Cơ sở xác định các thông số hình học và lực tác dụng lên hệ thống bốc gỗ nhỏ cho rơ mooc lâm nghiệp đặt sau máy kéo nông nghệp để vận xuất gỗ rừng trồng

KHOA HQC CONG N G H l c a S Q XAC DIIMH CAC THOIMG SO HllMH HOC V A LUC TAC DLJIMG LEIM HE THOIMG DOC G d IMHO CHO R O IVIOOC LAIVI IMGHIEP D A T S A U IVIAY K E O IMOIMG IMGHIEP D E VAlM XUAT G d RUIMG TROIMG Nguyin Van Quan' TOMTAT Bai viet trinh bay torn tit co so ly thuyet xac dinh cac thong sd hinh hoc va luc tac dung len he thdng boc gd nho bang toi cap vai su trg giup cua co cau nang gd thuy luc - mot phuong an boc gd nho kieu moi cho mooc lam nghiep dat sau may keo nong nghiep de van xuat gd rimg trdng Tir nguyen ly lam viec, de xac dinh dugc cac thong so hinh hoc va luc tac dung len he thdng boc gd, can phai giai quyet bai bai toan: Nang dau bo gd len cao cin thiet va keo bo gd tir true lan vao san mooc Tren co sd' phan tich cac luc tac dpng len he thdng keo gd, van dung cac phuang phap cua ca hpc giai tich thiet lap dugc cac phuang trinb dong hoc va he phuong trinh vi phan mo ta qua trinh keo go tir true lan vao san mooc Giai he phuang trinh theo phuang phap Runghe - Kutta voi su trg giiip cua may vi tinh, tir xay dung cac dd thi bieu diin su phu thuoc cua cac dai lugng nghien ciiu vao cac tham sd anh huang Khao sat dpng hpc va dpng b e hpc qua trinh nang dau gd tir mat dat len dp cao can thiet de keo gd vao san mooc, xac djnh dugc cac thong sd dpng hpc va lire tac dung len xi lanh thuy luc cua ca cau nang Tren co sa kit qua giai hai bai toan da dua trinh tu va phuong phap xac dinh cac thong sd chii yeu cua he thdng boc go Tir khoa: Dgng Itfc hgc mdy keo, mode mgt trtic, nghien curu thttc nghiem : - r ; w Ơ * ããã"":^ LDATVANDE CIc miy klo n6ng nghiep (MKNN) thudng Ilm viec theo thdi vu, khdi lugng cong viec nam phan bd khong diu, vay, d l nang cao hieu q u i vdn dau tu, phlf huy tdi da nang lire cua miy mdc thilt bi cd fhl sii dung MKNN de van xult gd bing d c h trang hi them cho miy d c thilt bi phfi hgp nhu tdi, ro mode, co d u hoc gd Tuy nhien mdi loai miy chi b m viec cd hieu qua nhung diiu kien nhlt dinh dugc xle lap tii fhilf ke, chi tao Do dd de cd the khai thic MKNN cd hieu qui d' nhung diiu kien sii dung mdi d n fhilf phii nghien cuu cu fhl d vl ly thuylt vl thuc nghiem de thilt k l hoac lira chgn cle thilt hi thich hgp kem theo cung nhu cle e h i su dung Bii vilt trinh bly tdm b t co sd' ly thuyet xle dinh d c thong sd hinh hge vl luc b e dung len he thdng hoc g6 nhd theo phuong phip boc dgc bing tdi d p vdi su trg giiip cua eo clu nang gd thuy b e mgt phuong In hoc gd nhd kieu mdi cho ro mode b m nghiep mgt true dat sau MKNN de van xuat gd rung ' TS Khoa Co dien vl C6ng trinh - Trudng Dai hgc Lam nghiep 104 Hmh May k l o n6ng nghiep dugc frang hi ro mooc va CO d u hoc g6 de van xuat g6 nhd rimg frdng Nguyen ly lam viec cua he thdng hdc g6 Ddi vdi viec bde gd nhd theo phuong phap bde dgc bing tdi d p thudng gap 6' chd: Do kich thudc cay gb nhd, d l bde du trgng b i mgt chuyin xe phai hoc rit nhiiu lln, vay nlu k i t d u cua he thdng hoc gd khong hgp ly, se din tdi tinh trang