A longan peeling and core removing device for a longan processing production line

Abstract

The present invention relates to the technical field of peeling and pitting of soft-shelled fruit with cores, and discloses a longan peeling and pitting device for a longan processing production line, comprising four main parts: a longan tray, a peeling mechanism, a pitting mechanism, and a peeling mechanism. The present invention distributes the peeling steps based on actual conditions, and adds a pitting knife to the pitting step, which not only ensures feasibility but also ensures stability and efficiency. At the same time, the present invention integrates multiple similar processes on the same driving device, and multiple processing links can be completed by only one action, which can greatly improve production efficiency. In addition, the designed parts have excellent interchangeability, which can greatly reduce the cost of the device. This method is not only suitable for longan, but can also be applied to the peeling and pitting of various soft-shelled fruit with cores through size adjustment and visual control adjustment.

Description

Technical Field

[0001] The invention relates to a peeling and core removing device for a longan peel, flesh and core separation processing production line. Background Art

[0002] Longan is produced in abundance in southern China and Southeast Asia, but it is not easy to store in its fresh state, so a considerable part of longan is made into dried longan for sale. The production of dried longan requires the longan to be pitted and peeled. The pitting method is relatively mature at present, mainly using a thimble to pierce the longan to eject the pit, but most of the design process does not take into account the internal structure of the longan. There is a connection between the longan core and the longan skin inside the longan. At the same time, the longan skin has high toughness. If the ejection force required for forced ejection is large, if the thimble is not inserted into the longan core very accurately, it may cause the position of the longan core to shift and fail to successfully eject the longan core, and also cause damage to the longan itself. Therefore, there is still room for improvement in this method. There is currently no mature method for peeling longan that can be used in a processing production line. The currently proposed method includes using a blade to cut the longan skin into two petals, but this method requires adding a self-rotation motion to each longan itself, which is difficult to control. At the same time, each longan is of different sizes, and a flexible device needs to be added to ensure the success rate. As a result, this method has high cost and low efficiency, and it is difficult to meet the growing production demand. Another method has been proposed, which uses a rotating blade to cut off the longan skin. However, this method is obviously difficult to ensure the integrity of the longan flesh and the integrity of the peeled skin.

[0003] At present, in the actual production process, peeling is mainly done by workers by hand. However, in addition to the difficulty in ensuring sanitary conditions, the efficiency of workers' direct hand operation is also very low. Currently, this method has become increasingly difficult to meet the industry's growing production needs. Summary of the invention

[0004] The problem to be solved by the present invention is to provide a peeling and core removing device for a longan processing production line, which can realize peeling and core removing with high efficiency, strong stability and greatly reduced cost compared with manual labor.

[0005] The longan peeling and core removing device for a longan processing production line of the present invention comprises: a plurality of through holes are opened on a fruit plate, the through holes are called support ring holes, the aperture of each support ring hole can pass through one of the fruits, a support ring is arranged at the lower end of the support ring hole, the ring diameter of the support ring is smaller than the outer diameter of the fruit and larger than the outer diameter of the fruit core; N elongated through holes are evenly opened along the radial direction of the circumference of the support ring hole, each elongated through hole is connected to the circumference of the support ring hole; N openings are evenly distributed on the support ring, and the openings on the support ring correspond to the positions of the elongated through holes in a vertical plane one by one;

[0006] The top plate is installed above the front of the fruit plate, and the top plate is connected to the first driving mechanism and can move up and down, and the first driving mechanism is connected to the control box;

[0007] The clamping claw plate is located above the top plate, and the clamping claw plate is connected to the second driving mechanism and can move up and down, and the second driving mechanism is connected to the control box; a central disk is fixedly installed below the clamping claw plate, and N pins are evenly distributed along the circumference of the central disk, and the value of N is a natural number of 3 to 6; each pin is connected to the upper part of a connecting rod, and the lower part of each connecting rod is movably connected to the upper part of a claw arm, and the lower part of a claw arm is movably connected to the upper part of a clamping claw, and the connection between the claw arm and the clamping claw is connected to the top plate; the two ends of a spring sheet that is bent in a free state are respectively fixed to a clamping claw and a claw arm, and the bend of the spring sheet is located at the movable connection between the clamping claw and the claw arm; claw teeth are provided at the bottom of each clamping claw; the position of each clamping claw corresponds to the opening position on the support ring;

[0008] A first through hole is opened at the axis of the central disk, a push rod is installed in the first through hole, the upper end of the push rod is above the clamping claw plate, and the lower end of the push rod extends to the fruit on the supporting ring; the push rod is connected to the third driving mechanism and can move up and down, and the third driving mechanism is connected to the control box.

[0009] Furthermore, the longan peeling and core removing device used in the longan processing production line further includes:

[0010] The bottom plate is installed on the back of the fruit plate, the bottom plate is connected to the fourth driving mechanism, and the fourth driving mechanism is connected to the control box; the bottom end of the knife handle is fixedly connected to the bottom plate, and a long through groove is opened on the knife handle body, the knife rod is bent, and the knife rod is installed at the upper end of the through groove through a pin at the bend, and part of the knife rod is accommodated in the through groove; the upper end of the skin cutting knife spring is connected to the knife rod head, and the lower end is connected to the lower end of the knife handle; the lower end of the knife rod is connected to the circular skin cutting blade through a pin, and the side of the skin cutting blade is provided with a circular boss, and the diameter of the circular boss is smaller than the diameter of the skin cutting blade; the number of the combination of the knife handle, the knife rod, the skin cutting knife spring, and the skin cutting blade is N.

[0011] Furthermore, the longan peeling and core removing device for a longan processing production line further comprises: the top of the push rod sleeve is fixedly connected to the bottom of the top plate, the upper section of the push rod is sleeved in the push rod sleeve, the lower end of the push rod is provided with a spring seat, the push rod exposed in the lower section of the push rod sleeve is covered with a push rod spring, the upper end of the push rod spring presses against the lower bottom surface of the push rod sleeve, and the lower end of the push rod spring presses against the spring seat;

[0012] A second through hole is axially opened in the ejector rod, and an ejector pin is installed in the second through hole; the ejector pin is connected to a fifth driving mechanism and can move up and down, and the fifth driving mechanism is connected to the control box;

[0013] The annular blade is fixed on the bottom plate, with the blade edge facing upwards, and the diameter of the annular blade is greater than the diameter of the fruit core.

[0014] Most preferably, the value of N is 3.

[0015] The present invention has the following advantages:

[0016] In view of the low efficiency of core and peeling in existing production lines for fruits like longan, the present invention proposes a longan core and peeling device for a longan processing production line. The device distributes the peeling steps based on the actual situation, and adds a core removal knife to the core removal step, which not only ensures feasibility but also ensures stability and efficiency. At the same time, the present invention integrates multiple similar processes on the same drive device, and multiple processing links can be completed with only one action, which can greatly improve production efficiency. In addition, the designed parts have excellent interchangeability, which can greatly reduce the cost of the device. This method is not only suitable for longan, but can also be applied to the peeling and core removal of various soft-shelled core fruits, such as lychee, etc. through size adjustment and visual control adjustment. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a schematic diagram of the overall structure of the device.

[0018] Figure 2 is a schematic diagram of a longan tray containing longans.

[0019] Figure 3 is a schematic diagram of the support ring.

[0020] Figure 4 It is a schematic diagram of the skin cutting mechanism.

[0021] Figure 5 It is a schematic diagram of the skin cutting knife.

[0022] Figure 6 It is a cross-sectional view of the dermatome portion.

[0023] Figure 7 It is a schematic diagram of the denucleation mechanism.

[0024] Figure 8 It is a cross-sectional view of the denuclearization mechanism.

[0025] Fig. 9 It is a schematic diagram of the clamping mechanism.

[0026] Fig.10 This is a schematic diagram of the baseboard integration.

[0027] Fig.11 It is a schematic diagram of the integration of the clamping mechanism and the clamping plate.

[0028] Fig.12 It is a schematic diagram of top plate integration.

[0029] Fig.13 This is a schematic diagram of the positioning screw installation.

[0030] In the figure: 1. longan, 2. supporting ring component, 3. fruit plate, 4. knife handle, 5. knife handle screw, 6. skin cutting knife, 7. skin cutting knife spring, 8. knife rod, 9. ejector sleeve, 10. ejector sleeve retaining spring, 11. ejector spring, 12. ejector, 13. core removing knife, 14. core removing knife retaining spring, 15. ejector pin, 16. ejector retaining spring, 17. clamping claw, 18. spring sheet, 19. clamping claw screw, 20. claw arm, 21. connecting rod, 22. center plate, 23. push rod, 24. push rod retaining spring, 25. bottom plate, 26. clamping claw plate, 27. top plate, 28. positioning pin, 29. positioning screw. DETAILED DESCRIPTION

[0031] like Figure 1 As shown, the longan peeling and core removing device used in the longan processing production line includes four main parts, namely a longan tray, a peeling mechanism, a core removing mechanism and a peeling mechanism.

[0032] The longan tray is composed of a fruit plate 3 and a supporting ring, wherein one supporting ring is composed of three identical supporting ring components 2, such as Figure 2 shown.

[0033] A fruit plate 3 is provided with 6 large through holes, the middle part of which is a support ring hole, the aperture of which is larger than that of the longan 1, so as to ensure that the longan 1 can pass through without obstacles. A fruit plate is provided with 6 support ring holes, which means that 6 longans can be processed at the same time. Of course, as long as the length of the fruit plate allows, more support ring holes can be provided. In the preferred embodiment, 3 elongated through holes are evenly distributed along the radial direction of the support ring hole, and the midline angle of each two elongated through holes along the radial direction of the circular hole is 120°, and the elongated through holes are connected to the support ring hole. For safety and aesthetic considerations, rounded corners are provided at the transition in the elongated through hole. The 3 elongated through holes mean that 3 tools at an angle of 120 degrees to each other are used to process a longan during the skinning and peeling process of the longan. Of course, those skilled in the art can also use 4 tools at an angle of 90 degrees to each other, and can also achieve the same technical purpose as the present invention, but the use of more than 3 tools is not the optimal solution. The fruit tray 3 is also provided with a series of through holes for screw connection, which are located at both ends of the length direction of the fruit tray 3 and between the midline angles of each two long through holes along the radial direction of the circular hole. The through holes distributed at both ends of the length direction of the fruit tray 3 are used to connect with the conveying mechanism. After completing the setting steps, the longan 1 can be directly sent to the next station by the conveying mechanism. During this process, the longan 1 does not need to be operated and only the conveying mechanism is running.

[0034] A support ring is composed of three identical support ring parts 2, such as Figure 3As shown, the support ring component 2 is designed with a flange, and two threaded holes are formed on the flange, which correspond to the two through holes located between the long through holes on the fruit plate 3, and are fixed under the fruit plate with screws. A supporting claw is designed at the lower part of the support ring component 2, and the part where the supporting claw contacts the longan 1 is in an arc shape, and the diameter of the arc is smaller than the diameter of the longan 1. Three support ring components 2 are evenly distributed along the circumference, and the corresponding surfaces are kept parallel to form a support ring. There is a certain distance between each two corresponding parallel surfaces of the support ring component 2 to form an opening, which does not affect the skin cutting knife 6 to contact the longan epidermis through the opening. During the processing, the longan 1 enters the support ring through the large circular hole on the fruit plate 3 and is supported by the supporting claw on the support ring component 2.

[0035] The skin cutting mechanism can be divided into two parts, namely the skin cutting knife part and the push rod part. Figure 4 The dermatome part includes: a handle 4, a handle screw 5, a dermatome 6, a dermatome spring 7 and a shank 8, as shown in FIG. Figure 5 As shown. The handle 4 is a quadrangular prism in appearance, and a long through slot is provided on the handle for mounting the shank 8. The handle 4 also has two threaded holes, of which the threaded hole located directly below is used for connecting with the bottom plate 25, and a longer handle screw 5 is installed on the other threaded hole. After tightening, a section of the handle screw 5 is exposed outside for connecting with the skin cutting knife spring 7. The shank 8 is bent, as shown in FIG. Figure 6As shown, the knife bar 8 is provided with three through holes and a square groove. The through hole at the longer end is used to connect with the skin cutting knife spring 7, and the other two through holes are connected with the knife bar 8 and the knife handle 4 and the knife bar 8 and the skin cutting knife 6 respectively by pins. The friction force of the pin connection is very small, so the knife bar 8 can rotate around the axis of the pin, and the skin cutting knife 6 can also rotate around the axis of the corresponding pin. In addition to the blade, the skin cutting knife 6 also has a boss at both ends. The diameter of the boss is smaller than the outer diameter of the blade of the skin cutting knife 6, so that the blade will not penetrate too deeply into the flesh after the skin cutting knife 6 cuts the longan skin. The push rod part includes: a push rod sleeve 9, a push rod sleeve retaining spring 10, a push rod spring 11, a push rod 12 and a push rod retaining spring 16. The push rod sleeve 9 can be divided into two sections according to the diameter. The larger diameter section has two retaining spring grooves for installing the push rod sleeve retaining spring 10, and the push rod part is fixed on the top plate 27. The top plate is installed above the front of the fruit plate. The top plate is connected to the first driving mechanism and can move up and down. The first driving mechanism is connected to the control box. A through hole is opened in the middle of the entire top rod sleeve 9 for installing the top rod 12. A countersunk groove is opened inside a section with a smaller diameter of the top rod sleeve 9, and the groove is mainly used to install the top rod spring 11. The top rod 12 is installed in the through hole of the top rod sleeve 9. The top rod 12 also has a through hole along the axial direction, and the hole is used to install the ejector pin 15 for core removal. There is also a hemispherical cover at the lower end of the top rod 12. This structure is mainly to evenly disperse the force while pressing the longan 1, so that the longan 1 can be compacted without crushing the longan 1. A retaining spring groove is opened at the upper end of the top rod 12 for installing the top rod retaining spring 16. The top rod spring 11 is installed on the top rod. In the actual operation process, the longan 1 is located on the support ring, and the longan pedicle is ensured to face downward. First, the top plate 27 drives the push rod sleeve 9 and then drives the push rod part to move downward, and the lower end of the push rod 12 contacts the longan 1. After that, the push rod sleeve 9 can continue to move downward until the push rod spring 11 contacts the lower end of the push rod 12 and then gradually increases the pressure. The applied pressure range can press the longan 1 onto the supporting ring, ensuring that the longan 1 will not change its posture during the skin cutting process and will not cause damage to the longan 1. After that, the bottom plate 25 drives the skin cutting knife part to move upward, and the blade of the skin cutting knife 6 first contacts the longan 1 and cuts the longan skin. After that, the boss on the skin cutting knife 6 contacts the longan skin and prevents the skin cutting knife 6 from going deeper. In the process of the skin cutting part gradually moving upward, since the skin cutting knife cannot continue to go deeper into the longan 1, the knife bar 8 will start to rotate to stretch the skin cutting knife spring 7. This stretching process has two main functions: 1. Increase the force to ensure successful cutting into the longan skin. If the skin cutting knife 6 does not cut in, the stretching will be more obvious, and the force on the skin cutting knife 6 will increase, thereby successfully cutting the longan skin. 2. Energy storage, automatic recovery after the action is completed. When there is no longan 1 after cutting, the knife bar 8 can automatically return to its original position under the spring force of the skin cutting knife spring 11. After the skin cutting process is completed, three knife edges will be left on the longan skin to facilitate the subsequent skinning process.Meanwhile, this process needs to be performed before the longan 1 is pitted, because the longan 1 is fuller before being pitted, and the skin cutting knife 6 can easily cut the longan skin.

[0036] The core removal mechanism also consists of two parts, namely the ejector part and the core removal knife part. Figure 7 As shown. The ejector part is basically the same as the ejector rod part of the above-mentioned peeling mechanism, except that an ejector pin 15 is installed inside the ejector rod 12, and the ejector pin 15 is connected to the fifth drive mechanism and can move up and down, and the fifth drive mechanism is connected to the control box. The core removing knife part includes a core removing knife 13 and a core removing knife retaining spring 14. There are two retaining spring grooves at the lower part of the core removing knife 13 for installing the core removing knife retaining spring 14, and the core removing knife retaining spring 14 can fix the core removing knife 13 on the bottom plate 25 and be driven by the bottom plate 25. The bottom plate is installed on the back of the fruit plate, and the bottom plate is connected to the fourth drive mechanism, and the fourth drive mechanism is connected to the control box. The upper end of the core removing knife 13 is a circle of sharp annular blades, and the blade edge faces upward. The interior of the core removing knife 13 is hollow, which is convenient for the falling of longan cores and part of the longan skin. In the actual operation process, such as Figure 8 As shown, first, the top plate 27 moves downward to drive the top rod 12 of the ejector part to press the longan 1 and fix it on the supporting ring; then the bottom plate 25 moves upward, and at the same time, the ejector 15 inside the ejector rod 12 moves downward to penetrate into the longan 1 and the longan core; at the same time, in the process of the core removal knife 13 moving upward, the longan skin around the longan core can be cut to form an annular incision, and after the ejector 15 penetrates the longan core, it can push out the longan core together with a part of the longan skin connected to the longan core when continuing to move downward, and discharge it downward along the core removal knife 13.

[0037] The peeling mechanism includes a clamping jaw part and a push rod 23. The clamping jaw part is composed of a clamping jaw 17, a spring sheet 18, a clamping jaw screw 19, a clamp arm 20, a connecting rod 21, a center disk 22 and a positioning pin 28. Fig. 9 As shown, in order to more clearly express the incision made by the skin cutting knife 6 on the longan 1, the longan 1 is rotated so that the incision is in the center of the field of vision and is not blocked by the clamping claw 17. In order to facilitate the description of the contact between the positioning screw 29 and the positioning pin 28, the figure also includes the positioning screw 29, which is installed on the top plate 27. Fig.13As shown. Among them, three structures that match the connecting rod 21 are evenly distributed along the circumference of the center disk 22, and the matching parts are connected by pins, and the connecting parts can rotate around the pin axis. The connecting rod 21 and the claw arm 20, as well as the claw arm and the clamping claw 17 are also connected by pins. Three threaded holes are evenly distributed along the circumferential direction on the center disk 22, which are used to connect with the clamping claw plate 26, and then the entire clamping claw part is connected to the clamping claw plate 26, and is driven by the clamping claw plate 26. The clamping claw plate 26 is connected to the second driving mechanism and can move up and down. The second driving mechanism is connected to the control box. There is a circular boss at the upper end of the center disk 22 for positioning when installed with the clamping claw plate. A through hole is opened at the axis of the center disk 22 for installing the push rod 23. The push rod 23 is connected to the third driving mechanism and can move up and down. The third driving mechanism is connected to the control box. There is a retaining spring groove on the push rod 23 for installing the push rod retaining spring 24. The push rod retaining spring 24 is to ensure that the displacement of the push rod will not be too large. A long positioning pin 28 is used to position the claw arm 20 and the clamping jaw 17. Both ends of the long positioning pin 28 extend out, and the positioning pin 28 itself is fixedly connected to the top plate 27 by positioning screws 29. A long spring piece 18 with a bent shape is fitted on the clamping jaw 17 and the claw arm 20. A rectangular through hole is provided on at least one of the clamping jaw 17 and the claw arm 20. The upper end and the lower end of the spring piece 18 are connected to the claw arm 20 and the clamping jaw 17 by clamping jaw screws 18, respectively, wherein at least one clamping jaw screw 18 is installed on two rectangular through holes and can move in the rectangular through holes. The part of the clamping jaw 17 that contacts the longan 1 is serrated. This design is to partially embed the clamping jaw 17 into the longan skin, increase the friction, and smoothly grab the longan skin.

[0038] In the actual operation process, the push rod 23 first moves downward to fix the longan 1 on the supporting ring, and then the top plate 27 moves downward until the clamping claw 17 reaches the appropriate position of the lower half of the longan and stops. Then the clamping claw plate 26 drives the central disk 22 to move downward, the upper end of the connecting rod 21 descends, and the lower end generates a downward and outward thrust on the upper end of the claw arm 20, which is transmitted to the upper end of the spring sheet 18, and the force on the upper end of the spring sheet 18 is transmitted to the lower end of the spring sheet 18, and an inward and upward force is generated at the lower end of the spring sheet 18, which acts on the clamping claw 17, so that the three clamping claws 17 work together to grasp the longan skin. Then the top plate 27 moves upward, driving the three clamping claws 17 with clamping force to move upward, while the push rod 23 remains pressed on the longan, so that the longan skin is peeled off from the longan by the three clamping claws 17 with clamping force. In addition, when the skin cutting process has been completed and three incisions are left on the longan skin, the longan skin is easier to peel off. After the skin and flesh are separated, the push rod 23 rises, and the clamping claw plate 26 and the top plate 27 keep rising synchronously, grabbing the longan skin from the supporting ring hole, and the longan flesh remains in the supporting ring hole; when the entire production line is advanced forward half a station, the clamping claw 17 is released to make the longan skin fall between the two longan trays.

[0039] The present invention integrates multiple processes that can be completed simultaneously by combining the consideration of the control part. The skin cutting knife part in the skin cutting mechanism and the core removing knife part in the core removing mechanism are integrated on the bottom plate 25, such as Fig.10 As shown, the ejector rod part in the skin cutting mechanism and the ejector pin part in the core removing mechanism are integrated into the ejector plate, as shown in FIG. Fig.12 All peeling mechanisms are integrated on the clamping claw plate 26, as shown. Fig.11 As shown, individual driving is possible.

Claims

1. A longan peeling and core removing device for a longan processing production line, characterized in that: include: The fruit plate is provided with a plurality of through holes, which are called support ring holes. The aperture of each support ring hole can pass a fruit. The support ring is arranged at the lower end of the support ring hole. The diameter of the support ring is smaller than the outer diameter of the fruit and larger than the outer diameter of the fruit core. N long through holes are evenly opened along the radial direction of the circumference of the support ring hole. Each long through hole is connected to the circumference of the support ring hole. N openings are evenly distributed on the support ring. The openings on the support ring correspond to the positions of the long through holes on a vertical plane. The top plate is installed above the front of the fruit plate, and the top plate is connected to the first driving mechanism and can move up and down, and the first driving mechanism is connected to the control box; A center plate is fixedly installed below the clamping jaw plate, and N pins are evenly distributed along the circumference of the center plate, and the value of N is a natural number of 3 to 6; each pin is connected to the upper part of a connecting rod, and the lower part of each connecting rod is movably connected to the upper part of a claw arm, and the lower part of a claw arm is movably connected to the upper part of a clamping jaw, and the connection between the claw arm and the clamping jaw is connected to the top plate; the two ends of a spring sheet that is bent in a free state are respectively fixed to a clamping jaw and a claw arm, and the bend of the spring sheet is located at the movable connection between the clamping jaw and the claw arm; claw teeth are provided at the bottom of each clamping jaw; the position of each clamping jaw corresponds to the opening position on the support ring; A first through hole is opened at the axis of the central disk, a push rod is installed in the first through hole, the upper end of the push rod is above the clamping claw plate, and the lower end of the push rod extends to the fruit on the supporting ring; The push rod is connected to the third driving mechanism and can move up and down, and the third driving mechanism is connected to the control box; It also includes: a bottom plate is installed on the back of the fruit plate, the bottom plate is connected to the fourth driving mechanism, and the fourth driving mechanism is connected to the control box; The bottom end of the knife handle is fixedly connected to the bottom plate, a long through slot is formed on the knife handle body, the knife rod is bent, the knife rod is installed at the upper end of the through slot at the bend through a pin, and part of the knife rod is accommodated in the through slot; the upper end of the skin cutting knife spring is connected to the knife rod head, and the lower end is connected to the lower end of the knife handle; the lower end of the knife rod is connected to the circular skin cutting blade through a pin, and the side of the skin cutting blade is provided with a circular boss, and the diameter of the circular boss is smaller than the diameter of the skin cutting blade; the number of the combination of the knife handle, the knife rod, the skin cutting knife spring, and the skin cutting blade is N.

2. The longan peeling and core removing device for a longan processing production line according to claim 1, characterized in that: Also includes: The top of the ejector sleeve is fixedly connected to the bottom of the ejector plate, the upper section of the ejector sleeve is sleeved in the ejector sleeve, a spring seat is provided at the lower end of the ejector, the ejector exposed at the lower section of the ejector sleeve is covered with an ejector spring, the upper end of the ejector spring presses against the lower bottom surface of the ejector sleeve, and the lower end of the ejector spring presses against the spring seat; A second through hole is axially opened in the ejector rod, and an ejector pin is installed in the second through hole; the ejector pin is connected to a fifth driving mechanism and can move up and down, and the fifth driving mechanism is connected to the control box; The annular blade is fixed on the bottom plate, with the blade edge facing upwards, and the diameter of the annular blade is greater than the diameter of the fruit core.

3. The longan peeling and core removing device for a longan processing production line according to claim 2, characterized in that: The value of N is 3.

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