Analysis of Measurement System as a Mechatronics System

Transcription

1 Analysis of Masurmnt Systm as a Mchatronics Systm M. RYBOKAS, D. BRUČAS, L. ŠIAUDINYTĖ 3, L. PUPEIKIENĖ 4,, 3, 4 Vilnius Gdiminas Tchnical Univrsity,, 3, 4 Saulėtkio ally, Vilnius LITHUANIA mindaugas.rybokas@vgtu.lt, domantas.brucas@vgtu.lt, 3 lauryna.siaudinyt@vgtu.lt, 4 lina.pupikin@vgtu.lt Abstract: - Th papr dals with th us of a mchatronic approach to an angl masuring systm application whr th objcts to b masurd ar circular rastr scals, rotary ncodrs and codd scals. Th ky task of th masuring systm is to dtrmin th bias of th angl masuring standard as a circular scal and to us th rsults for both rror corrction and achiving an improvmnt in accuracy of mtal cutting machins, coordinat masuring machins, robots, tc. Th tchnical solutions ar givn, togthr with th application of activ matrials for smart pizoactuators implmntd in svral positions of th angular masuring quipmnt. Th mchatronic masuring systm is analysd as a compl intgratd systm and som of its lmnts can b usd as sparat units. All ths functional lmnts ar dscribd and discussd in som dtail in th papr using diagrams and graphs illustrating th rrors prsnt, togthr with ampls of microdisplacmnt dvics using mchatronic lmnts of this typ. Ky-Words: - angl masurmnt systm, pizoactuators, mchatronics, accuracy, rror corrction. Introduction Th main constitunts of th masuring systm discussd in this work ar an air baring (of high prcision whr th uncrtainty of th run-out is ~ 0.05 µm), a rfrnc angl masurmnt dvic (a rotary ncodr of high accuracy), a pizolctric driv, a rotary adjustabl tabl (with th possibility of bing adjustd in at last thr dgrs of frdom), angular position rading dvics for th objct to b masurd (photolctric microscops or autocollimators with CCD matrics) and fiturs for thir adjustmnt in th radial, tangntial and angular dirctions. In addition, th systm involvs using signal outputs from all th activ lmnts bing inputtd to a PC, togthr with hardwar and softwar dsignd for us in systm adjustmnt, th control of th opration, transfr of th radings and procssing and prsntation of th rsults. Tchniqus for angl calibration hav bn dvlopd using mchatronic mthods. Th calibration quipmnt for th angl masurmnt compriss a numbr of lmnts spanning th filds of optics and lctronics, including drivs such as vibromotors and pizolctric or stppr motors, togthr with digital information links and data procssing tchniqus, involving computr control of all th procsss, making this quipmnt typical of mchatronic systms today. Th tchnical units from th tst bnch which ar linkd togthr includ information channls, photolctric microscops and an autocollimator, an optical standard multiangular prism (polygon) and a rotary tabl drivn by th stppr motor and controlld by photolctric rotary ncodr and a PC. Th PC srvs as th main control unit oprating not only for th control of th masuring procss, but also for th data slction and procssing oprations including mathmatical statistical valuation and th prsntation of th final rsults in th form of digital protocol or th diagrams of th rror distributions []. Prcision Positioning Evaluation It is important to dtrmin th quantity of information that can b obtaind from an objct that has bn valuatd in ordr to provid a mor thorough assssmnt and bttr accuracy during th calibration procsss. Th main problm that ists ariss from th significant amount of information that is obtaind in th calibration of scals, from masuring systms involving numrically-controlld machins and automatd masuring quipmnt such as ISBN:

2 coordinat masuring machins (CMMs), for ampl. Th typical lngth masurmnt intrval, in th cas of an valuation of th accuracy (th calibration) is such that fwr than 0 positions could b masurd, as it is indicatd in CMM tchnical documntation. This can hlp in th dtrmination of th impact of mchatronic systms on ths informationmasuring systms to achiv an limination of any systmatic rrors. Pizoplats and simplifid systms using pizomatrials ar usd to achiv micromtric displacmnt, to allow for th corrction of th systmatic rrors on th rastr scal. Th corrction of rrors occurs by control of th pizoplat, achivd by changing a voltag supplid to th lctrod lctromchanically coupld to th rastr scal, changing th width of th lctrod coating of th pizoplat. According to th principl of δu minimum of potntial nrgy 0, and taking δε into account that longitudinal displacmnts ar rlatd to dformations by th du rlationship ε ( ), it is possibl to obtain th d quation that rprsnts th quilibrium of th pizoplat that is usd and to control th accuracy achivd from a linar rastr scal. Th distributions of rrors for two-dimnsional or thr-dimnsional masuring systms can b prssd by two functions uy (, ) kδ ( y, ) and vy (, ) kδ y ( y, ), whr u, v ar th componnts of displacmnts at th zon controlld into th dirction of th appropriat coordinats and k, k ar th cofficints of th lctromchanical coupling. For a mor act assssmnt of th rror distribution and to allow for possibl corrctions, th rlativ ntropy paramtrs must b valuatd [5]. A pizolctric systm that was usd is shown in Fig. for incorporation in a rotary tabl usd for angl masurmnts, usd for th masurmnt of circular rastr and codd scals in conjunction with th stroks rading instrumnts with th photolctric microscops or th autocollimators usd for angl position dtrmination. Information on th rotation can b usd for manual control or an automatd systm dvlopd so that it is controlld by th output signal from th rotary ncodr. This can hlp in th dtrmination of th impact of this mchatronic dvic on th informationmasuring systm, thus allowing for th limination of systmatic rrors. A cas whr scal rrors hav bn corrctd is prsntd in th litratur [7, 8]. Pizoplats and simplifid dvics constructd from pizomatrials wr usd to achiv a micromtric displacmnt to allow for th corrction of th systmatic rrors of th rastr scal. Th corrction of such rrors is achivd through th voltag applid to th lctrod lctromchanically coupld to th rastr scal, changing th width of th lctrod coating of th pizoplat. Fig.. Eprimntal rotary tabl with th mchatronic parts Th rlativ ntropy is considrd in assuming th distribution of th random valu of q whn th tru distribution of this variabl is p. Basd on th planations givn abov, th mutual information approach appars to b th most accptabl mthod to allow for an assssmnt of th multi-coordinat masuring systms. This mutual information modl for 3D masurmnt is discussd blow. Hr th, y and z as ar subdividd into k, l and m stps (divisions), rspctivly, and Δ is th lngth of a singl stp of th scal of th information-masuring systm. Thrfor, th intrvals of th masurmnt valus tnd to 0 k, 0 y l and () ISBN:

3 0 z m. If all dimnsions ar indpndnt of ach othr, no information can b gaind about any of th variabls by fiing th valu in on dimnsion. Th cas whr th two rmaining dimnsions ar fid producs analogous rsults using th prvious quations: pxy (, Z) IXY ( ; Z) pyz (,, ) log p ( X Z ) py ( Z ) whil th m s and th σ s ar th mans and th standard dviations of th random variabls indicatd by th inds, rspctivly. In Fig. th rlationship btwn th total numbr of stroks on th scal m, its information, I, and th numbr of th strok positions alrady assssd on th scal b is displayd. It is assumd that th bas of th logarithm is. log kl log 0 klm klm k l () Th gnral prssion for a bivariat normal distribution is givn by th formula: py (, ) πσ σ r y y ( m ) ry ( m )( y my ) ( my ) + ( ry ) σ σσ y σy (3) Th prssions for th bivariat conditional normal distributions to b placd in th dnominator of quation () ar providd blow as: y my z m z r yz ( ryz ) σy σ z p( y z) σ r π y yz, (4) m z mz rz ( r ) σ σz z p ( z) σ r π z, (5) whr th r s ar corrlation cofficints btwn th corrsponding random variabls,. Fig.. Th rlationship btwn th total and assssd numbr of stroks with th quantity of information of th scal, whr m is th numbr of stroks on th scal, b is th numbr of th assssd stroks on th scal and I is th quantity of information 3 Thr Dimntional Cas Th masurmnts of th gomtrical paramtrs of th parts concrnd ar usually prformd using vry pnsiv 3D masuring quipmnt coordinat masuring machins (CMMs) having a high prcision mchanical bas quippd with vry high prcision slidways. Such CMMs ar ampls of highly compl, prcis and vry pnsiv quipmnt. Th most prcis mthods ar usd for th assssmnt of th accuracy of ths CMMs, to allow th us of mchatronic tchniqus for making corrctions. This approach is usd only at th initial phas of production of such machins and any furthr accuracy assuranc is carrid out using th ISBN:

4 mchatronic dvics, controlld by th PC that forms part of th masurmnt systm. Th main task hr is to dtrmin th corrctional displacmnt valus for all th rlvant co-ordinat displacmnts by us of a sris of calculations and thn to prform th additional movmnt rquird using th final part of th kinmatic chain of th machin. Eampls of this includ th grip on th arm of an industrial robot, th prob forming part of a CMM (a masuring robot), th cutting instrumnt of a mtal cutting tool, tc. In this cas, pizolctric plats, mad from cylindrical or sphrical componnts ar important dvics to b incorporatd into th final machin lmnt to achiv th corrctional microdisplacmnt rquird. Th final lmnt of CMM, a touch-prob with a pizolctric cylindr and th lctrods to provid th powr, is shown in Fig.3. Th pizolctric activ lmnts also ar implantd into th sliding parts of th machin i.. th consol moving along th y-ais, th carriag moving along th -ais and th arm with th touchprob moving in th dirction of th z-ais. Nw, activ matrials with high pizolctric or magntostrictiv proprtis (Trfnol-D, flibl pizoactiv matrials, tc.) show considrabl applications potntial with a high lvl of intgration and multi-functionality [9]. Thy may b implmntd as shown in Fig. 3, giving th possibility of achiving a corrction of th position of th part in 3D spac, thrby compnsating th systmatic rror in th masurd displacmnt. Final (instrumnt s) position Coordinat displacmnt corrction, Part s position Fig. 3. Corrction of displacmnt monitoring or th tip of cutting (masuring) instrumnt. Th mthods usd prmit th control of th accuracy of th displacmnt of various parts of th machin, or of th transducrs or th final lmnt in th kinmatic chain, such as th touch-prob or th cutting tool of th machin. 4 Conclusion An approach using mchatronic tchniqus for masurmnt using angl masuring systms is dscribd, thrby giving information on th accuracy of th angular displacmnt and dtrmining valus of rrors that could thn b corrctd by us of mchatronic tchniqus. Information is givn which allows th valuation of th calibration of th circular scals or rotary ncodrs and in addition giving information on what was assssd in total during this procss. Thus an ffctiv computrcontrolld rotary tabl for angular masurmnts has bn dvlopd for th masurmnt of th circular rastr scals, rotary ncodrs or angl masuring instrumnts. 5 Acknowldgmnts An approach using mchatronic tchniqus for Rfrncs: []. Bansvičius, R.and Tolocka, R. T. Pizolctric actuators. R. H. Bishop, Ed. in Chif. Th Mchatronics Handbook, CRC Prss; 00, pp []. Giniotis, V., Grattan, K.T.V., Rybokas, M.and Kulvitin, R. Uncrtainty and indtrminacy of masurmnt data, Masurmnt, Vol. 36, No, pp. 95-0, 004. [3]. Bansvicius, R., Giniotis, V. Mchatronic mans for machin accuracy improvmnt, Mchatronics, Vol., 00, pp [4]. Ash, R. B. Information Thory, Dovr Publications, Nw York, 990. [5]. Giniotis, V.; Rybokas, M.; Dmitrijv, G.; Sabaitis, D.; Šiaudinytė, L.a; Janulvičius, J.. Mchatronic lmnts for masuring systms // Mchatronic Systms and Matrials V. Solid Stat Phnomna. Switzrland : Trans Tch Publications Ltd. (Solid Stat ISBN:

5 Phnomna, Vol. 99, ISSN ). ISSN ISBN , Vol. 99, p [6]. Probst, R. Rquirmnts and Rcnt Dvlopmnts in High Prcision Angl Mtrology, Th 86th PTB-Sminar, 5 th Nov. pp. 4 3, 003. [7]. Bručas, D., Giniotis, V., Ptroškvičius, P. Th construction of th tst bnch for calibration of godtic instrumnts, Godzija ir kartografija (Godsy and Cartography), 006, Vol. XXXII, No. 3, pp [8]. Giniotis, V. and Grattan, K. T. V. Optical Mthod for th Calibration of Rastr Scals, Masurmnt, 00, Vol. 3/, p [9]. Rybokas, M.; Dmitrijv, G.; Šiaudinytė, L.; Bručas, D.. Th dtrmination of masurmnt accuracy using information ntropy // Vibronginring. Journal of Masurmnts in Enginring (JME). Kaunas : Vibromchanika. ISSN Vol., iss. (03), p ISBN: