Description:The present patent application has a reference to Indian Patent Application No. 201721030771 filed on date 30th August 2017. The present invention is improvement or modification of the invention claimed in specification the Indian Patent Application No. 201721030771.

Field of the invention:
The present invention relates to solar trackers and more particularly to damping apparatus for solar trackers.

Background of the invention:
Solar photovoltaic plants are huge power generation systems that are installed in remote locations where there might be harsh atmospheric conditions during their life cycle. The solar plants include trackers for maximization of the generation of energy from available sun light. The interaction between the solar tracker structure and the wind flowing over it causes vortices or eddies to be formed above and below the leading edge. The alternate shedding of these vortices causes the leading edge of the structure to move up and down causing twisting of the tracker structure.
There is a need of a damping apparatus for solar trackers to damp the twisting of the tracker structure. There is further need of damping apparatus along with driving and locking apparatus for solar trackers.

Summary of the invention:
A friction damping apparatus for providing friction damping a solar tracker includes a plurality of anchor assemblies, a tensioner unit, a driver and a plurality of wire ropes that are connected to a first pulley. The friction damping is achieved by a pair of opposed spool assemblies, a pair of opposed wire ropes that are connected to a first pulley forming a triangulated structure. It is noted that the solar tracker is a structure that include solar panels that follow a path of the sun for maximizing the energy yield.
The damping apparatus of the present invention advantageously provides damping, locking, and driving at one or more locations to the solar tracker. The spool assemblies are positioned on a beam such that the spool assemblies are connected to the first pulley positioned below the sector by respective wire ropes. The spool assemblies are connected to the first pulley by the pair of wire ropes that pass through a groove defined in the sector and provide damping to the tracker by rubbing action between the wire rope and groove of the sector.
A first spool assembly and a second spool assembly are opposedly positioned on a beam of a sector. The sector is a semi-circular shaped structure with the beam on the top. A first wire rope connects the first spool assembly with the first pulley. The first wire rope runs through groove defined along circumference of a first arcuate portion the sector making a tangential contact. A second wire rope connects the second spool assembly with the first pulley. The wire rope runs through groove along circumference of a second arcuate portion the sector making a tangential contact.
The tensioner unit is positioned below the cantilever to develop tension in respective wire ropes. The driver includes the first pulley, a shaft, and worm gear box. The first pulley is lockable during wind induced motion by the worm gear box. In accordance with the present invention, a rubbing action is generated between the first wire rope, the second wire rope, and the arcuate groove of the sector during the oscillatory motion of the tracker generating frictional damping effect for the tracker.
In a winding cycle, the first pulley is rotated to wind the first wire rope, and simultaneously the second wire rope is un-winded during the unwinding cycle of the second wire rope for driving the tracker. The apparatus also has a self-locking ability and controlled driving to the solar tracker.
A first end of the first wire rope is connected to the first spool assembly, and a second end of wire rope is connected to the first pulley. A first end of the second wire rope is connected to the second spool assembly, and a second end of the wire rope is connected to the first pulley.
The sector has a first arcuate portion, and second arcuate portion such that both of them include an arcuate groove including a receptacle receiving respective wire ropes running along respective arcuate portions of the sector. The first wire rope is wound in a clockwise direction and anchored on the driving pulley, and the second wire rope is wound in anticlockwise direction and anchored on the driving pulley simultaneously. The first pulley allowing both first and second wire ropes and to be alternately reeled in and out with the rotation of the worm gear box while driving the tracker. The first spool assembly includes a second pulley freely rotatably positioned at the movable end of the cantilever.
The cantilever includes a pair of parallel members that are mounted on the first beam 124, the cantilever includes a first end is hinged on a pair of parallel plates, and the other movable end including the second pulley. The second pulley is rotatably positioned on the open end of the cantilever by a bolt or pin, and the other end of the cantilever is pinned in the parallel plates by a hinge joint defined by a bolt or a pin. The tensioner unit including the cantilever, a base member, a spring, a stopper, a nut and a bolt, the tensioner unit developing tension in the respective wire ropes, and whereas the anchor holds the respective wire ropes without any slip.
The base member, and the stopper are positioned on the beam avoiding compression of the spring beyond a predefined limit. The cantilever having at least three positions including a first position is a primary position wherein the cantilever is approximately parallel to the beam, a second position wherein the cantilever is located at a lowest point relative to the first position, and a third position wherein the cantilever is located at the highest point relative to the first position. The cantilever oscillates between the second position and the third position such that the second pulley is rotated about the pin joint. The cantilever oscillates against the spring keeps the first wire rope under tension in all positions of the cantilever. The cantilever is defined by an envelope that includes a pair of approximately identical vertical plates is connected by a top horizontal plate.

