The planetary gear system is mainly composed of planetary gear g, central gear k, and planetary carrier H. The number of planetary gears is usually 2-6. But when calculating the transmission ratio, only the speed of one planetary gear is considered, and the rest of the planetary gears are not considered when calculating, which is called virtual constraint. Their function is to evenly distribute around the central wheel, allowing several planetary gears to share the load and reduce gear size; At the same time, it can balance the radial force components at each meshing point and the centrifugal force generated by the revolution of the planetary gear, reducing the force inside the main bearing and increasing the smoothness of operation. A planetary carrier is a component used to support planetary gears and enable them to revolve. In the center wheel, the outer gear center wheel is called the sun wheel, represented by the symbol a, and the inner gear center wheel is called the inner gear ring, represented by the symbol b. 2、 The classification of planetary gear systems can be divided into three types based on the composition of their basic components: 2K-H type, 3K type, and K-H-V. The 2K-H type has the advantages of fewer components, a wide range of transmission power and transmission ratio variations, and easy design, making it the most widely used. The 3K type has three central wheels, and its planetary carrier does not transmit torque but only serves to support the planetary wheels. Planetary gear systems are named NGW, NW, NN types according to their meshing methods. N represents internal meshing, W represents external meshing, and G represents the common planetary gear g.

The fundamental difference between a planetary gear system and a fixed axis gear system is that the planetary gear system has a rotating planet carrier, which allows the planetary gear system to have both rotation and revolution. Therefore, the calculation of the transmission ratio of planetary gear systems cannot be done using the calculation method of fixed axis gear systems. According to the principle of relative motion (reversal method), assuming that the planet carrier H does not move, that is, adding an angular velocity of (- ω H) to the system around the center of rotation of the planet carrier, the planetary gear train can be transformed into an imaginary fixed axis gear train, which is called the transformation gear train of the planetary gear train. The speed relationship between the gears in the converted fixed axis wheel system and the original revolving wheel system is:, and the calculation formula for the transmission ratio of the converted wheel system is: Therefore, for any two parallel axes of gear j and gear k in the planetary wheel system, their transmission ratios in the converted wheel system are: Given any two of nj, nk, and nH, the third term can be obtained, and the transmission ratio between any two components in the original planetary wheel system can be obtained.