Towards the Biped Walking Wheelchair

Transcription

1 Towards the Bped alkng heelchar Yusuke Sugahara, Kenj Hashmoto, Hroyuk Sunauka, Masamk Kawase, Akhro Ohta and Chak Tanaka Hun-ok Lm Atsuo Takansh Graduate School of Scence and Engneerng Department of Mechancal School of Scence and Engneerng Engneerng / Humanod Robotcs Insttute aseda Unversty Kanagawa Unversty aseda Unversty Tokyo, JAPAN Kanagawa, JAPAN Tokyo, JAPAN Emal: sugahara@suou.waseda.jp.abstract Ths paper descrbes the development of a prototype bped walkng wheelchar. Ths robot conssts of two Stewart Platform type legs and wast wth a passenger seat. The walkng control method based on ZMP crtera and vrtual complance control method for ths robot were also developed. Through varous experments, the effectveness of the developed hardware and the control method was confrmed. Index Terms Bped alkng, Bped Robot, heelchar, Bped Locomotor, Carryng Human. I. INTRODUCTION As the expected form of locomoton for robots s ultmately bped walkng, we have been studyng the mechansm and control of bped walkng robots for approxmately 35 years [1-4]. To date, however, most humanod robots have employed wheels and crawlers for ther locomoton mechansm. Ths s not only because bped robots are essentally unstable; another problem s that they are dffcult to treat as ndependent locomoton modules. Our ultmate research am s to develop a bpedal robot as a leg module that s suffcent for practcal use as a mult-purpose locomotor for robotc systems (Fgure 1). e am to provde a bpedal robot wth only lower-lmbs and a wast that can walk ndependently; allowng users to then buld the upper body accordng to ther needs. Ths bped locomotor would be applcable to the welfare feld as a walkng wheelchar or as a walkng support machne that s able to walk up and down stars carryng or assstng a human. Varous researches nto walkng robots for practcal use have been conducted [5-10], as well as other researches nto those of the bped walkng type. Regardng locomoton modules capable of human transport, researches on the alkng Char [9] or locomoton module called My Agent [10] have also been carred out. In addton and remanng n the welfare ndustry feld, the electrc wheelchar named BOT [11], capable of ascendng and descendng stars and slopes was released by Independence Technology L.L.C., although t employed wheels for ts locomotve mechansm. Some of these researches were performed wth the concept of reducng DOF [5, 6] whle other researches focused only on ascendng and descendng stars [7, 8]. Furthermore, not all these researches focused on dynamc bped walkng [9, 10]. Although such methods appear advantageous n terms of cost reducton and ease, ther ultmate goal s not versatlty. Although the am s to develop BOT as a sutable style of locomoton system on whch to rde, ts objectve does not nclude operaton n any narrow envronment wth obstacles scattered around such as a tradtonal Japanese house. Moreover, there are problems related to ts mechansm, such as requrng a rgd star ral to ascend and descend stars, and ts nablty to move sdeways. Therefore, we developed bped locomotors, L-15 (aseda Leg - No. 15), L-16, L-16R and L-16RII, whch have 6-DOF parallel mechansm legs [12-16]. Ths robot conssts of two legs and a wast. Usng ths robot, we studed how to apply the bped walkng robot to a moble base. In 2003, usng L-16, the world s frst dynamc bped walkng carryng an adult woman and a dynamc bped walkng carryng a 60 kg adult man were realed [13, 14], earler than the release of the Toyota Motor Corporaton s Toyota Personal Robot [17, 18]. In addton, bped walkng up and down stars carryng a human was also realed n 2005 [15].. * Ths research was done n collaboraton wth TMSUK Co., Ltd supported by Fukuoka Prefecture, Fukuoka Cty, SANYO Electrc Soft Energy Co., Ltd. and Sold orks Japan K.K. The authors would lke to express sncere thanks to them for ther fnancal and techncal support. Fgure 1. Applcatons of mult-purpose bped moble base.

