When robots work together with a human or contact with a human body directly in such as a medical welfare field, in order to avoid an accident from crash and so on, a flexibility is required for the robot. The purpose of this study is to realize a safe mechanism for a human-friendly robot. In this paper, the structure and the fundamental characteristics of a pneumatic rubber muscle and soft mechanism are described, and then the structure and the fundamental operation of the developed soft hand are shown. Finally, the shaking hands is discussed as an example of force communication tasks between a robot and a human. </p

Noritsugu, Toshiro

Sasaki, Daisuke

Takaiwa, Masahiro

Okayama University Digital Information Repository

Application of artificial pneumatic rubber muscles to a human friendly robot

Okayama University Scientific Achievement Repository

EngineeringIndustrial & Management Engineering fieldsOkayama University Year 2003Application of artificial pneumaticrubber muscles to a human friendly robotToshiro Noritsugu Daisuke SasakiOkayama University Okayama UniversityMasahiro TakaiwaOkayama UniversityThis paper is posted at eScholarship@OUDIR : Okayama University Digital InformationRepository.http://escholarship.lib.okayama-u.ac.jp/industrial engineering/74Proceedings of the 2003 IEEE Interoationai Conference on Robotics 61 Automation Taipei, Taiwan, Septembir 14-19, 2003 Application of Artificial Pneumatic Rubber Muscles to a Human Friendly Robot Toshiro Noritsugu , Daisuke Sasaki and Masahiro Takaiwa Faculty of Engineering, Okayama University 3-1-1 Tsushimanaka , Okayama , 700-8530 Japan Email  : toshiro~sys.okayama-u.ac jp  daisukeQmcrlab sys.okayama-u ac.jp takaiwa@sys.okayama-u.ac.jp Abstract  - When robots work together with a hu- man or contact with a human body directly in such as a medical welfare field, in order to avoid an acci- dent from crash and so on , a flexibility is required for the robot. The purpose of this study is to realize a safe mech- anism for a human-friendly robot. In this paper, the structure and the fundamental characteristics of a p neumatic rubber muscle and soft mechanism are d a  scribed, and then the structure and the fundamental operation of the developed soft hand are shown. Fi- nally, the shaking hands is discussed e an example of force communication tasks between a robot and a human. I. In t roduc t ion  For the coming advanced age society, there may not be enough working people in various fields. 5 specially, in the high physical burden field such as medical welfare , agriculture and so on , the lack of working people may become a serious problem. In order to  deal with such a situation, it is effective to  introduce a human friendly robot. Differently from conventional robots, robots are required a safety for a human because robots op- erate around a human and contact with a human body directly['!. In addition, the robot has to pre- pare with various communication functions such as vision, audition, tactile sensation and so on[21[3]. A wide usability of human hand is paid attention, various humanlike robot hands have been developed such as the Utah/MIT Dextrous Handl'1,the Star- ford/JPL hand[5] and so on. Their hands are op- erated by a tendon mechanism. The tendon mech- anism needs to  adjust a tension force so that the tension adjuster is incorporated into the mechanis- m. Therefore the mechanism becomes complicated. to realize a robot which can work together with human or handle fragile objects , a soft robot hand constructed with two, types of p- neumatic rubber muscle and a tactile soft s e n ~ o r [ ~ ] [ ~ !  In this study has been developed. The developed robot hand is made of silicone rubber body and driven with a p neumatic power A pneumatic rubber muscle and a soft mechanism provided with the flexibiiity owing t o  silicone r u b  ber can easily achieve bending and torsion motions without joint , bearing and so on. Depending on the flexibility of the hand , this hand can accom- plish almost the same motion as a human hand, therefore this hand can contact with a fragile and shapeless object without complicated control law. In addition, since this hand is directly driven by p- neumatic rubber muscles, the mechanism of hand can be made simpler than the above robot hands. In this paper ,  the structures and the fundamen- tal  characteristics of apneumatic rubber muscle and soft mechanism are described , and then the struc- ture and the fundamental operation of the soft hand are shown. Finally, a method of force communica- tion task is proposed, which controls a mutual com- munication based on the operating force between a robot and a human. This method is.appIied to their shaking hands motion. 