WO2011115482A1

WO2011115482A1 - Sorting device

Info

Publication number: WO2011115482A1
Application number: PCT/NL2011/050179
Authority: WO
Inventors: Peter Kok; Jan Poppe
Original assignee: Imix Vision Support Systems B.V.
Priority date: 2010-03-16
Filing date: 2011-03-15
Publication date: 2011-09-22
Also published as: NL2004406C2; EP2574177A1

Abstract

The invention relates to Sorting device for sorting objects. The device being configured to move at least one tray along a path between a blow unit positioned below said path and a suction unit positioned above said path. A tray comprises a topside and a underside. The topside is provided with an array of pockets. A pocket is coupled to an air channel from the underside to the pocket. The blow unit comprises adjacent outlets and is configured to blow air into corresponding adjacent air channels of a tray above the blow unit. The blow unit is configured to press the outlets against the underside of a tray to prevent a flow of air from one outlet into air channels of pockets adjacent to the pocket corresponding to said one outlet.

Description

Sorting Device

TECHNICAL FIELD OF THE INVENTION

The invention relates to a sorting device for sorting small, lightweight objects defined by the preamble of claim 1, more particular to a seed sorting device. The scope of application is for analysing, grading and sorting small, lightweight objects.

BACKGROUND OF THE INVENTION

A sorting device for sorting small, lightweight object, especially seeds is commercially available on the market and known as iXeed. The seed sorting device is configured to inspect each individual seed from a batch of seed and to remove seed with characteristics below required characteristics. In this way, the quality of a batch of seed is improved, which increases the value of the batch of seed.

The sorting device comprises an endless chain provide with trays along the length of the end less chain. Each tray comprises an array of pockets in its top surface. A pocket has a size and depth such that one piece of seed fits in the pocket and will normally stay in the pocket when the tray is moved back and forth in horizontal direction.

Furthermore, a pocket has a round, oval or elliptic shape such that after the pockets are filled with seed, the seed in the pockets have substantially the same orientation. The tray further comprises air channels from the underside of the tray to a pocket. When air is blown in the air channel from the underside, seed that is in a pocket will be blown out of the pocket.

In the known sorting device, the trays are coupled to the endless chain and go around with a speed and passes each round subsequently a tray filling part, a seed surplus removing part, a visual inspection part, a selective seed removal part and a remaining seed removal part. In the tray filling part, a continuous flow of seed is falling on each tray. In the seed surplus removing part, a tray is moved in a direction perpendicular to the direction of the endless chain. In this way, the seeds are moved in the pockets and a surplus of seed is shifted to the edges of the tray to fall off from the tray. After the seed surplus removing part only seed is in the pockets and no seed is present on the top surface of the tray between the pockets. Then the tray with seed in the pockets passes the visual inspection part. In this part by means of a camera one or more images taken from the upper side. Light sources positioned at the same side of the tray as the camera are used to improve the lighting of the tray and objects and to provide an image quality which is constant in time. The images are analysed to determine for each pocket the characteristics of the seed in said pocket. Characteristics of a seed that could be used be: surface, length, width, symmetry, colour, dent, deformations, twists, mechanical damage, colour distribution, more than one seed in pocket, etc.. The characteristics are used to determine for each individual seed a quality measure. This quality measure is used to determine whether a seed in a pocket has the minimal desired quality. If a seed in a particular pocket has at least the minimal desired quality, in the selective seed removal part, the seed is blown out of the pocket by means of a nozzle into the space above the tray. A puff of air from the nozzle is blown in the direction of the opening of a channel in the underside of a tray resulting in an air flow through the channel to the pocket. A seed in a pocket is above the opening of the channel. The puff resulting in the air flow causes the seed to move into the air above the tray. A first suction unit above the tray sucks away the seed blown out of the pocket and collects the seed with the desired quality in a container. Finally, the seeds not having the minimal desired quality which are still on the tray are removed from the tray and collected in another container. Then the empty tray is transported to the tray filling part again to start a subsequent sorting cycle.

