Elevator is a kind of permanent transportation equipment which serves several specific floors in the building, and its car runs on at least two rigid tracks which are perpendicular to the horizontal plane or the inclination angle with the plumb line is less than 15 degrees. Also has the step type, the step board installs on the crawler track continuous movement, commonly known as the escalator or the moving sidewalk. Fixed lifting equipment serving specified floors. The vertical elevator has a car running between at least two vertical or rigid rails with an inclination angle less than 15 degrees. The size and structural form of the car are convenient for passengers to enter and exit or load and unload goods. Traditionally, no matter how its driving mode is, the elevator is regarded as the general term of vertical transportation in buildings. According to the speed, it can be divided into low-speed elevator (below 4m / s), fast elevator (4-12m / s) and high-speed elevator (above 12m / s). Hydraulic elevators began to appear in the mid-19th century and are still used in low rise buildings. In 1852, e.g. Otis of the United States developed a safety hoist with wire rope. In the 1980s, the driving device was further improved, such as the winding drum driven by the motor through worm drive and the balance weight