Myoelectric Control Strategies for a Human Upper Limb Prosthesis

Transcription

1 CEAI, Vol.4, No., pp , 202 Print in Romni Myoltri Control Strtgis for Humn Uppr Lim Prosthsis Sorin Hrl, Srgiu Mn, Ghorgh Lz, Pul Ri Thnil Univrsity of Cluj-Npo, Dprtmnt of Automtion, G. Britiu Str., , Cluj-Npo (-mil: {Sorin.Hrl, Srgiu.Mn, Ghorgh.Lz, Astrt: Myoltri ontrol is nowys th most us pproh for ltrilly-powr uppr lim prosthss. Th myoltri ontrollrs us ltromyogrphi (EMG) signls s inputs. Ths signls, ollt from th surf of th skin, hv to prpross for ing us s inputs for th ontrollr. In this ppr w prsnt lssifir for surf ltromyogrphil signls s on n utorgrssiv (AR) mol rprsnttion n nurl ntwork, n two myoltri ontrol strtgis s on Finit Stt Mhin. Th rsults hv shown tht omining low-orr AR mol with f-forwr nurl ntwork, rt of lssifition rnging from 9% to 98% n hiv, whil kping th omputtionl ost low. On of th min vntgs of th propos strtgy is th ru ffort rquir to th ptint for ontrolling th prosthti vi. Kywors: EMG signl, myoltri ontrol, finit stt mhin, nurl ntwork, utorgrssiv mol. INTRODUCTION Th noninvsiv ttion of th signl on skin surf, with no n of surgry for th ptint, n th rltivly smll musl tivity rquir to provi ontrol signls r nfits tht mk myoltri ontrol th most wily us pproh for th ontrol of uppr lim prosthss (Hung t l.,2005), (Ping t l., 2006), (Chn t l., 2005), (Light t l., 2002). In orr to tt th movmnt intntion of th ptint, mny vis n us suh s: surf ltromyogrphi (SEMG) snsors, ortil n priphrl nrv implnts, implntl myoltri snsors, t. Th sist wy to tt th movmnt intntion is to us SEMG snsors. Although th myoltri prosthsis uss iologil signls to ontrol its movmnts, grt mntl ffort is rquir spilly uring th first months ftr fitting (Sors t l., 2002). This hppns us th prosthsis ontrol is vry unnturl; signls ollt from ru numr of musls r us to tivt movmnts tht r normlly ontroll y othr nrvous signls. Morovr, th ffort rquir to ontrol myoltri prosthss inrss with th lvl of mputtion. W propos two myoltri ontrol strtgis pl of ruing th rquir ffort. Our ontrol strtgis r s on hirrhil ontrollr. Th highr lvl of th ontrollr, implmnt using Finit Stt Mhin, is prsnt in this ppr. In th s of th first ontrol strtgy four lmntry motions of th prosthsis: opn hn, los hn, rott insi n rott outsi, n initit irtly y th ptint using SEMG signls ollt from snsors mount on xtnsor ommunis igitorum n flxor rpi rilis musls. In th s of th son ontrol strtgy six motions of th prosthsis: lowr rm flxion, lowr rm xtnsion, rott hn insi, rott hn outsi, los hn, n opn hn, n initit y th ptint using SEMG signls ollt from ips, trips n ptorlis mjor musls. Th first ontrol strtgy n us for ptints with n mputtion t wrist lvl n th son ontrol strtgy for ptints with n mputtion t th lowr rm lvl. For oth strtgis th lowr lvl of th ontrollr finlizs ths motions using lol los loop. Sin th ptint must only initit movmnt, th ffort rquir to ontrol th prosthsis will rs. As th following stions will show, th propos strtgis n ppli to ptints with ru musulr tivity. In signing myoltri ontrollrs, two min pprohs r us: th non-pttrn rognition- n th pttrnrognition s pproh (Oskoi t l., 2007). In th tgory of non-pttrn rognition-s mthos r inlu, mong