Hybrid Parallel Robot for the Assembling of ITER

Transcription

1 7 Hybrd Parallel Robot for the Aemblng of IER Huapeng Wu, Hekk Handroo and Pekka Pe Lappeenranta Unverty of ehnology Fnland. Introduton he nternatonal thermonulear expermental reator (IER) a jont nternatonal reearh and development projet that am to demontrate the entf and tehnal feablty of fuon power. he reator tokomak (vauum veel) made of tanle teel, and ontan nne etor welded together; eah etor ha about the ze of meter hgh and 6 meter wde. he etor of IER vauum veel (VV) (Fg. ) requre more trngent tolerane (±5mm) than normally expeted for the ze of the truture nvolved. he wall (nner wall and outer wall) of IER etor are of 6mm thk and are joned by hgh qualty leak tght weld. In addton to the ntal vauum veel aembly, the etor may have to be replaed for repar. Meanwhle, the mahnng operaton and lftng of a poble e-beam gun olumn ytem requre extreme tffne property and good auray for a mahne tool. he payload to weght rato alo ha to be gnfantly better than t n the ommeral ndutral robot. he onventonal robot, provdng a hgh nomnal payload, are lak of tffne and auray n uh mahnng ondton. Sne ommerally avalable mahne apable of handlng large payload requre floor mountng and ther workpae are nuffent for reahng the ro eton at a ngle mountng poton, a peal robot needed. Parallel robot have hgh tffne, hgh dynam performane and good payload to weght rato n omparon wth the onventonal eral robot. Stewart [] preented the novel dea of xdegree-of-freedom parallel robot n 96. A remarkable number of reearh artle and book about parallel manpulator have been publhed durng the lat two deade. here are alo a number of ueful ndutral applaton developed [2], [3], [4], [7]. he parallel manpulator have many potental advantage ompared wth the onventonal eral lnk manpulator. Parallel manpulator are loed-loop mehanm preentng good performane n term of auray, rgdty, hgh peed, and ablty to handle large load. hey are beomng popular n applaton uh a mahnng, weldng, aembly, flght and vehle mulator, mnng mahne, and pontng deve [2], [3], [4], [7]. he mot mportant drawbak of parallel robot the mall workpae, whh an be made larger by addng addtonal eral axe n the robot. For the aembly of the IER vauum veel etor, the pree potonng of weldng endeffetor at ome dtane n a onfned pae from the avalable upport wll be requred,

2 364 Parallel Manpulator, oward New Applaton whle t not poble ung onventonal mahne or robot. he parallel robot preented n th paper able to arry out weldng and mahnng proee from nde the IER vauum veel, ontng of a x degree-of-freedom parallel mehanm mounted on a arrage drven by eletr motor/gearbox on a rak. he robot arre both weldng gun (uh a a IG, hybrd laer or e-beam weldng gun to weld the nner and outer wall of the IER vauum veel etor) and mahnng tool (to ut and mll the wall wth neeary auray). It an alo arry other heavy tool and part to a requred poton nde the vauum veel. he robot offer not only a deve but alo a methodology for aemblng and reparng VV. For aemblng, an on-lne x-degree-of-freedom-eam-fndng algorthm ha been developed. he algorthm enable the robot to fnd weldng eam automatally n a very omplex envronment. For mahnng, the mult flexble mahnng proee arred out automatally by the robot have alo been nvetgated, nludng edge uttng, moothng, and defet pont mllng. he knemat degn of the robot ha been optmed for the IER ae and a hydraulally atuated prototype ha been bult. Fnally the expermental reult are preented and dued. he earler development phae of the robot are preented n [8] and [9]. 2. Struture of VV and aemblng proe he nner and outer wall of the VV of IER are made of 6mm-thk tanle teel 36L and are welded together through an ntermedate, o-alled ple plate, nerted between the etor to be joned. he ple plate have two mportant funton: () to allow ae to bolt together the thermal held between the VV and ol; and () to ompenate the mmath between adjaent etor to gve a good ft-up of the etor-etor butt weld. he robot end-effetor wll have to pa through the nner wall ple plate openng to reah the outer wall. A hown n Fg., the aembly and reparng proee have to be arred out from nde the vauum veel. Fg. IER and VV etor to be welded

