The gantry crane is a bridge-type crane supported on the ground track by two side legs. Structurally, it consists of the gantry, trolley running mechanism, hoist trolley, and electrical parts, etc. Some gantry cranes have legs only on one side, supported by the factory or pier on the other, known as semi-gantry cranes. The components of the gantry crane include the upper bridge girder (including the main beam and end beam), legs, lower crossbeam, etc. To expand the crane's working range, the main beam can extend beyond the legs to one or both sides, forming a cantilever. An overhead crane with an arm架 can also be used to expand the working range through the tilting and rotation of the arm.