Self-aligning decoupled nut mechanism

Abstract

A feed screw and nut mechanism includes a nut having an internally threaded bore which threadingly engages an externally threaded feed screw. A runner bearing is attached to the nut and projects outwardly therefrom, and a dummy runner bearing is attached to the nut and projects outwardly therefrom and is angularly displaced from the runner bearing about the feed screw axis. The mechanism includes a stationary runner defining a runner surface that is engaged by the runner bearing to prevent rotation of the nut, and a dummy runner defining a dummy runner surface that engages the dummy runner bearing. The dummy runner and dummy runner bearing are biased toward each other such that the nut is rotatably biased in a direction to urge the runner bearing against the runner surface. The nut includes at least one rotatable drive bearing having a rotation axis perpendicular to the feed screw axis, and at least one rotatable driven bearing connected to the carriage and having a rotation axis perpendicular to both the feed screw axis and to the axis of the drive bearing. The drive and driven bearings make contact at their cylindrical surfaces to form a crossed bearing coupling for minimizing transmission to a carriage of force components which are not parallel to the axial direction along which the carriage travels. In a preferred embodiment, the nut mechanism includes a slave carriage, connected to the carriage, which supports a pair of crossed bearing couplings and which is rotatably connected to the nut to isolate the slave carraige from rotation of the nut about a transverse axis.

What is claimed is:  
     
         1 . A nut mechanism for translating a carriage along an X-axis, and comprising: 
 an externally threaded feed screw which is rotatable about a fixed screw axis parallel to the X-axis;    a nut having an internally threaded bore which threadingly receives the feed screw;    a stationary runner adapted to be fixed relative to the feed screw axis, the stationary runner defining a stationary runner surface which extends parallel to the X-axis;    a runner bearing attached to the nut and projecting outwardly therefrom along a Y-axis which is perpendicular to the X-axis, the runner bearing engaging the stationary runner surface to prevent rotation of the nut when the feed screw is rotated such that rotation of the feed screw causes the nut to translate along the X-axis and the runner bearing to travel along the stationary runner surface;    a dummy runner bearing attached to the nut and projecting outwardly therefrom along an axis which is perpendicular to the X-axis and angularly displaced about the screw axis from the runner bearing; and    a dummy runner defining a dummy runner surface which extends parallel to the X-axis and engages the dummy runner bearing;    at least one of the dummy runner bearing and dummy runner being biased toward the other so as to rotatably bias the nut in a direction to maintain the runner bearing in contact with the stationary runner surface.    
     
     
         2 . The nut mechanism of  claim 1 , wherein the dummy runner bearing includes a shaft attached to and projecting outwardly from the nut, at least a portion of the shaft being resiliently bendable so as to bias the dummy runner bearing against the dummy runner surface.  
     
     
         3 . The nut mechanism of  claim 1 , wherein the dummy runner is movably mounted relative to the dummy runner bearing and is biased toward the dummy runner bearing for rotatably biasing the nut.  
     
     
         4 . The nut mechanism of  claim 1 , further comprising: 
 a drive bearing attached to the nut and projecting outwardly therefrom, the drive bearing having an outer generally cylindrical drive surface defining an axis which is perpendicular to the X-axis; and    a driven bearing which has an outer generally cylindrical driven surface defining an axis and which is adapted to be attached to the carriage such that the axis of the driven surface is perpendicular to both the axis of the drive surface and the X-axis, and such that the driven surface is engaged by the drive surface to form a crossed bearing coupling.    
     
     
         5 . The nut mechanism of  claim 4 , wherein the drive and driven bearings are freely rotatable about their respective axes such that the crossed bearing coupling is substantially incapable of transmitting forces to the carriage in directions non-parallel to the X-axis.  
     
     
         6 . The nut mechanism of  claim 1 , wherein the runner bearing and dummy runner bearing are on diametrically opposite sides of the nut with their axes collinear with each other and extending along the Y-axis.  
     
     
         7 . The nut mechanism of  claim 1 , wherein the runner bearing and dummy runner bearing are freely rotatable about their respective axes so as to roll along the stationary runner surface and dummy runner surface, respectively, when the nut is translated along the X-axis direction.  
     
     
         8 . The nut mechanism of  claim 5 , wherein the axis of the drive bearing defines a Z-axis which is mutually perpendicular to both the X-axis and the Y-axis.  
     
