Debjyoti Chowdhury. Arunabha Mitra Appld. Electron. & Instru. Engg. Heritage Institute of Technology, Kolkata , India. Madhurima Chattopadhyay

Transcription

1 Ral Tim Dsign and Implmntation of Brushlss DC Motor Driv basd Continuous Positiv Airway Prssur (CPAP) basd Rspirator Systm for Patints with Chronic Obstructiv Pulmonary Disass (COPD) Arunabha Mitra Dbjyoti Chowdhury Madhurima Chattopadhyay ABSTRACT This papr aims at dsigning a cost-ffctiv, portabl and asy-to-us brushlss DC (BLDC) motor drivn continuous positiv airway prssur (CPAP) basd rspirator for patints with acut brathing troubl. Th proposd systm is intndd to facilitat continuous monitoring of patint's condition with positiv airway support providd by a brushlss DC (BLDC) motor drivn rspirator blowr fan by masuring Rspiration Rat (RR). To masur th rspiration rat, a pair of capacitiv typ rspiration rat snsors ar mountd blow Right Nostril (RN) and Lft Nostril (LN), in such a way that th nasal airflow during inspiration and xpiration imping on th snsor diaphragms dirctly. Du to irrgularitis in nasal airflow in som rspiratory disass, th rspiration rat (RR) varis from th normal rat (12-20). Thus, a supporting airflow rgulatory systm has bn dsignd to rduc abnormalitis in rspiration rat (RR). In this cas a low cost snsorlss commutatd BLDC driv is implmntd with a thr phas invrtr and microcontrollr by using fdback of rotor rpm. A suitabl cost ffctiv algorithm has also bn dvlopd to gnrat an appropriat six transistor switching squnc to commut th BLDC motor according to th RR of th subjct. Th charactristics of th implmntd driv giv satisfactory outputs ovr a wid rang of controlld spd variation from 200 to 2440 rpm which rquirs a match with th patint s brathing dmand. Th ffctivnss of th dsignd systm is populatd by th ral tim xprimntal rsults. Kywords Positiv Airway Rspirator, Blowr Fan, Brushlss DC Motor, Rspiration Rat, Chronic Obstructiv Pulmonary Disass. 1. INTRODUCTION Chronic obstructiv pulmonary disas (COPD) has bcom th fourth lading rason of dath across th world which causd around 2.7 million daths in By th nd of 2020, COPD is xpctd to com up as a third most common caus of dath [1]. Thr ar two typs of COPD disass namly mphysma and chronic bronchitis. Emphysma (causd by continud smoking) and chronic bronchitis (causd by th xposur to indoor and outdoor air pollutants) both of thm ar major rasons of brathlssnss. Ths disass obstruct th windpip to th lung and which may in turn chok th rspiratory systm if it is not takn car proprly. In th arlir days, polysomnography was th mthod followd in ordr to diagnos th slp rlatd disordrs but it involvd tim consuming procdur, causd som amount of discomfort as a numbr of lctrods ar attachd to th patint s body and was costly as wll [2]. This ld to th furthr dvlopmnts of dvics such as rspiratory polygraphy which may b anothr option to dtct slp disordrs. Both of ths dtction tchniqus ar complx and rquird to b carrid out in th prsnc of qualifid halthcar staff. Bcaus of ths svr drawbacks, nw trnds in this fild of halthcar cam forward namly continuous positiv airway prssur (CPAP) machin which was invntd by Colin Sullivan in Jun 1980 and h applid this thrapy initially for fiv patints with svr obstructiv slp apna syndrom [3]. In this systm, air is pumpd undr prssur into th airway of th lung so as to kp th windpip to th lung opn at th tim of slping. This systm compriss of a small machin with a hos that is placd at th sid of th patint s bd. This papr bgins with introduction, givn in Sction I. In Sction II, w hav dscribd th condnsr typ capacitiv snsor. Sction III puts forward th dscription of th driv systm for thr phas BLDC motor. Aftr this, sction IV throws light on th ral tim implmntd hardwar. Followd by, Sction V which stablishs th rsults dscribing th rspons of th snsor and aptnss of th blowr. Sction VI concluds th work with th ssnc of outcom of this proposd schm. 2. OVERVIEW OF THE PROPOSED SYSTEM Th CPAP machin proposd hr provids a fixd airway prssur to th subjct undr study by liminating th nd of convntional cylindrs of lif-support gass. Morovr, th portability and robustnss of th dsignd machin maks it a quick option to b considrd into th fild of halthcar [4]. Whil taking th subjct undr study to hospital, th proposd dvic can b considrd as a vry ffctiv mans of providing continuous air support. 46

2 Control Circuit for 3-phas BLDC motor Suprvisory Controllr Blowr Fan drivn by BLDC motor Signal conditioning circuitry Mask Rspiration Rat (RR) Snsor Fig 1: Schmatic diagram of Positiv Airway Rspirator using BLDC drivn blowr fan In ordr to provid a variabl positiv airway prssur and to ovrcom th drawbacks of th xisting systms, this systm is intndd to srv for th patints with COPD. An ida of th proposd systm is illustratd in Fig DESCRIPTION OF THE PROPOSED SYSTEM 3.1 Snsor A pair of lctrt (a dilctric matrial having a quasiprmannt lctric charg or dipol polarization) condnsr typ capacitiv snsors of xactly sam mak is mountd vry clos to th human nostrils on th innr sid of a rspiratory mask. Th arrangmnt can b wll undrstood from a sid viw of th sam as dpictd in Fig. 1. Th ncssity of two snsors coms into play bcaus of th fact that human nostrils altrnat th brathing onc in a day and varis from prson to prson. Th rspiration is snsd by th diaphragm insid th snsor followd by a chang in th capacitanc and as a rsult, th voltag across it givs th intnsity of th xhald prssur. A cross-sctional viw of a traditional lctrt condnsr typ snsor is shown in Fig. 2 which illustrats that th JFET fabricatd insid th housing typically acts as a microphon pramplifir. Analog-to-Digital Convrtr (ADC) rquirs th analog signal ntring at its input to b of magnitud of th ordr of Volts (Rang: 0-5 V). Thus th rquirmnt of signal conditioning is wll undrstood. Th block diagrammatic rprsntation of th signal conditioning circuitry is shown in Fig. 3. Th Amplifir and th Filtr, togthr condition th RR signal. 3.3 Suprvisory Controllr Th oprational mthodology of th ntir systm is govrnd by an algorithm followd by th Suprvisory controllr. As th nam suggsts, it is simply a microcontrollr having a prwrittn program (as pr th algorithm) in it. A dtaild discussion of th algorithm is prsntd in Sction IV. 3.4 Control Circuitry for thr phas BLDC motor This sction puts forward th ida of controlld rotation in a thr phas BLDC motor using an xtrnal commutation circuit. Th driv powr is givn to motor windings via a thr phas invrtr consisting of six Bipolar Junction Transistor (BJT) switchs [7]. Th opration of th forsaid switchs insid th drivr follow a particular squnc which dpnds on th rotor position as wll as th rotor spd, shown by Tabl I. Th switching squnc is providd to th drivr by a microcontrollr, which taks a continuous fdback of th rotor position and th rotor spd [8]. Th rotor position is stimatd by zro crossing th back EMFs [9] gnratd in th thr windings of th BLDC motor [10]. Th rotor spd is masurd and fd back to th microcontrollr in ordr to vrify th achivmnt of th dsird rotational spd. Th block diagram of th spd control circuit is shown in Fig.3. Rf. Masurmnt Microcontrollr D 1 D 2 D 3 D 4 D 5 D 6 Motor drivr v a v b v c BLDC Motor Back EMF procssing circuitry Fig 1: A cross-sctional viw of th RR snsor [5] 3.2 Signal Conditioning Circuitry Th signal gnratd by th RR snsor is of th ordr of mv and contains nois gnratd du to th ambinc [6]. Th RR Snsor Amplifir Band Pass Filtr (1-2.5 Hz) ADC Fig 4: Block diagram of spd control circuit Th rfrnc spd is gnratd as th motiv to supply corrctional volum of air to th subjct undr obsrvation. This valu is gnratd by th microcontrollr and dirctly utilizd for th spd control algorithm. On th othr hand, back EMFs gnratd in th thr windings ar fd to th microcontrollr, and th rotor position is roughly stimatd which in turn dtrmins th xact commutation squnc. Th microcontrollr gnrats six signals i.., D 1, D 2, D 3, D 4, D 5 and D 6, which ar supplid to th bas trminals of th transistors usd. Th drivr givs thr phas supply to th motor i.., v a, v b and v c. Fig 3: Block diagram of th signal conditioning circuitry 47

3 D 1 V dc Q 1 Q 2 Q 3 Start D 2 D 3 D 4 D 5 D 6 A B C R L a R L R L I c b c I a I b Rspiration by subjct undr obsrvation Q 1 ' Q 2 ' Q 3 ' Fig 4: Six transistors basd thr phas invrtr Th thr phas six switch motor driv with th commutation lins by using transistor bass is shown in Fig.4. Th voltag across th RR snsor is quantizd by an ADC fabricatd within th microcontrollr. 3.5 Blowr Fan drivn by BLDC motor with Mask Th BLDC motor is coaxially coupld to a blowr assmbly of almost sam siz to that of motor [11]. Th commonly availabl mdical mask is usd in th dvlopd stup that houss th RR snsors optimally clos to th nostrils of th subjct undr study [12]. Th snsors ar mountd in such a fashion that thy can b rmovd whil strilizing th mask for r-using of th sam mask. On nd of a transparnt flxibl pip supplying th corrctional volum of air is attachd to th mask and th othr nd is connctd to th xhaust of th blowr assmbly. 4. ALGORITHM FOLLOWED BY THE SUPERVISORY CONTROLLER In this sction, th algorithm rsponsibl for supplying corrctional volum of air to th mask is dscribd. As soon as th dvic is powrd ON, th blowr starts to rotat at a prdfind spd, which is in proportion to RR of a halthy subjct. At first, th RR snsd is masurd with th standard/normal RR (of a halthy subjct) [13]. If th masurd RR coms to b normal, thn th prvious supply volum of air is maintaind. If th RR is found to b abnormal, thn th ncssary corrctional volum of air is gnratd by optimally altring th BLDC motor spd. This whol ida is prsntd by a flowchart shown in Fig. 5. Th Suprvisory controllr is programmd with th proposd algorithm as mntiond in subsction 3 of Sction REAL TIME IMPLEMENTATION OF BLOWER DRIVEN BY BLDC MOTOR Th implmntd hardwar is built using six pairs of BC548 transistors with IN4148 diods in anti-paralll connction opratd by an 8-bit Atml microcontrollr ATmga328p-pu. An appropriat algorithm considring a pr-dfind transistor switching squnc is writtn to th microcontrollr prsnt in th said commutation systm. Th rotor spd is masurd and fd back to th driv systm by a photo diod pair. Th voltag across th RR [11] snsor is quantizd by an ADC fabricatd within th microcontrollr [12]. This quantizd valu is mad us of by th algorithm to dtrmin th brathing pattrn and accordingly a corrction signal is gnratd. Th dsignd ral tim hardwar consisting of BLDC motor run blowr fan opratd by th 3 phas motor No RR Snsor Is RR Abnormal Fig 5: Flowchart of th proposd algorithm of opration for th suprvisory controllr drivr is shown in Fig.5. Th blowr is mad oprational at a dsird spd till abnormality in brathing prsists. Th proposd algorithm of opration for th PAR [14] systm is dscribd by a flow chart as shown in Fig.6. Fig 6: Ral tim implmntd hardwar Morovr, th systm is calibratd to cancl ffcts du to audio frquncy nois and dc biasing. Th signal conditioning circuit is chosn in such a fashion that low frquncy signals will b liminatd.? Ys Optimiz th BLDC Corrctiv volum of air is dlivrd by a BLDC drivn blowr 48

4 Rotor (rpm) Intrnational Journal of Computr Applications ( ) Tabl 1. Spcifications of th mployd BLDC motor Motor Paramtrs Ratd DC voltag Ratd Currnt Stator Rsistanc Torqu Constant Ratd Lif of working Valus 12 V 110 ma 1.7 Ω Nm 5400 rpm 50,000 hours Th paramtrs of thr phas BLDC motor usd in our work ar displayd in Tabl 1. It can b infrrd by taking a look at th paramtrs that th proposd systm can b a compltly portabl systm. W hav dsignd a rgulatd powr supply of 12 volts as a powr sourc from 230 V AC main. In ordr to mak th systm portabl, a LiPo battry of sam output can b mad us of. Th spcifications of th usd capacitiv snsor ar listd in Tabl 2.. Tabl 2. Spcifications of th RR snsor Snsor Spcifications Snsor typ Ratd DC Voltag Ratd Currnt Frquncy (F) Snsitivity (F =1 khz) Signal to Nois Ratio Valus Elctrt Condnsr 10 V 0.5 ma 50-60,000 Hz -42 ± 2 db 60 db 6. RESULTS This sction puts forward th ral tim xprimntal rsults Fig 7: Rspons of th RR Snsor obtaind from th dsignd positiv airway prssur rspirator. Th output of th RR snsor bing analog in natur is takn via a 10 bit analog to digital convrtr (ADC) and is rprsntd as quantizd digital valus ranging from 0 to 1023 ( ) in Fig.7 along with normal and abnormal brathing rgions for various groups. Th systm so dvlopd was tstd on thr diffrnt ag groups for bttr accuracy. Th brathing pattrn so obtaind from th RR snsor is fd to th suprvisory controllr which obtains rspiration rat to dtrmin th corrct rpm for th BLDC blowr, shown in Fig.8. Th xactnss of th achivd rpm for th BLDC blowr fan is cross chckd via a rotor rpm fdback assmbly. Thr diffrnt kinds of rspons indicat th aptnss in slcting th snsor. Th various paks indicat th minimum and maximum quantization lvls for brathing. Th paks ar a dirct indication of th prssur of inhald and xhald air. Also, th air supplid by th blowr is wll within inhalabl limits Tim (s) Fig 8: Variation of motor spd with brathing pattrn 7. CONCLUSION In this work, a pair of dispnsabl capacitiv microphons has bn considrd as a snsor. Th novlty of this systm lis with th us of dispnsabl articls for implmntation in ral tim. As w got th BLDC motor from scrap PC hard driv and snsors from thrown away ar phons. Thus, th ovrall systm costs around INR 1000 including th microcontrollr along with th associatd circuitry. Morovr, th choic of snsorlss driv of BLDC motor maks th systm powr fficint than convntional brushd DC motors. Th main challngs ar to modulat th spd of th BLDC motor mor ffctivly and prcisly position th snsors to obtain bttr rsult, though so far proportional modulation of motor spd has bn achivd. 8. REFERENCES [1] Surajit Bagchi, Dr. Madhurima Chattopadhyay, Prformanc analysis of an innovativ snsory systm basd spiromtr for diagnostic valuation of COPD and CRPD disass, Proc. of th Intl. Conf. on Advancs in Elctronics, Elctrical and Computr Scinc Enginring (EEC), 2012, DOI: / , pp [2] S. Bagchi, M. Chattopadhyay, Ral-Tim Monitoring of Rspiratory Disass of Distantly Locatd Eldrly Impaird Patints, Chaptr 2, Snsing Tchnology: Currnt Status and Futur Trnds, Springr Intrnational Publishing, Switzrland, 2014, DOI: / _2, pp [3] Ching Chih Tsaia, Tai Yu Wang, Zn Chung Wang & Chung-Yu Lai, Two dgr of frdom control for constant continuous positiv airway prssur of an 49

5 obstructiv slp apna tratmnt systm, Journal of Chins Institut of Enginrs, Vol.31, Issu 6, 2008, pp [4] Robrt M DiBlasi, Nasal Continuous Positiv Airway Prssur (CPAP) for th Rspiratory Car of th Nwborn Infant, Rspiratory Car, Spt. 2009, Vol.54, No. 9, pp [5] Enabling digital microphons, 5. [6] Madhurima Chattopadhyay, Dborshi Chakraborty, A Nw Schm for Dtrmination of Rspiration Rat in Human Bing using MEMS Basd Capacitiv Prssur Snsor: Simulation Study, Smart Snsors, Masurmnt and Instrumntation, ISSN: , Vol.16, pp , Springr Intrnational Publishing. [7] Dbjyoti Chowdhury, Madhurima Chattopadhyay, Priyanka Roy, Modlling and Simulation of Cost Effctiv Snsorlss Driv for Brushlss DC Motor, Intrnational Confrnc on Computational Intllignc: Modlling, Tchniqus and Applications (CIMTA), 2013, pp [8] Santanu Mondal, Arunabha Mitra, Dbjyoti Chowdhury, Madhurima Chattopadhyay, A nw approach of snsorlss control mthodology for achiving idal charactristics of brushlss dc motor using MATLAB/Simulink, IEEE confrnc on Computr, Communication, Control and Information Tchnology (C3IT), 2015, DOI: /C3IT , pp.1-4. [9] G. Prasad, N. Sr Ramaya, P.V.N. Prasad, G. Tulasi Ram Das, Modlling and simulation analysis of th brushlss dc motor by using MATLAB, IJITEE, ISSN: , vol-1, Octobr 2012, pp [10] Paul P. Acarnly, John F. Watson, Rviw of position opration of brushlss prmannt-magnt machins, IEEE Transactions on Industrial Elctronics, vol. 53, No. 2, April 2006, pp [11] Bikram Das, Suvamit Chakraborty, Abanishwar, Prabir Ranjan Kasari, Prformanc analysis of BLDC motor using basic switching convrtrs, IJITEE, ISSN: , vol-2, Issu-1, Dcmbr 2012, pp [12] Juan Apont Luis, Laura M. Roa Romro, Juan Antonio Gómz-Galán, David Naranjo Hrnándz, Migul Ángl Estudillo-Valdrrama, Grardo Barbarov-Rostán, Carlos Rubia-Marcos, Dsign and implmntation of a smart snsor for RR monitoring, ISNN, , Snsors 2014, MDPI journal, DOI: /s , pp [13] P. Dvndra, Madhavi TVVS, K Alic Mary, Ch. Saibabu, Microcontrollr basd control of thr phas bldc motor, JERS, vol. II, Issu IV, Octobr-Dcmbr, pp [14] Bhbhani, Khosrow, PLM Implmntation of a Multipl Closd-Loop Control Stratgy for a Microprocssor-Controlld Rspirator, Amrican Control Confrnc, Jun 1984, pp , IEEE Confrnc Procdings. IJCA TM : 50