Abstract:
In a fileting process for fish of the Siluridae species, for instance, catfish ( Ictalurus punctatus ), the bone plate present in the area of the dorsal fin of these species for supporting the dorsal spike is first undercut from the dorsal area without cutting through its connection to the bone structure, in order to obtain largely trim-free filets. This takes place by means of a cutting tool that makes incisions under the bone plate up to the ventral bones, so that, in the subsequent cutting free of the filet meat from the ventral bones, the outer parts of the bone plate accumulate separately from the filet meat.

Description:
FIELD OF THE INVENTION 
     The invention pertains to a process for decapitated fish of the Siluridae species, for instance, catfish ( Ictalurus punctatus ) as well as a machine for performing this process, comprising a device for transporting the fish in the direction of their longitudinal axis along a predetermined conveyance path, means arranged on either side for cutting the filet away from the bone structure and a measuring means for determining the size of the fish and controlling the processing tools as a function of the measurement result. 
     BACKGROUND OF THE INVENTION 
     When fileting fish, it is fundamentally important to maximize the yield of valuable filet meat and simultaneously to prevent undesired skeletal parts from remaining in the filet. If skeletal parts remain in the filet, expensive trimming work following the filet production is necessary to remove such parts from the filet meat. This trimming work is expensive particularly because only qualified personnel is eligible, which performs this processing manually. 
     A prerequisite for a filet production optimized in both senses is, among others, that the fish are aligned precisely in the position of their line of symmetry with respect to the fileting tools, so that cutting away the dorsal and ventral bones with narrowly spaced tools can take place without danger of skeletal parts being cut into. 
     In a known process, this problem is confronted in that the unpaired fins and fin-holders are first removed and then the fileting cuts for cutting away the dorsal and ventral bones are made. Such a process is known, for instance, from GB 466 674, in which, for fish conveyed in their longitudinal direction, incisions are made from both sides of the dorsal fins by cutters positioned at an angle, so that a strip of flesh comprising the fins and the fin-holder is cut out of the fish carcass. 
     For fish with an ordinary arrangement and formation of fins, this process leads to satisfactory fileting results, but cannot be applied to fish of the Siluridae species. The cause for this is the presence of a stable dorsal spike in front of the first dorsal fin and anchored by an internal column of bone to the front end of the spinal column and supported by a bone plate situated directly under the skin that holds the dorsal spike in place on the cranial roof. 
     In an ordinary back fileting cutting tool consisting of a pair of knives whose spacing is adapted to the width of the back ribs, the bone plate on either side of the dorsal spike is cut through, so that the outer parts of the bone plate remain in the filet meat and thus the aforementioned trimming work is necessary. 
     SUMMARY OF THE INVENTION 
     An aspect of the present invention is to specify a mechanical fileting method for fish of the Siluridae species by which filets can be obtained with a high yield of filet meat that make trimming work caused for the above reasons unnecessary. 
     The method involves that initially the bone plate (os exoccipitale) supporting the dorsal spike in the area of the first dorsal fin is first released from the filet meat by undercutting while leaving the connection to the bone structure intact, and then the filet meat is cut free from the bone structure. This method is preferably applied by a cutter tool processing the area of the dorsal spike. The cutter tool is arranged above the conveyance path and movable relative to the path of the fish and comprises two knives arranged symmetrical to the conveyance path and somewhat above. Each knife advantageously comprises a circular knife and is arranged with its cutting edge in a plane that is oriented essentially parallel to the conveyance path and, with the corresponding plane of the other knife, it encloses an obtuse angle opening away from the conveyance path. 
     Due to this method, the lateral parts of the bone plate are first released from the filet meat situated underneath and cut off by the following back fileting cut so that they fall off separately. 
     An additional optimization of effort and yield can be achieved in that the means for cutting the filet meat loose comprise a cutting tool for cutting away the dorsal bones with a pair of circular cutters that have a gap between them which can be controlled in width to pass through the dorsal bones. The gap between the circular cutters is established by means of an adjustment element that can be controlled by the measuring means. The gap is widened in the moment of arrival of the dorsal spike in the area of action of the circular cutters in order to avoid cutting into the bone column between the bone plate and the terminal area of the spinal column, as well as the edges of the dorsal spike. 
