exceptional low speed torque and position resolution. An advance on this technique is to normally run the motor in open loop mode, and only enter closed loop mode if the rotor position error becomes too large -- this will allow the system to avoid hunting or oscillating, a common servo problem.

Stepper motors are not just rated by voltage. The following elements characterize a given stepper motor:

ü     Voltage
Stepper motors usually have a voltage rating. This is either printed directly on the unit, or is specified in the motor's datasheet. Exceeding the rated voltage is sometimes necessary to obtain the desired torque from a given motor, but doing so may produce excessive heat and/or shorten the life of the motor.

ü     Resistance
Resistance-per-winding is another characteristic of a stepper motor. This resistance will determine current draw of the motor, as well as affect the motor's torque curve and maximum operating speed.

ü     Degrees per step
This is often the most important factor in choosing a stepper motor for a given application. This factor specifies the number of degrees the shaft will rotate for each full step. Half step operation of the motor will double the number of steps/revolution, and cut the degrees-per-step in half. For unmarked motors, it is often possible to carefully count, by hand, the number of steps per revolution of the motor. The degrees per step can be calculated by dividing 360 by the number of steps in 1 complete revolution Common degree/step numbers include: 0.72, 1.8, 3.6, 7.5, 15, and even 90. Degrees per step is often referred to as the resolution of the motor. As in the case of an unmarked motor, if a motor has only the number of steps/revolution printed on it, dividing 360 by this number will yield the degree/step value.

TYPES OF STEPPER MOTORS:
Stepper  motors  fall  into  two  basic  categories:  Permanent  magnet  and variable reluctance. The type of  motor  determines the type of drivers, and the type of translator used. Of the permanent magnet stepper motors, there are several "subflavors" available. These include the Unipolar, Bipolar, and Multiphase varieties.

    Permanent Magnet Stepper Motors

    Unipolar Stepper Motors
Unipolar motors are relatively easy to control. A simple 1-of-'n' counter circuit can generate the proper stepping sequence, and drivers as simple as 1 transistor per winding are possible with unipolar motors. Unipolar stepper motors are characterized by their center-tapped windings. A common wiring scheme is to take all the taps of the center-tapped windings and feed them +MV (Motor voltage). The driver circuit would then ground each winding to energize it.

Unipolar stepper motors are recognized by their center-tapped windings. The number of phases is twice the number of coils, since each coil is divided in two. So the diagram below (Figure 3.1), which has two center-tapped coils, represents the connection of a 4-phase unipolar stepper motor.

In addition to the standard drive sequence, high-torque and half-step drive sequences are also possible. In the high-torque sequence, two windings are active at a time for each motor step. This two-winding combination yields around 1.5 times more torque than the standard sequence, but it draws twice the current. Half-stepping is achieved by combining the two sequences. First, one of the windings is activated, then two, then one, etc. This effectively doubles the number of steps the motor will advance for each revolution of the shaft, and it cuts the number of degrees per step in half.

    Bipolar Stepper Motors
Unlike unipolar stepper motors, Bipolar units require more complex driver circuitry. Bipolar motorsare known for their excellent size/torque ratio, and provide more torque for their size than unipolar motors. Bipolar motors are designed with separate coils that need to be driven in either direction (the polarity needs to be reversed during operation) for proper stepping to occur. This presents a driver challenge. Bipolar stepper motors use the same binary drive pattern as a unipolar motor, only the '0' and '1' signals correspond to the polarity of the voltage applied to the coils, not simply 'on-off' signals. Figure 5.1 shows a basic 4-phase bipolar motor's coil setup and drive sequence.

