Industrial Automation and Robotics E-Book

Mercury Learning and Information

• Herausgeber: Packt Publishing
• Kategorie: Fachliteratur
• Sprache: Englisch

Seitenzahl: 745

Veröffentlichungsjahr: 2024

Beschreibung

This course offers an introduction to automation and robotics for industrial applications. It begins with essential concepts of hydraulics and pneumatics, explaining their roles in industrial automation. Next, it delves into circuits and their applications in hydraulic, pneumatic, and fluidic design. The latter part focuses on electric and electronic controls, ending with robotics, robotic programming, and their industrial applications.
Understanding these concepts is crucial for anyone looking to work in automation, as they provide the foundation for designing and maintaining automated systems. The course covers everything from basic laws and principles to advanced topics like the use of UAVs and AI in industrial automation.
Throughout the course, you'll explore real-world applications and see how these principles are applied in industry. This structured approach ensures you gain a comprehensive understanding, from fundamental concepts to advanced automation and robotics techniques, preparing you for a career in this dynamic field.

Leseprobe

LICENSE, DISCLAIMER OF LIABILITY, AND LIMITED WARRANTY

By purchasing or using this book and disc (the “Work”), you agree that this license grants permission to use the contents contained herein, including the disc, but does not give you the right of ownership to any of the textual content in the book / disc or ownership to any of the information or products contained in it. This license does not permit uploading of theWork onto the Internet or on a network (of any kind) without the written consent of the Publisher. Duplication or dissemination of any text, code, simulations, images, etc. contained herein is limited to and subject to licensing terms for the respective products, and permission must be obtained from the Publisher or the owner of the content, etc., in order to reproduce or network any portion of the textual material (in any media) that is contained in the Work.

MERCURY LEARNING AND INFORMATION (“MLI” or “the Publisher”) and anyone involved in the creation, writing, or production of the companion disc, accompanying algorithms, code, or computer programs (“the software”), and any accompanying Web site or software of the Work, cannot and do not warrant the performance or results that might be obtained by using the contents of the Work. The author, developers, and the Publisher have used their best efforts to insure the accuracy and functionality of the textual material and/or programs contained in this package; we, however, make no warranty of any kind, express or implied, regarding the performance of these contents or programs. The Work is sold “as is” without warranty (except for defective materials used in manufacturing the book or due to faulty workmanship).

The author, developers, and the publisher of any accompanying content, and anyone involved in the composition, production, and manufacturing of this work will not be liable for damages of any kind arising out of the use of (or the inability to use) the algorithms, source code, computer programs, or textual material contained in this publication. This includes, but is not limited to, loss of revenue or profit, or other incidental, physical, or consequential damages arising out of the use of this Work.

Companion files that are included with this book can be downloaded from an FTP site by writing to the publisher [e-mail].

The sole remedy in the event of a claim of any kind is expressly limited to replacement of the book and/or disc, and only at the discretion of the Publisher. The use of “implied warranty” and certain “exclusions” vary from state to state, and might not apply to the purchaser of this product.

Copyright ©2024 by MERCURY LEARNING AND INFORMATION. An Imprint of DeGruyter Inc. All rights reserved.

Portions of this book appeared in Industrial Automation and Robotics3/E

(978-8-131805-92-3). ©Copyright 2013. Laxmi Publications Pvt. Ltd.

This publication, portions of it, or any accompanying software may not be reproduced in any way, stored in a retrieval system of any type, or transmitted by any means, media, electronic display or mechanical display, including, but not limited to, photocopy, recording, Internet postings, or scanning, without prior permission in writing from the publisher.

Publisher: David Pallai

MERCURY LEARNING AND INFORMATION

121 High Street, 3rd Floor

Boston, MA 02110

[e-mail]

www.merclearning.com

800-232-0223

J. R. Westcott / A. K. Gupta / S. K. Arora. Industrial Automation and Robotics, Second Edition.

ISBN: 978-1-68392-961-1

The material in Chapter 18 and the videos on the companion files appear and were adapted from Real-Time Embedded Components and Systems with Linux and RTOS by S.Siewert and J. Pratt. Mercury Learning and Information, 2016. ISBN: 978-1-942270-04-1. Chapter 19 appeared in “Unmanned Aerial Vehicles,” by P.K. Garg, © Copyright 2021. Mercury Learning and Information. All Rights Reserved.

The publisher recognizes and respects all marks used by companies, manufacturers, and developers as a means to distinguish their products. All brand names and product names mentioned in this book are trademarks or service marks of their respective companies. Any omission or misuse (of any kind) of service marks or trademarks, etc. is not an attempt to infringe on the property of others.

Library of Congress Control Number: 2023944997

232425321 Printed on acid-free paper in the United States of America

Our titles are available for adoption, license, or bulk purchase by institutions, corporations, etc. For additional information, please contact the Customer Service Dept. at 800-232-0223(toll free).

All of our titles are available in digital format at academiccourseware.com and other digital vendors. Companion files for this title are available by contacting [e-mail]. The sole obligation of MERCURY LEARNING AND INFORMATION to the purchaser is to replace the disc, based on defective materials or faulty workmanship, but not based on the operation or functionality of the product.

CONTENTS

Preface

1.AUTOMATION

Introduction

Definition of Automation

Mechanization vs Automation

Advantages of Automation

Goals of Automation

Social Issues of Automation

Low Cost Automation

Types of Automation

Current Emphasis in Automation

Reasons for Automation

Reasons for No Automation

Issues for Automation in Factory Operations

Strategies for Automation

Exercises

2.BASIC LAWS AND PRINCIPLES

Fluid Properties

Exercises

3.BASIC PNEUMATIC AND HYDRAULIC SYSTEMS

Introduction to Fluid Power

Basic Elements of Fluid Power System

Advantages and Disadvantages of Fluid Power

Applications of Fluid Power

Pneumatics vs. Hydraulics

Advantages and Disadvantages of Pneumatics

Advantages and Disadvantages of Hydraulics

Applications of Pneumatics

Applications of Hydraulics

Basic Pneumatic System

Basic Hydraulic System

Hydraulic System Design

Fluids Used in Hydraulics

Exercises

4.PUMPS AND COMPRESSORS

Introduction

Pumps vs. Compressors

Positive Displacement vs. Non Positive Displacement Devices

Classification of Hydraulic Pumps

Positive Displacement Pumps

Rotary Pumps

Reciprocating Pumps

Metering Pump

Dynamic/Non Positive Displacement Pumps

Centrifugal Pumps

Pump Selection Parameters

Comparison of Positive and Non Positive Displacement Pumps

Air Compressors

Types of Air Compressors

Positive Displacement Compressors

Rotary Compressors

Reciprocating Compressors

Piston Compressors

Diaphragm Compressor

Dynamic Compressors

Comparison of Different Compressors

Specifications of Compressors

Exercises

5.FLUID ACCESSORIES

Introduction

Air Receiver

Aftercooler

Air Dryer

Air Filter

Pressure Regulator

Air Lubricator

Air Service Unit (F.R.L.)