2 Fgure 3. DOF confguraton of L-16RII. Fgure 2. Photograph of aseda Leg - No. 16 Refned II. In ths paper, our prevous steps toward the realaton of bped walkng wheelchar are descrbed. Our steps nclude the development of hardware, control method and varous experments of the newest prototype L-16RII (aseda Leg - No. 16 Refned II) shown n Fgure 2. II. HARDARE OF PROTOTYPE ASEDA LEG -NO.16 REFINED II A. Basc Desgn Ths bped machne was developed to be a leg module that s suffcent for practcal use as a mult-purpose locomotor of the robot system. Therefore, ths robot should be able to carry heavy load. To fulfl ths requrement, the DOF confguraton of the leg mechansm conssts of a Stewart Platform as shown n Fgure 3. The weght of L-16RII s 62 kg ncludng 5 kg battery weght. Each leg mechansm has 6 lnear actuators and passve jonts at the both sdes of each lnear actuator. Each lnear actuator conssts of a 150 DC servo motor and ball screw, and has a negatve operaton electro magnetc brake, so ths robot can hold ts posture wthout power supply. The control computer s arranged at the rear of the pelvs, and the batteres, DC servo drvers and a body angle detector are arranged nsde the pelvs. A passenger seat s on the pelvs. Fgure 4 shows the sometrc vew of ths robot, and Fgure 5 shows the exploded vew of the lnear actuator. B. Support Torque Reducton Mechansm On the desgn specfcaton of the lnear actuator of L-16RII, the maxmum payload s 60 kg. It s not too Fgure 4. Isometrc vew of L-16RII. Fgure 5. Exploded vew of lnear actuator. small, but t s nsuffcent to apply ths robot as a bped wheelchar. Ths s manly because the torque of the DC servomotor s not so large. So the easest way to ncrease the maxmum payload s to use other hgher power actuators, or to ncrease the torque usng reducton gears wth a hgher reducton rato. However, the former leads to beng more expensve to produce and too large n a human-lvng envronment, and the latter s dsadvantageous n walkng at hgher speed.

3 Fgure 6. Assembly drawng of L-16R wth support torque reducton mechansm. Fgure 8. Defnton of coordnate system and vectors. Rght STRM Left STRM Hard sprng Soft sprng Hard sprng Soft sprng Rght: support Rght: support Left: swng Left: swng Rght: support Left: support Instead, research on robot arms provdes a way of reducng the necessary torque of the actuator by compensatng for the robot s own weght mechancally. So we focused on the fact that most of the force actng on the foot durng walkng wth a heavy load s to support the robot s own weght, and developed the Support Torque Reducton Mechansm not to compensate for all of the robot s weght mechancally, but to reduce torques needed to support the robot s own weght usng a smpler mechansm. The Support Torque Reducton Mechansm conssts of two compresson gas sprngs wth dfferent sprng forces that have a lock functon, and are attached to each leg (Fgure 6). These mechansms lock and unlock each sprng accordng to the support / swng phase, and supports manly vertcal force. Fgure 7 shows the operaton sequence of swtchng gas sprngs. Durng the support phase, the gas sprng wth a large reacton force s unlocked and actvated, and the other s locked. Contrarwse, durng the swng phase, the gas sprng wth a small reacton force s unlocked and the other s locked. hen the supportng state changes, the effects of the two gas sprngs are swtched by pushng down and releasng the swtch pn of each gas sprng usng solenods. III. ALKING CONTROL METHOD Rght: swng Rght: swng Left: support Left: support Fgure 7. Operaton sequence of swtchng gas sprngs. Snce L-16RII s also a bped robot that has 6 DOF legs, the walkng control problem s bascally same as that of exstng bped robots that ncludes humanod robots. As the control method of ths robot, model based walkng control method based on ZMP crtera s used. The walkng control method of ths robot conssts of two man parts: frst s the walkng pattern generaton before walkng as the feed forward control of the bped walkng system, and second s the real-tme stablaton control durng walkng as the feed back control. A. alkng Pattern Generaton Ths algorthm conssts of the followng man parts: 1. Modellng of the robot 2. Dervaton of the ZMP equatons 3. Computaton of approxmate wast moton 4. Computaton of strct wast moton by teratvely computng the approxmate wast moton Let the walkng system be assumed as follows: (1). The robot s a system of partcles. (2). The floor for walkng s sold and cannot be moved by any force or moment. (3). A Cartesan coordnate system s determned as shown n Fgure 8. The X-axs and Y-axs form a plane that s the same as that of the floor. (4). The contact regon between the foot and the floor s a set of contact ponts. (5). The coeffcent of frcton for rotaton around the X, Y and Z-axes s ero at the contact pont. Frst, we defne an approxmaton model of the wast and the poston vectors lke Fgure 2. The moment balance around pont P on the floor can be expressed as below: all _ partcles m ( r - r ) ( r G) T 0 p If the pont P s defned as ZMP, T = 0. e denote the poston vector of P as P ZMP ( xzmp, yzmp,0). To consder the relatve moton of each part, a movng coordnate O - XYZ

