《工程测试与信号处理》课程教学资源（文献资料）Actuators_elecrical

McGraw-Hill CreateTM ReviewCopyforInstructorNicolescu.Notfordistribution88Measurement Systems432CHAPTER10Actuators4.Beabletoselectamotorforamechatronicsapplication5.Be able to identify and describe the components used in hydraulic andpneumaticsystems10.1INTRODUCTIONMost mechatronic systems involvemotion or action of some sort.This motion oraction can be applied to anything from a single atom to a large articulated struc-ture.It is created bya force ortorque that results inacceleration and displacement.Actuatorsarethe devices usedtoproducethis motionor action.Uptothispointinthebookwehavefocusedonelectroniccomponentsandsensors and associated signals and signal processing, all of which are required toproduce a specific mechanical actionor action sequence.Sensor inputmeasureshowwellamechatronicsystemproducesitsaction,openlooporfeedbackcontrolhelps regulatethe specific action, and much of the electronics welearned about isrequiredtomanipulateand communicatethisinformation.Actuatorsproducephysi-cal changes such as linear and angular displacement.They also modulatethe rateand power associated with these changes.An important aspect of mechatronic sys-tem design is selecting the appropriate type of actuator.This chapter covers someInternet Linkofthemostimportantactuators:solenoids,electricmotors,hydrauliccylindersandrotary motors,and pneumatic cylinders.Putting it poetically,this chapter is"where10.1Actuatorthe rubber meets the road." Internet Link 10.1 provides links to vendors and onlineonline resourcesandvendorsresourcesforvarious commercially availableactuatorsand supportequipment.10.2ELECTROMAGNETICPRINCIPLESMany actuators rely on electromagnetic forces to create their action.When a current-carrying conductor is moved in a magnetic field, a force is produced in a direc-tion perpendicular to the current and magnetic field directions.Lorentz's force law,whichrelatesforceonaconductortothecurrentintheconductorandtheexternalmagneticfield, in vectorformisF=IxB(10.1)where F is the force vector (per unit length of conductor), I is the current vector,and B is the magnetic field vector.Figure 10.1 illustrates the relationship betweenthese vectors and indicates the right-hand rule analogy,which states that if yourright-hand index finger points in the direction of the current and your middle fingerisaligned withthefield direction,thenyour extendedthumb(perpendiculartotheindex and middle fingers)will point in the direction of the force. Another way toapply the right-hand rule is to align your extended fingers in the direction of theivectorandorientyourpalm soyoucancurl(flex)yourfingerstowardthedirectionof theBvector.Yourhand will thenbe positioned suchthatyour extended thumbpoints in thedirectionofF

Confirming Pages Internet Link 10.1 Actuator online resources and vendors 432 C H A P T E R 10 Actuators 4. Be able to select a motor for a mechatronics application 5. Be able to identify and describe the components used in hydraulic and pneumatic systems 10.1 INTRODUCTION Most mechatronic systems involve motion or action of some sort. This motion or action can be applied to anything from a single atom to a large articulated struc￾ture. It is created by a force or torque that results in acceleration and displacement. Actuators are the devices used to produce this motion or action. Up to this point in the book, we have focused on electronic components and sensors and associated signals and signal processing, all of which are required to produce a specific mechanical action or action sequence. Sensor input measures how well a mechatronic system produces its action, open loop or feedback control helps regulate the specific action, and much of the electronics we learned about is required to manipulate and communicate this information. Actuators produce physi￾cal changes such as linear and angular displacement. They also modulate the rate and power associated with these changes. An important aspect of mechatronic sys￾tem design is selecting the appropriate type of actuator. This chapter covers some of the most important actuators: solenoids, electric motors, hydraulic cylinders and rotary motors, and pneumatic cylinders. Putting it poetically, this chapter is “where the rubber meets the road.” Internet Link 10.1 provides links to vendors and online resources for various commercially available actuators and support equipment. 10.2 ELECTROMAGNETIC PRINCIPLES Many actuators rely on electromagnetic forces to create their action. When a current￾carrying conductor is moved in a magnetic field, a force is produced in a direc￾tion perpendicular to the current and magnetic field directions. Lorentz’s force law, which relates force on a conductor to the current in the conductor and the external magnetic field, in vector form is F IB = × (10.1) where F is the force vector (per unit length of conductor), I is the current vector, and B is the magnetic field vector. Figure 10.1 illustrates the relationship between these vectors and indicates the right-hand rule analogy, which states that if your right-hand index finger points in the direction of the current and your middle finger is aligned with the field direction, then your extended thumb (perpendicular to the index and middle fingers) will point in the direction of the force. Another way to apply the right-hand rule is to align your extended fingers in the direction of the I vector and orient your palm so you can curl (flex) your fingers toward the direction of the B vector. Your hand will then be positioned such that your extended thumb points in the direction of F . alc80237_ch10_431-477_sss.indd 432 lc80237_ch10_431-477_sss.indd 432 10/01/11 10:24 PM 0/01/11 10:24 PM 88 Measurement Systems McGraw-Hill Create™ Review Copy for Instructor Nicolescu. Not for distribution

