Patent attributes
An electric direct-acting actuator is proposed which can maintain a large power increasing function without mounting a separate speed reducer. A plurality of planetary rollers (7) are disposed between the radially outer surface of a rotor shaft (5) of an electric motor and the radially inner surface of an outer ring member (1) fixed in position around the rotor shaft (5) so as to be rotatable about the rotor shaft (5) and about their own axes when the rotor shaft (5) rotates. A helical rib is defined by a rib member (9) engaged in a helical groove (8) formed in the radially inner surface of the outer ring member (1). The helical rib is engaged in circumferential grooves (10) formed in the radially outer surface of each planetary roller (7) at the same pitch as the turns of the helical rib. Thus, the rotary motion of the rotor shaft (5) is converted to a linear motion of the planetary rollers (7), so that it is possible to ensure a large power increasing function without mounting a separate speed reducer.
