Document Sample
Introduction Powered By Docstoc
					    Chapter One                                                  Introduction 1

       Lifts are installed into buildings to satisfy the vertical transportation
needs of their occupants and visitors and are necessary by virtue of human
comfort and convenience, or by statutory regulation [1]. In offices and other
commercial building, lifts are installed to aid efficiency by saving occupants
time, and hence money. These financial considerations do not apply for
residential property, quite the opposite money is saved by not providing a
lift, and statutory regulations are framed to ensure suitable lifts are installed
[2]. Generally may be classified to several characteristics. The most
important of a lift is its drive method, with different design principle and
different lift component construction. Classification from this aspect is as
electric lifts & hydraulic lifts [1].
  Electric lift may by:[3]
a- Traction drive,
b- Positive drive, in which chains suspend the lift or ropes driven by means
other than friction (drum drive).
c- Linear induction motor (LIM) drive, where the driving force generated by
the motor is acting readily upon lift car or counterweight.
d- Schindler Mobile: incorporates a self-supporting vertical column structure
and a self-propelled lift car.
Passenger traction drive is recommended in this work.

       The traction is a means of transmitting lifting force to the hoist ropes
of a lift by friction between the grooves in the machine drive sheave and the
hoist ropes. The ropes are simply connected from the car to the
   Chapter One                                                  Introduction 2

counterweight and wrapped over the machine drive sheave in grooves. The
weight of both the car and the counterweight ensure the seating of the ropes
in the groove or, for higher speed lifts, the ropes are double wrapped, i.e.,
pass over the sheave twice [4].
      The main advantage of the traction drive is that if either the car or
counterweight meets the buffers, the drive ceases or there is no danger of the
car being wound into the overhead structure, with very high-rise, however,
over winding of the car may be possible if the counterweight is on its
buffers. The weight of the ropes on the counterweight side may be sufficient
to provide traction to drive the ropes. Other advantage of this method is
cheapness, simplicity, and the fact that standard equipment may be used
irrespective of height of travel [5]. A typical installation of traction drive
passenger lift is shown in Figure (1-1).
       There are a number of different roping systems in existence, the
application of which depends upon the local conditions, particularly upon
the location of the machine, the rated load and rated speed of the car.
   Great attention should be given to the selection of the roping system to
achieve long life of lift ropes, high efficiency of the system and reasonable
power consumption. The machine is usually situated above the hoistway as
the overhead position of the machine facilitates the application of the
simplest roping schemes and the load exerted upon the building structure is
relatively low. With some installations , the machine is located in a
basement position near the bottom of the hoistway . The initial cost is
usually higher in this case [6], and the load imposed on the overhead pulleys
at the top of the hoistway and, thus on the supporting building structure, is
also considerably high. For these reasons, the basement location of the
   Chapter One                                                   Introduction 3

machine should be avoided wherever possible[5]. Schematic diagram of
principal roping system is shown in Figure (1-2).
1-3-1 Suspension Wire Ropes:
1-3-1-1 Selection of Wire Ropes:
     Wire ropes are affected by wear and bending as they operate over
sheave. When selecting a wire rope for a particular service in addition to the
minimum breaking load, the required resistance to abrasion and to bending
fatigue must be considered. Resistance to bending fatigue and resistance to
abrasion require two different types of ropes. Maximum resistance to
bending fatigue is obtained from a flexible rope with small outer wires
whereas to obtain maximum resistance to abrasion a less flexible rope with
larger outer wires is required. The correct selection of a wire rope involves a
compromise between these two characteristics [7].
1-3-1-2 Construction of Wire Ropes (Figure 1-3):
   Lift ropes are either of ordinary (regular) lay Figure (1-4) or of Lang's
lay Figure (1-5). With Lang's lay ropes, the direction of the lay of the strand
is the same as that of the outer wires in the strands while in the ordinary
construction, the direction of the lay of the outer layer of wires in the strands
is opposite to the direction of the lay of the strands in the rope. The
advantage of Lang's lay ropes is a larger contact surface and, consequently,
a lower unit pressure between the wires of particular strands, resulting in a
longer life of the rope. On the other hand, ordinary lay ropes can be handled
more easily, as the tendency to kink and untwist is smaller than with Lang's-
lay ropes [8]. Lift ropes are usually of right – hand lay, which means that the
strands are laid up to the right (clockwise direction when looking at the rope
   Chapter One                                                  Introduction 4

