Elevator Mechanical Design Lubomir Janovsky Pdf

[Malcolm Lozada]

Thisthird edition of Elevator Mechanical Design benefits from a logical and clear arrangement of the topics and many worked examples. The author describes how to achieve the mechanical aspects of the design of an electric elevator, as well as discussing why the designs are implemented in a particular way. The principles and concepts of all the mechanical components of an elevator are discussed in detail, supported wherever necessary by mathematical analysis, figures and examples. A full description and comparison of international standards is also included.

Readership: Designers, manufacturers, operators, maintenance management and safety personnel, electrical, mechanical, electromechanical, transportation and vertical transportation engineers, passenger control operators in the elevator industry, researchers and students of transportation science and architects and building service engineers.

Chapters include:Definition of the mechanical system and component partsSuspension of car and counterweightTypes of driveElevator MachinesBrakesCounterweightGuiding the car and counterweightSafety GearBuffersCar FrameDoors and door operatorsElevator hoistway and machine roomClick here to view the Table of Contents and Foreword.

Also available in a digital edition.

Hardcover 401 Pages 3 lbs.

Lubomir Janovsky was a Professor at the Faculty of Mechanical Engineering, Technical University of Prague. An elevator/escalator consultant and expert witness, he has been chairman or member of various prototype, technical and standard draft committees. The author has written numerous books and papers on vertical transportation and materials handling, published in many countries.

In order to do this, the elevetor turns electrical powerinto mechanical (rotational) power. The brake of the elevator must be designed in order toguarantee safety during normal day use. The brake must also be able to engage in extremecases in which the elevator cable is broken or otherunforeseen circumstances arise. In addition, the elevator must pick up and drop offpassengers as efficiently as possible. If a collection of elevators is used, a complexcontroller usually controls them.

The elevator must fit within the given space requirements of the building. It must bemade large enough to deal with the normal daily traffic and to move the necessary objectswithin the building. It cannot be made too large and, therefore, affect the structure ofthe building itself. Possible restrictions on the weight carried within the elevator maybe determined from the size of the motor and the other components within the elevatorsystem. This weight limit must be large enough to handle daily usage.

A roping system is used to attach the motor/gear reducer, the elevator car and thecounter weight. There are many different kinds of arrangements that can be used. In onepossible arrangement, such as shown in Figure 2, both ends of the elevator rope areanchored to the overhead beam. Both the elevator car and the counter weight are attachedto free moving pulleys. The traction drive is attached to a stationary pulley.

The traction drive is the method of converting the input mechanical power (in this casethe turning of a shaft) into useable mechanical power in the system (the vertical movementof the elevator). The friction between the ropes and the sheave grooves, which are cut onthe pulley, initiates the traction force between the traction drive and the rope.

When the traction drive is rotated power is transferred from the traction drive to theelevator car and counter weight. Power is only needed to move the unbalanced load betweenthe elevator and the counterweight.

An elevator's function is to convert the initial electrical power, which runs themotor, into mechanical power, which can be used by the system. The elevator is composed ofa motor and, most commonly, a worm gear reducer system. A worm gear system is made up of aworm gear, typically called the worm, and a larger round gear, typically called the wormgear. These two gears which have rotational axes perpendicular to each other, not onlydecrease the rotational speed of the traction pulley (1), but also change the plane ofrotation. By decreasing the rotation speed, with the use of a gear reducer, we are alsoincreasing the output torque, therefore, having the ability to lift larger objects for agiven pulley diameter. A worm gear is chosen over other types of gearing possibilitiesbecause of its compactness and its ability to withstand higher shock loads. It is alsoeasily attached to the motor shaft, sometimes through use of a coupling. The gearreduction ratios typically vary between 12:1 and 30:1.

The motor component of the elevator machine can be either a DC motor or an AC motor. ADC motor had a good starting torque and ease of speed control. An AC motor is moreregularly used because of its ruggedness and simplicity. A motor is chosen depending ondesign intent for the elevator. Power required to start the car in motion is equal to thepower to overcome static, or stationary friction, and to accelerate the mass from rest tofull speed. Considerations that must be included in the choice of an acceptable motor aregood speed regulation and good starting torque. In addition, heating ofvarious electrical components in continuous service should not be excessive.

The most common elevator brake is made up of a compressive spring assembly, brake shoeswith linings, and a solenoid assembly. When the solenoid is not energized, the springforces the brake shoes to grip the brake drum and induce a braking torque. The magnet canexert a horizontal force for the break release. This can be done directly on one of theoperating arms or through a linkage system. In either case, the result is the same. Thebreak is pulled away from the shaft and the velocity of the elevator is resumed.

In order to improve the stopping ability, a material with a high coefficient offriction is used within the breaks, such as zinc bonded asbestos. A material with too higha coefficient of friction can result in a jerky motion of the car. This material must bechosen carefully.

Typically the efficiency of the geared machine is 60 percent for the motor and gear boxassembly. This efficiency was estimated for a load of 2500lb, which matches a regularlysized residential elevator, being driven at 1.75 m/s.

The following analysis has been done for steady state (no acceleration )operation. Theforce on the driving pulley is equal to the difference of the two exerted tensions on eachside. On one side, this force is equal to We and on the other side, it is Wc.Therefore, the net force exerted on pulley 1 (the drivepulley) is:

In order to find the power required for elevator movement, either the rotational speedof the drive shaft (attached to pulley 1) or the velocity of the elevator must be known.The output power is (assumming 100% efficiency),

As explained above, the brake is held closed by a spring and released using a magnet.The free body diagram below shows how these forces are distributed. The force exerted bythe spring is much closer to the pin joint and, therefore, is easily overridden by theforce of the magnetic pull because of its longer moment arm (great distance from the pointof rotation).

3a8082e126