KHOA HOC CONG N G H l IMGHIEIM CUU XAC DflMH LUC cAlM CAY IMGAIVI KHI CAIMH TAC TREIM DAT LAIVI IMGHIEP Btii Hii Tri^uS Doin Vin Thu^ T6MTAT Luc can cay la thong sd ky thuat quan trpng quyet dinh mirc dp chi phi nang lugng, va la thong sd vao de nghien ciru tinh toan thiet kd, lap lien hgp cay Viec img dung ky thuat tenzo va thiet lap he thong da kenh k6t ndi voi may tinh de xac dinh luc can cay la cong nghe moi, hien dai, cho phep ddng thai nhieu thong sd ca hpc co lien quan voi dp chinh xac cao Ket qua nghien cuu thuc nghiem da xac dinh dugc he so luc can rieng (iQ cua cay ngam lien hgp voi may keo Komatsu D65A lam dat rimg o'Vinh Phuc la ca sa khoa hpc de nghien ciiu xac dinh cac thong sd tdi uu, nang cao hieu qua lam viec cua lien hgp cay ngam Tir khoi: Luc cdn cdy ngdm, diin tra bien dqng LDATVANDE Ciy ngim li mdt loai ciy khong lit, lim viec cic thin ciy tic ddng lim p h i vo' lien ket cua dat tao cic ranh dat toi xdp (rach ciy) theo dudng ddng mirc cd dd sau tfr 40 -^ 60 cm hoac hon nfra Trong sin xuat lam nghiep, sit dung ciy ngam de lim dat frdng rtmg li cong nghe cd rat nhieu uu diem: Dd siu lim dat ldn, fang k h i nang tham vi gift nudc, it lim xio trdn lop dat mat, ban che rira troi, xdi mdn dif, (Doin Van Thu, 1996) dap iing dugc cic tieu chi ciia phuang fhirc lim dat tdi thieu De thiet lip dugc mgt lien hgp miy (LHM) ciy ngam boat ddng cd hieu qui, ning cao nang suit, chat lugng lim dat, giam chi phi nang lugng cin phai nghien ciru xic dinh, phin tich vi dinh gii ve lire cin ciy LHM lim viec fren cic dieu kien dia hinh, dat dai khic Tuy nhien, lim viec fren dat lam nghiep, lire cin ciy ngim phti thudc vig rat nhieu yeu td: Dac diem dia hinh, tinh chat dat dai, ket cau cay vi che dg sir dung LHM nen khd cd the xic dinh dugc bang tinh toan ly thuyet Bii bio niy gidi thieu phuong phap va mdt sd ket qui nghien ctru xic dinh lire cin ciy ngim lien hgp vdi miy keg Kgmatsu D65A-8 lim viec fren dat lim nghiep II PHUDNG PHAP XAC D|NH LUC CAN CAY BANG THJ NGHIEM Ddi vdi ciy mdc Luc cin ciy chinh li luc keg d mdc, cd the xic dinh bing lire ke hgac cim bien luc, thief bi PGS.TS Truang Dai hoc Nong nghiep Ha Npi, Vien Khoa hpc Lam nghiep Viet Nam 90 dugc lip ndi tiep qua mdc nen chi xic dinh dugc thinh phan lire cin theg phuang ngang (P„) Ddi vdi ciy freo Sir dung khung phu (Hin Trung Diing, 2006) de bang lire ke hoac bing cim bien (tenzg) dien frd bien dang Trong trudng hgp niy, may ciy dugc mic giin tiep vdi ca cau freo qua mdt khung da, fren cic phin thing dimg cua lire can ciy da hi friet tieu, chi cdn thinh phan luc theg phuong ngang dugc tiep nhan bdi lire ke Sir dung cam bie'n dien frd bien dang din len cac vi fri thich hgp dg bien dang cic khau, chi tiet ciia din ciy cd chiu tic ddng ciia lire cin ciy (cic khdp ndi freg, fren cic treo hoac fren than ciy) Luc cin keo dugc xic dinh nhd mdt thuat fgan xir ly cac thinh phin luc tuong tfng fren cic freo Tuy nhien chinh xic chi dugc dam bag ddi vdi cic ca cau freo don giin dd thao lip de