     
         9 . A nut mechanism for translating a carriage along an X-axis by engagement with an externally threaded feed screw which is rotatable about a fixed screw axis parallel to the X-axis, and comprising: 
 a stationary runner adapted to be fixed relative to the X-axis, the stationary runner defining a stationary runner surface which extends parallel to the X-axis;    a nut having an internally threaded bore adapted to threadingly receive the feed screw;    a runner bearing attached to the nut and projecting outwardly therefrom, the runner bearing being rotatable about a Y-axis which is perpendicular to the X-axis, the runner bearing engaging the stationary runner surface to prevent rotation of the nut when the feed screw is rotated such that rotation of the feed screw causes the nut to translate along the X-axis and the runner bearing to travel along the stationary runner surface; and    a slave carriage connected with the nut and adapted to engage the carriage for transmitting force in the X-axis direction from the nut to the carriage, the slave carriage being connected to the nut so as to be rotatable relative to the nut about the Y-axis.    
     
     
         10 . The nut mechanism of  claim 9 , further comprising a pair of bearings mounted on opposite sides of the nut and connected to the slave carriage for rotatably connecting the slave carriage to the nut.  
     
     
         11 . The nut mechanism of  claim 10 , wherein the pair of bearings for mounting the slave carriage to the nut have axes which are collinear with the Y-axis.  
     
     
         12 . The nut mechanism of  claim 11 , further comprising a dummy runner bearing attached to the nut and projecting outwardly therefrom, the dummy runner bearing being rotatable about an axis which is perpendicular to the X-axis and angularly displaced about the screw axis from the runner bearing; and 
 a dummy runner defining a dummy runner surface which extends parallel to the X-axis and engages the dummy runner bearing;    at least one of the dummy runner bearing and dummy runner being biased toward the other so as to rotationally bias the nut in a direction to maintain the runner bearing in contact with the stationary runner surface.    
     
     
         13 . The nut mechanism of  claim 12 , wherein the dummy runner bearing includes a shaft which is resiliently bendable and is preloaded to urge the dummy runner bearing against the dummy runner surface.  
     
     
         14 . The nut mechanism of  claim 12 , wherein the dummy runner bearing and the runner bearing are mounted to the nut on diametrically opposite sides thereof and have their respective axes collinearly aligned along the Y-axis.  
     
     
         15 . The nut mechanism of  claim 12 , further comprising: 
 a first drive bearing attached to a first side of the slave carriage and projecting outwardly therefrom, the first drive bearing having an outer generally cylindrical drive surface defining an axis which is perpendicular to the X-axis; and    a first driven bearing which has an outer generally cylindrical driven surface defining an axis and which is adapted to be attached to the carriage such that the axis of the driven surface is perpendicular to both the axis of the drive surface and the X-axis, and such that the driven surface is engaged by the drive surface to form a first crossed bearing coupling.    
     
     
         16 . The nut mechanism of  claim 15 , further comprising: 
 a second drive bearing having an outer generally cylindrical drive surface defining an axis and attached to the slave carriage on a second side thereof opposite the first drive bearing, the two drive bearings being diametrically opposite each other and symmetrically disposed about the slave carriage; and    a second driven bearing having an outer generally cylindrical driven surface defining an axis and adapted to be attached to the carriage with the axis perpendicular to the X-axis and to the axis of the second drive bearing, the second drive and driven bearings being engageable to form a second crossed bearing coupling;    whereby the two crossed bearing couplings define a line of action for force transmitted to the carriage which is generally aligned with the screw axis.    
     
     
         17 . The nut mechanism of  claim 16 , further comprising a connector mounted to the slave carriage and adapted to be connected to the carriage for transmitting force thereto, the connector including first and second spaced-apart walls between which the slave carriage is disposed, the first wall having the first driven bearing mounted thereon and the second wall having the second driven bearing mounted thereon.  
     
     
         18 . The nut mechanism of  claim 16 , wherein each of the first and second drive bearings comprise a pair of rotatable bearings spaced apart in the direction of the X-axis, the rotatable bearings of each pair having outer generally cylindrical drive surfaces defining axes which are parallel to each other and perpendicular to both the X-axis and the axis of the respective driven bearing, and wherein each driven bearing is disposed between the rotatable bearings of the respective drive bearing to form a biaxial crossed bearing coupling for moving the carriage in two opposite directions along the X-axis.  
     
     
         19 . The nut mechanism of  claim 18 , wherein the pairs of rotatable bearings on the slave carriage have their axes oriented parallel to the Y-axis and the driven bearings have their axes oriented parallel to a Z-axis which is mutually perpendicular to both the X-axis and the Y-axis.  
     
     
         20 . The nut mechanism of  claim 18 , wherein the pairs of rotatable bearings on the slave carriage have their axes oriented parallel to a Z-axis which is mutually perpendicular to both the X-axis and the Y-axis and the driven bearings have their axes oriented parallel to the Y-axis.  
     
