Abstract:
A system for effecting the rotational movement of a solar tracker about an axis of rotation includes a bow mounted on the solar tracker and comprising a rack and a worm engaging with the rack to effect the rotational movement, the rack having a plastic tooth set and the bow having a damper configured to dampen the connection with the solar tracker.

Description:
This application claims priority to International Application No. PCT/FR2013/050997 filed May 3, 2013 and French Application No. 12 55 954 filed Jun. 22, 2012; the entire contents of each are incorporated herein by reference. 
     BACKGROUND 
     The invention relates to a system for moving a solar tracker in rotation about a predetermined axis of rotation, in particular in a solar tracking device comprising solar radiation processing means mounted on a solar tracker which is itself mounted to move in rotation on a frame. 
     SUMMARY 
     The solar tracking devices, like that illustrated in  FIG. 8 , comprise, mounted to move in rotation on a frame  62  about an axis  63 , a solar tracker  60  on which is mounted a series of solar radiation processing means  61 . In order to produce a rotational movement about the axis  63  of the solar tracker  60 , the solar tracking device further comprises a rotational movement system  10  comprising an arch  20  fixed to the solar tracker  60  and driven by a driving means  52  controlled by a transmission shaft  51 . Conventionally, the arch  20  is produced, just like the driving means  52 , in metallic materials. The contact between the metal of the driving means  52  and the metal of the arch  20  leads to screeching effects due to the vibrations generated at the contact level. Furthermore, these vibrations are transmitted directly to the solar tracker  60  by the arch  20  via fixing tabs  30  making it possible to fix the arch  20  to the solar tracker  60 . In order to reduce these screeching effects, and therefore the vibrations, greasing is implemented to reduce the friction at the level of the contact between the arch  20  and the driving means  52 . However, implementing such greasing involves heavy maintenance phases in a field comprising hundreds, even thousands, of solar tracking devices thus equipped with an arch  20  and a driving means  52  for said arch  20 . In effect, the grease used for the greasing disappears rapidly under the effect of the climatic conditions, in particular being washed away by bad weather. 
     One aim of the invention is to provide a system for moving a solar tracker in rotation about an axis of rotation which does not necessitate maintenance phases while making it possible to reduce the generation of vibrations which lead to screeching effects. 
     To this end, there is provided, according to the invention, a system for moving a solar tracker in rotation about an axis of rotation comprising: 
     an arch mounted on the solar tracker and comprising a rack; and, 
     a worm screw cooperating with the rack in order to produce the rotational movement, the rack comprising teeth made of plastic material and the arch comprising damping means linking with the solar tracker. 
     The fact that the rack comprises teeth made of plastic material makes it possible, on the one hand, to avoid any metal-metal contact as in the prior art, instead involving a metal-plastic contact which exhibits a very low coefficient of friction, which leads to a reduction in the generation of vibrations causing screeching effects. On the other hand, the use of plastic teeth for the rack makes it possible to not provide greasing, which makes it possible to eliminate the maintenance phases at this level. Finally, the use of linking damping means between the arch and the solar tracker makes it possible to eliminate the transmission of the residual vibrations between the arch and said tracker. 
     Advantageously, but optionally, the system for moving a solar tracker in rotation according to the invention comprises at least one of the following technical features: 
     the arch comprises a curved profile member on which is positioned a series of parts made of plastic material forming the rack; 
     the curved profile member comprises a gutter arranged in such a way as to receive the series of parts made of plastic material; 
     the rack is mounted to slide in the gutter, the arch further comprising abutment means for keeping the rack in position in the gutter; 
     the parts made of plastic material comprise tabs having a beveled form at a free end arranged in such a way as to cooperate by bearing with a wall of the gutter; 
     the rack is mounted in position by clipping into the gutter; 
     the rack is formed on a flank of the arch contained in a plane at right angles to the axis of rotation; 
     the linking damping means comprise damping blocks interposed between the arch and the solar tracker; 
     the damping blocks are produced in an elastomer of EPDM (Ethylene-Propylene-Diene Monomer) type; 
     the plastic material of the teeth includes fibres to reinforce it. 