Brief description of the drawings:
The objectives and advantages of the present invention will become apparent from the following description read in accordance with the accompanying drawings wherein:
FIG. 1A is a perspective view of the friction damping apparatus for solar trackers 100 in accordance with an embodiment of the present invention;
FIG. 1B shows an enlarged perspective view of a swivel joint of the friction damping apparatus 100 of FIG. 1A showing connection of a beam of a sector of the damping apparatus with a clamp of a torque tube of the solar tracker;
FIG. 1C is a front view showing a triangulated structure defined by a pair opposed spool assemblies, a pair of opposed wire ropes and a first pulley of the friction damping apparatus of FIG. 1A;
FIG. 1D shows an enlarged view of arcuate groove receiving a first wire rope in a sector of the damping apparatus of FIG. 1A;
FIG. 2 shows a perspective view of a first spool assembly of the friction damping apparatus of FIG.1A;
FIG. 3 shows a perspective view of a tensioner unit of the spool assembly of FIG. 2;
FIG. 3A shows a sectional perspective view of the spool assembly of FIG. 2 along axis-X of FIG 3;
FIG. 4A-C show a front view of a first neutral position, a second bottom position and a third top position of the cantilever of the first spool assembly of the damping apparatus of FIG. 1A;
FIG. 5A shows a side view of a driver of the damping apparatus of FIG. 1A;
FIG. 5B shows perspective view of a first end of wire rope being connected with a first spool assembly of the damping apparatus of FIG. 1A;
FIG. 5C shows perspective view of a second end of first and second wire rope being wound around a first pulley;
FIG. 5D shows a front view of the sector of the damping apparatus of FIG. 1A in a deflected position wherein the cantilever of the first spool assembly is in the second position, and the cantilever of second spool assembly is in the third position;
FIG. 6A shows side view of a tracker with the damping apparatus of FIG. 1A showing unbalanced loading due to wind induced forces on the tracker;
FIG. 6B shows a side view of a deflected position of the tracker of FIG. 1A;
FIG. 7A shows a perspective view of another embodiment of the damping apparatus of the present invention;
FIG. 7B shows a front view of the embodiment of the damping apparatus of FIG. 7A;
FIG. 8A shows a perspective view of a spool assembly of the damping apparatus of FIG. 7A;
FIG. 8B shows an exploded view of a drum including a rachet and clamp of the spool assembly of the embodiment of FIG. 7A;
FIG. 9 shows a perspective view of an envelope of the spool assembly of another embodiment of FIG. 7A; and
FIG. 10 shows a perspective view of the spool assembly of FIG. 7A while one wall of the envelope is removed.

Detailed description of the drawings:
The invention described herein is explained using specific exemplary details for better understanding. However, the invention disclosed can be worked on by a person skilled in the art without the use of these specific details.
References in the specification to "one embodiment" or "an embodiment" means that feature, structure, characteristic, or function described in connection with the embodiment is included in at least one embodiment of the invention. The appearances of the phrase “in one embodiment” in various places in the specification are not necessarily all referring to the same embodiment.
References in the specification to “preferred embodiment” means that a particular feature, structure, characteristic or function described in detail thereby omitting known constructions and functions for clear description of the present invention.
The foregoing description of specific embodiments of the present invention has been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the present invention to the precise forms disclosed, and obviously many modifications and variations are possible in light of the above teaching.
In general, the present invention is a friction damping apparatus for solar trackers. The apparatus also provides a self-locking ability and controlled driving to the solar tracker. The friction damping is achieved by a pair of opposed spool assemblies, a pair of opposed wire ropes that are connected to a first pulley forming a triangulated structure. The spool assemblies are positioned on a beam such that the spool assemblies are connected to the first pulley positioned below the sector by respective wire ropes. The spool assemblies are connected to the first pulley by the pair of wire ropes or more wire ropes that pass through a groove defined in the sector and provide damping to the tracker by rubbing action between the wire rope and groove of the sector.
It is understood that solar tracker is a structure that include solar panels that follow a path of the sun for maximizing the energy yield. The damping apparatus 100 of the present invention advantageously provides damping, locking, and driving at one or more locations to the solar tracker.
Referring to FIG. 1A-1D, the damping apparatus for solar trackers 100 includes a first spool assembly 104, a first wire rope 108, a first pulley 112, a second spool assembly 116, and a second wire rope 120. Each of the spool assemblies 104, 116 are opposedly positioned on beam 124 of a semi-circular sector 128 i.e. sector 128. The shape of the sector 128 is of approximately semi-circular in this embodiment. In other embodiments, the sector 128 may have other shapes such as parabolic, involute, curved or the like. The sector is defined by a first arcuate portion and a second arcuate portion. First end of the first wire rope 108 is connected to the first spool assembly 104, and another end i.e. the second end is connected to the first pulley 112.
Similarly, the first end of the second wire rope 120 is connected to the second spool assembly 116, and the second end is connected to the first pulley 112. Both the wire ropes 108, 120, run through and make a tangential contact with the sector 128 before reaching the first pulley 112 that is a driving pulley, in accordance with the present invention. The wire ropes 108, 120 are preferably made of stainless-steel. In this embodiment, the nominal diameter of each of the wire ropes 108, 120 is 6mm with construction of 7x19. In another embodiment the wire rope is replaced by a flat band, preferably made of stainless steel of width 20mm and thickness 1.5mm.
The beam 124 of the sector 128 is connected with a torque tube 132 of the tracker. The connection is defined by a split clamp 136 i.e. an upper clamp an and a lower clamp that are connected to torque tube 132 with multiple through bolts and side bolts for clamping. A swivel hinge joint 140 is defined by two thick plates that are connected to similar thick plates on beam 124 with two large bolts. The sector 128 includes an arcuate groove 144 that runs along the sector 128. The groove 144 defines a receptacle that receives respective wire ropes 108, 120.
The first wire rope 108 while passing from the first spool assembly 104 to the first pulley 112 runs through the groove 144 of the first arcuate portion defined along circumference of the sector 124. The second wire rope 120 while passing from the second spool assembly 116 to the first pulley 112 runs through the groove 144 of the second arcuate portion defined along circumference of the sector along the other side of the sector 128.
The first wire rope 108 is received in the groove 144 that is in the first portion i.e. first half of the sector, and the second wire rope 120 is received in the groove that is in an opposed second portion i.e. second half of the sector 128. In this embodiment, radius of the sector 128 is of approximately 0.9 meters. The length of the first wire rope and the second wire rope is approximately 4.8 meters. The diameter of the first pulley is approximately 100 mm. In other embodiments, the radius of the sector 128 is in the range of 0.75 to 1.75 meters.
In accordance with the present invention, the first pulley 112 is preferably a cylindrical metal body with a shaft 148. In this embodiment, the diameter of the first pulley is approximately 100 mm. The first pulley 112 is securely positioned on the member 152. The member 152 is a hot rolled or a cold formed section made of materials like steel, iron or the like. One end of the first pulley 112 and thereby the shaft 148 is coupled with a worm gear box 156, and other end is supportedly positioned in a lateral assembly 160 that includes a bushing that provides lateral support to the first pulley 112. The lateral assembly 160 advantageously transfers the shear load on the first pulley 112 to a base portion the member 152 in the form of torsion.
The first pulley 112 and the shaft 148 are a single unit such that the first pulley 112 is stepped down to define the shaft 148. The diameter of the shaft 148 is approximately little less than the half of the diameter of the first pulley 112. The assembly is preferably made of steel material. In other embodiments, the first pulley 112 may be made of materials like cast aluminum with steel inserts.
The first pulley 112 advantageously allows both first and second wire ropes 108 and 120 to be alternately reeled in and out with the rotation of the worm gear box 156. In accordance with the present invention, one of the wire ropes, for example, 108 is wound in a clockwise direction on the driving pulley 112, and at the same time the second wire rope 120 is wound in anticlockwise direction on the driving pulley 112. Accordingly, while the driving pulley 112 is rotated in clockwise direction, the wire rope 108 is reeled in and the second wire rope 120 is unwound i.e. paid out.
The first pulley 112 is rotatable with the rotation of the worm gear box 156. Ends of both the wire ropes 108 and 120 are connected to the pulley preferably by a clamp and set screw. It is, understood, that the clamp is permanently fitted to the first pulley 112. Just before the second end of the wire rope 108, the wire rope 108 is wound around the first pulley 112 to define at least three full dead turns around the first pulley 112, and then first wire rope 108 passes through the arcuate groove 144 of the sector 128 to the first spool assembly 104. In accordance with present invention, the portion of the wire ropes required for making the three dead turns are not to be counted in the winding or unwinding of the wire ropes 108, 120 during the rotation of the first pulley 112.
