Abstract:
A longitudinal cavity is defined in the fixed longitudinal support ( 2 ) preferably presenting a square section ( 7 ) within which a main sliding cursor ( 6 ) is held to which at least one auxiliary cursor ( 10 ) is associated, the two cursors together are suited to bearing rollers ( 8 ) that can slide along four races ( 9 ) coinciding with the sides of said longitudinal cavity set with a diagonal coinciding with the action line (II—II) of the load (P) supported by the linear guide (FIG.  3 ).

Description:
FIELD OF THE INVENTION 
     The present invention concerns a linear guide to support a sliding element, as, for example, a door or part of a machine. 
     THE PRIOR ART 
     The linear guides comprise a fixed longitudinal support and a mobile part on rollers that slides along the longitudinal support holding a sliding unit suspended or bearing from above. 
     In known guides the fixed longitudinal support is generally shaped so as to present one or two plane sliding races upon which at least two rollers for each race roll charging radially Generally the roller cursor runs astride the guide and the cross-sectional encumbrance is given by the sum of the dimensions of the guide plus the dimensions of the rollers; this solution is shown in FIG.  1 . Opposite versions are also known in which the guide has the inner sliding races and in these versions the guide is large enough to contain also the roller cursor and the cross-sectional encumbrance is similar to the version previously described. 
     SUMMARY OF THE INVENTION 
     The main purpose of the present invention is to offer a linear guide that features a smaller transversal section compared to known guides, at equal roller dimensions and load capacity. 
     This linear guide belongs to the type of guides with the sliding cursor within the fixed longitudinal support and is characterised by a cursor that comprises a main cursor bearing a main group of rollers and at least one auxiliary cursor which bears an auxiliary group of rollers, the auxiliary cursor being adjustable in respect of the main cursor in order to move with respect to the other group. The two cursors carry rollers that can roll along four races defined within a longitudinal cavity that has a parallelogram cross-section and is formed within the fixed longitudinal support in order that one of its diagonals coincides with the line of action of the load supported by the guide and to have a longitudinal aperture along one of the vertexes crossed by said line in order to allow the passage of the parts that connect the cursor to the sliding element, so that the latter and the cursor may slide along said support. One group of rollers can roll along the two races that will take the load and the other group can roll along the other two races, but the adjustment means allow to transfer the engagement of each group of rollers from the two races to the opposite two, so that the guide can work with the sliding element above or below the guide, the load being borne by the four rollers of the main group in any case. This characteristic of being able to use the guide with the sliding element above or else below the guide is conventionally called “guide inversion”. The longitudinal cavity will preferably have a square section and the description herein will relate to such square section embodiment. 
     The auxiliary cursor, preferably set at the centre of the main cursor, is fixed to the latter by means of a coupling in sliding-guiding engagement, sliding and fastening screws and spacing screws, all together suited to adjust the relative movement of the two cursors, as it will be explained in detail with the example of embodiment. 
     In one embodiment of the present invention, in which the load transmitted by the sliding element is applied above the guide, the main group of rollers bears at least one pair of rollers that are longitudinally spaced from one another and charge on a first common lower race and bears at least a second pair of longitudinally spaced rollers charging on a second common lower race positioned at 90° with respect to the first race; the auxiliary cursor is positioned between the said first and second pairs of rollers, preferably at the centre of the main cursor, and bears at least two rollers at 90° from one another that respectively charge upon the two upper races. 
     According to said embodiment we have a guide bearing at least six rollers, four of which charge upon the lower races supporting the load transmitted by the sliding element and two are just slightly engaged on the two lower races so that the cursor is held in all transversal directions during its sliding along the guide. 
