Optical sorting apparatus with multiple light beams and according method

Abstract

Sorting apparatus and method for detecting irregular products (7) in a product flow, wherein at least two light beams (8,9) are made to strike a rotating polygon mirror (12) such that said light beams (8,9) are directed towards the product flow in a detection zone (4) wherein the light beams (8,9) are each made to strike a different plane of the polygon mirror (12) so as to direct the light beams (8,9) to different parts (21,22) of said detection zone (4) and move them over said parts (21,22).

Description

[0001] OPTICAL SORTING APPARATUS WITH MULTIPLE LIGHT BEAMS AND ACCORDING METHOD

[0002] The invention concerns an optical sorting apparatus for detecting irregular products in a product flow moving through a detection zone in a direction of travel. This sorting apparatus has a detection device with one or several detectors and is equipped with at least one beam source to generate at least two light beams. Furthermore, a polygon mirror is provided which is rotatably mounted in relation to a scan axis to direct said light beams towards the detection zone via a corresponding optical path and move them across said zone in a scanning direction. The scanning direction extends practically transversely to the direction of travel of the product flow, so that the light beams in the detection zone are incident on said product flow and are reflected by products from said product flow. Thus, the light beams are reflected and directed at least partially, via said polygon mirror, to the detectors in order to generate detection signals. A control unit is provided to classify and / or sort the products from the product flow based on these detection signals.

[0003] In such a sorting apparatus, the width of the detection zone and therefore of the product flow is relatively limited to allow accurate detection of irregularities. Indeed, as the width of the detection zone increases, said light beams at the far ends of the detection zone will strike the mirror surface of the polygon mirror and the product flow at a smaller angle. This small angle, and the large distance that the light beam has to travel over the detection zone, increase the margin of error for detecting irregularities in the product flow and make this detection insufficiently accurate.

[0004] According to the present state of the art, this problem is solved by using multiple detection devices, each with its own light source and polygon mirror. Each polygon mirror ensures that an associated light beam covers part of the detection zone. Such an arrangement is presented for example in Figure 9 of document US 2014 / 0362382 Al, but it has the major disadvantage that the movement of the different light beams must be synchronised in order to avoid their simultaneous incidence in the same place of the product flow, which would generate an erroneous detection signal. In addition, such a sorting apparatus with multiple polygon mirrors and a synchronisation system is relatively complex and not very compact.

[0005] The invention aims to remedy these disadvantages and present a sorting apparatus that does not have these disadvantages and yet allows a relatively wide product flow to be scanned over a wide detection zone in order to detect irregular products. Thus, the invention aims to make it possible to develop a sorting apparatus that allows a product flow to be sorted at a higher flow rate and with more accuracy than is the case with existing sorting apparatuses.

[0006] To this end, said light beams are each incident on a different plane of said polygon mirror, as a result of which the light beams are directed towards different parts of said detection zone.

[0007] Practically, said different parts of the detection zone partially overlap.

[0008] Advantageously, said light beams are incident on the polygon mirror on opposite sides of a plane comprising said scan axis and which is transverse to said detection zone.

[0009] In an interesting manner, the sorting apparatus according to the invention comprises a first beam source which makes a first beam of light strike said polygon mirror in order to direct said light beam to a first part of said detection zone. Said first beam source thereby cooperates with at least one detector provided specifically for this purpose. Furthermore, a second beam source is provided which causes a second light beam to strike the polygon mirror in order to direct this light beam to a second part of the detection zone. This second beam source also cooperates with at least one detector provided specifically for this purpose.

[0010] According to an interesting embodiment of the sorting apparatus according to the invention, the detection device comprises a mounting plate on which at least the polygon mirror and said detectors are mounted. This mounting plate is parallel to a detection surface, the scan axis having an angle with respect to this detection plane and / or with respect to the mounting plate that is less than 90°. The detection surface is defined, for example, by the part of the optical path of the part of the reflected light beam that is incident on said detector downstream of the polygon mirror and by the part of the optical path of the light beam, connecting to the polygon mirror, emanating from said beam source which is incident on the polygon mirror.

