Four-point orthogonal coarse-fine composite mandrel precision aligning device and closed-loop aligning method thereof

Abstract

A four-point orthogonal coarse-fine composite mandrel precision centering device and its closed-loop centering method, relate to the field of precision measurement and assembly. The geometric center of the upper surface of the centering upper plate is set as the reference origin, and four radial notches are processed for the centering top block to extend along the circumferential direction at equal angles; the centering lower plate is a basic support element, and is connected with the centering upper plate through a center shaft to form an integrated body; four groups of ball screw coarse adjustment mechanisms are arranged orthogonally and symmetrically along the circumferential direction in the horizontal plane, and are installed in pairs on the upper surface of the centering lower plate along two orthogonal directions X and Y; four groups of piezoelectric ceramic stack micro-displacement centering mechanisms are fixed respectively on the moving platforms of the corresponding ball screw coarse adjustment mechanisms, and the centering operation on the mandrel is performed through the centering top block. The composite adjustment structure of ball screw coarse adjustment and piezoelectric ceramic fine adjustment is adopted, the centering strategy of four-point orthogonal symmetric layout and unilateral pushing is combined, a complete closed-loop centering mathematical model is established, and the micron-level precision centering of the mandrel in a large stroke range is realized.

Description

Technical Field

[0001] This invention relates to the field of precision measurement and assembly technology, specifically a four-point orthogonal coarse and fine composite mandrel precision self-aligning device and its closed-loop self-aligning method. Background Technology

[0002] Initial eccentricity error during mandrel clamping directly affects the accuracy of precision measurement. Automatic self-aligning systems are core equipment for correcting workpiece eccentricity and ensuring measurement accuracy. Currently, automatic self-aligning systems, both domestically and internationally, can be categorized by their drive mechanism into unidirectional self-aligning, bidirectional orthogonal self-aligning, and multi-point collaborative self-aligning.

[0003] Unidirectional self-alignment adjusts the workpiece position through an actuator in a single direction. While simple in structure and easy to control, it struggles to compensate for initial eccentricity errors in any direction during mandrel clamping. Bidirectional orthogonal self-alignment adjusts the workpiece cross-section center using micro-displacement mechanisms in both the X and Y directions. It decomposes the eccentricity between the platform reference center and the workpiece center into compensation amounts in two orthogonal directions, resulting in clearer control logic. Four-point orthogonal piezoelectric self-alignment arranges four sets of stacked piezoelectric ceramic micro-displacement mechanisms in a horizontal plane. Compensation in the X and Y directions is achieved through symmetrical drive units, improving self-alignment stability and response speed. However, the assembly and closed-loop control processes are relatively complex.

[0004] In general, existing self-aligning devices mostly adopt a single drive form, which makes it difficult to simultaneously take into account the initial position adjustment of a large stroke and the micron-level precision eccentricity compensation. Multi-point self-aligning methods are prone to over-constraint due to simultaneous clamping in multiple directions, increasing self-aligning frictional resistance and the risk of jamming. Furthermore, they lack a complete closed-loop self-aligning mathematical model that matches the structure, as well as an analysis of the applicable boundary of self-aligning accuracy, making it difficult to guarantee the stability and accuracy of self-aligning results under different working conditions. Summary of the Invention

[0005] To address the shortcomings of the prior art, this invention provides a four-point orthogonal coarse-fine composite mandrel precision self-aligning device and its closed-loop self-aligning method. It adopts a composite adjustment structure that combines ball screw coarse adjustment and piezoelectric ceramic fine adjustment in series, and combines a four-point orthogonal symmetrical layout with a single-sided push self-aligning strategy to establish a complete closed-loop self-aligning mathematical model, thereby achieving micron-level precision self-aligning of the mandrel within a large stroke range.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A four-point orthogonal coarse and fine composite mandrel precision self-aligning device, comprising:

[0008] The self-aligning lower plate, the self-aligning upper plate, four sets of ball screw coarse adjustment mechanisms, and four sets of piezoelectric ceramic stacked micro-displacement self-aligning mechanisms;

[0009] The upper self-aligning plate is a workpiece carrier, with its upper surface geometric center set as the reference origin, and four radial notches machined at equal angles along the circumference for the extension of the self-aligning top block; the lower self-aligning plate is a basic support component, used to support the upper self-aligning plate, the ball screw coarse adjustment mechanism, and the piezoelectric ceramic stacked micro-displacement self-aligning mechanism. The upper self-aligning plate and the lower self-aligning plate are connected as one unit through a central shaft.

[0010] The four sets of ball screw coarse adjustment mechanisms are orthogonally symmetrically arranged along the circumferential direction on a horizontal plane, and are installed in pairs on the upper surface of the self-aligning lower plate along the X and Y orthogonal directions. The four sets of piezoelectric ceramic stacked micro-displacement self-aligning mechanisms are respectively fixed on the moving platform of the corresponding ball screw coarse adjustment mechanism, forming four sets of series coarse and fine composite self-aligning units. The piezoelectric ceramic stacked micro-displacement self-aligning mechanism is equipped with a self-aligning top block to perform self-aligning operation on the mandrel. In the coarse adjustment stage, the ball screw coarse adjustment mechanism drives the piezoelectric ceramic stacked micro-displacement self-aligning mechanism to move radially along the mandrel. In the fine adjustment stage, the piezoelectric ceramic stacked micro-displacement self-aligning mechanism performs radial compensation on the mandrel.

[0011] Furthermore, the ball screw coarse adjustment mechanism includes a ball screw, a linear guide, a grating ruler, a moving platform, and a servo motor; the servo motor is connected to the ball screw via a coupling, the two ends of the ball screw are supported by a fixed end support and a supporting end support, respectively, the linear guide is arranged on both sides of the ball screw, the moving platform is connected to the ball screw nut and moves along the linear guide, and the grating ruler is used to detect the actual displacement of the moving platform and provide feedback.

[0012] Furthermore, the piezoelectric ceramic stack micro-displacement self-aligning mechanism includes a guide mechanism, a return spring, a support block, a piezoelectric ceramic stack, a self-aligning top block, a trapezoidal thread preload screw, and a locking nut. The guide mechanism is fixed on the moving platform and provides linear guidance and lateral constraint to the support block. The rear end of the piezoelectric ceramic stack is subjected to axial preload through the trapezoidal thread preload screw and locked by the locking nut. The front end of the piezoelectric ceramic stack is rigidly connected to the self-aligning top block through the support block. The return spring is supported between the guide mechanism and the support block to drive its return reset.

[0013] Furthermore, the piezoelectric ceramic stack micro-displacement self-aligning mechanism has two piezoelectric ceramic stacks arranged horizontally side by side. The two piezoelectric ceramic stacks correspond to two support blocks respectively. The two support blocks are connected as one unit by a T-shaped connector in the middle. The self-aligning top block is rigidly connected to the T-shaped connector.

[0014] A closed-loop self-aligning method for a four-point orthogonal coarse-fine composite mandrel precision self-aligning device includes the following steps:

[0015] S1. Establish the self-aligning coordinate system: The theoretical center is based on the geometric center of the self-aligning upper plate. Establish a plane rectangular coordinate system XOY, and arrange four sets of self-aligning units in the positive X, negative X, positive Y, and negative Y directions respectively;

[0016] S2. Core Center Recognition: Acquire images of the core cross-section and extract edge sampling points to fit the actual core center. ;

[0017] S3. Calculation of eccentricity and eccentricity angle: Based on the actual center coordinates of the mandrel, calculate the eccentricity and eccentricity angle of the mandrel relative to the theoretical center of the platform.

[0018] S4. Determine the termination condition for centering: If the eccentricity meets the allowable error requirement, the centering ends; otherwise, proceed to the next step.

[0019] S5. Four-point self-aligning compensation decomposition: Calculate the target compensation amount in the X and Y directions, and use a strategy of single-sided pushing as the main force and opposing units cooperating with retreat to distribute the compensation amount to the self-aligning units in the four directions.

[0020] S6. Coarse-fine adjustment displacement allocation: Based on the relationship between the total compensation displacement in one direction and the maximum effective fine adjustment stroke of the piezoelectric ceramic, allocate the coarse adjustment displacement of the ball screw and the fine adjustment displacement of the piezoelectric ceramic and perform the adjustment.

[0021] S7. Iterative Loop: After completing one adjustment, return to step S2 and repeat the detection and compensation process until the centering termination condition is met or the maximum number of iterations is reached.

[0022] Furthermore, in step S2, the algebraic least squares circle fitting method is used to obtain the center and radius of the mandrel cross section, a least squares objective function is constructed for all edge sampling points, the optimal parameters of the fitted circle are solved, and then the actual center coordinates and fitted radius of the mandrel are obtained.

[0023] Furthermore, in step S4, the centering termination condition only needs to satisfy any one of the following:

[0024] Record No. The eccentricity corresponding to this detection is , For the first The actual center of the mandrel obtained from the second test is used to set the allowable eccentricity error. The termination condition for mind adjustment is expressed as follows: ;

[0025] Set the allowable error in the X direction. Y-direction allowable error The termination condition for mind adjustment is expressed as follows: and ;

[0026] Set the maximum number of iterations. If the number of iterations reaches If the accuracy requirements are still not met, the centering process will stop and an error message will be output.

[0027] Furthermore, in step S5, the target compensation amounts in the X and Y directions are opposite to those in the eccentricity direction, and are expressed as follows: The compensation amounts in the four directions are distributed using a maximum value function:

[0028]

[0029]

[0030]

[0031]

[0032] In the formula, , , , These are the compensation amounts for the four-directional centering units. When the compensation amount is positive, the corresponding centering unit performs active pushing; when the compensation amount is zero, the corresponding centering unit maintains yielding.

[0033] Furthermore, in step S6, the first Total compensation displacement required for each directional self-aligning unit Decomposed into coarse adjustment displacement of ball screw fine-tuning displacement with piezoelectric ceramics :

[0034]

[0035] The coarse adjustment displacement of the ball screw is determined by the screw lead and the rotation angle:

[0036]

[0037] The fine-tuning displacement of piezoelectric ceramics can be approximated as a linear function of the driving voltage:

[0038]

[0039] In the formula, For the ball screw lead, For the first The rotation angle of the ball screw in each direction For the displacement sensitivity of piezoelectric ceramic stacks, For the first The driving voltage of the piezoelectric ceramic stack in each direction;

[0040] The maximum effective fine-tuning stroke of the piezoelectric ceramic is set to... The displacement allocation logic is as follows:

[0041] when At this time, the ball screw coarse adjustment mechanism first performs a coarse adjustment to adjust the remaining compensation amount. Entering the effective stroke range of the piezoelectric ceramic;

[0042] when At that time, fine adjustment is performed directly by the piezoelectric ceramic stack micro-displacement centering mechanism.

[0043] Compared with the prior art, the beneficial effects of the present invention are:

[0044] 1. This invention adopts a composite adjustment method that combines coarse adjustment of ball screw and fine adjustment of piezoelectric ceramics. The ball screw can realize the initial position adjustment of large stroke and the pre-adjustment of large eccentricity, while the piezoelectric ceramic stack can realize micron-level residual eccentricity compensation, thus taking into account both adjustment stroke and centering accuracy.

[0045] 2. The present invention adopts a four-point orthogonal symmetrical layout, which can decompose the planar eccentricity into two independent directions, X and Y, for decoupled control. The control logic is simple and avoids cross interference between movements of different axes.

[0046] 3. The present invention adopts a self-aligning strategy with unilateral pushing as the main method and opposing units cooperating with yielding, which avoids over-constraint caused by simultaneous multi-directional pressing, reduces frictional resistance and jamming risk during self-aligning, and improves self-aligning stability.

[0047] 4. This invention establishes a complete mathematical model for centering, including center identification, eccentricity calculation, compensation decomposition, coarse and fine allocation, and closed-loop iteration. Through closed-loop iterative control with visual feedback, the eccentricity of the spindle can be gradually corrected to ensure centering accuracy.

[0048] 5. This invention clarifies the stiffness characteristics and applicable mandrel mass range of the micro-displacement mechanism through finite element analysis, and verifies the convergence and stability of the closed-loop self-aligning algorithm through simulation, providing accuracy boundaries and parameter references for the practical application of the device. Attached Figure Description

[0049] Figure 1 This is a schematic diagram of the overall structure of the self-aligning device of the present invention;

[0050] Figure 2 This is a schematic diagram of the coarse adjustment mechanism of the ball screw in this invention;

[0051] Figure 3 This is a schematic diagram of the piezoelectric ceramic stacked micro-displacement self-aligning mechanism in this invention;

[0052] Figure 4 This is a flowchart of the closed-loop centering method of the present invention;

[0053] Figure 5This is a schematic diagram of the centering coordinate system and the arrangement of the four-point unit in this invention;

[0054] Figure 6 This is a schematic diagram of the finite element boundary conditions for the horizontal centripetal thrust in the embodiment;

[0055] Figure 7 These are the total deformation cloud diagrams of the micro-displacement self-aligning mechanism under different structural schemes in the embodiments;

[0056] Figure 8 These are the total deformation cloud diagrams of the micro-displacement self-aligning mechanism under different horizontal thrusts in the embodiments;

[0057] Figure 9 This is a diagram showing the trajectory of the mandrel center under the first set of initial eccentricities in the embodiment.

[0058] Figure 10 This is a diagram showing the trajectory of the mandrel center under the second set of initial eccentricities in the embodiment.

[0059] Figure 11 This is a comparison chart of centering error convergence under different control coefficients in the embodiment.

[0060] In the diagram: 1. Lower self-aligning plate; 2. Ball screw coarse adjustment mechanism; 3. Piezoelectric ceramic stacked micro-displacement self-aligning mechanism; 4. Upper self-aligning plate; 21. Support end bracket; 22. Ball screw; 23. Linear guide rail; 24. Grating ruler; 25. Moving platform; 26. Fixed end bracket; 27. Coupling; 28. Servo motor; 31. Guide mechanism; 32. Return spring; 33. T-type connector; 34. Support block; 35. Piezoelectric ceramic stack; 36. Top self-aligning block; 37. Trapezoidal thread preload screw; 38. Locking nut. Detailed Implementation

[0061] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the invention, not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0062] The core idea of ​​this invention is to use a four-point orthogonal symmetrical series coarse and fine composite adjustment unit, hereinafter referred to as the four-point unit, to complete the initial positioning of the large stroke through the ball screw 22, to complete the micron-level precision compensation through the piezoelectric ceramic stack 35, and to achieve high-precision center correction in the horizontal plane of the mandrel by combining the single-sided push self-aligning strategy and the closed-loop iterative control method.

[0063] A four-point orthogonal coarse and fine composite mandrel precision self-aligning device, with an overall structure combining Figure 1As shown, it includes a lower self-aligning plate 1, an upper self-aligning plate 4, four sets of ball screw coarse adjustment mechanisms 2, and four sets of piezoelectric ceramic stacked micro-displacement self-aligning mechanisms 3, wherein:

[0064] The upper self-aligning plate 4 serves as the workpiece support, with its upper surface geometric center set as the reference origin O, which is used as the reference for establishing the self-aligning coordinate system and calculating the eccentricity. Four radial notches are machined at equal angles along its circumference for the extension of the self-aligning top block 36 to perform self-aligning operations on the mandrel. The lower self-aligning plate 1 is the basic support, supporting the upper self-aligning plate 4, the ball screw coarse adjustment mechanism 2, and the piezoelectric ceramic stacked micro-displacement self-aligning mechanism 3. The upper self-aligning plate 4 and the lower self-aligning plate 1 are connected as a single unit via a central shaft to form the self-aligning base.

[0065] Four sets of ball screw coarse adjustment mechanisms 2 are orthogonally and symmetrically arranged along the circumferential direction on a horizontal plane, and are installed in pairs on the upper surface of the self-aligning lower plate 1 along the X and Y orthogonal directions; four sets of piezoelectric ceramic stacked micro-displacement self-aligning mechanisms 3 are respectively fixed on the moving platform 25 of the corresponding ball screw coarse adjustment mechanism 2. The piezoelectric ceramic stacked micro-displacement self-aligning mechanism 3 and the corresponding ball screw coarse adjustment mechanism 2 constitute a self-aligning unit, and the four self-aligning units constitute a four-point unit. In the coarse adjustment stage, the ball screw 22 drives the piezoelectric ceramic stacked micro-displacement self-aligning mechanism 3 to move radially along the mandrel, realizing the rapid adjustment of the relative position between the self-aligning top block 36 and the mandrel; in the fine adjustment stage, the piezoelectric ceramic stack 35 generates axial micro-displacement, which is transmitted to the mandrel through the support block 34, T-shaped connector 33 and self-aligning top block 36, realizing small stroke and high precision radial compensation.

[0066] Four sets of piezoelectric ceramic stacked micro-displacement self-aligning mechanisms 3 are evenly and symmetrically distributed at 90° intervals in the self-aligning base with the rotation center of the self-aligning upper plate 4 as the origin. Two sets of piezoelectric ceramic stacked micro-displacement self-aligning mechanisms 3 are symmetrically arranged above and below the Y-axis, with the driving direction along the Y-axis. The other two sets of piezoelectric ceramic stacked micro-displacement self-aligning mechanisms 3 are symmetrically arranged to the left and right of the X-axis, with the driving direction along the X-axis (see...). Figure 5 In part a), A and C are two sets of piezoelectric ceramic stacked micro-displacement self-aligning mechanisms 3 along the Y-axis, and B and D are two sets of piezoelectric ceramic stacked micro-displacement self-aligning mechanisms 3 along the X-axis. The self-aligning platform refers to the self-aligning upper plate 4, and the workpiece to be measured refers to the mandrel. By calculating the eccentricity of the detected workpiece center relative to the platform center and distributing the displacement to the piezoelectric ceramic stacked micro-displacement self-aligning mechanisms 3 in the X-axis and Y-axis directions respectively, the precise eccentricity adjustment of the platform in any horizontal direction can be achieved.

[0067] The structure of the ball screw coarse adjustment mechanism 2 Figure 2As shown, the coarse adjustment actuator of the self-aligning device mainly consists of a support end bracket 21, a ball screw 22, a linear guide rail 23, a grating ruler 24, a moving platform 25, a fixed end bracket 26, a coupling 27, and a servo motor 28. These components work together through rotary drive, screw transmission, guide rail constraint, and displacement feedback to ensure the feed stability and positioning accuracy of the coarse adjustment.

[0068] The ball screw coarse adjustment mechanism 2 is mounted on the upper surface of the self-aligning lower plate 1 and arranged radially along the spindle. The servo motor 28 is fixed to the edge of the self-aligning lower plate 1, and its motor shaft is connected to the screw shaft of the ball screw 22 via a coupling 27, used to transmit the motor output torque to the screw shaft. The two ends of the ball screw 22 are supported by a fixed end support 26 and a supporting end support 21, respectively. The fixed end support 26 is used to limit the axial movement of the ball screw 22 and ensure rotational positioning stability, while the supporting end support 21 is used to improve the slewing bearing stiffness of the ball screw 22 and reduce the sway and deformation of the ball screw 22 during operation. The coupling 27 can compensate for minor installation deviations between the servo motor 28 and the ball screw 22, reducing the impact of assembly errors on transmission smoothness.

[0069] During coarse adjustment, the servo motor 28 drives the ball screw 22 to rotate, and the screw nut of the ball screw 22 drives the moving platform 25 to move linearly along the linear guide rail 23. The piezoelectric ceramic stack micro-displacement self-aligning mechanism 3 is fixedly installed on the moving platform 25. The feed motion of the moving platform 25 can drive the entire piezoelectric ceramic stack micro-displacement self-aligning mechanism 3 to move synchronously along the spindle radially, realizing the large stroke initial radial position adjustment of the self-aligning operation.

[0070] Linear guides 23 are arranged on both sides of the ball screw 22 to bear the weight of the moving platform 25 and the upper piezoelectric ceramic stacked micro-displacement self-aligning mechanism 3, and to constrain the movement direction of the moving platform 25, limiting the lateral offset, rotation and lateral sway of the moving platform 25 during the coarse adjustment process, avoiding the ball screw 22 from directly bearing excessive lateral load, and improving the consistency of the coarse adjustment feed direction and the stability of the mechanism operation.

[0071] The grating ruler 24 serves as a displacement feedback element. Its body is fixed to the self-aligning lower plate 1 or the guide rail mounting reference surface, while the reading head is fixed to the moving platform 25, maintaining a certain non-contact gap with the ruler body. When the moving platform 25 moves, the reading head of the grating ruler 24 moves synchronously with it. By reading the relative displacement between the grating ruler and the ruler body, the actual feed amount of the coarse adjustment mechanism is obtained. This reduces the impact of ball screw 22 transmission error, backlash, and assembly error on the coarse adjustment positioning accuracy, providing a stable initial position basis for subsequent micro-displacement fine adjustment of the piezoelectric ceramic stack 35.

[0072] The structural combination of the piezoelectric ceramic stacked micro-displacement self-aligning mechanism 3 Figure 3As shown, the fine-tuning actuator of the self-aligning device mainly consists of a guide mechanism 31, a return spring 32, a T-shaped connector 33, a support block 34, a piezoelectric ceramic stack 35, a self-aligning top block 36, a trapezoidal thread preload screw 37, and a locking nut 38. Each component works together through guide constraints, preload support, elastic reset, and rigid force transmission to ensure the stability of the micro-displacement output and the repeatability of the positioning accuracy during fine-tuning.

[0073] The piezoelectric ceramic stack micro-displacement self-aligning mechanism 3 is mounted on the moving platform 25 of the ball screw coarse adjustment mechanism 2, and moves radially along the mandrel along with the ball screw coarse adjustment mechanism 2. The guide mechanism 31 is fixed on the moving platform 25. Its internal guide surface and support surface form linear guidance, lateral limit and anti-rotation constraint for two support blocks 34 arranged in parallel laterally. This ensures that the movement direction of the support blocks 34 is consistent with the drive axis of the piezoelectric ceramic stack 35, suppresses the sway, rotation and undesirable lateral displacement of the support blocks 34 during the micro-displacement transmission process, and improves the directional consistency and transmission stability of the piezoelectric drive displacement.

[0074] Two piezoelectric ceramic stacks 35 are installed side-by-side laterally inside the main body of the piezoelectric ceramic stack micro-displacement self-aligning mechanism 3. Axial preload is applied to their rear ends via trapezoidal threaded preload screws 37, and the preload position is locked by a locking nut 38. The trapezoidal threaded preload screws 37 convert rotational adjustment into a small axial feed through the threaded joint, thereby applying a stable preload to the piezoelectric ceramic stacks 35. This ensures that the piezoelectric ceramic stacks 35 remain under pressure throughout their entire working stroke, reducing the impact of initial gaps, loose contact, and uneven force on output accuracy. During preload adjustment, the trapezoidal threaded preload screws 37 are screwed in first, causing a small axial feed along the piezoelectric ceramic stacks 35 and gradually tightening the rear ends. Once the preload reaches the design requirements, the locking nut 38 locks the preload screws to prevent loosening during repeated self-aligning, vibration, or piezoelectric ceramic expansion and contraction.

[0075] The piezoelectric ceramic stack 35 has a contact-type force transmission relationship with the end face of the support block 34. After being energized, the piezoelectric ceramic stack 35 elongates axially based on the inverse piezoelectric effect and pushes the support block 34 forward along the guide mechanism 31 through the end face thrust. When the driving voltage decreases or the piezoelectric ceramic stack 35 returns to its initial length, the piezoelectric ceramic stack 35 does not bear the pulling force during the return process of the support block 34.

[0076] During displacement transmission, the two support blocks 34 are rigidly connected to the T-shaped connector 33 arranged in the middle, ensuring high connection stiffness and motion consistency at the input end. The axial micro-displacement output by the two piezoelectric ceramic stacks 35 is transmitted to the T-shaped connector 33 via the two support blocks 34. Then, the T-shaped connector 33 drives the self-aligning top block 36 to generate micro-displacement output along the horizontal radial direction, which finally drives the mandrel to complete the radial position adjustment, forming a continuous force transmission path of "piezoelectric ceramic stack 35 - support block 34 - T-shaped connector 33 - self-aligning top block 36 - mandrel".

[0077] Two return springs 32 are respectively supported between the guide mechanism 31 and the corresponding support block 34, and are used to push the support block 34, T-shaped connector 33 and self-aligning top block 36 back to the initial position after the piezoelectric ceramic stack 35 is unloaded.

[0078] Based on the aforementioned self-aligning device, a closed-loop self-aligning method for a four-point orthogonal roughing and finishing composite mandrel precision self-aligning device is provided, with the overall process combined with... Figure 4 As shown, it is based on visual detection of the center of the circle, and gradually corrects the spindle eccentricity through iterative compensation, specifically including the following steps:

[0079] Step 1: Establish a centering coordinate system

[0080] Combining the self-aligning coordinate system with the arrangement of four-point elements Figure 5 As shown in the figure, part a) represents the distribution of the centering positions, and part b) represents the centering coordinate system and the arrangement of the four-point units. The geometric center of the centering upper plate 4 is taken as the theoretical center of the platform. A Cartesian coordinate system XOY is established, where the theoretical center of the platform represents the ideal center position that the mandrel should reach. The X-axis coincides with the line connecting the centers of the left and right sets of self-aligning units, and the Y-axis coincides with the line connecting the centers of the upper and lower sets of self-aligning units. Four-point units are arranged in the positive X, negative X, positive Y, and negative Y directions of the platform, denoted as X0. + X - Y + Y - Alignment unit.

[0081] After the mandrel is installed, it is affected by errors. The actual center of the circle obtained through visual inspection or cross-sectional profile recognition is recorded as follows: ,in This indicates the deviation of the actual center of the mandrel in the X direction from the theoretical center. This represents the deviation of the actual center of the mandrel in the Y direction relative to the theoretical center; the centering objective is to gradually bring the actual center of the mandrel closer to the theoretical center of the platform through radial compensation using four-point elements. .

[0082] Because the four-point elements are arranged orthogonally and symmetrically in the structure, the eccentricity error of the mandrel in the horizontal plane can be decomposed into two independent components in the X and Y directions. The advantage of this approach is that it transforms the complex planar centering problem into a one-dimensional compensation problem in two orthogonal directions, and then the centering elements in the four directions perform the corresponding compensation actions respectively.

[0083] Step 2: Identification of the center of the mandrel cross section

[0084] Acquire images of the mandrel cross-section, extract the contour of the mandrel cross-section boundary, and obtain... edge sampling points .

[0085] The center and radius of the mandrel cross section are obtained using the algebraic least squares circle fitting method. The standard equation of the circle is:

[0086]

[0087] In the formula, Fit the center coordinates of the mandrel cross section. The fitted radius is denoted as .

[0088] Expand the equation of the circle and let... , , Transform into linear form:

[0089]

[0090] For all edge sampling points, construct the least squares objective function:

[0091]

[0092] When the objective function When the minimum value is obtained, the result is , , These are the optimal parameters for fitting the circle, which then yield the actual coordinates of the mandrel's center. , The fitting radius is: .

[0093] Step 3: Calculation of eccentricity and eccentricity angle

[0094] Based on the actual center of the mandrel Calculate the theoretical center of the mandrel relative to the platform. eccentricity :

[0095]

[0096] when At this time, the actual center of the mandrel coincides with the theoretical center of the platform, achieving an ideal self-aligning state; when At this time, the spindle is eccentric and needs to be compensated.

[0097] Calculate the eccentricity angle using the two-parameter arctangent function :

[0098]

[0099] Eccentricity and eccentricity Together they describe the deviation of the mandrel center, where: eccentricity It is mainly used to determine whether the centering error meets the requirements, and the eccentricity angle. It is mainly used to determine the quadrant where the eccentricity is located and the direction of active compensation. In the actual closed-loop alignment process, the mandrel center needs to be re-detected and the eccentricity recalculated after each adjustment. and eccentricity This will determine whether to proceed with the next round of compensation.

[0100] Step 4: Determining the conditions for terminating mindset adjustment

[0101] The basic idea of ​​closed-loop feedback control and closed-loop centering is: after each adjustment is completed, the cross-sectional image of the mandrel is re-acquired, the actual center position of the mandrel is re-identified, and then it is determined whether to continue compensation based on the new eccentricity.

[0102] If the comprehensive eccentricity is used as the criterion for judging the end of centering, let the first... The eccentricity corresponding to this detection is , For the first The actual center of the mandrel obtained from the second test is used to set the allowable eccentricity error. The termination condition for mind adjustment is expressed as follows: In addition to using the comprehensive eccentricity judgment, the component errors in the X and Y directions can also be judged separately, and the allowable error in the X direction can be set. Y-direction allowable error At this point, the termination condition for mind adjustment is expressed as: and .

[0103] Therefore, if the following conditions are met or satisfy and If the centering termination condition is met, the center position of the mandrel is considered to meet the centering accuracy requirements, and the centering process ends; if the centering termination condition is not met, the next step is to decompose the four-point centering compensation amount.

[0104] In addition, to prevent the system from looping infinitely due to center recognition failure, mechanism overtravel, abnormal contact of the top block, or unreasonable control parameter settings, a maximum number of iterations should be set. If the number of iterations reaches If the accuracy requirements are still not met, the centering process will stop and an error message will be output.

[0105] Step 5: Decomposition of Four-Point Heart Adjustment Compensation Amount

[0106] The essence of mandrel self-alignment is to align the actual center of the mandrel. Towards the theoretical center of the platform Movement. Therefore, the centering compensation direction should be opposite to the eccentricity direction, and the target compensation amounts in the X and Y directions are respectively:

[0107]

[0108] Since the self-aligning device of this invention consists of four sets of orthogonally symmetrically arranged self-aligning units, the target compensation amount needs to be allocated to X. + X - Y + Y - Four directions. Considering that the piezoelectric ceramic stack 35 mainly achieves active pushing through elongation and is not suitable for active pull-back, a compensation method is adopted with unilateral pushing as the main method and opposing units cooperating with yielding. The compensation amount is distributed to the centering units in four directions. The compensation amount in the four directions is distributed using a maximum value function, as shown below:

[0109]

[0110]

[0111]

[0112]

[0113] In the formula, , , , These are the compensation amounts for the four-directional self-aligning units. When the compensation amount in a certain direction is positive, the self-aligning unit in the corresponding direction performs active pushing; when the compensation amount is zero, the corresponding self-aligning unit does not perform active pushing, and if necessary, the ball screw coarse adjustment mechanism 2 maintains a yielding or light contact state to avoid over-constraint and reverse interference.

[0114] The four self-aligning units decompose the compensation amount according to the method of unilateral pushing and opposing yielding. The ball screw coarse adjustment mechanism 2 is responsible for large-range approach and initial position adjustment, while the piezoelectric ceramic stacked micro-displacement self-aligning mechanism 3 is responsible for micron-level residual error compensation. Through closed-loop detection and iterative judgment, the mandrel center position can be gradually corrected, providing a theoretical basis for subsequent self-aligning control and simulation analysis.

[0115] Step 6: Coarse-fine adjustment of displacement distribution

[0116] No. One direction ( X represents + X - Y + Y - Total compensation displacement required for the self-aligning unit (four directions) It can be decomposed into coarse adjustment displacement of the ball screw. fine-tuning displacement with piezoelectric ceramics :

[0117]

[0118] The coarse adjustment displacement of the ball screw is determined by the screw lead and the rotation angle:

[0119]

[0120] In the formula, For the ball screw lead, For the first The rotation angle of the ball screw in each direction. Since the ball screw 22 is used in conjunction with the grating ruler 24, the actual coarse adjustment displacement of the ball screw can be corrected through feedback from the grating ruler 24.

[0121] The fine-tuning displacement of piezoelectric ceramics can be approximately expressed as a linear function of the driving voltage within a small displacement range:

[0122]

[0123] In the formula, For the displacement sensitivity of piezoelectric ceramic stacks, For the first The driving voltage of the piezoelectric ceramic stack in each direction.

[0124] The maximum effective fine-tuning stroke of the piezoelectric ceramic is set to... The displacement allocation logic is as follows:

[0125] when At that time, the ball screw coarse adjustment mechanism 2 first performs coarse adjustment to adjust the remaining compensation amount. Entering the effective stroke range of the piezoelectric ceramic;

[0126] when At that time, fine adjustment is performed directly by the piezoelectric ceramic stack micro-displacement centering mechanism 3.

[0127] Step 7: Iteration Loop

[0128] After completing one adjustment, return to step 2 to reacquire the mandrel cross-sectional image, identify the actual center position of the mandrel, and calculate the eccentricity. Proceed to the next round of judgment and compensation until the centering termination condition is met or the maximum number of iterations is reached. .

[0129] Example

[0130] This embodiment uses a 190mm diameter mandrel as the adjustment object to specifically explain the parameter design, adjustment range, stiffness characteristics, and closed-loop self-aligning convergence effect of the self-aligning device of the present invention.

[0131] 1. Key component parameters and adjustment range

[0132] (1) Parameters of ball screw coarse adjustment mechanism

[0133] Select a 22mm ball screw with a nominal diameter of 8mm and a lead of [missing information]. The total length is 120mm; for every revolution of the servo motor 28, the moving platform 25 theoretically advances 2mm.

[0134] After deducting structural limitations such as the 16mm length of the ball screw nut, the 30.5mm length occupied by the fixed end support 26, the 14.9mm length occupied by the supporting end support 21, and the 5.5mm thickness of the fixed end limit ring, the maximum mechanical stroke of the ball screw coarse adjustment mechanism 2 is... .

[0135] Servo motor 28 uses a 50W small servo motor with a rated speed of Calculate the rated torque from the power relationship: Substitute ,have to .

[0136] Conservative design axial thrust Ball screw transmission efficiency Calculate the required driving torque for the ball screw: Substituting the data yields .

[0137] Take the torque safety factor The verification torque is The torque is less than the rated torque of the servo motor (28), and the driving capability meets the requirements.

[0138] Design coarse adjustment speed Corresponding motor speed It is far below the rated speed, with ample speed margin.

[0139] Linear guide rail 23 adopts a double-rail, double-slider support method. The effective length of a single guide rail is 81.60 mm, the guide rail width is 4.40 mm, the slider length is 11.00 mm, the slider height is 3.90 mm, and the center distance between the two guide rails is 51 mm. The theoretical allowable stroke of the guide rail pair is 70.60 mm, which is greater than the actual mechanical stroke of the coarse adjustment mechanism, and the range of motion meets the requirements. The design requires a rated static load of not less than 150 N and a rated dynamic load of not less than 100 N for a single slider, meeting the support and guiding requirements of the small self-aligning unit.

[0140] The grating ruler 24 has a total length of 91.00 mm, an effective installation length of 82.00 mm, a width of 6.00 mm, and a thickness of 0.50 mm. The reading head measures 15.00 mm × 6.00 mm × 6.80 mm, with a non-contact installation gap of approximately 1 mm between the reading head and the ruler. The effective measurement range of the grating ruler 24 is designed to be 64 mm, covering the entire coarse adjustment stroke; the design resolution is 1 μm, and the measurement accuracy is ±5 μm, meeting the requirements for coarse adjustment displacement feedback.

[0141] (2) Applicable mandrel diameter range

[0142] When the self-aligning top block 36 moves to its closest position, the distance from the center of the platform to the contact surface of the self-aligning top block 36 is... When moving to the farthest position, the distance The corresponding theoretically applicable mandrel diameter range is:

[0143]

[0144]

[0145] Mandrel diameter in this embodiment ,radius Radial margin with minimum contact radius It is within the applicable range and has sufficient margin.

[0146] (3) Initial eccentricity compensation range

[0147] For a 190mm diameter mandrel, the compensation amount for coarse adjustment in the single-axis direction is [missing information]. .

[0148] 35 Target Effective Fine-Tuning Stroke of Piezoelectric Ceramic Stack Therefore, the maximum compensation capability in a single-axis direction is approximately: , and These represent the maximum compensation capabilities in the X and Y directions, and the theoretical maximum eccentricity compensation in the plane, respectively. Therefore, for a mandrel with a diameter of 190 mm, under the current structural position, the mechanism can theoretically achieve a single-axis eccentricity compensation capability of approximately 15.89 mm and a maximum planar eccentricity compensation capability of approximately 22.47 mm. This compensation range is mainly determined by the radial margin between the current mandrel radius and the nearest contact position of the self-aligning top block 36. The piezoelectric ceramic stack 35 mainly undertakes the micron-level residual error correction after coarse adjustment. It should be noted that the coarse adjustment stage is responsible for driving the fine adjustment unit closer to the mandrel, so that the self-aligning top block 36 enters the working position, while the fine adjustment stage is responsible for micron-level residual error correction.

[0149] (4) Piezoelectric ceramic stacking and pre-tightening reset parameters

[0150] The piezoelectric ceramic stack 35 consists of 11 stacked piezoelectric ceramic sheets, each 2.00 mm thick, with a total stack length of 22.00 mm. The stack height is 10.00 mm, and the width is 16 mm to accommodate the assembly space. The target effective fine-tuning stroke is... The maximum driving voltage is taken according to the commonly used piezoelectric drive level. The corresponding displacement sensitivity is not less than 0.133μm / V; in order to ensure that the piezoelectric ceramic stack 35 has sufficient pushing ability, the maximum output force or blocking force of the piezoelectric ceramic stack 35 is set to not less than 500N in this embodiment.

[0151] The trapezoidal thread preload screw 37 and the locking nut 38 adopt a Tr4×1 trapezoidal thread structure. Recommended preload force. Approximately 10% of the maximum output force is used to eliminate the initial contact gap. The trapezoidal thread preload screw 37 is 18mm long, has a maximum diameter of 4mm, and is made of 45 steel; the locking nut 38 is 4mm thick and is also made of 45 steel.

[0152] The return spring 32 is made of 65Mn spring steel with a wire diameter of [missing information]. , outer diameter median diameter Total number of coils: 10; Effective number of coils: 8. The formula for calculating spring stiffness is: Take the shear modulus The stiffness of a single spring was calculated. .

[0153] Set precompression amount during installation. Initial return force of a single spring The total return force of the two springs is approximately 5.40 N. When the piezoelectric ceramic stack reaches its full stroke, the additional spring force of a single spring is approximately 0.036 N, and the total additional spring force of the two springs is approximately 0.072 N. Compared to the output force of the piezoelectric ceramic stack, this is relatively small, and its influence can be ignored.

[0154] 2. Finite Element Analysis of Stiffness of Micro-Displacement Mechanism

[0155] Taking the guide mechanism 31, support block 34, T-shaped connector 33, and self-aligning top block 36 as the analysis objects, a fixed constraint is set at the bottom of the guide mechanism 31, and a horizontal centripetal thrust is applied to the end face of the self-aligning top block 36. Static finite element analysis is carried out, and the finite element boundary conditions of the horizontal centripetal thrust are combined with... Figure 6 As shown.

[0156] The formula for calculating the applied horizontal centripetal thrust in finite element analysis is as follows: Take the coefficient of friction Thrust safety factor ,have to That is, for every 1kg increase in the mass of the mandrel, the corresponding horizontal centripetal thrust increases by approximately 8.82N.

[0157] (1) Structural optimization results

[0158] Initial finite element analysis results show that under horizontal centripetal thrust, the maximum deformation is mainly concentrated at the upper end of the self-aligning block 36 and near the T-shaped connector 33, indicating significant cantilever bending and local rotation in this area. To reduce the elastic deformation of the self-aligning block 36, this embodiment performs multiple rounds of dimensional optimization on the self-aligning block 36 and the T-shaped connector 33, including increasing the dimensions of key force transmission sections, adjusting the height and width of the self-aligning block, and increasing the size of the connection area of ​​the T-shaped connector. The total deformation cloud diagrams of the micro-displacement self-aligning mechanism under different structural schemes are combined. Figure 7 As shown in Table 1 (corresponding to the initial scheme, optimized scheme 1, optimized scheme 2, and final scheme from top to bottom), the corresponding maximum total deformation results are shown in Table 1.

[0159] Table 1 Record of the Structural Optimization Process of the Micro-Displacement Self-Aligning Mechanism

[0160]

[0161] Depend on Figure 7 As shown in Table 1, the initial structure exhibited a maximum total deformation of 0.058721 mm (58.721 μm) under a thrust of 100 N, with the deformation concentrated in the area connecting the upper end of the self-aligning top block 36 and the T-shaped connector 33. After multiple rounds of optimization, including increasing the critical force transmission section, optimizing the size of the self-aligning top block 36, and increasing the connection area of ​​the T-shaped connector 33, the final design reduced the maximum total deformation under a thrust of 100 N to 0.006009 mm (6.009 μm), a deformation reduction of approximately 89.77%, resulting in a significant improvement in structural stiffness.

[0162] (2) Deformation patterns under different loads

[0163] To further analyze the deformation characteristics of the self-aligning block 36 under horizontal thrust corresponding to different mandrel masses, horizontal centripetal thrusts of 10N, 20N, 40N, 60N, 80N, and 100N were applied based on the final design, and the maximum total deformation results under different load conditions were obtained. The total deformation contour maps of the micro-displacement self-aligning mechanism under different horizontal thrusts are combined with... Figure 8 As shown (corresponding to 10N, 20N, 40N, 60N, 80N, and 100N from top to bottom), the corresponding data are summarized in Table 2. It should be noted that because the deformation range varies under different working conditions, the color scale range of the ANSYS contour plot will automatically change with the maximum value. Therefore, it is not advisable to directly compare different contour plots solely based on color intensity; the maximum total deformation value in the upper left corner of the contour plot and the statistical data in Table 2 should be used as the primary basis for judgment.

[0164] Table 2. Maximum total deformation results of the micro-displacement self-aligning mechanism under different horizontal thrusts.

[0165]

[0166] Depend on Figure 8 As shown in Table 2, within the thrust range of 10N to 100N, the maximum total deformation increases approximately linearly with increasing thrust, and the deformation area is concentrated near the upper end of the self-aligning top block 36.

[0167] 10N thrust: maximum total deformation 0.6009μm, meeting the 1μm self-aligning accuracy requirement;

[0168] 20N thrust: maximum total deformation 0.90136μm, meeting the 1μm self-aligning accuracy requirement;

[0169] 40N thrust: maximum total deformation 2.4036μm, exceeding the 1μm accuracy requirement;

[0170] 100N thrust: maximum total deformation 6.009μm, exceeding the 1μm accuracy requirement.

[0171] Therefore, the finite element results show that the current structure can meet the 1μm level self-aligning accuracy requirement under horizontal thrust of 10N and 20N, but it can no longer meet the precision adjustment requirements starting from 40N.

[0172] (3) Applicable mandrel mass range

[0173] Based on the relationship between thrust and mass, the accuracy requirements for different mandrel masses can be obtained:

[0174] The mandrel weighs 1.13 kg (corresponding to a thrust of 10 N): the maximum deformation is 0.6009 μm, meeting the 1 μm accuracy requirement;

[0175] The mandrel weighs 2.27 kg (corresponding to a thrust of 20 N): the maximum deformation is 0.90136 μm, meeting the 1 μm accuracy requirement;

[0176] The spindle weighs 4.54 kg (corresponding to a thrust of 40 N): the maximum deformation is 2.4036 μm, which does not meet the 1 μm accuracy requirement.

[0177] Based on linear interpolation estimation, the critical mandrel mass that meets the 1μm accuracy requirement is approximately 2.42kg; conservatively speaking, the structural design of this embodiment can reliably meet the 1μm precision adjustment of mandrels weighing up to approximately 2.27kg.

[0178] In this embodiment, the target mandrel mass is 11.765 kg, corresponding to a horizontal thrust of approximately 103.77 N. The estimated maximum total deformation is approximately 6.235 μm, which is greater than the 1 μm accuracy requirement, indicating that the stiffness of this structure needs further optimization for a large-mass mandrel.

[0179] 3. Closed-loop self-aligning simulation verification

[0180] A closed-loop self-alignment simulation model was established using MATLAB, and allowable eccentricity error was set. maximum effective fine-tuning stroke of piezoelectric Maximum number of iterations Default control coefficient The center identification error is 0.15μm, and the execution error is 0.10μm. Control coefficient. Let X represent the compensation ratio for the current eccentricity error in each adjustment. Then, the theoretical compensation amounts in the X and Y directions can be expressed as: .

[0181] (1) Medium initial eccentricity condition

[0182] Set the first set of initial eccentricities , Initial overall eccentricity Simulation results show that the overall eccentricity decreases rapidly with increasing iteration count, dropping to 145.676 μm after the first iteration, indicating that closed-loop compensation can quickly reduce the large initial eccentricity error. As the iteration count continues to increase, the rate of error reduction gradually slows down, reaching 0.663 μm after the fifth iteration, which is less than the 1 μm accuracy requirement, indicating centering convergence. Therefore, under this initial eccentricity condition, the closed-loop centering model can achieve error convergence within a relatively small number of iterations.

[0183] The first set of initial eccentricity combined with the mandrel center motion trajectory Figure 9As shown in the figure, the mandrel center gradually approaches the theoretical center O(0,0) from the initial position (0.50, 0.30), and the overall trajectory converges along the line connecting the initial eccentric point and the theoretical center. This is because the present invention uses a decoupling compensation method in the X and Y directions, and uses the same control coefficients in both directions, so the errors in the two directions gradually decrease in a similar proportion. This result shows that under the first set of initial eccentric conditions, the closed-loop centering model can make the mandrel center stably approach the theoretical center of the platform.

[0184] (2) Large initial eccentricity condition

[0185] Set the second set of initial eccentricities , Initial overall eccentricity Simulation results show that the overall eccentricity also decreases rapidly with increasing iterations. After the first iteration, the eccentricity drops to 235.630 μm, and after the second iteration, it further decreases to 58.540 μm. As closed-loop compensation continues, it drops to 0.961 μm after the fifth iteration, meeting the 1 μm accuracy requirement. This result demonstrates that even with a large initial eccentricity and changes in the eccentricity direction, the established closed-loop centering model still exhibits good error convergence capability, verifying the adaptability of the compensation decomposition method to eccentricities in different quadrants.

[0186] The second set of initial eccentricity combined with the mandrel center motion trajectory Figure 10 As shown in the figure, the initial center of the second group is located in the positive X direction and the negative Y direction. During the closed-loop centering process, the trajectory of the center gradually approaches the theoretical center from the fourth quadrant. Similar to the results of the first group, the overall trajectory of the center shows a convergence characteristic along the direction from the initial eccentric point to the theoretical center. This indicates that the compensation quantity decomposition method established in this invention can automatically determine the compensation direction according to the positive and negative signs of the eccentric component, and has the ability to adjust the initial eccentricity in different quadrants.

[0187] The simulation results from the first and second groups show that when the initial eccentricity is 583.095 μm and 943.398 μm respectively, the closed-loop centering model can reduce the overall eccentricity to less than 1 μm within 5 iterations, verifying the effectiveness of the established closed-loop compensation model.

[0188] (3) Comparison of different control coefficients

[0189] Based on the initial eccentricity of the first group, control coefficients of 0.4, 0.6, 0.8, and 0.9 were used for comparison. The curves of the overall eccentricity changing with the number of iterations under different control coefficients were combined. Figure 11 As shown, it can be seen that:

[0190] It has a relatively slow convergence speed but good stability, making it suitable for scenarios with high stability requirements.

[0191] The convergence speed is moderate, the stability is good, and it is suitable for general centering processes.

[0192] It has a relatively fast convergence speed and good stability, with a good balance between convergence speed and stability.

[0193] It has the fastest convergence speed, but is more sensitive to error disturbances, and is suitable for scenarios with small errors and stable mechanism response.

[0194] In summary, a control coefficient of 0.75 to 0.8 can balance convergence speed and centering stability.

[0195] The parameters and results in this embodiment are used to illustrate the implementation process of the present invention. In practical applications, the component parameters and control strategies can be adjusted according to the requirements of mandrel size, quality, and precision.

[0196] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered illustrative and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of the equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

[0197] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A four-point orthogonal coarse-fine composite mandrel precision self-aligning device, characterized in that: It includes a lower self-aligning plate (1), an upper self-aligning plate (4), four sets of ball screw coarse adjustment mechanisms (2), and four sets of piezoelectric ceramic stacked micro-displacement self-aligning mechanisms (3). The upper self-aligning plate (4) is a workpiece carrier. Its upper surface geometric center is set as the reference origin, and four radial notches are machined at equal angles along the circumference for the extension of the self-aligning top block (36). The lower self-aligning plate (1) is a basic support component used to support the upper self-aligning plate (4), the ball screw coarse adjustment mechanism (2), and the piezoelectric ceramic stacked micro-displacement self-aligning mechanism (3). The upper self-aligning plate (4) and the lower self-aligning plate (1) are connected as one unit through a central shaft. The four sets of ball screw coarse adjustment mechanisms (2) are arranged orthogonally and symmetrically along the circumferential direction on the horizontal plane, and are installed in pairs on the upper surface of the self-aligning lower plate (1) along the X and Y orthogonal directions; the four sets of piezoelectric ceramic stacked micro-displacement self-aligning mechanisms (3) are respectively fixed on the moving platform (25) of the corresponding ball screw coarse adjustment mechanism (2), forming four sets of series coarse and fine composite self-aligning units. The piezoelectric ceramic stacked micro-displacement self-aligning mechanism (3) is equipped with a self-aligning top block (36) to perform self-aligning operation on the mandrel; in the coarse adjustment stage, the ball screw coarse adjustment mechanism (2) drives the piezoelectric ceramic stacked micro-displacement self-aligning mechanism (3) to move radially along the mandrel as a whole; in the fine adjustment stage, the piezoelectric ceramic stacked micro-displacement self-aligning mechanism (3) performs radial compensation on the mandrel.

2. The four-point orthogonal roughing and finishing composite mandrel precision self-aligning device according to claim 1, characterized in that: The ball screw coarse adjustment mechanism (2) includes a ball screw (22), a linear guide (23), a grating ruler (24), a moving platform (25), and a servo motor (28). The servo motor (28) is connected to the ball screw (22) via a coupling (27). The two ends of the ball screw (22) are supported by a fixed end support (26) and a supporting end support (21), respectively. The linear guide (23) is arranged on both sides of the ball screw (22). The moving platform (25) is connected to the screw nut of the ball screw (22) and moves along the linear guide (23). The grating ruler (24) is used to detect the actual displacement of the moving platform (25) and provide feedback.

3. The four-point orthogonal roughing and finishing composite mandrel precision self-aligning device according to claim 1, characterized in that: The piezoelectric ceramic stack micro-displacement self-aligning mechanism (3) includes a guide mechanism (31), a reset spring (32), a support block (34), a piezoelectric ceramic stack (35), a self-aligning top block (36), a trapezoidal thread preload screw (37), and a locking nut (38). The guide mechanism (31) is fixed on the moving platform (25) and forms a linear guide and lateral constraint on the support block (34). The rear end of the piezoelectric ceramic stack (35) is subjected to axial preload through the trapezoidal thread preload screw (37) and locked by the locking nut (38). The front end of the piezoelectric ceramic stack (35) is rigidly connected to the self-aligning top block (36) through the support block (34). The reset spring (32) is supported between the guide mechanism (31) and the support block (34) to drive its return reset.

4. The precision self-aligning device for a four-point orthogonal coarse-fine composite mandrel according to claim 3, characterized in that: The piezoelectric ceramic stack micro-displacement self-aligning mechanism (3) has two piezoelectric ceramic stacks (35) arranged horizontally side by side. The two piezoelectric ceramic stacks (35) correspond to two support blocks (34) respectively. The two support blocks (34) are connected as one unit by a T-shaped connector (33) in the middle. The self-aligning top block (36) is rigidly connected to the T-shaped connector (33).

5. A closed-loop self-aligning method for a four-point orthogonal roughing and finishing composite mandrel precision self-aligning device, characterized in that: According to claim 1, the closed-loop self-aligning method of the four-point orthogonal coarse-fine composite mandrel precision self-aligning device includes the following steps: S1. Establish the self-aligning coordinate system: The theoretical center of the platform is the geometric center of the self-aligning upper plate (4). Establish a plane rectangular coordinate system XOY, and arrange four sets of self-aligning units in the positive X, negative X, positive Y, and negative Y directions respectively; S2. Core Center Recognition: Acquire images of the core cross-section and extract edge sampling points to fit the actual core center. ; S3. Calculation of eccentricity and eccentricity angle: Based on the actual center coordinates of the mandrel, calculate the eccentricity and eccentricity angle of the mandrel relative to the theoretical center of the platform. S4. Determine the termination condition for centering: If the eccentricity meets the allowable error requirement, the centering ends; otherwise, proceed to the next step. S5. Four-point self-aligning compensation decomposition: Calculate the target compensation amount in the X and Y directions, and use a strategy of single-sided pushing as the main force and opposing units cooperating with retreat to distribute the compensation amount to the self-aligning units in the four directions. S6. Coarse-fine adjustment displacement allocation: Based on the relationship between the total compensation displacement in one direction and the maximum effective fine adjustment stroke of the piezoelectric ceramic, allocate the coarse adjustment displacement of the ball screw and the fine adjustment displacement of the piezoelectric ceramic and perform the adjustment. S7. Iterative Loop: After completing one adjustment, return to step S2 and repeat the detection and compensation process until the centering termination condition is met or the maximum number of iterations is reached.

6. The closed-loop self-aligning method of the four-point orthogonal roughing and finishing composite mandrel precision self-aligning device according to claim 5, characterized in that: In step S2, the algebraic least squares circle fitting method is used to obtain the center and radius of the mandrel cross section. A least squares objective function is constructed for all edge sampling points to solve for the optimal parameters of the fitted circle, thereby obtaining the actual center coordinates and fitted radius of the mandrel.

7. The closed-loop self-aligning method of the four-point orthogonal roughing and finishing composite mandrel precision self-aligning device according to claim 5, characterized in that: In step S4, the centering termination condition only needs to meet any one of the following: Record No. The eccentricity corresponding to this detection is , For the first The actual center of the mandrel obtained from the second test is used to set the allowable eccentricity error. The termination condition for mind adjustment is expressed as follows: ; Set the allowable error in the X direction. Y-direction allowable error The termination condition for mind adjustment is expressed as follows: and ; Set the maximum number of iterations. If the number of iterations reaches If the accuracy requirements are still not met, the centering process will stop and an error message will be output.

8. The closed-loop self-aligning method of the four-point orthogonal roughing and finishing composite mandrel precision self-aligning device according to claim 5, characterized in that: In step S5, the target compensation amounts in the X and Y directions are opposite to those in the eccentricity direction, and are expressed as follows: The compensation amounts in the four directions are distributed using a maximum value function: In the formula, , , , These are the compensation amounts for the four-directional centering units. When the compensation amount is positive, the corresponding centering unit performs active pushing; when the compensation amount is zero, the corresponding centering unit maintains yielding.

9. The closed-loop self-aligning method of the four-point orthogonal roughing and finishing composite mandrel precision self-aligning device according to claim 5, characterized in that: In step S6, the first Total compensation displacement required for each directional self-aligning unit Decomposed into coarse adjustment displacement of ball screw fine-tuning displacement with piezoelectric ceramics : The coarse adjustment displacement of the ball screw is determined by the screw lead and the rotation angle: The fine-tuning displacement of piezoelectric ceramics can be approximated as a linear function of the driving voltage: In the formula, For the ball screw lead, For the first The rotation angle of the ball screw in each direction For the displacement sensitivity of piezoelectric ceramic stacks, For the first The driving voltage of the piezoelectric ceramic stack in each direction; The maximum effective fine-tuning stroke of the piezoelectric ceramic is set to... The displacement allocation logic is as follows: when At that time, the ball screw coarse adjustment mechanism (2) first performs coarse adjustment to adjust the remaining compensation amount. Entering the effective stroke range of the piezoelectric ceramic; when At that time, fine adjustment is performed directly by the piezoelectric ceramic stack micro-displacement centering mechanism (3).

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