4 s establshed on the wast of the robot parallel to the fxed coordnate O - XYZ. Q x, y, ) s the poston vector of the orgn of ( q q q O - XYZ from the orgn of O - XYZ. Usng the movng coordnate frame, Equaton (1) can be modfed as follows: all _ partcles m ( r - r ) { r Q - G r 2 r ( r )} 0 where r s the poston vector of ZMP wth respect to the O. s the angular velocty vector of the orgn of O - XYZ. Assumng that a movng coordnate does not rotate, ths equaton s expanded nto Equatons (3) and (4) by puttng the terms representng the moment generated by the lowerlmb partcles on the rght-hand sde as known parameters, named M and M respectvely. x y m ( )( x xq g x ) m ( x x )( g ) M m m ( y ( y q )( w q g ) )( y y g ) M q y y x These equatons are nterferental and non-lnear. Thus, by assumng that the wast partcles move vertcally, the equatons can be decoupled and lneared wth the rght sde ncludng the known clause of the left sde beng newly replaced wth M * x and M * y, as follows. m m ( ( ZMP ZMP )x * m ( g )x M y )y * m ( g )y M x In these equatons, M * x and M * y are known because they are derved from the lower-lmb s moton and the tme trajectory of ZMP. In the case of steady walkng, M * x and M * y are perodc functons because each partcle of the lower-lmbs and the tme trajectory of ZMP move perodcally for the movng coordnate - XYZ. Thus, each equaton can be represented as a Fourer seres. By comparng the Fourer transform coeffcents from both sdes of each equaton, we can easly acqure the approxmate perodc soluton for the trunk moton. In order to obtan the strct solutons of the body, the approxmate solutons are subtracted nto Equaton (2) and ZMP s computed. Then, the strct moton of the body s obtaned usng an teraton method. The flowchart of ths method s shown n Fgure 9. B. Vrtual Complance Control Snce our walkng pattern generaton algorthm outputs a stable walkng pattern generated offlne beforehand, the robot becomes unstable due to the landng mpact accordng to modelng errors such as the deflecton of the structure. There s concern that ths landng mpact would be fatal when the robot walks under condtons that create large deflecton of structures and response error of the motor easly, such as walkng wth a heavy payload or carryng a human. Therefore, usng the vrtual complance control, we planned to moderate the landng mpact, and to stable walkng under such condtons. The moton that the leg should perform n order to reale vrtual complance can be gven by F Kxf Cx f 12 where FR s the force / moment vector actng on the 12 complance center, xf R s the desred poston error 12 vector of the foot orgn, and x f R s the desred velocty vector of the foot orgn KR and CR denote the stffness and dampng matrxes. The complance poston of the foot can be calculated by the dscretaton of Equaton (7) as follows: Fgure 9. Flowchart of walkng pattern generaton method. 1 C x f ( tt) xf () t K t F C t where x f () t s the present reference of foot coordnate orgn's error, x f ( tt) s the reference of foot

5 6-dmensonal Foot Poston x fpat + x f () t x fcc + Inverse Knematcs l f 1 ( x) l cc PATTERN GENERATOR Complance Controller 1 C x f ( tt) xf () t K t F C t BIPED LOCOMOTOR F Reacton Force Fgure 10. The block dagram of vrtual complance control. coordnate orgn's error before 1 control cycle, and t s the control cycle (1 ms). The desred complance poston of Equaton (8) s added to the reference poton generated by the pattern generator. Then, the reference lengths of the lnks are calculated by nverse knematcs, and are commanded to each jont by the poston control. The block dagram of poston-based vrtual complance control s shown n Fgure 10. Fgure 11. alkng experment carryng a 50 kg load. IV. EXPERIMENTS e conducted varous experments usng the developed robot. Fgure 11 shows the dynamc bped walkng experment carryng a 50 kg payload, and Fgure 12 shows the dynamc bped walkng experment carryng a 60 kg adult man. In both of these experments, the step length was 0.1 m/step and the walkng cycle was 0.96 s/step. By usng the developed hardware and control method, these experments were successfully completed. Fgure 13 shows the dynamc bped walkng experment carryng a 94 kg adult man usng the support torque reducton mechansm. The walkng cycle was 0.96 s/step and the step length was 0.1 m/step. By usng the developed support torque reducton mechansm, ths experment succeeded. Fgure 14 shows the bped walkng experment ascendng and descendng stars carryng a 60 kg adult man. The rse of the star was 200 mm and the walkng cycle was 5.76 s/step. Although the Stewart Platform has a generally narrow workspace, by twstng the wast accordng to the foot poston, ths experment also succeeded. Fgure 15 and 16 shows walkng experments conducted n the human-lvng envronment and on a publc road. Fgure 15 shows the walkng experment ascendng outdoor stars at the entrance of a Japanese shrne, and Fgure 16 shows the walkng experment on the crosswalk of a publc road. These experments demonstrate ts practcal applcaton. V. CONCLUSIONS AND FUTURE ORK e developed a prototype bped walkng wheelchar, L-16RII that conssts of two Stewart Platform type legs and wast wth a passenger seat was developed. e also Fgure 12. alkng experment carryng a 60 kg adult man. Fgure 13. alkng experment carryng a 94 kg adult man usng a support torque reducton mechansm. developed a support torque reducton mechansm that reduces the requred motor torque to carry a heavy load. In addton, we developed a walkng control method based on ZMP crtera and a vrtual complance control method for ths robot. Through varous experments, the effectveness of the developed hardware and control method was confrmed.

