Bidirectional active follow-up loading device and control method thereof

Abstract

The invention discloses a bidirectional active follow-up loading device and a control method thereof.According to the device, through the synergistic effect of a loading mechanism, a spherical hinge and a lower-layer follow-up mechanism, rapid and accurate compensation can be achieved according to the deviation angle, active detection and compensation of inclination angles in two directions are achieved, and the loading efficiency is improved. The loading force is always kept consistent with the normal direction of the loading force bearing surface; according to the method, the compensation displacement of the mobile platform is calculated through the inclination angle of the cross bearing, and the double-layer follow-up mechanism is driven to compensate the offset distance between the X axis and the Y axis, so that the loading direction is always kept consistent with the normal direction of the loading force bearing surface, and dynamic compensation in multiple directions is realized, thereby ensuring that the direction of the loading force is always kept accurate; the compensation amount is fed back and adjusted in real time, the influence of nonlinear change of the effective length of the loading hydraulic cylinder on the loading force is reduced, the compensation process in the control method is smooth, and the response speed and the compensation precision are improved.

Description

Technical Field

[0001] The present invention relates to the field of industrial testing, and particularly to a bidirectional active follow-up loading device and its control method. Background Art

[0002] In modern industrial production, loading devices play an important role in various working environments, especially in situations where precise control of force is required. These devices are widely used in material testing, mechanical engineering, and other fields to ensure the stability and accuracy of the loading force. However, existing loading devices have some significant problems in practical applications.

[0003] Existing loading devices usually adopt a fixed loading direction. When an object above is subjected to force, it is prone to tilting. As the loading load increases, the angle θ between the normal of the loading force bearing surface and the initial loading direction of the actuator will continuously increase, which will cause an angular deviation between the loading force output by the actuator and the expected loading force, resulting in a mismatch between the actual loading condition and the expected loading condition. This deviation not only affects the loading accuracy but may also lead to equipment damage and operation failure. In addition, existing systems lack an effective angle compensation mechanism and cannot dynamically adjust the loading direction when the load changes, further exacerbating this problem.

[0004] The material biaxial compression loading device with the publication number CN108896394B realizes uniaxial and biaxial compression loading through a unique composition structure of a first power device and a second power device, and can switch between displacement control and force control. Structurally, the device adopts a multi-layer board-axis combination form where the loading axes are coplanar while the mounting plates are not coplanar, and through a combination of active and follow-up movement methods, it ensures that the loading axes do not interfere with each other during the biaxial compression movement process. However, in this technical solution, the coplanar design of the loading axes and the multi-layer board-axis combination form may lead to a relatively high complexity of the device, increasing the manufacturing and maintenance costs. In addition, although the combination of active and follow-up movement methods can avoid the interference problem of the loading axes, there is still room for improvement in terms of accuracy and response speed.

[0005] The linear loading and measuring device of a transfer mechanism test bench with the publication number CN104634602B realizes linear loading and data measurement by setting multiple fixed rings and linear motors on the loading axis support, and can be adjusted in multiple degrees of freedom directions. The device ensures the stability and accuracy of the loading axis in different directions through a combination of a follow-up two-dimensional displacement table and an active two-dimensional displacement table. However, in this technical solution, the multiple fixed rings on the loading axis support and the complex displacement table structure will increase the overall weight of the device, affecting stability and accuracy. In addition, although the multi-degree-of-freedom adjustment improves the adaptability of the device, there is still room for improvement in terms of control accuracy and stability.

[0006] Most inventions can usually only compensate in a single direction and cannot solve the problem of multi-directional inclination. Most devices capable of two-way compensation require complex propulsion and moving devices, and cannot perform precise compensation according to the offset angle, and the compensation process is not smooth enough. Summary of the Invention

[0007] Object of the Invention: The present invention aims to provide a two-way active follow-up loading device that can achieve multi-directional dynamic compensation. Another object of the present invention is to provide a control method for a two-way active follow-up loading device that can quickly and accurately compensate according to the offset angle and has a smooth compensation process.

[0008] Technical Solution: The two-way active follow-up loading device described in the present invention includes a loading mechanism, a ball joint, and a double-layer follow-up mechanism. The loading mechanism is installed on the double-layer follow-up mechanism through the ball joint. The loading mechanism includes a loading hydraulic cylinder, a cross-bearing mounting bracket, and a loading connecting plate. The loading hydraulic cylinder is provided with a displacement sensor. The cross-bearing mounting bracket is fixed on the piston of the loading hydraulic cylinder. The cross-bearing mounting bracket is connected to the loading connecting plate through a cross-bearing; magnetic grating sensors for rotating around the X-axis and the Y-axis are provided at the steering shaft of the cross-bearing; when loading, the cross-bearing deflects, and displacements occur in both the X-axis and Y-axis loading directions. By moving the double-layer follow-up mechanism, the displacement is compensated to make the loading direction consistent with the normal direction of the loading force bearing surface.

