Keywords Wireless Inertial Measurement Unit (WIMU). Kalman Filter, Motion Tracking, algorithms.

Transcription

1 Moion Trcing Algorihms for neril Mesuremen Jvier Torres Tyndll Nionl nsiue Universiy College Cor relnd jvier.orres@yndll.ie Brendn O Flynn Tyndll Nionl nsiue Universiy College Cor relnd boflynn@yndll.ie Philip Angove Tyndll Nionl nsiue Universiy College Cor relnd pngove@yndll.ie Frn Murphy Tyndll Nionl nsiue Universiy College Cor relnd fmurphy@yndll.ie Cin O Mhun Tyndll Nionl nsiue Universiy College Cor relnd omhun@yndll.ie ABSTRACT n his pper, we describe he developmen of he sofwre lgorihms required o inerpre sensor d developed by werble miniurized wireless ineril mesuremen uni MU o enble rcing of movemen Trdiionlly, ineril rcing hs involved he use of off he shelf moion sensors in he form of n ineril mesuremen uni, in combinion wih GPS bsed receiver sysem for improved ccurcy. Severl immedie concerns re eviden when low cos, low power consumpion, miniurised soluion is needed in pplicions such s niml rcing. GPS soluions hve proven o be cosly requiring n epensive sellie lin & enil power supply nd size concerns when deployed on live nimls. n priculr pplicions, GPS coverge is no vilble for ll pplicion scenrios nd lernive mechnisms for moion rcing re required. MUs cnno be used in isolion for bsolue posiion rcing, since n MU clcules posiion uilising squre funcion of ime where he error is proporionl o he smpling ime, ny errors in he oupu of he sensors re herefore lso muliplied by ². This ypiclly leds o lrge posiionl errors in operion: These issues cn poenilly be ddressed by using only low cos modulr MU soluion o enble he mpping of movemen if pproprie lgorihms re implemened The gol of his pper is o presen mhemicl lgorihm h enbles n ineril -bsed rcing sysem o be relized. This lgorihm could hen be used wih GPS GPS is commonly used bu here re oher mehods lie ringulion long wih Klmn Filer lgorihm providing n ccure - Dimensionl rcing sysem. Keywords Wireless neril Mesuremen Uni WMU. Klmn Filer, Moion Trcing, lgorihms.. NTRODUCTON Auonomous posiion mpping cn be relized using miniurized wireless MU wih -is sensor oupus indicing ccelerion, ngulr velociy & mgneic field. Using his informion s inpus o sysem of equions represening MU moion, he resuln posiionl displcemen, ngulr roion & compss orienion relive o he erh s mgneic field, in ll - es cn be relized. This posiionl d could for insnce be uilised wih GS mpping sofwre o see he movemen of he body eiher in rel ime following d downlod, or inerc direcly wih he environmen [], depending on he pplicion. The inheren drif common in ll MU sensors cn be compensed for using n ddiionl sysem s pproprie e.g. n RFD sysem o give zero origin dum poin correcion, or noher pplicion specific zeroing mechnism GPS, ringulion ec.. Furhermore filering lgorihms such s Klmn filering [] [] [4] or digil filering of he sensor oupus cn be enbled for improved ccurcy.. WMU Hrdwre Developmen The 5mm WMU, hs been described previously [5], nd is 6 DOF MU module, which is mde up of n rry of ineril sensors coupled wih high resoluion nlog o digil converer ADC. The 5mm WMU module uilises he wireless communicion cpbiliies of he 5mm wireless node [6] [7] o relise fully uonomous WMU module. Cegories nd Subjec Descripors D..4 Algorihms, B.4. D Communicions Devices, E. D Srucures, F.. Numericl Algorihms & Problems Generl Terms Algorihms, Mesuremen, Design, Relibiliy, Eperimenion Permission o me digil or hrd copies of ll or pr of his wor for personl or clssroom use is grned wihou fee provided h copies re no mde or disribued for profi or commercil dvnge nd h copies ber his noice nd he full ciion on he firs pge. To copy oherwise, or republish, o pos on servers or o redisribue o liss, requires prior specific permission nd/or fee. Conference 4, Monh, 4, Ciy, Se, Counry. Copyrigh 4 ACM -58--//4 $5.. Figure. Tyndll's 5mm WMU Module

