SIRIUS: Improving the maneuverability of powered wheelchairs

Pmcsedngs ol he MO2 IEEE ln emabmal Can e em on Cmbd ApplicnDw Sep embe 1820.2W2.G$sgow.~~d.UK SIRIUS: IMPROVING THE MANEUVERABILITY OF POWERED WHEELCHAIRS A. Ci i -Balcells, F. Diaz del Rio, C. Jimenez, J.L. Se illano, C. Amaya, S. Vicen e. Escuela Supeno de lngeme ia In od ica U u e sidad de Se llla. A da Rem Me cedes dn. 41012 Se illa Spain Fax +34-954552759. Email cin @alc uses ‘Abspac - The indoo maneu e abili y o powe ed wheelchai s may he di licnl o bo he some in se e al ci cums ances. In his pape , we desc ibe an expe imen al powe ed wheelchai named SIRIUS, de eloped a he Uni e si y o Se ille, which in oduces some simple bu eKec i e na iga ion aids. Special emphasis is placed on he implemen a ion o eco ded ajec o y playback and in he sha ed con ol modes, i.e. he chai ’s guiding whe e bo h he use and he compu e collabo a e. Fu he mo e, SIRIUS is an open pla o m o essay ano he kinds o nne ional o na iga ional aids, because i s ha dwa e a chi ec u e is based on a comme cial PC. This would pe mi many de ices ha a e equen ly needed by he chai d i e o be in eg a ed smoo hly in o he chai con olle . I. INTRODUCTION. Powe ed wheelchai s a e one he mos impo an elemen s in he ield o ehabili a ion. Indeed powe ed wheelchai s a e no a luxu y o mos use s bu hei only way o li e independen ly. Much R&D wo k in he ield o ehabili a ion enginee ing is being ocused on he imp o emen o powe wheelchai s [l], [Z], [31, [4], [5]. In his con ex , au oma ion, obo ics and elema ics should play a e y impo an ole in hc ield o ehabili a ion enginee ing. Du ing he las decade ad anced wheelchai s ha e expe ienced a spec acula imp o emen om he echnical poin o iew, and many p o o ypes ha e been buil o o e come he limi a ions o cu en wheelchai s, Some o hem a e: di icul adap abili y, high cos , ou da ed designs, imp ecise ba e y gauges, di icul handling and lack o po abili y [4]. Besides, a wide ange o o - he-shel elec onic de ices and senso s can be ound oday a e y low cos . While, o example, mos o hese de ices a e being inco po a ed o au omobiles as luxu y componen s, hey can play a c ucial ole in ad anced wheelchai aids. Thus, we belie ha esea cbe s should do a special e o o inco po a e hese de ices o powe ed wheelchai s. An impo an e o is also equi ed o b ing hese de elopmen o he ma ke as, o he wise, hey will no bene i he inal use s. Du ing he las yea s in he Robo ics and Compu e o Rehabili a ion Lab a he Uni e si y o Se ille we ha e de eloped a sys em named SIRIUS ha embeds many * This wnl was suppo ed in pa by he Spanish “Minis e io de Cimcia y Temologis” h ough p ojec TlC-2MIO-0087-P443. mobile obo ics ea u es [6], [7]. I is based on a con en ional wbeelchai bu adding senso s and a con olle ; so i can be eleope a ed o na iga e in an au onomous way. Mo eo e SIRIUS can be used as a esea ch pla o m o es new ad anced ea u es: GPS na iga ion sys ems, elecommunica ion de ices, miiicial ision-based na iga ion, e c. In ac , we a e wo king nowadays in a esea ch p ojec in o de o inco po a e elecommunica ion sys ems o s anda d wheelchai s, and he possibili y o in e ac ing wi h adap i e en konmen s. In his pape , and using SIRIUS as a pla o m, we discuss bow he ad anced na iga ion sys em (usually ound in mobile obo s) can help a wheelchai use and, also, how he use can aid an ad anced na iga ion ea u e. In sec ion I1 we b ie ly desc ibe he main subsys ems inco po a ed o SIRIUS o imp o ing na igabili y. We discuss in sec ion ID he na iga ion aids expe imen ed un il now and inally he conclusions a e ound in sec ion N. n. THE Sms PROTOTYPE. SIRIUS is a wheelchai p o o ype ha has been buil based on a con en ional wheelchai , and ha emains open as a pla o m o es ing di e en hno a ions. The p o o ype is in ended o be a low cos SOM MI domes ic chai ha should inco po a e ad anced na iga ion ea u es. a mTIm -- W Fig. I: Subsys ems o SIRIUS 0-7803-73S3/WS17.00 0 2002 IEEE 790 Besides we can no o ge ha a pe sonal wheelchai can ne e be a ully au onomous sys em (like AGV, Au oma ed Guided Vehicles), bu a “semiau onomous- eleope a ion” sys em. We