Abstract:
A tracker including an outer post having elongated bore and a lower end mounted on a sub-structure, an inner pole rotatably received in the elongated bore, a lower bearing in the bore adjacent a lower end of the outer post and attached thereto to be constrained from lateral movement and mounted on the sub-structure such that a lower end of the inner pole rests on and is supported by the lower bearing, an upper bearing near an upper end of the outer post, a circumferential drive supported on the outer post for rotating the inner pole relative to the outer post, such that substantially a full weight of a load on the inner pole is directly transmitted to the sub-structure and lateral force and torque leverage are placed on a full length of the outer post by way of the upper and lower bearing.

Description:
STATEMENT 
     This invention was made with Government support under DE-FC36-07G017052 awarded by the Department of Energy. The government of the United States of America has certain rights in this invention. 
    
    
     FIELD 
     The present patent application relates to trackers for supporting solar panels, antennae and the like and, more particularly, to trackers for supporting and aligning such loads in three dimensions. 
     BACKGROUND 
     Solar panels typically include solar cells that convert solar energy into useable electrical energy. However, efficient operation of a solar panel generally requires precise alignment between the solar panel and the sun. Therefore, solar panels typically are mounted on trackers that maintain alignment between the associated solar panel and the sun as the sun moves across the sky. 
     A typical solar tracker includes a pedestal upon which a solar panel assembly is mounted. The pedestal is secured to a sub-structure, such as a post secured to the ground. The solar panel assembly may include an elevation actuator to tilt an angle of the solar panel with respect to the x-y horizontal plane. Additionally, a slew drive is positioned between the pedestal and the solar panel assembly to facilitate rotation of the solar panel assembly around the z-axis relative to the pedestal, thereby facilitating tracking in three dimensions. Therefore, the entire weight of the solar panel assembly rests on the slew drive. 
     Thus, typical solar trackers require slew drives capable of carrying the full weight of the solar panel assembly, and bearing the horizontal torque of the tilted panel with wind load, while still permitting rotation of the solar panel assembly relative to the pedestal. Therefore, the size of the slew drive and associated motor is highly dependent on the size of the solar panel assembly and, as such, substantially contributes to the overall cost of the system. Furthermore, due to the constant force being applied by the weight, tilting torque and wind load of the solar panel assembly, the wear and tear on the slew drive and associated motor may impact the tracking accuracy of the system. 
     Accordingly, those skilled in the art continue to seek alternative trackers for supporting and aligning loads, such as solar panels, antennae and the like. 
     SUMMARY 
     In one aspect, of the disclosed two-axis tracker may include an outer post defining an elongated bore and including a first end and a second end, the second end being secured to a sub-structure, the first end providing access to the elongated bore, an inner pole defining an axis of rotation and including a first end and a second end, the second end of the inner pole being received in the elongated bore to define an annular region between the inner pole and the outer post, a tapered roller bearing received in the elongated bore and disposed between the second end of the inner pole and the sub-structure, an annular bearing disposed in the annular region between the inner pole and the outer post, and a load connected to the first end of the inner pole, wherein the inner pole is rotateable relative to the outer post about the axis of rotation. 
     In another aspect, of the disclosed three-dimensional tracker may include an outer post defining an elongated bore and including a first end and a second end, the second end being secured to a sub-structure, the first end providing access to the elongated bore, an inner pole defining an axis of rotation and including a first end and a second end, the second end of the inner pole being received in the elongated bore to define an annular region between the inner pole and the outer post, a tapered roller bearing received in the elongated bore and disposed between the second end of the inner pole and outer post near the sub-structure, an annular roller bearing disposed in the annular region between the inner pole and the outer post, a circumferential drive assembly including a worm gear connected to the inner pole and a worm screw with motor drive connected to the outer post, the worm screw being engaged with the worm gear, and a load connected to the first end of the inner pole, wherein rotation of the worm screw causes corresponding rotation of the inner pole worm gear relative to the outer post around the z-axis of rotation. 
     In yet another aspect, the disclosed three-dimensional tracker may include an outer post defining an elongated bore and including a first end and a second end, the second end being secured to a sub-structure, the first end providing access to the elongated bore, an inner pole defining an axis of rotation and including a first end and a second end, wherein the second end of the inner pole includes a cylindrical neck end and is received in the elongated bore to define an annular region between the inner pole and the outer post, a tapered roller bearing defining a inner ring recess therein, the tapered roller bearing being received in the elongated bore such that the cylindrical neck end of the inner pole is received in the inner ring recess of the tapered roller bearing, an annular roller bearing disposed in the annular region between the inner pole and the outer post generally adjacent to the first end of the outer post, a circumferential drive assembly including a worm gear connected to the inner pole and a worm screw with motor drive connected to the outer post, the worm screw being engaged with the worm gear, and a solar panel assembly connected to the first end of the inner pole at a pivot point, the solar panel assembly including a linear actuator, wherein rotation of the worm screw causes corresponding rotation of the inner pole relative to the outer post about the axis of rotation. 
