Sensor Array for Evaluation of Gait Cycle

BIOMEDICAL ENGINEERING VOLUME: 17 |NUMBER: 4 |2019 |DECEMBER Senso A ay o E alua ion o Gai Cycle Sla omi KARDOS, S anisla SLOSARCIK, Pe e BALOG Depa men o Technologies in Elec onics, Facul y o Elec ical Enginee ing and In o ma ics, Technical Uni e si y o Kosice, Le na 9, 042 00 Kosice, Slo ak Republic sla omi .ka dos@ uke.sk, s anisla .slosa cik@ uke.sk, pe e .balog.2@ uke.sk DOI: 10.15598/aeee. 17i4.3352 Abs ac . The gai mo ion is an essen ial pa o he li e o e e y human being. The e alua ion o human mo ion is a subjec o complex app oach and knowl- edge in he biomechanics a ea wi h applica ion in o ho- pedics, he apy and comme cial spo ing applica ions. The moni o ing and diagnos ics allow de e mining he backg ound o mo ion indi iduali ies and he de ec s easons and impac s. The a icle desc ibes he pos- sibili ies o gai cycle sensing, which has he po en- ial o use in medical diagnos ics and ehabili a ion p ocess moni o ing. The sys em inco po a es a ma ix o ou FSR (Fo ce Sensing Resis o ) p essu e senso s and an accele ome ic uni o he possibili y o pos- u e and s ep cycle e alua ion so ha i can be u i- lizable a diagnos ic o ehabili a ion du ing gai cycle e- aining o spo ing ac i i ies moni o ing. Keywo ds Accele ome e , FSR senso , gai sensing, hu- man mo ion, mic ocon olle , senso a ay. 1. In oduc ion Real- ime o logged sensing o gai pa ame e s allows he human gai analysis in medical p axis, which has a wide applica ion a ea in he ehabili a ion p ocess and acco dingly allows ea ly disco e ing o some deg a- da ion p ocesses. Fo he pu pose o he gai cycle moni o ing, he o ce and ine ial senso s a e mainly used. The ollowing analysis is applied using known e e ence da a o no mal and de ec i e p o iles o gai [1], [2] and [3]. The senso s o mo emen , o ce, loading o p es- su e measu emen a e p oduced in a ious cons uc- ions. Acco ding o he applica ion and equi ed sen- si i i y o sensing, he conc e e ones a e used [4], [5] and [6]. In echnical as well as medical p axis, he FSRs a e widely applied o measu emen o p essu e o loading ela ed pa ame e s. They consis o a laye o a conduc i e polyme , which change i s nominal e- sis ance by applica ion o he o ce a he su ace o he senso ac i e a ea. The inne s uc u e inco po a es a sys em o elec ically conduc i e composi ion wi h he non-conduc i e pa icles suspended in he solid polyme ma ix. The size o he ac i e pa icles is in sub-mic ome e o de , and hey a e u he composed o compensa e o he esis i i y empe a u e depen- dence. The applica ion o he pe pendicula o ce a he su ace o he FSR senso causes he dila a ion o he s uc u e and consequen ly, he esis ance dec eas- ing as well. The meaning ul bene i o hese senso s is in he hin p o ile o less han 0.5 mm in hickness [7]. U iliza ion o accele ome ic uni s allows high sen- si i e ine ial measu emen s o mo ion pa ame e s, which has he impac in o a wide ange o indus ial ap- plica ions. Acco ding o he pa icula ype, hey ha e compa a i ely low p oduc ion cos s and good mechan- ical esis ance. Mo eo e , hey a e he only al e na i e in many applica ions due o he size and sensi i i y. 2. Senso Sys em wi h U iliza ion o FSR and Accele ome e The human pos u e and gai a e gi en by he indi idual gi enness and habi s ha a e in luenced by a kind o li e as well as degene a ion p ocesses. The human sole is an a ea o na u ally une