mean ha we canno elimina e he use ope a ion mainly because: a) complex na iga ion sys ems a e p ohibi i e due o he in ended low cos o he comme cial wheelchai s, b) ully au oma ic sys ems usually a e e used by use s and c) In houses, he e a e small innica e spaces whe e he chai mus na iga e in. So he use will some imes ha e o guide i (o show he ajec oly o he chai he i s ime), and we a e de eloping a mixed o “sha ed con ol” sys em: con ol p ocessing is sha ed be ween he use and he au oma ic senso -based con ol sys em 111. The new ha dwa e ha he SIRIUS p o o ype includes has been inco po a ed in o a con en ional powe wheelchai . The wheelchai has wo independen ly ea d i e wheels, which cause u ning by hei di e en ial speeds, and wo on cas o s o “ ee-wheels”. Below we desc ibe he main componen s ha ha e been added, and in Fig. 1 we show a schema ic o SIRIUS. PC-ba ed o chi ec u e. We ha e also eached he wheelchai p o o ype on he basis o a low cos high pe o mance sys em. So we ha e “adap ed” all subsys ems o go a ound a common CPU boa d and ba e simpli ied he elec onic de ices needed Ou CPU al ema i e is a PC boa d based chai . I a x86 based main boa d is used, con ol ci cui y can be inco po a ed as PCI o ISA based ca ds. This would also pe mi many de ices ha a e kquen ly needed by he cbai d i e o be in eg a ed smoo hly in o he chai con olle ( o example, oice ecogni ion sys ems, mo emen senso s, g aphic use in e aces, e c.). Besides, as he compu ing equi emen s ha e inc eased, he main boa d has been easily upda ed wi h mo e powe ul x86 p ocesso s. The only limi a ion is ha low powe e sions should be used. On he o he hand, PC a chi ec u e eases so wa e de elopmen , and in ac , he PC solu ion o embedded sys ems is being mo e and ’ mo e common [8]. Fo PC adap a ion we ha e used ou p e ious expe ience in he con e sion o obo con ol uni s, and ha e main ained SIRIUS as an open pla o m o imp o e mul isenso coo dina ion and na iga ion algo i hms. In his sense he m pu pose o SIRIUS was o de e mine wha na iga ion ea u es migh inco po a e a con en ional wheelchai in o de o acili a e he maneu e ing in small a eas. This will be discussed in nex sec ion. Powe mo o d i e s. The o me chai had a pai o elays in o de o change he di ec ion o u n. This makes impossible o build a high pe o mance con ol because he swi ching delays in oduce non-linea i y when c ossing he ze o. We inco po a ed a new powe d i e ha ensu es linea i y in bo h di ec ions and inc eases e iciency. The d i e is based in an H-b idge o MOS ansis o s, wi h a pai o BJT ansis o s as he d i e s age, ha a e commanded hy PWM wa es. Op ical encode s and coun e s. SIIUUS ge s he posi ion eedback h ough wo op ical encode s a each wheel, and sa es his in o ma ion in wo 16-bi s coun e s. Tha pe mi s us a high p ecision de e mina ion o he chai posi ion and an accu a e eco e ing o ajec o ies in his esea ch p o o ype (as we show in nex sec ion). Al hough hese eedback senso s gi e high p ecision, we a e conside ing a simple eedback, ha would a oid he encode s assembly in a p ospec i e comme cial chai . A possibili y is de ec ing he in ensi y changes in he mo o s blushes, which p ecision will be accu a e enough o allow he eco e ing o ajec o ies. Use In e lace. Designing a comple e use in e ace needs a mul i-disciplina y app oach, inclndiig ehabili a ion enginee ing, obo ics, e gonomics, psychology, compu e science, e c. Fo ou p o o ype we did no conside all hese aspec s. We a e using he o iginal joys ick and ha e included a 16 keys keyboa d o selec he di e en pa ame e s and ac ions. We ha e added a LCD display o in o m abou he s a e o he wheelchai . Finally, a special bu on ( he o me ho n) is used o play hack ajec o ies. O come all he inpu in o ma ion is digi ized o be supe ised by he CPU. Fig. 2: Possibili ies o low-le el eedback i e no1 simple senso ing in oma ion. Ul asound calcula ing he wo ld posi ion in a changeable en i onmen . ansduce s a e he cheapes way o measu ing dis ance and Al hough sona in o ma ion is no comple e, hei dis ance measu es can be in e es ingly exploi ed as explained in he ollowing sec ion. was done by