WO2008132300A2 - Solar collector - Google Patents

Abstract

The collector of the invention includes a convergent lens (2) having a focal distance f and an image focal plane (PFI). The convergent lens (2) defines one of the walls of a casing (1) defined by two pairs of side walls (4a, 4c), a bottom wall (3) and a front wall defined by the lens (2), the side and bottom walls on the inside of the casing being reflective, and the depth p of the casing being lower than the focal distance f of the lens so that after multiple reflections, the ray beam (R1, R2) thus reflected is concentrated on a final image focus (I') located inside said casing, said collector including a mobile receptor (6a) held inside the concentrated beam or in a position at least intersecting said beam by means controlling the movement of said collector (6a) with that of said beam.

Description

 Solar captor.

The present invention relates to a solar collector of the type comprising, as a collector, a convergent lens having, in a manner known per se, a focal distance and an image focal plane on which are concentrated, in a line, called "focus image primary ", the beam of solar rays that receives said lens, said concentrated beam moving with the course of the sun. Such a lens is said to be "linear" in that its focus is a line.

To account for the variation of the direction of the sun's rays during the day and during the seasons, known solar collectors or use expensive parabolic mirrors or are included in pivoting and motorized equipment, complicated and fragile.

The present invention proposes to provide a simple and effective solution to overcome these disadvantages.

To this end, the present invention provides a solar collector of the aforementioned type, wherein said convergent lens constitutes one of the walls of a box defined by: two pairs of side walls, a bottom wall and a front wall constituted by said lens, the side walls of each pair being parallel to each other, and each pair of side walls being perpendicular to the other pair, the side and bottom walls, inner side of the box being reflective, the depth p between the front wall and the bottom wall being smaller than the focal length f of the lens, so that, after multiple reflections, the ray beam thus reflected is concentrated on a line called "final image focus", symmetrical to said primary image focus relative to said bottom wall and belonging to a "close-up focal plane" itself symmetrical to said image focal plane with respect to said bottom wall, but located inside said box, said sensor enclosing a movable receiver held within said concentrated beam, or in a position at least secant to said beam, by means controlling the moving said receiver to move said beam.

In a preferred embodiment, the front wall and the bottom of the box are perpendicular to the side walls; in other words, the box takes the form of a rectangular parallelepiped.

In this particular case, the depth p of the box corresponds to the relation p = 0.5 * (f + e + b) where: e is the penetration depth of the lens in the box, and b is the distance between the lens and the focal plane close image or useful distance of operation, said sensor enclosing a mobile receiver held within said concentrated beam, or in a position at least secant said beam, by means slaving the displacement of said receiver to the displacement of said beam.

Thus, the structure of the sensor according to the invention makes it possible to follow the course of the sun, by slaving to this race, not the orientation of the box, but the position of the receiver in the box. It follows, on the one hand, that the servo-control means can be considerably lighter than if it were to move the whole box and, on the other hand, that the mobile element (the receiver) is protected from the outside by the box. In practice, the receiver is movably mounted in the focal plane image close to said lens or in a plane parallel to said close-up focal plane. Servo control means that can be used are in the field of skill of the person skilled in the art. In particular, they can apply principles similar to those implemented in the known sensors. It will be understood that in the absence of solar rays or insufficient radiation, the receiver can remain temporarily immobile in the box and come to reposition relative to the concentrated beam when the radiation has recovered to a sufficient level. In a possible embodiment, to control the speed and the direction of movement of said heat pipe, it is provided with a photonic flowmeter adapted to send signals to drive means to which the heat pipe is subjected. In order for the receiver position to be optimal, that is, to receive all the concentrated beam, the center of the receiver must be located within an area that ranges from + jc to -Jc on both sides of said close-up focal plane, median to said area, Jc satisfying the relation

où : r_ est le rayon de la section transversale du récepteur si cette section est circulaire ou du cercle inscrit dans la section du récepteur si cette section n'est pas circulaire, étant entendu que par "centre du récepteur" on entend la droite parallèle au foyer image final et qui passe par le centre dudit cercle ; sin[Atan] signifie sinus [arc tangente] ; . d est la distance entre l'axe optique de la lentille et le bord de la lentille, prise dans le plan contenant ledit axe optique et qui est perpendiculaire au fond du caisson et orthogonal au foyer image final. Cependant, il est possible de placer le centre du récepteur à l'extérieur de cette zone optimale en obtenant toujours un résultat acceptable, par exemple un résultat économiquement acceptable si la perte de performance est compensée par une réduction significative du coût du capteur. La lentille convergente peut revêtir diverses formes pourvu qu'elle concentre les rayons solaires selon une ligne. Ainsi, la lentille convergente pourra être plan- convexe, biconvexe ou ménisque convergente.

