You are an expert at summarizing long articles. Proceed to summarize the following text:

You are an expert at summarizing long articles. Proceed to summarize the following text: 
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a machine for paving concrete paths of the type in which a concrete mix, in a plastic condition, is spread over a certain width and is then levelled to a certain height, the machine consisting of a tractor section and a levelling section connected thereto. 
     2. State of the Prior Art 
     Such a device is known from WO-A-95/28525. 
     In this machine of the prior art the tractor section and the levelling section form one whole, the width of which can be adjusted to the width of the concrete path to be paved. 
     This machine of the prior art has in itself given great satisfaction and is still used to a large extent. Nevertheless there are some problems associated with the use of this machine. A first problem arises because it is always necessary to have space along the concrete path to be paved. This space is not always available due, for example, to the presence of buildings or plants immediately adjacent to the concrete path to be paved. Another difficulty arises when paving larger surfaces such as squares or wider paths. Here the work must always be carried out in such a manner that after a first strip is paved, the second adjacent strip must be temporarily omitted, but the third strip must be started. The second strip cannot then be paved until the first and second strips have sufficiently hardened. This often results in a loss of time due to the hardening time and may make it impossible for the side edge drop-off to be removed. Finally, the machine is difficult to control and drive when paving curves. 
     SUMMARY OF THE INVENTION 
     The object of the invention is to provide a machine of the above-mentioned type in which the above drawbacks are avoided. 
     This object is achieved according to the invention in that the adjustment of the working width of the tractor is independent of the adjustment of the working width of the levelling section. 
     Because the working width of both sections is made independent of each other, it is possible to make the working width of the tractor smaller than the working width of the levelling section, or vice versa, thus enabling the above-mentioned problems to be avoided or considerably reduced. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other features and advantages will become clear from the following description in which reference is made to the attached drawings, in which: 
         FIG. 1  shows a side view of a machine according to the invention, 
         FIG. 2  shows an elevation of the machine in  FIG. 1 , 
         FIG. 3  shows a front view of the machine in  FIG. 1 , 
         FIG. 4  shows a side view of the levelling system of the machine in  FIG. 1 , 
         FIG. 5  shows a side view similar to that of  FIG. 1  focusing on certain components of this machine, and 
         FIG. 6  shows an elevation view of the machine similar to  FIG. 2 , focusing on certain components of the machine. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     As shown in  FIG. 1 , the machine according to the invention consists of two sections, tractor section  1  and levelling section  2 . Tractor section  1  is a section that is displaceable by means of two caterpillar mechanisms  3 ,  4 , whilst levelling section  2  is a section coupled to the track section that does not have its own driving means but is propelled together with the tractor section. In the following description reference is made to horizontal and vertical directions, horizontal coinciding with the plane of the tread of caterpillar mechanisms  3 ,  4 , and the vertical plane referring to the plane that is perpendicular to it. 
     Each caterpillar mechanism  3  is mounted on two frame plates which lie on both sides of caterpillar mechanism  3  and are incorporated inside caterpillar track  6 .  FIG. 1  only shows frame plate  5 , the frame plates being mounted on the axles of driving wheel  7  and tensioning wheel  8  of caterpillar track  6 , whilst gauge wheels  9  are mounted against the underside of frame plates  5 . 
     Two vertical columns  10 ,  11  and  12 ,  13  respectively are mounted above each caterpillar mechanism  3 ,  4 . Vertical columns  10 ,  11 ,  12 ,  13  are identical and only the structure of vertical column  10  will be described in more detail below. 
     A bracket (only bracket  15  is shown in  FIG. 1 ) is fitted to the top of each of the frame plates belonging to caterpillar track  3  level with column  10 , each of which brackets supports an axle journal projecting from the caterpillar track (only axle journal  16  is visible in  FIG. 1 ). A largely U-shaped profile  17  is mounted on these axle journals  16  in a downward direction, two flange plates  18 ,  19  of which profile  17  extend along both sides of caterpillar track  3 . In this case flange plate  18 , which is located on the outside of the machine, is much shorter than the flange plate  19 . Flange plate  18  therefore extends to a point just above the level of the axles of driving wheel  7  and tensioning wheel  8  of caterpillar mechanism  3 , whilst flange plate  19  extends to a point just above the level of the supporting face of caterpillar track  6 . 