he use o by he CPU (see Fig. 2). When au oma ic eedback is no ac i a ed he only adjus able “pa ame e ” is he powe gi en o each wheel h ough he joys ick o any o he use in e ace (see Fig. 2, uppe d awing). This makes he use he con olle , con inuously adjus ing he joys ick depending on he ex e nal condi ions wo king wi h ’Ims p o ome and discussing hem o ine ia, loo slope, e c. Fo example, in he p esence o wi h many and educa o s we ha e O slopes he con ol sys em au oma ically changes he powe he na iga ion aids o be included in o de o imp o e he gi en o he wheels in o de o main ain he desi ed speed, and o a oid he chai ’s huns (mo e p obable when ising a maneu e abili y o powe ed wheelchai s. We delibe a ely ha e a oided beacons, ixed pa hs o any slope). This “open-loop manual con ol” inc eases he o he way o guiding he chai . Mos o bibliog aphy di icul y o handling he chai . In ac , wi h he usual open ocuses on au onomous obo s ha ollow ixed pa hs o a e loop con ol he use “closes” he eedback pa h nI. NAVIGATION MODES AND EXPERIMENTAL RESULTS. guided by beacons o a i icial ision. The las is non- iable in his momen because o i s cos and compu a ional equi emen s. On he o he hand, we hink ha adjus ing beacons o ixed pa hs in a domes ic en i onmen ha may equen ly change is no a good idea. This way o na iga ion only can i in places whe e changes o he scene can be es ic ed and ha ha e mo e open spaces like hospi als o indus ial en i onmen s; his is no he case o a pe sonal indoo wheelchai . The inal p o o ype can he conside ed lie a eleope a ed mobile obo wi h some amoun o au onomy. The complexi y o he in e ac ion buman-compu e in he na iga ion has implied he o ganiza ion o he unc ionali y in laye s o con ol. We ha e ollowed he classical laye s p oposed in [9], bu adding he use ac ion as a new agen ha can in e e e wi h hem. Tha is, om he mos “in elligen ” o highes o he lowes we ind Task planne . Ob iously he use always mus do his in wheelchai s. T ojec oiy planne . This can be done by he use (e.g. selec ing a ued ajec o y like a s aigh line). Bu he compu e o example can do i i he use had selec ed a ask lie “play back a ajec o y”. In his case, his planne will e ie e he las memo ized ajec o y and i will send i o he lowe le el. T ajec oiy gene a o . I gene a es he nex poin in he ajec o y sen by he immedia e uppe le el. Al hough he CPU (lie in mobile obo s) usually does his gene a ion, i he use mo es he wheelchai h ough he joys ick, hen hdshe is cons mc ing hidhe own haie n - 7 -----, . Con olle . This le el ies o con e ge eal pos u e o he desi ed pos u e gi en by la es le el. F om he p eceding. o ganiza ion we can dis inguish wo kinds o eedback, which can be al e na i ely done by he use o he compu e : 1) The low-le el eedback, done a he con olle le el. 2) The high-le el eedback, done a he ajec o y planne le el (in SIRIUS he ask le el eedback [coope 95]. O he wise, when a compu e is used o conml he wheelchai (see Fig. 2, lowe d awing), he joys ick command can be he linea and u ning eloci y (o he possibili ies include con e ing joys ick commands in o dis ance). This compu e based eedback con ol makes he chai mo ion mo e in ui i e and independen o ex e nal condi ions. He e he speed o he d i e wheels is sensed in o de o ob ain eedback in o ma ion. Fu he mo e, he exis ence o an au oma ic low-le el eedback can se e o une sys em pa ame e s o he use ’s needs. This imp o es he adap abili y o he chai making possible a “ unable con ol”. Fo u u e wo k e en he inpu signals om he use in e ace could also be p e-condi ioned, o example o neu alize in en ion emo . The second g oup o essays was based in he need o elie e he use . We mean o say ha in se e al si ua ions, he di icul o bo he same guiding o he joys ick (o any o he in e ace) can be subs i u ed o p e ixed ajec o ies. We ha e concluded ha h ee ajec o ies we e especially in e es ing o he use s: s aigh ahead o back, sligh changes o pa h’s cu a u e, and 90 deg ees u ns. These ajec o ies a e selec ed in SIRIUS h ough he keys 1 o 9 (‘2’ o wa d, ‘8’ backwa ds, ‘4’ 90 deg ees le u n and ‘6’ 90 deg ees igh u n, as shown in Fig. 3). When mo