McGraw-Hill CreateTM Review Copyfor Instructor Nicolescu.Not fordistributionIntroduction to Mechatronics and Measurement Systems, Fourth Edition8910.3Solenoids and Relays433extendedextended right handright hand thumbindex fingerdirectiondirectionflexed right handmiddle fingerdirectionFigure 10.1 Right-hand rule for magnetic forceAnother electromagnetic effect important to actuator design is field intensifica-tion withina coil.Recall that,when discussing inductors inChapter2,westated thatthe magnetic flux through a coil is proportional tothe current through the coil andthenumberofwindings.Theproportionalityconstant is afunctionof thepermeabil-ity of the material within the coil.Thepermeabilityof a material characterizes howeasilymagneticfluxpenetratesthematerial.Ironhas apermeability afewhundredtimesthatof air;therefore,acoilwound aroundan iron corecanproduceamagneticflux a few hundred times that of the same coilwith no core.Most electromagneticdevices we will presentuse iron cores of oneform or anotherto enhance magneticflux.Cores are usually laminated (made up of insulated layers of iron stacked par-allel tothecoil-axisdirection)to reducetheeddy currents inducedwhen thecoresexperiencechanging magneticfields.Eddy currents,which are a result of Faraday'slaw of induction, result in inefficiencies and undesirable core heating.10.3SOLENOIDSANDRELAYSAs illustrated inFigure 10.2,a solenoid consists of a coil and amovableiron corecalled the armature. When the coil is energized with current, the core moves toincrease the flux linkageby closing the air gap between the cores.The movable coreis usually spring-loaded to allowthe coreto retract when thecurrent is switched off.Theforce generated is approximately proportional to the square of the current andinversely proportional to the square of the width of the air gap. Solenoids are inex-pensive, and their use is limited primarily to on-off applications such as latching.locking,and triggering.They arefrequentlyused inhome appliances(e.g.,washingVideo Demomachine valves), automobiles (e.g.,door latches and the starter solenoid), pinballmachines (e.g,plungers and bumpers),and factory automation.VideoDemos 1o.110.1Magicpianothrough 10.3 showexamplesof interesting studentprojects using solenoids in cre10.2Automatedative ways.melodicaAn electromechanical relay is a solenoid used to makeorbreak mechanical con-10.3LEDtact between electrical leads.A small voltage input to the solenoid controls a poten-fountainsystemtially large current through the relay contacts.Applications include power switchesand electromechanical control elements.Arelayperforms afunction similartoapowertransistor switch circuitbuthasthecapabilitytoswitchmuch largercurrents

Confirming Pages Figure 10.1 Right-hand rule for magnetic force. F I B extended right hand index finger direction extended right hand thumb direction flexed right hand middle finger direction 10.3 Solenoids and Relays 433 Another electromagnetic effect important to actuator design is field intensifica￾tion within a coil. Recall that, when discussing inductors in Chapter 2, we stated that the magnetic flux through a coil is proportional to the current through the coil and the number of windings. The proportionality constant is a function of the permeabil￾ity of the material within the coil. The permeability of a material characterizes how easily magnetic flux penetrates the material. Iron has a permeability a few hundred times that of air; therefore, a coil wound around an iron core can produce a magnetic flux a few hundred times that of the same coil with no core. Most electromagnetic devices we will present use iron cores of one form or another to enhance magnetic flux. Cores are usually laminated (made up of insulated layers of iron stacked par￾allel to the coil-axis direction) to reduce the eddy currents induced when the cores experience changing magnetic fields. Eddy currents, which are a result of Faraday’s law of induction, result in inefficiencies and undesirable core heating. 10.3 SOLENOIDS AND RELAYS As illustrated in Figure 10.2 , a solenoid consists of a coil and a movable iron core called the armature. When the coil is energized with current, the core moves to increase the flux linkage by closing the air gap between the cores. The movable core is usually spring-loaded to allow the core to retract when the current is switched off. The force generated is approximately proportional to the square of the current and inversely proportional to the square of the width of the air gap. Solenoids are inex￾pensive, and their use is limited primarily to on-off applications such as latching, locking, and triggering. They are frequently used in home appliances (e.g., washing machine valves), automobiles (e.g., door latches and the starter solenoid), pinball machines (e.g., plungers and bumpers), and factory automation. Video Demos 10.1 through 10.3 show examples of interesting student projects using solenoids in cre￾ative ways. An electromechanical relay is a solenoid used to make or break mechanical con￾tact between electrical leads. A small voltage input to the solenoid controls a poten￾tially large current through the relay contacts. Applications include power switches and electromechanical control elements. A relay performs a function similar to a power transistor switch circuit but has the capability to switch much larger currents. Video Demo 10.1 Magic piano 10.2 Automated melodica 10.3 LED fountain system alc80237_ch10_431-477_sss.indd 433 lc80237_ch10_431-477_sss.indd 433 10/01/11 10:24 PM 0/01/11 10:24 PM Introduction to Mechatronics and Measurement Systems, Fourth Edition 89 McGraw-Hill Create™ Review Copy for Instructor Nicolescu. Not for distribution

