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Copyright 1998-2004 NJCATE, a National Center for AdvancedTechnological Education
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This material is based on work supported by the National ScienceFoundation Advanced Technological Education Program under NSF grant# ESI-9553749 and DUE-9813444. Any
opinions, findings, conclusions, or recommendations expressed inthis material are those of the authors and do not necessarilyreflect those of the National Science Foundation.
Module K: Applications of Electromechanical Systems ShamsaAnwar, M.S. Sohail Anwar, Ph.D. Richard Flack, Ph.D. Paula FordAndrew N. Vavreck, Ph.D.
Penn State University NJCATE Publications Coordinator:
Paula Neves
TABLE OF CONTENTS
HOW TO USE THIS MODULEGUIDE................................................................................1
MECOMTRONICS MODULE K COMPETENCIES............................................................ 2
MODULE OVERVIEW.........................................................................................................6
TERMINOLOGY AND CONCEPTS.....................................................................................8
INDUSTRIALCONTEXT....................................................................................................10
PROJECT OVERVIEW........................................................................................................13
SUPPLEMENTALMATERIALS.........................................................................................15
TECHNICAL ACTIVITIES
LEARNING ACTIVITY: MOUNT COMPRESSION TESTER DEVELOPMENT PROJECT:HYDRAULIC, PNEUMATIC, AND ELECTROMECHANICAL ACTUATOR APPLICATION#KPT1........................................................................16
LEARNING ACTIVITY: MOUNT COMPRESSION TESTER DEVELOPMENT PROJECT:TESTING AND TROUBLESHOOTING OF ELECTRICAL/ ELECTRONIC AND SENSINGDEVICES #KPT2...29
LEARNING ACTIVITY: MOUNT COMPRESSION TESTER DEVELOPMENT PROJECT:MECHANICAL DESIGN AND FABRICATION #KPT3. ............. 42
LEARNING ACTIVITY: PRELIMINARY DESIGN #KST1............................................. 63
LEARNING ACTIVITY: ELECTRONIC CONTROL AND SENSING INTEGRATION#KST2.....................................................................................................................................76
MATHEMATICS ACTIVITIES
LEARNING ACTIVITY: STATISTICAL CONCEPTS #KSM1........................................ 93
LEARNING ACTIVITY: SWITCHING ALGEBRA AND COMBINATIONAL LOGICSYSTEMS #KSM2.... ............................... 108 APPENDIX A..124
SCIENCE ACTIVITIES
LEARNING ACTIVITY: MECHANICAL AND THERMAL PROPERTIES OF MATTER#KSS1...................................................................................................................................125
LEARNING ACTIVITY: CONTROLLING OSCILLATIONS #KSS2............................ 140
RESEARCH, COMPOSITION, AND PRESENTATION (RCP) ACTIVITIES
LEARNING ACTIVITY: MOUNT COMPRESSION TESTER DEVELOPMENT PROJECT:DATA COLLECTION AND REPORTING #KPC1...................................... 151
LEARNING ACTIVITY: MOUNT COMPRESSION TESTER DEVELOPMENT PROJECT:TRAINING PROGRAM DEVELOPMENT #KPC2. ................ 160 EVALUATIONFORMS .. ......170
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HOW TO USE THIS MODULE GUIDE
This module guide contains several unique features: CompetenciesEach activity covers a list of technical competencies, which areresearched and verified by industry representatives. Thesecompetencies provide the conceptual framework for students todevelop knowledge and skills required by industry.
The list of competencies is broken out by Technical, PhysicalScience, Mathematics, and Research, Composition and Presentation(RCP). The level of mastery attained for each competency as itrelates to the material covered in corresponding modules, isindicated as Introduce (I), Develop (D), Master (M), and Reinforce(R). Therefore, you will find in the competency list an indicationof the level of mastery to be attained. Projects Each moduleincludes an industry-related capstone project. Learning activitiesin each module are classified by whether they are project-embedded(activities essential to the development and implementation of theproject) or stand-alone (activities guiding the student in thedevelopment of the core competencies of technical, mathematics,physical science, and research, composition, and presentationskills). The corresponding equations, tables, and figures for eachactivity follow the same classification system. Activity Codes Anactivity numbering key is followed throughout the module. Forexample, in codes KPT1 and KSM1, the first letter of the codesignifies that this is an activity of Module K. The second lettercan be either a P for a project embedded activity or an S for astand-alone activity. KSM1 then is a stand-alone activity. Thethird letter represents either T for Technical, S for PhysicalScience, M for Mathematics, or C for Research, Composition andPresentation. KSM1 is a mathematics activity. The last digit in thecode represents the order of the activity in a particulardiscipline. KSM1 is the first mathematics activity in Module K. Usethis key code to identify each learning activity.
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MECOMTRONICS MODULE K COMPETENCIES
The list of competencies in this module is broken down byTechnical, Physical Science, Mathematics, and Research,Composition, and Presentation (RCP). The codes I, D, M or R in eachcompetency indicate:
Introduce (I), Develop (D), Master (M), and Reinforce (R).
A spiral approach to learning reinforces competencies as theyare revisited each semester. Technical Competencies:
R 1.6 Create and modify spreadsheets for presenting data ingraphical
form. I,D 1.7 Construct, modify and manage databases; use forms,perform
queries, and generate reports. D 1.8 Create computer-generatedvisual aids using application software
and imported graphics. R 3.7 Identify and create electrical andlogic diagrams utilizing a library
of appropriate symbols. M 3.12 Read and interpret engineeringdrawings, wiring diagrams,
schematics and process diagrams. D 4.7 Demonstrate knowledge ofelectromagnetic principles, operation of
electromagnetic devices and their use in systems. D 4.8Demonstrate knowledge of electric motors and generator typesand
applications. D 4.9 Select and specify electric motors,generators and transformers.
Perform measurements to determine electric motorcharacteristics. I,D 4.25 Employ semiconductor switching devices inpower control systems
(ON/OFF, phase control, frequency control). I,D 6.3 Test,adjust, and repair electromechanical equipment. D 6.8 Maintainequipment maintenance and repair records. D 6.13 Maintain,troubleshoot, and repair hydraulic and pneumatic
control equipment and systems. R 7.1 Use measuring devices formeasuring linear and angular quantities. R 7.2 Use analog anddigital meters, oscilloscopes, and virtual instruments
to measure electrical and electronic parameters. D 7.6 Use avariety of instruments to determine the hardness, toughness
and impact of a material. R 7.7 Evaluate the measurementspecification and select the appropriate
instrument to accurately perform the measurement.
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R 7.9 Record and present data for evaluation and analysis. R7.10 Evaluate and analyze data obtained from measurements. D 8.1Employ safety procedures using manufacturer guidelines and
industry and government standards when working withelectrical/electronic equipment.
D 8.4 Demonstrate knowledge of effective troubleshootingtechniques; use manufacturers' documentation and software, flowcharts, and diagrams for efficient troubleshooting and repair ofelectrical/electronic system problems.
D 8.5 Calibrate/adjust electrical equipment. D 9.2 Assemble ordisassemble electrical and mechanical components and
systems. D 9.3 Select and use appropriate tools needed forassembling and
disassembling machine components. D 9.9 Calibrate/adjustmechanical equipment. I,D 9.13 Demonstrate knowledge ofcharacteristics, functions, and
applications of power transmission systems based on mechanicaland/or fluid components.
Physical Science Competencies:
R 15.A Demonstrate knowledge of the definitions of fundamentalphysical
quantities such as: length, time, mass, charge, etc. R 15.BDemonstrate knowledge of the definition of derived physical
quantities such as: velocity, acceleration, force, torque,energy, momentum, current, voltage, resistance, pressure,viscosity, power, inductance, capacitance, hardness, stress,strain, magnetic field strength, flux, etc.
D 15.1 Apply kinematics equations for translation and rotationto describe the motion of rigid bodies.
D 15.2 Draw (sketch) the free body diagram of a structure;determine the forces and/or torques acting on the structure byapplying Newtons Second law.
D 15.8 Calculate the stress on an object from a measurement ofthe strain.
R 15.9 Distinguish between gauge pressure and absolute pressure.D 15.10 Calculate the pressure exerted by or on a fluid. R 15.11Use Pascals Law to predict the ratio of the forces on the two
pistons of a hydraulic and/or pneumatic press. D,M 15.12 Analyzeand predict the rate of fluid flow through a system by use
of Bernoullis Law. D 15.13 Describe the effect of viscosity onflowrate and the variation of
viscosity as a function of temperature.
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D 15.15 Use Hookes Law, the equations of motion and the law ofconservation of energy to predict the frequency, period andamplitude of a mechanical oscillator.
M 15.16 Apply the concepts of simple harmonic motion (amplitude,frequency, energy transformations) to tuned circuits and mechanicaloscillators.
