Forearm-attachable EMG-based wireless controller

Recen Inno a ions in Mecha onics (RIiM) Vol. 3. (2016). No. 1-2. DOI: 10.17667/ iim.2016.1-2/18. Fo ea m-a achable EMG-based wi eless con olle Tamás Bán i BSc Budapes Uni e si y o Technology and Economics Facul y o Mechanical Enginee ing, Depa men o Mecha onics, Op ics and Mechanical Enginee ing In o ma ics Budapes , Hunga y ban i. [email protected] Pe a A adi PhD Budapes Uni e si y o Technology and Economics Facul y o Mechanical Enginee ing, Depa men o Mecha onics, Op ics and Mechanical Enginee ing In o ma ics a adi.p[email p o ec ed] Abs ac — This pape p esen s he de elopmen p ocess s a ing om a simple elec onic module o ampli ica ion o EMG signals. Du ing de elopmen he asks o be sol ed we e ex ended owa ds he c ea ion o an EMG-base con olle ha e en ually can be connec ed o a PC. Among he main goals we e he simplici y and low cos o p oduc ion. The e a e simila de ices comme cially a ailable, bu he main ocus was on he whole p ocess o design, es ing, ab ica ion and he explo a ion o applica ion a eas. I was impo an o use medical ecommenda ions. The de ice ma ches he sugges ion o SENIAM, excep o he esolu ion o A/D con e sion, which is pe missible due o he ac ha i was no designed o medical pu poses. The inal e sion is capable o de ec ing and ampli ying EMG signals, wi h he app op ia e il e ing and digi izing p ocedu es o u he p ocessing. Wi h he de elopmen o wi eless communica ion capabili ies, he de ice which can be a ached o he o ea m can be used as a USB HID de ice wi h a PC. A numbe o addi ional applica ions a e also discussed, poin ing ou he ac ha his piece o echnology o e s a wide ange o possibili ies. Keywo ds—elec omyog aphy, a m mo emen , A duino, STM32 mic ocon olle , signal p ocessing, USB HID con olle I. INTRODUCTION A. The pu pose o he wo k Elec omyog aphy (EMG) is a widely-used medical p ocess o examine he ac i i y o muscles. The de ice is called elec omyog aph, he diag am being de ec ed is he elec omyog am, which ep esen s he elec ical ac i i y o muscles in mV o μV ange o e ime. Du ing he measu emen elec odes a e a ached o he skin su ace o needles a e inse ed in o he muscles. The second solu ion is much mo e accu a e, bu i can sense he elec ic ac i i y o jus a ew mo o uni s. This is an in asi e me hod, so medical p o essionals use i mos ly o speci ic diagnos ic pu poses. The nonin asi e o m is applied o mo emen de ec ion o as a senso . The p esen ed de ice is based on he second me hod. In o de o measu e he muscle ac i i y, a pai o elec odes is a ached longi udinally o he skin su ace abo e he muscle. The muscles in his applica ion a e he o ea m muscles, esponsible o mo ing he w is and inge s. As su ace de ec ion is he chosen me hod, he p o ound muscles canno be examined. This is one o he easons, ha du ing de elopmen and es ing he de ice he loca ion, o ien a ion and unc ion o hese muscles mus be known [1], [2], [3]. To gain mo e in o ma ion abou he a m’s mo ion, a 6 deg ee o eedom accele ome e and gy oscope, an IMU (Ine ial Measu emen Uni ) is used. This senso de ec s angula and linea accele a ion. Fu he mo e, choosing he mos sui able mic ocon olle is also an impo an s ep. I mus be able o a end o se e al unc ions: digi izing 8 analog channels conside ing he Nyquis -Shannon sampling heo em, communica ing wi h he IMU and sending he da a o ano he con olle wi elessly. B. The cha ac e is ics