Note: Descriptions are shown in the official language in which they were submitted.
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POLYMER LINEAR GUIDE
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to linear guides having a slide body and a guide
rail. More
specifically, the present invention relates to a linear guide in which the
slide body, the guide rail,
or both are unitarily constructed of polymer, coated, or otherwise provided
with a polymer
bearing surface.
2. Description of the Prior Art
Linear motion guides are an important component in the construction of
automated and
other equipment. The linear motion guide (hereinafter just "linear guide")
provides for high
precision as a piece of equipment, such as a robotic arm or workpiece, is
linearly moved back
and forth over a relatively long distance. Since each linear guide has only a
single degree of
freedom, longitudinally along its guide rail, multiple linear guides may be
used in combination
to provide additional degrees of freedom for the moving of the equipment.
Generally, linear guides have two primary components, a guide rail (also known
as a
track and hereinafter referred to as a "rail") and slide body (hereinafter
just referred to as a
"slider"). The slider and rail are designed so that the slider mounts and
moves along the rail
without play or backlash. This is achieved by employing a bearing mechanism
between the
two.
In one variety of prior linear guide, recirculating ball bearings are captured
within the
slider and contact a bearing race formed in the rail. Such systems are
relatively costly to
produce and replace. When worn, the construction of the recirculating ball
bearing slider is
such that, at a minimum, the entire slider must be replaced and, more
typically, both the slider
and rail. It is not feasible to merely replace the ball bearings because of
the wear in the
raceways where the bearings contact the slider and the rail.
Another type of linear guide actually eliminates the use of recirculated ball
bearings
while still providing the necessary low sliding friction between the slider
and the rail. In this type
of linear guide, a bearing material is permanently bonded to the slider so as
to provide a contact
interface between the slider and the rail. Polymer materials used to form
these bearing
surfaces have included nylon, polytetrafluorethylene (PTFE) and numerous
others. Such a
design is generally considered to be maintenance free in that there is no need
for wet lubricants
since the polymer chosen typically provides a built-in and permanent
lubrication.
Some drawbacks on the above designs are the required separate manufacture of
the
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slider and bearing portion and the mounting of the bearing material to the
slider. Such mounting
typically involves the bonding of the polymer, in a predetermined thickness,
to areas of the
slider so as to engage the rail. The bonding procedure itself is sometimes
complex and costly,
depending on the specific polymer and slider materials involved. Additionally,
concerns may
arise regarding a failure of the bond during use and any resulting
consequences.
One alternative approach to bonding the polymer to the slider is disclosed in
U.S. Patent
No. 5,735,610, issued April 7, 1998, the subject matter of which is hereby
incorporated by
reference. In that patent the slider requires replaceable polymer inserts upon
which the slider
slides.
In view of the foregoing limitations and shortcomings of the prior art
devices, as well as
other disadvantages not specifically mentioned above, it should be apparent
that there still
exists a need in the art for an improved linear guide.
It is therefore a primary object of this invention to fulfill that need by
providing a linear
guide which eliminates the need for ball bearings or for the bonding of the
polymer material to
the slider.
Another object of the present invention is to provide a linear guide which
eliminates the
need for separately manufacturing the slider and the bearing.
A further object of the present invention is to provide a linear guide in
which the bearing
element and the slider or rail are formed as a unitary component.
SUMMARY OF THE INVENTION
Briefly described, these and other objects are accomplished according to the
present
invention by providing a linear guide, as with prior linear guides which
includes a slider that is
slidably mounted to a guide rail. However, in the present invention the
slider, and in alternate
embodiments the rail, defines the bearing surface which allows the slider and
rail to move
relative to each other.
The slider of the present invention includes a body having a top, a bottom,
opposing
sides and opposing ends. Portions of the body define a channel that extends
longitudinally
through the length of the body, between the opposed ends. The channel has an
open side
generally in the direction of the bottom of the body and exhibits a cross-
sectional shape which
allows the rail to be received therein. The rail has opposing ends that define
its length, which
is greater than the length of the body. The interaction between the cross-
sectional shape of the
body and the rail is of a low clearance and allows for movement of the body
along the rail
restricting movement to a single degree of freedom. Lateral or vertical
movement of the body
relative to the rail is accordingly inhibited.
