Bearings – Linear bearing – Recirculating
Reexamination Certificate
2003-05-30
2004-08-24
Butler, Douglas C. (Department: 3683)
Bearings
Linear bearing
Recirculating
C384S051000
Reexamination Certificate
active
06779923
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a roller retainer which is used in a direct-acting guide device, a roller screw, or the like, and in which a roller rolling in a circulation path is held so as to be rotatable/slidable.
2. Description of the Related Art
A roller screw having rollers interposed between a screw shaft and a nut member is known. When the screw shaft is rotated relative to the nut member, the nut member makes reciprocating motion in a direction of the axis of the screw shaft. The rollers make rolling motion so as to go around the outer circumference of a screw groove between the screw shaft and the nut member. Thus, the rollers circulate in a roller circulation path. A helical roller rolling groove is formed in the screw shaft. The roller circulation path containing a helical load rolling groove corresponding to the roller rolling groove is formed in the nut member. In the roller screw, the plurality of rollers may be arranged in the roller circulation path so as to be parallel to one another to keep the axes of adjacent rollers approximately parallel to each other, or the plurality of rollers may be arranged in the roller circulation path so as to cross one another to intersect the axes of adjacent rollers.
Generally, in the case of a full-roller type roller screw in which only rollers are arranged in the roller circulation path, the respective rollers make no consistent motion so that each of the rollers falls down in a plane containing the axis of the roller and the direction of the movement of the roller to cause skew. Hence, the rollers are prevented from circulating while arranged in the roller circulation path. Though not relating to the roller screw, a belt-like ball retainer for rotatably/slidably holding a plurality of balls of a ball screw to make arranged circulation of the balls is known (for example, see JP-A-11-223258). The ball retainer holds the balls in the form of a linear chain so that front-side and rear-side adjacent balls can circulate smoothly.
On the other hand, a cage for holding corresponding one of rollers arranged and received in a circulation path of a direct-acting guide device is known (see JP-A-60-205013).
FIG. 17
shows such cages circulating in the roller circulation path of the direct-acting guide device. A plurality of rollers
1
are cross-arranged in the roller circulation path
2
so that the axes of adjacent rollers
1
cross each other. The direction of the roller
1
is changed two-dimensionally in between a linear load passage
2
a
and a U-shaped changing-direction passage
2
b
.
FIG. 18
is a front view of a cage
3
with a roller
1
when viewed in the direction of the movement thereof.
FIG. 19
is a sectional view taken along the line A—A in FIG.
18
. Because of the cross arrangement of the rollers
1
, the roller circulation path
2
is shaped substantially like a square in section. The cages
3
rotatably/slidably hold the rollers
1
in container holes
3
a
of the cages
3
individually and correspondingly while the outer circumferences
1
a
of the rollers
1
are exposed partially slightly. The thickness of the cage
3
(the radial thickness of the roller) is set to be approximately equal to that of the roller
1
. As shown in the drawings, the shape of the cage
3
viewed from the front side in the direction of the movement forms a square approximately equal to the sectional shape of the roller circulation path
2
so that the roller
1
can be guided by the cage
3
. As shown in
FIG. 17
, two end surfaces
3
a
and
3
b
which form an angle of not smaller than 90° are formed at two ends of the adjacent cages
3
in the direction of the movement thereof. When the cage
3
is located on the linear load passage
2
a
, one end surface
3
a
is positioned so as to be approximately perpendicular to the load passage
2
a
. When the cage
3
is located on the U-shaped changing-direction passage
2
b
, the other end surface
3
b
is directed to the direction of the radius of the changing-direction passage
2
b
. Thus, the cages
3
with the rollers
1
circulate in the roller circulation path
2
while the end surfaces
3
a
and
3
b
of adjacent cages
3
press each other.
In the background-art ball retainer holding balls in the form of a straight chain, however, the circulation path of the ball screw draws a spiral. Hence, the ball retainer is twisted so spirally that load is applied on the ball retainer. There is a risk that the ball retainer may be broken by the load.
On the other hand, the cages
3
by which the rollers
1
arranged and received in the roller circulation path
2
of the direct-acting guide device are held individually are adapted to the case where the linear load passage and the U-shaped changing-direction passage are positioned on one plane so that the direction of the rollers
1
is changed two-dimensionally. For example, in a circulation path of a roller screw, however, not two-dimensional direction changing but three-dimensional direction changing and, accordingly, twisting motion around the direction of the movement, may be required. In the aforementioned cages
3
, the circulating cages
3
are not allowed to rotate slightly around the axes of the rollers
1
respectively so that the cages
3
can hardly make such complex motion. This is because the shape of each cage
3
is formed to be approximately equal to the sectional shape of the roller circulation path
2
and because adjacent cages
3
are in surface contact with each other at large-area flat end surfaces
3
a
and
3
b
. Moreover, a lubricant can hardly enter in between the cage
3
and a corresponding roller
1
because the circumference of the roller
1
except part of the outer circumference
1
a
is covered with the cage
3
. Hence, the roller
1
cannot be lubricated sufficiently. Moreover, the approximately whole section of the roller circulation path
2
is covered with the cage
3
. There is a problem that a support member for supporting the cage
3
to prevent the cage
3
from dropping down from the slide member when the slide member is removed from the race rail is hardly provided in the circulation path.
SUMMARY OF THE INVENTION
An object of the present invention has been made to solve the above object, and therefore an object of the invention is to provide a roller retainer which can circulate smoothly even in a complex kinetic condition such as a three-dimensional changing-direction passage and in which lubricating oil can be supplied sufficiently to rollers, and to provide a direct-acting guide device and a roller screw using such roller retainers.
The present invention will be described below. Although the reference numerals in the accompanying drawings are put in parentheses to make understanding of the present invention easy, the present invention is not limited to the embodiments based on the accompanying drawings.
To solve the problem, the inventor of the present invention provides a system in which rollers circulating in a circulating path are not held in the form of a straight chain but are held in roller retainers individually so that the rollers circulate in a circulation path while the rear-side roller retainer presses the front-side roller retainer. Further, because linear portions and curved portions mainly exit in the circulation path, the inventor considers the shape of each end of the roller retainer in a direction of the movement thereof so that pressing force is transmitted smoothly either in the linear portions or in the curved portions. Further, the inventor provides a system in which roller retainers can circulate while allowed to rotate slightly around the axes of the rollers respectively when the roller retainers circulate while pressing each other. Accordingly, the roller retainers can be adapted to a three-dimensionally complex circulation path on the assumption that the rollers are arranged in the circulation path and the axes of adjacent rollers are substantially kept parallel to each other.
Specifically, according to a first aspect
Butler Douglas C.
King Bradley
Morgan & Lewis & Bockius, LLP
THK Co. Ltd.
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