     A tube end  25 , which extends vertically upwards, is mounted on web  20  of profile  17 . Over tube end  25  is pushed a tube end  26  whose inner circumference almost coincides with the outer circumference of tube end  25  so that the two tube ends are able to slide over each other telescopically. 
     Inside tube ends  25 ,  26  pushed over each other is mounted a hydraulic cylinder piston system consisting of a cylinder  27  whose closed end is articulated to a plate  28  which seals the top of tube end  26 , and a piston which is connected by a piston rod  29  to web  20 . On plate  28  a vertical rod  30  is mounted on the top, a detection system  31  of which is fitted by means of which the height of system  31  can be adjusted to external reference systems. Such systems are generally known in this type of machine and will not be described in further detail here. By means of the piston cylinder system  27 ,  29  it is possible to adjust the height of tube end  26  relative to tube end  25  and hence relative to the ground level, wherein this height adjustment can be controlled by means of detection system  31 . 
     As already stated, the four columns  10 ,  11 ,  12  and  13  are identical and each of the four columns is therefore also provided with a piston cylinder system and means for detecting the height. 
     As shown in  FIG. 2 , columns  10 ,  11 ,  12  and  13  have a square cross-section. In principle they may assume a different cross-sectional shape, but because a square cross-section is used, where the diagonals of the square are perpendicular and parallel to the direction of movement of the machine, greater stability is obtained during the movement of the machine. 
     Plates  32  and  33  respectively are secured to the sides facing each other on the inner sides of columns  10 ,  11  and  12 ,  13  respectively. Plates  32  and  33  are in this case welded directly to the diagonals of columns  10 ,  11 ,  12  and  13 . Plates  34  and  35  respectively are also secured to the sides of columns  10 ,  11  and  12 ,  13  respectively, these sides facing away from each other, by welding to the diagonals of columns  10 ,  11 ,  12  and  13 . Plates  32 ,  33 ,  34  and  35  are rectangular in shape, two edges of each plate lying in a horizontal plane and the other two edges being vertically directed. In this case the upper edges of plates  32 ,  34  and  33 ,  35  respectively are connected by means of plates  36 ,  37  and  38 ,  39  respectively, both level with columns  10 ,  11  and  12 ,  13  respectively. The vertical dimension of plates  32  and  33  is greater than that of plates  34 ,  35 , the lower edge of plates  32 ,  33  lying approximately at the same height of the as the axles of driving wheels  7  and running wheels  8 , whilst the lower edge of plates  34  and  35  lies at a certain height above the level of flange plate  20 . The lower edge of plates  34 ,  35  is connected by means of horizontal plates  40 ,  41  to plates  32 ,  33 , which are therefore parallel to plates  36 ,  37 ,  38  and  39 .  FIG. 3  shows only plates  40  and  41 , but similar plates are located level with columns  11  and  13 . 
     Plates  36 ,  37 ,  38 ,  39 ,  40  and  41  are all provided with a rectangular recess through which extend columns  10 ,  11 ,  12  and  13 , and are in this case connected by welding to tube ends  26  belonging to these columns so that all plates  32 ,  33 ,  34  and  35  follow the movements of tube ends  26 . 
     Between plate  32  and flange plate  19  is fitted a plate  42  which is fixedly connected to flange plate  19  and which extends from the top of caterpillar mechanism  3  almost to the level of the bottom over which caterpillar track  6  is displaced. This plate  42  serves as a lateral limit for the concrete which is poured in front of the machine and is to be processed by the machine into concrete paths so that the machine does not end up directly below caterpillar track  6 . Plate  42  extends over the entire length of the tractor section and is also connected to the innermost flanged section of the U-profile which column  11  supports. Similarly such a plate  43  is mounted on the side of columns  12 ,  13  so that on the side of caterpillar mechanism  4  the concrete is also kept to the side inside the machine. 