11. P n e u m a t i c  Rubber Muscle  Linear-Type Ac tua to r  To realize components for a complicated motion such as the root of thumb , the small size linear- type soft actuator is developed. Since deformation of mechanism (bending , torsion) can be realized by the small sized linear-type soft actuator easily, many kinds of complicated motions become possi- ble. In the following , the structure and the funda- mental property of this linear-type soft actuator is described. Fig.1 shows the structure of the linear-type soft actuator. It consists of silicone rubber tube (outer diameter 4[mm] ~ inner diameter 3[mm]). The tube is reinforced with polyester fibers. 0-7803-7736-2/03/$17.00 02003 IEEE 2188 Silicone rubber tube Fiber Fig.1: Structure of linear-type soft actuator Fig.l(a) shows the initial state of the developed actuator. When the compressed air is supplied to this actuator , it contracts in the axial direction as shown in Fig.l(b). . , .I^  (a) Initial state (b) Pressurized state Fig.2: Operation of linear-type soft actuator Three kinds of linear-type soft actuators ( l o  = 40,70,95mm]) have been experimentally examined. lo is the initial length of this actuator. The dis- placement when the compressed air is supplied to the linear-type soft actuator from O[kPa] to  500[k- Pa] at SO[kPa] interval is measured. Fig.3 shows the relations between the inner pressure and the displacement. The experimental results show that the displacement saturates with an increase in the inner pressure . The elastic limit of silicone rubber c a m s  this saturation. 0 lnner pressure P [kI’a) Fig.3: Relation between P and 61 The relation between the inner pressure and the contraction force of the linear-type soft actuator is measured. The ectuator is fixed at the initial length in the measurement. The  experimental re- sult shown in Fig.4, it proves that  the contraction force increases with an increase in the length of the actuator. Inner pressure P [kPal Fig.4: Relation between P and F The relations between the contraction ratio and the contraction force of each actuator are shown in Fig.5. In the measurement , the fixed distance of this actuator is decreased at 61/10 =0.5 intervals at the constant inner pressure of SOO[kPa]. It is shown that the contraction force decreases almost linearly along with an increase in the contraction ratio. h I Contraction rate Sr / l o  Fig.5: Relation between e and F Rotary-Type Actuator Fig.6 shows a structure of the developed actua- tor. This actuator consists of a silicone rubber ball with an outer diameter of lZ[mm] , an inner diam- eter of 10[mm] and a silicone rubber bar with an outer diameter of lO[mm]. The silicone rubber ball is made by forming a liquid silicone rubber with a metal mold A rotary-type soft actuator of which the ball and the bar are covered with a fiber tube. This fiber tube is made from polyester fiber tube as shown in Fig.G(b). The bended side of actuator is reinforced with fiber to inhibit expanding in the axial direction. Therefore , when the compressed 2189 air is supplied into the actuator , it bends in only the circumferential direction without expanding in the awial direction as shown in Fig.7. (a) Silicone rubber (c) Ratruy-lype soft actuator Fig.6: Structure of rotary-type soft actuator (a) Initial state Fig.7. Operation of rotary-type soft actuator Fig.8 shows the relation between the inner pres- sure and the bending angle. The change of the angle becomes small over BOO[kPa] , because the extention of the silicone rubber gradually nears the elastic lim- it . Enough large bending angle can be obtained. (b) Pressurized state Inner pressure P [kPa] Fig.8: Relation between P and 60 111. Tactile Soft Sensor Sensors used in the soft hand should be provided with the flexibility to keep the softness of the mech- anism. For this purpose , the pressure measurement type tactile soft sensor is developed. Fig.9 shows the developed tactile sensor. (a) Structure (b) Outlook Fig.9: Tactile soft sensor This sensor consists of cylindrical silicone rub- ber with an outer diameter 