Question

Report About (( Lift Mechanism ))

1- Abstract 2-Introduction

3- Model Description 4- Discussion

5. Conclusions 6. References

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Answer 1

1.Abstract

The earliest known reference to an lifting mechanism is in the works of the Roman architect Vitruvius, who reported that Archimedes (c. 287 BC – c. 212 BC) built his first lifting mechanism probably in 236 BC. Some sources from later historical periods mention lifting mechanism as cabs on a hemp rope powered by hand or by animals.

In 1000, the Book of Secrets by al-Muradi in Islamic Spain described the use of an lifting mechanism -like lifting device, in order to raise a large battering ram to destroy a fortress. In the 17th century the prototypes of lifting mechanism were located in the palace buildings of England and France. Louis XV of France had a so-called 'flying chair' built for one of his mistresses at the Chateau de Versailles in 1743.

Ancient and medieval lifting mechanism used drive systems based on hoists or windlasses. The invention of a system based on the screw drive was perhaps the most important step in lifting mechanism technology since ancient times, leading to the creation of modern passenger lifting mechanism . The first screw drive lifting mechanism was built by Ivan Kulibin and installed in the Winter Palace in 1793, although there may have been an earlier design by Leonardo da Vinci. Several years later another of Kulibin's lifting mechanism was installed in the Arkhangelskoye near Moscow.

The hydraulic crane was invented by Sir William Armstrong in 1846, primarily for use at the Tyneside docks for loading cargo. These quickly supplanted the earlier steam driven lifting mechanism : exploiting Pascal's law, they provided a much greater force. A water pump supplied a variable level of water pressure to a plunger encased inside a vertical cylinder, allowing the level of the platform (carrying a heavy load) to be raised and lowered. Counterweights and balances were also used to increase the lifting power of the apparatus.

2.Introduction

The first lifting mechanism shaft preceded the first lifting mechanism by four years. Construction for Peter Cooper's Cooper Union Foundation building in New York began in 1853. A lifting mechanism shaft was included in the design, because Cooper was confident that a safe passenger lifting mechanism would soon be invented. The shaft was cylindrical because Cooper thought it was the most efficient design. Later, Otis designed a special lifting mechanism for the building.

The Equitable Life Building completed in 1870 in New York City was thought to be the first office building to have passenger lifting mechanism . However Peter Ellis, an English architect, installed the first lifting mechanism that could be described as paternoster lifting mechanism in Oriel Chambers in Liverpool in 1868.

The first electric lifting mechanism was built by Werner von Siemens in 1880 in Germany. The inventor Anton Freissler developed the ideas of von Siemens and built up a successful enterprise in Austria-Hungary. The safety and speed of electric lifting mechanism were significantly enhanced by Frank Sprague who added floor control, automatic lifting mechanism , acceleration control of cars, and safeties. His lifting mechanism ran faster and with larger loads than hydraulic or steam lifting mechanism , and 584 electric lifting mechanism were installed before Sprague sold his company to the Otis Lifting mechanism Company in 1895. Sprague also developed the idea and technology for multiple lifting mechanism in a single shaft.

In 1882, when hydraulic power was a well-established technology, a company later named the London Hydraulic Power Company was formed by Edward B. Ellington and others. It constructed a network of high-pressure mains on both sides of the Thames which, ultimately, extended to 184 miles and powered some 8,000 machines, predominantly lifting mechanism and cranes. Schuyler Wheeler patented his electric lifting mechanism design in 1883.

In 1874, J. W. Meaker patented a method which permitted lifting mechanism doors to open and close safely.^[19] In 1887, American Inventor Alexander Miles of Duluth, Minnesota patented a lifting mechanism with automatic doors that would close off the lifting mechanism shaft. The first lifting mechanism in India was installed at the Raj Bhavan in Calcutta (now Kolkata) by Otis in 1892. By 1900, completely automated lifting mechanism were available, but passengers were reluctant to use them. A 1945 lifting mechanism operator strike in New York City, and adoption of an emergency stop button, emergency telephone, and a soothing explanatory automated voice aided adoption. In 2000, the first vacuum lifting mechanism was offered commercially in Argentina.