     A U-shaped profile  44 ,  45  is mounted on each of the inner sides of plates  32 ,  33  facing towards each other close to the lower edge thereof. U-shaped profiles  44 ,  45  are secured to plates  32  with a head end  46 ,  47 , and the other ends  48 ,  49  of these profiles, located at a certain distance from each other, the function of which will be explained later. The U-shaped profiles consist of a web  44 ,  45 , which is horizontally directed, and two flange plates, only the leading flange plates  46 ,  47  being visible in  FIG. 3 . 
     Inside U-shaped profiles  44 ,  45  is placed a tray  60  in the shape of a parallelepiped which rests with its bottom plate on flange plates  52 ,  53  of U-shaped profiles  44 ,  45 . Two parallel side walls (only side wall  62  is shown in  FIG. 3 ) bear against the flange plates of U-shaped profiles  44 ,  45  so that tray  60  is laterally displaceable relative to the U-shaped profiles which at the same form a guide for tray  60 . 
     Flange plates  52 ,  53  of the U-shaped profiles have horizontal upper edges which lie level with plates  40 ,  41  and corresponding plates of columns  11  and  13 . Parallel side walls  62  of tray  60 , on the other hand, have horizontal upper edges which lie at the level of plates  36 ,  37 ,  38  and  39 . This means that the tray projects above the U-shaped profiles. 
     The two other side walls  63  and  64  of tray  60  therefore extend in the direction of movement of the machine. In the tray thus formed is incorporated the hydraulic drive for caterpillar mechanisms  3  and  4 , as are the operating and control means  59  for operating the machine. This will not be described in greater detail because it is clear to the person skilled in the art, without further explanation, how this can be achieved. 
     Above flange plates  44 ,  45  and between plates  32 ,  33  are fitted eight rectangular tubes extend in the horizontal direction and are perpendicular to the plates  32 ,  33 . One set of tubes has an inside diameter in which the other tubes have a sliding fit. One end of the one set of tubes is connected to plate  32 , whilst one end of the other tubes is connected to plate  33 . A system of four tubes that are telescopically displaceable into each other is formed which therefore interconnects plates  32  and  33 , the plates nevertheless being free to move in parallel with each other. 
     A piston cylinder system is installed inside each pair of the telescopic tubes connected between plates  32 ,  33 , the piston sections of two systems being connected to plate  32 , whilst the piston sections of two systems being connected to plate  33 . The cylinder sections of the first two systems, on the other hand, are connected to plate  34  and the other two cylinder sections are connected to plate  35 . The piston cylinder systems are double acting, i.e. a hydraulic pressure can be generated on both sides of the piston in order to displace the piston to one or the other side relative to the associated cylinder. 
     At the height of columns  11  and  13  is fitted a second system of tubes  81 ,  82  which interact telescopically with tubes  83  and  84 . Piston cylinder systems are fitted inside tube systems  81 ,  83  and  82 ,  84 , these systems consisting of cylinders  85  and  86  respectively, and pistons with piston rods  87  and  88  respectively. Tubes  81 ,  82  are also provided with closing plates  89  and  90  respectively. The arrangement of the tube systems is such that in one pair of tubes positioned one above the other the piston cylinder system of the uppermost tube system acts on plates  32 ,  34 , and in the other pair of tubes positioned one above the other the piston cylinder system of the bottommost tube acts on plates  33 ,  35  and vice versa. 
     Due to a suitable application of a hydraulic pressure in the piston cylinder systems in the tubes plates  32 ,  34  and  33 ,  35  can be moved away from each other and hence also can caterpillar mechanisms  3  and  4 , so that tractor section  1  becomes wider or plates  32 ,  34  and  33 ,  35  can be displaced towards each other so that tractor section  1  becomes narrower. The tractor section can therefore be set in a continuous way to any desired width. During this movement tray  60  may be displaced inside U-shaped profiles  44  and  45 , the bottom face and the leading face being formed by flange plates  44 ,  45  and side wall  62  continuing to form an almost closed surface. 
     Recesses through which tubes  72 ,  73  and  83 ,  84  can pass freely movably are installed in side walls  63  and  64  of tray  60 , whilst these side walls can serve as a closing plate for tubes  70 ,  71  and  81 ,  82 . Tubes  70 ,  71  and  81 ,  82  therefore form one whole. 
