TECHNICAL FIELD

The present invention relates to a photovoltaic apparatus, and more precisely to a single-axis solar tracker .

A single-axis solar tracker is an apparatus that supports one or more photovoltaic panels which can orient such panels in the direction of the sun, by turning them about an axis so that the sun's rays hit the panel or the panels perpendicularly, i.e. with an angle of incidence of about 90° in the plane of rotation of the solar tracker.

The photovoltaic apparatus in question is generally mounted on foundations that may be of different types: embedded poles, screwed poles, blocks of reinforced concrete and the like.

The solar tracker therefore comprises a support structure and the assembly of mounted panels must be rotated about an axis, generally horizontal but sometimes inclined according to the conformation of the ground on which the installation is to be performed. The axis of rotation of the panels coincides with the longitudinal axis of the apparatus, with lengths that exceed 90 metres.

The structure must withstand the forces of atmospheric agents and must maintain good orientation precision towards the sun; a further basic requirement of solar trackers is assembly simplicity and the possibility to correct any positioning errors of the foundations.

Furthermore, it is important at the same time to reduce the dimensions of the structure without altering the surface area dedicated to the photovoltaic modules and reduce the strains and deformations of the structure itself during the rotation of the panels, in order to guarantee greater orientation precision.

PRIOR ART

Various embodiments are known in the prior art, designed to face contrasting requirements.

To minimize imprecisions in movement and, therefore, in the capacity of the tracker to be correctly aligned with respect to the sun's rays, the choice of positioning of the tracker's axis of rotation is important .

Advantageous positions are at or around the centre of gravity of the structure, so as to make the apparatus balanced with respect to the rotation and therefore minimize efforts and torsional deformations during rotation due to the weight itself of the part of the structure in rotation, however in the section of the machine the area around the centre of gravity falls at the position of the panels themselves, and it is therefore impossible to position a rotation pin except by interrupting the succession of the panels.

The need to have a balanced apparatus with respect to the rotation, which leads to interrupting the surface defined by the photovoltaic panels, is therefore in contrast with the need to maximize such surface area, avoiding all types of interruption.

Furthermore, the interruption of the sequence of panels envisaging leaving the functional space for the rotation mechanisms between one panel or between a group of panels and the adjacent panel or group of panels, implies an increase in the overall dimensions of the structure for the same useful area for the installation of photovoltaic modules, with a consequent increase in the costs of the structure due to the higher dimensions and larger area of ground used for the same installed photovoltaic power.

Because of the need to face these contrasting needs in the state of the art, different solutions have been developed, however apparatuses of the known type can be grouped into two macro-categories.

A first category of apparatuses envisages the photovoltaic modules being adjacent to each other, creating a continuous surface, also known as a "board" without interruptions.

This category includes solutions that envisage solar trackers with an axis of rotation placed at or near the centre of gravity of the structure, and trackers with an axis of rotation centred on the beam, but wherein the structure is not however balanced from a torsional point of view (twisting efforts are therefore generated during the rotation of the panels) .

A second category of apparatuses envisages instead the photovoltaic modules being grouped into groups of modules (or "boards") with an empty space between one group and another, spaces intended to house elements of the support structure, in particular rotation pins. In this case, the axis of rotation is barycentric, however the surface of the modules undergoes an interruption at the rotation pins.

A further requirement that the solar tracker must satisfy is that of being able to manage the thermal expansions resulting from the heating of the structure itself . In fact, as mentioned, the structure generally comprises a steel beam consisting of various portions connected to each other to form a structure that can have a longitudinal extension of over 90 metres. In the presence of temperature changes (between day and night, but also between summer and winter) which may even be in the order of 50°C, a steel structure of such dimensions can even vary its total length (by extending/contracting) by about 30 mm on each side. For this reason, thermal expansions must be allowed at the various support points of the longitudinal beam.

Solutions of the known type are not free from drawbacks .

In particular, apparatuses belonging to the first macro-category (continuous "board") and with a barycentric position of the axis of rotation, are better from the point of view of the occupation of space (power density) and costs with respect to devices belonging to the second macro-category (groups of "boards") , and have better operating characteristics, i.e. lower deformations and efforts induced by weight during rotation, with respect to continuous "board" devices but with a non-barycentric axis of rotation. In any case, even the most advantageous solutions represented by continuous "board" solutions with a barycentric position of the axis of rotation are not free from drawbacks.

