METHOD AND APPARATUS FOR GRADING FISH ACCORDING TO SIZE

Abstract: Fish (17) of different sizes are graded by means of gently sloping grilles (2, 3, 4, 5) consisting of smooth rounded rods or tubes extending in directions parallel to the plane of the drawing, preferably being kept wet by water sprayed from nozzles (18). In this manner, rapid grading can be achieved without damage to the fish and using relatively light equipment, as dictinct from water-filled tanks previously used for this purpose.

Description: METHOD AND APPARATUS FOR GRADING FISH ACCORDING TO SIZE TECHNICAL FIELD The present invention relates to a method of grading fish according to size, said method being of the kind set forth in the preamble of claim 1. BACKGROUND ART SU 1 ,665,862-A discloses the use of vertical sorting grilles situated in a tank filled with water. This method suffers from two main disadvantages, i.e. the requisite apparatus, i.e. the tank, is very heavy and cannot easily be moved about, and the fish can swim freely about in the tank and are not urged particularly strongly to swim towards the grilles, through which only some of them may pass so as to be graded according to size. DISCLOSURE OF THE INVENTION It is the object of the present invention to provide a method of the kind referred to above, with which it is possible to achieve grading of fish according to size considerably faster than what is possible with the method referred to above, and this object is achieved by, according to the invention, proceeding in the manner set forth in the characterizing clause of claim 1. By proceeding in the manner indicated, the fish will be graded according to principles not differing greatly from those applying to the grading of e.g. potatoes, but in addition to this, it appears that the fish have a natural tendency to try to "hide" between the parallel rods or tubes, so that they are motivated both by gravity and by natural instinct to try to pass through the grille. As is well-known, many species of fish can survive being out of water for a short period, and for a somewhat longer period if sprayed with water. This fact is exploited in the method according to the invention, as the time taken for fish to pass through the requisite grading apparatus can be made to be considerably shorter than the survival period. The present invention also relates to an apparatus for carrying out the method of the invention, and this apparatus is characterized by the feature set forth in the characterizing clause of claim 7. Advantageous embodiments of the method and the apparatus, the effects of which - beyond what is obvious - are explained in the following detailed part of the present description, are set forth in claims 2-6 and 9-14, respectively. BRIEF DESCRIPTION OF THE DRAWINGS In the following detailed part of the present description, the invention will be explained in more detail with reference to the exemplary embodiment of an apparatus for grading fish according to size according to the invention shown highly simplified and diagrammatically in the drawings, in which Figure 1 shows the apparatus in vertical section through a plane parallel to the rods or tubes used in the grilles, Figure 2 is a perspective view of one of the grilles of the apparatus of Figure 1 , and Figures 3a-3c are cross-sectional views showing a grille of the kind shown in Figure 2 in three different adjustments. DESCRIPTION OF THE PREFERRED EMBODIMENT The fish-grading apparatus shown in Figure 1 comprises four grilles 2, 3, 4 and 5 placed one below the other and sloping gently in alternate directions as shown. In a manner to be explained below, each grille 2-4 consists of a number of parallel rods or tubes extending in directions parallel to the plane of the drawing in Figure 1. Below each of the first three grilles 2, 3 and 4 there is a guide plate 6, 7 and 8, respectively, each extending parallel to but ending short of the respective grille 2, 3 and 4 so as to leave a passage 9, 10 and 11 , respectively. The upper side of each of the grilles 2, 3, 4 and 5 communicates directly with an associated chute 12, 13, 14, 15, respectively, whereas the lower side of the lowermost grille 5 communicates with a final chute 16. All the chutes 12-16 extend transversely to the plane of the drawing in Figure 1 and independently of one another, such as by communicating with individual post-grading bins (not shown). In operation, fish 17 of different size are introduced at an entry region 1 , from which they slide, preferably "lubricated" by fresh water or sea water issuing from a number of spray nozzles 18, along the top of the first grille 2. Here, let it be assumed that the fish can be classified in five different size classes: "very large", "large", "medium", "small", and "very small". In the preferred embodiment, the first grille 2 is adapted to allow fish in the four smallest categories, i.e. "large" and smaller, to pass through to the guide plate 6, only the fish of the "very large" category landing in the chute 12. All the remaining fish, i.e. those in the categories "large" and smaller, will slide along the guide plate 6 and fall through the passage 9 onto the second grille 3. The spacing in this grille 3 is adjusted to allow fish of the category "medium" and smaller to pass through the grille so that only the fish of the category "large" will land in the second chute 13, whereas fish of the category "medium" and smaller will slide along the guide plate 7 and fall through the passage 9 onto the third gille 4. The grading continues in the third and fourth grilles 4 and 5, respectively, so that finally, fish of the categories "medium", "small" and "very small" will land in the chutes 14, 15 and 16, respectively. The grille shown diagrammatically in Figure 2 may be any one of the grilles 2-5 shown in Figure 1. The grille shown in Figure 2 consists of two sets of rods 19 and 20, of which the upper set 19 is secured to a first common frame 21 , while the second set 20 is secured to a second common frame 22. As shown in Figures 3a, 3b and 3c, the distance 23 between the first common frame 21 and the second common frame 22 can be adjusted, i.e. by moving one set of rods relative to the other set along a direction at right angles to the main plane of the grille concerned. With the adjustment shown in Figure 3a, the width 24 of the openings between the rods in the sets 19 and 20 is at a maximum, whereas with the adjustment shown in Figure 3c, this width 24 is at a minimum. As diagrammatically indicated in Figures 3a-3c, only fish 17 smaller than those of the category "very large" will pass through the grille shown in Figure 3a, whereas in the grille shown in Figure 3c, only fish of the category "very small" will pass. As can be seen from Figures 3a-3c, it is possible for all the grilles 2-5 in the apparatus shown in Figure 1 to be of identical construction, the only difference being that they are individually adjusted so as to have a width 24 varying from a large value in the uppermost grille 2 to a small value in the lowermost grille 5. In order to influence the speed, at which the fish slide down along the various grilles, their inclination may be adjusted by suitable means (not shown), preferably of a kind permitting adjustment during operation. In a further embodiment (not shown), the inclination of the two sets of rods 19 and 20 relative to each other may also be varied, so that the width 24 will increase or decrease along the length of the grille concerned. Like the means mentioned above for adjusting the inclination of the grilles, the means for adjusting the relative inclination of the two sets of rods 19 and 20 are also not shown, but a person skilled in the art of mechanics will be capable of devising and constructing the requisite means for these purposes. The same applies, of course, to the means used for adjusting the two frames 21 and 22 relative to each other. LIST OF PARTS 1 Entry region 2 Grille 3 Grille 4 Grille 5 Grille 6 Guide plate 7 Guide plate 8 Guide plate 9 Passage 10 Passage 11 Passage 12 Chute 13 Chute 14 Chute 15 Chute 16 Chute 17 Fish 18 Spraying nozzle 19 Set of rods (upper) 20 Set of rods (lower) 21 First common frame 22 Second common frame 23 Distance 24 Width