     
         21 . A nut mechanism for translating a carriage along an X-axis by engagement with an externally threaded feed screw which is rotatable about a fixed screw axis parallel to the X-axis, and comprising: 
 a frame defining an interior space therein and having an opening for passage of the feed screw into the interior space;    a nut disposed in the interior space and having an internally threaded bore adapted to threadingly receive the feed screw, the nut including a portion which is resiliently bendable relative to the remainder of the nut in a plane perpendicular to the X-axis;    a runner bearing attached to the nut and projecting outwardly therefrom along a first axis which is perpendicular to the X-axis, the runner bearing engaging a stationary runner surface to prevent rotation of the nut when the feed screw is rotated such that rotation of the feed screw causes the nut to translate along the X-axis and the runner bearing to travel along the stationary runner surface; and    a dummy runner bearing attached to the resiliently bendable portion of the nut and projecting outwardly therefrom along a second axis which is parallel to the first axis of the runner bearing and spaced apart therefrom, the dummy runner bearing engaging a dummy runner surface;    the resiliently bendable portion of the nut preloading the dummy runner bearing against the dummy runner surface so as to rotatably bias the nut in a direction to maintain the runner bearing in contact with the stationary runner surface.    
     
     
         22 . The nut mechanism of  claim 21 , wherein the runner bearing and dummy runner bearing are mounted on a first side of the nut, and further comprising a pair of rotatable drive bearings mounted on an opposite second side of the nut, the drive bearings having axes which are spaced apart from and parallel to each other and perpendicular to the X-axis.  
     
     
         23 . The nut mechanism of  claim 22 , further comprising a rotatable driven bearing adapted to be connected to the carriage with an axis of the driven bearing perpendicular to the X-axis and to the axes of the drive bearings, the driven bearing being disposed between the drive bearings so as to form a crossed bearing coupling.  
     
     
         24 . The nut mechanism of  claim 23 , wherein the frame includes an elongate slot parallel to the X-axis through which the driven bearing extends.  
     
     
         25 . A nut mechanism for translating a carriage along an X-axis by engagement with an externally threaded feed screw which is rotatable about a fixed screw axis parallel to the X-axis, and comprising: 
 a stationary runner adapted to be fixed relative to the X-axis, the stationary runner defining a stationary runner surface which extends parallel to the X-axis;    a nut having an internally threaded bore adapted to threadingly receive the feed screw;    a runner bearing attached to the nut and projecting outwardly therefrom along a Y-axis which is perpendicular to the X-axis, the runner bearing engaging the stationary runner surface to prevent rotation of the nut when the feed screw is rotated such that rotation of the feed screw causes the nut to translate along the X-axis and the runner bearing to travel along the stationary runner surface;    a drive bearing attached to the nut and projecting outwardly therefrom, the drive bearing having an outer generally cylindrical drive surface defining an axis which is perpendicular to the X-axis; and    a driven bearing which has an outer generally cylindrical driven surface defining an axis and which is adapted to be attached to the carriage such that the axis of the driven surface is perpendicular to both the axis of the drive surface and the X-axis, and such that the driven surface is engaged by the drive surface to form a crossed bearing coupling.    
     
     
         26 . The nut mechanism of  claim 25 , wherein the drive and driven bearings are freely rotatable about their axes.  
     
     
         27 . The nut mechanism of  claim 25 , further comprising a second rotatable drive bearing having an outer generally cylindrical drive surface defining an axis, the two drive bearings being mounted side-by-side on the nut with their axes spaced apart in the X-axis direction and parallel to each other, the driven bearing being disposed between the drive bearings.  
     
     
         28 . A nut mechanism for translating a carriage along an X-axis by engagement with an externally threaded feed screw which is rotatable about a fixed screw axis parallel to the X-axis, and comprising: 
 a nut having an internally threaded bore adapted to threadingly receive the feed screw;    a stationary runner fixed relative to the screw axis, opposite sides of the stationary runner respectively defining a stationary runner surface which extends parallel to the X-axis and a dummy runner surface which is spaced apart from and parallel to the stationary runner surface;    a runner bearing attached to the nut and projecting outwardly therefrom and being rotatable about a first axis which is perpendicular to the X-axis, the runner bearing engaging the stationary runner surface to prevent rotation of the nut when the feed screw is rotated such that rotation of the feed screw causes the nut to translate along the X-axis and the runner bearing to travel along the stationary runner surface; and    a dummy runner bearing attached to the nut and projecting outwardly therefrom and being rotatable about a second axis which is parallel to the first axis of the runner bearing and spaced apart therefrom, the dummy runner bearing engaging the dummy runner surface.    
     
     
         29 . The nut mechanism of  claim 28 , wherein the nut includes a resiliently bendable portion, the dummy runner bearing being attached to the resiliently bendable portion, and the resiliently bendable portion being preloaded to bias the dummy runner bearing against the dummy runner surface so as to rotatably bias the nut in a direction to maintain the runner bearing in contact with the stationary runner surface.