othrs, proportionl ontrol (Prkr t l.,2006), finit stt mhins (Moon t l., 2005), (Flzr t l., 2002), or thrshol ontrol (Sun t l., 2005). Proportionl ontrol uss th lvl of ontrtion of musl to ltr th sp or for of prosthti lim. Du to th omplxity of SEMG signl it is mntory to prpross th signl quir y snsors for using it s input for th proportionl ontrollr. Evn if it is sy to implmnt, it rquirs grt ffort for th ptint to prmnntly ontrol th prosthsis. Thrfor, this typ of ontrol is not suitl for ptint with low musulr tivity. Proportionl ontrol

2 CONTROL ENGINEERING AND APPLIED INFORMATICS 59 is typilly us in onjuntion with othr non-pttrn rognition-s or pttrn rognition-s mthos to inrs th ury of positioning. Finit Stt Mhin-s myoltri ontrol ws ppli y mny rsrhrs to riv rhilittion vis lik whlhirs (Moon t l., 2005), (Flzr t l., 2002), uppr n lowr lim prosthss, ssistn roots (Zhng t l., 2009), t. Using th finit stt mhin mtho, th ontrollr is sri y finit numr of pr-fin stts, trnsitions twn thm, n ommns. Th min rwk of this pproh is th ru numr of tions tht n implmnt. Howvr, th ru numr of motions prform y uppr-lim prosthsis mks this pproh suitl for implmnttion. In thrshol ontrol, signl lvl is us to isrimint twn two stts. If th mplitu of th surf EMG signl is ovr thrshol, ommn will gnrt. Fig. illustrts this mhnism. prours us to quir th surf EMG signls r prsnt in Stion 3. Th implmnt lssifirs us in our ontrol rhitturs r prsnt in Stion 4. Stion 5 will prsnt th high-lvl ontrollr s rhitturs. Th prformn of our pprohs is nlyz in Stion 6, n th finl onlusions r prsnt in Stion THE ARCHITECTURE OF THE MYOELECTRIC CONTROLLER Our ontrol strtgis r implmnt using th myoltri ontrol systm rhittur prsnt in Fig.2. Musls Dt quisition systm Eltromyogrphi snsors n goniomtrs Amplifir () Ptorlis mjor EMG snsor Commn gnrtor s on thrshol Convrtr () Fig.. () SEMG signl ror, () Thrshol ontrol ommn gnrt Th prformn of this typ of ontrollr n fft y mny ftors lik th hrtristis of th quisition systm us to tt n pross th ltromyogrphi signls, th ntomil n physiologil proprtis of musls, th position of th snsors on th skin n th musl ftigu (D Lu, 997) t. Clssifir Fturs xtrtion Autorgrssiv moling Fturs prossing Nurl Ntwork Controllr High lvl ontrollr Finit Stt Mhin Th lssifition of EMG signls is vry importnt prolm to rss for ny myoltri ontrollr. It hs th rol of hiving rtin lss ll for h input (.g. flxion, xtnsion, t.). Mny lssifition lgorithms s on pttrn-rognition mthos wr propos in rnt yrs. Th grtst suss in myoltri ontrol hs n rliz y pttrn rognition s ontrollrs using nurl ntworks (NN) (Englhrt t l., 999), fuzzy logi (Mir t l, 2000) n nurl-fuzzy systms (Krlik t l.,2003). Bus th rl-tim onstrints r n importnt issu, thr is tr-off twn th roustnss, rquir tim for lssifition n th omputtionl powr rquir. Th rminr of this ppr is orgniz s follows. Stion 2 sris th rhittur n th funtionlity of th ontrol systm propos. Th t quisition systm n th Prosthsis Low lvl ontrollr Sp, position n for ontrol Fk snsors -position -for -sp Fig. 2. Myoltri ontrol systm rhittur Th t quisition systm ompriss SEMG snsors, n mplifir n onvrtr. Th SEMG signls r ollt using singl iffrntil SEMG snsors. Th signls r mplifi, filtr n onvrt from nlog to igitl.