[0009] Further, the upper moving mechanism of the double-layer follow-up mechanism is installed on the lower base through the lower roller mechanism. The lower base is provided with an X-direction propulsion hydraulic cylinder, and the X-direction propulsion hydraulic cylinder is provided with an X-direction displacement sensor; the moving platform of the upper moving mechanism is installed on the upper base through the upper roller mechanism. The upper base is provided with a Y-direction propulsion hydraulic cylinder, and the Y-direction propulsion hydraulic cylinder is provided with a Y-direction displacement sensor; the loading mechanism is fixed on the moving platform through the ball joint.

[0010] Further, the lower roller mechanism includes an X-direction roller, an X-direction grid tray limit plate, and an X-direction grid tray; the upper roller mechanism includes a Y-direction roller, a Y-direction grid tray limit plate, and a Y-direction grid tray.

[0011] Further, an X-direction rolling slider is provided on the side of the upper base, and a Y-direction rolling slider is provided on the side of the moving platform.

[0012] The control method of the two-way active follow-up loading device described in the present invention is realized through the above two-way active follow-up loading device. The method includes the following steps:

[0013] (1) Move the two-way active follow-up loading device to the lower part of the force application point of the workpiece to be detected. The piston rod of the loading hydraulic cylinder extends along the Z-axis. The loading connecting plate is attached to the force application surface of the workpiece and the load reaches 3%-5% of the target load. The force loading speed is FV The target load is F and the initial loading force is F0. Through measurement by a magnetic grating sensor, the initial angle between the loading connecting plate and the X-axis is obtained as α0, and the initial angle between the loading connecting plate and the Y-axis is obtained as β0;

[0014] (2) The loading hydraulic cylinder continues to apply a load along the Z-axis direction. The angle between the loading connecting plate and the coordinate system plane increases. The current angles α1 between the loading connecting plate and the X-axis and β1 between the loading connecting plate and the Y-axis are obtained through the magnetic grating sensor, and the deflection angles Δα = α1 - α0 and Δβ = β1 - β0 are obtained;

[0015] (3) The displacement L1 of the piston rod of the loading hydraulic cylinder is obtained through a displacement sensor, and the distance L3 from the rotation center of the cross shaft to the center of the bottom fixed ball joint is obtained, which is the effective length of the loading hydraulic cylinder;

[0016] (4) Calculate the combined rotation matrix after the rotation of the loading connecting plate, determine the coordinate position of the center of the ball joint after rotation, obtain the reverse compensation displacement S, perform geometric correction, and calculate the compensation displacement of the moving platform;

[0017] (5) Judge the compensation displacement of the moving platform. If the compensation displacement distance exceeds the stroke of the X / Y-direction propulsion hydraulic cylinder, an alarm is issued and the loading hydraulic cylinder stops working. Otherwise, the X / Y-direction propulsion hydraulic cylinder starts working for angle compensation;

[0018] (6) Before the target load is reached, the continuous cyclic compensation mode is maintained until all the loads required for the workpiece are loaded. The loading hydraulic cylinder is depressurized until the loading force is 1% of the target load, and the angle compensation ends.

[0019] Further, step (4) is specifically as follows:

[0020] (41) Construct a three-dimensional space coordinate system model based on spatial pose decoupling;

[0021] (42) Construct rotation matrices about the X-axis and the Y-axis, and calculate the combined rotation matrix after the rotation of the loading connecting plate;

[0022] (43) Calculate the coordinate position of the center of the ball joint after rotation, and obtain the reverse compensation displacement S;

[0023] (44) According to the current system stiffness, predict the change in the loading force of the loading hydraulic cylinder during the compensation process, and correct the force loading speed of the loading hydraulic cylinder and the compensation distance of the double-layer moving platform.

[0024] Further, a three-dimensional space coordinate system model is constructed based on spatial pose decoupling, with the intersection point of the cross-axis as the origin O, one rotation center of the cross rotation axis as the X-axis, another rotation center perpendicular to and coplanar with it as the Y-axis, and the central axis of the loading hydraulic cylinder as the Z-axis; the initial position of the spherical hinge center is P0 = [0 0 L3] T , when the loading connecting plate rotates by Δα around the X-axis and by Δβ around the Y-axis, a mapping relationship is established through homogeneous coordinate transformation, and the new coordinate system is O'; the coordinates of point P in O' are (0, 0, L3), and the coordinates of point P are converted from O' to O, applying the inverse matrix of the homogeneous transformation matrix, that is, the inverse matrix of the transformation matrix from O to O'.

[0025] Further, step (42) is specifically as follows:

[0026] Construct a rotation matrix R for rotating by Δα around the X-axis x which is

[0027]

[0028] Construct a rotation matrix R for rotating by Δβ around the Y-axis y which is

[0029]

[0030] The combined rotation matrix R after the loading connecting plate rotates is

[0031]

[0032] Further, step (43) is specifically as follows:

[0033] The initial coordinates of the center of the spherical hinge before the loading connecting plate rotates are P0 = [0 0 L3] T , and the coordinates after rotation are

[0034] P′ = R T * [0 0 L3] = [x′ y′ z′]

[0035] Convert the rotated coordinates back to the original coordinate system to obtain the reverse compensation displacement S,

[0036]

[0037] where S1 is the compensation displacement in the X direction and S2 is the compensation displacement in the Y direction.

[0038] Further, step (44) is specifically as follows:

[0039] When the bottom hydraulic cylinders perform compensatory displacements S1 and S2, the effective length L3 of the loading hydraulic cylinder changes by ΔL. The initial effective length of the loading hydraulic cylinder in the Z-axis direction is L3 = L1 + L2. The bottom platform moves S1 (in the X direction) and S2 (in the Y direction) during the compensation process. The new effective length of the loading hydraulic cylinder is:

[0040]

[0041] The change in length is ΔL = L N - L3. Since the compensatory displacements S1 and S2 are less than the effective length L3 of the loading hydraulic cylinder, S1 2 + S2 2 <L3 2 That is Therefore, the new effective length of the loading hydraulic cylinder is:

[0042]

[0043] Furthermore, the change in the effective length of the loading hydraulic cylinder is The equivalent stiffness of the current system is K s The calculation formula is:

[0044]

[0045] Where, F a is the current loading force, F0 is the initial loading force, L a is the current effective length of the loading hydraulic cylinder, and L3 is the initial effective length of the loading hydraulic cylinder.

[0046] To predict the change in the loading force caused by the change in the effective length of the loading hydraulic cylinder, the calculation formula is:

[0047]

[0048] In the formula, ΔL is the change in the effective length of the loading hydraulic cylinder, and ΔF is the change in the loading force;

[0049] Then the force deviation caused by the change in the effective length of the loading hydraulic cylinder is ΔF = K s *ΔL.

[0050] If ΔF ≤ K a F, normal compensation is performed;

[0051] If K a F < ΔF ≤ K b F, the force loading speed of the loading hydraulic cylinder is corrected to λ1F V , the displacement distance of the moving platform in the X direction is corrected to λ2S1, and the displacement distance in the Y direction is corrected to λ2S2;

[0052] If Kb If F < ΔF, the system will sound an alarm, the hydraulic system will stop working, and implement safety self-locking protection. Generally, the empirical coefficient K a 0.01~0.05, K b is 0.05, λ1 is 0.1~0.2, and λ2 is 0.05~0.1.

[0053] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: 1. The device of the present invention realizes active detection and compensation of the tilt angles in two directions through the synergistic effect of the loading mechanism, the ball joint and the lower follower mechanism, ensuring that the loading force is always consistent with the normal direction of the loading force bearing surface; 2. The device of the present invention adopts a grid-fixed roller design to replace the traditional ball structure, thereby enhancing the directional control capability. The grid-fixed structure limits the movement direction of the roller through mechanical constraints, thereby avoiding the occurrence of slippage. Since the rollers are distributed under the moving platform, the compensation process is smoother, further improving the stability of the loading direction; 3. The method of the present invention calculates the compensation displacement of the moving platform through the inclination angle of the cross bearing, driving The dynamic double-layer follow-up mechanism compensates for the offset distance between the X-axis and the Y-axis, thereby ensuring that the loading direction is always consistent with the normal of the loading force bearing surface, realizing dynamic compensation in multiple directions, thereby ensuring that the direction of the loading force is always accurate; 4. The method of the present invention targets the influence of the nonlinear change of the displacement of the loading hydraulic cylinder on the follow-up compensation amount and its accuracy, and reduces the influence of the nonlinear change of the effective length of the loading hydraulic cylinder on the loading force. Compared with the traditional compensation method, it has better accuracy, adaptability and stability in the application of large-angle offset and dynamic loading, and can handle more complex working conditions; 5. The device of the present invention is simple, can quickly and accurately compensate according to the offset angle, and the compensation process in the control method is smooth, which improves the response speed and compensation accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] Figure 1 It is a structural schematic diagram of the device of the present invention;

[0055] Figure 2 is a structural schematic diagram of the loading mechanism;

[0056] Figure 3 It is a structural diagram of the cross bearing rotating in the X direction;

[0057] Figure 4 It is a schematic diagram of the structure of the cross bearing rotating in the Y direction;

[0058] Figure 5 It is the structural schematic diagram of the ball joint;

[0059] Figure 6 It is a structural schematic diagram of a double-layer follower mechanism;

[0060] Figure 7Schematic diagram of the upper moving mechanism;

[0061] Figure 8 Schematic diagram of the upper roller mechanism;

[0062] Figure 9 Schematic diagram of the lower roller mechanism;

[0063] Figure 10 Explosion diagram of the double-layer follower mechanism;

[0064] Figure 11 Schematic diagram of the coordinate system and deflection angle of the loading hydraulic cylinder;

[0065] Figure 12 Schematic diagram of the angle compensation of the bidirectional follower platform;

[0066] Figure 13 Flow chart of the method of the present invention. Detailed implementation manners

[0067] The present invention will be further described below with reference to the accompanying drawings.

[0068] The bidirectional active follower loading device of the present invention includes a loading mechanism 1, a ball hinge 2, and a double-layer follower mechanism 3.

[0069] The described loading mechanism includes: a loading hydraulic cylinder 11, a locking nut 12, a cross-bearing mounting bracket 13, an end cover 14, a cross-bearing 15, a loading connecting plate 16, an X-axis magnetic grating sensor 17, an X-axis magnetic grating ring 18, a Y-axis magnetic grating sensor 19, and a Y-axis magnetic grating ring 110. The loading hydraulic cylinder 11 is cylindrical and is installed above the ball hinge 2 by screws at the bottom. The top of the piston has a thread and is connected to the cross-bearing mounting bracket 13. The locking nut 12 is ring-shaped and is installed on the piston of the loading hydraulic cylinder 11 for fixation. The cross-bearing mounting bracket 13 is rectangular, with convex platforms on both sides, threaded holes are opened, and threaded holes are at the bottom, and are connected to the thread on the piston of the loading hydraulic cylinder 11. Through holes are opened on both sides of the cross-bearing mounting bracket for installing the end cover 14. There are four end covers 14, which are cylindrical, the protruding convex platforms cooperate with the cross-bearing 15, and threaded holes are opened at the ends, and are connected to the cross-bearing mounting bracket 13 by screws. The cross-bearing 15 is cross-shaped, with end covers 14 installed around it, two sides are installed on the bearing mounting bracket 13, and the other two sides are installed on the loading connecting plate 16. The loading connecting plate 16 is rectangular, with convex platforms on both sides, is installed above the cross-bearing 15, and is connected to the other two ends of the cross-bearing 15 through the end cover 14.

[0070] The described magnetic grating ring 17 around the X-axis is in a circular ring shape and is installed in the X direction of the cross bearing 15. The described magnetic grating sensor 18 around the X-axis is rectangular, has two through holes, and is installed on the loading connection plate 16.

[0071] The described magnetic grating ring 110 around the Y-axis is in a circular ring shape and is installed in the Y direction of the cross bearing 15. The described magnetic grating sensor 19 around the Y-axis is rectangular, has two through holes, and is installed on the cross bearing mounting bracket 13.

[0072] The described ball hinge 2 includes a support 21, a sphere 22, and a limit cover plate 23. The upper part of the support 21 is cylindrical and the lower part is rectangular. A groove is opened in the upper part of the support 21 for installing the sphere 22. Threaded holes are opened around for installing the limit cover plate 23. A through hole is opened in the lower part for installing the ball hinge 2 on the moving platform 311. The lower part of the sphere 22 is spherical and the upper part is a cylindrical disc. The lower sphere 22 is fitted with the groove on the support 21 and is installed on the support 21. A through hole is opened in the upper cylindrical disc and is connected to the loading hydraulic cylinder 11. The limit cover plate 23 is semi-circular and has an arc convex platform, with threaded holes, and is installed on the support 21 for restricting the ball hinge from exceeding the movement range.

[0073] The described double-layer follow-up mechanism includes an upper-layer moving mechanism 31, a large seal cover 32, an X-direction propulsion hydraulic cylinder 33, an X-direction displacement sensor 34, a lower base 35, an X-direction rolling slider 36, and a lower-layer roller mechanism 37. The large seal cover 32 is in a square frame shape and is installed above the lower base 35 for dust prevention. For the X-direction propulsion hydraulic cylinder 33, there are threaded holes on the cylinder flange, which are connected to the threaded holes on the lower base 35 with screws, and there is a thread on the piston rod for connecting to the upper-layer moving mechanism 31. The X-direction displacement sensor 34 is installed inside the X-direction propulsion hydraulic cylinder 33 for detecting the X-direction propulsion distance. The lower base 35 is rectangular, has a through hole for placing the piston of the Y-direction propulsion hydraulic cylinder 314, and has threaded holes for installing the X-direction propulsion hydraulic cylinder 34. The lower base has a square through hole to reserve a moving space for the upper-layer moving mechanism 31. The X-direction rolling slider 36 is rectangular and is respectively installed on both sides of the moving platform for guiding the upper-layer moving mechanism 31 to move along the X propulsion direction.

[0074] The upper moving mechanism 31 described above includes: a moving platform 311, Y-direction rolling sliders 312, an upper base 313, a Y-direction propulsion hydraulic cylinder 314, a Y-direction displacement sensor 315, an upper roller mechanism 316, and a small sealing cover 317. The moving platform 311 is in the shape of a cuboid, with grooves and threaded holes on the upper surface for installing the ball hinge 2. Four grooves are opened on both sides of the moving platform 311 for installing the Y-direction rolling sliders 312, and a threaded hole is opened on the front for connecting with the Y-direction propulsion hydraulic cylinder 33. There are four Y-direction rolling sliders 312, which are rectangular and are respectively installed in the grooves on both sides of the moving platform 311 by screws for guiding the moving platform 311 to move along the Y propulsion direction. The upper base 313 is rectangular, with threaded holes for connecting with the piston rod of the X-direction propulsion hydraulic cylinder 33. Grooves are opened on both sides for installing the X-direction rolling sliders 36, and a threaded hole is opened on the side for connecting with the flange on the Y-direction propulsion hydraulic cylinder 314. The Y-direction propulsion hydraulic cylinder 314 is in the shape of a cuboid, with a thread on the piston rod for connecting with the moving platform 311, and threaded holes are opened on the flange of the cylinder body and are connected to the upper base 313 by screws. The Y-direction displacement sensor 315 is installed inside the Y-direction propulsion hydraulic cylinder 314 for detecting the Y-direction propulsion distance. The small sealing cover 317 is in the shape of a square frame and is installed above the upper base for dust prevention.

[0075] The upper roller mechanism 316 described above includes Y-direction rollers 3161, Y-direction grille tray limit plates 3162, and Y-direction grille trays 3163. The Y-direction grille tray 3163 is rectangular, with square grooves opened on the upper and lower surfaces, making the middle thickness of the grille tray one-fourth of the roller diameter. A plurality of square through-holes are opened, and the through-holes are linearly arranged along the Y direction. The length and width of the through-holes are 1 mm greater than the length and width of the Y-direction rollers 3161. There are two Y-direction grille tray limit plates 3162, and their sizes are the same as the sizes of the grooves of the Y-direction grille tray 3163. A plurality of square through-holes are opened, and the through-holes are linearly arranged along the Y direction. The length of the through-holes is 1 mm greater than the length of the Y-direction rollers 3161, and the width of the through-holes is 1 mm less than the width of the Y-direction rollers 3161 for restricting the rollers. They are connected to the upper and lower surfaces of the Y-direction grille tray 3163 by screws. The Y-direction rollers 3161 are cylindrical, and there are a plurality of them installed in the square through-holes for assisting the platform to move.

[0076] The lower roller mechanism 37 described above includes X-direction rollers 371, X-direction grille tray limit plates 372, and X-direction grille trays 373. The X-direction grille tray 373 is rectangular, with square grooves on its lower two sides, such that the middle thickness of the grille tray is one-fourth of the roller diameter. It has multiple square through-holes, which are linearly arranged in the X direction. The length and width of the through-holes are 1 mm greater than the length and width of the X-direction rollers 371. There are two X-direction grille tray limit plates, whose sizes are the same as the groove sizes of the X-direction grille tray 373. They have multiple square through-holes, which are linearly arranged in the X direction. The width of the through-holes is 1 mm greater than the width of the X-direction rollers 371, and the length of the through-holes is 1 mm less than the width of the X-direction rollers 371, for restricting the X-direction rollers 371. They are connected to the upper and lower surfaces of the X-direction grille tray 373 with screws. The X-direction rollers 371 are cylindrical, there are multiple of them, and they are installed in the square through-holes for assisting the movement of the platform.

[0077] Through the coordinated action of the loading mechanism, the ball hinge structure, and the double-layer follow-up mechanism, this device realizes the active detection and compensation of the tilting angles in two directions, ensuring that the loading force always remains perpendicular to the normal of the loading force bearing surface. As Figure 11 shown, it is a diagram of the follow-up test platform and its coordinate system definition. Taking one of the rotation centers of the cross rotation shaft as the X-axis, the other rotation center perpendicular and coplanar to it as the Y-axis, and the central axis of the loading hydraulic cylinder as the Z-axis. When the loading hydraulic cylinder applies a load along the Z-axis direction, the loading force bearing surface rotates around the X and Y axes under the action of gravity offset, and deflection angles α and β are generated between the direction of the output force of the loading hydraulic cylinder and the normal of the bearing surface. By real-time detecting the deflection angles of the top cross rotation shaft and the telescopic displacement of the loading hydraulic cylinder, and dynamically adjusting the position of the moving platform according to the deviation of the two angles, when the angle deviation is 0, it can ensure that the direction of the output force of the loading hydraulic cylinder is perpendicular to the bearing surface.