Claims: CLAIMS 1. Method of grading fish according to size, said method being of the kind, in which the fish to be sorted are made or allowed to encounter at least one grille having openings allowing fish up to a certain size to pass therethrough, ch a racterized by the use of at least one grille consisting of parallel rods or tubes sloping gently in their longitudinal direction. 2. Method according to claim 1, ch a ra cte rize d by the use of a grille consisting of parallel rods or tubes, the surfaces of which encountered by the fish are smooth and rounded withouth sharp edges or points. 3. Method according to claim 1 or 2, ch a ra cte ri ze d by the use of an assembly of grilles placed one below the other in such a manner, that fish having passed through one grille will encounter the next grille below it. 4. Method according to any one or any of the claims 1-3, characterized by spraying a liquid, preferably fresh water or seawater, onto the fish being graded. 5. Method according to any one or any of the claims 1-4, characterized by the use of at least one grille consisting of at least two sets of parallel rods or tubes, of which sets at least one is movable relative to the other(s) in a direction at right angles to the main plane of the grille so as to vary the width of the openings between said rods or tubes. 6. Method according to any one or any of the claims 3-5, characterized by the use of grilles, in which the width of said openings decreases from the uppermost to the lowermost grille. 7. Apparatus for grading fish according to size by carrying out the method according to any one or any of the claims 1-6, characterized by at least one grille (2, 3, 4, 5) comprising parallel rods or tubes (19, 20) sloping gently in their longitudinal direction. 8. Apparatus according to claim 7, characterized in that the surfaces of said rods or tubes (19, 20) expected to be encountered by the fish (17) are smooth and rounded without sharp edges or points. 9. Apparatus according to claim 7 or 8, characterized by a) an assembly of grilles (2, 3, 4, 5) placed one below the other and sloping in alternate directions, and b) in the spaces between said grilles (2, 3, 4, 5): guide plates (6, 7, 8), each extending substantially parallel to and ending short of the grille (2, 3, 4) immediately above so as to leave a passage (9, 10, 11) for fish to pass to the next grille (3, 4, 5) below it. 10. Apparatus according to any one or any of the claims 7-9, ch a ra cter- i z e d in that at least one of the grilles (2, 3, 4, 5) consists of at least two sets of parallel rods or tubes (19, 20), of which sets at least one is movable relative to the other(s) in a direction at right angles to the main plane of the grille so as to vary the width (24) of the openings between said rods or tubes (19, 20). 11. Apparatus according to claim 9 or 10, characterized in that the width (24) of said openings decreases from the uppermost grille (2) to the lowermost grille (5). 12. Apparatus according to any one or any of the claims 7-11, ch a ra cte r- i z e d by spraying means (18) situated and adapted to spray a liquid onto the fish being graded by said grille or grilles (2, 3, 4, 5). 13. Apparatus according to any one or any of the claims 7-12, ch a ra cte rized in that the inclination of each grille (2, 3, 4, 5) can be adjusted individually during operation. 14. Apparatus according to any one or any of the claims 10-12, ch a racte rized in that each end of said at least one set of rods or tubes (19, 29) is movable independently of the other so as to produce openings having a width (24) gradually increasing or decreasing from one end to the other.

Inventors: PEDERSEN OLE ENGGAARD, PEDERSEN, OLE, ENGGAARD
Applicants: DIAT DEV APS, PEDERSEN OLE ENGGAARD, DIAT DEVELOPMENT APS, PEDERSEN, OLE, ENGGAARD
Application year: 1997
Main classification: A01K61
IPC codes: A01K61, A22C25, B07B1, B07B13