ing in a co ido , he selec ion o a s aigh pa h can be e y com o able. In his case i is necessa y o add some mechanism o neu alize he li le o ien a ion’s de ia ions o he wheelchai . We ha e ound wo simple mechanisms, which implan a ion will no inc ease he wheelchai ’s cos : sligh changes o pa h’s cu a u e ha can be chosen by he use ( o example in keys 1,3,7 and 9 o SIRIUS), o con inuous la e al dis ance measu es wi h an ul asonic senso . Changes o la e al dis ance will mean changes o o ien a ion. The las mechanism bas been ully es ed in AGV’s, whe e he sona s a e equen ly he only senso de ice o ollow a wall [IO]. Some imes hey inco po a e a ull a ay o sona s a ound he obo ( u he mo e hey a e in ended o o he easons like maps building). Al hough is always done by he use ). In he i s ials we show he di e ence when ac i a ing o no he con olle eedback, i.e., when he low-le el con ol some wo ks like [ 111 ha e conside ed his pckbili y, we hink ha his op ion is no obliga o y in wheelchai s because o i s complexi y and due o he p oblems 792 associa ed wi h sona s mul iple e lec ions and de ec ion aul s (e.g. i he objec is as na ow as some able legs). Mo eo e building a map may no be a good idea in en i onmen s like some use s’ homes, which may equen ly change. (supposing he ini ial wheelchai o ien a ion is acing he doo unde 30”, he maximum de ec ion angle o sona s). In addi ion he use ha guides he joys ick has he imp ession ha “someone” is helping himhe . OOOOl Fig. 3: Co espondence beh een keys andp ej xed ajec o ies. The hi d g oup o es s was done wi h senso s o ob aining ex e nal eedback in o ma ion. Due o he high p ecision o odome ic in e nal senso s (op ical encode s a each wheel), we do no conside complica ed senso ing o ge comple e in o ma ion, bu he simples ones, which a e su icien o help he in e nal senso s’ guiding. We inally decided o inco po a e ou ul asonic senso s: wo on al (a le and igh sides) wi h high each dis ance and wo la e al. The la e al ones we e in ended o guiding SIRIUS h ough a co ido as explained be o e. The hn al ones can be inac i e o p og”ed in wo main ways: Obs acle de ec ion and p og essi e speed educ ion used o app oach an objec acing i . We mix wo di e en e ec s: eloci y educ ion and um. The speed is educed as we app oach he obs acle, and each wheel’s speed educ ion is p opo ional o he in e se o he dis ance o he objec de ec ed by each sona . The di e en speed educ ions ansla e in small huns ha aces he chai o he objec . Obs acle a oiding wi hou changing he main wheelchai o ien a ion ( e y use ul o c oss a doo ) sa ing he use om bo he some guiding. He e we also mix he eloci y educ ion and he huning, bu in a di e en way. The speed is educed as we app oach he obs acle, and a he same ime when one o he sona de ec s a wall bu he o he does no a small um is pe o med o a oid he doo walls ( o example, he au oma ic igh u n in Fig. 4). The small ums a e eco ded; when he obs acle a e los he old o ien a ion is esumed ( he iinal le um in Fig. 4). This is done wi hou use in e en ion. Howe e i he use is guiding he joys ick, he au oma ic co ec ion o o ien a ion helps he use o c oss he doo . This is simply done by adding he joys ick command o he au oma ic command (wi h a scale ac o ). The esul is ha is almos impossible o collide wi h he doo walls Le sona I de ec ion Fig. 4: Obs acle a oiding helps o c oss a doo . Howe e ul asonic senso s su e om se e al d awback hey do no wo k p ope ly in e y noisy en i onmen s, hey ha e a limi ed sensing ange wi h signi ican minium dis ance, e c. Fo hese di icul ies i is easy desi able ha he sona s in o ma ion will be combined wi h o he senso s. The las g oup o na iga ion aids is he mos au oma ed playing back eco ded ajec o ies. The main in en ion o his is o a oid he use he di icul maneu e ing o e e se d i ing, and may be e y use ul in small a eas like ba h ooms. The e o e he CPU is always memo izing he ajec o y done by he chai (no ma e which agen has done i ). Fo example, in Fig. 5 he CPU will ha e memo ized he pa h om poin 1 (ini ial posi ion) o 2 ( inal posi ion in he ba h oom). When he use wan s o play back he ajec