Fluid Power Lab Material(reviced) 1.docx

EXERSICE – 1 INTRODUCTION TO FLUID POWER AND PNEUMATIC AUTOMATION & STUDY OF PNEUMATIC SYSTEM

FLUID POWER Machines often need means to transmit power over a distance. Power is the rate at which work is being done. If you lift a weight, your body is doing work to move the weight up. The work is being done against the force of gravity that is trying to pull the weight down. The faster you lift the weight, the more power you are generating. There are purely mechanical ways to do this. Think about the drive train of a car, where the torque of the engine is transmitted over a distance, through the gearbox and the drive shaft to the wheels to make the car move. There are also electrical ways to do this, like the power that flows over power lines to make your household appliances work. Hydraulics and pneumatics are a very common way to transmit power. Systems using hydraulics and pneumatics can be efficient and portable, can produce a lot of power but don’t need to weigh very much overall, and are fairly easy to maintain and design. Hydraulics and pneumatics offer efficiency, portability, good power-to-weight ratio and ease of maintenance and design. Hydraulics use liquids, pneumatics uses gases. Hydraulics use liquids (oil, generally) and pneumatics use gases (air, usually) to transmit power. Some of the systems using hydraulics and pneumatics include 1. 2. 3. 4. 5.

Excavators Presses Vehicle Brakes Construction Equipment Automated machinery (grippers, ejectors, actuators)

PNEUMATIC SYSTEM Pneumatics has for considerable time been used for carrying out the simplest mechanical tasks, but in recent times has played a more important role in the development of pneumatic technology for automation. In majority of applications compressed air is used for one or more of the following functions.    

The use of sensors to determine status of processors Information processing Switching of actuators by final control elements Carrying out the actual work

Pneumatic components can perform the following types of motion:  

Linear Swivel



Rotary

Some industrial applications employing pneumatics are listed below:

General methods of material handling:    

Clamping Shifting Positioning Orienting

General applications: o o o o o o o o o

Packaging Feeding Metering Door or Chute control Transfer of materials Turning and Inverting of parts Sorting of parts Stacking of components Stamping and Embossing of components

Pneumatics is used in carrying out machining and working operations. For example:      

Drilling Turning Milling Sawing Finishing Forming

The product development in Pneumatics can be considered in a number of areas : o o o o o

Actuators Sensors and Input devices Processors Control systems Accessories

Each of the above product groups is important in the development of pneumatic solutions. The demands are for components with,          

Accessibility for repair and maintenance Low cost of replacement Ease of mounting and connection Low plant maintenance requirements Interchangability and flexibility Compact design Costs commensurate with the above Readily available Documentation support Minimum training required to support the product

Pneumatics-An introduction: The surface of the earth is covered entirely by layers of air. It is an abundant gas mixture comprising

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Nitrogen (approximately 78% volume) Oxygen (approximately 21% volume)

When air is compressed and stored it can be used as a medium for making measurements and for controlling and operating equipment and plant. This is known as pneumatics . The word “Pneuma” comes from Greek and means breath or wind. The word “Pneumatics “, the study of air movement and air phenomena is derived from the word “Pneuma”.

PRESSURE: Pressure is force acting at right - angles onto a surface area. One (1) Pascal represents a constant pressure on a surface area of 1 sq. m. with a force of 1N (NEWTON) acting at right - angles to that surface area. 105 Pa or 100 K Pa is equal to 1 bar and this represents atmospheric air pressure. As can be seen, the Pascal is a small unit of pressure and hence we tend to use the bar. One (1) bar represents atmospheric pressure. Pressure is defined as force F per unit area A. P = F/A

N/m2

The unit of pressure is called Pascal. 1 Pa = 1 N/m2 100,000 Pa = 1 bar 100,000 N/m2 = 1 bar (or) 1 bar = 10 N/cm2

ADVANTAGES OF PNEUMATIC SYSTEMS: o

Availability - Air is available practically everywhere in abundant quantities

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Transport - Air can be transported in pipelines, even over large distances

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Storage - An air compressor need not be in continuous operation. Compressed air can be stored in a reservoir and removed as required.

