Jural Tekologi GRIP FORCE MEASUREMENT OF SOFT- ACTUATED FINGER EXOSKELETON I. N. A. M. Nordi a, A. A. M. Faudzi a,b,c*, M. Z. Kamarudi a, Dyah Ekashati Octoria Dewi c,d, Tariq Rehma a, M. R. M. Razif a a Cotrol ad Mechatroics Egieerig Departmet, Faculty of Electrical Egieerig, Uiversiti Tekologi Malaysia, 81310 UTM Johor Bahru, Johor, Malaysia b Ceter for Artificial Itelligece ad Robotics (CAIRO, Uiversiti Tekologi Malaysia, 81310 UTM Johor Bahru, Johor, Malaysia c IJN-UTM Cardiovascular Egieerig Ceter, Istitute of Huma Cetred Egieerig, Uiversiti Tekologi Malaysia, 81310 UTM Johor Bahru, Johor, Malaysia d Departmet of Cliical Sciece, Faculty of Bioscieces ad Medical Egieerig, Uiversiti Tekologi Malaysia, 81310 UTM Johor Bahru, Johor, Malaysia Full Paper Article history Received 3 November 2015 Received i revised form 24 March 2016 Accepted 24 March 2016 *Correspodig author athif@fke.utm.my Graphical abstract Abstract Over recet years, the reseach i the field of soft actuatio has bee extesively icreased for achievig more complex motio path with smooth, high flexible movemet ad high geerated force at miimum operatig pressure. This paper presets the study o grippig force capability of soft actuators applied o glove-type figer exoskeleto, developed i motivatio to assist idividuals havig weak figer grippig ability i their rehabilitatio exercise towards had fuctio restoratio. The exoskeleto utilizes five cylidrical shaped peumatic bedig actuators developed i the lab, which use fiber reiforcemet as a cause of bedig motio that drive figer s flexio movemet. Four right-haded healthy voluteers simulated paralysis participated i the study. At 200 safe operatig pressure, the soft exoskeleto wor by the subjects demostrates the ability to provide adequate grip force. The grip force geerated from exoskeleto wor o passive right had is 4.66 ± 0.2 N ad 3.61± 0.2 N from passive left had, both higher tha the miimum grip forces measured to hold the Had Dyamometer of 240 g. It shows good potetial to be used as a figer rehabilitatio assist device. Keywords: Figer exoskeleto; soft robotic glove; actuator soft actuator; peumatic rubber 2016 Peerbit UTM Press. All rights reserved 1.0 INTRODUCTION From the statistic of Natioal Stroke Associatio of Malaysia (NASAM, stroke is the third largest cause of death i Malaysia [1]. Nearly 40,000 people i Malaysia suffer from stroke every year, i most cases affectig adults compared to childre. Paralysis, the commo disabilities resultig from stroke which may ivolve complete or partial disability i body movemet, affectig the stroke survivors i their daily activities, such as walkig ad graspig objects. Through the use of rehabilitatio excercises ad equipmets at early stages of paralysis, the brai ca be traied to regai those forgotte body movmets sigificatly much faster. With aid from robotic devices, it might promote a cost-effective therapy for stroke survivors to maitai 78: 6-13 (2016 25 30 www.juraltekologi.utm.my eissn 2180 3722
Displacemet Z [mm] 26 I. N. A. M. Nordi et al. / Jural Tekologi (Scieces & Egieerig 78: 6-13 (2016 25 30 their movemet ability after receivig stadard i hospital rehabilitatio. Rehabilitatio device specifically desig for restorig had fuctio must be able to at least provide the most importat motio to the figer; e.g. flexio motio. Several studies i developig figer actuatio device for assistig stroke survivors i motor skills fuctio restoratio have bee coducted [2] [5]. Differet approaches are extesively beig studied for causig the bedig motio to follow figer flexio motio. Whether they are peumatic or hydraulic-based actuator, the actuators have bee developed based o bellow structure [6], [7], itegratio of bellows structure with strai limitig layer [5], fiber braided reiforcemet [8] [11], ad itegratio of fiber braided reiforcemet with strai limitig layer [3]. Most of the actuators shows promisig bedig capability at safe operatig pressure util 500 for peumatic drive [4], [5], [12] ad util 345 for hydraulic drive [13]. I additio to bedig capability, grip assistace produced by the figer exoskeleto should be eough to assist the stoke survivors i their rehabilitatio exercises. Not more tha 15 N graspig forces of healthy subjects was reported to