ELEVATORS - DESIGN AND DRIVES

摘要

Depending upon the type of service for which it is intended, a given elevator may be engineered in accordance with any of a number of basic design concepts. Apart from the standard lift used to transport passengers and loads, there are also very special designs, examples of which include the small goods lift, the construction lift or the facade lift. The present introduction to elevator engineering is intended to deal only with general-purpose passenger and freight elevators and with the types of designs most often utilized. Elevators are fitted with either electric or hydraulic drives. This difference in drive design has far-reaching consequences and, in the preparation of European Standard EN 81, has resulted in its division into two parts: "Electric lifts" and "Hydraulic lifts." A further major distinction is in regard to the suspension equipment. EN 81 makes reference to wire rope, steel link chain and hydraulic cylinders used to transmit power (while the TRA 200 Technical Rules for Elevators also mentions spindles and rack-and-pinion drives). The steel-chain and spindle options are now only very rarely used. Steel link chains suffer inherent disadvantages in terms of safety and, due to the so-called "polygon effect," do not run smoothly. They are consequently used only at low speeds and in particular when dealing with very deep cars where the tilting forces induced by off-center loads are not absorbed by the car guide system. Rack-and-pinion designs are used almost exclusively for construction lifts. The large majority of all lifts now in service are equipped with wire rope or hydraulic cylinders.