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Temperature - Compressed air is relatively insensitive to temperature fluctuations. This ensures reliable operation, even under extreme conditions.

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Explosion proof - Compressed air offers minimal risk of explosion of fire, hence no expensive protection against explosion is required.

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Cleanliness - Unlubricated exhaust air is clean. Any lubricated air which escapes through leaking pipes or components does not cause contamination.

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Components - The operating components for pneumatics are of simple construction and are therefore relatively inexpensive.

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Speed - Compressed air is very fast working medium. This enables high working speeds to be attained.

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Adjustable - With compressed air, speeds and forces are variable over wide ranges.

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Overload safety - Pneumatic tools and operating components can be loaded to the point of stopping and therefore overload safe.

DISADVANTAGES: o

Preparation - Compressed air requires good preparation. Dirt and condensate should not be present.

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Compressible - It is not always possible to achieve uniform and constant piston speeds with Compressed air.

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Force Requirements: Compressed air is economical only up to a certain force requirement. Under the normal working pressure of 6 to 7 bar and dependent on the travel and speed, the output limit is between 20,000 and 30,000 Newton’s.

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Noise Level - In pneumatic systems exhaust air is loud. This problem has now however, been largely solved due to the development of sound absorption materials and silencers.

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Costs - Compressed air is relatively expensive means of converting power. The high energy costs are partially compensated by inexpensive components and higher performance.

BASIC REQUIREMENT FOR MAINS AIR SUPPLIES: It is essential for proper and effective operation in all pneumatic systems that mains air supplies be   

Clean Dry Oil free

The preparation of the air starts from the point of generation, Contamination of the air can occur at many potential points in the generation and distribution systems right up to the point of use. The equipment to be considered in the generation, preparation and distribution of air includes:        

Compressor - It takes air at a lower pressure and delivers it at a higher pressure. Receiver - It is for storing and maintaining constant pressure of the compressed air. Filter - It is for filtering impurities and condensates. Drier - Depending on the application of the compressed air dryers may be used for necessary dehydration of the air. Lubricator - To provide lubrication for sliding parts in Pneumatic devices. Pressure Regulator - To reduce the primary pressure to the most suitable value for the equipment and application. Drainage Point - To drain the water contents in the flow lines and in the tanks. Oil Separator - To separate the compressor oil contents from the compressed air.

ELECTRO-PNEUMATICS: Integration of pneumatic and electrical technologies has played an important part in the development of a large range of industrial automation solutions. An electro-pneumatic control offers number of advantages to the developer of control systems. Where signals are transmitted over great distances in a control system, the time between transmission and signal reception is minimised using electricity as the transmission medium. Where future growth is anticipated, the incorporation of solenoid actuators and valves provides the option of developing the system to incorporate a controller that allows the system operating cycle to be altered as production requirements change. An electrical component in electro-pneumatics has the following roles:  Sensing Information  Processing Information The sensing of information can be carried out by the roller actuated limit switches, magnetically actuated switches or electronic sensors that sense whether or not a particular operation has occurred. This information is passed to the processing device, which may be a relay. The processor then has

the task of directing and modifying its received signal to drive the output stage of the system. This output stage has generally two parts: Firstly a final control element that is electrically actuated with a pneumatic output and secondly the pneumatic actuator.

ELECTRO-PNEUMATIC ELEMENTS: Actuators:  Pneumatic cylinders  Rotary Actuators  Lamps / Buzzers Control Elements:  Solenoid actuated Directional control valves  Relays Processors:  Solenoid actuated Directional control valves  Logic elements  Pneumatic - electric converter  Relays Sensors: o Limit switches o Push buttons o Proximity Sensors Energy Supply: o Compressor o Receiver The succeeding section contains various problems and solutions of pneumatic and electro-pneumatic systems for automation.

STRUCTURE AND SIGNAL FLOW IN PNEUMATIC SYSTEM Pneumatic system consists of an interconnection of different groups of elements.