maipulate objects that are ecoutered durig Activities of Daily Livig (ADL [14], while the graspig force for idividuals with differet severity of had impairmets is very small, some almost close to zero [15]. A figer soft exoskeleto should provide graspig force that is adequate to assist ADL, which varies betwee 0.1 N to 15 N depedig o the weight of the objects. Other factor cotributig to the grip assistace produced is the material of the actuator iterfacig huma body. Glove is usually beig used as the attachemet betwee the actuator ad figers for optimum force trasmissio [6], [13], [16]. Glove-type soft exoskeleto preseted i this paper utilized the potetial fiber reiforced soft bedig actuators to drive the figer s flexio motio. This paper presets the evaluatio of our first prototype of figer exoskeleto, operated util 200 of air pressure tested o the grip force by healthy simulated paralysis subjects. 2.0 SOFT EXOSKELETON DESIGN AND CONTROL 2.1 Braided Bedig-type Actuator The actuators used for actuatig the flexio motio of the figer were fabricated from two rubber layers, the ier ad the protective outer layer that were made from silicoe rubber, KE-1603 A/B from Shi-Etsu. A braided fiber layer composed from Aramid fiber was positioed aroud the ier rubber layer to restrict expasio i radial directio. The fibers were kitted i two patters, each coverig half of cylidrical segmets as ca be see i Figure 1. The 90 o fibers show by the gree segmet box o the left side of the cylidrical actuator have cotributed i the extesio motio of the actuator while the red segmet o the right side of the actuator that shows the kitted fibers of 35 o fiber agle has lead to cotractio motio, thus iduced bedig motio. A small tube was iserted ad mouted at the top of the actuator to eable the air pressure iput supply. The actuator fabricatio method of combiig two fiber agles of extesio ad cotractio characteristics, represeted by fibers of 90 o ad 35 o was prove to successfully produce bedig motio. A very smooth curlig trajectory of the actuator s tip is demostrated i Figure 2. Figure 1 Costructio of soft actuator braided with two differet characteristics of fiber agles By referrig to Figure 3, 84.66 o bedig agle, θ, is show through experimetal testig whe operated at 300 air pressure. The bedig agle icreases liearly as the pressure icreases. R-squared measures from the liear tred lie is 0.995 (very close to 1, explai a good fit of liear model show by the graph. 180 160 140 120 100 80 60 40 20 0 79, 153 0 20 40 60 80 100 120 Displacemet Y [mm] Figure 2 Trajectory of actuator s tip (tip was show i blue marker i Figure 1
Bedig Agle [degree] 27 I. N. A. M. Nordi et al. / Jural Tekologi (Scieces & Egieerig 78: 6-13 (2016 25 30 90 80 70 60 50 40 30 20 10 y = 0.2821x R² = 0.995 84.66 0 0 50 100 150 200 250 300 350 Pressure [] Figure 3 Bedig agle of actuator as the pressure icreases Vcc 100 150 200 250 300 Cotrol Box microcotroller uc 3/2 Directioal Cotrol Valve Actuator 1 Actuator 2 Actuator 3 Actuator 4 Actuator 5 2.2 Glove Desig & Actuator Itegratio Five soft actuators of the same desig characteristics were fabricated to fit five figered comfortable eopree glove attachmet, positioed alog the top surface of figers ad thumb, as show i Figure 4. Rubber bads were icorporated to the glove to fix the actuators o the figers boes ad joits. Velcro strap was placed aroud the forearm to prevet the uwated movemet from the air tubes. Velcro tape at the wrist will perfect the fittig of the glove to the user s had. Aother same structure of the glove is used for right had. Figure 5 Schematic diagram of the soft exoskeleto system Figure 6 shows the cotrol box of the system. I case of ay emergecy coditio, the emergecy butto to stop the operatio i case of ay malfuctio of the exoskeleto is located o further right o top of the box. 100 Butto for selectig air pressure supply 150 200 250 300 Air service uit Reset butto O/off switch Air tubes coector to soft actuators Emergecy butto Figure 6 Cotrol box Figure 4 The prototype showig the soft actuator attachmet to the glove for the left had 2.3 Cotrol System Overview Air is pressurized by the air compressor, trasferred by peumatic tubes ad push buttos were used to activate the desired amout of air pressure supplied to the soft actuators. The amout of air pressure supplied to the exoskeleto was regulated by usig o-off valve. A microcotroller was programmed to have a five selectios of pressure supply, 100, 150, 200, 250 ad 300. The cotrol box is powered from wall mouted power source of 24 V. The workflow of the system ca be summarized as i Figure 5. 