Loading bay vehicle docking and automatic leveling system

Abstract

This invention relates to the field of automatic control technology, and more specifically, to a vehicle docking and automatic leveling system for loading positions. The system includes a loading platform, a docking platform, a linear guide rail, a sliding platform, a servo motor, a two-dimensional linear scanning laser sensor on the platform side, four-corner hydraulic cylinder assemblies, a cross-balancing valve assembly, a servo valve, a cylinder pressure sensor, a magnetostrictive displacement sensor, and a controller. The linear guide rail is mounted on the top crossbeam of the loading platform. The sliding platform is mounted on the linear guide rail and driven to reciprocate by the servo motor. The two-dimensional linear scanning laser sensor on the platform side is fixed to the sliding platform, with its laser emission plane perpendicular to the longitudinal axis of the loading platform. The four-corner hydraulic cylinder assemblies are located at the bottom of the docking platform and support it. The cross-balancing valve assembly connects to the rodless chambers of two opposite diagonal hydraulic cylinders. This invention can stably acquire the spatial pose information of the rear opening of the vehicle compartment even when the vehicle's parking posture exhibits lateral offset, pitch, or roll.

Description

Technical Field

[0001] This invention belongs to the field of automatic control technology, specifically relating to a vehicle docking and automatic leveling system for loading positions. Background Technology

[0002] In loading operations involving hazardous materials, bulk materials, and large industrial products, the docking and leveling between the loading platform and the vehicle is a crucial step in ensuring operational safety and efficiency. Current loading operations generally rely on fixed-height platforms, liftable platforms, or simple hydraulic leveling devices. The platform height and the rear position of the vehicle's cargo compartment are adjusted manually or through semi-automatic control to create a relatively continuous transition structure in the loading aisle. However, with increasing loading frequency, diversified vehicle types, and higher safety requirements, traditional loading docking and leveling technologies are gradually revealing problems such as insufficient precision, poor stability, and limited adaptability to complex working conditions.

[0003] In existing technologies, a common approach is to use a single-cylinder or dual-cylinder hydraulic leveling mechanism, which raises and lowers the docking platform via manual operation or simple control logic. This approach is relatively simple in structure, but due to the limited number of hydraulic cylinders, the docking platform is prone to tilting or twisting under uneven load conditions. This is especially true when the vehicle is parked incorrectly, tires are under uneven stress, or the load changes significantly during loading. Maintaining a balanced stress state on the docking platform is difficult, increasing the risk of localized contact, structural impact, or even hydraulic component overload. Furthermore, the displacement feedback from a single hydraulic cylinder is usually insufficient to accurately reflect the overall platform posture, leading to leveling accuracy relying on manual experience or repeated adjustments, resulting in low efficiency. Another existing technology uses multiple hydraulic cylinders arranged in parallel, achieving platform leveling through synchronous control. This approach improves load-bearing capacity and posture adjustment capabilities to some extent, but most synchronous control relies on the electronic synchronization of servo valves, lacking a direct hydraulic-side balancing path between the hydraulic cylinders. When the docking platform is subjected to uneven loads or transient impacts, the pressure in the rodless chambers of each hydraulic cylinder rapidly differentiates, requiring the control system to repeatedly correct via electronic means, easily introducing response lag and oscillation. Meanwhile, due to changes in oil temperature, drift in hydraulic component parameters, or the elasticity of pipelines, the synchronization accuracy of the electronic control system further decreases, making it difficult to guarantee the long-term stability of the platform's posture. Summary of the Invention

[0004] The main objective of this invention is to provide a vehicle docking and automatic leveling system for loading positions. This system not only reduces the reliance on manual intervention and experience-based judgment during loading operations, but also achieves automation and repeatability of docking, leveling, and contact force control under complex working conditions. It improves the safety margin, operational efficiency, and long-term reliability of loading operations for hazardous materials and bulk materials, and has good engineering applicability and promotion prospects.

[0005] To solve the above problems, the technical solution of the present invention is as follows: a vehicle docking and automatic leveling system for loading positions, including a loading platform, a docking platform, a linear guide rail, a sliding platform, a servo motor, a two-dimensional linear scanning laser sensor on the platform side, a four-corner hydraulic cylinder assembly, a cross-balancing valve assembly, a servo valve, a cylinder pressure sensor, a magnetostrictive displacement sensor, and a controller; the linear guide rail is located on the top crossbeam of the loading platform, the sliding platform is located on the linear guide rail and is driven to reciprocate by the servo motor, the two-dimensional linear scanning laser sensor on the platform side is fixed to the sliding platform and the laser emission plane is perpendicular to the longitudinal axis of the loading platform; the four-corner hydraulic cylinder assembly is located at the bottom of the docking platform and supports the docking platform, and the cross-balancing valve... The components are connected to the rodless chambers of the two diagonal hydraulic cylinders respectively; the controller is connected to the servo motor, the platform-side two-dimensional linear laser sensor, the servo valve, the cylinder pressure sensor, and the magnetostrictive displacement sensor. The controller is configured to generate the spatial pose data of the car opening based on the two-dimensional contour data output by the platform-side two-dimensional linear laser sensor and the displacement of the sliding platform. Based on the spatial pose data of the car opening, the controller calculates the target extension amount of the four corner hydraulic cylinders and controls the four corner hydraulic cylinder components to complete the diagonal alternating progressive leveling control process. After the spatial pose data of the car opening indicates that the docking and fitting is completed, the controller enters the contact force holding control stage and runs the inner loop interference observer module in the force control loop to perform interference compensation on the servo valve control current command.

[0006] Furthermore, the controller is configured to trigger the pose measurement process after the vehicle to be loaded enters the loading position and completes the parking brake, drive the servo motor to move the sliding platform from the starting end of the linear guide to the ending end of the linear guide, control the two-dimensional line scan laser sensor on the platform side to continuously collect two-dimensional contour data of the rear area of ​​the carriage at a fixed sampling period, and then perform spatiotemporal registration of the two-dimensional contour data at each sampling time with the corresponding sliding platform displacement to generate a three-dimensional original point cloud of the rear area of ​​the carriage.

[0007] Furthermore, the controller is configured to perform octree voxel partitioning on the original 3D point cloud, dividing the 3D space into cubic cells with equal side lengths, calculating the average coordinates of the points falling into each cubic cell, and using the average coordinates as the representative point of the cell, and constructing a voxel downsampled point cloud from all the representative points.

[0008] Furthermore, the controller is configured to search for all neighboring points within a preset neighborhood radius for each point to be determined in the voxel downsampled point cloud, calculate the mean distance and standard deviation of the distance from the point to be determined to all neighboring points, and mark the point to be determined as an outlier and perform removal processing when the mean distance exceeds a preset multiple of the standard deviation of the distance. The filtered point cloud is formed by the points after the removal processing.

[0009] Furthermore, the controller is configured to perform region growth segmentation in the filtered point cloud: select a seed point, search for adjacent points within a preset growth radius, calculate the local fitting plane normal vector of the seed point and the local fitting plane normal vector of each adjacent point, and when the angle between the local fitting plane normal vector of the adjacent point and the local fitting plane normal vector of the seed point is less than a preset normal vector angle threshold, the adjacent point is assigned to the growth region and updated as a new seed point until the growth region is completed, and the growth region is output as a segmentation patch; the controller further repeats the region growth segmentation on the points in the filtered point cloud that have not yet been assigned to any segmentation patch until all points are assigned; the controller selects the segmentation patch with the largest number of points and whose normal vector points to the loading platform direction from all segmentation patches as the segmentation patch of the rear opening plane of the carriage, and performs principal component analysis on the segmentation patch of the rear opening plane of the carriage, taking the eigenvector corresponding to the smallest eigenvalue of the covariance matrix as the unit normal vector of the rear opening plane of the carriage, taking the mean coordinate of all points in the segmentation patch of the rear opening plane of the carriage as the coordinate of the center point of the rear opening plane of the carriage, and outputting the combination of the unit normal vector and the center point coordinate as the spatial pose data of the carriage opening.

[0010] Furthermore, the four-corner hydraulic cylinder assembly includes a first hydraulic cylinder, a second hydraulic cylinder, a third hydraulic cylinder, and a fourth hydraulic cylinder. The first hydraulic cylinder is installed at the left front corner of the docking platform, the second hydraulic cylinder is installed at the right front corner of the docking platform, the third hydraulic cylinder is installed at the right rear corner of the docking platform, and the fourth hydraulic cylinder is installed at the left rear corner of the docking platform. The first hydraulic cylinder and the third hydraulic cylinder form a first diagonal hydraulic cylinder pair, and the second hydraulic cylinder and the fourth hydraulic cylinder form a second diagonal hydraulic cylinder pair.

[0011] Furthermore, the cross-balancing valve assembly includes a first cross-balancing valve and a second cross-balancing valve. The first cross-balancing valve has its first port connected to the rodless chamber of the first hydraulic cylinder via a first hydraulic line and its second port connected to the rodless chamber of the third hydraulic cylinder via a second hydraulic line. The second cross-balancing valve has its first port connected to the rodless chamber of the second hydraulic cylinder via a third hydraulic line and its second port connected to the rodless chamber of the fourth hydraulic cylinder via a fourth hydraulic line. Both the first and second cross-balancing valves are differential pressure sensing bidirectional relief valves and are configured to open the relief channel when the pressure difference across the valve core exceeds the opening differential pressure threshold corresponding to the valve core spring preload, allowing hydraulic oil on the high-pressure side to flow to the low-pressure side, and to close the relief channel when the pressure difference falls back to within the opening differential pressure threshold.

[0012] Furthermore, the controller is configured to calculate the target extension amounts of the first, second, third, and fourth hydraulic cylinders corresponding to the docking platform reaching the target docking posture based on the spatial pose data of the carriage opening, and execute a diagonal alternating progressive leveling control process: controlling the first diagonal hydraulic cylinders to move synchronously and sending the same valve core displacement command to the servo valves of the first and third hydraulic cylinders to drive the first and third hydraulic cylinders to extend synchronously. During the synchronous extension process, the first cross-balancing valve automatically opens or closes the overflow channel based on the pressure difference in the rodless chamber to adjust the balance state of the pressure in the rodless chamber of the first and third hydraulic cylinders; when the piston rod displacement of the first hydraulic cylinder reaches the target docking posture, the controller is configured to execute a diagonal alternating progressive leveling control process. When the target extension amount is reached and the piston rod displacement of the third hydraulic cylinder reaches the target extension amount, the action of the first diagonal hydraulic cylinder pair stops; the second diagonal hydraulic cylinder pair is controlled to move synchronously and the same valve core displacement command is sent to the servo valves of the second and fourth hydraulic cylinders to drive the second and fourth hydraulic cylinders to extend synchronously. During the synchronous extension process, the second cross equalization valve automatically opens or closes the overflow channel according to the pressure difference of the rodless chamber to adjust the balance state of the pressure in the rodless chamber of the second and fourth hydraulic cylinders; when the piston rod displacement of the second hydraulic cylinder reaches the target extension amount and the piston rod displacement of the fourth hydraulic cylinder reaches the target extension amount, the action of the second diagonal hydraulic cylinder pair stops, thereby completing the diagonal alternating progressive leveling control process.

