Lubrication reservoir for lead screw assembly
A nut driven by a lead screw and stepper motor has an internal concave recess for holding high viscosity grease that is semi-solid at ambient temperature and spaced from the lead screw. Grease flow ensues with lead screw motion causing a slow flow of grease coating the lead screw with a thin coating of grease as the nut travels back and forth over the lead screw. The nut may be an anti-backlash nut or a single member nut with both having a concave recess about the lead screw for the grease.
1. A lead screw assembly comprising:
(a) a lead screw driven in rotation by contact with a motor, the lead screw having an axis with helical threads about the axis;
(b) a nut having internal threads in drive relation with the helical threads of the lead screw, the nut having a concave recess forming a lubrication reservoir extending from the lead screw threads transverse to the axis;
wherein the nut has a first tubular member with a first portion of said internal threads and external threads about the tubular periphery of the member with a central annular first boss dividing the member into first and second sections, the first boss having upright shoulders extending transverse to the screw axis, the first section of the first member having said concave recess as a channel with a rectangular cross section extending transverse to the axis;
a second tubular member with a second portion of said internal threads and a first section having first and second opposed flange members that fit into the concave recess of the first tubular member, serving to selectively size a volume for said recess, and
an annular spacer having internal threads that engage the external threads about the first section of the first tubular member, stopping the approach of the second tubular member towards the first tubular member when the lead screw is inserted into the nut, thereby selecting the volume of the concave recess on the lead screw; and
(c) lubricant that is semi-solid at ambient temperatures disposed in the nut recess at a distance spaced from the lead screw helical threads, the lubricant having a flow property upon rotation of the lead screw whereby the lead screw is coated with lubricant upon lead screw rotation.
2. The apparatus of claim 1 wherein an external injection port is disposed in the nut that is open transverse to the lead screw axis and is aligned with the recess for introducing lubricant into the recess.
3. The apparatus of claim 1 wherein an annular spring washer is disposed on the first section of the first tubular member, separating the annular spacer from the first tubular member.
4. The apparatus of claim 1 further comprising a stepper motor driving said lead screw in rotation.
5. The apparatus of claim 1 wherein the concave recess is an annular space within the nut.
6. The apparatus of claim 1 wherein the lubricant is grease that has a viscosity in the range of 135 cSt to 165 cSt at temperature up to 40° C.
7. The apparatus of claim 5 wherein the concave recess is defined in a nut member made of a first material surrounded by a nut member made of a second material.
8. The apparatus of claim 1 wherein the nut is an anti-backlash nut.
9. The apparatus of claim 8 wherein the anti-backlash nut is formed by first and second tubular members separated by an annular spacer and said concave recess is defined by one of the tubular members.