H-BRIDGE CIRCUIT

A circuit known as an "H-bridge" (shown below) is used to drive Bipolar stepper motors. Each coil of the stepper motor needs its own H-bridge driver circuit. Typical bipolar steppers have 4 leads, connected to two isolated coils in the motor. ICs specifically designed to drive bipolar steppers (or DC motors) are available (Popular are the L297/298 series from ST Microelectronics, and the LMD18T245 from National Semiconductor). Usually these IC modules only contain a single H-bridge circuit inside of them, so two of them are required for driving a single bipolar motor. One problem with the basic (transistor) H-bridge circuit is that with a certain combination of input values (both '1's) the result is that the power supply feeding the motor becomes shorted by the transistors. This could cause a situation where the transistors and/or power supply may be destroyed. A small XOR logic circuit was added in figure 6.1 to keep both inputs from being seen as '1's by the transistors.
Another characteristic of H-bridge circuits is that they have electrical "brakes" that can be applied to slow or even stop the motor from spinning freely when not moving under control by the driver circuit. This is accomplished by essentially shorting the coil(s) of the motor together, causing any voltage produced in the coils by during rotation to "fold back" on itself and make the shaft difficult to turn. The faster the shaft is made to turn, the more the electrical "brakes" tighten.

    Variable Reluctance Stepper Motors
Sometimes referred to as Hybrid motors, variable reluctance stepper motors are the simplest to control over other types of stepper motors. Their drive sequence is simply to energize each of the windings in order, one after  the  other  (see drive pattern table below) This type of stepper motor  will  often  have  only one lead, which is the common lead for all the other leads. This type of motor feels like a DC motor  when  the shaft is spun by hand; it turns freely and you cannot feel the steps. This type of stepper motor is not permanently magnetized like its unipolar and bipolar counterparts.

There are several standard stepper motor translation circuits which use discrete logic ICs. Below you will find yet another one of these. The circuit in Figure 10.1 has not been tested but theoretically should work without problems.

WORKING OF STEPPER MOTOR CONTROL CIRCUIT

In this project when we interface the data from the computer then firstly we interface the circuit with the optocoupler. In optocoupler circuit we use ic 817 optocoupler. Here we use four optocoupler with this circuit. Output of the optpcoupler is negative. So to convert this negative output to the positive we use one inverter ic. In this project we use ic 4049 as a inverter. Pin no 3,5,7,9,11 is the input pin and pin no 2,4,6,10, 12 is the output pin. . from the output pin we interface the transistor circuit. Here we use NPN transistor. Emitter of the NPN transistor is connected to the negative voltage. Collector of the NPN transistor is connected to the coil of the stepper motor . Here we use total four transistor’s . collector of the transistor is connected to the each coil of the stepper motor.

ELECTRONICS

PART OF

SYSTEM

WORKING OF INFRA RED TRANSMITTER AND RECIEVER CIRCUIT

Photo Transistor

A phototransistor is in essence nothing more than a normal bipolar transistor that is encased in a transparent case so that light can reach the Base-Collector diode. The phototransistor works like a photodiode, but with a much higher sensitivity for light, because the electrons that tunnel through the Base-Collector diode are amplified by the transistor function.

Phototransistors are specially designed transistors with the base region exposed. These transistors are light sensitive, especially when infrared source of light is used. They have only two leads (collector and emitter). When there is no light the phototransistor is closed and does not allow a collector-emitter current to go through. The phototransistor opens only with the presence of sufficient light

An auto electronic device that conducts current when exposed to light is the PHOTOTRANSISTOR. A phototransistor, however, is much more sensitive to light and produces more output current for a given light intensity that does a photodiode. Figure 3-32 shows one type of phototransistor, which is made by placing a photodiode in the base circuit of an NPN transistor. Light falling on the photodiode changes the base current of the transistor, causing the collector current to be amplified. Phototransistors may also be of the PNP type, with the photodiode placed in the base-collector circuit.

Applications

Infrared (IR) radiation is electromagnetic radiation of a wavelength longer than visible light, but shorter than microwave radiation. The name means "below red" (from the Latin infra, "below"), red being the color of visible light of longest wavelength. Infrared radiation has wavelengths between 700 nm and 1 mm.

