Bai Giang FMS & CIM - Chuong 3

7/25/2019 Bai Giang FMS & CIM - Chuong 3

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HC VIN K THUT QUN SKHOA HNG KHNG V TR

BI GiNG MN HC

H THNG SN XUT LINH HOT

TS. Trnc Tng

Bmn CNTB & HKVTin thoi: 0973 991486

Email: [email protected]

GV: TS. Trn c Tng Khoa HKVT

2. Cng c m phngNi dung

3. S mng li Petri net

1. Cc cng c k hoch ha

Chng 3: Cc cng c phn tch HTSX


2/45


1. Cc cng c k hoch ha

Lp khoch l mt phn ca mi hotng sn xut, n l

mt cng vic lin quann khoch thi gian v khochha chi tit.

- Khoch ha thi gian lin quann thi gian trong mt

cng vicc thc hin.

- Khoch ha chi tit lin quann schun bv khai thc

tiu tt ccc ngun lc sn xut.

Kh khn ca vic lp khoch l mi cng vic sn xut yu

cu phng php lp khoch ring, v cc phng php

ngy cng thayi.


V d, phng php lp khoch c trgip ca my tnh

khc rt nhiu so vi phng php lp khoch bng tay s

dng cchy 30 nm.

Khng c khi nim chung vni dung v cu trc ca tng

cng clp khoch.

V d, cng clp khoch cho pht trin phn mm s

khc cng csdng cho lp khoch sn xut.

Cc cng cdng cho hthng khoch ha thng xydng thnh cc khi m c thp dng cho cc vnkhc

nhau.


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Hthng lp khoch phc tp c thsdng cc biu,quy hoch tuyn tnh v quy hochng, m phng, mng

li Petri, v phng php tr tunhn to.

Thng thng rt khxcnh cng cno c lis

dng trong gii quyt 1 vn a ra.

Nu mt hthng lp khoch ln, c cu to tcc cng

clp khoch cbn, cc giao tip bn trong phic

thit kcn thnc slin kt hiu qugia cc bphn.


Nhim vca lp khoch tri qua vi giaion:

Khoch btu vi khi nim vsn phm v kt thc vi

sbo qun, bo dng chng.

Mt phn quan trng ca lp khoch l khnng sn c ca

csdliu, lu cc thng tin vcc sn phm, qu trnh,

ngun lc sn xut, scnh tranh, v.v.

Ngi lp khoch phi truy cp vo tt ccc dliu cn

thit v cp nht csdliu m bo l thng tin lun

lun mi.


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Trong nhiu trng hp, lp khoch l mt cng vic lp li

v cc cng ccbn thngc sdng nhiu ln.

V vy, hthng khoch ha phic thit ktheo mun,

cc mun c th c tham sha bi ngi sdng t

kinh nghim.

Cng c thcung cp dng thvin cc thnh phn, t

thit lp nn hthng lp khoch cho tng mcch.


Hai cng vic lp khoch lin quann qu trnh sn xut l

khoch vtrang bv cc nguyn cng.

Trong FMS hai cng vic ny khngc phn chia mt cch

r rng.

y, iu quan trng l cung cp mt s btr ca cc

thit bgip cc my cng c, cc thit bvn chuyn c thddngc thit lphthng c thlm vic theo khi nim

sn xuto.


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Cc giai on lp KH cho 1 HTSX & cc cng c h tr lp KH

Phn tch yu cu

Thu thp vnh gidliu

Btr hthng vnh gi kthut

Phn tch tnh kinh t

Thit khthng vlp ti liu

Hin thc ha hthng v kim tra

Cc giaion lp khoch

- Hthng htrqun l dn

- Cc cng ckthut cho vic m t- Thit bsn xut- Btr hthng sn xut- Thit kb iu khin my tnh- Thit kphn mm

- Mi trng lp trnh cho- Cc tbo sn xut- Cc my cng cNC- Cc robot

- Cc thit bph- Cc cng cm hnh ha v m phng chott ccc thit bsn xut- Chng trnh vvnu t- Ti liu v cc cng cto biu- Cc cng ckthut phn mm cho lptrnh v hthng cstri thc

Csdliu cho lp khoch

Cc cng clp khoch


2. Cng c m phng

2.1 Cc cng c m phng

M phng trgip rt tt cho lp khoch v cc hotng

ca mt hthng sn xut.

Trcy ngnh cng nghip xem m phng nhmt cng

cngoi lai chhu dng trongo to, do hthng m phng

kh p dng v cn my tnh ln.

Trong nhng nm gny, tnh hnh thayi. Cc h

thng m phngc tng ln vi thit kgiao din hngngi sdng, v cc my chcngc pht trin. Thm

vo, vi vic pht trin ca mng my tnh, cho php cc

my chlin kt vi nhau to thnh mt mng my tnh ln.


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Ngi ksxy dng m hnh ton hay ha cc qu trnh

cn nghin cu (vi sm phngc htrca my tnh)

v quan st trng thi, slm vic ca n.