The first pulley 112 is rotatable when the worm gear box is activated, and also retains the wire ropes 108, 120 with minimum three dead turns without any slip at any given point, and even when the tracker is rotated to its full design tilt, or under maximum design wind loads. The first pulley 112 includes a second end of the first wire rope 108, and the second end of the second wire rope 120 that are wound on the first pulley 112.
Referring to FIG. 2, the first spool assembly 104 includes a second pulley 200 that is freely rotatably positioned at the end of a cantilever 204 defined by a pair of parallel members 204 and 204’, hereinafter, referred as the cantilever 204. It is noted that the cantilever 204 has two ends. A first end is hinged on a pair of parallel plates 208, 208’, and the other end i.e. the open end includes the second pulley 200. The plates 208, 208’ are perpendicularly fixedly mounted on one end of the beam 124. The members of the cantilever 204 has a section, for example, a C-section, or rectangular section or the like.
The second pulley 200 is rotatably positioned on the open end of the cantilever 204 by a bolt or pin 212, and the other end of the cantilever 204 is pinned in the parallel plates 208, 208’ by a hinge joint 216 defined by a bolt or a pin. The second pulley 200 is rotatable about the bolt 212 in clockwise as well as anticlockwise directions as indicated by arrow ‘A’ (Ref. FIG. 4A). Similarly, the cantilever 204 is rotatable about the hinge joint 216 in directions as indicated by arrow ‘B’.
The second end of the cantilever 204 also includes an anchor 220 which defines a cylindrical drum that is fixedly positioned between the opposed plates 208, 208’. The anchor 220 is fixed between plates 208, 208’. It is noted that there is no relative movement between the anchor 220 and the plates 208, 208’. In accordance with the present invention, the tensioner unit 222 is positioned below the cantilever 204 to guide the oscillatory movement of the cantilever 204. It is noted, however, that the cantilever 204 is part of the tensioner unit 222.
As shown in FIG. 3 and 3A, the tensioner unit 222 includes cantilever 204, a base member 300, a spring 304, a stopper defined by a cylindrical pipe 320, a nut 312 and a bolt 316. The tensioner unit 222 is securely mounted on the main beam 124 such that a longitudinal axis of the bolt 316 is approximately normal to the beam 124. The tensioner unit develops tension in the respective wire ropes 108, and 120, whereas the anchor 220 holds the respective wire ropes without any slip.
Now referring to FIG. 2, 3 and 3A, the spring 304 of the tensioner unit 222 is advantageously positioned between the cantilever 204 and the beam 124. The bolt 316 and spring 304 are positioned on the beam 124 such that the bolt 316 is approximately normal to the beam 124. The bolt 316 is secured with the beam 124 by the nut 312. The structure defined by the arrangement of the nut 312- bolt 316 assembly, the base member 300, and the stopper 320 is advantageously positioned on the beam 124 to avoid the compression of the spring 304 beyond a predefined limit. The bolt 316 guides the spring 304 that maintains tension in the respective wire rope 104.
For example, in this embodiment the specifications of the spring 304 were as follows: the free length i.e. length of the spring 304 was 80mm, spring rate was 247 N/mm, wire diameter was 8mm. The spring 304 was compressed by 9mm in the first position of the cantilever 204 that developed tension in the wire rope 108. In the second position of the cantilever 204, the maximum compressive movement of the spring 304 was by approximately 5mm. In the third position of the cantilever 204, the maximum expansive movement of the spring was approximately 5 mm.
The stopper 320 is a cylindrical construction like a pipe. The nut 312 and bolt 316 allow compression of the spring 304 during installation of wire ropes 108 and 120 at their respective spooling assemblies 104, 116. The respective wire rope, for example, wire rope 108 is wound around the anchor 220 such that at least three turns of the wire rope 108 are wound around the anchor 220, before fixing it in a clamp with a set screw (Not shown).
The spring 304 is pushed against the base member 300 which is pushed against the cantilever beam 204 (Ref. FIG. 2, FIG 3A and FIG 4A), and that keeps the wire rope 108 under tension. Accordingly, the first wire rope 108 under tension exerts a pressure which is radially compressive force inward towards the center on the sector 128. It is noted, however, that bolt 316 compresses the spring 304 when the wire rope 108 is being wound and installed on the anchor 220. The stopper 320 advantageously limits compression of the spring 304 and thereby avoids full compression and damage of the spring 304.
A preferred method of installation of the first end of the first wire rope 108 is discussed. Initially, in a first step, the second end of the wire rope 108 is fixed (REF FIG 5C) in the clamp 506 with the set screw 508. In a second step, the wire rope 108 is wound on first pulley 112 and is then received in groove 144 of sector 128.
In a next step, the wire rope 108 is inserted into through a hole defined in the beam 124, and then passed over the second pulley 200. In a next step, the spring 304 is compressed by the installation nut 312 and bolt 316 so that the tensioning pulley 200 configured on the cantilever 204 of the spool assembly 104 is configured closer to the beam 124. After the installation of the wire rope 108 on the anchor 220, the bolt 316 is loosened that act as a guide for the spring 304 and allows full movement of the spring 304.
As shown in FIGS. 4A, 4B, and 4C, the first spool assembly 104 includes the second pulley 200 positioned at the open end of cantilever 204, that is also a movable end of the cantilever 204. The other end of cantilever 204 is hingedly connected on the pair of plates 208, 208’ that are fixed on the first end of beam 124. The hinge joint 216 is defined by a nut and bolt arrangement. In accordance with the present invention, the cantilever 204 has at least three positions. A first position is a natural and primary position adopted during the installation of the damping apparatus 100. In this first position, the cantilever 204 is approximately parallel to the beam 124.
In a second position, the cantilever 204 is moved down to a lowest point till the stopper 320 constrains the cantilever 204 to move any lower. In this one embodiment, in the second position, the cantilever beam 204 is moved by approximately 3° (In words: three degrees) around the hinge joint 216 in lower direction relative to the first position. Similarly, in a third position, the cantilever 204 is moved upwards to a highest point till the cantilever 204 is constrained from moving any higher by the stopper 320 on the opposite side. In this one embodiment, in the third position, the cantilever beam 204 is moved by, for example, approximately by 3° (In words: three degrees) around the pin joint 216 in an upper direction relative to the first position. The cantilever 204 oscillates between the second position and the third position.
The oscillatory movement of the cantilever 204 and therefore of the second pulley 200 is about the pin joint 216 that defines the pivot for the cantilever 204. The cantilever 204 oscillates against the spring 304 that keeps the first wire rope 108 under tension in all positions of the cantilever 204. The second spool assembly 116 has approximately identical structure and components as that of the first spool assembly 104.