     The efficiency of the cutting tool processing the area of the dorsal spike can be limited in that the control of the cutting tool is accomplished by means of an adjustment element whose time of activation and actuation path are determined by the measuring means, the signal of which takes into account the size of the respective fish. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The foregoing features and other features of the present invention will now be described with reference to the drawings of a preferred embodiment of an interface module. The illustrated embodiment is intended to illustrate, but not to limit the invention. The drawings include the following figures: 
     FIG. 1 shows a partial perspectival representation of a fileting machine for fish of the Siluridae species with a processing unit in the area of the dorsal spike; 
     FIG. 2 shows a cross section through the fish in the area of the dorsal spike with the cutting tool for undercutting the bone plate in the operating position; 
     FIG. 3 shows a cross section through the fish in the area of the dorsal spike after performance of the back fileting cut; 
     FIG. 4 shows a perspectival view of a catfish skeleton; 
     FIG. 5 shows a cross section through the fish in the area of the dorsal spike with the cutting tool for undercutting the bone plate in the operating position; 
     FIG. 6 shows a partial perspective view of a fileting machine for fish of the Siluridae species with a processing unit in the area of the dorsal spike, with a unit for pivoting and raising the height of the circular cutters; 
     FIG. 7 shows a partial perspectival view of a fileting machine for fish of the Siluridae species with a processing unit in the area of the dorsal spike, with circular cutters that can be pivoted with respect to their axis of rotation. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 shows a partial perspectival representation of a fileting machine for fish of the Siluridae species with a processing unit in the area of the dorsal spike. In a frame, not shown, of the fileting machine for fish, a conveyance path  2  for the fish is formed. The conveyance path  2  is determined by the path of an endless chain conveyor  1 , only suggested (in the drawing), which is equipped with push saddles  3  for holding the fish by their abdominal cavity and transporting the fish tail-first. Along the conveyance path  2 , more specifically, above and below it, pairs of dorsal cut guides  4  and ventral cut guides  5  extend, leaving gaps  6  and  7 , respectively, between one another and leaving a common lateral gap  8 . Pairs of dorsal and ventral fileting knives  9  and  10 , respectively, each consisting of a pair of axially opposing circular cutters  11  and  12 , are located upstream of the guides  4  and  5  and essentially in their planes. 
     The dorsal fileting knives  10  are each seated on pivoting levers  13 , which can be pivoted about axes  14  stationary with respect to the chassis and running parallel to the conveyance path  2  in the sense of modifying the spacing of the circular cutters  11 . The pivot levers  13  are in synchronizing engagement with one another and an actuation element  15  acts on one of the pivoting levers  13 . 
     Upstream of the dorsal fileting knives  10  and above the path of the fish is located a cutting tool  16 , consisting of a pair of driven circular cutters  17 , as shown in FIGS. 1 and 2. The circular cutters  17  are arranged with their cutting edges  18  in planes essentially parallel to the conveyance path and enclose an obtuse angle opening upwards between them. The circular cutters  17  are seated on a crank  19  that is seated on a shaft  20  stationary with respect to the chassis and perpendicular to the conveyance path  2 . An actuation element  21 , which upon activation causes a shift in height of the circular cutters  17  with respect to the path of the fish, acts on the crank  19 . 
     Upstream of the cutting tool  16  there is a measuring unit  22 , illustrated in FIG. 1 for the sake of example and schematically as a sensing lever  23 , which influences an angle encoder  24  such that, alternatively, a determination of the length or of the thickness of the fish is possible. Various alternative mechanical detecting systems could be used to indicate or measure the size of the fish in terms of its length, height or thickness as it is moved along the processing path by saddles  3  in order to provide information to position various cutters. The detection of the height of the fish is advantageous for positioning the cutters. Similarly, various optical systems could be used, such as an optical system reflecting radiation off the sides of the fish, or a photo-detector system sensing blockage or passage of light along axes corresponding to the width or height dimensions of the fish when its length is placed along the axis in which the fish moves for processing. 