2.4 Grip Test Setup Grip force test was coducted to assess the efficiecy of the soft exoskeleto i providig grippig stregth to simulated paralyzed hads. A digital Had Dyamometer HD-BTA (Verier Lab used by researchers i coductig grip stregth measuremet [17] [20] was used i this study. The sesor is a isometric force sesor (strai gauge amplifier-based that sese the force applied to its pressure pads. It is coected the device iterface, Verier LabQuest 2 ad coected to the laptop for better visualizig of the output by usig Logger Lite software. Grip test was performed o four healthy subjects from a mixed sample of uiversity studets, composed of two males ad two females (weight 45-70 kg, aged from 20-27 years. Voluteer exclusio criteria iclude left had as the domiat had, eurological disorder, stroke survivors, ijured hads ad disable people. Two experimets were coducted, grip forces were take
28 I. N. A. M. Nordi et al. / Jural Tekologi (Scieces & Egieerig 78: 6-13 (2016 25 30 from subjects without wearig the soft exoskeleto (i Experimet A ad with wearig the soft exoskeleto (i Experimet B. I Experimet A, all subjects were asked to grip the had dyamometer just eough for holdig the gauge. The results of Experimet A were preseted i Sectio 3.1. I Experimet B, the subjects were simulated paralysis by beig totally passive durig the force measuremet. The soft actuators that actuate the flexio movemet of figers were cotrolled by selectig the modes of operatio at three differet iput pressure: 100, 150 ad 200. Pressure 250 ad 300 were excluded i the measuremet to comply with safety regulatio. The maximum compressed air give or i direct cotact with the ski, as regulated by Uited States OSHA (Occupatioal Safety ad Health Admiistratio i 1910.242.b is 210 (30 psi. The results were tabulated i Sectio 3.2. To achieve a paralyzed coditio, subjects were asked to close their eyes, sat o a chair with relaxed back ad arm, feet flat o the groud ad arm supported by the chair armrest, perpedicular to the body. Figure 7 shows the grippig posture followig the maual of Verier Had Dyamometer, i measurig the grip force of both experimets. The had dyamometer held i a vertical positio ad should ot i cotact with aythig else except the figer. Figure 8 Verier Logger Lite software iterface showig cotiuous grip force Three cotiuous grip trials were measured for subjects s both right ad left hads. Every trial was coducted i 60 s, but were aalyzed i the last 40 s (samples of data highlighted i gray whe the outputs are more stable. The mea grip force to hold the had dyamometer calculated from the data gaied from their right had is 1.15 ± 0.2 N ad from left had is 0.98 ± 0.2 N. 3.2 Grip Force from Experimet B The grip force of had assisted by the soft exoskeleto was measured 6 times per subject per operatig pressure. The statistics for every grip trials were obtaied by movig the brackets to the rages of each plateau gaied. The box show i Figure 9 cotais the statistical data (mi, max, mea ad media. The mea value of oe plateau (at the peak was tabulated as grip force of oe trial. Figure 7 Stadard positio of had grip test measuremet. The had dyamometer was weighted as 240 grams equivalet to 240 ml bottled mieral water. 3.0 RESULTS AND DISCUSSION 3.1 Grip Force from Experimet A The data recorded by the had dyamometer were collected by Verier LabQuest 2 iterface ad displayed by the Logger Lite software. Figure 8 shows a trial of cotiuous iitiative grip forces acquired by the right had of oe subject to hold the had dyamometer. Figure 9 Grip forces measured at 200 supplied air pressure of Subject 1 s right had. The mea grip forces were recorded to the earest 0.1 N as show i Table 1, 2 ad 3. The measuremet were collected at both left ad right hads. Six grippig trials were recorded per had at three differet operatig pressure, 100 i Table 2, 150 i Table 3 ad 200 i Table 4.