en dis ibu ed loading du - ing he gai cycle. The dis ibu ion o he sole loading leads o sense i by a mul i-channel senso sys em wi h app op ia e dis ibu ed senso segmen s in he a ange- men which allow he analysis o he gai . Wi h ega d o he cha ac e o he p oblema ics, he ou -channel loading senso sys em was designed as an op imal se - up which co esponds o he measu emen in ou sole c 2019 ADVANCES IN ELECTRICAL AND ELECTRONIC ENGINEERING 459 BIOMEDICAL ENGINEERING VOLUME: 17 |NUMBER: 4 |2019 |DECEMBER a eas (see Fig. 1). The i s wo measu emen poin s we e de e mined in he heel oo a ea, and he nex wo poin s a e localized in on o he plan a a ch a ea. Such applica ion ypes equi e he implemen a ion o he senso ma ix in he insole, including he equi e- men s o he compac and hin p o ile acco ding o i s speci ic localiza ion, esis ance o he p essu e and shea ela ed mechanic s ess and o he p esence o he mois u e in a ull ela i e humidi y ange due o agg essi e swea in luence possibili y. Flexible polyu e hane oam Alloca ion o plan a a ch FSR senso s Alloca ion o heel FSR senso s FSR senso s ou pu s S ainless s eel pla e Fig. 1: Alloca ion o he FSR senso a ay embedded in he insole. Assuming he men ioned equi emen s, he Tekscan FlexiFo ce A201 o ce senso s (see Fig. 2) we e applied as he sensing elemen s a he sensing poin s. P essu e sensi i e a ea wi h esis i e laye Connec o Polyes e subs a e Ag elec odes The leng h adjus able om 51 o 152 mm (a) ADHESIVE LAYER PRESSURE- SENSITIVE LAYER CONDUCTIVE LAYER FLEXIBLE SUBSTRATE (b) Fig. 2: The Tekscan FlexiFo ce A201 mechanical o ce / loading senso (a) and he simpli ied s uc u e o he senso in decomposed iew (b) [7]. The senso elemen is 0.2 mm hin, lexible compo- nen , which is easy o in eg a e in o a ge applica- ions which ha e he space limi a ions. The o e all senso wid h is 14 mm, and he diame e o he ac i e a ea is 9.53 mm. The cons uc ion o he senso inco - po a es wo lexible polyes e subs a es on which he conduc i e sil e in e connec ion laye is applied. The mechanical s ess-sensi i e laye is applied be ween he subs a es, and he o e all s uc u e is lamina ed using polyme adhesi e. The ac i e sensing a ea is de ined by ci cula sil e laye elec odes, which a e elonga ed h ough he lexible in e connec ion cable o he con- nec o , whe e he leng h can be adjus ed. The ope a- ional empe a u e ange o he senso is de ined om −40 o 60 ◦C. The signal esponse ime is gua an eed less han 5µs, which is ully su icien o he applica- ion [7] due o gai equency and dynamics. The sensing a ea o he p essu e senso is no su - icien enough o he dis ibu ed load sensing in he sense o he su ace a ea so he addi ional mechani- cal elemen s we e added in he o m o he mechani- cal ansduce and loading ac ua o . The mechanical ansduce allows expanding he loading a ea o he ou e pa o he insole and he loading ac ua o allows he concen a ion o he loading o he sensing a ea (see Fig. 3). The ou mechanical ansduce s we e ealized using molded polyamide. The inco po a ed loading ac ua o s a e disc-like p o ile elemen s wi h a ound base, which a e abou 70 % o sensing a ea o he p essu e senso acco ding o p oduce ecommen- da ions in he p oduc ion da a lis . The loading o ce applica ion has inco po a ed a shea o ce componen which can cause he displacemen o he disc elemen ou o he sensing a ea. Fo he pu pose o elimina- ion o ha un a o able e ec , he PET oil