2 The wireless node hs n inegred ATMEL ATMeg8 [8] microconroller for he developmen of cusomised embedded proocol lgorihms for he neworing of he modules. This feure coupled wih he.4ghz rnsceiver, RF Nordic nrf4 [9], produces very powerful cusomisble wireless node. Alernive implemenions enble he Zigbee EEE communicions in he 5mm form fcor if required. The 5mm WMU cn be seen in Figure. The ineril sensor rry consiss of hree single is gyroscopes, ADXRS5 [] from Anlog Devices, wo dul is cceleromeers, ADXL [] from Anlog Devices, nd wo dul is mgneomeers, HMC5L [] from Honeywell. The sensor rry ws designed wih novel D srucure, which produces he 6 required degrees of freedom DOF necessry o deermine posiion. The module lso hs - bi ADC chip, AD749 [] from Anlog Devices, hndling he d conversion. This chip hs Seril Peripherl nerfce SP, which llows esy inerfcing o he ATMEL microconroller, s oulined in Figure. The Roc n Roll pplicion ws developed o provide visul nlysis of he sensor d being produced by he WMU. This pplicion llowed for he viewing of he sensor signls in rel ime nd conined inegred clibrion rouines h llowed for he clculion of he resoluion of ech he sensors. The oscilloscope syle inerfce of he Roc n Roll pplicion cn be seen in Figure. Figure. WMU Bloc Digrm The D srucure ws implemened using moherbord/dugherbord configurion. Miniure slos were drilled in he moherbord o llow he dugherbord o be oriened 9 ngle wih respec o he moherbord. The moherbord nd dugherbord were designed so h heir respecive pds would regiser ccurely nd llow for 9 solder connecion. The moherbord ws configured so he sensors would me up he relevn rry o genere he 6 degrees of freedom required for he module.. 5mm WMU Chrcerision The WMU module hs been developed using off he shelf componens from suppliers such s Anlog Devices nd Honeywell. The performnce of he module hd o be esed for bsic funcionliy nd hen for he generion of se of sysem specificions. A number of eperimens were designed nd eecued o crry ou his chrcerision. The sysem ws conneced o PC wirelessly o log he informion received from he WMU for off bord nlysis. Ech of he sensors ws subjec o condiions h ecied he respecive sensing properies il, roion, mgneic field nd he resuls were recorded nd compred o mnufcurers specificions. The cceleromeers were subjec o il eremes o mesure he m, min nd zero offses. The gyroscopes were ecied using clibred roing ble while he mgneomeers were ecied using Helmholz coil se up. All of he d ws recorded nd nlysed used cusomised C pplicion. Figure. Roc n Roll Applicion The Roc n Roll pplicion lso hs Klmn Filer module inegred o enble he fusion of he sensor signls nd rel ime monioring of he orienion of he module. Using his pplicion, he Gyroscopes, Acceleromeers nd Mgneomeers were ll esed nd shown o be woring wihin he epeced prmeers. The Gyroscopes recorded sensiiviy ws wihin % of he epeced vlue. The Acceleromeers ll produced sensiiviy fcors wihin 5% of heir epeced specified vlues. The mgneomeers were shown o hve reduced sensiiviy bu sill minined sub degree resoluion for high specificion nvigion pplicions. Rese of he mgneomeers under conrol of he microconroller s required increses drmiclly he resoluion of he mgneomeers.. Sensor Chrcerision.. Acceleromeers As he nme suggess, he MU provides ineril ccelerion mesuremens, herefore resuling mesuremens mde by he cceleromeers re sum of effecs due o liner ccelerion, orienion of he plform wih respec o he grviy vecor, ngulr ccelerion of he plform s i moves round curve, he effecs of he Coriolis force, nd finlly he cenrifugl ccelerion cused by he erh roion round iself. gnoring he ls wo ccelerion componens we cn consider h he mesuremens mde by he cceleromeers re in fc sum of effecs due o liner ccelerion, orienion of he plform wih respec o he grviy vecor nd ngulr ccelerion of he plform s i moves round curve [4]. However cceleromeers sensors will be mosly sensiive o he grviy vecor elemen nd herefore cn lso be used s il sensor [5], heir role when used s n inclinomeer cn be improved by using n pproprie low pss filer.