M 15.17 Define the three types of damping (under, critical,over) and describe the motion associated with each.
R 15.21 Determine the capacitance of a capacitor in terms of itsphysical characteristics.
R 15.22 Calculate the energy stored in a system of capacitors. R15.23 Predict and measure the time constant of a RC circuit. R15.24 Predict and measure the time constant of a RL circuit. M15.25 Measure current as a function of frequency and calculatethe
resonant frequency of an AC circuit. M 15.26 Predict and measurethe power of an AC circuit. R 15.27 Predict and plot B (totalmagnetic field) vs. Bo (externally applied
magnetic field) for a paramagnetic, diamagnetic andferromagnetic material.
M 15.28 Calculate the magnetic force on a current carrying wire,and the torque on a current loop.
R 15.29 Predict the self-inductance of a coil in terms of itsgeometry. R 15.30 Calculate the energy stored in a system ofinductors. R 15.40 Differentiate between conductors, semiconductorsand insulators
based on their atomic structure. I 15.48 Use the law ofconservation of energy to predict state and
temperature changes of a thermally isolated system. I 15.49Employ the first law of thermodynamics and the gas laws to
predict the state variables of an ideal gas. MathCompetencies:
R 14.1 Perform numerical computations using decimals, fractions,and
percents. R 14.2 Raise numbers to powers and take roots ofnumbers. D 14.3 Estimate and approximate answers to multipleoperation problems,
and evaluate the reasonableness of the results. R 14.4 Useratios and proportions to solve technical problems. R 14.5 Usescientific, engineering and prefix notation to simplify
computations and to represent data. R 14.6 Use a calculator toperform multiple operation problems. R 14.7 Convert between U.S.customary and SI units.
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R 14.8 Translate problem situations into their symbolicrepresentations and use those representations to solve theproblem.
R 14.9 Solve technical problems involving polynomial, rational,and radical equations graphically, numerically andanalytically.
D 14.10 Identify, describe, compare and classify geometricfigures. R 14.13 Graph empirical data and determine the functionthat the graph
represents. R 14.14 Graph a straight line on a rectangularcoordinate system, and
determine its slope and intercept from the graph of a linearfunction.
D 14.27 Analyze collected data and use probability andstatistical models to make decisions about technicalsituations.
D 14.28 Collect, organize and describe data from real worldsituations. D 14.30 Use Boolean algebra to perform logicoperations. RCP Competencies:
D 13.1 Convey ideas and facts by composing, revising andediting
memoranda and letters, reports, articles, proposals, and essays.D 13.2 Use varied and precise technical language appropriatelyin
written documents and oral presentations. D 13.3 Determine theform, length, content and styleeither oral or
writtenfor presenting material to an intended audience. D 13.4Eliminate errors in Standard American English (SAE) grammar,
syntax, usage, punctuation and spelling. D 13.9 Use specificfactual data to provide instructions and explanations
of processes and technical concepts, and to recommend a courseof action.
D 13.10 Classify information into related groups, and analyzedata to discover or present similarities and differences, todiscover or present relationships, to explain unfamiliar conceptsand to highlight specific details.
D 13.12 Plan, organize, rehearse, and make effective oralpresentations. D 13.13 Prepare visual materials for oralpresentations.
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MODULE OVERVIEW
Applications of Electromechanical Principles
Apply electrical, electronic, and mechanical principles to thedevelopment and installation of
systems designed to perform a useful task. Study the life-cyclerepair and maintenance requirements for electromechanicalsystems.
Learning Activity Code Time Allocation
Introductory Session 1.0 hour Hydraulic, Pneumatic, andElectromechanical Actuator Application
KPT1 5.0 hours
Testing and Troubleshooting of Electrical/Electronic and SensingDevices
KPT2 4.0 hours
Mechanical Design and Fabrication KPT3 9.0 hours PreliminaryDesign KST1 4.0 hours Electronic Control and Sensing IntegrationKST2 4.0 hours Statistical Concepts KSM1 2.0 hours SwitchingAlgebra and Combinational Logic Systems KSM2 2.0 hours Mechanicaland Thermal Properties of Matter KSS1 6.0 hours ControllingOscillations KSS2 2.0 hours Data Collection and Reporting KPC1 2.0hours Training Program Development KPC2 4.0 hours
TOPIC
OBJECTIVES
LEARNING ACTIVITIES
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To ensure your success in this module, the followingprerequisites and corequisites are recommended:
Prerequisites
Module B: Electrical and Mechanical Components and SystemsModule D: Electrical and Mechanical Principles
Corequisites
Module H: Electrical and Mechanical Power Components andApplications
PREREQUISITES/COREQUISITES
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TERMINOLOGY AND CONCEPTS
Upon completion of this module, you should be able to use incontext the following terminology and concepts: absolute pressureempirical AC circuit experts AC motors ferromagnetic amplitudefield-effect transistor (FET) angles first law of thermodynamics B(total magnetic field) flat-file database B0 (externally appliedmagnetic field) flowrate Bernoullis constant fluid Bernoullis Lawfluid power cylinders binary variable fracturing bipolar junctiontransistor(BJT) frequency diagram Boolean function breakdown gasturbine engines brittle gauge pressure calibrate gear motorcapacitor generalists cells graphics Charpy test hardness circuitbreaker harmonic oscillators coil heat combinational logic systemsheat of fusion complex audience heat of vaporization compressorshistogram conductor hydraulic conservation of energy hydraulicmotors damping ideal gas database impact database management systeminductive statistics DC motors inductor descriptive statisticsinsulator diamagnetic internal energy dielectric junctionfield-effect transistor(JFET) displacement kinematics DPST (DoublePole Single Throw) kinetic energy ductile linear function elasticlimit linear spring elasticity linear variable differentialtransformer (LVDT)elastomer magnetic force elastomer isolators meanelectromagnetic measures of central tendency electropneumaticregulator measures of dispersion
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mechanical linkages silicon-controlled rectifier(SCR) mediansimple harmonic motion
sine wave metal-oxide semiconductor field-effecttransistor(MOSFET) SI unit mode slope and intercept momentarypush-button switch solenoids motor SPDT relay mount specific heat /specific heat capacity NC (normally closed) push button switchspecimen NO (normally open) push button switch spreadobject-oriented database spreadsheet operational amplifiers springconstant oscillatory motion SPST (Single Pole Single Throw) Pascalslaw standard deviation period state periodic statistical analysisphase control statistics PN junction diode stepper motors pneumaticstrain pneumatic motors stress population switch potential energyswitching algebra power tensile stress primary audience thermallyisolated query thermodynamic system range thyristor RC circuit timeconstant rectangular coordinate system torque rectifiers torsionrelational database toughness relay transistor relay controlcircuit transmitter resonance triac resonant frequencytroubleshooting rigid truth table RL circuit turbine Rockwell testturned circuits root ultimate strength rotary switch unijunctiontransistor rotary variable differential transformer U.S. customaryunit sample viscosity secondary audience workbook semiconductorworking fluid semiconductor switching device worksheets servomotorsYoungs Modulus shroud zener diode
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INDUSTRIAL CONTEXT
Systems Integration
Intermech Ltd. is a small electromechanical systems integrator.The company, which has 100 employees, designs, develops, fields,and maintains electromechanical devices such as mechanized partfeeders, metal-forming equipment, automated packaging and labelingequipment, and machine vision-based inspection systems. Much of thecompanys work involves integrating Original Equipment Manufacturer(OEM) components into complete automated electromechanical systems.The company primarily serves the metalworking industry.
Gas turbine engines have sets of disks, around which are mountedmany blades, like blades on a fan. These fans serve as compressorsof incoming air (in the compressor section) or extract energy fromthe jet exhaust to operate the compressor (in the turbine section).Each blade has a root area, which mounts in the disk, and a shroudarea, which mates to adjoining blades to form a ring (Figure1).
This ring is part of the seal for the outside edge of thecompressor or turbine fan. It is very important that the root andshroud have a specific angle (around the long axis of the blade)relative to each other. If they do not, shrouds in the outer ringcan wear against each other incorrectly, and can experienceexcessive stress. The angle can change because of creep due to thehigh temperatures and pressures the blades may experience.
During maintenance, when blades are removed from their disks forinspection and repair, they undergo a process of inspection andadjustment of the root-to-shroud angle. The angle is measured andthe blades are carefully twisted to restore the correct angle. Amanual process is currently used, during which the blade root isheld in a fixture. The blade shroud is twisted by hand with a barclamped to the shroud, then measured, then re-twisted. The manualprocess is inaccurate, leads to too many scrapped blades, and istoo slow.
