Note: Descriptions are shown in the official language in which they were submitted.
WO 95/27858 PCT/US95l04381
LINEAR MOTION BEARING
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to anti-friction linear motion bearings and,
more particularly, to linear motion bearing assemblies which facilitate ease
of
manufacture and installation while effecting optimization of contact angle
with the
rolling elements.
2. Descrietion of the Related Art
Linear motion bearing assemblies are well known in the art and are
used extensively in a wide variety of machines, machine tools, transfer
systems and
other equipment where machine elements move with respect to one another. These
assemblies typically include a bearing carriage mounted for movement along a
modified Y-beam, I-beam or T-beam shaped rail. Load bearing and return tracks
are
provided in association with the bearing carriage for a plurality of
recirculating rolling
elements such as, for example, balls or rollers. These rolling elements travel
alternately through the load bearing tracks and return tracks to facilitate
movement of
the bearing carriage along the rail with minimum friction.
End caps are usually located on the ends of the bearing carriage and
may have turnarounds formed therein for transferring the rolling elements from
the
load bearing tracks to the return tracks. The turnarounds typically comprise a
semi-
toroidal shaped track dimensioned and configured for the particular rolling
element
being employed. At the center of the semi-toroid, an internal guide may be
provided
to smooth the movement of the rolling elements in the turnarounds.
The return tracks typically take the form of bores or channels
conforming in size to the dimensions of the rolling elements which are cut or
drilled
into the depending legs of the bearing carriage. See, for example, U.S. Patent
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Nos. 4,932,067 to Pester et al. The overall structure of this type of linear
motion
bearing assembly typically requires the extensive use of expensive high
quality
bearing steel in order to yield a bearing of sufficient strength and
longevity. This is
at least partially necessitated by the fact that load bearing portions require
the strength
and rigidity of bearing steel and are usually monolithically formed directly
in the
structure of the bearing carriage and/or the rail. See, for example, U.S.
Patent No.
4,637,739 to Hattori. Fabrication of the rails and/or carriages from such
material
requires numerous precision machining steps as well as hardening processes on
designated areas such as, for example, the contact portions of the load
bearing tracks
in both the carriage and the rail. This process is extremely costly and,
depending on
the bearing assembly structure, requires elaborate and expensive machining
equipment. In addition, one characteristic of high quality bearing steel is
its rigidity.
This characteristic results in a requirement for extreme precision in grinding
the load
bearing tracks and highly accurate installation of the linear motion bearing
assembly
to avoid overly stressing the contact portions.
Attempts have been made in the past to isolate the highly stressed
contact points within the linear motion bearing assemblies by providing
inserts which
are mounted to conventional rail or carriage structure. See, for example, U.S.
Patent
Nos. 3,900,233 and 4,025,995 to Thomson. Load bearing track inserts are also
shown in U.S. Patent Nos. 4,515,413, 4,527,841, 4,531,788 and 4,576,421 to
Teramachi and U.S. Patent No. 4,576,420 to Lehmann et al. However, these
linear
motion bearings do not address or overcome the inherent rigidity problem
characteristic of these materials. Thus, extreme precision and accurate
placement are
still very definite factors affecting the operation and longevity of the
linear motion
bearing assembly.
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Attempts have also been made in the past to reduce this inherent
rigidity of structures formed entirely of high quality bearing steel. For
example, U.S.
Patent No. 5,217,308 to Schroeder discloses an internal carriage structure for
a
linear motion bearing assembly. The carriage is configured to be supported
within a
frame structure by four inward facing steel raceways mounted to the frame
structure.
The frame structure is constructed of aluminum and is configured to allow for
flexure
of the upper races to take up clearances within the assembly.
Therefore, it would be highly desirable to have an easily manufactured
linear motion bearing assembly which reduces the need for extensive precision
drilling, hardening and/or grinding of contacting surfaces on the carriage and
on the
rail while providing a dependable bearing assembly which is capable of a high
degree of flexural movement when placed under load to optimize the contact
angle
of the rolling elements in the load bearing tracks.
