WO2009141468A1 - Actuation device enabling the relative rotation of structures and a solar tracker - Google Patents

Abstract

The invention relates to a device including: a drive pulley (1) mounted on a shaft (3) supported by a first structure (30) and actuated by a motor (5), a driven pulley (2) secured to a second structure (40) and mounted coaxially in relation to a reference axle (4a) enabling relative rotation between the first and second structures (30, 40), and a cable (6) disposed around part of the drive and driven pulleys (1, 2). The cable (6) surrounds the drive pulley (1) at an angle greater than 180° and less than 360°, and two segments (6a, 6b) of the cable (6) intersect between the drive pulley (1) and the driven pulley (2). The axis (3a) of the shaft (3) of the drive pulley (1) is sufficiently inclined in relation to the reference axis (4a) such that said two segments (6a, 6b) of the cable (6) do not come into contact at the intersection point.

Description

 DRIVING DEVICE FOR RELATIVE TURN OF STRUCTURES. Y

SOLAR TRACKER

Field of the technique The present invention concerns an actuation device for relative rotation of structures, applicable to apparatus provided with relatively bulky structures and provided with relative rotation, such as solar trackers, wind generators, construction cranes or other types, mooring or anchor windlass and net drums for boats, etc. The present invention also concerns a solar tracker provided with such a drive device.

Background of the invention

In many devices there is a need to rotate a structure, relatively bulky and heavy, with respect to another, either in turn portions lower than one full turn in opposite directions or in consecutive full turns in either of the two directions, at a speed relatively low and with high torque. The rotation of such structures requires drive devices that are simple, robust, economical and easy to maintain. In addition, many of the devices of this type, such as solar trackers, wind generators, construction or other cranes, mooring or anchor windlass and net drums for boats, etc., are installed to operate outdoors , and therefore require drive devices that are resistant to atmospheric agents, sunlight, and little sensitive to dust and dirt.

Patent application US-A-2007/0034205 discloses a drive device for a solar tracker structure, where a parabolic solar reflector is installed on a first structure arranged to rotate around a first vertical axis with respect to a second structure fixed to the ground. The first structure has a large coaxial diameter drum with said first axis and the second structure has a support on which a small diameter drum is installed that rotates around a second axis parallel to the first axis and driven by a motor. An endless cable is wound more than one turn on the large diameter drum and several turns on the small diameter drum, and has a crossing point between the two drums. The various turns of the cable on the drums ensure greater static friction or adhesion and therefore better traction. However, a drawback of this construction is that the winding of the cable both on the large diameter drum and on the small diameter drum is necessarily helical, and this causes a displacement of the cable in the axial direction of the drums as they rotate. The axial direction of the displacement of the helical winding will depend on the direction of rotation of the drum and the direction of the propeller. Consequently, if the drums rotate consecutive full turns in one direction or another the cable could escape the drums. In addition, for the same propeller passage, the axial displacement speed of the cable will be greater in the small diameter drum than in the large diameter drum, so that, with relatively high transmission ratios, the differences in axial displacement speeds in both drums they can cause undesired tension in the cables with risk of damage to the cable and / or the drums. The different speeds of axial displacement can be compensated with different propeller passages, but in this case the axial dimension required for both drums increases considerably and this makes it practically unfeasible to use multiple cables with the same pair of small and large diameter drums. Patent GB-A-1121220 describes a rope and pulley system for an elevator with a noise damping device and improved traction. Each pulley defines at its edge a channel in which a strip of elastomeric material is inserted that defines a circular groove configured to support the rope and prevent the rope from touching other parts of the pulley while passing over it. For this, the circular groove has a cross-section in the form of half a circle. In the circular groove, contact areas with the rope are formed separated by transverse holes to improve the tensile stress. From the outer ends of the channel of the pulley, lips that inwardly secure the strip of elastomeric material within the channel extend inwards. However, said contact areas separated by transverse holes may be insufficient to ensure high static friction or adhesion and a high degree of traction between the rope or a cable and the pulley when the rope or cable embraces an angle less than 360 ° of The pulley. On the other hand, obtaining the strip of elastomeric material with the longitudinal groove and the transverse holes can be excessively laborious. The GB-A-1294524 patent discloses an annular insert of elastomeric material to cover a channel of a pulley on which a metal wire cable is supported without any traction between the cable and the pulley, in order to reduce noise and Protect the cable. The annular insert has in its circular periphery a groove to support the cable and a plurality of transverse grooves distributed along the circumference. In an alternative embodiment, the annular insert is formed by a plurality of separate plugs of elastomeric material fixed to the bottom of the channel of the Ia pulley for dovetail-shaped lace. In another alternative embodiment, the annular insert is formed by several narrow rings of elastomeric materials of different adjacent hardnesses in the axial direction. In any case, the circular groove has a cross-section in the form of half a circle or less than a half circle.

