22-10-2016, 10:52 AM
1460451396-REPORTPNEUMATICCLUTCH.doc (Size: 780 KB / Downloads: 4)
SYNOPSIS
The technology of pneumatics has gained tremendous importance in the field of workplace rationalization and automation from old-fashioned timber works and coal mines to modern machine shops and space robots. It is therefore important that technicians and engineers should have a good knowledge of pneumatic system, air operated valves and accessories. The air is compressed in an air compressor and from the compressor plant the flow medium is transmitted to the pneumatic cylinder through a well laid pipe line system. To maintain optimum efficiency of pneumatic system, it is of vital importance that pressure drop between generation and consumption of compressed air is kept very low.
The aim is to design and develop a control system based an intelligent electronically controlled automotive braking system is called “PNEUMATIC CLUTCH”. Sensor Operated Pneumatic Brake is consists of IR transmitter and Receiver circuit, Control Unit, Pneumatic breaking system. The IR sensor is used to detect the obstacle. There is any obstacle in the path, the IR sensor senses the obstacle and giving the control signal to the breaking system. The pneumatic breaking system is used to break the system.
INTRODUCTION
We have pleasure in introducing our new project “PNEUMATIC CLUTCH”, which is fully equipped by IR sensors circuit and Pneumatic circuit. It is a genuine project which is fully equipped and designed for Automobile vehicles. This forms an integral part of best quality. This product underwent strenuous test in our Automobile vehicles and it is good.
The “PNEUMATIC CIRCUIT” can stop the vehicle within 2 to 3 seconds running at a speed of 50 KM. The intelligent system is a fully automation project.
This is an era of automation where it is broadly defined as replacement of manual effort by mechanical power in all degrees of automation. The operation remains an essential part of the system although with changing demands on physical input as the degree of mechanization is increased.
Degrees of automation are of two types, viz.
Full automation.
Semi automation.
In semi automation a combination of manual effort and mechanical power is required whereas in full automation human participation is very negligible.
NEED FOR AUTOMATION:
Automation can be achieved through computers, hydraulics, pneumatics, robotics, etc., of these sources, pneumatics form an attractive medium for low cost automation. The main advantages of all pneumatic systems are economy and simplicity. Automation plays an important role in mass production.
For mass production of the product, the machining operations decide the sequence of machining. The machines designed for producing a particular product are called transfer machines. The components must be moved automatically from the bins to various machines sequentially and the final component can be placed separately for packaging. Materials can also be repeatedly transferred from the moving conveyors to the work place and vice versa.
Nowadays almost all the manufacturing process is being atomized in order to deliver the products at a faster rate. The manufacturing operation is being atomized for the following reasons.
To achieve mass production
To reduce man power
To increase the efficiency of the plant
To reduce the work load
To reduce the production cost
To reduce the production time
To reduce the material handling
To reduce the fatigue of workers
To achieve good product quality
Less Maintenance
The aim is to design and develop a control system based on pneumatic breaking system of an intelligent electronically controlled automotive braking system. Based on this model, control strategies such as an 'antilock braking system' (ABS) and improved maneuverability via individual wheel braking are to be developed and evaluated.
There have been considerable advances in modern vehicle braking systems in recent years. For example, electronically controlled ABS for emergency braking, electronically controlled hydraulically actuated individual brake-by-wire (BBW) systems for saloon cars and electronically controlled pneumatically actuated systems for heavy goods vehicles. The work of recent years shall form the basis of a system design approach to be implemented. The novelty of the proposed research programmed shall lie in the design and evaluation of control systems for achieving individual wheel motion control facilitated by BBW. In the case of BBW the brake pedal is detached from the hydraulic system and replaced by a 'brake pedal simulator'. The simulator provides an electrical signal for the electronic control system.
Preliminary modeling and simulation work considers a quarter cars initially followed by a natural progression to the half car and full four wheel station cases. The model is to be constructed in modular form thus allowing the replacement / interchange of the various blocks and their associated technologies. Upon completion of the full vehicle braking model, sensitivity analyses will be carried out. Once the preliminary simulation model has been thoroughly benchmarked and existing control system strategies evaluated, an audit of the technology used is to take place and this will provide a basis for comparison of iterative technologies / techniques.
