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INTRODUCTION

Elevators are used to move loads from one height to another without disturbing the load itself.

The prime mover of an elevator can be given by an electric motor. Suspension systems driven

by electric motors are the ideal choice for applications having minimal space and great heights

because these systems do not require infrastructure to be built beneath the floor of the elevator

and are limited in height only by the ability of the electric drive to overcome static forces such

as gravity and dynamic forces such as friction and air drag.

The physical model of elevator is analysed and converted the physical model into

mathematical equations to find the transfer function. The purpose to find the transfer function

is that we can see the behaviour of system theoretically using software and design the

physical model accordingly. We can compare the theoretical results and practical results to

improve response of elevator for the comfort passengers.

Electronic control systems (we have used) for control of lift are composed of hardware

components. Using Electronic a control system to dictate the position of an elevators electric

drive increases the accuracy and precision with which the elevator system responds to position

commands. DC motor is as simple as changing the magnitude of voltage applied to the motors

armature circuit; to make the motor operate in the opposite direction the polarity of the supply

voltage needs to only be reversed.. In our system, as box moves upward and reaching its top

position it stops automatically by touching limiting switch then polarity reverses of motor to

move lift downward and it stops again following same mechanism.

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Mathematical modelling of elevator

Motors Electrical Equations

The elevator is driven by a DC motor. The equivalent circuit of the DC motor is confined to the

armature circuit which is illustrated as

Equivalent circuit of armature of DC motor

The motor voltage equation of the armature circuit is

= . () + . () . . ()

= . () is the electro-motive force developed in the armatures winding

K is the motor constant

() is the angular speed of the motors shaft

is the voltage difference between the armature terminals

is the resistance of the armature circuit

() is the current form armature

The electro-magnetic torque = . () is the torque developed by the motor

Mechanical Systems Motion Equations

The motion equation of the entire system from the motors perspective is

() = . () () ()

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Where:

is the motors moment of inertia

is the friction coefficient of the motor

is load torque placed on motors shaft

The load torque that is placed on the drive pulley which is mounted on the motors shaft is

expressed as

= . ()

Where:

is the radius of the drive pulley

is the force exerted on the drive pulley

If the elevator car is moving upwards the load force is defined by Equation

=1

2[. +

] ()

Where:

is the gravitational constant

is the mass of the car

is the linear speed of the car

() ()

= [1

2(. +

)] . ()

()

() = . () () 1

2[. +

]

= .

() = . () () 1

2.

1

2

2

()

4

() + 1

4

2() = . () () 2

= . () () 2 . . ()

= + 1

42.

2 = 1

2. ()

,

= . () + . () . ()

= . () () 2 . . ()

() () = ()

()

() = [ ()

] () 2

. () = . 2() () 2

. . () = . ()[2 + . ] 2

() .

2 + . =

2 + . ()

2 + . (2)

1(). = 2 () 1. 2 . . ()

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1 =

2 + .

2 =

2 + .

()

1. . (). = 2() () 1

2

. [1. + 1]()

()= 2

()

()

1()

2

As () =1

( )

So

. [1. + 1]()

()= 2

()

() . 1. 2

()

()=

2 1. 21. + 1

. ()

As = . ()

() = ()

()

()

()=

(2 1. )

1. . + 1 . ()

() = . ()

()

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()

()=

(2 1 . )

(1. + 1) ()

Equation () is transfer function for position of the car

Conclusion from transfer function:

As we have found the transfer function for Speed & Position of Elevator by putting the values

of unknown parameters (which can be the parameters of a particular system), We can see the

behaviour of our system that is settling time, rise time, steady state error, percentage

overshoot and peak time.

We can get the response as we desire by changing the values of parameters.

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Different Components used in Lift Control Mechanism

Toggle Switch

Limiting Switch

Diode

Power Supply

Power Window Motor

Bread board

LED

Description of Components

Toggle Switch:-

Toggle Switches have a to and fro switching movement. The most familiar form of switch

is a manually operated electromechanical device with one or more sets of electrical

contacts, which are connected to external circuits. Each set of contacts can be in one of two

states: either "closed" meaning the contacts are touching and electricity can flow between

them, or "open", meaning the contacts are separated and the switch is non-conducting. The

mechanism actuating the transition between these two states (open or closed) can be either

a "toggle" (flip switch for continuous "on" or "off") or "momentary" (push-for "on" or push-

for "off") type.