[0013] Furthermore, the controller is configured to enter the contact force holding control stage after the docking platform and the rear opening of the carriage have completed docking and fitting. The contact force holding control stage adopts a force-position cascade control architecture, which includes a position control loop and a force control loop. The inner loop interference observer module is embedded in the force control loop and generates interference-compensated servo valve control current commands based on the servo valve control current value, cylinder pressure sensor output, and magnetostrictive displacement sensor output, and sends them to the servo valve to maintain the actual contact force applied by the docking platform to the rear opening of the carriage to track the target contact force set value.

[0014] Furthermore, the inner-loop interference observer module is configured to execute the following operating procedure in each control cycle: acquire the servo valve control current value and the current measured piston rod displacement value output by the magnetostrictive displacement sensor at the start of the control cycle; convert the servo valve control current value into the nominal hydraulic oil volume flow rate entering the rodless chamber based on the nominal flow gain coefficient of the hydraulic cylinder; convert the nominal hydraulic oil volume flow rate entering the rodless chamber into the nominal piston rod speed based on the nominal effective piston area; generate the nominal piston rod displacement increment from the nominal piston rod speed based on the control cycle duration; and superimpose the nominal cumulative displacement value at the end of the previous control cycle with the nominal piston rod displacement increment to obtain the nominal predicted displacement value of the control cycle. The displacement residual is obtained by performing a difference between the measured displacement value and the nominal predicted displacement value of the piston rod. A first-order inertial filter is then performed on the displacement residual to obtain a filtered displacement residual. Based on the nominal hydraulic stiffness coefficient of the hydraulic cylinder, the filtered displacement residual is converted into an equivalent lumped disturbance force estimate. The equivalent lumped disturbance force estimate characterizes the disturbance caused by the elastic deformation reaction force of the vehicle tires, the transient force disturbance caused by the impact of the loaded material, and the drift of system parameters caused by the change in hydraulic oil temperature. The equivalent lumped disturbance force estimate is then inversely multiplied and superimposed on the output of the force control loop controller to generate a disturbance-compensated servo valve control current command. This disturbance-compensated servo valve control current command is then sent to the corresponding servo valve of the four-corner hydraulic cylinder assembly.

[0015] The loading platform vehicle docking and automatic leveling system of the present invention has the following beneficial effects: In terms of spatial perception, the present invention uses the coordinated motion of the two-dimensional line scanning laser on the platform side and the sliding platform to obtain continuous contour information of the rear area of ​​the carriage, and obtains stable and consistent carriage opening spatial pose data through spatial reconstruction, so that the docking platform has clear and reliable geometric reference before entering the leveling stage, thereby avoiding the uncertainty caused by traditional single-point distance measurement or manual judgment.

[0016] At the execution level, the present invention adopts a structure of four-corner hydraulic cylinders combined with cross-balancing valves. Through the diagonally coupled hydraulic self-balancing mechanism, the docking platform can still maintain the overall force coordination and consistency under the condition of uneven load or unsatisfactory vehicle posture, effectively suppressing platform torsion and local overload, reducing the risk of structural impact, and reducing excessive reliance on the synchronization accuracy of electronic control.

[0017] At the control level, this invention introduces force-position cascade control after the docking and bonding process is completed, and runs an inner-loop disturbance observer within the force control loop to estimate and compensate for disturbances such as vehicle tire elastic deformation, loading process impact, and hydraulic system parameter changes in real time. This ensures that the contact force can be maintained smoothly around the target state, avoiding safety hazards caused by sudden changes in contact force. Through the synergy of the above technologies, this invention not only improves the accuracy and smoothness of the docking and leveling process, but also significantly enhances the system's adaptability to complex working conditions and dynamic loads, reduces the need for manual intervention, and lowers the reliance on operator experience. It provides a reliable, repeatable, and engineering-feasible technical solution for loading operations in hazardous materials and high-safety-requirement scenarios, demonstrating significant comprehensive technical effects and application value. Attached Figure Description

[0018] Figure 1 A schematic diagram of the overall mechanical structure and hardware layout of the loading bay vehicle docking and automatic leveling system provided in an embodiment of the present invention;

[0019] Figure 2 This is a schematic diagram illustrating the connection principle of the hydraulic drive system and the cross-balancing valve assembly provided in an embodiment of the present invention.

[0020] Figure 3 This is a schematic diagram of the time response curve of the diagonal alternating progressive leveling control process provided in an embodiment of the present invention;

[0021] Figure 4 A schematic diagram of the comparative experimental curves of the system's anti-disturbance performance during the contact force holding control stage provided in an embodiment of the present invention. Detailed Implementation

[0022] This solution provides a vehicle docking and automatic leveling system for loading positions, comprising a loading platform 10, a docking platform 50, a linear guide rail 20, a sliding platform 30, a servo motor 31, a platform-side two-dimensional linear scanning laser sensor 40, a four-corner hydraulic cylinder assembly 60, a cross-balancing valve assembly, a servo valve 80, a cylinder pressure sensor 92, a magnetostrictive displacement sensor 91, and a controller 110. The linear guide rail 20 is mounted on the top crossbeam 11 of the loading platform 10. The sliding platform 30 is mounted on the linear guide rail 20 and is driven to reciprocate by the servo motor 31. The platform-side two-dimensional linear scanning laser sensor 40 is fixed to the sliding platform 30, and its laser emission plane is perpendicular to the longitudinal axis of the loading platform 10. The four-corner hydraulic cylinder assembly 60 is located at the bottom of the docking platform 50 and supports it. The cross-balancing valve assembly... The rodless chambers of the two diagonal hydraulic cylinders are connected respectively. The controller 110 is connected to the servo motor 31, the platform-side two-dimensional line scan laser sensor 40, the servo valve 80, the cylinder pressure sensor 92, and the magnetostrictive displacement sensor 91. The controller 110 is configured to generate spatial pose data of the rear opening 100 of the carriage based on the two-dimensional contour data output by the platform-side two-dimensional line scan laser sensor 40 and the displacement of the sliding platform 30. Based on the spatial pose data of the rear opening 100 of the carriage, the controller calculates the target extension amount of the four corner hydraulic cylinders and controls the four corner hydraulic cylinder assembly 60 to complete the diagonal alternating progressive leveling control process. After the spatial pose data of the rear opening 100 of the carriage indicates that the docking and fitting is completed, the controller enters the contact force holding control stage and runs the inner loop interference observer module in the force control loop to perform interference compensation on the control current command of the servo valve 80.

[0023] When arranging the linear guide rail 20 on the top crossbeam 11 of the loading platform 10, a reference line is usually drawn first, using the longitudinal axis of the loading platform 10 as a reference, and then the linear guide rail 20 is fixed against the reference line in the transverse direction. The top crossbeam 11 is chosen instead of the side beam because the top crossbeam 11 has better structural continuity, less local deformation when the vehicle impacts the platform, and the straightness of the linear guide rail 20 is easier to maintain; at the same time, the top position is less likely to be obstructed by ground oil, water, and debris, and the two-dimensional contour data obtained by the two-dimensional line scan laser sensor 40 on the platform side is more stable. The effective stroke of the linear guide rail 20 can be between 1000 mm and 1600 mm, depending on the transverse coverage width of the rear opening 100 of the car body and the allowable installation space. In order to maintain the dimensional and positional accuracy of the linear guide 20 under long-term vibration environment, a positioning pin is usually installed between the linear guide 20 and the top crossbeam 11 of the loading platform 10. The number of positioning pins can be 2 or 4. The positioning pins are distributed near both ends of the linear guide 20 to suppress the slight movement caused by temperature changes or loose bolts.

[0024] When the sliding stage 30 is mounted on the linear guide rail 20, a preloaded rolling guide structure is preferred. The advantage of preload is that the lateral clearance of the sliding stage 30 is smaller during reciprocating motion, which reduces the attitude jitter of the two-dimensional line scan laser sensor 40 on the platform side. The sliding stage 30 and the servo motor 31 can be driven by a ball screw or a rack and pinion. When using a ball screw, the transmission efficiency is high and the return clearance is easy to control, making it suitable for spatiotemporal registration of two-dimensional contour data with the displacement of the sliding stage 30. When using a rack and pinion, it is more resistant to dust and oil mist, easier to maintain, and suitable for long-term operation in the loading position. The servo motor 31 can be arranged at one end of the linear guide rail 20, with the output shaft connected to the screw or gear through a coupling; or it can be arranged on the side of the top crossbeam 11, with the screw end driven by a synchronous belt. The purpose is to keep the servo motor 31 away from the laser emission area and reduce the disturbance of the motor's heat dissipation airflow to the laser beam path.

[0025] When the two-dimensional line-scanning laser sensor 40 on the platform side is fixed on the sliding stage 30, it is necessary to ensure that the laser emission plane is perpendicular to the longitudinal axis of the loading platform 10. The direct benefit of this arrangement is that the two-dimensional contour data obtained from a single sampling corresponds to a cross-section of the area of ​​the rear opening 100 of the carriage, and the geometric abrupt changes of the carriage frame, sill, and opening edge in the cross-section are more obvious; the sliding stage 30 moves laterally along the linear guide 20, which is equivalent to allowing the cross-section to gradually sweep across the area of ​​the rear opening 100 of the carriage laterally, thereby forming a three-dimensional structure by superimposing continuous two-dimensional contour data. Compared with setting the laser emission plane to be parallel to the longitudinal axis of the loading platform 10, the vertical arrangement is less likely to produce long strip-shaped obstructions on the longitudinal stiffeners of the carriage, and there are fewer gaps after the contour is spliced, which is more conducive to the stability of subsequent spatial pose measurement of the rear opening 100 of the carriage. The sampling frequency of the platform-side 2D line-scan laser sensor 40 can be from 2000 Hz to 10000 Hz, with 5000 Hz being a common setting; the uniform moving speed of the sliding stage 30 can be from 80 mm / s to 200 mm / s, with 120 mm / s being a common setting. With this combination, the displacement of the sliding stage 30 corresponding to two adjacent frames of 2D contour data is on the order of 0.016 mm to 0.1 mm, which is beneficial for maintaining sufficient density of the 3D point cloud in the lateral direction and avoiding contour "jawing" caused by sparse sampling.

[0026] To ensure repeatable registration between the 2D contour data and the displacement of the sliding stage 30, a displacement encoder or linear encoder is typically installed on the sliding stage 30. Installing the displacement encoder on the shaft end of the servo motor 31 offers the advantage of structural simplicity; installing the linear encoder on the side of the linear guide 20 allows for direct measurement of the sliding stage 30's displacement, reducing displacement errors caused by elastic deformation of the transmission chain. The displacement resolution can be 0.01 mm or 0.05 mm. In actual operation, the starting and stopping of the servo motor 31 will cause speed fluctuations, which will be reflected in local density changes in the 3D point cloud. To mitigate this effect, the pose measurement process typically includes an acceleration section at the beginning of the linear guide 20 and a deceleration section at the end, with each section ranging from 80 mm to 150 mm. 2D contour data is only acquired after the sliding stage 30 enters the uniform speed section, ensuring more consistent point spacing in the original 3D point cloud.

[0027] When the four-corner hydraulic cylinder assembly 60 is installed at the bottom of the docking platform 50, the installation reference for the four-corner hydraulic cylinder assembly 60 is generally taken as the geometric center line and two diagonals of the docking platform 50. A common arrangement is to install the four hydraulic cylinders of the four-corner hydraulic cylinder assembly 60 at the left front corner, right front corner, right rear corner, and left rear corner of the docking platform 50 respectively, so that the force path of the docking platform 50 is as symmetrical as possible. The rated stroke of each hydraulic cylinder can be 200 mm to 450 mm, with 300 mm being common; the rated thrust can be 80 kN to 200 kN to meet the load-bearing and impact margins during the loading of hazardous materials. A ball joint or universal joint is usually installed between the four-corner hydraulic cylinder assembly 60 and the docking platform 50. This prevents the hydraulic cylinder piston rod from generating lateral bending moment when the docking platform 50 tilts slightly, and the measured displacement value of the piston rod measured by the magnetostrictive displacement sensor 91 is closer to the true axial displacement.

[0028] The cross-balancing valve assembly connects the rodless chambers of the two diagonally opposite hydraulic cylinders, focusing on using diagonal coupling to suppress the torsional tendency of the docking platform 50 under off-center load. When off-center load occurs on the docking platform 50, it often manifests as a rapid rise in pressure in the rodless chamber of one corner of the hydraulic cylinder, while the pressure in the rodless chamber of the hydraulic cylinder at the opposite corner rises more slowly. If there is no balancing path between the two, the docking platform 50 is prone to diagonal torsional deformation, manifested as one side rising first and the other side lagging behind, which is then forcibly corrected by the controller 110, thus introducing repeated oscillations. After the cross-balancing valve assembly connects the rodless chambers of the diagonally opposite hydraulic cylinders with a differential pressure sensing bidirectional relief valve, when the diagonal pressure difference reaches the valve core opening condition, the hydraulic oil on the high-pressure side will flow back to the low-pressure side, and the diagonal support forces will converge more quickly. The advantage of this is that the pressure difference caused by off-center load is converted into a self-balancing flow within the oil, rather than relying entirely on the controller 110 and the servo valve 80 to "chase" it, reducing the torsional excitation of the docking platform 50 and making the leveling process smoother. The opening differential pressure of the cross equalization valve assembly can be set in the range of 1.5 MPa to 3.0 MPa, with 2.0 MPa being a common setting. Setting it too low will cause even slight disturbances to trigger frequent backflow, slowing down the response. Setting it too high will cause torsional loads to accumulate on the structure for longer, making it easier for sudden changes to occur during release.

[0029] The servo valve 80 and the four-corner hydraulic cylinder assembly 60 typically employ a rodless chamber for oil inlet and a rod chamber for oil return to complete the extension action. To ensure the consistency of the four corner movements of the docking platform 50, servo valves 80 are preferably selected from the same series and have the same rated flow rate, and each servo valve 80 undergoes zero-position offset calibration during assembly. The rated flow rate can range from 40 liters per minute to 80 liters per minute. To avoid flow gain drift caused by oil temperature changes, the hydraulic station can be equipped with an oil temperature control device to maintain the oil temperature within the range of 35 degrees Celsius to 45 degrees Celsius. The oil temperature control device can use an air-cooled radiator or a water-cooled heat exchanger. If the hazardous materials loading area is sensitive to electrical sparks, a water-cooled heat exchanger is more likely to meet the on-site explosion-proof requirements.

[0030] When installing cylinder pressure sensors 92, one is typically placed in each of the rodless and rod chambers of each hydraulic cylinder. The range of cylinder pressure sensors 92 can be from 0 MPa to 25 MPa, and the accuracy can be 0.5% of full scale or higher. The advantage of this arrangement is that it can be used for contact state identification during mating and for differential pressure verification when the cross-balancing valve assembly is in operation. For example, after the diagonal pressure difference rises and exceeds the opening pressure difference, the cross-balancing valve assembly begins to backflow, and the diagonal pressure difference measured by cylinder pressure sensor 92 will fall back to near the opening pressure difference. This provides the controller 110 with actual measurement evidence that "balancing action has occurred," allowing the controller 110 to be more conservative when issuing commands to the servo valve 80, avoiding repeated pulling. If on-site cost or wiring is limited, cylinder pressure sensors 92 can also be placed only in the rodless chamber, with the rod chamber pressure approximated by the hydraulic station return oil pressure. This method is simpler, but the sensitivity to rapid impacts will decrease.

[0031] refer to Figure 2 The hydraulic system comprises four main actuating hydraulic cylinders: a first hydraulic cylinder 61, a second hydraulic cylinder 62, a third hydraulic cylinder 63, and a fourth hydraulic cylinder 64. Spatially, these correspond to the left front, right front, right rear, and left rear support points of the docking platform 50, respectively. In the hydraulic circuit design, these four hydraulic cylinders are divided into two diagonal pairs: the first hydraulic cylinder 61 and the third hydraulic cylinder 63, located diagonally opposite it, form the first diagonal pair; the second hydraulic cylinder 62 and the fourth hydraulic cylinder 64, located diagonally opposite it, form the second diagonal pair. Each hydraulic cylinder is controlled by an independent high-response servo valve 80. The servo valve 80 is typically an electro-hydraulic servo valve with linear flow characteristics or a high-frequency response proportional valve. Its inlet is connected to a constant pressure oil source, and its working ports are connected to the rodless and rod chambers of the corresponding hydraulic cylinder, respectively. The controller 110 sends independent control current commands to the four servo valves 80. It can precisely adjust the flow rate of hydraulic oil entering each hydraulic cylinder. This allows for the control of the extension speed and position of the piston rods in each hydraulic cylinder. To achieve high-precision closed-loop control, each hydraulic cylinder is equipped with a magnetostrictive displacement sensor 91, either internally or externally, for real-time measurement of the absolute extension amount of the piston rod. The measurement accuracy can reach the micrometer level. Simultaneously, a cylinder pressure sensor 92 is installed on the rodless chamber side (and optionally the rod chamber side) of each hydraulic cylinder to monitor the working pressure inside the hydraulic cylinder in real time. .

[0032] Figure 2The core innovation of the system shown lies in the introduction of a cross-balancing valve assembly to achieve pressure self-balancing between the diagonal hydraulic cylinders. Specifically, the two ports of the first cross-balancing valve 71 are connected via hydraulic lines to the rodless chambers of the first hydraulic cylinder 61 and the third hydraulic cylinder 63, respectively; the two ports of the second cross-balancing valve 72 are connected to the rodless chambers of the second hydraulic cylinder 62 and the fourth hydraulic cylinder 64, respectively. Both the first cross-balancing valve 71 and the second cross-balancing valve 72 are bidirectional pressure differential sensing relief valves. When the docking platform 50 is in an ideal stable state, the load pressure of the diagonal hydraulic cylinders is basically the same, the cross-balancing valves are closed, and each hydraulic cylinder is independently controlled. However, when the docking platform 50 is subjected to an off-center load torque due to uneven settlement of the carriage or initial contact deviation during leveling, a significant pressure difference will occur between the diagonal hydraulic cylinders. Taking the first diagonal group as an example, if the first hydraulic cylinder 61 bears a large downward pressure, causing its rodless chamber pressure to... The pressure increased dramatically, while the load on the diagonally opposite third hydraulic cylinder 63 was relatively small, resulting in... Lower, once the pressure difference between the two is... Exceeding the preset opening threshold of the first cross equalization valve 71 (For example The valve core will open rapidly. At this time, the hydraulic oil on the high-pressure side (the rodless chamber of the first hydraulic cylinder 61) will be diverted to the low-pressure side (the rodless chamber of the third hydraulic cylinder 63) through the first cross equalization valve 71. This physical fluid interaction can instantly reduce the torsional torque transmitted by the rigid structure, forcing the output force of the diagonal hydraulic cylinders to tend to be balanced, thereby eliminating internal stress before the mechanical structure undergoes plastic deformation.

[0033] Controller 110, acting as the system's nerve center, aggregates position feedback signals from magnetostrictive displacement sensor 91 and pressure feedback signals from cylinder pressure sensor 92 via a high-speed bus. In terms of control logic, controller 110 employs a hierarchical control architecture. During the leveling motion phase, controller 110 primarily executes a diagonal synchronous progressive strategy based on position feedback. This involves sending synchronous position increment commands to the servo valves 80 of the first hydraulic cylinder 61 and the third hydraulic cylinder 63, and then alternately sending commands to the second hydraulic cylinder 62 and the fourth hydraulic cylinder 64, utilizing the passive balancing characteristics of the cross-balancing valve assembly to compensate for open-loop synchronization errors. During the force-holding phase after docking, controller 110 switches to a force-position hybrid control mode, using data from cylinder pressure sensor 92 to estimate the actual contact force and combining it with an inner-loop interference observer algorithm to dynamically compensate for the control current of the servo valve 80. Through this hardware-software collaborative approach, controller 110 ensures the stability and safety of the four-corner hydraulic cylinder assembly 60 when driving the high-inertia docking platform 50 to perform complex attitude adjustments, effectively preventing equipment damage or operational accidents caused by "virtual legs" or "single-point overload."