Pipeline Layout

Seals

Hydraulic Fluids

Hydraulic Reservoir

Hydraulic Filter

Pressure Gauges and Volume Meters

Hydraulic Accumulator

Intensifier

Lines

Fittings and Connectors

Hydraulic Seals

Exercises

6.CYLINDERS AND MOTORS

Introduction

Cylinders

Classification of Cylinders

Classification of Cylinders on the Basis of Construction

Single-Acting Cylinder

Double-Acting Cylinder

Types of Single-Acting Cylinders

Types of Double-Acting Cylinders

Other Types of Cylinders

Classification of Cylinders on the Basis of Working Medium

Hydraulic Cylinders

Pneumatic Cylinders

Applications of Cylinders

Cylinder Cushioning

Cylinder Mountings

Cylinder Sizing

Cylinder Specification

Introduction to Motors

Motor Ratings

Hydraulic and Pneumatic Motors

Symbol of Motors

Classification of Fluid Motors

Gear Motors

Vane Motors

Piston Motors

Application of Motors

Exercises

7.CONTROL VALVES

Introduction

Classification of Valves

Direction Control Valves

Symbol and Designation of Direction Control (DC) Valve

Classification of DC Valves

Classification of DC Valves on the Basis of Methods of Valve Actuation

Symbols for Valve Actuators

Examples of DC Valves With Actuators

Classification of DC Valves on the Basis of Construction

2/2 DC Valves

3/2 DC Valves

4/2 DC Valves

Center Conditions in 4 Way DC Valves

Check Valve

Pilot Operated Check Valve

Pressure Control Valves

Pressure Relief Valve

Pressure Reducing Valve

Sequence Valve

Counterbalance Valve

Flow Control Valves

Non Return Flow Control Valve

Quick Exhaust Valve

Time Delay Valve/Air Timer

Pneumatic Logic Valves

Twin Pressure Valve

Shuttle Valve

Servo Valves

Torque Motor and Armature Assembly

Classification of Servo Valves

Single-Stage Servo Valve

Multistage Servo Valve

Servo System

Example of a Servo Control System

Hydraulic and Pneumatic Symbols

Exercises

8.CIRCUITS

Introduction

Building up the Circuit Diagram

Designation of Components in a Circuit Diagram

Pneumatic Circuits

Pneumatic Circuit for Control of Single-Acting Cylinder

Pneumatic Circuit for Control of Double-Acting Cylinder

Application of 2/2 and 3/2 DC Valves

Circuit with Mechanical Feedback

Speed Control Circuits

Use of Flow Control Valve to Control Single-Acting Cylinder

Use of Quick Exhaust Valve in Pneumatic Circuits

Time Delay Circuit

Circuits with Necessary Conditions

Application of the Twin Pressure Valve

Application of the Shuttle Valve

Hydraulic Circuits

Hydraulic Circuit for Control of Single-Acting Cylinder

Hydraulic Circuit for Control of Double-Acting Cylinder

Circuits Using 3 Position Valves

Speed Control in Hydraulic Circuits

Bleed off Circuit

Regenerative Circuit

Circuit Showing Application of Counter Balance Valve

Sequencing Circuit

Pressure Reduction Circuit

Problems in Circuit Design

Exercises

9.PNEUMATIC LOGIC CIRCUITS

Introduction

Control System

Open Loop Control System

Closed Loop Control System

Circuit Design Methods

Motion Sequence Representation

Motion Diagrams

Control Diagram

Cascade Design

Steps Involved in Cascade Design

Sign Conventions

Sequencing

Examples

Exercises

10.FLUIDICS

Introduction

Boolean Algebra

Laws of Boolean Algebra

Truth Table

Logic Gates

Origin and Development of Fluidics

Coanda’s Effect

Tesla’s Valvular Conduit

Fluidic Devices

Fluidic Logic Devices

Fluidic Sensors

Fluidic Amplifier

Advantages and Disadvantages of Fluidics

Exercises

11.ELECTRICAL AND ELECTRONIC CONTROLS

Introduction to Sensors and Transducers

Sensor Terminology

Selection of a Transducer

Classification of Sensors

Classification of Transducers

Temperature Sensors

Light Sensors

Position Sensors

Piezoelectric Sensors

Pressure Sensors

Strain Gauges

Microprocessor

Microcontroller

Programmable Logic Controller (PLC)

Exercises

12.TRANSFER DEVICES AND FEEDERS

Introduction

Fundamentals of Production Lines

Types of Assembly Lines

Reasons for Using Automated Assembly Lines

Transfer Systems in Assembly Lines

Automatic Machines

Transfer Devices/Machines

Selection of Transfer Devices

Transfer Mechanism in Transfer Devices

Linear Transfer Mechanism

Rotary Transfer Mechanism

Classification of Transfer Devices

Advantages and Disadvantages of Transfer Machines

Conveyor Systems Used in Transfer Devices

Feeders

Classification of Feeders

Criteria for Feeder Selection

Parts Feeding Devices

Types of Feeders

Apron Feeders

Reciprocating Feeders (Plate Feeders)

Reciprocating-Tube Hopper Feeder

Reciprocating Plate Feeder

Vibratory Bowl Feeder

Screw Feeders

Belt Feeders

Rotary Plow Feeders

Rotary Table Feeders

Centrifugal Hopper Feeder

Centerboard Hopper Feeder

Flexible Feeders

Exercises

13.ROBOTICS

Introduction

History of Robots

Definition of a Robot

Industrial Robot

Laws of Robotics

Motivating Factors

Advantages and Disadvantages of Robots

Characteristics of an Industrial Robot

Components of an Industrial Robot

Comparison of the Human and Robot Manipulator

Robot Wrist and End of Arm Tools

Robot Terminology

Robotic Joints

Classification of Robots

Robot Classification on the Basis of Co-Ordinate Systems

Robot Classification on the Basis of Power Source

Robot Classification on the Basis of Method of Control

Robot Classification on the Basis of Programming Method

Robot Selection

Robot Workcell

Machine Vision

Robotics and Machine Vision

Robotic Accidents

Robotics and Safety

Robots Maintenance

Robots Installation

Exercises

14.ROBOTIC SENSORS

Introduction

Types of Sensors in Robots

Exteroceptors or External Sensors

Tactile Sensors

Proximity Sensors (Position Sensors)

