In this study, in order to realize an assist of independent life for the elderly or people in need of care and relieve a physical burden for care worker, an active support splint driven by pneumatic soft actuator (ASSIST) has been developed. ASSIST consists of a plastic interface with the palm and arm and two rotary-type soft actuators put in both sides of appliance. In this paper, the fundamental characteristics of ASSIST is described, and then the effectiveness of this splint is experimentally discussed. Finally, the operation of ASSIST based on a human intention is described. </p

Noritsugu, Toshiro

Sasaki, Daisuke

Takaiwa, Masahiro

Okayama University Digital Information Repository

Development of Active Support Splint driven by Pneumatic Soft Actuator (ASSIST)

Okayama University Scientific Achievement Repository

EngineeringIndustrial & Management Engineering fieldsOkayama University Year 2005Development of Active Support Splintdriven by Pneumatic Soft Actuator(ASSIST)Daisuke Sasaki Toshiro NoritsuguOkayama University Okayama UniversityMasahiro TakaiwaOkayama UniversityThis paper is posted at eScholarship@OUDIR : Okayama University Digital InformationRepository.http://escholarship.lib.okayama-u.ac.jp/industrial engineering/70Development of Active Support Splintdriven by Pneumatic Soft Actuator (ASSIST)Daisuke Sasaki , Toshiro Noritsugu and Masahiro TakaiwaFaculty of EngineeringOkayama University3-1-1 Tsushimanaka, Okayama, 700-8530, Japan[daisuke,toshiro,takaiwa]@sys.okayama-u.ac.jpAbstract— In this study, in order to realize an assist ofindependent life for the elderly or people in need of care andrelieve a physical burden for care worker, an active supportsplint driven by pneumatic soft actuator (ASSIST) has beendeveloped. ASSIST consists of a plastic interface with thepalm and arm and two rotary-type soft actuators put in bothsides of appliance. In this paper, the fundamental character-istics of ASSIST is described, and then the effectiveness ofthis splint is experimentally discussed. Finally, the operationof ASSIST based on a human intention is described.Index Terms— Power Assist, Wearable Robot, Pneumatics,Artificial Rubber MuscleI. INTRODUCTIONIn recent years, owing to a great advance of medicaltechnology and a decrease of birth rate, a growth ofadvanced age society has become a serious problem inJapan. Therefore, it is becoming difficult to secure enoughcare workers for the elderly or people in need of care.In addition, relieving a physical burden of care work isimportant subject because it is hard physical work. In thiscase, if a slight symptom people in need of care is possibleto have a daily life independently by some way, that wayis one of effective means to solve the above problemabout a care worker shortage. From above reasons, manykinds of power assist device have been developed [1,2,3].The exoskeleton to assist a human upper-limb motion[1],the power-assisting device for the assist of self-transferbetween a bed and a wheel chair[2] are floor type devices,they can realize effective assist according to the enoughgenerated force. That is the strong point of both devices,but the movement in an arbitrary place is not supposedin these devices. To realize the movement in an arbitraryplace for a user equipped with a device, a wearable typedevice has been adopted. Berkeley Exoskeleton [3] is oneof wearable type devices. Berkeley Exoskeleton assistsa lower limb motion by a pneumatic cylinder. Howeversince the cylinder is constructed with rigid components,the cylinder lacks a flexibility except a moving direction.On the other hand, the soft actuator constructed with a softmaterial such as a rubber has an inherent flexibility besidesa moving direction. It is the main advantage for the medicalor the welfare application that the developed device has aflexibility due to not only the power source but also thebody of actuator.To assist people in need of care to be independent andrelieve the burden on care workers, an active support splintdriven by pneumatic soft actuator(ASSIST) for bendingmotion assist at a wrist has been developed. Since the massand hardness of device involve the danger of causing aserious accident for the users or neighbors, this device isconstructed with an appliance made by forming a plastic asan interface with human body, and by using a pneumaticsoft actuator[7] which has a mechanical softness accordingto a material and a power source.In this paper, the structure of developed power assistsplint is described, and then the effectiveness of this deviceis experimentally discussed based on the experiments forthe assisting both movable range and muscular endurance.Finally, the operation of ASSIST based on a human inten-tion is described.II. STRUCTURE OF ASSISTFig.1 