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The slider or rail is made from one of several preferred polymeric materials
having a low
coefficient of friction, high load capacity and good wear characteristics
which facilitates the
longitudinal sliding movement of the slider relative to the rail. The present
invention
encompasses embodiments where the slider is composed of polymer and the rail
is a non-
polymeric material, where the rail is composed of polymer and the slider is a
non-polymeric
material, where both the rail and slider are composed of polymer, where the
rail has polymer
bonded to a non-polymeric core, and where the rail includes replaceable
polymer bearing
inserts. In embodiments where both the rail and slider are made of polymeric
materials, it is
preferable that they be made from different polymeric materials.
By providing the bearing element as outlined above, several of the embodiments
of this
invention have the slider directly engaging the rail, eliminating the need for
a separate bearing
carried by the slider or bonded to the slider.
Additional benefits and advantages of the present invention will become
apparent to
those skilled in the art to which the present invention relates from the
subsequent description
of the preferred embodiments and the appended claims, taken in conjunction
with the
accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view of a linear guide embodying the principles of the
present
invention;
FIG. 2 is an exploded view of a linear guide according to the principles of
the present
invention;
FIG. 3 is a sectional view taken substantially along line 3-3 in FIG. 1
illustrating various
features of the present invention;
FIGS. 4-7 are a sectional views taken substantially along line 3-3 in FIG. 1
of alternate
embodiments of the present invention;
FIGS. 8a-8b are alternate views of an alignment mechanism for the slider of
the present
invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Refen-ing now in detail to the drawings, there is shown in FIG. 1 a linear
guide, generally
designated at 10, embodying the principles of the present invention. The
linear guide 10
principally includes a guide rail ("rail 12") on which is supported a slide
body ("slider 14").
Depending on the specific embodiment of the present invention which is being
referred to for
discussion, the rail 12 or slider 14 may be constructed out of aluminum,
steel, polymer or other
suitable material.
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The rail 12 is a longitudinal member and includes a top surface 16, a bottom
surface 18,
and opposing side surfaces 20. Vertical bores 22 are provided in the rail 12,
extending from
the top surface 16 to the bottom surface 18, to enable the securing of the
rail 12 to a suitable
base or table by fasteners such as screws (not shown). The bores 22 are
provided in a manner
which will allow the heads of the fasteners to be counter sunk beneath the top
surface 16. In
this way, the fasteners will not interfere with movement of the slider 14
along the guide rail 12.
The side surfaces or sides 20 of the rail 12 are profiled such that inclusions
24 are
directed generally toward one another inwardly of the rail 12. The inclusions
24 are provided
in the shape of trapezoidal indentations into the sides 20. As further
discussed below, the
inclusions 24 cooperate with protruding portions of the slider 14 to retain
the slider 14 on the
rail 12 and limit relative movement between the two to an axial or
longitudinal direction along
the rail 12.
Referring now to FIGS. 2 and 3, the slider 14 is a generally rectangular body
which
includes a top surface 26, a bottom surface 28, opposed side surfaces 30 and
opposed end
surfaces 32. The top surface 26 forms a generally planar surtace to which at
least a portion of
the component to be guided by the linear guide 10 is mounted. To facilitate
this mounting,
mounting bores 34 are vertically provided in the top surface 26 and into the
slider 14. Bolts or
other fasteners (not shown) can be extended through the slider 14 and through
the mounting
bores 34 allowing a nut or other engagement mechanism (not shown) to engage
the opposing
end of the fastener. If desired, the bores 34 may be threaded or provided with
threaded inserts
(molded or otherwise formed therein) to engage the fastener, without further
engagement with
the nuts. Cut-outs 36, axially aligned with the mounting bores 34, are formed
in the slider 14
to recess the nuts (if utilized) within the exterior dimensions of the slider
14. The cut-outs 36
are illustrated as extending upward from the bottom surface 28 and inward from
the side
surfaces 30 and end surfaces 32 to locate the cut-outs 36 generally in the
four corners of the
slider 14. Obviously, alternative locations and configurations, or even
complete elimination
thereof of the cut-outs 36 could be employed depending on the specific design
criteria of the
linear guide 10 and its intended application.
Formed longitudinally through the slider 14 and generally being open in the
direction of
the bottom surface 28, is a channel 38 whose cross-sectional shape generally
corresponds to
the cross-sectional shape of the rail 12. As seen in FIG. 3, the cross-
sectional shape of the
channel 38 is closely dimensioned to conform to the cross-sectional shape of
the rail 12.
Adjacent to the bottom surface 28, the protrusions 40 define a necked-down
entrance area into
the channel 38 and this cooperates with the channel to inhibit vertical and
lateral movement of
the slider 14 relative to the rail 12.
While the above discussed shapes of the rail and the channel have been
detailed with
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some particularity, it will be understood that these shapes can be provided in
numerous
alternative configurations. All such shapes are therefore considered to be
equivalents of the
illustrated shape, so long as the above general operating parameters of the
linear guide are
met.
As briefly mentioned above, the slider 14 rests directly on the rail 12 and
its channel 38
defining surfaces function and operate as a bearing element. Alternatively,
the surfaces
defining the channel 38 can include a series of protuberances or raised
sections not shown,
extending partially or fully along the length of the channel 38, which engage
the rail 12 and
operate as a bearing surface of the slider 14.
The slider 14 in the preferred embodiment utilizes a self alignment mechanism
47
which includes spring biased plungers 48, as seen in FIGS. 8a and 8b. The
plungers 48
provide for self alignment of the slider 14 relative to the rail 12. A
plurality of bores 46 extend
laterally through slider 14 so that the plungers 48 (three in the illustrated
embodiment) contact
the rail 12 at an upper vertical face 49 thereof. Notably, the bores 46 are
equidistantly located
along the length of the slider 14 for equalizing the loading and self
alignment of the slider 14
relative to the rail 12. The contact between the plungers 48 and the rail 12
is adjustably
provided by the incorporation of coil springs 50 or other biasing mechanism
/member between
the plunger 48 and a set screw 52 which is threadably received in the bore 46.
The force
exerted by the plungers 48 on the rails 12 is varied by progressively
advancing or retracting
the set screws 52. This change in position varies the force exerted by the
plungers 48 upon the
rail 12 and allows the position of the slider 14 to self-align relative to the
rail 12. In the preferred
embodiment three plungers 48 are used to self-align said slider 14 with said
rail 12, although
a greater or lesser number could be used. The plungers 48 are themselves made
of a low
friction polymeric material, such as one of the materials described below,
since they too contact
and slide along the rail 12.
In another preferred embodiment, the plungers 48 are retained in threaded
casings that
are threaded into the bores 46. Within the casing is a spring that biases the
plunger such that
the plunger partially protrudes from a necked down portion of the casing. The
opposite end of
the casing is closed to retain the spring and include a drive socket or head
allowing it to be
advanced or retracted in the bore 46. By advancing or retracting the casing
relative to the bore
46, or by providing a more or less stiff spring within the casing, the force
is exerted by the
plungers 48. While the plungers 48 may directly contact the rail 12, they also
may all contact
a common gib which is itself in contact with the rail 12. The gib is supported
by the body 14 or
may extend approximately the length of the body 14. As such, the gib may be
received in an
axial slot formed in the body 14 and is mounted with respect thereto for a
limited amount of
transverse movement, for example 0.001 inches. Since it contacts the rail 12,
the gib is made
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of a low friction polymer and, in this embodiment, the plunger 48 may be of a
different material,
such as steel.
To form the slider 14, the polymer material may be cast or otherwise molded
into the
desired end shape, may be extruded into the desired end shape, or may be
initially formed in
any manner and then machined into the desired shape. The bores 34 and 46
mentioned above
are machined or molded into the slider 14. If the bores 34 and 46 are
threaded, the internal
threads are either tapered into a machined bore or internally threaded inserts
(of metal or other
suitable material), known as hell-coils, are molded in place within the body
of the slider 14 or
mounted into the bores 34.
The basic operating limits for a linear guide 10 according to the present
invention are
anticipated to be: load (300-750 Ibs./slide body); pressure/velocity level
(approximately 7500);
and maximum operating temperature (300-500° F) up. Obviously, operating
parameters
beyond the above listed parameters could be employed upon appropriate design
considerations
being employed. For example, the load capacity of the linear guide 10 might be
increased by
the inclusion of reinforcement members (such as rods, mesh, grids or other
structures) within
the body of the slider 14 during initial formation.
As seen above, in addition to withstanding the anticipated operating
parameters, the
material from which the slider 14 is formed needs to have a low coefficient of
friction, good wear
capabilities and not necessarily require wet lubricants. Any suitable material
which meets the
above criteria therefore constitutes a preferred material of this invention.
