Mechatronics Lect7 Introduction to Pneumatics PDF

ACE 352 Introduction to Mechatronics Level 3 – 1st Semester Prepared by: Dr.\ Emad A. Elsheikh Faculty of Electronic Engineering, Menoufia University.  Actuation Systems Pneumatic, Hydraulic, and Electric Systems Pneumatic Actuation Systems What i...

ACE 352 Introduction to Mechatronics Level 3 – 1st Semester Prepared by: Dr.\ Emad A. Elsheikh Faculty of Electronic Engineering, Menoufia University.  Actuation Systems Pneumatic, Hydraulic, and Electric Systems Pneumatic Actuation Systems What is pneumatics? Pneumatics is the branch of science and technology, which deals with the study and application of use pressurized air—using piped, compressed air (or a similar gas, such as nitrogen) to transmit force and energy. Pneumatic systems are similar to hydraulic systems but in these systems compressed air is used in place of hydraulic fluid.  A pneumatic system is a system that uses compressedair to transmit and control energy. Pneumatic systems are used extensively in various industries. Most pneumatic systems rely on a constant supply of compressed air to make them work. This is provided by an air compressor. ▪ The compressor sucks in air from the atmosphere and stores it in a high pressure tank called a receiver. ▪ This compressed air is then supplied to the system through a series of pipes and valves. ❑ The word ‘Pneuma’ means air or gas. ❑ Pneumatics is all about using compressed air to do the work. ❑ Compressed air is the air from the atmosphere which is reduced in volume by compression thus increasing its pressure. ❑ It is used as a working medium normally at a pressure of 6 kg/sq mm to 10 kg/sq mm. ❑ For using pneumatic systems, maximum force up to 50 kN can be developed. Where Is Pneumatics Used? Air brakes on buses and trucks: These systems use a type of friction brake in which compressed air presses on a piston, and then applies the pressure to the brake pad that stops the vehicle. Exercise machines can be built on pneumatic systems. A pneumatic cylinder creates resistance that can be adjusted with air pressure. Compressed-air engines: also called pneumatic motors, do mechanical work by expanding compressed air. Usually the compressed air is converted to mechanical action by rotary or linearmotion.  Pressure regulators are valves designed to automatically stop the flow of a liquid or gas when it reaches a certain pressure. Pneumatic mail systems deliver letters through pressurized air tubes. This was invented by a Scottish engineer in the 1800 s.  A vacuum pump removes gas molecules from a sealed container, leaving behind a partial vacuum. This concept was invented in1650. Pressure switches close an electrical contact when a certain vacuum pump amount of pressure has been reached. Pneumatic air guns use pre-compressed air as an energy source to put a projectile in motion. Pressure switches Pneumatic air guns  Pneumatic tires are created with compressed air to inflate and form the body of a tire on a bike, car, or other vehicle. A handheld jackhammer is a tool that combines a hammer and a chisel.  Pneumatics also has applications in Dentistry , Construction , Mining, … and other areas This compressed air is then supplied to the system through a series of pipes and valves provide motive power in a cheaper, safer, more flexible, and more reliable way than a large number of electric motors andactuators. Gases used in pneumaticsystems ❑ The air usually has moisture removed (‫ )إزالة الرطوبة‬and a small quantity of oil added at the compressor, to avoid corrosion )‫ (تآكل‬of mechanical components and to lubricate )‫ (تشحيم‬them. ❑ Factory-plumbed, pneumatic-power users need not worry about poisonous leakages as the gas is commonly just air. ❑ Smaller or stand-alone systems can use other compressed gases which are an asphyxiation hazard (‫)خطر االختناق‬, such as nitrogen –often referred to as OFN (oxygen-free nitrogen), when supplied in cylinders. Any compressed gas other than air is an asphyxiation hazard - including nitrogen, which makes up approximately 80% ofair. Compressed oxygen (approx. 20% of air) would not asphyxiate, but it would be an extreme fire hazard, so is never used in pneumatically powered devices. ❑ Portable pneumatic tools and small vehicles such as Robot Wars machines and other hobbyist applications are often powered by compressed carbon dioxide because containers designed to hold it such as soda stream canisters and fire extinguishers are readily available, and the phase change between liquid and gas makes it possible to obtain a larger volume of compressed gas from a lighter container than compressed air would allow. Carbon dioxide is an asphyxiant and can also be a freezing hazard when vented inappropriately. Advantages of pneumatics Simplicity of Design And Control Machines are easily designed using standard cylinders & other components. Control is as easy as it is simple ON - OFF type control. Reliability ▪ Pneumatic systems tend to have long operating lives and require very little maintenance. ▪ Because gas is compressible, the equipment is less likely to be damaged by shock. The gas in pneumatics absorbs excessive force, whereas the fluid of hydraulics directly transfers force. Storage ▪ Compressed Gas can be stored, allowing the use of machines when electrical power is lost. Safety ▪ Very low chance of fire (compared to hydraulic oil). ▪ Machines can be designed to be overload safe. Environmental friendly – The operation of pneumatic systems do not produce pollutants. Pneumatic systems are environmentally clean and with proper exhaust air treatment can be installed to clean room standards. Therefore, pneumatic systems can work in environments that demand high level of cleanliness. One example is the production lines of integrated circuits. Economical – As the