3.Model Description

Hydraulic lifting mechanism

In Conventional hydraulic lifting mechanism, They use an underground hydraulic cylinder,are quite common for low level buildings with two to five floors (sometimes but seldom up to six to eight floors), and have speeds of up to 1 m/s (200 ft/min). For higher rise applications, a telescopic hydraulic cylinder can be used. Hole less hydraulic lifting mechanism were developed in the 1970s, and use a pair of above ground cylinders, which makes it practical for environmentally or cost sensitive buildings with two, three, or four floors. Roped hydraulic lifting mechanism use both above ground cylinders and a rope system, allowing the lifting mechanism to travel further than the piston has to move.

The low mechanical complexity of hydraulic lifting mechanism in comparison to traction lifting mechanism makes them ideal for low rise, low traffic installations. They are less energy efficient as the pump works against gravity to push the car and its passengers upwards; this energy is lost when the car descends on its own weight. The high current draw of the pump when starting up also places higher demands on a building's electrical system. There are also environmental concerns should the lifting cylinder leak fluid into the ground.

The modern generation of low-cost, machine room-less traction lifting mechanism made possible by advances in miniaturization of the traction motor and control systems challenges the supremacy of the hydraulic lifting mechanism in their traditional market niche.

4- Discussion

Geared traction machines are driven by AC or DC electric motors. Geared machines use worm gears to control mechanical movement of lifting mechanism   by "rolling" steel hoist ropes over a drive sheave which is attached to a gearbox driven by a high-speed motor. These machines are generally the best option for basement or overhead traction use for speeds up to 3 m/s (500 ft/min).

Historically, AC motors were used for single or double-speed lifting machines on the grounds of cost and lower usage applications where car speed and passenger comfort were less of an issue, but for higher speed, larger capacity lifting mechanism s, the need for infinitely variable speed control over the traction machine becomes an issue. Therefore, DC machines powered by an AC/DC motor generator were the preferred solution. The MG set also typically powered the relay controller of the lifting mechanism , which has the added advantage of electrically isolating the lifting mechanism s from the rest of a building's electrical system, thus eliminating the transient power spikes in the building's electrical supply caused by the motors starting and stopping (causing lighting to dim every time the lifting mechanism s are used for example), as well as interference to other electrical equipment caused by the arcing of the relay contactors in the control system.

The widespread availability of variable frequency AC drives has allowed AC motors to be used universally, bringing with it the advantages of the older motor-generator, DC-based systems, without the penalties in terms of efficiency and complexity. The older MG-based installations are gradually being replaced in older buildings due to their poor energy efficiency.

Gearless traction machines are low-speed (low-RPM), high-torque electric motors powered either by AC or DC. In this case, the drive sheave is directly attached to the end of the motor. Gearless traction lifting mechanism s can reach speeds of up to 20 m/s (4,000 ft/min), A brake is mounted between the motor and gearbox or between the motor and drive sheave or at the end of the drive sheave to hold the lifting mechanism stationary at a floor. This brake is usually an external drum type and is actuated by spring force and held open electrically; a power failure will cause the brake to engage and prevent the lifting mechanism from falling (see inherent safety and safety engineering). But it can also be some form of disc type like 1 or more calipers over a disc in one end of the motor shaft or drive sheave which is used in high speed, high rise and large capacity lifting mechanism s with machine rooms(an exception is the Kone MonoSpace's EcoDisc which is not high speed, high rise and large capacity and is machine room less but it uses the same design as is a thinner version of a conventional gearless traction machine) for braking power, compactness and redundancy (assuming there's at least 2 calipers on the disc), or 1 or more disc brakes with a single caliper at one end of the motor shaft or drive sheave which is used in machine room less lifting mechanism s for compactness, braking power, and redundancy (assuming there's 2 brakes or more).