is inse ed be ween he mechanical ansduce elemen and disc ac ua o . In such a con igu a ion, he p o ec i e oil will shi i shea o ce is p esen . So he disc elemen e ains ixed o he p essu e senso . The men ioned senso sys em a angemen is inse ed be ween he wo s ainless-s eel pla es. The polyu e hane oam was used as he illing medium o he es o he sys em. Dis ibu ed loading S ainless s eel pla es Mechanical ansduce FSR senso 14 mm wid h P essu e sensi i e laye 9.53 mm wid h Disc loading ac ua o Flexible polyu e hane oam P o ec i e PET oil Fig. 3: The cons uc ion a angemen o an elemen al sensing elemen wi h he mechanical ansduce and he loading ac ua o . The ADXL345 (Analog De ices) was u ilized as he accele ome ic uni o mo ion sensing, which p o ides p econdi ioned da a in digi al o m (see Fig. 3). The accele ome e is based on a ia ion o mo ion eloc- i y sensing and in he o hogonal sys em, he 3-axis in e p e a ion is needed [8]. In case o wide u ilized c 2019 ADVANCES IN ELECTRICAL AND ELECTRONIC ENGINEERING 460 BIOMEDICAL ENGINEERING VOLUME: 17 |NUMBER: 4 |2019 |DECEMBER capaci i e MEMS (Mic o-Elec o-Mechanical-Sys em) accele ome ic sys em, he ac ual accele a ion is p o- po ional o he capaci ance change and a e con e - sion o he ol age change by: a=kd mU U0(m·s−2),(1) whe e kis he sp ing cons an (s i ness o polyc ys- alline silicon sp ing), dis he idle-s a e gap be ween he elec odes in (m), and min (kg) is ela ed o a mass o he polyc ys alline silicon seismic elemen . 3-AXIS SENSOR SENSE ELECTRONICS ADC DIGITAL FILTER 32 LEVEL FIFO SERIAL I/O CONTROL AND INTERRUPT LOGIC POWER MANAGEMENT T ADXL345 Fig. 4: The ADXL345 3-axis accele ome e uni wi h he signal p econdi ioning and I2C digi al d i e [8]. The accele ome e da a a e in o ma ion abou ac ual accele a ion in (m ·s−2) so ha i is possible o e alu- a e he dynamic a ia ion o eloci y in ime unde he gi en bandwid h. Indi idual accele ome e changes i s measu emen sensi i i y ( he change in ou pu by he co esponding change in inpu ) due o sinusoidal de- pendence. I means ha he g a i y p oduces he ac- cele a ion ou pu p opo ional o he sine o he angle be ween he senso (a he equipmen ) and he na u al ho izon (o hogonal o he g a i y ec o ): a(g)=gsin θ(m·s−2),(2) whe e gis he g a i a ional o s a ic accele a ion in (m·s−2), and θis he inclina ion angle in ( ad) ela i e o he ho izon, so ha i s alue is p opo ional o he in e se sine unc ion o he o hei a io: θ= sin−1a(g) g( ad).(3) Consequen ly, he angle change du ing accele ome e da a in e p e a ion can be calcula ed by he iangle cosine heo em: φ= cos−1axbx+ayby+azbz qa2 x+a2 y+a2 zqb2 x+b2 y+b2 z ( ad),(4) whe e aand bin (m·s−2) a e he accele a ion alues be- ween he wo accele ome e eadings in he espec i e di ec ions [9], [10] and [11]. 3. The FSR and Accele ome e Signal P ocessing The senso sys em is ollowed by he elec onic ci - cui , including ou -channel FSR senso signal p econ- di ioning, mic ocon olle o da a acquisi ion and p e- p ocessing, powe managemen including cha ging and wi eless module o da a ansmission. P econdi ioning o he signal om FSR senso s is ealized by MCP6004 in eg a ed quad uple analog ope a ional ampli ie (see Fig. 5(a)). The p essu e sensing ange and he sensi- i i y a e adjus able by he e e ence and eedback o he ampli ie . (a) (b) Fig. 5: The FSR senso s signal p econdi ioning ampli ie ci - cui y (a) and he accele ome e senso in e acing ci - cui y (b). The single-sou ce ope a ion is mo e sui able o he po able applica ion, mo eo e , wi hou he meaning- ul linea i y d op-ou , bu he eedback ange is mo e limi ed han wi h he dual (symme ic) sou ce. So ha he signal condi ioning o such ype was used wi h he ou pu ol age delimi ed by: Vou =V e RF B RF F (V),(5) whe e V e is he e e ence ol age in (V), RF B is he eedback esis o esis ance in (Ω) (Rsin he schema - ics on he Fig. 5), and RF F is he senso esis ance in (Ω) (FlexiFo ce connec o in Fig. 5). The signal om he ADXL345 is condi ioned by e - e encing a he e e ence condi ions by he so wa e. Also, he measu emen ange o he accele ome e is adjus able by so wa e and is su icien as ±2g o s an- da d gai . Due o I2C ype digi al bus, only he 10 kΩ pull-up esis o s we e added o he SDA and SCL com- munica ion pins (see Fig. 5(b)). c 2019 ADVANCES IN ELECTRICAL AND ELECTRONIC ENGINEERING 461 BIOMEDICAL ENGINEERING VOLUME: 17 |NUMBER: 4 |2019 |DECEMBER The digi aliza ion o he signal om he FSR sen- so s is ealized by he 10-bi ADC o A mel AT- mega328 mic ocon olle [12]. The p e-p ocessed da a a e di ec ed o SPP-C ype Blue oo h 2.0 uni , which allows he communica ion wi h he mic ocon olle h ough s anda d UART se ial bus. The powe man- agemen o he mic ocon olle module includes he MCP73831T in eg a ed cha ge d i e , he minia u e p isma ic 130 mAh accumula o and he 10A45 5 V Swi ched-Mode Powe Sou ce (SMPS) boos con e e [13], [14] and [15]. The o e all elec onic sys em unc- ional block schema ic diag am is desc ibed in Fig. 6 and he ealized module in Fig. 7 wi h he desc ip ion o he main componen s. USB/UART ex . module Ex . USB connec o Powe managemen Cha ge uni Blue oo h Accumula o Condi ioning + - Mic o- con olle 3-axis accele ome e 4x FSR Fig. 6: The block diag am o he FSR and accele ome ic sen- so sys em wi h signal p ocessing ci cui y and mic o- con olle module componen s. The accumula o ene gy capaci y was calcula ed e- ga ding he ene ge ic needs o he o e all sys em. Due o a ious componen s, he ol age le els also had o be adap ed. The ope a ional cu en consump ion o he ou FSR senso s is 0.4 mA including condi ion- ing ope a ional ampli ie , and is limi ed by he cu - en noise and in e e ence le el. The mic ocon olle cu en consump ion is 9 mA, he Blue oo h uni con- sumes 8 mA du ing communica ion so ha he powe consump ion o he o e all sys em wi h addi ional loses a 5 V cha ge pump boos swi ching sou ce is 100 mW in maximum. Tha esul s in app oxima ely 5–6 hou s o 130 mAh accumula o ope a ion wi h he elec oni- cally limi ed ol age. The p isma ic Li-ion accumula o was selec ed due o i s e y low p o ile which wi h he su ace moun ed de ices a he ibe -glass epoxy subs a e esul s in o only 3 mm o e all hickness and 48 ×55 mm size o he module. This p ope y pe spec i ely allows he in eg a ion o he module in o shoe insole oge he wi h he FSR senso s. MCP73831T cha ging uni 130 mAh Li-ion acc Powe swi ch 10A45 boos DC/DC con e e P og amming and cha ging connec o MCP6004 quad uple ope a ional ampli ie ATmega328 mic ocon olle Blue oo h uni FSR senso s inpu ADXL345 3-axis accele ome e Fig. 7: The FSR and accele ome ic senso sys em signal p o- cessing mic ocon olle module including powe man- agemen . The mic ocon olle code p o ides ini ializa ion o senso channels, se ing o communica ion p o ocols and ans e a es o he digi al buses, he da a