In accordance with the present invention, a relative movement between the first wire rope 108 and the sector 128 advantageously provides damping to the tracker, and the damping is achieved during the oscillatory movement of the cantilever 204 between second and third positions. It is noted that the damping effect is advantageously generated by the friction between the first wire rope 108 under tension and the arcuate groove 144 of the sector 128 during the oscillatory motion of the cantilever 204.
Now referring to FIGS. 5A, 5B, 5C, and 5D a driver 500 in accordance with the present invention is described. The driver 500 includes the shaft 148 coupled with the first pulley 112. The shaft 148 is coupled with the worm gear box 156. The first pulley 112 is positioned between the worm gear box 156 and a lateral assembly 160 providing lateral support to the first pulley 112. The lateral assembly 160 is fixedly mounted on the vertical member 152. The worm gear box 156 has an input side and an output side.
The input side includes drive line and other gear boxes such as a bevel gear box. It is, noted, that the drive line receives rotary movement as input from a motor in order to rotate the tracker in desired directions. The drive line also connects and mechanically synchronizes other drivers 500 in the solar tracker such that all the drivers 500 rotate the tracker at the same angle in a synchronised manner. From the input side, the drivers include devices such as motors known in the art. The drive line transfers torque from one such motor to all the other drivers installed in the tracker. Such drivers are approximately identical with the driver 500. The output side includes shaft 148 that is coupled with the first pulley 112.
The first pulley 112 includes ends of first wire rope 108 and second wire rope 120. The first pulley 112 includes a second end of the first wire rope 108 and second end of the second wire rope 120 that are inserted in holes of clamps 506 and fixed by set screw 508 that constrains the second ends of respective wire ropes 108, 120. The clamps 506 are fixedly configured on the first pulley 112.
The respective second ends of the first wire rope 108, and the second wire rope 120 are installed securely on the driving pulley i.e. the first pulley 112 such that the first wire rope 108 is wound on the first pulley 112 in the clockwise direction, and the second wire rope 120 is wound on the driving pulley 112 in anticlockwise direction.
Accordingly, the worm gear box 156 drives the first pulley 112. The efficiency and ratio of the worm gear box 156 is selected such that the worm gear box 156 is driven from only the input side by of the worm gear box 156 by motors or the driveline, and that is not driven from the output side. In other words, driver 500 doesn’t work in reverse direction and this arrangement advantageously defines self-locking in the output side of the worm gear box 156. The self-locking, in accordance with present invention is defined to the solar tracker by the driver 500 through the worm gear box 156. The self-locking counteracts wind induced moment by stopping undesired rotation in the tracker.
It is understood, however, from the above description that the driver 500 drives the tracker. Hence, the rotation of the driving pulley i.e. the first pulley 112 by the worm gear box 156 results in one wire rope 108 being reeled in while the other wire rope 120 is paid out. This motion causes the rotation of the tracker via displacement mechanism.
Now referring to FIG, 6A, and 6B movement of the sector 128 while providing damping effect to the sector 128 is discussed. When the module 600 of the tracker receives wind for example in a direction indicated by arrows ‘D’, a plurality of forces (F1, F2,…..Fn), hereinafter referred as, ‘forces’ are developed on the module 600 of the tracker. The forces being unbalanced, develop a moment in the tracker around the torque tube 132. The moment is developed in a direction as indicated by as ‘M’. Accordingly, the moment twists or rotates the structure about a longitudinal axis of the torque tube 132.
Due to the moment ‘M’ the tracker is deflected from an initial position as shown in FIG. 6A to the deflected position as shown in FIG. 6B. Arrow ‘Z’ shows the direction of rotation of the tracker and sector 128 under the influence of moment ‘M’. While the tracker is moved from the initial position to the deflected position, the cantilever 204 of the first spool assembly 104 moves in a direction indicated by arrow ‘X’, and a cantilever of the second spool assembly 116 moves in a direction indicated by arrow ‘Y’. It is noted that the cantilever 204 of the first spool assembly 104 moves from its first position to the second position, and the other cantilever of second spool assembly 116 moves from a first position to the third position.
It is, clear, from the above disclosure that while the tracker moves in the direction ‘Z’, the first pulley 112 is locked in its original position. As a result, the relative motion caused between the first wire rope 108 and the sector 124 generates a first portion of the friction forces that provides damping to the tracker. Similarly, the relative motion caused between the second wire rope 120, and the relevant portion of the sector 124 generates a second portion of the friction forces that also provides damping to the tracker. It is understood however that the first portion of frictional forces and the second portion of the frictional forces provide the damping to the tracker simultaneously during the motion of the sector 124 from the initial position to the deflected position. While the moment ‘M’ is in the opposite direction, damping is provided in similar fashion by the damping apparatus 100 to the tracker.
Now referring to FIGS. 1 to 6C, the operation of the damping apparatus 100 is described. In normal working conditions of the apparatus 100, the tension in the wire ropes 108, 120 is preferably initially developed by the springs 304. This causes inward radial pressure on the sector 128 directed towards the centre of the torque tube 132. The wind induced moment ‘M’ that produces deflection as indicated by arrow 'Z’ in the tracker causes the spring 304 to compress while the damping is being provided to the tracker by the apparatus 100.
As the spring 304 compresses and releases, there is angular movement in the cantilever 204 of the respective spool assembly 104 about the hinge joint 216 that is installed on the two vertical plates 208, 208’. During the angular movement of the cantilever 204, movement of the wire rope 108 is observed over the second pulley 200 in the spool assembly 104 and sliding movement of the wire rope 108 is observed in the arcuate groove 144 of sector 128.
As the wind induced eddies or vortices are generated and alternately shed from above and below leading edges of the module 600, an alternating moment is generated that twists the tracker. The movement of the wire rope 108 slidingly generates a rubbing action between the surface of the arcuate groove 144 of the sector 128, and the wire rope 108. The friction generated by the rubbing action advantageously provides damping effect to the oscillatory or twisting motion of the tracker. The rubbing action is simultaneously observed on the other side of the sector 128 with the second wire rope 120 also.