     There is also provided, according to the invention, a solar tracking device comprising solar radiation processing means mounted on a solar tracker which is itself mounted to move in rotation on a frame and further comprising a rotational movement system with at least one of the preceding features. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other features and advantages of the invention will become apparent from the following description of an embodiment of the invention. In the attached drawings: 
         FIG. 1  is a front view of an arch of a system for moving a solar tracker in rotation according to the invention; 
         FIG. 2  is a partial view of the detail II of  FIG. 1 ; 
         FIG. 3  is a partial three-dimensional view of the detail II of  FIG. 2 ; 
         FIG. 4  is a partial view of the detail IV of  FIG. 1 ; 
         FIG. 5  is a cross-sectional view on V-V of the detail of  FIG. 4 ; 
         FIG. 6  is a three-dimensional partial view illustrating the mounting of the teeth on the arch in the system for moving a solar tracker in rotation of  FIG. 1 ; 
         FIG. 7  is a cross-sectional view of the system for moving a solar tracker in rotation according to the invention; and 
         FIG. 8  is a three-dimensional view of a solar tracking device comprising a system for moving a solar tracker in rotation. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIG. 1 , the system for moving a solar tracker in rotation  10  according to the invention comprises an arch  20  forming a circular arc whose centre is on the axis of rotation  63 . The arch  20  is fixed at each of its ends to a link part  30  making it possible to link the arch  20  to the framework of the solar tracker  60 . The link between each of the ends of the arch  20  with the link parts  30  is illustrated in detail in  FIGS. 2 and 3 . Each of the ends of the arch  20  has orifices passing through the arch  20 . Here, there are two of these orifices. Also, they are at right angles to a plane of the arch and come, when the arch  20  is mounted on the link parts  30 , to face equivalent orifices situated at an end of each of the link parts  30 . When the arch  20  is mounted on the link parts  30 , a screw  41  is introduced into each of the orifices passing through the arch  20 , then a first damping means  45  is positioned on each of the screws  41 , then the link part  30  is put in place on the two screws  41  so as to sandwich the first damping means  45  between the link part  30  and the arch  20 . Then, each of the screws  41  has a second damping means  44  threaded onto it, followed by a washer  43 , the duly produced stack assembly then being tightened using a nut  42  screwed onto a threading situated at the end of each of the screws  41 . The first damping means  45  and the second damping means  44  are of “Silentbloc” type. In particular, the first damping means  45  and the second damping means  44  take the form of washers or blocks made of elastomer of EPDM (Ethylene-Propylene-Diene Monomer) type. The advantage of using an elastomer of EPDM type is that it makes it possible to obtain first damping means  45  and second damping means  44  which withstand the outside conditions, that is to say, in particular, water and ultraviolet rays due to the solar radiation. Once mounted, the link part  30  is, from the vibrational point of view, insulated from the arch  20  by the first  45  and second  44  damping means. Other elastomers can be used for this purpose. 
     In a variant embodiment, the first  45  and second  44  damping means form a single part so that, when mounting, the part is introduced through the orifice of the link parts  30 . Other damping means can be used. 
     Referring to  FIGS. 4 to 6 , there now follows a more detailed description of the arch  20  of the rotational movement system  10  according to the invention. The arch  20  comprises a profile member  21 . The profile member  21  is made of a metallic material, preferably of aluminium. In order to keep it as light as possible, the profile member  21  is hollow and has a rectangular section with the small sides respectively forming a radially outer periphery and a radially inner periphery of the arch  20 . The small sides are linked to one another by large sides forming flanks of the arch  20 . The profile member  21  is curved. One  210  of the flanks of the arch  20  comprises a gutter  29  delimited at the radially outer periphery and the radially inner periphery of the arch  20  by walls  23  extending facing one another and protruding from the flank  210 . Furthermore, the walls  23  are inclined towards one another in order to form means for retaining a rack  22  in the gutter  29 . The teeth  22  are then added to the profile member  21  of the arch  20  by the insertion thereof into the gutter  29 . The rack  22  is produced in a plastic material possibly fibre-reinforced in order to form a composite plastic material. The rack  22  can be of a single piece. However, in a preferred embodiment, the rack  22  is made up of a series of plastic parts which are placed end to end in the gutter  29 . 