where: r_ is the radius of the cross-section of the receiver if this section is circular or of the circle inscribed in the section of the receiver if this section is not circular, it being understood that by "center of the receiver" is meant the line parallel to the focus final image and passing through the center of the circle; sin [Atan] means sinus [arc tangent]; . d is the distance between the optical axis of the lens and the edge of the lens, taken in the plane containing said optical axis and which is perpendicular to the bottom of the box and orthogonal to the final image focus. However, it is possible to place the center of the receiver outside this optimal zone by obtaining always an acceptable result, for example an economically acceptable result if the loss of performance is offset by a significant reduction in the cost of the sensor. The converging lens can take various forms as long as it concentrates the sun's rays along a line. Thus, the convergent lens may be plane-convex, biconvex or convergent meniscus.

Preferably and without being limiting, the convergent lens will be a Fresnel lens, for reasons of reducing the size and weight of the lens. A Fresnel lens also has the advantage of less absorbing rays that pass through it than other lenses. In the case of a plano-convex Fresnel lens, that is to say a lens having a flat face and a sawtooth face, said lens will preferably be mounted so that its face plane is turned towards the outside of said box. This orientation has the advantage of placing inside the box the face of the lens that is most likely to trap dirt, the flat face, outside, obviously being easier to clean. For the same reason, if the Fresnel lens is biconvex, i.e. a lens having a convex smooth face and a sawtooth face, the lens will preferably be mounted so that its convex face is turned towards the outside of said box.

In another embodiment, the lens may be a convergent meniscus lens, i.e. a lens having a convex face and a concave face; such a lens will necessarily be mounted so that its convex face is facing outwardly of said box. The receiver is advantageously a heat pipe covered with a material whose absorption coefficient of the heat is greater than the heat emission coefficient.

In a particular embodiment of the invention, more particularly intended for solar power plants, the heat pipe takes the form of a tube, possibly flexible, included in a vacuum tube, to limit the heat loss.

The heat pipe is advantageously connected to an extraction exchanger fed with a heat transfer fluid to exploit the heat obtained, for example to heat water or another fluid, to heat a device or to generate solar cold.

In another embodiment, the receiver is an extraction exchanger supplied with a heat transfer fluid. In yet another embodiment, the receiver may be a photovoltaic cell receiver.

In a preferred embodiment, the receiver is capable of occupying two positions, namely a service position in which it receives a certain thermal energy and a retracted position in which it receives a lower thermal energy than in the service position. , retractable means being able to move the receiver from its operating position to its retracted position, in the event of risk of overheating, for example, in the event that the circulation of coolant no longer occurs in the extraction exchanger .

The receiver can be connected to a Stirling engine, that is to say an engine that exploits a temperature difference between a hot source and a cold source, especially for the purpose of generating electricity.

Preferably, the surfaces of the lens are treated so as to reduce their potential deterioration with time, alterations which may consist, mainly on the outside, in soiling, and on the inner side in depositing metal particles ejected from the reflective surfaces. Such treatment may consist of a non-stick surface treatment increasing the wettability and obtained by application of thin layers consisting of SiOx-based compounds (SiO _2, etc.) and / or coatings which make it possible to reduce the adhesion of various pollutants, such as TiO ₂ type photocatalytic compounds.

It may be, in addition, protection against aging of the lens material, obtained by deposition on the outer surface of the lens of conventional optical layers in anti-reflection treatment. Such an antireflection treatment has, in addition, the advantage of reducing the reflection, by the lens, the rays it receives according to certain incidences.

The same is true of the reflective walls of the box which will advantageously be treated so as to reduce their potential deterioration with time.

Regarding the reflective walls, alternatively, they may be made of removable reflective panels for cleaning, replacement or complete flattening of the box for transport or displacement.

The invention will be better understood on reading the following description given with reference to the accompanying drawings in which:

FIG. 1 is a diagram, in perspective, cutaway, of an embodiment of a box according to the invention,

FIGS. 2a, 2b and 2c illustrate various types of lenses that can be used according to the invention with identification of the thickness e_;

FIGS. 3a and 3b are diagrams of one embodiment of the box according to the invention, illustrating the effect of the useful distance b on the depth of the box;

FIGS. 4a and 4b are diagrams of one embodiment of a box according to the invention, seen in section in a plane perpendicular to the general direction of the lens, and illustrating the path of the solar rays in two angles. different; FIGS. 5a and 5b are diagrams illustrating the parameter k and the optimal positioning zone of the receiver, FIG. 5b being a view on a larger scale of the area of the final image focus of FIG. 5a, and FIG. a diagram illustrating an embodiment of a drive mechanism for the heat pipe.

As is apparent from FIG. 1, the casing 1, in this embodiment of the invention, is of rectangular parallelepipedal shape, composed of a front wall consisting of a linear converging lens 2, a rear wall or bottom 3 and side walls 4a-d. The inner faces of the side walls 4a-d and bottom 3 of the box 1 are reflective, either they are coated with a reflective film or they are lined with a removable reflective wall.

The side wall 4b has a slot such as 5, in which is slidable a heat pipe 6 in a plane parallel to the general plane of the lens 2, the heat pipe being supported, opposite the slot, by appropriate means ( not shown) allowing this sliding.

The heat pipe 6 is sheathed with a material having a heat dissipation coefficient lower than its thermal absorption coefficient to limit the losses as much as possible. An extraction exchanger 7, fed with cold fluid according to 7a hot spring 7b, removes heat from the heat pipe for proper operation.

The casing 1 is extended by a housing 8 (dashed in FIG. 1) for the extraction exchanger 7 and a drive mechanism not shown in FIG. 1

(see Figure 6). The housing 8 may have the same rectangular section as the casing 1 and be closely connected to avoid infiltration of rainwater or dust. It can be advantageously opaque to slow the aging of the hoses 9a and 9b (Figure 6). The lens 2 of the box 1 is struck by the sun's rays at an incidence that varies with the time of day, the season, and so on. and two such different incidences are illustrated by the rays R and R ¹ . If we come to the optical plane, FIG. 4a, which represents the casing 1 without the heat pipe 6 nor the extraction exchanger 7 for the clarity of the representation, we see that the lens 2 is constituted by a lens of Fresnel 2 convex plane whose flat face is turned towards the outside of the box. The thickness of the lens has been exaggerated in the figure also for the sake of clarity. The lens 2 has an optical axis AA, a focal length f greater than the depth p of the box 1 and an image focal plane PFI which is beyond the bottom 3 of said box 1. As indicated above, the depth p of the box must answer the relationship: p = 0.5 * (f + e + b)

This relationship is explained with reference to Figures 2a-2c and 3a-3b. FIGS. 2a, 2b and 2c respectively show a plano-convex lens 2a, in this case a Fresnel lens, a biconvex lens 2b, and a meniscus lens 2c, forming one of the walls of a box which can be seen in FIG. primer of the side walls 4a and 4c.

In the case of the Fresnel lens 2a, the plane face of the lens coincides with the plane FF passing through the adjacent edge of the side walls 4a-4d, and the penetration thickness e is the distance between this plane FF and the TT plane tangent to the most prominent part of the lens inside the box.

In the case of the biconvex lens 2b, one of the convex faces of the lens protrudes outwardly of the casing 1 and the other convex face protrudes towards the inside of the casing. The thickness e_ of penetration is the distance between the median plane of the lens, which is confuses with the plane FF, passing through the adjacent edge of the side walls 4a-4d, and the plane TT tangent to the most prominent part of the lens inside the box. In the case of the meniscus lens 2c, no part of the lens enters the casing (when the lens is attached), so that the thickness e_ is substantially zero.

As is apparent from FIGS. 3a and 3b, where the lens has been schematized in the form of a simple rectangle designated 2a-c, to show that it may be any of the types of lenses 2a, 2b or 2c illustrated in Figures 2a to 2c, the parameters necessary for the determination of the depth of the box are indicated. In FIGS. 3a and 3b, it can be seen that the lens 2a-c has a thickness e_ and a focal distance f_, which distance determines the image focal plane PFI.

In the case of Figure 3a, there is provided a useful distance bl, distance which must allow to accommodate the receiver, in other words the heat pipe 6 in the embodiment of Figure 1, and its support opposite the slot 5, taking into account the heat sensitivity of the lens, thus the material of the lens.

In the first place, for simplicity, it will be considered that the receiver 6 is in the plane PFIR situated at e + b1 of the plane FF, which is a special case, as will be seen with reference to FIGS. 5a and 5b. The bottom 3 of the box must be equidistant from the PFIR plane and the PFI plane.

In the case where b = bi (FIG. 3a), the distance between PFIR

In the case where b = b ₂ with b ₂ > bi (FIG. 3b), the distance between PFIR and PFI is 2 * x ₂ .

The choice of b is within the reach of those skilled in the art. It depends on the size of the receiver 6 and the means associated with it and the material of the lens.

By way of example, for a plano-convex Fresnel lens of 50 cm × 100 cm, made of glass having a refraction n = 1.5, a focal length f of 80 cm and a thickness e = 1.5 cm, with respect to a useful distance b = 15 cm, the depth p of the box 1 will be equal to the product 0.5 (f + e + b) = 0.5 * (80 + 1, 5 + 15) = 48.25 cm. It is understood that these values are given only to allow the reader to understand the principle of the invention. In practice, these values can be other and the depth of the box even smaller compared to the focal length. Returning to FIG. 4a, in the absence of the bottom of the box, sun rays striking the lens 2 parallel to the ray R would focus on a primary image focus in the image focal plane PFI. However, the lateral reflecting walls, such as 4a, and the reflecting bottom 3 of the box stop the R-rays and reflect them until they focus on a final image focal point, in a close-up image plane PFIR parallel to the plane focal image PFI, but inside the box 1. In FIG. 4a, this final image focus is seen in section, thus in the form of a point I.

FIG. 4b is similar to FIG. 4a except that it illustrates another orientation of impact of the rays, such as R ', on the lens 2. As can be seen, at the end of multiple reflections, these rays R 'focus on a final image focus, also located in the PFIR plane, and this final image focus is seen in section in Figure 4b, thus in the form of a point I'.

Thus, the final image focus of the R-rays and that of the R 'rays are located in the same plane PFIR, but along two different lines or, expressed otherwise, the linear final image focus moves in translation in the plane PFIR as and when measure of the sun's course.

The heat pipe 6 which, in the particular case envisaged, is arranged in the plane PFIR, moves to follow this displacement in translation of the final linear image focus. To this end, there are provided motor means enslaving the displacement of the heat pipe to the race of the sun, or more precisely to the race of the concentrated ray beam towards the final image focus. This enslavement takes into account the location of the caisson, the season, the time of day, etc.

As indicated above, the heat pipe may, in addition, be subjected to retractable means adapted to move it, if necessary, out of its operating position, to avoid overheating. To this end, the retracting means will move the heat pipe from its service position where it receives a certain thermal energy to a retracted position where it receives a lower thermal energy than in the service position.

As is apparent from the numerical example indicated above, the invention considerably reduces the distance required between the lens and the heat pipe. Without the invention, in the example given, this distance would be fe = 80-1.5 = 78.5 cm, whereas according to the invention and still in the example in question, it is only 48. , 25 cm.

If we come to Figure 5a, there is the box 1 with its lens 2 and its bottom 3. It also shows a receiver 6a which has been presented in the form of a circular section device of radius r (see Figure 5b), but not necessarily circular. If the receiver is not circular, consider the circle in the non-circular section. The distance d used in the calculation of the value I is also identified in this figure. In R ₁ and R _Σ are indicated solar rays forming the outer boundaries of the beam of rays striking the lens 2 with zero incidence. The beam bounded by Ri and R ₂ converges towards the plane PFI but is stopped and reflected by the bottom 3 to converge in a concentrated beam towards the plane PFIR that crosses along a line seen in section I ", corresponding to the focus image final, to diverge beyond the RETP plan. concentrated beam thus delimits, on either side of the final image center I ", two X planes forming an angle α between them.

As long as these planes are tangent to the receiver (position 6a - FIGS. 5a and 5b) or secant to the receiver (position 6b - FIG. 5b), the receiver receives the entire concentrated beam. On the other hand, if the receiver is well located between these planes, without these planes being intersecting or tangent (position 6c - figure 5d), a part of the concentrated beam, namely the part which lies between, respectively, the plane of R 1 and R ₂ and the tangents T ₁ and T ₂ to the receiver 6c do not hit the receiver.

