Patent ID: 7404782

Claim:
A reduction gear for a walking assistance system that, in order to assist walking movement by extending/bending a user's leg joint, reduces the speed of rotation of an input shaft (Si) driven by a motor ( 48 ) and transmits the rotation to an output shaft (So) connected to the leg joint, the reduction gear comprising: the input shaft (Si), the output shaft (So), a first planetary gear mechanism (P 1 ), and a second planetary gear mechanism (P 2 ) disposed coaxially on an axis (L), the second planetary gear mechanism (P 2 ) being disposed so as to substantially overlap the radially outer side of the first planetary gear mechanism (P 1 ), the rotation of the input shaft (Si) being reduced in speed by the first planetary gear mechanism (P 1 ) and the second planetary gear mechanism (P 2 ) and transmitted to the output shaft (So); the first planetary gear mechanism (P 1 ) comprising a first sun gear (ZS 1 ) provided on the input shaft (Si), a first ring gear (ZR 1 ) rotatably disposed so as to surround the outer periphery of the first sun gear (ZS 1 ), a plurality of first planetary gears (ZP 1 ) meshing simultaneously with the first sun gear (ZS 1 ) and the first ring gear (ZR 1 ), and a first carrier (C 1 ) rotatably supporting the first planetary gears (ZP 1 ), and; the second planetary gear mechanism (P 2 ) comprising a second sun gear (ZS 2 ) provided on the outer periphery of the first ring gear (ZR 1 ), a second ring gear (ZR 2 ) disposed so as to surround the outer periphery of the second sun gear (ZS 2 ), a plurality of second planetary gears (ZP 2 ) meshing simultaneously with the second sun gear (ZS 2 ) and the second ring gear (ZR 2 ), and a second carrier (C 2 ) rotatably supporting the second planetary gears (ZP 2 ), wherein the first carrier (C 1 ) of the first planetary gear mechanism (P 1 ) is fixed to a casing ( 41 ), the second ring gear (ZR 2 ) of the second planetary gear mechanism (P 2 ) is fixed to the casing ( 41 ), and the second carrier (C 2 ) of the second planetary gear mechanism (P 2 ) is connected to the output shaft (So).