chuan tin hieu Ddi vdi ciy ngim Udn hgp vdi miy kdo Komatsu Ciy ngam dugc hen hgp vdi miy keg bang ca cau freg hinh bmh hinh, viec dieu khien nang ciy tbuc hien bdi xi lanh thuy luc (hmh 1) Khi LHM cay lam viec dn dinh, xi lanh lire d vi tri khda cd dinh (kb6ng cd thd boi nhu ciy lat cd binh tua ddng) nen cfing chiu tic dgng ciia luc keo nen nhu cic freo Ke't cau miy ciy ddi xung hai ben qua mat phing OXZ chira frnic dgc LHM vi vugng ggc vgi nen dat, cd the quy din ciy vd eg ciu phang khdp ban le nim fren mat phing OXZ Sg dd cic luc tic dgng len din ciy dugc m6 fa fren hinh 2, frong dd: Pt^, P^, la lire kea nen NONG NGHIEP VA PHAT TRIEN NONG THON - SO - THANG 6/2009 KHOA HOC CONG NGHE tic dgng len cic freg fren vi dudi; P^ li luc tac dgng len xi lanh thuy lire ciy lim viec Hmh K^t ciu ciy ngim Ii6n hgp vdi miy kdg xich Komatsu D65A- Luc cin cua dat tic ddng vio cic thin ciy dugc xac dinh theg cong thuc: P, = V^^J^^^/^ (1-1); P„ li tdng hgp cic luc cua dat vig thin cay theg phuang ngang; P„ li tdng hgp cic luc len than ciy theg phuong thing dung Pcx=(Ptr+Pd)C0SY2+PxlC0SYi (1-2) P„ = (Ptr + Pel) siny2 + P^ siny (1-3) Trong dd: yi vi y2 li gdc nghieng ciia xi lanh thuy luc vi cic treo so vdi phuang thing dimg, gii fri ciia nd phu thugc vio vi tri cua dan ciy nang (vdi mdi gia fri dg sau ciy h^ se cd cic gia fri Yiviyz tuong ling) Plr_ , Lire can ciy theo hai phucmg cd the dugc xac dinh bing each tdng hgp luc fren cac freo ciia ca cau freo hinh binh hinh vi ap suit dau tren xy lanh thuy lire Luc fren cac treo dugc xac dinh bang phucmg phip cim bien dien frd bien dang, luc tic ddng len xilanh thiiy luc bang sensor da ap suit, tir dd xac dinh dugc lire can cay Tuy nhien, cic freo ciy ngam dugc che tao cd dd ben cao, ciy lim viec bien dang cua chiing rat nhd, cha nen tin hieu nhan dugc tir cic cam bien khd cd dll dd nhay de xac dinh chinh xac su thay ddi ciia lire can ciy frgng qua trinh thi nghiem Mat khac, ket cau cac freg nguyen bin ciia ciy ngam khgng the hieu chuan fin hieu Do viy, mudn lire keo, nen ciia cic freo bang cim bien dien frd bien dang, can phai thief ke mgt bg freg mdi de ciy lim viec bien dang ciia chiing dii ldn vi nim frong gidi ban dan hdi, dam bio cac cim bien cd the nhan biet dugc tin hieu dg chuan xic III XAY DUNG HE THOniG DO LUC CAN CAY NGAM Thidt k^ Iai cic thanhfreocua ca ciu freo hinh binh hinh Cac freo dugc gitr nguyen chieu dii de kh6ng lam thay ddi kich thudc cua ca ciu freg, fren dd doan dan cam bie'n (khau do) cd tiet dien ngang dugc tinh fgan, lira chgn de cay lam viec chung cd dd bien dang nim frgng gidi han dan hdi vi dam big dd nhay tin hieu Hinh dang cic freo cua din cay dugc thief ke nhu hinh Khau Nc 'o O Hmh SCT dd thi^t k^ freo Dd dan dii ty ddi £ cua khau dg fren cic treo dugc tinh bing cgng fhtrc: Z A o Hinh SCT dd ckn bing ItK vi m6 menfr6ndin ciy ^^ ^ to^^ E- — = (2-1) / E.F Trgng dd: vi Al - li chieu dii va dd dan dii ciia khiu do; P - Luc keo, nen tic dgng fren cic freo (kN); E - Mo duyn din hdi cua vit