The international patent application WO-A-99/53223 discloses a pulley that has a circumferential channel within which a sandwich configuration band composed of three concentric layers in the radial direction is arranged, where the inner layer, which It is closer to the center, and the outer layer, which is further away from the center and supports a cable, is made of elastomeric materials of different characteristics, and the intermediate layer is made of a material that provides rigidity to the whole. The outer layer is of greater hardness than the inner layer in order to create a surface of high resistance to abrasion on which the cable runs, and defines a circular groove of cross section in the form of a portion of circumference substantially less than average circumference. The outer layer has no other configuration aimed at providing an increase in static friction and greater traction between the cable and the pulley.

Document DE-A-10014903 describes a drive for an elevator that includes a pulley driven around which a textile cable is guided several times each time hugging an angle greater than 180 ° and less than 360 °. To this end, the driven pulley has several parallel circular grooves on its edge and a guide pulley, which is smaller in diameter than the driven pulley and has its axis of rotation inclined with respect to the axis of rotation of the driven pulley, is arranged to forward the cable from one of said circular grooves to another. The guide pulley is not a driving pulley and the cable has no cross portions between the guide pulley and the driven pulley, so that the cable hugs the guide pulley at an angle less than 180 °. The driven pulley has a metal core covered by a ring of elastomeric material that forms the parallel circular grooves to provide a high degree of static friction between the cable and the pulley. However, the circular grooves are of approximately semicircular cross-section and the elastomeric material ring has no other configuration aimed at providing an increase in static friction and greater traction between the cable and the pulley.

Pulleys for belts of trapecial cross-section are well known in the market, in which the circular groove supporting the belt comprises a mouth, a bottom, and a pair of opposite inclined surfaces that converge towards the bottom such that the V-belt tends to "get stuck" by wedge effect on the groove of the pulley providing a high degree of static friction and a great traction capacity between the belt and the pulley. However, pulleys with circular groove of trapezoidal cross-section are not known to support and / or pull cables such as twisted filament metallic cables or textile cables, the metallic cables being much more resistant and less elastic than the trapecial belts for an area of equivalent cross section.

GB-A-106658 discloses a planetarium composed of several spheres connected to a driven mechanism to provide a predetermined relative movement between the spheres. The mechanism includes several transmissions by endless cable and pulleys. At least one of the pulleys is diametrically divided into two halves so that it can be expanded to allow a fine adjustment of the transmission ratio. One of the halves is fixed to the hub while the other can be displaced by means of a screw to bring it closer or away from the other. Once in the desired position, the movable half can be immobilized by means of a fixing screw.

Exhibition of the invention

According to a first aspect, the present invention provides a drive device for relative rotation of structures, applicable to solar trackers, wind generators, cranes for construction or other types, mooring or anchor windlass and net drums for boats, between others, which have in common relatively voluminous structures endowed with relative rotation at relatively low speed. The device comprises a driving pulley associated with a first structure and mounted on a shaft driven by a motor, a driven pulley associated with a second structure and coaxially mounted with respect to a reference axis, and at least one flexible traction member arranged around at least part of said drive and driven pulleys. The device is characterized by the following combination of features: the shaft on which said drive pulley is mounted is supported on said first structure; said driven pulley is fixed to said second structure; the reference axis with respect to which the driven pulley is coaxially mounted is a relative axis of rotation between the first and second structures; said flexible traction member embraces the drive pulley by an angle greater than 180 ° and less than 360 °; two sections of said flexible traction member intersect at a crossing point between the driving pulley and the driven pulley; Y The axle bearing shaft of the driving pulley has an axis that is inclined with respect to the reference axis at a sufficient angle so that said two sections of the flexible traction member do not touch each other at said crossing point.

Preferably the drive pulley, and more preferably both driven and driven pulleys have a perimetric coating of an elastomeric material that improves the coefficient of static friction between the flexible traction member and the pulleys. Preferably, the flexible traction member is a cable and said perimetric coating of elastomeric pulley material defines at least one coaxial throat with the respective axes, formed at the peripheral edge of each pulley. Each of said throats comprises a mouth, a bottom, and a pair of opposite inclined surfaces that converge in a radial direction from said mouth to said bottom. These opposite inclined surfaces are configured to act as a wedge to allow a predetermined degree of cable interlock in the throats and ensure a predetermined degree of static friction or adhesion between the cable and the driven and driven pulleys.

donde:In an alternative embodiment, the cable used has a coating of elastomeric material, and the drive pulley, or both driven and driven pulleys have at least one peripheral region of a rigid material that defines respective throats with a mouth, a bottom, and a pair of opposite inclined surfaces that converge in a radial direction from said mouth to said bottom. These opposite inclined surfaces are configured to act as a wedge to allow a predetermined degree of interlocking of the cable in the throats and ensure a predetermined degree of static friction or adhesion between the coating of elastomeric material of the cable and the driven and driven pulleys. It is known that the efficiency of a drive device by flexible traction member and pulley depends on the angle of the pulley embraced by the flexible traction member and the coefficient of static friction between the flexible traction member and the pulley, according to the following equation:

where:

F is the useful tensile force, that is, the tensile force exerted by the portion of the more tensile flexible member (not supported by the pulley), which performs the work;

F ₁ is the tensile force of the portion of the flexible traction member (not supported by the pulley) less tense, which does not perform the work; θ is the angle of the pulley embraced by the flexible traction member; Y μ is the coefficient of static friction between the flexible traction member and the pulley

It will be observed that the useful tensile force F increases exponentially with the embraced angle θ and with the coefficient of static friction μ. Thus, in the device of the present invention, the fact that the two sections more tense and less tense of the cable intersect between the driving pulley and the driven pulley allows substantially increasing the angle θ of the driving pulley embraced by the cable to values greater than 180 °, which can be, for example, around 300 ° with high transmission ratios, and the fact that the throats of both pulleys are formed in respective elastomeric material coatings and configured in wedge, or the construction Inverse, in which the wedge throats are made of a rigid material and the cable has a coating of elastomeric material, it provides a very high static friction coefficient μ between the cable and the pulley, which gives the cable a very high tensile force. in comparison with known devices without crossing point and pulleys without coating of elastomeric material and / or without throat configured in wedge. The fact of arranging the axle of the driven pulley with respect to the reference axis, that is to say, the axis of the driven pulley, allows to cross the two sections of the cable between the driving pulley and the driven pulley without touching, avoiding with it a deterioration of the cable, particularly if it is a braided or textile cable, and friction losses. Since the gauge of the cable can be comparatively small in relation to the diameters of the two pulleys, and the diameter of the drive pulley can be comparatively small in relation to the diameter of the driven pulley, a relatively small angle of inclination is sufficient to ensure that the cable portions are sufficiently separated at the crossing point. In addition, the fact that for a cable a single throat is required in each pulley makes the axial dimension of the pulleys very small compared, for example, with the drums of the drive device described in the cited US patent application. A-2007/0034205, which allows the use of multiple parallel cables with a single set of pulleys provided with multiple throats. In an exemplary embodiment, the cable is an endless cable (that is, forming a closed loop) of a predetermined length, whereby the cable also embraces the pulley driven by an angle greater than 180 ° and less than 360 ° and the mentioned relative rotation between the first and second structures admit consecutive complete turns in either of both directions. In this case, the driven pulley can be optionally divided diametrically into two halves installed on the second structure so that the two halves can be guided in a guided manner. with respect to the other in opposite directions in order to bring them mutually sufficient distance to allow the installation of the cable around the driven and driven pulleys, and then mutually move them a sufficient distance to provide a desired tension to the cable. In another example of embodiment, the cable is a finite cable of a predetermined length with two ends fixed to the driven pulley or to the second structure, whereby the relative rotation between the first structure and the second structure admits only turn portions less than a complete turn in either direction. In this case, the driven pulley can be a pulley sector with a throat sector comprising only a portion of circumference less than a complete circumference. Said pulley sector can be fixedly installed with respect to the second structure with its corresponding throat sector coaxial with the reference axis. In any case, when the cable has two ends, at least one of said two ends is preferably fixed to the driven pulley or to the second structure by means of an adjustable tensioning device or calibrated to provide a desired tension to the cable.

In any of the exemplary embodiments, the respective perimetric coatings of elastomeric material of the driven and driven pulleys may have formed several of the parallel throats, which allows several of said cables to be arranged around the driven and driven pulleys so that Each cable is coupled to one of the throats of the drive pulley and one of the throats of the driven pulley. This multiplies the traction capacity between the driving pulley and the driven pulley.

Optionally, the device includes a torque limiting device disposed between the drive pulley and the shaft to protect the cables, pulleys and overload structures. according to a second aspect, the present invention provides a solar tracker equipped with one or more drive devices according to the first aspect of the present invention.

Brief description of the drawings

The foregoing and other features and advantages will be more fully understood from the following detailed description of some embodiments with reference to the accompanying drawings, in which: Fig. 1 is a bottom plan view of a drive device for relative rotation of structures according to a first generic embodiment of the present invention;

Fig. 2 is a side elevation view of the device of Fig. 1; Fig. 3 is a profile view of the device of Fig. 1;

Fig. 4 is a side elevational view of a drive device for relative rotation of structures according to a second generic embodiment of the present invention;

Fig. 5 is a cross-sectional view of a driving pulley according to another alternative embodiment;

Fig. 6 is a cross-sectional view of a pulley driven in accordance with said alternative embodiment; Figs. 7A and 7B are enlarged details of one of the throats of the driving pulley of Fig. 5 with a cable in a low voltage and high tension arrangement, respectively, with the understanding that the details of Figs. 7A and 7B are also applicable for the driven pulley of Fig. 6;

