采用壓電蜂鳴器設(shè)計和啟用壓電離合器?【中文6190字】【PDF+中文WORD】,中文6190字,PDF+中文WORD,采用,壓電,蜂鳴器,設(shè)計,啟用,離合器,中文,6190,PDF,WORD Available online at Sensors and Actuators A 141(2008)515522Design and implementation of a piezoelectric clutch mechanismusing piezoelectric buzzersKuo-Tsai Chang,Hsuang-Chang Chiang,Chun-Wei LeeDepartment of Electrical Engineering,National United University,1,Lien Da,Kungching Li,Miaoli 36003,Taiwan,ROCReceived 20 December 2006;received in revised form 10 July 2007;accepted 3 October 2007Available online 16 October 2007AbstractThis paper develops a novel piezoelectric clutch mechanism,including a driving member and a driven member,and investigates the clutchingperformance of the clutch mechanism.Each member is based on a thin-disk piezoelectric buzzer as a frictional member under coupling mode and amechanical vibrator under non-coupling mode.In doing so,the clutch mechanism and its experimental set-up namely a power transmission systemare first expressed.Then,operating principles such as inverse piezoelectric effect and ultrasonic levitation for separating two facing surfaces of themembers are stated,and a carbon-powder imaging method for observing the vibration mode of the piezoelectric buzzer is introduced.Moreover,a DC/AC resonant inverter for converting a DC source to a sinusoidal source applied to energize the piezoelectric buzzer is constructed.Finally,relationships between rotational speeds and electrical conditions as well as the transient response of the rotation speed with the condition of changeare investigated.2007 Elsevier B.V.All rights reserved.Keywords:Piezoelectric clutch;Piezoelectric buzzer;Vibration mode;Piezoelectric effect1.IntroductionConventional clutches,including electromagnetic clutches,gear clutches,friction clutches,overrunning clutches and cen-trifugalclutches,areusuallyappliedtostartorstopamechanicalload,and even to control a revolving speed of the mechanicalload in power transmission systems.For the electromagneticclutches,some magnetic powders with magnetic flux linkagesenclosed by an exciting coil are needed to transmit the torquefromthedrivingtodrivenendaftermagnetization.Thetransmit-ted torque is approximately proportional to the magnetic fieldor magnetization current.Each electromagnetic clutch is capa-ble of connecting the driving and driven members at the samespeedorundercontrollablespeeddifference.Unfortunately,anyelectromagnetic clutch has its inherent shortcoming such as agreat electromagnetic interference(EMI),which is unfavorableat free-of-EMI sites such as hospitals or precision laboratories,during the running of the clutch 14.Corresponding author.Tel.:+886 37 381372;fax:+886 37 327887.E-mail address:ktchangnuu.edu.tw(K.-T.Chang).For the gear clutches,protrusions such as gear teeth or keysare built in the driving and driven members.The differencebetween the driving and driven speeds is small in order to avoidan excessive impact or damaging the gear clutches under cou-pling and non-coupling modes 58.For the friction clutches,the driving and driven members are connected with each otherusing frictions,which enable the driving member to drive thedriven member indeed.They are promptly connected or sep-arated by a small impact force or a little vibration.However,an abrasive slip at the contact of the members is caused by aheavy load to shorten the durability of the clutching materialsor maintain the members frequently 911.For the overrun-ning clutches,an overrunning clutch comprises ratchet wheels,ratchet pawls,rotary cylinders and wedge blocks.This clutch isused to transmit the torque or motion from the driving to drivenend in one-way direction.In spite of its simple construction,a considerably bulky size and a loud noise arising at the tran-sientmomentofthemembersfromthecouplingtonon-couplingmode restrict this type of mechanism can only applicable forlow-speed and non-precision machines 12,13.For the centrifugal clutches,the contact of the driving anddriven members is automatically connected or separated by acentrifugal force if the desired speed at the driving or driven0924-4247/$see front matter 2007 Elsevier B.V.All rights reserved.doi:10.1016/j.sna.2007.10.018516K.