Lift Controller

8/13/2019 Lift Controller

1/7

LIFT CONTROLLERSubmitted by

Sandesh.N.S,

1st Mtech, CEDT,

S.R.NO 461!"1!41!##4$.

%&'b(em) Design a lift controller for 2 lifts with the following

specifications.

1. If one goes up the other goes down.

*. Call a lift.

#. Select to stop at a floor.

4. Open time for the door.

". Emergency exit.

+LOC DI-R-M OF T/E LIFT CONTROLLER)

Ca((012)3

C'unt01#)3

Se(ect012)3

C'unt0*#)3

Ca((0*2)3

M'de01

Se(ect0*2)3

M'de0*

Eme&ency0e5it01 Oen01

Eme&ency0e5it0* Oen0*

C('c7

Sta&t01

Reset

Sta&t0*

LIFT

CONTROLLER


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De8inin the inut sina(s) Separate call and select buttons are used for

each lift. Each floor has has two call buttons , which is specific for each lift.

ift!" responds only to select!" and call!" buttons and the same assumption

is made for lift!2 also. #ut the mo$ements of the lifts is restricted by the fact

that both ha$e to mo$e in the opposite direction.%ere it is assumed that there

are "& floors in the building. %ence to represent each floor we re'uire ( bits.

De8inin the 'utut sina(s)

C'unt ) )sed to indicate the position of the lift i.e the floor number.

M'de ) *his is used to indicate the direction of the lifts.

1 + Indicates the lift is mo$ing up.

+ Indicates the lift is mo$ing down.Oen-

1+ Indicates that the door is open.

+ Indicates the door is closed.

Sta&t ) *his signal maes the lift mo$e from its current position or stop the

lift at a floor.

1 9: /o$e the lift

9: Stop the lift.

-&'ach used in desinin the c'nt&'((e& ) 0s the specification demands

that both the lifts should mo$e in the opposite direction, the logic

implemented uses toggling of the modes of the 2 lifts. *o mae this more

clear let us see an e5am(e .

0ssume that both the lifts are starting from the ground floor. One lift is

assigned mode up and the other mode down.

/ode down /ode up

1nd floor 1nd floor

ift!2 ift!"


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ets say that a person from thfloor calls the lift!" . 0fter some time another

person calls lift!2 from the "st floor before the lift!" reaches the th floor.

3ow lift!2 cannot go up as lift!" is already mo$ing up. Only when the

lift!" comes to idle state4i.e it has no more calls from the floors abo$e it5

lift!2 can go up in response to the caller at "stfloor.

0t this point the modes of the 2 lifts ha$e to be changed.

1nd floor thfloor

0fter the modes of the lifts ha$e been changed lift!2 can go to the first

floor.

"st floor thfloor

-ssumti'ns made-

". *o chec whether a lift has reached a particular floor or not, a position

sensor is used. *his can be simulated by generating an interrupt when a lift

reaches a particular floor. *o generate the interrupt it is assumed that the

time the lift taes to tra$el between two successi$e floors is a constantonce the lift starts mo$ing.

2. 6hen the lift reaches a particular floor an open signal is asserted high to

open the door. If the lift has no more callers the door remains open,

otherwise the door closes after a fixed amount of time. *he lift can mo$e

only when the door is closed.

ift!2 ift!"

ift!2 ift!"


4/7

Inte&na( b('c7 dia&am '8 the (i8t c'nt&'((e&)

&eset0se(012)3 se(012)3 &eset0se(012)3

&eset0ca((2)3 ca(012)3 &eset0ca((012)3

se(ect012)3 c'unt01#)3 'en01

ca((012)3 int&01 'en0id(e1

d''&0c('sed01 id(e0st1'en01

ca(0se(01 sta&t01

m'de01 ca(0se(0* cen01cen01

m'de01

c(7 &eset

c(7 &eset

&eset0se(0*2)3 ca(0se(0# m'de0*

&eset0ca((0*2)3 ca(0se(04 cen0*

se(ect0*2)3 int&0* sta&t0*

ca((0*2)3 d''&0c('sed0* 'en0*

'en0* sel!247-&5 'en0id(e*

m'de0* cal!247-&5 id(e0st*

cen0* c'unt0*2)3 &eset0se(0*2)3

&eset0ca((0*2)3

c(7 &eset

c(7 &eset

L'ic F'&

ene&atin

c'nt&'( sina(s

F'& FSM01 FSM01

L'ic F'&

ene&atin

c'nt&'( sina(s

F'& FSM0*FSM0*


5/7

Desc&iti'n '8 the inte&na( c'nt&'( sina(s used)

M'de01,M'de0*) *his signal indicates whether the lift is mo$ing up or

down for the 2 lifts.

Int&01,Int&0*- 1enerates an interrupt when the lift reaches a particular

floor.

Se(01,Se(0*,Ca(01,Ca(0*- *hese are the flip flop outputs for the call and

select switches.

Ca(0se(01,Ca(0se(0#- 0 high on this signal indicates that there is a re'uest

for the lift from the floors abo$e the current floor .*he re'uest may be due to

call or select buttons.

Ca(0se(0*,Ca(0se(04- 0 high on this signal indicates that there is a re'uest

for the lift from the floors below the current floor. *he re'uest may be due to

call or select buttons .

Reset0se( -6hen a lift reaches a particular floor this signal goes high after

the lift has ser$iced the select re'uest. *his resets the select flipflop for that

floor .*his ascertains that any re'uest coming after that is recogni8ed by the

lift.

Reset0ca(( -6hen a lift reaches a particular floor this signal goes high after

the lift has ser$iced the call re'uest. *his resets the call flipflop for that

floor .*his ascertains that any re'uest coming after that is recogni8ed by the

lift.

D''&0c('sed) 1oes high when the door is closed.

Oen,Oen0id(e) *he open signal goes high when the lift stops at a

intermediate floor and has to further ser$ice re'uests, whereas the the

open!idle signal goes high when the lift stops at a particular floor and hasno more re'uests.*hese to separate signals are needed as the logic to to close

the door at these two states are different.

Cen- *his enables the counter when the lift starts mo$ing to eep trac of

the current position of the lift.


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State machine 8'& the (i8t c'nt&'((e&) *he state machine for one of the lift

is shown below. *he state machine for the other lift is similar e5cetthat

u'n &eset the initia( state is m'de d';n.

&eset

if tog!2+"

M'de9d';n M'de9u

If cal!sel!2+" If tog!"+" If cal!sel!"+"

if 99 99 if em!exit+" door!closed+" door!closed+" em !exit +"

If4 sel4cnt5 or If4 sel4cnt5 or

Cal4cnt5 5 +" If cal!sel!"+" cal4cnt5 5 +"

intr!"+" 9 door!closed+" 9

If cal!sel!2+" 9 intr!"+" if

if door!closed +" cal!sel!"+&

cal!sel!2+&

Desc&iti'n '8 the states)*he important part of the state diagram is thetoggling of the modes between idle!" and idle!2 states.*he lift can change

states only in these states.

Id(e0*Id(e01

M'


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M'de u

Id(e1 ) %ere the lift is waiting for a re'uest from the floors abo$e the current

floor.)pon a re'uest it waits for the door to be closed and it goes to the

mo$ing state. If there is no re'uest and the other lift has a re'uest from the

floors abo$e then it goes to the idle!2 state where the mode of the lift is

down. *his is re'uired as the 2 lifts must operate in opposite modes. *he lift

can also go to idle!2 state when there is a re'uest from the floors below the

current floor, wherin the lift has to change the direction .It can start mo$ing

down only when the other lift is not mo$ing downwards and is in the idle

state.

M'

Lift Controller

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