The working principle of the double girder overhead crane is: by operating the control system, the crane's driving unit converts dynamic energy into mechanical energy (i.e., appropriate force or motion speed), then transmits it to the gripping device. The crane's picking device connects the transported material to the crane, and the working mechanism moves individually or in combination to complete the material handling task. The movable metal structure connects all components into a single unit, supporting the crane's own weight and the load it lifts.