[0011] According to a preferred embodiment of the sorting apparatus according to the invention, the detection surface forms an angle with a horizontal plane that is between 30° and 80° and in particular is of the order of magnitude of 45°.

[0012] According to a particular embodiment of the sorting apparatus according to the invention, a fixed aiming mirror is provided for each of said light beams which is positioned in said optical path between the polygon mirror and the detection zone, so that each light beam is directed from the polygon mirror to the detection zone via the corresponding aiming mirror.

[0013] The invention also concerns a method for detecting irregular products in a product flow. The product flow is moved in a direction of travel through a detection zone, and at least two light beams are made to strike a rotating polygon mirror driven about a scan axis so that said light beams are directed towards the detection zone via a corresponding optical path. The light beams are thereby moved across the detection zone in a scanning direction extending practically transversely to said direction of travel, so that the light beams in the detection zone are incident on said product flow and are reflected by products from said product flow onto which they hit. These reflected light beams are directed at least partially through the polygon mirror to detectors of a detection device in order to generate detection signals. The products are thus sorted and / or classified based on these detection signals.

[0014] This method is characterised in that said light beams each strike a different plane of said polygon mirror in order to direct the light beams to different parts of said detection zone and move them over these parts. Other particularities and advantages of the invention will become apparent from the following description of a few specific embodiments of the sorting apparatus and method according to the invention. This description is given by way of example only and does not limit the scope of the protection claimed; the reference numbers used hereinafter refer to the appended figures.

[0015] Figure l is a schematic view in perspective of a sorting apparatus with a detection device and a removal device according to the invention.

[0016] Figure 2 is a schematic view in perspective of a detection device of a sorting apparatus according to the invention with a polygon mirror and two beam sources.

[0017] Figure 3 is a schematic view in perspective of a detection device with a polygon mirror onto which several light beams are incident according to the invention.

[0018] Figure 4 is a schematic side view of the detection device from Figure 3.

[0019] In the different figures, the same reference numbers refer to the same or analogous elements.

[0020] In general, the invention concerns a sorting apparatus for detecting irregular products in a product flow and for possibly removing these irregular products from the product flow.

[0021] The invention thus relates to a sorting apparatus for sorting, preferably, granular products such as, for example, peas, nuts, raisins, potatoes, frozen food products, etc. The invention can also be used for sorting non-granular products such as, for example, leafy vegetables, tobacco leaves, etc.

[0022] The products are transported in the form of a wide product flow along a detection device wherein at least one concentrated light beam strikes the product flow in order to detect irregular products and thus allow them to be classified or possibly removed from the product flow.

[0023] More specifically, in this description, by sorting is understood identifying and removing irregular products such as foreign elements, impurities or products that do not meet set quality requirements, etc., from a product flow. Said light beam consists, for example, of one or more laser beams.

[0024] A first embodiment of such a sorting apparatus is shown in Figure 1. The products 1 to be sorted are placed on a conveyor belt 2 where the products 1 are transported as a product flow at a speed determined by the travel speed of the conveyor belt 2 towards an inclined plane 3. The products 1 then move downward by gravity over this inclined plane 3 so that the products 1 leave the inclined plane 3 in a wide flow having the thickness of almost one product 1 and move through a detection zone 4 of the sorting apparatus.

[0025] Alternative ways of feeding the products 1 through the detection zone 4 can of course also be provided. For example, the inclined plane 3, as represented in Figure 1, may not be present. If that is the case, the products 1 will be ejected from the conveyor belt 2 at a speed which is sufficient to move the products 1 in free flight at an almost uniform speed through the detection zone 4. Such a product feed to the detection zone 4 is represented, for example, in Figure 1 of documents US 4723659 or US 4634881.