     All ropes have fibers core, impregnated with a special lubricant in order
to reduce friction between the inner wires and extend their life by preserving
them from dampness deterioration, especially when the rope is not in use.
Fiber cores may be made of natural or synthetic material new sisal or
manilla is usually used as natural fiber material, while synthetic fiber cores
are made of polypropylene, polyamide or polyester [8]. Two numbers (A ×
B) represent rope code, the first symbol (A) represents the number of strand
while the second symbol (B), represents number of wires in each strand. The
three principal kinds of ropes most commonly used now a days are as
follows [3]:
 a) Round-Strand Equal Lay 6×19 (12/6+6F/1):
   In this rope, there are six-filler wires with small diameters inserted
between the inner and outer wires in each strand filling interstices between
both wire layers. They improve the contact between the layers and facilitate
the rope to retain its shape. In calculating the rope strength, the filler wires
are considered as not bearing any load. This rope construction is
recommended for use on Vee-groove traction lifts. Due to its larger metallic
area, it possesses greater resistance to crushing and distortion than a rope
type of eight strands. This quality is desirable where groove       walls exert
pressure on the rope [8]. Its cross-section is shown in Figure (1-6).
 b) Round-Strand Equal Lay 8×19 (9/9/1):
   The rope is of the Seale construction and is composed of eight strands. It
is superior to a six – strand rope in several respects, it is more flexible and
fatigue – resistant, it conforms better to the shape of the sheave grooves and
is smoother in running, the contact area between the wires and the grooves is
larger, it sustains a greater number of bending so that its life may be longer.
The rope has less resistance to abrasion, when compared with the equivalent
   Chapter One                                                 Introduction 5

size of 6×19 (9/91) ropes, because the outer wires are of a smaller diameter
[7]. In addition, the breaking load is lower than with the 6×19 rope. This
rope construction is recommended for use on Round – groove installation
[11]. In Figure (1-7), the rope construction is depicted.
c) Round-Strand Equal Lay 6×19 (9/9/1):
   This rope construction is less flexible than the two previous
constructions. Where it is possible to employ sheaves large enough to
prevent premature fatigue of the wires this rope it is recommended for all
installation as large outer wires provide greater wearing area than the 6×19
(12/6+6F/1) and their core being smaller provides a greater resistance to
crushing and distortion than the 8×19 (9/9/1) [8]. A cross – sectional view of
the rope is shown in Figure (1-8).
1-3-2 Traction Sheaves:
    Sheave is the name given to a pulley to which power is applied and is
that part of the lift machine transmitting driving power to the lift ropes [6].
The ratio between the pitch diameter of sheave, and the nominal diameter or
the suspension ropes shall be at least 40 regardless of the number of strands
in the ropes [9]. However where 6×19 (9/9/1) construction ropes are
employed, recommendation of a minimum sheave diameter to nominal rope
diameter ratio of (47) [10]. Moreover, the types of sheave groove are:
a) Vee – groove (Figure 1-9): The type of sheave groove usually employed
is Vee-shaped and includes angle (γ) from (35º to 40º) [9].
    Traction increases when the angle of groove decreases, and so does the
specific pressure and resultant wear of both the grooves and suspension
ropes [12].
b) Round groove -semicircular (Figure 1-10): with the round grooves, the
traction is much lower, so the double wrap drive is most often used,
    Chapter One                                                Introduction 6

particularly, with high – speed lifts [6]. However, this type of groove has a
great advantage in its longer rope life, which is due to lower specific
pressure in the contact area between the rope and the groove. A second
advantage is the lower degree of noise, which is especially noticeable at high
speeds [7].
c) Undercut groove (Figure 1-11): the properties of an undercut groove are
intermediate between those of a Vee-groove and a round groove [6]. The
angle of the undercutting (β) should be preferably under (90º) and must not
be greater than (106º) [10].
1-3-3 Diverter Pulleys (Figure 1-12):
   These are idle pulleys used to change the direction of ropes, these pulleys
are of similar construction to the sheave [6], the minimum ratio between
diameter of the diverting pulleys and the nominal diameter of the rope is
specified equal to (30) [13]. Generally, the diverting pulley is located in the
machine room. However, if a long span between the centre lines of the car
and counterweight is required, it is mounted at the top of the hoistway to
reduce the loss of angle of wrap [4].
Traction sheaves are usually made of grey cast iron of Brinell hardness
number (220 to 230) in the area of sheave grooves , pulleys are made of
either grey cast iron or cast steel [3].
    The lift braking system, which must be set in operation automatically in
the event of loss of power supply and/or loss of supply to the control
circuits, must be provided with an electromechanical friction brake [3]. This
brake must be capable of stopping the machine when the car is with 125 %
of rated speed and must hold the system at least afterwards [9].
   Chapter One                                                 Introduction 7