d c bd gd hoc sau se bi thfic diu vio ldp go da dugc hoc len trudc tren sin mode, vi thi khong fhl boc xip gd len cao dugc D l trinh hien tugng nly trorg sudt qua trinh tdi keo gd, diu bd gd d n dugc nang b n mgt cao thich hgp De giii quyit van de nly da dung co d u nang gd din dgng bing thuy luc dat phia cudi mode Co clu nly gdm bai ddn nang ndi voi khung NONG NGHIEP VA PHAT TRIEN NONG THON - SO 12 - THANG 12/2009 KHOA HOC CONG NGHE mode b i n g khop quay, diu mut cua hai don nang dugc ndi vdi bing true lan Hai don nang cung true b n dugc nang len, xudng nho hai xi lanh thuy luc b m viec ddng thoi dat d phia sau khung mode (hinh 1) Qua trinh hoc gb len san mode dugc filn hinh theo frinh tu sau: Ha true lan cua ca cau nang nlm sit mat dat; diiu khiln tdi keo gd, mot dau bd g6 glc len true lan lap tiic ngif truyin dgng din tdi; diiu khiln he thdng thuy luc nang true lan cfing mgt dau bd gd len cao thich hgp; diiu khiln tdi tilp tuc keo gd tir true lan vao vi tri mong mudn tren sin mode Viec hoc chuyin tilp theo, cle thao tie dugc lap lai theo frinh tu tren Tfr nguyen ly bde go neu fren dat bii toln nhu sau: Gil sir vdi mgt ro mode cd kich thuoc vl trgng bi da chgn, d n phii xic dinh d c th6ng sd hinh hge cua he thdng bde g6 de cd the keo dugc go len ldp tren ciing eua mode vdi chilu cao bde da dinh (Hi) Ngoli ra, d n xle dinh lire ldn nhlt b e dung len d c pbin tfr eua co' eau nang vl co d u keo go de b m eo sd tinh toan sue ben cho d c chi fief cQng nhu xle dmh b i ldn nhat m l LHM ed the keo vl nang dugc Vi d c thong sd tren lien quan chat che vdi nhau, vay d l cd co so lira ebon vl xle dinh d c tb6ng sd nly mgt d c h hgp ly d n phai khao sit mgt cich tdng fhl d c mdi quan he giiia chiing vdi Hmh So dd khao sit qua tiinh k l o gd tii true lan vio dau sin mode Xem bd go nhu mot cay go co chilu dai L, trgng tam C, khdi lugng m, mo men quan tinh ddi vdi trgng fam J Chon he true toa XOY khIo sit chuyin dpng cua cay gd, he true nly ed gdc friing vdi true lan do' cay go a vi tri cao nhat, OX song song vdi mat dit, OY vuong gdc vdi mat dit Vi tri ciia cay gd he true toa XOY duge xle dinh bdi trpng b m C (xc ,yc ) • Ggi (cp) 11 gdc quay cua cay gd so vdi tnrc OX Luc b e dung len cay gd gom: Luc keo cua day d p tdi F ; frgng lue G; phin luc Ng vl luc ma sit F^^ true b n b e dung b i diem O; phan luc N^vl luc ma sit FJ mat dat tic dung tai diem A Tfr so (hinh 1) ta vilt dugc he phuong trinh: \gcp = Xg = x^ - L^coscp II niOl DUniG, PHUONG PHAP NGHIEN CUU yg = y,- -L^sincp Khao sat qua trinh k l o g6 tfr true eon lan vao san mode FQIYE -YB) (l) X^ = X^ -I- L|C0S99 YA =yc+LiSin99 Giai doan l:.Tu tdi bit diu klo din foln bo cay gd dugc nhac len khdi mat dat, giai doan nly cay gd hi k l o lit tren mat dit tai diem A Giai doan 2: Tu kit fhuc giai doan den dau cay g6 glc vio sin mode hoac ddng go da cd tren mode, giai doan nly cay go dugc keo trugt tren true lan ciia eo d u nang De keo dugc bd go len ldp tren cfing vdi chilu eao xip g6 Hi cho truoc fhi diu bd go a vi tri eao nhlt phii eao hon hoac phii ngang bing ddng go da xip tren mode nlu khong se thuc vio