3 .. Mgneomeers The mgneomeers inegred ino he MU sysem mesure he erh mgneic field on hree orhogonl es. Figure 6 shows he mgneomeer oupu in he Wes direcion see Figure 7 while we were chnging is orienion from norh o souh. Figure 4: Signl oupu of he cceleromeer wih sensiive is in he U direcion. Figure 4 bove grphiclly shows he signl oupu of he cceleromeer which hs is sensiive is in he U direcion see Figure 8. The firs segmen of he wve form shows he ccelerion mesured while we were chnging he U is from plne in which i s prllel o he erh s surfce o plne in which i poins owrd he erh s core nd he sensor is eperiencing force of g 9.8m/s. This is he ccelerion due o il respec o grviy. The second segmen shows he ccelerion mesured wih he sme moion s he firs secion, bu wih simulneous inclusion of dynmic ccelerion. The Erh s mgneic field inensiy is bou.5 o.6 Guss, i is pproimed wih dipole model nd hs componen prllel o he Erh s surfce h lwys poining owrd mgneic norh nd is used o deermine compss direcion. For esblishing device orienion, he ey componens of he mgneomeers sensor d re prllel o he erh s surfce nd b in he direcion of he erh s mgneic norh. These vecors cn be used o esime he direcion cosine mri i will be clled Orienion Mri from now on defined in secion 4.. The end resul of hese clculions is n orienion esimion referenced wih respec o he mgneic norh, which differs from geogrphic norh, by bou 5 degrees in geogrphic locions found in relnd. Geogrphic norh is loced he erh s roionl is nd is referenced by he meridin lines found on mps. A differen locions round he globe, mgneic nd geogrphic norh cn differ by ±5 degrees. This difference is clled he declinion ngle nd cn be deermined from looup ble bsed on he geogrphic locion... Gyroscopes Gyroscopes re ngulr velociy sensing devices. They provide he ngulr velociy round he hree orhogonl es. The firs ime inegrion of he ngulr velociy leds o he Euler ngles h re necessry o describe he orienion of he MU. The Euler ngles re usully given in eronuicl erm s Pich, Roll nd Yw See Figure 8, where: Pich is he roion round he lerl V is, Roll round he longiudinl U is nd Yw round he perpendiculr W one. Figure 6: Mgneomeers oupus Generlly i is possible o obin he orienion of he MU wih high ccurcy by fusing Gyroscope, Acceleromeer, nd Mgneomeer signls vi Klmn Filering [6,7]. n his cse, he cceleromeers re used s il sensor, under his pproch is useful o use n pproprie low pss Filer h me he cceleromeers signl more sensiive o grviy [8] nd he mgneomeers re used s compss. Figure 5. Gyroscopes oupus

4 4. neril Sysems Equions. 4. Frmes Mesuremens mde direcly from he MU re referenced wih respec o he MU sensors es, which re fied by he physicl orienion of he sensors. These es Figure 7 re clled he MU-Fied Frme nd ll he sensor oupus re referenced o his frme. 4. Algorihms Developmen for ineril MU-bsed rcing sysem The -is ccelerion & ngulr velociy sensor oupu vlues cn be combined in non-liner mri equion o give boh posiion & orienion informion. The sysem cn be visulized by using fied frme of reference for posiion mesuremen, y, z: The Erh-Fied Frme nd uilizing moving non-ineril frme u, v, w: MU- Fied Frme wih is es prllel o he MU sensors es see Figures 7, 8 nd 9 Figure 7. WMU gyro, cceleromeer nd mgneomeer lyou nd MU-Fied Frme. To enble he rcing of posiioning nd orienion, we need o reference he d o nown origin reference frme. To chieve his we use he Erh-Fied Frme Figure 8 h is defined wih is X-is prllel o he Erh s surfce nd poining owrd he Erh mgneic Norh, is Z-is prllel o he grviy vecor nd herefore perpendiculr o he Erh s surfce nd Y- is will be he cross