Range Sensors

Machine Vision Sensors

Velocity Sensors

Proprioceptors or Internal Sensors

Robot with Sensors

Exercises

15.ROBOT END EFFECTORS

Introduction

End Effector

Classification of End Effectors

Grippers

Selection of Gripper

Gripping Mechanisms

Tools

Types of Tools

Characteristics of End-of-Arm Tooling

Elements of End-of-Arm Tooling

Types of Grippers

Finger Grippers

Mechanical Grippers

Vacuum/Suction Grippers

Magnetic Grippers

Exercises

16.ROBOT PROGRAMMING

Introduction

Robot Programming

Robot Programming Techniques

Online Programming

Lead-Through Programming

Walk-Through Programming or Teaching

Offline Programming

Task Level Programming

Motion Programming

Overview of Robot Programming Languages

Requirements for a Standard Robot Language

Robot Languages

Types of Robot Languages

Example of a Robot Program Using VAL

Review Exercises

17.APPLICATIONS OF ROBOTS

Introduction

Robot Capabilities

Applications of Robots

Manufacturing Applications

Material Handling Applications

Cleanroom Robots

Exercises

18.ROBOTS USING REAL-TIME EMBEDDED SYSTEMS

Introduction to Robots Using Real-Time Embedded Systems

Robotic Arm

Actuation

End Effector Path

Sensing

Tasking

Automation and Autonomy

Exercises

19.THE USE OF UNMANNED AERIAL VEHICLES (UAVS) IN INDUSTRIAL AUTOMATION

Introduction

Historical Developments

Uses of UAVs

Some Technical Terms

Characteristics of UAVs

Working of a UAV

Advantages and Disadvantages of UAVs

Summary

Exercises

20.THE PROMISE OF ARTIFICIAL INTELLIGENCE (AI) IN INDUSTRIAL AUTOMATION

What is Artificial Intelligence?

Applications to Industrial Automation and Robotics

Factors to be Considered Using Artificial Intelligence in Industrial Automation

Planning and Implementation

Preparing the Workforce for AI Implementation

Evaluating for Safety and Efficiency

Exercises

REFERENCES

INDEX

PREFACE

The purpose of this book is to present an introduction to the multidisciplinary field of automation and robotics for industrial applications. The book initially covers the important concepts of hydraulics and pneumatics and how they are used for automation in an industrial setting. It then moves to a discussion of circuits and using them in hydraulic, pneumatic, and fluidic design. The latter part of the book deals with electric and electronic controls in automation, robotics, robotic programming, and applications of robotics in industry. New chapters on unmanned aerial vehicles and the promise of AI in industrial automation have been added. Companion files are available with applications and videos.

Companion Files

Companion files (videos, lab projects, and figures from the book) for this title are available by contacting the publisher at [e-mail].

Acknowledgments

The material in Chapter 18 and the videos on the companion files appear in and were adapted from Real-Time Embedded Components and Systems with Linux and RTOS by S.Siewert and J. Pratt. Mercury Learning and Information, 2016. ISBN: 978-1-942270-04-1. I would like to thank Jen Blaney of Mercury Learning for her professional and patient assistance with this product, Sean Westcott for his input and support, and to dedicate this project to the truest friend, Sandy.

Jean Riescher WestcottOctober 2023

CHAPTER1

AUTOMATION

INTRODUCTION

The word automation comes from the Greek word “automatos,” meaning self-acting. The word automation was coined in the mid-1940s by the U.S. automobile industry to indicate the automatic handling of parts between production machines, together with their continuous processing at the machines. The advances in computers and control systems have extended the definition of automation. By the middle of the 20th century, automation had existed for many years on a small scale, using mechanical devices to automate the production of simply shaped items. However the concept only became truly practical with the addition of the computer, whose flexibility allowed it to drive almost any sort of task.

DEFINITION OF AUTOMATION

Automation can generally be defined as the process of following a predetermined sequence of operations with little or no human labor, using specialized equipment and devices that perform and control manufacturing processes. Automation in its full sense, is achieved through the use of a variety of devices, sensors, actuators, techniques, and equipment that are capable of observing the manufacturing process, making decisions concerning the changes that need to be made in the operation, and controlling all aspects of it.

OR

Automation is the process in industry where various production operations are converted from a manual process, to an automated or mechanized process.

Example: Let’s assume that a worker is operating a metal lathe. The worker collects the stock, already cut to size, from a bin. He then places it in the lathe chuck, and moves the various hand-wheels on the machine to create a component; a bolt could be such an item. When finished the worker begins the process again to make another item. This would be a manual process. If this process were automated, the worker would place long lengths of bar into the feed mechanism of an automatic lathe. The lathe mechanisms feed the material into the chuck, turn the piece to the correct shape and size, and cut it off the bar before beginning another item. This is an example of an automated machine in a manufacturing process.

Automation is a step beyond mechanization, where human operators are provided with machinery to help them in their jobs. Industrial robotics are said to be the most visible part of automation. Modern automated processes are mostly controlled by computer programs, which through the action of sensors and actuators, monitor progress and control the sequences of events until the process is complete. Decisions made by the computer ensure that the process is completed accurately and quickly.

Many people fear that automation will result in layoffs and unemployment; they believe that its evils considerably outweigh its benefits. Basically, automation does take over jobs performed by workers; but automation does not need to bring about unemployment, as some people fear, for three very positive reasons:

First, in terms of the numbers of workers required to produce a product, the reduction is a temporary displacement which can be offset by the demands of a broadening market, as well as the creation of new industries. It still takes many workers to build, service, and operate any automatic machine.

Second, automation does not happen overnight; it is an evolutionary process. Manual, direct-labor work will be progressively transformed into work, which will be cleaner, easier, safer, and more rewarding to the worker, who, through the process of automation itself, will be trained for the more skillful accomplishments required in the better jobs of the future.

Third, and most important, automation is the necessary solution to a predicted shortage of labor. It is designed to do the work of people who are not there; it is a solution to a problem, not a cause.

Automation is a technology dealing with the application of mechatronics and computers for production of goods and services. Manufacturing automation deals with the production of goods. It includes:

Automatic machine tools to process parts.

Automatic assembly machines.

Industrial robots.

Automatic material handling.

Automated storage and retrieval systems.

Automatic inspection systems.

Feedback control systems.

Computer systems for automatically transforming designs into parts.

Computer systems for planning and decision making to support manufacturing.

The decision to automate a new or existing facility requires the following considerations to be taken into account:

Type of product manufactured.

Quantity and the rate of production required.

Particular phase of the manufacturing operation to be automated.

Level of skill in the available workforce.

Reliability and maintenance problems that may be associated with automated systems.

Economics.

MECHANIZATION VS AUTOMATION

Mechanization refers to the use of powered machinery to help a human operator in some task. The use of hand-powered tools is not an example of mechanization. The term is most often used in industry. The addition of powered machine tools; such as the steam powered lathe dramatically reduced the amount of time needed to carry out various tasks, and improves productivity. Today very little construction of any sort is carried out with hand tools. Automation and mechanization are often confused with each other, though it should not be too hard to keep them apart. Mechanization saves the use of human muscles; automation saves the use of human judgment. Mechanization displaces physical labor, whereas automation displaces mental labor.

Mechanization is the replacement of human power by machine power. Mechanization often replaces craftwork and creates jobs for unskilled labor. It also only affects one or two industries at a time. Mechanization moves slowly and the job displacement is short-term. Mechanization is what occurred during the industrial revolution. Automation is the replacement of human thinking with computers and machines. Automation tends to create jobs for skilled workers at the expense of unskilled and semi-skilled workers. It affects many industries at the same time, moving rapidly. It also creates longer-term job displacement and has been more characteristic since the 1950s.