Kt quca m phng l cc bn ghi hay hnhnhng trc

quan trn mn hnh. V vy ngi ksc thkho st cc

hotng sn xut khc nhau m khng cn setup my hay

cc qu trnh gia cng tht.

M hnh thng chgm cc bphn thit yu ca qu trnh

cn kho st. Do , vic xy dng v thc hin ca m hnhsnhanh.


N cho php kho st cc qu trnh sn xut khc nhau

nhanh.

N cng cho phpiu chnh tng tc hay lm chm mt qu

trnh sn xutc mt ci nhn tng qut hay chi tit vqu

trnh sn xut. Ngoi ra c ththm cc nhiu lonxem

nh hng ca n.

M phng cngc dng choiu khin qu trnh sn xut.Trong trng hp ny, m hnhiu khin hotng song

song vi hthng sn xut.


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2.2 Cc phng php m hnh ha

C cc m hnh khc nhaum hnh ha mt nh my sn

xut.M hnh

Ton hc ha Vt l

Tnh ng Tnh ng Tnh ng

S Phn tch S


M hnh ton hc

- Trong m hnh ton hc, cci tng ca 1 hthng sn

xut v cc thuc tnh ca nc trnh by bng cc bin.

- Cc hotngc m tbng cc hm ton hc, nh ngha

mi tng quan gia cc bini trong sn xut.

- M hnh ton hc c thl kiu tnh hocng.

- Vi kiu tnh, m hnh hthng trong trng thi cn bng;

- Vi kiung, hthng c thtrong trng thi thayi lin

tc.

- Trong thc tc2 kiuc sdngm tcc hot

ng ca hthng sn xut.


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- Cc phng php vn tr hc cung cp cc cng ccho vic

xy dng m hnh hthng sn xut. Cc cng cny c ththy trong m hnh ha lp khoch, iuviu khin

cc chc nng cuqu trnh sn xut.

- Cc phng php vn tr hc bao gm quy hoch tuyn tnh,

quy hochng, phn tch mng, m hnh hngi, v m

phng s.

- Cc phng php vn tr thngc p dnggii quyt

cc vnca nhng lnh vc khc nhau; chng hn, thut

ton vn chuyn cho vic phn bcc chi tit ti cc my

cng cc th c p dnglp khoch thtgia cngcc ltrong mt chi tit kim loi mng c hnh dng phc tp.


- Cc phng php vn tr chyu hu dng cho lp khoch

offline.

- V d, nu mt my cng cbhng, khoch phic

lmi lm li trong ch offline.

- y l mt hn chca phng php vn tr hc. Phng

php ny cng gp kh khn nu mt qu trnh sn xut c

cc nhiu lon v m hnh khng thm tchng mt cch

ph hp


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M hnh ha

Cc m hnhha l cc cng cquan trngbiu din

hotng ca hthng sn xut. Hotng sn xut c th

c hin thha bng cc biu tng hoc k hiu.

Cc biu tng l cc cng cl tng cho m phng khi hnh

nh ca chng ging cc thit bsn xut. Tuy nhin xy dng

thvin cc biu tng l cng vic bun tv tn thi gian.

C nhiu cch khc nhauk hiu ha mt hotng sn

xu

t. Cc cng cm

i g

n

y s

dng m

ng Petri.


M hnh vt l

Cc hotng sn xut thngc m hnh bng cc m

hnh thnghim hay hotng thnghim. Mcch l xy

dng mt hnhnh vt l ca nh my hay mt thnh phn

ca n.

Cc m hnh ny bao gm tt ccci tng chc nng cn

thit cho vic biu din hotng sn xut tht. V vy c th

mt nhiu thi gian vt.

Php ngoi suy ccng sca m hnh vi hthng tht

cng c thdn ti cc kt qukhng thc t.

M hnh vt l s c thay bi cc m hnhha hay ton

hc


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2.3 Cc phng php m phng

Nu mt qu trnh sn xutc m phng:

Trc tin m hnhi tng m phng phic xy

dng.

Trong trng hp l tng, i vi mt qu trnh lin tc,

m hnhc xy dng tcc phng trnh ton hc m

ttrng thi vt l cai tng.

Tuy nhin cch ny t khic thc hin cho qu trnh sn

xut bi v khng thm t o cc nguyn tc vt l bn

trong di mt kiu chnh xc.


Cc phng php m phng cbn sdng cho ccng

dng sn xut l:

M phng cc skin ri rc

V m phngha.

C nhiu hthng m phng kt hp c2 phng php.

Hthng m phng skin ri rc ph hp cho nghin cu

dng lu thng mt hotng sn xutxcnh kh

nng ca n, xcnh cc bottlenecks, quan st sphn

phi cc chi tit ti cc trm lm vic. Cci tngc

biu din bng cc biu tng hay k hiu vi m phng

ha.


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Khi dng biu tng, hthng sn xut c th c hin thng trc tip trn mn hnh vc quan stcc mc

chi tit khc nhau. N rt hu dng trong vic quan st dng

vt liu, qu trnh gia cng v lp rp sn phm.