produc beween he Z nd X es. Figure 8. Erh Fied Frme. The Orienion Mri is Mri h rnsforms ny vecor given respec o he MU fied-frme nd herefore given by he sensors oupus ino he nown reference Erh-Fied Frme. Figure 9. Moving nd Reference frmes 4.. Orienion Esimion Clculions The Orienion of he MU will hve wo sources of esimion: gyroscopes oupus nd he oupus from he cceleromeers nd mgneomeers. Gyroscopes cnno be used in isolion for obining bsolue Orienion becuse of he drif ssocied wih heir redings. Mgneomeers & cceleromeers led o orienion esimion wih long-erm sbiliy bu shorerm occsionl inccurcy due o he presence of ferromgneic merils or oher mgneic fields differen o he erh s mgneic field nd due o liner nd roionl ccelerions h disurb he orienion esimion. Thus we cn combine he dvnge of he shor-erm precision of Gyroscopes nd he long-erm sbiliy of Acceleromeers nd Mgneomeers vi Klmn Filer Orienion esimion from gyroscope oupus Every ime sep we re ble o now he Euler nglesα, φ, θ, we cn eep he order of roion nd follow i every ime sep s follows: Definiion of Angles & θ & θ θ Yw & φ & φ φ Pich & α & α α Roll 4

5 where: θ denoes he incremenl ngle round he W-is, α denoes he incremenl ngle round he U-is. φ denoes he incremenl ngle round he V-is. denoes he ime sep. nd is he ime inde. Noe h he rpezium rule hs been used in equions,&4 s numericl inegrion mehod. Given roions mri denoed s R round ech priculr is [8]: cosθ sinθ R W, θ, sinθ cosθ 5 cosφ sinφ R V, φ, 6 sinφ cosφ R U, α, cosα sinα 7 sinα cosα nd given generl roion mri [8]: Roion R W, θ, R V, φ, R U, α, 8 We define n Orienion mri s follows: Orienion Roion Orienion 9 The orienion mri conins informion bou he orienion of he MU nd he order of roion followed unil his orienion is chieved. Th mens we cn rnsle he coordines of ny vecor from he MU-Fied Frme o he Erh- Fied Frme using he Orienion Mri Orienion esimion from Acceleromeers nd Mgneomeers oupus Reminding h he Orienion Mri is Mri h rnsforms ny vecor given respec o he MU fied-frme nd herefore given by he sensors oupus ino he nown reference Erh-Fied Frme, so h he Orienion Mri rnsforms coordines from he MU-fied frme o he Erh-fied frme nd, equivlenly, is inverse rnsforms coordines from he Erh-fied frme o he MU-fied frme. Defining he Orienion Mri inverse s: Orienio n The mgneomeer mesuremens provide d regrding he erh s mgneic field on hree orhogonl es. This mgneic field vecor is used o direcly clcule he firs column of he inverse of Orienion Mri. Considering h he erh mgneic field vecor, referenced o he Erh Fied Frme, is prllel o he X is nd h H denoes he erh mgneic field mgniude in he region of ineres, hen, he Erh mgneic field coordines in he Erh Fied frme re H nd, if H u H v H w is he mgneic field vecor direcly mesured from he MU oupus, nd herefore represening is coordines respec wih he MU Fied frme, hen: Hu H Hv Hw So he Firs column of he inverse of he Orienion Mri is given s: Hu Hv H Hw As well s he mgneic vecor, he cceleromeer field vecor is used o direcly clcule he hird column of he inverse of Orienion mri. Since he grviy vecor, referenced o Erh fied-frme, is prllel o he Z is nd g denoes he grviy ccelerion mgniude, hen, he grviy vecor coordines in he Erh Fied frme re g nd, if ugrviy vgrviy wgrviy is he ccelerion field vecor direcly mesured from he MU oupus, nd herefore represening is coordines respec wih he MU Fied frme, hen: ugrviy vgrviy wgrviy g So he Third column of he inverse of he Orienion Mri is given s: ugrviy vgrviy g wgrviy 4 Finlly he second column of he inverse of he orienion mri will be direcly clculed from he cross produc beween he hird nd firs columns.