     The rack  22  comprises, on one face, teeth  26  substantially at right angles to a longitudinal axis of the rack  22 . Furthermore, the rack  22  comprises, on a face intended to be facing the flank  210  of the profile member  21 , a central rib  25  and lateral tabs  24  situated on either side of the central rib  25 . The tabs  24  extend laterally protruding from the rack  22 . The tabs  24  are continuous and extend along the rack  22 . In a variant, the tabs  24  are discontinuous. Also, the tabs  24  have a beveled form arranged in such a way that, when one of the tabs  24  bears on the corresponding wall  23  of the gutter  29 , the beveled form of the tab  24  adopts the form of the inclined wall  23 . Thus, when mounting the rack  22  in the gutter  29  of the profile member  21  of the arch  20 , the tabs cooperate with the lateral walls  23  of the gutter  29  so as to keep the rack  22  in the gutter  29 . In a first embodiment, the rack  22  is mounted to slide in the gutter  29 . Such a mounting makes it possible to correctly position the rack  22  or the series of plastic parts forming the rack  22  on the arch  20  of the system for moving a solar tracker in rotation  10  according to the invention. Once the rack is positioned, abutment-forming means  27  are positioned in the gutter  29  so as to block the rack  22  in position on the profile member  21  of the arch  20 . The abutments  27  are immobilized in position using fixing means  28 , here rivets. In a variant, the abutment-forming means  27  are arranged in such a way as to be retained by the lateral walls  23  of the gutter  29 . In a variant embodiment, the rack  22  or the series of plastic parts forming the rack  22  have lateral tabs  24  arranged in such a way as to allow the rack  22  to be clipped into the gutter  29 . Other means for blocking the rack  22  in the gutter  29  are possible, such as riveting or screwing. When the abutment-forming means  27  are put in place, the rack  22  is compressed on itself between said abutment-forming means in such a way that one of the tabs  24  situated at the radially outer periphery of the arch  20  comes to bear on the corresponding wall  23  of the gutter  29 , the beveled form of the tab  24  ensuring, by cooperation with the corresponding wall  23 , that the rack  22  is kept immobile in the gutter  29 . 
     Referring to  FIG. 7 , the rotational movement system  10  according to the invention comprises means for driving the rack  22  of the arch  20 . These driving means comprise a cage  52  in which is formed a housing to receive a worm screw  50 . The worm screw  50  is received to move rotationally about its axis in said housing of the cage  52  and is driven by a shaft  51  in this rotational movement. Once mounted to rotate in the cage  52 , the worm screw  50 , having an external threading, protrudes into an adjacent passage  55 . The passage  55  is U-shaped and open on a bottom part of the cage  52 . The passage  55  is intended to receive the arch  20 , in such a way that the rack  22  cooperates with the external threading of the worm screw  50 . In order to ensure this cooperation, the cage  52  has a cover  53  removably fixed to each of the ends  54  of the branches of the U delimiting the passage  55 . The cover  53 , once put in place on the cage  52 , makes it possible to avoid any disengagement of the teeth  26  of the rack  22  and of the threading of the worm screw  50  throughout the relative movement between the cage  52  and the arch  20 . In effect, before the disengagement occurs, the cover  53  comes to bear on the flank opposite the flank  210  of the profile member  21 , then ensuring the cooperation between the rack  22  of the arch  20  and the worm screw  50 . The worm screw  50  is made of stainless steel for example. 
     The fact of using a rack made of plastic material coming into contact with a metal worm screw, in particular made of stainless steel, makes it possible to reduce the friction and therefore the vibrations which generate the screeching effects previously described while avoiding providing for greasing of the rack  22  and of the worm screw  50 . Thus, any maintenance phases (greasing) are eliminated. However, the contact between the worm screw and the rack  22  does generate residual vibrations which are absorbed by the first  45  and second  44  damping means situated between the arch  20  and the parts  30  for mounting the arch on the solar tracker  60 . 
     Another advantage of mounting a rack made of plastic material in a gutter  29  formed on a flank  210  of the arch  20  is that it makes it possible to take up any mounting play, which can be significant, of the solar tracking device, like that illustrated in  FIG. 8 , comprising a system for moving a solar tracker in rotation  10  according to the invention. This allows for extremely simplified and rapid mounting and placement of the solar tracking device on its site S while ensuring optimum accuracy of the solar tracking during the operation of the solar tracking device comprising the system for moving a solar tracker in rotation  10  according to the invention. 
     Obviously, it is possible to add many modifications to the invention without in any way departing from the framework thereof. For example, the rack  22  can be positioned on an edge of the arch  20 , in particular on a radially outer peripheral edge.