3 Hybrd Parallel Robot for the Aemblng of IER 365 he aembly or repar wll be performed aordng to four phae: uttng, edge mahnng and moothng, weldng, and non-detrutve tet (ND) ontrol. he robot wll arry out weldng, mahnng, and npetng nde the VV. he maxmum robot fore are from uttng. It an be up to 3kN. Fg.2 he trak ral mounted nde VV and robot on the trak In order that the robot an operate n the ro eton of the veel, a trak aembled nde the etor. he trak ha a rak on one de of the ral and t upported by manfold and beam (hown n Fg. 2). he robot drven on the ral arre out weldng or mahnng along the edge of the etor. After fnhng the aembly of two etor, the robot ha to be moved to the next etor where there alo a trak aembled. After fnhng the aembly of all the etor, the robot an be taken out va the port of VV. 3. Knemat of parallel robot 3. Struture of parallel robot he propoed parallel robot ha ten degree of freedom (Fg. 3). It ont of two relatvely ndependent ub-truture: () arrage, whh provde four addtonal degree of freedom,.e., rotaton, lnear moton, tlt rotaton and trakng moton, and thee four degree are added to enlarge the workpae and to offer hgh moblty; and () the Hexa-WH parallel mehanm drven by x hydraul ylnder ontrbute x degree of freedom for the endeffetor. hu the robot a hybrd redundant manpulator wth four extra degree of freedom provded by eral knemat lnk. a). Carrage mehanm he arrage manly ont of 5 unt. ) Carrage frame: he arrage frame a omplex truture welded by mult-teel-plate, and t able to arry hgh payload and offer enough room to mantan mehanm. Stffne and weght are the mot mportant onderaton n the degn, and they have been optmzed to aheve neeary tffne

4 366 Parallel Manpulator, oward New Applaton wth lght weght. ) rakng drve unt: he trakng drve unt ont of eletr motor, reduton unt CYCLO, V-hape bearng, and drvng gear. he eletr ervo motor wth Fg. 3 Parallel robot poton feedbak ontroller offer the hgh aurate moton. In order to output large torque to drve the heavy ma and payload, the reduton unt CYCLO added to the motor to redue peed and to tranmt hgh torque to the drvng gear. wo V-haped wheel keep the arrage on the trakng ral at rght poton to avod the ro moton. wo drve unt are ued n the arrage to offer enough torque n order to drve the robot and payload around nde the VV. ) Compenaton mehanm: he ompenaton ytem an mportant unt that lmt the baklah aued by the naurate aemblng of the trakng ral and ompenate the dtane hangng between the wheel n bendng area. A the hape of the VV very omplated, t dffult to keep the trakng ral lyng on the VV urfae n the aurate poton. he poton tolerane an be up to ±2mm. he dtane of the oupled wheel ha to be adjuted to follow the hange of the ral, and all the wheel mut touh the parallel ral wth ertan fore durng moton; hene an adaptve dtane ompenaton ytem needed and t hould be able to undertake the ummed weght of the robot and the payload, when the robot upde down at the top poton nder VV. Sne the total

5 Hybrd Parallel Robot for the Aemblng of IER 367 payload very heavy, a hydraul ylnder appled to jutfy the ompenaton fore aordng to the poton where the robot loated. Fg. 4 how the ompenaton ytem, where the upde the tolerane adaptve mehanm that pavely follow the hange of trak ral and the downde the hydraul dtane ompenaton ytem that enure a ontant fore appled to the ral. v) Lnear drve unt: he lnear drve unt enlarge the workpae of the robot, and ont of fve part: ball rew drve unt, ervo motor, ral, lnear bearng, and a table. wo parallel ral are fxed on the arrage frame to offer the moton rong the frame and to extend the dtane of the robot n dreton Y. In dreton Y, the dtane from the nner board to the outer board an be 9mm n one VV etor,.e., the robot need longer reah n th dreton, and the lnear drve unt help the robot endeffetor to reah the farther border of the VV. v) Rotaton drve unt: h unt offer a rotaton moton about the Z ax, o that the robot an mahne the flexble houe on the nner wall at any poton. he rotaton drve unt ont of lewng bearng, drve gear, reduton unt CYCLO, and ervo motor. he lewng bearng ntegrate bearng and gear together, leadng to a ompat truture wth lght weght. he rotaton of the unt an reah ±8. Fg. 4 Compenaton mehanm b). Hexa-WH A Stewart baed mehanm, drven by x ervo ontrol water hydraul ylnder, offer x-degree freedom to the end-effetor, where the mahnng head and weldng gun are mounted. Beaue of the peal hape of the VV, a full x-degree freedom moton for tool needed to enable the robot to arry out weldng and mahnng. he Hexa-WH an offer the requred auray and the hgh fore apaty due to t novel onfguraton and the hydraul drve. 3.2 Knemat model he knemat model very mportant for the robot moton ontrol. A the robot ha redundant degree freedom, t dffult to fnd the knemat oluton dretly. he knemat model an frt be et up for the arrage and the Hexa-WH eparately, and then be ombned together by ung an optmzaton algorthm n olvng the redundant problem [4], [5]. a). Forward knemat A derbed above, the arrage offer the robot the four-degree freedom: two lnear moton and two rotaton; whle the Hexa-WH offer the end-effetor the full x-degree freedom. he tranformaton matrx of the robot an be defned a:

6 Parallel Manpulator, oward New Applaton 368 = , (2) where = Z Y X, = Z Y X, = Z Y X φ φ φ φ, = Z Y X ϕ ϕ ϕ ϕ, + + = Z Y X. One the parameter of jont are gven, the forward knemat of the robot an be defned a P P P = =. (2) o olve the forward knemat model of the Hexa-WH, the numer teratve method an be employed and t an be olved from t nvere kenamat model gven later n the hapter. b). Invere knemat model of robot A the robot ha four-degree freedom of redundany, we gve an nvere knemat model frt to the arrage, then to the Hexa-WH. Invere knemat model of arrage: he nvere knemat model of the arrage defned to fnd the value of the four atuator wth repet to the frame o for a gven poton and an orentaton of P 4 on the Hexa-frame. he prnple of the arrage mehanm hown n Fg. 5. In the applaton, rotaton angle φ fxed only at a few value,, ±9, and 8, and we an alulate the value of other atuator by fxng φ,.e., for a gven poton P 4 (x, y, z), the entre of the Hexa-Frame, we have

7 Hybrd Parallel Robot for the Aemblng of IER 369 X + ( r + r oϕ) oφ = x, (3) Y + r + r oϕ) nφ = y, (4) ( hen r nϕ = Z. (5) ϕ = arn( Z / r ), (6) X = x r + r oϕ) oφ, (7) ( Y = y r + r oϕ) nφ. (8) ( Fg. 5 a) Mehanm of arrage, b) Hexa-WH Invere knemat model of Hexa-WH: he nvere knemat model for the Hexa-WH defned to fnd the value for eah ylnder at a gven poton and an orentaton of the end-effetor wth repet to the Hexa-frame. Here O 4 onded wth P 4 on the arrage de. Fg.5 b) demontrate the oordnate of the Hexa-WH. he nvere knemat model for the Hexa-WH where L = O4 O5 + R r r ( =, 2,,6), (9) ' + R = +,

8 37 Parallel Manpulator, oward New Applaton r denote the vetor of the jont of the th ylnder on the Hexa-frame wth repet to frame ' o 4 and r the vetor of the jont of the th ylnder on the end-effetor wth repet to frame o 5. he length of eah ylnder an be found, when (x, y, z,,, ) defned wth repet to frame o 4. l ' ' = L = ( O 4 O 5 + R r r ) ( O 4 O 5 + R r r ). () here are two way to ombne the two nvere knemat model to get the oluton of the whole robot. One mple way to alulate the oordnate (x, y, z,,, ) of the endeffetor wth repet to {O 4 } and the value for eah atuator from equaton (3-) for the gven oordnate of the end-effetor wth repet to frame {o}, whle fxng {O 4 } at a ertan poton wth repet to frame {o} aordng to experene. he another way to ue an optmzaton algorthm to fnd redundant oluton, whh ubjeted to mnmze the defleton of the robot durng moton,.e., mnf ( q, l ), where f the defleton model of the l robot, q the poton vetor of the end-effetor, and l the value vetor of ten atuator. For a gven q we an fnd l by olvng the optmzaton problem mnf ( q, l ). l 4. Control ytem 4. Hydraul ontrol ytem Fg.6 how the water hydraul ytem. Preure ervo ontrol appled n lokng ylnder. Poton ervo ontroller ued n ylnder -7. here are three loop n the ervo poton ontrol: the poton loop together wth the peed loop that provde an aurate and fat trajetory trakng; and the load preure feedbak loop that appled to dampng the elf-exted ollaton, whh normally our n the natural frequeny. he peed loop an elmnate the peed error, whle the preure feedbak damp the vbraton of hydraul atuator (Fg. 7). Fg.6 Water hydraul rle