ADVANTAGES OF AUTOMATION

Manufacturing companies in virtually every industry are achieving rapid increases in productivity by taking advantage of automation technologies. When one thinks of automation in manufacturing, robots usually come to mind. The automotive industry was the early adopter of robotics, using these automated machines for material handling, processing operations, and assembly and inspection. Automation can be applied to manufacturing of all types. The advantages of automation are:

Increase in productivity.

Reduction in production costs.

Minimization of human fatigue.

Less floor area required.

Reduced maintenance requirements.

Better working conditions for workers.

Effective control over production process.

Improvement in quality of products.

Reduction in accidents and hence safety for workers.

Uniform components are produced.

GOALS OF AUTOMATION

Automation has certain primary goals as listed below:

Integrate various aspects of manufacturing operations so as to improve the product quality and uniformity, minimize cycle times and effort, and thus reduce labor costs.

Improve productivity by reducing manufacturing costs through better control of production. Parts are loaded, fed, and unloaded on machines more efficiently. Machines are used more effectively and production is organized more efficiently.

Improve quality by employing more repeatable processes.

Reduce human involvement, boredom, and possibility of human error.

Reduce workpiece damage caused by manual handling of parts.

Raise the level of safety for personnel, especially under hazardous working conditions.

Economize on floor space in the manufacturing plant by arranging the machines, material movement, and related equipment more efficiently.

SOCIAL ISSUES OF AUTOMATION

Automation has contributed to modern industry in many ways. Automation raises several important social issues. Among them is automation’s impact on employment/unemployment. Automation leads to fuller employment. When automation was first introduced, it caused widespread fear. It was thought that the displacement of human workers by computerized systems would lead to unemployment (this also happened with mechanization, centuries earlier). In fact the opposite was true, the freeing up of the labor force allowed more people to enter information jobs, which are typically higher paying. One odd side effect of this shift is that “unskilled labor” now pays very well in most industrialized nations, because fewer people are available to fill such jobs leading to supply and demand issues.

Some argue the reverse, at least in the long term. First, automation has only just begun and short-term conditions might partially obscure its long-term impact. For instance many manufacturing jobs left the United States during the early 1990s, but a massive up scaling of IT jobs at the same time offset this as a whole. Currently, for manufacturing companies, the purpose of automation has shifted from increasing productivity and reducing costs to increasing quality and flexibility in the manufacturing process.

Another important social issue of automation is better working conditions. The automated plants needs controlled temperature, humidity, and dust free environment for proper functioning of automated machines. Thus the workers get a very good environment to work in.

Automation leads to safety of workers. By automating the loading and unloading operations, the chances of accidents to the workers get reduced.

Workers expect an increase in standard of living with the help of automation. Standards of living go up with the increase in productivity, and automation is the sure method of increasing productivity. The cost of color TVs, washing machines, and stereos has declined, thus enabling a large number of households to buy these products.

LOW COST AUTOMATION

Low cost automation (LCA) is a technology that creates some degree of automation around the existing equipment, tools, methods, people, etc. by using standard components available in the market with low investment, so that the payback period is short.

The benefits of low cost automation are numerous. It not only simplifies the process, but also reduces the manual content without changing the basic set up. Major advantages of low cost automation are low investment, increased labor productivity, smaller batch size, better utilization of the material, and process consistency leading to less rejections.

A wide range of activities such as loading, feeding, clamping, machining, welding, forming, gauging, assembly, and packing can be subjected to low cost automation systems adoption. Besides, low cost automation can be very useful for process industries manufacturing chemicals, oils, or pharmaceuticals. Many operations in food processing industries, which need to be carried out under totally hygienic conditions, can also be rendered easy through low cost automation systems.

A wide variety of systems (mechanical, hydraulic, pneumatic, electrical, and electronics) are available for deployment in LCA systems. However, each has its own advantages as well as limitations. For uncomplicated situations, one can build a simple LCA device using any of the above systems, through a rapid techno-economic evaluation. However, in most of the practical applications, hybrid systems are used because that can allow use of the advantages of different devices, while simultaneously minimizing individual disadvantages.

Issues in Low Cost Automation

1.Assessment of the Current Productivity Level: There are some simple procedures for this. Work sampling (activity sampling) is one of them. It needs no equipment and little time to collect the data. If the data is processed, considerable information will come out about the current productivity level.

2.PMTS: Predetermined Motion and Time Studies is a very useful tool to check whether an existing manual operation is correctly pasted. If the time taken is more than desirable, PMTS will help in identifying it and improving it.

3.Design for Automation and Assembly: When components are made and assembled manually one may not have thought about the complexity of automation. For example, putting together half a dozen nuts and bolts is very easy in a manual assembly but very complex for an automatic system.

TYPES OF AUTOMATION

Fixed Automation (Hard Automation)

Fixed automation refers to the use of special purpose equipment to automate a fixed sequence of processing or assembly operations. It is typically associated with high production rates and it is relatively difficult to accommodate changes in the product design. This is also called hard automation. For example, GE manufactures approximately 2 billion light bulbs per year and uses fairly specialized, high-speed automation equipment. Fixed automation makes sense only when product designs are stable and product life cycles are long. Machines used in hard-automation applications are usually built on the building block, or modular principle. They are generally called transfer machines, and consist of the following two major components: powerhead production units and transfer mechanisms.

Advantages

Maximum efficiency.

Low unit cost.

Automated material handling—fast and efficient movement of parts.

Very little waste in production.

Disadvantages

Large initial investment.

Inflexible in accommodating product variety.

Programmable Automation

In programmable automation, the equipment is designed to accommodate a specific class of product changes and the processing or assembly operations can be changed by modifying the control program. It is particularly suited to “batch production,” or the manufacture of a product in medium lot sizes (generally at regular intervals). The example of this kind of automation is the CNC lathe that produces a specific product in a certain product class according to the “input program.” In programmable automation, reconfiguring the system for a new product is time consuming because it involves reprogramming and set up for the machines, and new fixtures and tools. Examples include numerically controlled machines, industrial robots, etc.

Advantages

Flexibility to deal with variations and changes in product.

Low unit cost for large batches.

Disadvantages

New product requires long set up time.

High unit cost relative to fixed automation.

Flexible Automation (Soft Automation)

In flexible automation, the equipment is designed to manufacture a variety of products or parts and very little time is spent on changing from one product to another. Thus, a flexible manufacturing system can be used to manufacture various combinations of products according to any specified schedule. With a flexible automation system, it is possible to quickly incorporate changes in the product (which may be redesigned in reaction to changing market conditions and to consumer feedback) or to quickly introduce a new product line. For example, Honda is widely credited with using flexible automation technology to introduce 113 changes to its line of motorcycle products in the 1970s. Flexible automation gives the manufacturer the ability to produce multiple products cheaply in combination than separately.

Advantages

Flexibility to deal with product design variations.

Customized products.

Disadvantages

Large initial investment.

High unit cost relative to fixed or programmable automation.

CURRENT EMPHASIS IN AUTOMATION

Currently, for manufacturing companies, the purpose of automation has shifted from increasing productivity and reducing costs, to broader issues, such as increasing quality and flexibility in the manufacturing process. The old focus on using automation simply to increase productivity and reduce costs was short-sighted, because it is also necessary to provide a skilled workforce who can make repairs and manage the machinery. Moreover, the initial costs of automation were high and often could not be recovered by the time entirely new manufacturing processes replaced the old. (Japan’s “robot junkyards” were once world famous in the manufacturing industry.)

Automation is now often applied primarily to increase quality in the manufacturing process, where automation can increase quality substantially. For example, automobile and truck pistons used to be installed into engines manually. This is rapidly being transitioned to automated machine installation, because the error rate for manual installment was around 1–1.5%, but is 0.00001% with automation. Hazardous operations, such as oil refining, the manufacturing of industrial chemicals, and all forms of metal working, were always early contenders for automation.

Another major shift in automation is the increased emphasis on flexibility and convertibility in the manufacturing process. Manufacturers are increasingly demanding the ability to easily switch from one manufacturing product to other without having to completely rebuild the production lines.

REASONS FOR AUTOMATION

1.Shortage of labor

2.High cost of labor

3.Increased productivity: Higher production output per hour of labor input is possible with automation than with manual operations. Productivity is the single most important factor in determining a nation’s standard of living. If the value of output per hour goes up, the overall income levels go up.

4.Competition: The ultimate goal of a company is to increase profits. However, there are other goals that are harder to measure. Automation may result in lower prices, superior products, better labor relations, and a better company image.

5.Safety: Automation allows the employee to assume a supervisory role instead of being directly involved in the manufacturing task. For example, die casting is hot and dangerous and the work pieces are often very heavy. Welding, spray painting, and other operations can be a health hazard. Machines can do these jobs more precisely and achieve better quality products.

6.Reducing manufacturing lead-time: Automation allows the manufacturer to respond quickly to the consumers needs. Second, flexible automation also allows companies to handle frequent design modifications.

7.Lower costs: In addition to cutting labor costs, automation may decrease the scrap rate and thus reduce the cost of raw materials. It also enables just-in-time manufacturing which in turn allows the manufacturer to reduce the in-process inventory. It is possible to improve the quality of the product at lower cost.

REASONS FOR NO AUTOMATION

1.Labor resistance: People look at robots and manufacturing automation as a cause of unemployment. In reality, the use of robots increases productivity, makes the firm more competitive, and preserves jobs. But some jobs are lost. For example, Fiat reduced its work force from 138,000 to 72,000 in nine years by investing in robots. GM’s highly automated plant built in collaboration with Toyota in Fremont, California employs 3,100 workers in contrast to 5,100 at a comparable older GM plant.

2.Cost of upgraded labor: The routine monotonous tasks are the easiest to automate. The tasks that are difficult to automate are ones that require skill. Thus, manufacturing labor must be upgraded.

3.Initial investment: Cash flow considerations may make an investment in automation difficult even if the estimated rate of return is high.

ISSUES FOR AUTOMATION IN FACTORY OPERATIONS

Task is too difficult to automate.

Short product lifecycle.

Customized product.

Fluctuating demand.

Reduce risk of product failure.

Cheap manual labor.

STRATEGIES FOR AUTOMATION

Specialization of operations.

Combined operations.

Simultaneous operations.

Integration of operations.

Increased flexibility.

Improved material handling and storage.

On-line inspection.

Process control and optimization.

Plant operations control.

Computer Integrated Manufacturing.

EXERCISES

1. Differentiate between mechanization and automation.

2. Identify some of the major reasons for automation.

3. List the levels of automation.

4. Discuss the concept of low cost automation with the help of suitable examples.

5. What are the types of automation that can be used in a production system? Compare them for their features and drawbacks.

6. Discuss the various levels of automation.

7. Write short notes on “low cost automation.”

8. Identify major socio-economic considerations favoring automation.

9. State the advantages of automating production operations.

10. List the strategies for automation.

11. Compare hard automation with soft automation.

12. List the advantages of flexible automation.

13. List at least four reasons why automation is required in industry.

CHAPTER2

BASIC LAWS AND PRINCIPLES

FLUID PROPERTIES

Force

A force is a push or a pull, or more generally anything that can change an object’s speed or direction of motion. The International System of Units (SI) unit used to measure force is the Newton (symbol N).

where F stands for force in Newton, m stands for mass in Kg and a represents acceleration expressed as meters divided by seconds squared m/s2.

Pressure

Pressure is the ratio of force to the area over which the force acts.

Mathematically, it can be expressed as:

where p is pressure, F is force, and A represents area. Pressure is usually expressed in Newton per square meter, given the name Pascal, and traditionally, it was expressed in pounds force per square inch (PSI).

Atmospheric Pressure

Atmospheric pressure is defined as the pressure due to the weight of the atmosphere (air and water vapor) on the earth’s surface. Atmospheric pressure is determined by a mercury column barometer, that is why it is sometimes called as barometric pressure. The average atmospheric pressure at sea level has been defined as 1.01325 bars, or 14.696 pounds per square inch absolute (PSIA).

FIGURE 2.1 Pressure Relationship.

Absolute Pressure

Absolute pressure can be given as gauge pressure plus barometric or atmospheric pressure. Absolute pressure is referenced against absolute zero pressure, or a complete vacuum. The units of absolute pressure are followed by suffix “a,” such as psia. If we hold an absolute pressure instrument in the open air, the reading should be well above zero, in the range of 14.7 to 12 psia.

Gauge and Vacuum Pressure

Gauge pressure is referenced against the atmospheric pressure at the measurement point. The units of gauge pressure are followed by a “g,” such as psig. A gauge pressure instrument should always read zero when exposed to atmospheric pressure. Similarly, when the pressure falls below atmospheric, it is called vacuum pressure, sometimes it is also called negative gauge pressure.

Based upon the above discussions, the following equations can be derived:

Where

Conversion of various units of pressure in Pascal

Unit

Symbol

No. of pascals

Bar

bar

1 × 105 Pa

Millibar

mbar

100 Pa

Hectopascal

hPa

100 Pa

conventional mm of Hg

mmHg

133.322 Pa

conventional inch of Hg

in Hg

3,386.39… Pa

Torr

torr

101325/760 ≈ 133.322 Pa

pound-force per square inch

lbf/in2

6,894.76 ≈ 6895 Pa

Pascal’s Law

Blaise Pascal formulated this basic law in the mid-17th century. His law states that pressure in a confined fluid is transmitted undiminished in every direction and acts with equal force on equal areas and at right angles to container walls. Hydraulic brakes, lifts, presses, syringe pistons, etc. work on the principle of Pascal’s law.