Purpose of Toggle Switch in our project is to change the polarity of motor that is when

it is pressed at one side it performs the switching action and give polarity to the motor

so that it rotates clockwise. At centre, toggle switch do not any current to the motor

and when pressed at an other side the motor rotates anticlockwise.

Toggle Switch

http://en.wikipedia.org/wiki/Electromechanicalhttp://en.wikipedia.org/wiki/Electrical_contactshttp://en.wikipedia.org/wiki/Electrical_contacts

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Limit Switch:-

A limit switch is an electromechanical device that consists of an actuator mechanically linked

to a set of contacts. When an object comes into contact with the actuator, the device operates

the contacts to make or break an electrical connection. As its name suggests, a limit

switch regulates the operations of machines that are equipped with moving parts connected to

a switching action mechanism. A wide range of industrial machinery uses limit switches to

control the movement of devices performing on a production line, but these switches are also

found in non-industrial applications, such as electric motor operation and garage door opener

units. The switch also deactivates the motor as the door closes, preventing it from being pushed

into the ground. A limit switch is typically composed of a series of electrical contacts coupled

to an actuator that controls the mechanical device responsible for on and off functions.

.

Diode:-

In electronics, a diode is a two-terminal electronic component . it has low (ideally

zero) resistance to current in one direction, and high (ideally infinite) resistance in the other.

A semiconductor diode, the most common type today, is a crystalline piece

of semiconductor material with a pn junction connected to two electrical terminals.

The most common function of a diode is to allow an electric current to pass in one direction

(called the diode's forward direction), while blocking current in the opposite direction

http://www.thomasnet.com/products/limit-switches-81912800-1.html?WTZO=NTKG+Body+Linkhttp://www.thomasnet.com/products/limit-switches-81912800-1.html?WTZO=NTKG+Body+Linkhttp://en.wikipedia.org/wiki/Electronicshttp://en.wikipedia.org/wiki/Terminal_(electronics)http://en.wikipedia.org/wiki/Electronic_componenthttp://en.wikipedia.org/wiki/Electrical_resistance_and_conductancehttp://en.wikipedia.org/wiki/Electric_currenthttp://en.wikipedia.org/wiki/Infinityhttp://en.wikipedia.org/wiki/Crystallinehttp://en.wikipedia.org/wiki/Semiconductorhttp://en.wikipedia.org/wiki/P%E2%80%93n_junction

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(the reverse direction).. This unidirectional behaviour is called rectification, and is used to

convert alternating current to direct current,

The function of diode on our project is that to allow the current in one direction (close

switch) and block the current in other direction (open switch) for control mechanism of

Lift.

Diode Symbol Diode

Power Supply:-

A power supply unit (PSU) converts mains AC to low-voltage regulated DC power.

An AC powered unregulated power supply usually uses a transformer to convert the voltage

from the wall outlet (mains) to a different, nowadays usually lower, voltage. If it is used to

produce DC, a rectifier is used to convert alternating voltage to a pulsating direct voltage,

followed by a filter, comprising one or more capacitors, resistors, and sometimes inductors, to

filter out (smooth) most of the pulsation. For purposes such as charging batteries the ripple is

not a problem, and the simplest unregulated mains-powered DC power supply circuit consists

of a transformer driving a single diode in series with a resistor.

The power window motor we have used required 12V input DC voltage. For this purpose

we used power supply which convert 220V AC to 12V DC.