Thus, as is apparent from FIG. 5b, for the receiver to occupy an optimum position, the line which passes through the center of the receiver and which is parallel to the final image focus I "(line C ₃ for the receiver in position 6a, line C _b for the receiver in position 6b) must be located in a zone of extent E ranging from + k to -k, on either side of the plane PFIR, k having to satisfy the relation

où r, d et f sont tels que définis plus haut, le centre du récepteur pouvant éventuellement se confondre avec ledit foyer image final I" (cas particulier précité) . Une position du récepteur telle que 6c, où la ligne C_c est à l'extérieur de la zone d'étendue E, n'est cependant pas un cas de figure sortant de la portée de l'invention : cette position peut être acceptable, même si le récepteur ne reçoit pas la totalité du faisceau concentré, par exemple s'il est moins coûteux de positionner le récepteur en 6c qu'en 6a ou 6b.

where r, d and f are as defined above, the center of the receiver possibly being confused with said final image focal point I "(special case mentioned above) A receiver position such as 6c, where the line C _c is However, the outside of the area of extension E is not a case in point outside the scope of the invention: this position may be acceptable, even if the receiver does not receive the entire concentrated beam, for example it is cheaper to position the receiver at 6c than at 6a or 6b.

Naturally, positions 6a, 6b and 6c could just as easily be on the other side of the PFIR plane.

FIG. 5b shows, in addition, for the receiver 6a a service position (in this case, within the beam concentrated and tangent to the planes bounding this beam) and a retracted position, illustrated in 6a 'or the receiver is totally out of the concentrated beam. The position βc could also be considered to constitute the retracted position of the receiver 6a.

If one comes to Figure 6, the references E1 and E8 respectively designate the interior space of the box 1 and the interior space of the housing 8, separated by the partition 4b, slotted at 5. There is found the heat pipe 6 and the exchanger 7 with its cold fluid supply according to 7a and its discharge in hot fluid according to 7b, as shown in FIG. 1. More specifically, this supply and this evacuation are done via flexible hoses, respectively 9a and 9b, connected to tubings, respectively 10a and 10b, themselves in fluid communication with the inside of the exchanger 7. Flexible tubes 9a and 9b are used, obviously, to allow the displacement of the heat pipe 6.

To ensure this displacement, the heat pipe 6 is connected, via a collar 11 provided with a fork 12a, 12b, to the axis of rotation of a pinion 13 which meshes with a rack 14, pinion 13 which is itself driven in rotation by a motor 15.

It is schematized in 16 a photonic flowmeter which sends signals to said motor means to control the direction and speed of rotation of the pinion 13, and therefore the heat pipe 6.

It is understood that the invention is not limited to the embodiments described and shown. Thus, the lens and the bottom of the box are not necessarily perpendicular to the side walls of said box, and not necessarily parallel to each other. Instead of incorporating a heat pipe, the box could contain an extraction exchanger supplied with heat transfer fluid or a linear volume coated with photovoltaic cells, both mobile as has been described for the heat pipe. Moreover, it is possible to juxtapose several lenses each forming a face of a "sub-well", the sub-boxes thus juxtaposed having components in common, in particular a common drive mechanism, to limit the amount of constituent materials used and to reduce the number of servocontrols for the displacement of the receiver.