3 60 CONTROL ENGINEERING AND APPLIED INFORMATICS Bus of th omplxity of SEMG signl, it is not fsil to intify movmnt irtly from th quir signl. Thrfor, first imnsionlity rution hs to ppli, using th ftur xtrtion moul of th lssifir. Th purpos of this moul is to xtrt st of fturs hrtrizing th signl. Thy r furthr us s inputs for th ftur prossing moul tht will isrimint four lsss of signls. A til sription of ths lsss will prsnt in Stion 4. In th s of th first ontrol strtgy th four outputs of th lssifition lok r ppli to th high lvl moul of th ontrollr. In th s of th son strtgy itionlly to th four outputs of th lssifition lok, n output from th ptorlis mjor musl is ppli to th high lvl moul of th ontrollr. Thn, th high lvl ontrollr omputs ommns for th low lvl ontrollr. Th low lvl ontrollr will ontrol oring with th ptint intntion, th movmnts of th prosthsis vi using los loop ontrol shm. Du to th smll mplitu of th SEMG signl (μv to mv), th quir signl is fft y nois. In orr to inrs s muh s possil th ury of th signls quir th nois ws rfully onsir. A 2 n orr noth filtr ws implmnt for supprssing th 50 Hz frquny nois gnrt y th min lin. Th istn twn th ltros n lso fft th qulity of th signl tt (Mrltti t l., 2004). To limint this prolm, th snsors mnufturr us fix istn of 0 mm twn ltros. Th SEMG signls wr mplifi y ftor of Th SEMG signl quisition for th first ontrol strtgy Th positions of th snsors on th uppr lim r illustrt in Fig. 5 n Fig DATA ACQUISITION SYSTEM Fig. 3 illustrts th omponnts of th Bgnoli 4 t quisition systm ( us in our work. 2 3 Fig. 5. Position of th snsors (outsi viw of th forrm): - SEMG snsor, 2-smll goniomtr, 3- lrg goniomtr. Fig. 3. Bgnoli 4 quisition systm for SEMG signls: -top right: th min mplifir; -ottom lft; th input moul; -top lft: th onvrtr. Th mplifir unit (Fig. 3, top right) hs gin ftor justl from 0 to 0000 n nwith twn 20 n 450 Hz ±0%. Th singl-iffrntil SEMG snsors, illustrt in Fig.4, wr onnt to th mplifir using n input moul (Figur 3, ottom lft) whih is n intrf twn snsors n th mplifir. Th mplifi signls r fil into th onvrtr rprsnt y NI USB-6009 DAQ r (Figur 3, top lft) from NATIONAL INSTRUMENTS. Th DAQ ws st to us 000 Hz smpling frquny. Fig. 4 Singl-iffrntil SEMG snsor Fig. 6. Position of th snsors (insi viw of th forrm): - rfrn ltro, 2- SEMG snsor 2 On SEMG snsor ws pl t istn of 40 mm from th low, on th xtrnl si of th forrm (Fig. 5) in orr to tt myoltril signl from xtnsor ommunis igitorum. Th son SEMG snsor ws position on th intrnl f of th forrm t istn of 70 mm from th low (Fig. 6) n ws us to ollt signl from flxor rpi rilis. W hos ths two musls ftr mny trils, us thy r th most importnt ontriutors to th flxion-xtnsion movmnts of th hn. In orr to iffrntilly tt th SEMG signls, rfrn ltro ws nssry. This ltro is rommn to pl wy from th SEMG 2

4 CONTROL ENGINEERING AND APPLIED INFORMATICS 6 snsors. Thrfor, w pl th rfrn ltro wy from th two EMG snsors, on th joint of th hn (Fig. 6). Bus surf ltromyogrphi signls r fft y mny isturns it is vry importnt to know whn movmnt is initit, in orr to know th strting point for th quir signl onsir for lssifition. Thr r svrl mthos us nowys for this rson. Th simplst on is th us of thrshol. Unfortuntly, th vlu of th thrshol is hosn mpirilly; thrfor tht vlu nnot work in ll ss. Othr mthos, lik vio ttion of th movmnt, or th us of pushutton tht hs to prss whn th ptint intn to mk movmnt, n lso ppli. W us two itionl goniomtrs to tt th ginning of movmnt. Using th goniomtrs, th informtion from ths vis n us for th implmnttion of th los-loop low-lvl ontrollr too. 3.2 Th SEMG signl quisition for th son ontrol strtgy Th positions of th snsors on th rm r illustrt in Fig. 7 (th snsor on trips not visil in th pitur). On SEMG snsor ws pl t istn of 80 mm from th low joint ovr th ips musl. Th son SEMG snsor ws position on th trips t istn out 0 mm from th low. Th thir SEMG snsor ws position ovr th