     To provide adequate rigidity, rods  90 ,  94  are fitted which connect the upper wall of tube  70  to the upper wall of tube  81 . A second pair of rods  96 ,  97  connects the upper wall of tube  81  to the upper edge of vertical plate  98 , which forms a rear wall of tray  60 . Because of this construction spaces are freely maintained between plate  98 , whose lower edge connects to bottom plate  61  and side walls  62  and  63 , as a result of which the hydraulic pipes from the tray to the various hydraulic units can be guided outside the tray. 
     Close to the upper end and on the outside of tray  60 , two piston cylinder systems  100 ,  101  can be mounted on rear wall  98  with a vertical action. The piston is in this case located near the upper edge of plate  98 , whilst the downwardly projecting end of the piston rod is connected to a plate  103  which is parallel with plate  98  and can be displaced along the plate by means of the piston cylinder systems  100 ,  101 . 
     Plate  103  has a rectangular shape and is located opposite the bottommost part of plate  98 . Plate  103  can be displaced vertically up and down by means of piston cylinder systems  100  and  101 , as a result of which the height of plate  103  can be adjusted and hence also the quantity of concrete which is admitted to the levelling section. U-shaped brackets  107  are fitted to the outwardly and rearwardly directed wall of the tube ends of columns  11  and  13 , which tube end corresponds to tube end  16  of column  10 , in which brackets are placed vertically directed rotary shafts  108 ,  109 , which are connected to one end of a cylinder of a piston cylinder systems  110 ,  111  having ends of piston rods  112 ,  113  connected by means of brackets  114 ,  115  with vertical rotary shafts  116 ,  117  to a sub-frame  118 . 
     Sub-frame  118  is also connected by means a second pair of piston cylinder systems  120 ,  121  to the rear ends of plates  32 ,  37  and  33 ,  39  respectively. For this purpose a support plate  122  is secured to the rear ends of plates  32 ,  37 , and a support plate  123  is supported to the rear ends of plates  33 ,  39 , to which support plates are fitted a bracket  124  and  125  respectively with horizontal rotary shafts  126 ,  127  as the fastening point of one of the ends of piston cylinder systems  120 ,  121 . Support plates  122  and  123  may possibly also be secured to plate  98 . 
     Sub-frame  118  consists of a tray in the shape of a parallelepiped, with a horizontal bottom  129 , a vertical rear wall  130 , two vertical side walls  131 ,  132 , and a leading wall  133 . The connection between leading wall  133  and side walls  131 ,  132  is formed by inclined wall sections to which brackets  116  and  117  are secured. The second ends of piston cylinder systems  120 ,  121  are connected to horizontal rotary shafts  134 ,  135  incorporated in brackets  136 ,  137 , which are connected to tray  118 . In this manner sub-frame  118  is connected in a rigid manner to the caterpillar tracks of tractor section  1 . 
     A rectangular tube  138  is formed against the inside of side wall  131 , which tube extends in the vertical direction above the height of side wall  131 . Rectangular tube  138  lies with a side that is long in cross-section against the inside of side wall  131 . Square tubes  139 ,  140  are formed inside tube  138  against each short side, which tubes also extend in the vertical direction and up to a certain height project above the level of side wall  131 . The upper ends of tubes  139 ,  140  are interconnected by means of a bridge  141 , which supports a vertical rod  142  on which a system  143  is positioned for, detecting the height. 
     Square tubes  144 ,  145  are incorporated in tubes  139  and  140  so that they have a sliding fit, which tubes project downwards outside tubes  139 ,  140 , with their bottommost ends connected to a sub-frame  146  which is fitted under sub-frame  118  and which will be described in greater detail later. Between tubes  139 ,  140  there is a vertically directed piston cylinder system whose cylinder  147  is connected to tube  138  and where the downwardly projecting end of the piston rod is connected to sub-frame  146 . In this manner the height of sub-frame  146 , guided through tubes  139 ,  140  and  144 ,  145 , can be displaced vertically up and down and can be adjusted to the desired height. 
