Eccentric rolling cutting device and plate production system

Abstract

The present invention provides an eccentric rolling cutting device and a plate production system, which relate to the technical field of shearing equipment and include: a frame; an upper knife frame and a lower knife table arranged relatively to each other, the upper knife frame being swingably arranged on the frame; a shearing blade arranged on the upper knife frame, the upper knife frame being able to drive the shearing blade to controllably shear with the lower knife table; a guide limiting mechanism, the guide limiting mechanism being able to guide the upper knife frame along a first direction of the frame; an eccentric rotating mechanism, the eccentric rotating mechanism being arranged between the upper knife frame and the frame, the upper knife frame being able to drive the shearing blade to eccentrically swing through the eccentric rotating mechanism; and a driving mechanism. The present invention can control the eccentric swing path of the upper knife frame by cooperating with the eccentric rotating mechanism, thereby better controlling the rolling cutting trajectory between the shearing blade and the lower knife table, thereby improving the rolling cutting quality of the plate, and eliminating the need for an additional control system on the driving mechanism, thereby reducing the manufacturing and maintenance costs of the eccentric rolling cutting device.

Description

Technical Field

[0001] The present invention relates to the technical field of shearing equipment, and in particular to an eccentric rolling cutting device and a plate production system. Background Art

[0002] Existing rolling shears are primarily mechanical and hydraulic. Mechanical shears are relatively complex and bulky, often achieving rolling shearing by reverse engineering and optimizing the connecting rod length, crank radius, and phase angle based on key locations along the curved blade's rolling shearing trajectory. Furthermore, the shearing drive mechanism, which primarily consists of a motor, reducer, crankshaft, connecting rod, and curved blade, presents challenges during use, including complex structure, high machining and assembly precision requirements, high equipment cost, and high maintenance costs.

[0003] Hydraulic shearing machines usually use two hydraulic cylinders to drive a composite connecting rod mechanism to achieve rolling shearing of the upper shear blade. In order to make the hydraulic cylinders work according to the trajectory and speed required for rolling cutting, an additional servo control system needs to be set on the two hydraulic cylinders. This increases the complexity of the electronic control and hydraulic systems, resulting in the large-scale and complex hydraulic and control systems, increasing the equipment cost and the maintenance cost of subsequent debugging and production. Summary of the Invention

[0004] In order to overcome the above-mentioned defects of the prior art, the technical problem to be solved by the embodiments of the present invention is to provide an eccentric rolling cutting device and a plate production system for improving the control accuracy of the rolling shearing trajectory and simplifying the complexity of the control system to reduce manufacturing and maintenance costs.

[0005] The above-mentioned object of the present invention can be achieved by adopting the following technical solutions. The present invention provides an eccentric rolling cutting device, comprising:

[0006] frame;

[0007] An upper tool holder and a lower tool table are arranged opposite to each other, wherein the upper tool holder is swingably arranged on the frame;

[0008] A shearing blade is provided on the upper tool holder, wherein a shearing station is formed between the shearing blade and the lower tool table, and the upper tool holder can drive the shearing blade and the lower tool table to shear in a controllable manner;

[0009] a guide and limiting mechanism, disposed between the upper tool holder and the frame, wherein the guide and limiting mechanism is capable of guiding the upper tool holder along a first direction of the frame;

[0010] An eccentric rotating mechanism, the eccentric rotating mechanism being arranged between the upper knife holder and the machine frame, and the upper knife holder being able to drive the shear blade to eccentrically swing through the eccentric rotating mechanism;

[0011] and a driving mechanism, wherein the driving mechanism is connected to the upper tool holder and can drive the upper tool holder to swing reciprocatingly and eccentrically.

[0012] In a preferred embodiment of the present invention, the upper tool holder includes a horizontal upper tool platform and a mounting portion protruding from the middle of the upper tool platform, the shear blade is arranged on the upper tool platform, and the guide limiting mechanism is arranged between the mounting portion and the frame.

[0013] In a preferred embodiment of the present invention, the cutting blade is an arc-shaped cutting blade protruding from the bottom of the upper cutting platform, and the arc-shaped cutting blade is arranged along the longitudinal extension direction of the upper cutting platform.

[0014] In a preferred embodiment of the present invention, the guide and limiting mechanism includes a guide groove provided on the frame, and a guide block slidably provided in the guide groove, and the mounting portion is rotatably connected to the guide block.

[0015] In a preferred embodiment of the present invention, a first rotating shaft is provided on the guide block, the first rotating shaft is arranged on the frame along the second direction, and the mounting portion is rotatably connected to the first rotating shaft.

[0016] In a preferred embodiment of the present invention, the eccentric rotating mechanism includes a second rotating shaft arranged on the frame, and an eccentric member sleeved on the second rotating shaft, the second rotating shaft is arranged on the frame along a third direction, and the upper tool holder is rotatably connected to the eccentric member.

[0017] In a preferred embodiment of the present invention, the eccentric member is an eccentric sleeve disposed between the second rotating shaft and the mounting portion, and the diameter of the eccentric sleeve is set to a first size.

[0018] In a preferred embodiment of the present invention, the first direction is the height direction of the rack, the second direction and the third direction are parallel, and the second direction and the third direction are both perpendicular to the first direction.

[0019] In a preferred embodiment of the present invention, the driving mechanism includes a first driving device and a second driving device relatively arranged on both sides of the eccentric rotation mechanism, the first driving device has a first telescopic rod, the first driving device is hinged to the frame, the first telescopic rod is hinged to the upper tool holder, the second driving device has a second telescopic rod, the second driving device is hinged to the frame, and the second telescopic rod is hinged to the upper tool holder.

[0020] The present invention also provides a plate production system, comprising the aforementioned eccentric rolling cutting device.

[0021] The technical solution of the present invention has the following significant beneficial effects:

[0022] When the eccentric rolling cutting device described in the present invention is used, an upper blade holder and a lower blade table are positioned relative to each other on a machine frame. The upper blade holder is provided with a shearing blade, and a shearing station is formed between the shearing blade and the lower blade table. The upper blade holder is swingably mounted on the machine frame, and an eccentric rotation mechanism is provided between the upper blade holder and the machine frame. The eccentric rotation mechanism enables the upper blade holder to swing eccentrically on the machine frame. A guide and limit mechanism is also provided between the upper blade holder and the machine frame. The guide and limit mechanism can guide the upper blade holder along a first direction of the machine frame, such as along the height direction of the machine frame. Furthermore, by drivably connecting the drive mechanism to the upper blade holder, the drive mechanism can drive the upper blade holder to swing eccentrically back and forth, thereby continuously driving the shearing blade to cooperate with the lower blade table to perform rolling cutting operations.

[0023] The present invention can control the eccentric swing path of the upper tool holder by cooperating with the eccentric rotation mechanism and the guide limit mechanism, thereby better controlling the rolling cutting trajectory between the shear blade and the lower tool table, improving the rolling cutting quality of the plate, and eliminating the need for an additional control system on the drive mechanism, thereby reducing the manufacturing and maintenance costs of the eccentric rolling cutting device.

[0024] For example, when the driving mechanism uses two hydraulic cylinders, it is only necessary to detect the signals emitted by each hydraulic cylinder at the extension and retraction limit points, and control the two hydraulic cylinders to reverse to drive the upper tool holder to swing back and forth eccentrically. The two hydraulic cylinders only need to provide reciprocating power and do not need to participate in controlling the rolling cutting trajectory of the shear blade, so there is no need to set up an additional control system. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0026] The drawings described herein are for illustrative purposes only and are not intended to limit the scope of the present invention in any way. In addition, the shapes and proportional dimensions of the various components in the drawings are merely illustrative and are used to help understand the present invention, and are not intended to specifically limit the shapes and proportional dimensions of the various components of the present invention. Those skilled in the art can select various possible shapes and proportional dimensions to implement the present invention according to specific circumstances under the guidance of the present invention.

[0027] Figure 1 This is a schematic diagram of the main structure of the eccentric rolling cutting device of the present invention;

[0028] Figure 2A schematic diagram of the three-dimensional structure of the eccentric rolling cutting device of the present invention;

[0029] Figure 3 This is a schematic diagram of the main structure of the upper knife platform of the present invention;

[0030] Figure 4 This is a schematic diagram of a three-dimensional structure of the upper knife platform of the present invention;

[0031] Figure 5 A schematic diagram of a three-dimensional structure of the eccentric sleeve of the present invention;

[0032] Figure 6 The figure is a schematic diagram of the process of forming a rolling cutting track by the eccentric rolling cutting device of the present invention.

[0033] Reference numerals in the above drawings:

[0034] 1. Frame; 11. Upper crossbeam;

[0035] 2. Upper tool holder; 21. Upper tool platform; 22. Installation part;

[0036] 3. Lower the knife platform;

[0037] 4. Shear blade;

[0038] 5. Guide limit mechanism; 51. Guide groove; 52. Guide block; 53. First rotating shaft;

[0039] 6. Eccentric rotating mechanism; 61. Second rotating shaft; 62. Eccentric member; 621. Eccentric sleeve;

[0040] 7. Driving mechanism; 71. First driving device; 711. First telescopic rod; 72. Second driving device; 721. Second telescopic rod. DETAILED DESCRIPTION

[0041] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0042] Implementation Method 1

[0043] Please refer to Figure 1 and Figure 2As shown, an embodiment of the present invention provides an eccentric rolling cutting device, comprising: a frame 1; an upper tool holder 2 and a lower tool table 3 arranged opposite to each other, the upper tool holder 2 being swingably arranged on the frame 1; a shearing blade 4 arranged on the upper tool holder 2, a shearing station being formed between the shearing blade 4 and the lower tool table 3, the upper tool holder 2 being able to drive the shearing blade 4 and the lower tool table 3 to controllably shear each other; a guide and limiting mechanism 5, arranged between the upper tool holder 2 and the frame 1, the guide and limiting mechanism 5 being able to guide the upper tool holder 2 along a first direction of the frame 1; an eccentric rotating mechanism 6, the eccentric rotating mechanism 6 being arranged between the upper tool holder 2 and the frame 1, the upper tool holder 2 being able to drive the shearing blade 4 to perform eccentric swinging through the eccentric rotating mechanism 6; and a driving mechanism 7, the driving mechanism 7 being connected to the upper tool holder 2, the driving mechanism 7 being able to drive the upper tool holder 2 to perform reciprocating eccentric swinging.

[0044] In general, when the eccentric rolling cutting device is in use, the upper tool holder 2 and the lower tool table 3 are positioned relative to each other on the machine frame 1. The upper tool holder 2 is provided with a shearing blade 4, forming a shearing station between the shearing blade 4 and the lower tool table 3. The upper tool holder 2 is swingably mounted on the machine frame 1, and an eccentric rotation mechanism 6 is provided between the upper tool holder 2 and the machine frame 1. The eccentric rotation mechanism 6 enables the upper tool holder 2 to swing eccentrically on the machine frame 1. A guide and limit mechanism 5 is also provided between the upper tool holder 2 and the machine frame 1. The guide and limit mechanism 5 can guide the upper tool holder 2 along a first direction of the machine frame 1. Furthermore, by drivably connecting the drive mechanism 7 to the upper tool holder 2, the drive mechanism 7 can drive the upper tool holder 2 to swing eccentrically back and forth, thereby continuously driving the shearing blade 4 to shear against the lower tool table 3 to perform the rolling cutting operation.

[0045] The eccentric rolling cutting device cooperates with the guide limit mechanism 5 through the eccentric rotating mechanism 6, which can control the eccentric swing path of the upper tool holder 2, thereby better controlling the rolling cutting trajectory between the shear blade 4 and the lower tool table 3, thereby improving the rolling cutting quality of the plate, and eliminating the need to set up an additional control system on the driving mechanism 7, thereby reducing the manufacturing and maintenance costs of the eccentric rolling cutting device.

[0046] Designers can adjust the first direction according to usage requirements, for example, setting the first direction to the height direction of the rack 1, which is not specifically limited here.

[0047] In a specific embodiment, the frame 1 includes an upper crossbeam 11 and multiple pillars arranged at both ends of the upper crossbeam 11. The lower tool platform 3 is arranged directly below the upper crossbeam 11, and the upper tool holder 2 is swingably connected to the upper crossbeam 11 through an eccentric rotating mechanism 6.

[0048] In an embodiment of the present invention, Figure 3 and Figure 4In the embodiment shown, the upper tool holder 2 includes a horizontal upper tool platform 21 and a mounting portion 22 protruding from the middle of the upper tool platform 21, the shear blade 4 is arranged on the upper tool platform 21, and the guide and limiting mechanism 5 is arranged between the mounting portion 22 and the frame 1.

[0049] By cooperating with the eccentric rotating mechanism 6 and the guide limiting mechanism 5, the reciprocating swing path of the upper knife table 21 can be controlled, so that the upper knife table 21 can reciprocately drive the shear blade 4 and the lower knife table 3 to shear to form a rolling cutting trajectory.

[0050] Specifically, the upper tool platform 21 is connected to the upper crossbeam 11 through the eccentric rotating mechanism 6 , and the mounting portion 22 is slidably connected to the upper crossbeam 11 through the guide and limiting mechanism 5 .

[0051] The sliding guide amount of the guide limiting mechanism 5 is not less than the eccentric amount of the eccentric rotating mechanism 6 , so that the guide limiting mechanism 5 and the guide limiting mechanism 5 will not be stuck.

[0052] In a feasible embodiment of the present invention, the cutting blade 4 is an arc-shaped cutting blade protruding from the bottom of the upper cutting platform 21 , and the arc-shaped cutting blade is arranged along the longitudinal extension direction of the upper cutting platform 21 .

[0053] By utilizing the arc-shaped shear blade, better cooperation with the lower cutter table 3 can be performed in rolling cutting, thereby improving the uniformity of rolling cutting of the plate and further improving the rolling cutting quality.

[0054] Designers can adjust the curvature and length of the curved shear blade according to the cutting requirements of the plate, and no specific numerical restrictions are imposed here.

[0055] In other embodiments, designers can adjust the shape of the shear blade 4 according to shearing needs. For example, the shear blade 4 can be a combination of an arc shape and a straight line shape. No specific limitation is made here.

[0056] In an embodiment of the present invention, the guide and limiting mechanism 5 includes a guide groove 51 provided on the frame 1 and a guide block 52 slidably provided in the guide groove 51 , and the mounting portion 22 is rotatably connected to the guide block 52 .

[0057] Specifically, the guide block 52 is provided with a first rotating shaft 53, which is disposed on the frame 1 along the second direction, and the mounting portion 22 is rotatably connected to the first rotating shaft 53. Furthermore, a guide groove 51 is provided on the upper crossbeam 11 along the height direction of the frame 1, and the guide block 52 is slidably disposed in the guide groove 51. The middle portion of the upper tool platform 21 is rotatably connected to the guide block 52.

[0058] The guide groove 51 can serve as a guide and limit for the upper knife table 21. The guide groove 51 can provide the upper knife table 21 with a displacement in the height direction and limit the displacement of the upper knife table 21 in the horizontal direction, so that the upper knife table 21 can swing symmetrically and eccentrically relative to the guide groove 51, thereby driving the shear blade 4 to cut the plate more evenly.

[0059] In an embodiment of the present invention, the eccentric rotation mechanism 6 includes a second rotating shaft 61 arranged on the frame 1, and an eccentric member 62 sleeved on the second rotating shaft 61, the second rotating shaft 61 is arranged on the frame 1 along the third direction, and the upper tool holder 2 is rotatably connected to the eccentric member 62.

[0060] Specifically, such as Figure 3 and Figure 5 In the illustrated embodiment, the eccentric member 62 is an eccentric sleeve 621 disposed between the second rotating shaft 61 and the mounting portion 22. The diameter of the eccentric sleeve 621 is set to a first size. The upper cutter platform 21 is provided with a mounting hole, through which the upper cutter platform 21 is rotatably mounted on the eccentric sleeve 621.

[0061] Please combine Figure 6 The rolling cutting trajectory formation flow chart shown in the figure illustrates that the upper cutter table 21 is rotatably mounted on the eccentric sleeve 621. Under the eccentric action of the eccentric sleeve 621, the upper cutter table 21 is able to oscillate eccentrically around the second rotating shaft 61, thereby driving the shear blade 4 to form a rolling cutting trajectory on the lower cutter table 3, thereby evenly cutting the plate. Designers can adjust the first magnitude value to control the swing amplitude of the upper cutter table 21 according to actual needs, thereby effectively cutting plates of varying thicknesses. No specific numerical limit is imposed herein.

[0062] In other embodiments, designers may adjust the specific structure of the eccentric member 62 according to usage requirements, such as setting the eccentric member to a block structure, or setting the eccentric member 62 to a connecting rod structure, which is not specifically limited here.

[0063] In a feasible embodiment of the present invention, the first direction is the height direction of the rack 1 , the second direction and the third direction are parallel, and the second direction and the third direction are both perpendicular to the first direction.

[0064] By setting the first direction along the height direction of the frame 1 and making the second direction and the third direction perpendicular to the first direction, the upper knife table 21 can drive the shear blade 4 to form a rolling cutting track along the horizontal direction, so as to evenly shear the horizontally transported plate.

[0065] In other embodiments, designers may adjust the orientations of the first direction, the second direction, and the third direction according to the shearing requirements of the plate, and no specific limitation is imposed herein.

[0066] In an embodiment of the present invention, the driving mechanism 7 includes a first driving device 71 and a second driving device 72 relatively arranged on both sides of the eccentric rotation mechanism 6, the first driving device 71 having a first telescopic rod 711, the first driving device 71 being hinged to the frame 1, the first telescopic rod 711 being hinged to the upper tool holder 2, the second driving device 72 having a second telescopic rod 721, the second driving device 72 being hinged to the frame 1, the second telescopic rod 721 being hinged to the upper tool holder 2.

[0067] In the embodiment of the present invention, the first driving device 71 and the second driving device 72 are hydraulic cylinders symmetrically arranged on both sides of the eccentric rotating mechanism 6. By symmetrically arranging the two hydraulic cylinders, the driving uniformity of the two hydraulic cylinders on the upper tool table 21 is improved, and a better driving effect is achieved.

[0068] Designers can adjust the extension and contraction of the telescopic rod of the hydraulic cylinder according to shearing needs to control the swing and floating of the shear blade 4, thereby better shearing plates of different thicknesses.

[0069] In one feasible embodiment, when the two hydraulic cylinders are driven, when the extension amount of the telescopic rod of one hydraulic cylinder reaches the maximum, the telescopic rod of the hydraulic cylinder is at the extension limit point. At the same time, when the extension amount of the telescopic rod of the other hydraulic cylinder reaches the minimum, the telescopic rod of the hydraulic cylinder is at the retraction limit point.

[0070] At this time, it is only necessary to detect the signals emitted by the telescopic rod of each hydraulic cylinder at the extension limit point and the retraction limit point, and then control the telescopic rods of the two hydraulic cylinders to reverse to drive the upper tool table 21 to swing back and forth eccentrically, so that the shear blade 4 can cooperate with the lower tool table 3 to form a rolling cutting trajectory.

[0071] Therefore, the two hydraulic cylinders only need to provide reciprocating power and do not need to participate in controlling the rolling cutting trajectory of the shear blade 4, so there is no need to set up an additional control system.

[0072] In other embodiments, designers may adjust the specific structures of the first driving device 71 and the second driving device 72 according to driving requirements, for example, setting the first driving device 71 and the second driving device 72 as cylinders, which is not specifically limited here.

[0073] Implementation Method 2

[0074] An embodiment of the present invention also provides a sheet metal production system, including the aforementioned eccentric rolling cutting device. The specific structure, operating principle, and beneficial effects of the eccentric rolling cutting device are the same as those in the first embodiment and will not be further described here. By utilizing the eccentric rolling cutting device, the sheet metal production system can more conveniently control the eccentric swing path of the upper tool holder 2, thereby better controlling the rolling cutting trajectory between the shear blade 4 and the lower tool holder 3, thereby improving the rolling cutting quality of the sheet metal. This eliminates the need for an additional control system and reduces manufacturing and maintenance costs.

[0075] Furthermore, the plate production system may further include a plate conveying device, and the eccentric rolling cutting device is arranged on the plate conveying path of the plate conveying device, so that the plate can be rolled and cut by using the eccentric rolling cutting device.

[0076] All articles and references disclosed, including patent applications and publications, are incorporated herein by reference for all purposes. The term "essentially consisting of..." describing a combination should include the identified elements, ingredients, parts or steps and other elements, ingredients, parts or steps that do not substantially affect the basic novel features of the combination. The use of the terms "comprising" or "including" to describe the combination of elements, ingredients, parts or steps herein also contemplates an embodiment that is essentially composed of these elements, ingredients, parts or steps. By using the term "may", it is intended to illustrate that any attribute described that "may" include is optional. Multiple elements, ingredients, parts or steps can be provided by a single integrated element, ingredient, part or step. Alternatively, a single integrated element, ingredient, part or step can be divided into separate multiple elements, ingredients, parts or steps. The disclosure "one" or "an" used to describe an element, ingredient, part or step is not intended to exclude other elements, ingredients, parts or steps.

[0077] Each embodiment in this specification is described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the embodiments can be referred to each other. The above embodiments are only for illustrating the technical concept and features of the present invention. Their purpose is to enable people familiar with this technology to understand the content of the present invention and implement it accordingly, and they cannot be used to limit the scope of protection of the present invention. Any equivalent changes or modifications made according to the spirit of the present invention should be included in the scope of protection of the present invention.

Claims

1. An eccentric rolling cutting device, characterized in that: include: frame; An upper tool holder and a lower tool table are arranged opposite to each other, wherein the upper tool holder is swingably arranged on the frame; A shearing blade is provided on the upper tool holder, wherein a shearing station is formed between the shearing blade and the lower tool table, and the upper tool holder can drive the shearing blade and the lower tool table to shear in a controllable manner; a guide and limiting mechanism, disposed between the upper tool holder and the frame, wherein the guide and limiting mechanism is capable of guiding the upper tool holder along a first direction of the frame; an eccentric rotating mechanism, the eccentric rotating mechanism being arranged between the upper knife holder and the machine frame, and the upper knife holder being able to drive the shear blade to eccentrically swing through the eccentric rotating mechanism; and A driving mechanism connected to the upper tool holder, the driving mechanism being capable of driving the upper tool holder to swing reciprocatingly and eccentrically; The upper tool holder includes a horizontal upper tool platform and a mounting portion protruding from the middle of the upper tool platform, the shear blade is arranged on the upper tool platform, and the guide and limiting mechanism is arranged between the mounting portion and the frame; The guide and limiting mechanism includes a guide groove provided on the frame, and a guide block slidably provided in the guide groove, and the mounting portion is rotatably connected to the guide block; The guide block is provided with a first rotating shaft, the first rotating shaft is arranged on the frame along the second direction, and the mounting portion is rotatably connected to the first rotating shaft; The eccentric rotating mechanism includes a second rotating shaft provided on the frame, and an eccentric member sleeved on the second rotating shaft, wherein the second rotating shaft is provided on the frame along a third direction, and the upper tool holder is rotatably connected to the eccentric member; The driving mechanism includes a first driving device and a second driving device arranged on both sides of the eccentric rotation mechanism. The first driving device has a first telescopic rod, which is hinged to the frame, and the first telescopic rod is hinged to the upper tool holder. The second driving device has a second telescopic rod, which is hinged to the frame, and the second telescopic rod is hinged to the upper tool holder.

2. The eccentric rolling cutting device according to claim 1, characterized in that: The shearing blade is an arc-shaped shearing blade protruding from the bottom of the upper knife platform, and the arc-shaped shearing blade is arranged along the longitudinal extension direction of the upper knife platform.

3. The eccentric rolling cutting device according to claim 1, characterized in that: The eccentric member is an eccentric sleeve arranged between the second rotating shaft and the mounting portion, and the diameter of the eccentric sleeve is set to a first size.

4. The eccentric rolling cutting device according to claim 1, characterized in that: The first direction is the height direction of the rack, the second direction and the third direction are parallel, and the second direction and the third direction are both perpendicular to the first direction.

5. A plate production system, characterized in that: The method comprises the eccentric rolling cutting device according to any one of claims 1 to 4.

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