ddng gd tren mode (hinh 2) ^ S" = (Xf - LjCosK - Xg)^ -I- (y^ - L^sin^j - y^)^ Trong dd, S - khoang d c h giua diem B (diim bugc g6) vl diem E (diim treo puly tdi) Phuang trinh dgng luc hgc Giai doqn - keo lit tren mat ddt: Lap phuong trinh vi phan ehuyen dgng eua cay gd dudi b e dung ciia he luc tren, ta dugc he phuong trinh sau: (2) + H 0C6CP + N , + H ^ , sincp = ni/c + ng I;|(XE- J I Y E - YB) - (YE - Y B K - X B ) ] - H(ycsincp+Xc0oscp) + ^[x^-\ + f^Yc-YA = Jcp Trong he phuong frinh 2: fo, f,, - he sd cin giira true lan va mat dat voi cay gd NONG NGHIEP VA PHAT TRIEN NONG THON - SO 12 - THANG 12/2009 105 KHOA HOC CONG N G H l Tir he phuong trinh (1) lap dugc d c phuong trinh sau: y P = - (p Ll cosf (3); (4) X, = ( — ^ + L, sin cp)cp sin" cp -S.S (5) (p = -F(L| -)-L2)coscp-i-Xg + (L| -i-U)cos(f[h-i-(L| -i-L,).smcp-i-yEj -i-(L, -i-L2)4'sir'(p sin" cp tgcp Phuong frinh (5) dugc giai vdi diiu kien diu: diem B friing vdi diem 0, dd ta cd: + yi eua dp VQ tdi; f arctg ; Vfl - van tdc keo Yc _ Dieu kien d l kit thuc giai doan b diu A ciia cay gd dugc nhlc khdi mat dit, N,, = CIc luc N,i, Fo, N„ dugc xac dmh tfr he phuong frinh (2) Cac gil fri yc, Xc , f cung nhu y ^ X ^ , cp dugc xic dinh nhd phuong trinh vi phan (3), (4), (5); y ^, \^, cp xac dinh nhd' tich phan sd arctg V(L, + L , ) ^ FQIXE - X B ] Giai doqn - cdy gd dug'c nhde khdi mat ddt: giai doan nly N^= 0, he phuong trinh dgng luc hoc cua cay go ed dang: -h' - No sincp -HNQ^ ooscp = niic (6) FO(YE - Y B ) + NQ ooscp -h -f- N^^ sincp = n f c + n g ( X E - XB)(YE - YB) - (YE - YB)(XC-XB) - No(ycSincp+XcOOS(p) Day 11 he phuong trinh vi phan vdi an sd, d n lap them phuong trinh: All X ^ + A , y ^ + A i =Bi B,= (7) Jcp x^cp ^ x^cp-tgcp cos cp cos cp Kit hgp (6); (7); (8) dugc he phuong trinh vdi Trong : All = (xc - L2 cosf - xg ) ; A^ = ( yc L2sinf - ye ); A13 = AnL^sinf - A12L2 cosf ; - B] = an la X^ ; y^;Cp ; NQ; FQ Cd fhl giai dugc he cp^L2Cosf (xc-L2Cosf -XE)-I- (X^ -^ (pL2sinf)' phuong frinh tren theo phuong phip Runghe - kutia vdi su trg giiip cua miy vi tinh -i-cp^L2Cosf (yc-L2sinf - yE)-i- (Yc - (plvjcosf )' - III KET QUA VA THAO LUAN Vo^; Qua trinh k l o g6 tu true eon lan vio san mode A21X +A22 Vc +A23 qp = B (8) Trong dd: A21 = - tgf ; A22 = 1; A23 = - X, COS' cp F,No,Nd (N) 6000 T XB(m Xc(m) r*-, Hinh Quy dao chuyen dong ciia dau cay g6 qua trinh keo go tii' true lan vao san mooc 106 —^ oc OJ • 0 ^O ly-, 0 X ^ CM — Hinh - Su phu thuoc ciia cac luc vao tam cay gd NONG NGHIEP VA PHAT TRIEN NONG THON - SO 12 - THANG 12/2009 KHOA HOC C b N G NGHE c De Ilm CO sd lua chpn va xic d b h cic thong sd a Quy dqo chuyen ddng cua ddu cdy go (diem B) hmh hpc ciia he thdng bde gd, tinh toan sue ben cac chi tie true ldn vdo t&i ddu sdn mdc YB = f(xB) vdi d c tilt cua he thdng bde gd; tinh toan tieu hao cong suit, tham sd khac d i u ed dang tuong tu nhu hinh chi phi nhien lieu LHM tu bde gd da tien hanh: b Su phu thudc cua lite keo cdp t&i (F), phdn luc - Khao sit anh hudng cua d c tham sd: Chilu cao cua true ldn tin cdy gd (Ng), phdn luc cua mat ddt frue lan (h), vi fri treo puly tdi (xg, y^) den