Heu khiu do, vdi thep CT-3cdE = 2L10^N/mm2; NONG NGHIEP V A PHAT TRIEN NONG THON - SO - THANG 6/2009 91 KHOA HOC CONG NGHE F - Dien tich tiet dien ngang khiu (m^ Bien dang dii mi tenzo cam nhin dugc li: s = 10"' ^10"^ Bang tinh toin ly thuyet ta xic dinh dugc khoang lire tic dgng len cic treo (P,), tir dd chgn dugc tiet dien cin thief cua cic khiu da freg fren va dudi (Ftr, F^) li: Cam bien dien trd loai day det cd uu diem li: Dien tich tiep xtic din len chi tiet ldn hon nen cd dd vting chac vi kha nang nhin tin hieu bien dang cua chi tiet tdt hon; he sd tda nhiet cao hon nen cd the cho ddng dien di qua ldn hon, nhd vay mi dp nhay cao hon so vai day trdn b Phuang phdp ddn cdm bien len khdu treo: F^ = 3200 (mm^); kich thudc tiet dien: 80 x 40 mm Cim bien dien frd bien dang dugc din frtrc tiep Fd = 6500 (mm^); kich thudctie'tdien: 100 x 65 mm len khiu dg bing keg dac biet, tiiy thugc vig tinh Lua chgn cim bi^n, lip dat vi kdt ndi thidt bl dg chat lire tic dung de lira chgn vf fri vi phuong phap din cim bien cho phu hgp, dam bag dd nhay ciia tin a Cdm bien dien tr& bien dgng: hieu dg Tren hinh frinh biy cic phucmg phap dan Cam bien dien frd bien dang (chuyen ddi tenzo) cam bien day dien frd de lire keo nen vi m6 men cd kich fhudc rat nhd nen cd the dan true tiep len chi udn cua tiet can d vi fri hep, tin hieu dn dinh vi co nhay Theo sa dd hinh 6-a (do luc keo) cd mpt caa Cim bien dien trd bien dang chii yeu de lire nhanh lim viec Rj (nhinh do) thi cim bien bit trir tic ddng udn, xain, keg, nen len cic khau dg nhiet R4 dugc din vuong gdc vdi phuang tic dung lire Cam bien dien frd cd laai day tie't dien trdn vi keo P Ngoii viec bu trtr inh hudng cua nhiet dg, loai day fief dien chir nhat (day det), hinh 4, din cim bien R4 theg vi tri nhu tren se bii trir dugc ca su mit mit dd nhay d nhinh lim viec dg cim bien hi bien dang theg chieu ngang -C3 -a In U Neu din cim bien theg so dd hinh 6-b se tang nhay len hai lan cd cim bien bii nhiet Nggai frong sa dd cdn bit frir dugc ci inh hudng bi udn c Ket ndi mach dien tr& bien dgng: Hmh Cim bi^n didnfrdrloai diy ti^t didn frdn Mach ciia fhi nghiem dugc ket ndi theo phugng phip ciu khdng cin bing Tren hinh trinh biy sa dd nguyen ly lire keo nen Cim bie'n day dien trd dugc din tren keo vi li mdt nhinh ciia ciu Khi cd lire P tic dung len keg se lim thay ddi dien frd cua cim bien din fren nd, dg dd ciu dg bi mat can bang, fren nhinh cheo xuat hien the hieu (U) Tin hieu dien ip niy dugc khue'ch dai nhd bo khuech dai 4, sau dd dua vio bd chuyen ddi A/D de chuyen fin hieu sd rdi dua den miy tinb cd cii dat phin mem thu thap vi xu ly sd lieu Dasylab 7.0 Sd lieu thu dugc sau xir ly se cho gii tri ciia lire can ciy ngim lim viec d Dinh chudn khdu do: Hmh Cim bidn difn frg loai diy det 92 Cac khau sau din cim bien phii dugc dinh chuan fren thief bi chuyen dimg de dam big dg chinh xic qui trinh thi nghiem NONG NGHIEP VA PHAT TRIEN NONG THON - SO - THANG 6/2009 KHOA HOC CONG NGHl R4 'A - Rl 'I e Cdm bie'n dp sudt thuy luc: R2 Rl > - > P R4 R3 Ap suit xi lanh thuy luc (PJ dugc xac dinh bang cam bien dg ip suit SIO, day li loai cam bien da ap suit hang WIKA Alexander Wiegand GmbH & Co.KG CHLB Ditc sin xuat, lim viec theo nguyen tac ap - dien, dii ip suit tir + 1000 bar / Bdtri lap ddt cdm bien: Cim bien dien trd bien dang luc keo nen dugc din len cic khau dg fren cic freo Cim bien i p suit SIO dugc lap fren dudng dng din diu de dg i p suit diu chenh lech frgng xylanh thuy luc nang ciy Hinh So dd din cim bi^n difnfrdrd^ Itic kdo ndn a) Mdt nhdnh ldm viec vd cd bii tru nhiet; b) Hai nhdnh ldm viec vd cd bit trie nhiet Ngoii q u i frmh khia nghiem he thdng cdn ke't ndi cic cim bie'n de mgt sd thong sd khac cd lien quan nhu: van tdc tien cua LHM (vj), sd vdng quay ddng ca, binh (n^^, n^s), chi phi nhien lieu gid (Gt) DASYLAB / A/D I \ CPU N Hinh SCT dd m i c c i m bi^n vio ciu d^ Itrc kdo 1- Thanh keo; 2- Cdm bien ddy dien tr&; 3- Cdu do; 4- Bd khuyech dgi; 5- Bd chuyen ddi A/D; 6- Mdy tinh cua thie't bi chuyen ddi Analog - Digital (ggi li Card Kdt ndi hf thdng v i xu ly tin hidu A/D) den may tinh cd cii dat phan mem thu nhan vi Qui frinh lim viec cua LHM ciy ngim didn xu ly sd lieu Dasylab rat phirc tap, bi tic dgng bdi nhieu yeu td ngiu nhien, cic dai lugng frong eg he cung cd tic dgng qua lai Iin frgng qua frinh Do vay khio nghiem ong gom tin (do lire can ciy) can xic dinh nhieu thong sd vi cac th6ng sd dd phii dugc dg ddng thdi De thuc MAY TINH hien dugc vin de niy phii xay dtmg mdt he thdng Phan mem gdm nhieu phan tu (he thdng da kenh) ke't ndi cic DASYLAB diu vdi cic cim bien de xic dinh cic th6ng sd cin thiet nhu: luc keo, nen cic freo, i p suit dau Bp chuyen doi tin hieu ciia xi lanh thuy lire, tdc dd quay dgng eg, banh sag, van tdc LHM, chi phi nhien lieu He thdng dg da kenh niy dugc kef ndi vdi miy tinh cd cai dat phan Hmh SCT dd k^t ndi cic phin tii hf thdng dg mem Dasylab, vtra cd tinh nang thu thap, tinh toin xir ly sd lieu vfra hd trg dieu khien thi nghiem frong Wgrksheet chucmg frinh fhi nghiem de thu thip qui frinh da vi xir ly tin hieu dugc lap fren eg sd cic mo dun Sa dd he thdng dugc m6 phdng fren hinh 8, cac tin hieu dg dugc truyen qua cic cdng tuong img CO sin ciia phin mem Dasylab va ke't ndi lai thinh chudi cic mo dun theo yeu cau cua fhi nghiem (Hinh NONG NGHIEP VA PHAT TRIEN NONG THON - SO - THANG 6/2009 93 KHOA HOC CONG NGHE 9) Ket qua fhi nghiem dugc hien thi frtrc tiep d dang dd thi hoac bang sd tren hinh miy tinh (hinh 10), viy cd the quan sif dugc ket qui frong qui trinh Hinh Worksheet chuong trinh thi nghifm IV TO CHUC THl NGHIEM DO VA KET QUA Cic phuang in thi nghif m - Kef qua fhi nghiem cho thay: i) Lire thinh phan fren cic freo tren P,r lu6n cd gii tri im cdn lire fren freo duoi P^ luon cd gia tri duong, cd nghia li frgng sudt qui frinh lim viec fren mdi dudng ciy freo fren lu6n chiu nen cdn treo dudi luon chiu keo, ii) Do tinh khong ddng nhat ciia dat dai tren moi dudng ciy nen tin hieu ciia cic thong sd thay ddi vai bien dd ldn Tdng