[0034] The magnetostrictive displacement sensor 91 is preferably installed inside the hydraulic cylinder or in an external sleeve coaxial with the piston rod. Compared to a rotary encoder, the magnetostrictive displacement sensor 91 is more resistant to oily environments and directly outputs the measured displacement value of the piston rod, facilitating correlation with the control current value of the servo valve 80. The range of the magnetostrictive displacement sensor 91 is consistent with the stroke of the hydraulic cylinder; for example, a stroke of 300 mm corresponds to a range of 300 mm. The resolution can be from 0.01 mm to 0.1 mm, with 0.05 mm being a common setting. To ensure the displacement consistency between the four corner hydraulic cylinder assemblies 60, a mechanical zero-point alignment is typically performed after installation: the docking platform 50 is lowered to the mechanical support point, and the readings of the four corner magnetostrictive displacement sensors 91 are recorded as the zero-point reference. All subsequent displacements are offset and compensated based on this zero-point reference.

[0035] In the implementation of the connection between the controller 110 and the servo motor 31, the platform-side two-dimensional line-scan laser sensor 40, the servo valve 80, the cylinder pressure sensor 92, and the magnetostrictive displacement sensor 91, the platform-side two-dimensional line-scan laser sensor 40 and the controller 110 can communicate via Ethernet or a serial bus, with the sampled data marked with timestamps. The servo motor 31 receives speed and position commands from the controller 110 and reads the displacement of the sliding platform 30. The servo valve 80 receives current or voltage commands from the controller 110, and the signals from the cylinder pressure sensor 92 and the magnetostrictive displacement sensor 91 are read by the analog acquisition channel of the controller 110. To synchronize the two-dimensional contour data with the displacement of the sliding platform 30, the controller 110 typically uses the same hardware clock source to uniformly mark the sampling time of the platform-side two-dimensional line-scan laser sensor 40 and the displacement sampling time of the sliding platform 30, and pairs them according to the nearest timestamp during data stitching. This reduces the "stretching" or "compression" of the original three-dimensional point cloud caused by communication delay fluctuations, making the three-dimensional geometry of the rear opening 100 area of ​​the carriage closer to the real shape.

[0036] In terms of optional implementation methods, the linear guide rail 20 can be changed from one to two parallel arranged rails, with the sliding platform 30 straddling the two linear guide rails 20 to improve lateral stiffness, which is suitable for loading platforms 10 with large spans of the top crossbeam 11 or strong on-site vibration. The servo motor 31 can also be replaced by a linear motor instead of a rotary servo motor. The linear motor has less speed ripple in the low-speed uniform speed range, and the point spacing of the three-dimensional original point cloud is more uniform. The two-dimensional line scan laser sensor 40 on the platform side can be changed from a single sensor to two arranged side by side. The two laser emission planes keep in the same direction and have a fixed spacing. When the sliding platform 30 moves, it forms a double-strip scan, which makes it easier to fill in contour gaps when encountering local occlusion. The four-corner hydraulic cylinder assembly 60 can also be arranged in a "front and back two rows" arrangement closer to the docking end at the bottom of the docking platform 50, so that the docking end has higher stiffness when docking. At this time, the cross equalization valve assembly is still connected to the rodless chambers of the two diagonal hydraulic cylinders to maintain the diagonal self-balancing characteristics. The cross equalization valve assembly can be integrated on the hydraulic manifold. The first, second, third, and fourth hydraulic lines are connected to the rodless chamber of the hydraulic cylinder with short pipes to reduce the pressure differential response lag caused by hose expansion. Alternatively, the cross equalization valve assembly can be arranged close to the four corner hydraulic cylinder assemblies 60 to shorten the diagonal return path and make the equalization action more timely when eccentric load occurs.

[0037] Reference Figure 1 The loading platform 10 forms the physical base of the entire system. It is typically constructed of reinforced concrete or welded heavy-duty steel, possessing the structural strength to withstand the impact of heavy trucks and frequent loading and unloading operations. Above the loading platform 10, the top beam 11 serves as a crucial mounting carrier, spanning the space above the loading bay. The top beam 11 not only provides robust mechanical support but also, due to its elevated position, effectively avoids dust, oil, and forklift collisions from the ground-level work area, thus providing a relatively clean and stable working environment for precision measuring equipment. The linear guide 20 is rigidly fixed to the lower or side surface of the top beam 11 in the horizontal transverse direction, and its mounting reference line maintains a strictly geometrically perpendicular relationship with the longitudinal center axis of the loading platform 10. The linear guide 20 is typically a high-rigidity, heavy-duty roller linear guide, with its effective stroke length set to cover the width of a standard truck bed, for example… to To accommodate lateral position deviations when different vehicles are parked, the sliding platform 30 is mounted on the linear guide rail 20 via a preloaded slider, enabling it to perform low-friction reciprocating linear motion along the guide rail direction. The servo motor 31 serves as the drive source, connected to the sliding platform 30 via a precision ball screw pair or synchronous toothed belt transmission mechanism, driving the sliding platform 30 at a controllable speed. The servo motor 31 performs lateral scanning motion with precise positioning. To achieve real-time closed-loop control of the sliding stage 30's position, a high-resolution absolute encoder is integrated at the end of the servo motor 31 shaft, or a linear grating ruler is arranged parallel to the linear guide rail 20 to feed back the real-time lateral displacement coordinates of the sliding stage 30 to the system. .

[0038] The platform-side two-dimensional line-scan laser sensor 40 is mounted upside down or side-mounted on a dedicated bracket of the sliding platform 30, with its optical window facing the vehicle's entry direction. The internal laser emission module of the platform-side two-dimensional line-scan laser sensor 40 is precisely calibrated so that its projected fan-shaped laser plane is perpendicular to the extension direction of the linear guide rail 20, i.e., the laser plane is parallel to the longitudinal axis of the loading platform 10. This orthogonal arrangement ensures that when the sliding platform 30 moves the platform-side two-dimensional line-scan laser sensor 40 laterally, the laser beam can scan the three-dimensional contour of the rear opening 100 of the carriage layer by layer, like a slicer. The controller 110 synchronously acquires the displacement data fed back from the servo motor 31 and the cross-sectional contour data output by the platform-side two-dimensional line-scan laser sensor 40, and uses a coordinate transformation algorithm to stitch the two-dimensional cross-sectional data back into a highly dense three-dimensional point cloud model of the rear opening 100 of the carriage. This three-dimensional point cloud model contains the spatial geometric information of key features such as the carriage frame, floor edge, and door locks, serving as the navigation reference for subsequent automatic docking control.

[0039] Below or in the front recessed area of ​​the loading platform 10, a docking platform 50 is arranged for carrying personnel and goods. The docking platform 50 is welded from a box-shaped steel structure and has high torsional rigidity. Four-corner hydraulic cylinder assemblies 60, serving as the power actuators of the docking platform 50, are symmetrically distributed at the four corner points below the docking platform 50. Specifically, the four-corner hydraulic cylinder assembly 60 includes four independently actuating single-rod double-acting hydraulic cylinders. The cylinder bases are fixed to the pit foundation, and the piston rod ends are connected to the bottom bearing points of the docking platform 50 via ball joint bearings or universal joints. This flexible connection method removes the rigid couple constraint between the docking platform 50 and the hydraulic cylinders, enabling the docking platform 50, under the differential drive of the four-corner hydraulic cylinder assembly 60, not only to achieve vertical lifting and lowering but also to adjust its pitch and tilt attitude within a certain angle range. This allows it to adapt to the complex spatial posture of the rear opening 100 of the car body caused by uneven vehicle load distribution or uneven ground. Once the controller 110 calculates the target pose of the rear opening 100 of the carriage, it will coordinate the extension length of the four-corner hydraulic cylinder assembly 60 to drive the front contact surface of the docking platform 50 to precisely dock with the lower edge plane of the rear opening 100 of the carriage, thus establishing a stable loading and unloading channel.

[0040] The connections between the controller 110 and the servo motor 31, the platform-side 2D line-scan laser sensor 40, the servo valve 80, the cylinder pressure sensor 92, and the magnetostrictive displacement sensor 91 are typically built according to the principles of "unified timing, diagnostic link, and closed-loop execution." When the platform-side 2D line-scan laser sensor 40 outputs 2D contour data, the 2D contour data naturally carries sampling time information. However, the displacement of the sliding stage 30 comes from the motion chain driven by the servo motor 31. If pairing is based solely on communication arrival times, mismatches can easily occur during network jitter or load fluctuations in the controller 110, resulting in lateral stretching or compression during 3D reconstruction. To address this, the controller 110 provides a unified clock source at the hardware level. Each frame of 2D contour data from the platform-side 2D line-scan laser sensor 40 is written with a timestamp under the same timing reference when it enters the controller 110, and the displacement of the sliding stage 30 is also written with this timestamp during sampling. In engineering practice, a common approach is for the controller 110 to provide a single periodic trigger signal as a sampling reference. The trigger period can be set to 1 millisecond or 2 milliseconds. The platform-side 2D line-scan laser sensor 40 outputs 2D contour data according to the trigger cycle, and the servo motor 31 provides position feedback by sampling the displacement of the sliding stage 30 according to the same trigger cycle. The advantage of this approach is that the matching of the 2D contour data and the displacement of the sliding stage 30 does not depend on software thread scheduling. The main source of registration error degenerates into the sensor's own delay and a small amount of fixed delay, which can be compensated for by a one-time calibration.

[0041] On the data link, the platform-side two-dimensional linear laser sensor 40 and the controller 110 can communicate via Ethernet. The number of two-dimensional contour data points per frame can be set from 800 to 1600 points, with 1200 points being common. The output frequency can be set from 5000 Hz to 8000 Hz, with 5000 Hz being common. The displacement of the sliding stage 30 can be read from either the encoder of the servo motor 31 or the linear encoder. When using the encoder of the servo motor 31, the controller 110 reads the position of the encoder and calculates the displacement of the sliding stage 30 by combining it with the lead screw. When using the linear encoder, the controller 110 directly reads the displacement of the sliding stage 30 output by the linear encoder. The resolution of the linear encoder can be set to 0.01 mm, and the equivalent resolution after conversion by the encoder of the servo motor 31 can be set to 0.02 mm. The advantage of linear grating rulers is that they isolate factors such as transmission chain elasticity, backlash, and belt elongation from the measurement chain. The displacement of the sliding stage 30 is closer to the actual displacement, and the cumulative drift during the splicing of two-dimensional contour data is smaller. The advantage of servo motor encoders 31 is that the wiring is simple and suitable for cost-sensitive loading positions.