acqui- si ion, i s p ocessing and consequen wi eless ans e h ough he SPP-C Blue oo h uni o he PC applica- ion. An FSR senso applica ion is p eceded by ini ial- iza ion using he me hodology s a ed in he p oduc da ashee . The p ocess s a ed by loading o each sen- so by 110 % o he ope a ional ange du ing 3 seconds and epea ed i e imes. The nex s ep included p o- g essi e loading by 1/3, 2/3 o he ull loading. The ini ializa ion was no applied on a ba e senso , bu he ull mechanical chain desc ibed in Fig. 3 wi h esul an con e sion cu es in Fig. 8 was e alua ed. 1 2 3 4 5 5 15 25 35 45 Vol age (V) Load (kg) Senso 1 Senso 2 Senso 3 Senso 4 Linea 1 Linea 2 Linea 3 Linea 4 Fig. 8: The g aphical dependencies o FSR senso s ou pu s which we e condi ioned by a ecommended mechanical loading. A e he condi ioning, measu emen ange and sen- si i i y se ing, he senso segmen s we e e alua ed o hys e esis in he loading ange om 5 o 50 kg due o c 2019 ADVANCES IN ELECTRICAL AND ELECTRONIC ENGINEERING 462 BIOMEDICAL ENGINEERING VOLUME: 17 |NUMBER: 4 |2019 |DECEMBER mechanical ansduce and loading ac ua o in luence. The esul an hys e esis (see Fig. 8) means up o 2 % de ia ion be ween inc easing and dec easing loading a he pa icula senso segmen . 1 2 3 4 5 5 15 25 35 45 Vol age (V) Load (kg) Senso 1 (5 kg → 50 kg) Senso 1 (50 kg → 5 kg) (a) Senso 1. 1 2 3 4 5 5 15 25 35 45 Vol age (V) Load (kg) Senso 3 (5 kg → 50 kg) Senso 3 (50 kg → 5 kg) (b) Senso 3. Fig. 9: G aphical dependencies o condi ioned FSR senso hys- e esis ( he Senso 1 om heel oo a ea and he Senso 3 om he plan a a ch a ea). The expe imen al mechanical loading es ing was e- alized a Tes ome ic M250-2.5CT equipmen . The esul an con e sion cha ac e is ics o he senso ma- ix we e used o e alua ion o loading in e p e a ion, which is in luenced by o e all mechanical s uc u e. 4. In e p e a ion So wa e The FSR senso s da a a e help ul o pos u e as well as gai cycle loading analysis. In he module, he senso s a e dis ibu ed acco ding o ele an loading poin s in he plan a a ea so ha he subs an ial di e ences be- ween he le and igh oo as well as de ia ions in compa ison wi h a no mal gai can be iden i ied and analyzed. Fo he loading ac i i y moni o ing, he da a acquisi ion wi h he g aphical use in e ace (see Fig. 10) unde he LabVIEW applica ion was c ea ed wi h he u he possibili y o s a is ical ea men . The pos -p ocessing o acqui ed da a is ealized in he Mo ion Logge applica ion unde he LabVIEW sys em [16], which was de eloped o he pu poses o ine ial senso s da a p ocessing. Fig. 10: The Foo Balance applica ion g aphical use in e ace in he LabVIEW sys em [15] o oo loading e alua- ion du ing a gai cycle. Fig. 11: The Mo ion Logge g aphical use in e ace in he Lab- VIEW applica ion o measu emen o mo ion dynam- ics by he 3-axis accele ome e du ing a gai cycle. The condi ioning includes digi al il a ion ealized by con igu able bandpass Bu e wo h ype il e [17], [18], [19], [20] and [21]. The pu pose o he il e is o elimina e he s a ic accele a ion (g a i y) componen s as well as he elimina ion o highe equency compo- nen s which occu by noise and signals gene a ed by human body biological p ocesses and o he ou e in lu- ences. In he LabVIEW applica ion, he e is a possi- bili y o selec he measu emen mode and addi ional pa ame e s including ype and pa ame e s o he il a- ion. The addi ional pa ame e s and unc ions a e a ail- able