SUMMARY OF THE INVENTION

The object of the invention is to provide an improved sorting device.

According to the invention, this object is achieved by sorting device having the features of Claim 1. Advantageous embodiments and further ways of carrying out the invention may be attained by the measure mentioned in the dependent claims.

According to the invention, a sorting device is characterized in that, the blow unit is configured to press the outlets against the underside of a tray to prevent a flow of air from one outlet into air channels of pockets adjacent to the pocket

corresponding to said one outlet.

The invention is based on the recognition that a puff of air directed to an associated pocket to blow the object in the pocket into the suction device sometimes causes an airflow through the channel of an neighbouring pocket. This airflow to a neighbouring channel could occur as the outlets of the blow unit and the inlet of an associated channel in the known device does not form a contiguous air channel. The airflow could result in that the object in said neighbouring pocket is blown in to the airflow of the suction device. If said object didn't have the required quality, the object is erroneously added to a batch of objects. It could also happen that the object is moved such that is could not be blown out of the pocket in to the airflow of a suction device. Consequently, the object will erroneously be added to a batch of rejected objects. A solution to this problem is found in providing an arrangement which presses the outlets against the underside of a tray. The underside of a tray will slide over the outlets of the blowing unit. When a channel of a pocket will pass the corresponding outlet, a puff of air will be blown in to the channel. The amount of air that will not go through the air channel will be reduced significantly and the consequently said air has less force to move the object in a neighbouring pocket.

In an embodiment of the invention, the outlets are movable between a first position and a second position, in the first position the outlets being positioned against the underside of a tray and in the second position the outlets being positioned above the path of the underside of a tray. This allows us to have a very simple construction to press the outlets to the underside of a tray. In an advantageous embodiment of the invention, the blow unit comprises one or more spring elements to move the outlets to the second position.

In an embodiment of the invention, the blow unit comprises a top surface including a first part and a second part, the first part of the top surface comprises the two or more adjacent outlets and forms a plane parallel to the path of the tray, the second part of the top surface is linked up to the first part and is a sloped with respect to the first surface wherein a border of the second part opposite to the first part has a position in the second position which is below the path of the underside of a tray. These features provides an arrangement with the following functionality when a tray passes the blow unit. In use, a front side of a tray will butt the sloped part of the top surface and will move the blow unit down when sliding over the sloped part to the surface with the outlets. As the blow unit is always forced into a direction perpendicular to the path of the tray and to the second position, the outlets will be pressed to the underside of the tray ensuring that the underside with air channels will slide over the outlets.

In an embodiment of the invention, the top surface further comprises a third part linked up to the first part and opposite to the second part, wherein part has a slope with respect to the first surface wherein a border of the third part opposite to the first part has a position in the second position which is below the path of the underside of a tray. These features ensures that when a tray has passed the outlets will smoothly be moved to the second position.

In an embodiment of the invention, the top surface comprises grooves positioned between the outlets. This feature reduced the possibility that some air for a pocket will flow to a neighbouring pocket. If there is some space between the outlet and the underside, some air of a puff will flow through this space in to the groove. Even if the neighbouring outlet is at some distance from associated channel forming a small opening for an airflow from a neighbouring outlet, the pressure of said airflow will be reduced significantly by the groove. The groves direct the airflow to another direction than the neighbouring pocket.

In an embodiment of the invention, the blow unit comprises a guiding groove and a tray comprises guiding extension dimensions to pass through the guiding groove when said tray passes the blow unit. These features enables us to position the outlet with respect to an associated channel.

In an embodiment of the invention, the device further comprises an airflow reduction device configured for reducing airflow caused by the suction unit on the top surface of the tray. This feature enables us to reduce the chance that an object which is not blown out of a pocket is suck in to the suction unit.