     Other aspects of the disclosed three-dimensional tracker will become apparent from the following description, the accompanying drawings and the appended claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-sectional, schematic view of the lower portion of one aspect of the disclosed two-axis tracker; and 
         FIG. 2  is a side elevational, schematic view of the upper portion of the three-dimensional tracker of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION 
     As shown in  FIG. 1 , one aspect of the disclosed three-dimensional tracker, generally designated  10 , may include an outer post  12 , an inner pole  14 , a circumferential drive assembly  16 , an upper bearing  18  and a lower bearing  20 . As shown in  FIG. 2 , a load  22  (discussed below) may be connected to the upper end  24  of the inner pole  14 . 
     Referring to  FIG. 1 , the outer post  12  may be a post having a first, upper end  26 , a second, lower end  28  and an elongated bore  30  extending therebetween. The bore  30  may have an inner diameter D 1 . The upper end  26  may include an opening  32  to provide access to the bore  30 . The lower end  28  of the outer post  12  may be fixedly and securely connected to a sub-structure  34 , such as the ground. In one example, the outer post  12  may be cemented into a hole formed in the sub-structure  34 . In another example, the outer post  12  may be connected to the sub-structure  34  using mechanical fasteners, such as bolts extending from the sub-structure  34 . In yet another example, an extra long post  12  equipped with a helical blade screw may be driven directly into the sub-structure  34 . 
     The outer post  12  may have a height H 1  above the sub-structure  34  and a thickness T, which may be selected based upon the overall size of the tracker  10 . Specifically, the height H 1  and thickness T of the outer post  12  may be selected to resist lateral forces presented when the inner pole  14  is received within the bore  30 , as shown in  FIG. 1 . Furthermore, the outer post  12  may be formed from a rigid material, such as galvanized steel. 
     In one aspect, the bore  30  defined by the outer post  12  may be generally cylindrical in shape. However, those skilled in the art will appreciate that an outer post  12  having various shapes and bore geometries may be used without departing from the scope of the present disclosure. For example, the bore  30  may be generally elliptical or rectangular in cross-section. As such, reference to the diameter D 1  of the bore  30  broadly refers to the cross-section width of the bore  30 . 
     The inner pole  14  may be an elongated pole having a first, upper end  24  ( FIG. 2 ) and a second, lower end  33  ( FIG. 1 ), and may define an axis A 1  of rotation ( FIG. 1 ). As discussed above and shown in  FIG. 2 , the upper end  24  of the inner pole  14  may be connected to a load  22 . As shown in  FIG. 1 , the lower end  33  of the inner pole  14  may be received in the bore  30  defined by the outer post  12  and may be engaged with the lower bearing  20  to define an annular region  36  between the inner pole  14  and the outer post  12 . 
     The inner pole  14  may have a height H 2  ( FIGS. 1 and 2 ) and a diameter D 2 , which may be selected based upon the overall size of the tracker  10 . Specifically, the height H 2  and diameter D 2  of the outer post  12  may be selected to resist lateral forces acting on the inner pole  14  when the lower end  33  of the inner pole  14  is received within the bore  30 , as shown in  FIG. 1 . Furthermore, the inner pole  14  may be formed from a rigid material, such as steel, and may be solid, hollow or partially hollow. 
     In one aspect, the inner pole  14  may be generally cylindrical in shape. However, those skilled in the art will appreciate that an inner pole having various shapes and cross-sectional geometries may be used without departing from the scope of the present disclosure. For example, the inner pole  14  may be generally elliptical or rectangular in cross-section with select portions of the inner pole  14  configured to facilitate rotation about the axis A 1  of rotation. As such, reference to the diameter D 2  of the inner pole  14  broadly refers to the cross-sectional width of the inner pole  14 . 
     At this point, those skilled in the art will appreciate that the diameter D 2  of the inner pole  14  and the diameter D 1  of the bore  30  may be selected to minimize the radial length of the annular region  36 , while still providing space in the annular region  36  for receiving the upper and lower bearings  18 ,  20 , e.g., annular roller bearings, annular bearings. 
     The upper bearing  18  may be positioned in the annular region  36  between the inner pole  14  and the outer post  12  and may carry the radial load of the inner pole  14  relative to the outer post  12 . In one aspect, the upper bearing  18  may be a ring bearing, such as a roller bearing. In one particular aspect, the upper bearing  18  may include roller bearings (not shown) received in a circumferential race (not shown), as is known in the art. 
     While the upper bearing  18  is shown disposed at or near the upper end  26  of the outer post  12 , those skilled in the art will appreciate that the upper bearing  18  may be positioned at various locations in the annular region  36  between the inner pole  14  and the outer post  12 . Furthermore, those skilled in the art will appreciate that additional upper bearings (not shown) may be included without departing from the scope of the present disclosure. 
     The lower bearing  20  may be a thrust bearing or tapered roller bearing positioned in the bore  30  defined by the outer post  12  generally adjacent to the lower end  28  of the outer post  12  such that the lower bearing  20  is statically coupled with the sub-structure  34 . Like the upper bearing  18 , the lower bearing  20  may include roller bearings (not shown) or the like to facilitate circumferential rotation. Therefore, in one aspect, the lower bearing  20  may transfer the axial weight of the inner pole  14  to the sub-structure  34 , while facilitating rotation of the inner pole  14  about the axis A 1  relative to the sub-structure  34  and the outer post  12 . 
     In another aspect, the lower bearing  20  may be a tapered roller bearing that supports the axial weight of the inner pole  14 , as discussed above, and may also maintain radial spacing of the lower end  33  of the inner pole  14  relative to the lower end  28  of the outer post  12 . For example, as shown in  FIG. 1 , the lower end  33  of the inner pole  14  may include a smaller, cylindrical neck end  38  and the lower bearing  20  may include a corresponding inner ring recess  40  such that the cylindrical neck end  38  of the inner pole  14  may be received in the ring recess  40  in the lower bearing  20 , thereby maintaining radial spacing of the inner pole  14  relative to the outer post  12 . While the cylindrical neck end  38  shown in  FIG. 1  fits directly into the tapered roller bearing  20 , those skilled in the art will appreciate that the cylindrical neck end  38  may be a rounded tapered end. Furthermore, the lower bearing  20  may be sized to support the full diameter D 2  of the inner pole  14 , thereby permitting the use of a thrust roller bearing (e.g., a “Lazy Susan” roller). 
     The circumferential drive assembly  16  may be any apparatus or system capable of applying a rotational force to the inner pole  14  such that the inner pole  14  rotates about the axis A 1  relative to the outer post  12 . In one aspect, the circumferential drive assembly  16  may include a worm gear  42  securely and fixedly connected to the inner pole  14  and a worm screw  44  connected to the outer post  12 . The worm screw  44  may be meshed with the worm gear  42  such that rotation of the worm screw  44  about its axis A 2  of rotation (which extends into the page in  FIG. 1 ) causes corresponding rotation of the inner pole  14  about its axis A 1  of rotation relative to the outer post  12 . 
     Those skilled in the art will appreciate that the mechanics of the circumferential drive assembly  16  may be selected to provide the desired amount of axial rotation of the inner pole  14 , as well as the desired stepping of the rotation. In one aspect, the inner pole  14  may rotate 1 degree relative to the outer post  12  with a stepping function of about 360 degrees in worm screw rotation. In another aspect, the inner pole  14  may rotate 0.5 degrees relative to the outer post  12  with a stepping function of about 360 degrees in worm screw rotation. In yet another aspect, the inner pole  14  may rotate 0.1 degrees relative to the outer post  12  with a stepping function of about 360 degrees in worm screw rotation. 
     The load  22  may be any apparatus or system capable of, or in need of, being supported on the inner pole  14  and rotated about the axis A 1 . For example, the load  22  may be a solar panel, an antenna, a telescope or the like. 
     In one particular aspect, as shown in  FIG. 2 , the load  22  may be a solar panel assembly  46 , which may include a solar panel  48 , a mount  50  and an actuator assembly  52 . The mount  50  may be connected to the upper end  24  of the inner pole  14  at a pivot point  54  and the solar panel  48  may be connected to the mount  50  using fasteners  56 A,  56 B,  56 C or the like. The actuator assembly  52  may include a linear actuator  58  and a support structure  60 . The first end  62  of the linear actuator  58  may be pivotally connected to the mount  50  and the second end  64  may be connected to the inner pole  14  by way of the support structure  60 . 
     Thus, actuation of the linear actuator  58  (either extension or retraction) may cause corresponding movement of the solar panel  48  about the pivot point  54 , which provides tracking of the solar panel assembly  46  tilting in elevation. Furthermore, actuation of the circumferential drive assembly  16  may cause corresponding rotation of the inner pole  14  around the axis A 1  (i.e., about the z axis), thereby providing three-dimensional tracking of the solar panel assembly  46 . 
     Accordingly, the disclosed tracker  10  may transfer the full weight of the load  22  directly to the sub-structure  34 , while placing the lateral force and torque leverage on the full length of the outer post  12  by way of the upper and lower bearings  18 ,  20 . Therefore, there is little or no load on the circumferential drive assembly  16 , thereby allowing for the use of smaller and less expensive drive assemblies, while maintaining precision. Furthermore, by attaching the linear actuator  58  to the inner pole  14  away from the circumferential drive assembly  16 , the solar panel  48  may be maintained closer to the inner pole  14 , thereby enabling near zero elevation angle. 
     Although various aspects of the disclosed three-dimensional tracker have been shown and described, modifications may occur to those skilled in the art upon reading the specification. The present application includes such modifications and is limited only by the scope of the claims.