Gio n s: 2 S tit: 1 Tng s tit ging: Lp C C in t Ngy thc hin

4

- Tn bi hc: Cm bin o v tr v dch chuyn - Mc ch: + Trang b cho sinh vin kin thc c bn v nguyn l, phng php o v cc ng dng ca cm bin o dch chuyn v v tr trong thc t. + Rn luyn t duy logic, tnh t ch. - Yu cu: Sau bi hc sinh vin cn phi: + Nm vng kin thc c bn v o dch chuyn v v tr: Nguyn l, cu to v u, nhc im v mt vi ng dng ca cm bin. + T tm hiu cc loi cm bin o dch chuyn v v tr trong thc t, hiu c mt s c tnh k thut c bn ca cm bin ny. C th vn dng la chn c cm bin o v tr v dch chuyn ph hp vi u bi t ra. I. N NH LP : Ni dung cn nhc nh: II. KIM TRA BI C Khng kim tra bi c. III. GING BI MI : - dng dy hc: o My chiu, my tnh o Bng, phn o Gio n, slide bi ging o cng bi ging, s tay ging vin o Ti liu tham kho - Ni dung, phng php. TT Ni dung ging dy 2.3 Cm bin o dch chuyn v v tr 2.3.1 Gii thiu chung a,nh ngha v tr v dch chuyn b, Phng php o v tr v dch chuyn 2.3.2 Cm bin kiu bin tr a, Cu to b, Nguyn l o Thi gian Phng (pht) php thc hin 2 Thuyt trnh, ging gii minh ha bng hnh nh Thuyt trnh, ging gii minh Thi gian: 2 pht Thi gian: 0 pht

1

2

14

c, Mch o 2.3.2.4 u nhc im 3 2.3.3 B m ho vng quay (encoder) a, Encoder tng i ( incremental encoder) Cu to Nguyn tc hot n u nhc im b, Encoder tuyt i Cu to Nguyn tc hot ng u nhc im 2.3.4 ng dng a,Dng cho ng c servo b, ng dng ca encorder trong my CNC 18

ha bng hnh nh Thuyt trnh, ging gii minh ha bng hnh nh

5

Thuyt trnh, ging gii minh ha bng hnh nh Thi gian: 2 pht

IV. TNG KT BI Nhc li nhng ni dung chnh dy: - Nguyn tc hot ng ca cm bin kiu bin tr - Cu to v nguyn tc hot ng ca Encoder

V. CU HI V BI TP: Thi gian: 2 pht VI. T NH GI CA GIO VIN V: Cht lng, ni dung, phng php, thi gian thc hin bi ging trn .. THNG QUA T B MN Ngy .. thng . nm Ch k gio vin

V TR BI GING Chng 1 : Nhng nguyn l c bn v cc c trng o lng 1.1 nh ngha v c trng chung 1.2 Cm bin tch cc 1.3 Cm bin th ng 1.4 Cc i lng nh hng n cm bin 1.5 Mch o ghp ni vi cm bin 1.6 Sai s ca php o nh hng ti cm bin 1.7 nh chun cc b cm bin 1.8 nhy 1.9 c tuyn ca b cm bin 1.10 Gii hn s dng cm bin Chng 2 : Cc loi cm bin, nguyn l v ng dng 2.1.1Cm bin quang 2.1.2Cm bin o nhit 2.1.3Cm bin o v tr v dch chuyn 2.1.4 Cm bin o bin dng 2.1.5Cm bin o vn tc 2.1.6Cm bin o lc 2.1.7Cm bin o gia tc v rung 2.1.8Cm bin o vn tc, lu lng v mc lu cht 2.1.9Cm bin o p sut cht lu 2.1.10 Cm bin o m 2.1.11 Cm bin in ha Chng 3 : o lng v x l tn hiu 3.1 Khi nim c bn v o lng v x l tn hiu 3.2 Cc thit b o lng vn nng v chuyn dng 3.3 Chuyn i tng t - s v s - tng t 3.4 Ghp ni cm bin vi vi iu khin 3.5 LabView v phng php thu thp d liu t cm bin 3.6 ng dng Matlab trong x l tn hiu 3.7 Cc bi thc hnh - Ghp ni mch cm bin bin dng o bin dng trc - Ghp ni mch cm bin t trng xc nh tc bnh rng tr - Ghp ni mch cm bin t trng xc nh khong cch - Ghp ni mch cm bin nhit o nhit vng ct khi tin

2.3 CM BIN O V TR V DCH CHUYN 2.3.1 Gii thiu chung a, nh ngha v tr v dch chuyn V tr l thut ng ch to ca mt i tng so vi mt chun chn trc. Dch chuyn l s chuyn ng ca i tng t v tr ny n v tr khc vi mt khong cch hay mt gc no . b, Phng php o v tr v dch chuyn: Phng php th nht: B cm bin cung cp tn hiu l hm ph thuc vo v tr ca mt trong cc phn t ca cm bin, ng thi phn t ny c lin quan n vt di ng cn xc nh di chuyn. Phng php th hai ng vi mt dch chuyn c bn, b cm bin s pht ra mt xung. Vic xc nh v tr ca vt da vo vic m s xung pht ra. Mt s loi cm bin khng i hi kt cu c hc gia cm bin v i tng o. Mi lin h ny thng c thc hin thng qua in trng, t trng, nh sng 2.3.2 Cm bin kiu bin tr a, Cu to ca cm bin Cc dng hnh hc in k gm mt in tr c nh Rn , trn c mt tip xc in c th di chuyn gi l con chy. Con chy ny c gn c hc vi vt chuyn ng cn nghin cu (nhng hon ton cch in vi nhau). Ph thuc vo dng hnh hc v dng chuyn ng ca con chy, ngi ta phn bit hai loi in k: - in th k dch chuyn thng - in th k dch chuyn trn in tr Cc in tr c th tn ti di dng cun dy hoc bng dn. - in tr dng cun dy phi khng b mi mn, ng thi h s nhit R ca in tr cng phi nh v n nh. Cc dy dn ny c cun trn li cch in (bng thu tinh, gm, nha), cn bn thn dy th c cch in bng may hoc bng mt lp xt trn b mt. - Cc in tr dng bng dn c ch to bng cht do trn bt dn in l carbon hoc kim loi c kch thc ~10-2 m . Tip xc in (con chy) Con chy phi m bo tip xc in tt, ngha l khng gy nn sut in ng tip xc, in tr tip xc phi nh v n nh. Ngoi ra phi m bo cc tiu chun trn trong iu kin c dao ng v tc dch chuyn ln.

Hnh 2.1 Cc dng cm bin in tr o dch chuyn v v tr b, Nguyn l o Da trn cng thc tnh in tr:R= l S

(1.1)

R- in tr dy; l- chiu di dy; - in tr sut; S- tit din dy. v S khng i, in tr ca cm bin ph thuc vo di l. ViR = K .l

(1.2)

K-h s Quan h gia i lng ra ca cm bin v i lng o c biu din di dng biu thc: RX = f ( X V ) (1.3) X V - l i lng o Vi bin tr di chuyn thng:RX = x R0 l

(1.4)

x- l khong di chuyn l-chiu di ca bin tr R- in tr ton phn Vi bin tr loi trn:R =

di chuyn :gc quay ton phn. i vi in th k dch chuyn trn < 3600 cn vi in k xon >3600. R0: in tr ton phn c, Mch o

x -gc

x R0

(1.5)

C th thc hin theo cc dng sau: Mch phn p

Hnh 2.2 Mch o kiu phn p a, o trc tip; b, o qua mch khuych i T s trn ta c biu thc sau:U ra R2 = E R1 + R2

(1.6) (1.7)

Vi mch s dng khuych i:U ra R R = 2 . X E R1 R0

E-ngun nui Mch cu phn p S mc:

Hnh 2.3 Mch o kiu mch cu T s trn ta c:U ra R2 R4 = E R1 + R2 R3 + R4

(1.8)

d,u nhc im u im: - Nguyn l o n gin, Gi c va phi, Tn hiu o ln v khng i hi mch in c bit x l tn hiu. Nhc im: - Kh nng p ng chm, rng thang o gii hn. - C s c xt gy ra ting n - B mi mn, s ln s dng hn ch - Chu nh hng ca mi trng ( bi, bn). 2.3.3 B m ho vng quay (Encoder)