16[mm] , inner diameter 15[mm]. The cylindrical silicone rubber is made by forming a liquid silicone rubber with a metal mold. Fig.lO(a) shows the initial state of the sensor. When the external force is applied to it , the inner pressure of the sensor increases according to the de- formation of cylindrical silicone rubber as shown in Fig.lO(b). A tactile information can he detected by measuring the inner pressure change with a pressure sensor. -- (a) Initial state (b) Force applied state Fig.10: Principle of tactile soft sensor Fig.11 shows the relation between the applied external force and the inner pressure of the sensor. It is difficult for this sensor to detect the applied force smaller than l.O[N] , where the inner pressure is very small. Almost linear relation is obtained over l.O[N]. 0 2 4 6 8 1 0  Applied Force F ;NI Fig.11: Relation between F and P IV. Soft Hand Fundament a1 Operat ion Fig.12 shows the structure and the outlook of the soft hand. This soft hand consists of the soft finser and the linear-type soft actuator. The mass of hand is 9OO[g]. The length is 185[mm]. It has 21 90 the same size as human. The soft finger has three joints as shown in Fig.13. The rotary-type soft actuators are put in position at intervals of 25[mm]. The disposition of the iinear-type soft actuator is decided by referring the human muscle. This hand can operate almost same as a human hand as shown in Fig.14. (a) Structure (b) Outlook Fig.12: Soft hand (a) Initial state Fig.13: 0 (b) Pressurized state utlo&.of soft finger istics such as a shape and a weight , depending on the flexibility of the mechanism. . .  . .  Softball Cubical wood , . .  Balloon Fig.15: Scene of grasping motion C o n t a c t  Mot ion  By installing tactile soft sensor at the top of the finger , the soft hand can detect contact force. In the following , the contact motion with a constant force is discussed. This hand contacts with a soft ball and a balloon a t  the constant force as shown in Fig.16. . .  . .  , . ., The scene when the hand grasps three kinds of objects is shown in Fig.15. The grasping objects are a soft ball with an outer diameter of 90[mm] , a mass of 17O[g] , a cubical wood with a length of 50[mm] , a mass of 75[g] and a balloon with an outer diameter of 95[mm] , a mass of 2[g]. The com- mon and constant inner pressures are applied to  the linear-type soft actuator and the actuator. The in- ner pressures are 400 and 150 [kPa] , respectively. This hand can grasp objects with various character- Softball Balloon Fig.16: Scene of contact motion In the experiment , the inner pressure of the ro- tary actuator is defined by the force control sys- tem as shown in Fig.17. The inner pressure of the linear-type soft actuator is constant value. F, , P, represent the desired contact force and the reference inner pressure of the rotary actuator , respectively. F , P represent the measured values of the rotary 2191 actuator. F , P are detected by the tactile soft sen- sor and the pressure sensor. C represents PI con- troller. In the case of the softball and the balloon, the inner pressures of the linear-type soft actuator are 150 and SO[kPa] , respectively. Fig.18 shows the experimental results of contact motion. The desired contact force F, is 1.0,1.5,2.O[N]. In the case of the softball , the little finger can not contact with the object , then the little finger is not used in this experiment. As shown in the figures , this hand can contact with a objects with vari- ous characteristics , depending on detecting contac- t force. Especially , where this hand can contact with a softness object such as a balloon , this hand is effective to contact with a fragile object. Time I [SI Time l [I] 0 I . .  P Time I [I] (a) Softball I ......... * 1 -  -- 0 Time I [SI (b) Balloon Fig.18: Contact motion with object Fig.19 shows the experimental results of contact motion when a vibration is applied to the softball in the x axis direction. In the experiment , the vi- bration with an amplitude of 2.5[mm] , a frequency of 5[Hz] starts at lO[s]. When the vibration is a p  plied to the object, the contact forces agree with the desired contact force From the results mentioned above , when the external force is applied to this hand , this hand can grasp objects certainly too. &YJ 0 T i 3  I I*] Fig.19: Contact motion with softball Force Communication Task with Human physical