6 ACKNOLEDGMENT Ths study was conducted as part of the humanod project at the Humanod Robotcs Insttute, aseda Unversty. Ths study was supported n part by the Mnstry of Educaton, Scence, Sports and Culture, Grant-n-Ad for Young Scentsts (B), , It was also supported n part by the Robotcs Industry Development Councl. Part of ths study has been conducted thanks to a aseda Unversty Grant for Specal Research Projects (2004A-159). Ths study was supported n part by the The nnovatve research on symboss technologes for human and robots n the elderly domnated socety, 21st Century Center of Excellence Program, Japan Socety for the Promoton of Scence. In addton, the authors would lke to thank the cty employees and resdents of Fukuoka Cty for ther help n conductng experments. REFERENCES Fgure 14. alkng experment ascendng and descendng 200 mm stars carryng a 60 kg adult man. Fgure 15. alkng experment ascendng outdoor stars. Fgure 16. alkng experment on the crosswalk at the publc road. Our next goal s to conduct varous experments and mprove the hardware and control method toward practcal applcaton. [1] A.Takansh, et al., The realaton of dynamc walkng by the bped walkng robot, Proc. of the IEEE ICRA 85, pp , St.Lous, MO, March, [2] A.Takansh, et al., A control method for dynamc walkng under unknown external force, Proc. of the IEEE/RSJ IROS 90, pp , Tsuchura, Japan, July, [3] J. Yamaguch, A. Takansh and I. Kato, Development of a Bped alkng Robot Adaptng to a Horontally Uneven Surface, Proc. of the IEEE/RSJ IROS 94. [4] H. O. Lm, Y. Sugahara and A. Takansh, Stablaton walkng control for human-lke bped robots, Proc. of the 2002 CISM- IFToMM Symp. on Theory and Practce of Robots and Manpulators, pp , Udne, Italy, July, [5] K. Takta, et al., Fundamental mechansm of dnosaur-lke robot TITRUS-II utlng coupled drve, Proc. of the IEEE/RSJ IROS 2000, pp , Takamatsu, Japan, October, [6] Y. Ota, T. Tamak, K. Yoneda and S. Hrose, Development of walkng manpulator wth versatle locomoton, Proc. of the IEEE ICRA 2003, pp [7] Y. Konuma and S. Hrose, Development of the star-clmbng bped robot Zero alker-1, Proc. of the 19 th Annual Conf. of the RSJ, pp , [8] Y. Konuma and S. Hrose, Development of 2 types of leg-wheel vehcle wth the functon of stable star-clmbng, Proc. of the 8 th RSJ/JSME/SICE Robotcs Symposa, pp , Shuoka, Japan, March, [9] Y.Takeda, M.Hguch and H.Funabash, Development of a walkng char (Fundamental nvestgatons for realng a practcal walkng char), Proc. of the CLAAR2001, pp , Karlsruhe, Germany, September, [10] T. Kamada, My Agent: A Practcal Personal Assstant, Proc. of the JSME ROBOMEC 94, pp , Kobe, Japan, [11] [12] Y. Sugahara, et al., Control and Experments of a Mult-purpose Bpedal Locomotor wth Parallel Mechansm, Proc. of the IEEE ICRA 2003, pp , Tape, Tawan, September, [13] Y. Sugahara, et al., Realaton of Dynamc alkng by a Bped Locomotor Carryng a Human, Proc. of the 9 th RSJ/JSME/SICE Robotcs Symposa, pp , Oknawa, Japan, March 8 th -9 th, [14] Y. Sugahara, et al., Realaton of Dynamc Human-Carryng alkng by a Bped Locomotor, Proc. of the IEEE ICRA 2004, pp , New Orleans, USA, Aprl, [15] Y. Sugahara, et al., Support Torque Reducton Mechansm for Bped Locomotor wth Parallel Mechansm, Proc. of the IEEE/RSJ IROS 2004, pp , Senda, Japan, October, [16] Y. Sugahara, et al., alkng Up and Down Stars Carryng a Human by a Bped Locomotor wth Parallel Mechansm," Proc. of the IEEE/RSJ IROS 2005, pp , Edmonton, Canada, August, [17] March 11 th, [18] December 3 rd, 2004.