   Retraction must not be in excess of that resulting from the operation of
the safety gear or stopping the car on its buffers [10]. The brake is usually
mounted on the high-speed shaft (motor shaft), because the braking torque is
relatively small, provided that the shaft is coupled to the sheave by direct
mechanical means. The brake must be applied by compression spring or by
gravity. It can be released either electromagnetically or electro hydraulically
[6]. When the machine is fitted with a manual emergency operating device,
the brake must be so designed as to enable releasing by hand and effort must
be exerted to keep the brake open [1].
Type of Brakes [32]:
a) Drum brakes (Figure 1-13): The most common form of drum brake is
electromagnetic brake, consisting of a spring assembly, two brake shoes
with lining and a magnet assembly. The release of the brake is effected by
energizing the solenoids; when de -energized, the brake shoes grip the brake
drum under the influence of the compression spring and induce the braking
and torque . Drum brakes are mostly external contracting type. However,
large dimensional gearless machines may have internal expanding – type
b) Disc brakes: A disc brake system currently contains a disc, brake caliper
with actuate, power pack and controller. On request, the system may be
equipped with a monitoring device that allows the brake to be integrated into
the control system of the lift by supplying pad replacement and adjustment
   Chapter One                                                 Introduction 8

a) Geared Traction Machines (Figure 1-14): In a traction machine the
power from the motor is transmitted to the drive sheave through reduction
gears. Geared machines are applied for lower speeds. Spur gears were used
occasionally in the past, but with the advancement of design and production
techniques, worm gearing has become the accepted standard for
conventional geared lift machines Figure (1-15). Helical gears are expected
to be used for speed in excess of 2.5 m/s while for lower speeds ; worm
gearing will remain the standard. A number of machines equipped with
planetary gearing have appeared in the market [3].
   The machines are normally located overhead, directly over the hoistway,
but can be mounted to the side and below. Typically, AC motors are used for
geared traction machines [5].
b) Gearless Traction Machines: There is no gearing between the rotor and
the traction sheaves. Gearless traction machines are used for high-speed
passenger lift applications (2 – 10) m/s , the machine should be located over
the hoistway in overhead machine room. A typical gearless traction machine
employs double – wrap roping. The gearless machine is equipped with a
special low – speed DC motors; the progress in the development of AC
speed regulation systems enabled the AC gearless machines to be introduced
in the lift market [3]. A gearless machine is shown in Figure (1-16).
1-6 OVERSPEED GOVERNOR (Figure 1-17):
    A schematic arrangement of the overspeed governor system is shown in
Figure (1-18). The governor is provided with the governor rope(1), passing
round the governor pulley (2), down to a tensioning pulley(3)in the pit and
back again to the governor pulley. The car to which the governor rope is
   Chapter One                                                  Introduction 9

attached at point (4) drives the system. When the tripping speed of the
governor rope is achieved, the governor stops the rope. Since the car
continues in a downward motion, the tension in the governor rope is
increased; exceeding the value necessary to engage the safety gear and,
consequently, the safety gear is set in operation. The governor is usually
located in the machine room [5].

   Safety gear is invariably fitted to lift cars, with the object of preventing
any uncontrolled movement of the car in a downward direction, by clamping
the car to its guides should the lifting ropes break or the speed of the car, in
descent, exceeds a certain predetermined value. The gear is sometimes
arranged to operate and clamp the car to its guides if the lifting ropes stretch
unequally. Car is always fitted under the car framing Figure (1-19), as cases
have been recorded where the car has broken away from the safety gear
when the latter has been fitted to the top of the car. Counterweights are
sometimes provided with safety equipment in addition to that installed under
the car, in order to stop an over-speeding ascending car and this is invariably
the practice when the lift does not extend to the basement, and occupied
spaces are under the well [4]. Car safety gears are classified based on their
performance characteristics, they are as follows:
a) Instantaneous type: This exerts a rapidly increasing pressure on the
guide rails during the stopping period. The stopping time and distance are
very short; no flexible medium is introduced limit to the retarding force and
the stopping distance [6]. The type can be employed for rated speeds not
exceeding 0.63 m/s [14].
   Chapter One                                                 Introduction 10

b) Instantaneous type with buffered effect: incorporates an elastic system
of either the energy accumulation type with buffered return movement or
the energy dissipation type [3]. It is usually represented by one or more oil
buffers interposed between the lower members of the car frame and a safety
plank applied on the guide rails, and develops retarding forces during the
compression stroke of the buffers [6]. The stopping distance is equal to the
effective stroke of the buffers. They may be used for rated speeds up to 1
m/s [14].
 c) Progressive type: applies limited pressure on the guide rails during the
stopping interval. After the safety gear is fully applied, retarding forces are
reasonably uniform. The stopping time and distance are related to the mass
of the movable system being stopped and speed at which the application of
the safety gear is initiated [6]. This type must be used for rated speed in
excess of 1 m/s [14].
  The object of the counterweight is to provide traction and to balance the
weight of the car plus a predetermined proportion, usually (40 to 50) per
cent, of the maximum carload, and thereby to reduce the size of the motor
[15]. The most usual construction consists of cast-iron sections firmly
secured against movement by at least two steel tie rods having lock nuts or
split pins at each end, and passing through each section, as shown in Figure
(1-20). In addition to tie rods, the sections are sometimes mounted in a steel
framework. For heavy loads, the sections are sometimes weighted with lead
to reduce the size of the counterweight [6].
    Chapter One                                                Introduction 11

