Abstract:
A linear guide including a guide rail, a carriage, a drive screw and a connection arrangement is provided. The guide rail defines a linear travel path. The carriage is mounted to the guide rail for motion along the linear travel path. The drive screw is operably mounted to the guide rail. The connection arrangement couples the drive screw to the carriage to convert rotary motion of the drive screw to linear actuation of the carriage along the linear travel path. The connection arrangement provides a single degree of linear freedom between the drive screw and the carriage in a direction that is generally perpendicular to the linear travel path. The single degree of linear freedom permits relative motion between the screw and the carriage to relieve internal binding between the relative components.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention generally relates to linear guides and particularly to linear guides that drive a carriage along a guide rail using a drive screw. 
       BACKGROUND OF THE INVENTION 
       [0002]    Linear guides are used to guide devices along a predetermined linear pathway in a highly accurate and repeatable fashion. Typically, these linear guides will include a guide rail, a carriage that is driven along the guide rail and a device for driving the carriage along the guide rail. In some embodiments, a screw may be the device for driving the carriage along the guide rail. 
         [0003]    In highly precise applications, there is very limited, if any, clearance between the guide rail and the carriage and the screws are designed to have very high straightness. However, tolerance stack up between the guide surfaces of the guide rail and carriage as well as the screw in addition to any flexure in the components or variations due to machining can cause binding within the linear guide, as well as high or variable running torque. This variation in forces within the linear guide can affect the positional control of the carriage along the guide rail. 
         [0004]    The present invention relates to improvements over the current state of the art in linear guides. 
       BRIEF SUMMARY OF THE INVENTION 
       [0005]    A new and improved linear guide is provided to overcome some of the limitations of prior linear guides. The new and improved linear guide includes a guide rail, a carriage, a drive screw and a connection arrangement. The guide rail defines a linear travel path. The carriage is mounted to the guide rail for motion along the linear travel path. The drive screw is operably mounted to the guide rail. The connection arrangement couples the drive screw to the carriage to convert rotary motion of the drive screw to linear actuation of the carriage along the linear travel path. The connection arrangement provides a single degree of linear freedom between the drive screw and the carriage in a direction that is generally perpendicular to the linear travel path. The single degree of linear freedom permits relative motion between the screw and the carriage to relieve some of the internal binding between the relative components. 
         [0006]    In one embodiment, the connection arrangement provides a slot and receiver arrangement that permits the linear degree of freedom. 
         [0007]    In another embodiment, the slot and receiver arrangement has cooperating anti-rotation features to prevent relative rotation due to rotational torques presented by the drive screw and particularly backlash when the drive screw changes rotational direction. 
         [0008]    In one embodiment, the connection arrangement includes a nut and a cradle arrangement. The nut threadably cooperates with the drive screw. The nut and cradle arrangement have cooperating anti-rotation features to prevent relative rotation therebetween due to rotational torques presented by the drive screw. 
         [0009]    In one embodiment, the nut includes a head portion that is received in a slot of the cradle arrangement. The engagement between the head portion and the cradle arrangement prevents rotation between the nut and the cradle arrangement. The engagement between the head portion and the cradle arrangement prevents linear motion therebetween in a direction parallel to the travel path. 
         [0010]    In one embodiment, the carriage includes a mounting arrangement for mounting the carriage to the guide rail. The mounting arrangement is configured to prevent linear motion of carriage relative to the guide rail in a plane generally orthogonal to the travel path. 
         [0011]    In one embodiment, the mounting arrangement includes first and second channels formed in arm portions of the carriage. Each channel receives a corresponding portion of the guide rail. The channels are bounded by sliding surfaces that slide on corresponding surfaces of the guide rail. Preferably, the sliding surfaces are provided by low friction material. 
         [0012]    In one embodiment, the slot defines parallel sides that extend generally perpendicular to the travel path. The head has parallel sides that extend generally perpendicular to the travel path that cooperate with the parallel sides of the slot. 
         [0013]    In one embodiment, the connection arrangement includes a first component that defines at least one slot and a second component that mates with the slot. The second component is slidable within the slot along the single degree of linear freedom. In one embodiment, the first component is fixedly part of the carriage and the second component is a nut having a head portion that is received within the slot of the first component. 
         [0014]    In one embodiment, the linear guide further includes a pair of end blocks. The end blocks are attached to the guide rail and rotationally support the drive screw. 
         [0015]    In one embodiment, cradle arrangement includes a pair of transversely inward facing surfaces that face one another and that bound opposed ends of the slot and extend parallel to the single degree of linear freedom. The head portion of the nut includes a pair of transversely outward facing surfaces that face away from one another and extend parallel to the single degree of linear freedom. The outward facing surfaces slide relative to the inward facing surfaces to provide the single degree of linear freedom. Preferably, the inward and outward facing surfaces are planar. 
