An adaptive compensation multi-point support fixture for displacement measurement in the machining of thin-walled spherical shells

Abstract

The present invention belongs to the field of mechanical design technology and discloses an adaptive compensating multi-point support fixture for measuring displacement during the machining of thin-walled spherical shell parts. The fixture comprises a single-degree-of-freedom support unit, a mounting plate, and a displacement measuring device. The fixture forms a support system with axial displacement as the control variable in terms of spatial positioning and motion. This fixture replaces the full internal support of the spherical shell, offers excellent fit and a wide support adjustment range. By controlling spring limits to provide a set support force for the workpiece and adaptively compensating when the workpiece deforms, it can meet the support requirements of workpieces of varying diameters and heights. Furthermore, the arrangement of the support units allows the inner surface of the spherical shell to be reconstructed in conjunction with information from displacement sensors, enabling detection of deformation during the spherical shell machining process.

Description

Technical Field

[0001] The invention belongs to the technical field of mechanical design, and in particular relates to an adaptive compensation multi-point support fixture for measuring displacement during machining of spherical shell thin-walled parts. Background Art

[0002] With the continuous expansion of application areas and the continuous improvement of performance indicators, the aerospace, energy and power, defense and military industries, and other fields have higher requirements for the instruments and equipment used. All types of structural components are moving towards lightweighting. Among them, large thin-walled spherical shells are a typical structural component. For a given volume, the spherical shell has the smallest surface area, the lightest weight, and the lowest equipment cost. They offer advantages such as large internal space, low density, high specific surface area, and excellent stability. Therefore, they are widely used in engine cases, fuel tanks, engine nacelles, and aircraft auxiliary fuel tanks. The complex application scenarios of spherical shell parts dictate that they must withstand thermal loads such as high temperatures, high pressures, and strong thermal shock, placing stringent requirements on the mechanical properties of the parts themselves. However, large thin-walled spherical shell parts are characterized by high internal residual stresses, large structural dimensions, high material removal rates, complex overall stiffness, and uneven and difficult-to-control residual stress distribution. These components present various technical challenges in actual machining. This can lead to instability or vibration during machining due to insufficient rigidity, making it difficult to ensure machining accuracy. Therefore, for the clamping of spherical shell-like thin-walled parts, in addition to requiring the fixture to provide the main positioning and clamping, it is also necessary to add auxiliary supports to the weak rigid parts of the workpiece to improve its rigidity on the basis of ensuring the fit.

[0003] At present, the support structure for processing spherical shell thin-walled parts mostly adopts spherical shell-shaped internal support blocks that match the inside of the spherical shell workpiece for auxiliary support. The deformation mechanics analysis and control of thin-walled spherical shell vacuum adsorption clamping adopts vacuum adsorption fixtures to process spherical shell thin-walled parts. The basic research on precision turning technology of pure iron thin-walled spherical shells adds soft auxiliary support to provide support force on this basis. However, these support methods have obvious problems in the support process. First, full support cannot guarantee the fit, and the stiffness of the spherical shell parts is uneven. Due to insufficient rigidity, static deformation, instability or vibration of the spherical shell processing occurs. Secondly, during the processing of spherical shell parts, the residual stress inside the spherical shell changes as the processing progresses. Combined with material removal, the spherical shell will be deformed. Therefore, the above-mentioned support force method cannot provide online adaptive support force compensation for the deformation, which in turn causes processing wall thickness errors. Summary of the Invention

[0004] In view of the problem that the existing technology cannot meet the support requirements for different parts of the spherical shell workpiece when it is deformed during the processing, and cannot ensure the overall stiffness of the spherical shell while ensuring the fit, the present invention provides an adaptive compensation multi-point support fixture for measuring the displacement of spherical shell thin-walled parts. Combined with simulation means, it can not only efficiently complete the support fit, but also use precision rectangular springs to achieve adaptive compensation for the deformation of the spherical shell during the processing, provide uniform support force for the fixation of thin-walled parts, and can use simulation means to determine the weakest point of the stiffness of the spherical shell thin-walled parts, and complete the reconstruction of the inner surface of the spherical shell after deformation.