     The functioning of the machine is as follows: 
     A decapitated fish  25  (see FIGS.  1  and  3 ), opened at its abdominal cavity  26  and gutted, is placed with its abdominal cavity on a push saddle  3  advanced by the endless chain conveyor  1  such that its tail points in the conveyance direction, the spinal column  27  rests on the saddle ridge and the end of the push saddle  3  pointing forward makes contact with the end of the abdominal cavity. The fish thus first moves into the area of the measuring unit  22 , where it displaces the sensing lever  23 . The maximal displacement travel of the sensing lever  23  is recorded by way of the angle encoder  24 , as is the end of the fish in the form of the trailing head cut surface in relation to the position of the push saddle  3  in the machine and thus the position of the end of the fish&#39;s abdominal cavity. The measurement signal is processed in the ordinary manner, as explained further for FIGS. 6 and 7, in order to be provided as a control signal for the subsequent fileting processing of the fish. This begins by means of the cutting tool  16 , which is initially held in such a position above the path of the fish that the circular cutters  17  pass over the fish without effect. The computer has determined from the measurement signal the position of the push saddle  3  at which the dorsal fin enters into the area of action of the cutting tool  16  and by what amount the latter is to be lowered in order to undercut said bone plate  28 . At the moment of arrival of the dorsal fin in the area of the cutting tool  16 , the latter is accordingly lowered by appropriate activation of the actuation element  21 , so that the circular cutters  17  penetrate into the dorsal area of the fish and remain in this position until the head cut surface has passed through the area of the circular cutters  17 . The incision is made up to the dorsal bones  29  without, however, cutting through the bone column  33  between the dorsal spike  30  and the bone structure. 
     Alternatively, the cutters  17  may be held at a stationary height relative to the fish and the saddle  3  raised so the cutters  17  engage the dorsal area of the fish at the desired location. In either embodiment, the cutting apparatus is always held in the same position relative to the dorsal surface regardless of the size of the fish. 
     Subsequently the fish  25  moves into the area of action of the dorsal fileting knives  10 , which cut into the fish on both sides of the dorsal bones  29 , starting from the tail end. Upon entry of the dorsal fin  31  into the area of the circular cutters  12 , the processed measurement signal brings about the activation of the actuation element  15 , so that the circular cutters  12  are controlled to move apart, with the effect that the dorsal spike  30  can pass between the circular cutters  12  without being cut into. The spacing between the cutting edges of blades  12  is about 4 mm, increasing to about 6-8 mm to accommodate the dorsal bone and allow passage of the dorsal spike  30  between the cutters  12 . The wider bone plate  28  is cut through on both sides of the dorsal spike  30  by this dorsal fileting cut, the cut planes of the circular cutters  12  intersecting those of the circular cutters  17  (see FIG.  3 ), so that the outer parts of the bone plate  28  fall off and thus accumulate separately from the filet meat. The ribs  32  are shown in FIGS. 3 and 4. 
     After this preparation the filet processing can take place in the usual manner, i.e., cutting the filet meat away from the belly, bones, ribs and the sides of the spinal column, as described, for instance, in DE 36 32 561, the disclosure and drawings of which are incorporated herein by reference. 
     FIGS. 6 and 7 show the conveyance path  2  of a fileting machine for fish. The conveyance path  2  is determined by the path of a schematically illustrated endless chain conveyor  1 , which is equipped with push saddles  3  for accommodating in their abdominal cavity and conveying the fish tail first. Along the conveyance path  2 , above and below it, pairs of dorsal cut guides  4  and ventral cut guides  5  extend, leaving gaps  6  and  7 , respectively, between one another and leaving a common lateral gap  8 . Pairs of dorsal and ventral fileting knives  9  and  10 , respectively, each consisting of a pair of axially opposing circular cutters  11  and  12 , are located upstream of the guides  4  and  5  and essentially in their planes. 
     The dorsal fileting knives  10  are each seated on pivoting levers  13 , which can be pivoted about axes  14  stationary with respect to the chassis and running parallel to the conveyance path  2  in the sense of modifying the spacing of the circular cutters  11  relative to each other. The cutting edges of the two cutters  11  are separated by about 4 mm, when the tail of the fish is first engaged for cutting. The spacing between the cutting edges of blades  11  increases to about 6-11 mm allow the saddles  3  to pass between the blades  11 , although different designs could be used to accommodate relative movement of blades  11  and saddles  3 . The pivot levers  13  are in synchronizing engagement with one another and an actuation element  15  acts on one of the pivoting levers  13  to allow movement of blades  11 . The cutters  11  provide a counter pressure for cutter  12  as well as cutting the fish. 
     Upstream of the dorsal fileting knives  10  and above the path of the fish is located a cutting tool  16 , consisting of a pair of driven circular cutters  17 . The circular cutters  17  are arranged with their cutting edges  18  in planes essentially parallel to the conveyance path and enclose an obtuse angle opening upwards between them, the latter angle being variable in the embodiments of FIGS. 6 and 7. Whether the angle between the blades  17  is fixed as in the first embodiment, or variable as in the embodiment of FIGS. 6 and 7, the angle is advantageously about 150°-180°. According to the embodiment of FIG. 6, the circular cutters  17  are seated on a crank  19  that is seated on a shaft  20  stationary with respect to the chassis and perpendicular to the conveyance path  2 . An actuation element  21 , which upon activation causes a shift in height of the circular cutters  17  with respect to the path of the fish, acts on the crank  19 . 
     Upstream of the cutting tool  16  there is a measuring unit  22 , illustrated in FIGS. 6 and 7 for the sake of example and schematically as a sensing lever  23 , which influences an angle encoder  24  such that, alternatively, a determination of the length or of the thickness of the fish is possible. 
     The functioning of the machine is as follows: 
     A decapitated fish  25 , opened at its abdominal cavity  26  and gutted, is placed with its abdominal cavity on a push saddle  3  advanced by the endless chain conveyor  1  such that its tail points in the conveyance direction, the spinal column  27  rests on the saddle ridge and the end of the push saddle  3  pointing forward makes contact with the end of the abdominal cavity. The fish thus first moves into the area of the measuring unit  22 , where it displaces the sensing lever  23 . The maximal displacement travel of the sensing lever  23  is recorded by way of the angle encoder  24 , as is the end of the fish in the form of the trailing head cut surface in relation to the position of the push saddle  3  in the machine and thus the position of the end of the fish&#39;s abdominal cavity. The measurement signal is fed via the measuring line  42  to a computer  41  and processed there in order to be supplied via control line  43  or  44  for the subsequent fileting processing of the fish. This begins by means of the cutting tool  16 , which is initially held in such a position above the path of the fish that the circular cutters  17  pass over the fish without effect. The computer has determined from the measurement signal the position of the push saddle  3  at which the dorsal fin enters into the area of action of the cutting tool  16  and by what amount the latter is to be lowered, or by what angle relative to the rotating bearing  40  the circular cutters  17  are to be pivoted, in order to undercut said bone plate  28 . At the moment of arrival of the dorsal fin in the area of the cutting tool  16 , the latter is accordingly lowered by appropriate activation of the actuation element  21  and/or the rotating bearing is activated, so that the circular cutters  17  penetrate into the dorsal area of the fish and remain in this position until the head cut surface has passed through the area of the circular cutters  17 . Advantageously, the incision is made up to the dorsal bones  29  without, however, cutting through the bone column  33  between the dorsal spike  30  and the bone structure. As needed, the cutters  17  can be configured to cut the dorsal bone  29 , with or without cutting through the bone column  33 . 
     In the alternative configuration according to FIG. 7, the height adjustment of the circular cutters  17  is omitted, since they need merely be pivoted about the rotating bearing  40 , the signal for pivoting or for the angle at which to pivot reaching the computer  41  and, from there, the rotating bearing; this also applies to the seating of the circular cutters  17  illustrated in FIG.  6 . 
     In another alternative configuration, the individually driven circular cutters  17 , visible in FIG. 5, can be introduced into the area underneath the bone plate  28  individually suspended from, for instance, a guide essentially perpendicular to the long direction of the fish  25 . So that they cut up to the dorsal bones  29  with their cutting edges  18  without cutting through them. 
     Subsequently the fish  25  moves, both in FIG.  6  and in FIG. 7, into the area of action of the dorsal fileting knives  10 , which cut into the fish on both sides of the dorsal bones  29 , starting from the tail end. Upon entry of the dorsal fin  31  into the area of the circular cutters  12 , the processed measurement signal brings about the activation of the actuation element  15 , so that the circular cutters  12  are controlled to move apart, with the effect that the dorsal spike  30  can pass between the circular cutters  12  without being cut into. The wider bone plate  28  is cut through on both sides of the dorsal spike  30  by this dorsal fileting cut, the cut planes of the circular cutters  12  intersecting those of the circular cutters  17 , so that the outer parts of the bone plate  28  fall off and thus accumulate separately from the filet meal. After this preparation the filet processing can take place in the usual manner, as was discussed in the description of FIGS. 1-3. 
     In a further embodiment the dorsal spike is detected and used to start and position the cutters  17 . As the fish moves on the saddle  3  the dorsal fin  31  passes between parallel guides spaced apart sufficiently to allow passage of the fin  31  between the guides. Erecting hubs protrude into the space separating the parallel guides to offer resistance to the flexible posterior dorsal fin as it passes through the guides. Positioned after the erecting hubs are a series of erecting fingers that ensure the fin stays erected through the fin guiding plates. Within the fin guiding plates is a capacitive sensor that senses the flexible extended rays of the dorsal fin  31 . Output from the capacitive sensor is input to computer  41 . The dorsal spike  30  is located at the end of the dorsal fin nearest the head. As the fish is moving tail first, the dorsal spike  30  is the last portion of the dorsal fin detected by the sensor. Thus, when the dorsal fin is no longer sensed the location of the dorsal spike  31  is known. Using the signal from the capacitive sensor, and based on the travel speed of the saddle  3  and fish, the location of the cutters  17  relative to the capacitive sensor, the computer  41  can determine when to start the cutters  17 . Photo sensing or mechanical sensing of the dorsal fin can also be used in place of the capacitive sensor. 
     Referring to FIGS. 8 and 9, a further embodiment for rotating the cutters  17  is shown. Each of the cutters  17  is mounted to the end of a motor  100  which is in turn mounted to a bracket  104  that pivots about pivot  102   a ,  102   b  at one end to rotate about a point offset from the axis of rotation of cutters  17 . The pivots  102   a ,  102   b  are on opposing sides of the conveyance path and on opposing sides of the dorsal fin of a fish passing between the cutters  17 . Extendible pistons  106   a ,  106   b  have an extendible end  107   a ,  107   b , rotatably connected to the bracket  104   a ,  104   b , respectively. The pistons  106  may comprise solenoids, linear actuators, or other extensible members. An opposing end  109   a ,  109   b  of each piston  106   a ,  106   b  is rotatably mounted to a support  108 , advantageously on the opposing side of the conveyance path as the bracket  104  to which the piston is connected. The opposing ends  109  of the pistons  106  may be adjustably positioned relative to the support  108  by sliding the ends  109  along slots  110 , in order to adjust the location of the cutters  17 . Once positioned the ends  109  are fastened so they only rotate but do not translate. The pistons  106 , brackets  104  and support  108  provide a three-bar linkage that moves the cutters  17  into cutting position by extending one member of the three-bar linkage. 
     When the pistons  106  are extended as in FIG. 9, the brackets  104  pivot about pivot  102  to rotate the cutters  17  into a position to engage and cut the fish as it passes between the cutters. When the pistons  106  are retracted as in FIG. 8, the cutters do not engage the fish. Generally parallel channels  112  are shown between cutters  17 , with the channels having openings to accommodate passage of the cutters  17 , and to allow the dorsal fin of a fish to pass between the channels  112 . There is thus provided a means for moving the cutters  17  into engagement with the dorsal fin area of a fish passing between the cutters. 
     While the above detailed description has shown, described and identified several novel features of the invention as applied to a preferred embodiment, it will be understood that various omissions, substitutions and changes in the form and details of the described embodiments may be made by those skilled in the art without departing from the spirit of the invention. Accordingly, the scope of the invention should not be limited to the foregoing discussion, but should be defined by the appended claims.