Fig. 8 is an enlarged detail illustrating one of the throats of a drive pulley with a cable according to an alternative embodiment, with the understanding that the detail of Fig. 8 is also applicable for a driven pulley ;

Fig. Θ is a cross-sectional view of a driving pulley associated with a torque limiting device;

Fig. 10 is a rear perspective view of a solar tracker to which another embodiment of the drive device of the present invention is applied;

Fig. 11 is the detail Xl of the enlarged Fig. 10;

Fig. 12 is an enlarged bottom perspective view of the same area shown in the detail of Fig. 11;

Fig. 13 is a schematic representation of the driving pulley, the driven pulley and the cable of the device of the present invention according to the example of embodiment applied to the solar tracker of Fig. 10, where the driven pulley is divided into two halves, in an installation position; Y

Fig. 14 is a schematic representation of the driving pulley, the driven pulley and the cable of the additional embodiment example in a working position.

Detailed description of some embodiments Referring firstly to Figs. 1 to 3, the drive device for relative rotation of structures of the present invention comprises, according to a first example of generic embodiment, a driving pulley 1 associated with a first structure 30 and a driven pulley 2 associated with a second structure 40 The first and second structures 30, 40 are provided with relative rotation around a coaxial rod 4 with a reference axis 4a. Said drive pulley 1 is mounted to rotate together with a shaft 3 driven by a motor 5 (Figs. 2 and 3), and this shaft 3 on which the drive pulley 1 is mounted is supported on the first structure 30. The pulley driven 2 is fixed to the second structure 40 coaxially with respect to said reference axis 4a. A flexible tensile member, such as a metallic cable 6 of twisted filaments or a textile cable, is arranged around part of said drive and driven pulleys 1, 2. Said cable 6 is an endless cable of a predetermined length and has two sections 6a, 6b (Fig. 1) that intersect at a crossing point between the driving pulley 1 and the driven pulley 2. Consequently, the cable 6 embraces both the driving pulley 1 and the driven pulley 2 on respective angles comprised between 180 ° and 360 °, and in addition the aforementioned relative rotation between the first and second structures 30, 40 admits consecutive complete turns in either of both directions.

As best shown in Fig. 3, the axis 3a of the shaft 3, that is, the axis of the drive pulley 1, is inclined with respect to the reference axis 4a, that is, the axis of the driven pulley 2, a angle α sufficient to ensure that said two sections 6a, 6b of the cable 6 do not touch each other at said crossing point.

In Fig. 4 a driving device for relative rotation of structures according to a second generic embodiment of the present invention is shown, which is of inverse construction with respect to the first embodiment. In Figs. 1 to 3, the first structure 30 could be, for example, a rotating support and the second structure 40 could be, for example, a base structure fixed to the ground, in which case the motor 5, the shaft 3 and the driving pulley 1 they would rotate together with the first structure 30 around the driven pulley 2, which would be stationary. In the second embodiment of Fig. 4, the first structure 30 could be the base structure fixed to the ground and the second structure 40 a rotating support, in which case, the motor 5, the shaft 3 and the driving pulley 1 would remain stationary installed on a support 17 fixed to the first structure 30, and the driven pulley 2 would rotate together with the second structure 40 with respect to the first stationary structure 30. Exemplary embodiments are also possible in which both the first structure 30 and the second structure 40 are provided with relative turning capacity with respect to the ground in addition to relative turning capacity between them, although in any case the generic conditions described in relation to Figs. 1 to 4

In relation to Figs. 5 to 8, the construction of the driving and driven pulleys 1, 2 is described below. The driving pulley 1, shown in Fig. 5, comprises a rigid core 12, for example, of a metallic material, which has a central hole 19 and a perimeter edge 20 coaxial with the axis 3a. The central hole 19 is configured to receive the shaft 3, and fixing means (such as, for example, a cotter device not shown) are arranged to rigidly fix the drive pulley 1 to the shaft 3. On the perimeter edge 19 is provided a perimeter covering 7 of an elastomeric material defining a number of parallel throats 8, coaxial with said shaft 3a of the shaft 3. Given the relatively small diameter of the drive pulley 1, the perimeter coating 7 can be obtained by molding or machining , or by a combination of both procedures.