Encoder c chia thnh 2 loi l encorder tng i v encoder tuyt i. a, Encoder tng i Cu to: Gm mt thc m ho v b thu pht tia quang hc: -B thu pht quang hc: B pht: l cc i t pht tia hng ngoi (Led) hoc n pht quang, c s dng nh mt ngun pht sng. B thu: c th l mt i t quang cho php dng in chy theo mt hng khi c tia hng ngoi chiu ti, nu khng n hot ng nh mt mch h; hoc tranzito quang. Trong mt tranzito quang, tia hng ngoi ti nh mt dng in base ca tranzito dng trn cc C s t l vi cng nh sang ti; quang in tr c in tr t l vi cng nh sng chiu ti.

Hnh 3.1 Cc k hiu mch quang in t v cu hnh mt b thu pht in hnh - Thc m ho gm 2 loi: Loi thc thng v dng a trn Loi thc thng: gm cc vch chia . Vch chia c th l vch en, hoc trng, nh sng xuyn qua hoc phn x trn cc vch khc . Loi a trn: a c th lm bng nha trong hoc knh vi cc vch hng tm hoc nha m vi cc khe nh, v vy khi a quay th cc vch ny s ngn hoc cho tia sng i qua ti thit b d quang hc.

Hnh 3.2 B m ho Encoder tng i

Nguyn tc hot ng

-Vi loi thc thng:

Hnh 3.3 S nguyn l hot ng Mi ln nh sng xuyn qua 1 vch, t bo quang in nhn c mt xung nh sng v to ra mt xung in. m s xung ta c th suy ra c di chuyn v ta c: D X = Nd 0 (2.1) D X - khong dch chuyn; N- s xung m c; d 0 - gi tr ca vch chia . -Vi loi a trn Xt encoder nh trn hnh 3.2 s c 3 knh to ra xung A, B, Z. Cng thc xc nh gc ln lt theo raian v x =n k 2

X =

K la tong so vach Xc nh chiu quay: C hai chui xung l A v B vung gc vi nhau. V d: A tng ln 1 khi B=0 chuyn ng ngc chiu kim ng h, ngc li khi A tng ln 1 B=1th chuyn ng l thun theo chiu kim ng h. Knh Z: c tc dng m s nguyn vng.

n 360 0 k

Hnh 3.4 Nguyn tc hot ng b m ho encoder tng i Cc phng php gii m: php vi phn gii 1X, 2X, 4X. Trong phng php 1X, gi tr ca b m s tng ln 1 n v khi gp mt sn ln

hoc xung ca ch mt chui xung, do tng s m ca b m ho cho mt vng quay bng tng s vch trn a. Trong phng php 4X, gi tr ca b m tng ln mt n v khi c mt sn ln hoc xung ca mt trong hai chui xung. V vy phn gii gc c tng ln 4 ln.

Hnh 3.5 Gin xung ca Encoder tng i vi 3 rnh 1x lay suon len cua 1 xung 2x ca suon len ca xuong cua 1 xung hoac 2 suon len cua 2 xung 4x ca suon len ca suon xuong cua 2 xung

u nhc im: u im: - C tn hiu dng xung in c th s dng dng s. - C phn gii cao. Nhc im: - Khng cho php bit c v tr tuyt i ca trc. - Khng thch hp s dng trong mi trng vi nhit cao v dao ng ln. b, Encoder tuyt i Cu to: Gm: mt a m ha k vnh ng tm v k b ngt quang hc, m ho sinh ra mt t nh phn k bit biu din 2k v tr khc nhau ca a v a ra phn gii gc l 360/2k.