From a mechanical point of view, the constraint between the beam and the pole is considerable as a hinge in the longitudinal plane of the machine.

The forces that develop on the beam are not contrasted by systems of constraint to the pole of the known type. This represents a drawback since the aerodynamic forces that develop because of the thrust of the wind on the structure can cause the oscillation of the structure in the perpendicular direction to the photovoltaic modules. If the connection is more rigid, the oscillations are limited, by eliminating or however reducing the need for dynamic dampers.

Furthermore, another drawback that affects solutions of the known type consists of the fact that they are free from any possibility of adjustment against possible "twist" errors.

Since it is difficult to maintain a high level of precision during the realization of foundations and/or while embedding the poles in the ground, the pole must be tilted with respect to the vertical axis Z by an angle known as the "tilt", or rotated about the axis Z, i.e. with the axis of the pole section rotated with respect to the longitudinal axis of the machine ("twist") .

In general, single-axis trackers of the known type have the possibility of adjustment to balance the "tilt" effect .

On the other hand, not all the solutions have the possibility of adjustment to balance the "twist" effect, and in particular, as mentioned, the so-called continuous "board" solutions and those with a barycentric position of the axis of rotation are not equipped with such possibility.

SUMMARY OF THE INVENTION

The main task of the present invention is to obviate the drawbacks affecting solutions of the known type.

Within this task, it is an object of the present invention to provide a single-axis solar tracker that allows the connection between the support element and the tubular element of the support structure to be made more rigid.

A further object of the present invention is that of providing a single-axis solar tracker that allows a possibility of adjustment of the connection between the support element and the tubular element of the support structure about the vertical axis Z (twist) .

Yet another object of the present invention is that of providing a single-axis solar tracker that allows the thermal expansions of the structure to be managed.

It is a further object of the present invention to provide a single-axis solar tracker that allows axial fixing in one point of the tracker, also allowing installation on sloping ground.

This task, as well as these and other objects according to the present invention are achieved by a single-axis solar tracker according to the accompanying claim 1. In particular, the single-axis solar tracker according to the present invention comprises a support structure comprising one or more support elements adapted to be constrained to the ground and defining a substantially vertical direction, at least one tubular element for the support of one or more photovoltaic panels, said tubular element extending along a longitudinal direction substantially parallel to the installation ground, and with which said one or more photovoltaic panels are associated, side-by-side, said solar tracker comprising also connection means of said tubular element to said one or more support elements configured to allow the rotation of said tubular element about an axis substantially parallel to the longitudinal direction, characterized in that said connection means comprise at least one substantially plate-shaped connection element with a half-moon conformation and associated with said tubular element, comprising at least one curved guide element which is integral with said connection element and extends in a direction substantially orthogonal to the plane on which said plate-shaped connection element lies, said guide element being slidably associated with support and guide means integrally associated with said support element .

Further characteristics of the single-axis solar tracker according to the present invention are the subject matter of the dependent claims.

More in particular, the single-axis solar tracker according to the present invention constitutes a solution in which the axis of rotation of the tracker is positioned at the centre of gravity of the structure itself, so as to make the apparatus balanced with respect to the rotation and therefore minimize the efforts and torsional deformations during rotation due to the weight itself of the part of the structure in rotation even without interrupting the succession of the panels, thus creating a continuous structure.

More specifically, and as will be seen more clearly below, the specific shape of the guide element which is typically, but not necessarily, circular, when appropriately sized, allows the centre of rotation of the rotating part of the photovoltaic tracker to be positioned in proximity to its centre of gravity, without the need to interrupt the continuity of the photovoltaic modules.

The present invention thus solves the opposing requirements to balance the apparatus with respect to the rotation, a need that would lead to the interruption of the surface defined by the photovoltaic panels, with the requirement to maximize such surface area, avoiding all types of interruption.