show the structure of ASSIST. In this study, twotypes of ASSISTs are developed. Fig.1(i) shows Type I ofASSIST is developed for realizing the assisting increasein movable range. Type II is developed for realizing theincrease muscular endurance. The difference of both typesis the existence of the McKibben type rubber muscle. TheMcKibben type pneumatic rubber muscles are attachedfor relieving a restrained feeling by releasing the palmappliance when the device is not operated.Fig.2 shows the outlook of ASSIST. ASSIST is con-structed with an appliance and two rotary-type soft actua-tors put in both sides of appliance. The width and length ofsplint are 150[mm] and 280[mm], respectively. The mass is390[g]. Where a general baseball glove is compared withASSIST as another device mounted to a hand, ASSISTis lighter than an baseball glove since the mass of gloveis about 500!A600[g]. Therefore this splint is lightweightcomparatively in devices mounted to a hand. In this section,the structure and fundamental characteristics of ASSISTare discussed.ApplianceFig.3 shows the appliance as an interface between ahuman body and the actuator. If the stiffness of applianceProceedings of the 2005 IEEEInternational Conference on Robotics and AutomationBarcelona, Spain, April 20050-7803-8914-X/05/$20.00 ©2005 IEEE. 520(i) Type I(ii) Type IIFig. 1. Structure of ASSIST.Fig. 2. Outlook of ASSIST.is not enough, owing to the deformation of the palm witha complicated structure, and of a fixed part of actuatordue to a high bending moment, it becomes difficult totransfer the generated torque from actuator to the humanbody efficiently. From the above, this appliance is madeof a plastic same as the usual appliance. The shape ofappliance is decided referring a shape of extension splintfor a disabled person. Two cylindrical plastics are attachedto the both sides of the palm and arm in order to fix theactuators.Rotary-Type Soft ActuatorFig.4 shows the structure of rotary-type soft actuator fortype I. The rotary-type soft actuator consists of a rubbertube and two silicone rubber tubes, a polyester bellows.In order to bend circumferentially, the polyester bellowsis reinforced with fiber as shown with the solid line inFig.4(c). The both sides with length 50[mm] from the endare reinforced for inhibiting axial expansion. The bendingside at center part of bellows with length 60[mm] is rein-forced. Since the other side of the bellows expands to the(a) Palm side(b) Arm sideFig. 3. Shape of appliance.axial direction by reinforcement at the only bending side,this actuator bends circumferentially when the compressedair is supplied into the actuator. The part between thebending and fixed parts of the bellows is not reinforced forreleasing the palm appliance. Fig.5 shows the outlook ofactuator. Depending on the reinforcement of bellows, whenthe compressed air is supplied to the actuator, the actuatorexpands to the axial direction as shown in Fig.5(b). Fig.6shows the size of the rotary-type soft actuator used fortype II. The outer and inner diameter and length of rubbertube are 16, 12, 180[mm], respectively. The outer andinner diameter of polyester bellows are 28, 22, respectivelyThe both sides of the bellows with length 60[mm] fromthe end are reinforced for inhibiting axial expansion. Thebending side at center part of bellows with length 60[mm]is reinforced. Fig.7 shows the fundamental characteristicsof actuator. Enough bending angle δθ for assisting withhuman wrist can be obtained as shown in Fig.7(a). Fig.7(b)show the relation between a bending angle and a maximumgenerated torque with 500[kPa].The mass of average Japanese male palm is about560[g][4]. It supposes that the position of the center ofgravity is the center of the palm[5], the required torque forsupport the palm is about 250[Nmm] per one actuator. Thedashed line in the figure shows this required torque. Fromthe result, an assisted bending angle of about 80[deg.] canbe expected. The almost satisfactory bending angle can beobtained, since an average bending angle of a Japanesemale is about 86[deg.][4,5].Fig.8 shows the torque characteristic of the actuator usedfor TypeII. To realize the assisting increase in muscularendurance, the required torque is more than type I. Fromthe figure, the generated torque which is 5 times as much asone of actuator for type I can be obtained. For protecting521the wrist, the stopper is attachd to the bending side forinhibiting the increase in the bending angle over 80[deg.].(a) Rotary-type soft actuator(b) Rubber tube(c) Polyester bellowsFig. 4. Structure of rotary-type soft actuator used for type I.(a) Initial state(b) Pressurized stateFig. 5. Outlook of rotary-type soft actuator.Fig. 6. Size of rotary-type soft actuator used for Type II.Fundamental Characteristics of ASSISTFig.9 shows the generated torque of ASSIST. As com-pared with Fig.7(b),8, the torque which is twice as bigas one of one actuator can be obtained. In contrast, thegenerated one with Type II decreases sharply with theincrease in the bending angle. The decrease in the torqueis caused principally by the deformation of the rotary-typesoft actuator at the fixed part on the appliance. However,type II can apply the generated force of about 20[N] tothe palm with keeping bending angle of 80[deg.]. Fig.10(a) P -δθ(b) δθ-τmaxFig. 7. Fundamental characterisics of actuator.Fig. 8. Torque characterisic of actuator used for typeII.shows the pressure response of ASSIST. In addition, theangle responses of the actuator attached with ASSIST arealso shown in this figure. The bending angles of both typessaturate mechanically over 400[kPa], the dynamic charac-teristics is measured under 400[kPa] in this experiment.From the figures, although the increase of the angle issmall in the lower pressure region under 200[kPa] due tothe non-linear characteristic of the actuator, the delay tothe pressure do not appear in the high pressure region.III. INCREASE IN MOVABLE RANGEIn this section, an effectiveness of the assisting increasein movable range for a muscularly weak human is discussedexperimentally.Fig.11 shows the assisting scene. In this experiment,a human wrist is bended by ASSIST without a humanmuscular force. For evaluating the assist effectiveness, thebending angle at human wrist is measured. In addition,EMG is measured in order to confirm the muscular powerfrom human. The wrist operates stepwise and sinusoidallyboth cases with and without the splint. EMG is measuredat a flexor carpi ulnaris as shown in Fig.12. A flexor carpiulnaris is one of muscles for bending a wrist[6], therefore522(a) Type I(b) Type IIFig. 9. Relation between δθ and τmax.(a) Type I(b) Type IIFig. 10. Relation between t and P ,δθ.it is selected as a measured point of EMG. ASSIST iscontrolled by the pressure control system.Fig.13 shows the experimental results with and withoutASSIST when the wrist is bended stepwise. The bendingangle without assist is about 86[deg.]. This value is roughlyequivalent to an average bending angle of Japanese male.The bending angle with the assist is about 80[deg.]. The al-most satisfactory bending angle can be obtained. The largedifference in the amplitude of EMG can be confirmed inthe cases with and without ASSIST. Since the amplitude ofEMG with ASSIST decreases compared with the amplitudewithout one, the burden for the muscle can be decreasedby the generated torque from ASSIST. Fig.14 shows theexperimental results with and without ASSIST when thewrist is bended sinusoidally. The generated torque fromASSIST can also decrease the burden at muscle. By usingASSIST, the bending motion can be realized even when ahuman does not generate a muscular force.(a) Initial state(b) Pressurized stateFig. 11. Assisting sceneFig. 12. Measured point for EMG.IV. INCREASE IN MUSCULAR ENDURANCEFor evaluating the effectiveness of muscular enduranceassist quantitatively, the method of Mosso’s ergographknown as one of method to measure muscular fatigueis applied to this experiment. In the method of Mosso’sergograph, a periodical motion of the measured bodypart is repeated under the applied load, and the changingamplitude of displacement with time is measured.In this experiment, the angles at the wrist are measuredwith and without ASSIST Type II as shown in Fig.15, andthe load is 3[kg], the period of bending motion is 2[s], theexperimental time is 400[s].The subjects are 5 Japanese males. Fig.16 shows tworesults as the examples of the large and the small effect .In the case of the experiment without ASSIST, the bendingangle decreases steeply or the magnitude of bending anglevaries widely according to the muscular fatigue. In thecase of using ASSIST, although the bending angle alsodecreases, the decreased angle is smaller than the decreasedone without ASSIST. In addition, though the tendenciesof both results in the case without ASSIST are differentquite each other, the difference of the tendency becomessmall by using ASSIST. From these results, ASSIST is523(a-1) Angle (a-2) EMG(a) Without ASSIST(b-1) Angle (b-2) EMG(b) With ASSISTFig. 13. Experimental results (Step motion).(a-1) Angle (a-2) EMG(a) Without ASSIST(b-1) Angle (b-2) EMG(b) With ASSISTFig. 