hgp, tinh toin Itrc cin ciy ngim Cac thuat toan xac dinh luc can cay dugc tich hgp tren cac mo dun ciia chugng trinh Dasylab, chi viec lay vi ket ndi thinh chudi cic m6 dun ggi la Worksheet de tinh toin va hien thi kef qui theo cac yeu ciu khac ciia muc dich nghien cuu Tren ca sd he fhdng da dugc xiy dung d tren, tien hinh lap dat he thdng thief bi, chay thu de kiem fra tin hieu cua tirng diu tren may tinh Cic phuang in thi nghiem dugc fhay ddi thea thir tir cic yeu fd thuc nghiem sau: Sd than cay n = 1, 2, Loai mui cay voi bd rgng b = 0,12,0,23, 0,30 (m) Van tdc ciy (cay vdi cic sd fruyen 1, 2, 3) Dg ciy sau h, = 0,35, 0,45, 0,50, 0,55, 0,60 (m) Thi nghiem dugc thuc hien tai Trung tam Khga hgc sin xuat Lam nghiep Dong Bic bg, Nggc Thanh, Phiic Yen, Vinh Phuc Dieu kien hien trudng: Do ddc ddi tir + 8%, dat cd am: 17%, chat: 35 kg/cm^, thuc bi li Sim, Mua vi gdc Bach dan sau khai thic cd mat khoing 700 + 800 cay/ha Mgt sd kdt qui thi nghifm vi nhin xft Ket qui thi nghiem thu thap dugc luu d dang cac file dtf lieu ciia phan mem Dasylab, tin hieu dugc hien fhi theo dang dd thi (hinh 10) Aj TiVtH,'lli".i^'-'W.lUAI>"j^.l'/u'^T„.\l"tl»'-'Ar ",'V'1-i_»Ui;u I - fl^ _r' o -'-i \^ I—? iJff" Hmh 11 Worksheet tdng hgp, tinh toin Itrc cin ciy ngim Cac phan luc cin ciy ngim Pcx, Pcz theo cac cong thirc (1-2) vi (1-3) dugc tdng hgp tif cac tin hieu luc P^, Pt,., p^i, thuat toan cii dat mo dun fx - Pcx, Pcz (hinh 11) Gii tri Pcx vi Pcz dugc bieu dien d dang dd fhi hoac bang sd cfing vdi van tdc V,, n^s va chi phi nhien lieu gid Gt de thuan tien cho viec phin tich tiep theo (hinh 12) \iit^MlW^*-tL93utifijtM^'(>'!'f AJ.'K v''W' ^ ^•''''^'*'"-''•-.^vA-^v-''>••••'^''•V••'•"-^•'~^^^^^^^^ VVU>\>'^^^''^^ m 20 30 40 SD GO 70 M 100 110 120 130 140 15 Hmh 10 K^t qui dg cic thdng sd: V, nbs, Pd, Pfr, pxl, Msc dr phuong in thi nghif m 11^04 (n = 2, b = 0,12 m, he = 0,55 m) 94 so un Hmh 12 Dd thi Pcx.Pcz phuong in thi nghifm 04 Ket qui do, tinh toin gii fri trung binh ciia P„, P„, he sd can Ko tuong ung vdi van tdc ciy d mgt sd phuong an fhi nghiem dugc ghi frong bang dudi day NONG NGHIEP VA PHAT TRIEN NONG THON - SO - THANG 6/2009 KHOA HOC CONG NGHE TT 01 02 07 08 14 15 04 05 09 19 14 15 Bing L Gii fri P,„P„,hf so cin Ko b mdt sd phuong in thi nghif m K, (kN/m^) V Ocm/h) P„ ftN) P„ (kN) n n n n n n n n n n n n Phuong an thi nghiem = 2, b = 0,12 m h,= 0,35 m = 2, b = 0,12 m h„= 0,35 m = 2, b = 0,23 m h,= 0,35 m = 2, b = 0,23 m h,= 0,35 m = 1, b = 0,30 m h,= 0,40 m = 1, b = 0,30 m h,.= 0,40 m = 2, b = 0,12 m h,= 0,55 m = 2, b = 0,12 m h,= 0,55 m = 2, b = 0,23 m h,= 0,55 m = 2, b = 0,23 m h,= 0,55 m = 1, b = 0,30 m h,= 0,55 m = 1, b = 0,30 mh,= 0,55 m V KET LUAN 2,1 2,4 2,2 2,9 2,1 2,4 1,7 2,1 1,7 2,1 1,8 2,2 23,6 24,3 39,9 44,1 24,5 24,5 74,7 75,1 95,0 113,3 51,00 53,2 3,8 3,98 6,5 7,23 3,2 3,9 22,1 22,5 36,6 43,8 16,9 19,6 89,28 91,97 117,26 129,60 102,93 103,37 133,03 134,70 124,76 148,86 137,10 144,68 TAI UEU THAM KHAO Su dung cim bien dien frd bien dang de dg lire