McGraw-HillCreateTM ReviewCopyforInstructorNicolescu.Notfordistribution90MeasurementSystems434CHAPTER10Actuatorsmovablespringarmaturecorecoilspninstationary(a) plunger typeiron core(b) nonplunger typeFigure10.2Solenoidsmovablecoilpermanentmagnetstationaryiron coreFigure10.3Voicecoil.Relays,becausethey createa mechanical connection and don't require voltagebias-ing,can be used to switch either DC or AC power.Also, the input circuit of arelayiselectricallyisolatedfromtheoutputcircuit,unlikethecommon-emittertransistorcircuit, where there is a common ground between the input and output. BecauseVideo Demotherelayis electrically isolated, noise, induced voltages, and groundfaults occur-10.4Relayring in the output circuit have minimal impact on the input circuit. One disadvan-andtransistortage of relays is thattheyhaveslowerswitching times than transistors.And becauseswitching circuitthey contain contacts and mechanical components,theywearout muchfaster.VideocomparisonDemo10.4demonstrates how relays and transistors respond to different switching10.5Computerspeeds.hard-drive withAs illustrated in Figure 10.3, a voice coil consists of a coil that moves in avoice coilmagnetic field produced by a permanent magnet and intensified by an iron core.10.6ComputerFigure1o.4showsthecoilandironcoreofacommerciallyavailablevoicecoil,hard-drivewhich can be used as either a sensor or an actuator.When used as an actuator,thetrack seekingforceon the coil is directlyproportional to the current in the coil.The coil is usuallydemonstrationattachedtoamovableloadsuchasthediaphragmofanaudiospeaker.thespoolof10.7Computera hydraulicproportional valve,or theread-writehead of a computer diskdrive.Thehard-drive super-linearresponse,smallmassofthemovingcoil,andbidirectionalcapabilitymakeslow-motion videovoicecoilsmoreattractivethan solenoidsforcontrol applications.of track findingVideoDemos10.5and10.6showhowacomputerdiskdrivefunctions,whereavoicecoilisused toprovidethepivotingmotion of theread-writehead.VideoDemo10.7 shows a super-slow-motion clip, filmed with a special high-speed camera,which dramatically demonstrates the accuracy and speed of the voice coil motion.The read-write head comes to a complete stop on one track beforemoving to another.In real-time (e.g., in Video Demo 10.6), this motion is a total blur

Confirming Pages Figure 10.2 Solenoids. (a) plunger type (b) nonplunger type movable armature core coil stationary iron core spring spring 434 C H A P T E R 10 Actuators Relays, because they create a mechanical connection and don’t require voltage bias￾ing, can be used to switch either DC or AC power. Also, the input circuit of a relay is electrically isolated from the output circuit, unlike the common-emitter transistor circuit, where there is a common ground between the input and output. Because the relay is electrically isolated, noise, induced voltages, and ground faults occur￾ring in the output circuit have minimal impact on the input circuit. One disadvan￾tage of relays is that they have slower switching times than transistors. And because they contain contacts and mechanical components, they wear out much faster. Video Demo 10.4 demonstrates how relays and transistors respond to different switching speeds. As illustrated in Figure 10.3 , a voice coil consists of a coil that moves in a magnetic field produced by a permanent magnet and intensified by an iron core. Figure 10.4 shows the coil and iron core of a commercially available voice coil, which can be used as either a sensor or an actuator. When used as an actuator, the force on the coil is directly proportional to the current in the coil. The coil is usually attached to a movable load such as the diaphragm of an audio speaker, the spool of a hydraulic proportional valve, or the read-write head of a computer disk drive. The linear response, small mass of the moving coil, and bidirectional capability make voice coils more attractive than solenoids for control applications. Video Demos 10.5 and 10.6 show how a computer disk drive functions, where a voice coil is used to provide the pivoting motion of the read-write head. Video Demo 10.7 shows a super-slow-motion clip, filmed with a special high-speed camera, which dramatically demonstrates the accuracy and speed of the voice coil motion. The read-write head comes to a complete stop on one track before moving to another. In real-time (e.g., in Video Demo 10.6), this motion is a total blur. Video Demo 10.4 Relay and transistor switching circuit comparison 10.5 Computer hard-drive with voice coil 10.6 Computer hard-drive track seeking demonstration 10.7 Computer hard-drive super￾slow-motion video of track finding Figure 10.3 Voice coil. movable coil stationary iron core permanent magnet N S alc80237_ch10_431-477_sss.indd 434 lc80237_ch10_431-477_sss.indd 434 10/01/11 10:24 PM 0/01/11 10:24 PM 90 Measurement Systems McGraw-Hill Create™ Review Copy for Instructor Nicolescu. Not for distribution