The student is part of a design and development team withinIntermech Ltd., an electromechanical design and developmentcompany, which has been contracted to design,
INDUSTRY TYPE
COMPANY PROFILE
PROBLEM/SITUATION
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construct, install, and maintain a prototype, automatedelectromechanical system to twist used gas turbine engine blades torestore specified root-to-shroud angles for reuse.
root
blade airfoil
shroud
1.5 inches
Figure 1. J-52 High-Pressure Turbine Engine Compressor Blade
The industrial development encompasses three major phases:
Phase I: Specification of Machine Requirements
1. Develop database of part specifications
2. Prepare graphs of blade torque-strain response ranges
3. Review operator requirements (cycle times, ergonomics)
4. Report on blade forming requirements
Phase II: Machine Design, Development and Integration
5. Specify hydraulic components for blade twist
6. Specify electromechanical components for blade shroudgripping
7. Machine mechanical design and fabrication
8. Design and fabricate machine electrical/electronics
9. Operate prototype machine on sample blades, gathering andanalyzing data
on blade torque response to strain
10. Measure blade material properties before and afterforming
11. Report on machine design and testing
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Phase III: Installation and Life-Cycle Support
12. Install machine at customer site
13. Adjust head design, mechanics, electronics andhydraulics
14. Provide training for customer operator personnel
15. Maintain machine, field troubleshoot and repair
Module K will help students understand the process of design,development, and maintenance through activities involving all areasof product development and fielding.
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PROJECT OVERVIEW
Module Ks Mount Compression Tester Development Project focuseson electromechanical system integration. Students will:
Develop, test, install, and maintain an elastomer mountcompression tester. Use a pneumatic cylinder to compress anelastomer specimen. The compression of the
specimen and the force on the specimen will be measuredelectronically.
Part 1: Hydraulic, Pneumatic and Electromechanical ActuatorApplication (KPT1)
1. State the Problem
2. State the Goal
3. Data Collection - Industrial Applications
4. Approach Listing
5. Actuator Approach Weighting and Selection
Part 2: Testing and Troubleshooting of Electrical/Electronic andSensing Devices (KPT2)
1. LVDT Testing
2. Using an Operational Amplifier
Part 3: Mechanical Design And Fabrication (KPT3)
1. Design the Frame
2. Fabricate and Assemble Components of the Mount CompressionTester Frame
3. Assemble and Test the Complete Mount Compression Tester
4. Measure Mount Parameters
5. Calculate the Modulus of Elasticity and Power
6. Fluid Flow Calculations
7. Thermodynamic Relationships
PROJECT NAME, FOCUS & DESCRIPTION
PROJECT PROCEDURE
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Part 4: Data Collection and Reporting (KPC1)
1. Use Word Processing to Write a Memo Report
2. Write a Report Using Data from the Database Created inKST1
Part 5: Training Program Development (KPC2)
1. Find Examples of Warnings
2. Prepare a Diagram of the Mount Compression Tester
See AlsoEight challenges in developing theory of intelligence[PDF] Study Guide for Test Technician Test - Free Download PDF[PDF] invitation to negotiate (itn) registration - Free Download PDF[PDF] Book Template - Stevenson University - Free Download PDF3. Make a List of the Steps in Your Instructions
4. Rehearse the Presentation
5. Make Training Presentation to the Class
The project will result in the development of anelectromechanical/pneumatic compression tester. The project willserve as the core of the technical activities, and will encompassactivities involving electronics, mechanics, pneumatics, design,maintenance, troubleshooting, assembly, measurement, safety, andthe machine shop.
OUTLINE OF PROJECT OUTCOMES OR SPECIFICATIONS
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SUPPLEMENTAL MATERIALS
Bogart, Theodore F. Jr. 1992. Introduction to Digital Circuits.Glencoe. Dueck, Robert K. 1994. Fundamentals of DigitalElectronics. West Publishing Company. Floyd, Thomas L. 1997.Principles of Electric Circuits. New Jersey: Prentice-Hall.Honeycutt, Richard A. 1986. Electromechanical Devices. New Jersey:Prentice-Hall. Kissell, Thomas E. 1997. Industrial Electronics. NewJersey: Prentice-Hall. Ledolter, Johannes and Claude W. Burrill.1999. Statistical Quality Control: Strategies and Tools forContinual Improvement. John Wiley and Sons. Majumdar, S. J. 1996.Pneumatic Systems. New York: McGraw-Hill. Maloney, Timpoty J. 1996.Modern Industrial Electronics. New Jersey: Prentice-Hall. Norton,Robert L. 1992. Design of Machinery. New York: McGraw-Hill. Reeves,William W. 1987. The Technology of Fluid Power. New Jersey:Prentice-Hall. Smith, Gerald M. 1998. Statistical Process Controland Quality Improvement. New Jersey: Prentice-Hall.
Allied Electronics Catalog (1-800-433-5700),www.allied.avnet.com
Jameco Catalog (1-800-831-2424), www.jameco.com
Mouser Electronics Catalog (1-800-346-6873), www.mouser.com
http://www.ggrweb.com for GeoWeb jobssearch in engineeringtechnology.
http://www.prosci.com for discussions of product realizationprocesses, best practices, and participating companies.
http://www.asme.org/codes/ for ASME standards and reports.
BOOKS
INDUSTRIAL CATALOGS
WEBSITES
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Project-Embedded Stand-Alone
5 hours
To develop an understanding of the application of motors andgenerators, and hydraulic and pneumatic power transmission devicesby selecting an actuator approach for use in the mount compressiontester.
Understand the engineering design process Understand the rangeof suitable applications for actuators Explore applications ofhydraulic, pneumatic, and motor actuators in real industrialmachines Identify appropriate types of actuators to compresselastomer specimens in the mount
compression tester
Establish performance requirements for selected actuators
LEARNING ACTIVITY MOUNT COMPRESSION TESTER DEVELOPMENT PROJECT:HYDRAULIC, PNEUMATIC, AND ELECTROMECHANICAL ACTUATOR APPLICATIONKPT1
TIME ALLOCATION
STATEMENT OF PURPOSE
OBJECTIVES
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Your instructor will assess you on the following:
Correct answering of all review questions within this activityIdentification of appropriate actuators Identification ofindustrial actuator applications
The blade twist machine must have elastomer (elastic,rubber-like material) isolators installed on its base to reduce thetransmission of vibration from the machine to the floor on which itis mounted. The proper selection of the elastomer for the isolationmount requires the use of a tensile test machine. Your companycurrently employs the tensile test machine to measure thecompression characteristics of samples of material. Your team isassigned to automate this purely mechanical tensile test machine tofacilitate the selection of the isolation mount elastomer.
The current machine uses a simple, mechanical worm screw-springarrangement to compress a sample in incremental steps (see FigureKPT1-1). The specimen to be tested is held between two plates thatcan slide on four rods. The rods are attached to end plates that donot move. A crank turns a worm screw, which pushes on the firstfloating plate (specimen plate). The displacement of the specimenplate relative to the spring plate is measured with a scale. Thismeasurement is used to calculate the strain on the specimen. Thedeflection of the spring (the relative displacement of the springplate and right end plate) gives a measurement of the force on thespecimen, which can be used to calculate the stress.
crankframe rods
worm screw specimen
left end plate
specimen plate
springspring plate
right end plate
Figure KPT1-1. Current Compression Tester
ASSESSMENT
SITUATION
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The compression tester is slow, inaccurate, and very difficultto maintain. Your team is assigned to apply electromechanicaldevices to automatically:
1. compress the sample 2. measure the force (stress) on thesample 3. measure the compression (strain) on the sample
In this activity, your design team must identify an initialapproach for an actuator to replace the worm screw and mechanicalcrank in the device currently used to compress elastomermounts.
In order to modify the compression tester, your engineering teammust make an initial selection of the types of actuators that canbe used to compress the elastomer mounts. Later, in learningactivities KPT2 and KPT3, the selected actuator will be combinedwith both the compression testers mechanical structure, and theelectronics for sensing and power transmission. You shall thenprepare a detailed machine design. In KPT1, you will be followingthe engineering design process, which is a formal means ofaddressing a problem by identifying and following through with aselected approach. The process helps designers be unbiased towardtheir own preferences by performing a thorough, objectiveidentification of approaches, and then rating the value of thevarious approaches in different categories. The process also helpsuncover potential problems that could cause delays or incur costsin later parts of the development.
THE ENGINEERING DESIGN PROCESS
1. State the Problem Clearly identify just what problem is beingaddressed. Try to be as general as possible. For instance, if youare designing a new vacuum cleaner because an older model makes toomuch noise, do not say, The old models fan is too noisy. Maybe itis not just the fan, but other parts of the machine, and you willhave just biased the process. The correct statement would be, Thecleaner is too noisy.
2. State the Goal Clearly and briefly state the objective of theproject. For the vacuum cleaner example above, the goal might be,Reduce the noise level of the cleaner by 10 decibels withoutincreasing the unit production cost. Any performance specificationsrequired of the design should also be identified and listed at thistime.