[0026] According to yet another method of feeding the products 1 to the detection zone 4, they are made to move in free fall through the detection zone 4. In this case, the products 1 are supplied, for example by means of a vibrating table, to a curved plate whose surface approximates a falling parabola of the products 1. Upon leaving the plate, the products 1 move through the detection zone 4 in a single layer at an almost uniform speed. This is described, for example, in document WO 98 / 31477 or WO 2014 / 013421. Said plate is not necessarily curved but may also be straight.

[0027] In general, the detection zone 4 preferably extends almost parallel to the product flow and transverse to the direction of travel of the product flow. It is further ensured that the product flow in this detection zone 4 has a thickness that practically corresponds to a product 1.

[0028] In the detection zone 4, each product 1 is scanned by means of a detection device 5 and it is checked whether a product 1 is a desired product 6 or an undesired one, more specifically an irregular product 7. The detection device 5 allows at least two light beams 8 and 9 to be directed towards the detection zone 4. To this end, at least one beam source is provided which cooperates, for example, with a beam splitter to generate these two light beams 8 and 9.

[0029] In the embodiment of the invention shown in Figure 2, the detection device 5 comprises two beam sources 10 and 11, with each beam source generating a corresponding light beam 8 or 9.

[0030] The beam sources 10 and 11 preferably allow the generation of a highly concentrated light beam 8 or 9 and include, for example, one or more laser sources or, for example, a supercontinuum light source. The beam of rays thus comprises, for example, one or more laser beams. The wavelength of the beams can also be selected according to the nature and type of the products to be sorted. For example, the beams may include IR light, NIR, UV light, or visible light. Preferably, the beams comprise mainly coherent light.

[0031] Further, the detection device 5 comprises scanning means for moving the light beams 8 and 9 in a direction that is practically transverse to the direction of travel of the product flow so that practically all products 1 are struck by at least one of the light beams 8 or 9 in the detection zone 4. The movement of the light beams 8 and 9 is schematically indicated by arrows 8a and 9a.

[0032] Said scanning means for moving the light beams 8 and 9 preferably comprise what is called a polygon mirror 12 which is subjected to a rotational movement about a scan axis 13, as indicated by arrow 14. More specifically, such a polygon mirror 12 is preferably formed of a straight prism having a regular polygon as its ground plane and with rectangular reflective side surfaces.

[0033] Thus, the polygon mirror 12 is formed of successive mirrors, aligned on the perimeter of the polygon mirror 12 and preferably flat, which form said side surfaces.

[0034] The scan axis 13 extends centrally through the polygon mirror 12 and is parallel to its reflective side surfaces. As is schematically shown in Figure 2, the light beams 8 and 9 are incident on the polygon mirror 12 in a direction perpendicular to its central axis. Thus, these light beams 8 and 9 strike the reflective side surfaces of the polygon mirror 12 and are directed towards the product flow. In doing so, the light beams 8 and 9 strike the products 1 of the product flow in said detection zone 4.

[0035] As a result of the rotation of the polygon mirror 12 about said scan axis 13, the light beams 8 and 9 are moved over the product flow in a direction that is practically transverse to the direction of travel of the product flow, so that practically all products 1 are struck by at least one of the light beams 8 or 9 in said detection zone 4. The light beams 8 and 9 thus scan the product flow in the detection zone 4.

[0036] In doing so, the light beams 8 and 9 strike the products 1 located in the detection zone 4 and are reflected by them so that a corresponding reflected stream of light 15 or 16 is generated. These reflected streams of light 15 and 16 are directed back to the detection device 5 via the polygon mirror 12. In the detection device 5, these reflected streams of light are directed to detectors 17 and 27 via optical aids such as, for example, mirrors, lenses, diaphragms, etc., in a manner known to those skilled in the art.

[0037] In this process, the detectors 17 and 27 generate detection signals as a function of the measured reflected stream of light 15 or 16. The detectors 17 and 27 cooperate with a control unit, not shown in the figures, to sort the products 1 by means of the detection signals. This is sufficiently known to those skilled in the art. To this end, as shown in Figure 1, a removal device 18 is provided downstream of the detection zone 4 that includes, for example, a row of compressed air valves extending across the full width of the product flow. When the presence of an unwanted product 7 in the product flow is detected by means of the detectors 17 or 27, this product 7 will be removed from the product flow by the removal device 18. As shown in Figure 1, a compressed air valve of the removal device 18 is activated by the control unit to this end, so that a short air flow 19 is created that blows the unwanted product 7 out of the product flow. As shown in Figure 1, in some embodiments of the sorting apparatus, the detection device 5 may cooperate with a background element 20 in the form of, preferably, a tube whose colour or other optical properties, for example, match those of the desired products 6 in the product flow to be sorted. This ensures that the removal device 18 is not activated when the light beam 8 or 9 strikes the background element 20 instead of a product 1 to be sorted. The background element

[0038] 20 is elongated and extends transversely to the direction of travel of the product flow and practically parallel to the latter. Consequently, the products 1 move between the background element 20 and the polygon mirror 12.

[0039] When the light beam 8 or 9 strikes an irregular or undesired product 7, the amount or nature of the reflected light will be different from that for a desired product 6. Thus, this reflected light is detected by the detectors 17 or 27 in order to distinguish undesired products 6 from desired products 5.

[0040] According to the invention, said light beams 8 and 9 from the respective beam sources 10 and 11 strike different reflecting surfaces of said polygon mirror 12, such that the light beams are directed to different parts of said detection zone 4.

[0041] It is thereby ensured that the light beams 8 and 9 strike the polygon mirror 12 such that each light beam 8 or 9 travels over a different part 21 or 22 of the detection zone 4, as schematically shown in Figure 2. These different parts 21 and 22 of the detection zone 4 may connect so that both parts 21 and 22 together cover practically the entire width of the detection zone 4. Preferably, however, parts 21 and 22 of the detection zone 4 partially overlap. Because the parts

[0042] 21 and 22 overlap, it is ensured that all products 1 in the product flow are scanned by at least one of the light beams 8 or 9.

[0043] As the light beams 8 and 9 each strike a different reflective side surface of the polygon mirror, it is prevented that these light beams 8 and 9 cross each other while the polygon mirror 12 is being driven and rotates about the scan axis 13. This also ensures that both light beams 8 and 9 do not simultaneously strike the same position of the detection zone 4 and therefore do not simultaneously strike the same product 1. Compared to the present state of the art, with two polygon mirrors being used, for example, this offers the advantage that synchronisation of the rotation speed of different polygon mirrors is no longer required.

[0044] In addition, this allows a wider detection zone 4 to be covered compared to the situation where only one beam strikes the polygon mirror 12, as is the case in the prior art.

[0045] According to a preferred embodiment of the sorting apparatus according to the invention, the light beams 8 and 9 strike the polygon mirror 12 on opposite sides of a plane 23 which is transverse to said detection zone 4 and which includes the scan axis 13 of the polygon mirror. In this way, the light beams 8 and 9 can cover a detection zone 4 that is almost nearly twice the width of the detection zone that can be achieved when a light beam strikes the polygon mirror in only one spot.

[0046] Preferably, the detection device 5 comprises associated optical elements for each beam 8 and 9 that direct the reflected light stream 15 and 16 from the polygon mirror 12 to associated detectors 17 and 27.

[0047] Thus, the detection device 5 comprises a first beam source 10 which causes a first light beam 8 to strike the polygon mirror 12 in order to subsequently direct this light beam 8 towards a first part 21 of the detection zone 4. This first beam source 10 cooperates with at least one detector 17 provided specifically for this purpose, which detects the stream of light 15 reflected by products 1 from the product flow and emanating from the first beam source 10. Furthermore, a second beam source 11 is provided which also makes the second light beam 9 strike the polygonal mirror 12 so that this light beam 9 is directed towards a second part 22 of the detection zone 4. This second beam source 11 also cooperates with at least one detector 27 specifically provided for this purpose. Thus, this detector 27 receives light from the stream of light 16 that is reflected by the products as a result of the second beam 9 striking them.

[0048] In other embodiments of the sorting apparatus according to the invention, more than two light beams may possibly strike the side surfaces of the polygon mirror in different spots and be directed towards the product flow to scan the latter. Matching detectors are provided in this case for each light beam, for example, and these light beams travel over different, preferably overlapping parts of the detection zone 4.

[0049] Figures 3 and 4 show yet another embodiment of the sorting apparatus according to the invention. In these figures, a mounting plate 24 of the detection device 5 is shown. Said polygon mirror 12 as well as said detectors 17 and 27 and the optical aids of the detection device such as, for example, mirrors, lenses, diaphragms, etc., are fixed to this mounting plate 24.

[0050] In this embodiment of the invention, the polygon mirror 12 is inclined with respect to the surface of the mounting plate 24 on which it is mounted. More specifically, the scan axis 13 of the polygon mirror forms an angle a in relation to the mounting plate that is less than 90°. This angle a is preferably between 30° and 80° and, in the embodiment shown in Figures 3 and 4, for example, it is of the order of magnitude of 45°. The mounting plate 24 normally has a substantially flat surface on which mounting elements such as, for example, recesses and / or raised elements are present that allow said optical aids and the detectors 17 and 27 to be positioned and fixed on the mounting plate.

[0051] In general, a detection plane 25 may be defined which is usually parallel to the surface of the mounting plate 24. This detection plane 25 is defined by:

[0052] (a) the straight part of the optical path of the part of the reflected stream of light 15 and 16 incident on said detectors 17 and 27 downstream of said polygon mirror 12, and by

[0053] (b) the straight part of the optical path of the light beam 8 and 9 incident on the polygon mirror 12 emanating from said beam sources 10 and 11.

[0054] According to this embodiment of the invention, the scan axis 13 of the polygon mirror 12 consequently forms an angle a with respect to the detection plane 25 that is smaller than 90°. This angle a is preferably between 30° and 80° and is, for example, in the embodiment shown in Figures 3 and 4, of the order of magnitude of 45°.

[0055] This inclination of the scan axis 13 of the polygon mirror 12 with respect to the mounting plate 24 or with respect to the detection plane 25 offers the major advantage that the detection device 5 is easily accessible to a technician 26 for performing maintenance on the detection device 5 or, for example, for adjusting or calibrating optical elements mounted on the mounting plate.

[0056] Figure 5 schematically shows a detection device 5 of such a sorting apparatus according to the invention in which the angle a between the scan axis 13 and the surface of the mounting plate 24 is different from 90°. In the embodiment shown, this angle a is of the order of magnitude of 35°, for example. The surface of the mounting plate 24 or said detection surface 25 in this case forms an angle P in relation to a horizontal plane situated between 30° and 80°, and in particular of the order of magnitude of 45°.

[0057] This angle P between the mounting plate 24 and a horizontal plane ensures that virtually all parts of the detection device 5 are easily accessible to a technician 26 standing directly opposite the detection device 5. In the proposed sorting apparatus, the polygon mirror is located at a vertical distance H from the floor on which the technician 26 is standing.

[0058] An existing sorting apparatus according to the state of the art is shown in Figure 6. In this sorting apparatus, the polygon mirror 12 is also situated at the same vertical distance H from the floor on which a technician 26 is standing. The scan axis 13 of the polygon mirror extends perpendicular to the mounting plate 24 or to the detection surface 25. As can be deduced from the figure, the technician from Figure 6 cannot reach the optical elements of the detection device 5 attached to the mounting plate 24 without any aids such as a ladder or a stepladder and without moreover bending over considerably.

