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BACKGROUND OF THE INVENTION 
     The invention relates to an arrangement of grinding modules with grinding tools in track grinders. Such arrangements are used in reprofiling the head of a track profile, in removal of short waves (groovings) as well as in truing long waves in a driving direction. Mostly grinding wheels are used as grinding tools. 
     Track grinding machines are already known in which a surface pressure of a grinding module is increased or reduced, depending on whether the grinding module moves over a wave trough or over the top of a wave, so that any such waves are leveled, refer to DE-OS 2 037 461. Furthermore, track grinding machines with hydrostatic control are known which, irrespective of the rising of the line or the train resistance, keep to the rate of advance with high precision. A precise positioning of the grinding wheels is essential for the regeneration of the rails, refer to the grinding machine LRR 8-M of the Speno Company. This, however, is particularly problematic with small radii of curvature (&lt;30 m) since there is a comparatively large radial departure of the grinding modules due to common wheel center distances, in particular when both rails are simultaneously ground. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide an arrangement of grinding modules in a track grinding machine which permits to exactly involve a radial departure in narrow rail curvature radii (&lt;15 m) without provoking reactive forces, and which allows reprofiling in a reproducible and simple way. 
     The object is realized by the the present invention providing an arrangement of grinding modules with grinding tools in track grinders, characterized in that each grinding tool has five degrees of freedom of movement, whereby two linear movements are transverse to the rail to be ground, two linear movements are at least approximately vertically to the rail to be ground and one rotational movement is about an axis which is directed in parallel to the rail at the respective grinding site. Thereby it is of no concern whether or not the arrangement has to grind only one rail or to simultaneously grind both rails of a track. In the latter case the arrangement can be used with particular effectiveness. Furthermore, the number of grinding modules, which are comprised to a reprofiling unit in a frame, is insignificant, whereby the frame can be made, for example, of tubular steel. 
     An advantageous arrangement according to the present invention is obtained when at least one grinding module is at least approximately vertically adjustably seated in a frame and at least approximately horizontally and adjustably seated on a mount via the frame. In the mount, there is provided a housing pivotally arranged about an axis, the axis is at least approximately parallel to a rail to be ground, and in the housing a grinding cylinder is at least approximately displaceable at right angles to the rail to be ground. Preferably a measuring wheel is provided for each grinding module and means for carrying out a relative movement between the grinding module and the measuring wheel. In this way it is possible to include a radial deviation for each grinding module, particularly in narrow curves. 
     In order to have the measuring wheels always engage via their wheel flanges the rail to which they are associated, each measuring wheel is rotationally seated in a seating mount, which is adjustable, transversely to the rail to be worked on, along a guiding means on the frame, by aid of a servo-drive or a drive means and gearing, preferably a lever system. Preferably, horizontal transversal movement of the mount seated on the frame is carried out by way of a fluid transmission gear in dependence on the transversal movement of the measuring wheel. Thus it is possible to drive into three defined positions (driving the reprofiling unit into operation position, into positioning of the grinding modules, and in pressing the grinding modules to the rail) without the necessity of employing expensive sensing means for each position. 
     Advantageously, the fluid transmission gear comprises a double cylinder with two opposing pistons in a cylinder chamber of the double cylinder. This design permits using the arrangement according to the invention on different rail gauges, whereby the rail gauge setting range preferably lies between 1000 mm and 1458 mm. Means for blocking the fluid transmission gear are preferably provided for passing complicated curves in the track and points, whereby the fluid transmission gear can be designed as a cylinder-piston-arrangement. The blocking means can be entirely or partially arranged in the vicinity of gearing for the transversal movement of the mount. It is, however, also possible to arrange the blocking means in the vicinity of the measuring wheels of corresponding grinding modules for both rails. 
     In a further arrangement according to the present invention a plurality of grinding modules can be seated on the frame and corresponding front and rear measuring wheels, considered in the direction of the grinding carriage, can be pivotally joined to the frame for executing movements in vertical directions. 
     In a further favorable embodiment, provided that the requirements to accuracy are satisfactory for an actual case of application, the grinding modules can be combined in groups on a frame, and each grinding module group is attached to a support which is pivotally seated on the frame in a plane at least approximately parallel to one of the rails. In this case, the measuring wheels are advantageously associated to the grinding module groups. Each of the measuring wheels which are arranged between the grinding module groups is active for the two neighboring grinding module groups which, in the vicinity of the measuring wheels located between them, are pivotally joined to one another about an axis which is arranged substantially at right angles to the rail to be ground. 