During operation of the damping apparatus 100, the rubbing of the wire ropes 108, 120 with the arcuate groove 144 causes friction and dissipates mechanical energy in the form of heat that results in providing damping to the tracker. The friction between the wire ropes 108, 120 and the arcuate groove 144 is generated by the radial inward force developed by the tension in the wire ropes 108, 120 that is advantageously generated by the tensioner unit 222.
The radially inward force on the sector 128 and the tension in wire rope 108 is directly proportional to the stiffness of the spring 304. The energy dissipation due to friction advantageously defines friction damping as per the present invention.
The damping effect provided by the apparatus 100 is controllable by factors such as the spring properties, the surface finish of the arcuate groove, type of the wire ropes 108, 120 and the type of coating of the arcuate groove.
In accordance with the present invention, the material of the sector 128 is preferably chosen to provide a non-shiny or dull layer of higher surface roughness during galvanization. In this embodiment, the surface coating of the acuate groove 144 is hot dip galvanized layer of Zinc. The roughness value of the coating on the arcuate groove 144 is greater than 5µm Ra.
For example, on 22nd Feb 2022 during a testing cycle using pluck testing method, the damping effect achieved by the damping apparatus 100 was found to be 13%. It is noted that pluck testing, wherein externally supplied impulse of force causing twisting in a structure is imparted to the tracker, is a method for measuring free vibrations of the tracker structure using accelerometers and the analysis of these vibrations results in measuring damping and other modal characteristics of the tracker structure. In another testing cycle on 4th April 2022, the damping effect achieved by the damping apparatus 100 was found to be 15%.
Referring to FIGS. 7A, and 7B, another embodiment 700 of the damping apparatus 100 is shown. The damping apparatus for solar trackers 700 includes a first spool assembly 704, a first wire rope 708, a first pulley 712, a second spool assembly 716, and a second wire rope 720. Each of the spool assemblies 704 and 716 are opposedly positioned on beam 724 of sector 728. All elements and the structure of this embodiment 700 are approximately identical to the embodiment 100, except the spool assemblies 704, 716, and the beam 724.
Referring to FIG. 8A and FIG 8B the spool assembly 704 includes a wire rope winding drum 800, an envelope 804, a tensioner (Not seen), a second pulley 808 and a ratchet 812. The wire rope winding drum 800 includes a plurality of angled teeth 816 that mesh with angled teeth 816’ of the clamp 814 to form the ratchet 812. The opposed clamp 814 is coupled with the wire rope winding drum 800 such that the diameter of the wire rope winding drum 800 and the opposed clamp 814 is approximately identical. It is, noted, however, that the ratchet 812 allows the rotation of the drum 800 in only one direction ‘R1’ to tighten the respective wire rope 708/716 around the drum-ratchet assembly comprising of the wire rope winding drum 800 and opposed clamp 814. The clamp 814 includes protrusions 822.
The wire rope winding drum 800 includes a clamp 820 fixedly circumferentially positioned on the wire rope winding drum 800. The clamp 820 has a first hole 824 to receive the wire rope 708/720 and has second intersecting hole 828 to receive the set screw 832. The set screw 832 is screwed into second intersecting hole 828 after receiving the wire rope 708/720 in first hole824 to fix the same. The wire rope winding drum 800 also includes a central hub 836 that receives a bolt 840 which is tightened by a washer 844 and nut 848.
As shown in FIGS. 8A, 8B, 9 and 10, the envelope 804 includes a pair of approximately identical vertical plates 900 that are connected by a top horizontal plate 904. The envelope 804 includes a first end 908 and second end 912. The second end 912 includes a through hole 916 for the purpose of hingedly positioning the envelope 804 on the beam 724. The second end 912 also includes through holes 920 that receive protrusions 822 of the opposed clamp 814, and two slots 924 to seat the drum-ratchet assembly.
Another end of the opposed clamp 814 includes a set of angled teeth 816’ that is meshed with a plurality of projections 816 of the drum 800 to define the drum ratchet assembly allowing the wire rope winding drum 800 to rotate only in one direction that allows the wire rope to tighten on it.
The second pulley 808 is positioned in the first end 908 of the envelope 804 and the wire rope winding drum of drum-rachet assembly 800 is positioned in the second end 912. The tensioner unit also includes a spring 1000, and a horizontal member 1004. The tensioner unit is positioned between the top plate 904 and the horizontal member 1004 that is fixedly positioned on the beam 724. In accordance with the present invention, in this embodiment, the envelop 804 defines a cantilever that is hinged about a bolt 1008. The bolt 1008 is receivable in the hole 916 of the envelope 804. The envelope 804 has three positions such as a first normal position, a second bottom position and a third top position.
The clamp 820 on the wire rope winding drum 800 receives a first end of the first wire rope 708 or a first end of the second wire rope 720. The first end of the wire rope 708 is received in the hole 824 of clamp 820 and fixed by inserting a set screw 832 in the hole 828. The wire rope 708 is then wound by preferably making least three turns around the drum-ratchet assembly. The wire rope winding drum 800 is locked by the rachet 812. During installation of the drum–ratchet assembly, the bolt 840 is inserted into the slots 924 in envelope 804 and is used to wind the wire rope 708/720 on the wire rope winding drum 800. The bolt 840 is advantageously tightened with the nut 848 to securely fix the ratchet-drum assembly between vertical plates 900 of the envelope 804.
In accordance with the present invention, there is no relative motion between the clamp 814 and wire rope winding drum 800 or between the clamp 814 and the body of the envelope 804 because of the projections 822. In this embodiment, the envelope 804 defines the cantilever that oscillates between two positions. In this one embodiment, the beam 724 is defined by a pair of opposed C-type cross sections. The beam 724 advantageously allows assembling or removably positioning of various components of the damping assembly, using fasteners, on the beam 724 instead of permanently welding said components on the beam 724.
In this one embodiment, the movement of the envelope 804 of spool assembly 704 from the first position to second position is constrained by the beam 724 itself as the first end 908 of envelope 804 touches the beam 724 and thereby constraining further lower movement of the first end 908. When the first spool assembly 704 is in the second position, the second spool assembly 716 achieves its third position and vice versa. As the movement of each of the spool assembly 704/716 is constrained in its second position, the other spool assembly is constrained in the third position at the same time. The first, second and third positions of the envelope are approximately identical with the first, second and the third position of the cantilever 204 of the previous embodiment.
Referring to FIGS. 1 to 6D, the operation of the damping apparatus 100 during tracking of the solar tracker is discussed. When the tracker is in normal operational cycle, during the daytime while tracking the sun, the whole tracker assembly rotates about the longitudinal axis of torque tube 132.