[0078] The control method of the two-way active follow-up loading device described in this invention includes the following steps:

[0079] S1. Move the loading hydraulic cylinder of the multi-point coordinated loading follow-up test control system to below the force application point of the workpiece to be detected. Through speed control, the loading hydraulic cylinder moves along the Z-axis, with 3% - 5% of the target load as the preloading starting point, and the force loading speed is F V , the target load is F, the initial loading force is F0. When the loading connecting plate is in contact with the workpiece force application surface and the load reaches the preloading range, at this time, measure and feedback through the magnetic grating sensor at the cross steering shaft, and obtain the tilting angle information of the loading force bearing surface in real time through the detection system. Record the initial angle between the loading connecting plate and the X-axis as α0, and the initial angle between the loading connecting plate and the Y-axis as β0;

[0080] S2. The loading hydraulic cylinder continues to apply a load along the Z-axis direction. As the load increases, the angle between the loading connecting plate and the coordinate system plane also continuously increases. Through the measurement and feedback of the magnetic grating sensor at the cross steering shaft, the current X-axis angle α1 and Y-axis angle β1 are recorded in real time, and then the deflection angles Δα = α1 - α0 and Δβ = β1 - β0 are obtained.

[0081] S3. The elongation displacement L1 of the loading hydraulic cylinder is measured and feedback in real time through the displacement sensor in the loading hydraulic cylinder, and then the distance L3 from the cross rotation center to the bottom fixed ball joint center is obtained, where L3 = L1 + L2. In the formula, L3 is the fixed structure parameter from the top of the loading hydraulic cylinder to the ball joint rotation center, as Figure 12 shown;

[0082] S4. The above feedback parameters Δα, Δβ, and L are input into the control system, and the actuation compensation in the X and Y directions is adjusted by means of error, as Figure 13 shown, to obtain the adaptive compensation displacement.

[0083] S4.1. Establish a three-dimensional space coordinate system model based on spatial pose decoupling

[0084] Taking the intersection point of the cross shaft as the origin O, one rotation center of the cross steering shaft as the X-axis, the other rotation center perpendicular to and coplanar with it as the Y-axis, and the central axis of the loading hydraulic cylinder as the Z-axis. The initial position of the ball joint center is P0 = [0 0 L3] T . When the loading connecting plate rotates by Δα around the X-axis and by Δβ around the Y-axis, a mapping relationship is established through homogeneous coordinate transformation, and the new coordinate system is O'. The coordinates of point P in O' are still (0, 0, L3). To convert the coordinates of point P from O' to O, the inverse matrix of the homogeneous transformation matrix needs to be applied, that is, the inverse matrix of the transformation matrix from O to O';

[0085] S4.2. Construct the rotation matrices around the X-axis and Y-axis;

[0086] The matrix for rotating by Δα around the X-axis is

[0087]

[0088] The matrix for rotating by Δβ around the Y-axis is

[0089]

[0090] S4.3. The combined rotation matrix is

[0091]

[0092] S4.4. Calculate the position of the ball joint center in the rotated coordinate system;

[0093] The initial coordinates of the spherical hinge center before the loading connection plate rotates are P0 = [0 0 L3] T , and the coordinates after rotation are

[0094] P′ = R T *[0 0 L3] = [x′ y′ z′]

[0095] Convert the rotated coordinates back to the original coordinate system to obtain the reverse compensation displacement S

[0096]

[0097] In the formula, S1 is the compensation displacement in the X direction, and S2 is the compensation displacement in the Y direction;

[0098] When the bottom hydraulic cylinder performs the compensation displacements S1 and S2, in order to make up for the lack of loading force, the effective length of the loading hydraulic cylinder will change. The change amount is ΔL. The initial effective length of the loading hydraulic cylinder along the Z-axis direction is L3 = L1 + L2. The bottom platform moves S1 (in the X direction) and S2 (in the Y direction) during the compensation process. The new effective length of the loading hydraulic cylinder is:

[0099]

[0100] The change amount of the effective length of the loading hydraulic cylinder is ΔL = L N - L3. Because the compensation displacements S1 and S2 are less than the effective length L3 of the loading hydraulic cylinder, so S1 2 + S2 2 <L3 2 , that is Therefore, the new effective length of the loading hydraulic cylinder is:

[0101]

[0102] Furthermore, the change amount of the effective length of the loading hydraulic cylinder is The equivalent stiffness of the current system is K s , and the calculation formula is:

[0103]

[0104] Among them, F a is the current loading force, F0 is the initial loading force, L a is the current effective length of the loading hydraulic cylinder, and L3 is the initial effective length of the hydraulic cylinder.

[0105] Predict the force change caused by the change of the effective length of the loading hydraulic cylinder, and the obtained formula is as follows:

[0106]

[0107] Where, ΔL is the change in the effective length of the loading hydraulic cylinder, and ΔF is the change in the loading force;

[0108] Then the force deviation caused by the change in the effective length of the loading hydraulic cylinder is ΔF = K s *ΔL.