In an embodiment of the invention, the sorting device further comprises visual inspection device for inspecting characteristics of the objects, wherein the visual inspection device is arranged such that a tray comprising objects passes a beam of X-rays from a X-rays source to an imaging device, the tray comprises a top layer and a transparent layer positioned below said top layer, wherein the top layer comprises through holes forming at least a part of the volume of a pocket and the bottom of the pockets is formed by the transparent layer and the transparent layer comprises through holes forming the associated air channels. These features enable us to analyse characteristics like transparency or translucency of the object.

In an embodiment, the tray is configured to move the transparent layer with respect to the top layer such that in a first position the through holes of the transparent layer at one end are positioned such that objects in the through holes of the top layer cover the through holes of the transparent layer and in a second position the through holes of the transparent layer at said one end are positioned next to the through holes of the top layer. These features enables the device to have a transparent layer with even transparency over the whole area of the pocket when obtaining an image of the pocket and object in the pocket and to blow an object out of a pocket by means of the blow unit.

To improve the transparency of the transparent layer, the transparent layer comprises in the surface opposite to surface facing the top layer for each pocket a corresponding recess, wherein a cross section of the recess in the second position t overlaps at leas the through hole of the corresponding pocket. In a further embodiment of the invention, each recess has a cylindrical shape with a cylinder axis, wherein the cylinder axes of the recesses coincide with the direction of the X-rays passing through the recess when the imaging device captures an X-ray image of the X-rays passing through the recess. These features results in recesses which provides a transparent layer with even transparency across the area of the pockets and with smallest cross-section. As the underside will have the smallest possible holes, the underside will be the most durable.

It is a further object of the invention to provide an improved method of sorting, analyzing or grading small lightweight objects. The method comprises providing a multitude of small lightweight object to an arrangement comprising all technical features of a sorting device according to the invention to obtain two or more batch of sorted lightweight objects.

It will be clear that the various aspects mentioned in this patent application may be combined and may each be considered separately for a divisional patent application. Other features and advantages of the invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawing which illustrate, by way of example, various features of preferred embodiments of the invention.

BRIEF DESCRIPTION OF THE FIGURES

These and other aspects, properties and advantages of the invention will be explained hereinafter based on the following description with reference to the drawings, wherein like reference numerals denote like or comparable parts, and in which:

Figure 1 shows a profile of an embodiment of the invention;

Figure 2 shows a top-view of an embodiment of the blow unit according to the invention;

Figure 3 shows a sectional- view of the embodiment of the blow unit shown in figure 2;

Figure 4 shows another sectional- view of the embodiment of the blow unit shown in figure 2;

Figure 5 shows a top-view of a tray;

Figure 6 shows a sectional- view of the embodiment of the tray shown in figure 5;

Figure 7 shows a top-view of a protection device according to the invention; Figure 8 shows a perspective top view of another embodiment of a tray; Figure 9 shows a perspective top view of the tray of fig 8 with the top layer removed;

Figure 10 shows a perspective bottom view of the embodiment shown in figure 8;

Figure 11 shows a top view of the embodiment shown in figure 10;

Figure 12 shows a sectional view of the embodiment shown n figure 11, and,

Figure 13 illustrates the visual inspection device.

DESCRIPTION OF EMBODIMENTS

Figure 1 shows a profile of the a selective seed removal part of a sorting device 1 according to the invention. The sorting device is arrange for sorting small light weight object. In the context of the present invention, small light weight objects are objects which can easily be moved in an air stream through a duct. Examples of small light weight object are seeds, pills or any other object in the form of a pill. The object are preferably objects of a batch. The sorting section comprises two blow units 4, 4A, 4B and two suction units 5, 5A, 5B. An endless chain, not shown moves trays coupled to the endless chain between the blow unit 4 and the suction unit 5. In figure 1 only one tray 2 is shown. The tray follows a path 3 between the suction unit 5 and the blow unit 4. The path of the underside of a tray is indicated by the arrow indicated with 3A. The tray 2 comprises pockets. The blow unit 4 is arranged for selectively blowing small lightweight objects out of the pockets. The suction unit 5 comprises a duct with an opening for sucking the objects blown out of the pockets and is arranged to transport said objects to the desired container (not shown). Each pair of blow unit and suction unit enables the sorting device to select object with a determined characteristic, i.e. seed quality, from a tray 2. For example, with two pairs of blow unit 4 and suction unit 5, three batches of objects with different quality can be obtained with one run. The amount of pairs of blow unit and suction unit may be adjusted/extended to the desired requirements of the sorting device.

