Design of a patient-tailored active knee-ankle-foot orthosis to assist the gait of spinal cord injured subjects

 Abs ac —This pape p esen s he main design s eps in he de elopmen o an ac i e knee-ankle- oo o hosis (KAFO) concei ed o assis he gai o incomple e spinal co d inju ed (SCI) subjec s. The design app oach is based on he idea o modi ying he a ailable passi e o hoses by adding adap able mecha onic modules a he join s. This app oach has esul ed in a p o o ype ha has been es ed on SCI pa ien s. The design and con ol p oblems ound and hei adop ed solu ions a e ho oughly desc ibed. I. INTRODUCTION HE design o powe ed o hoses and exoskele ons ha assis human gai is an open ield o esea ch ha co e s se e al a eas such as biomechanics, mechanical design, obo ics and neu o ehabili a ion. Those ac i e de ices a e designed o help pa ien s wi h disabili ies, caused o example by a spinal co d inju y (SCI) o acqui ed b ain damage, and ha e shown o be use ul o eco e ing locomo o unc ion a e he inju y [1], and o a ou ing physical ac i i y la e , hus imp o ing he pa ien s’ heal h and quali y o li e a e ehabili a ion. In he las yea s, a numbe o obo ic de ices aimed a assis ing human gai ha e been de eloped [2]. The objec i e o his wo k is o p esen he p og ess o an ongoing p ojec aimed a designing a pa ien - ailo ed ac i e o hosis o assis he gai o incomple e SCI subjec s. A pai o o hoses ha e been buil so a and hey a e now being es ed on pa ien s o he SCI Uni o he “Complejo Hospi ala io Uni e si a io de A Co uña” (CHUAC). The design o he o hosis is based on he ideas o he Head o he SCI Uni o he CHUAC, who wan ed o imp o e he comme cial passi e o hoses ha SCI pa ien s o his uni a e using a p esen . I mus be no ed ha he a ge pa ien s a e able o con ol hip lexo muscles, being classi ied unde le els C o D in he ASIA impai men scale (AIS). The cu en comme cial o hoses include wo basic pa s: a) a knee locking sys em, which is essen ial o bea he pa ien ’s weigh du ing he s ance phase due o he lack o This wo k has been suppo ed by he Spanish Minis y o Economy and Compe i i eness unde p ojec s DPI2009-13438-C03 and DPI2012-38331- C03, co inanced by he Eu opean Union h ough EFRD. J.M. Fon -Llagunes and D. Clos a e wi h he Depa men o Mechanical Enginee ing and he Biomedical Enginee ing Resea ch Cen e o he Technical Uni e si y o Ca alonia, Ba celona, Spain (e-mail: [email p o ec ed]). F. Rome o and F.J. Alonso a e wi h he Depa men o Mechanical, Ene ge ics and Ma e ials Enginee ing o he Uni e si y o Ex emadu a, Spain. U. Lug ís and J. Cuad ado a e wi h he Labo a o y o Mechanical Enginee ing o he Uni e si y o La Co uña, Spain. o ce a he quad iceps muscle; and b) a passi e ankle join (klenzak join ) ha cons ains ankle plan a lexion du ing he swing phase, hus a oiding d op- oo gai . Comme cial knee-locking sys ems a e shape o ic ion-based, being ac i a ed upon heel s ike de ec ion, usually by means o an on-o con ac senso . The klenzak join consis s o a sp ing ha applies an ex e nal do si lexion o que. Those de ices a e essen ially passi e, being he only semi-ac i e sys em ha o med by he knee locking mechanism and he on-o con ac senso . Those cu en o hoses ep esen he s a ing poin o he p o o ypes ha ha e been de eloped in he p ojec . Wi h he aim o ob aining a pa ien - ailo ed, low-cos and low-weigh p oduc , ou design app oach is based on using as much as possible he exis ing o hopaedic de ices and de eloping mecha onic modules ha can be a ached o hem. The ollowing sec ion p esen s he mechanical design and senso s o he buil ac i e o hoses, highligh ing he design p oblems ound and solu ions adop ed. Finally, he main u u e de elopmen s o he p ojec a e ou lined. II. MECHANICAL DESIGN AND SENSORS The main modi ica ions o he cu en de ices sugges ed by he medical s a o he SCI Uni a CHUAC we e he ollowing ones: a) in oducing, besides he locking sys em, ac ua ion a he knee join because he conside ed subjec s do no ha e enough muscle o ce o lex and ex end he lowe limb du ing he swing phase; and b) including some addi ional senso s on he p o o ype o he body in o de o be e con ol he knee-locking sys em and ac ua ion. Fig. 1. CAD design o he i s p o o ype o ac i e KAFO. Mo o g oup Knee-locking de ice Klenzak and encode Design o a Pa ien -Tailo ed Ac i e Knee-Ankle-Foo O hosis o Assis he Gai o Spinal Co d Inju ed Subjec s J. M. Fon -Llagunes, U. Lug ís, F. Rome o, D. Clos, F.J. Alonso, and J. Cuad ado T Based on ha , a i s knee-ankle- oo o hosis (KAFO) p o o ype was designed [3], Fig. 1. In his p o o ype, a s anda d klenzak join was sligh ly modi ied including an op ical inc