Low-scattering regular prismatic table screw and design method thereof

Abstract

The invention relates to a low-scattering regular prismatic table screw and a design method thereof, belongs to the technical field of radar detection, and solves the technical problem of strong scattering of the screw, the screw is of an integral structure, the head is in a regular prismatic table shape, the head is provided with a groove used for dismounting the screw, and the upper bottom of the groove is in a regular n-polygon shape, and the edge of the n-regular polygon at the upper bottom of the groove is overlapped with the edge of the n-regular polygon at the upper bottom of the head part. And the groove surface comprises a triangular plane formed by two adjacent vertexes of the regular n-polygon at the upper bottom of the groove to the nearest secondary vertex of the groove, and a triangular plane formed by the vertexes of the regular n-polygon at the upper bottom of the groove, the secondary vertex of the groove and the vertex of the groove. The lower bottom of the head is connected with the screw. The screw design method comprises the steps of designing the number of the bottom edges of the bottom face of the head, designing the side face structure of the head, designing the groove of the head, setting the screw rod and setting the threads. The method is used for designing the weak scattering source screw of the stealth equipment.

Description

Technical Field

[0001] The present invention belongs to the technical field of radar detection for mechanical components, and particularly relates to a low-scattering regular frustum screw and its design method. Background Technique

[0002] The low-detectability technology can effectively reduce the probability of a weapon system being discovered, identified, tracked, and attacked, thereby enhancing its battlefield survivability. It is the most important penetration tactic in modern warfare. In medium- and long-range air combat, the stealth threat to aircraft mainly comes from electromagnetic detectors. The radar cross section (RCS) is a main index characterizing the scattering ability of a stealth target to incident waves. For conventional aircraft, in addition to the three major strong scattering sources of the radar compartment, cockpit, and intake duct, the gaps, steps at places where the covers are not often opened, and the fastening rivets, screws, etc. of each component will form electrically discontinuous structures, which are the main scattering sources affecting the stealth performance of the whole machine after the strong scattering sources are effectively reduced. Research indicates that the total radar cross-sectional area of an array of ten screws can reach 1 m 2 , therefore, the scattering reduction and suppression of weak scattering sources such as screws and rivets are also crucial for improving the low-detectability ability of weaponry.

[0003] Currently, the research on weak scattering sources such as screws and rivets mainly qualitatively analyzes their influence on the overall low-detectability of weaponry from the perspective of scattering mechanism. There is no scattering reduction design and quantitative analysis of RCS for them, making it difficult to further improve the overall low-detectability of the target. Summary of the Invention

[0004] In order to reduce the weak scattering of screws, the present invention proposes a low-scattering regular frustum screw and its design method.

[0005] The technical solution adopted by the present invention to solve its technical problems is as follows:

[0006] A low-scattering regular frustum screw, which is an integral structure and can be divided into a head and a screw rod.

[0007] The central axis of the head coincides with the central axis of the screw rod.

[0008] The head is in the shape of a regular frustum. The side length of the regular n-sided polygon on the upper base of the head is less than the side length of the regular n-sided polygon on the lower base of the head, where n is the number of sides of the base of the regular frustum of the head. The lower base of the head is connected to the screw rod, and threads are provided on the circumferential surface of the screw rod.

[0009] The head is provided with a groove, which is used for fixing the screw for disassembly and assembly and is matched with the disassembly and assembly tool.

[0010] The upper base of the groove is a regular n-sided polygon, and the sides of the regular n-sided polygon on the upper base of the groove coincide with the sides of the regular n-sided polygon on the upper base of the head.

[0011] The groove is provided with 1 groove vertex and n groove secondary vertices. The groove vertex is located on the central axis of the head. The n groove secondary vertices are located in the same vertical plane of the central axis of the head and on the concentric circle of the central axis of the head, and are evenly distributed. Each groove secondary vertex is located in the vertical bisecting plane of the nearest side line of the regular n-sided polygon on the upper bottom surface of the groove. The depth of the groove secondary vertex is less than the depth of the groove vertex.

