The concept of the crane

Crane (Crane) is a crane is a for loop, intermittent movement of machinery. A work cycle include: extract extract means to put items from the lift, and then move to the designated place lower level items, followed by a reverse movement, so extract unit returns to original position for the next cycle.

Usually by a  hoist gantry crane  hoisting mechanism (the items up and down movement), operating agencies (the lifting movement), luffing and slewing mechanism (the article for horizontal movement), plus the metal body, power units, steering control and the necessary combination of auxiliary devices.
In bridge construction crane used in accordance with its structure and performance of different, generally can be divided into small light lifting equipment, overhead type crane and jib type crane three categories. Small light lifting equipment such as: jacks, hoists, winches, etc.. Girder bridge type lifting machinery such as  bridge crane  , gantry cranes. Such as fixed jib type crane slewing cranes, tower cranes, truck cranes, tires, crawler cranes.

Within a certain range vertical lifting and horizontal multi-action lifting heavy lifting machinery. Also known as the gantry crane . Belong material handling machinery. Crane's work is characterized by intermittent exercise to do that in a work cycle reclaimer, transport, unloading and other activities of the appropriate agency is working alternately.