A ballscrew assembly comprises a ballnut having a first helical groove and a ballscrew comprising a second helical groove opposed to the first helical groove so as to form a helical raceway. A plurality of balls is disposed in the helical raceway. A first seal is disposed at a first axial end of the ballnut to seal between the ballscrew and the ballnut. A second seal is provided for selectively sealing between the ballscrew and a second axial end of the ballnut, the second seal comprising a ballscrew seal mounted for axial movement with the ballscrew, and configured to make sealing engagement with the ballnut when the ballscrew is in a first axial position relative to the ballnut to form a chamber between the first and second seals, but not to make sealing engagement with the ballnut when the ballscrew assembly is in a second axial position relative thereto.

In one embodiment, an actuator has a roller, a helical track, and at least one track follower. The roller has a cylindrical body that has a first end, a second end that is offset from the first end along a central axis, and a cylindrical outer surface that extends from the first end to the second end. The helical track is disposed around the cylindrical outer surface in a helical pattern. The at least one track follower can be attached to a load, and rides along the helical track when the roller is rotated about the central axis so as to translate the load along an axial direction that is substantially parallel to the central axis. In some embodiments, the roller has an internal motor that is disposed within the cylindrical body.

A ballscrew assembly comprises a ballnut having a first helical groove and a ballscrew comprising a second helical groove opposed to the first helical groove so as to form a helical raceway. A plurality of balls is disposed in the helical raceway. A first seal is disposed at a first axial end of the ballnut to seal between the ballscrew and the ballnut. A second seal is provided for selectively sealing between the ballscrew and a second axial end of the ballnut, the second seal comprising a ballscrew seal mounted for axial movement with the ballscrew, and configured to make sealing engagement with the ballnut when the ballscrew is in a first axial position relative to the ballnut to form a chamber between the first and second seals, but not to make sealing engagement with the ballnut when the ballscrew assembly is in a second axial position relative thereto.

Provided is an electric actuator (1), including: a motor part (A); and a motion conversion mechanism part (B). The motion conversion mechanism part (B) includes: a screw shaft (33); a nut member (32); and a planetary gear speed reducer (10) configured to reduce a speed of rotation of the rotor (24) and output the rotation. The screw shaft (33) is configured to advance toward one side in an axial direction or retreat toward another side in the axial direction in accordance with a rotation direction of the nut member (32), and the nut member (32) is arranged on an inner periphery of the rotor (24), and is coupled to a planetary gear carrier (43), which is an output member of the planetary gear speed reducer (10), so as to be capable of transmitting torque.