The final phase of the new modern vehicle shall include:
• Development of improved ABS control systems
• Development and assessment of an electro-hydraulic-BBW (EH-BBW) system
• Individual wheel braking combined with traction control
• Assessing sensor failure and fault tolerant control system design
• Preliminary studies into an electrically actuated system
• Re-engineering using simplified models.
PNEUMATICS
The word ‘pneuma’ comes from Greek and means breather wind. The word pneumatics is the study of air movement and its phenomena is derived from the word pneuma. Today pneumatics is mainly understood to means the application of air as a working medium in industry especially the driving and controlling of machines and equipment.
Pneumatics has for some considerable time between used for carrying out the simplest mechanical tasks in more recent times has played a more important role in the development of pneumatic technology for automation.
Pneumatic systems operate on a supply of compressed air which must be made available in sufficient quantity and at a pressure to suit the capacity of the system. When the pneumatic system is being adopted for the first time, however it wills indeed the necessary to deal with the question of compressed air supply.
The key part of any facility for supply of compressed air is by means using reciprocating compressor. A compressor is a machine that takes in air, gas at a certain pressure and delivered the air at a high pressure.
Compressor capacity is the actual quantity of air compressed and delivered and the volume expressed is that of the air at intake conditions namely at atmosphere pressure and normal ambient temperature.
The compressibility of the air was first investigated by Robert Boyle in 1962 and that found that the product of pressure and volume of a particular quantity of gas.
The usual written as
PV = C (or) PıVı = P2V2
In this equation the pressure is the absolute pressured which for free is about 14.7 Psi and is of courage capable of maintaining a column of mercury, nearly 30 inches high in an ordinary barometer. Any gas can be used in pneumatic system but air is the mostly used system now a days.
MECHANICAL BRAKE:
In a motor vehicle, the wheel is attached to an auxiliary wheel called drum. The brake shoes are made to contact this drum. In most designs, two shoes are used with each drum to form a complete brake mechanism at each wheel. The brake shoes have bake linings on their outer surfaces. Each brake shoe is hinged at one end by on anchor pin; the other end is operated by some means so that the brake shoe expands outwards. The brake linings come into contact with the drum. Retracting spring keeps the brake shoe into position when the brakes are not applied. The drum encloses the entire mechanism to keep out dust and moisture. The wheel attaching bolts on the drum are used to contact wheel and drum. The braking plate completes the brake enclosure, holds the assembly to car axie, and acts the base for fastening the brake shoes and operating mechanism
HYDRAULIC BRAKES:
The hydraulic brakes are applied by the liquid pressure. The pedal force is transmitted to the brake shoe by means of a confined liquid through a system of force transmission.
The force applied to the pedal is multiplied and transmitted to brake shoes by a force transmission system. This system is based upon Pascal’s principle, which states that “The confined liquids transmit pressure without loss equally in all directions”.
It essentially consists of two main components – master cylinder and wheel cylinder the master cylinder is connected by the wheel cylinders at each of the four wheels. The system is filled with the liquid under light pressure when the brakes are not in operation. The liquid is known as brake fluid, and is usually a mixture of glycerin and alcohol or caster-oil, denatured alcohol and some additives Spring pressure, and thus the fluid pressure in the entire system drops to its original low valve, which allows retracting spring on wheel brakes to pull the brake shoes out of contact with the brake drums into their original positions. This causes the wheel cylinder piston also to come back to its original inward position. Thus, the brakes are released.
AIR BRAKE:
Air brakes are widely used in heavy vehicle like buses and trucks which require a heavier braking effort that can be applied by the driver’s foot. Air brakes are applied by the pressure of compressed air, instead of foot pressure, acting against flexible diaphragms in brake chamber. The diaphragms are connected to the wheel brakes. These diaphragms are controlled through a hand or foot operated valve. The brake valve controls brake operation by directing the flow of air from a reservoir against diaphragms in the brake chamber when the brakes are applied and from brake chambers to tube atmosphere when the brakes are released. The air compressor, driven by the engine furnishes compressed air to the reservoir fall below a set valve.
ELECTRIC BRAKE:
Electric Brakes are also used in some motor vehicles, although these are not very popular. Warner electric brake is one of the examples of such brakes. An electric brake essentially consists of an electromagnet within the brake drum. The current from the battery is utilized to energize the electromagnet, which actuates the mechanism to expand the brake shoe against the brake drum, thus applying the brakes. The severity of braking is controlled by means of a rheostat, which is operated by the driver through the foot pedal.