-T.Chang et al./Sensors and Actuators A 141(2008)515522Fig.1.Piezoelectric clutch mechanism.end is arrived.But this clutch has a considerably bulky mecha-nism 14,15.To mitigate or solve the aforementioned problemsregarding the above conventional clutches,an ultrasonic clutchfor a driving power control of multi-fingered exoskeleton hapticdevice with passive force feedback control has been developed16.And,an ultrasonic clutch,including two ultrasonic trans-ducers as mechanical vibrators and frictional members as well,for controlling the contact or non-contact between the drivingand driven shafts has been investigated 17.These ultrasonicclutches are heavy and bulky.Based on the above,this paper develops a novelpiezoelectricclutchmechanism,includingtwothin-diskpiezoelectricbuzzersas mechanical vibrators and frictional members as well,to min-imize the clutch mechanism,cancel the EMI effect,decline theimpact of the members at the transient state from the couplingto non-coupling mode,and control the power transmitted fromthe driving to driven end.2.Mechanism designFrom Fig.1,the piezoelectric clutch mechanism containsa driving member and a driven member,each of which con-tains a thin-disk piezoelectric buzzer(TE41208-26,SeahornInc.,Taipei,Taiwan),a driving or driven shaft,a plastic fixer,aFig.2.Structure of piezoelectric buzzer.Fig.3.Electrical drive of piezoelectric buzzer.conductive tap and two electric wires.The piezoelectric buzzercomprises a piezoceramic disk(diameter,24.8mm;thickness,0.1mm),a nickel-alloy disk(diameter,41.0mm;thickness,0.1mm)and a silvering electrode(diameter,24.8mm;thick-ness,0.02mm),as shown in Fig.2.The piezoceramic disk has apolingdirectionatitsthicknessdirection.Themassofthepiezo-electric buzzer is approximately 1.5g.For the electrical drive,an electrical sinusoidal source is supplied to the piezoelectricbuzzer via the nickel-alloy disk and the silvering electrode,asdepicted in Fig.3.Intheassemblyoftheclutchmechanism,theconductivetapisadheredtotheoutsideoftheplasticfixer.Theaxisofthedrivingshaft is aligned that of the driven shaft.The piezoelectric buzzerisfixedtotheedgeoftheplasticfixerbyviscoseatanodalcircleof the vibration mode on the nickel-alloy disk.For the electricwires,one is mounted between the driving(driven)shaft andthe silvering electrode,and the other is mounted between theconductive tap and the nickel-alloy disk.Fig.4.Power transmission system.K.-T.Chang et al./Sensors and Actuators A 141(2008)515522517Fig.5.Inverse piezoelectric effect.Fig.6.Near-field acoustic levitation.From Fig.4,the power transmission system comprises theclutchmechanism,anelectricalcontrolsystem,twopreloadcon-trollers,two plastic couplings,and others.The electrical controlsystem includes an AC power supply system,two switches S1and S2,two conductive taps,four carbon brushes,and a sourcebase.This system is used to control electrical drive conditionsof the members and determine the coupling or non-couplingmode of the clutch mechanism.Each preload controller con-tains a stainless spring,two metal washers,and a linear bearing,where the washers are mounted at both ends of the spring,andthe bearing is needed to support and guide the driving or drivenshaft along a center line of the clutch mechanism.This con-troller provides a preload force to the driving or driven memberFig.7.Principle of carbon-powder imaging method:(a)movement of powders;(b)distribution of electrical charges.Fig.8.Patternsofvibrationmode:(a)front-viewpattern;(b)back-viewpattern.soastoensurethatfacingsurfacesofthemembersareconnectedwith each other under coupling mode.For specifications of thespring,the plastic coefficient is about 1.15g/cm,the length isapproximately18mm,andthediameterisapproximately4mm.Thus,the preload force on the contact of the facing surfacesis approximately 0.46g.In the connection of the plastic cou-plings,one is linked between the driving shaft and a motorshaft,and the other is linked between the driven shaft and aload shaft.3.Operating principleThe non-coupling mode of the clutch mechanism is basedon near-field acoustic levitation 1820,which is caused byinverse piezoelectric effect.For the inverse piezoelectric effect,518K.