9 Hybrd Parallel Robot for the Aemblng of IER 37 he hydraul ylnder normally lak dampng that make the ylnder ontrol dffult by ung onventonal PID-ontroller. he dampng an effetvely be nreaed by mean of load preure feedbak. he major drawbak n ung preure feedbak t negatve effet on the tat tffne of the atuator. o overome th problem, the hgh pa flter are ued n the load preure feedbak loop. he hgh pa flter remove the negatve effet of preure feedbak at low frequeny. Fg.7 Hydraul ervo poton ontrol 4.2 Motor ontrol wo drve motor ontrbute effort for the trakng moton of the robot. A the trakng ral are not alway traght, the peed of the two motor are not the ame when the robot movng. he torque ontrol together wth a poton feedbak algorthm mplemented. Fg. 8 how the ontrol prnple. Fg. 8 rakng motor ontrol

10 372 Parallel Manpulator, oward New Applaton In th method, one motor work a mater, and another one work a lave. For the mater motor, the poton ontrol plu the peed ontrol appled to guarantee the requred peed and poton auray of the arrage on the trakng ral. For the lave motor, the torque ontrol appled, whh ontrbute the drvng torque for the robot. 4.3 Control of hardware and oftware Beaue there are no ommeral ontroller and oftware avalable for the peal funton of the parallel robot, an open arhteture of hardware and programmable oftware are beng developed. Fg. 9 how the truture of hardware ontrol ytem. he ontroller an ndutral-pc-baed moton ontroller. It provde a relable and eay-at-ue envronment for ontrollng the robot beaue Earthnet bu ued n the onneton of PC and I/O nterfae. Fg.9 Struture of robot ontroller he oftware defned n Fg., nludng graphal nterfae, trajetory plannng, forward and nvere knemat model, nterpolator, ontroller, and I/O nterfae funton. And

11 Hybrd Parallel Robot for the Aemblng of IER 373 thoe funton have to be ntegrated wth the program offered by PC and run ompletely n real tme. Graphal nterfae a hgh level program, t nlude parameter ettng, ondton montorng, and graphal vualzaton funton. Uer an ealy exhange nformaton wth th program. rajetory plannng alo a hgh level program. A the robot ha redundant atuator, the trajetory plannng muh more dffult than uual, o an optmzaton algorthm, whh ubjeted to mnmze the defleton of the robot durng moton, ha been employed. Forward and nvere knemat model and nterpolator are real tme funton, whh generate data for moton ontroller. Controller a real tme funton nludng water hydraul ontroller and motor ontroller. A the robot ha two trakng motor and the peed of the motor are not alway the ame at ome poton, a mater lave ontrol algorthm ha been ued. I/O nterfae funton are real tme funton, whh enable tranferrng date from enor to ontroller and from ontroller to drver. Fg. Struture of oftware 5. Mahnng and weldng tetng mok-up he parallel robot ha been bult n Lappeenranta Unverty of ehnology and the mahnng and weldng tet mok-up degned hown n Fg.. he mok-up one

12 374 Parallel Manpulator, oward New Applaton quarter of a etor bult up for tetng the mahnng and weldng funton of the robot. Before the mok-up, ome weldng and mahnng tet have been arred out wth the frt prototype of the parallel robot named Penta-WH. he laer weldng wth eam traker ha been teted n tanle teel and the mahne uttng wth d aw ha been teted n the tanle teel mahnng proe. he robot perform well n the tet. 5. Mahnng he uttng tet wa arred out wth tanle teel. he hgh peed teel uttng tool wa ued n the tet. It 2mm n dameter and 4mm n thkne. he problem n the experment wa that the hgh peed uttng tool wore out qukly durng the uttng. he arbde tool, whh are muh more utable for uttng tanle teel, are uggeted to be ued n the uttng operaton n the IER. Fg. VVPSM mok-up and fnal veron of parallel robot 5.2 Laer weldng tet In the IER aembly, the hgh qualty weld are requred to avod the leak of trtum. hey an be aheved by a hghly automat and remotely ontrolled weldng proedure. o guarantee the weldng qualty, a eam traker, whh gude the robot moton along the enter of a weldng eam, employed. Wth a eam traker, the parallel robot ha the apablty to orret the moton trajetory on-lne to keep the weldng head at the rght poton and orentaton n relaton to the weldng eam. he poton error of the weldng head related to the weldng eam aued by the dtorton of materal and the mpree trak ral are derbed n Fg.2.