Accordingly, it is a feature of one embodiment of the present invention
to provide an easily manufactured linear motion bearing assembly which
minimizes
the use of expensive high quality bearing steel while providing the capability
of
optimizing the contact angle of the rolling elements and load bearing tracks.
It is a further feature of the present invention to provide a linear motion
bearing wherein, in preferred embodiments, the contacting load bearing
portions of
the carriage and rail are formed of high quality steel inserts which are
fitted into
relatively flexible carrier structure.
It is also a feature of the present invention to provide, in preferred
embodiments, a reliable linear motion bearing assembly which can be easily
fabricated with a minimum of bearing steel elements without the need for
precision
grinding and hardening directly on the carriage block and/or rail.
These and other highly desirable features are accomplished by the
present invention in a linear motion bearing having bearing steel track
inserts fitted
into the depending legs of the bearing carriage and the rail. The balance of
the
bearing assembly is constructed of more flexible material such as, for
example,
machine grade aluminum, plastics or less expensive grades of steel to
facilitate easy
and accurate assembly of the linear motion bearing assembly. The parts are
configured without the need for precision grinding or hardening of tracks
directly on
the carriage and/or rail.
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Advantages of the invention are set forth in part herein and in part will
be obvious therefrom, or may be learned by practice with the invention, which
is
realized and attained by means of the instrumentalities and combinations
pointed out
in the appended claims. The invention consists of novel parts, constructions,
arrangements, combinations, steps and improvements herein shown and described.
SUMMARY OF THE INVENTION
In accordance with the present invention, there is provided a linear
motion bearing having load bearing tracks formed of high quality bearing steel
load
bearing track inserts mounted in the bearing carriage assembly and/or the rail
assembly. Axial grooves are also formed in both the bearing carriage assembly
and/or the rail assembly to optimize the contact angle of the rolling elements
under
load. This construction simplifies manufacture and avoids the need for
difficult and
expensive grinding and hardening of load bearing tracks directly on the
bearing
carriage and rail.
In accordance with one embodiment of the present invention there is
provided a linear motion bearing assembly comprising: a rail assembly
including an
elongate base member having a pair of vertical arms, the vertical arms having
respective inner surfaces and outer surfaces, the vertical arms being flexible
with
respect to the base member; a bearing carriage assembly including a bearing
carriage, a pair of depending legs extending therefrom, the depending legs
having
respective facing and opposing sides, the facing sides defining a longitudinal
channel for accommodating the rail assembly, the depending legs being flexible
with
respect to the bearing carriage; a plurality of load bearing inserts, each of
the inserts
defining a portion of at least one load bearing track thereon, the inserts
being
positionable on the facing sides of the depending legs to define a plurality
of load
bearing tracks between the vertical arms and the depending legs; and a
plurality of
rolling elements disposed in the load bearing tracks.
In accordance with another embodiment of the present invention there
is provided linear motion bearing assembly comprising: an elongate rail
assembly
including an aluminum base member having a pair of substantially parallel arm
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members extending the longitudinal length of the rail assembly, the arm
members
having respective inner surfaces and outer surtaces, the inner surtaces
defining a
longitudinal groove, the outer surfaces defining rail assembly insert
receiving
structure; a plurality of rail assembly load bearing inserts, said inserts
having an
outer surface and an inner surface, the outer surface having a plurality of
parallel
grooves formed therein defining a portion of a plurality of load bearing
tracks, the rail
assembly load bearing inserts being disposed in the insert receiving structure
formed
in the outer surfaces of the parallel arm members; a bearing carriage assembly
including an aluminum bearing carriage, a pair of depending legs extending
therefrom, the depending legs having respective facing and opposing sides, the
facing sides defining a longitudinal channel for accommodating the rail
assembly, the
facing sides further including carriage assembly insert receiving structure; a
plurality
of carriage load bearing inserts, each of the inserts including a plurality of
parallel
grooves formed therein defining a portion of a plurality of load bearing
tracks, the
carriage load bearing inserts being disposed in the carriage assembly insert
receiving structure of the faces sides of the depending legs; and a plurality
of rolling
elements disposed in the load bearing tracks such that upon loading of the
bearing
carriage assembly, the load bearing inserts are flexible into an optimized
contact
angle with respect to the rolling elements.