chieu len cdy gd (NJ vdo toq trgng tdm cdy go (XQ) cd cao bde go (Ygmax) vl khoang each da dau gd (Xgo); dang dd thi nhu hinh - KhIo sit Inh hudng cua cic tham sd h, x^, y^, Ttr quy dao hinh cho thay: Khi k l o gd tfr true m den luc keo d p tdi ldn nhlt (Fn^^x) vl ap b e Ion lan vio san mode diu cay gd dugc nang din len nhlt cua cay gd xudng true lan (Nomax) • din vifricao nhat (yB= yBm.ix) sau dd di xudng: Chilu cao diu cay gd giam din b e dau vdi tdc cham sau Xle dinh d c kich thudc dgng hge v l luc b e dd giim rat nhanh- dd chinh 11 giai doan cay g6 hi lao dung lln xi lanh thuy lue cua co d u nkng go xudng Tai thdi diim dau cay g6 d vi fri eao nhat n l u Luc b e dung len xi lanh thuy b e ciia co clu khong dugc ty vio ddng g6 da cd tren mode hoac nang dugc trinh bly d hinh Lap he true toa khung mode hay ndi d c h khic khong cd vat gi do' nd XOY frong dd gdc O frfing vdi khdp quay O3; frue va nlu tilp tuc dfing tdi k l o thi diu cay gd se bi chui OX song song vdi mat dat Luc b e dung len cay gd xudng rdi thiic vio ddng g6 hoac lao xudng dit, gdm: Trpng luc G; phin luc NQ va luc ma sat F^^do vay kh6ng fhl klo cay gd len mode dugc Ddi vdi r a frue b n tic dung tai diim O; phan luc Npvl luc mode chd g6, khiic gd dugc xep thd ngoli khung ma sat F^ mat dat b e dung fai diim A mode mpt khoang nIo dd, diem da dau cay gd chmh 11 duoi ddng gd da cd fren mode Goi holnh diim B (dau cay gd) yB= ysmax 11 Xgo , nlu khoing d c h tii true lan din du6i ddng gd ldn hem Xgo thi se xly hien tugng diu cay gd bi thiic vio ddng gd Ngugc lai, n l u khoang d c h tfr true lan din ddng gd nhd hon Xgo, diu cay gd se dugc ty vio ddng gd, dd cd fhl tilp tuc keo Hinh Sa dd x^c dinh d e kich thudc d6ng hgc cay gd len mode mdt d c h de ding Nhu vay Xgo v l luc tic dung b n xi lanh thuy luc chinh 11 khoang d c h da dau cay gd ldn nhlt cho ciia ca d u ning gh phip de frinh hien tugng diu cay gb hi thuc vio - Ttr so dd hinh 4, dua vio d c quan he hinh hoc ddng gd hoac lao xudng dat Tu quy dao chuyin xle dinh dugc c6ng thfrc bilu thi mdi quan he giffa dpng cua diu cay gd, cho phip xic dinh dugc thong sd: Khoang d c h tii true eon lan tdi ddng gd d c thong sd dong hoe cua ea cau nang: ldn nhat cho phip (XBQ); chilu cao xip gd ldn nhlt Gi+la) = 7'o+>3-21„l3Cos(p3 (9) (thong qua Yemax) ma he thdng ed fhl thuc hien Hinh trinh cua pit t6ng se 11: dugc S= Dd thi hinh m6 b su thay doi ciia d e lue b e dung len cay g6 frong q u i frinh k l o g6 vl cho bilf thdi diem vl giafrid e lire fren dat cue dai ^ L,l , fb-i-lsincp , r- • O l + U ^ a x - ai+l2)n,in (10) - Xit can bang luc eho ca d u xle dinh dugc luc b e dung len xi lanh thuy luc: - I, (coscp-i-foSincp;., - I b-i-lsin(p^ -i- b-)-lsin(p _ ^(IQCOSCP-sincp) Iglj sin((p-I-Y -I-a) (11) V'o + l3+21ol3COs((p + Y + a ) Trong cong thuc (9), (10), (11): NONG NGHIEP VA PHAT TRIEN NONG THON - SO 12 - THANG 12/2009 107 KHOA HQC CONG N G H l P - luc tic dung len xi lanh thuy luc, (N); S hinh trinh pit tong, (m); m - khdi lugng cay go (kg); L - chieu dii cay go, (m); t,- he sd d n gitra cay gd vl true lan; L, - khoang each tu dau cay go fy vio dit