13 Hybrd Parallel Robot for the Aemblng of IER 375 Durng tetng, the laer weldng head mounted on the end-effetor of the parallel robot whle the eam trakng enor mounted n the front of the weldng head for gudng the robot weldng (Fg.2). he work pee aembled randomly n the y and z dreton durng tetng. It ha approxmately a one-degree angle about the Y and Z-axe. he poton of eam unknown for the robot before the eam fndng. he maxmum output power ued n the tetng 3 kw YAG. It ha a 2mm foal length reultng n a.6 mm dameter foal pot on the work pee. he beam parameter produt 25 mm-mrad. he work pee made of tanle teel AISI 36LN. It ha a 7mm-thkne, 6mm-length, and.2mm-root gap for weldng. Fg.2 Prnple of eam traker wo eam trakng algorthm were teted durng laer weldng tral. One the off-lne teahng algorthm that ha two tep: () the robot follow the planned trajetory of the eam and reord the data from the eam traker; and after that () the robot ompenate the moton trajetory from the data reorded and tart weldng followng the new moton trajetory. Fg.3 how the weldng reult. he eond algorthm the on-lne teahng algorthm. In the algorthm, the robot orret the trajetory on-lne ung data from the eam traker durng the weldng moton. Fg.4 how the weldng reult aheved durng the tet.from the tet reult, we an onlude that the on-lne teahng algorthm better than the off-lne teahng algorthm, beaue the on-lne teahng algorthm ompenate the dtorton of the work pee durng the weldng proe.

14 376 Parallel Manpulator, oward New Applaton Fg.3 Off-lne teahng weldng reult Fg.4 On-lne trakng weldng reult

15 Hybrd Parallel Robot for the Aemblng of IER Conluon A hybrd parallel robot wth four addtonal eral moton axe developed for arryng out the neeary mahnng and weldng tak n the aemblng and reparng of the IER Vauum Veel. he robot apable of holdng all neeary mahnng tool and weldng end-effetor n all poton aurately and tably. he knemat analy of the robot preented. he model are omplex beaue of the redundant truture of the robot. he model are eparately derved for the Hexa-WH and the arrage mehanm. An optmzaton algorthm fnd the oluton n the trajetory plannng, enurng the maxmum tffne durng the robot moton. he experment of the laer weldng tet wth the eam traker have been arred out. Both the on-lne and off-lne teahng algorthm have been developed and the reult how that the onlne teahng algorthm better. he mahnng uttng tet wth tanle teel have been teted. he entre degn and tetng proe of the robot a very omplex tak due to the hgh pealzaton of the manufaturng tehnology needed n the IER reator. he reult demontrate the applablty of the propoed oluton qute well. 7. Aknowledgement he laer weldng tet arred out n ollaboraton wth the laer laboratory of V n Lappeenranta, Fnland, the whole work, upported by the European ommunte under the ontrat of Aoaton between EURAOM/Fnnh EKES, wa arred out wthn the framework of the European Fuon Development Agreement, and the vew and opnon expreed heren do not neearly reflet thoe of the European Common. 8. Referene D. Stewart (965), A platform wth x degree of freedom, Pro. Int. Meh. Eng., London, Vol. 8, pp C. Ara, K. Homma, H. Adah, and Nakamura (99), Development of parallel lnk manpulator for underground exavaton tak, Pro. Int. Sympoum on Advaned Robot ehnology, pp C. Goeln and J. Hamel (994), he agle eye: A hgh-performane three degree of freedom amera orentng deve, Pro. IEEE Int. Conferene on Robot and Automaton, pp L. W. a (999), Robot analy: he mehan of eral and parallel manpulator, A Wley-Interene Publaton, John Wley & Son In. G. Lebret, K. Lu, and L. Lew (993), Dynam analy and ontrol of a Stewart platform manpulator, J. Robot Sytem, Vol. 5, No., pp G. Zheng, L. S. Hayne, J. D. Lee and R. Carroll(992), On the dynam model and knemat analy of a la of Stewart platform, Robot and Autonomou Sytem, Vol. 9, pp K. H. Häfele, H. Haffner, and P. Spener (992), Automat Fettlng Cell- An Example for Applyng Computer- Aded Robot, Indutral Robot. Vol.9 No. 5. pp.3-34

16 378 Parallel Manpulator, oward New Applaton H.Wu, H. Handroo, P. Pe, J. Klkk, L. Jone (25), Development and ontrol toward a parallel water hydraul weld/ut robot for mahnng proee n IER vauum veel, Fuon Engneerng and Degn. H. Wu, H. Handroo (26), Mehatron degn and development toward a heavy-duty waterhydraul weldng/uttng robot n Book: Mehatron for Safety, Seurty and Dependablty n a New Era. Elever.