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Further, less expensive materials of construction such as, for example,
aluminum, plastic or non-bearing quality steel may be used to mount the
inserts. The
material of construction may also be selected based on its desirable flexural
characteristics without being constrained to the use of relatively rigid high
quality
S bearing steel.
This structure provides an inexpensive and dependable linear motion
bearing assembly that is easy to fabricate, assemble and install.
BRIEF DESCRIPTION OF THE DRAWINGS
The accompanying drawings, referred to herein and constituting a part
hereof, illustrate the preferred embodiments of the apparatus of the present
invention,
and, together with the description, serve to explain the principles of the
invention.
FIG. 1 is a perspective view of an assembled linear motion bearing
assembly in accordance with a preferred embodiment of the present invention.
FIG. 2 is a perspective view similar to FIG. 1 with one of the carriage
end caps removed.
FIG. 3 is a perspective view with parts separated of the carriage of the
linear motion bearing assembly in FIG. 1.
FIG. 4 is a perspective view with parts separated of the rail assembly
of the linear motion bearing assembly of FIG. 1.
FIG. 5 is an end view with the end cap removed of the assembled
linear motion bearing assembly of FIG. 1.
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DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
Referring now to the drawings in detail, and initially to FIGS. 1 and 2,
a fully assembled linear motion bearing assembly 20 in accordance with the
present
invention is shown. The assembly includes an inverted substantially U-shaped
bearing
carriage 22 configured and dimensioned to move along a rail assembly 24 on
rolling
elements 25. Although shown here as balls, other rolling elements are also
contemplated including rollers. End caps 26 are positioned on each
longitudinal end
of the bearing carriage 22. The end caps 26 include semi-torridal turnarounds
29
integrally formed in each of the end caps 26 and serve to enclose and connect
corresponding load bearing and return tracks, 28 and 30 respectively, located
in
depending legs 32 of the bearing carriage 22. As best seen in FIG. 2, return
tracks
28 comprise parallel longitudinal bores drilled axially through the depending
legs 32
of the bearing carriage 22. Mounting holes 34 are formed in the upper planar
surface
of the bearing carriage 22 and facilitate engagement of the bearing assembly
to
desired machinery components. Longitudinal mounting bores 36 are formed in
each
longitudinal end face of the bearing carriage 22 and serve to attach end caps
26.
Inner guides 27 are positioned between the ends of the load bearing tracks 28
and
return tracks 30. These inner guides 27 ease the movement of the rolling
elements 25
between the respective tracks.
Refernng now to FIG. 3, the individual components of the bearing
carriage 22 are shown in detail. The bearing carriage 22 is preferably formed
of a
relatively flexible machine grade material such as, for example, aluminum,
plastic or
steel. The interior facing surfaces 38 of depending legs 32 are configured and
dimensioned to receive load bearing track inserts 40. These inserts 40 are
formed of
a high quality bearing steel and include a pair of parallel grooves 42 formed
in an
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inner face 44. These grooves 42 make up a portion of the load bearing tracks
28 and
are configured and dimensioned in an appropriate cross-sectional shape to
conform to
the rolling elements 25 employed in the bearing assembly 22.
The load bearing track inserts 40 can be easily and efficiently formed
in long sections by known cold drawing processes and subsequently cut to the
desired
length prior to assembly. To facilitate manufacture, the cross-sectional area
of the
load bearing track inserts is preferably substantially uniform in thickness.
