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1)Introduction
๏ In roped elevators, the car is raised and lowered by traction steel ropes rather than pushed from below. ๏ The ropes are attached to the elevator car, and looped around a sheave. A sheave is just a pulley with grooves around the circumference. The sheave grips the hoist ropes, so when you rotate the sheave, the ropes move too. ๏ The sheave is connected to an electric motor. When the motor turns one way, the sheave raises the elevator. When the motor turns the other way, the sheave lowers the elevator. Typically, the sheave, the motor and the control system are all housed in a machine room above the elevator shaft. ๏ The ropes that lift the car are also connected to a counterweight, which hangs on the other side of the sheave. The purpose of this balance is to conserve energy. With equal loads on each side of the sheave, it only takes a little bit of force to tip the balance one way or the other. ๏ Both the elevator car and the counterweight ride on guide rails along the sides of the elevator shaft.
2) Need
The basic need of elevator is to move people between floors of building.
3) Specifications
๏ Maximum height elevator can travel =88ft=26.8m ๏ Maximum no of stops = ๏ Maximum persons the car can carry= ๏ Height of car=8ft ๏ Top of the car is a square. each side has length=4ft
4) Sketch and free body diagrams
Figure 1: sketch of rope elevator
4.1.2 Free body diagram of sheeve
Figure 3: FBD of sheeve
4.1.3Free body diagram of motor
Figure 4: FBD of motor
4.1.4Free body diagram of shaft
Figure 5: FBD of shaft
4.1.5Free body diagram of drum
=1519.14N
6) SELECTION OF ROPE
We have to select rope according to following criteria.
Load lifted by the rope=W=5.317KN
Depth=26.
Time =t=10sec
Procedure
Speed of the cabin=v=s/t=2.6 m/s
From table
Table 1: steel wire suspension ropes for lift, elevators and hoists.
We find that steel wire suspension ropes for elevators is of two types i.e. 6ร19 and 8ร19.let we take 8ร19. from table we take factor of safety 5.since design load is calculated by taking a factor of safety 2 to 2.5 times greater than F.O.S given in table so we take F.O.S
design load for rope=53170N From table 20.7 we find that tensile strength of 8ร19 rope is 1300MPa is equating this tensile strength to design load.
d=11mm
Table 2 : diameter of wire and wire rope
Area of rope=
=42.
from table 20.7 we find that weight of rope.
w= w= 4.1140N
From table 20.12 diameters of sleeve and drum may be taken 21 to 31 times the diameter of rope. So D =28d=308mm
Table 3:sheave diameters for wire ropes
Where k=1 for full depth teeth
=20 for full depth
7.2 Diametrical pitch
7.3 Module
7.4 Circular pitch
=1.54in
7.5 Tooth thickness
=.77in
7.6 Addendum(a) and dedendum(b)
=.228in
=.2857in
7.7 Outer diameter
=(4.372+2)*.228=1.45in
8) Design of shaft
We have to design shaft form the following criteria.
Power transmitted by the shaft=P=27.5 kw
Diameter of gear=1.45in
Take shear stress =60N/mm^2 this is for steel
Pressure angle of gear= =
8.1 Torque to be transmitted by shaft is given as
=875N.m
8.2 Transmitted force
9) DESIGN OF SPRING
We have to design spring according to following data.
Variation of load=2177 To 5317.2 N
Spring index=C=D/d=
Modulus of rigidity=G=70 MPa
Shear stress= =350 Mpa
9.1 We know twisting moment on spring
D/
AS
D=6d 6d/ 3d
9.2 Also we know that twisting moment
By comparing
3d=
d=15mm
Mean diameter of spring coil =D=90mm
outer diameter of spring coil=D+d=105mm
inner diameter of coil=D-d=75mm
Number of turns of coil is calculated by
n=
10) Considerations
- Elevators also have electromagnetic brakes that engage when the car comes to a stop.