Now a winding cycle and unwinding cycle of the driver 500 is discussed. In the winding cycle, the input to the worm gear box 156 from the motor or the drive line rotates the shaft 148, and the first pulley 112. The rotation of the first pulley 112 causes one of the wire ropes 108 to be wound or reeled-in and the other, 120 to be unwound or paid out. The wire rope, for example, 108, configured on spool assembly 104 on one end of the sector 128 is reeled-in on the first pulley 112. Accordingly, the portion of beam 124 on the side of the spool assembly 104 is pulled towards the first pulley 112.
In the unwinding cycle, the second wire rope 120 is unwound on the first pulley 112, simultaneously, while wire rope 108 is being wound on the first pulley 112 during the winding cycle. The second wire rope 120 is configured to be unwound or reeled-out on the first pulley 112 simultaneously while wire rope 108 is being reeled-in on the first pulley 112. The second end or wire rope 120 is configured on the spool assembly 116 on the second end of beam 124 of sector 128.
Thus, this winding and unwinding of the wire ropes 108 and 120 during, the winding and unwinding cycles of the driver 500 causes one spool assembly 104 to be pulled in while the other spool assembly 116 is moved in the opposite direction. This results in a driving moment to be applied to the beam 124 which in turn transfers this driving moment to the clamp 136 thereby resulting rotation of the module 600 of the tracker.
The driving moment in clamp 136, results in rotation of the torque tube 132 about its own longitudinal axis, as clamp 136 is fixed to torque tube 132, and no relative motion is possible in between clamp 136 and torque tube 132. Further, the torque tube 132 rotates the modules as they are firmly connected the torque tube 132.
The operation of the damping apparatus 100 while wind induced moment is exerted on module 600 is discussed. The eccentric or unbalanced forces tend to rotate the tracker about the torque tube 132. It is understood that when a flat plate structure, for example, the PV solar module 600 mounted on the torque tube 132 and when tracker is subjected to wind flow across the tracker, unbalanced forces are developed by fluid-structure interaction between body of the module 600 and wind in motion. This causes moment ‘M’ to be generated about the longitudinal axis of the torque tube 132.
The wind tends to rotate the tracker about the longitudinal axis of the torque tube 132. This torsion is transferred to sector 128 via the sector clamp 136. The clamp 136 applies a force couple to the beam 124 via the connection of the swivel pins 140. The beam 124 then in turn tries to rotate to sector 128 about the longitudinal axis of the torque tube 132. Thus, one end of the beam 124 tries to move upward and the other downward due to this force couple or moment.
The driving pulley 112 is advantageously rotationally locked by worm gear box 156 whenever wind induced moment ‘M’ is observed in the tracker. During the attempted rotation of the sector 128, one wire rope 108 experiences an increase in tension, and the other wire rope 120 a decrease in tension.
This phenomenon is observed because the second end of the wire ropes 108, 120 are wound and stay locked on the driving pulley 112. When there is wind induced moment ‘M’ (Ref. FIG. 6A), the spring 304 of the first spool assembly 104 compresses due to the rotation of the torque tube 132 about its longitudinal axis, and at the same time the spring of the second spool assembly 116 expands. The expanded spring of the tensioner unit 222 of the second spool assembly 116 maintains tension in the wire rope 120, however, of a lower value relative to the tension in the first wire rope 108.
As described above, the wire rope 108 experiences an increase in tension when the wind tries to rotate the tracker. This increased tension tries to compress the spring 304, but this compression is restricted until the stopper 320 is touching the member 300 and beam 124. The stopper 320 limits the compression of the spring 304. This clockwise and anti-clockwise nature of the winding of the wire ropes 108 and 120 on the driving pulley 112 leads to a couple on the driving pulley 112, and and this couple attempts to rotate the first pulley 112 which in turn imposes torque on the worm gear box 156. Accordingly, the self-locking worm gear box 156 stops the first pulley 112 from rotating and advantageously locks the tracker.
The damping effect is advantageously generated by the friction damping apparatus 100 of the present invention by the rubbing action between the first wire rope 108 and the second wire rope 120 under tension, and the arcuate groove 144 of the sector 128 during the oscillatory motion of the tracker. The oscillatory motion of the tracker generates angular oscillatory displacement of the cantilevers 204 of respective spool assemblies 104, 116 leading to the rubbing action between the wire ropes 108, 120 and the arcuate grooves 144 of the sector 128 in order to provide friction damping to the tracker.
The foregoing description of specific embodiments of the present invention has been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the present invention to the precise forms disclosed, and obviously many modifications and variations are possible in light of the above teaching.
The embodiments were chosen and described in order to best explain the principles of the present invention and its practical application, to thereby enable others, skilled in the art to best utilize the present invention and various embodiments with various modifications as are suited to the particular use contemplated. It is understood that various omission and substitutions of equivalents are contemplated as circumstance may suggest or render expedient, but such are intended to cover the application or implementation without departing from the scope of the present invention.
, Claims:Claims:
We claim:
1. A friction damping apparatus for solar tracker 100 for providing damping to the solar tracker comprising:
a first anchor assembly 104 and a second anchor assembly 116 opposedly positioned on a beam 124 of a sector 128;
a first wire rope 108 connecting the first spool assembly 104 with the first pulley 112, wherein the first wire rope 108 running through groove 144 along circumference of a first arcuate portion the sector 128 making a tangential contact,
a second wire rope 120 connecting the second spool assembly 116 with the first pulley 112, wherein the wire rope120 running through groove 144 along circumference of a second arcuate portion the sector 128 making a tangential contact;
a tensioner unit 222 being positioned below the cantilever 204 to develop tension in respective wire ropes 108, 120;
a driver 500, the driver 500 including the first pulley 112, a shaft 148, and worm gear box 156 wherein the first pulley 112 being lockable during wind induced motion by the worm gear box 156;
a rubbing action between the first wire rope 108, the second wire rope 120, and the arcuate groove 144 of the sector 128 during the oscillatory motion of the tracker generating frictional damping effect for the tracker; and
a winding cycle, rotating the first pulley 112 to wind the first wire rope 108, and simultaneously unwinding the second wire rope 120 during the unwinding cycle of the second wire rope 120 for driving the tracker.
2. The friction damping apparatus of claim 1, wherein a first end of the first wire rope 108 being connected to the first spool assembly 104, and a second end of wire rope 108 being connected to the first pulley 112.

3. The friction damping apparatus of claim 1, wherein a first end of the second wire rope 120 being connected to the second spool assembly 116, and a second end of the wire rope 120 being connected to the first pulley 112.

4. The friction damping apparatus of claim 1, wherein the sector 128 having a first arcuate portion, and second arcuate portion, both including an arcuate groove 144 including a receptacle receiving respective wire ropes 108, 120 running along respective arcuate portions of the sector 128.

5. The friction damping apparatus of claim 1, wherein the first wire rope 108 is wound in a clockwise direction and anchored on the driving pulley 112, and the second wire rope 120 is wound in anticlockwise direction and anchored on the driving pulley 112 simultaneously.
6. The friction damping apparatus of claim 1, wherein the first pulley 112 allowing both first and second wire ropes 108 and 120 to be alternately reeled in and out with the rotation of the worm gear box 156 while driving the tracker.

7. The friction damping apparatus of claim 1, wherein the first spool assembly 104 including a second pulley 200 freely rotatably positioned at the movable end of the cantilever 204.

8. The friction damping apparatus of claim 1, wherein the cantilever 204 including a pair of parallel members 204 and 204’ mounted on the first beam 124, the cantilever including a first end being hinged on a pair of parallel plates 208, 208’, and the other movable end including the second pulley 200.

9. The friction damping apparatus of claim 1, wherein the second pulley 200 is rotatably positioned on the open end of the cantilever 204 by a bolt or pin 212, and the other end of the cantilever 204 is pinned in the parallel plates 208, 208’ by a hinge joint 216 defined by a bolt or a pin.

10. The friction damping apparatus of claim 1, wherein the tensioner unit 222 including the cantilever 204, a base member 300, a spring 304, a stopper 320, a nut 312 and a bolt 316, the tensioner unit 222 developing tension in the respective wire ropes 108, and 120, whereas the anchor 220 holding the respective wire ropes without any slip.

11. The friction damping apparatus of claim 1, wherein the base member 300, and the stopper 320 being positioned on the beam 124 avoiding compression of the spring 304 beyond a predefined limit.

12. The friction damping apparatus of claim 1, wherein the cantilever 204 having at least three positions including a first position being a primary position wherein the cantilever 204 is approximately parallel to the beam 124, a second position wherein the cantilever 204 is located at a lowest point relative to the first position, and a third position wherein the cantilever 204 is located at the highest point relative to the first position.

13. The friction damping apparatus of claim 12, wherein the cantilever 204 oscillating between the second position and the third position such that the second pulley 200 being rotated about the pin joint 212.

14. The friction damping apparatus of claim 1, wherein the cantilever 204 oscillating against the spring 304 keeping the first wire rope 108 under tension in all positions of the cantilever 204.
15. The friction damping apparatus of claim 1, wherein the cantilever 204 being defined by an envelope 804 including a pair of approximately identical vertical plates 900 being connected by a top horizontal plate 904.

Dated this 11th day of June 2022
For, SCORPIUS TRACKERS PRIVATE LIMITED,

Mahurkar Anand
IN/PA-1862
(Agent for Applicant)