Abstract:
A linear unit has a drive unit, a stator, a drive roller connected to the drive unit, a freewheeling roller supported on the stator adjacent to one of longitudinal ends of the stator, the drive belt being wound around the drive roller and around the freewheeling roller, a traveler movable along the stator by the drive belt, the drive belt being connected to the traveler in at least one fastening point, so that a distance between an end of the traveler which is oriented toward an end of the stator associated with the freewheeling roller, and the fastening point situated the closest to the end of the traveler is at least equal to a radius of the freewheeling roller.

Description:
CROSS-REFERENCE TO A RELATED APPLICATION 
       [0001]    The invention described and claimed hereinbelow is also described in German Patent Application DE 20 2007 004 693.6 filed on Mar. 30, 2007. This German Patent Application, whose subject matter is incorporated here by reference, provides the basis for a claim of priority of invention under 35 U.S.C. 119(a)-(d). 
       BACKGROUND OF THE INVENTION 
       [0002]    The invention relates to a linear unit with a traveler that can be moved along a stator by means of a drive belt, in which the drive belt is wound around a drive roller, which is connected to a drive unit, and around a freewheeling roller; the freewheeling roller is supported on the stator adjacent to one of the longitudinal ends of the stator; and the drive belt is connected to the traveler in at least one fastening point. 
         [0003]    A linear unit of this kind is known, for example, from DE 37 43 577 C1. In this linear unit, the freewheeling roller is supported on an end plate of the linear unit by means of tensioning screws that engage in threaded bores of the bearing shaft of the freewheeling roller. In addition, the drive belt is connected to the traveler at two fastening points, which are situated adjacent to the ends of the traveler oriented toward the freewheeling roller and oriented away from it. In this arrangement, it is disadvantageous that the traveler cannot make use of the full length of the stator as it travels along it. 
       SUMMARY OF THE INVENTION 
       [0004]    By contrast, the object of the invention is to disclose a linear unit of the type mentioned at the beginning in which the traveler can make use of a greater length of the stator when moving along it. 
         [0005]    This object is attained according to the invention by means of a linear unit of the type mentioned at the beginning in which the distance between the end of the traveler, which is oriented toward the end of the stator associated with the freewheeling roller, and the fastening point situated the closest to this end of the traveler is at least equal to the radius of the freewheeling roller. Since at a maximum, the traveler can move in the direction toward the freewheeling roller until the fastening point closest to the freewheeling roller is situated precisely at the apex of the freewheeling roller, i.e. the point at which the drive belt comes into contact with the freewheeling roller and begins its deflection movement around the freewheeling roller, and according to the invention, in this position, there is still a segment of the traveler protruding beyond the apex, the length of which is at least equal to the radius of the freewheeling roller, the traveler is therefore able to make use of a significantly greater length of the stator for its movement. 
         [0006]    In order to be able to make use of an even greater length of the stator for the movement of the traveler, according to a modification of the invention, the distance is at least equal to the radius of the freewheeling roller determined by taking into account the drive belt that is wound around it. 
         [0007]    Depending on the respective construction of the linear unit, when determining the distance, it is additionally or alternatively possible to also take into account the thickness of the end plate of the linear unit. 
         [0008]    As is intrinsically known from the prior art, the position of the freewheeling roller can be adjustable relative to the stator, which is particularly advantageous for tensioning the drive belt. 
         [0009]    In order to stabilize the position of the freewheeling roller in the vertical direction of the linear unit and thus to be able to assure a smoother running of the drive belt, according to another aspect of the invention, it is possible for the axle or shaft of the freewheeling roller to be supported in a carriage whose position in relation to the stator can be adjusted in the longitudinal direction of the stator, for example through the use of at least one tensioning screw supported on the stator, preferably on an end plate of the stator. Since the provision of such a carriage is not yet known from the prior art, separate protection is being sought for this idea. 
         [0010]    The carriage can advantageously be guided on the stator. If one of the parts here, i.e. the stator or carriage, has an undercut groove that encompasses associated projections of the respective other part, i.e. the carriage or stator, then this can produce a stable guidance of the carriage in both the vertical direction and the transverse direction of the linear unit. 
         [0011]    Since the play present in the vertical direction in particular plays a decisive role in a smooth running of the drive belt, according to a modification of this aspect of the invention, play-adjusting means are provided that make it possible to adjust, preferably to reduce or eliminate, the play between the carriage and the stator. In this case, the play-adjusting means should adjust the play in the vertical direction in such a way that it is still possible, preferably just barely, to tension the drive belt, i.e. to adjust the carriage in the longitudinal direction of the stator. After the belt is tensioned, the play-adjusting means is firmly tightened in order to prevent the carriage from vibrating. 
         [0012]    The carriage can have an essentially U-shaped form in a section extending orthogonal to the movement direction. In this case, the axle or shaft of the freewheeling roller can be supported in the two side legs of the U-shape and/or the at least one tensioning screw can engage in an end surface of at least one side leg of the U-shape and/or the carriage can be guided on the stator by means of the base leg of the U-shape and/or the play-adjusting means can be associated with the base leg of the U-shape. 
         [0013]    In order to be able to minimize the generation of noise caused by the drive belt slapping against the traveler when the traveler is moving along the stator, according to a modification of the invention, when a plurality of fastening points are provided, they are distributed asymmetrically over the length of the traveler in its movement direction. In particular, it is advantageous if the distance between the end of the traveler oriented away from the freewheeling roller and the fastening point situated the closest to this end of the traveler is as small as possible, preferably the fastening point situated the closest to this end of the traveler is situated adjacent to the end of the traveler oriented away from the freewheeling roller. 
         [0014]    As is intrinsically known, it is also possible according to the invention for the stator to be composed of the housing of a linear module, preferably produced from an extruded profile. 
         [0015]    In addition, the drive belt can be a toothed belt, which is likewise intrinsically known. 
         [0016]    The novel features which are considered as characteristic for the present invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]      FIG. 1  is a perspective view of a linear unit according to the invention; 
           [0018]      FIG. 2  is an end view of the linear unit according to  FIG. 1 ; 
           [0019]      FIG. 3  is an exploded view of the tensioning device of the linear unit according to the invention; and 
           [0020]      FIG. 4  is a schematic side view of the linear unit according to the invention. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0021]    In  FIG. 1 , a linear unit according to the invention is labeled as a whole with the reference numeral  10 . It includes a drive unit  12  and a main module unit  14 ; in  FIG. 1 , an end plate  16  of the main module unit  14  is only depicted with dashed lines in order to provide a view of the inner structure of the main module unit  14 . The inner structure of the main module unit  14  is also shown in the end view according to  FIG. 2 . 
         [0022]    The main module unit  14  has a housing  18  that is advantageously composed of an extruded profile with an essentially U-shaped cross-section. The base leg of the U-shape of the housing  18  has two guide rails  20  mounted to it on which guide units  24  support a table part  22  so that it is able to slide in the longitudinal direction L of the linear unit  10 . As is shown only in  FIG. 2 , the opening between the free ends of the side legs of the U-shape of the housing  18  is covered over the length of the housing  18  by a cover plate  26  so that only two longitudinal slots  28  remain, through which two fastening strips  22   a  of the table part  22  protrude. A component that is to be slid by means of the linear unit  10  can be attached to the table part  22  by means of these fastening strips  22   a . The cover plate  26  is fastened to the drive unit  12  at one end and to the end plate  16  at the other. 
         [0023]    As is particularly clear from  FIG. 1 , the linear unit  10  according to the invention is equipped with a belt drive. The drive belt  30  of the belt drive, which is closed into an endless loop, on the one hand winds around a driven roller that is situated in the drive unit  12  and is therefore not visible in the drawing and on the other hand, winds around a freewheeling roller  32 , which is situated adjacent to the end plate  16 . In order to be able to tension the drive belt  30 , which can for example be embodied in the form of a toothed belt, the freewheeling roller  32  is situated in a tensioning device  34  whose design and function will be explained in greater detail below particularly in conjunction with  FIG. 3 : 
         [0024]    The tensioning device  34  has a carriage  36  that has an essentially U-shaped cross-section in the view shown in  FIG. 2 . The side legs  36   a  of the carriage  36  are provided with through openings  36   b , which serve to accommodate the axle or shaft  32   a  of the freewheeling roller  32 . To support the freewheeling roller  32  in rotary fashion on the axle/shaft  32   a , roller bearings  32   b  are provided, which are secured to the axle/shaft  32   a  by means of shim rings  32   c . On its base leg  36   c , the carriage  36  is provided with an undercut groove  36   d  that engages with correspondingly embodied projections  18   a  of the base leg  36   c  of the housing  18  (see  FIG. 2 ). Threaded bores  36   f  extending in the longitudinal direction L are let into the end surfaces  36   e  of the side legs  36   a  of the carriage  36 . Two tensioning screws  36   g , which pass through the end plate  6  engage in these threaded bores  36   f  and rest with their heads against the end late  16 . In this way, tightening the tensioning screws  36   g  causes the carriage  36  to move toward the endplate  16 , thus making it possible to tension the drive belt  30 . 
