Abstract:
A inverted spline rail system is provided. The inverted spline rail system includes a drive motor that rotates a drive screw. The drive screw has a associated nut body. The nut body includes a attachment portion that a user can attach a device that requires linear motion control. Furthermore, the nut body is located inside of a cylindrical body that encases the drive screw. The nut body has guide teeth that mate with an internally splined guide rail of the cylindrical body that contains both the nut and the drive screw. The reciprocating nature of the guide teeth of the nut and the internally splined guide rail of the cylindrical body translate the rotational motion of the drive screw into linear motion of the nut body. The inverted spline rail system is protected from its operating environment by a seal.

Description:
FIELD OF THE INVENTION 
     This invention generally relates to linear motion rail systems, and more particularly relates to devices utilizing splines to transfer rotational motion into linear motion. 
     BACKGROUND OF THE INVENTION 
     Linear motion rail systems are used in many industries such as robotics, manufacturing, food processing, medical device industries, etc. Many of, these linear motion rail systems are composed of a motor actuated drive screw that mates with a nut. The nut has one or more threads that engage cooperating threads of the drive screw. Additionally, the nut mates with a guide rail. The guide rail prevents the nut from rotating when the motor actuates the drive screw. Because the nut is prevented from rotating with the drive screw the rotational motion of the drive screw is turned into linear motion of the nut. Thus, actuating the drive screw causes the nut to slide in a linear direction along the guide rail. An example of the current state of the art of linear motion rail systems is shown in U.S. Pat. No. 7,552,657. 
     As previously mentioned, linear motion rail systems are used in a variety of industrial applications. Many of these applications expose the rail system to various types of particulate and liquid matter. This matter will be able to collect on various surfaces of the linear motion rail system. Particularly, when the guide rail is an outwardly projecting splined guide rail, matter will gather on the outwardly projecting splines. Because the nut must slide along the outwardly projecting splines, any matter that gathers on the splines will become a hindrance to the linear motion of the nut. 
     Additionally, impact damage is potentially possible for the outwardly projecting splines. If the linear motion rail system is inadvertently impacted by some other device damage may be caused to the rail system, which could potentially hinder the linear motion rail system&#39;s ability to operate, or to operate with high precision. 
     Therefore, the linear motion rail system requires routine servicing at the cost of downtime for operation of the device and other attendant expenses related to maintenance of the device. 
     There exists, therefore, a need in the art for an improved guide rail system. The invention provides such an improved guide rail system. These and other advantages of the invention, as well as additional inventive features, will be apparent from the description of the invention provided herein. 
     BRIEF SUMMARY OF THE INVENTION 
     In one embodiment, the present invention is directed toward a splined rail system comprising a lead screw, an internally splined guide rail, a nut, and a seal. The lead screw rotates about a rotational axis. The internally splined guide rail defines an internal cavity in which the lead screw extends, and the guide rail includes a plurality of guide teeth extending longitudinally parallel to the rotational axis, being angularly spaced apart, and extending radially inward. Additionally, the nut is attached to the lead screw positioned within the internal cavity, the nut includes a plurality of guide teeth extending radially outward and being angularly spaced apart, the guide teeth mate with the guide teeth of the guide rail. Further, the guide rail defines a mouth and the nut includes a first portion extending radially through the mouth and external of the internally splined guide rail. A seal substantially seals the mouth of the guide rail with the first portion extending through the seal and external of the internal cavity. 
     In another embodiment, the splined rail system further comprises a drive motor. The drive motor is configured to rotate the lead screw about the rotational axis. 
     In another embodiment, the portion of the nut that radially extends through the mouth of the guide rail is configured to be attached to an external component for driving the external component parallel to the rotational axis. 
     In another embodiment, the nut includes a nut body that defines a screw receiving aperture that includes internal threading through which the lead screw extends, the lead screw having external threading engaging the internal threading of the nut body. 
     In yet another embodiment, the splined rail system further comprises a second drive motor. The second drive motor is operably coupled to the guide rail for rotationally driving the guide rail about the rotational axis. 