According to Pascal’s law, inside the pipes of a confined system pressure is uniform at all points. Mathematically,

FIGURE 2.2 Pascal’s Law Illustrated

Flow and Flow Rate

The volume of a substance passing a point per unit time is called flow and the volume of water, a pump or a compressor can move during a given amount of time is called, “flow rate.”

Volumetric Flow Rate

It is the volume of the fluid flowing through a cross section per unit time. Air related flows are usually expressed in cubic feet per minute (CFM) and for liquid-based fluids, they are expressed as liters or gallons per minute (LPM or GPM) or cubic meters per second, etc.

Volumetric Flow Rate = Area × Velocity

Mass Flow Rate

Volumetric flow rate times density, i.e., pounds per hour or kilograms per minute.

Mass Flow Rate = Area × Velocity × Density

Conversion of various flow rate units into m3/s

Unit

Symbol

No. of m3/s

Liters/second

l/s

10−3 m3/s

Gallons/second

gps

0.003788 m3/s

cubic feet/min

cfm

4.719 × 10−4 m3/s

Bernoulli’s Equation

It states that, for a non-viscous, incompressible fluid in steady flow, the sum of pressure, potential, and kinetic energies per unit volume is constant at any point. Mathematically, it can be expressed as:

Where

Bernoulli’s principle states that in fluid flow, an increase in velocity occurs simultaneously with a decrease in pressure. It is named for the Dutch/Swiss mathematician/scientist Daniel Bernoulli; this phenomenon can be seen in airplane lift, a carburetor, the flow of air around the ball, etc.

Venturi Effect

A fluid passing through smoothly varying constrictions is subject to changes in velocity and pressure, as described by Bernoulli’s principle. In case of fluid or airflow through a tube or pipe with a constriction in it, the fluid must speed up in the restriction, reducing its pressure, and producing a partial vacuum.

FIGURE 2.3 Venturi’s Law Illustrated.

Continuity Equation

It is simply a mathematical expression of the principle of conservation of mass. Mass is neither created nor destroyed. For a steady flow, it states that:

The “continuity equation” is a direct consequence of the rather trivial fact that what goes into the pipe must come out. This has the important consequence that as the area of the hole decreases, the velocity of the fluid must increase, in order to keep the flow rate constant.

Specific Weight, Density, and Specific Gravity

(a)Specific Weight or Weight Density

The weight per unit volume of a substance. Usually it is expressed in N/m3 or lbs/ft3. Mathematically,

Where

(b)Density

Density is defined as the ratio of the mass of an object to its volume; usually it is expressed in kg/m3 or g/cm3. Mathematically,

Where

(c)Specific Gravity

The ratio of the density (or specific weight) of a substance to the density (or specific weight) of a standard fluid is called Specific gravity or Relative density. The usual standard of comparison for solids and liquids is water at 4°C at atmospheric pressure. Gases are commonly compared to dry air, under standard conditions (0°C and atmospheric pressure).

Specific gravity is not expressed in units, as it is purely a ratio. Mathematically,

Where

Compressibility and Bulk Modulus

Compressibility is the measure of change in volume of substance when pressure is exerted on it. Liquids are incompressible fluids. For each atmosphere increase in pressure, the volume of water would decrease 46.4 parts per million. The hydraulic brake systems used in most cars operate on the principle that there is essentially no change in the volume of the brake fluid when pressure is applied to this liquid.

On the other hand, the volume of the gases can be readily changed by exerting an external pressure on the gas. An internal combustion engine provides a good example of the ease with which gases can be compressed.

The compressibility is the reciprocal of the bulk modulus. Compressibility is denoted by “k” and is expressed mathematically as:

Where B is called the bulks modulus of elasticity and is defined as the ratio of change in pressure to volumetric strain (change in volume/original volume) over a fluid element. It is expressed as follows:

Where

Viscosity and Viscosity Index

Viscosity is the measure of the internal friction of a fluid or its resistance to flow. A hydraulic fluid that is too viscous usually causes high-pressure drop, sluggish operation, low-mechanical efficiency, and high-power consumption. Low-viscosity fluids permit efficient low-drag operation, but tend to increase wear, reduce volumetric efficiency, and promote leakage.

Viscosity index is an arbitrary scale, which indicates how the viscosity of a fluid varies with changes in temperature. The higher the viscosity index, the lower the viscosity changes with respect to temperature and vice versa. Ideally, the fluid should have the same viscosity at very low temperatures as well as at high temperatures. In reality, this cannot be achieved. This change is common to all fluids. Heating tend to make fluids thinner and cooling makes them thicker.

Gas Laws

(a)Boyle’s Law

English scientist Robert Boyle investigated the relationship between the volume of a dry ideal gas and its pressure. It states that at constant temperature, the pressure is inversely proportional to the volume of a definite amount of gas. Mathematically,

thereforeWhere

(b)Charle’s Law

French scientist Jacques Charles experimented with gas under constant pressure and his observations have been formalized into Charle’s law.

The volume of a gas at constant pressure is directly proportional to the absolute temperature. Mathematically, it can be expressed as:

thereforeWhere

(c)Gay-Lussac’s Law

French scientist Joseph Gay-Lussac investigated the relationship between the pressure of a gas and its temperature. It states that the pressure of a gas at constant volume is directly proportional to the absolute temperature. The mathematical statement is as follows:

thereforeWhere

(d)Combined Gas Laws

Any two of the three gas laws of Boyle, Charles, or Gay-Lussac can be combined, hence the name, combined gas law. In short, this combined gas law is used when it is difficult to keep either the temperature or pressure constant:

This relationship can be used to predict pressure, volume, and temperature relationships where any five of the six variables are known.

Moisture in the Air

(a)Humidity

Humidity is the concentration of water vapor in the air. The concentration can be expressed as specific humidity, absolute humidity, or relative humidity. A device used to measure humidity is called a hygrometer.

(i)Specific humidity. Is defined as mass of water vapor present per kg of dry air. It is expressed in g/kg of dry air. Humidity is measured by means of a hygrometer.

(ii)Absolute humidity. Is expressed as the mass of water vapor contained in a given volume of air. The hotter the air is, the more water it can contain. It may be measured in grams of vapor/cubic meter of air. Absolute humidity finds greatest application in ventilation and air-conditioning problems.

(iii)Relative humidity. Is defined as the ratio (usually expressed as a percentage) of the mass of water in a given volume of moist air divided by the maximum mass of water that can be held by that same volume of air (saturated air) at a given temperature. We can compare how much water vapor is present in the air to how much water vapor would be in the air if the air were saturated. A reading of 100 percent relative humidity means that the air is totally saturated with water vapor and cannot hold any more.

Practically, “relative humidity” is the amount of moisture in the air at a certain temperature. It is called “relative” because it is being compared to the maximum amount of moisture that could be in the air at the same temperature.

