Reduction gear

A reduction gear that decelerates and transmits rotation of an input side rotation body to an output side rotation body, the reduction gear comprising:

• an eccentric cam that turns together with the input side rotation body;
• a first swing body relatively turnably fitted to the eccentric cam and swung by the eccentric cam that turns in an eccentric state with respect to a rotation shaft center of the input side rotation body;
• a second swing body that is relatively turnably fitted to the eccentric cam, swung by the eccentric cam that turns in an eccentric state with respect to the rotation shaft center of the input side rotation body, and swung in a state of being shifted by 180° in phase with respect to the first swing body;
• a plurality of round rod shaped pins that extend across and contact outer peripheries of the first swing body and the second swing body and are swung by swing motions of the first swing body and the second swing body;
• a first radial direction groove forming body, a direction extending radially from the rotation shaft center of the input side rotation body being defined as a radial direction, a direction along a circumference of a virtual circle centering on the rotation shaft center of the input side rotation body being defined as a circumferential direction, at least a same number of radial direction grooves as a number of the pins being formed in the first radial direction groove forming body, the radial direction grooves allowing one end sides of the pins swung and moved by the first swing body and the second swing body to slidingly move along the radial direction;
• a second radial direction groove forming body integrated with the first radial direction groove forming body, at least a same number of radial direction grooves as the number of the pins being formed in the second radial direction groove forming body, the radial direction grooves allowing other end sides of the pins swung and moved by the first swing body and the second swing body to slidingly move along the radial direction;
• and
• a wave shape depressed portion forming body positioned on radially outward sides of the first swing body and the second swing body and having a wave shape depressed portion formed along the circumferential direction, the wave shape depressed portion being into contact with the pin slidingly moved along the radial direction groove, wherein
• one of the first radial direction groove forming body and second radial direction groove forming body or the wave shape depressed portion forming body is secured to a member to be fixed,
• another of the first radial direction groove forming body and second radial direction groove forming body or the wave shape depressed portion forming body is arranged relatively turnably with the one of the first radial direction groove forming body and second radial direction groove forming body or the wave shape depressed portion forming body, the first swing body, and the second swing body, and
• when the number of grooves of the radial direction grooves is defined as Za and the number of the wave shape depressed portions is defined as Zb, a plurality of the wave shape depressed portions are formed along the circumferential direction of the wave shape depressed portion forming body such that a difference between Za and Zb becomes 1.