     The advantages of this guide lie in that, given the same load capacity, compared to a known guide, it allows for a greater compactness and lightness, a protected positioning of the roller system and the fact that all the rollers conveniently charge on the respective races in order to provide a sliding free of undesirable transversal jolting and the possibility of guide inversion. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will be described in further detail by means of an example of embodiment and the support of the attached drawings in which 
     FIG. 1 is a part section that serves as reference to the state of the art, 
     FIG. 2 is a first longitudinal view, 
     FIG. 3 is a first transversal section, 
     FIG. 4 is a first part section transversal section, 
     FIG. 5 is a second part section transversal section, 
     FIG. 6 is first perspective view, and 
     FIG. 7 is a second partly blown-up perspective view. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 is a transversal section of a guide that responds to the state of the art and bears a pair of upper rollers  1   a  and a pair of lower rollers  1   b  astride the longitudinal support  2  fixed to a vertical wall  3 ; the rollers are hinged according to the I—I axes onto cursor  4  that supports the sliding door  5 . 
     FIGS. 2 and 3, and the others, show a guide bearing six rollers, as featured by a preferred embodiment of the guide invented. It is useful to consider FIGS. 2 and 3 together. A vertical load P acting according to the transversal symmetry axis II—II of the square longitudinal cavity  7 , weighs upon the fixed longitudinal support  2  through the main cursor  6  that is held in a sliding manner within cavity  7  as it carries the main group of rollers made up of two pairs  8   a  and  8   b  one on one side and the other on the other side of the centre of the main cursor  6 . The  8   a  pair of rollers charges and can roll along the lower race  9   a  of the longitudinal support  2  and the  8   b  pair of rollers charges and can slide along the lower race  9   b  of the longitudinal support  2 , the two races obviously being at 90° from one another. The auxiliary cursor  10 , engaged in an adjustable manner in a suitable seat at the centre of the main cursor  6  with adjustment means of which only the spacing screws  12  are shown herein, bears the auxiliary group of rollers made up by a roller  8   c  just slightly engaged upon the upper race  9   c  and a roller  8   d  just slightly engaged upon the upper race  9   d  this just slight engagement being a desired light pressure upon the races, obtained by means of the said adjustment of the auxiliary cursor compared to the main one. An extension of the main cursor  6  passes through aperture  11  of the longitudinal support  2  in order to be fitted to the sliding element (not shown) and an extension of the auxiliary cursor  10  passes through aperture  11  to be fastened to the main cursor. 
     FIG. 4 shows the main cursor  6  and relative rollers  8   a ,  8   b , that can rotate round axes A—A. 
     FIG. 5 shows the auxiliary cursor  10  and related rollers  8   c ,  8   d  that can rotate around axes B—B. 
     FIGS. 6 and 7 show in detail a solution for fixing the auxiliary cursor  10  to the main cursor  6  in an adjustable manner in order that the two groups of rollers move within a given field, so as to transfer the engagement of each group of rollers from two races to the other two opposite races and realise the guide inversion. The tongue  13  is held in the calibrated aperture  14  (sliding-guiding engagement); the sliding and locking screws  15  are made to pass through the holes  15   a  and slits  16  behind which screws  15  are fitted with a washer and a lock-nut that are not shown; a covering plate  17  is fixed to the flat part  17   a  of the main cursor  6  with screws that are not shown engaged in holes  18 ,  18   a  in correspondence with the spacing screws  12  that pass through the flat part  17   a  to be engaged in the threaded holes  12   a  of the auxiliary cursor; on plate  17  holes  19  are foreseen, tighter than the heads of screws  12 , through which screws  12  can be fully fastened or unfastened in order to end up forcing against the plate  17  with their heads so that the auxiliary group of rollers are forced against races  9   a ,  9   b  and the main group of rollers are forced against races  9   c ,  9   d . It is understood that the “screwing field” assigned to the screws  12  allows to adjust the distance between the two cursors as required in the direction of the transversal symmetry, axis  11 — 11  and, hence, the position of the rollers with respect to the races and, which is very important, to cause the guide inversion. After having chosen the relative position of the two cursors  6  and  10 , the screws  15  are locked into the desired position. 
     It is also understood that this linear guide can bear more than two pairs of rollers  8   a , and  8   b  on the main cursor  6  and can comprise more than one auxiliary cursor  10 , each bearing one or more pairs of rollers  8   c ,  8   d , depending on the working conditions of the guide; with only one auxiliary cursor it could be at the centre of the main cursor and if there are two auxiliary cursors they can, each of them, be at opposite ends of the main cursor.