LIST OF FIGURES

The characteristics and advantages of the single-axis solar tracker according to the present invention will become more apparent from the following detailed description, provided by way of non-limiting example, with reference to the schematic attached drawings, wherein :

- figure 1 shows an overall perspective view of the single-axis solar tracker according to the present invention;

- figure 2 shows an overall side view of the single- axis solar tracker of Figure 1 ;

- figure 3A shows a perspective view of the connection means of said single-axis solar tracker;

- figure 3B shows a front view of the connection means of figure 3A;

- figure 4 shows a perspective view of the connection means of said solar tracker in the motorized version; figure 5 shows a further perspective view of the motorized connection means of figure 4;

- figure 6A shows a detailed view of the guide rollers integral with the support element which are part of the connection means in the version without twist adj ustment ;

- figure 6B shows the same detail of figure 6A in the version equipped with twist adjustment;

- figures 7 and 8 show detailed perspective view of the connection means;

figure 9 shows a front view of the motorized connection means;

- figure 10 shows a perspective view of the connection means only of said single-axis solar tracker in accordance with a further embodiment of the present invention;

- figure 11 shows a side view of the connection means of figure 10;

- figures 11D and HE show sectional views of figure 11 according to planes D-D and E-E respectively;

- figure 12 shows a perspective view from above of the connection means of figure 10;

- figure 13 shows a perspective view of the connection means only of said single-axis solar tracker in accordance with a further embodiment of the present invention;

- figure 14 shows a side view of the connection means of figure 13;

- figures 14D and 14E show sectional views of figure 14 according to planes D-D and E-E, respectively;

- figure 15 shows a perspective view from above of the connection means of figure 13.

DE TAILED DESCRIPTION OF THE INVENTION

Figure 1 shows a perspective view of a solar tracker 1 according to the present invention.

The tracker is of the single-axis type with a prevalently longitudinal extension, the longitudinal axis being indicated with the letter X in the triad of Cartesian axes again visible in figure 1. The solar tracker 1 according to the present invention comprises a support structure 10 in turn comprising one or more support elements 11 adapted to be constrained to the ground and arranged according to a substantially vertical direction Z.

Said support structure 10 further comprises at least one tubular element 12 for supporting one or more photovoltaic panels 20, said tubular element 12 extending along said longitudinal direction X which is substantially parallel to the installation ground.

One or more photovoltaic panels 20 are associated, side-by-side, with said tubular element 12.

According to a preferred embodiment of the single-axis solar tracker 1 according to the present invention, said photovoltaic panels 20 are adjacent to each other without any break in continuity, defining a continuous surface known as a "board".

The solar tracker 1 according to the present invention further comprises connection means 13 of said tubular element 12 to said one or more support elements 11.

Said connection means 13 are configured to allow the rotation of said tubular element 12 about an axis of rotation substantially parallel to the longitudinal direction X.

Said connection means 13 comprise at least one substantially plate-shaped connection element 14 with a half-moon conformation and associated with said tubular element 12, said connection element 14 comprising in turn at least one guide element 14a for the rotation of said connection element with respect to the support element 11, said guide element 14a defining at least one outer guide surface 14b having, on the plane in which the connection element 14 lies, a curved profile that follows the half-moon profile of said connection element 1 .

Said outer guide surface 14b extends, at least for a portion thereof, in a substantially orthogonal direction to the plane in which said plate-shaped connection element 14 lies, projecting orthogonally at least from one side of said plate-shaped connection element .

Said connection means 13 further comprise support and guide means, for example comprising guide rollers 15 or sliding shoes 15d associated by means of a pair of flanges 11a with said support element 11.

More in particular, each of said support elements 11 is, as mentioned, suitable to be stably fixed to the ground at an end thereof, while at the other end they comprise said connection means 13.

In the preferred embodiment shown in the appended figures, the support elements comprise poles 11 embedded in the ground. With reference to figures 3A and 3B, for example, the head of the pole 11 opposite the end embedded into the ground preferably supports a pair of flanges 11a constrained to the head of the pole and to which said guide rollers 15 are in turn constrained.

As can be seen more clearly below in the detailed description of the single-axis photovoltaic tracker provided herein by way of non-limiting example of the present invention, said support and guide means may be configured differently, both in terms of type and dimensions, number and positioning, according to the embodiment of the connection means. According to a first embodiment of the present invention, said connection means 13 are configured according to what can be seen in figures 3A and 3B, wherein said guide element 14a of said plate-shaped connection element 14 extends substantially orthogonally to the plane in which said plate-shaped connection element 14 lies.

As mentioned, the plate-shaped connection element 14 lies in one plane, and said guide element 14a which follows the half-moon profile of the connection element itself projects orthogonally from said plane towards the outside, projecting from both sides of said plate- shaped connection element 14.