    
    
     The invention will be explained in more detail by virtue of the schematical drawings. 
     BRIEF DESCRIPTION OF THE FIGURES 
     FIG. 1 a plan view of a grinding carriage substantially characterized by wheel axles between which arrangements according to the present invention (reprofiling units) are provided, 
     FIG. 2 a lateral view of an arrangement according to the present invention with three grinding modules, 
     FIG. 3 a plan view of the arrangements according to the present invention of FIG. 2, 
     FIG. 4 an end view of a grinding module of the reprofiling unit, 
     FIG. 5 a perspective view of a grinding module, 
     FIG. 6 a lateral view of a second arrangement according to the present invention, and 
     FIG. 7 a control logic of a fluid transmission gear with a double cylinder. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In FIG. 1 a grinding carriage  10  moving in x-direction and having a central line m is provided with two wheel axles  11 ,  12 , whereby the wheel axles  11 ,  12  are seated for rotation substantially about vertical axes X—X on the carriage. Pairs of wheels  13 ,  14  of the grinding carriage  10  run on rails  15 ,  16  of a track, rail heads of which shall be worked on and reprofiled. Thereby wheel flanges  17 ,  18  of the wheels  13 ,  14  run on inner edges of the rails  15 ,  16 , indicated by dashed curved line. Reprofiling units  19 ,  20 ,  21 ,  22  are attached to the grinding carriage  10  between the wheel axles  11 ,  12 . By use of the reprofiling units  19 ,  20 ,  21 ,  22 , the heads of the rails  15 ,  16  will be worked on. Due to the curvature of the rails  15 ,  16 , the wheel axles  11 ,  12  are inclined relative to the central line m of the grinding carriage  10  by an angle of ±φx towards a not shown center of curvature. The curvature of the rails  15 ,  16  also effects deviations of secants gx for the reprofiling units fixedly connected to the grinding carriage  10 , whereby these secant deviations also affect the grinding tools in the reprofiling units  19  to  22  and their position relative to the rails  15 ,  16 . With too small radii of curvature of the rails  15 ,  16 , the grinding tools will not work the entire width of the rail head, respectively they will work on the rail head in an improper manner. This disadvantage is eliminated by the arrangement according to the present invention. 
     In FIGS. 2 and 3, the arrangement according to the present invention comprises a frame  23  with grinding modules  24 ,  25 ,  26 , whereby the frame  23 , by the aid of drive means  29 ,  30 , is arranged vertically displaceable in the direction of a double arrow  56  at guide means  27 ,  28  which, in turn, are secured to the (here not shown) grinding carriage. The drive means  29 ,  30  can be pneumatically operating ones. Each of the grinding modules  24 ,  25 ,  26  is provided with a grinding disk  31 ,  32 ,  33  which is driven by an electric-motor arranged in a housing  34 ,  35 ,  36  to grind a rail head (surface)  37  of a rail  15  (FIG. 1) and which will be, along guides  57 ,  58 ,  59 , driven by respective electric-motors  60 ,  61 ,  62  substantially at right angles to the respective rail  15 , transported to the respective rail  15  and pressed onto the same. The housing  34 ,  35 ,  36  is pivotally seated at a respective mount  38 ,  39 ,  40  about an axis at least approximately in parallel to the rail  15  to be ground, for grinding the cross-profile of the rail head. To his end electric-motors  63 ,  64 ,  65  are provided at the mounts  38 ,  39 ,  40  which, via respective motion transmission means  66 ,  67 ,  68 , effect the pivotal movement of the housing  34 ,  35 ,  36  and of the guides  57 ,  58 ,  59  in bearings  69 ,  70 ,  71  at the respective mount  38 ,  39 ,  40 . The mount  38 ,  39 ,  40  is arranged on the frame  23  for displacements along guides  41 ,  42 ,  43  which are substantially horizontally positioned and transversal to the rail head  37 . Drive means  44 ,  45 ,  46 , for example, pneumatic double cylinders are employed for transverse displacing the mounts  38 ,  39 ,  40 , whereby the drive means are partially attached to the associated grinding module  24 ,  25 ,  26  and partially to a suitably location on the frame  23 . The action of the grinding modules can be neutralized by blocking means  47 ,  48   49 , for example, hydraulic blocking cylinders. 