McGraw-Hill CreateTM ReviewCopyforInstructorNicolescu.Notfordistribution91IntroductiontoMechatronicsandMeasurementSystems,FourthEdition10.4Electric Motors435CLASS DISCUSSION ITEM 1O.1Examples of Solenoids,VoiceCoils,andRelaysMake a list of common household and automobile devices that contain solenoidsvoice coils, and relays. Describe why you think the particular component wasselected for each of the devices you cite.Figure1o.4Photographofavoicecoil ironcoreandcoil.10.4ELECTRICMOTORSElectric motors arebyfar themostubiquitous of theactuators,occurring invirtuallyallelectromechanicalsystems.Electricmotorscanbeclassifiedeitherbyfunctionorby electrical configuration.Inthefunctional classification,motors aregivennamesVideo Demosuggesting how the motor is to be used.Examples of functional classifications10.8ACinclude torque,gear, servo,instrument servo, and stepping.However, it is usuallyinduction motornecessarytoknowsomethingabout theelectrical design of themotortomake judg-(single phase)ments about its application for delivering power and controlling position.Figure 10.510.9ACprovides a configuration classification of electrical motors found in mechatronicsinductionmotorapplications. The differences are due to motor winding and rotor designs, resultingwithasoftstartforin a largevariety of operating characteristics.The price-performance ratio of electricawaterpumpmotors continuesto improve,makingthemimportant additions toall sortsofmecha-10.10ACtronic systems from appliances to automobiles.AC induction motors are particularlyinduction motorimportantinindustrialandlargeconsumerapplianceapplications.Infact,theACvariablefrequencyinductionmotorissometimescalledtheworkhorseofindustry.VideoDemos10.8driveforabuildingthrough10.10 showsomeexamples anddescribehowthemotorsfunction.air handlerunit

Confirming Pages 10.4 ELECTRIC MOTORS Electric motors are by far the most ubiquitous of the actuators, occurring in virtually all electromechanical systems. Electric motors can be classified either by function or by electrical configuration. In the functional classification, motors are given names suggesting how the motor is to be used. Examples of functional classifications include torque, gear, servo, instrument servo, and stepping. However, it is usually necessary to know something about the electrical design of the motor to make judg￾ments about its application for delivering power and controlling position. Figure 10.5 provides a configuration classification of electrical motors found in mechatronics applications. The differences are due to motor winding and rotor designs, resulting in a large variety of operating characteristics. The price-performance ratio of electric motors continues to improve, making them important additions to all sorts of mecha￾tronic systems from appliances to automobiles. AC induction motors are particularly important in industrial and large consumer appliance applications. In fact, the AC induction motor is sometimes called the workhorse of industry. Video Demos 10.8 through 10.10 show some examples and describe how the motors function. Video Demo 10.8 AC induction motor (single phase) 10.9 AC induction motor with a soft start for a water pump 10.10 AC induction motor variable frequency drive for a building air handler unit ■ CLASS DISCUSSION ITEM 10.1 Examples of Solenoids, Voice Coils, and Relays Make a list of common household and automobile devices that contain solenoids, voice coils, and relays. Describe why you think the particular component was selected for each of the devices you cite. Figure 10.4 Photograph of a voice coil iron core and coil. 10.4 Electric Motors 435 alc80237_ch10_431-477_sss.indd 435 lc80237_ch10_431-477_sss.indd 435 10/01/11 10:24 PM 0/01/11 10:24 PM Introduction to Mechatronics and Measurement Systems, Fourth Edition 91 McGraw-Hill Create™ Review Copy for Instructor Nicolescu. Not for distribution

McGraw-Hill CreateTM Review Copyfor Instructor Nicolescu.Not fordistribution.92MeasurementSystems436CHAPTER10Actuatorspermanent magnetvariable reluctanceseries woundshunt woundcompound woundpermanent magnetbrushlessvariable reluctancewound rotornductiorsquirrel cagesingleshaded polehysteresisreluctancepermanent magnetACmotowound rotorductiorsquirrel cageuniversal motorFigure 10.5Configurationclassificationofelectricmotorsair gapOstatorshaf/rotorT77laminatedironcorewindingpolecommutatorlaminated iron core polesegment包bearingLSshaftwindingrotorrotorstator (end vicw section)Figure 10.6 Motor construction and terminology.Figure10.6 illustratesthe construction and componentsof a typical electricmotor.The stationary outer housing,called the stator,supportsradial magnetizedpoles.These poles consist of either permanent magnets or wire coils, called fieldcoils, wrapped around laminated iron cores. The purpose of the stator poles is to pro-videradial magneticfields.The iron core intensifies the magnetic field inside the coildue to its permeability.The purpose forlaminating the core is to reduce the effectsofeddy currents,which are induced in a conducting material (see Class DiscussionItem 10.2).The rotor is the part of themotor that rotates. It consists of a rotatingshaft supported by bearings,conducting coils usuallyreferred to as the armaturewindings,and an iron core that intensifies thefields created bythewindings.There

Confirming Pages DC motors single phase induction synchronous shaded pole hysteresis reluctance permanent magnet polyphase synchronous universal motor AC motors wound rotor squirrel cage induction wound rotor squirrel cage brushed brushless permanent magnet variable reluctance series wound shunt wound compound wound permanent magnet variable reluctance Figure 10.5 Configuration classification of electric motors. 436 C H A P T E R 10 Actuators Figure 10.6 illustrates the construction and components of a typical electric motor. The stationary outer housing, called the stator, supports radial magnetized poles. These poles consist of either permanent magnets or wire coils, called field coils, wrapped around laminated iron cores. The purpose of the stator poles is to pro￾vide radial magnetic fields. The iron core intensifies the magnetic field inside the coil due to its permeability. The purpose for laminating the core is to reduce the effects of eddy currents, which are induced in a conducting material (see Class Discussion Item 10.2). The rotor is the part of the motor that rotates. It consists of a rotating shaft supported by bearings, conducting coils usually referred to as the armature windings, and an iron core that intensifies the fields created by the windings. There Figure 10.6 Motor construction and terminology. stator shaft/rotor air gap shaft commutator segment laminated iron core pole winding bearing rotor stator (end view section) winding laminated iron core pole rotor alc80237_ch10_431-477_sss.indd 436 lc80237_ch10_431-477_sss.indd 436 10/01/11 10:24 PM 0/01/11 10:24 PM 92 Measurement Systems McGraw-Hill Create™ Review Copy for Instructor Nicolescu. Not for distribution