ptorlis mjor musl. W hos th ips n trips musl us thy r th most importnt ontriutors to th flxion-xtnsion movmnts of th forrm. Also th ptorlis mjor musl ws hosn us it is lrg musl, mning tht vn smll ontrtions will tt y th snsor ruing th ptint s ffort. Th rfrn ltro ws pl on th joint of th hn. On of thm ws pl on th joint of th hn in orr to tt flxion-xtnsion movmnts. Th son goniomtr ws pl long th smll fingr in orr to tt th losing of th hn. As Fig. 5 illustrts w pl th goniomtrs on th sm hn on whih w pl th SEMG snsors, us w ollt t from l-ois sujts. In th s of th prsons with mputtions t th wrist lvl, th goniomtrs will mount on th othr hn. During th t olltion sssion th ptint will simultnously mk th rqust movmnt with oth th hlthy n th ill hn. W onsir tht using this strtgy th ptint will nourg to ontrol oth hns. For th implmnttion of th first ontrol strtgy, w us t ollt from fiv l-oi sujts, ftr riving thir inform onsnt. Thr movmnts (hn flxion, hn xtnsion n tight losing of th hn) wr us uring th quisition of th signls, in orr to isrimint thr stts: oth musls ontrt, on ontrt, th othr rlx n vi vrs. Th quir signls plus th signls ror from th two musls whn non of th thr movmnts ws prform (th rpos stt) wr us to ontrol four movmnts of th prosthti vi: rott insi; rott outsi, los hn, opn hn. Eh of th thr movmnts ws prform 75 tims y h sujt. Also, 75 t sts wr ror from h sujt in th s whn no movmnt ws prform. A totl of 500 movmnts rsult ((3 movmnts x 75 tims +75 t sts orrsponing to th s whn no movmnt ws prform) x 5 sujts). Bus for h movmnt, t wr ollt from two musls, totl of 3000 signls wr pross y th lssifir. During th quisition sssion th sujt st own with th low lning on hir rm in orr to ttr isolt th ontrtions of th musls for h motion Fig. 7. Position of th snsors on th uppr lim: -rfrn ltro, 2-th goniomtr for prontionsupintion, 3-th goniomtr for flxion-xtnsion, 4- SEMG snsor on ips, 5-SEMG snsor on ptorlis mjor Lik for th first ontrol strtgy, s illustrt y Fig. 7, th two goniomtrs wr pl on th sm uppr lim s th SEMG snsors, us w ollt t from l-ois sujts. For th son ontrol strtgy, t wr ollt, lik for th first ontrol strtgy, from fiv l-oi sujts ftr riving thir inform onsnt. Four movmnts of th forrm (flxion, xtnsion, prontion n supintio wr prform uring th quisition of th signls. For th flxion n xtnsion movmnts, th sujt st own with th uppr rm in position tht mks n ngl of out 30 gr with th longituinl xis of th oy. Th low ws ln on hir rm in orr to isolt ttr th ontrtions of th musls for th motions. Th flxion movmnt ws roun ninty grs n th xtnsion movmnt ws m s muh s ws possil y th sujt. For prontion n supintion th sujt stoo up with th rm nr th oy in n ntomil position. Th prontion n supintion movmnts wr out ninty grs towr n outwr th oy, rsptivly.

5 62 CONTROL ENGINEERING AND APPLIED INFORMATICS During th quisition of th SEMG, th sujts wr nourg to mk movmnts in wy whih ws omfortl for thm. Eh of th four movmnts ws prform 77 tims y h sujt. A totl of 540 movmnts rsult ((4 movmnts x 77 tims) x 5 sujts). Prforming lrg numr of motions for h movmnt typ rsults in ollting signls vn whr musls om ftigu, whih orrspon ttr to th lttr us of rl prosthsis. Bus for h movmnt, t wr ollt from two musls, totl of 3080 signls wr pross y th lssifir. 4. THE ELECTROMYOGRAPHIC CLASSIFIER As Fig. 2 illustrts, th ltromyogrphi lssifir hs two mouls: th ftur xtrtion moul n th ftur prossing moul. In orr to ru th prossing tim it is importnt to xtrt rlvnt fturs from th rw signls, tsk tht is prform y th ftur xtrtion moul. This stp is nssry us fing th SEMG signl s tim squn, irtly into th lssifir, xssivly inrss th prossing tim. Th ftur xtrtion lgorithms ttmpt to prsrv from th rw signl only th informtion tht is rlvnt for lssifition n to rmov runnt informtion. Th ftur prossing moul is us to lssify th fturs xtrt y th first moul, into istintiv lsss tht orrspon to th sir motion pttrns. 4. Ftur xtrtion moul Whn vloping ontrol systm for prosthti vi n importnt ftor is th rl-tim implmnttion. Th gnrlly pt ly twn inititing mov ommn t th mntl lvl n th strt of tht movmnt is pprox. 300 ms. (Oskoi t l, 2007). In orr to rspt this onstrint, quir t hv to sgmnt, n thn sgmnts will pross on y on. Th lngth of th tim sgmnt pns on th smpling frquny us in quisition n on th omputtionl powr of th systm. W tst th prformn of th lssifition lgorithm whn using sgmnts rnging from 32 to 256 t st vlus. W osrv tht th lssifition prformn is irtly rlt to th lngth of th sgmnt, th 256 vlus t sts yiling th lowst rror rt in lssifition. Bs on this osrvtion w hoos to work on 256 ms tim sgmnts orrsponing to 256 t st vlus, sin w us smpling frquny of 000 Hz. As th strutur of th ltromyogrphi signl is omplx on (Oskoi t l, 2007) n th signl is strongly rlt to th sujt s musl n tissu strutur, simpl thrshol s lgorithm os not offr suffiint informtion for th lssifition of th signl in iffrnt movmnt lsss. Diffrnt pprohs (tim omin, frquny omin n tim-sl omin nlysis) wr us prviously for ftur sltion (Hugins t l., 993), (Hrl t l., 2008), (Krlsson t l., 999), (Krlsson t l., 2000). In this ppr w us n utorgrssiv s lgorithm for ftur xtrtion. Th utorgrssiv (AR) moling of th SEMG offrs vry goo prformns in myoltri signls lssifition. On of th min vntgs is tht it omins two stgs: ftur xtrtion n imnsionlity rution. This ls to smll siz ftur vtor, n in ition, to rution of th prossing tim. Eqution () sris th AR mol: M x( i x( n i) (, n 0.. N () whr i r th AR offiints, N is th imnsion of th tim sgmnt, M is th mol orr, x( r th smpls of th signl, n x( r th smpls of th mol signl. Stuis hv shown tht n utorgrssiv mol of finit orr (suffiintly lrg) n pproximt ny systm with spifi gr of ury (Prkr t l, 2006). Th lgorithm for th utorgrssiv offiints lultion suggst y (Sors t l.,2002) follows th stps llow: i. initiliz th offiints ii. lult th prit vlu of th signl M x( x( n i) (2) i iii. stimt th rror ( x( x( (3) iv. upt th offiints i ( n ) i ( 2 ( x( n i) (4) Using this short lgorithm for th n vlus of th signl, w fin th offiints of n M th orr mol. Th trm μ is th onvrgn offiint. Bs on multipl trils w us vlu μ=0.0. Th pproprit mol orr nnot foun nlytilly. Frrin n Mrltti (Frin t l., 2007) foun tht mol of orr 0 works for most of th sgmnt lngths onsir, n Sors t l. (Sors t l., 2003) show tht fourth mol orr n qutly rprsnt th strutur of th EMG signl. W srh for th st pproximtion in mols with orrs twn 2 n 2 n foun tht fifth orr mol offrs th st lssifition prformn. AR moling provis us with two min vntgs onrning th lssifition prolm. Th first vntg in using th utorgrssiv mol is th imnsion of th ftur vtor tht is f into th nurl ntwork s lssifir. In our s, th 2x256 t points h n rpl y 2x5 vlus. This llows th lssifir to prform muh fstr n with highr gr of ury. Th son vntg, th roustnss is nssry u to th omplxity of th EMG signl. As mntion ov, th EMG signl is irtly pnnt of th musl strutur, th skin thiknss n th ftigu of th musl. An mplitu s ftur lik thrshol vlu or mn vlu is not nssrily irtly

6 CONTROL ENGINEERING AND APPLIED INFORMATICS 63 rlt to th lvl of ontrtion (Oskoi t l., 2007) n thrfor nnot rflt th struturl proprtis of th EMG. On th fturs wr xtrt, thy wr lssifi using th ftur prossing moul, in orr to isrimint th uppr lim movmnts. 4.2 Ftur prossing moul A. Th ftur prossing moul for th first ontrol strtgy Th fturs xtrt using th ov mntion lgorithm (i.. th offiints of th utorgrssiv mol) wr us in trining lssifir to isrimint twn 4 iffrnt lsss: (i) flxor ontrt n xtnsor rlx, (ii) flxor rlx n xtnsor ontrt, (iii) oth musls ontrt, n (iv) no movmnt. Th outputs pttrns of th lssifir r 000, 000, 000, n 000 orrsponing to th four lsss A two lyr nurl f-forwr ntwork lssifir ws us for lssifying th utorgrssiv offiints into ths four lsss of movmnt. In trining th lssifir, st of 200 of pttrns (from th totl of 300) ws us for h sujt. Th