Knee Joint Movement Monitoring Device Based on Optical Fiber Bending Sensor

Transcription

1 Knee Jont Movement Montorng Devce Based on Optcal Fber Bendng Sensor G.M. Salm and M.A. Zawaw Faculty of Electrcal & Electroncs Engneerng, Unverst Malaysa Pahang, Pekan, Pahang Abstract Ths paper dscusses the possble mplementaton of an optcal fber bendng sensor for knee jont montorng applcaton. The studed technque s based on the use of an ntensty modulated optcal fber va angular dsplacement between two separated fbers, whch approach has been mplemented prevously n spne movement and respraton rate measurement. To estmate the sutablty of ths technque for knee montorng applcaton, the maxmum range of detecton of the sensor s estmated usng the output ntensty equaton for plastc optcal fber. Based on the estmated output ntensty graph wth respect to bendng angle, t s concluded that the amed technque s not perfectly sutable for the knee montorng due to lmted sensor s range of moton, whch renders a lmted the sensor detecton range for knee jont movement. In addton to ths, several other types of knee jont montorng devces are also presented and summarzed n a table form to hghlght the contrbuton of other devces. as ce-hockey, handball, soccer, downhll skng and basketball. In ths study, t was summarzed that knee njures from sports actvtes comprsed 10% of all njures n males and 13% n females [5]. Most knee njures are smlar and often related ether to the lack of tranng or to overuse and fatgue. It was also mportant to note that most knee njury persons are between 20 to 29 years old (50%). Ths statstcs was publshed from a 10-year perod on a study among athletes aged between 10 to 69 years old [6]. These fndngs hghlght the needs for the relable devce at low operatonal cost by researchers n the bomedcal feld so that the amed users (e.g. physotherapst) can have more alternatve devces n knee njury treatment and recovery. Index Terms Health Montorng; Knee Injury; Knee Montorng; Optcal Fber Sensor. I. INTRODUCTION Health montorng applcatons for human cover dfferent body areas such as respraton assessment, heart rate montorng, gat montorng, heart rate montorng, glucose level measurement as well as lower and upper lmb moton detectons [1]. Among all jont movements related to the lower lmb moton, the knee jont s consdered among the most mportant and crtcal health assessment due to the hgh exposure of ths area to njures. Knee problems and njures most often occur durng sports or recreatonal actvtes, work-related tasks, or home projects. The knee s the largest jont n the body [2]. The upper and lower bones of the knee are separated by two dscs (mensc) [3]. The upper leg bone (femur) and the lower leg bones (tba and fbula) are connected by lgaments, tendons, and muscles. Fgure 1 llustrates the typcal range of moton of the human knee. The surface of the bones nsde the knee jont s covered by artcular cartlage, whch absorbs shock and provdes a smooth, gldng surface for jont movement. [2, 3]. Many heavy jobs, sports and recreaton actvtes, gettng older or havng a dsease such as osteopoross or arthrts ncrease the chances of havng knee problems. Sudden (acute) knee njures may be caused by a drect blow to the knee or from abnormal twstng, bendng the knee, or fallng on the knee [4]. Based on a 7-year study among sports athletes n 12 dfferent sports n Europe county, nvolvng 3864 knee njury cases, t was found that female athletes were sgnfcantly at rsk n sx sports; alpnsm, downhll skng, gymnastcs, volleyball, basketball and handball. Meanwhle, male athletes were more exposed to a knee njury n sports actvtes such Fgure 1: Illustraton of human knee range of moton [4] Although t s possble to prevent knee njures from sports actvtes [7], there are lttle optons that can be done for athletes especally when they nvolve n tght schedules of tranng and tournaments. For ths reasons, health practtoners and physotherapsts are nconsstently suggestng dfferent approaches to knee njury treatment among athletes. Among these optons are detary nterventon, exercse, drug therapy and surgcal nterventons [8]. Due to the adverse effects of drug therapy and the hgh cost of surgcal nterventon, ntensve exercse s a popular choce for the athletes. To effcently montor the condton of the knee njury after each treatment, a relable montorng devce s thus needed, so that more nformaton on the knee condton could be retreved by the user for further consultaton and treatment. For ths reason, majorly avalable knee montorng devces are dscussed n detals here. As far as laboratory scale tests are concerned, several dfferent devces have been developed and nvestgated for ths applcaton so far, ncludng usng accelerometer [9], torsometer [10], conductve fber [11], and sde-polshed fber optc [12]. These devces offer dverse characterstcs and measurement e-issn: Vol. 10 No