Representative materials include, without limitation, thermosetting polymers
such as
epoxy resins, allyl esters, amino polymers, phenolics, polyesters, polyamides
and nylons,
cyanoacrylates, polyurethanes, silicones and mixtures thereof; thermoplastic
polymers such as
polystyrene, polyethylene, polyvinyl chloride, polyethylene terapthalate, and
mixtures thereof;
materials with characteristics of both of the above varieties of polymers; and
plastic lubricants
such as polytetrafluroethylene (PTFE) and filled PTFE. The polymer could also
include known
self or solid lubricating components. Generally, an acceptable polymer will be
any polymer
capable of carrying an adequate load while maintaining low friction
characteristics.
One specific preferred polymer material, having a PV of 7500, an operating
temperature
range of over 300° F, is an extruded polyamide-imide commercially
available from the DSM
Polymer Corporation, Reading, Pennsylvania under the tradename of TORLON. The
coefficient friction of this material is 0.20, the operating temperature range
of this material is
over 500° F (making the material much stronger at elevated
temperatures), the thermal
expansion rate of the material is significantly low (allowing for closer
tolerances between the
parts) and the PV limit (45,000) greatly exceeds the anticipated requirements
for most known
applications of linear guides 10. Another preferred material is commercially
available under the
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tradename NYLATRON from the above mentioned company.
As seen in the embodiment of FIG. 3, the rail 12 is made from a suitable
materials, such
as aluminum or steel, and is coated or otherwise provided with an exterior
surface having a low
coefficient of friction. One such method of providing the low coefficient
surface is via a
synergistic coating. Such coatings are advantageous because of their
wearability, low friction,
anticorrosion and non-sticking characteristics. Such coatings are well known
and involve the
conversion of the base metal surface into an oxide (ceramic) surface and the
disposition or
infusion of a polymer (such as a fluropolymer) into the oxide surface
resulting in a new surface
with superior performance characteristics.
In an alternate embodiment, seen in FIG. 5, the rail 12 is polymeric and the
slider 14 is
made of a non-polymeric material such as aluminum or steel. As with the
embodiment of FIG.
3, the non-polymeric material is provided with an exterior surface (at least
where it contracts
the rail) having a low coefficient of friction. Again, such a surface may be
provided via a
synergistic coating. The rail 12, is constructed of the materials mentioned
above in connection
with the slider 14 of the embodiment seen in FIG. 3 and can be manufactured by
any of the
aforesaid methods.
Referring now to FIG. 4, the slider 14 and rail 12 are both shown as being
composed
of polymeric materials. In the preferred embodiment the slider 14 and the rail
12 are made of
different polymeric materials. The dissimilarity in polymeric materials
between the slider 14 and
rail 12 decreases the friction between the slider 14 and rail 12, as the
slider 14 traverses the
rail 12.
In the embodiment seen in FIG. 6, the rail 12 of the embodiment therein has
bonded to
it a corresponding covering 60 of suitable polymeric material. The covering 60
provides a
bearing surface, at least in those areas engaging the slider 14, similar to
the bearing surtaces
previously discussed. Various methods are known for bonding polymer to
aluminum or steel
and such methods are employed in this embodiment.
In the embodiment seen in FIG. 7, a non-polymeric rail 12 is provided with
longitudinal
slots 62 in which removable polymeric inserts 64 are mounted. The polymeric
inserts 64 serve
as a bearing surface between the slider 14 and rail 12. The polymeric inserts
include feet 66
or are otherwise shaped or keyed to matingly engage and be retained in the
slots 62. The
inserts 64 are easily removed or installed by sliding the inserts 64,
specifically the feet 66, in
a longitudinal direction along the rail 14 in and out of the correspondingly
shaped slots 62.
Once the inserts 64 are in place, the ends of the rail 12, which give access
to the installation
and removal of the inserts 64, receive end caps (not shown) which cover the
ends of the slots
62 into which the inserts 64 are inserted. The end caps are shaped to
correspond to the profile
or cross-sectional shape of the rail 12 and are secured thereto by screws or
other suitable
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fasteners. In this manner, the inserts 64 are captured and retained in the
slots 62 of the rail 12.
The inserts 64 are again formed of one of the above mentioned or similar
materials and may
be formed by any appropriate method, including casting, machining, extruding
or other method.
Accordingly, the feet 66 similarly cooperating with the slots 62 prevent the
lateral dislodgment
of the inserts 64 so that a rigid installation of the inserts 64 is possible.
While the above description constitutes the preferred embodiment of the
present
invention, it will be appreciated that the invention is susceptible to
modification, variation and
change without departing from the proper scope and fair meaning of the
accompanying claims.
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