pneumatic system components are not expensive, the costs of pneumatic systems are quite low. Moreover, as pneumatic systems are very durable, the cost of maintenance is significantly lower than that of other systems. Limitations of pneumatic systems Relatively low accuracy – As pneumatic systems are powered by the force provided by compressed air, their operation is subject to the volume of the compressed air. As the volume of air may change when compressed or heated, the supply of air to the system may not be accurate, causing a decrease in the overall accuracy of the system. Low loading – As the cylinders used in pneumatic systems are not very large, a pneumatic system cannot drive loads that are too heavy. Processing required before use – Compressed air must be processed before use to ensure the absence of water vapour or dust. Otherwise, the moving parts of the pneumatic components may wear out quickly due to friction. Uneven moving speed – As air can easily be compressed, the moving speeds of the pistons are relativelyuneven. Noise – Noise is usually produced when the compressed air is released from the pneumatic components. Leaking A basic pneumatic system consists of the following two main sections. ❑ Compressed air production, transportation, and distributionsystem ❑ Compressed air consuming system The main components of the compressed air production, transportation, and distribution system consistof air compressor, electric motor and motor control center, pressure switch, check valve, storage tank, pressure gauge, auto drain, air dryer, filters, air lubricator, pipelines, and different types ofvalves.  Main Components of Pneumatic System Major components of pneumaticsystem Intake filter also known as air filter is used to filter out the contaminants from the air. Electric motor transforms electrical energy into mechanical energy. It is used to drive the aircompressor. Air compressor converts the mechanical energy of an electric or combustion motor into the potential energy of compressed air. There type of compressor is selected based on the basis of desired maximum delivery pressure and the required flow rate of the air. There are several types of compressors in the compressed air systems are: (i) piston or reciprocating compressors, (ii)rotary compressors, (iii)centrifugal compressors, and (iv)axial flow compressors. For satisfactory operation of the pneumatic system the compressed air needs to be cleaned and dried. Atmospheric air is contaminated with dust, smoke and is humid. These particles can cause wear of the system components and presence of moisture may cause corrosion. Hence it is essential to treat the air to get rid of these impurities. Further during compression operation, air temperature increases. Therefore cooler is used to reduce the temperature of the compressed air. The water vapour or moisture in the air is separated from the air by using a separator or airdryer. This treatment is called primary air treatment. The compressed air coming from the compressor is stored in the air receiver. The purpose of air receiver is: To smooth the pulsating flow from the compressor. Also helps the air to cool and condense the moisture present. The air receiver is to be large enough to hold all the air delivered by the compressor. The pressure in the receiver is held higher than the system operating pressure to compensate pressure loss in thepipes. Also the large surface area of the receiver helps in dissipating the heat from the compressed air. In the third stage which is the secondary air treatment process, further filtering is carried out. Control valves are used to regulate, controland monitor for control of direction flow, pressureetc. The main function of the control valve is to maintain constant downstream pressure in the air line, irrespective of variation of upstream pressure. Due to the high velocity of the compressed air flow, there is flow-dependent pressure drop between the receiver and load (application). Hence the pressure in the receiver is always kept higher than the system pressure. At the application site, the pressure is regulated to keep it constant. Air cylinders and motors are the actuators which are used to obtain the required movements of mechanical elements of pneumaticsystem. Actuators are output devices which convert energy from compressed air into the required type of action ormotion. Actuators can be classified into three types which are (i) linear actuators which convert pneumatic energy into linear motion, (ii) rotary actuators which convert pneumatic energy into rotary motion, and (iii) actuators to operate flow control valves- these are used to control the flow and pressure of fluids such as gases, steam or liquids. The construction of hydraulic and pneumatic linear actuators is similar. However they differ at their operating pressure ranges. Typical pressure of hydraulic cylinders is about 100 kg/sq mm and that of pneumatic cylinders is around 10 kg/sq mm. (i) linear actuators (Cylinders) which convert pneumatic energy into linear motion, Pneumatic cylinder, also known as air cylinder, is a mechanical device which uses the power of compressed gas to produce a force in a reciprocating linear motion. Pneumatic cylinders are divided into ▪ single-acting and ▪ double-acting cylinders. Rotary pneumatic actuator In the Rotary pneumatic actuator category, the Vane style and the Rack and Pinion style are very common. 1- Vane Actuator Vane Actuators have a cylindrical chamber in which a movable vane is mounted on a shaft. Pneumatic air under pressure applied on one side of the vane causes it to rotate through its stroke. 2- Rack and pinion Rack and Pinion actuators use a piston attached to rack gear. When pneumatic pressure is applied, the piston and rack move linearly rotating the pinion gear and driveshaft.