Hnh 3.6 a m ho tuyt i

Nguyn tc hot ng: Chm tia sng 2 c i qua a m ho 1 ti cm bin quang 4. Khi a m ho quay cc tia sng tc ng ti cm bin quang hnh thnh cc xung in. Cc tn hiu c a ti thit b tnh gii m gc quay. Nguyn tc m ha: - Vnh trong cng gm mt na m, mt na trong. Vic c vnh ny (bit c trng s cao nht) cho php xc nh ang na vng no. - Vnh tip theo c chia thnh 4 phnm v trong lin tip. c vnh ny kt hp vi vnh trong cho php xc nh ang gc phn t no. - Cc vnh tip theo cho php lin tip xc nh ang gc 1/8, 1/16, - ng ngoi cng cho chnh xc cui cng, goi l LSB (bt c trng s thp nht). ng ny gm 2 k im (n s vnh trn a) tng ng vi phn gii ca b m ho.

Hnh 3.7 S nguyn tc o ca encoder tuyt i

Hnh 3.8 Gin xung ca encoder tuyt i Bng m ho ca encoder vi 4 vnh:

Hnh 3.9: Bng m ha ca encoder 4 vnh T bng m ho nh phn ta c th chuyn v thp phn vi 16 v tr c m ho. 23 22 21 20 Th p ph n 0 0 0 0 0 0 0 0 1 1 0 0 1 0 2 0 0 1 1 3 0 1 0 0 4 0 1 0 1 5 0 1 1 0 6 0 1 1 1 7 1 0 0 0 8 1 0 0 1 9 1 0 1 0 1 0 1 0 1 1 1 1 1 1 0 0 1 2 1 1 0 1 1 3 1 1 1 0 1 4 1 1 1 1 15

Hnh 3.10 Bng m ho nh phn ca encoder tuyt i Khong dch chuyn c tnh theo biu thc sau:N1 N2d0 D X = ( N 2 N 1 )d 0

(2.2)

con s ch gi tr v tr ban u con s ch gi tr v tr sau dch chuyn gi tr ca vch chia

u nhc im: u im: - Lun xc nh chnh xc v tr tuyt i ca vt. - C tn hiu dng xung in c th s dng dng s. Thun li cho qu trnh tnh ton v giao tip vi cc chip x l. - C phn gii cao. `Nhc im - C mc gi cao hn so vi encoder tng i - Khng c kh nng lm vic trong mi trng chu lc, v c nhit cao. 2.3.4 Gii thiu mt s ng dng Encoder a, ng dng trong ng c servo

Hnh 4.1 ng c servo v nguyn l iu khin ng c servo l thit b c iu khin bng chu trnh kn. T tn hiu hi tip vn tc/v tr, h thng iu khin s s iu khin hat ng ca mt ng c servo. Vi l do nu trn nn sensor o v tr v tc l cc b phn cn thit phi tch hp cho mt ng c servo. Vi cc loi encoder quang hc ta c Tnh v tr theo cng thc:D X = ( N 2 N1 ) d 0

Tnh vn tc theo cng thc sau:

S=

60 N kt

t Trong : : l khong thi gian m x,k : l s im m ho trn mt vnh, : Tng s xung m c N

b, ng dng trong cc my CNC

Hnh 4.2 Mt s dng encoder dng trong my CNC Cc encoder dng thng (lineare encoder) s xc nh cc trc di chuyn theo cc chiu thng. Cc loi thc m ho thng ny thng c lm t thu tinh, knh chuyn dng t b nh hng bi s thay i nhit . Do my thng c 3 bc t do dch chuyn dc trc nn s b tr 3 encoder dng thng

Cc encoder dng a ( rotary encoder) s kim sot cc chuyn ng quay. Trong cc my CNC tu theo s bc t do m s lng b m ho ny c th 1, 2 hoc nhiu hn Tt c c b m ho s o c v tnh ra cc khong dch chuyn hay gc quay gia cng sn phm theo chng trnh c lp trnh. Mt s encoder c s dng: Loi c ng knh l trc 8-10mm phn gii 2000 xung trn mt vng Knh u ra A/B/Z Loi c ng knh a 60-80 mm phn gii 100 xung trn mt vng Knh u ra A v B Ngun nui 5v BI TP: Bi 1:

Cho mch o nh hnh v. E=5v, R3=R4=2 R0=10 v biu s ph thuc Ura vi R2 thay i 0-10 Bi 2: Cho encoder tuyt i dng a m ho 32 v tr ng knh 60 mm. Tnh s vnh m ho. S vch trn cc vnh. V gin xung ca encoder ny.