-T.Chang et al./Sensors and Actuators A 141(2008)515522Fig.9.Dimensional view of the front-view pattern.the shape of a piezoelectric element extends by a positiveDC driving voltage,and contracts by a negative DC driv-ing voltage,as shown in Fig.5.For the acoustic levitation,an object with a planar-and-rigid bottom suspends above aradiation surface of a piezoelectric vibrator using a radia-tion pressure (kgw/m2)on the bottom of the object,and apiston-like acoustic wave occurs in the space between the lev-itation object and the radiation surface,as depicted in Fig.6.Generally,the levitation height is much less than the wave-length of the acoustic wave.This height,h(m),is expressedbyh=a0?1+4ac2a(1)where a0is the vibration amplitude(m),ais the sound den-sity of medium(kg/m3),cais the sound velocity of medium(m/s),and is the specific heat ratio 21.Using Eq.(1),thelevitation height increases with the vibration amplitude if theparameters such as a,ca,and are constant.Additionally,the non-coupling mode of the clutch mechanism results largelyfromtheacousticlevitationsothatthedrivenshaftalmoststops,but the driving shaft still rotates.From Figs.1 and 4,the members are arranged to rotate abouta common axis of rotation to be in contact with each other in aFig.10.Schematic vibration mode.Fig.11.AC power supply system.Fig.12.Speed measuring system.first state if both piezoelectric buzzers in the members are elec-trically energized by low AC power.These members are furthermovedintoasecondstatewherebythedrivingmemberisdiscon-nectedfromthedrivenmemberusingastrongradiationpressurefield on the facing surface of the piezoelectric buzzer if one ortwo piezoelectric buzzers in the members are electrically ener-gizedbyhighACpower.Bothmembersmaybeinterchangeablewith one another,if necessary.Then,the contact surfaces of themembers are tightly coupled together without electrically ener-gizing the piezoelectric buzzers,so as to get the fact that thedriving member drives the driven member.These surfaces arealso separated for disconnecting the members,so as to stop thedriven member,but still rotate the driving member,if one ortwo piezoelectric buzzers are electrically energized by high ACpower.Fig.13.Speeds vs.DC input voltage at the frequency of 76.0kHz.K.-T.Chang et al./Sensors and Actuators A 141(2008)515522519Fig.14.Speeds vs.frequency under different voltages:(a)Vdc=1,2,3V;(b)Vdc=4,5,6V;(c)Vdc=7,8,9V;(d)Vdc=10,11,12V.4.Mechanical analysisAsreferringtoRef.22,thevibrationmodeoftheelectricallyenergized piezoelectric buzzer is observed by a carbon-powderimagingmethodsoastoelucidatethedisconnectionbetweenthefacingsurfacesofthemembers.Tooperatetheimagingmethod,some carbon powders are first uniformly spread on both sidesof the piezoelectric buzzer.Then,the powders are moving fromthe loops to nodes in the axialsymmetrical flexural vibration ofthe piezoelectric buzzer,as shown in Fig.7(a),until revealinga pattern of the vibration mode after electrically turning on.The pattern of the vibration mode still holds on both sides ofthe piezoelectric buzzer due to positive and negative chargescaused by a residual electric field Er,as shown in Fig.7(b),afterelectricallyturningoff.Moreover,patternsofthevibrationmodeat both sides of the piezoelectric buzzer are depicted in Fig.8(a)and(b)if the piezoelectric buzzer is electrically energized byan electrical sine source,involving the amplitude of 5V andthe frequency of 73.25kHz.In the patterns,dark areas indicatenodes of the vibration mode,and bright areas indicate loops ofthe vibration mode.From Fig.9,the diameter of the first nodalcircle,n1,is approximately 5.9mm,the diameter of the secondnodal circle,n2,is approximately 14.0mm,and the diameterof the third nodal circle,n3,is approximately 21.2mm.Next,a two-dimensional(2D)wave equation of a thin-diskpiezoelectric element such as a thin-disk piezoelectric buzzer isdefined as follows2u(r,t)=1c22t2u(r,t)(2)wherec=?THere,u is the vibration amplitude,r is the radius,and is thegeometrical angle;c is the sound velocity,T is the horizontaltension,and is the mass density.Thus,c is constant if T and areconstant.ThevariableisfurtherwithdrawnfromEq.