     In a further embodiment, the seal includes a pair of seal flaps extending towards one another, each flap having a distal end, the distal ends abutting one another to form a seal interface therebetween. 
     In another embodiment of the present invention, the pair of seal flaps include a seal head that is inserted in a head interface at the mouth of the guide rail, such that the seal prevents debris from entering the guide rail radially. 
     In another embodiment, the distal ends angularly abut the portion of the nut extending through the mouth. 
     In a further embodiment, the portion of the nut extending through the mouth includes seal separating wedges facing axially away from one another. The wedges assist in separating the distal ends of the seal flaps at the seal interface to permit passage of the nut along the guide rail. 
     In a further embodiment, the guide rail has a generally cured periphery. 
     In another embodiment the invention includes an anti-backlash nut that cooperates with a lead screw. The anti-backlash nut comprises a first nut body including a first internally threaded through hole defining a central axis and configured to mate with the lead screw. The anti-backlash nut also comprises a second nut body including a second internally threaded through hole configured to mate with the lead screw. The anti-backlash nut also comprises a biasing spring operably biasing the first nut body relative to the second nut body in opposed axial direction. Further, the anti-backlash nut also comprises an anti-rotation interface between the first nut body and the second nut body to prevent relative rotation therebetween. 
     In a further embodiment of the anti-backlash nut, the first nut body includes a first biasing surface facing axially outward and orthogonal to a central axis of the internally threaded through hole. And the second nut body includes a second biasing surface facing axially outward and orthogonal to a central axis of the internally threaded through hole and facing the first biasing surface. 
     In another embodiment of the anti-backlash nut, the first nut body includes a first anti-rotation surface radially offset from the central axis. The second nut body further includes a second anti-rotation surface radially offset from the central axis. The first anti-rotation surface radially engaging to prevent relative rotation between the first and second nut bodies about the central axis; wherein the first and second anti-rotation surfaces permit relative axial translation between the first and second nut bodies parallel to the central axis. 
     In a further embodiment of the anti-backlash nut, the first nut body and the second nut body have radially outward projecting splines forming an outer periphery thereof. 
     In another embodiment of the anti-backlash nut, the first and second surfaces are planar and parallel to the central axis. 
     In a further embodiment of the anti-backlash nut, the biasing spring provides a force biasing the first nut body away from the second nut body. 
     In another embodiment of the present invention, an anti-backlash nut comprises a body, a plurality of flexible fingers defining an inner periphery circumference having a first radial dimension axially extending from the body and connected to one another through the body. Further, the anti-backlash nut comprises a circumferential groove formed in a radially outer periphery of the plurality of fingers, the groove having a groove bottom having a second radial dimension greater than the first radial dimension. Further, the anti-backlash nut comprises a snap ring inserted in the circumferential groove applying a radially inward directed pressure on the flexible fingers, the snap ring having a radially inner periphery being smaller than the dimension of the bottom of the groove. 
     In further embodiment of the anti-backlash nut, the plurality of flexible fingers are internally threaded. 
     In another embodiment of the anti-backlash nut, the snap ring decreases the first radial dimension when inserted in the circumferential groove. 
     In yet another embodiment, the present invention is directed toward a splined rail system comprising a lead screw, a first drive motor, an internally splined guide rail, a second drive motor, and a nut. A first drive motor is configured to rotate the drive screw about a rotational axis. The internally splined guide rail defines an internal cavity in which the lead screw extends. The guide rail includes a plurality of guide teeth extending longitudinally parallel to the rotational axis, spaced apart, and extending radially inward. The second drive motor is operably coupled to the guide rail for rotationally driving the guide rail about the rotational axis. The nut is attached to the lead screw and includes a plurality of guide teeth extending radially outward, and angularly spaced apart such that the guide teeth mate with the guide teeth of the guide rail. 