A blow unit 4 comprises a blow head 12A and spring elements 12. The spring elements 12 in figure 1 are in the form of a spiral spring but other arrangements are possible. The spring elements 12 are arranged to move the blow head in to the direction of the suction unit 5. The blow head 12A comprises a surface with outlets. If no tray is present between the blow head 12 A and the suction unit 5, the surface with outlets has second position which is between the path of the underside 3 a of the tray 2 and the suction unit 5. If a tray is moved between the blow head 12A and the suction unit 5, the surface with outlets is moved by the underside of the tray from the second position to a first position. In the first position, the surface with outlets coincides with the path 3a of the underside of a tray 2. As the spring elements forces the blow head 12A to the second position, the outlets are pressed against the underside of a tray. In this way is prevented that a flow of air from one outlet will flow into an air channel of an adjacent pocket.

Optionally, the seed removal part comprises an airflow reduction device 18. The airflow reduction device 18 is disclosed in more detail in figure 7. The airflow reduction device 18 is positioned between the blow unit 4 and the suction unit 5 such that the trays can pass underneath at a short distance, for example 0,5 -1,0 cm. The airflow reduction device 18 is in the form of a plate with a though hole at the position of the outlets of a blow head. The airflow reduction device 18 reduces the airflow across the surface a tray due to the suction unit 5. In this way, the possibility that an object is erroneously moved out of a pocket and/or suck into the suction unit 5 is reduced. The size of the through hole in the direction of the path is the trays depends on the distance between the airflow reduction device and the inlet of the suction device and the airflow in to the inlet of the suction device. The profile of the through hole 19 is smaller than the profile of the inlet of the duct of a suction unit 5.

The airflow reduction device 18 could further be configured such that it improves the out blow behaviour of the blow head. In this case, the through holes in the airflow reduction device are aligned with pockets when objects are blown out of said pockets and have a cross section which corresponds to the opening of a pocket in the top surface of a tray. The through hole of the airflow reduction device functions as a channel to increase the maximum speed when blowing the object out of the pockets. Furthermore, the through hole enables the system to blow more accurately the object out of the pocket in to the direction of the suction unit.

Figures 2 - 4 show a top-view, and two sectional views of an embodiment of the blow head of a blow unit 4 according to the invention. The blow head comprises outlets 8 thought which a puff of air is forced at the moment an air channel of a tray to a pocket of said tray. A controller 9 controls whether or not a puff is produced when an air channel is above the outlet. The controller enables the sorting device to sort the objects and to blow only the objects on a tray having desired characteristics.

The blow head 5 comprises top surface 13 with a first part 13 a, a second part 13b and a third part 13c. The first part 13a comprises the outlets 8 and forms a plane that is in use parallel to the path of a tray. The second part 13b is linked up to the first part 13a and has a surface with a first slope 14 with respect to the surface of first part 13a. A border 15 of the second part 13b opposite to the first part 13a has a position which is in use below the path 3a of the underside of a tray 2.

The third part 13c is linked up to the first part and is opposite to the second part 13b. The third part 13c has a surface with a second slope 16 with respect to the surface of the first part 13 a. A border 17 of the third part opposite to the first part has a position which is in use of the sorting device below the path of the underside of a tray. The position of the border 16 of the third part 13c is preferably at least below the position of the border 15 of the second part 13c. The slope 16 of the third part 13c is at least smaller than the slop 14 of the second part 13b.

