Planetary gear reducer with double input and double output

A double-input and double-output planetary gear reducer is provided with a shell, three planetary gear trains are sequentially arranged in the shell from left to right, the first planetary gear train comprises an input sleeve, a first inner gear ring frame, a first inner gear ring, an input planet carrier, a first planet gear and a center wheel shaft, and the input sleeve is connected with the first inner gear ring through the first inner gear ring frame; a first planet wheel is mounted on the input planet carrier and is respectively meshed with the first inner gear ring and the central wheel shaft; the second planetary gear train comprises a center wheel and planetary gear shafts, the center wheel is connected to the output end of the center wheel shaft and meshed with the planetary gear shafts which do not do revolution, and the third planetary gear train comprises a second planetary wheel, a second inner gear ring, a second inner gear ring frame and an output sleeve. The right end of the planetary gear sha