     In a comparable manner a rectangular tube  148  is formed against the inside of side wall  132 , in which tube two tubes  149  and  150  are fitted whose upper ends can be interconnected by means of a bridge which supports a vertical rod on which is positioned a system for detecting the height. Two tubes  154  and  155  are incorporated displaceably inside tubes  149 ,  150 , and are connected with their lower ends to a sub-frame which is comparable to sub-frame  146 . The movement of this sub-frame is controlled by means of a piston cylinder system  157 . 
     Sub-frame  146  is shown in greater detail in  FIG. 4 . In practice the other sub-frame connected to side wall  132  is designed identically but is mirror symmetrical to it. 
     Sub-frame  146  consists of a vertical, mainly rectangular side wall  160  which lies underneath side wall  131 . A bent plate  161  is secured to the vertical leading edge of the side wall and the lower wall, the angle between these two edges being rounded, which plate extends from the side wall up to a certain distance inside it. Plate  161  forms part of the levelling plate, as will be described below. Levelling plates  161  in the two sub-frames therefore lie opposite each other and together support a central levelling plate which rests on plates  161 . 
     Two rectangular tubes  163  and  164  are mounted on the central levelling plate, for example by means of welding. These tubes are horizontally directed and are perpendicular to side walls  160  of sub-frames  146 . A vertical plate  165  is secured to one of the vertical walls of tube  163 , which plate extends close to the upper edge of side wall  160 . A rectangular tube  166  is mounted near the upper edge on the other side of plate  165  relative to tube  163 , which rectangular tube is orientated in exactly the same direction as tubes  163  and  164 . In the same way a tube  167  is secured to a vertical side wall of tube  164 , a tube  168  being mounted near the upper edge of plate  160  against plate  167 , which tube lies on the other side of plate  167  relative to tube  164  and has the same orientation and construction. The four tubes  163 ,  164 ,  166  and  168  are similarly rigidly connected to the central levelling plate. 
     Rectangular tubes  170 ,  171 ,  172  and  173  are each incorporated inside the tubes so that they have a sliding fit, so that tubes  170 ,  171 ,  172  and  173  can be displaced horizontally inside tubes  163 ,  164 ,  166  and  168  and therefore form telescopic systems. The ends of tubes  171  and  173  projecting outside tubes  163  and  168  are connected to side wall  160  of sub-frame  146 , whilst the ends of tubes  170  and  172  projecting outside tubes  164  and  166  are connected to the side wall of the other sub-frame. 
     Two cylinders  174 ,  175  of two cylinder piston systems are also connected to central levelling plate  162 , but this connection is not shown in greater detail. The end of piston rod  176  belonging to cylinder  174  is connected to side wall  160 , whilst the end of piston rod  177  belonging to cylinder  175  is connected to the side wall of the other sub-frame. It is possible, by means of the cylinder piston systems, to displace the sub-frames  146  laterally relative to the central section supporting levelling plate  162 , and the width of levelling can therefore be steplessly adjusted by plates  161  and the central levelling plate. In this case plates  161  and the central levelling plate are constructed as described in more detail in the Dutch patent application in the name of the applicant and filed on Dec. 10, 2007. This applies particularly to the trailing end of levelling plates  161  and the central levelling plate, which are inclined so that the levelling height of plates  161  and the central levelling plate is the same. 
     A hinge  180 , by means of which a finishing plate  181  is articulated, is mounted on the rear end of the central levelling plate. A number of reinforcing ribs  182 , which keep plate  181  very flat, are fitted to the upper side of finishing plate  181 . The finishing plate serves to correct minor irregularities which cannot be compensated for by the levelling plates, and extends over the maximum width of the machine. In this case finishing plate  181  is positioned slightly inclined with the leading edge slightly higher than the trailing edge. 
     In order to retain plate  181  further in the desired position, a chain or cord  183  is fitted which is on the one hand secured to the vertical rear edge of side wall  160 , close to the upper end thereof, and on the other hand to a point  184  on the finishing plate in the vicinity of the rear end of plate  181 . The inclination of plate  181  can be set by adjusting the length of the cord or chain  183 . On the other hand plate  181  can be rotated away not only for possible maintenance or cleaning, but also in the event that n unexpected obstacle should be found in the concrete mass. 