McGraw-Hill CreateTM Review Copyfor Instructor Nicolescu.Not fordistributionIntroduction to Mechatronics and Measurement Systems,Fourth Edition9343710.4Electric Motorsis a small air gap between the rotor and the stator where the magneticfields interact.In many DC motors,the rotor also includes a commutator that delivers and con-trols the direction of current through the armature windings.For motors with a com-mutator,“brushes"provide stationary electrical contact to the moving commutatorconductingsegments.Brushes inearlymotors consisted of bristles of copper wireflexedagainst thecommutator,hencethetermbrush;butnowtheyare usuallymadeof graphite,which provides a larger contact area and is self-lubricating.Thebrushesare usually spring-loaded to ensure continual contact with the commutator.VideoDemo10.11 showsa small,brushed,permanent-magnetDCmotordisassembled soyou can see the various components and how theyfunction.Abrushless DC motor has permanent magnets on the rotor and a rotatingfieldin the stator.The permanent magnets on the rotor eliminate the need for a commuta-tor.Instead, the DC currents in the stator coils are switched in response to proximitysensors that are triggered as the shaft rotates.Video Demos 10.12 and 10.13 showtwoexamplesof brushlessDC motors.One advantageofa brushlessmotoristhatit does notrequiremaintenancetoreplaceworn brushes.Also,becausethere arenorotor windings or iron core, the rotor inertia is much smaller, sometimesmakingcontrol easier.There arealsonorotor heat dissipationproblems,becausethere are noVrotor windings and henceno FRheating.Anotheradvantage of not havingbrushesVideo Demois that there is no arcing associated withmechanical commutation.Therefore,brush-lessmotorscreatelessEMI andaremoresuitableinenvironmentswhereexplosive10.11DC motorgases mightbepresent.Onedisadvantage ofbrushlessmotors is that they can costcomponentsmore due to the sensors and control circuitry required.10.12BrushlessFigure 10.7 shows examples of commercially available assembled motors.InDCmotorfromathe top figure, the motor on the left is an AC induction motor with a gearhead speedcomputerfanreduction unit attached.The motor on the right is a two-phase stepper motor.Motors10.13Brushlesscome in standard sizes with standard mounting brackets,and theyusuallyincludeDC motorgearnameplates listing someof themotor's specifications.Thebottomfigure showsthepumpinternalconstructionofapermanent-magnet-rotorsteppermotor.VideoDemo1o.1410.14DCandsteppermotorshowsotherexamplesof commerciallyavailableregularDC motors and stepperexamplesmotors.CLASS DISCUSSIONITEM1O.2Eddy CurrentsDescribe the causes of eddy currents that are induced in a conducting material expe-riencing a changing magnetic field.The iron core in a motor rotor is usuallylami-nated.Explain why.What is the best orientation for the laminations?Torque is produced by an electric motor through the interaction of either statorfields and armaturecurrents or statorfields and armaturefields.We illustrate bothprinciples starting with the first.Figure 10.8 illustrates a DCmotor with six armaturewindings.Thedirection of current flow in the windings is illustrated in the figure

Confirming Pages is a small air gap between the rotor and the stator where the magnetic fields interact. In many DC motors, the rotor also includes a commutator that delivers and con￾trols the direction of current through the armature windings. For motors with a com￾mutator, “brushes” provide stationary electrical contact to the moving commutator conducting segments. Brushes in early motors consisted of bristles of copper wire flexed against the commutator, hence the term brush; but now they are usually made of graphite, which provides a larger contact area and is self-lubricating. The brushes are usually spring-loaded to ensure continual contact with the commutator. Video Demo 10.11 shows a small, brushed, permanent-magnet DC motor disassembled so you can see the various components and how they function. A brushless DC motor has permanent magnets on the rotor and a rotating field in the stator. The permanent magnets on the rotor eliminate the need for a commuta￾tor. Instead, the DC currents in the stator coils are switched in response to proximity sensors that are triggered as the shaft rotates. Video Demos 10.12 and 10.13 show two examples of brushless DC motors. One advantage of a brushless motor is that it does not require maintenance to replace worn brushes. Also, because there are no rotor windings or iron core, the rotor inertia is much smaller, sometimes making control easier. There are also no rotor heat dissipation problems, because there are no rotor windings and hence no I 2 R heating. Another advantage of not having brushes is that there is no arcing associated with mechanical commutation. Therefore, brush￾less motors create less EMI and are more suitable in environments where explosive gases might be present. One disadvantage of brushless motors is that they can cost more due to the sensors and control circuitry required. Figure 10.7 shows examples of commercially available assembled motors. In the top figure, the motor on the left is an AC induction motor with a gearhead speed reduction unit attached. The motor on the right is a two-phase stepper motor. Motors come in standard sizes with standard mounting brackets, and they usually include nameplates listing some of the motor’s specifications. The bottom figure shows the internal construction of a permanent-magnet-rotor stepper motor. Video Demo 10.14 shows other examples of commercially available regular DC motors and stepper motors. Video Demo 10.11 DC motor components 10.12 Brushless DC motor from a computer fan 10.13 Brushless DC motor gear pump 10.14 DC and stepper motor examples ■ CLASS DISCUSSION ITEM 10.2 Eddy Currents Describe the causes of eddy currents that are induced in a conducting material expe￾riencing a changing magnetic field. The iron core in a motor rotor is usually lami￾nated. Explain why. What is the best orientation for the laminations? Torque is produced by an electric motor through the interaction of either stator fields and armature currents or stator fields and armature fields. We illustrate both principles starting with the first. Figure 10.8 illustrates a DC motor with six armature windings. The direction of current flow in the windings is illustrated in the figure. 10.4 Electric Motors 437 alc80237_ch10_431-477_sss.indd 437 lc80237_ch10_431-477_sss.indd 437 10/01/11 10:24 PM 0/01/11 10:24 PM Introduction to Mechatronics and Measurement Systems, Fourth Edition 93 McGraw-Hill Create™ Review Copy for Instructor Nicolescu. Not for distribution