2 Journal of Telecommuncaton, Electronc and Computer Engneerng performances, but most of them do not support n-stu measurement that s requred for contnuous knee assessment [13]. Moreover, n some cases such as the accelerometer devce, t has qute a large overall devce dmenson (and weght) that could cause dscomfort to devce s wearer [14]. Further dscusson on varous types of knee montorng devces s presented n the next secton. As an overall, the objectve of ths research s to develop a non-nvasve knee montorng devce based on optcal fber technology. The nvestgated extrnsc optcal fber sensor must have a small sensor dmenson, lghtweght, easy to wear and requre mnmum experence for devce handlng. These advantages can be made possble due to the small fbre optc cable dmenson (typcally 1 mm dameter for plastc fbre) [15]. In addton, the nherent advantage of mmunty to electromagnetc dsturbances of the optcal fbre technque also makes t sutable for hgh-rsk applcaton such as n hazardous places [16]. In ths paper, a possble mplementaton of an ntensty modulated optcal fber bendng sensor for knee montorng applcaton s nvestgated. Ths approach, whch uses the lght attenuaton resulted from the angular dsplacement between two separated optcal fbers, has been mplemented n other health montorng applcatons such as spne movement [17] and respraton montorng [18]. Due to the dfferent background between the knee montorng applcaton and the above-mentoned applcatons [17, 18], ths paper presented the output estmaton of the optcal fber, n order to fnd the maxmum range of moton of the sensor usng ths approach. The obtaned results are crtcal to establsh further development work of the knee montorng devces usng the nvestgated technque. II. DIFFERENT TYPES OF KNEE JOINT MOVEMENT MONITORING DEVICES The frst devce dscussed here has been appled on elte athletes as hs subjects for the study. A montorng devce called electrogonometer s used, whch comprsed of optcal fbres to measure moton, usng a fxed end-block and a telescopc end-block [19] as llustrated n Fgure 2. Ths study measured knee jont angles n three dfferent startng postons whch are supne, sttng, and standng [20]. The results proved that usng a standardsed protocol mnmses measurement error, and performance was relable. It s concluded that a flexble and lghtweght electrogonometer s relable for the statc type of measurements for knee jont angles n supne, sttng and standng postures [21]. Another method proposed by Dejnabad. et al. [22] obtaned knematc data from gat analyss to evaluate and quantfy knee jont angle. Ths research asssts physotherapsts to decde sutable treatments for the patent. The sensors appled n ths research are accelerometer and gyroscope, whch are mounted on the subject s thgh and calf as close as possble to the knee jont as llustrated n Fgure 3. Fgure 2: Knee montorng usng electrogonometer [19] Fgure 3: Knee montorng usng accelerometer at 2 locatons; a & b [22] The same sensors combnaton (accelerometer and gyroscope) have also been ntroduced to measure the angular movement of shoulder and elbow [23]. The popularty of nertal based sensor to detect human jont angle s due to ts smple (straghtforward) technology, unobstructed and selfcontaned characterstcs. The accelerometer s used to provde translatonal and gravtatonal acceleratons whle gyroscope s for angular velocty data [24]. However, the use of the accelerometer to measure the knee angle could lead to sgnal drft when the subject under study s not n moton, render a poor devce accuracy. The ntegraton of gyroscope alongsde wth the accelerometer s also not possble to solve ths problem because of rapd accuracy degradaton as shown by Roetenberg. [25]. The next type of devce applcable for knee montorng s based on small three degrees of freedom sensor modules contanng angular rate sensors, accelerometers, and magnetometers [26]. Ths sensor combnaton was able to elmnate the drft errors by usng flter technque. However, varatons n the drecton of the local magnetc feld reference vector can cause errors n the knee orentaton, thus reducng the sensor s accuracy. The next technque for knee montorng applcaton nvolves the use of conductve fbers nto flexble, skn-tght fabrcs surroundng the knee jont [27] as shown n Fgure 4. Resstance changes across these conductve fbers are measured and drectly related to specfc sngle or mult-axs jont angles through the use of a non-lnear predctor after a sngle ntal calbraton. a b 26 e-issn: Vol. 10 No. 1-3