[0109] If ΔF ≤ K a F, normal compensation is performed;

[0110] If K a F < ΔF ≤ K b F, the force loading speed of the loading hydraulic cylinder is corrected to λ1F V , the displacement distance of the moving platform in the X direction is corrected to λ2S1, and the displacement distance in the Y direction is corrected to λ2S2;

[0111] If K b F < ΔF, the system issues an alarm, the hydraulic system stops working, and safety self-locking protection is implemented.

[0112] (The empirical coefficient K a is 0.01 - 0.05, K b is 0.05, λ1 is 0.1 - 0.2, and λ2 is 0.05 - 0.1)

[0113] S5. Judge the obtained compensated displacement. If the required moving distance of the auxiliary platform exceeds the stroke pushed by the pushing hydraulic cylinder, the system issues an alarm, and at the same time, the hydraulic system stops telescoping, and safety self-locking protection is implemented. If it is within the hydraulic pushing stroke, the system responds to the instruction and performs angle compensation;

[0114] S6. Before the target load is reached, the system enters a continuous cyclic compensation mode. Through the magnetic grating sensor and the displacement sensor, continuously obtain the tilt angle of the loading connecting plate and the actuator telescopic amount, update the compensated displacement amount in combination with the real-time parameters, and perform angle cyclic compensation, that is, keep the loading direction always consistent with the normal direction of the bearing surface. The bottom hydraulic cylinder continuously compensates through absolute displacement control until the angle compensation ends when all the required loads of the workpiece are loaded;

[0115] S7. After the target load is reached, the loading hydraulic cylinder is depressurized until the loading force is 1% of the target load. From the start of loading to the end of depressurization, the compensation cycle runs continuously to ensure that the loading direction always tracks the change of the bearing surface normal direction.

Claims

1. A two-way active follow-up loading device, characterized in that It includes a loading mechanism (1), a spherical hinge (2) and a double-layer follow-up mechanism (3). The loading mechanism (1) is installed on the double-layer follow-up mechanism (3) through the spherical hinge (2). The loading mechanism (1) includes a loading hydraulic cylinder (11), a cross-bearing mounting bracket (13) and a loading connecting plate (16). The loading hydraulic cylinder (11) is provided with a displacement sensor. The cross-bearing mounting bracket (13) is fixed on the piston of the loading hydraulic cylinder (11). The cross-bearing mounting bracket (13) is connected to the loading connecting plate (16) through a cross-bearing (15); magnetic grating sensors for rotating around the X-axis and the Y-axis are provided at the steering shaft of the cross-bearing. When loading, the cross-bearing (15) deflects, displacements occur in both the X-axis and Y-axis loading directions. By moving the double-layer follow-up mechanism (3), the displacements are compensated to make the loading direction consistent with the normal direction of the loading force bearing surface.

2. The two-way active follow-up loading device according to claim 1, characterized in that The upper moving mechanism (31) of the double-layer follow-up mechanism (3) is installed on the lower base (35) through the lower roller mechanism (37). The lower base (35) is provided with an X-direction propulsion hydraulic cylinder (33), and the X-direction propulsion hydraulic cylinder (33) is provided with an X-direction displacement sensor (34); the moving platform (311) of the upper moving mechanism (31) is installed on the upper base (313) through the upper roller mechanism (316). The upper base (313) is provided with a Y-direction propulsion hydraulic cylinder (314), and the Y-direction propulsion hydraulic cylinder (314) is provided with a Y-direction displacement sensor (315); the loading mechanism (1) is fixed on the moving platform (311) through the spherical hinge (2).

3. The bidirectional active follow-up loading device according to claim 2, wherein The lower roller mechanism (37) includes an X-direction roller (371), an X-direction grid tray limit plate (372) and an X-direction grid tray (373); the upper roller mechanism (316) includes a Y-direction roller (3161), a Y-direction grid tray limit plate (3162) and a Y-direction grid tray (3163).

4. The bidirectional active follow-up loading device according to claim 3, characterized in that, An X-direction rolling slider (36) is provided on the side of the upper base (313), and a Y-direction rolling slider (312) is provided on the side of the moving platform (311).