Power Supply

http://en.wikipedia.org/wiki/Rectification_(electricity)http://en.wikipedia.org/wiki/Alternating_currenthttp://en.wikipedia.org/wiki/Direct_currenthttp://en.wikipedia.org/wiki/Mains_electricityhttp://en.wikipedia.org/wiki/DC_powerhttp://en.wikipedia.org/wiki/Alternating_currenthttp://en.wikipedia.org/wiki/Transformerhttp://en.wikipedia.org/wiki/Direct_currenthttp://en.wikipedia.org/wiki/Rectifierhttp://en.wikipedia.org/wiki/Electronic_filterhttp://en.wikipedia.org/wiki/Capacitorhttp://en.wikipedia.org/wiki/Resistorhttp://en.wikipedia.org/wiki/Inductorhttp://en.wikipedia.org/wiki/Diodehttp://en.wikipedia.org/wiki/Resistor

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Power Window Motor:-

Power window motor is DC motor which converts electrical energy into mechanical energy.

The power window motor is used in vehicle, usually in car windows to lift the window glass

up and down in vehicles. To operate this motor (to move the window glass), we press an

automated button then the motor shaft rotates in clockwise direction. The glass is attached to

shaft of the motor and as motor rotates clockwise the glass moves upward. When we press

the button again, the motor rotates anticlockwise and glass moves downward. Same

mechanism is used in the upward and downward movement of the cabin of the lift. When

toggle switch is pressed at one side, motor rotates clockwise and when toggle switch is

pressed towards other direction, the polarity of the motor changes and it rotates in

anticlockwise direction.

Bread Board:-

A breadboard is usually a construction base for prototyping of electronics. Because the solder

less breadboard for electronics does not require soldering, it is reusable. This makes it easy to

use for creating temporary prototypes and experimenting with circuit design.

http://en.wikipedia.org/wiki/Prototypehttp://en.wikipedia.org/wiki/Electronic_circuithttp://en.wikipedia.org/wiki/Soldering

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Light-Emitting Diode (LED):-

A light-emitting diode (LED) is a two-lead semiconductor light source that resembles a basic

PN-junction diode, except that an LED also emits light. Light emitting diode emits light when

current is passed through the LED. The maximum voltage it can bear is 5V

http://en.wikipedia.org/wiki/Semiconductorhttp://en.wikipedia.org/wiki/Pn-junction

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Control Mechanism of lift:

As we seen that the purpose of the toggle switch is to change the polarity of the motor, so for

upward movement of the lift one positive end of the wire of the motor is connected to the

positive end of the toggle switch and negative end is connected to limit switch. The other end

of limit switch is connected to positive end of diode. The negative end of the diode is

connected to the negative end of the toggle switch.

When toggle switch is pressed at one side, the current flow from toggle switch through limit

switch and diode. As the current flow through motor, it will rotate clockwise and life move

upward, as the life strike to the limit switch, the circuit will break and motor will which will

result in stopping of cabin.

For downward movement of the lift, the positive end of the motor is connected to the positive

end of the toggle switch as above and the negative end of the motor is connected to an other

limit switch which is attached at the elevator base. The other end of this limit switch is

connected to the negative end of the diode and the positive end of the diode is connected to

negative end of toggle switch. But important point is that as the toggle switch is pressed in

the other direction, it will change the polarity automatically. Now the positive end of motor

will become negative and negative end of motor will become positive. The motor will move

downward, as it strikes the limit switch, the circuit will break and motor will stop. As the

circuit break motor will stop which will result in stopping of cabin.

As the cabin strike the limit switch, the circuit will break and current cannot flow through an

other path because in this path a diode is connected at reverse polarity which will block the

current.

And other addition is made in the circuit, 2 LEDs are connected with reverse polarities to

each other parallel to the motor. As LEDs conduct in only one direction so when motor

move upward one LED will be ON and when motor moves downward other LED will be ON.

Two resistances are connected in series and parallel to each LED to limit the value of voltage

and current across LED. As it can bear 5V maximum voltage and we have used a 12V power

supply as shown in the circuit:

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Conclusion:

The mathematical modelling has been done successfully to find the transfer function of the

lift. The transfer function helps us to see the response of lift and selecting the values of

different parameters for comfort of passengers. Physical model has been prepared

successfully and motion of motor and hence cabin is controlled as we desired. Different

components have been used for control mechanism.

Bibliography:

www.wikipedia.com

www.fordthesis.com