         [0016]    In one embodiment, a method of reducing binding within a linear guide is provided. The linear guide has a guide rail a guide rail defining a linear travel path; a carriage mounted to the guide rail for motion along the linear travel path; a drive screw operably mounted to the guide rail; and a connection arrangement coupling the drive screw to the carriage to convert rotary motion of the drive screw to linear actuation of the carriage along the linear travel path. The method includes providing a single degree of linear freedom between the drive screw and the carriage in a direction that is generally perpendicular to the linear travel path. 
         [0017]    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 
         [0018]    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: 
           [0019]      FIG. 1  is a top perspective illustration of a linear guide according to an embodiment of the present invention; 
           [0020]      FIG. 2  is a bottom perspective illustration of the linear guide of  FIG. 1 ; 
           [0021]      FIG. 3  is a bottom exploded illustration of the linear guide of  FIG. 1  with the guide rail removed; 
           [0022]      FIG. 4  is a bottom perspective illustration of the linear guide of  FIG. 1  with the guide rail removed; 
           [0023]      FIG. 5  is an enlarged illustration of the connection arrangement between the carriage and drive screw of the linear guide of  FIG. 1 ; 
           [0024]      FIG. 6  is an enlarged illustration of the bottom side of the carriage of the linear guide of  FIG. 1  showing the portion of the connection arrangement that is part of the carriage; 
           [0025]      FIG. 7  is an enlarged illustration of the bottom side of the carriage showing the connection arrangement of the linear guide of  FIG. 1 ; and 
           [0026]      FIG. 8  is a cross-sectional end view of the linear guide of  FIG. 1  taken about line  8 - 8 . 
       
    
    
       [0027]    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 
       [0028]      FIGS. 1 and 2  illustrate a linear guide  100  according to an embodiment of the invention. The linear guide is configured to guide an attached device along a predetermined pathway. The linear guide  100  includes a carriage  102  mounted to a guide rail  104  and a drive screw  106  that operably drives the carriage  102  along the guide rail  104 . Rotational motion of the drive screw about axis  108  will drive the carriage  102  linearly along the guide rail  104 . 
         [0029]    The drive screw  106  and guide rail  104  are mounted to end blocks  110  at opposed ends thereof. The end blocks  110  may include bearings or bushings for rotationally supporting the drive screw  106 . The ends of the guide rail  104  are inserted into grooves or slots formed in the end blocks  110 . Further, screws or other fasteners may be provided to secure the ends of the guide rail  104  into the grooves or slots of the end block  110 . The end blocks  110  may include slots or apertures for allowing a user to mount the end blocks  110  to another support surface. 
         [0030]    With additional reference to  FIGS. 3 and 8 , the carriage  102  generally defines channels  112  that receive raceway portions  114  of the guide rail  104 . The channels  112  are bounded by a low friction material such as a lubricious material that may be in the form of FREELON, which is a polytetrafluoroethylene (PTFE) based material. The channels  112  are generally formed by three sidewalls or surfaces that have two of the sidewalls or surfaces parallel to one another with a third sidewall or surface extending perpendicular therebetween. These three sidewalls or surfaces are generally coated with or provided by the lubricious or self-lubricating material such as PTFE. This self-lubricating material can be adhered or otherwise secured to the body of the carriage  102 . The three sidewalls or surfaces defining each of the channels  112  cooperate with a corresponding one of three sides of the raceway portions  114 . There is a close tolerance relationship between the channels  112  and the raceway portions  114  in order to prevent play therebetween and to provide accurate motion for the carriage  102  along the axis  108  and guiderail  104  when driven by drive screw  106  in reciprocating motion along the guiderail  104 . 
         [0031]    The carriage  102  generally includes a body  116  with a pair of arms  118  extending away from a top surface  120 . The top surface  120  is configured for mounting additional structures that are to be driven linearly along axis  108 . The guiderail  104  is positioned transversely between the arm portions  118  as is the drive siren  106  when assembled. 
         [0032]    The sides of the raceway portions  114  that cooperate with the channels  112  of the arms  118  of the carriage  102  have very high tolerance characteristics such that they are very straight and smooth. This promotes improved accuracy of the travel of the carriage  102  therealong. 
         [0033]      FIG. 3  illustrates the linear guide  100  from the bottom in exploded form with the guiderail  104  removed.  FIG. 4  illustrates the linear guide  100  with the guide rail  104  removed and viewed from a bottom thereof. The linear guide  100  includes a connection arrangement  130  for operably connecting the drive screw  106  to the carriage  102  to convert rotary motion of the drive screw  106  into linear motion of the carriage  102 . 