(b)Dew Point Temperature and Holding Capacity of Air

Air present at certain temperatures could consume a certain quantity of water in it, likewise when this temperature is attained, air becomes completely saturated. If the air is further cooled then water will start condensing out of it. Dew point is the temperature at which water vapor begins to condense out of the air. Dew points can be defined and specified for ambient air or for compressed air. Dew point normally occurs when a mass of air has a relative humidity of 100%. This temperature can be recorded by a thermometer.

(c)Atmospheric Dew Point

Atmospheric dew point is the value of the temperature at which moisture present in the air begins to condense at atmospheric pressure, i.e., at 1.01325 bar. Atmospheric dew point is not at all important for pneumatics, as pressure is always more than atmospheric pressure in a pneumatic line.

(d)Pressure Dew Point

Pressure dew point is the value of the temperature at which moisture present in the air begins to condense at pressures more than the atmospheric pressure. As pressures encountered in pneumatics are generally more than atmospheric so it is of great importance. Obviously, at higher pressures, the water present in air condenses at higher temperatures in comparison to atmospheric pressure, so dew point should be kept very low so as to ensure the least amount of moisture in the pneumatic line (as moisture is the biggest enemy in pneumatics).

Energy, Work, and Power

Energy is the ability to do work and is expressed in foot pound (ft lb) or Newton meter (Nm). The three forms of energy are potential, kinetic, and heat. Work measures accomplishments; it requires motion to make a force do work. Power is the rate of doing work or the rate of energy transfer.

Potential Energy

Potential energy is energy due to position. An object has potential energy in proportion to its vertical distance above the earth’s surface. For example, water held back by a dam represents potential energy because until it is released, the water does not work. In hydraulics, potential energy is a static factor. When force is applied to a confined liquid, potential energy is present because of the static pressure of the liquid. Potential energy of a moving liquid can be reduced by the heat energy released. Potential energy can also be reduced in a moving liquid when it transforms into kinetic energy. A moving liquid can, therefore, perform work as a result of its static pressure and its momentum.

Kinetic Energy

Kinetic energy is the energy a body possesses because of its motion. The greater the speed, the greater the kinetic energy. When water is released from a dam, it rushes out at a high velocity jet, representing energy of motion—kinetic energy. The amount of kinetic energy in a moving liquid is directly proportional to the square of its velocity. Pressure caused by kinetic energy may be called velocity pressure.

Heat Energy and Friction

Heat energy is the energy a body possesses because of its heat. Kinetic energy and heat energy are dynamic factors. Pascal’s Law dealt with static pressure and did not include the friction factor. Friction is the resistance to relative motion between two bodies. When liquid flows in a hydraulic circuit, friction produces heat. This causes some of the kinetic energy to be lost in the form of heat energy. Although friction cannot be eliminated entirely, it can be controlled to some extent. The three main causes of excessive friction in hydraulic systems are:

(i) Extremely long lines.

(ii) Numerous bends and fittings or improper bends.

(iii) Excessive velocity from using undersized lines.

EXERCISES

1. What are the differences between a liquid and a gas?

2. What do you mean by pressure dew point? Does it have any importance in pneumatics?

3. State the importance of gas laws.

4. Define the terms specific weight, density, and specific gravity.

5. What is the effect of temperature on viscosity of fluids?

6. State continuity equation.

7. Differentiate between the terms viscosity and viscosity index.

8. What is the difference between pressure and force?

9. Explain venturi effect. Give the name of important pneumatic equipment, which uses this principle.

10. State Bernoulli’s equation.

11. What is meant by the term bulk modulus?

12. State and prove Pascal’s law.

13. What is the relationship between atmospheric, absolute, and vacuum pressure?

14. Differentiate between absolute and relative humidity.

CHAPTRE3

BASIC PNEUMATIC AND HYDRAULIC SYSTEMS

INTRODUCTION TO FLUID POWER

A fluid power system transmits and controls energy through the use of pressurized fluid. The term fluid power applies to both hydraulics and pneumatics. With hydraulics, that fluid is a liquid such as oil or water. With pneumatics, the fluid is typically compressed air or inert gas. Hydraulics uses oil or liquid as the medium that cannot be compressed and pneumatics, which involves gases, uses air or gas as the medium that can be compressed. It is a term, which was created to collect the generation, control, and application of smooth, effective power of pumped or compressed fluids (either liquids or gases). This power is used to provide force and motion to various mechanisms. This force and motion may be in the form of push, pull, rotate, regulate, or drive.

Fluid power is one of three commonly used methods of transmitting power in an industry; the others are electrical and mechanical power transmission. Electric power transmission uses an electric current flowing through a wire to transmit power. Mechanical power transmission uses gears, pulleys, chains, etc. to transmit power. Fluid power’s motive force comes from the principle that pressure applied to a confined fluid is transferred uniformly and undiminished to every portion of the fluid and to the walls of the container that holds the fluid. A surface such as a cylinder piston will move if the difference in force across the piston is larger than the total load plus frictional forces. The resulting net force can then accelerate the load proportionately to the ratio of the force divided by the mass.

Fluid power encompasses most applications that use liquids or gases to transmit power in the form of mechanical work, pressure, and/or volume in the system. This definition includes all systems that rely on pumps and compressors to transmit specific volumes and pressures of liquids or gases within a closed system. Fluid power is used in the steering, brake system, and automatic transmissions of cars and trucks. In addition to the automotive industry, fluid power is used to control airplanes and spacecraft, harvest crops, mine coal, drive machine tools, and process food. Fluid power can be effectively combined with other technologies through the use of sensors, transducers, and microprocessors.

BASIC ELEMENTS OF FLUID POWER SYSTEM

The basic elements of fluid power system are:

Power device: Pump or Compressor

Control valves

Actuators: Cylinders or Motors

Figure 3.1 shows the basic elements of a fluid power system connected by fluid power lines. These elements are discussed in detail in next chapters.

FIGURE 3.1 Elements of Fluid Power System.

ADVANTAGES AND DISADVANTAGES OF FLUID POWER

Advantages

There are few advantages, which make fluid power so popular. These are listed below:

No need of intermediate equipment: They eliminate the need for complicated systems of gears, cams, and levers. Motion can be transmitted without the slack inherent in the use of solid machine parts.

Less wear and tear: The fluids used are not subject to breakage as are mechanical parts, and the mechanisms are not subjected to great wear.

Multi-function control: A single hydraulic pump or air compressor can provide power and control for numerous machines or machine functions when combined with fluid power manifolds and valves.

Constant force or torque: This is a unique fluid power attribute.

Flexibility: Hydraulic components can be located with considerable flexibility. Pipes and hoses instead of mechanical elements virtually eliminate location problems.

Comparatively small pressure losses: The different parts of a fluid power system can be conveniently located at widely separated points, because the forces generated are rapidly transmitted over considerable distances with small loss. These forces can be conveyed up and down or around corners with small loss in efficiency and without complicated mechanisms.

Multiplication and variation of force: Very large forces can be controlled by much smaller ones and can be transmitted through comparatively small lines and orifices. Linear or rotary force can be multiplied from a fraction of an ounce to several hundred tons of output.

