Patent Publication Number: US-2010129013-A1

Title: Guide Rail Having Base Rail And Gear Rack, Method Of Making Same, Guide Assembly Including Same

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATIONS 
     This patent application claims the benefit of U.S. Provisional Patent Application No. 61/117,795, filed Nov. 25, 2008, the disclosure and teachings of which are incorporated herein, in their entireties, by reference thereto. 
    
    
     FIELD OF THE INVENTION 
     This invention generally relates to guide assemblies and more particularly to guide rails for linear motion. 
     BACKGROUND OF THE INVENTION 
     Guide assemblies have been used for assisting in guided linear motion of many products including medical scanners, printer devices, machining devices and automatic door openers, such as for elevators. 
     Typically, a guide assembly will include a guide rail and a carriage or frame. The carriage or frame and the guide rail move relative to one another for coordinated linear motion. Typically, the carriage or frame will include at least one guide roller or similar rolling element that interacts with and rides on a raceway of the guide rail to provide smooth controlled linear relative motion between the guide rail and carriage or frame. In some instances, the carriage or frame may include a motor that operably engages the guide rail to drive the relative motion between the carriage or frame and the guide rail. 
     Unfortunately, due to standard methods of forming such guide rails, tolerances between the raceway and the portion of the guide rail operably engaged by the motor are insufficient and promote increased ware on the motor and structure that operably engages the guide rail. 
     The present invention relates to providing guide rails with increased precision to promote consistent and improved engagement between the guide rail and a cooperating motor over the current state of the art. 
     BRIEF SUMMARY OF THE INVENTION 
     Embodiments of the present invention relate to guide rails having gear racks that are precision located relative to raceways of the guide rail along which motors that include gears that engage the gear racks move. 
     In one embodiment, a guide rail comprising at least one raceway, a gear rack and a base rail is provided. The at least one raceway interacts with a rolling member of a cooperating carriage or frame member. The raceway defines a reference point. The gear rack is mounted to the base rail and interacts with a pinion of a cooperating carriage or frame member. The gear rack and the reference point of the at least one raceway have a parallelism per linear foot of the guide rail of less than or equal to 0.005 inches. 
     In one embodiment, the parallelism is less than or equal to 0.001 inches per linear foot of the guide rail. Further, in some embodiments, the raceway may be provided by a hardened rail mounted to the base rail. In alternative embodiments, the raceway may be directly provided by the base rail. 
     Further yet, in an embodiment, the gear rack is mounted to the base rail free of any threaded connectors. In one implementation, the gear rack is mounted to the base rail by spring pins press fit through apertures formed through the base rail and the gear rack. This arrangement prevents the gear rack from loosening relative to the base rail due to vibrations within the structure. This arrangement also prevents additional areas for tolerance loss due to tightening of a threaded connector that can result in undesirable biasing of the gear rack relative to the base rail. 
     A method of forming a guide rail is also provided. The method includes forming a guide rail having at least one raceway and a gear rack mounted to a base rail. The method comprises the step of machining a first qualified reference point on the guide rail. The qualified reference point relating to the location of the raceway. The method also includes the step of machining a gear rack seat in the base rail. Further, the step of machining the gear rack seat in the base rail includes locating the gear rack seat off of the qualified reference point on the guide rail during the step of machining a gear rack seat. 
     In some methods, the first qualified reference point is directly provided by the raceway of the guide rail, thus machining of the reference point is provided by machining of the raceway. 
     In some methods, the guide rail includes a hardened rail, the hardened rail providing the raceway, the method further comprising the step of securing the hardened rail to the base rail. The step of securing the hardened rail to the base rail may occur prior to the step of machining the first qualified reference point and the step of machining a gear rack seat in the base rail. In this method, the step of machining a first qualified reference point may include machining a raceway onto the hardened rail, and the first qualified reference point is directly provided by the raceway. 
     The step of machining a first qualified reference point and the step of machining a gear rack seat in the base rail may be performed simultaneously on a continuous length of the guide rail. However, although they may be simultaneously performed, the step of machining a gear rack seat may be performed on a given axial location of the guide rail along its length after the step of machining a first qualified reference point at that same axial location. In other words, the machining devices need not be axially located at the same axial position along the guide rail during formation. 
