A land LNG double-truck arm fine positioning docking system and docking method

Abstract

The application discloses a land LNG double-loading vehicle arm fine positioning butt joint system, which comprises an LNG double-loading vehicle arm, a stand column camera arranged on the upper part of a support stand column, a liquid-phase camera and a liquid-phase marker arranged on the hard pipe at the end of a liquid-phase arm, a gas-phase camera and a gas-phase marker arranged on the hard pipe at the end of a gas-phase arm, a liquid-phase arm flange arranged at the end of the liquid-phase arm and used for butt joint with a tank car liquid-phase flange, and a gas-phase arm flange arranged at the end of the gas-phase arm and used for butt joint with a tank car gas-phase flange. The application further discloses a land LNG double-loading vehicle arm fine positioning butt joint method. The first virtual flange position is taken as a coarse positioning terminal point, three virtual flanges are arranged along the central axis direction of the tank car liquid-phase flange after the first virtual flange as transition positions for step-by-step fine positioning butt joint, and the step-by-step positioning butt joint realizes multi-step control step-by-step butt joint in the fine positioning process, thereby improving the butt joint precision.

Description

Technical Field

[0001] The present invention belongs to the technical field of LNG loading arm docking, and in particular relates to a land-based LNG double loading arm precise positioning docking system and a docking method. Background Art

[0002] LNG receiving stations require dual LNG loading arms for loading and unloading. These arms consist of supporting columns, along with a liquid-phase arm and a gas-phase arm mounted on them. Each arm consists of five joints and five rigid tubes, each driven by a servo motor. The joints share the same structural principles, primarily comprising a servo motor, a reducer, a drive gear, and a driven gear. Each servo motor has a built-in explosion-proof encoder that transmits the motion angles of each joint to the host computer in real time. During loading and unloading, the control system uses the corresponding actuators to control the liquid-phase arm to reach the tank truck's liquid-phase flange for docking, or the gas-phase arm to reach the tank truck's gas-phase flange for docking.

[0003] Currently, docking between the dual LNG loading arms and the target flange at the rear of a tank truck is typically accomplished through coarse and fine positioning. After coarse positioning is complete, fine positioning is accomplished through a single motion control. This involves controlling the loading arms to move from the coarse positioning endpoint to the tank truck's target flange position in a single motion. This one-step motion control fine positioning docking method suffers from low docking accuracy, making docking errors more likely to occur.

[0004] Based on the above problems, this application proposes an onshore LNG double loading arm precision positioning docking system and docking method to achieve multi-step controlled gradual docking between the LNG double loading arm and the target flange at the rear of the tank truck after rough positioning, thereby improving docking accuracy. Summary of the Invention

[0005] The purpose of the present invention is to overcome the above-mentioned deficiencies in the prior art and to provide an onshore LNG double loading arm precise positioning docking system and docking method.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] A land-based LNG double-loading arm precision positioning and docking system comprises an LNG double-loading arm, wherein the LNG double-loading arm comprises a supporting column and a liquid phase arm and a gas phase arm mounted on the supporting column, wherein the liquid phase arm and the gas phase arm respectively comprise five joints and five rigid tubes, and each joint is driven by a servo motor; a column camera is provided on the upper portion of the supporting column, a liquid phase camera and a liquid phase marker are provided on the rigid tube at the end of the liquid phase arm, and a gas phase camera and a gas phase marker are provided on the rigid tube at the end of the gas phase arm; a liquid phase arm flange is provided at the end of the liquid phase arm for docking with the liquid phase flange of a tank truck, and a gas phase arm flange is provided at the end of the gas phase arm for docking with the gas phase flange of a tank truck.

[0008] The invention also discloses a method for precise positioning and docking of onshore LNG double loading vehicle arms.

[0009] A method for precisely positioning and docking a land-based LNG dual-loading vehicle arm is implemented using a land-based LNG dual-loading vehicle arm precisely positioning and docking system, comprising the following steps:

[0010] For the liquid phase arm:

[0011] Step 1: Determine four virtual flanges between the end of the liquid phase arm and the liquid phase flange of the tank truck along the central axis of the liquid phase flange of the tank truck. The position of the first virtual flange is the end point of the rough positioning, and the positions of the remaining three virtual flanges and the liquid phase flange of the tank truck are the target positions of the liquid phase arm's fine positioning step-by-step movement;

[0012] Step 2: Control the end of the liquid phase arm to move to the first virtual flange position through PLC;

[0013] Step 3: The liquid phase arm remains stationary, and the column camera photographs the liquid phase marker and the liquid phase flange of the tank truck. The column camera positions the tank truck liquid phase flange based on the two simultaneously taken photos.

[0014] Step 4, establishing the liquid phase arm coordinate system based on the DH method;

[0015] Step 5, use i to represent the sequence number, let i = 2;

[0016] Step 6: Read the current angle value of each joint of the liquid phase arm and calculate the homogeneous transformation matrix of each joint Get the pose matrix of the liquid phase arm end coordinate system relative to the earth coordinate system As shown in formula (1):

[0017]

[0018] Step 7: Collect the pose matrix of the tank truck’s liquid phase flange relative to the liquid phase arm’s end coordinate system based on the column camera

[0019] Step 8: According to the pose matrix of the liquid phase arm end coordinate system relative to the earth coordinate system Combined with the position matrix of the tank truck liquid phase flange relative to the liquid phase arm end coordinate system Calculate the position matrix of the tank truck liquid phase flange relative to the geodetic coordinate system As shown in formula (2);

[0020]

[0021] Step 9: Pose matrix based on target position i Calculate the pose matrix of the target position i with respect to the earth coordinate system As shown in formula (3);

[0022]

[0023] Step 10: Inversely solve to obtain the joint angles when the end of the liquid phase arm reaches the target position i;

[0024] Step 11, controlling the end of the liquid phase arm to move from the current position to the target position i through PLC;

[0025] Step 12: Obtain the distance between the current end of the liquid phase arm and the target position i through the column camera;

[0026] If the distance between the end of the current liquid phase arm and the target position i is less than the error setting value, the liquid phase arm reaches the target position i, and then proceeds to step 13;

[0027] Otherwise, repeat steps 6 to 12;

[0028] Step 13: When i < 5, set i = i + 1, take the position of the end of the liquid phase arm as the current position, and repeat steps 6 to 12;

[0029] Otherwise, the docking operation is terminated;

[0030] For the gas phase arm, the process is the same as above.

[0031] Preferably, in step 1, the pose matrix of the first virtual flange is The first virtual flange position is a position 250 mm away from the tank truck's liquid phase flange plane along the center axis of the tank truck's liquid phase flange;

[0032] The pose matrix of the second virtual flange is The second virtual flange position is a position 150 mm away from the tank truck's liquid phase flange plane along the center axis of the tank truck's liquid phase flange;

[0033] The pose matrix of the third virtual flange is The third virtual flange position is a position 100 mm away from the tank truck's liquid phase flange plane along the center axis of the tank truck's liquid phase flange;

[0034] The pose matrix of the fourth virtual flange is The fourth virtual flange position is a position 50 mm away from the tank truck's liquid phase flange plane along the center axis of the tank truck's liquid phase flange;

[0035] The pose matrix of the tank truck liquid phase flange is

[0036] Preferably, step 10 uses Newton's iteration method to perform inverse kinematics solution.

[0037] Preferably, the step 11 includes the following sub-steps:

[0038] Step 11.1, calculate the difference between the current joint angle and the corresponding joint angle at the target position i, and record it as the joint angle difference;

[0039] Step 11.2: Set the ratio of the joint speeds to the ratio of the joint angle differences to be consistent, and determine the speed of the corresponding servo motor based on the ratio of the joint speeds.

[0040] Step 11.3, driving the liquid phase arm to move for a time t according to the rotation speed of each servo motor;

[0041] Preferably, in step 11.3, t is 0.5 s.

[0042] Preferably, in step 12, the error setting value is 0.1 mm.

[0043] The beneficial effects of the present invention are:

[0044] (1) The present invention uses the first virtual flange position as the rough positioning end point, and sets three virtual flanges along the central axis of the tank truck's liquid phase flange after the first virtual flange as transition positions for fine positioning step-by-step docking, wherein the step-by-step positioning docking realizes multi-step control and gradual docking in the fine positioning process, thereby improving docking accuracy.

[0045] (2) The present invention sets a virtual flange along the central axis of the tank truck's liquid phase flange, so that the liquid phase arm and the tank truck's liquid phase flange are first aligned during the step-by-step docking process; at the time of final docking, if alignment is not performed first, the guide rod will touch the tank truck's liquid phase flange first. When the guide rod touches the tank truck's liquid phase flange first, the liquid phase arm will no longer be able to move, and ultimately the docking will fail. The present application sets a virtual flange along the central axis of the tank truck's liquid phase flange, and by performing alignment first, avoids the situation where the guide rod touches the tank truck's liquid phase flange first, thereby improving the success rate of docking.

[0046] (3) In the present invention, three virtual flanges are set along the central axis of the tank truck's liquid phase flange after the first virtual flange as transition positions for precise positioning and step-by-step docking. When controlling from the current position to the target position, after the current angle of each joint and the angle of each joint at the corresponding target position are determined, the planned trajectory is realized by controlling the speed of each joint. This control method can make the loading arm movement smoother, avoid jamming during the movement process and frequent starting and stopping of the motor, improve the service life of the motor, and avoid energy loss.