In each case, cables are attached to a hitch plate on top of the cab or may be "underslung" below a cab, and then looped over the drive sheave to a counterweight attached to the opposite end of the cables which reduces the amount of power needed to move the cab. The counterweight is located in the hoist-way and is carried along a separate railway system; as the car goes up, the counterweight goes down, and vice versa. This action is powered by the traction machine which is directed by the controller, typically a relay logic or computerised device that directs starting, acceleration, deceleration and stopping of the lifting mechanism cab. The weight of the counterweight is typically equal to the weight of the lifting mechanism cab plus 40–50% of the capacity of the lifting mechanism. The grooves in the drive sheave are specially designed to prevent the cables from slipping. "Traction" is provided to the ropes by the grip of the grooves in the sheave, thereby the name. As the ropes age and the traction grooves wear, some traction is lost and the ropes must be replaced and the sheave repaired or replaced. Sheave and rope wear may be significantly reduced by ensuring that all ropes have equal tension, thus sharing the load evenly. Rope tension equalisation may be achieved using a rope tension gauge, and is a simple way to extend the lifetime of the sheaves and ropes.

Lifting mechanism s with more than 30 m (98 ft) of travel have a system called compensation. This is a separate set of cables or a chain attached to the bottom of the counterweight and the bottom of the lifting mechanism cab. This makes it easier to control the lifting mechanism, as it compensates for the differing weight of cable between the hoist and the cab. If the lifting mechanism cab is at the top of the hoist-way, there is a short length of hoist cable above the car and a long length of compensating cable below the car and vice versa for the counterweight. If the compensation system uses cables, there will be an additional sheave in the pit below the lifting mechanism, to guide the cables. If the compensation system uses chains, the chain is guided by a bar mounted between the counterweight tracks.

5. Conclusions

Some people argue that lifting mechanism began as simple rope or chain hoists . An lifting mechanism is essentially a platform that is either pulled or pushed up by a mechanical means. A modern-day lifting mechanism consists of a cab (also called a "cage", "carriage" or "car") mounted on a platform within an enclosed space called a shaft or sometimes a "hoistway". In the past, lifting mechanism drive mechanisms were powered by steam and water hydraulic pistons or by hand. In a "traction" lifting mechanism, cars are pulled up by means of rolling steel ropes over a deeply grooved pulley, commonly called a sheave in the industry. The weight of the car is balanced by a counterweight. Sometimes two lifting mechanism are built so that their cars always move synchronously in opposite directions, and are each other's counterweight. The friction between the ropes and the pulley furnishes the traction which gives this type of lifting mechanism its name. Hydraulic lifting mechanism use the principles of hydraulics (in the sense of hydraulic power)to pressurize an above ground or in-ground piston to raise and lower the car (see Hydraulic lifting mechanism below). Roped hydraulics use a combination of both ropes and hydraulic power to raise and lower cars. Recent innovations include permanent magnet motors, machine room-less rail mounted gearless machines, and microprocessor controls. The technology used in new installations depends on a variety of factors. Hydraulic lifting mechanism are cheaper, but installing cylinders greater than a certain length becomes impractical for very-high lift hoistways.For buildings of much over seven floors, traction lifting mechanism must be employed .

6. References

1. ^ Edmund F. Tweedy, Commercial Engineering for Central Stations. New York, McGraw-Hill (1912)
2. ^ Howard B. Cook, Passenger Elevator Service. Cincinnati, Warner Elevator Manufacturing Company (1920)
3. ^ Bassett Jones, “The Probable Number of Stops Made by an Elevator”. General Electric Review, Vol. 26, 583-587 (August 1923)
4. ^ Bassett Jones, “Note on Probable Number of Stops Made by an Elevator”. General Electric Review, Vol. 29, 425-426 (1926)
5. ^ Strakosch, G.R., 1967, "Elevators and escalators", 1/ed, Wiley
6. ^ Barney, G.C. and Dos Santos, S.M., 1975, "Improved traffic design methods for lift systems", Bldg. Sci.
7. ^ Peters R D Improvements to the Up Peak Round Trip Time Calculation (Technical Note) International Journal of Elevator Engineers, Volume 3 No 1 (2000)
8. ^ Inglis, Cooper, Barney Elevator & Escalator Micropedia 5^th edition (2009)
9. ^ Lift Traffic Analysis: Formulae for the General Case Building Services Engineering Research and Technology, volume 11 No 2 (1990)