     When no hardened rails are included, the step of machining the qualified reference point may include directly machining a raceway into the base rail. 
     Methods may also include the step of securing the gear rack to the base rail. This step may be performed free of threaded fasteners and may further comprise forming cooperating apertures through the base rail and gear rack and inserting a pin through the cooperating apertures. The step of forming cooperating apertures through the base rail and gear rack can occur in a single machining step. 
     Further, in those methods that require mounting a hardened rail, the step of securing the hardened rail to the base rail can occur after the step of machining the first qualified reference point. In this implementation, the base rail is most typically machined to provide the reference point and this machining of the base rail provides increased accuracy for locating the hardened rail. Further, the reference point is related to the raceway as the location of the raceway is related to the accuracy of the machining of the base rail prior to mounting the hardened rail onto the base rail. 
     Guide assemblies incorporating guide rails identified and manufactured by the methods identified are also provided. These guide assemblies include a pinion for engaging the gear rack and at least one guide roller or similar structure for interacting with the raceways of the guide rail. The parallelism between the gear rack and reference point relating to the raceway maintain a desired mesh between the pinion gear and the gear rack even if slight bows or variations for true straight occur in 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 isometric illustration of a guide assembly according to an embodiment of the present invention. 
         FIG. 2  is an end profile illustration of the guide assembly of  FIG. 1 ; 
         FIG. 3  is a bottom view illustration of the guide assembly of  FIG. 1 ; 
         FIG. 4  is an isometric partial exploded illustration of the guide assembly of  FIG. 1 ; 
         FIG. 5  is an end profile illustration of the guide rail of the guide assembly of  FIG. 1 ; 
         FIG. 6  is an end profile illustration of an alternative embodiment of a guide rail according to the teachings of the present invention; 
         FIG. 7  is an end profile illustration of an alternative embodiment of a guide rail according to the teachings of the present invention; and 
         FIG. 8  is an end profile illustration of the guide rail of  FIG. 5  with the hardened rails removed therefrom. 
     
    
    
     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 
       FIGS. 1-4  illustrate an embodiment of a guide assembly  100  that includes a carriage assembly  102  and a linear guide rail  104 . The carriage assembly  102  and linear guide rail  104  are coupled for relative motion. Therefore, the carriage assembly  102  can be driven along the linear guide rail  104  to position devices attached to the carriage assembly  102  relative to the linear guide rail  104 . Alternatively, the carriage assembly  102  could be in the form of a fixed position frame member that is in fact a stationary component relative to which the linear guide rail  104  moves. In this alternative arrangement, the linear guide rail  104  would be attached to a device to move the attached device relative to the carriage assembly  102 . 
     The carriage assembly  102  generally includes a base member  106 , a motor  108  and a plurality of guide rollers  110 ,  112 ,  114 . The motor  108  and guide rollers  110 ,  112 ,  114  are operably mounted to the base member and are generally carried thereby. The motor  108  includes a pinion gear  116  that interacts with the linear guide rail  104  to drive the linear guide rail  104  and carriage assembly  102  relative to one another. The pinion gear  116  and guide rollers  110 ,  112 ,  114  have axes of rotation that are fixed relative to one another. 
     With further reference to  FIG. 5 , the linear guide rail  104  generally includes a pair of hardened rails  118 ,  120 , a base rail  122  and gear rack  124 . The hardened rails  118 ,  120  define raceways  126 ,  128  of the guide rail  104  upon which the guide rollers  110 ,  112 ,  114  ride and otherwise interact. In the illustrated embodiment, each of the hardened rails  118 ,  120  are V-shaped. Consequently, raceways  126 ,  128  defined by the hardened rails  118 ,  120  are similarly V-shaped and are defined by a pair of surfaces  130 ,  132  and  134 ,  136 , respectively, upon which the guide rollers  110 ,  112 ,  114  directly ride. However, in other embodiments, the raceways  126 ,  128  could be provided by other profiles such as for example gothic arch profiles, a single groove, and the like for interacting with various guide rollers or alternatively directly with ball bearings. Thus, the raceways could be provided, for example, by convex and concave profiles depending on the cooperating structure of the carriage assembly  102 . 
     By using V-shaped or similar raceways  126 ,  128 , the raceways  126 ,  128  have lateral positioning structure that provides lateral stability in a direction parallel to the axis of rotation of a guide roller or other rolling member of a cooperating carriage assembly  102 , as the carriage assembly  102  travels along the length of the linear guide rail  104 . Other shapes of raceways can be used to provide for lateral stability. 
     Typically, base rail  122  is a light weight material such as aluminum while the hardened rails  118 ,  120  are formed from a harder material such as steel. However, other materials can be used. 
     The hardened rails  118 ,  120  are preferably swaged to the base rail  122 . More particularly, fingers  140  are bent over (i.e. swaged) distal ends of the hardened rails  118 ,  120  to secure the hardened rails  118 ,  120  to the base rail  122 . However, in alternative embodiments, the hardened rails  118 ,  120  could be secured to base rail  122  using other means such as mechanical fasteners. 
     The gear rack  124  is mechanically fastened to the base rail  122 . More particularly, the base rail  122  includes a gear rack mounting channel  164  in which the gear rack is mounted. The gear rack channel  164  is laterally offset from the hardened rails  118 ,  120  and arranged such that the axis of rotation  135  of pinion  116  is parallel to the axes of rotation  137  of the guide rollers  110 ,  112 ,  114  (the axes illustrated schematically as dashed lines in  FIG. 5 ). The gear rack mounting channel  164  includes a gear rack seat  160  upon which a bottom surface  162  of the gear rack  124  is mounted. The bottom surface  162  faces away from and is on the opposite side of teeth  165  of gear rack  164  As will be more fully described below, the gear rack seat  160  is a precision located and machined surface that has a high tolerance related to one or more of the raceways  126 ,  128  to provide precision interaction between the gear rack  124  and a cooperating pinion gear  116  of the carriage assembly  102 . 
     In the illustrated embodiment, the gear rack  124  is mounted to the base rail  122  free of threaded fasteners. This eliminates a first location for tolerance to be lost. More particularly, the use of threaded fasteners can result in the fasteners jacking the gear rack  124  relative to the base rail  122  thereby changing the desired position of the gear rack relative to the raceways  126 ,  128 . Further, the use of threaded fasteners is time consuming and costly during manufacture because this method of connection requires tapping and threading the base rail  122  for receipt of a cooperating screw or bolt. Additionally, the threaded fasteners are more expensive than other modes of connection, such as laid out below. Further, threaded fasteners are source of potential loosening between the gear rack  124  and base rail  122  due to vibrations. 
     With primary reference to  FIG. 4 , in the illustrated embodiment, the gear rack  124  is mechanically fastened to the base rail  122  using pins  166  pressed through aligned holes  168 ,  170  of the base rail  122  and gear rack  124 , respectively. In one embodiment, the holes  168 ,  170  are formed simultaneously with the gear rack  124  affixed or located within the gear rack mounting channel  164 . Thus, when hole  168  is drilled through base rail  122  cooperating hole  170  of the gear rack  124  is also simultaneously formed. Pin  166  is then inserted through the pair of holes  168 ,  170  to prevent any shifting or misalignment of the gear rack  124  relative to the base rail  122 . 
     In the illustrated embodiment, pins  166  are spring pins that are press fit into holes  168 ,  170  to prevent any clearance between the pins  166  and inner diameters of holes  168 ,  170 . 
     Rack and pinion systems are only as accurate as the running relationship between the pinion and the gear rack. A predetermined gap setting is specified for optimal rack and pinion gear life and for minimal backlash, as well as reduced friction. Older methods of shimming or jacking the rack into a position to maintain the optimal gap settings are time consuming and often unattainable. Thus, a highly precise relationship between the raceways and the gear rack substantially improves performance of systems incorporating such guide rails that include gear racks. 
     With reference to  FIG. 5 , a linear guide rail  104 , but not all linear guide rails, according to one embodiment will have a non-accumulative per foot parallelism between a plane defined by the pitch diameter of the gear rack  124  and a reference point defined by at least one of the raceways  126 ,  128  that is less than or equal to 0.005 inches, and more preferably less than or equal to 0.002 inches and most preferably less than or equal to 0.001 inches. 