McGraw-Hill CreateTM ReviewCopyforInstructorNicolescu.Notfordistribution94MeasurementSystems438CHAPTER1oActuatorsom电旺话0(@) AC induction and stepper motorBracketRotorStatorFlange(b) exploded view of stepper motor with apermanent magnet rotorFigure1o.7Examplesofcommercialmotors.(CourtesyofOrientalMotorTorrance,CA)stator ficldstatoXorqucrotcX?ROcurent outarmaturefieldO?currentinCarmatureoOwindingsstator ficeldFigure1o.8 Electricmotorfield-currentinteractionAs a result of Equation 10.1,the interaction of thefixed stator field and the currentsinthearmaturewindingsproduceatorqueinthecounterclockwisedirection.Youcan verify this torque direction by applying the right-hand rule to the armature cur-rent and statorfield directions.To maintain thetorque as the rotor rotates,the spatialarrangementof thearmaturecurrentsrelativetothestatorfieldmustremainfixed

Confirming Pages 438 C H A P T E R 10 Actuators As a result of Equation 10.1 , the interaction of the fixed stator field and the currents in the armature windings produce a torque in the counterclockwise direction. You can verify this torque direction by applying the right-hand rule to the armature cur￾rent and stator field directions. To maintain the torque as the rotor rotates, the spatial arrangement of the armature currents relative to the stator field must remain fixed. Figure 10.7 Examples of commercial motors. (Courtesy of Oriental Motor, Torrance, CA) (a) AC induction and stepper motor (b) exploded view of stepper motor with a permanent magnet rotor Case Bracket Rotor Stator Flange Figure 10.8 Electric motor field-current interaction. 1 1 2 2 3 3 4 4 5 5 6 6 stator stator stator field stator field current out current in torque rotor armature windings armature field alc80237_ch10_431-477_sss.indd 438 lc80237_ch10_431-477_sss.indd 438 10/01/11 10:24 PM 0/01/11 10:24 PM 94 Measurement Systems McGraw-Hill Create™ Review Copy for Instructor Nicolescu. Not for distribution

McGraw-Hill CreateTM ReviewCopyforInstructorNicolescu.NotfordistributionIntroduction to Mechatronics and Measurement Systems, Fourth Edition9510.4ElectricMotors439A commutatoraccomplishes this by switchingthecurrents inthearmaturewindingsin the correct sequence as the rotor turns.Figure 10.9 illustrates an example commutator. It consists of a ring of alternat-ing conductive and insulating materials connected to the rotor windings.Current isdirected throughthewindings viathebrushes,which slideonthesurface of thecom-mutator as it rotates.In theposition shown,the current flows through windingsA,B,and Cintheclockwisedirection and throughF,E,andDinthecounterclockwisedirection.When the rotor turns clockwise one sixth of a full rotation from the positionshown, the currents in windings C and F switch directions. As the brushes slide overtherotatingcommutator,thisprocess continuesin sequence.Withappropriatewind-ing configurations, thecommutator maintains a consistent spatial arrangement of thecurrents relativetothefixed statorfields.This continuallymaintainsthetorqueinthedesireddirectionAnothermethod bywhichelectricmotors can createtorqueisthroughthe inter-action of stator and rotormagnetic fields.The torqueisproduced bythefact thatlike field poles attract and unlike poles repel.Figure 10.10 illustrates this principleof operation witha simple two-poleDC motor.The statorpolesgeneratefixed mag-netic fields with permanent magnets or coils carrying DC current.The winding in therotor is commutated to cause changes in direction ofits magnetic field.The interac-tion of the changingrotor field and thefixed stator fields produce atorqueon theshaft,causing rotation.With the rotor in position i, the right brush contacts commu-tator segmentAand theleftbrush contacts segmentB,creating acurrent in therotorwinding,resulting inthemagneticpoles as shown.Therotormagneticpoles opposethe stator magnetic poles, creating a torque causing clockwise motion of the rotor.Inpositioni,thestatorpolesbothopposeandattracttherotorpolesto enhancetheclockwiserotation.Between positions iiand vthe commutator contacts switch,changingthedirectionoftherotorcurrentandhencethedirectionofthemagneticfield.Inpositioniv,bothbrushestemporarilylosecontactwiththecommutator,butconductorB0insulatoarmatureQwindingsEFigure10.9Electricmotorsix-windingcommutator

Confirming Pages A commutator accomplishes this by switching the currents in the armature windings in the correct sequence as the rotor turns. Figure 10.9 illustrates an example commutator. It consists of a ring of alternat￾ing conductive and insulating materials connected to the rotor windings. Current is directed through the windings via the brushes, which slide on the surface of the com￾mutator as it rotates. In the position shown, the current flows through windings A, B, and C in the clockwise direction and through F, E, and D in the counterclockwise direction. When the rotor turns clockwise one sixth of a full rotation from the position shown, the currents in windings C and F switch directions. As the brushes slide over the rotating commutator, this process continues in sequence. With appropriate wind￾ing configurations, the commutator maintains a consistent spatial arrangement of the currents relative to the fixed stator fields. This continually maintains the torque in the desired direction. Another method by which electric motors can create torque is through the inter￾action of stator and rotor magnetic fields. The torque is produced by the fact that like field poles attract and unlike poles repel. Figure 10.10 illustrates this principle of operation with a simple two-pole DC motor. The stator poles generate fixed mag￾netic fields with permanent magnets or coils carrying DC current. The winding in the rotor is commutated to cause changes in direction of its magnetic field. The interac￾tion of the changing rotor field and the fixed stator fields produce a torque on the shaft, causing rotation. With the rotor in position i, the right brush contacts commu￾tator segment A and the left brush contacts segment B, creating a current in the rotor winding, resulting in the magnetic poles as shown. The rotor magnetic poles oppose the stator magnetic poles, creating a torque causing clockwise motion of the rotor. In position ii, the stator poles both oppose and attract the rotor poles to enhance the clockwise rotation. Between positions iii and v the commutator contacts switch, changing the direction of the rotor current and hence the direction of the magnetic field. In position iv, both brushes temporarily lose contact with the commutator, but Figure 10.9 Electric motor six-winding commutator. A B C D E F armature windings Iin Iout brush conductor insulator 10.4 Electric Motors 439 alc80237_ch10_431-477_sss.indd 439 lc80237_ch10_431-477_sss.indd 439 10/01/11 10:24 PM 0/01/11 10:24 PM Introduction to Mechatronics and Measurement Systems, Fourth Edition 95 McGraw-Hill Create™ Review Copy for Instructor Nicolescu. Not for distribution

McGraw-Hill CreateTM ReviewCopyforInstructorNicolescu.Notfordistribution96Measurement Systems440CHAPTER10ActuatorsstatorcommutatorbrushsegmentOACVBUtorquces(ii)(iv)(i)(v)Figure10.10 Electricmotorfield-fieldinteractiontherotor continues to move dueto itsmomentum.Inpositionvreversed magneticfieldintherotoragainopposesthestatorfield,continuingtheclockwisetorqueandmotion.CLASS DISCUSSIONITEM 1O.3Field-Field Interaction ina MotorDoes thearmature field inFigure 10.8 have any effect on the torque produced bythe motor?Aproblemwiththe simple two-poledesignillustrated inFigure10.10 is thatstarting would not occur if the motor happens to be in position iv, where the brushesare located overthecommutator gaps.Thisproblemcan be avoided by designing theVideoDemomotorwithmorepolesand morecommutatorsegmentswith overlappingswitching.This allowsthebrushesto alwayscontacttwoactivesegments,even whileswitching10.11DCmotor(seeVideoDemo10.11andClassDiscussionItem10.4).components

Confirming Pages Figure 10.10 Electric motor field-field interaction. + stator N S A B commutator segment brush stator pole torque (i) N S A B N S (iii) N S A B N S A B (iv) N S (v) N S B A S N (ii) N B A S N S Video Demo 10.11 DC motor components 440 C H A P T E R 10 Actuators the rotor continues to move due to its momentum. In position v reversed magnetic field in the rotor again opposes the stator field, continuing the clockwise torque and motion. ■ CLASS DISCUSSION ITEM 10.3 Field-Field Interaction in a Motor Does the armature field in Figure 10.8 have any effect on the torque produced by the motor? A problem with the simple two-pole design illustrated in Figure 10.10 is that starting would not occur if the motor happens to be in position iv, where the brushes are located over the commutator gaps. This problem can be avoided by designing the motor with more poles and more commutator segments with overlapping switching. This allows the brushes to always contact two active segments, even while switching (see Video Demo 10.11 and Class Discussion Item 10.4). alc80237_ch10_431-477_sss.indd 440 lc80237_ch10_431-477_sss.indd 440 10/01/11 10:24 PM 0/01/11 10:24 PM 96 Measurement Systems McGraw-Hill Create™ Review Copy for Instructor Nicolescu. Not for distribution