Claims

1. Solar collector of the type comprising _/ as collector, a convergent lens (2; 2a; 2b; 2c) having a focal length f_ and an image focal plane (PFI), on which are concentrated, in a line, called "image focus primary ", the beam of solar rays (R; R '; Ri, R2) that receives said lens, said concentrated beam moving with the race of the sun, characterized in that said convergent lens (2; 2a; 2b; 2c) constitutes one of the walls of a box (1) defined by: two pairs of side walls (4a, 4c and 4b, 4d), a bottom wall (3) and a front wall (2; 2a; 2b; 2c; ) constituted by said lens, the side walls (4a, 4c and 4b, 4d) of each pair being parallel to each other, and each pair (4a, 4c) of side walls being perpendicular to the other pair (4b, 4d), the side and bottom walls (4a-d, 3), on the inside of the box, being reflective, the depth p between the front wall (2; 2a; 2b; 2c) and the bottom wall (3) being smaller than the focal length f_ of the lens, so that, after multiple reflections, the ray beam thus reflected is concentrated on a line called "final image focus"(I; I '; I "), symmetrical to said primary image focus with respect to said bottom wall (3) and belonging to a "close-up focal plane" (PFIR) itself symmetrical to said image focal plane (IFP) with respect to said bottom wall (3), but located inside said box, said sensor enclosing a mobile receiver (6; 6a; 6b; 6c) maintained within said concentrated beam, or in a position at least secant said beam, by means enslaving the movement of said receiver (6; 6a; 6b; 6c) the displacement of said beam. 2. Sensor according to claim 1, characterized in that said box (1) is parallelepiped rectangle eten what the depth p of the box responds, to do this, to the relation p = 0.5 * (f + e + b) where: • e is the thickness of penetration of the lens (2; 2a; 2b; 2c) in the casing (1), and B is the distance between the lens (2; 2a; 2b; 2c) and the close-up focal plane (PFIR) or operating distance of operation, 3. Solar collector according to claim 1 or 2, characterized in that the center of said receiver (6; 6a; 6b; 6c) is located within an area which affects a range (E) from + k to -Jc on either side of said close-image focal plane (PFIR), median to said zone, Jc satisfying the relation

or : • r is the radius of the cross-section of the receiver if this section is circular or of the circle inscribed in the section of the receiver if this section is not circular, it being understood that by "center of the receiver" is meant the straight line (C _{a Cb} ; C _c ) parallel to the final image focus (I; I '; I ") and passing through the center of said circle; • sin [Atan] means sinus [tangent arc]; D is the distance between the optical axis (A-A ') of the lens and the edge of the lens, taken in the plane containing said optical axis (AA') and which is perpendicular to the bottom (3) of the box and orthogonal to the final image focus (I; I '; I "). 4. Sensor according to any one of claims 1 to 3, characterized in that said convergent lens is plano-convex (2; 2a), biconvex (2b) or meniscus convergent (2c). 5. Sensor according to any one of claims 1 to 4, characterized in that said convergent lens is a Fresnel lens (2; 2a). 6. A sensor according to claim 4, characterized in that the convergent lens is a plano-convex Fresnel lens (2; 2a) mounted so that its planar face is turned towards the outside of said box (1). 7. Sensor according to claim 4, characterized in that the convergent lens is a biconvex Fresnel lens mounted so that its convex smooth face is facing outwardly of said box (1). 8. Sensor according to any one of claims 1 to 7, characterized in that said receiver (6; 6a; 6b; 6c) is a heat pipe covered with a material whose heat absorption coefficient is greater than the coefficient of heat emission. 9. Sensor according to claim 8, characterized in that the heat pipe takes the form of a tube included in a vacuum tube. 10. Sensor according to claim 8 or 9, characterized in that the receiver (6; 6a; 6b; 6c)) is connected to an extraction exchanger (7) supplied with a heat transfer fluid. 11. Sensor according to any one of claims 1 to 7, characterized in that the receiver is a photovoltaic cell receiver. 12. Sensor according to any one of claims 1 to 7, characterized in that said receiver (6; 6a; 6b; 6c) is an extraction exchanger supplied with heat transfer fluid. 13. Sensor according to any one of claims 1 to 12, characterized in that said receiver is capable of occupying two positions, namely a service position (6a) in which it receives a certain thermal energy and a retracted position ( 6a ¹ ) in which it receives a lower thermal energy than in the service position. Sensor according to one of claims 1 to 13, characterized in that the receiver (6; 6a; 6b; 6c) is connected to a Stirling motor. 15. Sensor according to any one of claims 1 to 14, characterized in that the surfaces of the lens (2; 2a; 2b; 2c) and / or the reflective walls (3,4a-4d) of the box are treated so as to reduce the potential deterioration of their material with time. 16. Sensor according to any one of claims 1 to 15, characterized in that the outer surface of the lens (2; 2a; 2b; 2c) comprises anti-reflective treatment. 17. Sensor according to any one of claims 1 to 16, characterized in that the reflective walls (3,4a-4d) consist of removable reflective panels. 18. Sensor according to any one of claims 1 to 16, characterized in that, to control the speed and direction of movement of the receiver (6), it is provided with a photonic flowmeter (16) adapted to send signals to drive means to which said receiver is subjected.