emen al encode o con ol pu poses. The knee join inco po a ed wo powe ed sys ems ac ing in pa allel. In o de o lock he knee du ing s ance, he con ollable shape- locking mechanism Neu o T onic, manu ac u ed by Fio & Gen z (Ge many), was used. An on-o con ac -de ec ion senso p o ided by he company con olled his sys em. Rega ding he knee ac ua ion, an elec ical EC 45 la mo o , manu ac u ed by Maxon Mo o (Swi ze land), oge he wi h a 1:156 plane a y gea box was used. The mo o included an op ical encode o i s posi ion con ol. The objec i e o using he wo sys ems was o a oid he use o he mo o o locking he knee du ing s ance, hus educing he powe consump ion o he o hosis. Rega ding he con ol, apa om he men ioned senso s, a hip elec o-goniome e was also included. Since he a ge pa ien s a e able o con ol (up o a ce ain deg ee) he hip join o a ion, his angula measu emen was in ended o be used as a e e ence o he knee lexion-ex ension ac ua ion du ing swing. I mus be men ioned ha his p o o ype had leng h-adap able la e al ba s, so ha i could be used wi h di e en SCI subjec s. Fig. 2. (a) P o o ype wi h emu -aligned mo o . (b) Expe imen al es o a SCI subjec wea ing he ac i e KAFO. Labo a o y es ing e ealed se e al d awbacks o he i s p o o ype, which a e desc ibed in wha ollows. A i s incon enien was ela ed o he ho izon al a angemen o he mo o axis, which could collide wi h he c u ches du ing walking. This was amended using a 1:1 be el gea and placing he mo o axis pa allel o he emu , Fig. 2(a). Howe e , he lack o obus ness o he gea se o ced o e u n o he o iginal ho izon al layou . Rega ding he shape-locking mechanism, a conside able ex ension o que om he mo o was equi ed o unlock he join in o de o s a he swing, hus inc easing he powe consump ion and ime o esponse. So i was decided o use he mo o o lock he knee, since i p o ed o be capable o locking ha join du ing s ance. In wha e e s o he oo -g ound con ac de ec ion, he on- o ansduce s we e e y un eliable, so hey we e eplaced by con inuous o ce-sensing esis o s. Finally, he inabili y o p ope ly measu ing he hip angle by means o elec o-goniome e s led o disca d i as a con ol inpu . The men ioned imp o emen s led o a second p o o ype, illus a ed in Fig. 2(b), his ime speci ically ailo ed o he a ge emale pa ien , since he p e ious adap able design showed o be p oblema ic due o he wide ange o mo phologies ound among pa ien s. Each o hosis weigh s less han 2 kg, which was he ini ial speci ica ion o he medical s a . A PID con olle is used o con ol he posi ion o he knee ac ua o as a unc ion o he ankle angle o he con ala e al leg. A eal- ime GUI has been de eloped in o de o pa ame ically une his unc ion du ing he es s, so ha i adap s o he gai s yle o he pa ien . Acco ding o he physicians, his con ol has yielded a mo e na u al gai pa e n o he SCI subjec , who has been so a walking wi h he aid o pa allel ba s. III. FUTURE DEVELOPMENTS AND CHALLENGES The e a e s ill se e al challenges o ace in he p ojec . Fi s o all, o he pa ien o be able o walk long dis ances so ha he pe o mance can be objec i ely measu ed, po abili y o he sys em is being add essed. The objec i e is o in eg a e powe and con ol de ices inside a 2 kg backpack ca ied by he pa ien . As o he mechanical design, a no el ac ua ion sys em is unde de elopmen and he use o se ies elas ic sys ems o educe ene gy consump ion is being in es iga ed. Mo eo e , he use o elec omyog aphy (EMG) o ac i e muscles o con ol, and he use o unc ional elec ical s imula ion (FES) oge he wi h he cu en ac ua ion (hyb id ac i e o hosis) a e also being explo ed. IV. CONCLUSION This ex ended abs ac p esen s he wo k being done in a p ojec aimed a designing an a o dable and pa ien - ailo ed ac i e o hosis o gai ehabili a ion o SCI subjec s. The main ea u es o he p o o ypes and he decisions made du ing he design s age, which a e based on p ac ical expe ience on ac ual SCI pa ien s, a e ou lined. F om his expe ience, se e al design and con ol challenges a e cu en ly aced in o de o ob ain a p oduc ha could be in oduced in hospi als and ehabili a ion cen e s. REFERENCES [1] M. Hubli, and V. Die z, “The physiological basis o neu o ehabili- a ion – locomo o aining a e spinal co d inju y,” J. Neu oeng. Rehabil., ol. 10:5, Jan. 2013, pp. 1–8. [2] A.M. Dolla , and H. He , “Lowe ex emi y exoskele ons and ac i e o hoses: challenges and s a e-o - he-a ,” IEEE T. Robo ., ol 24:1, Feb. 2008, pp. 1–15. [3] J.M. Fon -Llagunes, R. Pàmies-Vilà, J. Alonso, and U. Lug ís, “Simula ion and design o an ac i e o hosis o an incomple e spinal co d inju ed subjec ,” P oc. IUTAM, ol. 2, Jun. 2011, pp. 68–81.