In use, a tray will approach the blow head from the side of the third part 13c. After the front of the tray hits the blow head, the front will slide over the third part 13c and forces the blow head to move down until the front of the tray reaches the first part 13a with the outlet. The spring element of the suction unit press continuously the blow head in the opposite direction of the movement. In this way during a puff the leakage of air between the underside of the tray and the surface of first part will be minimised. After the underside of the tray 2 has passed the first part 13a, the rear of the tray will slit along the second part 13b until the blow head is in its end position. By means of the first and second slope the tray will not shake when is passes the blow head. Consequently, the objects in the pockets will not be bumped out of a pocket. The slope 16 of the third part 13c is in the given embodiment smaller than the slop 14 of the second part 13b. In this way the top surface of the blow head 12a is optimized for wear.

Three spring elements 12a are used to press the surface with the outlets 13a of the blow head against the underside of the tray. One spring element is positioned at the side of third part 13c and two spring are positioned at the opposite side, the side of the second part 13b of top surface of the blow head unit. The springs are dimensioned such that they press the surface with the outlets 13a evenly against the underside of a tray without tilting the surface 13a with respect to the underside of the tray.

The blow head further comprises parallel grooves 28. Grooves are present between adjacent outlets and interrupts the surface of the first part 13a between two adjacent outlets. In this way, if some air during a puff will escape between the first part 13a and the underside of the tray around an outlet, the air flow is guide away from the adjacent outlet. The orientation of the grooves is in the given embodiment parallel to the direction of the trays.

The blow head further comprise a guiding groove 29. The guiding groove 29 enables a guiding rail attached to a tray and extending below the underside of the tray to position to outlet with respect to the channels with inlet at the underside of a tray such that the opening of the outlet 8 is aligned with a channel to a pocket in the tray.

Figures 5 and 6 show a top-view and sectional view of a tray 2 suitable for use in the sorting device in combination with the blow head shown in figures 2 - 4. A tray comprises a 2-D array (7 X 8) of pockets 6 in the topside 2a of the tray 2. However the size of the 2-D array depend on the size of a tray and the size of the objects and is not limited to the examples given. The blow head comprises 7 outlet for cooperation with each time a line of 7 pockets. The pockets have an oval form. The form of a pocket should be chosen such that is could hold one object and that the object can easily be shifted in to a pocket by rapid asymmetric horizontal movement of a tray and that the object stay in the pocket during the rapid asymmetric movement. Asymmetric means that during an alternating movement of the tray, the acceleration in forward direction differs from the acceleration in reverse direction. From the bottom of a pocket 6 to the underside 2b of a tray 2 is a channel 7 for guiding a puff out of the blow unit to blow the object that is in the pocket out of the pocket in the airflow of the suction unit. The channel should be positioned such that it could blow an object out of the pocket. For large objects one pocket could comprise two or more air channels to blow the object out of a pocket. Furthermore, in figures 5 and 6, the opening of the air channel in the pocket is in the middle of the pocket. Depending on the type of object is might be suitable to have the opening out of the centre of the pocket. In figure 6, the channels have the same cross section along the channel. In another embodiment the channels tapper inward from the underside of the tray to the bottom of a pocket. In the present embodiment the bottom of the pockets is parallel to the top side of the tray. In another embodiment, the bottom is slanted forming a pocket with a cross section having the form of a wedge. In this embodiment, the movement of the tray will determine whether the objects will be moved in to the pockets or will be moved out of the pockets to fall down from the tray. In another embodiment, the bottom of a pocket is parallel to the top side of the tray. One side of the pockets is perpendicular to the bottom. A side opposite to said one said is sloped such that the pocket widens from the bottom of the pocket to the top surface of the tray. This form has the advantage that an object in the pocket will always be released out of a pocket when giving a puff through the air channel below said pocket.,

Figures 8 - 12 show another embodiment of a tray. This type of tray is used to irradiate objects by means of X-rays. In the context of the present invention X-rays have a wavelength in the range of 10 to 0.01 nanometres, corresponding to frequencies in the range 3 x 10¹⁶ Hz to 3 x 10¹⁹ Hz.