Accurate and easy to control: We can start, stop, accelerate, decelerate, reverse, or position large forces with great accuracy.

High horsepower and low weight: Pneumatic components are compact and lightweight.

Smoothness: Fluid systems are smooth in operation. Vibration is kept to a minimum.

Overload protection: In case of an overload, an automatic release of pressure can be guaranteed; automatic valves guard the system against a breakdown from overloading so that the system is protected against breakdown or strain.

Wide variety of motions: Fluid power systems can provide widely variable motions in both rotary and straight-line transmission of power.

Low speed torque: Unlike electric motors, air or hydraulic motors can produce large amounts of torque (twisting force) while operating at low speeds. Some hydraulic and air motors can even maintain torque at zero speed without overheating.

Less human intervention: The need for control by hand can be minimized.

Low operating costs: Fluid power systems are economical to operate their high efficiency with minimum friction loss keeps the cost of a power transmission at a minimum.

Safety in hazardous environments: Fluid power can be used in mines, chemical plants, near explosives, and in paint applications because it is inherently spark-free and can tolerate high temperatures.

Better force control: Force control is much easier with fluid systems than for electric motors. Fluid actuators, either hydraulic or pneumatic, are well suited to walking robots because they are high force, low speed actuators. They provide much higher force densities than electric systems.

Simpler design: In most cases, a few pre-engineered components will replace complicated mechanical linkages.

Disadvantages

The main disadvantage of a fluid system is maintaining the precision parts when they are exposed to bad climates and dirty atmospheres. Protection against rust, corrosion, dirt, oil deterioration, and other adverse environmental conditions is very important.

APPLICATIONS OF FLUID POWER

Mobile

Fluid power is used to transport, excavate, and lift materials, as well as control or power mobile equipment. End use industries include construction, agriculture, marine, and the military. Applications include backhoes, graders, tractors, truck brakes and suspensions, spreaders, and highway maintenance vehicles.

Industrial

Fluid power is used to provide power transmission and motion control for the machines of industry. End use industries range from plastics to paper production. Applications include metal working equipment, controllers, automated manipulators, material handling, and assembly equipment.

Aerospace

Fluid power is used for both commercial and military aircraft, spacecraft, and related support equipment. Applications include landing gear, brakes, flight controls, motor controls, and cargo loading equipment.

PNEUMATICS VS. HYDRAULICS

Fluid power can be broadly divided into two fields: pneumatics and hydraulics. Both pneumatics and hydraulics are applications of fluid power.

Pneumatic systems use compressed gas such as air or nitrogen to perform work processes whereas hydraulic systems use liquids such as oil and water to perform work processes. Pneumatic systems are open systems, exhausting the compressed air to the atmosphere after use whereas hydraulic systems are closed systems, recirculating the oil or water after use.

A fluid power system uses hydraulics or pneumatics to deliver extremely powerful pushing and pulling forces to machinery. Much of the factory equipment used to lift and move large components is powered by hydraulics. For example, forklift trucks, opencast mining equipment, and multi-purpose agricultural spraying equipment all use hydraulic systems to operate their lifting arms. Pneumatics, on the other hand, are used for a variety of purposes that include delivering power to tools like jack hammers, air guns, and complex industrial equipment for conveying, separating, and air handling goods.

The extensive use of hydraulics and pneumatics to transmit power is due to the fact that properly constructed fluid power systems possess a number of favorable characteristics. They eliminate the need for complicated systems of gears, cams, and levers. The fluids used are not subject to breakage as are mechanical parts, and the mechanisms are not subjected to great wear.

Some points of difference between hydraulics and pneumatics are shown in Table 3.1.

TABLE 3.1 Difference between Hydraulics and Pneumatics.

Pneumatics

Hydraulics

Pressure level

5–10 bar

Up to 200 bar

Actuating forces

Pneumatic actuators can produce only low or medium size forces.

Hydraulic actuators are suitable for very high loads.

Element cost

Pneumatic elements such as cylinders and valves are less costly as compared to hydraulic elements.

Hydraulic elements can cost from 5 to 10 times more than similar size pneumatic elements.

Transmission lines

Transmission lines in pneumatics are made up of inexpensive flexible plastic tubing. Only single line is needed in pneumatics to simply exhaust the air into atmosphere.

Transmission lines in hydraulics are made up of metal tubing with expensive fittings to withstand high working pressure and to avoid leaks. Also return lines are needed in hydraulics to return the oil from each cylinder back to reservoir.

Stability

Low stability because air is compressible.

High stability because oil is incompressible.

Speed control

Difficult to control the speed of pneumatic cylinders or motors.

Easy to control the speed.

ADVANTAGES AND DISADVANTAGES OF PNEUMATICS

Advantages

Pneumatic systems are clean because they use compressed air. If a pneumatic system develops a leak, it will be air that escapes and not oil.

Pneumatic systems are cheaper to run than other systems.

Inherently modulating actuators and sensors.

Explosion proof components.

High efficiency, example, a relatively small compressor can fill a large storage tank to meet intermittent high demands for compressed air.

Ease of design and implementation.

High reliability, mainly because of fewer moving parts.

Compressed gas can be stored, allowing the use of machines when electrical power is lost.

Easy installation and maintenance.

Disadvantages

Low accuracy and control limitation because of compressibility.

Noise pollution.

Leakage of air can be of concern.

Need for a compressor producing clean and dry air.

Cost of air piping.

Need for regular component calibration.

ADVANTAGES AND DISADVANTAGES OF HYDRAULICS

Advantages

Through the use of simple devices, an operator can readily start, stop, speed up, slow down, and control large forces with very close and precise tolerance.

High power output from a compact actuator.

Hydraulic power systems can multiply forces simply and efficiently from a fraction of an ounce to several hundred tons of output.

Force can be transmitted over distances and around corners with small losses of efficiency.

There is no need for complex systems of gears, cams, or levers to obtain a large mechanical advantage.

Extreme flexibility of approach and control. Control of a wide range of speed and forces is easily possible.

Safety and reliability.

Hydraulic systems are smooth and quiet in operation. Vibration is kept to a minimum.

Disadvantages

Hydraulic systems are expensive.

System components must be engineered to minimize or preclude fluid leakage.

Protection against rust, corrosion, dirt, oil deterioration, and other adverse environment is very important.

Maintenance of precision parts when they are exposed to bad climates and dirty atmospheres.

Fire hazard if leak occurs.

Adequate oil filtration must be maintained.

APPLICATIONS OF PNEUMATICS

Operation of heavy or hot doors

Lifting and moving in slab moulding machines

Spray painting

Bottling and filling machines

Component and material conveyor transfer

Unloading of hoppers in building, mining, and chemical industry

Air separation and vacuum lifting of thin sheets

Dental drills

APPLICATIONS OF HYDRAULICS

Machine tool industry

Plastic processing machines

Hydraulic presses

Construction machinery

Lifting and transporting

Agricultural machinery

BASIC PNEUMATIC SYSTEM