Depending
legs 32 are further provided with a longitudinal relief 66 on an outer surface
thereof
adjacent the intersection of the depending legs 32 with the remainder of the
carriage
22. This relief 66 provides additional flexural characteristics to the
depending legs 32
as discussed below.
With reference to FIG. 4, the rail assembly 24 in accordance with a
preferred embodiment of the present invention includes a substantially U-
shaped base
member 46 formed of a machine grade aluminum and is extruded using known
production techniques. The base member 46 includes a pair of parallel vertical
arms
48 defining an axial groove 50 along the longitudinal length of the base
member 46.
This configuration provides an advantageous degree of flexibility to the
vertical arms
48.
Dove-tailed channels 52 are formed in opposed sides of vertical arms
48 substantially parallel to axial groove 50. A load bearing track insert 54
is
configured and dimensioned to fit within each of the channels 52 and defines a
portion
of load bearing tracks 28. As in the carriage load bearing track inserts 40
discussed
above, rail load bearing track inserts 54 are produced from a high quality
hardenable
bearing steel using known cold drawing processes. The inserts are hardened in
line
by known techniques such as, for example, induction heating and quench.
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The inserts 54 are preferably formed with a longitudinal relief 56 on an
inner surface thereof. This relief 56 gives the insert 54 a degree of
flexibility which
enhances its final assembly to the rail. The inserts 54 preferably have a
substantially
uniform thickness in cross-section and include parallel load bearing grooves
58.
The load bearing track inserts 54 are easily mounted to the base
member 46 by configuring the relative dimensions of dove-tailed channels 52
and
insert 54 such that the inserts fit into the channels with some clearance. The
upper
flange 60 of the channel 52 is plastically deformed over the uppermost portion
of the
insert 54, effectively locking it into place on the base member 46. During
this plastic
deformation process, the insert 54 will deform, much as a spring, by virtue of
the
shape and design of the longitudinal relief 56. The tendency of the insert 54
to return
to its original unstressed configuration produces a secure connection between
the
insert 54 and the base 46.
Referring to FIG. 5, the advantageous features of this construction are
graphically presented. With the application of a load or force "F" in the
direction of
the arrow, load is transmitted through the carriage 22, load bearing tracks
28, and
rolling elements to the fixed rail assembly 24. Axial groove 50 formed in the
base
member 46 allows the rail assembly to deform in response to the applied load.
This
allows for the correct compliance and orientation of each of the vertical arms
48 and
allow for translation of the carriage load bearing track centerline 62. As
this
centerline 62 moves with respect to the rail load bearing centerline 64, the
angle of
contact rotates from its initial position represented by angle "A" to its
loaded position
represented by angle "B" . Since the final angle "B" is more aligned with the
orientation of the applied load, the contact angle is effectively optimized.
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Where a load is applied in an opposite direction, i.e. a "lift-off' force,
a similar reaction occurs. Because the carriage is formed of a relatively
flexible
material such as, for example, aluminum, the depending legs 32 can flex
outward to
again optimize the contact angle. In addition, relief 66 referred to above,
may be
formed on the outer opposing surfaces of the depending legs 32 at the
intersection
between the legs 32 and the carriage 22. This relief 66 provides a flexure
line for
allowing realignment and/or reorientation of the carriage load bearing track
portions
formed in insert 40.
In addition to the optimization of contact angle provided by this
construction, the manufacture and assembly of this linear motion bearing
assembly is
greatly simplified over the prior art. This results from the optimizing
compliance
described above that allows the use of materials, processes and tolerances
that are
much less costly than those in existing product manufacture.
To the extent not already indicated, it also will be understood by those
of ordinary skill in the art that any one of the various specific embodiments
herein
described and illustrated may be further modified to incorporate features
shown in
other of the specific embodiments.
The invention in its broader aspects therefore is not limited to the
specific embodiments herein shown and described but departures may be made
therefrom within the scope of the accompanying claims without departing from
the
principles of the invention and without sacrificing its chief advantages.
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