contact. A human can recognize some in- formations such as a feeling , a physical condition and so on. Then, the contact force is one of im- portant informations. That is the same about a communication between a human and a robot. In this section, a force communication with a hu- man is proposed. In the following, the shaking hands is discussed as one of fundamental force com- munication tasks with a human. This hand shakes with a human one as shown in Fiv.2fl When a human communicates with someone through Fig.20: Scene of Shaking hands The small size pneumatic chamber is installed be- tween the fingers as shown in Fig.20. This pneumat- ic chamber is connected with the pressure sensor. When the human shakes with this hand, this pneu- matic chamber is deformed by the grasping force. The inner pressure of the pneumatic chamber in- creases according to  this deformation. Therefore, the inner pressure expresses the magnitude of the grasping force. The desired contact force F, is defined as shown in Fig.21. When the human applies the grasping force Fh to  the soft hand, F, is calculated from the force communication law. It is difficult to  detect Fh directly, then the inner pressure of the pneumatic 21 92 chamber defines as Fh, which expresses the magni- tude of grasping force. In this experiment, the magnitude of the contac- t force is changed according to the grasping force of human. Where, the force communication law is defined as a simple proportional factor a(= 0.2). Fig22 shows the inner pressure of the pneumat- ic chamber. From the figure, it is shown that the human changes the force intensity with time. - :b 0 10 20 30 Tune t [SI Fig.22. Inner pressure of pneumatic chamber Fig.23 shows the contact force of each finger. The desired force and the measured one are shown by a dashed line and a solid one, respectively. From the figure, it is shown that this soft hand can change the magnitude of the contact force according to the grasping force intensity of the human. V. Conclusion In the paper , the structures and the fundamen- tal characteristics of pneumatic rubber muscles and tactile soft sensor have been described , and then the structure and the fundamental operation of the soft hand have been described. After that, the force communication with a human have been proposed as an application of this hand. By applying the flexibility to the hand ,  the hand can operate almost same as a human hand. When a robot contacts with a fragile object such as a human body or fruits , a robot is required a delicate motion. In this case , the soft hand is effec- tive because this hand with a flexibility can contact with a fragile object without complicated control method. Finally, in this paper, the force communication law is defined as a simple proportional factor. The various responses of the force contact can be real- ized by changing the force communication law. It is the next subject to investigate the force commu- nication law for a highly human communication. _ _ _  Desired fome --Measured forss I Fig.23: Shaking hands VI. References [I] Y.K.Lee,I.Shimoyama"A Skeletal Framework Artificial Hand Actuated by Pneumatic Artificial Muscles". in Pmc. of Int. Conf. on Robotics and Automation. pp.92&931, 1999. [2] T.Fukuda,J.Taguri.F.Arai,M.Nakashima,D.T~hibana, Y.Hasegawa"Facial Expression of Robot Face for Human-Robot Mutual Communication". in Pme. of IEEE Int. Conf. o n  Robotics and Automation. pp.4& [3] T.Kanda.H.Ishiguro,T.Ono,M.Imai,R.Naluit~~ 51, 2002. "Development and Evaluation of an Interactive Hu- manoid Robot "Robovie" ". in Pmc. of IEEE In- 1.  Conf. on Robotics and Automotion. pp.1848-1855, 2002. [4] S.C.Jacobsen,J.E.Wood,D.FKnutti,K.B.Bigg~~: "The UtahJMIT Dextrous Handwork in Progress", Robotics Research(The First Internattonal Sympo- sium). pp.601-653, 1984 [5] M.T.MaSOn,J.K.SalisbUr:Rob~t Hands and the Me- chanies of Manipulation. MIT Press. 1985. [6] T.Noritsugu.D.Kar,eshiro and T.Inoue :"Soft Planar Actuator using Pneumatic-Rubber Balls", Journal of Robotics and Mechatronics. Vo1.12, No.3. pp.254-260, (71 T.Noritsugu,M.Kubota and S.Yosimatsu :"Develop ment of Pneumatic Rotary Soft Actuator Made of Sili- cone Rubber", Journal of Robotics and Mechatmnics, znno. v01.13, ~ 0 . 1 .  pp.17-22. 2001. 21 93 

Application of artificial pneumatic rubber muscles to a human friendly robot

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