McGraw-Hill CreateTM Review Copyfor Instructor Nicolescu.Not fordistributionIntroduction to Mechatronics and Measurement Systems,Fourth Edition9744110.5DC Motors3Other problems not discussed with these simple models are a back electromo-tive force (emf) and induction. As the rotor windings cut through the stator magneticfield,a back emfis induced opposing the voltageapplied to the rotor.Also,whenthe commutator switches thedirection ofcurrent,a voltage is inducedto oppose thechangeincurrentdirection.The principles of operation of AC motors are similar regarding interaction ofthe magnetic fields, but commutation is not required.This is becausethe magneticfield rotates around the stator as aresult of the AC voltages and the arrangement ofthe coils around thestatorhousing.Therotorwindingsof asynchronous AC motorshave no external voltage applied; rather, voltages are induced in the rotor windingsdue to the rotating fields around the stator. The rotor rotates at slower speeds thanthe rotating stator fields (this is called slip),making the induction possible, hencethetermasynchronous.Becauseofthis action,asynchronousmotorsaresometimesreferred toas induction machines.With synchronous AC motors,therotor wind-ings are energized but through sliprings instead of a commutator.Brushes provideconstant uninterrupted contact with the slip rings,causingfields torotate around therotorwindingsatthesamerateasthefieldsrotatearoundthestator.Duetotheinteraction of thesefields,the rotorrotates atthesamespeed asthe statorfields, hencetheterm synchronous.CLASS DISCUSSIONITEM 1O.4DissectionofRadio ShackMotorPurchase an inexpensive 1.5-3-V DC motor (e.g-,Radio Shack Catalog No.273-223)and disassemble it.Identifythebrushes,the commutator segments,thearmature windings, the laminated rotor poles, and the stator permanent magnets.Sketchthemagnetic field produced by the stator permanent magnets.Fordifferentcommutator positions, determine the direction of current flow (and theresultingfield direction) in the armature windings.Determine the direction of torque pro-duced by the field-field and field-current interactions. Which effect do you think isstrongerin this motor?Internet Link 10.2 provides excellent illustrations and animations showing thefundamentalsofhowvariousmotors,generators,andtransformersfunction.Internet Link10.5DC MOTORS10.2ElectricDirect current (DC) motors are used in a large number of mechatronic designsmotor illustrationsbecause of thetorque-speed characteristics achievablewithdifferent electrical con-andanimationsfigurations.DC motor speedscanbe smoothlycontrolled andinmost casesarereversible. Since DC motors have a high ratio of torque to rotor inertia, they canrespond quickly.Also, dynamic braking,where motor-generated energy is fed to a

Confirming Pages ■ CLASS DISCUSSION ITEM 10.4 Dissection of Radio Shack Motor Purchase an inexpensive 1.5–3-V DC motor (e.g., Radio Shack Catalog No. 273-223) and disassemble it. Identify the brushes, the commutator segments, the armature windings, the laminated rotor poles, and the stator permanent magnets. Sketch the magnetic field produced by the stator permanent magnets. For different commutator positions, determine the direction of current flow (and the resulting field direction) in the armature windings. Determine the direction of torque pro￾duced by the field-field and field-current interactions. Which effect do you think is stronger in this motor? Other problems not discussed with these simple models are a back electromo￾tive force (emf) and induction. As the rotor windings cut through the stator magnetic field, a back emf is induced opposing the voltage applied to the rotor. Also, when the commutator switches the direction of current, a voltage is induced to oppose the change in current direction. The principles of operation of AC motors are similar regarding interaction of the magnetic fields, but commutation is not required. This is because the magnetic field rotates around the stator as a result of the AC voltages and the arrangement of the coils around the stator housing. The rotor windings of asynchronous AC motors have no external voltage applied; rather, voltages are induced in the rotor windings due to the rotating fields around the stator. The rotor rotates at slower speeds than the rotating stator fields (this is called slip ), making the induction possible, hence the term asynchronous. Because of this action, asynchronous motors are sometimes referred to as induction machines. With synchronous AC motors, the rotor wind￾ings are energized but through slip rings instead of a commutator. Brushes provide constant uninterrupted contact with the slip rings, causing fields to rotate around the rotor windings at the same rate as the fields rotate around the stator. Due to the inter￾action of these fields, the rotor rotates at the same speed as the stator fields, hence the term synchronous. Internet Link 10.2 Electric motor illustrations and animations Internet Link 10.2 provides excellent illustrations and animations showing the fundamentals of how various motors, generators, and transformers function. 10.5 DC MOTORS Direct current (DC) motors are used in a large number of mechatronic designs because of the torque-speed characteristics achievable with different electrical con￾figurations. DC motor speeds can be smoothly controlled and in most cases are reversible. Since DC motors have a high ratio of torque to rotor inertia, they can respond quickly. Also, dynamic braking, where motor-generated energy is fed to a 10.5 DC Motors 441 alc80237_ch10_431-477_sss.indd 441 lc80237_ch10_431-477_sss.indd 441 10/01/11 10:24 PM 0/01/11 10:24 PM Introduction to Mechatronics and Measurement Systems, Fourth Edition 97 McGraw-Hill Create™ Review Copy for Instructor Nicolescu. Not for distribution