Patent ID: 6857981

Claim:
A rotary actuator according comprising: a synchronous motor; an internally meshing planetary reduction gear having a first shaft rotated by said synchronous motor; an outer gear mounted to said first shaft with an eccentric part so as to be eccesntrially rotatable around said first shaft; an inner gear with which said outer gear meshes internally; a second shaft connected to said outer gear with transmission means that only transmits said outer near rotation on its axis to said second shaft, and an incremental encoder provided along said first shaft of said synchronous motor for detecting a rotation angle of a rotor of said synchronous motor in a rotating direction of said synchronous motor, wherein said incremental encoder further comprises: a magnet that rotates integrally with said rotor and has multiple poles along a rotating direction; magnetic flux detecting means fixed to the housing for detecting a change in magnetic flux when said magnet is rotated; and said incremental encoder is an incremental encoder for detecting the rotation angle of the rotor through said magnetic flux detecting means by counting the number of repetitions of the change in the magnetic flux, which is induced by the rotation of the magnet.