[0012] The groove surface includes a first triangular plane and a second triangular plane. The first triangular plane is a triangular plane formed by two adjacent vertices of the regular n-sided polygon on the upper bottom surface of the groove to the nearest groove secondary vertex. The second triangular plane is a triangular plane formed by the vertex of the regular n-sided polygon on the upper bottom surface of the groove, the groove secondary vertex and the groove vertex.

[0013] For the above low-scattering regular prism head screw, the head is in the shape of a regular triangular prism, and the height of the head is 6.3 mm; the dihedral angle formed by the first triangular plane and the upper bottom surface of the head is 22°, and the dihedral angle formed by the first triangular plane and the side surface of the adjacent regular prism head is 106°. The depth of the groove vertex is 6 mm, and the depth of the groove secondary vertex is 3 mm.

[0014] For the above low-scattering regular prism head screw, the included angle between the connection line of the vertex of the regular n-sided polygon on the upper bottom surface of the groove and the groove vertex and the central axis of the head is 124.6°.

[0015] For the above low-scattering regular prism head screw, the screw rod is a plain screw rod, with a height of 11.6 mm and a thread pitch of 0.9 mm.

[0016] A design method for a low-scattering regular prism head screw includes the following steps:

[0017] Step 1, design the number of sides of the bottom edge of the head bottom surface

[0018] When the key angular range of radar low detectability is [-θ, θ], the number of sides n of the regular n-sided polygon on the bottom surface of the regular prism head satisfies the following conditions:

[0019]

[0020] Step 2, design the head side structure

[0021] The n side surfaces of the head are regular trapezoids. According to the contribution of the side surface of the regular prism head screw to the overall RCS of the screw, the base angle of the regular trapezoid on the side surface of the regular prism head is given.

[0022] Step 3, design the head groove

[0023] Give the included angle between the connection line of the vertex of the regular n-sided polygon on the upper bottom surface of the head groove and the groove vertex and the central axis of the head, as well as the positions of the n groove secondary vertices.

[0024] Step 4, give the screw rod

[0025] The screw is cylindrical.

[0026] Step 5: Specify the thread

[0027] The thread is an equally spaced plain weave, and the thread type is the same as that of the international standard screw.

[0028] In the above low-scattering regular prism screw design method, in Step 1, the number of sides of the bottom surface of the head regular prism is 3.

[0029] In the above low-scattering regular prism screw design method, in Step 2, the bottom angle of the regular trapezoid on the side of the head is specified as 51.8°.

[0030] In the above low-scattering regular prism screw design method, in Step 3, the angle between the line connecting the vertex of the upper base regular n-gon of the groove and the vertex of the groove and the central axis of the head is 124.6°.

[0031] The beneficial effects of the present invention are:

[0032] A low-scattering regular prism screw design method gives the lowest RCS shape according to the detection angle of the detector, and the design method is flexible and the effect is remarkable.

[0033] A low-scattering regular prism screw has a significantly reduced RCS compared with the traditional frustum countersunk screw. The simulation results show that: under horizontal and vertical polarizations, for the incident electromagnetic wave in the range of [-θ, θ], the multi-sided prism screw has a significantly reduced RCS compared with the traditional frustum countersunk screw; taking θ = 45° as an example, the head of the regular triangular prism screw of the present invention has an average RCS reduction of 13.3 dB and a maximum reduction of up to 30.1 dB compared with the traditional frustum cross countersunk screw. It shows that the low-scattering regular prism screw of the present invention solves the problem of "strong" weak scattering of the existing screw from the perspective of the outer shape design. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is a three-dimensional structure schematic diagram of the triangular prism screw in Embodiment 1 of the present invention;

[0035] Figure 2 It is a top view of the triangular prism screw in Embodiment 1 of the present invention;

[0036] Figure 3 It is a detailed top view of the head of the triangular prism screw in Embodiment 1 of the present invention;

[0037] Figure 4 It is a schematic diagram of the incident wave direction setting of the triangular prism screw when vertically incident in the present invention;

[0038] Figure 5 It is a schematic diagram of the incident wave direction setting of the triangular prism screw when horizontally incident in the present invention;