M phng cc s kin ri rc

- Phn ln cc qu trnh sn xut l cc skin ri rc v phi

c m tnhnhng skin ri rc.

- Trcy cc ngn nglp trnh bc cao nhFortran,

Pascal, c sdng cho vic m phng cc skin ny.

- Trong qu trnh sn xut cc chi tit ring bit, dng sn phm

hay thng tin xy ra ngu nhin, v dcc chi tit ti cc trm

theo hm phn bxc sut. Hm ny bit trc vc nhp

vo hthng m phng.- Trong nhiu trng hp kinh nghim tcc qu trnh tng t

v gissphn bxc sutca vo tnh ton. Trong

mt strng hp khc c thgishm hoc ly dliu

thc nghim tqu trnh chy th


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- M phng thc hin vi ngn ngbc cao c th c bao

gm khi dng vt liu phic m t, v l do ny cc ngnngringc pht trinnghin cu cc skin ri

rc.

- Cc hthng m phng skin ri rc nh: GPSS

(general purpose simulation system), SIMULA (simulation

language),

- C cc chng trnh m phng sn xutc thn gin ha

cc hotng ca nh my, nh: Witness, Promod,

STARCELL,


M phngha c th c phn thnh 3 phng php:

M phng dng biu tng (icons)

- Vi kiu m phng ny, cci tng ca hthng sn xut

c biu din bng cc hnhnhn gin (biu tng) v

lu trong csdliuhac cu trc nhcc lpi

tng.

- Cci tng c thl my cng c, xe thnh, robot, .- Khi hotng ca hthng sn xutc m phng, cci

tngcc ra tcsdliu vc cu hnhthit

lp hotng

M phng ha


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- Hotng ca hthngc hin thtrong thi gian thc v

c thtng tc vi cci tng hin th thcc chcnng khc nhau.

- Kiu m phng ny chyu hu dng trong gri, chnh l v

quan st dng vt liu

- M hnh biu tng cng ph hp cho la chn cc thnh

phn ca hthngthit lp hthng. Trong trng hp

ny cc biu tngc lp cho cci tng khc nhau

m phng.


- Cc biu tng c th c hin thtrn mn hnh v h

thng s a ra mt mu cnin cho ngi sdng nh

ngha shotng cai tng.


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- Vi phng php ny, cc k hiuhac gn cho ccchc nng hthng.

- V ds i ti ca mt chi tit, gn mt chi tit cho mt

my, bngm sn phm,

- Cc tham scngi cc chc nngc ngi sdng

nhp. Ngi sdng c thhin thv quan st hotng

ca cc thit btrn mn hnh vi strgip ca cc k hiu,

cc k hiu ny c tht mu.

M phng s dng cc k hiu logic


- Vi phng php ny, i tngc m tbng mt biu

tng:

V dbiu din nhitbng mt nhit k, p sut nn

bng mt mi tn,

- Khi hin thtrn mn hnh, mt shthng cho php nhn hot

ng ca cc biu tng:

V dstng ca p sutc chra bng cp sut.

Cng c thhin thmu.

M phng s dng k hiu ha


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2.4 Chu k m phng

Xem xt mcch, yucu kthut

Phn tch vn, thuthpv lc dliu

Thit km hnh

Vit phn mm

Thc hin m phng

nh gi v phn tchkt qu

Lp ti liu

- Dliu nhp- Phng php sdng- Cng cm phng- Cc kt qu

Csdliu

Cc giaion cam phng


Sthc hin ca cc giaion c th c thc hin lp li

vi lnn khi nhnc gii php c thchp nhnc.

Trong rt nhiu trng hp dliu cs m phng khng

, v dliu thc nghim c thphi nhn tchy sn xut

th.


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2.5 Cng c m phng ton b

Cng cm phng mt nh my sbao gm mt smuncho cc thnh phn ca ton bhthng.

Khng sn c mt hthng m phng cho tt ccc mcch

m ngi sdng phi tlin kt cc cng cm phng.

Thng thng cc hthng m phng cbn nhGPSS,

SLAM c thmua, tuy nhin rt nhiu qu trnh trong nh my

l ccng dngc th, v vy ngi sdng phi txy

dng cc mun.


Hthng m phng ton bsrt phc tp bi v khng d

dng lin kt cc mun cng nhau thnh mt khi v vn

l thi gian chy ca my tnh sdi.

Cng khng c sbom l cc mun c thtch hp

thnh mt hthng hiu qu.

Trong nhiu trng hp, hthng m phng bao gm vi

mun, vi cu trc nhp/xut ring v c thc csd

liu ring cho tng mun


17/45


Ccn vsn xut c thbao gm cc my cng c, cc

robot, v cc xe vn chuyn vt liu. Hthngc xy dng

t5 mun: m hnh ha, m phng, lp trnh, m phng v

ha. Dliuc lu trong csdliu m phng.


- Mun ny cha tt ccc mun cn thit cho m phng,

bao gm sn phm, cc my cng c, robot, xe vn chuyn

vt liu.

