Lead screw apparatus, linear actuator, and lift apparatus

A lead screw apparatus comprising:

• a screw shaft having a spiral channel on an outer circumferential surface thereof;
• a plurality of rollers configured to revolve around the screw with contact with the spiral channel;
• a roller cage configured to rotatably support the rollers, the lead screw apparatus providing conversion between a relative rotary motion between the screw shaft and the roller cage and a relative linear motion in axial direction of the screw shaft between the screw shaft and the roller cage bi-directionally;
• bearings configured to rotatably support the rollers, each of bearings including an outer ring supported by a holder supported by the roller cage, wherein the outer ring includes a protrusion on an outer circumference thereof on a side of the outer circumference closer to the screw shaft, and the holder abuts the protrusion from a side farther than the protrusion from the screw shaft.

A lead screw apparatus comprising:

• a screw shaft having a spiral channel on an outer circumferential surface thereof;
• a plurality of rollers configured to revolve around the screw with contact with the spiral channel;
• and
• a roller cage configured to rotatably support the rollers, the lead screw apparatus providing conversion between a relative rotary motion between the screw shaft and the roller cage and a relative linear motion in axial direction of the screw shaft between the screw shaft and the roller cage bi-directionally;
• bearings, each including an outer ring supported by the roller cage and a plurality of tapered rollers, configured to rotatably support the rollers, wherein the tapered rollers are disposed on an inner circumferential surface in a circumferential direction of the outer ring with substantially no gaps so that adjoining rollers of the tapered rollers can contact with each other.

A lead screw apparatus comprising:

• a screw shaft having a spiral channel on an outer circumferential surface thereof;
• a plurality of rollers configured to revolve around the screw with contact with the spiral channel;
• a roller cage configured to rotatably support the rollers, the lead screw apparatus providing conversion between a relative rotary motion between the screw shaft and the roller cage and a relative linear motion in axial direction of the screw shaft between the screw shaft and the roller cage bi-directionally;
• and
• bearings, each including an outer ring supported by the roller cage, configured to rotatably support the rollers, wherein the outer ring and the holder include a thread part configured to allow the outer ring to be screwed with the holder to allow the roller to shift in an axial direction of a rotation axis of the roller.