Electric brakes are simpler. These brakes do not require complicated operating linkage. Only cable is required to take current from the battery to the electromagnet. Also, these are very quick in action as compared to other types of brakes.
VACUUM BRAKES / SERVO BRAKES:
A serve mechanism fitted to the braking system reduces the physical effort the driver has to use on the brake pedal most servo mechanisms are of the vacuum assistance type. A pressure differential can be established by subjecting one side of the piston to atmospheric pressure and the other side to a pressure below atmospheric pressure by exhausting air from the corresponding end of the servo cylinder.
REGENERATIVE BRAKING:
Electricity powered vehicles use regenerative braking for stopping the vehicle. With regenerative braking pressing the brake pedal does not necessarily activate a conventional friction brake. The motor controller controlling the vehicle is treated as a generator which slows the vehicle and simultaneously provides an output for charging the battery. The effectiveness of regenerative braking falls of with vehicle speed. Electric vehicles will have to be fitted with conventional hydraulic friction brakes as well as with regenerative systems.
SELECTION OF PNEUMATICS:
Mechanization is broadly defined as the replacement of manual effort by mechanical power. Pneumatics is an attractive medium for low cost mechanization particularly for sequential or repetitive operations. Many factories and plants already have a compressed air system, which is capable of providing both the power or energy requirements and the control system (although equally pneumatic control systems may be economic and can be advantageously applied to other forms of power).
The main advantages of an all-pneumatic system are usually economy and simplicity, the latter reducing maintenance to a low level. It can also have out standing advantages in terms of safety.
PNEUMATIC COMPONENTS AND ITS DESCRIPTION
The pneumatic bearing press consists of the following components to fulfill the requirements of complete operation of the machine.
1) PNEUMATIC SINGLE ACTING CYCLINDER
2) SOLENOID VALVE
3) FLOW CONTROL VALVE
4) IR SENSOR UNIT
5) WHEEL AND BRAKE ARRANGEMENT
6) PU CONNECTOR, REDUCER, HOSE COLLAR
7) STAND
8) SINGLE PHASE INDUCTION MOTOR WITH PULLEY
1) PNEUMATIC SINGLE ACTING CYLINDER:
Pneumatic cylinder consist of
A) PISTON B) CYLINDER
The cylinder is a Single acting cylinder one, which means that the air pressure operates forward and spring returns backward. The air from the compressor is passed through the regulator which controls the pressure to required amount by adjusting its knob.
A pressure gauge is attached to the regulator for showing the line pressure. Then the compressed air is passed through the single acting 3/2 solenoid valve for supplying the air to one side of the cylinder.
One hose take the output of the directional Control (Solenoid) valve and they are attached to one end of the cylinder by means of connectors. One of the outputs from the directional control valve is taken to the flow control valve from taken to the cylinder. The hose is attached to each component of pneumatic system only by connectors.
CYLINDER TECHNICAL DATA:
Piston Rod:
M.S. hard Chrome plated
Seals:
Nitrile (Buna – N) Elastomer
End Covers:
Cast iron graded fine grained from 25mm to 300mm
Piston:
-Aluminium.
Media:
-Air.
Temperature Range:
0^c to 85^c
Parts of Pneumatic Cylinder
Piston:
The piston is a cylindrical member of certain length which reciprocates inside the cylinder. The diameter of the piston is slightly less than that of the cylinder bore diameter and it is fitted to the top of the piston rod. It is one of the important parts which convert the pressure energy into mechanical power.
The piston is equipped with a ring suitably proportioned and it is relatively soft rubber which is capable of providing good sealing with low friction at the operating pressure. The purpose of piston is to provide means of conveying the pressure of air inside the cylinder to the piston of the oil cylinder.
Generally piston is made up of
Aluminium alloy-light and medium work.
Brass or bronze or CI-Heavy duty.
The piston is single acting spring returned type. The piston moves forward when the high-pressure air is turned from the right side of cylinder.
The piston moves backward when the solenoid valve is in OFF condition. The piston should be as strong and rigid as possible. The efficiency and economy of the machine primarily depends on the working of the piston. It must operate in the cylinder with a minimum of friction and should be able to withstand the high compressor force developed in the cylinder and also the shock load during operation.
The piston should posses the following qualities.
a. The movement of the piston not creates much noise.
b. It should be frictionless.
c. It should withstand high pressure.