Said guide element 14a extends in a preferably symmetrical way from said plate-shaped connection element 14.

Such configuration of the connection means is preferred for the realization of the idle connections between said tubular element 12 and said support elements 11. In fact, with reference to figure 1, it can be noted how a plurality of support elements 11, preferably comprising poles, are arranged at regular distances to support said tubular element 12 along the whole of its longitudinal extension.

To move, in particular as mentioned to turn, the tubular element 12 about an axis substantially parallel to the longitudinal axis of the structure, advantageously coinciding with the longitudinal axis of the tubular element 12 itself, and thus obtain the rotation of the "board" of photovoltaic panels 20 in the plane YZ according to what can be seen for example in figure 2, it is not necessary for all the connection means 13 to be motorized.

It is therefore possible and preferable to use in most of the connections of the tubular element 12 to the support element 11, connection means 13 comprising a simplified structure, in particular wherein said connection means comprise only one plate-shaped connection element 14 comprising only one guide element 14a which extends symmetrically orthogonally from said plate-shaped element 14.

Said guide element 14a has, on the plane in which the connection element 14 lies, a curved profile that follows the half-moon profile of said connection element 14.

Said connection means 13 in the non-motorized configuration further comprise guide rollers 15 associated with said support element 11 preferably configured according to what is illustrated, for example, in figures 3A and 3B, wherein said guide rollers 15 are preferably supported by a pair of flanges 11a for the connection to the support element 11 and comprise at least one lower guide roller 15a and at least one upper guide roller 15b, preferably at least one pair of upper rollers 15b side-by-side on the same axis, where the terms lower and upper refer to the positioning of the rollers with respect to the guide element 14a.

In even more detail, still with reference to the drawings, it is possible to identify on said guide element 14a an outer guide surface 14b and an inner guide surface 14c which is divided into two parts by the presence of said plate-shaped connection element Said at least one lower guide roller 15a contacts the outer guide surface 14b, while at least one upper guide roller 15b contacts the inner guide surface 14c.

In even more detail, the reference is in particular to the view of figure 7, in this preferred embodiment of the non-motorized connection means, the connection means 13 comprise at least one pair of lower rollers 15a on which said outer guide surface 14b rests, and opposing two pairs of upper rollers 15b which rest on said inner guide surface 14c of said guide element 14a. Said guide element 14a is inserted between said lower rollers 15a and said upper rollers 15b thus realizing a rigid constraint that can be likened to a joint in the direction of the tracker axis.

Preferably, each lower roller 15a is radially opposed to a pair of said upper rollers 15b.

As mentioned, according to the preferred embodiment of the present invention, in the case of a non-motorized connection, two lower rollers 15a and two pairs of upper rollers 15b are provided.

With particular reference to figures 4 and 5, a preferred embodiment of the motorized connection means according to the present invention is now described. In the motorized version, the connection means 13 comprise a pair of plate-shaped connection elements 14', 14'' each comprising a guide element 14a', 14a'' which extends orthogonally from said plate-shaped elements 14' , 14' ' .

In more detail, said connection means 13 in the motorized version, comprise a first 14' and a second 14'' connection element, with which a first 14a' and a second 14a' ' guide element are respectively associated, each of which extends orthogonally from a respective connection element towards the other connection element, defining the configuration that can be seen in figure 4, wherein the guide rollers 15 and the two guide elements 14a' , 14a' ' are closed between said first 14' and second 14'' connection element.

Also in this case, the connection means 13 further comprise guide rollers 15a' , 15a' ' , 15b' , 15b' ' associated through a pair of flanges 11a with said support element 11 and preferably configured according to what is shown for example in figures 4, 6A, 6B and 9, wherein said guide rollers comprise at least two pairs of lower guide rollers 15a' , 15a' ' and at least two pairs of upper guide rollers 15b' , 15b' ' being opposed with respect to a respective guide element 14a' , 14a' ' .

More preferably, the connection means 13, in the case of a motorized configuration, comprise at least one pair of lower guide rollers and at least one pair of upper guide rollers for each of said guide elements of said plate-shaped connection elements.

