Elevators, Escalators and moving walks are the safest form of transportation. In 1853, American inventor Elisha Otis demonstrated a freight elevator equipped with a safety device to prevent falling in case a supporting cable should break. The electric motor was introduced in elevator construction in 1880 by the German inventor Werner von Siemens. His car, carrying the motor below, climbed its shaft by means of revolving pinion gears that engaged racks at the sides of the shaft. Within the next 12 years, electric elevators with worm gearing connecting the motor and drum came into general use except in tall buildings. In the drum elevator the length of the hoisting rope, and therefore the height to which the car can rise, are limited by the size of the drum; space limitations and manufacturing difficulties prevented the use of the drum mechanism in skyscrapers. The advantages of the electric elevator, however, including efficiency, relatively low installation costs, and virtually constant speed regardless of the load, spurred inventors to search for a way of using electric motive power in skyscrapers. Counterweights creating traction on electrically driven sheaves solved the problem. Since the introduction of electric motive power for elevators, various improvements have been made in motors and methods of control. At first, single-speed motors only were used. Because a second, lower speed was desirable to facilitate leveling the car with landings, low-speed auxiliary motors were introduced, but later several systems were devised for varying speed by varying the voltage supplied to the hoisting motor. There are two main types of elevators in use today: The hydraulic elevator and the traction elevator. A hydraulic elevator uses a pressurized piston to move the elevator. For elevators coursing more than a few floors, hydraulic elevators do not work well. A traction elevator uses steel ropes that glide over pulleys, and the elevator car is balanced with counterweights. The friction of the ropes on the pulley creates traction – hence the name traction elevator. In the past 150 years, technology has come a long way. Elevators falling due to rope breakage are unheard of since modern elevators are supported by multiple steel ropes each one with a safety factor of five or more. Electric operations are monitored by modern microprocessors that serve to ensure the ride is safe. A trip on an elevator servicing about six to a hundred stories is by a traction elevator whereas a low rise building may have a hydraulic elevator supported by a steel column and oil pressure. Elevators have become a medium of architectural expression as compelling as the buildings, in which they’re installed, and new technologies and designs regularly allow the human spirit to soar! For More detail:-http://bit.ly/1ZLlLS8
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