IR is often subdivided into near-IR (NIR, 0.7-5 µm in wavelength), mid-IR (MIR (also intermediate-IR (IIR)), 5 - 30 µm) and far-IR (FIR, 30 - 1000 µm). However, these terms are not precise, and are used differently in the various study. Infrared radiation is often linked to heat, since objects at room temperature or above will emit radiation mostly concentrated in the mid-infrared band

Uses

Infrared is used in night-vision equipment, when there is insufficient visible light to see an object. The radiation is detected and turned into an image on a screen, hotter objects showing up brighter, enabling the police and military to chase targets.

Smoke is more transparent to infrared than to visible light, so fire fighters apply infrared imaging equipment when working in smoke-filled areas.

A more common use of IR is in television remote controls. In this case it is used in preference to radio waves because it does not interfere with the television signal. IR data transmission is also employed in short-range communication among computer peripherals and personal digital assistants. These devices usually conform to standards published by IrDA, the Infrared Data Association. Remote controls and IrDA devices use infrared light-emitting diodes (LEDs) to emit infrared radiation which is focused by a plastic lens into a narrow beam. The beam is modulated, i.e. switched on and off, to encode the data. The receiver uses a silicon photodiode to convert the infrared radiation to an electric current. It responds only to the rapidly pulsing signal created by the transmitter, and filters out slowly changing infrared radiation from sunlight, people and other warm objects.

The light used in fiber optic communication is typically infrared.

Diode

A diode functions as the electronic version of a one-way valve. By restricting the direction of movement of charge carriers, it allows an electric current to flow in one direction, but blocks it in the opposite direction.

Light-emitting diode

A light-emitting diode (LED) is a semiconductor device that emits incoherent monochromatic light when electrically biased in the forward direction. This effect is a form of electroluminescence. The color depends on the semiconducting material used, and can be near-ultraviolet, visible or infrared. Nick Holonyak Jr. (1928 - ) developed the first practical visible-spectrum LED in 1962.

Light-emitting diodes

LED Technology

A LED is a special type of semiconductor diode. Like a normal diode, it consists of a chip of semiconducting material impregnated, or doped, with impurities to create a structure called a pn junction. Charge-carriers (electrons and holes) are created by an electric current passing through the junction, and release energy in the form of photons as they recombine. The wavelength of the light, and therefore its colour, depends on the band gap energy of the materials forming the pn junction. A normal diode, typically made of silicon or germanium, emits invisible far-infrared light, but the materials used for a LED have band gap energies corresponding to near-infrared, visible or near-ultraviolet light.

Conventional LEDs are made of inorganic minerals such as:

• aluminium gallium arsenide (AlGaAs) - red and infrared
• gallium arsenide/phosphide (GaAsP) - red, orange and yellow
• gallium nitride (GaN) - green
• gallium phosphide (GaP) - green
• zinc selenide (ZnSe) - blue
• indium gallium nitride (InGaN) - blue
• silicon carbide (SiC) - blue
• diamond (C) - ultraviolet
• silicon (Si) - under development

LED development began with infrared and red devices, and technological advances have made possible the production of devices with ever shorter wavelengths.

The semiconducting chip is encased in a solid plastic lens, which is much tougher than the glass envelope of a traditional light bulb or tube. The plastic may be coloured, but this is only for cosmetic reasons and does not affect the colour of the light emitted.

Why Use Phototransistors?

Phototransistors are solid-state light detectors that possess internal gain. This makes them much more sensitive than photodiodes of comparably sized area. These devices can be used to provide either an analog or digital output signal. This family of detectors offers the following general characteristics and features:

• Low cost visible and near-IR photodetection
• Available with gains from 100 to over 100,000
• Moderately fast response times
• Available in a wide range of packages including epoxy coated, transfer molded, cast, hermetic packages and in chip form
• Usable with almost any visible or near infrared light source such as LEDs, neon, fluorescent, incandescent bulbs, laser, flame sources, sunlight, etc....
• Same general electrical characteristics as familiar signal transistors (except that incident light replaces base drive current)
• Can be specially selected to meet the requirements of your particular application

Why Use IREDs?