keg, nen fren cic freo, tfr dd xic dinh dugc lire cin ciy li phugng phip kha fhi vi cho phep xic dinh chinh xic gii fri luc can ciy ngam frong dieu kien dat dai cua lam nghiep Vdi mgt LHM cu the (miy keo Kgmatsu D65A - ciy ngam), can nghien cuu tinh fgin thiet ke, dinh chuin cic khiu dg de dim bag nhay vi dd chinh xic cua tin hieu nhin dugc frgng qui frinh thi nghiem (1) Nguydn Can (2005) Nghien cim mdt sd thgng sd dn dinh ngang cua lien hgp miy keo xich ciy ngim lam viec fren dat ddi mien Bac Viet Nam Luan an TS KT, H i Ngi Thief lip he thdng dg da kenh ket ndi vdi may tinh cd phin mem Dasylab li cang nghe hien dai, cho phep xic dinh ddng thdi nhieu thgng sd eg hgc cd lien quan vdi dd chinh xic cao (3) Pham Thugng Han v i cac cgng su (1996) Ky thuat ludng cic dai lugng vit ly, tip N h i xuat ban Giio due Ket qua fhi nghiem cho thiy, lire can ciy ngim cd gii fri ldn vi bien thien frong khoing rgng, phan anb tinh kh6ng ddng nhat ciia dat dai frgng lam nghiep, day li dac diem cin luu y tinh fgan thief ke vi thinh lip lien hgp ciy (2) Hin Trung Dung (2006) Nghien cuu mdt so tinh chat boat ddng cua miy keo nong nghiep boat dgng d vfing ddng bing sgng Hdng Bio cio tdng ket de tai cap Bg, ma sd: B2004-32-76 Trudng Dai hgc N6ng nghiep I (4) Ngo Dien Tap (2001) Do ludng va dieu khien bing miy tmh Nxb Khga hgc vi Ky thuat H i Ndi (5) Dgin Van Thu (1996) Nghien ctht mdt sd tinh chat sir dung ciia lien hgp miy ciy lim dat frdng rfmg g tinh Vinh Phii Luin van thac sy, Dai hgc Ngng nghiep I RESEARCH AND DETERMINE RESISTANCE DYNAMICS OF CULTIVATOR RIPPING ON THE SITES OF PLANTATION Bui Hai Trieu, Doan Van Thu Summary Resistance dynamics of ripping is a significant technical parameter to decide the energy consumption, and its parameters to use on designated research and establish the conjoint ripping machine Appling Tenzo technical method and establishing the multi canal measurement system to determine the ripping resistance dynamics is a new and modern technology The results of experimental reseach identify the resistance dynamic coefficient (K,) of Komatsu D65A ripping on forest land in Vinh Phuc province, and its scientific basis to research determining the optimal parameters to raise efficiency of the ripping machine Keywords: Ripping resistance dynamics, deformed resistance electronics Ngudi phin hifn: GS TSKH Pham Ykn Lang NONG NGHIEP VA PHAT TRIEN NONG THON - SO - THANG 6/2009 95 ... E.F Trgng dd: vi Al - li chieu dii va dd dan dii ciia khiu do; P - Luc keo, nen tic dgng fren cic freo (kN); E - Mo duyn din hdi cua vit Heu khiu do, vdi thep CT-3cdE = 2L10^N/mm2; NONG NGHIEP... A PHAT TRIEN NONG THON - SO - THANG 6/2009 91 KHOA HOC CONG NGHE F - Dien tich tiet dien ngang khiu (m^ Bien dang dii mi tenzo cam nhin dugc li: s = 10"'' ^10"^ Bang tinh toin ly thuyet ta xic... dinh dugc khoang lire tic dgng len cic treo (P,), tir dd chgn dugc tiet dien cin thief cua cic khiu da freg fren va dudi (Ftr, F^) li: Cam bien dien trd loai day det cd uu diem li: Dien tich