- Cc m hnh m tthuc tnhng hc cng nh ng lc

hc, ng scai tng nghin cu.

- M hnh nh myc sdng cho vic cu hnh hotng

ca ton bnh my. C mt mun cho sensor v mt m

un choiu khin vng lpkho st ccng scbn

ca cc thnh phn.

M un m hnh ha


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- Mun m phngc sdng cho vic trnh din hotngca thit bsn xut v cc thnh phn ca n.

- Motion planning c thc hin cho tt ccc thit bdi

chuyn nhrobot, my cng c, hthng vn chuyn.

- Cc mun sensor viu khin cho php m phng ccho

viu khin cc hotng. Cng c cc mun cho vic ra

quytnh v cc chin lc khoch ha

M un m phng


- Cc robot, my cng c, c lp trnh nhnhng mun

ny.

- Vic lp trnh c th c thc hin theo dng text, ha,

hay hng nhim v.

Trgip m phng

- Bthng dch l giao tip gia hthng lp trnh v m phng.

M chng trnhc bin dch v sau hin thnhcc

biu tngng trn mn hnh.

M un lp trnh


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- Bgrixcnh v sa li trong lp trnh

- Mun xcnh va chm kho st tt ccc chuynng ca

thit bv tm va chm. Thng cc va chm c thxy ra l

cc tay robot, stng tc gia dao v phi, v cc xe t

hnh.

Trgip ha

- Mun ny bao gm tt ccc cng cmy tnh cn thit cho

vic m hnh ha v m phng


3. S mng Petri Nets

3.1 Gii thiu

Trong qu trnh sn xut, cci tng nhdng vt liu

trong nh my c thdi chuyn: tun t, khng tun thoc

song song.

- mi trm gia cng, cc cng vicc thc hin vii

tng, nh: ct vt liu, xl nhit, lp rp, v.v.

- Mi cng vic (hay gi l mt svic) c thc hin bicc ngun lc sn xut (cci tng sn xut) cc my

cng c, robot, cng nhn,


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Nm 1964, Carl A. Petri gii thiu m hnh Petri nets:

M hnh Petri nets sauc pht trin rng ringhin cu cu trc, iu khin ca cc hthngng thi

v song song.

Lcu ncng dng chyu trong cc hthng my

tnh v giao thc mng, sau Petri nets cng dng

trong cc hthng sn xut.

Petri net chng minh rt hu dng trong m hnh ha, kim

tra, phn tch, viu khin cc hthng sn xut, v n c

ththu thp hay bt gi(capture) ccc tnh chyu canhng hthng ny:


- c tnhng thi hay song song (trong thc trt nhiu

cng vicc thc hinng thi)

- Khngng b(do thi gianhon thnh cc cng vic

l khc nhau)

- Sxungt do vic dng chung cc ngun lc sn xut

(cc my c ththc hin cc cng vic khc nhau)

- Cc qu trnh ri rc (cc qu trnh sn xut c th c

xem nhsni tip ca cc skin ri rc)

c tnh vthi gian Petri nets rt hu dng trong nghin cu

sthc hin ca cc hthng FMS thu nhn cc thng tin

nhnng sut, khnng khai thc my ca hthng, v.v.


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3.2 L thuyt v Petri nets

3.2.1 Cc thut ng v khi nim c bn

3.2.1.1 Cu trc ca Petri nets Cu trc ca mt Petri net l mtthhng 2 phn, bao

gm:

- 2 kiu nt (node) c gi l Place (vtr) v Transition (schuyn tip).

- Cc cungnh hng (directed arcs) ni cc Places v ccTransitions.

Petri net c m tnhbba: N = (P, T, F)

Trong:- P = {p1, p2, p3,pn} l tp hu hn ca cc vtr, k hiu:


P1t1 P3

P2

- P1- Vtru vo (Input place) ca t1

- P2, P3- Vtru ra (Output place) ca t1

- Inp (t1) = {P1} (tp ca ccu vo ca t1)

- Out (t1) = {P2, P3} (tp ca ccu ra ca t1)

M hnh Petri net

V d:

- T = {t1, t2, t3,tn} l tp hu hn ca cc Transitions, k hiu:

- F (P x T) (T x P) l tp ca cc cungnh hng, k hiu:


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3.2.1.2 Ma trn lin thuc

Cu trc ca Petri net c th c m tbng ma trn lin

thuc ca cc places v transitions:A = [ aij]nm

Trong:( )

( )ij

1 p

1 p

0 Otherwise

i j

i j

Out t

a Inp t

+

=

P1

t1

P3

P2

t2

t3

Ma trn lin thuc ca m hnh Petri net trong v dtrn nhsau:

-1

-1

+1

t3

+1+1P3

0+1P2

-1-1P1

t2t1


3.2.1.3 nh du (marking)

nh du ca mt mng Petri net N l mt hm:

M: P {0, 1, 2, . . .} (tp ca cc snguyn dng)

- Gn mt skhng m ca cc token (k hiu bng du chm

muen) cho mi vtr (place) ca mng Petri.

- Mt vtr (place) picnh du nu M(pi) 0

- K hiu M0 l du ban u (initial marking).


23/45


V d v nh du ban u (Initial marking)

0

10

2

0

3

( ) 1

( ) 0

( ) 2

M P

M P

M P

=

=

=

P1

t1

P3

P2

t2

t3

n gin k hiu chng ta cng c thk hiunh duca Petri net bng n-vector:

0 [1, 0, 2]M =

Trong thnh phn thitngng vinh du ca vtr(place) thi (i = 1,,n)


3.2.1.4 Nguyn tc firing (firing rules)

- nh du (marking) c ththayi bifiring transitions (th

hin tnhng trong Petri nets)

- Mttransition tc gi lfireablebinh duMnu v ch

nu miu vo p Input (t) cha t nht mt token, ngha l

M(p)>0

- Mitransitionc khing binh duMc thfiring

- Khi mt transitition t nofiring, mt token c loi bkhi

input place, v mt token c thm vo ccoutput placeca

n => To ra mt s nh du mi ca mng Petri nets.


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V d:

P1

t1

P3

P2

t2

t3

- t1v t2c khnngfiringbinh du ban u M0, tuy nhin t3khng c khnng (u vo ca (p

2) khng c token)

-Firingca t1loi mt token t u vo p1, thm mt token cho

miu ra p2v p3

- Kt qu nh du mi M1=[0,1,3]

M0 = [1,0,2]

P1

t1

P3

P2

t2

t3

M1 = [0,1,3]


P1

t1

P3

P2

t2

t3

M1 = [0,1,3]

P1

t1

P3

P2

t2

t3

M0 = [1,0,2]

P1

t1

P3

P2

t2

t3

M0 = [1,0,2]

P1

t1

P3

P2

t2

t3

M1 = [0,0,3] DEAD


25/45


t1v t2trong trng hp th2 gi l xungt vi nhau. V vycn phi la chn transition m sfiring.

Stin trin tip ca cc mng Petri c thkhc nhau, ph

thuc vo transition noc chnfiring.

Petri net khng yu cu stoken cn phi bo tn, do tng s

ca token c ththayi sau mi lnfiring. Trong trng hp

thnht ca v dtrn, firingca t1loi bmt token nhng

to ra 2 token, v vy tng tng sca token thm 1.


3.2.1.5 Cc thuc tnh c bn ca Petri net

Firingca mt transition trong thc tc th c din gii

nhsxy ra ca mt svic (event), n tiu tn mt ngun

lc v to ra cc ngun lc khc.

Token biu din cc ngun lcmt trng thi bit, c

thhin bi cc places

Stn ti ca mt hay nhiu cc token chra ssn sng ca

cc ngun lc, v vy c thlm cho cc svic (event) c thxy ra; ngc li nu khng c token ngha l cc ngun lc

cha sn sng.


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Token cng c th c xem nhcciu kin, c trnhby bi cc places. Phthuc vo cciu kin c tha mnhay khng m mt ssvic (event) xy ra, n slm choiu kin cmti v to ra cciu kin mi (m tbinhdu mi)

Trong mi trng sn xut:

Cctokensbiu din cc ngun lc nh: my, chi tit, v.v.

Transition firingbiu din sbtu hay kt thc ca mtcng vic.

Cc places v transition cng biu din cciu kin v ccmi quan hvtht u tin trong cc hotng ca hthng sn xut.


nghin cung hc ca cc hthng m hnh ha bng

Petri net, mt vic rt quan trng l kim tra trng thi sng -

hotng (liveness) v gii hn - chn (boundedness) ca m

hnh mng li.

Mt m hnh Petri net hotng (live) nu minh du

(marking) c thquay trv nh du ban u (sau mt chui

ca cc transition firing), tn ti mt thtfiringfiring

cho mi transition.

Thuc tnh sng-hotng (live) bom l hthng khng

c deadlock (s nh trhay tc nghn)


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V d

Petri net di khng hotng, do nh du M2 (t nh duban u qua firing t2) xy ra deadlock

P1

t1

P3

P2

t2

t3

S Petri net ny cstc nghn (deadlock)


Mt m hnh Petri net bgii hn (bounded) nu tn ti mt

gii hn trn vstoken trong trong mi place ca mng cho

minh du (marking) t nh du ban u. Thuc tnh ny

bom l cc token trong bt k1 place no khng thtch

ly mt cch v hn.

P1

t1

P3

P2

t2

t3

S Petri net ny bgii hn (chc mt khnngnh du tM0 lM1, M2, v M0 )


28/45


Thuc tnh sng-hotng (liveness) v gii hn

(boundedness) rt kh kim tra. N yu cu xy dngthm ttt cccnh du c tht nh du ban u.

i vi cc mng ln, thny khng dkim sot v s

ca ccnh du c thti tng theo hm m.

Liveness v boundedness cng bom l hthng c th

lm vic lin tc vi mt sngun lc nhtnh. Chnh v vy

cc thuc tnh ny thu ht squan tmc bit khi nghin cu

ng hc ca cc hthng m hnh ha bng Petri nets.


V d v m hnh ha bng Petri nets:

Xem xt hotng ca mt r bt gp vt chi tit:

Robot ny gp mt chi tit saut n vo vtr mong

mun.

Nhvy c 2 svic l gpvtchi tit.

Svic thnht c thxy ra nu chi tit sn c v robot

sn snggp.


29/45


P1biu din robot, P2biu din chi tit (cc token -nh du

thhin robot v chi tit sn sng)

t1biu din svic gp chi tit, t2biu din svict chi tit.

Sau khi robot gp chi tit, mt trng thi mic to (robot

gichi tit), c biu din bng P3, sau svict chi tit

c biu din bng transition t2.

Khi robot t chi tit n

sn sng cho hotng

gp chi tit tip theo,

v vy cn mtngni tt2ti P2

P2

t1P3

t2P1

Chi tit sn c

Robot sn sng

Gp chi tit t chi tit

Robot gichi tit


3.2.1.6 c tnh thi gian (Timed Petri nets)

Timed Petri nets c gii thiu lnu tin vo nm 1974

bi Ramchandani.

Hm thi gian (Firing time funtion) :+:T IQ (Tp ca cc shu tdng)

Mi transition t ly mt thi gian thc(t) firing

(a) Btu (a) Thc hin (a) Kt thc

Thi gianfiringca transition thhin khong t.gian hotng


30/45


3.2.1.7 th biu din s vic (event graphs)

nh ngha:mt event graph l mt mng Petri m mi place

c chnh xc mt input v mt output

P1

t1

P3

P2

t2

t3P1t1

P3

P4

t2

t3 P2

Mt event graph Khng phi l mtevent graph


S mng li c bn:

Mt s mng li cbn trong mt event graph l mt

ng hng kni tmt nt (placehoctransition) v quay

trli nt ny, khng lp licc nt khc.

P1t1

P3

P4

t2

t3 P2

V ds bn gm 2 mng

li cbn:

1 1 2 4 1 1( , , , , )p t p t p =

2 1 2 2 3 3 1 1( , , , , , , )p t p t p t p =


31/45


- Tng stoken trong mt s mng li cbn khng thay

i do vicfiringcc transition- Mt event graph sng - hotng (live) nu v chnu tn ti

t nht mt token mi s mng li cbn.

P1t1

P3

P4

t2

t3 P2

0 0

1 2

0 0

3 4

( ) 1, ( ) 0,

( ) 1, ( ) 1

M P M P

M P M P

= =

= =

1 1 4

2 1 2 3

( ) ( ) ( )

( ) ( ) ( ) ( )

M M P M P

M M P M P M P

= +

= + +

0

1 10

2 2

( ) ( ) 2( ) ( ) 2

M MM M

= == =

Cc thuc tnh event graphs


Phn tch c tnh thi gian trong th Event Graph

Tng thi gian firing trong mt mng li cbn() :

1

( ) ( )n

i

i

t =

=

Stoken M() trong mt mng li cs

0

1

( ) ( )n

i

i

M M p=

= (M0 lnh du ban u)

Thi gian lp li C() (chu k) ca mng li cs c xc

nh bi:( )

( )( )

CM

=


32/45


Hthng quay li chu kban u sau mt thi gian nhtnh.

Thi gian lp lic xcnh bi thi gian ln nht tiu tntrong scc s mng li cbn, ngha l:

ax(C( ))C M

=

Ni cch khc, tn sut (hs) m transition fire l:

1 1( )

( )Min

C C

= =

Mng li cs* c thi gian lp li (chu k) ln nht (ngha

l C=C(*)) c gi l mng gii hn (critical circuit).


V d

Xt event graph nhhnh bn. Gisgi trthi gian firing

nhsau:

P1t1

P3

P4

t2

t3 P2

1 2 3( ) ( ) 2, ( ) 1t t t = = = (n vthi gian)

Chng ta nhnc:

1 1 2

2 1 2 3

1 2

( ) ( ) ( ) 4

( ) ( ) ( ) ( ) 5

( ) 2, ( ) 2

t t

t t t

M M

= + =

= + + =

= =

V vy:

1 2( ) 4 / 2 2, ( ) 5 / 2 2.5C C = = = = Thi gian lp li (chu k) ca event graph l:

1 2 2ax(C( ), C( )) = C( ) = 2.5C M =

2l mng gii hn


33/45


P4

P1t1

P3

t2

t3 P2

P4

P1t1

P3

t2

t3 P2

P4

P1t1

P3

t2

t3 P2

P4

P1t1

P3

t2

t3 P2

M0 Sau 2 n vt.gian Sau 3 n vt.gian

Sau 4 n vt.gian

P4

P1t1

P3

t2

t3 P2

Sau 5 n vt.gian


3.3 M hnh ha FMS bng Petri net

Xem xt mt hthng sn xut gm:

mmy, k hiu: M1, M2,Mm

nkiu cng vic (hay chi tit) khc nhau: P1, P2,Pn

Ltrnh sn xut mi chi tit c chra bi thtchi tit n

cc my

Thi gian xlc cho trc v xcnh.