IRED's are solid state light sources which emit light in the near-IR part of the spectrum. Because they emit at wavelengths which provide a close match to the peak spectral response of silicon photodetectors both GaAs and GaAlAs LEDs are often used with phototransistors and photodarlingtons. Key characteristics and features of these light sources include:

• Long operating lifetimes
• Low power consumption, compatible with solid state electronics
• Narrow band of emitted wavelengths
• Minimal generation of heat
• Available in a wide range of packages including epoxy coated, transfer molded, cast and hermetic packages
• Low cost
• Can be specially selected to meet the requirements of your particular application

Applications

Phototransistors can be used as ambient light detectors. When used with a controllable light source, typically and LED, they are often employed as the detector element for optoisolators and transmissive or reflective optical switches. Typical configurations include:

Optoisolator The optoisolator is similar to a transformer in that the output is electrically isolated from the input.
Optical Switch An object is detected when it enters the gap of the optical switch and blocks the light path between the emitter and detector.
Retro Sensor The retrosensor detects the presence of an object by generating light and then looking for its reflectance off of the object to be sensed.
Computer/Business Equipment track zero detector - floppy drive margin controls - printers read finger position - touch screen detect holes - computer card monitor paper position - copiers Consumer coin counters position sensors - joysticks remote controllers - toys, appliances, audio/visual equipment games - laser tag Industrial LED light source - light pens security systems safety shields encoders - measure speed and direction Medical provide electrical isolation between patient and equipment monitor intravenous injection rates

Basic of the ic 555 as a monostable timer.

The 555 timer IC was first introduced around 1971 by the Signetics Corporation as the SE555/NE555 and was called "The IC Time Machine" and was also the very first and only commercial timer IC available. It provided circuit designers and hobby tinkerers with a relatively cheap, stable, and user-friendly integrated circuit for both monostable and astable applications. Since this device was first made commercially available, a myrad of novel and unique circuits have been developed and presented in several trade, professional, and hobby publications. The past ten years some manufacturers stopped making these timers because of competition or other reasons. Yet other companies, like NTE (a subdivision of Philips) picked up where some left off.

CAPACITOR

Capacitance is the property of opposition to a change in voltage. Capacitance has the same reaction to voltage as the inductance has to the current.  That is the voltage across circuit increases.  Capacitor will resist the change and if the voltage applied to a circuit is decreased and try to maintain the original voltage.

The property of capacitor is to store charge and release.  The storing capacity of capacitor is depend upon the value of capacitor as defined in micro farad.

A basic capacitor consists of two conducting metal plates separated by a layer of air or other insulating material.  The insulating layer is called dilectric layer. All capacitor have two plates and seperating layer. In practice the dilectric layer are often staked and even rolled into compact form.  The capacitor areas classified by the name of dielectric, used in the particular:

1.  Paper capacitor

2.  Mica capacitor

3.  Ceramic capacitor

4.  Electrolytic capacitor

All electrolytic capacitors are above 1 micro farad.  All electrolytic capacitor having two legs one is positive and second is negative , bigger leg is positive and smaller leg is negative.

RESISTANCE

The unit being ohm, the greater the ohmic value the greater is the opposition to the flow of current causes.  The heating effect and causes a loss of electrical energy in the form of heat energy, greater the ohmic value greater the loss.

Types of Resistance

1.  Fixed value

2. Variable value

Normally fixed type of resistance are carbon resistance value of resistance in ohm printed on the body of resistance in colour code.

 

TRANSISTOR

Transistor are tiny semiconductor device that provide current  amplification. A transistor has three leads indentified as emitter  Base and collector. A small current to say 1mA flowing between base and emitter produce a large current of 100ma or more in the widely used as a current amplifier circuit transistor are also very useful in switching circuit.

We use normally two type of transistor one is NPN and second in PNP. In PNP transistor conduction is conducting between emitter and collector with the help of electron flow. In PNP transistor conduction is conducting between emitter and collector with the help of holes.

We normally give a forward bias to the emitter point and reverse bias to the collector point with the help of load resistance and for the base point. We give a very low voltage by resistance or any other circuit control devices.

 

Working of

Complete System

When any object comes in front of the vehicle, the IR rays emitted by LED are reflected back to photo diode and also the radiations falling on photo diode faces obstruction. This causes a negative pulse at the start of the IC resulting in its actuation. Then the two autocouplers comes into act which generates a positive-negative potential difference at meeting points of the ‘H’ Bridge terminals. This potential difference starts the motor attached to the brakes.

Now at place of brake, a dynamo with a traction motor is fixed to generate electrical energy by using the frictional energy generated during the application of brakes. This energy can be directly used or it can also be stored in a battery for future applications.

I.C. 555

The 555 timer IC was first introduced around 1971 by the Signetics Corporation as the SE555/NE555 and was called "The IC Time Machine" and was also the very first and only commercial timer IC available. It provided circuit designers and hobby tinkerers with a relatively cheap, stable, and user-friendly integrated circuit for both monostable and astable applications. Since this device was first made commercially available, a myriad of novel and unique circuits have been developed and presented in several trade, professional, and hobby publications. The past ten years some manufacturers stopped making these timers because of competition or other reasons. Yet other companies, like NTE (a subdivision of Philips) picked up where some left off.
     This primer is about this fantastic timer which is after 30 years still very popular and used in many schematics. Although these days the CMOS version of this IC, like the Motorola MC1455, is mostly used, the regular type is still available, however there have been many improvements and variations in the circuitry. But all types are pin-for-pin plug compatible. Myself, every time I see this 555 timer used in advanced and high-tech electronic circuits, I'm amazed. It is just incredible.
     In this tutorial I will show you what exactly the 555 timer is and how to properly use it by itself or in combination with other solid state devices without the requirement of an engineering degree. This timer uses a maze of transistors, diodes and resistors and for this complex reason I will use a more simplified (but accurate) block diagram to explain the internal organizations of the 555. So, lets start slowly and build it up from there.

      The 555, in fig. 1 and fig. 2 above, come in two packages, either the round metal-can called the 'T' package or the more familiar 8-pin DIP 'V' package. About 20-years ago the metal-can type was pretty much the standard (SE/NE types). The 556 timer is a dual 555 version and comes in a 14-pin DIP package, the 558 is a quad version with four 555's also in a 14 pin DIP case.
The supply current, when the output is 'high', is typically 1mA or less. The initial monostable timing accuracy is typically within 1% of its calculated value, and exhibits negligible (0.1% / V) drift with supply voltage. Thus long-term supply variations can be ignored, and the temperature variation is only 50ppm / °C (0.005% / °C).    

All IC timers rely upon an external capacitor to determine the off-on time intervals of the output pulses. As you recall from your study of basic electronics, it takes a finite period of time for a capacitor (C) to charge or discharge through a resistor (R). Those times are clearly defined and can be calculated given the values of resistance and capacitance.

The basic RC charging circuit is shown in fig. 4. Assume that the capacitor is initially discharged. When the switch is closed, the capacitor begins to charge through the resistor. The voltage across the capacitor rises from zero up to the value of the applied DC voltage. The charge curve for the circuit is shown in fig. 6. The time that it takes for the capacitor to charge to 63.7% of the applied voltage is known as the time constant (t).