     This parallelism maintains the desired gap spacing between a pinion gear  116  (illustrated by axis of rotation  137 ) mounted to a carriage assembly  102  and the gear rack  124 . Variations in this gap will cause premature wear, excessive backlash, noise, and friction. 
     Because the pinion gear  116  is carried by the carriage assembly  102 , its position relative to the gear rack  124  is directly influenced by raceways  126 ,  128 . Thus, if the raceways  126 ,  128  remain parallel to the pitch diameter  140  of the gear rack  124 , the pinion gear  116 -to-gear rack  124  spacing will remain constant and the desired mesh between the two components will be maintained to prevent unnecessary wear or friction between the two components or alternatively inadequate mesh that can create damage to the teeth of either gear component. 
     The non-accumulative per foot parallelism can be measured as any one of the per foot variation in distances D 1 , D 2  or D 7  illustrated in  FIG. 5 . Distance D 7  is a distance between a theoretical point  174  defined by a theoretical intersection of surfaces  130 ,  132  of raceway  126 . 
     However, because the desired precision relates to a variation (i.e. delta) in distances D 1 , D 2 , D 7  between a reference point defined by the raceways  126 ,  128  and the plane defined by the pitch diameter  180  of the gear rack, any point that a guide roller or cooperating portion of the carriage assembly  102  would ride on raceways  126 ,  128  can be used to measure the parallelism. For example reference points  142 ,  146  are theoretical locations where a guide roller may ride on raceways  126 ,  128 . For the illustrated embodiment, reference points  142 ,  146  are planes or lines that extend perpendicular relative to a central dividing line/plane  144  that passes through the theoretical intersections of the surfaces of raceways  126 ,  128 . Thus, a tool that includes a cooperating profile of the raceways  126 ,  128  could be mounted to the raceways  126 ,  128  and used as a constant reference point relative to the gear rack  124  during determining the variation in parallelism. Most preferably, the parallelism determined from the desired location on the raceways where the cooperating guide rollers or similar structure will ride on the raceways. 
     By maintaining the desired parallelism, if a slight variation from true straight occurs in the raceways  126 ,  128 , the variation should also be found in the gear rack  124 , within the desired tolerance. The variation maintains the proper spacing between the pinion gear  116 , whose position is ultimately determined by raceways  126 ,  128 , and the gear rack  124 . 
       FIG. 6  illustrates another embodiment of a linear guide rail  204  having a different configuration than that of  FIG. 1 . In this arrangement, the linear guide rail  204  includes a pair of hardened rails  218 ,  220  mounted to a base rail  222 . The linear guide rail  204  also includes a gear rack  224  mounted within a gear rack channel  264  of the base rail  222 . Again, the gear rack channel  264  defines a gear rack seat  260  upon which a bottom surface  262  of the gear rack  224  abuts when the gear rack  224  is mounted to base rail  222 . 
     However, in this embodiment, the gear rack  224  is mounted in a side  229  of the base rail  222  that is angularly oblique to the sides  231 ,  233  (perpendicular in the illustrated embodiment) that includes hardened rails  218 ,  220 , respectively. This arrangement is used when a pinion gear that engages gear rack  224  is driven about an axis  235  that is perpendicular to axis  237  about which a guide roller that rides on hardened rails  218 ,  220  rotates. However, as the position (i.e. mesh) of the pinion relative to the gear rack  224  is determined by the relative position of raceways defined by hardened rails  218 ,  220 , parallelism between the raceways and the gear rack  224  is important to maintain the desired gear mesh between the gear rack  224  and a cooperating pinion. 
     In this arrangement, parallelism can be measured as the variation (also referred to as a delta) in lateral distance D 4  along the length of the linear guide rail  204 . Distance D 4  is defined between the pitch diameter  280  of gear rack  224  and a hypothetical axis  244  defined by reference points  273 ,  274  defined by hardened rails  218 ,  220 , respectively. Reference points  273 ,  274  are defined by the intersection of surfaces  232 ,  230  and  234 ,  236 , respectively. Again, further locating can be used to measure the parallelism. 
     A further embodiment of a guide rail  304  is illustrated in  FIG. 7 . This embodiment is similar to the embodiment of  FIG. 6  in that gear rack  324  is formed in side  329  of base rail  322 . Side  329  extend obliquely to sides  331 ,  333  of base rail  322 . However, this embodiment is free of hardened rails to define the raceways. 
     In this embodiment, raceways  326 ,  328  are formed directly in to the base rail  322 . More particularly, raceway  326  is formed by side  331  and raceway  328  is formed by side  333 . 
     In this embodiment, parallelism is the variation in distance D 6  and is substantially similar to distance D 4  for the previous embodiment. 
     Returning to the embodiment of  FIGS. 1-5 , methods of forming the linear guide rails  104  to establish this high-precision parallel relationship between the pitch diameter  180  of the gear rack  124  and the raceways  126 ,  128  will now be described. 
     To provide the high tolerance desired by the linear guide rail  104  of the instant invention, the relative location of the gear rack  124  relative to the raceways  126 ,  128  is the desired parameter to control. 
     One method of forming the linear guide rail  104  includes machining a qualified reference point defined by the linear guide rail  104  as well as machining a gear rack seat  160  in a base rail  122  of the linear guide rail  104 . The step of machining the gear rack seat  160  in the base rail  122  includes locating the machining processes of the gear rack seat  160  off of the first qualified reference point. In a preferred embodiment, the qualified reference point is defined by at least one of the raceways  126 ,  128  of the linear guide rail  104 . To locate off of the first qualified reference point, the reference point may ride on a predefined structure of the machining apparatus, such as a guide roller having a known position. 
     In one implementation of a method of forming the linear guide rail  104 , the raceways  126 ,  128  of the linear guide rail  104  and the gear rack seat  160  are machined simultaneously and at a same axial position. This arrangement prevents multiple positioning steps of the base rail  122  during machining 
     Further yet, in another implementation, the method includes first securing hardened rails  118 ,  120  to the base rail  122  and then simultaneously machining the raceways  126 ,  128  onto hardened rails  118 ,  120 , respectively, along with machining the gear rack seat  160 . 
     While the steps of machining raceways  126 ,  128  and gear rack seat  160  may be performed simultaneously, the simultaneous machining may be performed at different axial locations along the linear guide rail  104 . For instance, the step of machining the raceways  126 ,  128  may be performed axially upstream on a length of the linear guide rail  104  relative the step of machining the gear rack seat  160 . Alternatively, this may be reversed. 
     In other words, a given axial location of the raceways  126 ,  128  of a linear guide rail  104  may be machined prior to the machining of the gear rack seat  160  for that same axial position along the length of the linear guide rail  104 . 
     Alternatively, when no hardened rails are used, such as in the embodiment of  FIG. 7 , the raceways  326 ,  328  may be machined directly into base rail  322  as gear rack seat  360  is machined into base rail  322 . Thus, in this embodiment, the raceways  326 ,  328  and gear rack seat  360  are formed in and provided by a single piece of material. Again, the machining of the raceways  326 ,  328  and gear rack seat  32  may be performed simultaneously or subsequently, but are preferably performed simultaneously. 
     Further implementations of methods of forming the linear guide rail  104  may not require having the raceways  126 ,  128  define reference point for locating the gear rack seat  160 . With reference to  FIG. 8 , the method may use support surfaces  180 ,  182 ,  184 ,  186  that support hardened rails  118 ,  120  to define the reference point for locating machining of gear rack seat  160 . Again, the reference point may be the hypothetical intersections  188 ,  190  of support surfaces  180 ,  182  and  184 ,  186 . Alternatively, the reference point could be the tips  192 ,  194  of the support profiles of the base rail  122  merging surfaces  180 ,  182  and  184 ,  186  into one another. Thus, in some embodiments, the reference point may not be directly established by the raceways of the linear guide rail. 
     In  FIG. 8 , support surfaces  180 ,  182 ,  184 ,  186  are precision machined prior to addition of hardened rails  118 ,  120 . By precision machining support surfaces  180 ,  182 ,  184 ,  186  prior to mounting hardened rails  118 ,  120  to base rail  122 , the hardened rails  118 ,  120  are more precisely located relative to base rail  122 . In some embodiments, the location is sufficient that hardened rails  118 ,  120  need not be subsequently machined after being mounted to base rail  122 . 
     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.