den frong tam (m); - chieu dai nang (0;jD), (m); ly - chieu dii gil cua co clu nang, (m); l, chieu dii dong hoc cua khau (O3F) (m); b - khoing each tfr khdp quay nang den mat dat, (m); y gdc hinh dang nang, (") ; cp - gdc quay ctia nang, (") ; a - gdc hgp bdi dudng ndi O1O3 vl phuong nam ngang, (") ; g - gia tdc truong, (m/s^ ; ^'- hinh frinh (gdc lie) eua nang, (") De phan tich mdi quan he giua lire tac dung len xi lanh thuy b e vl cac ylu td Inh hirdng ciing nhu mdi quan he giira cac th6ng sd dgng hgc cua eo cau nang, bai toan dugc giii tren may vi tinh Tir ket qua nhan dirge cho thay: Hanh trinh pit tong (S) chu ylu phu thudc vao (I3) vl (W) - dd fhi hinh 5; Inh hudng cua lo den S la khong dang ke; Luc tie dung len xi lanh thuy luc ldn nhlt (P„„) chu yeu phu thugc vio khdi lugng cay gd (m) va ehilu dai l, - dd fhi hinh 6, cdn anh hudng cua 1„ den Pmax b khong dang kl Pmax (KN) 120 T m=1000kc m=900 kg ni=cS000kg m=7000kg m=6000kg llllllllllllllllllllllllllllllllllllllllllllll I3 (m d d d d d 00 d ON —' d Hinh Su phu thuoc ciia hanh trinh pit tong vao chilu dai I3 Cae dd thi SO3, ^ ) vl P^^d^, m) 11 co sd' d l chgn xi lanh thuy b e din dgng cho co clu vl xle dinh cle thong sd dgng hgc ciia co d u nang gd Trinh tu vl phuang phip xae dmh d c thdng sd hmh hgc v l luc b e dung len he thdng bde gd Tfr d c kit qua nghien cuu 6' mue vl da dua trinh tu vl phuong phip xae dinh eac th6ng sd hinh hge ehu ylu vl luc b e dung len d e pliln tii cua he thdng bde gd phuc vu cho viec tinh foln thiet k l gdm 10 buoc: Xac dinh chilu cao xep gd (H,); Chgn chieu cao true b n (b) vl holnh puly tdi (XE) tuc 11 chgn truoc vi fri cao nhat cua true eon lan; Xac dmh ehilu cao diu bd gd ldn nbat tren quy dao chuyen dgng cua nd (yB,„,J d n thiet de co fhl keo dugc bd gd len cao H,; Xle dmh chilu cao puly tdi (H); Xle dinh khoing each diu gd ldn nhat cho phep (XBO); 108 I I I I I 11 I I I I I I I I I I I I I I I I I I l3(m) —' 'O r^i d -: ^ 30 01 d NO d d Hinh Su phu thuoc ciia luc tac dung len xi lanh thuy luc Ion nhat vao chieu dai I3 Xle dinh lue keo ldn nhat eua d p tdi (F^^J, Ip lire len true eon b n ldn nhat (No^ax); Xle dinh gdc quay d n thilt ciia nang (W); Chgn ehilu dii gil eo d u nang (lo) vl chilu dii dgng hgc cua nang G3); Xle dmh hinh trinh tdi thieu cua xi lanh thuy Ifrc (S„,„); 10 Xle dinh lue b e dung len xi lanh thuy b e ldn nhat(P„,J IV KET LUAN Tren eo sd' phan tich luc fac dgng len he thdng keo gd, bii bio da xay dung dugc he phuong trinh vi phan mo b qui trinh keo gd tfr true eon lan vao sin mode: Giai doan 1- tfr tdi bit diu k l o din toan bg cay gd dugc nhac len khdi mat dit (he phuang trinh 2); giai doan - fir kit thuc giai doan den dau cay gd glc vio sin mode (he phuong trinb 6) Da xay dung duge bilu thfrc toan hge xac dbh hinh trinh pit tong (10) vl lue tac dung len xi lanh thuy b e cua ca cau nang gd (11) NONG NGHIEP VA PHAT TRIEN NONG THON - SO 12 - THANG 12/2009 KHOA HOC CONG NGHE Khao sat cic phuong trinh dong luc hoc, xle dinh dugc quy dao chuyen dgng cua cilu cay gd, lire keo elp tdi, Inh hudng cua cac thong sd hinh hge den d c luc tac dimg