     Other aspects, objectives and advantages of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings incorporated in and forming a part of the specification illustrate several aspects of the present invention and, together with the description, serve to explain the principles of the invention. In the drawings: 
         FIG. 1  is an exemplary embodiment of a inverted spline rail system in accordance with the teachings of the present invention; 
         FIG. 2  is a exploded view of the inverted spline rail system, in accordance with the teachings of the present invention; 
         FIG. 3  is a top view of the inverted spline rail system, in accordance with the teachings of the present invention; 
         FIG. 4  is a lengthwise cross section of the linear drive system, in accordance with the teachings of the present invention; 
         FIG. 5  is a close up of the cross section of  FIG. 4 , in accordance with the teachings of the present invention; 
         FIG. 6  is a frontal view cross section of the linear drive system facing toward the nut and the drive motor, in accordance with the teachings of the present invention; 
         FIG. 7  is a frontal view of the linear drive system facing away from the nut and the drive motor, in accordance with the teachings of the present invention; and 
         FIG. 8  is another embodiment of the nut, in accordance with the teachings of the present invention. 
     
    
    
     While the invention will be described in connection with certain preferred embodiments, there is no intent to limit it to those embodiments. On the contrary, the intent is to cover all alternatives, modifications and equivalents as included within the spirit and scope of the invention as defined by the appended claims. 
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  shows a guide rail system in the form of an inverted spline rail system  100  in accordance with a particular embodiment of the present invention. The inverted spline rail system  100  includes a drive motor  102  that rotates a lead screw  104 , or by another name a drive screw  104 . While in the particular embodiment of the invention shown in  FIG. 1  a drive motor  102  rotates the drive screw  104 , it is contemplated that other methods of rotating the drive screw  104  are possible, such as a crank or handle mechanism that attaches to the drive screw  104 . The drive screw  104  interfaces with a nut  106  to create linear motion along a central or linear axis  144 . The nut  106  includes a nut attachment section  108  to which devices such as medical devices or machining tools can be attached for corresponding linear motion parallel to axis  144 . 
     The inverted spline rail system  100  further includes a cylinder body  126  having an internally splined guide rail  118 . The inner periphery of the cylinder body  126  includes a plurality of teeth  146 . The nut  106  has guide teeth  136  that mate with the internally splined guide rail  118  and particularly with the teeth  146 . 
     The inverted spline rail system  100  can translate rotational motion of the drive screw  104  to linear motion of the nut  106 . As the drive motor  102  rotates the drive screw, the internally splined guide rail  118  prevents the nut  106  from rotating. Because the nut  106  is not allowed to rotate, the rotational motion of the drive screw  104  is transferred into linear motion of the nut  106  along axis  144 . 
     The nut  106  has a attachment section  108 , which allows the system user to attach various devices to the inverted spline rail system  100 . The attachment section  108  extends outside of the internal cavity  116  of the internally splined guide rail  118  through a mouth  138  of the cylinder body  126 . This allows a device mounted to the attachment section  108  to move along with the nut  106 . 
     In the embodiment of the invention shown in  FIG. 1 , the inverted spline rail system  100  includes a seal  142  formed by a first and a second seal flaps  120 ,  122 , that operably seal with one another. The first and second flaps  120 ,  122  engage one another such that the first and second flaps  120 ,  122  form a seal interface at the mating distal ends  140  of each seal flap  120 ,  122 , in the center of the mouth  138  of the cylinder body  126 . The first and second seal flaps  120 ,  122  are held in the cylinder body  126  by an enlarged head portion  124  of each flap  120 ,  122 . The head portions  124  are received in a corresponding head interface or groove in the cylinder body  126  that have a reduced width mouth through which the head portions  124  cannot laterally pass. Additionally, the first and second seal flaps  120 ,  122  are of such a length that they span the length of linear motion capable of the inverted spline rail system  100 , and the first and second seal flaps  120 ,  122  are long enough and wide enough that they seal off the opening made in the cylinder body  126  (e.g. mouth  138 ), from the outside environment. 
     The seal  142 , or at least the mating distal ends  140  of the first and second seal flaps  120 ,  122  are made from a flexible material such that they allow the attachment portion  108  of the nut  106  to protrude through the seal. Therefore the device attached to the attachment portion  108  of the nut  106  can move linearly, but the internal cavity  116  of the cylinder body  126  is protected from the outside environment. Furthermore, the attachment portion  108  includes wedges  128 . The wedges  128  separate the seal flaps  120 ,  122  to allow the flexible material of seal  142  to wrap around the wedges  128  during motion of nut  106 . Therefore, little to no particulate or liquid matter from the industrial application of the linear rail system  100  will be deposited in the internal cavity  116  of the internally splined guide rail  118 , or any other structure contained in the internal cavity  116 . 
     In the particular embodiment of the invention shown in  FIG. 1 , the inverted spline rail system  100  includes both the drive motor  102  and a second drive motor  130 . The second drive motor allows the inverted spline rail system  100  to rotate a device attached to the attachment portion  108  of nut  106  in a circular path around the longitudinal center axis  144  of the inverted spline rail system  100 . 
     The second drive motor  130  rotates the cylinder body  126  relative to drive motor  102  through the interaction of a pinion gear  132  and a spur gear  134 . The second drive motor  130  rotates the pinion gear  132 , which in turn rotates the spur gear  134 , which is operably coupled to the cylinder body  126 . 
     Furthermore, the drive screw  104  is connected to the drive motor  102  and is otherwise freestanding within the internal cavity  116 . Because the drive screw  104  is only attached to the drive motor  102 , the nut  106  is allowed to travel the full length of the drive screw  104  along axis  144 . 
       FIG. 2  illustrates an exploded view of the inverted spline rail system  100  of  FIG. 1 . Nut  106  is illustrated in greater detail. In the particular embodiment of the invention illustrated in  FIG. 2 , the nut  106  is an anti-backlash nut  106 . The anti-backlash nut  106  includes a first nut body  110  and a second nut body  112  and a biasing spring  114 . The first and second nut bodies  110 ,  112  are internally threaded to engage the drive screw  104 . The exterior of the first and second nut bodies  110 ,  112  contain guide teeth  136  that engage and cooperate with the teeth  146  of the internally splined guide rail  118 . 
     The biasing spring  114  of the anti-backlash nut  106  acts to eliminate backlash between the nut  106  and drive screw  104  experienced when the drive screw  104  changes rotational direction. As the inverted spline rail system  100  ages, the threads of the drive screw  104  and/or the inner threads of the anti-backlash nut  106  will wear. Therefore, some unwanted linear motion could potentially occur during system operation. This unwanted motion is protected against by the biasing spring  114 . The biasing spring  114  provides a constant force between the first and the second nut bodies  110 ,  112  such that the first and second nut bodies  110 ,  112  continuously seat against the cooperating threads of the drive screw without any unwanted linear motion. 
     The anti-backlash nut  106  also includes a surface rotation prevention interface  150 . Interface  150  includes a first radially outward rotation prevention surface  152  of the first nut body  110 , and a second radially outward rotation prevention surface  154  of the second nut body  112 . During operation of the inverted spline rail system  100 , the first and the second nut bodies  110 ,  112  will be close in proximity. The first surface  152  will over lap with the second surface  154 . This over lap creates the interface  150 . The interface  150  prevents non-uniform rotation by forcing a common rotational angle for the first and the second nut bodies  110 ,  112 . 
       FIG. 2  also illustrates the first and second seal flaps  120 ,  122  removed from the cylinder body  126 . As was discussed in relation to  FIG. 1 , the first and second seal flaps  120 ,  122  connect to the cylinder body  126  at the head portions  124 , which engage the grooves  148  that run the length of the cylinder body  126 . The first and second seal bodies  120 ,  122  are flexible such that the attachment portion  108  of anti-backlash nut  106  can protrude through the mating distal ends when the first and second seal flaps  120 ,  122  are installed. 
       FIG. 4  is a cross-section of the cylinder body  126 , the drive screw  104 , and the nut  106 .  FIG. 5  shows how the bias spring  114  engages both the first and second nut bodies  110 ,  112  during operation of the inverted spline rail system  100  to bias the nut bodies  110 ,  112  axially away from one another. 
     Furthermore,  FIG. 5  illustrates the operation of the surface rotation prevention interface  150 . Interface  150  includes a first radially outward rotation prevention (or anti-rotation) surface  152  of the first nut body  110 , and a second radially outward rotation prevention (or anti-rotation) surface  154  of the second nut body  112 . As mentioned above, during operation the first and the second nut bodies  110 ,  112  are close in proximity such that the first surface  152  overlaps with the second surface  154 . The mating of these two surfaces creates the interface  150 . The interface  150  forces a common rotational angle for both the first and the second nut bodies  110 ,  112 . The interface  150  permits relative axial translation between the first and the second nut bodies parallel to the linear axis  144 . 
       FIG. 6  is a cross-sectional illustration of the nut  106  and the inverted spline rail system  100  looking axially down axis  144  the front lengthwise toward the drive motor  102 . From this perspective, the engagement between the guide teeth  136  of nut  106  and the internally splined guide rail is illustrated. In this particular embodiment of the invention, this relationship between these two components exists through the entire length of the cylinder body  126 . However, other embodiments where the spline structure is not uniform throughout the length of the cylinder body  126  are contemplated. 
     Additionally,  FIG. 6  shows the attachment portion  108  of nut  106 . The attachment portion  108  is shown protruding from the first and second seal flaps  120 ,  122 . 
       FIG. 7  shows another lengthwise cross-section looking away from the drive motor  102  and not including the nut  106 . In  FIG. 7 , the first and second seal flaps  120 ,  122  are illustrated mating distal ends  140 . Further, each of the first and second seal flaps  120 ,  122  connect to the cylinder body  126  at the head portion  124 . From this perspective, it can be seen that the seal  142  forms a radially directed barrier protecting the internally splined rail  118  and the drive screw  104  from the broader environment in which the inverted spline rail system  100  is used. Therefore, debris is kept out of the internal cavity  116 . 
       FIG. 8  shows another embodiment of an anti-backlash nut  200  in accordance with an embodiment of the present invention. The anti-backlash nut  200  of  FIG. 8  includes splined teeth  202  that engage with the internally splined guide rail  118 , and an attachment portion  204  that passes through seal  142 , similar to the anti-backlash nut  106  (e.g.  FIG. 2 ). However, the linear position of anti-backlash nut  200  is maintained, and backlash prevented, by the operation of a snap ring  208  and flexible fingers  206 . 
     The nut body  212  includes flexible fingers  206  and a snap ring  208  received in groove  210  to cause fingers  206  to engage screw  104 . The flexible finger  206  are biased radially against screw  104  by the snap ring  208 , which fits in groove  210 . The snap ring  208  applies a force between the flexible fingers  206  and the drive screw  104 . This force helps to maintain the linear position of nut  200  when slop is present between the threads of the nut  200  and the drive screw  104  biased radially against screw  104 . 
     The embodiment of the nut  200  shown in  FIG. 8  shows three flexible fingers  206 . The invention is not limited to three flexible fingers  206 , and it is contemplated that more or less flexible fingers  206  could be present. 
     All references, including publications, patent applications, and patents cited herein are hereby incorporated by reference to the same extent as if each reference were individually and specifically indicated to be incorporated by reference and were set forth in its entirety herein. 
     The use of the terms “a” and “an” and “the” and similar referents in the context of describing the invention (especially in the context of the following claims) is to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. The terms “comprising,” “having,” “including,” and “containing” are to be construed as open-ended terms (i.e., meaning “including, but not limited to,”) unless otherwise noted. Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”) provided herein, is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention. 
     Preferred embodiments of this invention are described herein, including the best mode known to the inventors for carrying out the invention. Variations of those preferred embodiments may become apparent to those of ordinary skill in the art upon reading the foregoing description. The inventors expect skilled artisans to employ such variations as appropriate, and the inventors intend for the invention to be practiced otherwise than as specifically described herein. Accordingly, this invention includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the invention unless otherwise indicated herein or otherwise clearly contradicted by context.