o he EMG signal Figu e 1 shows an elec omyog am measu ed by a medical de ice. The elec odes a ached o he pa ien s’ o ea m de ec muscles’ ac i i y while g abbing. Du ing he esea ch, he pa ien ’s ask was o g ip a dynamome e , hen elax he muscles. This p ocedu e had o be epea ed i e imes while inc easing he o ce. The i s g aph ep esen s he dynamome e ’s alues in kg, he second one shows he aw-, he hi d one he il e ed EMG signals in mV, all o hem o e ime. Fig. 1. Elec omyog am [7] I can be easily obse ed ha EMG signals a y, while he g abbing o ce is cons an . Acco ding o he en elopes, i would be eally di icul o de e mine he ix g abbing o ce. Ano he obse a ion is ha he huge o ce one exe s, he highe he g aph’s g adien is. This e ec is explained by he s ia ed muscles’ a igue. Mo eo e , he en elope’s smoo hness can be inc eased by educing he low-pass il e ’s equency. Howe e , his would wo sen he eac ion ime. Las , bu no leas , i is a di icul ask o di e en ia e low- o ce g abbing signals om noise. Recen Inno a ions in Mecha onics (RIiM) Vol. 3. (2016). No. 1-2. DOI: 10.17667/ iim.2016.1-2/18. Summing up he consequences o he measu emen , i is clea ha du ing he p ocessing o EMG signals, one has o deal wi h se e al di icul ies. II. HARDWARE INTERFACE A. Designing and building he ci cui I was necessa y o design and build a ci cui o measu ing and ampli ying he EMG signals. A i s , a es - panel was buil o he de ec ion o only one EMG channel, based on ideas om [8]. A common A duino panel was used o digi iza ion o he measu ed EMG signal. Gaining expe ience om his unc ioning ci cui , he inal panel, which can measu e 8 channels was designed and c ea ed. I con ains an accele ome e and gy oscope, as well as a wi eless adio module. The A/D con e sion o signals was pe o med by an STM32F4 Disco e y panel, because i s speed and esolu ion a e much highe , han ha o he i s choice o A duino Mega. The ol age supply was a 9V ba e y. B. The panels in he de ice The de eloped panels can be di ided in o wo g oups based on hei unc ions: ins umen a ion ampli ie panels and ope a ional ampli ie panel. The second one is also a shield o he STM32. The ins umen a ion ampli ie de ec s he po en ial di e ence be ween he wo ends o he muscle ha is how he EMG signal is gene a ed. Mo eo e , hese panels p o ide ampli ica ion by 20. As i ope a es om an asymme ic powe supply, he signals ha e o be pu on o a 1,5 V o se be ween 0 and 3V. Then a band-pass il e was applied, which emo es he unnecessa y high and low equency componen s. By cu ing he low band, he d i and he DC o se a e elimina ed. High- equency il e ing ex ac s he noises and p e en s aliasing. Acco ding o SENIAM (Su ace Elec oMyoG aphy o he Non-In asi e Assessmen o Muscles) [5], o su ace elec odes 5-10 Hz high-passing and 500 Hz low-passing should be used (Figu e 2). In he cou se o he de elopmen , based on he ga he ed da a, 7.23 Hz high- and 482.29 Hz low-passing equencies we e se . Fig. 2. Schema ic ou line o a sEMG eco ding sys em [6] C. The inal PCBs A e planning he ci cui s, NI Mul isim simula ion so wa e we e used o es s. Figu e 3 shows he Bode diag am esul s om he simula ion. Fig. 3. Bode diag am esul o he simula ion The PCBs we e designed wi h a p og am called DipT ace. PCB e ching and solde ing he componen s we e he inal manu ac u ing s eps. All in all, 8 smalle panel (Figu es 4 and 5), as well as a la ge shield we e made (Figu es 6 and 7). Fig. 4. PCB design o he small ins umen a ion ampli ie ’s’ panel Fig. 5. PCB o he small ins umen a ion ampli ie ’s’ panel Recen Inno a ions in Mecha onics (RIiM) Vol. 3. (2016). No. 1-2. DOI: 10.17667/ iim.2016.1-2/18. Fig. 6. PCB design o he shield Fig.7. PCB o he shield wi h he ope a ional ampli ie s, he wi eless adio module and he IMU III. SOFTWARE INTERFACE Fo he compu e p ocessing o he signal, a digi al low- pass il e is needed because o he i ing o he en elope. Fi s , he signal mus be ec i ied: he p og am measu es he EMG signals symme ic o 1.5V, hen subs ac s he mean alue om hem, so ha he o se will be 0. A e ha nega i e numbe s will be in e ed. As o he il e ype, he usage o IIR (In ini e Impulse Response) is easonable, because i p o ides highe p ocessing speed and esul s in a smoo he en elope, han FIR (Fini e Impulse Response) il e s. A 2nd o de Bu e wo h il e wi h 5 Hz cu was chosen a e ex ensi e es ing. A. Tes ing The boa d was es ed wi h an A duino Mega a i s . To display he signals, a ba e y-powe ed lap op was chosen, in o de o elimina e mains dis u bance. The p og am sen he aw and he il e ed EMG signals wi h se ial communica ion o he PC, whe e hey we e eco ded. These esul s we e isualized wi h Mic oso Excel. Figu e 8 shows he aw (uppe ) and he il e ed (lowe ) EMG signals using 5 Hz cu . The ho izon al axis shows ime in seconds, he e ical axis shows he digi ized alue, whe e 1023 bi co esponds o 5V. Fig. 8. The aw (uppe diag am) and he il e ed (lowe diag am) EMG signals using 5 Hz cu B. Final boa d The inal de ice unc ions (Figu e 9) as a con olle a ached wi elessly o a PC. I is able o handle 8 di e en EMG signals and he da a o he IMU simul aneously. The ci cui s a e loca ed in di e en plas ic boxes, which can be a ached o he o ea m wi h an elas ic band. The STM32 and i s shield a e in a bigge box. The nRF24L01+ communica ion module p o ides he high ange wi eless communica ion wi h he PC. Fi s , he ansmi e p og am eads he signals o he 8 analog inpu s. Each o hem a e a e aged, o ming he channels’ o se s. O se s a e sub ac ed om aw signals, so hei mean alue will be 0. Nega i e signals a e in e ed, hen a 2nd o de Bu e wo h il e p ocesses hem. These signals and he IMU’s da a a e sen o he ecei e . The da a a i e in an a ay o he ecei e , which disassembles and pu s hem o di e en a iables. The ecei e con e s IMU’s da a in o he i ems o X and Y axes. Two EMG signals, gene a ed by a lexo and an ex enso muscle, a e u ned in o a logical alue. I he muscle is ac i e, a bu on is pushed. All he da a a e sha ed wi h he PC. Fig. 9. The inal de ice Recen Inno a ions in Mecha onics (RIiM) Vol. 3. (2016). No. 1-2. DOI: 10.17667/ iim.2016.1-2/18. IV. CONCLUSION The i s expe imen al esul s came om es ing he panel made o A duino. A e ha a p in ed ci cui boa d was designed, buil and es ed, so ha inciden al e o s could be ecognized and co ec ed. Then he digi al il e s app op ia e o adjus ing he en elope we e selec ed. La e on he inal de ice was made "mobile" wi h a 433 MHz communica ion module. Du ing he p ojec , he e o s we e iden i ied and co ec ed, so ha in he inal de ice hey we e omi ed. Wi h he expe ience gained du ing de elopmen and es ing, a much as e sys em was designed and c ea ed, ha is capable o moni o ing 8 muscles, and can be placed on he o ea m wi hou elec ode cables. STM32F4-Disco e y handles digi iza ion, and includes a much as e mic ocon olle han A duino, so ha he sampling equency could ha e been inc eased. Fu he ad an age o STM32F4- Disco e y is a 12 bi A/D con e e compa ed o A duino's 10 bi sys em, inc easing he esolu ion o he sampled signals. Choosing he new, high pe o mance 2.4 GHz wi eless communica ion ins ead o he 433MHz modules, he ope a ional ange and da a speed inc eased conside ably. By upg ading he de ice wi h a Six-Axis Mo ion T acking De ice, he a m's posi ion and mo emen could be moni o ed wi h mo e de ails. The ci cui boa d o he ecei e , which is able o communica e se ially wi h he compu e was also designed and buil . Fu he mo e, he inal de ice can be connec ed o he compu e as an USB HID (Human In e ace De ice). The e is no need o ins all a d i e , he de ice can be used soon a e connec ion. This unc ion was es ed on a ocke powe ed ai c a simula o game called HAWX, whe e he igh e je s we e con olled by he de ice a ached o he playe 's o ea m (Figu e 10). Fig. 10. Playing wi h he simula o V. FURTHER APPLICATION AND TASKS A. Examina ion o muscle a igue The o ea m muscles a e olun a ily mo eable s ia ed muscles, which a e p one o a igue. This ea u e can be de ec ed wi h an EMG boa d. All one has o do is o pu he elec odes on o he biceps muscle. Then a hea ie weigh should be li ed and hold as long as possible. Du ing he exe cise he ampli ude o he EMG signal educes slowly. I is also a good idea o use he de ice o wo kou ollow-up. B. Follow-up o physio he apy ea men s When someone needs o do physio he apy egula ly, he e iciency could be supe ised, as well as he buildup o s eng h. Fo ins ance, du ing he exe cise he pa ien should epea edly push a small ubbe ball. The mic ocon olle coun s one up a e he EMG signal eaches a ce ain analog alue. C. Con olling a d one o mobile obo The 2,4 GHz communica ion module can be used o con ol d ones o e en obo s because o i s qui e la ge ange. Mo ing he gy oscope, i can di ec he con olled ehicle’s mo emen . Wi h he s e ching o elaxing o muscles di e en o de s can be gi en. One o i s ad an ages is ha he hand emains ee. D. Examining walk and balance The inal de ice shows muscles’ elec ic ac i i y in a sui able way, so a aching i o he leg, he ac i a ion le el can be sensed while walking o balancing. E. Redesign I is wo h o examine he possibili ies o edesign he de ice in a mo e compac o ma , o a wide ange o applica ions. REFERENCES [1] A. Fonyó A ila: Medical Physiology (Az o osi éle an anköny e). 7 h Ed.. Budapes , Medicina, 2014. [2] M. Ré helyi, J. Szen ágo hai: Func ional Ana omy (Funkcionális ana ómia). Band I. Budapes , Medicina, 2006. [3] F ied ich Paulsen, Jens. Waschke: Sobo a A las o Human Ana omy (Az embe ana ómiájának a lasza). 22nd Ed. Band I. Budapes , Medicina, 2012. [4] William Rose: Elec omyog am analysis. 2014. h p://www.udel.edu/biology/ osewc/kaap686/no es/EMG%20analysis.p d [5] SENIAM 8 Eu opean Recommenda ions o Su ace Elec oMyoG aphy. Published by Roessingh Resea ch and De elopmen b. . 1999. [6] D.F. S egeman, H.J. He mens: S anda ds o su ace elec omyog aphy: he Eu opean p ojec "Su ace EMG o non-in asi e assessmen o muscles (SENIAM)". h p://www.med.uni- jena.de/mo o ik/pd /s egeman.pd [7] L. Dé á i: In es iga ion o muscle ac ion wi h elec omypg aphy (Az izomműködés anulmányozása elek omiog á ia segí ségé el) h p://de a i.web.el e.hu/gyak_jegyze /emg.pd [8] Backya d B ains. Neu oscience o E e yone! h ps://www.backya db ains.com/