Cc cng vic gisc tnh chu k(cycle).


34/45


V d: Phn xng gm 3 my M1, M2, M3

Phn xng sn xut 3 sn phm (3 kiu cng vic): P1, P2, P3

Thtthc hin cc cng vic trn cc my nhsau:

P1: M1(1), M2(9)

P2: M1(2), M3(4)

P3: M1(3), M3(2)

Nhvy, chi tit P1c xlmy M1trong khong 1 n

vthi gian, saumy M2trong 9 n vthi gian v cngvicc hon thnh.

(Gi trtrong ngoc lthi gian xl)

(1)


Giscc cng vicc xl theo cc tlnhnhau.

Nhvy hn hp sn phm nhnhau v bng 1/3 cho cckiu cng vic.

Nhm chi tit nhnht (minimum part set - MPS): nhm nhnht cha tt ccc kiu cng vic (job) theo tlvcc tlsn xut.

Trong v dtrn:

S = {P1, P2, P3} do tt ccc chi titc sn xut theo tlging nhau (product mix: 1/3P11/3P21/3P3)

Gisnu tlsn xut l (1/2 1/4 1/4), tc l gp 2 ln schi tit 1 (hay kiu cng vic 1) c sn xut. Khi MPSsl: S = {P1, P1, P2, P3}


35/45


Gisthtthc hin trn cc myM1, M2, M3nhsau:

M1: S1= {P1, P2, P3}

M2: S2= {P1} (2)

M3: S3= {P2, P3}

Hthng c 2 phn phn bit:

Phn vn hnh (operative part): c chra bi thtsn

xut

Phniu khin (control part): chra bi thtcc my


Operative part: c m hnh ha nhl nhm ca cc mch(circuits) ca event graphs, c gi l ccprocessing circuits.

Mi circuite biu din chu kqu trnh sn xut ca mt cng

vic ca MPS theo thtsn xutc cho trc (1).

(processing circuits)P1

P2

t1 t2

(M1) (M2)

P1

P3

P4

t3 t4

(M1) (M3)

P2 P6

P5

t5 t6

(M1) (M3)

P3


36/45


Quy tc m hnh ha nhsau:

Mi transition biu din mt hotng (operation) thc hinbi mt my, firing time = thi gian xl ca my.

Trong v dtrn t1biu din hotngu tin trong qu

trnh sn xut ca chi tit (hay cng vic) P1thc hin

trn my M1

Token biu din cng vic trong qu trnh xl. Gisl

mi cng vic (chi tit) c mang bi mt thit bvn

chuyn nhpallet (mi pallet mang mt chi tit). V vy

token lun chuyn trong mt processing circuit biu dinchu trnh sn xut ca mt kiu cng vic (chi tit)


Place biu din rng buc vtht u tin gia cc hot

ng.

Token trong place biu din cng vic (chi tit) angi

c xl. V vy cc place cng c th c xem nh

cc trmi


37/45


Control part:

m hnh ha th

t

th

c hin cc cng vi

ctrn mt my,

Tt ccc transition m biu din mt operation thc hin

bi mt myc lin kt trong mt mch (circuit), c

gi l control circuit (mchiu khin).

Thtca cc transition trong mch xcnh bi tht

cc cng vicc xl trn my.

Mchiu khin theo thtcc myc cho(2) nh

sau:


Processing v control circuite

P1

P2

P2

P1t1 t2

(M1) (M2)

P3

P4

t3 t4

(M1) (M3)

P6

P5

t5 t6

(M1) (M3)

P3

c1

c5 c3

c2

c6 c4

phn bit placeca processing circuitev place ca controlcircuite (gi l controlplace) - k hiu c csdng

Control place m ttrng thi c thcamt my.

Chc mt v chmttoken lun chuyn trongmi control circuit,ngha l mi my chthc hin mt cng vicmt thi gian


38/45


Vtr ca token trong control circuit xcnh trng thi ca

my:

Token nm trong transition ngha l transition ang firing

hay myc khai thc

Token nm trong place ngha l myithc hin cng

vic tip theo theo thth c lp

nh du ban u (initial marking) c xcnh bi cng

vicu tin theo tht cho (2). Trong v dtrn, token

trong control circuit ca my M1ctplace c5bi v

cng vicu tinc xl l P1


M hnh trn minh ha nhngcim cbn ca Petri nets.

Transition biu din cc hotng khc nhau ca hthng

Token biu din cc ngun lc sdng.

Trong m hnh v dtrn c 2 kiu ngun lc cbn l

ngun lc vvn chuyn (nhcc pallets) v cc my.

Place v token cng m ttrng thi ca hthng.