5. A control method for a bidirectional active follow-up loading device, which is implemented by the bidirectional active follow-up loading device described in claims 1 to 4, characterized in that, The method includes the following steps: (1) Move the bidirectional active follow-up loading device to the position below the force application point of the workpiece to be detected. Extend the piston rod of the loading hydraulic cylinder along the Z-axis until the loading connecting plate fits the force application surface of the workpiece and the load reaches 3%-5% of the target load, with the force loading speed being F V , the target load being F, and the initial loading force being F0. Measure through the magnetic grating sensor to obtain the initial angle between the loading connecting plate and the X-axis as α0 and the initial angle between the loading connecting plate and the Y-axis as β0; (2) The loading hydraulic cylinder continues to apply a load along the Z-axis direction, the angle between the loading connecting plate and the coordinate plane increases. The current angles α1 between the loading connecting plate and the X-axis and β1 between the loading connecting plate and the Y-axis are obtained through the magnetic grating sensors, and the deflection angles Δα = α1 - α0 and Δβ = β1 - β0 are obtained. (3) The displacement L1 of the piston rod of the loading hydraulic cylinder is obtained through the displacement sensor, and the distance L3 from the rotation center of the cross shaft to the center of the bottom fixed spherical hinge is obtained, which is the effective length of the loading hydraulic cylinder. (4) Calculate the combined rotation matrix after the loading connecting plate rotates, determine the coordinate position of the center of the spherical hinge after rotation, obtain the reverse compensation displacement amount S, perform geometric correction, and calculate the compensation displacement of the moving platform. (5) Judge the compensation displacement of the moving platform. If the compensation displacement distance exceeds the stroke of the X / Y-direction propulsion hydraulic cylinder, an alarm is issued and the loading hydraulic cylinder stops working. Otherwise, the X / Y-direction propulsion hydraulic cylinder starts to work for angle compensation. (6) Before the target load is reached, the continuous cyclic compensation mode is maintained until all the required loads of the workpiece are loaded. The loading hydraulic cylinder is depressurized until the loading force is 1% of the target load, and the angle compensation ends.

6. The control method of the bidirectional active follow-up loading device according to claim 5, characterized in that (4) The specific steps are as follows: (41) Construct a three-dimensional space coordinate system model based on spatial pose decoupling; (42) Construct rotation matrices about the X-axis and Y-axis, and calculate the combined rotation matrix after the loading connecting plate rotates; (43) Calculate the coordinate position of the center of the spherical hinge after rotation to obtain the reverse compensation displacement S; (44) According to the current system stiffness, predict the change in the loading force of the loading hydraulic cylinder during the compensation process, and correct the force loading speed of the loading hydraulic cylinder and the compensation distance of the double-layer moving platform.

7. The control method of the bidirectional active follow-up loading device according to claim 6, characterized in that, Construct a three-dimensional space coordinate system model based on spatial pose decoupling. Take the intersection point of the cross axis as the origin O, one rotation center of the cross rotation axis as the X-axis, and the other rotation center perpendicular to and coplanar with it as the Y-axis. The central axis of the loading hydraulic cylinder is the Z-axis; the initial position of the spherical hinge center is P0 = [0 0 L3] T , when the loading connecting plate rotates by Δα around the X-axis and by Δβ around the Y-axis, establish a mapping relationship through homogeneous coordinate transformation to obtain a new coordinate system O'; the coordinates of point P in O' are (0, 0, L3). To convert the coordinates of point P from O' to O, apply the inverse matrix of the homogeneous transformation matrix, that is, the inverse matrix of the transformation matrix from O to O'.

8. The control method of the bidirectional active follow-up loading device according to claim 7, characterized in that, (42) The specific steps are as follows: Construct the rotation matrix \(R\) that rotates by \(\Delta\alpha\) about the \(X\)-axis x is Construct the rotation matrix R that rotates by Δβ about the Y-axis y be (42) The combined rotation matrix R after the loading connecting plate rotates is 9. The control method of the bidirectional active follow-up loading device according to claim 8, wherein (43) The specific steps are as follows: The initial coordinates of the center of the spherical hinge before the loading connection plate rotates are P0 = [00L3] T , and the coordinates after rotation are P′ = R T *[00L3] = [x′y′z′] (43) Convert the rotated coordinates back to the original coordinate system to obtain the reverse compensation displacement S, (43) where S1 is the compensation displacement in the X direction and S2 is the compensation displacement in the Y direction.

10. The control method of the bidirectional active follow-up loading device according to claim 9, characterized in that, (44) The specific steps are as follows: (44) The change in the effective length ΔL of the loading hydraulic cylinder is The equivalent stiffness of the current system is K s , and the calculation formula is Among them, F a is the current loading force, F0 is the initial loading force, L a is the current effective length of the loading hydraulic cylinder, and L3 is the initial effective length of the loading hydraulic cylinder; (44) Predict the change in the loading force caused by the change in the effective length of the loading hydraulic cylinder. The calculation formula is (44) where ΔL is the change in the effective length of the loading hydraulic cylinder and ΔF is the change in the loading force; (44) Then the force deviation caused by the change in the effective length of the loading hydraulic cylinder is ΔF = K s *ΔL If ΔF ≤ K a F, perform normal compensation; If K a F < ΔF ≤ K b F, then correct the force loading speed of the loading hydraulic cylinder to λ1F V , correct the displacement distance of the moving platform in the X direction to λ2S1, and the displacement distance in the Y direction to λ2S2; K a , K b are empirical coefficients, and λ1, λ2 are correction coefficients; If K b F < ΔF, the system will issue an alarm, the hydraulic system will stop working, and implement safety self-locking protection.

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