Figure 8 shows a perspective top view of a tray. The tray 2 comprises a top layer 20 and a transparent layer 21 positioned below said top layer. The top layer 20 comprises through holes forming at least a part of the volume of a pocket. The bottom of the pockets is formed by the transparent layer. According to the invention, the material of the transparent layer should be X-ray transparent. The transparent layer comprises through holes 22 forming the associated air channels. The transparent layer is movable with respect to the top layer. Figure 9 shows a perspective top view of the tray of fig 8 with the top layer removed. The tray comprises a transparent layer with two parts. By means of a displacement device 32 the two parts can be moved with respect to the top layer 20. In the present embodiment the displacement device comprises a wedge for forcing the two transparent parts in two opposite direction. By pushing the displacement device 32 in to the tray, the two parts are moved away from each other. When the displacement device is released, spring elements (not shown), e.g. spiral springs, in openings 30 force the transparent part to move to each other and force the displacement device outwards.

A housing 31 encompasses the transparent parts. By the movement of the transparent layer 21 with respect to the top layer 20, the air channels from the underside of the tray to the bottom of a pocket can be moved between a first position and a second position. In the first position the through holes of the transparent layer at the end in the bottom of a pocket are positioned such that objects in the through holes forming a pocket in the top layer cover the through holes of the transparent layer. In the second position the through holes of the transparent layer at said one end are positioned next to the through holes of the top layer. In the embodiment given, in the first position the openings of the through holes facing the top layer are positioned in the middle of the through holes forming the pockets. It might be clear, that in dependence of the shape and size of the object, i.e. seed, each pocket comprises one or more associated through holes in the transparent layer.

Figure 10 shows a perspective bottom view of the embodiment shown in figure 8 which comprises optionally recesses for each of the pockets. The thickness of the transparent layer determines the absorption of X-rays and thus the transparency. The recesses allows to reduce the thickness of the transparent layer when the transparent layer is in the second position. Each recess has a cylindrical shape with a cylinder axis, wherein the cylinder axes of the recesses coincide with the direction of the X-rays passing through the recess when the imaging device captures an X-ray image of the X-rays passing through the recess. This is illustrate in more detail in the figures 11 - 13.

Figure 13 illustrates a configuration of an inspection device 24 using X- rays. The visual inspection device 24 comprises a X-ray source 26, X-ray detector 27 and tray 2 passing the source 26 and detector 27. The X-ray source 26 emits a beam 25 of X- rays in the direction of the tray 2. The recesses 23 have an orientation in the direction of the X-rays coming from the X-ray source. In this way, an object in a pocket is homogenous irradiated from below and the internal structure of the object can be captured be means of detecting the intensity of the X-rays passing through the tray and objects. The X-ray detector is preferably a line-scan X-ray camera, a linear array camera or any other suitable device for capturing X-ray images. The detector 27 is oriented such that is captures the width of tray perpendicular to the direction of the path of said tray when passing between the X-ray source and X-ray detector.

In figure 11 is illustrate the difference in position of the profile 23b of the recess at the side of the underside of the tray and the profile 23a forming the bottom of the recess. It can further been seen the position of the air channels 7. The transparent part 21 at the upper part of the figure is in the second position, i.e. the position for irradiating the objects. The transparent part 21 at the bottom part of the image is in the first position, i.e. the position for blowing the objects out of the pockets. Similarly, in figures 8 - 10, the left part of the transparent layer 21 is in the first position and the right part of the transparent layer 21 is in the second position.

The measures described hereinbefore for embodying the invention can obviously be carried out separately or in parallel or in a different combination or if appropriate be supplemented with further measures; it will in this case be desirable for the implementation to depend on the field of application of the sorting device. The invention is not limited to the illustrated embodiments. Changes can be made without departing from the idea of the invention.