Said guide rollers comprise a pair of first lower guide rollers 15a' that support and contact the first outer guide surface 14b' of said first guide element 14a' , and a pair of first upper guide rollers 15b' that contact the first inner guide surface 14c' of said first guide element 14a' , a pair of second lower rollers 15a' ' that support and contact the second outer guide surface 14b' ' of said second guide element 14a' ' , and a pair of second upper rollers 15b' ' which contact the second inner guide surface 14c' ' of said second guide element 14a' ' . In the event of motorized connection means, actuator means 18 are appropriately connected to said connection means 13.

By way of example, with reference to figure 5, said actuator means 18 may comprise a linear actuator 18' preferably electric, or alternatively a pneumatic or hydraulic piston, a connection pin 16 or similar device being advantageously provided integrally with at least one of said first 14' or second 14'' connection elements, for the connection of the free end of the stem 18' ' of said piston 18' , the body of said piston 18' preferably being connected to the support element 11.

Preferably, said connection pin 16 is arranged between said first 14' and second 14'' connection elements.

The movement of the stem 18' ' of the piston 18' causes the rotation, or the rototranslation according to the configuration of the curved profile of said plate- shaped connection elements 14, of said tubular element 12 substantially about its own longitudinal axis.

In fact, the sliding of said first and second guide elements 14a', 14a'' of said first 14' and second 14'' plate-shaped connection elements between said lower guide rollers 15a' , 15a' ' and upper guide rollers 15b' , 15b' ' , transforms the axial movement of the stem 18' ' of the piston 18' into a rotation movement of the connection elements 14', 14'' and, therefore, of the tubular element 12 to which said connection elements are constrained.

Also in this case, like in the case of non-motorized connection means, the width, i.e. the extension in the longitudinal direction, of the surfaces 14b' , 14b' ' , 14c' , 14c' ' of the guide elements 14a' , 14a' ' and the width of the lower rollers 15a' , 15a' ' on which said guide elements rest, like the presence of the upper guide rollers 15b' , 15b' ' allow a "two point" coupling, making the coupling itself very stable, and suitable to contrast the "hinge-like" behaviour of solutions of the known type.

Further measures have been studied by the applicant to optimize the possibilities to adjust the positioning of the single-axis solar tracker 1 according to the present invention.

In particular, with reference to figure 6B, "twist" adjustment means 30 are provided, i.e. means for the adjustment of the angular positioning of the support element 11 with respect to the direction identified by the longitudinal axis of the apparatus.

Such twist adjustment means 30 preferably comprise a pair of adjustment flanges 31 integrally associated with said flanges 11a for supporting the guide rollers 15, preferably arranged orthogonally to the latter i.e. lying in a substantially horizontal plane.

Each of said adjustment flanges 31 comprises at least one guide groove 32 inside which a screw or a fixing bolt 33 is inserted for the tightening of said adjustment flange 31 to a counter-flange, also substantially horizontal integral with the head of the support element 11.

Said guide grooves extend parallel to the direction Y, substantially orthogonally to the direction X parallel to the longitudinal axis of the tubular element 12 when the structure is assembled, so that the flanges 11a for the support of the guide rollers 15 have an opportunity to adjust both transversely to the structure (direction y) , and with respect to the rotation about the vertical axis Z of the support element 11.

A further adjustment possibility, this time to allow, without contrasting them, the thermal expansions which the structure with a prevalent longitudinal extension encounters mainly in the parallel direction to the longitudinal axis X, is shown, for example in figures 7 and 8.

According to the preferred embodiment shown in such figures, the solar tracker 1 according to the present invention therefore comprises, still at said connection means 13, means for compensating for the thermal expansions preferably comprising a U-shaped flange 40 for the connection of said flanges 11a for the support of the guide rollers 15 to said support element 11, said U-shaped flange 40 comprising in turn one pair of parallel surfaces 41 and a connection stretch 42.

Said U-shaped flange 40 faces downwards, so that between the parallel surfaces 41 of the U-shaped flange 40 the head of said support element 11 is inserted, on which said connection stretch 42 rests.

In this configuration, said parallel surfaces 41 of said U-shaped flange 40 are each provided with a pair of holes, which are aligned with corresponding pairs of holes provided on the head of the support element 11, so that pins 43 are inserted in such holes in order to be fixed stably to said parallel surfaces 41 of said U- shaped flange and slidable along the longitudinal direction X with respect to the holes provided on the support element 11.