3 Knee Jont Movement Montorng Devce based on Optcal Fber Bendng Sensor Conductve fber Pezoelectrc Flm MEMS mcrophone Elastc Cord Wre Contact Pont Electret mcrophone Reference sensor Fgure 4: Knee montorng usng conductve fber [27] The last approach for knee montorng devce to be dscussed n ths secton s based on acoustcs sensor va ar mcrophones [28]. Three dfferent type acoustc sensors are appled; electret, MEMS and pezoelectrc flm. These devces were appled on a human subject, as he performed three cycles of seated, unloaded knee flexon/extenson wth two electret mcrophones postoned at the lateral sde of the patella, one on the skn and one located 5 cm off the skn. In ther study, the researchers concluded that practcal mplementaton of contact mcrophones n a wearable devce requres further nterface nose reducton. The sensor placement n the knee area usng ths devce s llustrated n Fgure 5. For comparson purpose, the advantages and lmtatons of each knee montorng devces that have been descrbed here are summarzed n Table 1. Fgure 5: Knee montorng usng acoustc sensor [28] III. COMPARISON OF DIFFERENT TYPE OF KNEE MONITORING DEVICES Based on the dscusson on several man examples of knee montorng devces presented above, ther respectve advantages and constrants are presented n ths secton va a smple table form to allow drect comparson between each devce. In addton to ths, other related health montorng devces for dfferent human jonts are also presented n the same table to allow dverse technology comparson. The comparson of the sensors characterstcs s presented n Table 1. Table 1 Lst of Dfferent Human Jont Angle Movement Sensors and Ther Advantages/Lmtatons. No Human Advantages / Type of Sensor Parameter Jont Lmtatons 1 Knee Electrogono meter Stran Adv. based on stran gauge applcaton, straghtforward measurement Lm. hgh cost (hardware and software sold separately) 2 Knee Accelerometer, Velocty Adv. basc nstallaton, low component cost gyroscope Lm. sgnal drft f not n moton 3 Shoulder Inertal sensor Angular rate Adv. basc nstallaton, low component cost, elbow Lm. sgnal drft f not n moton 4 Knee Angular rate 3D coordnate Adv. reduce the problem wth sgnal drft accelerometer, (va angular Lm too many sensor elements, complcated crcut arrangement magnetometer rate) 5 Knee, Conductve fber Electrc Adv. small fber s used, possble for wearable devce hp conductvty Lm dffcult to dentfy multple movement poston along the conductve fber 6 Knee Acoustcs sensor Soundwave Adv. wreless detecton s possble, does not lmt patent movement travel tme 7 Knee Conductve wre Electrc conductvty 8 Fngers Resstve bend sensor Stran due to compresson 9 Fngers Flexpont bend sensor Stran due to compresson 10 Knee (moton) Pezoresstve sensor strps Stran due to compresson Lm sgnfcant nose level (uncontrolled room condton) Adv. smplcty of the measurement, low cost, and the sturdness of the sensor Lm use dfferental Wheatstone brdge crcut, so output sgnal s dependent on the temperature. Range of detecton of up to 50 deg. only. Adv. embedded nto a glove, hgh resoluton (0.1 deg.) Lm requre careful knttng work to place the sensor on the glove. Adv. no movng parts, slent n operaton, lghtweght Lm requre assocated components such as wreless board, data storage etc. (place n a box at arm poston) Adv. lghtweght, fast response Lm requre extended crcut to record the movement (large sze, dffcult to attach to the body) Ref. No. [19, 20] [22] [23] [26] [27] [28] [29] [30] [31] [32] e-issn: Vol. 10 No

4 Normalzed ntensty (%) Journal of Telecommuncaton, Electronc and Computer Engneerng The lst of crtcal concerns for each jont sensor n Table 1 can be summarzed as follow: a) Accelerometer / nertal sensor drft ssue when statc b) Electrogonometer hgh operatonal and mantenance cost. c) Conductve fber/wre requre to be attached to a flexble garment, not applcable for dfferent body szes d) Acoustc sensor prone to nose dsturbance (error) e) Resstve bend requre care to attach to the garment, or could damage the sensor. f) Pezoresstve sensor requre brdge crcut (dffcult to balance the offset), large crcut assembly. As summarzed above, there are stll many mprovements can be made to overcome the lmtatons of other knee montorng devces. The applcaton of plastc optcal fber for knee measurement offers several advantages ncludng; small sensor component (due to relatvely small n fber dameter), low cost for sensor component assembly (usng vsble wavelength LED and photodode) and less susceptble to nose when appled wth approprate flterng crcut. The problem wth sgnal drft can also be elmnated va sutable ntensty referencng method for optcal fbers. IV. KNEE MONITORING SENSOR BASED ON OPTICAL FIBER BENDING SENSOR: A PRELIMINARY RESULT In general, optcal fber sensor can be categorzed based on ts modulaton technques, such as the ntensty-based, frequency-based and phase-based modulaton technques [16]. An ntensty-based optcal sensor s appled where the magntude of lght s beng modfed by the parameter of nterest by ntatng a loss n the lght ntensty (.e. lght attenuaton). Ths technque requres the use of low-cost lght sources and multmode fbre types together wth smple optcal components, renderng an economcally low-cost system. Meanwhle, for phase and frequency modulatons, they represent modulaton approaches, n whch the varable to be measured wll cause a phase shft or frequency change of the coherent lght wave. Opposte to the low-cost ntensty modulaton technque, these approaches are only possble through the use of a coherent lght source, sngle mode fbre and a complex devce for sgnal detecton (e.g. nterferometer), whch are more expensve and complex. The descrpton on the sensor confguraton amed to be used for the knee montorng applcaton s presented n the followng secton. A. Sensor Confguraton under Investgaton Bendng movement or sometmes knows as angular dsplacement can be measured usng ntensty modulaton technque va the followng approaches : a) Longtudnal dsplacement Ths method uses 1 nput fber and 1 output fber. b) Dfferental dsplacement Ths method uses 1 nput fber and 2 output fber. c) Angular dsplacement Ths method uses 1 nput fber and 1 output fber as shown n Fgure 6. As far knee montorng applcaton s concerned, the longtudnal dsplacement (a) and the dfferental dsplacement (b) methods requre further calbraton steps n order to represent the angular movement n the form of lnear dsplacement. The use of angular dsplacement method n (c) s straghtforward and enable drect representaton of the knee jont movement usng optcal fber, thus beng appled here. The sensor output estmaton from the optcal fber sensor usng ths method s presented n the next secton. Fgure 6: Lght attenuaton based on angular dsplacement fbers B. Output Estmaton Result The output estmaton for the optcal fber sensor confguraton usng the angular dsplacement method s obtaned usng the fber loss equaton [15]: 2 2 A L L0I 0 x y I x, y, z exp exp 2 nr 2 (1) ( z ) ( z ) Where: A s the -th output fbre core area. L s the losses n the -th output fbre. L 0 s the losses n the nput fbre. I 0 s the lght ntensty at pont (x, y, z) of the -th output fbre. exp n r s the addtonal losses parameters n the -th output fbre caused by mcrobends. a o s the output fbre core radus. s the coeffcent parameter of the lght source. c s the fbre acceptance angle = sn-1 (NA/n 0). The characterstcs of output ntensty level (brghtness of the lght) wth respect to the dfferent bendng angle (degree) are presented n Fgure 7. The objectve s to nvestgate the maxmum angular dsplacement (degree) that can be detected usng ths confguraton. Ths s mportant to ensure that the studed technque can be appled to knee measurement applcaton, whch has a large range of moton that spne and respraton cases Input lght Output lght Fber bendng angle vs. Output ntensty Maxmum bendng angle, 50 deg Bendng angle/deg. ( o ) Fgure 7: Output ntensty varaton wth respect to jont angle movement The varaton of the lght ntensty output wth respect to the detecton angle (.e. knee movement angle) s presented n Fgure-7. The output ntensty s presented n a normalzed form, whch ranged between 1.0 to 0.58 for bendng angles (knee jont movement) between 0 deg. and 50 deg. The slope 28 e-issn: Vol. 10 No. 1-3

5 Knee Jont Movement Montorng Devce based on Optcal Fber Bendng Sensor of the output n Fgure 7 represents the sensor output resoluton. From the graph, t s shown that flat slope towards hgher bendng angle (above 40 deg.) gves a poor sensor resoluton at hgh bendng angle. As the maxmum knee movement s typcally up to 140 deg. for the full range of moton (R.O.M.), the nvestgated technque n ths study s not lkely sutable for ths applcaton. Fnally, another method s needed or at least some modfcatons to ths technque are requred to allow the detecton of knee jont movement usng an ntensty-based optcal fber sensor. V. CONCLUSION A possble mplementaton of ntensty modulated optcal fber bendng sensor for knee montorng applcaton has been nvestgated, whch technque has been prevously appled for the detecton of spne movement and respraton rate montorng. For ths study, the lght ntensty of the output fber s estmated usng the fber loss equaton, whch results n the output ntensty changes wth respect to the mposed bendng angle/angular dsplacement. From the calculated output, t was found that the maxmum detectable angular dsplacement s only 50 deg., whch s far lower than the typcal rotaton range for knee applcaton. As a concluson, the nvestgated technque requres further modfcatons to allow possble mplementaton of knee montorng area. Several other types of knee jont montorng devces have also been presented to hghlght the contrbuton of other devces. ACKNOWLEDGMENT The authors wsh to thank Unverst Malaysa Pahang for the fnancal support provded to carry out the study presented n ths artcle under the grant no. RDU REFERENCES [1] M. A. Zawaw, S. O Keeffe, and E. Lews, Intensty-modulated fber optc sensor for health montorng applcatons: a comparatve revew, n Sensor Revew, vol. 33, no. 1, pp , [2] M. A. H. Mohd Adb and M. F. 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