Mea Grip Force [Newto] 29 I. N. A. M. Nordi et al. / Jural Tekologi (Scieces & Egieerig 78: 6-13 (2016 25 30 Table 1 Grip force at 100 operatig air pressure Grip Force by Left Exoskeleto Trial 1 0.62 0.63 0.86 1.14 Trial 2 0.65 0.66 0.87 0.91 Trial 3 0.58 0.73 0.93 0.92 Trial 4 0.72 0.79 1.10 1.06 Trial 5 0.67 0.81 1.07 0.94 Trial 6 0.60 0.87 1.11 1.03 Mea (SD Mea (SD 0.64(0.05 0.75(0.09 0.84 (0.16 0.99(0.12 1.00(0.09 Grip Force by Right Exoskeleto Trial 1 1.55 0.76 0.77 1.55 Trial 2 1.48 0.74 0.81 1.48 Trial 3 1.52 0.74 0.78 1.52 Trial 4 1.42 0.63 0.77 1.42 Trial 5 1.26 0.64 0.81 1.26 Trial 6 1.42 0.64 0.78 1.42 Mea (SD 1.44(0.10 Mea (SD a SD represets Stadard Deviatio. 0.69(0.06 1.09 (0.35 0.79(0.02 1.44(0.10 Table 2 Grip force at 150 operatig air pressure Grip Force by Left Exoskeleto Trial 1 1.39 0.97 1.94 2.07 Trial 2 1.50 0.92 1.90 2.08 Trial 3 1.33 1.11 1.91 2.02 Trial 4 1.51 0.89 1.96 1.93 Trial 5 1.80 0.81 1.92 1.95 Trial 6 1.90 0.88 1.96 1.91 Mea (SD 1.57(0.23 0.93(0.10 1.93(0.03 1.99(0.07 Mea (SD 1.61 (0.42 Grip Force by Right Exoskeleto Trial 1 3.82 3.09 2.97 1.38 Trial 2 3.58 3.26 2.87 1.50 Trial 3 3.64 3.40 2.85 1.52 Trial 4 3.72 2.99 3.03 2.16 Trial 5 3.70 3.14 2.97 2.04 Trial 6 3.51 3.11 3.07 2.09 Mea (SD Mea (SD 3.66(0.11 3.17(0.14 2.89 (0.69 2.96(0.09 1.78(0.35 Table 3 Grip force at 200 operatig air pressure Grip Force by Left Exoskeleto Trial 1 3.39 3.52 3.66 4.17 Trial 2 3.46 3.55 3.51 3.73 Trial 3 3.82 3.42 3.61 3.53 Trial 4 3.81 3.71 3.02 3.66 Trial 5 3.89 3.83 3.32 3.70 Trial 6 3.88 3.88 3.03 3.67 Mea (SD 3.71(0.22 3.65(0.19 3.36(0.28 3.74(0.22 Mea (SD 3.61 (0.15 Grip Force by Right Exoskeleto Trial 1 6.50 4.10 4.10 4.53 Trial 2 5.72 3.62 4.47 4.69 Trial 3 6.04 3.72 4.03 4.80 Trial 4 5.73 3.38 4.03 5.15 Trial 5 5.71 3.60 3.83 5.39 Trial 6 5.71 3.83 3.37 5.73 Mea (SD Mea (SD 5.90(0.32 3.71(0.24 4.66 (0.88 3.97(0.36 5.05(0.46 Figure 10 shows the average force of passive had assisted by had exoskeleto i several coditios of air pressure supply. Red bar represets the forces measured from right had ad blue bar from left had. The referece value of the miimal force to grip the had dyamometer as described i Experimet A are preseted by the dashed lie i blue represets the referece value of grip force measured o the left had (0.98 N, ad the red lie o the right had (1.15 N. 5 4 3 2 1 0 0.84 Left Had Liear (Left Had 1.09 1.15 N 0.98 N 1.61 2.89 Liear (Right Had 4.66 3.61 100 150 200 Iput Air Pressure Right Had Figure 10 Mea Grip Force of whole populatio. From the results, the grippig forces produce by the exoskeleto wor o right had (1.09 N ad left had (0.84 N at operatig pressure of 100 are iadequate to hold a 240 g had dyamometer. Sufficiet grippig force ca be achieved whe the actuators were supplied 150 ad more. I all cases, the forces show by right had are higher tha the left had. The differece is ragig from (0.25-1.28 N which might be due to the uiteded force iitiated by their domiat right had. Cosiderig the grip force measured from left had exoskeleto as the referece to evaluate the effectiveess i grippig, the grip force show (1.61 N to 3.61 N that ca be achieved at 150-200
30 I. N. A. M. Nordi et al. / Jural Tekologi (Scieces & Egieerig 78: 6-13 (2016 25 30 operatig pressure proved that the soft exoskeleto is applicable to be used i assistig lightweight task. From the plots i Figure 10, the grip force is directly proportioal with icrease i air pressure. 4.0 CONCLUSION This paper has preseted a lightweight exoskeleto drive by soft bedig actuators ad its performace i actuatig healthy subject s figer flexio motio. From the data of four healthy subjects participated i the study, results showed that the soft exoskeleto has a sigificat effect o the grip force. 3.61 N of grip force at 200 operatig iput pressure is sufficiet to hold lightweight objects. It shows some potetial to provide assistace i grippig. Future works will iclude optimizatio works of the actuator desig i achievig higher grippig forces at lower air operatig pressure ad higher degree-offreedom (DOF that icludes figer abductio/ adductio movemet. 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