14. Experimental results (Sinusoidal motion).effective to decrease not only the muscular fatigue but alsothe difference among the human capability.V. OPERATION BASED ON A HUMAN INTENTIONFrom the above experiments, the effectiveness of AS-SIST is verified experimentally through the assisting in-crease in movable range and muscular endurance. In orderto operate ASSIST based on a human intention, the inputdevice for ASSIST must be developed. For realizing thesimple structure and operation of ASSIST, it is desirablethat also the input device has a simple structure. Thenthe bend sensor which the resistance is increased withincrease in the bending angle is equipped to the side ofappliance, the inner pressure of the rotary-type soft actuatoris determined from the change of bending angle of ASSISTaccording to the increase or decrease in the bending angleof the human wrist. The outlook and characteristic of thebend sensor are shown in Fig.17. As one of control methodof the inner pressure based on the bending angle, ASSIST(a)Without ASSIST (b)With ASSISTFig. 15. Shene of muscular endurance assistWithout ASSIST With ASSIST(a) Subject AWithout ASSIST With ASSIST(b) Subject BFig. 16. Experimental resultsis switched ON or OFF using a threshold determined fromthe absolute bending angle of wrist. However, since amovable range differs in every human, different thresholdvalues must be determined. In this study, by using themoving average of bending angle of ASSIST, the innerpressure is switched as follows and shown in Fig.18 whenthe difference of the measured angle and the movingaverage one becomes over or under the threshold.P = Pmax (θ − θa ≥ θt)P = 0 (θ − θa≤− θt)θ, θa, θt represent the measured angle, the moving averageone and the threshold, respectively. The moving averagetime is 1[s], and θt is 5[deg.]. Fig.19 shows the experi-mental result. In this experiment, the wrist with ASSIST isbended with frequency of 0.5[Hz], and the bending angleof wrist and EMG at a flexor carpi ulnaris are measured.As can be seen in the figures, ASSIST can be switchedON or OFF when the human bends or extends the wristunder the condition of keeping the inner pressure of theactuator constant. It can be verified from the EMG signalthat the muscular power is hardly required even when thehuman intends to bend his wrist. From the results, ASSISTcan operate based on a human intention.524(a) Outlook(b) CharacteristicFig. 17. Bend sensor.Fig. 18. Principle of operation.VI. CONCLUSIONIn this paper, the structure and the fundamental char-acteristics of ASSIST have been described, and then theeffectiveness of ASSIST has been verified experimentallythrough the assisting both movable range and the muscularendurance. The main results and the future works of thisstudy can be summarized as follows:1) The bending angles at the stepwise motion withoutand with ASSIST are about 86, 80[deg.], respectively.The almost satisfactory bending angle can be ob-tained with ASSIST in the condition that the humangenerate no muscular power.2) There is the large difference in the amplitudes ofEMG at stepwise and sinusoidal motions with andwithout ASSIST. Therefore, it can be proved thatASSIST can be realized an bending motion evenwithout a human muscular power. In addition, thefact (1) has been proved from EMG signal.3) ASSIST is effective to decrease not only the muscularfatigue but also the difference among the humancapability.4) By using a bend sensor, the operation based ona human intention can be realized. To realize the(a) Angle (Wrist)(b) EMG(c) Angle (ASSIST)Fig. 19. Experimental results.complicated motion and the control method are thefuture works.5) The power source of ASSIST is supplied from theexternal compressor. To improve the wearability, theminiaturization of the compressor is the future work.REFERENCES[1] K.Kiguchi,T.Tanaka,K.Watanabe,T.Fukuda:“Exoskeleton for HumanUpper-Limb Motion Support”,Proc. of the 2003 IEEE InternationalConference on Robotics & Automation, pp.2206-2211 (2003)[2] K.Nagai,I.Nakanishi,H.Hanafusa:“Assistance of Self-Transfer of Pa-tients Using a Power-Assisting Device”,Proc. of the 2003 IEEEInternational Conference on Robotics & Automation, pp.4008-4015(2003)[3] J.M. Tressler,T.Clement,H.Kazerooni,M.Lim :“Dynamic Behaviorof Pneumatic Systems for Lower Extremity Extenders”,Proc. of2002 IEEE International Conf. on Robotics and Automation,pp.3248-3253 (2002)[4] J.Kohara, et al.:“Measurement of human body”,Japan PublicationService, (1986) (in Japanese)[5] M.Sato, et al.:“Human engineering numerical standard hand-book”,Gihodo Shuppan Co.,Ltd., (1999) (in Japanese)[6] O.FUKUDA, T.Tsuji, A.Ohtsuka, M.Kaneko:“EMG-based Human-Robot Interface for Rehabilitation Aid”,Proc. of the 1998 IEEEInternational Conference on Robotics & Automation, pp.3492-3497(1998)[7] T.Noritsugu,D.Sasaki,M.Takaiwa:“Application of Artificial Pneu-matic Rubber Muscle to a Human Friendly Robot”,Proc. of the 2003IEEE International Conference on Robotics & Automation,pp.2188-2193 (2003)525

Development of Active Support Splint driven by Pneumatic Soft Actuator (ASSIST)

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