The plate-shaped connection element or elements 14 are thus movable in the longitudinal direction X with respect to the support element 11.

To allow the thermal expansions, at each support element 11 of the single-axis solar tracker 1 the tubular element 12 is therefore free to slide longitudinally, the stroke being exclusively limited by the length of the pins.

In another possible configuration of the single-axis solar tracker the pins 43 can coincide with the assembly pins of the guide rollers 15a, which guide rollers therefore slide longitudinally integrally with the element 14 (and with the tubular element 12) during the thermal expansions.

It is therefore necessary to create a fixed point along the structure, both to improve the overall stability of the structure itself, and especially to allow its installation on ground that is not perfectly level. The fixed point may preferably be created at the centre of the structure, i.e. approximately at the centre of the tubular element 12 with respect to its longitudinal extension .

Therefore, preferably, the fixed point of the structure will be created in the presence of the motorized connection means, which are also preferably provided exclusively at the halfway plane of the tubular element of the structure.

This situation is shown by way of example in figure 9, where connection means in the motorized version are shown provided with means 50 for blocking the axial sliding, comprising at least one pair of blocking rollers 51 preferably supported by said connection flanges 11a having a substantially vertical axis arranged resting against the outer side surface of each of said plate-shaped connection elements 14', 14'' of said connection means.

The presence of blocking rollers 51 prevents the plate- shaped elements 14', 14'' of the motorized connection means 13 being able to move axially, and therefore the entire tubular element 12 is fixed with respect to the possibility of axial movements.

With particular reference to figures 10 to 12, a further preferred embodiment of the present invention is now illustrated.

In accordance with such embodiment, the connection means 13' comprise at least one substantially plate- shaped connection element 14 having a half-moon conformation and that can be associated with said tubular element 12, not shown, said connection element 14 in turn comprising at least one guide element 14a for the rotation of said connection element 14 with respect to the support element 11, said guide element 14a which extends symmetrically orthogonally from said plate-shaped element 14 defining at least one outer guide surface 14b having, on the plane in which the connection element lies 14, a curved profile that follows the half-moon profile of said connection element 14.

In accordance with this preferred embodiment of the present invention, the connection means 13' further comprise lower guide rollers 15a associated with said support element 11 and adapted to abut said outer surface 14b of said guide element 14a, whereas with respect to the embodiment illustrated in figure 3A, the upper guide rollers 15b are replaced by upper sliding shoes 15c integral with said connection flanges 11a of said support element 11 and configured to abut on the inner guide surface 14c of said guide element 14a.

Preferably said upper sliding shoes 15c are positioned at said lower guide rollers 15a so that said guide element 14a is inserted between said lower guide rollers 15a and said upper sliding shoes 15c.

Similarly, according to an alternative embodiment visible in figures 13 to 15, the connection means 13' ' further comprise a substantially plate-shaped connection element 14 having a half-moon conformation and being associable with said tubular element 12, not shown, said connection element 14 comprising in turn at least one guide element 14a for the rotation of said connection element 14 with respect to the support element 11. Also in this case, the guide element 14a extends orthogonally from said plate-shaped element 14 symmetrically defining an outer guide surface 14b having, on the plane in which the connection element 14 lies, a curved profile that follows the half-moon profile of said connection element 14, and an inner surface 14c.

This further preferred embodiment of the present invention envisages that with respect to the embodiment illustrated in figure 3A not only the upper guide rollers 15b are replaced by upper sliding shoes 15c, as in the embodiment shown in figures 10 to 12, but the lower guide rollers are also in this case replaced by lower sliding shoes 15d configured to abut the outer guide surface 14b of said guide element 14a.

Also in these cases, therefore, the same concept already seen to characterize the other embodiments of the present invention shown herein, is referred to again: the presence of opposing pairs of sliding shoes or of sliding shoes opposing rollers allows the use of a guide element 14a that offers an outer resting surface 14b and an inner resting surface 14c which have an extension in the orthogonal direction to the plane in which the connection element 14 lies, which allows a more rigid connection to be realized between the tubular element 12 and the support element 11.

From the description provided up to now, the characteristics of the single-axis solar tracker according to the present invention are clear, as are the relative advantages.

It is also to be understood that the single-axis solar tracker as conceived herein is susceptible to many modifications and variations, all falling within the invention; furthermore, all the details are replaceable by technically equivalent elements.