The weight of a planetary gear transmission device is generally proportional to the weight of the gear, and the weight of the gear is closely related to its material and heat treatment hardness. For example, at the same power, the weight of carburized and quenched gears will be about one-third of the weight of quenched and tempered gears. Therefore, in response to the structural characteristics of planetary gear reducers and the load properties of gears, hard tooth surface gears should be widely used.