Operative part m tqu trnh sn xut lp li ca cc cngvic

Control part m tthtca cc cng vic trn cc my


39/45


nh gi kh nng thc hin

Tnh ton cycle time

Bcu tin l xcnh tt ccc mch trong m hnh

mng li (cc processing circuit v control circuit). Ngoi

ra cn c thm cc mch m cha ccc buffer v control

place cc mch ny gi l cc mch hn hp (mixed

circuit)

M hnh Petri net m t v dtrn c 8 mch:


Xc nh cc mch c bn trong m hnh

1 1 2 2 1 1

2 3 4 4 3 2

3 6 6 5 5 3

( , , , ) ( )

( , , , ) ( )

( , , , ) ( )

p t p t job P

p t p t job P

p t p t job P

=

=

=

4 1 3 3 5 5 1 1

5 2 2 2

6 4 6 6 4 3

( , , , , , ) ( )

( , ) ( )

( , , , ) ( )

c t c t c t M

c t M

c t c t M

=

=

=

P1

P2

P2

P1t1 t2

(M1) (M2)

P3

P4

t3 t4

(M1) (M3)

P6

P5

t5 t6

(M1) (M3)

P3

c1

c5 c3

c2

c6 c4

Processing circuits:

Control circuits:

7 1 3 3 4 4 6 5 5 5 1

8 3 5 6 6 6 4 4 3

( , , , , , , , , , )

( , , , , , , , )

c t p t c t p t c t

c t p t c t p t

=

=

Mixed circuits:


40/45


i vi cc mng li nhchng ta c thddng xcnh

cc circuits, vi s mng li ln ta khng dxcnh mtcch thcng, tuy nhin c cc thut ton c ththc hin

cng vic ny mt cch ddng (Martinez v Silva, 1980).

Gisl cc cng vic sn sng ngoi hthng vang

i c xl (cha c cng vic no hon thnh), v

gisl cc cng vic (chi tit) lun chuyn cng vi pallet,

cng gisl c 3 pallet dngphn phi cho mi cng vic

(chi tit) ca MPS.


Theo (1) transition firing time c cho nhsau:

1

2

3

4

5

6

1

9

2

4

3

2

=

=

=

=

=

=

(n vthi gian)


41/45


P1

P2

P3

P2

P1t1 t2

(M1) (M2)

P3

P4

t3 t4

(M1) (M3)

P6

P5

t5t6

(M1) (M3)

c1

c5c3

c2

c6 c4

M hnh vi 3 pallet

Trng thi

ban u

c m t

nhhnh v

bn.


Bng cycle time ca cc mch

5.566965610C()

22111111M()

11126965610()

87654321

Mixed circuitControl circuitProcessing cirtcuit


42/45


Thi gian chu k:

1ax( ( )) ( ) 10C m C C

= = =

1l mch gii hn, ngha l nng sut bgii hn bi chu ksn xut ca cng vic (chi tit) P1

Do chu ksn xut bao gm 3 kiu cng vic (P1, P2, P3) v tlxl l=1/C = 0.1,

Tng nng sut l:

TH = 3 x 0.1 = 0.3 job/n vthi gian


Nng cao kh nng thc hin ca m hnh

Gista thm mt pallet v phn bcho P1.

Nhvy sc 2 tokens trong mch1 (nhm t hnh

bn)

Cycle time cho mch1l C(1) = 10/2 = 5 n vthi gian

Cycle time ca cc mch cn li khng thayi.

V cycle time ln nht l C = 9 (tngng vi mch5). Mch

5( l mch control M2) trthnh mch gii hn.


43/45


M hnh vi 4 pallet

P1

P2

P3

P2

P1t1 t2

(M1) (M2)

P3

P4

t3t4

(M1) (M3)

P6

P5

t5

t6

(M1) (M3)

c1

c5c3

c2

c6 c4


Kt qu chra rng:

Sthc hin ca hthng phthuc vo sphn bca

cc pallet cho cc kiu cng vic cng nhthtthc hin

trn cc my.

thy riu ny, gista khng thm mt pallet cho

job P1m phn bcho P2hoc P3.

Cycle time ca1vn l 10 v nhvy sthc hin ca hthng khng c sthayi.


44/45


Gisby gita vn thm mt pallet v phn bcho P1

nhng tai thtthc hin ca cng vic trn my M3theotht:

S3= {P3, P2} (thay v S3= {P2, P3} nhban u).

Trong m hnh mng Petri net by gitoken control circuit 6(M3) nmplace c4(thay v c6) (nhhnh vbn)

Trong trng hp ny stoken trong 2 mixed circuit thay

i:

(M(7)=3) v C(7) = 12/3 = 4; C(8) = 11/1 = 11.


P1

P2

P3

P2

P1t1 t2

(M1) (M2)

P3

P4

t3t4

(M1) (M3)

P6

P5

t5 t6

(M1) (M3)

c1

c5c3

c2

c6 c4


45/45


Nhvy8by gitrthnh mch gii hn v cycle time l

C = 11.Nng sut tngng l;

TH = 3/11 = 0.273 job/n vthi gian

Nhvy sthc hin ca hthng phthuc rt nhiu vo s

phn bca cc pallets v thtthc hin ca cc my ch

khng phthuc vo spallet c thdng.

Documents

Bai Giang FMS & CIM - Chuong 3