[0059] Not only does the inclination of the scan axis 13 with respect to the mounting plate 24 according to the invention ensure that the detection device is much easier to reach for maintenance or repair, but it also allows for a more compact design of the sorting apparatus. Thus, the sorting apparatus according to the invention occupies less floor space than existing sorting apparatuses.

[0060] Obviously, such an inclination of the scan axis 13 with respect to the mounting plate can be applied in almost any sorting apparatus where a movable mirror, such as a polygon mirror, is used to scan products in the detection zone.

[0061] According to an interesting variant embodiment of the sorting apparatus according to the invention, the detection device 5 of the sorting apparatus includes a fixed aiming mirror 28 and 29 for each of said light beams 8 and 9, respectively, as shown in Figures 3 and 4. This aiming mirror 28 and 29 is placed for each of the light beams 8 and 9 in the optical path of these light beams between the polygon mirror 12 and the detection zone 4. In this way, each light beam 8 or 9 is directed from the polygon mirror 12 to the detection zone 4 via the corresponding aiming mirror 28 or 29.

[0062] The presence of these aiming mirrors 28 and 29 allows the detection device 5 to be made relatively compact when the scan axis 13 of the polygon mirror is inclined with respect to the plane of the mounting plate 24 or with respect to the detection surface 25.

[0063] The target mirrors 28 and 29 are positioned such that an imaginary plane parallel to said scan axis 13 and extending in the direction of the part of the optical path of the light beams 8 or 9 incident on the polygon mirror 12, emanating from said beam source 10 or 11, extends between said detection zone 4 and the aiming mirror 28 or 29, respectively.

Claims

CLAIMS1. Sorting apparatus for detecting irregular products (7) in a product flow moving through a detection zone (4) in a direction of travel, having a detection device (5) comprising one or several detectors (17,27) and equipped with at least one beam source (10,11) for generating at least two light beams (8,9), a polygon mirror (12) being provided which is rotatably mounted with respect to a scan axis (13) for directing said light beams (8,9) to the detection zone (4) via a corresponding optical path and for moving said light beams (8,9) over the detection zone (4) in a scanning direction (8a, 9a) extending practically transversely to said direction of travel so that the light beams (8,9) are incident on said product flow in the detection zone (4) and are reflected by products (1) from said product flow onto which they strike, generating reflected light beams (15,16) which are directed at least partly through said polygon mirror (12) to said detectors (17,27) in order to generate detection signals, a control unit being provided for sorting said products(I) on the basis of these detection signals, characterised in that said light beams (8,9) each strike a different plane of said polygon mirror (12) so that the light beams (8,9) are directed towards different parts (21,22) of said detection zone (4).

2. Sorting apparatus according to claim 1, wherein said different parts (21,22) of the detection zone partially overlap.

3. Sorting apparatus according to claim 1 or 2, wherein said light beams (8,9) strike the polygon mirror (12) on opposite sides of a plane extending transversely to said detection zone (4) and comprising said scan axis (13).

4. Sorting apparatus according to any one of claims 1 to 3, comprising a first beam source (10) which makes a first light beam (8) strike said polygon mirror (12) in order to direct this light beam (8) to a first part (21) of said detection zone (4), wherein this first beam source (10) cooperates with at least one detector (17) specifically provided for this purpose, whereas a second beam source(I I) is further provided which makes a second light beam (9) strike said polygonmirror (12) in order to direct this light beam (9) to a second part (22) of said detection zone (4), wherein this second beam source (11) also cooperates with at least one detector (27) specifically provided for this purpose.

5. Sorting apparatus according to any one of claims 1 to 4, wherein said detection zone (4) extends practically parallel to the product flow and practically transversely to the direction of travel of the latter.

6. Sorting apparatus according to any one of claims 1 to 5, wherein said detection device (5) comprises a mounting plate (24) having a surface on which at least said polygon mirror (12) and said detectors (17,27) are mounted, said scan axis (13) forming an angle (a) with respect to this surface of the mounting plate which is smaller than 90°.

