An indoor gantry crane is a bridge-type crane in which the bridge is supported on the ground track by legs on both sides. Structurally, it consists of a mast, a trolley operating mechanism, a lifting trolley and electrical parts. Some gantry cranes only have outriggers on one side, and the other side is supported on the factory building or trestle, which is called a semi-gantry crane. The gantry crane is composed of the upper bridge frame (including main beam and end beam), outriggers, lower beam and other parts. In order to expand the operating range of the crane, the main beam can extend beyond the outriggers to one or both sides to form a cantilever. A lifting trolley with a boom can also be used to expand the crane's operating range through the pitching and rotation of the boom. Gantry cranes can be classified according to the structure of the door frame, the form of the main beam, the structure of the main beam, and the form of use.