6 4.. Sysem equion for rcing posiion The generl lgorihm used o obin posiion is presened in flow-chr in Figure. Figure. neril rcing lgorihm flow chr cn be seen h hree differen elemens comprise he lgorihm: The op elemen, which corresponds o he Orienion esimion. b The middle elemen, which corresponds o he liner ccelerion ercion. c The buon elemen, which corresponds o he sysem equion for obining posiion The sysem equions for rcing posiion re hen summrized in he following se equion ] [ ] [ U U n Orienio B X Ro A X 5 Noe h he rpezium rule hs been used in equion 5 s numericl inegrion mehod. Where: z y z y X & & & re he posiions nd velociies. 6 O A 7 w v u U re he ccelerions. 8 B 9 Roion O O Ro where nd O denoe he deniy nd Null mrices respecively. The lgorihm o obin posiion uses liner ccelerion, herefore i is necessry o remove boh grviy nd cenripel force componens from he sensor d o obin he liner ccelerion in previous sep see Figure nd Figure. The Grviy ccelerion in he MU-fied frme cn be clculed s: Roion Wgrviy Vgrviy Ugrviy Wgrviy Vgrviy Ugrviy or using his oher represenion wih he Orienion Mri: g Orienion Wgrviy Vgrviy Ugrviy where g denoes he grviy ccelerion mgniude. g denoes he grviy ccelerion vecor referenced o he Erh Fied-Frme nd Wgrviy Vgrviy Ugrviy denoes he grviy ccelerion vecor referenced o he MU Fied-Frme Figure. Acceleromeer oupus n generl wo inds of roion cn e plce in generl movemen; he firs consiss of he roion of he body round iself nd he second consiss of he roion of he body round poin in he spce. This is nlogous o he movemen of he Erh which eperiences wo roionl movemens: One roion round iself nd noher one is orbi round he Sun, noher ypicl emple would be he generl movemen of spinning op. For his pplicion he firs roionl elemen cn be negleced due o is smll mgniude, he second however mus be en in o ccoun s follows:

7 ucenripel ωw ωv VU vcenripel ωw ωu VV wcenripel ωv ωu VW The cenripel force is given s he cross produc of he ngulr velociy nd he liner velociy. This velociy is he liner velociy on he MU es obined in he MU Fied-frme, ccording o he nomenclure followed; his is he velociy in he es U, V, W. 5. MU Grphicl nerfce for Orienion As n id o evluing he efficiency of he lgorihms under developmen, grphicl ool ws genered o show visully he rcing nd moion nlysis lgorihms wor. This consiss of represenion of cube on PC screen wih 6 differen colours on ech of is sides. As he ineril mesuremen uni is moved nd roed in rel ime, his movemen is wirelessly rnsmied o bse sion nd he pproprie equions in MATLAB implemened on he sensor d. The virul cube hen mps nd replices in rel ime he movemen of he rel WMU which i represens s shown in Figure. Figure. MU Grphicl nerfce for Orienion The cube is defined by eigh verices h form si sides. Figure shows he coordines of he verices defining cube in which he sides re one uni in lengh: Figure. Cube coordines The coordines of ll cube verices cn be reclculed fer ny roion using he Orienion Mri nd herefore he Grphicl inerfce for orienion consiss of collecing he d from he MU sensors nd reclculing he orienion of he rel WMU cube, before redrwing he virul cube in rel ime using hree differen lgorihms. The firs lgorihm clcules he orienion mri from he gyroscopes oupus, he second lgorihm clcules he orienion mri from he mgneomeers oupus s compss nd from he