BACKGROUND
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3. Collect Background Information Examine potential approachesto solve the problem. What have others done in the past? Identifyanalysis tools you might have to use, including applicableequations, computer design tools, books, articles, patentsanythingthat builds up your background enough to tackle the problem.
4. Identify Potential Approaches List as many approaches tosolve the problem as possible, keeping in mind that no idea is abad one at this point. A good technique is called brainstorming,where a group gets together in a room and writes down potentialapproaches that come to mind.
5. Analyze Potential Approaches Determine which measures ormetrics shall allow you to make an unbiased evaluation of eachapproach. All approaches are analyzed for performance, cost, impacton other parts of the system, etc. For example, in the vacuumcleaner problem, some categories might include risk, cost, weight,tooling impact, supply impact, and size. Each of these categoriesgets a score for each approach.
6. Select Single Approach Choose one approach with which toproceed. Your analysis should have yielded scores in differentcategories for each approach. The most common way now to select anapproach is to weight each category by how important it is. Forinstance, if cost is most important, the weighting for cost mightbe 5, while the weighting for weight, which is less important,might be 1. Each category score is then multiplied by the weightingfactor for that category, and the total weighted score for eachapproach is calculated by adding up the weighted category scores.The highest composite score indicates the best approach.
7. Modeling and Testing After choosing your conceptual design,model and test this approach in more detail than you used in theanalysis step above. The model might be a real, physicalconstruction, like an aircraft wing in a wind tunnel, or a computermodel. This step allows you to try out and refine many scenarios ona small scale, before selecting a final design.
8. Production Use the final design to produce tooling,manufacturing equipment, and a manufacturing process, ending inproduction of the product.
In this activity, you shall explore the first six steps of theengineering design process. You will state the problem and goal,and identify and select approaches to the actuation needs of themount compression tester. First, you need to review a littlebackground information on the types of actuators from which youhave to choose.
ACTUATOR TYPES Actuators are devices that convert or transmitenergy to apply mechanical force or torque to a mechanism. They areoften provided with some control of position or speed. A rangeof
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alternatives to apply force or torque exists, includingelectrical motors and fluid power systems. Mechanical linkages canalso be applied to trade off force or torque for speed from anactuator to some other part of a mechanism.
DC Motors The primary characteristic of DC motors is that theirtorque and speed vary strongly in some way. A permanent magnet DCmotor might have a torque-speed curve that resembles the one inFigure KPT1-2.
torque
speed
voltageincrease
Figure KPT1-2. DC Motor Speed-Torque Curves
Therefore, if the motor voltage is held constant, a given loadwould result in a given speed for the motor, with higher loadsincreasing torque on the motor and reducing speed. If theapplication requires constant speed for a range of loads, suchbehavior would be unacceptable.
DC motors come in a number of forms, each with functions andsuitable types of applications. The most common type is theseries-wound motor, which has the field coil in series with thearmature coil. These motors are called universal motors, becausethey can be operated from either AC or DC. Because they are lightand cheap, they are used in many portable power applications likehand drills.
One solution to the speed-load variation problem is to use aspeed-controlled DC motor, which has electronics to vary thecurrent to the motor to adjust for different loads. This type ofmotor will run from an AC source as well since the controllerconverts AC to DC. Speed-controlled DC motors, however, are moreexpensive than uncompensated DC motors.
As a reminder, DC generators function as the reverse of the DCmotor operation. A rotary input to the motor rotor generates acurrent in the field coil. Brushes are used to switch the coilcurrent direction through the commutator, producing a DCwaveformthe more windings available, the smoother the output.
AC Motors AC motors are often the most inexpensive solution tocontinuous rotary motion. Most of the motors in use in industry areAC motors. AC motors can be found with a variety oftorque-speed
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curves, most of which are much flatter than DC motor curves.That is, the motor speed does not vary much over a range ofloads.
AC motors are often limited to only a few speeds, which are afunction of the AC line frequency. The most common no-load speedsare 1725 and 3450 revolutions per minute (rpm). More expensivesynchronous AC motors can give corresponding speeds of 1800 and3600 rpm exactly, which represent no slippage from the standardmotors. If speeds other than those related to the AC line voltageare needed, a common solution is to employ a gearbox to reduce orincrease the speed (with a corresponding change in torque, ofcourse).
AC generators (usually called alternators) do not use acommutator. The simple rotation of the armature within the fieldcoil creates an AC output. The alternator in your car, for example,outputs AC, which is rectified into DC to charge the battery. Thebattery in turn provides field current for the alternator.
Servomotors Servomotors have electronic speed controls thatautomatically adjust the motors current flow in response to thetachometers measurement of the motor speed. The motor in the systemcan be either AC or DC. The controller compares the tachometerspeed to the commanded speed, and adjusts the current tocompensate. Servomotors are capable of extremely precisepositioning of a load but are very expensive and have lower powerand torque capacity than straight AC or DC motors.
Gearmotors Gearmotors represent one solution to the inability ofstraight motors to operate below several hundred RPM, and to theinefficiency, complex circuitry, and expense of stepper andservomotors. Incorporating a gearmotor, a gearbox within the motorhousing, provides, in most cases, a smaller shaft output speed thanthe motor speed and a larger torque output. With the integratedgearbox, which can allow for a straight, offset, or angled shaftoutput relative to the motor rotor shaft, maintenance will beslightly increased, and efficiency, in comparison to straightmotors, will be reduced. The cost will also be higher than forstraight motors.
Stepper Motors Stepper motors have toothed rotors and speciallydesigned field coils to allow the rotor to turn in very small,angular increments (or small steps). The motor has complex controlcircuitry to maintain a speed (steps per second) or position veryaccurately. Stepper motors can withstand lower torque loads than ACor DC motors, generally, and are expensive.
Pneumatic and Hydraulic Cylinders (or Fluid Power Cylinders)Fluid power cylinders are linear actuators (often pistons incylinders) which give a limited stroke in a straight line. They arepreferable in situations where straight-line motion is required butactuator speed is not an issue. If speed control is necessary,expensive servovalves will do the
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job, but at a cost. Output forces can be very high, especiallyfor hydraulic systems. If fluid sources are already available, thecost of fluid power systems can be very low. However, the cost fora system will be very high if a hydraulic or a pneumatic powersource is not available. Also, in the case of hydraulic devices,there exists potential for contamination of the machine withoil.
Pneumatic and Hydraulic Motors Pneumatic and hydraulic motorsare rotary devices using hydraulic or pneumatic power that functionin a similar way to the pumps used to pressurize fluid in hydraulicor pneumatic cylinders. However, instead of inputting rotary motionto yield a pressure increase, these devices reverse the process,inputting pressure to extract rotary motion. These devices sharethe same advantages and disadvantages as hydraulic and pneumaticcylinders, including high cost (if a hydraulic or pneumatic powersource is not available), limited speed and position accuracy, and,for hydraulic devices, the potential for contamination of themachine with oil.
Solenoids Solenoids are purely electromechanical devices thatuse a coil to move a magnetic core very rapidly over a smallstroke. They are very cheap and compact, but have low loadcapability and poor speed control. One very common application isin camera shutters and in electric car door locks, where theirsimple construction, small size, high speed, and low cost are majoradvantages.
Mechanical Linkages Mechanical linkages, which can multiplyavailable force or displacement or alter the direction of powertransmission, can be joined to any of the devices described above.Gears are just like rotary linkages, trading torque for speed ordisplacement. A pneumatic cylinder, which produces only a limitedforce, can be used to move a linkage that can multiply the force bythe lever effect while the stroke is reduced. Linkages can be madeinexpensively, and are low maintenance, especially if pinned(rotary) joints are used.
high force,small stroke
low force,large stroke
pneumatic cylinder
Figure KPT1-3. Mechanical Linkages
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MACHINE DESIGN REQUIREMENTS Returning to the engineering designprocess that you shall undertake, each teams goal statement mustinclude a listing of the design performance requirements for themount compression tester, as shown below.
Table KPT1-1. Performance Specifications for Mount CompressionTester Actuator
Maximum force 500 pounds (high)
Maximum displacement 2 inches (moderate)
Portability High
Position accuracy 0.01 inches (high)
Maximum speed 1 inch per second (low)
Speed accuracy 0.1 inch per second (low)
Actuator cost Very low
Hydraulic power availability None expected
Pneumatic power availability Yes
Note: Remarks in parentheses refer to the relative importance ofthe criteria listed.
Identify and discuss real industrial applications of motors,generators, and hydraulic and
pneumatic cylinders
Brainstorm actuator applications Select an actuator type forcompressing the specimen
TEAM EXPLORATION
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State the Problem In this task, your team will develop, discuss,and refine a statement of problem involving the selection ofactuator types for the mount compression tester.
Step Result 1. Write down a statement of the problem that
your team is trying to solve, as clearly and briefly aspossible.
1. Each team prepares a problem statement.
2. Share your teams problem statement with other teams in theclass.
2. Class teams share problem statements.
3. Discuss your problem statements. 3. The class discussesproblem statements. 4. Select one of the teams problemstatement
to use for the activity. 4. Teams select a single problemstatement for
the activity.
1. Are the problem statements from different teams similar? 2.How do they differ? 3. Why should the problem statement be writtenas broadly as possible?
Statement of Goal In this task, your team will develop, discuss,and refine a statement of the goal of the project involvingselection of actuator types for compressing specimens.
Step Result 1. Write down as clearly and briefly as
possible a statement of the goal of your teams actuatorproject.
1. Each team prepares a statement of the project goal.
2. Share your teams goal statement with other teams in theclass.
2. Class teams share project goals.
3. Discuss your goal statements. 3. The class discusses projectgoals.
TASK #1
REVIEW QUESTIONS
TASK #2
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4. Select one teams goal statement to use for the activity.
4. The class chooses a single goal statement for theactivity.
5. Review the list of performance specifications given in TableKPT1-1.
5. Teams review the performance requirements for theactuator.
1. Why should the goal statement be written as broadly aspossible?
Collect Background Information In this task, you willindividually collect data on examples of the actuator typesdescribed in the Background section of this activity. You willlearn about real-world applications of the various actuator types,and discuss the applicability of these actuators to the compressiontester design.
Step Result 1a. Outside of class time (or in class if timeand
facilities permit), identify real-world applications of each ofthe potential actuator types, using:
The Internet Product literature Observation of actualindustrial
equipment or equipment at your school
Any other source b. Outside of class time, gather one exampleof
each type of actuator from the Background section of thisactivity. For instance, construction equipment often uses hydraulicactuators for providing force to parts of a mechanism, like thebucket of a loader. Write a short paragraph on how the loader usesa hydraulic cylinder, and include a small sketch of the set-up. Dothis for all of the actuator types.
1a. Team members produce lists of examples of actuators in usein industry.
b. Team members prepare written summaries on the use of eachtype of actuator provided in the Background section.
REVIEW QUESTIONS
TASK #3
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2. Bring your examples to class and discuss
with the other students. Determine if some of the applicationsare relevant to the tester design problem, and list them.
2. Teams produce a list of actuator examples that are relevantto the mount tester.
1. Where are some potential sources for approaches? 2. Whatother types of background information will you need?
Identify Potential Approaches In this task, you will listapproaches to the actuator selection problem.
Step Result 1. Discuss with your team the actuation
problem and identify potential approaches. Do not discard anypotential approach. You may use the industrial examples you foundto help suggest approaches.
1. Teams discuss the actuation problem and identify potentialapproaches.
2. Submit all potential approaches to the instructor foridentification and listing on the blackboard. Do not discard anyapproach unless it is a duplicate of another.
2. The instructor lists all the teams potential approaches.
3. Write down the complete list of approaches. 3. Each studentrecords a list of potential approaches.
1. Why should you not immediately discard approaches that youfeel are clearly not going to work very well?
REVIEW QUESTIONS
TASK #4
REVIEW QUESTION
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Analyze Potential Approaches and Select a Single Approach Inthis task, you will weight the actuator approaches objectively andselect the best overall approach.
Step Result 1. List categories in which you will rate the
actuator approaches for the mount compression tester. Somepotential categories are:
Cost Torque Angular speed accuracy Power source compatibilityMaintenance Portability
1. Teams list categories in which actuator approaches will berated.
2. Discuss within your team and select weightings for eachcategory. Use your best judgment as to how to weight thecategories. For instance, the machine MUST produce the force anddisplacement specified, but cost may be more flexible.
2. Each team selects weightings for each category.
3. List each approach for the actuation design on the board.
3. Each team lists the approaches for the actuation design onthe board.
4. Next to each approach, create columns for all the ratingcategories and a last column for the total score for each approach.The table on the board should look something like the examplebelow, Table KPT1-2.
4. Each team produces a chart on the board showing approachesand categories.
5. Average the category weightings from each team. (Note: Sincethere may be some variation among the selected rating categoriesfrom each team, average those weightings whose categories werechosen by more than one team.)
5. Teams average the weightings assigned by each team to thevarious rating categories.
TASK #5
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Table KPT1-2. Example of Actuator Approach Table
Rating Categories
Actuator Approach Cost Size Force Speed Total
Score Weighted Score
Score Weighted Score
Score Weighted Score
Score Weighted Score
1. DC motor with worm gear 2. DC motor with linkages 3.Pneumatic cylinder 4. etc.
6. List the category weightings next to the
category names at the top of the chart. For instance, Force(5).
6. Teams list the category weightings.
7. Within each team, score each of the approaches for everycategory.
7. Each team scores their approaches.
8. As a class, average the scores for each approach, weightthem, and enter the weighted value in the chart.
8. The class produces a list of scores for all approaches.
9. Add up the weighted values for each approach and enter thesum in the last column.
9. The class produces a sum of weighted scores for eachapproach.
10. Identify the approach having the highest overall weightedscore.
10. The class selects the highest rated actuation approach thatwill replace the mechanical crank and worm screw in the currentcompression tester.
11. Discuss the selected approach. 11. Teams discuss the chosenapproach.
1. How is the weighting for each category selected? 2. Whatwould be the impact of a change to one of the categories after theprocess is complete
(e.g., if cost suddenly became the most important, for instance,due to budget reductions)?
REVIEW QUESTIONS
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Project-Embedded Stand-Alone
4 hours
To learn how to test and troubleshoot electrical/electronicdevices and sensors which can be integrated into the mountcompression tester.
Learn how a displacement transducer works Learn how anoperational amplifier works Understand the general principles oftroubleshooting Learn how to troubleshoot variouselectrical/electronic devices
Your instructor will assess you on the following:
Knowledge of electrical/electronic devices and sensors which canbe integrated into a mount compression tester
LEARNING ACTIVITY MOUNT COMPRESSION TESTER DEVELOPMENT PROJECT:TESTING AND TROUBLESHOOTING OF ELECTRICAL/ELECTRONIC AND SENSINGDEVICES KPT2
TIME ALLOCATION
STATEMENT OF PURPOSE
OBJECTIVES
ASSESSMENT
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Performance of all tasks and answering all questions listed inthis learning activity.
Intermech Ltd. is considering the integration of electronics andsensors into the design of the new mount compression tester, whichwill be developed in Learning Activity KPT3. Most of the electronicand control devices that can be integrated into the mountcompresssion tester are described in this learning activity and inModule H. In addition, this learning activity describes the sensorsthat can be integrated into the compression tester and focuses onthe troubleshooting of electrical/electronic devices.
ELECTRICAL/ELECTRONIC DEVICES AND SENSORS DisplacementTransducers Displacement is defined as the distance between theposition and a reference point. Displacement can be linear orrotary. The linear variable differential transformer (LVDT) can beused to measure linear displacement. It is shown in FigureKPT2-1.
I n p u tS h a f t
S e c o n d a r y 1 P r im a r y
S e c o n d a r y 2
C O R E
Figure KPT2-1. Linear Variable Differential Transformer(LVDT)
It consists of a primary, two secondaries, and a movable core.The primary is excited by an AC source. When the core is in itscenter location, the amplitude of the voltage induced into onesecondary will be the same as the voltage induced into the othersecondary. The secondaries are connected so as to cancel out theequal voltages, and so the output voltage will be zero (when thedisplacement equals zero). Figure KPT2-2 shows what happens to theoutput voltage as the core is moved to points A and B. Themagnitude of the output voltage is a linear function of the coreposition and the phase of the output is determined by the side ofthe zero or null position on which the core is located.
SITUATION
BACKGROUND
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The excitation frequency for an LVDT varies according to itsdesign and the application. If the LVDT has to accurately trackrapidly changing displacement, the higher frequencies are better.Typical values of excitation frequency range from 50 Hz to 30 kHz.The magnitude of the voltage applied to the primary is usuallyabout 10V.
Core at A Core at 0 Core at B
Output Voltage
PositionA 0 B
Figure KPT2-2. Output Voltages as a Function of CoreDisplacement
Figure KPT2-3 shows a rotary variable differential transformer(RVDT) which measures angular displacement up to 90. This range ofangular measurement may be extended with gearing.
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PrimaryWinding
Secondary1
Secondary2
DifferentialVoltage
Out
Core
InputShaft
Figure KPT2-3. Rotary Variable Differential Transformer(RVDT)
Operational Amplifiers
An electronic circuit, called an amplifier, is used to enlarge arelatively small signal at the input and produce a larger signal atthe output. Operational amplifiers are high-gain amplifiers usuallypowered by a dual supply. Dual power supply allows operationalamplifiers to amplify signals near ground potential. It also makesit possible for the output of operational amplifiers to swing aboveand below ground potential. An operational amplifier is shown inFigure KPT2-4.
In ve r t in gInp u t
N o n -Inv e r t ing
In p u t
+ V
-VD iffe re n t ia lIn p u t
A m p lifie r
In te rm e d ia teV o lta g e
A m p lifie r
O u tp u tA m p lifie r
O u tp u t
Figure KPT2-4. Operational Amplifier
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The output of an operational amplifier is usually single-ended.The first stage in an operational amplifier is an operationaldifferential amplifier circuit. It has two inputs. One of theinputs is in phase with the output and is called the non-invertinginput. It is marked plus (+). The other input is out of phase withthe output. It is called the inverting input and is marked minus(-).
The second stage in an operational amplifier is called anintermediate voltage amplifier. It follows the differentialamplifier stage to provide high gain. The third stage consists ofan output amplifier that provides a low output impedance so thatthe operational amplifier can drive most loads. Figure KPT2-5 showsa widely used operational amplifier package called a dual-in-linepackage (DIP). The dual-in-line package shown in Figure KPT2-5houses two 741 operational amplifiers.
1
2
3
4
5
6
7
14
13
12
11
10
9
8
-In A
+In A
Offset Null A
V-
Offset Null B
+In B
-In B
Offset Null A
V+ A
Out A
NC
Out B
V+ B
Offset Null B
-+
+
-
A
B
Figure KPT2-5. Dual-In-Line Package (DIP)
This package uses a separate V+ pin for each operationalamplifier. Both pins must be energized when both amplifiers areused. Operational amplifiers are extensively used because theyapproach ideal amplifiers, especially for DC and low-frequencysignals. The ideal amplifier has an infinite input impedance sothat it can be connected to any signal source with no loading. Anoperational amplifier such as the 741 approaches the ideal with aninput impedance of 6M. Another characteristic of an ideal amplifieris infinite gain. Operational amplifiers usually provide gainsexceeding 100dB at low frequencies. An ideal amplifier has zerooutput impedance and is capable of driving any load. Operationalamplifiers such as the 741 can provide at least 5mA to a 2000 load.An ideal amplifier has infinite bandwidth, which means it canamplify any signal frequency. Here, the operational amplifiers areat a disadvantage. The useful gain provided by an
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operational amplifier usually extends only into the tens of kHzrange. Some of the common applications of an operational amplifierare shown in Figures KPT2-6 to KPT2-9.
-
+
Vin
R2
R1
Vout
Vout = Vin R2R1
R3
Figure KPT2-6.
-
+VinVout
Vout =Vin
Figure KPT2-7.
-
+Vin
R2
Vout
Vout =Vin R1 +R2R1
R1
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Figure KPT2-8.
-
+
Vin, 1
R2
Vout
Vout = Vin,2 Vin,1( )R2R1R4
Vin, 2
R1
R3R1 = R3
R2 = R4
Figure KPT2-9. TROUBLESHOOTING PROCESS Troubleshooting can bedescribed as a logical system of investigation for determining thecorrect cause of breakdown in the shortest possible time and withthe least likelihood of error. Breakdown is a term used to indicateany machine condition that is considered to be less thansatisfactory according to the factors listed below:
performance downtime service life efficiency safetyenvironmental impact cost
Whenever a machine fails to meet the criteria of satisfactoryoperation, the process of troubleshooting must be employed todetermine why. When confronted with a problem, technicians mustmake sure that they:
have an adequate knowledge and understanding of the machineneeding troubleshooting use common sense and a step-by-stepapproach draw on their own experience and that of others when aneed arises
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To troubleshoot a problem quickly and effectively, it isnecessary that all relevant information be available. Theinformation needed for troubleshooting falls into two categories.The first one comprises background information, which includesinformation regarding the function, design characteristics, andmaintenance instructions of the machine.
The second category of information comprises operational data,including the conditions of operation at the time of breakdown.Therefore, it is important for a technician who is troubleshootingthe problem to be aware of the potential sources of such data. Thesources of background information include manufacturersinformation, maintenance history, systems drawings, processdrawings and troubleshooting charts. The sources of operationaldata are operating records, observers reports, test readings,condition monitoring equipment, and metallurgical analysis.
The process of troubleshooting consists of a series of basicsteps that apply to fault location for all types of machinery. Theyare summarized in Table KPT2-1 below.
Table KPT2-1. Troubleshooting Process
STEP DESCRIPTION
1. Problem Analysis The first step involves gatheringinformation about the fault so that the problem can be defined asaccurately as possible.
2. Preliminary Inspection
Once the problem has been defined, a more detailed inspection ofthe equipment can be conducted.
3. Fault Zone Location If the fault has not been located by thistime, the equipment should be mentally divided into functionalzones that can be checked for operation. Fault zone locationinvolves checking inputs and outputs.
4. Zone Investigation Once a fault has been traced to aparticular zone, a thorough examination should be initiated. Themore components that can be eliminated as functioning correctly,the simpler it becomes to find the component that is functioningimproperly.
5. Finding the Cause The objective of a troubleshootingprocedure is not to simply locate the fault but also to find outits cause. The cause can be categorized according to the manner inwhich a failure occurs. The following types of failures arepossible:
a. wear out failures b. misuse failures c. inherent weaknessfailures
6. Replacement/Repair The decision whether to repair or replacea faulty device depends on the organizations maintenance policiesand the downtime involved.
7. Performance Checks Once the repair of the faultydevice/machine is made, it is important to check its performance tomake sure that the fault has been eliminated. Tests should beconducted to ensure that the machine/device is functioningproperly.
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TROUBLESHOOTING OF ELECTRICAL/ELECTRONIC DEVICES Due to anextremely wide variety of electrical/electronic devices and systemsused in industry, it is not possible to cover the troubleshootingprocedures for every electrical/electronic device. Therefore, thematerial covered in this section of Module K is limited to thegeneral principles for troubleshooting an electrical/electronicdevice. Because the integration of electronics into the mountcompression tester would include operational amplifiers, a generaldiscussion of their troubleshooting is included.
Observation of Symptoms Troubleshooting of anelectrical/electronic system starts with an observation of thesymptoms. A technician should check all control settings, externalconnections, and power to the system before opening it up. Once thetechnician confirms that there are no obvious external reasons forthe system to malfunction, then the system is powered down. In anindustrial situation, the usual procedure is to lock off the faultysystems and tag them to inform others that maintenance is inprogress.
Visual Inspection After opening up the faulty system, it isvisually inspected for problems such as leaking capacitors, brokenwires, burned components, foreign substances, cracks in the circuitboards, components that are improperly held in their sockets,circuit boards that are improperly held in their connectors, dirt,loose connectors, and leaking batteries. Sometimes it is found thatthe faulty equipment is loaded with dirt and dust. Washing thecircuit boards after removing them from the system is recommendedin such a situation. The manufacturers specifications must bechecked before proceeding any further. Some manufacturers specifythe use of a solution of 90% ethyl alcohol and 10% water forwashing the circuit boards. If the circuit board has corrosivematerials on it, a solution of water and soda bicarbonate may beused to wash the circuit board. The circuit boards should bethoroughly rinsed with deionized water and must be dried beforethey are installed back in the systems.
Troubleshooting of an amplifier should be started with adetailed visual inspection. Sockets, connectors, and cables must bechecked. Devices in sockets should be checked because they can turnloose due to vibration of any kind. Any device that lookssuspicious should be reseated.
Supply Voltage Check If everything looks good during visualinspection, the supply voltages should be checked. A completesupply voltage check may include an oscilloscope test. After thesupply voltage has been checked, trouble symptoms must beconsidered. The possible symptoms include no output at all, weakoutput, unstable amplifier, distorted output, or output signalnoise. If the amplifier is part of a system with motors, or withhydraulic or pneumatic actuators, care must be taken so that adisturbance of an electrical device does not result in an undesiredmechanical disturbance. Manufacturers specifications must beconsulted when servicing such systems.
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1. Compute the dB power gain for an amplifier with an inputsignal of 5mW and an output signal of 25W.
2. Determine the dB voltage gain of an amplifier with an inputsignal of 0.25V peak-to-peak
and an output signal of 10V peak-to-peak. 3. Which operationalamplifier input is in phase with the output, and how is it markedon a
schematic? 4. What is the input impedance of an ideal amplifier?Why? 5. What is the output impedance of an ideal amplifier? Why? 6.Use Figure KPT2-6 to calculate the voltage gain of an invertingamplifier if R1 = 1k and R2
= 200 k. What is the input impedance? 7. What is an LVDT usedfor?
1k potentiometer Resistors: 18 k (1), 10 k (2), 2 k (1)Capacitors: 0.47F (2) Power Supplies: 15V (2) 741 OperationalAmplifier (1) DMM (digital multimeter) Two diodes Standard LVDT (Anappropriate LVDT for this activity is model LMT-711P33,
manufactured by G. L. Collins Corporation, Long Beach, CA. Thespecifications for this model include an input voltage of 5 8 8Vrms, a frequency range of 2kHz to 10 kHz, a null voltage value ofless than 50 mVrms, a non-linearity value of 0.5% of full range,and a sensitivity value of 0.465 mV/V/0.001 inch. Other LVDT modelsfrom this company include LMT-711P36, LMT-711P35 andLMT-711P34.)
Function generator (AC voltage source) Mounting devices Wire
REVIEW QUESTIONS
FACILITIES & EQUIPMENT
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Testing an LVDT
PrimaryWinding
Secondary1
Secondary2
Core
R1
R2
+
-
-
+
A
B
Figure KPT2-10. LVDT Circuit for Task #1
Step Result 1. Install the LVDT into an appropriate
mounting device. 1. You have seated the LVDT onto a mounting
device. 2. Attach the primary leads to the given AC
voltage source as shown in Figure KPT2-10. 2. You have connectedprimary leads to the
given AC voltage source.
3. Attach the secondary leads, S1 and S2, to the phase cancelingcircuit shown in Figure KPT2-10.
3. You have connected the secondary leads of the LVDT as shownin Figure KPT2-10.
4. Center the core of the LVDT. 4. You have centered the core ofthe LVDT. 5. Apply the AC voltage to the primary leads. 5. You haveapplied the AC voltage to the
primary leads. 6. Measure the output of each phase for azero
voltage condition. 6. The output of each phase is measured fora
zero condition. 7. Move the LVDT through its entire range of
motion in each direction, in ten equal steps, recording outputvoltages for each phase at every position.
7. The output voltages of each phase are recorded while the LVDTis moved through its entire range of motion. Voltages are recordedat ten, equally-spaced locations.
8. Note the values of each phase compared to each other.
8. You have noted the values of each phase in comparison witheach other.
TASK #1
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9. Interpolate and calibrate the voltages for the lineardistance traveled by the LVDT.
9. You have interpolated and calibrated the voltages.
10. Remove power from the circuit. 10. You have removed thepower from the circuit.
11. Disassemble the circuit. 11. The circuit isdisassembled.
1. Using the data collected in Task #1, draw a graph showingoutput voltage values corresponding to the LVDT core positions.
2. Explain how the circuit in Figure KPT2-10 works.
Using an Operational Amplifier as a Voltage Amplifier
-
+
1k
741
10k
18k 10k
2k
0.47F
0.47F
+15V
-15V
+
-
Figure KPT2-11. Voltage Amplifier Circuit
REVIEW QUESTIONS
TASK #2
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Step Result 1. Set up the circuit shown in Figure KPT2-11. 1.You have set up the circuit illustrated in
Figure KPT2-11. 2. For the various DC input voltages listed
below, measure the DC output voltages and record them. Each DCinput voltage listed below is obtained by adjusting thepotentiometer in Figure KPT2-11.
DC Input Voltages (V): 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.8,1.0
2. After adjusting the potentiometer in Figure KPT2-11 to obtainthe given DC input voltages, you have measured and recorded thecorresponding DC output voltages.
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Project-Embedded Stand-Alone
9 hours
To design and fabricate the mechanical/pneumatic portion of theautomated tensile test device.
Design mount tester frame Fabricate components Assemble frameand install air cylinder Connect pneumatic system Test device
Your instructor will assess you on the following:
Adherence to design requirements in the constructed deviceResponses to review questions
LEARNING ACTIVITY MOUNT COMPRESSION TESTER DEVELOPMENT PROJECT:MECHANICAL DESIGN AND FABRICATION KPT3
TIME ALLOCATION
STATEMENT OF PURPOSE
OBJECTIVES
ASSESSMENT
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The blade twist machine must have elastomer isolators installedon its base to reduce the transmission of vibration from themachine to the floor on which it is mounted. The proper selectionof the elastomer for the isolation mount requires the use of atensile test machine. Your company currently employs the tensiletest machine to measure the compression characteristics of samplesof material. Your team assignment is to automate this purelymechanical tensile test machine to facilitate the selection of theisolation mount elastomer.
The current machine uses a simple, mechanical worm, screw-springarrangement to compress a sample in incremental steps (see FigureKPT3-1 below). The specimen to be tested is held between two platesthat can slide on four rods. The rods are attached to end platesthat do not move. A crank turns a worm screw which pushes on thefirst floating plate (specimen plate). The displacement of thespecimen plate relative to the spring plate is measured with ascale. This measurement is used to calculate the strain on thespecimen. The deflection of the spring (the relative displacementof the spring plate and right end plate) gives a measurement of theforce on the specimen, which can be used to calculate thestress.
crankframe rods
worm screw specimen
left end plate
specimen plate
springspring plate
right end plate
Figure KPT3-1. Current Compression Tester
The compression tester is very difficult to maintain, and isslow and inaccurate. Your team is assigned to applyelectromechanical devices to automatically:
1. compress the sample 2. measure the force (stress) on thesample 3. measure the compression (strain) on the sample
Activity KPT2 introduced one of the sensing devices involved inthe mechanical tester, a linear variable differential transformeror LVDT. Learning Activity KPT2 also involved
SITUATION
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troubleshooting, maintenance and calibration of the compressiontester that you will build. This activity (KPT3) involves themechanical aspects of the design and development of the newcompression tester.
The new compression tester will use a pneumatic cylinder to pushthe sample to a certain displacement. The pressure on the cylinderwill be controlled by an electromechanical device, anelectropneumatic regulator, to compress the sample to a certainlength. The sample will be held between two plates. The cylinderwill be attached to the plate fixture at one end of the sample. Theother end of the sample will be pressed against a fixed endplate.
The pressure required in the cylinder will be the force requiredto compress the sample divided by the area of the piston in thecylinder. The maximum force can be calculated from the change inthe length of the sample when it is compressed. The change inlength divided by the original, unstressed length gives the strainassociated with the compression.
= xx0
(KPT3-1)
where
= strain (inches/inches) x = change in the length of the sample(inches)
x0 = initial uncompressed length of the sample (inches)
The stress in the sample is the force on the sample divided bythe cross-sectional area of the sample:
= FA
(KPT3-2)
where
= stress (pounds per square inch) F = force on the sample(pounds force)
BACKGROUND
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A = cross-sectional area of the sample (inches squared)
If we ignore the change in the cross-sectional area of thesample as it is being strained, the ratio of the stress to thestrain (for small strains which do not permanently deform thematerial) is a quantity known as the modulus of elasticity, E, ofthe material.
E = (KPT3-3)
The modulus of elasticity, E, has the units of pounds per squareinch. To calculate the force for any displacement, we can thencombine these equations to get
F = AxEx0
(KPT3-4)
or
E = FA
x0x
(KPT3-5)
The compression tester can thus be used to estimate the modulusof elasticity.
The force exerted by the cylinder times the displacement in thedirection of the force gives a measure of the work performed by thecylinder.
W = Fx (KPT3-6)
where
W = work performed (foot-pounds or inch-pounds)
x = displacement in the direction of the force (feet orinches)
F = force exerted (pounds force)
The elastomer mount develops a force proportional to thedisplacement
F = kx (KPT3-7) where
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k = spring constant (pounds per inch)
x = displacement of the mount (inches)
So the work the cylinder does on the elastomer is given bycombining Equations KPT3-6 and KPT3-7 as
W = kx2 (KPT3-8)
The power generated by the cylinder into the elastomer is givenby
P = Fv (KPT3-9)
where
v = velocity of the cylinder (feet per second)
P = power (horsepower or foot-pounds per second)
In terms of displacements and velocity,
P = kxv (KPT3-10)
In terms of the pressure in the cylinder, the force developed bythe cylinder is
F= PPAP (KPT3-11)
where
AP = area of the piston in the cylinder (inches squared or feetsquared)
PP = pressure in the cylinder (pounds per square inch)
We will also explore the pneumatic circuit in terms of theeffect on the air of compression and flow. Bernoullis Law statesthat, in the absence of losses, including heat transfer andfriction,
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and with no work done on or by the fluid, a fluid will flow withthe following sum of terms constant:
constantzg
Vg
P =++2
2
(KPT3-12)
where
P = static pressure, as measured by a pressure probe out of theflow (pounds per square inch)
= density of the fluid (slugs per foot cubed) g = gravitationalacceleration (feet per second per second)
V = average velocity of the fluid (feet per second)
z = elevation above some arbitrary datum (feet)
This constant is known as Bernoullis constant. Boyles Law isanother relationship governing the air, which involves theproperties: pressure, temperature, and density. If the air isconsidered an ideal gas, that is, if the temperature is high enoughand the pressure low enough (room temperature and atmosphericpressure, for instance) the following law holds:
P = RT (KPT3-13)
where
P = pressure (pounds per square inch)
= density (slugs per foot cubed) R = gas constant for that gas(BTUs per pound per degree Rankine) T = absolute temperature(degrees Rankine)
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Lastly, a thermodynamic system, with a constant quantity of massin the system, will have the following energy relationships as itchanges from a state 1 to a state 2, if the potential energy andkinetic energy of the mass do not change appreciably:
1Q2 1W2 = U2 U1( ) (KPT3-14)
where
1Q2 = heat transfer taking place during the transition (BTUsconverted to foot-pounds)
1W2 = work transfer taking place during the transition(foot-pounds)
(U2 U1) = change in internal energy of the system(foot-pounds)
The internal energy of an ideal gas is related to thetemperature through
U2 U1 = mcv T2 T1( ) (KPT3-15)
where
m = mass of the gas (slugs)
cv = constant volume specific heat of the gas (which can betaken to be constant over a broad range of selected temperaturesfor most materials, and has the units of BTUs per slug per degreeRankine)
(T2 T1) = change in temperature of the gas (degrees Rankine)
In this learning activity, you will electronically take readingsof compression and the resultant force at that compression when thedevice is completed. In addition, you will estimate the modulus ofelasticity of the specimen material, and will calculate the powerinput and work done by the cylinder on the specimen. An exercisewill also explore the effect of flow and pressure changes on thegas.