[0039] Figure 6RCS simulation effect diagrams of the triangular prism screw and the standard circular table screw under horizontal polarization for an incident angle of 45°;

[0040] Figure 7 RCS simulation effect diagrams of the triangular prism screw and the standard circular table screw under horizontal polarization for an incident angle of 0°;

[0041] Figure 8 RCS simulation effect diagrams of the triangular prism screw and the standard circular table screw under horizontal polarization for an incident angle of -45°;

[0042] Figure 9 RCS simulation effect diagrams of the triangular prism screw and the standard circular table screw under vertical polarization for an incident angle of 45°;

[0043] Figure 10 RCS simulation effect diagrams of the triangular prism screw and the standard circular table screw under vertical polarization for an incident angle of 0°;

[0044] Figure 11 RCS simulation effect diagrams of the triangular prism screw and the standard circular table screw under vertical polarization for an incident angle of -45°.

[0045] In the figure: 1. Head, 2. Polygonal prism, 3. Groove, 4. Screw rod, 5. Thread, 6. Secondary vertex of the groove, 9. Vertex of the groove, 11. RCS of the triangular prism screw, 12. RCS of the standard circular table screw. Specific implementation mode

[0046] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0047] Embodiment 1

[0048] A multi-sided regular prism screw is composed of a head, a screw rod and a thread. The head is a regular prism. The groove inclines from the vertex of the top surface of the regular prism towards the inside of the prism, and its projection on the top surface of the regular prism is an n-shaped fork extending from its center to the vertex, as Figure 1 shown.

[0049] The head includes a multi-sided regular prism and a groove. The bottom projection of the multi-sided prism is a regular n-sided polygon. The n side surfaces of the prism are all trapezoids. The top projection of the prism is a regular n-sided polygon. The regular n-sided polygon on the top surface of the multi-sided prism is directly fixedly connected to the sunken n-shaped fork groove.

[0050] Inside the prism of the head is an n-sided groove, as Figure 3As shown, the groove cross-section is designed as an n-shaped fork from the center to the vertex. The grooves are all inclined and sunken from the vertices of the regular n-sided polygon on the top surface of the frustum to the bottom surface. From the vertices of the regular frustum's top surface, they are inclined and sunken into the frustum. On the surface that is vertically downward from the top surface of the regular frustum by a height of h1 = 3 mm, three sub-vertices 6 of the groove are taken, such that the dihedral angle formed by the plane formed by any one of them and the two adjacent vertices on the top surface of the regular frustum and the top surface is θ1 = 22°, and the dihedral angle formed with the trapezoidal side surface of the regular frustum is θ2 = 106°. On the surface that is vertically downward from the top surface of the regular frustum by a height of h2 = 6 mm, the center of this triangular surface is selected as the vertex 9 of the groove. The sub-vertices 6 of the groove are respectively connected to the vertex 9 of the groove to form n internal edges of the groove. The projection on the top surface of the regular frustum is an n-shaped fork from its center to the vertex. Through simulation comparison, this inclined design reduces by an average of 13 dB compared to the traditional vertical cross groove, and the maximum reduction can reach 30 dB.

[0051] The screw rod is a cylinder connected to the bottom surface of the head.

[0052] The thread is a plain thread wound around the screw rod.

[0053] Step 1, design the bottom surface of the multi-sided regular frustum of the head

[0054] Assume that the bottom surface of the multi-sided regular frustum is a regular n-sided polygon. According to the mirror scattering mechanism and combined with the key low-detectable angular range [-θ, θ] of the radar, the number of sides n of the regular polygon satisfies the following rule, which can make the scattered echo deviate from the detection angular range, that is, the screw has low detectability

[0055]

[0056] Step 2, specify the side surfaces of the multi-sided frustum of the head

[0057] According to the contribution of the side surfaces of the multi-sided frustum of the screw to the overall RCS of the screw, the n side surfaces of the frustum of the head are designed as trapezoids, and the base angle is specified as 51.8°.

[0058] Step 3, design the groove of the multi-sided frustum of the head

[0059] Inside the frustum of the head is an n-sided groove. The groove cross-section is designed as an n-shaped fork from the center to the vertex. The grooves are all inclined and sunken from the vertices of the regular n-sided polygon on the top surface of the frustum to the bottom surface, and the inclination angle is set to 124.6°. Through simulation comparison, this inclined design reduces by an average of 13 dB compared to the traditional vertical cross groove, and the maximum reduction can reach 30 dB.

[0060] Step 4, specify the screw rod of the screw

[0061] The screw rod of the screw is a cylinder connected to the regular n-sided polygon of the bottom surface of the frustum of the head, and its height is the same as that of the traditional round frustum countersunk head screw.

[0062] Step 5, specify the thread of the screw

[0063] The screw thread is a constant pitch plain weave, and the pitch and thread type are the same as those of the international standard screw.

[0064] Embodiment 2

[0065] A design method for a low-scattering regular frustum screw, which is applicable to the design of the low-scattering structure of the screw. To illustrate the technical content, structural features, and achieved purposes and effects of the present invention in detail, the specific implementation manners will be combined with the design method for description:

[0066] Refer to Figure 1 , the present invention includes a head 1, a screw 4, and a thread 5; wherein, the head 1 includes a regular frustum 2 with multiple sides and an embedded groove 3, and the height of the regular frustum of the head is 6.3 mm; the screw 4 is a cylinder connected to the regular n-sided polygon at the bottom surface of the head, with a height of 11.6 mm; the thread 5 is a plain weave, evenly spaced around the rod body, with a spacing of 0.9 mm.

[0067] Refer to Figure 2 , for the regular frustum 2 with multiple sides of the head 1, both the upper and lower bottom surfaces are regular n-sided polygons. For the incident electromagnetic wave with a detection angle of the screw [-θ, θ], according to the specular scattering mechanism and the low RCS requirement, the number of sides n of the regular n-sided polygon should satisfy the following conditions:

[0068]

[0069] Wherein, n is the number of sides of the regular polygon, and θ is the refractive index at the center of the semi-fish-eye lens of the incident angle of the detected electromagnetic wave.

[0070] Refer to Figure 2 , for the regular frustum 2 with multiple sides of the head 1, the n side surfaces are all isosceles trapezoids, and the upper and lower bases of the isosceles trapezoids are respectively the sides of the regular n-sided polygons on the upper and lower bottom surfaces of the frustum. The included angles between the two waists and the base of each isosceles trapezoid on the side surfaces are all 51.8°.

[0071] Refer to Figure 2 , for the embedded groove 3 of the head 1, it is inclined and recessed from each vertex of the regular n-sided polygon on the top surface of the frustum to the bottom surface, and the inclination angle is all 124.6°.

[0072] Embodiment 3

[0073] Suppose the incident angle of the detection wave θ = 45°, and the working frequency band is 8 GHz to 10 GHz. Change the number of sides n of the frustum head of the screw. From the relationship between the number of sides of the regular n-sided polygon and the incident angle, the maximum value of n is obtained, that is, n < 8. Select n = 3, then the head of the screw is a regular triangular frustum, and the groove is a "Y" shape. Figures 4 to 5 They are schematic diagrams of the incident wave direction settings when the incident wave is vertical and horizontal respectively.

[0074] Figures 6 to 11They are respectively the RCS simulation effect diagrams of the regular triangular prism screw head and the standard frustum screw head involved under horizontal and vertical polarizations at different incident angles. Among them Figures 6 to 8 is the RCS distribution curve of the triangular prism screw head and the standard frustum screw head under horizontal polarization for incident angles of 45°, 0°, and -45°, Figures 9 to 11 is the RCS distribution curve of the triangular prism screw head and the standard frustum screw head under vertical polarization for incident angles of 45°, 0°, and -45°.

[0075] From Figures 6 to 11 it can be seen that under horizontal and vertical polarizations, the triangular prism screw head has an average RCS reduction effect of 13.3 dB and a maximum reduction of up to 30.1 dB compared to the traditional standard frustum screw head in the incident angle range of [-45°, 45°]; in addition, this screw head also has significant low detectability in the incident angle range of [-90°, 90°]. The above simulation results show that the multi-sided regular prism screw designed by the present invention has low scattering characteristics.

[0076] Embodiment 4

[0077] A low-scattering regular prism screw, which is an integral structure and can be divided into a head 1 and a screw rod 4.

[0078] The central axis of the head 1 coincides with the central axis of the screw rod 4.

[0079] The head 1 is in the shape of a regular prism. The side length of the regular n-sided polygon at the upper bottom of the head 1 is smaller than the side length of the regular n-sided polygon at the lower bottom of the head. n is the number of sides of the regular polygon at the bottom of the regular prism of the head 1. The lower bottom of the head 1 is connected to the screw rod 4, and a thread 5 is provided on the circumferential surface of the screw rod 4.

[0080] A groove 3 is provided on the head 1. The groove 3 is used for fixing the disassembly and assembly of the screw and is matched with the disassembly and assembly tool.

[0081] The upper bottom of the groove 3 is a regular n-sided polygon, and the sides of the regular n-sided polygon at the upper bottom of the groove 3 coincide with the sides of the regular n-sided polygon at the upper bottom of the head.

[0082] The groove 3 is provided with 1 groove vertex 9 and n groove sub-vertices 6. The groove vertex 9 is located on the central axis of the head 1. The n groove sub-vertices 6 are located in the same vertical plane of the central axis of the head 1 and on the concentric circle of the central axis of the head 1, and are evenly distributed. Each groove sub-vertex 6 is located in the mid-perpendicular plane of the nearest side line of the regular n-sided polygon at the upper bottom of the groove. The depth of the groove sub-vertex 6 is less than the depth of the groove vertex 9.

[0083] The groove surface includes n first triangular planes and 2n second triangular planes. The first triangular plane is a triangular plane formed by two adjacent vertices of the regular n-sided polygon at the upper bottom of the groove 3 to the nearest groove sub-vertex 6. The second triangular plane is a triangular plane formed by the vertex of the regular n-sided polygon at the upper bottom of the groove 3, the groove sub-vertex 6, and the groove vertex 9.

[0084] The distance from the vertex 9 of the groove to the upper bottom of the head 1 is the depth of the vertex 9 of the groove, and the distance from the secondary vertex 6 of the groove to the upper bottom of the head 1 is the depth of the secondary vertex 6 of the groove.

[0085] For example, the head 1 is in the shape of a regular triangular frustum, and the structure is as Figure 1 , 2 shown.

[0086] A design method for a low-scattering regular frustum screw includes the following steps:

[0087] Step 1, design the number of sides of the regular n-sided polygon at the bottom of the head

[0088] When the key angular domain of low radar detectability is [-θ, θ], the number of sides n of the regular n-sided polygon at the bottom of the regular frustum head satisfies the following conditions:

[0089]

[0090] Step 2, design the structure of the head side

[0091] The n sides of the head are regular trapezoids. According to the contribution of the side of the regular frustum head to the overall RCS of the screw, the base angle of the regular trapezoid on the side of the regular frustum head is given.

[0092] For example, the base angle is 51.8°.

[0093] Step 3, design the head groove

[0094] Given the included angle between the line connecting the vertex of the regular n-sided polygon on the upper bottom of the head groove 3 and the vertex 9 of the groove and the central axis of the head 1, and the positions of the n secondary vertices 6 of the groove.

[0095] For example, the included angle between the line connecting the vertex of the regular n-sided polygon on the upper bottom of the groove 3 and the vertex 9 of the groove and the central axis of the head 1 is 124.6°.

[0096] Step 4, specify the screw rod

[0097] The screw rod is cylindrical.

[0098] Step 5, specify the thread

[0099] The thread is an equally spaced plain weave, and the thread type is the same as that of the international standard screw.

[0100] Figures 6 - 11 It is a comparison curve of the scattering effects between the designed screw and the existing screw.

Claims

1. A low-scattering regular frustum screw, characterized in that, It is an overall structure and can be divided into a head (1) and a screw rod (4). The central axis of the head (1) coincides with the central axis of the screw rod (4). The head (1) is in the shape of a regular frustum of a pyramid. The side length of the regular n-sided polygon at the upper base of the head (1) is less than the side length of the regular n-sided polygon at the lower base of the head. n is the number of sides of the regular polygon at the bottom surface of the regular frustum of the pyramid of the head (1). The lower base of the head (1) is connected to the screw rod (4), and a thread (5) is provided on the circumferential surface of the screw rod (4). A groove (3) is provided on the head (1), and the groove (3) is used for fixing a dismounting and assembling screw and is matched with a dismounting and assembling tool. The upper base of the groove (3) is a regular n-sided polygon, and the sides of the regular n-sided polygon at the upper base of the groove (3) coincide with the sides of the regular n-sided polygon at the upper base of the head. One groove vertex (9) and n groove sub-vertices (6) are provided in the groove (3). The depth of the groove sub-vertices (6) is less than the depth of the groove vertex (9). The groove vertex (9) is located on the central axis of the head (1). The n groove sub-vertices (6) are located in the same vertical plane of the central axis of the head (1) and on the concentric circle of the central axis of the head (1), and are evenly distributed. Each groove sub-vertex (6) is located in the vertical plane of the mid-perpendicular of the nearest side line of the regular n-sided polygon at the upper base of the groove. The groove surface includes a first triangular plane and a second triangular plane. The first triangular plane is a triangular plane formed by two adjacent vertices of the regular n-sided polygon at the upper base of the groove (3) and the nearest groove sub-vertex (6). The second triangular plane is a triangular plane formed by the vertex of the regular n-sided polygon at the upper base of the groove (3), the groove sub-vertex (6), and the groove vertex (9).

2. The low-scattering regular frustum screw according to claim 1, wherein The head (1) is in the shape of a regular triangular frustum, and the height of the head (1) is 6.3 mm. The dihedral angle formed by the first triangular plane and the upper bottom surface of the head is 22°. The dihedral angle formed by the first triangular plane and the side surface of the regular frustum of the pyramid of the adjacent head is 106°. The depth of the groove vertex (9) is 6 mm, and the depth of the groove sub-vertex (6) is 3 mm.

3. The low-scattering regular frustum screw according to claim 3, wherein The included angle between the connection line of the vertex of the regular n-sided polygon at the upper base of the groove (3) and the groove vertex (9) and the central axis of the head (1) is 124.6°.

4. The low-scattering regular frustum screw according to claim 1, wherein The screw rod (4) is a plain-thread screw rod, with a height of 11.6 mm and a thread pitch of the thread (5) of 0.9 mm.

5. A design method for a low-scattering regular frustum screw, characterized in that, It includes the following steps: Step 1, design the number of sides of the bottom edge of the head: When the key angular range of low detectability of the radar is [-θ, θ], the number of sides n of the regular n-sided polygon at the bottom surface of the regular frustum of the pyramid of the head satisfies the following conditions: Step 2, design the side structure of the head: The n side surfaces of the head are regular trapezoids. According to the contribution of the side surface of the regular frustum of the pyramid of the screw head to the overall RCS of the screw, the base angle of the regular trapezoid of the side surface of the regular frustum of the pyramid of the head is given. Step 3, design the head groove: The included angle between the connection line of the vertex of the regular n-sided polygon at the upper base of the head groove (3) and the groove vertex (9) and the central axis of the head (1) is given, as well as the positions of the n groove sub-vertices (6). Step 4, given the screw rod: The screw rod is cylindrical. Step 5, given the thread: The thread is an equally spaced plain thread, and the thread type is the same as that of the international standard screw.

6. The design method of the low-scattering regular frustum screw according to claim 5, characterized in that In the said Step 1, the number of sides of the bottom surface of the regular frustum of the pyramid of the head is 3.

7. The design method of the low-scattering regular frustum screw according to claim 6, characterized in that, In the said Step 2, the base angle of the regular trapezoid of the side surface of the head is given as 51.8°.

8. The design method of the low-scattering regular frustum screw according to claim 7, characterized in that, In the step 3, the included angle between the line connecting the vertex of the regular n-sided polygon on the upper bottom of the groove (3) and the vertex of the groove (9) and the central axis of the head (1) is 124.6°.

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