[0042] After the two-dimensional contour data and the displacement of the sliding stage 30 are registered in the controller 110, the controller 110 assigns a spatial position to each frame of two-dimensional contour data according to the displacement of the sliding stage 30, forming a three-dimensional original point cloud of the rear opening 100 area of ​​the carriage. The reason for using the displacement of the sliding stage 30 as the main index for stitching is that the two-dimensional contour data output by the two-dimensional line scan laser sensor 40 on the platform side corresponds to the cross-sectional curve in the fixed scanning plane, and the displacement of the sliding stage 30 provides the displacement coordinates of the scanning plane in the lateral movement. The combination of the two can transform the two-dimensional contour data from a "set of cross-sections" into a "spatial point cloud". When the movement speed of the sliding stage 30 remains constant, the displacement interval between two adjacent frames of two-dimensional contour data is stable, the lateral sampling density of the point cloud is uniform, and it is less likely to cause patch breakage during region growth and segmentation. In actual use, the constant speed of the sliding stage 30 can be set to 120 mm per second, the effective scanning length of the linear guide 20 can be set to 1200 mm, and the time for a single complete scan is about 10 seconds. To avoid the speed fluctuation caused by start and stop affecting the stitching accuracy, the controller 110 can reserve a 100 mm acceleration section at the beginning of the scan and a 100 mm deceleration section at the end of the scan, and only collect two-dimensional contour data in the constant speed section.

[0043] The generation of spatial pose data for the rear opening 100 of the carriage is carried out within the controller 110 in the following order: downsampling, filtering, segmentation, planar extraction, and pose output. When downsampling the point cloud using octree voxel partitioning, the voxel side length can be set to 5 mm or 8 mm. A smaller voxel side length retains more detail but increases computational complexity and makes it more sensitive to local noise, while a larger voxel side length weakens the geometric abrupt changes at the door frame edge, resulting in less clear boundaries for the planar segmented patches of the rear opening 100 of the carriage. In the outlier removal stage, the controller 110 searches for neighboring points within a neighborhood radius for each point to be judged. The neighborhood radius can be set to 30 mm, and the lower limit for the number of neighboring points can be set to 20. When the mean distance from the point to be judged to its neighboring points exceeds three times the standard deviation, the controller 110 removes the point to be judged. The reason for using a combination of the mean distance and the standard deviation of distance instead of simply using a fixed distance threshold is that different car body surface materials, reflectivity and point cloud density will change the local point spacing distribution. The standard deviation can reflect the dispersion of the local point cloud. After binding the threshold and the standard deviation, the elimination rule will adapt to the local point cloud quality, which can filter out floating noise and is less likely to accidentally delete sparse points on the edge of the door frame.

[0044] When using region growing for patch segmentation, the angle threshold of the controller 110 for the local fitting plane normal vector can be set from 8 to 12 degrees, with 10 degrees being common; the growth radius can be set to 40 mm. A smaller angle threshold will result in the same plane being over-segmented, while a larger angle threshold may cause the plane of the rear opening 100 of the carriage to be bonded to the adjacent sidewall into the same segmented patch. After segmentation, the controller 110 selects the segmented patch with the largest number of points and whose normal vector points towards the loading platform 10 from all segmented patches as the segmented patch for the plane of the rear opening 100 of the carriage, and performs principal component analysis on this segmented patch to obtain the unit normal vector and the coordinates of the center point. The segmented patch with the largest number of points is selected because the plane of the rear opening 100 of the carriage usually has the largest coverage area and the most point cloud points within the scanning range; the constraint that the normal vector points towards the loading platform 10 can eliminate large-plane interference formed by the ground, guardrails, or other facilities. After combining the unit normal vector with the center point coordinates to form the spatial pose data of the rear opening 100 of the carriage, the controller 110 further converts the spatial pose data of the rear opening 100 of the carriage to the coordinate system of the loading platform 10, ensuring that the subsequent calculation and control of the actuators are unified under the same coordinate reference.

[0045] When calculating the target extension amount of the four corner hydraulic cylinders based on the spatial pose data of the rear opening 100 of the cargo compartment, the controller 110 first determines the target docking pose. The target docking pose typically includes the target gap from the center point of the docking platform 50 to the center point of the plane of the rear opening 100 of the cargo compartment, as well as the alignment relationship between the normal of the docking platform 50 and the unit normal vector of the plane of the rear opening 100 of the cargo compartment. The target gap can be set from 2 mm to 6 mm, with 4 mm being a common setting; this gap can both prevent the docking platform 50 from having a hard collision with the cargo compartment during the approach phase and be small enough to facilitate the contact force maintenance control phase after docking and fitting. The significance of aligning the normal of the docking platform 50 is to make the mating surface of the docking platform 50 as parallel as possible to the plane of the rear opening 100 of the cargo compartment, reducing the high stress concentration caused by local point contact after docking, thereby reducing the risk of structural vibration and sealing failure during the loading of hazardous materials.

[0046] When the controller 110 maps the target docking pose to the target extension amount of the four corner hydraulic cylinders, it uses the geometric parameters of the docking platform 50 for calculation. The lateral and longitudinal distances between the installation positions of the four corner hydraulic cylinders and the center point of the docking platform 50 can be set to 800 mm and 700 mm, respectively. The controller 110 calculates the target height of the four corners of the docking platform 50 based on the target docking pose, and then converts the target height into the target extension amount of the four corner hydraulic cylinders. If the docking platform 50 has a zero-point deviation in the initial state, the controller 110 uses the measured displacement value of the magnetostrictive displacement sensor 91 as the initial extension amount reference, and expresses the target extension amount as an increment based on the initial extension amount, avoiding the accumulation of absolute stroke calculation errors due to mechanical assembly differences. The sampling frequency of the magnetostrictive displacement sensor 91 can be set to 1000 Hz, the sampling frequency of the cylinder pressure sensor 92 can be set to 1000 Hz, and the control cycle of the controller 110 can be set to 2 milliseconds to 5 milliseconds, with 5 milliseconds being the most common setting, which can cover the main dynamics of the hydraulic system and allow sufficient calculation time.

[0047] When controlling the four-corner hydraulic cylinder assembly 60 to complete the diagonal alternating progressive leveling control process, the controller 110 follows a rhythm of "first diagonal synchronization, then diagonal synchronization again, and cyclical approximation." The controller 110 first sends the same valve core displacement command to the servo valve 80 corresponding to the first diagonal hydraulic cylinder pair, causing the first diagonal hydraulic cylinder pair to extend synchronously. The purpose of synchronous extension is to maintain the geometric symmetry of the docking platform 50 along the diagonal direction and reduce the torsion introduced by single-corner lifting. During synchronization, the cross-balancing valve assembly connects to the rodless chamber of the diagonal hydraulic cylinders. When the pressure difference between the diagonal rodless chambers exceeds the opening pressure difference threshold, the cross-balancing valve assembly opens the overflow channel, allowing the high-pressure side hydraulic oil to flow to the low-pressure side. After the pressure difference returns, the overflow channel closes. Releasing the diagonal pressure difference through self-balancing via the cross-balancing valve assembly reduces the reverse action amplitude applied by the controller 110 for correction, thus mitigating the swaying of the docking platform 50 under off-center loading conditions. After the first pair of diagonal hydraulic cylinders reaches their respective target extension amounts, the controller 110 switches to the second pair of diagonal hydraulic cylinders, sending the same valve core displacement command to complete the synchronous extension. To avoid impact caused by a single-stage extension, the controller 110 can adopt a progressive setting method, limiting the displacement increment of each diagonal synchronization to 3 mm to 8 mm, with 5 mm being a common setting. After each progression, the controller 110 uses the magnetostrictive displacement sensor 91 to verify displacement convergence and the cylinder pressure sensor 92 to verify the pressure balance before entering the next round of progression, until the target extension amounts of all four corner hydraulic cylinders are met.

[0048] refer to Figure 3 The horizontal axis represents time. The unit is seconds; the vertical axis represents the extension amount of the piston rod of the hydraulic cylinder. The unit is millimeters. This curve visually reflects the dynamic process of the controller driving the four-corner hydraulic cylinder assembly to approach the target docking position from its initial position. The entire leveling process is divided into several alternating "synchronous progression" stages. Within the time interval... to Inside, the controller first activates the first diagonal pair of hydraulic cylinders (i.e., the first and third hydraulic cylinders), sending the same target position increment command to the servo valves of these two hydraulic cylinders. (For example As shown in the figure, the curve representing the displacement of the first diagonal hydraulic cylinder pair rises in a sloping manner, indicating that the hydraulic cylinders are extending at a controlled speed. During this period, the second diagonal hydraulic cylinder pair (i.e., the second and fourth hydraulic cylinders) remains in its current position, and its displacement curve is a horizontal straight line. This strategy ensures that the docking platform has at least two diagonal support points that are relatively stationary at any given time, thus maintaining the geometric stability of the platform.

[0049] When the first diagonal hydraulic cylinder is aligned at time After reaching the preset incremental target, the controller enters a waiting confirmation state, checks the feedback data from the cylinder pressure sensor, and confirms whether the cross-balancing valve has completed pressure self-balancing (i.e., diagonal pressure difference convergence). After confirming that there are no abnormalities, it enters the time interval. to The controller switches the driving object, activating the second pair of diagonal hydraulic cylinders to perform the same synchronous progressive action, while the first pair of diagonal hydraulic cylinders remains stationary. This cycle repeats, forming a stepped upward displacement trajectory. As the docking platform gradually approaches the rear opening plane of the carriage (i.e., the target extension),... The controller will gradually reduce the incremental increment. For example, from Reduce to ,like Figure 3 The curve slope becomes gentler and the steps become denser in the mid-to-late stages, as shown. This variable step size approximation strategy ensures both the leveling efficiency in the early stages and avoids overshooting and collisions in the later stages. Figure 3 The diagram also demonstrates the effect of the cross-balancing valve: during each section of the ramp ascent, the actual displacement curve may experience slight fluctuations or corrections. This is because the cross-balancing valve opens to overflow when the pressure difference exceeds a threshold, causing some hydraulic oil to be diverted, thus physically forcing the forces on the diagonal hydraulic cylinders to become more consistent. Finally, when the displacements of all four corner hydraulic cylinders reach the target extension calculated by the vision system, and the pressure sensors detect the establishment of contact force, the curve stabilizes at the final height, marking the end of the leveling process and the system's readiness to switch to the contact force holding control phase. This control timing diagram clearly illustrates the control concept that combines "geometric symmetry drive" and "physical pressure equalization."

[0050] The determination of successful docking is supported by the spatial pose data of the rear opening 100 of the carriage and the cylinder pressure sensor 92. The spatial pose data of the rear opening 100 of the carriage is used to determine the attitude residual and gap residual between the docking platform 50 and the plane of the rear opening 100 of the carriage. The attitude residual can be set to less than 0.2 degrees, and the gap residual can be set to less than 1 mm. The cylinder pressure sensor 92 is used to determine the contact state. When the docking platform 50 moves further, the pressure in the rodless chamber of the four corner hydraulic cylinders rises synchronously and the rise exceeds 0.5 MPa. At the same time, the magnetostrictive displacement sensor 91 shows a significant decrease in the displacement change. The controller 110 uses this combination of features as the trigger condition for successful docking. The reason for using the pose residual and pressure rise together instead of relying on a single signal is that visual measurement may fluctuate briefly under strong reflection or partial obstruction, while the pressure signal may drift due to slow changes in temperature or load. The combination of the two can reduce the probability of misjudgment and make the switching of the contact force holding control phase more reliable.

[0051] After entering the contact force holding control phase, the controller adopts a force-position cascade control architecture. The position control loop is responsible for maintaining the macroscopic position of the docking platform to prevent cumulative drift, while the force control loop is responsible for ensuring that the actual contact force applied by the docking platform to the rear opening of the carriage tracks the target contact force setpoint. The target contact force setpoint can be set from 20 kN to 60 kN according to the loading process requirements, with 35 kN being a common setting. The feedback from the force control loop comes from the thrust calculated by the cylinder pressure sensor and the effective area of ​​the hydraulic cylinder, combined with the equivalent contact force geometrically distributed to the contact direction by the docking platform. To allow the force control loop to respond more quickly to external disturbances, its update frequency can be consistent with the controller's control cycle, for example, 5 milliseconds; the position control loop can be slower, for example, 20 milliseconds, to avoid the position control loop and force control loop competing for the actuator and causing jitter.

[0052] When the inner-loop disturbance observer operates within the force control loop, the controller 110 takes the control current command from the servo valve 80, the measured displacement value from the magnetostrictive displacement sensor 91, and the measured pressure value from the cylinder pressure sensor 92 as inputs to form a real-time estimate of the "equivalent lumped disturbance." This estimate is then superimposed onto the control current command from the servo valve 80 as a compensation term. The equivalent lumped disturbance includes the reaction force disturbance caused by the elastic deformation of the vehicle tires, the transient force disturbance caused by the impact of the loaded material falling, and the flow gain drift and internal leakage changes caused by changes in hydraulic oil temperature. The reason for using the inner-loop disturbance observer is that these disturbances often change rapidly and have large amplitudes. If they are only offset by the error integral of the force control loop, it is easy to cause response lag and overshoot. The inner-loop disturbance observer makes the disturbances "explicit" in advance, and the compensation action is earlier, resulting in smaller contact force fluctuation amplitude.

[0053] One easily implemented method for calculating the inner-loop disturbance observer is to characterize the disturbance using the difference between the predicted displacement and the measured displacement. The controller 110 calculates the predicted displacement based on the control current command from the servo valve 80 and the nominal parameters of the hydraulic cylinder. This predicted displacement is then subtracted from the measured displacement by the magnetostrictive displacement sensor 91 to obtain the displacement residual. This residual is then converted into an equivalent lumped disturbance after being filtered by a first-order inertial filter and used for compensation. If the predicted displacement and displacement residual are described by an expression, it can be written as: and .in, Indicates the control cycle number. Indicates the first Predicted displacement for each control cycle This represents the predicted displacement from the previous control cycle. Indicates the first Prediction speed per control cycle Indicates the duration of the control cycle. Indicates the first Displacement residual for each control cycle Indicates the first The measured displacement of each control cycle is collected by the magnetostrictive displacement sensor 91. Displacement residuals are used instead of pressure errors to estimate disturbances because the pressure signal contains multiple rapid components such as valve dynamics, oil compression, and pipeline elasticity. Directly treating pressure errors as disturbances can easily lead to mistaking the system's own dynamics for external disturbances, introducing compensating oscillations. Displacement residuals are closer to the "deviation of execution results" and are more indicative of external disturbances.

[0054] The first-order inertial filter of the displacement residual is used to suppress high-frequency noise from the magnetostrictive displacement sensor 91 and to prevent the compensation term from generating high-frequency excitation on the servo valve 80. The filter time constant can be set from 30 milliseconds to 80 milliseconds, with 50 milliseconds being a common setting; a time constant that is too small will make the compensation term too sensitive, while a time constant that is too large will cause the compensation to lag. When the compensation output is superimposed on the control current command of the servo valve 80, the controller 110 can also add a current change rate limit, for example, limiting the current change in each control cycle to within 0.2 amperes, in order to reduce the impact and heat generation of the hydraulic system.

[0055] The four-corner hydraulic cylinder assembly 60 and the cross-balancing valve assembly are used for docking and leveling, which can be implemented simultaneously from two lines: the hydraulic force path and the control scheduling. After the initial installation of the first hydraulic cylinder 61, second hydraulic cylinder 62, third hydraulic cylinder 63, and fourth hydraulic cylinder 64 at the bottom of the docking platform 50, the controller 110 first performs a geometric zero-position alignment: the docking platform 50 is placed on the mechanical support point, the measured displacement value of the piston rod of the four magnetostrictive displacement sensors 91 is read and written into the zero-position offset table; then the docking platform 50 is raised by 20 mm under no-load conditions, and then lowered by 20 mm, and the displacement hysteresis of the rising and falling segments is recorded respectively, which is used for compensation of the displacement command to the displacement response of the valve core. The advantage of this approach is that it makes the initial deviation caused by assembly and the small hysteresis of the hydraulic system explicit. When calculating the target extension of the first hydraulic cylinder 61, the second hydraulic cylinder 62, the third hydraulic cylinder 63, and the fourth hydraulic cylinder 64, it is not necessary to treat these errors as unknown disturbances and repeatedly try to find them. The progressive leveling is more straightforward.

[0056] The diagonal alternating progressive leveling control process adopts a rhythm of "diagonal synchronization, pressure self-balancing, and then diagonal synchronization again" in its execution sequence. The core consideration is not to pursue the rapid positioning of a single hydraulic cylinder, but to maintain low torsion of the docking platform 50 under off-center load. The first hydraulic cylinder 61 and the third hydraulic cylinder 63 form the first diagonal hydraulic cylinder pair, and the second hydraulic cylinder 62 and the fourth hydraulic cylinder 64 form the second diagonal hydraulic cylinder pair. When the controller 110 sends the same valve core displacement command to the two servo valves 80 of the first diagonal hydraulic cylinder pair, it is equivalent to applying the same lifting driving torque in the same direction and intensity to both ends of the diagonal of the docking platform 50. The platform tends to perform overall translation and overall pitch, rather than to twist around the vertical axis. Once torsion occurs, it will squeeze one side of the plane of the rear opening 100 of the carriage more tightly and the gap on the other side will be larger. The contact position becomes a local point contact, and the cylinder pressure sensor 92 will show a "pressure in a certain corner is continuously too high" state. Subsequent correction will introduce a reverse impact, which is detrimental to stability when loading dangerous goods.

[0057] When the cross-balancing valve assembly connects to the rodless chambers of the two diagonal hydraulic cylinders respectively, the first cross-balancing valve 71 connects the rodless chambers of the first hydraulic cylinder 61 and the third hydraulic cylinder 63, and the second cross-balancing valve 72 connects the rodless chambers of the second hydraulic cylinder 62 and the fourth hydraulic cylinder 64. During the diagonal synchronous extension process, if the docking platform 50 is subjected to an off-center load, causing the pressure in the rodless chamber of the first hydraulic cylinder 61 to rise rapidly, while the pressure in the rodless chamber of the third hydraulic cylinder 63 rises more slowly, when the pressure difference between the two exceeds the opening pressure difference threshold, the valve core inside the first cross-balancing valve 71 moves towards the low-pressure side and opens the overflow channel, allowing the high-pressure side hydraulic oil to flow back to the low-pressure side rodless chamber along the diagonal channel. The direct effect of this is that the diagonal support force tends to be consistent, and the platform is more like being "diagonally flattened" rather than being forcibly pressed down by the controller 110. The differential pressure threshold can be set to 2.0 MPa. When the oil temperature is around 40 degrees Celsius, the reflux build-up time is usually within 30 milliseconds. Setting the threshold too low will cause even slight fluctuations to trigger reflux, reduce the equivalent stiffness, and slow down the leveling response. Setting the threshold too high will cause torsional loads to accumulate on the structure for a longer time, making it easier for sudden changes to occur when released.

[0058] The progressive approach is typically not implemented by providing the target extension amount for each hydraulic cylinder all at once and then waiting for it to reach its position. Instead, the diagonal synchronous displacement increment for each round is limited to a small range, and the command for the next round is dynamically adjusted based on sensor feedback. For example, when the docking platform 50 approaches the rear opening 100 plane of the carriage from its initial height, the progressive displacement increment for each round can be set to 5 mm. Once it enters the final stage and the gap at the rear opening 100 plane of the carriage is shown to be less than 10 mm in the scanning data, the progressive displacement increment for each round can be reduced to 2 mm. The reason for reducing the progressive increment is straightforward: the smaller the gap, the more likely any small overshoot is to cause a contact impact. Reducing the progressive increment is equivalent to releasing the system's kinetic energy in stages. The pressure rise seen by the cylinder pressure sensor 92 is more gradual, and the cross-balancing valve assembly can more easily achieve equalization within a small pressure difference, preventing the platform from being suddenly "bounced" by the backflow.

[0059] To incorporate the self-balancing behavior of the cross-balancing valve assembly into the diagnostic scope, the controller 110 records the outputs of four cylinder pressure sensors 92 and four magnetostrictive displacement sensors 91 during each round of diagonal synchronous extension. A commonly used criterion is the "diagonal pressure difference convergence time": for example, if the difference between the pressure in the rodless chamber of the first hydraulic cylinder 61 and the pressure in the rodless chamber of the third hydraulic cylinder 63 exceeds the opening pressure difference threshold, it should fall back to within the opening pressure difference threshold within 100 milliseconds; if the fallback time continues to exceed 200 milliseconds, the controller 110 will reduce the rate of change of the valve core displacement command of the servo valve 80, for example, limiting the change of the valve core displacement command in each control cycle to 50% of the original, and reducing the incremental displacement from 5 mm to 2 mm. The advantage of this approach is that even if the cross-balancing valve assembly slows down due to oil contamination or valve core friction, the movement of the docking platform 50 will automatically become gentler, preventing platform torsion caused by forceful pushing when "balancing cannot keep up".