len he thdng boc gd, anh hudng , ,, , • , , 4-' cua cae tham so xac dinh vi tn tnic lan den cac , -•,.,, , ', ; ,' - , , , , - , thong so hmh hgc cua he thong boc go, hanh trmh va b e b e dung len xi lanh thuy luc Tfr kit qua nghien cfm bai bao da d l xult phuong phip vl trinh tu xle dmh eac thong sd chu yeu cua he thdng bde gd, b m co sd' cho viec tinb toan thiet ke he thdng boc gd cho ro mooc dat sau miy keo nong nghiep de van xuat gd rung trdng jA| UEU THAM KHAO n^ r^- TT, u nnncN A,.- •• -• ^-' ^ (1) E)ang The Huy (1995) Mot so van cle ve co •-^ - , - x, , „ T ' , •- T, ,NThocgiai tich va CO hoc may Nxb Nong nghiep Ha Noi c, o i (2) Forsyfhe G E, Mabolm M A, Moler C B (1990) Computer Methods for Mathematical Computation, Prentice Hall NC Englewood Cliffs Nj 07632 BASE TO DETERMINE GEOMETRICAL P/\RAMETERS AND FORCES EFFECTING ON SM/^L LOG LO/\DING SYSTEM FOR FORESTTRAILER CONNECTED WITH AN AGRICULTURAL TRACTOR TO EXTRACT LOGS FROM PLANTATION Nguyen Van Quan Summary The paper gives a brief theoretical base to determine geometrical parameters and forces effecting on a small log-loading system by winch which is supported by a lift hydraulic mechanism - a new small logloading method for forest trailer connected with an agricultural tractor to extract logs from plantation From operational principle, in order to determine the geometrical parameters and forces effecting on the loading system, it is needed to solve two problem: lift one end of the load to the necessary heigh and pull the load from the roller shaft to the flat of the trailer Based on annalysis of the forcess effecting on the loading system, by applying methods of analytic mechanics, kinematic and dynamic equations expressing log pulling from the roller shaft to the flat of the trailer have been eshtablished Solve these equations by Runghe-kutta method on computer, from that the graphs expressing the relations between studied and affected parameters have been eshtablished The kinematic parameters and forces effecting the hydraulic cylinder of the lift mechanism have been determined by studying kinematic and dynamic process of lifting one end of the load from the ground to the determined heigh Based on the studied result, the proceduce and method to determine the main parameters of the log-loading system have been presented Keywords: Dynamics tractors, two wheel trailer, experimental studies Ngudi phan bien: GS TSKH Pham Van Lang NONG NGHIEP VA PHAT TRIEN NONG THON - SO 12 - THANG 12/2009 109 ... trinh tu xle dmh eac thong sd chu yeu cua he thdng bde gd, b m co sd'' cho viec tinb toan thiet ke he thdng boc gd cho ro mooc dat sau miy keo nong nghiep de van xuat gd rung trdng jA| UEU THAM KHAO... cay gd xudng true lan (Nomax) • din vifricao nhat (yB= yBm.ix) sau dd di xudng: Chilu cao diu cay gd giam din b e dau vdi tdc cham sau Xle dinh d c kich thudc dgng hge v l luc b e dd giim rat nhanh-... quan he giffa dpng cua diu cay gd, cho phip xic dinh dugc thong sd: Khoang d c h tii true eon lan tdi ddng gd d c thong sd dong hoe cua ea cau nang: ldn nhat cho phip (XBQ); chilu cao xip gd ldn