[0005] The technical solution of the present invention:

[0006] An adaptive compensation multi-point support fixture for displacement measurement of spherical shell thin-walled parts processing, comprising a single-degree-of-freedom support unit, a mounting plate 1, a base 2, a column 3, and a screw-nut mechanism 4;

[0007] Multiple single-degree-of-freedom support units of different heights are fixed to the mounting plate 1 through the base plate 2 via the column 3, and the spherical shells of different sizes and different eccentricities can be matched by adjusting the length of the column 3; the single-degree-of-freedom support unit includes an adjustment plate 5, a guide sleeve 6, a rectangular spring 7, a baffle 8, a point support rod 9 and a contact displacement sensor 10; both ends of the column 3 are threaded, the lower end of which is fixed to the mounting plate 1 through the base plate 2 by bolts, and the upper end of which is fixed to the lower end flange of the guide sleeve 6 through the screw nut mechanism 4 by bolts; a screw nut mechanism 4 is installed under the guide sleeve 6, and the lower end surface of the nut of the screw nut mechanism 4 contacts the shaft shoulder of the column 3, and the screw nut mechanism The lead screw 4 is connected to the adjustment plate 5 by a thread, which provides auxiliary supporting force and adjusts the preload force of the rectangular spring 7 by adjusting the position of the lead screw; a rectangular spring 7 is placed inside the guide sleeve 6, and the rectangular spring 7 is sleeved on the point support rod 9. The boss in the middle of the point support rod 9 is used to limit the rectangular spring 7 and transmit the axial support force provided by the rectangular spring 7 to the ball head part of the point support rod 9; the top of the guide sleeve 6 is fixedly connected to the baffle 8 by a nut, and the baffle 8 provides a guide for the contact support part of the point support rod 9, limiting its upward movement and ensuring uniform force on the thin-walled part of the spherical shell; the baffle 8 also provides an installation position for the contact displacement sensor 10.

[0008] During the support process, the synchronous axial movement of the floating auxiliary support assembly is achieved through the joint action of the spring adjustment mechanism and the connected point support rod. Combined with the sensors of the seventeen support units, the adaptive compensation multi-point support fixture for measuring the displacement of spherical shell thin-walled parts in processing forms a support system with the axial displacement at the bottom position as the control variable in terms of spatial positioning and movement mode; one is to detect the axial displacement of the point support rod and determine the spring support force; the other is to detect the change in the position of the spherical shell at this point and determine the deformation of the spherical shell during processing, providing a basis for planning the processing path and compensating for the spring adaptive support force.

[0009] The mounting plate includes a base, positioning holes, and positioning slots. The base is an octagonal structure with a positioning hole on its upper end surface for positioning the support unit. 3N (N is the number of single-degree-of-freedom support units) threaded holes are provided circumferentially around the positioning hole on the upper end surface of the base for connecting to the column and securing the support unit. Positioning slots are provided on the side of the base for mounting the fixture on the machine tool worktable.

[0010] There are 3N columns in total, which are determined by the number N of single-degree-of-freedom support units. They are installed on the upper surface of the base according to the positioning holes, and the length of the column is determined by the position of the support unit. The column is an overall columnar structure, the lower part is a cylinder, and the upper part is processed to form two parallel side surfaces and shoulders, which are used to limit the movement of the screw and nut mechanism in the vertical direction; threaded holes are processed at both ends of the column for fixing the support unit and connecting the guide sleeve. The bottom end of the column is fixed to the upper surface of the mounting plate through a base with a through hole, and the upper end is fixed to the flange of the guide sleeve by threads.

[0011] The screw and nut mechanism includes a disc-shaped structure with a threaded hole in the middle and a cylindrical adjusting nut. The disc-shaped structure with the threaded hole is pressed down on the shoulder of the column shaft, and the adjusting nut passes through the threaded hole and is connected to the top adjusting plate by a thread; the upper end of the adjusting plate contacts the rectangular spring in the guide sleeve; during the support process, the moving component can be moved up and down along the auxiliary support frame by rotating the adjusting nut, and the axial supporting force control of the floating auxiliary support component is realized by the rectangular spring.

[0012] The guide sleeve is a stepped cylindrical structure with a smooth cylinder in the middle, a flange at the bottom, and threads arranged on the upper end and the circumference of the flange. The bottom flange is connected to the column by threads. The structure of the sleeve is different depending on the position of the support unit. The guide sleeve plays a positioning and guiding role for the spring installed inside. The upper part is connected to the baffle through a nut to limit the axial movement of the support rod.

[0013] There are N precision rectangular springs in total, which are determined by the number N of single-degree-of-freedom support units. The support position is the weakest point selected based on the stiffness simulation results of the unsupported spherical shell, and is arranged in combination with the point where the overall deformation of the workpiece is the largest. The magnitude of the support force is determined based on the simulation, and after experimental correction, it is pre-tightened with a safety margin of 1.5 times.

[0014] The baffle is an annular structure with threaded holes on all sides. When installed, a locking bolt is set above the through hole. The through hole and the point-type support rod are clearance-matched. The baffle plays a positioning and guiding role for the support rod and also serves as an upper limit.

[0015] The point-type support rod has a spherical head, a cylindrical center with the same radius as the rectangular spring, and a smooth cylindrical lower end that fits the rectangular spring. The overall shape is a stepped cylinder. The shoulder of the stepped shaft compresses the spring, providing axial support for the support rod. The spherical head is pressed against the inner surface of the spherical shell, ensuring a complete fit by being tangential to the inner surface of the shell.

[0016] The contact displacement sensor measures the downward displacement of the point-type support rod during clamping by contacting the inner surface of the spherical shell. The spring preload must be set to ensure a tight fit without damaging the shell. The spring must provide sufficient support to maintain the overall rigidity of the shell. The deformation of the shell during processing is measured by comparing the positioning holes on the base plate with the displacement of the sensor. Matlab is used to reconstruct the inner surface of the shell, measure the shell deformation, and provide support for the next step of path planning.

[0017] Furthermore, the number N of the single-degree-of-freedom support units is a natural number, preferably N≥6, and the specific number needs to be determined according to the diameter size of the spherical shell thin-walled part.

[0018] Beneficial effects of the present invention:

[0019] (1) The single-degree-of-freedom support unit used in the present invention adopts tangential contact between the ball head point and the inner surface of the spherical shell, which can ensure the absolute fit of each support point. At the same time, combined with simulation, the position and number of support units are set at the weakest point of rigidity, thereby improving the overall rigidity of the spherical shell workpiece during machining, thereby effectively suppressing machining deformation and vibration of the workpiece and ensuring machining quality and precision;

[0020] (2) Using a contact displacement sensor to measure the absolute displacement of the spherical shell and the point support rod, controlling the preload force while ensuring a safety margin, and using a rectangular spring to adaptively compensate for the deformation of the spherical shell workpiece during the machining process;

[0021] (3) The sensor detects the deformation during the machining process and can reconstruct the inner surface according to the axial displacement of the contact displacement sensor at the corresponding position, thereby correcting the tool path and completing the tool clearance planning;

[0022] (4) The present invention can also reduce the noise generated during workpiece processing and create a pleasant human-computer interaction environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] FIG1( a ) is a perspective schematic diagram of the present invention;

[0024] Figure 1(b) is a schematic diagram of the internal structure and positioning installation of the single-degree-of-freedom support unit;

[0025] Figure 2 (a) is a top view of a single-degree-of-freedom support unit;

[0026] Figure 2 (b) is a cross-sectional view of a single-degree-of-freedom support unit;

[0027] Figure 3 for Figure 2 A partial enlarged view of the structure at position Ⅰ in the middle;

[0028] Figure 4 for Figure 3 A partial enlarged view of the structure at center Ⅱ;

[0029] Figure 5 Schematic diagram of the number and position arrangement of single-degree-of-freedom support units.

[0030] In the figure: 1 mounting plate, 2 base, 3 column, 4 screw nut mechanism, 5 adjustment plate, 6 guide sleeve, 7 rectangular spring, 8 baffle, 9 point support rod, 10 contact displacement sensor. DETAILED DESCRIPTION

[0031] The present application is further described in detail below in conjunction with the accompanying drawings. The description in this section is only exemplary and explanatory and does not limit the scope of protection of the present invention in any way.

[0032] As shown in Figure 1, the displacement measurement type adaptive compensation multi-point support fixture for the processing of spherical shell thin-walled parts includes a mounting plate 1, a base 2, a column 3, a screw nut mechanism 4, an adjustment plate 5, a guide sleeve 6, a rectangular spring 7, a baffle 8, a point support rod 9, and a contact displacement sensor 10.

[0033] Seventeen single-degree-of-freedom support units of different heights are fixed on the mounting plate 1. Each single-degree-of-freedom support unit is connected to the base plate through three columns 3 with threads. The lower part of the column 3 is fixed to the mounting plate 2 by bolts. The single-degree-of-freedom support units have different positions and different lengths of columns 3 to meet the needs of spherical shells of different sizes and different eccentricities. The upper part of the column 3 is fixed to the lower end flange of the guide sleeve 6 by bolts. A screw nut mechanism 4 is installed under the guide sleeve 6. The lower end face of the nut of the screw nut mechanism 4 is in contact with the shaft shoulder of the column 3. The screw of the screw nut mechanism 4 is connected to the adjustment plate 5 through The threaded connection provides auxiliary supporting force and the preload force of the rectangular spring 7 can be adjusted by adjusting the position of the screw. A rectangular spring 7 is placed inside the guide sleeve 6, and the rectangular spring 7 is sleeved on the point support rod 9. The boss in the middle of the point support rod 9 is used to limit the rectangular spring 7, and the axial support force provided by the rectangular spring 7 is transmitted to the ball head part of the support rod. The top of the guide sleeve 6 is fixedly connected to the baffle 8 by a nut. The baffle 8 provides guidance for the contact support part of the support rod, limits the upper limit, and ensures uniform force on the workpiece; at the same time, it provides an installation position for the contact displacement sensor. During the support process, the synchronous axial movement of the floating auxiliary support assembly is achieved through the joint action of the spring adjustment mechanism and the point support rod 9. Combined with the sensors of the seventeen support units, the adaptive compensation multi-point support fixture for measuring the displacement of spherical shell thin-walled parts forms a support system with the axial displacement at the bottom position as the control variable in terms of spatial positioning and movement mode; one is to detect the axial displacement of the point support rod and determine the supporting force of the rectangular spring 7; the other is to detect the change in the position of the spherical shell at this point and determine the deformation of the spherical shell during the processing, providing a basis for the planning of the processing path and the compensation of the spring adaptive support force.

[0034] The mounting plate 1, shown in Figure 1, comprises a base, positioning holes, and positioning slots. The base is an octagonal structure with positioning holes on its top surface. Each positioning hole is surrounded by three sets of threaded holes for connecting the columns 3 and securing the single-degree-of-freedom support unit. Positioning slots are provided on the sides of the base for mounting and securing the fixture to the machine tool's workbench.

[0035] There are 3N columns 3 in total, which are installed around the positioning holes of the mounting plate 1; the upper part of the column 3 is a columnar structure with flat surfaces on both sides, and threaded holes are processed at the upper and lower ends; the column 3 is fixedly installed on the mounting plate 1 through a base with a through hole at the bottom end, and the upper end of the column 3 is connected to the flange of the guide sleeve 6 by bolts.

[0036] like Figure 2The screw nut mechanism 4 shown includes an annular threaded disk and a cylindrical adjusting nut; the threaded disk is provided with a through hole corresponding to the outer contour of the upper part of the column 3, and the lower end face contacts the shoulder of the column 3 under the action of the spring preload, and the shoulder limits the axial displacement of the threaded disk, and the adjusting nut passes through the threaded hole of the threaded disk and is connected to the top adjusting plate 5 by a thread; the upper end of the adjusting plate 5 contacts the rectangular spring 7 in the guide sleeve 6; during the support process, the moving component can be moved up and down along the auxiliary support frame by rotating the adjusting nut, and the axial support force control of the floating auxiliary support component is realized by the rectangular spring 7.

[0037] like Figure 3 The point-type support rod 9 shown has a spherical head, a cylindrical center with the same radius as the rectangular spring 7, and a smooth cylindrical lower end that provides a clearance fit with the rectangular spring 7, creating a stepped cylindrical shape. The shoulder of the stepped shaft compresses the spring, providing axial support for the entire support rod. The spherical head is pressed against the inner surface of the spherical shell, ensuring a complete fit through tangential contact.

[0038] like Figure 4 The baffle 8 is an annular plate with circumferential holes corresponding to the threaded holes on the upper end of the guide sleeve 6 and a central hole that fits the support rod. The baffle 8 is bolted to the upper end of the guide sleeve 6 and has a groove on its upper end for mounting the displacement sensor 10. A small baffle is mounted in the middle of the push rod on the point-type support rod 9. This baffle moves synchronously with the point-type support rod 9 and is used to synchronously convert the displacement of the support rod to the sensor contact.

[0039] like Figure 5 As shown, the single-degree-of-freedom support units used to coordinate with the sensor in the longitudinal direction of the spherical shell should be arranged with less than one at 20°, one at 45°, and one at 90°. In the latitudinal direction, the number of support rods should increase with the increase in deformation accuracy and the radius of the spherical shell. The number should increase in a power of two manner based on an arc length of 500.

[0040] Furthermore, the number M of the lower pressure plate assemblies is a natural number, preferably M≥6, and its function is to press the spherical shell onto the fixture. The specific number is determined according to the diameter size of the spherical shell thin-walled part.

[0041] For those skilled in the art, the above description is only a preferred embodiment of the present invention. The scope of the present invention is limited by the appended claims rather than the above description. Therefore, all changes within the meaning and scope of the equivalent elements of the claims of the present invention should be included in the scope of protection of the present invention.

Claims

1. An adaptive compensation multi-point support fixture for displacement measurement of spherical shell thin-walled parts, characterized in that: The self-adaptive compensation multi-point support fixture comprises a single-degree-of-freedom support unit, a mounting plate (1), a base (2), a column (3), and a screw-nut mechanism (4); A plurality of single-degree-of-freedom support units of different heights are fixed on a mounting plate (1) through a column (3) through a base (2), and spherical shells of different sizes and different eccentricities are matched by adjusting the length of the column (3); the single-degree-of-freedom support unit comprises an adjustment plate (5), a guide sleeve (6), a rectangular spring (7), a baffle (8), a point-type support rod (9) and a contact displacement sensor (10); both ends of the column (3) are threaded, the lower end of the column (3) is fixed to the mounting plate (1) through a bolt through the base plate 2, and the upper end of the column (3) is fixed to the lower end flange of the guide sleeve (6) through a bolt through a screw nut mechanism (4); a screw nut mechanism (4) is installed below the guide sleeve (6), and the lower end surface of the nut of the screw nut mechanism (4) contacts the shaft shoulder of the column (3), and the screw nut mechanism (4) is fixed to the lower end flange of the guide sleeve (6). The lead screw of the structure (4) is connected to the adjustment plate (5) through a threaded connection, providing auxiliary supporting force while adjusting the preload force of the rectangular spring (7) by adjusting the position of the lead screw; a rectangular spring (7) is placed inside the guide sleeve (6), and the rectangular spring (7) is sleeved on the point support rod (9); the boss in the middle of the point support rod (9) is used to limit the rectangular spring (7), and transmit the axial support force provided by the rectangular spring (7) to the ball head part of the point support rod (9); the top of the guide sleeve (6) is fixedly connected to the baffle (8) through a nut, and the baffle (8) provides a guide for the contact support part of the point support rod (9), plays an upper limit role, and ensures uniform force on the thin-walled part of the spherical shell; the baffle (8) also provides an installation position for the contact displacement sensor (10); The contact displacement sensor (10) measures the downward displacement of the point-type support rod (9) of the spherical shell thin-walled part when the spherical shell thin-walled part is clamped by contacting the inner surface of the spherical shell thin-walled part; the setting of the preload force of the rectangular spring (7) needs to ensure that the support force does not damage the spherical shell while ensuring the fit, and the rectangular spring (7) needs to provide a support force that ensures the overall rigidity of the spherical shell thin-walled part.

2. The adaptive compensation multi-point support fixture for displacement measurement of spherical shell thin-walled parts according to claim 1 is characterized in that: The mounting plate (1) comprises a base, a positioning hole and a positioning groove; the base is an octagonal structure, the upper end face is provided with a positioning hole to realize the positioning of the single-degree-of-freedom support unit, 3N threaded holes are provided in the circumferential direction of the positioning hole on the upper end face of the base for connecting the column (3); the side of the base is provided with a positioning groove for fixing the clamp on the machine tool workbench; wherein N is the number of the single-degree-of-freedom support units.

3. The adaptive compensation multi-point support fixture for displacement measurement of spherical shell thin-walled parts according to claim 1 is characterized in that: There are 3N columns (3) in total, which are determined by the number N of single-degree-of-freedom support units. The columns (3) are installed on the upper surface of the mounting plate (1) according to the positioning holes. The length of the columns (3) is determined by the position of the single-degree-of-freedom support units. The columns (3) are generally columnar structures, with the lower part being a cylinder and the upper part being processed into two parallel side surfaces and a shoulder, which are used to limit the movement of the screw nut mechanism (4) in the vertical direction.

4. The adaptive compensation multi-point support fixture for displacement measurement of spherical shell thin-walled parts according to claim 1 is characterized in that: The screw nut mechanism (4) comprises a disc-shaped structure with a threaded hole in the middle and a cylindrical adjusting nut. The disc-shaped structure is pressed down on the shaft shoulder of the column (3). The adjusting nut passes through the threaded hole and is connected to the top adjusting plate (5) by a thread. The upper surface of the adjusting plate (5) contacts the rectangular spring (7) in the guide sleeve (6). During the supporting process, the adjusting plate (5) can be moved up and down in the axial direction by rotating the adjusting nut, and the axial supporting force of the point-type supporting rod (9) is controlled by the rectangular spring (7).

5. The adaptive compensation multi-point support fixture for displacement measurement of spherical shell thin-walled parts according to claim 1 is characterized in that: The guide sleeve (6) is a stepped cylindrical structure with a smooth cylinder in the middle, a flange at the bottom, and threads arranged on the upper end and the circumference of the flange. The bottom flange is connected to the column (3) through threads; the guide sleeve (6) plays a positioning and guiding role for the rectangular spring (7) installed inside, and the upper part is connected to the baffle (8) through a nut to limit the axial movement of the point support rod (9).

6. The self-adaptive compensation multi-point support fixture for displacement measurement of spherical shell thin-walled parts according to claim 1 is characterized in that: The baffle (8) is an annular structure with threaded holes on all sides. When installed, a locking bolt is provided above the threaded holes. The through hole in the middle of the baffle (8) is clearance-matched with the point-type support rod (9). The baffle (8) plays a positioning and guiding role for the point-type support rod (9) and also plays an upper limit role.

7. The self-adaptive compensation multi-point support fixture for displacement measurement of spherical shell thin-walled parts according to claim 1 is characterized in that: The head of the point-type support rod (9) is spherical, the middle is a cylinder with the same radius as the rectangular spring, and the lower end is a smooth cylinder with a clearance fit with the rectangular spring (7). The whole is in the shape of a stepped cylinder, and the shoulder of the stepped shaft presses the rectangular spring (7) to provide axial support force for the support rod; the head is pressed against the inner surface of the spherical shell thin-walled part, and is ensured to be completely fitted by being tangent to the inner surface of the spherical shell thin-walled part.

8. The self-adaptive compensation multi-point support fixture for displacement measurement of spherical shell thin-walled parts according to claim 1 is characterized in that: The number N of the single-degree-of-freedom support units is ≥6, and the specific number needs to be determined according to the diameter size of the spherical shell thin-walled part.

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