The pneumatic cylinder will be attached to supply air pressure.An electropneumatic regulator will be inserted in the circuit tomaintain a specified pressure to the cylinder. A schematic of yoursystem will be as shown in Figure KPT3-2.
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Filter/Lubricator
Supply Air
ElectropneumaticRegulator
Air Cylinder
Frame
Specimen
DisplacementProbe
Load Cell
Bleed Valve
Overpressure Valve
PressureGauge
Supply Valve
Figure KPT3-2. New Compression Tester
The new compression tester is mechanically similar to the oldtester, but instead, the crank and worm screw have been replaced byan air cylinder, and the spring has been replaced by a load cell.The supply air is filtered and lubricated, and the regulator tracksits pressure. The regulator controls the output air pressure to thecylinder, which exerts a force on the specimen.
The specimen compresses (displaces) an amount proportional tothe force applied to it by the testing machine. A displacementprobe measures the linear motion of the interface between theelastomer and the cylinder and the load cell measures the force onthe specimen. Both the force on the specimen and its displacementwill be used to estimate the modulus of elasticity of theelastomer.
Review Module H.
You will build a mechanical device that will have pinch points.In addition, the pneumatic system can generate high pressures. Aloose connection or ruptured tube can cause injury. Wear safetygoggles at all times when pressure is applied to the system, andavoid pinch points by keeping your hands away from the compressiontester at all times when pressure is applied.
PREPARATION
SAFETY ISSUES
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You will also be fabricating components in your machine shop.Always use standard shop safety practices for metalworking.
Air compressor, piston type, single stage, rated at 3.5 cfm(cubic feet per minute, free flow), maximum pressure 100 psig, suchas Gast Manufacturing (Benton Harbor, Michigan) model 4H (or shopair supply capable of 3.5 cfm and 100 psi)
Machine shop equipment including, at a minimum, a band-saw, adrill press, drill bits, and a tap and die set
Single-acting air cylinder, such as ControlAir (Amherst, NH)S-4-L, effective area 4 sq. in, 1.8 in stroke
Electropneumatic regulator, such as ControlAir Type 500X (3-100psig) Pneumatic overpressure valve, such as Flow Safe (OrchardPark, NY) F84M/F85M Micro
Safety Relief (15 to 6600 psig)
Pneumatic bleed valve, such as Pneumadyne (Plymouth, MN) # PBV-4with an operating pressure range of 0-150 psi
Load cell, compact-type, 250 pound capacity, such as EntranDevices (Fairfield, NJ) ELA-B2 Pneumatic pressure gauge, standardtype, such as Wika Instrument Corporation
(Lawrenceville, Georgia) Model 113.13
Linear variable differential transformer (LVDT) as specified inLearning Activity KPT2 Fasteners Metal stock (for machining)
-- T6061 aluminum plate, -inch thickness, or appropriatedimension based on design -- steel rods, -inch diameter orappropriate dimension based on design
Air tubing Elastomer specimens, in cylinder form (instructorspecified)
Design the Frame
FACILITIES & EQUIPMENT
TASK #1
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Step Result 1. Measure and record the uncompressed
specimen height. 1. You have measured and recorded the
uncompressed specimen height. 2. Measure and record the minimumair
cylinder height. 2. You have measured and recorded the
minimum air cylinder height. 3. Determine the load cell and LVDTmounting
requirements (height, mounting holes, diameter).
3. The machine dimensional specifications are listed.
4. Sketch the frame. The frame should be designed to have fourrods of an appropriate diameter at the corners of two thick steelplates. The cylinder will be mounted on one plate. A plate attachedto the piston rod will compress the specimen. A second plate willinterface between the specimen and the load cell. The frame willconsist of:
a. specimen end plate
b. cylinder end plate
c. plate connection rods (4)
d. rod/plate fasteners (nuts and lock washers)
e. cylinder mounting fasteners
f. cylinder rod-to-specimen plate
g. cylinder rod-to-specimen plate fasteners
4. You have sketched a frame layout.
5. Using mechanical drafting tools, draw the detail views andassembly view of the frame and attachment plates. Check fortolerances and fit with OEM parts (the air cylinder, load cell anddisplacement probe).
5. The frame design is complete.
1. What functions do the floating plates serve? 2. For whatcalculation will the uncompressed specimen height be used? 3. Whatfunction does the load cell serve? 4. Why are there four connectingrods?
REVIEW QUESTIONS
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Fabricate and Assemble Components of the Mount CompressionTester Frame
Step Result 1. Select stock from aluminum plate of
appropriate dimensions and steel rods of appropriatedimensions.
1. Machine stock materials are selected.
2. Set up machines for fabrication. 2. You have prepared themachine shop equipment for fabrication.
3. Fabricate all device parts. 3. You have fabricated the deviceparts. 4. You are now ready to assemble the mount
tester frame.
Insert the floating plates, connect the rods to the end plates,connect the cylinder to the end plate, and connect the specimenplate to the cylinder.
Upon inspection, you may need to make some adjustments. Begin bychecking that the rods are tightly held in the end plates. Ensurethat the end plates are parallel to each other AND perpendicular tothe rods. Also, the floating plate should slide with very littleresistance along the connecting rods.
4. The frame is completely assembled and inspected.
1. Why must the plates be parallel and the rods perpendicular tothe plates? 2. What would be the effect of poor fit, i.e., highfriction between the rods and floating plate?
TASK #2
REVIEW QUESTIONS
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Assemble and Test the Complete Mount Compression Tester
Step Result 1. Gather system components, consisting of:
a. air tubing b. electropneumatic regulator (or manual
regulator) c. cylinder/frame assembly d. air tubing fittings e.bleed valve f. pressure gauge g. overpressure valve h. load cell i.linear variable differential transformer
1. System components are gathered and laid out.
2. Assemble the components according to Figure KPT3-2 and insertan elastomer specimen between the floating plate and the load cellplate.
Adjust the connecting rod positions until the cylinder in itsretracted position just touches the specimen.
2. You have assembled the testing device and pneumaticsystem.
3. Turn on the compressor and VERY SLOWLY increase pressure (oropen valve to air supply VERY SLOWLY). Watch the cylinder end plate(floating plate) as the pressure is increased. The cylinder willcompress the specimen. When the cylinder has extended approximatelyone-half inch, stop increasing the pressure.
Note: The cylinder may move RAPIDLY. Be careful to SLOWLYincrease pressure!
WARNING!!!! Do not place hands in or otherwise handle the testerduring this step. The cylinder can crush your hands orfingers!!!
3. The cylinder is extended and the specimen compressedapproximately one-half inch.
TASK #3
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4. Close the valve to the air supply or turn off thecompressor.
4. The air supply is disconnected.
5. Bleed the air pressure in the circuit with the reliefvalve.
5. The system is depressurized.
6. Notice that the cylinder has returned to the originalposition, in which the specimen is unloaded.
6. The specimen is unloaded, and the system depressurized.
1. List the functions of the following components:
a. air tubing b. electropneumatic regulator (or manualregulator) c. cylinder/frame assembly d. air tubing fittings e.bleed valve f. pressure gauge g. overpressure valve h. load cell i.linear variable differential transformer
2. Why is the air pressure bled off at the end?
Measure Mount Parameters
Step Result 1. Connect the electropneumatic regulator
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