     To each grinding module  24 ,  25 ,  26  belongs a measuring wheel  50 ,  51 ,  52  with a wheel flange  50 ′,  51 ′,  52 ′, which is seated in an associated bearing block  53 ,  54 ,  55  and which can be put on the rail head  37  by displacing the frame  23  along the guides  27 ,  28 . Rollers  501 ,  502 , and  521 ,  522 , respectively advance and trail the measuring wheels  50  and  52  in order to prevent short waves and grooves in the surface of the rail from being followed. By the aid of adjusting screws  110 , the bearing block  53 ,  55  with the corresponding measuring wheel  50 ,  52  and the respective rollers, advancing respectively trailing the latter, is pivotally seated at the respective grinding module  24 ,  25 ,  26 , with the definable pivotal movement being about a substantially horizontal axis and transverse directed to the rail head  37 . Additionally, the measuring wheels  50 ,  51 ,  52  and their bearing bodies  53 ,  54 ,  55  are displaceably arranged at the respective mount  38 ,  39 ,  40  transverse to the rail head  37  and parallel to the respective guide  41 ,  42 ,  43 . To this end respective drive means  72 ,  73 ,  74 . of the grinding modules  24 ,  25 ,  26  are provided, which are exemplarily and in more detail shown and explained in the FIGS. 4 and 5 with slight differences. To avoid any reactive forces, there is provided a tolerance s (about 0.3 to 0.8 mm) for the mean grinding module  25  relative to the rail head  37 , when the measuring wheels  50  and  52  bear upon the rail surface  37 , whereby the tolerance can be finely adjusted by a cam screw  75 . Provided that the grooving wave peaks are greater than the given tolerance, the mean grinding module  25  can escape in vertical direction by an amount f, which is indicated by a dash-point curved line  76 , so that the bridge length or the measuring length  1  between the outside measuring wheels  50 ,  52  is maintained. When g 1  is the distance of the axis of rotation of the trailing roller  502  from the axis of rotation of the measuring wheel  51 , and g 2  the distance of the axis of rotation of the advancing roller  521  from the axis of rotation of the measuring wheel  51 , and when p is the projection of the distance of the axis of rotation of the measuring wheel  51  from the nearest positioned horizontal guide  42  onto the rail surface  37 , then under the condition that p&lt;&lt;g 1 , there will approximatively result in the point A 
     
       
           f =( FA·h/E·I )· gi ·( l−gi ), 
       
     
     where I is the surface momentum, E is the elastic modulus, FA is the force in the point A. When the grinding carriage  10  is moved to a place of work or from one place of work to the next one, then the grinding tools  31 ,  32 ,  33  are up over the rail level, that is, they and their reprofiling units  19 ,  20 ,  21 ,  22  are withdrawn from the rails  15 ,  16  and from the rail surface  37 , respectively. After the distances between the grinding tools of the reprofiling units associated to the rails  15  and  16  have already been adjusted by the aid of the drive means  44 ,  45 ,  46 , the frames  23  of the individual reprofiling units  19  to  21  are lowered in such a way that the grinding wheels  31 ,  32 ,  33  are directly positioned above the rails  15 ,  16  to be ground. Simultaneously the measuring wheels  50 ,  51 ,  52  of all reprofiling units  19  to  22  are lowered down to the rails  15 ,  16  and the rail surface  37 , respectively. The drive means  44 ,  45 ,  46  ensure that, during the grinding process, the wheel flanges  50 ′,  51 ′,  52 ′ of all the measuring. Wheels of the reprofiling units  19  to  22  are in contact to the rail heads  37 , in other words, that the measuring wheels are backlash-free guided by the rails  15 ,  16 . The electric motors  34 ,  35 ,  36  rotate the grinding wheels  31 ,  32 ,  33  about the axes  77 ,  78 ,  79 . The inclination of the grinding wheels  31 ,  32 ,  33 , corresponds to the transversal profile of the rail heads  37  and is accordingly variable in transversal planes relative to the rails  15 ,  16  together with the electric motors  63 ,  64 ,  65  and the motion transmission means  66 ,  67 ,  68 . Together with the variation of inclination there also are changed the positions of the guides  57 ,  58 ,  59  and of the slides  83 ,  84 ,  85 , guided by the former. The advance of the grinding tools  31 ,  32 ,  33  to and pressing them into contact with the rails is achieved by the electric-motors  60 ,  61 ,  62  via motion transmission means  80 ,  81 ,  82  and slides  83 ,  84 ,  85 . On the slides  83 ,  84 ,  85  there are the motor housings  34 ,  35 ,  36  provided for rotationally driving the grinding wheels  31 ,  32 ,  33  and there are seated the drive shafts  86 ,  87 ,  88  of the grinding wheels, themselves. After completion of the grinding process, the frame  23  is moved along the guides  27 ,  28  substantially in vertical direction by aid of the drive means  29 ,  30 . Thus the grinding wheels  31 ,  32 ,  33  are withdrawn from the rail heads  37  and all the drive means and the motors are turned off. The entire arrangement according to the present invention is made ready for transportation. 
     FIG. 4 substantially comprises a section along a line S—S in FIG. 2, and represents an end view of the grinding module  26 : The mount  40  is pneumatically preset to the distance of the rails  15 ,  16 . This is achieved, substantially in horizontal directions indicated by the double arrow  97 , by aid of the double cylinders  46  and by the pistons  94 ,  95  sliding within the former. One of the pistons, in the present case piston  94  (FIG. 3) is attached to the frame  23  and the other one,  95 , is attached to the mount  40 . The blocking means  49 , which here operates pneumatically, allows to arrest the presetting, whereby the arrest is, for example, necessary when a point is passed. The piston  96  of the blocking means is, for example, fixedly connected to the mount  40  and the cylinder  49  accordingly to the frame  23 . Furthermore, the frame  23  is substantially vertically displaceable by pneumatic cylinders  30  along guides  28  in the directions indicated by the double arrow  56 . In the represented state, the frame  23  is in the upper (transportation) position. 
     In the frame  23 , the guides  43  are arranged in pairs upon which the mount  40  may slide in axial bearings  89 . There are only one guide and two associated axial bearings  89  visible. 
     The drive  62 , preferably an electric motor, which is fixedly connected to the guides  59  via a base  90 , moves the slide  85  via the drive transmission means, which here is a push rod  82 , the drive transmission means being pivotally connected to the slide. Thus the housing (motor)  36 , which is secured to the slide  85 , with the grinding tool  33  is pressed against the surface  37  of the rail  15 , whereby the grinding tool  33  is mounted on a not visible motor shaft. Thereby the measuring wheel  52  contacts the rail surface  37 . 
     In order to rectify the transversal profile of the rail head, the base  90  is pivotally seated at the mount  40  in bearings  71 , which are in the vicinity of the rail  15 , the base  90  including the guides  59 , the slide  85 , to which the housing  36  for driving the grinding tool  33  and, hence, the grinding tool  33  itself, is secured. The grinding tool  33  has axial pivots  91  which are substantially in parallel to the rail  15 . A drive  65 , realized by an electric-motor, provides for a pivot motion, whereby the drive is pivotally connected to a lever  93 , which is secured to a pivot  91  by way of a push rod  92 . 
     In FIG. 5, a measuring wheel  50  having a wheel flange  50 ′, as well as a roller  501  advancing the measuring wheel  50 , and a roller  502  trailing the measuring wheel  50 , are rotatable about axes, which are parallel to one another, and, together with the grinding module  24 , are seated in a bearing block  53  for displacements in directions indicated by the double arrow  102 . The bearing block  53  is seated for rotation about an axis U—U in a holder  98 . The holder  98  is slidingly engaged in a guidance  99 , preferably a dovetail guideway, which is in parallel to the axes of rotation of the measuring wheel  50 , the roller  501  and  502 , and is rigidly connected to a mount  38 . An adjustment screw  110  permits to adjust the bearing block  53  by pivotal movements about the axis U—U. A drive means in the form of an electric-motor  72  is secured to the mount  38 , which moves a push rod  100  in its axial direction. To the end of the push rod  100 , projecting from out of the electric-motor  72 , one arm of a three-armed lever  101  is pivotally connected, the lever, which is seated at the mount  38 , is connected to the holder  98  via another arm. The drive means  72  with the lever  101 , the holder  98  and its guiding device  99  is, for the grinding process, adjusted in a manner that the measuring wheel  50  with its wheel flange  50 , is positioned as desired relative to the mount  38  according to the set grinding angle a with respect to the transversal profile of the rail. 