Claims

CLAIMS:

1. Sorting device for sorting small light weight objects, the device being configured to move at least one tray (2) along a path (3) between a blow unit (4) positioned below said path and a suction unit (5) positioned above said path;

wherein each of the at least one tray comprises a topside (2a) and a underside (2b), the topside being provided with an array of pockets (6), wherein a pocket (6) is dimensioned to keep one object in the pocket, each pocket having an associated air channel (7) from the underside to the pocket, the air channel being configured to pass an airflow into the pocket to move a seed in the pocket into the air above the pocket;

the blow unit (4) comprising two or more adjacent outlets (8) and configured to blow air into corresponding two or more adjacent air channels of a tray above the blow unit;

wherein the sorting device comprise a control unit (9) configured to control the two or more adjacent outlets independently to enable selective move of seed out of corresponding pockets;

characterized in that,

the blow unit is configured to press the outlets against the underside of a tray to prevent a flow of air from one outlet into air channels of pockets adjacent to the pocket

corresponding to said one outlet.

2. Sorting device according to claim 1, characterized in that, the outlets are movable between a first position (10) and a second position (11), in the first position the outlets being positioned against the underside of a tray and in the second position the outlets being positioned above the path (3a) of the underside of a tray.

3. Sorting device according to claim 2, characterized in that, the blow unit comprises one or more spring elements (12) to move the outlets to the second position.

4. Sorting device according to any of the preceding claims, characterized in that, the blow unit comprises a top surface (13) including a first part (13a) and a second part (13b), the first part of the top surface comprises the two or more adjacent outlets and forms a plane parallel to the path of the tray, the second part of the top surface is linked up to the first part and is sloped (14) with respect to the first surface wherein a border (15) of the second part opposite to the first part has a position in the second position which is below the path (3 a) of the underside of a tray.

5. Sorting device according to claim 4, wherein the top surface further comprises a third part (13c) linked up to the first part and opposite to the second part, wherein part has a slope (16) with respect to the first surface wherein a border (17) of the third part opposite to the first part has a position in the second position which is below the path of the underside of a tray.

6. Sorting device according to claim 4 or 5, wherein the top surface (13) comprises grooves positioned between the outlets (8).

7. Sorting device according to any of the preceding claims, wherein the blow unit (4) comprises a guiding groove and a tray comprises guiding extension dimensioned to pass through the guiding groove when said tray passes the blow unit.

8. Sorting device according to any of the preceding claims, wherein the device further comprises an airflow reduction device (18) configured for reducing airflow caused by the suction unit on the top surface of the tray.

9. Sorting device according to any of the preceding claims, wherein the device further comprises a device (18) fixed above the path of the tray and having through holes which are aligned with pockets when objects are blown out of said pockets.

10. Sorting device according to any of the preceding claims, wherein the sorting device further comprises visual inspection device (24) for inspecting characteristics of the objects, wherein the visual inspection device is arranged such that a tray comprising objects passes a beam of X-rays (25) from a X-ray source (26) to an imaging device (27), the tray (2) comprises a top layer (20) and a transparent layer (21) positioned below said top layer, wherein the top layer (20) comprises through holes forming at least a part of the volume of a pocket and the bottom of the pockets is formed by the transparent layer and the transparent layer comprises through holes (22) forming the associated air channels.

11. Sorting device according to claim 10, wherein the tray is configured to move the transparent layer with respect to the top layer such that in a first position the through holes of the transparent layer at one end are positioned such that object in through holes of the top layer cover said one end of the through holes of the transparent layer and in a second position the through holes of the transparent layer at said one end are positioned next to the through holes of the top layer.

12. Sorting device according to claim 11, wherein the transparent layer comprises in the surface opposite to surface facing the top layer for each pocket a corresponding recess, wherein a cross section of the recess in the second position at least overlaps the through hole of the corresponding pocket.

13. Sorting device according to claim 12, wherein each recess has a cylindrical shape with a cylinder axis, wherein the cylinder axes of the recesses coincide with the direction of the X-rays passing through the recess when the imaging device captures an X- ray image of the X-rays passing through the recess.

14. Method of sorting, analyzing or grading small, lightweight objects, the method comprising, supplying a batch of small lightweight objects to an arrangement comprising all technical features of a sorting device according any of the claims 1 - 13, to obtain two or more batches of sorted small lightweight objects.