     In order to apply sufficient pressure to the finishing plate  181  a piston cylinder system  185  is fitted between on the one hand side wall  160  and on the other hand plate  181 . This system is positioned so that it exerts a certain pressure on plate  181 , but it also enables the plate to be displaced in the presence of obstacles. This is possible by making use of so-called gas springs which allow compression of the gas and therefore turning away of plate  181 . Instead of gas springs use can also be made of pressure-compensated hydraulic cylinders. 
     A number of devices are fitted in the space between plates  98 ,  103  and plates  133  and the vertical section of plates  161 ,  162  for homogenizing the concrete before it is levelled by plates  161 ,  162 . 
     These devices consist on the one hand of two mixing screws  189  and  190 . The mixing screws consist of a shaft  191  and  192  respectively, around which a rod  193  and  194  respectively is spirally wound. Shafts  191  and  192  are on the one hand rotatably mounted against side walls  131  and  132  respectively, and on the other hand are secured in brackets against sub-frames  146  and  156 . Driving means for the rotary driving of shafts  191  and  192  are present but are not shown. 
     In addition vibrating bars  199  are fitted. The vibrating bars are bars consisting of a vertically suspended section, which extends to the rear viewed in the direction of movement of the machine. Each vibrating bar  199  is connected, with the upper end of the vertical section, to a resilient element that is further suspended by means of a bar, not shown, on either levelling walls  161  or on the central levelling plate. For this purpose collecting tubes are fitted behind the upper edge of those plates, in which tubes these bars can be suspended. At the minimum width of the machine all the vibrating bars will be suspended on levelling plates  161 . If the machine is made wider, additional vibrating bars can be placed on the central levelling plate. The vibration of these vibrating bars  199  is obtained by the movement of the machine, but it is also possible to use hydraulically or electrically driven vibrating bars. 
     The operation of the machine is as follows: 
     The width of the tractor section and of the levelling section is adjusted according to the width of the concrete path to be paved. The width of the tractor section is adjusted in a continuous way by means of piston systems  77 ,  79 ;  78 ;  86 ,  88  and  85 . The width chosen depends on the circumstances. In practice a width will often be chosen that is smaller than the concrete path to be paved since this guarantees a pavement free from obstacles. The height of tray  60  together with U-shaped profiles  44  and  45  is also adjusted. The adjustment is a function of the final desired thickness of the concrete path, as will be described below. 
     The width of levelling section  2  is also adjusted in a continuous way and independently from the width of the tractor section by reinforcing piston cylinder systems  174 ,  176  and  175 ,  177 . This is adjusted as accurately as possible to the desired width, the particular advantage of the construction according to the invention consisting in the complete symmetry of the adjustment of the width, thereby improving the stability of the machine and quality of the end product. The thickness of the concrete path is also adjusted by means of piston cylinder system  147 . 
     After these adjustments have been carried out the machine can be started. For the paving of a concrete path a quantity of concrete is poured in front of the machine, and the machine is then moves forwards and backwards over it. On the one hand plates  52 ,  53  and  62  will together push the uppermost part of the deposited concrete mass forwards, whilst on the other hand a quantity will be admitted underneath U-shaped profiles  44 ,  45  and tray  60 . This pushing exerts a distributing effect on the concrete mass, so that it will also be spread width-wise. The adjustment of the height of U-shaped profiles  44 ,  45  and tray  60  is preferably chosen so that the quantity of concrete admitted is slightly higher than the quantity of concrete required to pave the concrete path. This also has a distributing effect width-wise on the concrete mass and surplus that is admitted is simply pushed forward through the mass of concrete present in front of levelling plates  161  the central levelling plate. Any deviations in the height of the machine relative to the wearing surface on which the concrete mass has to be spread and levelled can be compensated for by the height determinations and corrective height adjustments of U-shaped profiles  44 ,  45  and tray  60 . 