         [0025]    In order to reduce a play that exists between the carriage  36  and the housing  18  or to set it to an amount that permits a desired mobility of the carriage  36  in the longitudinal direction L, threaded bores  36   h  extending in a vertical direction H are provided in the base leg  36   c  of the carriage  36  on both sides of the groove  36   d ; these threaded bores  36   h  extend through the base leg  36   c  and set screws  36   i  can be screwed into them. If the lower end surfaces of the set screws  36   i  rest against the base leg of the housing  18 , then the projections  36   d   1  delimiting the groove  36   d  are pressed against the projections  18   a , thus reducing or eliminating a play that may be present between the carriage  36  and the housing  18 . 
         [0026]    It should also be noted that in order to stabilize the shape of the carriage  36 , reinforcing bridge pieces  36   j  are also provided that extend parallel to the carriage&#39;s base leg  36   c.    
         [0027]    It should further be noted that if the width of the base leg  36   c  essentially corresponds to the width of the roller  32 , then it is possible to achieve a particularly compact design. 
         [0028]    As shown in  FIG. 1 , the drive belt  30  is fastened to the table part  22  at four fastening points  38   a ,  38   b ,  38   c , and  38   d . As is easily visible, these fastening points are distributed nonuniformly in the longitudinal direction L of the table part  22 . The fastening points  38   c  and  38   d  are situated closer to the end  22   b  of the table part  22  oriented away from the freewheeling roller  32  than the fastening points  38   a  and  38   b  situated at the end  22   c  of the table part  22  oriented toward the freewheeling roller  32 . The important thing for the present invention is the fact that, as particularly shown in  FIG. 4 , the fastening point  38   a , which is the fastening point situated closest to the end  22   c  of the table part  22 , has a distance x from this end  22   c  that is greater than the radius r of the freewheeling roller  32 , and preferably, is even greater than the sum of the radius r and the thickness d of the drive belt  30 . 
         [0029]    If a freewheeling roller  32  of the kind shown in  FIG. 2  is used, i.e. a roller whose cylindrical deflection surface  32   d  is bounded by two limiting disks or limiting rings  32   e , then when the radius R of the limiting disks/limiting rings  32   e  is greater than the sum of the radius r of the cylindrical deflection surface  32   d  and the thickness d of the drive belt  30 , it is preferable for the distance x to be greater than this radius R. 
         [0030]    If the main module unit  14  is embodied so that the top  22   d  of the table part  22  is not flush with the top  16   a  of the end plate  16 , but instead protrudes beyond it so that the table part  22  can be moved until it is above the end plate  16 , then the distance x can be selected to be even greater, for example by the thickness D of the end plate  16  so that the end  22   c  of the table part  22  ends essentially flush with the end surface  16   b  of the end plate  16 . 
         [0031]    In this way, the entire length of the main module unit  14  can be used for the movement of the table part  22 . 
         [0032]    It should also be noted that a recess  22   e  is provided in the end  22   c  of the table part  22 , which extends into the table part  22  from this end  22   c . In the position of the linear unit  10  shown in  FIG. 1 , the freewheeling roller  32  is at least partially accommodated in this recess  22   e . It is therefore possible to assure that the housing  18  of the main module unit  14  has a low structural height, i.e. a small dimension in the vertical direction H, despite the implementation of the present invention. 
         [0033]    It should furthermore be noted that at least the drive unit  12 , the housing  18 , the end plate  16 , and the guide rails  22  constitute the stator  40  of the linear unit  10  and that at least the table part  22  and the guide units  24  constitute the traveler  42  of the linear unit  10 . 
         [0034]    It will be understood that each of the elements described above, or two or more together, may also find a useful application in other types of constructions differing from the type described above. 
         [0035]    While the invention has been illustrated and described as embodied in a linear unit, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of the present invention. 
         [0036]    Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can, be applying current knowledge, readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention.