Actuator for electric parking brake

An actuator of an electric parking brake, comprising:

• a driving unit configured to provide a rotational force through a driving shaft;
• a first gear unit configured to receive the rotational force from the driving unit;
• a second gear unit including a rotation shaft configured to receive the rotational force from the first gear unit to rotate;
• a driving shaft control unit disposed on the driving shaft, and configured to provide a degree of rotational freedom to the driving shaft during braking and fix the driving shaft to prevent reverse rotation of the driving shaft due to a reverse rotation torque when the braking is ended;
• a speed reduction unit configured to increase a rotational torque transmitted by the second gear unit, the speed reduction unit comprising a non-rotatable ring gear and a plurality of planetary gears rotatably engaged with an inner gear and the non-rotatable ring gear while gear teeth provided on an inner circumferential surface of the ring gear are engaged with the planetary gears,
• wherein the second gear unit further includes:
• the inner gear coupled to the rotation shaft;
• and
• an outer gear having an inner circumferential surface coupled to the inner gear and an outer circumferential surface, on which gear teeth engaged with the first gear unit are provided, and formed in a ring shape,
• wherein the inner circumferential surface of the outer gear has a plurality of coupling protrusions coupled with a corresponding plurality of coupling grooves formed on an outer circumferential surface of a larger diameter portion of the inner gear, and gear teeth formed on an outer circumferential surface of a smaller diameter portion of the inner gear are engaged with the plurality of planetary gears.