7. Sorting apparatus according to any one of claims 1 to 5, wherein said detection device (5) comprises a mounting plate (24) on which at least said polygon mirror (12) and said detectors (17,27) are mounted, wherein a detection surface (25) is defined by the straight part of the optical path of the part of the reflected stream of light (15,16) striking said detectors (17,27) downstream of said polygon mirror (12) and by the path of the light beam (8,9) emanating from said beam source (10,11) and striking the polygon mirror, wherein said scan axis (13) forms an angle (a) with respect to the detection surface (25) which is smaller than 90°.

8. Sorting apparatus according to claim 6 or 7, wherein said angle (a) is between 25° and 50° and in particular in the order of magnitude of 35°.

9. Sorting apparatus according to any one of claims 6 to 8, wherein said mounting plate (24) forms an angle (P) with a horizontal plane between 30° and 80° and in particular in the order of magnitude of 45°.

10. Sorting apparatus according to any one of claims 1 to 9, wherein a fixed aiming mirror (28,29) is provided for each of said light beams (8,9), placed in said optical path between the polygon mirror (12) and the detection zone (4) so that each light beam (8,9) is directed from the polygon mirror (12) to the detection zone (4) via the corresponding aiming mirror (28,29).

11. Sorting apparatus according to claim 10, wherein a plane which is parallel to said scan axis (13) and which extends in the direction of the part of the optical path of the light beams (8,9) emanating from said beam source (10, 11) which strike the polygon mirror (12), extends between said detection zone (4) and said aiming mirrors (28,29).

12. Sorting apparatus according to any one of claims 1 to 11, wherein said control unit cooperates with a removal device (18) to remove irregular products (7) from the product flow.

13. Sorting apparatus according to any one of claims 1 to 12, wherein said polygon mirror (12) has consecutive adjacent mirrors, preferably flat, extending along the circumference of the polygon mirror and parallel to said scanning axis.

14. Method for detecting irregular products (7) in a product flow, wherein said product flow is moved in a direction of travel through a detection zone(4), wherein at least two light beams (8,9) are made to strike a rotating polygon mirror (12) driven about a scan axis (13), so that said light beams (8,9) are directed to the detection zone (4) via a corresponding optical path and are moved over the detection zone (4) in a scanning direction (8a, 9a) extending practically transversely to said direction of travel, so that the light beams (8,9) in the detection zone (4) are incident on said product flow and are reflected by products (1) from this product flow onto which they strike, wherein these reflected light beams (15, 16) are directed at least partly via said polygon mirror (12) to detectors (17,27) of a detection device(5) for generating detection signals, wherein said products (1) are sorted on the basis of these detection signals, characterised in that said light beams (8,9) are each made to strike a different plane of said polygon mirror (12) in order to direct the light beams (8,9) to different parts (21,22) of said detection zone (4) and to move them over these parts (21,22).

15. Method according to claim 14, wherein said parts (21,22) of the detection zone (4) are selected such that they partially overlap and together cover the entire detection zone (4).

16. Method according to claim 14 or 15, wherein said light beams (8,9) are made to strike the polygon mirror (12) on opposite sides of a plane extending transversely to said detection zone (4) and comprising said scan axis (13).

17. Method according to any one of claims 14 to 16, wherein said first beam source (10) is provided to make a first light beam (8) strike said polygon mirror (12) so as to direct this light beam (8) to a first part (21) of said detection zone (4), wherein said first light beam (8) is made to strike at least one detector (17) which is specifically provided for this first light beam (8) after it has been reflected by said products (1), while a second beam source (11) is further provided to make a second light beam (9) strike said polygon mirror (12) in order to direct this light beam (9) to a second part (22) of said detection zone (4), wherein this second light beam (9) is made to strike at least one detector (27) which is specifically provided for this first light beam (9) after it has been reflected by said products (1).

Images