[0060] The switching after docking can also be clearly defined from the perspective of hydraulic characteristics, without relying on a single geometric residual. After completing the last few rounds of progression, the controller 110 allows the docking platform 50 to approach at a lower speed. The spatial pose data of the rear opening 100 of the carriage corresponding to the displacement of the sliding platform 30 is used to confirm that the attitude residual between the docking platform 50 and the plane of the rear opening 100 of the carriage is within the set range. At the same time, the cylinder pressure sensor 92 is used to confirm that contact has been established. A usable combination of conditions is: within 300 milliseconds, the pressure of the four rodless chambers simultaneously shows an upward trend with a cumulative increase of more than 0.5 MPa, and the change in the measured displacement value of the four piston rods is simultaneously less than 0.2 mm. The increase in pressure indicates that the docking platform 50 has begun to apply force to the plane of the rear opening 100 of the carriage, and the decrease in the displacement change indicates that the platform's continued advancement has been "held back" by the contact constraint. When both conditions are met simultaneously, the contact force holding control phase is more stable and less prone to accidental switching due to short-term visual fluctuations.

[0061] From another perspective, contact force disturbance suppression control can focus on the reliability of force estimation and the boundaries of compensation terms. When using a force-position cascade control architecture in the contact force holding control phase, the position control loop is responsible for locking the macroscopic position reference of the docking platform 50, preventing slow crawling due to internal oil leakage or temperature drift; the force control loop is responsible for suppressing short-term impacts, ensuring the actual contact force tracks the target contact force setpoint. The estimation of the actual contact force can preferentially utilize the cylinder pressure sensor 92, as the pressure signal is more sensitive than the pose signal at the moment of contact. If the first hydraulic cylinder 61 simultaneously collects the pressure in the rodless chamber and the pressure in the rod chamber, it can be expressed using the following expression... Calculate the first hydraulic cylinder 61 in the first... Axial thrust per control cycle. This indicates the thrust of the first hydraulic cylinder 61. This indicates the effective area of ​​piston 61 in the first hydraulic cylinder. This indicates the pressure in the rodless chamber of the first hydraulic cylinder 61. This indicates the pressure in the rod chamber of the first hydraulic cylinder, 61. This indicates the control cycle number. The advantage of using the pressure difference between the two chambers instead of just the rodless chamber pressure is that pressure changes caused by back pressure fluctuations in the return oil or throttling in the rod chamber are included in the calculation, making the thrust estimate less prone to drift during return oil fluctuations. If only the rodless chamber pressure is collected, the controller 110 can approximate the rod chamber pressure as the hydraulic station return oil pressure and introduce a back pressure term corrected for oil temperature. The thrust estimation accuracy decreases slightly, but the wiring is simplified.

[0062] When combining the thrust of the four hydraulic cylinders into the actual contact force, the direction of the force on the docking platform 50 also needs to be considered. If the normal vector of the docking platform 50 is aligned with the unit normal vector of the plane of the rear opening 100 of the carriage, the actual contact force can be approximated by summing the components of the thrust of the four cylinders in the normal direction. The expression can be written as: .in, Indicates the first The actual contact force per control cycle Indicates the first The thrust of each hydraulic cylinder Indicates the first The angle between the axial direction of the hydraulic cylinder and the contact normal. This angle is introduced because, during slight pitch or roll of the docking platform 50, the hydraulic cylinder thrust does not act entirely along the contact normal. Incorporating the geometric projection into the calculation reduces the risk of overestimating the thrust due to slight attitude deviations. After leveling, the angle of the docking platform 50 is typically small, for example, less than 0.5 degrees. Even when the value is close to 1, the calculation remains simple.

[0063] When the inner-loop disturbance observer is placed inside the force control loop, the emphasis is placed on "identifying the disturbance first, then suppressing it," rather than relying on error accumulation to gradually correct the deviation. Disturbances typically originate from the elastic deformation reaction force of vehicle tires, transient force disturbances from the impact of loaded materials, system parameter drift caused by changes in hydraulic oil temperature, and rebound caused by slight elasticity in the docking platform 50 structure. In each control cycle, the inner-loop disturbance observer first calculates a "displacement change that the actuator should cause," then compares it with the actual displacement change given by the magnetostrictive displacement sensor 91. The greater the difference, the stronger the external disturbance or parameter drift. This can be achieved using... and Describe this process. Among them, Indicates the first Displacement is predicted per control cycle. This indicates the predicted displacement from the previous control cycle. Indicates the first Predicting speed per control cycle Indicates the duration of the control cycle. Indicates the first The measured displacement output by the magnetostrictive displacement sensor 91 in each control cycle This represents the displacement residual. Predicted velocity. The displacement can be calculated from the control current command of the servo valve 80. The calculation uses the valve's nominal flow gain and the effective area of ​​the hydraulic cylinder piston, thus ensuring causal consistency between the predicted displacement and the control input. The advantage of basing the prediction on the control input rather than on past displacement differences is that when external disturbances suddenly occur, the displacement residual will immediately increase, and the compensation term will appear earlier.

[0064] Using displacement residuals directly for compensation would amplify sensor noise; therefore, a first-order inertial filter is required. This can be written as... .in, Indicates the first Displacement residual after filtering in each control cycle This represents the displacement residual after filtering in the previous control cycle. Represents the filter weight coefficients. Represents the current displacement residual. Filter weight coefficients. A value between 0.8 and 0.95 can be selected, with 0.9 being a common choice. A smaller value will make the filter output closely follow the changes in displacement residuals, resulting in a more aggressive compensation action, while a larger value will make the compensation action smoother but slightly lagging. The basis for selecting the range is that the main dynamics of the hydraulic system are usually on the order of tens of milliseconds. When the rate of change of the filter output matches the system dynamics, the compensation can both suppress disturbances and avoid exciting high-frequency oscillations at the valve orifice.

[0065] When converting the filtered displacement residual into an equivalent lumped disturbance force estimate, an equivalent stiffness can be used to map the "displacement deviation" to the "force deviation," written as: .in, Indicates the first Estimated equivalent lumped disturbance force for each control cycle Indicates equivalent stiffness. This represents the displacement residual after filtering. The equivalent stiffness is not required to be an invariant constant. In practice, it can be slowly updated during the contact force holding control phase based on the ratio of cylinder pressure sensor 92 to displacement change, for example, once per second. This makes the equivalent stiffness more closely match the current tire compression and platform structure state. The benefit of this is that when the vehicle tires are softer or the impact of loaded materials is stronger, the same displacement residual corresponds to a larger real force disturbance. The corresponding update of the equivalent stiffness allows for a more reasonable compensation term amplitude, avoiding undercompensation or overcompensation.

[0066] When the compensation term is added to the control current command of servo valve 80, it is usually canceled out by taking the opposite number, written as... .in, Indicates the first The servo valve 80 receives a control current command after interference compensation in each control cycle. Indicates the first The uncompensated servo valve 80 control current command output by the force control loop in each control cycle. This represents the conversion gain from force to current. This represents the estimated equivalent lumped disturbance force. (Converted gain) If the value is too large, compensation overshoot will occur, and the pressure ripple displayed by the cylinder pressure sensor 92 will increase; if the value is too small, the compensation effect will be insignificant. In engineering, it is often... The adjustment target is set as follows: within 200 milliseconds after the impact of the loaded material, the actual contact force returns to near the target contact force setting value, and the control current command of the servo valve 80 does not exhibit continuous saturation. To avoid pushing the servo valve 80 to its limit due to transient compensation, the controller 110 will also... Incorporate rate-of-change limits, such as limiting the current change in each control cycle to within 0.2 amperes, to reduce shock and heat generation in the hydraulic system.

[0067] In an alternative implementation, the inner-loop disturbance observer does not necessarily rely solely on the displacement residual. Another approach is to utilize the cylinder pressure sensor 92 simultaneously: when the displacement residual increases but the cylinder pressure change is minimal, it is more likely sensor noise or structural elastic rebound; when both the displacement and pressure residuals increase simultaneously, the reliability of external disturbances is higher. The controller 110 can introduce consistency discrimination before compensation, for example, only amplifying the compensation gain when the displacement residual and pressure difference have the same sign within 50 consecutive milliseconds, thus reducing noise-triggered invalid compensation. Alternatively, the diagonal pressure difference can be used as the basis for compensation suppression: if the first cross-balancing valve 71 is frequently open, it indicates that the diagonal is still undergoing pressure self-balancing. The controller 110 slightly reduces the compensation gain, allowing the cross-balancing valve assembly to first complete hydraulic-side balancing, and then the inner-loop disturbance observer finely suppresses disturbances, resulting in greater overall stability.

[0068] Reference Figure 4 The horizontal axis represents time. The unit is seconds; the vertical axis represents the actual contact force applied by the docking platform to the rear opening of the carriage. The unit is kilonewton (kN). The target contact force is defined in the figure. for The figure is represented by a horizontal dashed line. The experiment simulated severe disturbance conditions commonly encountered during loading, such as a forklift entering the truck bed or a heavy object being placed, causing instantaneous compression of the vehicle's suspension and impacting the docking platform. The figure compares two curves: the dashed line represents the system response using a traditional force-position cascade PID controller, and the solid line represents the system response using the inner-loop disturbance observer (DOB) enhanced controller proposed in this invention.

[0069] exist At a certain moment, a simulated disturbance occurs. It can be seen that the dashed line under traditional PID control exhibits significant fluctuations in contact force, with the maximum deviation... The contact force deviates significantly from the target value, and due to the hysteresis effect of the integral element, it takes time for the contact force to return to the target value. It had previously undergone a relatively long period of oscillation and adjustment, with an adjustment period of [duration missing]. This indicates that traditional control systems lack sufficient stiffness and respond slowly to rapidly changing load disturbances, potentially leading to momentary separation or excessive compression of the mating surfaces. In contrast, the solid line using the inner-loop disturbance observer of this invention exhibits superior robustness under the same disturbance. Its maximum deviation... much smaller And adjustment time Significantly shorter than The contact force can quickly return and stabilize at Nearby. This is thanks to the inner-loop disturbance observer in each control cycle. Fast estimation algorithm executed internally: The controller is based on servo valve control current. Calculate and predict displacement using hydraulic cylinder model and compared it with the measured displacement obtained by the magnetostrictive displacement sensor. By comparison, the displacement residuals are obtained. .

[0070] After being processed by a first-order low-pass filter, the residual is mapped to an equivalent lumped disturbance force. The controller then superimposes a reverse compensation amount onto the current command. This allows the disturbance to be canceled out at the level of the inner loop current before it manifests in the outer loop force error. Figure 4 Through intuitive comparison, the results demonstrate that the proposed control scheme effectively suppresses contact force fluctuations caused by vehicle settling, material impact, or hydraulic parameter drift, ensuring the reliability and safety of the docking seal during the loading of hazardous materials. This result indicates that introducing a model-based inner-loop disturbance compensation mechanism plays a decisive role in improving the dynamic force control performance of large-inertia hydraulic systems.