     At the mount  38 , a housing  103  is seated for rotations on pivots  104  in bearings  69 , only one of which is visible in the vicinity of the bearing block  53 , whereby the rotations are about an axis, which is in parallel to the double arrow  102 . Similar as in FIG. 4, an electric motor  63 , which is secured to the mount  38 , provides for the rotations, whereby the electric motor  63  acts upon a lever  105  via an axially displaceable push rod  92 . The lever  105  is rigidly connected to a not visible pivot. In the housing  103 , a substantially not visible slide  106  (similar to the slide  83  in FIG. 2) is displaceable along guides  57  substantially vertically and at right angles to the direction of displacement  102 . The slide  106  supports the housing  34  of the drive motor for the grinding tool  31 . An electric motor  60  which is attached to the outside of the housing  103  is employed for displacing the slide  106 , whereby the electric motor cooperates with a motion transmission means  80  which is engaged with the slide  106 . 
     Sliding elements  108  for the not shown guides ( 41  in FIG. 2 and 3) are attached to the mount  38 . Furthermore, a bearing block  109  is provided at the mount  38  for pivotally seating the pistons which, according to FIG. 3 slide within the cylinder  47  and in a part of the double cylinder  44 . 
     In FIG. 6, a frame  23  with slide bearing pairs  111 ,  112  are displaceable along vertical guide pairs  27 ,  28 , whereby the left half shows the frame in a sectional view, and the right half in a side view. The frame  23  is substantially aligned parallel to the rail head  37  to be worked on, and it is provided with at least one stabilizing cross-tie  107 , approximately in the center of its long side. To the right and to the left of the cross-tie  107 , there are arranged, on each side, three cylindrical guides  113  and  114 , respectively. The three cylindrical guides  113  and  114  are arranged in a horizontal plane in parallel to the rail head  37  and at right angles to the drawing plane, whereby respective guide elements  115  and  116 , respectively, of a slide  117  and  118 , respectively, are dispiaceably seated on the respective three cylindrical guides. One support plate  121  and  122 , respectively, is pivotally (by about 15°) seated approximately centrally on each slide  117 ,  118  by way of a bearing bolt  119  and  120 , respectively, each, for rotating about a vertical axis V—V and W—W, respectively. On each side of the bearing bolt  119 , a mount  123 ,  124  each including one grinding module  125 ,  126 , is attached to the support plate  121 . In the same way on each side of the bearing bolt  120 , a mount  127 ,  128  each including one grinding module  129 ,  130 , is rigidly connected to the support plate  122 . The mounts  123 ,  124 ,  127 ,  128  and the grinding modules  125 ,  126 ,  129 ,  130  are designed and arranged in analogy to FIGS  2 ,  4 ,  5 . Hence, the grinding modules  125 ,  126 ,  129 ,  130  can be rotated about axes Y—Y in their respectively associated mounts  123 ,  124 ,  127 ,  128 , whereby the axes Y—Y are in parallel to the rail heads  37 ; thereby the amounts of rotation of the grinding modules on the support plate  121  can differ (by 1-3) from the amounts of rotation of the grinding modules on the support plate  122 , when grinding different facings, since the modules attached to one support plate only are provided with one device  145 ,  146 , each, for rotations about the axis Y—Y. In FIG. 6, the grinding modules  125  and  130  are shown in sectional view, whereas the grinding modules  126  and  129  are shown in elevation. In the representation, all grinding modules are shown in a vertical plane parallel to the rail head  37 . 
     Two measuring wheels  131 ,  132  and  133 ,  132 , respectively, are associated to the respective support plates  121  and  122 , and the grinding modules  125 ,  126  and  129 ,  130 , respectively, which are correspondingly associated to the support plates. Thereby the mean measuring wheel  132  acts for both support plates  121 ,  122 . The measuring wheels  131 ,  132 ,  133  are seated in respectively associated bearing blocks  134 ,  135 ,  136  and are seated at the respective mount via axes U—U transverse to the rail head  37 . Adjustment screws  137 ,  138 ,  139 ,  140  are adapted to improve the position of the measuring wheels  131 ,  132 ,  133  relative to the corresponding mount  125 ,  126 ,  129 ,  130 . Suitable drive means  147 ,  148 ,  149 ,  150  are provided for each mount for adjustment of the measuring wheels  131 ,  132 ,  133  relative to the respective mount  123 ,  124 ,  127 ,  128 . 
     The common measuring wheel  132  is rigidly connected to the support plate  121  via an arm  141  and the mount  124 . The two units secured to the support plates  121  and  122  are articulated to one another by a hinge  142  in the vicinity of the common measuring wheel  132 . Due to an elongated slot  143 , the hinge  142  allows for a slight clearance, which is adapted to permit the passage through the smallest curves to be passed by the respective grinding carriage, and which is parallel to the driving direction and, hence, parallel to the rall head  37 . In analogy to FIG. 2 and 5, rollers  144  are associated to the measuring wheels  131 ,  132   133 . 
     Two drive means  151 ,  152  and  153 ,  154 , respectively, are associated to eah support plate unit  121 ,  122 , the drive means being in the form of pneumatically operating double cylinders are provided for executing the transversal motion of the support plates  121 ,  122 . Thereby, the individual cylinders of each double cylinder are arranged on top of each other. Each drive means  151  to  154  is additionally provided with a blocking means  155 ,  156 ,  157 ,  158  for blocking the drive action, the blocking means  155 ,  156 ,  157 ,  158  being designed as a hydraulically operating cylinder-piston combination. The pneumatically and hydraulically operating cylinders and pistons are in a suitable manner connected partially to the framne  23  and partially to the mounts  123 ,  124 ,  127 ,  128 . 
     Due to the articulated connection of the support plate units  121  and  122  it is ensured that the grinding procedure can be efficiently and precisely carried out even with the smallest radii (15-20 m), hence, that the measuring wheels neither jump off the rail heads to be ground nor reactive forces result. As to the remaining, the disclosure with respect to FIGS. 1 to  5  is valid in its general sense. 
     In FIG. 7 there are substantially shown a fluid gear  159  for a grinding module  160  for a right rail  15  and a fluid gear  161  for a grinding module  162  for a left rail  16 . Each of the fluid gears  159 ,  161  is gas driven and comprises a double cylinder, in the cylinder chambers of which,  1591  and  1611 , respectively, and  1592  and  1612 , respectively, pistons  1593  and  1613 , respectively, and  1594  and  1614 , respectively, are arranged for being displaced in opposition to one another. The pistons  1593  and  1613  are each articulated to the respective module  160 ,  162  and pistons  1594  and  1614 , respectively, are articulated to the associated frame  167 ,  168 . A measuring wheel  163  and  164 , respectively, having each a respective wheel flange  163 ′,  164 ′ is associated to each grinding module  160 ,  162 . 
     Furthermore, a fluid blocking device  165  is represented, which blocks the action of the right and the left fluid transmission gear  159 ,  161  when, for example, the grinding carriage ( 10  in FIG. 1) passes a point. The blocking device  165  prevents the fluid transmission gear  159 ,  161  from pressing the wheel flanges  163 ′,  164 ′ of the measuring wheels  163 ,  164  against the rails within the point. This is of importance as to the operation of the arrangement according to the present invention since only the wheel flanges  163 ′,  164 ′ are provided with sensorial functions in the grinding procedure. The blocking device  165  is hydraulically operated (for example, by glycol) and has two cylinders  1651 ,  1652  which are articulated to the corresponding frame  167  and  168 , respectively. In the cylinders, pistons  1653  and  1654 , respectively, are slidingly arranged which are articulated to the respectively associated grinding modules  160 ,  162 . The cylinders  1651 ,  1652  are connected to a fluid reservoir  171  via two-way valves  169 ,  170 . Furthermore, control means  166  are provided which control the state of pressure in the fluid transmission gear  159 ,  161  in dependence on the operation position, the positioning position and the position of rest of the grinding modules  160 ,  162 . 
     In the following, the cylinders  1591  and  1611  are referred to as positioning cylinders P 1 , and the cylinders  1592  and  1612  are referred to as working cylinders P 2 . Each cylinder P 1  can take the positions A 1 , B 1 , C 1 , and each cylinder P 2  can take the positions A 2 , B 2 , C 2 . Before the grinding procedure can start, the grinding modules  160 ,  162  have to be set to the rail gauge S, whereby there remains at first, for safety reasons, an air gap between the wheel flanges  163 ′,  164 ′ and the rails  15  and  16 , respectively, on a straight line, before a lowering between the rails  15 ,  16  can take place. A rail gauge r is available for the grinding module  160  (or for both grinding modules  160 ,  162 ) and, correspondingly, for the measuring wheel  163  (or for both measuring wheels  163 ,  164 ) for setting the rail gauge. The rail gauge r can be varied by Ar by varying the pivotal connection of the grinding modules  160 ,  162  to the pistons P 1  ( 1591 ,  1611 ) and to the pistons  1651 ,  1652 . Only after the measuring wheels  163 ,  164  have been lowered onto the respective rails  15 ,  16  the fluid transmission gears  159 ,  161  and the fluid blocking devices  165  are activated by the control means  166 . 
     In the positioning operation, starting from a position of rest, which can be, in principal, as desired, the pistons  1593  and  1613  take within the positioning cylinders P 1  the positions C 1 , and the pistons  1594  and  1614  take within the working cylinders P 2  the position C 2 . In the working position the control means  166  affects the cylinders P 1  and P 2  in such a way that the pistons  1593  and  1613  in the positioning cylinders P 1  are retained in the positions C 1 , and in the working cylinders P 2  the positions A 2  are on the way to be taken. With straight rails  15 ,  16 , however, the position C 2  in the working cylinders P 2  is kept to, and the control means  116  biases the working cylinders P 2  to the preset nominal pressure. When the grinding machine according to FIG. 1 is now driving into an arc of circle, and when taking into consideration the module  160  across the rail  15 , then the grinding module is displaced by a distance gx relative to the center m (FIG. 1) of the carriage. The piston  1594  moves from C 2  towards A 2  by the distance gx, since the piston  1593  already takes its end position C 1 . Conversely, with respect to the outer curve rail  16 , there is valid that the piston  1613  from C 1  and, hence, the grinding module  162  by the distance gx will be forced to the outside in direction of A 1 , since the piston  1612  is already in its end position C 2 . When passing through alternating curves, the pistons of P 1  and P 2  move in direction of B 1  and B 2 , due to the equal gas pressure in P 1  and P 2  initiated by the control means. Thus, a dynamic balance of displacement is possible in horizontal direction, when there are curves passed through. In the transportation state of the grinding carriage, that is, when there are no reprofiling operations carried out, the grinding modules are entirely displaced to the interior, relative to the center m of the carriage. 
     The blocking device  165  of FIG. 7 allows the same adjustment path for each piston  1653  and  1654 , respectively, in the associated cylinder  1651  and  1652 , respectively, as the fluid transmission gear  159 ,  161  does for the pistons  1593 ,  1594  and  1613 ,  1614 , respectively, in the double cylinders  1591 ,  1592  and  1611 ,  1612 , respectively. The two-way valves  169 ,  170  are pneumatically controlled by the control means  166 . 
     FIG. 7 shows the hydraulic circuit at a zero pressure state, the two-way valves  169 ,  170  do not block the hydraulic circuit to the fluid reservoir  171 . In this state the grinding modules  160 ,  162  can be freely positioned, pressed into contact and lowered. When the two-way valves  169 ,  170  are blocked towards the reservoir  171 , the fluid can only move between and in the cylinders  1651 ,  1652 , the action of the fluid transmission gear  159 , 161  is blocked, the grinding modules  160 ,  162  and their measuring wheels  163 ,  164  are maintained in the blocked state. Thus, one measuring wheel will always be the guiding one at superelevations in the rails and in points. This will be the measuring wheel in the inner curve at superelevations and the track-bound measuring wheel in the points. 
     The hydraulic duct can be extended mirror-invertedly for further modules, so that further modules can be added and can be combined to form groups. However, one group should not comprise more than three or four module pairs. It is also possible to attach the blocking means to the bearing blocks and/or to have the blocking means manufactured with one cylinder only. 
     All features disclosed in the specification, in the subsequent claims, and in the drawing can be substantial for the invention both, individually and in any combination with one another.

Summary:
An arrangement of grinding modules in a track grinder wherein a radial mismatch in narrow track bend radii can be considered in an exact manner without occurrence of constraining forces, enabling reprofiling to be reproduced in a simple manner. The arrangement provides a grinding tool with five degrees of freedom. Each grinding module is accommodated in an at least approximately vertical manner with a frame and in an at least horizontally manner on the frame with a holder. A housing in the holder is pivotably arranged around a shaft that is at least approximately parallel to the track to be ground. The grinding tool in the housing can be adjusted in a rectangular manner in relation to the track to be ground.