rst of 00 pttrns for h sujt ( totl of 500 pttrns for th fiv sujts) wr us for tsting th lssifir. W tun th numr of nurons in th hin lyr. Aftr multipl tris, w onlu tht lyr with 3 nurons offrs th st lssifition n still vois th phnomnon of ovrtrining, whih woul l to wors lssifition rt on unsn t. For th ips n trips musls, th offiints of th utorgrssiv mol wr us in trining lssifir to isrimint twn 4 iffrnt lsss: (i) flxion, (ii) xtnsion, (iii) prontion, n (iv) supintion, s on two lyr f-forwr nurl ntwork. Th lssifir ws trin using st of 26 pttrns (from th totl of 308) for h sujt. Thus, totl numr of 080 pttrns wr involv in th trining tion. Th rst of 92 pttrns for h sujt ( totl of 460 pttrns for th fiv sujts) wr involv in tsting th lssifir. Aftr multipl tsts, w onlu tht hin lyr of th nurl ntwork, with 4 nurons offrs th st lssifition n still vois th phnomnon of ovrtrining, whih woul l to wors lssifition rt on unsn t. Th output pttrns of th lssifir (nurl ntwork) r 000, 000, 000, n 000 orrsponing to th four lsss: flxion, xtnsion, prontion n supintion. Th tsting sts of signls wr prsnt to th nurl ntwork ftr trining. A 98% rognition rt ws hiv for th four movmnt lsss. Fig. 9 illustrts th xpt rsults n th lssifir s output. Aftr trining, tsting st of signls ws prsnt to th nurl ntwork. A 9% rognition rt ws hiv for th four movmnt lsss, rnging from 90% to 95% pning on th movmnt. Fig. 8 illustrts th xpt rsults n th lssifir s output. Flxor ontrt Extnsor ontrt Simultnous ontrt No ontrtion (intivity) Dt st Dt st Dt st Dt st Fig. 9. Th lssifir outputs. Comprison twn th xpt n th otin rsults Though w n to know if th ptorlis mjor musl is ontrt or not, spil lssifir is not rquir for this purpos. A thrshol ws us in this s. 5. THE HIERARCHICAL CONTROLLER As Fig. 2 lry illustrt, th ontrollr hs two lvls. Th purpos of th high lvl ontrollr is to trnsform th lsss isrimint y th lssifir into th inputs for th low-lvl ontrollr. Th high lvl moul is implmnt using finit stt mhin. 5. Th high-lvl ontrollr us in th first ontrol strtgy Fig. 8. Comprition twn th xpt n th otin rsults B. Th ftur prossing moul for th son ontrol strtgy In Fig. 0 is illustrt th stt trnsition igrm tht sris th ontrollr funtions, whr f stns for flxor rpi rilis n for xtnsor ommunis igitorum. Th initor os th prsn of ontrtion, n 0 its sn.

7 64 CONTROL ENGINEERING AND APPLIED INFORMATICS Th motions ontroll r: opn hn, los hn, rott insi, n rott outsi. Th signl from flxor rpi rilis musl is us to ommns two motions los hn n rotts insi. Th signl from xtnsor ommunis igitorum is us to ommn th opn hn n th rott outsi motions. Bus h musl ommns two f=,=0 movmnts, it is nssry to isrimint twn ths movmnts. Thrfor two mos r us. In mo opn n los motion r xut. In mo 2, rott insi n rott outsi motions r xut. In orr to swith twn th two mos, oth musls hv to simultnously ontrt. f=,=0 Clos hn f=,= f=,= Rott insi f=,=0 f=,=0 f=,=0 f=0,= Mo f=,= f=,= Mo 2 f=,=0 f=0,= f=0,= f=0,= Opn hn f=,= f=,= Rott outsi f=0,= f=0,= Fig.0 Stt trnsition igrm of finit stt mhin s ontrollr for hn prosthsis 5.2 Th high-lvl ontrollr us in th son ontrol strtgy For th son ontrol strtgy th high lvl ontrollr trnsform th lsss isrimint y th lssifir (flxion, xtnsion, prontion, n supintio into tul six movmnts of th prosthsis. Bus th finit stt mhin us to implmnt th high lvl ontrollr ns onition to kp stt, n us th lssifir implmnt n not offr suh onition w tri to moify th lssifir using thrshol inst of goniomtr for ttion of th strt of th movmnts. Th rognition rt of th lssifir ws roun 8% s fig. shows. prformn of th originl lssifir for th four movmnts of th forrm n to onsir th signl from th ptorlis mjor musl s onitionl signl to jump from on stt to nothr. Figur 2 illustrts th stt trnsition igrm tht sris th ontrollr funtions, whr th onitions to swith from on stt to nothr r o in th following wy: if f= n pm= thn if = n pm= thn if pm=0 thn if p= n pm= thn if s= n pm= thn whr f stns for flxion, for xtnsion, p for prontion, s for supintion, n pm for ptorlis mjor. Fig.. Comprison twn th xpt n th otin rsults of th lssifir whn thrshol ws us Morovr, n inrs numr of t wr nssry for th lssifir sin thrshol ws us to intify movmnt. Thrfor w i to prsrv th Th initor nos th prsn of ontrtion, n 0 its sn. For h joint of th prosthsis on mo is fin. Th suffixs ls n hs stn for low sp, n high sp. Th motions ontroll r: forrm flxion, forrm xtnsion, hn prontion, hn supintion, los hn, n opn hn. From mo th flxion n xtnsion of th low joint n ontroll using th flxion n xtnsion movmnts

8 CONTROL ENGINEERING AND APPLIED INFORMATICS 65 tt y th lssifir n th signl from th ptorlis mjor. In mo 2, th flxion n xtnsion ommns from th lssifir r us in onjuntion with th signl from th ptorlis mjor to ontrol th prontion n supintion movmnts of th prosthti hn. In mo 3, th flxion n xtnsion outputs of th lssifir r us in onjuntion with th signl from th ptorlis mjor to ontrol th los n opn movmnts of th prosthti hn. Th prontion n supintion outputs of th lssifir r us in onjuntion with th signl from th ptorlis mjor to swith twn mos. Eh of th six movmnts n ontroll using two lvls of sp. In this wy, if th ptint sirs to inrs th sp of movmnt h or sh hs to rpt on gin th onition tht llows th xution of tht movmnt. Flxion-hs Flxion-ls Mo Extnsion- Extnsion-hs Prontion-hs Prontion-ls Mo 2 Supintion-ls Supintion-hs Clos hn-hs Clos hn Mo 3 Opn hn-ls Opn hn-hs Fig.2 Stt trnsition igrm of finit stt mhin s ontrollr for n uppr-lim prosthsis 6. DISCUSSION Th rognition rt of 9% hiv y th first ontrol strtgy is smllr thn in our prvious stuy (Hrl t l., 2008). Th itionl signl ror whn no movmnt ws prform ltr th prformns of th lssifir, ut this itionl signl ws nssry to mintin th finit stt mhin in rtin stt. Howvr, thr is tr of twn th roustnss, rquir tim for lssifition n th rt of rognition. Using this pproh th lssifition tim ws rstilly ru. Th totl tim twn th momnt whn th rw EMG signl ws prsnt to th lssifir n th momnt whn th high lvl ontrollr rls ommn ws roun 6 ms, whn th tst wr m on PC Intl ul or t 2.66 GHz. In orr to improv th prformn of th lssifir, without inrsing th prossing tim w implmnt th son ontrol strtgy tht not only inrs th rognition rt to 98% ut llows lso ontrolling prosthti vi with mor grs of from using iffrnt lvls of sp. Th totl tim twn th momnt whn th rw EMG signl ws prsnt to th lssifir n th momnt whn th high lvl ontrollr rls ommn ws roun 9 ms, whn th tst wr m on th sm omputr lik tht on us for th first ontrol strtgy. Sin 300 ms is onsir to th mximum tim twn th intntion of movmnt n th strt of it, n tking into ount our rsults, w onsir tht our pproh is fsil for implmnttion into rl prosthsis. Comining this lssifition strtgy with finit stt mhin s high lvl ontrollr will ru signifintly th ffort rquir to ontrol rl prosthsis. Th high-lvl ontrollr llows th usrs with ru musulr tivity to sily ontrol th prosthsis, us th ptint must only initit or stop movmnt n th low-lvl ontrollr will fftivly ontrol tht movmnt using informtion from th lol snsors (.g. for or prssur snsors). Using goniomtrs, inst of thrshol-s mthos, w nsur high roustnss of th lssifir n ru omputtionl tim. 7. CONCLUSIONS In this stuy w propos n pproh for SEMG signl lssifition n two hirrhil ontrollrs for prosthti uppr-lim. W us lssifir s on utorgrssiv mol omin with nurl ntwork to tt of movmnt intntions. By using goniomtrs, inst of