o y (e.g. when he wan s o go ou he ba h oom), he/she pushes a bu on and he wheelchai began o au oma ically mo e in he e e se di ec ion and eco e ing he las mo emen s. Fo example, in Fig. 5 SIRIUS eco e s he ajec o y om poin 2 o 3 (posi ion a e i s eco e y). When he use decides ha he pa h eco e y was enough (e.g. i he chai is ou o he ba h oom a poin 3), he/she can p ess one o he s op bu ons, and he chai lea es his au oma ic mode and s ops. F om he e he CPU con inues again o eco d he ajec o y and he eco e ed pa h was los ( agmen 2 o 3 in Fig. 5). The e o e i in some me e s he ajec o y eco e bu on was p essed again, he eco e y will be done o ge ing he p e iously eco e ed pa h. Then i he bu on we e p essed in poin 4 o Fig. 5, he eco e y will pass h ough poin s 4, 3 and 1, o ge ing he p e iously 793 eco e ed ajec o y (inside he ba h oom). This pe mi s o “nes ” he epe i ion o ajec o ies. 4. Final Posi ion 3. Posi ion a le I. Ini ial Posi ion i s eco e y 2. Final posi ion in he ba hmom 1 Fig. 5: Playing backpa hs in SIRIUS: hepossibili y o nes ed eco e ies In o de o play again a p e iously eco ded ajec o y we mus choose a con ol law o he wo d i en wheels, conside ing SIRIUS as a mobile obo . This is a classical p oblem in non-holonomic sys ems lie mobile obo s [12] and se e al solu ions ha e been p oposed. We ha e p e e ed o use he “pa h ollowing” app oach which igno es he ime o ollow he ajec o y [12]. In ou sys em his ime is o no conce n, and his way we a oid he d adacks o conside ing desi ed ime e olu ion (“ ajec o y acking” app oach) such as discon inui ies in ansien esponses. The whole p ocedu e o selec ing a good con ol law o unicycle obo s (like SWS) is explained in [ 131 and i is a om he scope o his pape . The expe imen al esul s o pa hs eco e ies a e good enough when hese pa hs does no ha e many o a ions. Bu we ha e obse ed ha he o ien a ion e o s due o slippage ha e o be conside ed. Al hough he con ol law ensu es ha obo ollow he in emal memo ized pa h wi h li le e o s, slippage e o s could accumula e and he de ia ion om he o iginal pa h may be 4 o 5cm o each 1Om o pa h. No e ha he con olle acks he pa h using in emal odome ic eedback, i.e. i can no es ima e slippage e o s. The e o e we mus in oduce some mechanism o ex emal eedback o co ec his p oblem. In his ield he e is lo s o esea ch in ully au onomous AGV’s, bu all o hem implies a complica ed senso ing in o ma ion and p ocessing, as one can imagine. Al hough he e ha e some ials o his kind in ad anced wheelchai s (ul asonic a ay in [Ill, s e eo ision in [3], e c.) we ha e inco po a ed a e y simple solu ion: he use himhe sel can in oduce li le co ec ions o he au oma ic eco e y. Tha is, i he use sees ha he chai is de ia ed some cen ime e s o example o he igh , he/she can push he joys ick o he le o in o m he compu e o he de ia ion. The mo e helshe pushes he joys ick, bigge will be he co ec ion in oduced in he ajec o y. I is a ac ha he use usually o e es ima es he de ia ion and hen in a ew me e s hdshe ac s again (in he opposi e di ec ion) un il he chai ecupe a es app oxima ely he o iginal pa h. This human- compu e coope a ion can be conside ed as ano he kind o sha ed con ol [I]. O iginal pa h ----_ Pa h eco e ing Righ de ia ion: he use pushes he joys ick o he le Fig. 6: Sha ed con ol in a pa h eco e y. N. CONCLUSIONS. he maneu e abili y o powe ed wheelchai s. All hese ea u es ha e been included wi hou elimina ing he use 794 na iga ion sys ems, b) he use ’s ejec ion o ully au onomous sys ems, and c) he di icul y small spaces whe e he chai mus na iga e. The main conclusions a e cen e ed in a) The ad an ages o closed loop con ol ( ia in e nal adome ic eedback) ha educes bo he some guiding in many cases; b) The bene i s ob ained when mixing compu e and human con ol. He e we p esen wo cases: compu e co ec ion o he use guiding ia simple sona in o ma ion ( e y e icien o c oss doo s) and use co ec ion o au oma ic pa h eco e y (co ec ion o slippage de ia ions, e y di icul o de ec ia ex e nal eedback). REFERENCES 1. Coope , R A. In elligen Con ol o Powe Wheelchai s. 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