That time can be calculated with the simple expression:

t = R X C

Assume a resistor value of 1 MegaOhm and a capacitor value of 1uF (micro-Farad). The time constant in that case is:

t = 1,000,000 X 0.000001 = 1 second

Assume further that the applied voltage is 6 volts. That means that it will take one time constant for the voltage across the capacitor to reach 63.2% of the applied voltage. Therefore, the capacitor charges to approximately 3.8 volts in one second.
Fig. 4-1, Change in the input pulse frequency allows completion of the timing cycle. As a general rule, the monostable 'ON' time is set approximately 1/3 longer than the expected time between triggering pulses. Such a circuit is also known as a'Missing Pulse Detector'.

Operating Modes

The 555 timer has two basic operational modes: one shot and astable. In the one-shot mode, the 555 acts like a monostable multivibrator. A monostable is said to have a single stable state--that is the off state. Whenever it is triggered by an input pulse, the monostable switches to its temporary state. It remains in that state for a period of time determined by an RC network. It then returns to its stable state. In other words, the monostable circuit generates a single pulse of a fixed time duration each time it receives and input trigger pulse. Thus the name one-shot. One-shot multivibrators are used for turning some circuit or external component on or off for a specific length of time. It is also used to generate delays. When multiple one-shots are cascaded, a variety of sequential timing pulses can be generated. Those pulses will allow you to time and sequence a number of related operations. The other basic operational mode of the 555 is as and astable multivibrator. An astable multivibrator is simply and oscillator. The astable multivibrator generates a continuous stream of rectangular off-on pulses that switch between two voltage levels. The frequency of the pulses and their duty cycle are dependent upon the RC network values.

PRECAUTIONS

1.        Mount the components at the appropriete places before soldering. Follow the circuit discription and components details, leads identification etc. Do not start soldering before making it confirm that all the component are mounted at the right place.

2.        Do not use a spread solder on the board, it may cause short circuit.

3.   Do not sit under the fan while soldering.

4.     Position the board so that gravity tends to keep the solder where you want it.

5.     Do not over heat the components at the board. Excess heat may damage the components or board.

6.     The board should not vibrate while soldering otherwise you have a dry or a cold joint.

7.     Do not put the kit under or over voltage source. Be sure abort the voltage either do or ac while operating the gadget.

8.     Do spare the bare ends of the components leads otherwise it may short circuit with the other components. To prevent this use sleeves at the components leads or use sleeved wire for connections.

9.     Do not use old dark colors solder. It may give dry joint. Be sure that all the joints are clean and well shiny.10.  Do make loose wire connections specially with cell holder, speaker, probes etc. Put knots while connections to the circuit board, otherwise it may get loose.

ADVANTAGES

·        This system can be installed at front of vehicle to prevent against ‘Head-On’ collision.

The two sensors installed detects the presence of a foreign object in front of vehicle and applies the using the brake using an IC circuit.

·        The response of this system is much higher than human response. So it decreases the chances of accidents.

·        It can be used as collision detection system in aircrafts, trains, etc.

·        The regenerative braking system is used to produce electricity, which can be used in brake lights and can be stored in batteries for horn and lighting.

DISADVATAGES

·        The dynamo installed at brake causes dis-balancing of vehicle.

·        If this is not installed in all the vehicles on road it will not effectively reduce the tendency of no-road accidents.

APPLICATIONS

·        In all on road vehicles like cars, tractors, busses, etc.

·        In aero planes as collision detection system.

·        In trains, but this system requires a large amount of space and expertise, as large amount of power is required to apply brakes in trains. But in trains the principle of regeneration is used at a very large scale.

BIBLIOGRAPHY

1.     DIODE AND ITS APPLICATION -  TURNER

2.     ELECTRICITY AND GENERAL MAGNETISM - KEMP & YOUNG

3.     FUNDAMENTALS OF PHYSICS  -   SUBRAHMANYAM  AND

           BRIJLAL.

4.     BASIC RADIO (VOLUME - 5) - MARVIN TELER.

5.     PHYSICS  FUNDAMENTAL  OF  A B C  - GUPTA

6.     BASIC ELECTRONIC   -   T.T.T.I.  CHANDIGARH