Machine element or mechanism – Mechanical movements – Reciprocating or oscillating to or from alternating rotary
Reexamination Certificate
1998-11-13
2001-03-20
Fenstermacher, David (Department: 3682)
Machine element or mechanism
Mechanical movements
Reciprocating or oscillating to or from alternating rotary
C074S424830
Reexamination Certificate
active
06202498
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to ball screw arrangements, and more particularly, to a compact recirculating ball linear bearing arrangement wherein ball recirculation is effected within a recess in the ball screw whereby axial translation of the ball screw along the length of an elongated nut is achieved the response to the application of a rotatory drive to the nut.
2. Description of the Related Art
A number of arrangements are available in the prior art wherein a ball screw and nut mechanism include an insert in the nut whereby balls are recirculated in the nut. Other known recirculating ball screw arrangements include a ball recirculating member that cooperates with a lead screw to urge the balls out of their normal track to transfer the balls over the lead screw in an axial direction and then deposit same back onto the ball track.
All of the known arrangements are large in the radial direction and therefore cannot be accommodated in a compact environment. Thus, for example, the known arrangements cannot readily be accommodated within the confines of a drive motor to achieve an arrangement having a compact radial dimension and that facilitates a linear displacements of the ball screw to an extent that corresponds to a significant proportion of the overall axial dimension of the motor drive.
It is, therefore, an object of this invention to provide a compact linear drive arrangement that has a reduced radial dimension requirement.
It is another object of this invention to provide a ball screw arrangement wherein ball recirculation does not require displacement of a ball further radially outward than the helical groove of the race.
It is also an object of this invention to provide an arrangement for facilitating assembly of the compact ball screw arrangement of the present invention.
It is additionally an object of this invention to provide a compact drive arrangement wherein a linear translation bearing is contained within a drive motor system.
It is yet a further object of this invention to provide a compact linear translation bearing arrangement wherein linear translation is achieved from within the motor drive arrangement and extends for a significant portion of the overall length of the drive arrangement.
It is yet an additional object of this invention to provide a splined linear bearing arrangement wherein an actuator element is coupled thereto in rotatively fixed relation, and is axially translatable with respect thereto.
SUMMARY OF THE INVENTION
The foregoing and other objects are achieved by this invention which provides, in a first apparatus aspect thereof, an axial displacement arrangement having a ball screw shaft with an external helical ball race formed therein. The helical ball race has a predetermined pitch and is arranged at a predetermined race groove radius with respect to a longitudinal axis of the ball screw shaft. Additionally, there is provided a recirculation arrangement in the ball screw shaft for recirculating balls in the helical race of the ball screw shaft whereby a ball recirculation circuit is formed.
In one embodiment of the invention, the recirculation arrangement is provided with a recirculation race formed in the ball screw shaft for forming an axial race path between predetermined points of the helical race. Such interconnection of the predetermined points of the helical race by the recirculation race forms the recirculating ball circuit. In addition, there is provided a recirculation race cover arranged to overlie the recirculation race. The race cover maintains the balls within the ball screw shaft during their respective traverse of the recirculation race. Additionally, the outer surface of the race cover does not extend outward of the maximum diameter of the ball screw shaft with the balls thereon, and therefore recirculation within the ball screw shaft is insured. Thus, the recirculation race has a predetermined race groove radius with respect to the longitudinal axis of the ball screw shaft which is shorter than that of the race groove radius. The recirculating balls, therefore, are rolled closer to the central axis of the ball screw shaft during recirculation.
In a highly advantageous embodiment of the invention, there is provided an axial support that is disposed in an axial hollow portion of the ball screw shaft. The ball screw shaft is axially translatable along the axial support. Preferably, the axial support is provided with longitudinal splines extending there along, the longitudinal splines operating to prevent rotation of the ball screw shaft with respect to the axial support. Thus, the ball screw shaft can translate axially along the axial support, but is not rotatable with respect thereto.
In a preferred embodiment, there is provided a plurality of ball bearings interposed between the axial support and the ball screw shaft. The ball bearings are circumferentially confined within respective support races that are disposed between circumferentially adjacent ones of the longitudinal splines. Thus, the ball bearings interposed between the axial support and the ball screw shaft are relegated to travel axially along the axial support. In a practical embodiment, the ball bearings interposed between the axial support and the ball screw shaft are confined to remain within the axial dimension of the ball screw shaft by operation of segmented ball recirculation end caps. Thus, as the ball screw shaft is translated along the axial support, the interposed ball bearings travel with the ball screw shaft.
In accordance with a further apparatus aspect of the invention, there is provided an axial displacement arrangement having a support having a longitudinal axis defining the axial displacement. An actuator element is coupled to the support means and is axially displaceable with respect thereto for effecting the axial displacement. Ball bearing supports are interposed between the support and the actuator element. On the outer surface of the actuator element there is provided a helical ball recirculation arrangement that is axially displaceable with respect to the support. The helical ball recirculation arrangement is provided with an external helical race having a predetermined external race pitch and is arranged to surround at least a portion of the helical ball recirculation arrangement. Additionally, the helical ball recirculation arrangement is provided with a transfer race for coupling the external helical race axially to itself whereby a ball recirculation circuit is formed. A ball recirculation cover is arranged to overlie the transfer race. Moreover, a nut having an internal helical race formed therein, the internal helical race having an internal race pitch that corresponds substantially to the predetermined external race pitch, is provided and has an internal helical race that is axially longer than the external helical race of the helical ball recirculation arrangement.
In one embodiment of this further aspect of the invention, there is provided a rotatory drive arrangement for turning the nut with respect to the support. Such rotation of the nut causes the helical ball recirculation arrangement and the actuator coupled axially thereto to be translated axially among the support and the interior of the nut. In one embodiment, the rotatory drive arrangement is in the form of an electric motor that is coupled to the nut. In a highly advantageous embodiment of the invention, the electric motor surrounds the nut. The electric motor is mechanically coupled to the support. This precludes any rotation of the electrical motor with respect to the support.
In such an embodiment of the invention, the axial length of the helical ball recirculation arrangement is responsive to the number of ball recirculation circuits thereon, and is significantly shorter than the axial length of the nut. The maximum translation, therefore, is responsive to the difference between the length of the helical ball recirculation arrangement and the axial length of the internal helical race of the nut.
In acc
Beaver Aerospace & Defense, Inc.
Fenstermacher David
Rohm & Monsanto, P.L.C.
LandOfFree
Screw with recirculating ball arrangement does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Screw with recirculating ball arrangement, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Screw with recirculating ball arrangement will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2503669