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 structure. 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 physical changes such as linear and angular displacement. They also modulate the rate and power associated with these changes. An important aspect of mechatronic system 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 currentcarrying conductor is moved in a magnetic field, a force is produced in a direction 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 intensification 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 permeability 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 parallel 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 inexpensive, 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 creative ways. An electromechanical relay is a solenoid used to make or break mechanical contact between electrical leads. A small voltage input to the solenoid controls a potentially 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 biasing, 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 occurring in the output circuit have minimal impact on the input circuit. One disadvantage 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 superslow-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 judgments 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 mechatronic 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 provide 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