The driven pulley 2, shown in Fig. 6, also comprises a rigid base body 13, for example, of a metallic material, which has an inner portion provided with several holes 18 to allow the fixing of the driven pulley 2 to the second structure, for example, by means of rollers, and a perimeter edge 21 coaxial with the axis 4a. On this perimeter edge 21 there is also a perimetric coating 9 of an elastomeric material defining a number of parallel throats 10, coaxial with said axis 4a. Due to the relatively large diameter of the driven pulley 2, the perimetric coating 9 will be obtained in this case preferably from an extruded or machined strip, cut to size and applied on the perimeter edge 21. Alternatively, perimeter coating 9 of the pulley Conducted 2 can also be obtained by molding. Among the materials suitable for perimetric coatings 7, 9 are, for example, polyurethane, rubber, and in general any elastomer that provides the required mechanical properties, and perimeter coatings 7, 9 can be adhered respectively to the core 12 of The driving pulley 1 and the base body 13 of the driven pulley 2 by means of an adhesive. The number, configuration and arrangement of the throats 8 in the driving pulley 1 is equal to the number, configuration and arrangement of the throats 10 in the driven pulley 2, so that several identical, independent endless cables 6 can be arranged around the driven and driven pulleys 1, 2, with each cable 6 coupled to one of the throats 8 of the driving pulley 1 and one of the throats 10 of the driven pulley 2 to multiply the traction capacity. Thus, the number of throats on both pulleys will be determined by the needs of each application, and it will be understood that at least one throat in each pulley is within the scope of the present invention.

With reference to Figs. 7A and 7B now describe the configuration of the throats δ of the driving pulley 1. Each of said throats 8 comprises a mouth, a bottom δc, and a pair of opposite inclined surfaces 8a, 8b that converge in a radial direction from said mouth to the mentioned bottom 8c. These opposite inclined surfaces 8a, 8b are substantially flat and form an acute angle selected to act as a wedge in order to allow, in cooperation with a certain deformation of the elastomeric material from which the perimeter coating 7 is made, a predetermined degree of interlocking the cable 6 in the throat 8 and ensuring a predetermined degree of static friction between the cable 6 and the driving pulley 1. The interlocking degree of the cable 6 in the throat 8 will depend essentially on the tension of the cable 6. Thus, the Cable 6 can be installed with a predetermined tension that at rest, or working with low traction, will produce only a slight interlocking of cable 6 in the δ throat (Fig. 7A). When there is an increase in tensile requirements, the tension of the cable 6 increases and the cable 6 locks deeper into the throat δ (Fig. 7B), so that the static friction between the cable and the driving pulley increases. Optionally, the configuration of the throat δ can be selected in accordance with the maximum efforts envisaged so that the cable 6 comes to rest on the bottom δc of the throat 8, in which case it would be advantageous if the bottom δc of the throat had a approximately semicircular cross-sectional shape to provide the greatest possible static friction.

The throats 10 of the driven pulley 2 are identical to the throats δ of the driving pulley 1, so that their description will be omitted and all the characteristics of the throats 8 of the driving pulley 1 will be applicable to the throats 10 of the pulley driven.

In Fig. Δ an alternative embodiment example is shown, where the cable 6 carries a coating of elastomeric material 37 and where at least one perimeter region of the driving pulley 1 is of a rigid material, such as steel, and defines one or more throats 38 coaxial with the axis 3a of the shaft 3. Each throat 38 comprises a mouth, a bottom 3δc, and a pair of opposite inclined surfaces 3δa, 3δb that converge in a radial direction from said mouth to said bottom 38c. In a manner analogous to that described above in relation to Figs. 7A and 7B, the opposite inclined surfaces 38a, 38b are configured to act as a wedge in order to allow a predetermined degree of interlocking of cable 6 in Ia throat 38, but here in cooperation with a certain deformation of said elastomeric material coating 37 of the cable 6. This ensures a predetermined coefficient of static friction or adhesion between the cable 6 and the drive pulley 1. In this alternative embodiment, the Throats of the driven pulley 2 are also identical to the throats 38 of the driving pulley 1, so that their description will be omitted.

As shown in Fig. 9, in certain applications it may be convenient to provide a torque limiting device 11 between the driving pulley 1 and the shaft 3 in order to protect the driving pulley 1, the cable 6, the motor 5, and in general an associated reduction transmission of overloads. In the exemplary embodiment illustrated in Fig. 9, the core 12 of the drive pulley is mounted so that it can rotate on the shaft 3 thanks to a sliding bearing 22. The core 12 forms a cavity around a portion of the shaft 3 and within this cavity a plurality of alternating friction discs 15a, 15b are installed, which are integral with the rotation of the core 12 and with the rotation of the shaft 3, respectively, by means of cotter devices or the like. The friction discs 15a, 15b are axially compressed by a screw 16 in cooperation with one or more discoidal springs 14. It will be understood, however, that according to the present invention any other type of torque limiter is applicable as long as it allows a relative rotation of the driving pulley 1 with respect to the shaft 3 when a predetermined upper torque threshold is exceeded.

In Fig. 10 a solar tracker is shown comprising several structures provided with relative turning capacity, which are actuated by the drive device of the present invention. The solar tracker comprises a column 23 with a base 24 configured to be fixed to the ground. On a top end of the column 23 there is mounted a rotating support 24 that can rotate about a vertical axis V. On the rotating support 24 a tilting frame 25 is mounted so that it can pivot about a horizontal axis H. The tilting frame 25 supports a solar energy sensing device composed, for example, of a plurality of photovoltaic panels 26. A first drive device according to the present invention is arranged to drive turns of the rotating support 24 around the vertical axis V with respect to the column 23, which is stationary, to effect an azimuthal orientation of the photovoltaic panels 26. A second drive device according to the present invention is arranged to drive turns of the pivoting frame 25 around the horizontal axis H with respect to the rotating support 24, the which can be in any angular position with respect to column 23, to perform an overhead orientation of the photovoltaic panels 26.