Piston Rod
The piston rod is circular in cross section. It connects piston with piston of other cylinder. The piston rod is made of mild steel ground and polished. A high finish is essential on the outer rod surface to minimize wear on the rod seals. The piston rod is connected to the piston by mechanical fastening. The piston and the piston rod can be separated if necessary.
One end of the piston rod is connected to the bottom of the piston. The other end of the piston rod is connected to the other piston rod by means of coupling. The piston transmits the working force to the oil cylinder through the piston rod. The piston rod is designed to withstand the high compressive force. It should avoid bending and withstand shock loads caused by the cutting force. The piston moves inside the rod seal fixed in the bottom cover plate of the cylinder. The sealing arrangements prevent the leakage of air from the bottom of the cylinder while the rod reciprocates through it.
Cylinder Cover Plates
The cylinder should be enclosed to get the applied pressure from the compressor and act on the pinion. The cylinder is thus closed by the cover plates on both the ends such that there is no leakage of air. An inlet port is provided on the top cover plate and an outlet ports on the bottom cover plate. There is also a hole drilled for the movement of the piston.
The cylinder cover plate protects the cylinder from dust and other particle and maintains the same pressure that is taken from the compressor. The flange has to hold the piston in both of its extreme positions. The piston hits the top plat during the return stroke and hits the bottom plate during end of forward stroke. So the cover plates must be strong enough to withstand the load.
Cylinder Mounting Plates:
It is attached to the cylinder cover plates and also to the carriage with the help of ‘L’ bends and bolts.
2. SOLENOID VALVE WITH CONTROL UNIT:
The directional valve is one of the important parts of a pneumatic system. Commonly known as DCV, this valve is used to control the direction of air flow in the pneumatic system. The directional valve does this by changing the position of its internal movable parts.
This valve was selected for speedy operation and to reduce the manual effort and also for the modification of the machine into automatic machine by means of using a solenoid valve. A solenoid is an electrical device that converts electrical energy into straight line motion and force. These are also used to operate a mechanical operation which in turn operates the valve mechanism. Solenoids may be push type or pull type. The push type solenoid is one in which the plunger is pushed when the solenoid is energized electrically. The pull type solenoid is one is which the plunger is pulled when the solenoid is energized.
The name of the parts of the solenoid should be learned so that they can be recognized when called upon to make repairs, to do service work or to install them.
Parts of a Solenoid Valve
1. Coil
The solenoid coil is made of copper wire. The layers of wire are separated by insulating layer. The entire solenoid coil is covered with an varnish that is not affected by solvents, moisture, cutting oil or often fluids. Coils are rated in various voltages such as 115 volts AC, 230 volts AC, 460 volts AC, 575 Volts AC, 6 Volts DC, 12 Volts DC, 24 Volts DC, 115 Volts DC & 230 Volts DC. They are designed for such frequencies as 50 Hz to 60 Hz.
2. Frame
The solenoid frame serves several purposes. Since it is made of laminated sheets, it is magnetized when the current passes through the coil. The magnetized coil attracts the metal plunger to move. The frame has provisions for attaching the mounting. They are usually bolted or welded to the frame. The frame has provisions for receivers, the plunger. The wear strips are mounted to the solenoid frame, and are made of materials such as metal or impregnated less fiber cloth.
3. Solenoid Plunger
The Solenoid plunger is the mover mechanism of the solenoid. The plunger is made of steel laminations which are riveted together under high pressure, so that there will be no movement of the lamination with respect to one another. At the top of the plunger a pin hole is placed for making a connection to some device. The solenoid plunger is moved by a magnetic force in one direction and is usually returned by spring action. Solenoid operated valves are usually provided with cover over either the solenoid or the entire valve. This protects the solenoid from dirt and other foreign matter, and protects the actuator. In many applications it is necessary to use explosion proof solenoids.
WORKING OF 3/2 SINGLE ACTING SOLENOID (OR) CUT OFF VALVE:
The control valve is used to control the flow direction is called cut off valve or solenoid valve. This solenoid cut off valve is controlled by the emergency push button. The 3/2 Single acting solenoid valve is having one inlet port, one outlet port and one exhaust port. The solenoid valve consists of electromagnetic coil, stem and spring. The air enters to the pneumatic single acting solenoid valve when the push button is in ON position.