Patent ID: 7909722

Claim:
A structure of a swing part of an industrial robot provided with a fixed part and a rotary part, said structure comprising a front stage speed reducer which reduces speed of rotation inputted from a drive motor and outputs the rotation at the reduced speed, and a main speed reducer which reduces the speed of the rotation inputted from the front stage speed reducer and outputs the rotation to the rotary part, said main speed reducer is an eccentric oscillation speed reducer which includes a casing provided with a number of pin teeth on an inner periphery thereof, a pinion contained in said casing and having external teeth in mesh with said pin teeth, a carrier inserted into said casing and adapted to rotate relative to said casing, and a plurality of crank pins rotatably supported by said carrier and having eccentric parts respectively inserted into said pinion, said crank pins being rotated synchronously with the rotation from said front stage speed reducer thereby to rotate the pinion eccentrically, wherein either one of said casing and said carrier is fixed to said fixed part, and the reduced rotation is outputted from the other of said casing and said carrier to the rotary part, said front stage speed reducer including an external gear speed reducer which has first external gears which are provided at input side ends of all the crank pins, and a second external gear which is coaxial with said casing or said carrier and to which the rotation from the drive motor is inputted, characterized in that: total reduction ratio of said external gear speed reducer and said eccentric oscillation speed reducer is 80 to 200, a diameter D of a circle passing a center of the pin teeth being in a range of 150 to 200 mm, and a value N obtained by dividing reduction ratio M of said eccentric oscillation speed reducer by said diameter D is smaller than 0.20.