    Guide rails are manufactured from a structural steel having a tensile
strength of not less than (370 N/mm2). According to EN81, guide rails must
be made of cold drawn steel or the rubbing surfaces must be machined if the
rated speed exceeds (0.4 m/s), and progressive safety gears are employed
regardless of the speed [38]. The Sectional view of machined guide rail is
shown in Figure (1-21), and Figure (1-22) explains the movement of the car
and counterweight on the guide rail.
  A device designed to stop a descending car or counterweight beyond its
normal limit of travel by storing or by absorbing and dissipating the kinetic
energy of the car or counterweight . Lifts must be equipped with buffers
located in the pit at the bottom limit of travel [3].
There are two principal types of buffers in existence:
a) Energy accumulation type: A buffer where the kinetic energy of motion
is stored in the gradual compression of a spring provides a progressive
retarding force. Spring buffer is shown in Figure (1-23).
 b) Energy dissipation type: A buffer where the kinetic energy of motion is
 dissipated, by converting the energy into heat applying a constant force of
 retardation. Oil buffers can be designed to induce a constant force during
 the stopping action, resulting in constant retardation [3]. Sectional view of
 oil buffer is shown in Figure (1-24).
       Chapter One                                                 Introduction 12

1-11 Objective:

         The aim of this study is to collect the equations related with the

design of the elevators parts especially people elevators type traction drive,

and the European code EN81 was adapted in this process because it is one of

the popular type in Iraq and the region. The equations were used to built-up

a Passenger Lifts Design Package (PLDP) program using Visual Basic

Language to develop the best method for designing. The desired engineering

parts, the equation related with the design and manufacturing of the

elevators parts were derived to permit flexibility to change and replace parts,

which sometimes do not be compatible with the related equations because of

  changes of the manufacturing material or change in the shape of the parts.

          Selected local case studies were chosen for check and verifying the

PLDP program. Some of the important parts were selected in the checking

process, especially those related to human safety, such as safety gears, rope

Chapter One                                              Introduction 13

              Fig. (1-1) A typical passenger lift [16]
 Chapter One                                              Introduction 14

                   Fig. (1-2)-Roping systems [16]

 Fig. (1-4)                Fig. (1-3)               Fig. (1-5)
Ordinary (regular) lay [16] Construction of rope [16]     Lang lay [16]
                   Chapter One                                             Introduction 15

                    Fig. (1-6) Round-Strand equal
                        lay 6 X 19 (12/6+6F/1)            Fig. (1-7) Round-Strand equal
                          Suspension rope[17]              lay 8 X 19 (9/9/1) Suspension
                                                                      rope [17]

Fig. (1-8) Round-Strand equal
                              Fig. (1-9) Vee-groove of
 lay 6 X 19 (9/9/1) Suspension
                                traction sheave [17]
            rope [17]

                       Fig. (1-10) Round (semicircular)    Fig. (1-11) Undercut groove of
                        groove of traction sheave [17]           traction sheave [17]
Chapter One                                            Introduction 16

Fig. (1-12) Diverting pulley [16]
                                      Fig. (1-13) Drum Brake [18]

          Fig. (1-14)               Fig. (1-15) A typical under driven
    Geared lift machine [16]                 worm gear [16]
Chapter One                                                 Introduction 17

     Fig. (1-16) Gearless
    traction machine [16]
                                      Fig. (1-17) Overspeed governor [16]

      Fig. (1-18) Arrangement of
     overspeed governor System:
 1.governor rope; 2.governorpulley;
 3. Tensioning pulley; 4.Attachment                Fig. (1-19) Safety gear
               point [16]                            under car frame [16]
Chapter One                                    Introduction 18

              Fig. (1-20) Counterweight [16]

                      Fig. (1-21)
                Section of guide rail [4]
Chapter One                                               Introduction 19

        Fig. (1-22) car and Counterweight on the guide rail [16]

   Fig. (1-23) spring buffer [16]        Fig. (1-24) oil buffer [16]

Shared By: