A method, apparatus, and storage medium for relieving stress in sheet metal cutting.

Abstract

This invention discloses a method, apparatus, and storage medium for stress-relieving sheet metal cutting. The method includes: setting stress-relieving regions of the sheet metal to be cut based on customized cutting data, wherein the stress-relieving regions are arranged at local edges or local centers of the sheet metal; issuing at least two cutting commands, controlling a sawing mechanism to cut the stress-relieving regions according to the first cutting command to release the sheet metal stress, and then cutting the stress-relieving sheet metal according to the second cutting command to obtain the finished sheet metal. This invention divides stress-relieving regions on the uncut sheet metal, which can be located at the two edges or the center of the uncut sheet metal. Pre-cutting local areas of the sheet metal can release stress, avoiding repeated corrections due to stress issues during subsequent processing, and improving the efficiency of sheet metal production.

Description

Technical Field

[0001] This invention relates to the field of sheet metal processing technology, and specifically to a sheet metal cutting method, apparatus, and storage medium for relieving sheet metal stress. Background Technology

[0002] In the sheet metal processing industry, most sheets are currently composite, and under various conditions, stress accumulates within the sheet. If this stress is not released before cutting, the resulting sheet will be affected by the stress, leading to unevenness and deformation.

[0003] When stress deformation occurs, the usual method to smooth the deformed sheet is to cut it again. This is very time-consuming, labor-intensive, and material-intensive. Often, during the processing of sheet materials, multiple sheets belong to the same batch. If one sheet shows a stress reaction, the rest will show stress reactions of varying degrees. Therefore, each time the sheet materials are processed, they must be trimmed first, which is very time-consuming and labor-intensive. Summary of the Invention

[0004] In order to overcome the shortcomings of the prior art, one of the objectives of the present invention is to provide a plate cutting method that releases plate stress in advance and improves plate production efficiency.

[0005] The second objective of this invention is to provide a plate cutting device that releases plate stress, which can automatically achieve the effects of plate stress release and cutting into shape, thereby improving efficiency.

[0006] The second objective of this invention is to provide a computer-readable storage medium.

[0007] One of the objectives of this invention is achieved through the following technical solution:

[0008] A method for cutting sheet metal to relieve stress includes:

[0009] The stress relief area of ​​the sheet material to be cut is set based on custom cutting data. The stress relief area is arranged at a local position at the edge of the sheet material to be cut or at a local position at the center of the sheet material to be cut.

[0010] At least two cutting instructions are issued to control the sawing mechanism to cut the stress-relieving area according to the first cutting instruction to release the stress of the board, and then the stress-relieving board is cut according to the second cutting instruction to obtain the desired finished board.

[0011] Furthermore, the cutting data includes stress relief mode, dimensional information of the sheet material to be cut, and dimensional information of the finished sheet material.

[0012] Furthermore, the method for setting the stress relief area is as follows:

[0013] The position on the sheet material to be cut is determined according to the stress relief mode;

[0014] Based on the size information of the board to be cut and the size information of the finished board, determine the arrangement direction of the finished board on the board to be cut and the reserved size of the excess material on the board to be cut.

[0015] Furthermore, the method for cutting the stress-relieving region includes:

[0016] The sawing mechanism is controlled according to the stress relief area, starting from the edges on both sides of the board to be cut and gradually cutting inwards, ensuring that a specified length of uncuttered area is retained in the middle of the board; or,

[0017] According to the stress relief area, the sawing mechanism is controlled to gradually cut from the middle of the board to be cut towards both sides of the board edge, and to ensure that the board edge on both sides retains a specified length of uncut area.

[0018] Furthermore, after cutting the two side edges of the board to be cut, it is necessary to ensure that the uncut area in the current cutting direction accounts for 45% to 55% of the total length of the board.

[0019] Furthermore, after cutting the middle part of the board to be cut, it is necessary to ensure that the uncut area retained at any edge of the board in the current cutting direction accounts for 10% to 30% of the total length of the board.

[0020] Furthermore, the method for cutting the stress-relieved sheet material according to the second cutting instruction includes roughening the sheet material and cutting the uncut area and the remaining material after stress relief on the sheet material.

[0021] The second objective of this invention is achieved by the following technical solution:

[0022] A plate cutting device for relieving plate stress includes a frame, a clamping mechanism and a sawing mechanism installed in the frame, and a central control device that is signal-communicated with the clamping mechanism and the sawing mechanism;

[0023] The clamping mechanism is used to clamp and fix the board to be cut and transport the fixed board to the designated position of the sawing mechanism;

[0024] The central control device executes the plate cutting method described above for releasing plate stress, and is used to control the sawing mechanism to cut the plate to be cut when it reaches the designated position.

[0025] Furthermore, the frame is also equipped with a pressure beam mechanism, which is connected to the central control equipment via a signal. The central control equipment controls the pressure beam mechanism to press the plate to be cut so as to facilitate cutting the plate.

[0026] The third objective of this invention is achieved by the following technical solution:

[0027] A computer-readable storage medium storing a computer program that, when run on one or more processors, performs the sheet metal cutting method described above for relieving sheet metal stress.

[0028] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0029] This invention divides stress-relief areas on an uncut sheet material. These stress-relief areas can be located at the two edges of the uncut sheet material or at the center of the uncut sheet material. By pre-cutting local areas of the sheet material, stress can be released, avoiding repeated corrections of the sheet material due to stress issues during subsequent processing, and improving the efficiency of sheet material production and manufacturing. Attached Figure Description

[0030] Figure 1 This is a top view of the plate cutting device for relieving plate stress according to the present invention.

[0031] Figure 2 This is a side view of the plate cutting device for relieving plate stress according to the present invention;

[0032] Figure 3 for Figure 2 Enlarged structural diagram of the sawing mechanism;

[0033] Figure 4 This is a schematic diagram of the sheet material to be cut.

[0034] Figure 5 This is a diagram showing the gaps that appear after the board material to be cut has undergone conventional cutting.

[0035] Figure 6 This is a schematic diagram showing a non-right angle formed after cutting a board material with a central protrusion.

[0036] Figure 7 This is a schematic diagram of a right-angled plate obtained after pressing and cutting using the plate cutting method of the present invention to release plate stress;

[0037] Figure 8 This is a schematic diagram of the first stress mode of the present invention;

[0038] Figure 9 This is a schematic diagram of the second stress mode of the present invention;

[0039] Figure 10 This is a schematic diagram of the finished sheet material formed after cutting according to the present invention.

[0040] In the diagram: 1. Frame; 2. Material support beam; 3. Robot arm; 4. Pressure beam mechanism; 5. Sawing mechanism; 51. Main saw motor; 52. Main saw blade; 53. Main saw transmission components; 54. Main saw cylinder; 55. Linear bearing; 56. Guide rod; 57. Saw carriage seat; 58. Drive wheel. Detailed Implementation

[0041] The present invention will now be further described in conjunction with the accompanying drawings and specific embodiments. It should be noted that, without conflict, the various embodiments or technical features described below can be arbitrarily combined to form new embodiments.

[0042] Example 1

[0043] This embodiment provides a plate cutting device for relieving plate stress. This device can release the stress of the plate in advance and can also automate the plate cutting process, thereby improving production efficiency.

[0044] like Figure 1 , Figure 2 As shown, the sheet metal cutting device mainly includes a frame 1, a clamping mechanism, a sawing mechanism 5, and a central control device. The clamping mechanism and the sawing mechanism 5 are installed inside the frame 1. The central control device is connected to the clamping mechanism and the sawing mechanism 5 by signal, and is used to control the clamping mechanism to clamp and fix the sheet metal to be cut and transport the fixed sheet metal to the designated position of the sawing mechanism 5 for cutting. At the same time, the central control device is also used to control the sawing mechanism 5 to cut the sheet metal to be cut.

[0045] In this embodiment, the frame 1 is equipped with multiple longitudinally arranged support beams 2 for supporting the sheet metal. The spacing between the support beams 2 gradually increases along the width of the frame 1 to facilitate the movement of the sheet metal on the support beams 2. The support beams 2 can be unpowered column structures, unpowered column structures that can rotate under external force, or column structures connected to a motor and driven to rotate by the motor. The support beams 2 primarily function to support the sheet metal; their specific structure can be set according to actual conditions and is not limited here.

[0046] A guide rail is provided along the length of the frame 1, and a clamping mechanism is mounted on the guide rail, allowing the clamping mechanism to move back and forth along the guide rail along the length of the frame 1. The clamping mechanism includes a robotic arm 3 driven by a servo motor. The robotic arm 3 can be a clamping tool or an adsorption tool, etc. In this embodiment, the robotic arm 3 fixes the plate by clamping. When the robotic arm 3 moves along the guide rail, it can drive the plate to the position of the sawing mechanism 5 for cutting.

[0047] like Figure 3 As shown, the sawing mechanism 5 in this embodiment includes a main saw section and an auxiliary saw section. The main saw and the auxiliary saw can be used simultaneously, or only one of them can be activated. The main saw and / or the auxiliary saw are controlled to cut the board according to actual needs. The main saw section includes a saw carriage 57 and a main saw motor 51, a main saw blade 52, and a main saw transmission component 53 installed in the saw carriage 57. The main saw motor 51 and the main saw blade 52 are respectively installed in the upper and lower positions of the main saw transmission component. The main saw motor 51 drives the main saw blade 52 to rotate through the main saw transmission component 53, thereby realizing the board cutting function. The main saw transmission component 53 can be a gear or a belt or other power transmission component.

[0048] In addition, the saw carriage 57 also includes a main saw cylinder 54, which is connected to the main saw transmission component 53. A linear bearing 55 is fixedly mounted on the main saw transmission component 53, and a guide rod 56 is fixedly mounted on the saw carriage 57. The main saw transmission component 53 is slidably connected to the guide rod 56 via the linear bearing 55. When the main saw cylinder 54 rises or falls, the main saw transmission mechanism can move up and down along the guide rod 56. The auxiliary saw works similarly, achieving the same cutting and vertical movement.

[0049] A transmission wheel 58 can be installed on the outside of the sawing mechanism 5. The transmission wheel 58 is driven to rotate by a servo motor, so as to drive the sawing mechanism 5 to move left and right in the width direction of the frame 1, thereby cutting different positions of the board.

[0050] All cylinders and electric motors of the sawing mechanism 5 are connected to the central control equipment and are controlled by the central control equipment to achieve automation.

[0051] To secure the sheet metal during sawing, a pressure beam mechanism 4 can be installed on the frame 1. The pressure beam mechanism 4 clamps the sheet metal, allowing the sawing mechanism 5 to move beneath it and cut the stress-relieving areas to release stress. The pressure beam mechanism 4 can be hydraulically lowered to the surface of the sheet metal to press it down and prevent displacement during cutting. The specific structure of the pressure beam mechanism 4 is already disclosed in the prior art and will not be described in detail here.

[0052] The beam pressing mechanism 4 is also connected to the central control equipment. The central control equipment controls the beam pressing mechanism 4 to press the board to be cut so that the board to be cut can be cut.

[0053] Example 2

[0054] This embodiment provides a plate cutting method for relieving plate stress. By using the plate cutting device for relieving plate stress described in Embodiment 1, and then matching it with the method of this embodiment, the plate stress is relieved and the plate is cut, which can improve the plate production efficiency and reduce the number of times the plate is reworked.

[0055] The stress relief and sheet metal cutting steps in this embodiment include:

[0056] Step S1: Set the stress relief area of ​​the board to be cut based on the custom cutting data. The stress relief area is arranged at a local position on the edge of the board to be cut or at a local position in the center of the board to be cut.

[0057] Step S2: Issue a clamping instruction to the clamping mechanism to control the clamping mechanism to clamp and transport the board to be cut to the location of the sawing mechanism 5;

[0058] Step S3: Issue at least two cutting commands to the sawing mechanism 5, control the sawing mechanism 5 to cut the stress-relieving area according to the first cutting command to release the stress of the board, and then cut the stress-relieving board according to the second cutting command to obtain the desired finished board.

[0059] The cutting data includes a custom stress relief mode, the dimensions of the board to be cut, and the dimensions of the finished board. The stress relief mode includes at least two stress modes, which are primarily determined by the location of the stress relief area on the board.

[0060] In the first stress mode of this embodiment, the stress relief areas are arranged at local positions on the edge of the sheet material to be cut (e.g., ...). Figure 8 As shown, if three longitudinally arranged finished boards need to be cut from a complete board to be cut, two longitudinally arranged stress relief areas need to be planned on both the left and right edges of the board to be cut, and the width of the board between the longitudinal stress relief areas needs to be greater than or equal to the width of the finished board. In this case, there are four stress relief areas on both sides of the entire board to be cut.

[0061] In the second stress mode, the stress release area is distributed in a localized area at the center of the material to be cut (e.g., ...). Figure 9 (As shown); If three longitudinally arranged finished boards need to be cut from a complete board to be cut, then two longitudinally arranged stress relief areas need to be arranged in the middle of the board to be cut, and the width of the board between the longitudinal stress relief areas needs to be greater than or equal to the width of the finished board. In this case, there are two stress relief areas in the whole board to be cut.

[0062] Furthermore, based on the custom dimensions of the boards to be cut and the custom dimensions of the finished boards, the distribution of the required number of finished boards on the boards to be cut can be planned, and the arrangement and orientation of the boards can be determined. The principle of this planning is to plan the maximum number of finished boards in the limited area of ​​the boards to be cut, so as to avoid excessive waste.

[0063] At the same time, while planning the distribution of the boards, it is also necessary to reserve a certain amount of excess material on the boards to be cut, such as... Figure 8 , Figure 9 As shown, when planning the finished panels on the board to be cut, a certain gap needs to be maintained between adjacent finished panels to facilitate cutting. Therefore, when planning the distribution of panels based on the cutting data, it is also necessary to determine the size of the reserved excess material on the board to be cut; generally, an excess material of about 10mm-20mm is reserved at the stress relief position.

[0064] Before cutting the board, you can customize the cutting data on the PC, select the corresponding stress release mode, and then arrange the boards according to the size of the board to be cut and the size of the finished board. The arrangement data will be transmitted to the central control equipment to control the various mechanisms to cooperate with each other to perform the stress release and board cutting process.

[0065] The choice between the first and second stress modes can be made based on the stress state of the material to be cut; specifically: after obtaining... Figure 4 After the board to be cut is shown, its appearance can be observed beforehand. If the board to be cut is placed flat on a plane, and there is a gap between the bulge in the middle of the board and the plane ( Figure 6 (There is a gap in the middle of the board). This type of board, after being cut, will have gaps due to bending. Figure 6 The non-right angle case is shown; therefore, this type of board can be used as follows: Figure 9 The second stress mode shown is achieved by compressing and cutting to obtain, as... Figure 7 The right-angled plate shown.

[0066] If so Figure 4 If the appearance of the board to be cut is normal, it can be cut using the conventional sawing method, that is, cut directly to the required location in one step. Observe whether there are gaps between the cut finished products. Figure 5 As shown, there are gaps between the finished products. In this case, you can use... Figure 8 The first stress mode is shown.

[0067] After selecting the stress mode, the board is placed on the frame 1 and pushed onto the support beam 2. A clamping command is sent to the clamping mechanism to control the robot arm 3 to clamp the board and move it to the designated position of the sawing mechanism 5. At this time, the central control equipment can send a pressing command to the pressing beam mechanism 4 to control the pressing beam mechanism 4 to press the board to be cut, so as to stabilize the board to be cut and cut the stress-relieving area on the board to be cut.

[0068] If the first stress mode is selected, the central control device issues the first cutting command to the sawing mechanism 5. The sawing mechanism 5, according to the location of the stress relief area, controls itself to gradually cut inwards from the edges on both sides of the board to be cut, ensuring that a specified length of uncut area remains in the middle of the board in the current cutting direction. Specifically, after cutting the edges on both sides of the board, it is necessary to ensure that the uncut area in the current cutting direction accounts for 45% to 55% of the total length of the board, achieving the stress relief effect; a complete cut is not required.

[0069] If the second stress mode is selected, the method for cutting the stress relief area is to control the sawing mechanism 5 to gradually cut from the middle of the board to be cut towards both sides of the board according to the position of the stress relief area, ensuring that a specified length of uncut area is retained on both sides of the board edge. Specifically, after cutting the middle position of the board to be cut, it must be ensured that the uncut area retained at any edge of the board in the current cutting direction accounts for 10% to 30% of the total length of the board.

[0070] It should be noted that the cutting direction and sequence of the above-mentioned boards can be adjusted according to actual needs during the cutting process.

[0071] After stress-relief cutting is completed, a second cutting can be performed. During this second cutting, the clamping and transporting commands and the sawing mechanism 5 work together. The board is clamped and transported to the sawing mechanism 5, where rough edges are removed and uncut areas and excess material after stress relief are cut. Specifically, the central control equipment sends clamping commands to the clamping mechanism, which uses the robotic arm 3 to clamp the board along its length and move it to the sawing mechanism 5. Once the robotic arm 3 or the sawing mechanism 5 is aligned with the desired cutting position, a cutting command is sent to the sawing mechanism 5 to cut the board. This cutting process involves multiple repetitive steps: clamping followed by cutting, ultimately yielding multiple finished boards.

[0072] The following examples illustrate the two stress modes:

[0073] If the first stress mode is used, such as Figure 8As shown, the board to be cut needs to be cut into three finished boards, namely Finished Board 1, Finished Board 2, and Finished Board 3. A 10mm allowance is left between Finished Board 1 and Finished Board 2, and a 10mm allowance is left between Finished Board 2 and Finished Board 3. Stress relief areas 1, 2, 3, and 4 are provided on the two edges of the boards to be cut. The stress relief and board cutting steps are as follows:

[0074] 1) Place the sheet material to be cut on the support beam 2 and push the sheet material to be cut to the position of the robot arm 3;

[0075] 2) Control the robotic arm 3 to grip the sheet material to be cut and pull it to the straight line position where stress relief area one and stress relief area two are located;

[0076] 3) Control the pressure beam mechanism 4 to descend and press the sheet material to be cut;

[0077] 4) The sawing mechanism 5 saws at the stress release area one and stress release area two of the board to be cut (according to the length of the board to be cut, 50% of the total length of the board to be cut should be reserved in the middle as an uncut area).

[0078] 5) The robotic arm 3 grips the sheet material to be cut and pulls it to the straight line position where stress relief area 3 and stress relief area 4 are located;

[0079] 6) Control the pressure beam mechanism 4 to descend and press the sheet material to be cut;

[0080] 7) The sawing mechanism 5 performs sawing at the stress release area three and stress release area four of the board to be cut (according to the length of the board to be cut, 50% of the total length of the board to be cut should be reserved in the middle as an uncut area).

[0081] 8) The robotic arm 3 grips the long side of the finished board, controls the sawing structure to trim the rough edges of the board, and saws the edge of the finished board to obtain the finished board.

[0082] 9) The robotic arm 3 grips the finished product position of the board, uses the sawing structure to remove the excess material that has released stress, and saws the edge of the finished product to obtain the finished product.

[0083] 10) The robotic arm 3 grips the finished sheet at position three, uses the sawing structure to remove the excess material to release stress, and saws the edges of finished sheet three to obtain finished sheet three, as shown. Figure 10 As shown.

[0084] Similarly, if the second stress mode is used, such as Figure 9As shown, the board to be cut needs to be cut into three finished boards, namely finished board one, finished board two and finished board three; among them, a 10mm excess material is reserved between finished board one and finished board two, and a 10mm excess material is reserved between finished board two and finished board three; stress relief area five and stress relief area six are arranged in the middle of the board to be cut.

[0085] The stress relief and sheet cutting steps are as follows:

[0086] 1) Place the sheet material to be cut on the support beam 2 and push the sheet material to be cut to the position of the robot arm 3;

[0087] 2) Control the robotic arm 3 to grip the sheet material to be cut and pull it to the straight position of the stress release area 5;

[0088] 3) Control the pressure beam mechanism 4 to descend and press the sheet material to be cut;

[0089] 4) The sawing mechanism 5 saws at position 5 of the stress relief area of ​​the board to be cut (20% of the board length is reserved on both sides as an uncut area according to the length of the board to be cut);

[0090] 5) The robotic arm 3 grips the sheet material to be cut and pulls it to the straight position of the stress relief area 6;

[0091] 6) Control the pressure beam mechanism 4 to descend and press the sheet material to be cut;

[0092] 7) The sawing mechanism 5 performs sawing at the stress relief area three and stress relief area four of the board to be cut (based on the length of the board to be cut, 20% of the board length of the uncut area is reserved on both sides).

[0093] 8) The robotic arm 3 grips the long side of the finished board, controls the sawing structure to trim the rough edges of the board, and saws the edge of the finished board to obtain the finished board.

[0094] 9) The robotic arm 3 grips the finished product position of the board, uses the sawing structure to remove the excess material that has released stress, and saws the edge of the finished product to obtain the finished product.

[0095] 10) The robotic arm 3 grips the finished sheet at position three, uses the sawing structure to remove the excess material to release stress, and saws the edges of finished sheet three to obtain finished sheet three, as shown. Figure 10 As shown.

[0096] This method divides stress-relief areas on the uncut board, which can be located at the two edges or the middle of the uncut board. Pre-cutting local areas of the board can release stress and avoid repeated corrections due to stress issues during subsequent processing, thereby improving the efficiency of board production.

[0097] Example 3

[0098] This embodiment provides a computer-readable storage medium storing a computer program thereon, which, when executed, implements the above-described method for cutting sheet metal to relieve stress.

[0099] The storage medium in this embodiment and the method in the foregoing embodiments are based on another aspect of the same inventive concept. The implementation process of the method has been described in detail above, so those skilled in the art can clearly understand the structure and implementation process of the storage medium in this embodiment based on the foregoing description. For the sake of brevity, it will not be described again here.

[0100] The above embodiments are merely preferred embodiments of the present invention and should not be construed as limiting the scope of protection of the present invention. Any non-substantial changes and substitutions made by those skilled in the art based on the present invention shall fall within the scope of protection claimed by the present invention.

Claims

1. A method for cutting sheet metal to relieve stress, characterized in that, include: The stress relief area of ​​the sheet material to be cut is set based on custom cutting data. The stress relief area is arranged at a local position at the edge of the sheet material to be cut or at a local position at the center of the sheet material to be cut. At least two cutting commands are issued, controlling the sawing mechanism to cut the stress-relief area according to the first cutting command to release the stress in the board, and then cutting the stress-relieved board according to the second cutting command to obtain the desired finished board. The cutting data includes stress relief mode, dimensional information of the board to be cut, and dimensional information of the finished board. The method for setting the stress relief area is as follows: The position on the sheet material to be cut is determined according to the stress relief mode; Based on the size information of the board to be cut and the size information of the finished board, determine the arrangement direction of the finished board on the board to be cut and the reserved excess material size on the board to be cut. The method for cutting the stress relief region includes: The sawing mechanism is controlled according to the stress relief area, starting from the edges on both sides of the board to be cut and gradually cutting inwards, ensuring that a specified length of uncuttered area is retained in the middle of the board; or, According to the stress relief area, the sawing mechanism is controlled to gradually cut from the middle of the board to be cut towards both sides of the board edge, and to ensure that the board edge on both sides retains a specified length of uncut area.

2. The plate cutting method for relieving plate stress according to claim 1, characterized in that, After cutting the two sides of the board to be cut, it is necessary to ensure that the uncut area in the current cutting direction accounts for 45% to 55% of the total length of the board.

3. The plate cutting method for relieving plate stress according to claim 1, characterized in that, After cutting the middle part of the board to be cut, it is necessary to ensure that the uncut area retained at any edge of the board in the current cutting direction accounts for 10% to 30% of the total length of the board.

4. The plate cutting method for relieving plate stress according to claim 1, characterized in that, The method for cutting the stress-relieved sheet material according to the second cutting instruction includes roughening the edges of the sheet material and cutting the uncut areas and the remaining material after stress relief.

5. A sheet metal cutting device for relieving sheet metal stress, characterized in that, It includes a frame, a clamping mechanism and a sawing mechanism installed in the frame, and a central control device that is signal-connected to the clamping mechanism and the sawing mechanism; The clamping mechanism is used to clamp and fix the board to be cut and transport the fixed board to the designated position of the sawing mechanism; The central control device executes the plate cutting method for releasing plate stress as described in any one of claims 1 to 4, and is used to control the sawing mechanism to cut the plate to be cut when it reaches the designated position.

6. The plate cutting device for relieving plate stress according to claim 5, characterized in that, The frame is also equipped with a pressure beam mechanism, which is connected to the central control equipment via a signal. The central control equipment controls the pressure beam mechanism to press the plate to be cut so as to facilitate the cutting of the plate.

7. A computer-readable storage medium, characterized in that, The computer-readable storage medium stores a computer program that, when run on one or more processors, performs a plate cutting method for relieving plate stress as described in any one of claims 1 to 4.

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