SIGNAL FLOW This group of elements forms a control path for signal flow, starting from the signal selection (input) through to the actuating section (output).

Control elements control the actuating elements in accordance with the signals received from the processing elements. The primary levels in a pneumatic system are :     

Energy supply Input elements (sensors) Processing elements (Processors) Control elements Power components (Actuators)

The elements are represented by symbols which indicate the funtion of the element. PNEUMATIC CONTROL SYSTEM

PNEUMATIC COMPONENT SYMBOLS 0

Air Compressor

Pressure Regulator

Filter

Lubricator

Pressure Relief Valve

OR valve

Pressure line _____________________ Pilot line

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Pressure Gauge

AND valve

COMPONENT AND ITS SYMBOL

DESCRIPTION

1. COMPRESSOR

Compressor – It takes air at a lower pressure and delivers it at a higher pressure. Receiver - It is for storing and maintaining constant pressure of the compressed air. An air compressor is a device that converts power (usually from an electric motor, a diesel engine or a gasoline engine) into kinetic energy by compressing and pressurizing air, which, on command, can be released in quick bursts. 2. F.R.L Filter regulator and Lubricator Unit (FRL)    

This unit consists of two ports It consists of filter unit to filter the unwanted dust particle in the air. It consists of pressure regulator unit to regulate the pressure of the air from the source. For industrial applications recommended pressure is a 5 to 8 bar. In our lab 1.5 to 2 bar pressure is used for experiment purpose.

3. 3/2 D.C.V Detent Operated

3/2 D.C.V Detent operated     

This valve consists of three ports This valve operates in two positions Position shift carried out by detent type switch The position shift can be done manually This valve is used in temporary stop applications.

4. 3/2 D.C.V Push Button Operated with spring return 3/2 D.C.V Push button operated with spring return    

This valve consists of three ports This valve operates in two positions Position shift carried out by Push Button type switch The position shift can be done manually



The retrieval of position is taken care by the spring once the pressure is removed This valve is used in instant applications.



5. 3/2 D.C.V Roller Operated with spring return 3/2 D.C.V Roller operated with spring return      

This valve consists of three ports This valve operates in two positions Position shift carried out by Roller type switch Movement of piston in actuator can do the position shift Once the piston moves back ,the position is retained due to spring action This valve is used in sequential applications.

6. 5/2 D.C.V Pilot operated with spring return

5/2 D.C.V Pilot operated with spring return     

This valve consists of five ports This valve operates in two positions Position shift carried out by air from other DCVs or source The retrieval of position is taken care by the spring once air is removed This valve is used in where air flow to be changed in opposite directions.

7. 5/2 D.C.V Double side Pilot operated 5/2 D.C.V Double side pilot operated     

This valve consists of five ports This valve operates in two positions Position shift carried out by air from other DCVs or source The retrieval of position is taken care by air from other side of valve This valve is used in where air flow to be changed in opposite directions.

8. 5/2 D.C.V Solenoid operated with spring return 5/2 D.C.V Solenoid operated with spring return   

This valve consists of five ports This valve operates in two positions Position shift carried out by 24 v D.C Power supply

 

The retrieval of position is taken care by the spring once power supply is removed This valve is used in where air flow to be changed in opposite directions.

9. 5/2 D.C.V Double Solenoid operated with spring return 5/2 D.C.V Double side Solenoid operated     

This valve consists of five ports This valve operates in two positions Position shift carried out by 24 v D.C Power supply The retrieval of position is taken care by 24 v D.C Power supply This valve is used in where air flow to be changed in opposite directions.

10. Variable NR Throttle Valve

Variable NR Throttle Valve

   

This valve consists of two ports Fixed air flow and adjustable air flow are the two types available The valve has inbuilt check valve so that flow of air is allowed in one direction This valve is used to adjust the quantity of air flow according to requirement

11. Single Acting Cylinder Single Acting cylinder (Spring Return)    

12. Double Acting Cylinder

This consists of one port. The compressed air is fed only in one side. This can produce work only in one direction. The return movement of the piston is effected by a built-in spring or by application of external force.

Double Acting (DA) cylinder   

This consists of two ports. The compressed air is fed in both sides. This can used particularly when the piston is required to perform work not only on the advance movement but also on return.

EXCERSICE-2 DESIGN & SIMULATION OF PNEUMATIC SYSTEM USING SINGLE AND DOUBLE ACTING CYLINDER

a) Single Acting cylinder (SA cylinder spring return)

b) Double Acting (DA) cylinder

c) Double acting (DA) cylinder with logic elements (Roller operated DCV)

EXCERSICE-3 DESIGN & SIMULATION OF ELECTRO- PNEUMATIC SYSTEM USING SINGLE AND DOUBLE ACTING CYLINDER

a) Single Acting cylinder (spring return)

b) Double Acting (DA) cylinder

EXCERSICE-4 PROGRAMMABLE LOGIC CONTROLLER (PLC) INTRODUCTION

Programmable logic controller (PLC) is a microprocessor-based system designed to perform logical decision making for industrial control applications. According to National Electrical Manufacturers Association (NEMA), a PLC is " a digitally operating electronic apparatus which uses a programmable memory for the internal storage of instructions for implementing specific functions such as logic, sequencing, timing, counting and arithmetic operations through input / output modules for automating various types of machines or processes. ". Pneumatic control is widely used in conjunction with PLCs and industrial computers in many machines and process-control applications. The programme or software in a PLC, models and emulates the modulating control that had been previously achieved by hard-wiring discrete gates, encoders/decoders, counters, timers, flip-flops and similar digital circuitry. With its dedicated I/O modules (analogue and digital), hardened hardware, scan processing and ladder logic programming, PLC represents the optimum way to achieve industrial control in automation applications. PLC has unique components and architecture to make it better for industrial control. It also has software designed for a particular job. Furthermore, because it has cyclical scans that can be easily monitored, the PLC is relatively easy to diagnose and troubleshoot when compared to a PC. BASIC PARTS OF A PLC Regardless of size, cost and complexity, all PLCs share the same basic parts and functional characteristics. A PLC consists of an input module, an output module, memory, a processor and a programming device. The basic block diagram of the PLC is given in the Fig. The inputs are used to give information about the outside system to the PLC. The inputs are processed in the processor using the ladder logic stored in the memory. The ladder logic consists of several combinations of input and output data which are needed to carry out the control plan. Based on the results of the processing, an appropriate output signal is generated which is used to communicate with the outside system. The programming device is used to load the ladder diagram into the memory of the PLC.

Block diagram of a PLC The input module and output module are the connections to the industrial process that is to be controlled. The inputs to the controller are signals from limit switches, pushbuttons, sensors and other on/off devices. In addition to this, most PLC’s are capable of accepting signals from mechanical systems (spring-mass-damper), electrical circuits (resistance- inductance-capacitance circuits), hydraulic systems (fluid power mechanism). Some out put devices are contactor, Directional Control Valves, Motors, Stepper motors, conveyor belts etc., The processor is the central processing unit (CPU) of the PLC. It executes the various logic and sequencing function by operating the PLC inputs to determine the appropriate output signals. The processor is a microprocessor, very similar in construction to those used in personal computers and other data processing equipment. The memory is tied to the CPU. Memory contains the program of logic, sequencing and other input and output operations. Advantages of PLCs over conventional electrical relay panels The advantages of PLCs over conventional electrical relays are listed below: 1. Solid state devices are used for maximum reliability. 2. Easily reprogrammable. 3. It can be reused for other applications if no longer required in the original application. 4. Indicator lights have been provided at major diagnostic points to simplify trouble shooting 5. Powerful software features like timers, counters, logic operations etc., are also available. 6. Availability of unlimited no. of NO/NC contacts for input /output/internal logic coil (flag). 7. Very compact and rugged design leading to less downtime. 8. Small cabinet size leading to less floor space requirement.

9. Easy installation, Low cost. Hardware costs less than the installed relays.