Excavator movable arm energy-saving device based on spring set and variable-diameter roller and working method of excavator movable arm energy-saving device

The invention discloses an excavator movable arm energy-saving device based on a spring set and a variable-diameter roller and a working method of the excavator movable arm energy-saving device. The excavator movable arm energy-saving device is suitable for an excavator. The excavator movable arm energy-saving device comprises a potential energy storage device connected with a movable arm and a hydraulic system connected with a movable arm hydraulic cylinder of the excavator. The potential energy storage device is arranged on an upper rotary table and comprises a support, a large roller is arranged on the support through a rotating shaft and connected with a pull rod of a movable arm through a wound thin steel wire rope, two speed reducers are arranged on the two sides of the large roller, each speed reducer is provided with the variable-diameter roller, a thick steel wire rope is wound on each variable-diameter roller, the two variable-diameter rollers are connected with a spring force storage device through