         [0034]    With additional reference to  FIGS. 5-7 , the connection arrangement  130  generally includes a cradle mechanism  132  that slideably cooperates with a lead screw nut  134 . The cradle mechanism  132  is formed as part of carriage body  116  or otherwise attached to the carriage body  116 . In the instant embodiment, the cradle mechanism  132  is provided by a pair of attachment brackets  136  that are operably mounted to an underside of the carriage body  116 . The attachment brackets  136  are attached by screws  138  that are threaded into the underside of the body  116 . The attachment brackets  136  define grooves  140  that are in opposed and spaced relation such that the openings or mouths thereof face one another to form a receiving slot thereby. 
         [0035]    The lead screw nut  134  includes a head portion  142  that is configured to be received in the grooves  140  of the attachment brackets  136 . The axial width w1 of the head portion  142  is substantially equal to the axial width w2 of the grooves  140  when measured parallel to the axis  108  of the drive screw  106 . As such, there is substantially no axial clearance or play between the opposed axial end faces  144 ,  146  of the head portion  142  and the opposed facing surfaces on each of the attachment brackets  136 . 
         [0036]    Each of the grooves  140  is bound, in part, by a transversely facing surface  152 . These transversely facing surfaces  152  face one another when mounted to the carriage body  116 . Preferably, these transversely facing surfaces  152  are generally planar surfaces that extend generally perpendicular to the axes  108  of the drive screw  106 . 
         [0037]    The head portion  142  of the nut  134  has corresponding transversely facing surfaces  154  that face transversely away from one another. These transversely facing surfaces  154  cooperate with and abut against corresponding ones of the transversely facing surfaces  152  of the attachment brackets  136  that face one another when the head portion  142  is operably received in grooves  140 . The transversely facing surfaces  154  of the head portion  142  are also generally planar and will extend perpendicularly to the top surface  120  of the carriage like transversely facing surfaces  152 . 
         [0038]    Preferably, the head portion is sized such that it can slide axially within the grooves  140  in a direction generally perpendicular to the length of the drive screw  106 , as well as perpendicular to top surface  120 . More particularly, the nut  134  is permitted to move in an axial direction, illustrated by arrow  151  in  FIG. 7 , that is generally perpendicular to a plane defined by the top or bottom surfaces of the guide rail  104 . 
         [0039]    This arrangement allows for any tolerance stack up or variation between the guide rail  104  and the drive screw  106 . As used herein, a single linear degree of freedom shall not include the rotational degree of freedom between the screw and nut. More particularly, if there are variations in the straightness of either the drive screw or the guide rail, the first degree of freedom provided by the sliding arrangement between the head portion  142  of nut  134  and the grooves  140  of the attachment brackets  136  allows for some relief of any friction or forces that are applied between the drive screw and the carriage due to binding in the connection between the two components. More particularly, the head portion  142  is permitted to slide within the grooves  140  of the attachment brackets  136 . This can also compensate for slight tolerance variation in the components of the linear guide  100 . 
         [0040]    The connection arrangement  130  also provides anti-rotation features/structures. The transversely facing surfaces  152 ,  154  cooperate with one another to prevent rotation of the nut  134  within the grooves  140  in an angular direction about axis  108  of the drive screw  106 . This prevents any torsional backlash between the drive screw  106  and the carriage  102 , particularly when the drive screw  106  changes rotational direction about axis  108  to change the linear direction of movement of the carriage  102  along the guide rail  104 . This maintains the accuracy of the position of the carriage  102  along the axis  108 , particularly when changing axial direction of movement. 
         [0041]    Again, this sliding interface between the head portion  142  and the attachment brackets  136  helps reduce binding between the drive screw  106  and the connection arrangement  130 , and particularly the lead screw nut  134  thereof during operation of the linear guide  100 . 
         [0042]    The nut  134  preferably includes a plurality of flexible fingers  156  having threads formed from a low friction or self-lubricating material such as PTFE to reduce friction between the nut  134  and the drive screw  106 . The flexible fingers  156  may be integrally formed with the head portion  142  into a single piece of material, such as being molded as a single component. Alternatively, the flexible fingers  156  could be formed from a separate component as the head portion  142 . 
         [0043]    While the illustrated embodiment includes a head portion  142  formed or provided by the nut  134  and grooves provided by the brackets  136  (or the carriage  102  generally), an alternative embodiment could have these features reversed. More particularly, the nut could provide one or more grooves that receive one or more posts or wall portions of the carriage  102  that slide within the grooves formed by the head portion that provides a single linear degree of freedom. 
         [0044]    The use of separate attachment brackets  136  allows for an adjustment of the mounting of the grooves  140  to the rest of the carriage  102 . 
         [0045]    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. 
         [0046]    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. 
         [0047]    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.