     The concrete mass then attains the height of plate  103 , which is adjusted to a height which corresponds very accurately to the quantities of concrete required to pave the concrete path. This can be achieved by continuously adjusting the height of plate  103  on the basis of a determination of the height of the concrete mass in the space between plate  103  and plate  133 . In this space is placed, at a certain height, a height sensor which can be actuated by the concrete mass in this space. When the concrete mass in this space becomes too great, the height of the concrete mass rises and the sensor is actuated, as a result of which plate  103  is allowed to drop further and the quantity of concrete supplied to the space in which the sensor is placed is reduced. As soon as the height of the concrete mass in the space has dropped below a certain level, the sensor is no longer actuated and plate  103  will be displaced upwards causing the concrete mass admitted to rise again. The quantity of concrete in the space between plates  103  and  133  may therefore be kept almost constant, ensuring a highly uniform layer of concrete during the subsequent levelling of the concrete by means of levelling plates  161  the central levelling plate. In practice plate  103  is adjusted to a certain height that corresponds to the expected concrete consumption, and the control system will regulate variations around the adjustment by means of the sensor. 
     The concrete then passes underneath the levelling section, where the concrete is levelled flat because the end edges of levelling plates  161  the central levelling plate lie on the same horizontal line. Height variations of the machine can be compensated for by device  185 , which adapts the height of the levelling plates and compensates for any local irregularities in height. By means of this machine not only is a concrete layer with a constant height applied in one operation, but the concrete mass is homogenised, spread and distributed in a highly efficient manner. 
     Because the entire machine is only provided with a single caterpillar mechanism, comprising two caterpillar track mechanisms, the machine can easily be additionally adjusted when the concrete path describes a curve. In the embodiment described and illustrated, an additional adjustment of the position of the levelling section can be obtained by correct actuation of piston cylinder systems  110 ,  112 ,  120 ,  111 ,  113  and  121 . This should possibly be combined with the readjustment of the position of edge plates  202 ,  203  by means of piston cylinder systems  174 ,  176 ;  175 ,  177 . This is an important advantage over the machines of prior art, all of which have a double caterpillar mechanism where such an additional adjustment in curves encounters considerable problems. 
       FIGS. 5 and 6  illustrate the machine in a simplified manner, focusing on the piston cylinder systems  110 ,  112 ,  120 ,  111 ,  113  and  121 . As is clear from the drawing figures and the mechanical arrangement that has been described so far, these piston cylinder systems allow the levelling section to not only be moved rearwardly relative to the tractor section (which is illustrated by comparing  FIG. 6  with  FIG. 2 , for example), but also allows adjustment when a concrete path is describing a curve. That is, the levelling section can be adjusted relative to the tractor section by the piston cylinder systems  110 ,  112 ,  120 ,  111 ,  113  and  121  by, for example, extending piston  113  and retracting piston  112 . This allows the levelling section to, for example, describe an angle with respect to the tractor section. It should also be noted that the levelling section, being suspended by the two pairs of piston cylinder systems  110 ,  112  and  120 , and  111 ,  113  and  121 , with a pair of the piston cylinder systems being fitted on each side, each piston cylinder system forms an angle with a direction of movement of the tractor. As can also be seen from  FIG. 5 , piston cylinder systems  147  at both ends of the paving pan enable further vertical adjustment of the paving pan independently of the tractor section. As a result, the orientation of the levelling section including the paving pan can be independently adjusted with the present invention with respect to the orientation of the tractor, not only in the vertical plane, but also in the horizontal plane. 
     A different design may be chosen for the additional adjustment of the levelling section in curves, the sub-frame being placed in a slewing ring which is connected, by means of a telescopic system that can be actuated by means of a piston cylinder system, to tray  60 . Due to the extension and retraction of the telescopic system and the rotation of the slewing ring the levelling section can be kept in the correct orientation and position at all times. This system may provide particular advantages when GPS systems are used. 
     It is clear that the invention is not limited to the embodiment described and illustrated but that numerous modifications can be made within the scope of the claims.

Summary:
A machine for paving concrete paths, of the type in which a concrete mix, in a plastic condition, is spread over a certain width, and is then levelled to a certain height. The machine includes a tractor and a levelling section connected to it, wherein the working width of the tractor and levelling section are adjustable and wherein the adjustment of the working width of the tractor is independent of the adjustment of the working width of the levelling section. The tractor is provided with an element whose width is adjustable and which distributes the concrete mix over a certain width and to a certain height.