[0071] At the hardware layout level, there are some alternative solutions that would affect the aforementioned execution details. The cross-balancing valve assembly can be integrated onto the hydraulic manifold and placed as close as possible to the four-corner hydraulic cylinder assembly, shortening the diagonal return path and allowing for faster pressure differential establishment and release. If longer on-site piping is required, damping orifices can be added to the diagonal return piping to limit instantaneous return peaks and prevent visible rebound of the docking platform during return. If a larger cylinder diameter is used in the four-corner hydraulic cylinder assembly to increase load capacity, the cylinder pressure sensor range can be adjusted from 0 MPa to 25 MPa to 0 MPa to 35 MPa to avoid approaching the upper limit during the contact phase, which could lead to a decrease in resolution. The control cycle can also be adjusted from 5 milliseconds to 2 milliseconds, at the cost of increased computational load, but allowing the inner-loop interference observer to capture impact disturbances more quickly, making it suitable for loading conditions with more frequent impacts.

[0072] In summary, the above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A vehicle docking and automatic leveling system for loading bays, characterized in that, The system includes a loading platform, docking platform, linear guide rails, sliding platform, servo motors, platform-side 2D linear scanning laser sensors, four-corner hydraulic cylinder assemblies, cross-balancing valve assemblies, servo valves, cylinder pressure sensors, magnetostrictive displacement sensors, and a controller. The linear guide rails are mounted on the top crossbeam of the loading platform. The sliding platform is mounted on the linear guide rails and driven to reciprocate by the servo motors. The platform-side 2D linear scanning laser sensors are fixed to the sliding platform, with the laser emission plane perpendicular to the longitudinal axis of the loading platform. The four-corner hydraulic cylinder assemblies are located at the bottom of the docking platform and support it. The cross-balancing valve assemblies connect to the rodless chambers of two opposite diagonal hydraulic cylinders. The controller... Connected to a servo motor, a platform-side 2D line-scan laser sensor, a servo valve, a cylinder pressure sensor, and a magnetostrictive displacement sensor, the controller is configured to generate spatial pose data of the car opening based on the 2D contour data output by the platform-side 2D line-scan laser sensor and the displacement of the sliding platform. Based on the spatial pose data of the car opening, the controller calculates the target extension amount of the four corner hydraulic cylinders and controls the four corner hydraulic cylinder assemblies to complete the diagonal alternating progressive leveling control process. After the spatial pose data of the car opening indicates that the docking and fitting are completed, the controller enters the contact force holding control stage and runs the inner loop interference observer module in the force control loop to perform interference compensation on the servo valve control current command.

2. The system according to claim 1, characterized in that, The controller is configured to trigger the pose measurement process after the vehicle to be loaded enters the loading position and completes the parking brake. It drives the servo motor to move the sliding platform from the starting end of the linear guide to the ending end of the linear guide. During the movement, it controls the two-dimensional line scan laser sensor on the platform side to continuously collect two-dimensional contour data of the rear area of ​​the carriage at a fixed sampling period. The two-dimensional contour data at each sampling time is spatiotemporally registered with the corresponding sliding platform displacement and then stitched together to generate a three-dimensional original point cloud of the rear area of ​​the carriage.

3. The system according to claim 2, characterized in that, The controller is configured to perform octree voxel partitioning on the original 3D point cloud, dividing the 3D space into cubic cells with equal side lengths, calculating the mean coordinates of the points falling into each cubic cell, and using the mean coordinates as the representative point of the cell. The voxel downsampled point cloud is composed of all the representative points.

4. The system according to claim 3, characterized in that, The controller is configured to search for all neighboring points within a preset neighborhood radius for each point to be determined in the voxel downsampled point cloud, calculate the mean distance and standard deviation of the distance from the point to be determined to all neighboring points, and mark the point to be determined as an outlier and perform removal processing when the mean distance exceeds a preset multiple of the standard deviation. The filtered point cloud is formed by the points after the removal processing.

5. The system according to claim 4, characterized in that, The controller is configured to perform region growth segmentation in the filtered point cloud: select a seed point, search for adjacent points within a preset growth radius, calculate the local fitting plane normal vector of the seed point and the local fitting plane normal vector of each adjacent point, and when the angle between the local fitting plane normal vector of the adjacent point and the local fitting plane normal vector of the seed point is less than a preset normal vector angle threshold, the adjacent point is assigned to the growth region and updated as a new seed point until the growth region is completed, and the growth region is output as a segmentation patch; the controller further repeats the region growth segmentation on the points in the filtered point cloud that have not yet been assigned to any segmentation patch until all points are assigned; the controller selects the segmentation patch with the largest number of points and whose normal vector points to the loading platform direction from all segmentation patches as the segmentation patch for the rear opening plane of the carriage, and performs principal component analysis on the segmentation patch for the rear opening plane of the carriage, taking the eigenvector corresponding to the smallest eigenvalue of the covariance matrix as the unit normal vector of the rear opening plane of the carriage, taking the mean coordinate of all points in the segmentation patch for the rear opening plane of the carriage as the coordinate of the center point of the rear opening plane of the carriage, and outputting the combination of the unit normal vector and the center point coordinate as the spatial pose data of the carriage opening.

6. The system according to claim 1, characterized in that, The four-corner hydraulic cylinder assembly includes a first hydraulic cylinder, a second hydraulic cylinder, a third hydraulic cylinder, and a fourth hydraulic cylinder. The first hydraulic cylinder is installed at the front left corner of the docking platform, the second hydraulic cylinder is installed at the front right corner of the docking platform, the third hydraulic cylinder is installed at the rear right corner of the docking platform, and the fourth hydraulic cylinder is installed at the rear left corner of the docking platform. The first hydraulic cylinder and the third hydraulic cylinder form a first diagonal hydraulic cylinder pair, and the second hydraulic cylinder and the fourth hydraulic cylinder form a second diagonal hydraulic cylinder pair.

7. The system according to claim 6, characterized in that, The cross-balancing valve assembly includes a first cross-balancing valve and a second cross-balancing valve. The first cross-balancing valve has its first port connected to the rodless chamber of a first hydraulic cylinder via a first hydraulic line, and its second port connected to the rodless chamber of a third hydraulic cylinder via a second hydraulic line. The second cross-balancing valve has its first port connected to the rodless chamber of a second hydraulic cylinder via a third hydraulic line, and its second port connected to the rodless chamber of a fourth hydraulic cylinder via a fourth hydraulic line. Both the first and second cross-balancing valves are differential pressure sensing bidirectional relief valves and are configured to open the relief channel when the pressure difference across the valve core exceeds the opening differential pressure threshold corresponding to the valve core spring preload, allowing hydraulic oil on the high-pressure side to flow to the low-pressure side, and to close the relief channel when the pressure difference falls back to within the opening differential pressure threshold.

8. The system according to claim 7, characterized in that, The controller is configured to calculate the target extension amounts of the first, second, third, and fourth hydraulic cylinders based on the spatial pose data of the carriage opening, corresponding to the docking platform reaching the target docking pose. It then executes a diagonal, alternating, progressive leveling control process: controlling the first diagonal hydraulic cylinders to move synchronously and sending identical valve core displacement commands to the servo valves of the first and third hydraulic cylinders to drive them to extend synchronously. During this synchronous extension, the first cross-balancing valve automatically opens or closes the overflow channel based on the pressure difference in the rodless chamber to adjust the balance between the pressure in the rodless chambers of the first and third hydraulic cylinders; when the piston rod displacement of the first hydraulic cylinder reaches the target extension amount... When the output volume and the piston rod displacement of the third hydraulic cylinder reach the target extension volume of the third hydraulic cylinder, the action of the first diagonal hydraulic cylinder pair stops; the second diagonal hydraulic cylinder pair is controlled to move synchronously and the same valve core displacement command is sent to the servo valves of the second and fourth hydraulic cylinders to drive the second and fourth hydraulic cylinders to extend synchronously. During the synchronous extension process, the second cross equalization valve automatically opens or closes the overflow channel according to the pressure difference of the rodless chamber to adjust the balance state of the pressure of the rodless chamber of the second and fourth hydraulic cylinders; when the piston rod displacement of the second hydraulic cylinder reaches the target extension volume of the second hydraulic cylinder and the piston rod displacement of the fourth hydraulic cylinder reaches the target extension volume of the fourth hydraulic cylinder, the action of the second diagonal hydraulic cylinder pair stops, thereby completing the diagonal alternating progressive leveling control process.

9. The system according to claim 1, characterized in that, The controller is configured to enter the contact force holding control stage after the docking platform and the rear opening of the carriage have completed docking and fitting. The contact force holding control stage adopts a force-position cascade control architecture, which includes a position control loop and a force control loop. The inner loop interference observer module is embedded in the force control loop and generates interference-compensated servo valve control current commands based on the servo valve control current value, cylinder pressure sensor output, and magnetostrictive displacement sensor output, and sends them to the servo valve to maintain the actual contact force applied by the docking platform to the rear opening of the carriage to track the target contact force set value.

10. The system according to claim 9, characterized in that, The inner-loop interference observer module is configured to execute the following operation flow in each control cycle: acquire the servo valve control current value and the current measured piston rod displacement value output by the magnetostrictive displacement sensor at the start of the control cycle; convert the servo valve control current value into the nominal hydraulic oil volumetric flow rate entering the rodless chamber based on the nominal flow gain coefficient of the hydraulic cylinder; convert the nominal hydraulic oil volumetric flow rate entering the rodless chamber into the nominal piston rod speed based on the nominal effective piston area; generate the nominal piston rod displacement increment from the nominal piston rod speed based on the control cycle duration; and superimpose the nominal cumulative displacement value at the end of the previous control cycle with the nominal piston rod displacement increment to obtain the nominal predicted displacement value for the control cycle; for the current... The measured displacement value of the piston rod is compared with the nominal predicted displacement value to obtain the displacement residual value. A first-order inertial filter is applied to the displacement residual value to obtain the filtered displacement residual value. Based on the nominal hydraulic stiffness coefficient of the hydraulic cylinder, the filtered displacement residual value is converted into an equivalent lumped disturbance force estimate. The equivalent lumped disturbance force estimate characterizes the disturbance caused by the elastic deformation reaction force of the vehicle tires, the transient force disturbance caused by the impact of the loaded material, and the drift of system parameters caused by the change in hydraulic oil temperature. The equivalent lumped disturbance force estimate is inversely multiplied and superimposed on the output of the force control loop controller to generate a disturbance-compensated servo valve control current command. The disturbance-compensated servo valve control current command is then sent to the corresponding servo valve of the four corner hydraulic cylinder assembly.

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