In relation to Figs. 11 and 12 the implementation of said first and second drive devices in the solar tracker is described in detail. With respect to the first drive device, the rotating support 24 of the solar tracker corresponds to the first structure 30 described above in relation to the first and second embodiments of Figs. 1 to 4, column 23 of the solar tracker corresponds to the second structure 40 of Figs. 1 to 4, and the vertical axis V of the solar tracker corresponds to the reference axis 4a of Figs. 1 to 4. The other elements of the first drive device maintain the same numerical references. In the solar tracker, the rotating support 24 carries a first inclined plate 28 on which an actuating group comprising the motor 5 and a gear reducer 27 that drives the shaft 3 to which the driving pulley 1 is coupled by means is installed of the torque limiter 11. The inclination of the first inclined plate 28 provides the angle α (Fig. 3) of inclination of the axis 3a of the shaft 3 with respect to the vertical axis V (corresponding to the reference axis 4a of Figs. 1 to 4 ). The driven pulley 2 is fixed to the column 23 coaxially with the vertical axis V.

As best shown in Figs. 13 and 14, in the solar tracker, the driven pulley 2 is diametrically divided into two halves 2a, 2b installed on the column 23 (corresponding to the second structure 40 of Figs. 1 to 4) so that they can be displaced so guided one relative to the other in opposite directions in order to bring them mutually sufficient distance to allow the installation of the cable 6 around the driven and driven pulleys 1, 2 (Fig. 13), and mutually move them a distance sufficient to provide a desired voltage to cable 6 (Fig. 14). Thus, the driven pulley 2 has the ability to contract and expand to a limited extent. For this, the column 23 is of square cross-section and each of the halves 2a, 2b of the driven pulley 2 has a cutout 29a, 29b forming edges adjusted to lateral walls of the column 23 so that said cutout 29a, 29b cooperates with column 23 in guiding the movements of the corresponding half 2a, 2b of the driven pulley 2. In each half 2a, 2b of the driven pulley 2 a block 32 is provided provided with a threaded hole in which it is coupled a screw 33 arranged to interfere with a stop 34 fixed to a fixing plate 31 attached to the column 23 (see also Fig. 12). The screws 33 can be operated to carry out the aforementioned movements of approach and / or mutual separation of the two halves 2a, 2b of the driven pulley 2, thus acting as a means of regulation. Reversible fixing means, such as logs passed through holes 35 provided in halves 2a, 2b of the driven pulley 2 and corresponding elongated holes provided in the fixing plate 31, can be operated to fix the corresponding half 2a, 2b of the driven pulley 2 with respect to Ia column 23 (corresponding to the second structure 40 of Figs. 1 to 4) in a selected position. Alternatively, other guiding means can be used other than the mentioned cuts in cooperation with the square section of the column. For example, the aforementioned elongated holes of the fixing plate 31, or other similar configurations, can serve as guide means for the movements of the two halves 2a, 2b of the driven pulley 2. The driving pulley 1 and the two halves 2a , 2b of the driven pulley 2 include respective perimetric coatings 7, 9a, 9b (analogous to the perimeter coatings 7, 9 shown in Figs. 5 to 9), each of which defines several throats 8, 10. Several cables 6 auger, of a predetermined length, are installed around the driving and driven pulleys 1, 2, with sections 6a, 6b of the cable 6 crossing at a crossing point between the driving pulley 1 and the driven pulley 2 (Fig. 14) , so that said relative rotation between the rotating support 24 and the column 23 around the vertical axis H admits consecutive complete turns in either of both directions. Alternatively, if complete turns are not necessary, the cable 6 could be a finite cable of a predetermined length with two ends fixed to the driven pulley 2 itself or to the column 23 (corresponding to the second structure 40 in Figs. 1 4), so that the relative rotation between the rotating support 24 and the column 23 around the vertical axis H would admit only lower turn portions to a complete turn in either of both directions. In a variant not shown in the embodiment shown in Figs. 13 and 14, only one of said halves 2a, 2b of the driven pulley 2 is mobile while the other is stationary and is fixedly attached to column 23. In any case, the effects of the slight eccentricity of the driven pulley 2 and / or the small variation in the speed ratio between the driving pulley 1 and the driven pulley 2 caused by the expansion of the two halves 2a, 2b of the driven pulley 2 can be easily corrected by controlling the motor 5 by means of electronic control means including an encoder or the like, which are usually part of the equipment of any solar tracker. In other applications, such as cranes or mooring winches, the aforementioned effects are irrelevant and electronic control means may be omitted. Alternatively, in the first driving device of the solar tracker, the driven pulley 2 could be integral and the desired tension in the cables could be achieved by incorporating a tensioning device of a known or other type that could occur to a person skilled in the art.