as he o se , sample a e and a e aging o da a (see Fig. 11). c 2019 ADVANCES IN ELECTRICAL AND ELECTRONIC ENGINEERING 463 BIOMEDICAL ENGINEERING VOLUME: 17 |NUMBER: 4 |2019 |DECEMBER In Fig. 12 and Fig. 13, he expe imen al plo s ep e- sen he single s ep signal o 2 selec ed channel FSR and 3-axis accele ome e ou pu . Fig. 12: The single s ep sample signal o he 2-channel FSR ( o he heel oo a ea in blue and o he plan a a ch a ea in ed). Fig. 13: The single s ep sample signal o he 3-axis accele om- e e ( o ans e sal axis in blue, o longi udinal axis in ed and o e ical axis in g een (un il e ed g)). Based on FSR senso s and accele ome e da a in e - p e a ion, he a ious ypes o pos u e and gai aul a ia ions due o a ious ac o s can be ecognized by he medical s a : •une en pos u e ela i e p oblems, •p og essing os eopo osis, •muscula dys ophy, • a ious gai i egula i ies. The egene a ion p ocesses a e he inju y acciden s can also be e alua ed by compa ison measu emen s. In addi ion, spo s ac i i ies in ama eu o p o essional scale can be e alua ed using gai moni o ing as well. 5. Conclusion In he a icle, he ou -channel loading and 3-axis mo- ion senso sys em wi h signal p ocessing elec onics module was designed and ealized by he applica ion equi emen s. The buil senso sys em consis s o ou FSR p essu e senso s which we e embedded in he heel and plan a a ch a ea acco ding o he physiology o he human oo , and he 3-axis accele ome e was a - ached o he p ocessing elec onics module. The mi- c ocon olle module includes he condi ioning, digi al- iza ion, p e-p ocessing and wi eless ansmission wi h he in eg a ed accumula o and powe managemen . The module was designed as a la 3 mm s uc u e which is applicable o embedding in o a cus omized shoe insole. The sys em can be u ilized o lowe limb gai and loading analysis wha means he ac i e sens- ing o mo ion ac i i ies including ehabili a ion d i e simula o and o o he spo s and ehabili a ion pu - poses. The con inuing wo k is aimed o signal il a ion and de ailed in e p e a ion o he accele ome e da a. Acknowledgmen This con ibu ion is as a pa o he wo k unde he VEGA 1/0224/18 p ojec . Special hanks belong o Ma in S upak o ac i e pa icipa ion on he wo k. Re e ences [1] DUNGL, P. O opedie. 1s ed. 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DOI: 10.12700/APH.15.6.2018.6.9. [21] SEEL, T., J. RAISCH and T. SCHAUER. IMU- Based Join Angle Measu emen o Gai Analy- sis. Senso s. 2014, ol. 14, iss. 4, pp. 6891–6909. ISSN 1424-8220. DOI: 10.3390/s140406891. Abou Au ho s Sla omi KARDOS de ended his Ph.D. hesis in he ield o capaci i e posi ion senso s in 2007 a he Depa men o Technologies in Elec onics, Technical Uni e si y o Kosice. His wo k is ocused on in e - connec ion echniques, ine hick ilm echnologies, passi e componen s and MEMS echnologies. S anisla SLOSARCIK is a ull p o esso a he Depa men o Technologies in Elec onics, Tech- nical Uni e si y o Kosice. His wo k is ocused on in e connec ion and moun ing echnologies in elec- onics, LTCC-based 3D-shaped modules, senso s and echnologies o 3D in eg a ion o sys ems. Pe e BALOG de ended his diploma hesis in 2014 a he Depa men o Technologies in Elec onics, Technical Uni e si y o Kosice whe e he de ended his Ph.D. hesis in he same yea . The heme o his disse a ion hesis was "Sys em o Mo emen o Pa aplegics". c 2019 ADVANCES IN ELECTRICAL AND ELECTRONIC ENGINEERING 465