(2)duetotheaxialsymmetricalmodeofthepiezoelectricbuzzer.Thus,the solution of the 2D wave equation contains a term of zero-order first-kind Bessel function J0and a term of Euler functionejtif the piezoelectric buzzer is electrically energized by an520K.-T.Chang et al./Sensors and Actuators A 141(2008)515522electrical sine source.This solution indicating the mechanicalvibration is expressed byu(r,t)=AmJ0(kr)ejt(3)wherek=2=cHere,Amis the vibration amplitude,k is the wave num-ber,is the wavelength,and is the angular frequency.Aschematic diagram of the vibration mode is revealed in Fig.10.Additionally,n1:n2:n3=01:02:03,calculatedby01=2.4,02=5.6,and03=8.6,where 01,02and 03are the first,second and third zeros of zero-order first-kind Bessel func-tion J0,respectively 23.This finding indicates that Eq.(3)is available for analyzing the vibration behavior of the piezo-ceramic part.Therefore,the axialsymmetry flexural vibrationmode almost dominates the vibration behavior of the piezoelec-tricbuzzerunderfreeboundaryconditionsbecausethediameter2greatly exceeds that of the thickness t2in the piezoceramicdisk 24.Also,2/t2=248,calculated by 9=24.8mm,andt2=0.1mm.5.Experimental setupAn AC power supply system for generating an electrical sinesource at input terminals of the piezoelectric buzzer is shownin Fig.11.This system includes a DC/AC resonant inverter,adriven and isolated circuit,a DC power supply(LPS305,Amer-ican Reliance Inc.,EI Monte,CA)and a function generator(FG506,American Reliance Inc.,EI Monte,CA).The resonanttank consists of a series inductance Lf(=64?H)and a parallelcapacitance Cf(=0.1?F).The resonant inverter contains a full-bridge chopper with four MOSFET devices(IRF840,UnitrodeInc.,Dallas,TX),a resonant tank and an equivalent circuit ofthe piezoelectric buzzer.The MOSFET devices are controlledby four rectangular triggering signals vgs1 vgs4,respectively,which are produced from the driven and isolated circuit andcontrolled by the function generator.A pulse width modulationsignal vpwmas an input signal of the driven and isolated circuitis generated from the function generator.Thus,the amplitudeof the sine source is controlled by the DC power supply,andthe frequency of the sine source is controlled by the functiongenerator.From Fig.12,a speed measuring system,includingtwo digital optical tachometers(RM-1501,Prova Inc.,Taipei,Taiwan)and two optical reflectors,is constructed to measurerotational speeds of the shafts in the members.Each reflector isadheredontheoutsideoftheplasticfixerinthedrivingordrivenmember.6.Results and discussionAccording to Fig.4,the piezoelectric buzzer in the drivenmemberiselectricallyenergizedbyelectricalsinesourcesatthesame frequency of 76.0kHz that is the resonance frequency ofthe piezoelectric buzzer using different voltages,which are con-trolledbytheDCpowersupplyshowninFig.11.TheamplitudeFig.15.Measured transient responses of the driven speed using Vdc=12V andf=76.0kHz under different conditions of changes:(a)from the non-contact tocontact modes;(b)from the contact to non-contact modes.of electrical sine source approximately increases with the DCinput voltage if the driving frequency is constant.From Fig.13,the driving speed indicating a speed of the driving shaft almostequals the driven speed indicating a speed of the driven shaftfor the coupling mode of the clutch mechanism if a low DCinput voltage(7V)is supplied.Each speed is varying from 20to 23rps.Here,rps means the revolution per second.Also,thedriving speed is up to 29rps,and the driven speed is down tozeroforthenon-couplingmodeoftheclutchmechanismifahighDC input voltage(8V)is supplied.Therefore,a function ofthe clutch mechanism from the coupling to non-coupling modeis enhanced by increasing the DC input voltage or the amplitudeof the sine source if the driving frequency is constant.Next,effects of driving frequencies on the speeds are stated.From Fig.14(a)(d),the driving and driven speeds are almostunaffected by driving frequencies from 70 to 80kHz,and thedrivingspeedisapproximatelyequivalenttothedrivenspeedforthe coupling mode if a low DC input voltage(7V)is supplied.Each speed is varying from 20 to 23rps.But these speeds arehighly affected by the frequencies if a high DC input voltageK.-T.Chang et al./Sensors and Actuators A 141(2008)515522521Fig.16.Friction time-response of the facing surfaces in the members.(8V)is supplied.For example,the driving speed approxi-mately equals the driven speed for the coupling mode at thelow frequencies(73.0kHz)or high frequencies(78.5kHz).Each speed is still varying from 20 to 23rps.Notably,the drivenspeed is greatly down to zero,and the driving speed is slightlyup to 29rps at the frequency of 76.0kHz due to the change fromthe coupling to non-coupling mode if a high DC input voltage(11V)is supplied.Therefore,the clutch mechanism can beused for speed variation in the driven part if the piezoelectricbuzzer in the driving or driven member is electrically energizedat the frequency of 76.0kHz near the resonant frequency of thepiezoelectric buzzer under different voltages.Regarding the transient response of the driven speed,theresponse time(=1.5s,as shown in Fig.15(a)under the condi-tion of change from the non-contact to contact modes slightlyexceeds that(=0.9s,as shown in Fig.15(b)under the condi-tion of change from the contact to non-contact modes.FromFig.15(a)and(b),the driven speed of the non-contact mode iszero,and that of the contact mode is approximately 22rps insteady state when one of the buzzers in the clutch is electricallyenergized by the driving voltage(i.e.Vdc=12V)and the opera-tion frequency(i.e.f=76.0kHz).To measure the transient andsteady results of the driven speed indirectly,a mini DC motor(TS10SA,Teco Electric Inc.,Hong Kong,China)with 25mmlength,20.1mm width and 15.1mm height for playing the gen-eratingorsensingroleisconnectedtotheendofthedrivenshaftalong an aligning axis.For specifications of the DC motor,theterminal voltage almost equals the generated voltage which islinearlyincreasedwithrotationalspeedunderopen-circuitoper-ations if the DC motor plays the generating role.Meanwhile,aslope of a linear relationship between the terminal voltage andtherotationalspeedisapproximately6.8mV/rps.Fromthemea-sured results,the terminal voltage of 150mV in the DC motorapproximately indicates the driven speed of 22rps in the clutch.Based on the above results,a friction time-response of thefacing surfaces of the members is discussed.From Fig.16,thefacing surfaces are fully contact with each other,and the drivinganddrivenshaftsarestaticatthepoint(I)ifthedriveconditions,including VM=Vdc=0V,are used.Then,the facing surfacesare still fully contact with each other,and the static friction,fs,between the facing surfaces is increased from zero to themaximum static friction,fs,max,at the path(II)if the drive con-ditions,including VM3V and Vdc=0V,are used.Moreover,the facing surfaces are contact with each other by points,andthe maximum static friction is down to the kinetic friction,fk,at the path(III)if the drive conditions,including VM=3V andVdc7V,areused.Furthermore,thefacingsurfacesarenotcon-tact with each other,and the kinetic friction is almost constantby using a strong ultrasonic levitation in the space between thefacing surfaces at the path(IV)if the drive conditions,includ-ing VM=3V and Vdc8V,are used.The critical point shownin the top of Fig.16 indicating the maximum friction will be522K.-T.Chang et al./Sensors and Actuators A 141(2008)515522measured or estimated by friction measuring devices or