cceleromeers oupus s n inclinomeer, nd finlly he hird lgorihm clcules he orienion mri s n oupu of ll MU sensors using Klmn filer nd digil filers. This resuls in he cube on he screen mirroring he movemen nd roion of he WMU in rel ime. 6. RESULTS As niciped, he orienion esimion using only he gyroscope oupus resuled in shor-erm ccurcy of ineril mesuremen in he order of few seconds cused by he drif inheren in hese ype of sensors, since we were clculing ngles by muliplying he oupu of gyroscope by ime -, ny errors in he oupu of he gyroscope were lso muliplied by. This leds o lrge error coefficien in he ngle clculions. The described bove ws eperimened using he firs lgorihm of MU Grphicl nerfce for Orienion s described in secion 5. Orienion esimion from hree is compss uilising he mgneomeer oupus nd he d from he cceleromeers cing s il sensor resuled in n improved level of ccurcy. However he level of precision decreses when he MU is subjeced o rpid movemens, or is in presence of ferromgneic merils or oher mgneic fields ner he sensor module, s hese disurb he locl erh mgneic field nd, herefore, he orienion esimion. All of his ws observed using he second lgorihm of MU Grphicl nerfce for Orienion see secion 5. The fusion of he d from he mgneomeers, cceleromeers nd gyroscopes sensors using Klmn Filering lgorihms, long wih he use of n pproprie low pss Digil Filer h improves he role of he cceleromeers s n inclinomeer, elimined he ccurcy decrese discussed bove yielding precise D Orienion esimion which ws observed using he hird lgorihm of MU Grphicl nerfce for Orienion see secion 5. As regrds rcing of movemen, ccurcy is n issue due o sensor drif since n MU clcules posiion by muliplying he oupu of n cceleromeer by ²; ny errors in he oupu of he cceleromeer re lso muliplied by ². This leds o huge posiion errors: in jus 6 seconds, one-dimensionl MU using n cceleromeer wih n oupu noise level of jus.4 g yields posiion unceriny of bou 7 meers. For dimensionl rcing, he siuion ges worse. We cn see his effec in Figure 4, which is he resul of one of he preliminry ess we hve crried ou. Noe h his es ws crried ou prior o he implemenion of he orienion lgorihms using he mgneomeers nd cceleromeers oupus s described, nd herefore he orienion mri esimion in his cse is poor s resul of being clculed using only sensor d from he gyroscope oupus. This demonsres he requiremen for sophisiced lgorihms o mp movemen using hese ypes of sensors. Figure 4. Comprison of nown MU rjecory versus mesured es resuls

8 7. CONCLUSONS & FUTURE WORK As fr s bsolue posiion rcing is concerned, i hs been shown h MUs cnno be used in isolion for bsolue posiion rcing, however, low cos rcing of movemen using ineril MEMS bsed sensors is conceivble, uilising ddiionl nown posiion inpu updes s he sme mnner s he drif in he orienion esimion using gyroscopes ws removed using compss nd inclinomeer updes inegred in he lgorihms developed. A mhemicl lgorihm for bsolue posiion rcing, which is implemened wihin wireless ineril mesuremen uni WMU bsed rcing sysem, hs been presened. Fuure wor, will invesige vrious mechnisms o reduce he drif elemen ssocied wih ypicl ineril sensors when used for moion rcing, e.g., GPS, RFD or ringulion bsed receiver sysem o give precise posiionl updes. These posiionl updes could hen be used long wih he mhemicl lgorihm o provide