With respect to the second drive device, the rotating support 24 of the solar tracker corresponds to the first structure 30 described above in relation to the first and second embodiments of Figs. 1 to 4, the pivoting frame 25 of the solar tracker corresponds to the second structure 40 of Figs. 1 to 4, and the horizontal axis H of the solar tracker corresponds to the reference axis 4a of Figs. 1 to 4. The other elements of the second drive device maintain the same numerical references. In the solar tracker, the rotating support 24 carries a second inclined plate 36 on which an actuating group comprising the motor and a gear reducer (not shown) that drives the shaft 3 to which the driving pulley 1 is coupled is installed by means of the torque limiter 11. The inclination of the second inclined plate 36 provides the angle α (Fig. 3) of inclination of the axis 3a of the shaft 3 with respect to the horizontal axis H (corresponding to the reference axis 4a of Figs. 1 to 4). The driven pulley 2 is fixed to the pivoting frame 25a coaxially with the horizontal axis H. However, in this second driving device of the solar tracker, the driven pulley 2 is a pulley sector that covers only a portion of circumference less than a circumference complete.

In this second drive device, the drive pulley 1 and the driven pulley sector 2 include respective perimetric coatings (analogous to the perimeter coatings 7, 9 shown in Figs. 5 to 9), each of which defines several throats. The cables 6 are here finite cables of a predetermined length with two ends fixed on opposite sides of the driven pulley sector 2 or the pivoting frame 25, whereby the relative rotation between pivoting frame 25 and the rotating support 24 around the horizontal axis H admits only lower portions of a turn in one of both directions, which in this case is not an inconvenience since the rotation of the pivoting frame 25 is also limited by interference with the column 23. The various cables 6 are installed around the driven and driven pulleys 1, 2, with sections 6a, 6b of the cable 6 crossing at a crossing point between the driving pulley 1 and the driven pulley 2. To provide the required tension to the cables, at least one of the ends of each cable 6 is fixed to the driven pulley 2 or to the second structure 40 by means of a tensioning device (not shown), such as a tension spring or the like r.

The second aspect of the present invention contemplates that the first and second driving devices of the solar tracker are in accordance with other variants of the driving device of the first aspect of the present invention, or that only the first drive device or only the second drive device of the solar tracker are in accordance with any of the variants of the drive device of the first aspect of the present invention.

One skilled in the art will be able to make modifications and variations from the examples of embodiment shown and described without departing from the scope of the present invention as defined in the appended claims.

Claims

1.- Drive device for relative rotation of structures, of the type it comprises; a drive pulley (1) associated with a first structure (30) and mounted on a shaft (3) driven by a motor (5); a driven pulley (2) associated with a second structure (40) and coaxially mounted with respect to a reference axis (4a); and at least one flexible traction member (6) disposed around at least part of said driven and driven pulleys (1, 2), characterized in that: said shaft (3) on which said driving pulley (1) is mounted is supported in said first structure (30); said driven pulley (2) is fixed to said second structure (40); said reference axis (4a) with respect to which the driven pulley (2) is coaxially mounted is a relative axis of rotation between the first and second structures (30, 40); said flexible traction member (6) embraces the drive pulley (1) by an angle greater than 180 ° and less than 360 °; two sections (6a, 6b) of said flexible traction member (6) intersect at a crossing point between the driving pulley (1) and the driven pulley (2); and said shaft (3) has an axis (3a) that is inclined with respect to the reference axis (4a) an angle (α) sufficient so that said two sections (6a, 6b) of the flexible traction member (6) do not touch each other at said crossing point. 2. Device according to claim 1, characterized in that the drive pulley (1) has a perimetric coating (7) of an elastomeric material with which the flexible traction member (6) makes contact. 3. Device according to claim 2, characterized in that the flexible tensile member is a cable (6), and because said perimetric coating (7) of the driving pulley (1) defines at least one throat (8) coaxial with said shaft (3a) of the shaft (3), wherein said throat (8) comprises a mouth, a bottom (8c), and a pair of opposite inclined surfaces (8a, 8b) converging in a radial direction from said mouth to said bottom (8c), said opposite inclined surfaces (8a, 8b) being configured to act as a wedge in order to allow, in cooperation with a certain deformation of the elastomeric material, a predetermined degree of interlocking of the cable (6) in the throat (8) and ensuring a predetermined coefficient of static friction or adhesion between the cable (6) and the drive pulley (1). 4. Device according to claim 3, characterized in that the driven pulley (2) also has a perimetric coating (9) of an elastomeric material that defines at least one throat (10) coaxial with the reference axis (4a) , wherein said throat (10) comprises a mouth, a bottom, and a pair of opposite inclined surfaces that converge in a radial direction from said mouth to said bottom, said opposite inclined surfaces being configured to act as a wedge in order to allow, in cooperation with a certain deformation of the elastomeric material, a predetermined degree of interlocking of the cable (6) in the throat (10) and ensuring a predetermined coefficient of static friction or adhesion between the cable (6) and the driven pulley (2). 5. Device according to claim 4, characterized in that said perimeter covering (7) of the drive pulley (1) defines several of said parallel throats (8), said perimetric coating (9) of the driven pulley (2) defines several of said parallel throats (10), and several of said cables (6) are arranged around the driven and driven pulleys (1, 2), with each cable (6) coupled to one of the throats (8) of Ia drive pulley (1) and one of the throats (10) of the driven pulley (2). 6. Device according to claim 1, characterized in that the flexible traction member is a cable (6) with a coating of elastomeric material (37), and because the drive pulley (1) defines at least one throat (38 ) coaxial with said shaft (3a) of the shaft (3), wherein said throat (38) is of a rigid material and comprises a mouth, a bottom (38c), and a pair of opposite inclined surfaces (38a, 38b) that converge in a radial direction from said mouth to said bottom (38c), said opposite inclined surfaces (38a, 38b) being configured to act as a wedge in order to allow, in cooperation with a certain deformation of said elastomeric material coating (37) of the cable (6), a predetermined degree of interlocking of the cable (6) in the throat (38) and ensuring a predetermined coefficient of static friction or adhesion between the cable (6) and the driving pulley (1). 7. Device according to claim 6, characterized in that the driven pulley (2) also defines at least one coaxial throat with the reference axis (4a), wherein said throat is made of a rigid material and comprises a mouth, a bottom, and a pair of opposite inclined surfaces converging in a radial direction from said mouth to said bottom, said surfaces being opposite slopes configured to act as a wedge in order to allow, in cooperation with a certain deformation of the elastomeric material covering (37) of the cable (6), a predetermined degree of interlocking of the cable (6) in the throat and ensuring a predetermined coefficient of static friction or adhesion between the cable (6) and the driven pulley (2). 8. Device, according to claim 7, characterized in that the drive pulley (1) defines several of said parallel throats (38), the driven pulley (2) defines several of said parallel throats, and several of said cables (6 ) coated with elastomeric material (37) are arranged around the driving and driven pulleys (1, 2), with each cable (6) coupled to one of the throats (38) of the driving pulley (1) and one of the throats of the driven pulley (2). 9. Device according to any one of claims 2 to 8, characterized in that the cable (6) is an endless cable of a predetermined length, whereby said relative rotation between the first and second structures (30, 40 ) supports consecutive complete turns in either direction. 10. Device, according to claim 9, characterized in that the driven pulley (2) is diametrically divided into two halves (2a, 2b) installed on the second structure (40) so that they can be guidedly guided in relation to one The other in opposite directions in order to bring them mutually sufficient distance to allow the installation of the cable (6) around the drive and driven pulleys (1, 2), and move them apart a sufficient distance to provide a desired tension to the cable ( 6). 11. Device, according to claim 10, characterized in that at least one of said halves (2a, 2b) of the driven pulley (2) is associated with regulation means that can be operated to effect said approach movements and / or mutual distance and reversible fixing means that can be operated to fix the corresponding half (2a, 2b) of the driven pulley (2) with respect to the second structure (40) in a selected position. 12. Device according to any one of claims 2 to 8, characterized in that the cable (6) is a finite cable of a predetermined length with two ends fixed to the driven pulley (2) or to the second structure (40) , so that the relative rotation between the first and second structures (30, 40) admits only lower portions of a turn in one of both directions. 13. Device, according to claim 12, characterized in that the driven pulley (2) is a pulley sector that covers only a portion of circumference inferior to a complete circumference and that is fixedly installed with respect to the second structure (40). 14. Device, according to claim 12 or 13, characterized in that at least one of said ends of the cable (6) is fixed to the driven pulley (2) or to the second structure (40) by means of a tensioning device. 15. Device according to any one of the preceding claims, characterized in that a torque limiting device (11) is disposed between the driving pulley (1) and the shaft (3). 16.- Solar tracker, of the type comprising a column (23) to be fixed to the ground, a rotating support (24) installed on said column (23) so that it can rotate around a vertical axis (V), and a tilting frame (25) installed on said rotating support (24) so that it can pivot around a horizontal axis (H), the tilting frame (25) supporting a solar energy sensing device, characterized in that it comprises a first driving device of according to any one of the preceding claims for actuating rotations of the rotating support (24) around the vertical axis (V) with respect to the column (23) in order to effect an azimuthal orientation of said solar energy sensing device, and / or a second drive device according to any one of the preceding claims for driving pivoting frame turns (25) around the horizontal axis (H) with respect to the rotating support (24) with the in order to perform an overhead orientation of the solar energy sensing device.