9 66 CONTROL ENGINEERING AND APPLIED INFORMATICS mthos s on thrshols, w nsur high roustnss of th lssifir. Our futur work will fous on th implmnttion of th low lvl ontrollr. Sin w us goniomtrs w intn to xtrt not only informtion rlt to th strt of th movmnt, ut lso informtion rlt to th sp. This informtion will usful for th low lvl ontrollr in orr to just ontinuously th sp of th prosthti vi oring to th intntion of th wrr. This is n vntg with rspt to most of th urrnt ommril prosthss, whih only prform movmnts with onstnt sp. Anothr improvmnt for th lssifir will th us of th onlin trining of th nurl ntwork. This will inrs th ptility of th lgorithm to h iniviul usr. ACKNOWLEDGMENT This work ws support y th Romnin Rsrh Grnt 4-050/2007 (OSMOCEL). REFERENCES Chn, A. D. C. n Englhrt, K.B.(2005). Continuous myoltri ontrol for powr prosthss using hin Mrkov mols. IEEE Trnstion on Biomil Enginring, Volum (52), D Lu, C. J.(997) Th us of surf ltromyogrphy in iomhnis, Journl of Appli Biomhnis, Volum(3), Englhrt, K., Hugins, B., Prkr, P. n Stvnson, M.(999). Clssifition of th myoltri signl using tim-frquny s rprsnttions. Journl of Mil Enginring n Physis, Volum(2), Frin, D. n Mrltti, R.(2007). Comprison of lgorithms for stimtion of EMG vrils uring voluntry isomtri ontrtions. Journl of Eltromyogrphy n Kinsiology, Volum(0). Flzr T. n Frisln, B.(2002) HWCoS: th hns-fr whlhir ontrol systm. Proings of th ACM SIGCAPH Confrn on Assistiv Thnologis, ACM Prss, Hrl, S., Ri, Pul, Lz, Gh., Rootin, R., Mru, C. n Tms, L.(2008). Clssifition of surf ltromyogrphi signls for ontrol of uppr lim virtul prosthsis using tim-omin fturs. Proings of 2008 IEEE Intrntionl Confrn on Automtion, Qulity n Tsting, Rootis, Cluj-Npo, Hugins, B., Prkr, P. n Sott, R. N.(993). A nw strtgy for multifuntion myoltri ontrol. IEEE Trnstion on Biomil Enginring, Volum(40). Hung, I., Englhrt, K.B., Hugins, B. n Chn, A.D.C.(2005). A Gussin mixtur mol s lssifition shm for myoltri ontrol of powr uppr lim prosthss. IEEE Trnstion on Biomil Enginring, Volum (52), Krlik, B., Tokhi, M.O. n Ali, M.(2003). A fuzzy lustring nurl ntwork rhittur for multifuntion uppr-lim prosthsis, IEEE Trnstion on Biomil Enginring, Volum(50), Krlsson, S., Yu J. n Aky, M. (999). Enhnmnt of sptrl nlysis of myoltri signls uring stti ontrtions using wvlt mthos, IEEE Trnstion on Biomil Enginring, Volum(46), Krlsson, S., Yu, J., n Aky, M.(2000). Tim frquny nlysis of myoltri signls uring ynmi ontrtions: omprtiv stuy, IEEE Trnstion on Biomil Enginring, Volum(47), Light, C.M., Chppll, P.H., Hugins, B. n Englhrt, K. (2002) Intllignt multifuntion myoltri ontrol of hn prosthsis. Journl of Mil Enginring n Thnology, Volum (26), Mrltti R. n Prkr P.(2004). Eltromyogrphy: Physiology, Enginring, n Non-Invsiv Applitions, Wily-IEEE Prss. Mir, S., Stini, A. M., n Drio, P.(2000). On utomti intifition of uppr-lim movmnts using smll-siz trining sts of EMG signls, Journl of Mil Enginring n Physis, Volum(22), Moon, I., L, M. Chu, J. n Mun, M.(2005). Wrl EMH-s HCI for ltri-powr whlhir usrs with motor isilitis. Proings of th IEEE Intrntionl Confrn on Rootis n Automtion, Oskoi, M. n Hu, H.(2007) Myoltri ontrol systms A survy, Biomil Signl Prossing n Control, Volum (2), Prkr, P., Englhrt, K. n Hugins, B.(2006). Myoltri signl prossing for ontrol of powr lim prosthss, Journl of Eltromyogrphy n Kinsiology, Volum(6), Ping, Z., Lowry, M.M., Dwl, J.P.A. n Kuikn, T.A. (2006). Towrs Improv Myoltri Prosthsis Control: High Dnsity Surf EMG Roring Aftr Trgt Musl Rinnrvtion. 27th Annul Intrntionl Confrn of th Enginring in Miin n Biology Soity, Volum (), Sors, A. B., Brzin, F. n Anr, A. O. (2002) Powr sptrum stimtion of EMG signls vi Chirp-Z trnsform, in Proings of th XIVth Congrss of th Intrntionl Soity of Eltrophysiology n Kinsiology, p.43. Sors, A., Anr, A., Lmounir, E. n Crrijo, R.(2003). Th Dvlopmnt of Virtul Myoltri Prosthsis Controll y n EMG Pttrn Rognition Systm Bs on Nurl Ntworks. Journl of Intllignt Informtion Systms, Volum(2), Sun, Q., Sun, Y., Ding, X. n M, Z.(2005) Onst trmintion of musl ontrtion in surf ltromyogrphy signls nlysis. Proings of IEEE Intrntionl Confrn on Informtion Aquisition, Zhng, X., Wng, X., Wng, B., Sugi T. n Nkmur, M.(2009), Finit stt mhin with ptiv ltromyogrm (EMG) ftur xtrtion to riv ml ssistn root, IEEJ Trnstions on Eltronis, Informtion n Systms, Volum(29),