n ccure -Dimensionl rcing sysem. The ccure resuls given by he orienion esimion will be he sring poin o invesige new lgorihms under n pproch differen from he serch of bsolue posiion rcing, he relive posiion rcing, h is, if we e he Humn body s n emple of his, one could use n MUs newor wih MUs ched o specific poins of he body nd use he relive orienion of ech oher long wih he inheren consrins of he humn body model e.g. fied disnce from wris o elbow nd from elbow o shoulder nd so on.. o elimine ny inegrion drif. 8. ACKNOWLEDGMENTS The uhors would lie o hn ll he members of he Ambien Elecronic Sysems em who hve conribued o he projec o de. We would lie o eend our hns o Kiern Hrney, Anlog devices Micromchining Division nd Michel Coln, SAR ADC Group Anlog Devices, for he provision of devices for his wor. We would lie o hn he Europen Commission for funding he MULTPLEYE projec in he ST progrmme ST- 58 nd he res of he MULTPLEYE consorium, he rish Nionl Ars council for heir suppor, nd we would lie o cnowledge he suppor of Enerprise relnd in funding he D-SYSTEMS projec ATRP-/7A. Thns lso o Science Foundion relnd for funding he Tyndll Nionl Access Progrm NAP under which some of his wor ws crried ou. 9. REFERENCES [] Brendn O'Flynn, Giuseppe Torre, Miel Fernsrom, Todd Winler, Andy Lynch, John Bron, Philip Angove, Cin O'Mhun " Celeris A Werble Sensor Sysem for nercive Digil Dnce There Proc, BSN7 - Body Sensor Newors, 4h nernionl Worshop on Werble nd mplnble Body Sensor Newors [] G. Welch nd G. Bishop, An nroducion o he Klmn Filer. Upded 4. Deprmen of Compuer Science, Universiy of Norh Crolin. [] P. Zhng, J. Gu, E. Milios nd Peer Huynh Nvigion wih MU/GPS/Digil Compss wih Unscened Klmn Filer. Proceedings of he EEE nernionl Conference on Mechronics & Auomion, Nigr Flls, Cnd. July 5. pges 497-5, 5 [4] Dn Simon. Using non Linel Klmn Filering o esime signls nd Klmn Filering. Clevelnd Se Universiy, Deprmen of Elecricl nd Compuer Engineering. [5] A Lynch, B Mjeed, B O Flynn, J Bron, F Murphy, K Delney, S C O Mhun A wireless ineril mesuremen sysem WMS for n inercive dnce environmen, Proc. Sensors & heir Applicions X,, Greenwich, Ken, Englnd, pp 95-, Sepember 5. [6] Brendn O Flynn, S. Bellis, K.Mhmood, M. Morris, G. Duffy, K. Delney, C. O Mhun, A -D Miniurised Progrmmble Trnsceiver Microelecronics nernionl, Volume, Number, pp. 8-, 5. [7] hp:// [8] hp:// d8 [9] [] hp:// 5.pdf [] hp:// E.pdf [] hp:// [] hp:// [4] J. Robers nd P. Core nd J. Cunninghm nd B. Coo Eperimens in Auonomous Underground Guidnce Proceedings of he 997 EEE nemionl Conference on Roboics nd Auomion, Albuquerque, New Meico, pp 898-9, April 997. [5] B. Kemp, A. J. M.W. Jnssen, nd B. vn der Kmp, Body posiion cn be moniored in -D using miniure cceleromeers nd erh-mgneic field sensors, Elecroencephlogr. Clin. Neurophysiol. /Elecromyogr.Moor Conr., vol. 9, pp , 998. [6] Hen J. Luinge nd Peer H. Velin, Member, EEE nclinion Mesuremen of Humn Movemen Using -D Acceleromeer Wih Auoclibrion, EEE Trnscions on Neurl Sysems nd Rehbiliion Engineering, VOL., NO., pp -, MARCH 4 [7] Dniel Roeenberg, Hen J. Luinge, Chris T. M. Ben, nd Peer H. Velin, Member, EEE Compension of Mgneic Disurbnces mproves neril nd Mgneic Sensing of Humn Body Segmen Orienion EEE Trnscions on Neurl Sysems nd Rehbiliion Engineering, VOL, NO., pp 95-45, SEPT 5 [8] hp:// cion.pdf