[0047] (4) In the present invention, after the liquid phase arm reaches the first virtual flange and completes rough positioning, the column camera photographs the liquid phase marker while the liquid phase arm is stationary, and at the same time, the liquid phase camera photographs the liquid phase flange of the tank truck, and the column camera positions the liquid phase flange based on the two photos taken at the same time; since the liquid phase arm is in a stationary state, the two pictures collected by the two cameras are pictures at the same time, which avoids the time asynchrony during dynamic collection and can perform positioning more accurately. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] The drawings in the specification, which constitute a part of this application, are used to provide further understanding of this application. The illustrative embodiments of this application and their descriptions are used to explain this application and do not constitute improper limitations on this application.

[0049] Figure 1 It is a structural schematic diagram of the onshore LNG double-loading vehicle arm precise positioning docking system of the present invention.

[0050] Figure 2 This is a schematic diagram of the angle between the gas phase III hard tube and the gas phase IV joint of the gas phase arm;

[0051] Figure 3 This is a schematic diagram of the angle between the liquid phase III hard tube and the liquid phase IV joint of the liquid phase arm;

[0052] Figure 4 It is a schematic diagram of the liquid phase arm flange and the tank truck liquid phase flange.

[0053] Figure 5 It is a schematic diagram of the liquid phase arm DH coordinate system of the present invention.

[0054] Figure 6 It is a flow chart of the onshore LNG dual-loading vehicle arm precise positioning and docking method of the present invention.

[0055] in:

[0056] 1-Support column;

[0057] 2-Liquid phase arm, 21-Liquid phase I joint, 22-Liquid phase I hard tube, 23-Liquid phase III hard tube, 24-Liquid phase IV joint, 25-Liquid phase II joint, 26-Liquid phase II hard tube, 27-Liquid phase III joint, 28-Liquid phase V joint, 29-Liquid phase V hard tube, 210-Liquid phase IV hard tube;

[0058] 3-gas phase arm, 31-gas phase I joint, 32-gas phase I hard tube, 33-gas phase III hard tube, 34-gas phase IV joint, 35-gas phase II joint, 36-gas phase II hard tube, 37-gas phase III joint, 38-gas phase V joint, 39-gas phase V hard tube, 310-gas phase IV hard tube;

[0059] 4-liquid phase actuator, 41-liquid phase arm flange, 42-guide rod, 5-gas phase actuator;

[0060] 6- Tank car liquid phase flange;

[0061] 71-Gas phase camera, 72-Gas phase marker, 73-Liquid phase camera, 74-Liquid phase marker, 75-Column camera. DETAILED DESCRIPTION

[0062] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which the present application belongs.

[0063] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, they indicate the presence of features, steps, operations, devices, components and / or combinations thereof.

[0064] In the present invention, the directions or positional relationships indicated by terms such as "upper", "lower", "bottom", and "top" are based on the directions or positional relationships shown in the accompanying drawings. They are relational words determined only for the convenience of describing the structural relationships of the various parts or elements of the present invention. They do not specifically refer to any part or element in the present invention and cannot be understood as limitations on the present invention.

[0065] In the present invention, terms such as "connected" and "connection" should be interpreted broadly to mean a fixed connection, an integral connection, or a detachable connection; a direct connection or an indirect connection through an intermediary. Relevant researchers or technicians in this field may determine the specific meanings of these terms in the present invention based on specific circumstances, and they should not be construed as limitations on the present invention.

[0066] The present invention will be further described below with reference to the accompanying drawings and examples.

[0067] Example 1:

[0068] An onshore LNG double loading arm precise positioning docking system, including LNG double loading arm, such as Figures 1-3As shown, the LNG dual loading arm includes a support column 1 and a liquid phase arm 2 and a gas phase arm 3 mounted on the support column 1. The liquid phase arm 2 and the gas phase arm 3 each include five joints and five rigid tubes, each driven by a servo motor. A column camera 75 is mounted on the upper portion of the support column 1. A liquid phase camera 73 and a liquid phase marker 74 are mounted on the rigid tube at the end of the liquid phase arm 2. A gas phase camera 71 and a gas phase marker 72 are mounted on the rigid tube at the end of the gas phase arm 3. The end of the liquid phase arm 2 is provided with a liquid phase arm flange 41 for docking with the liquid phase flange 6 of the tank truck, and the end of the gas phase arm 3 is provided with a gas phase arm flange for docking with the gas phase flange of the tank truck. Guide rods 42 for centering are provided on the radially outer sides of the liquid phase arm flange 41 and the radially outer sides of the gas phase arm flange.

[0069] Specifically, the liquid phase arm 2 includes a liquid phase I joint 21, a liquid phase I hard tube 22, a liquid phase II joint 25, a liquid phase II hard tube 26, a liquid phase III joint 27, a liquid phase III hard tube 23, a liquid phase IV joint 24, a liquid phase IV hard tube 210, a liquid phase V joint 28, a liquid phase V hard tube 29 and a liquid phase actuator 4 connected in sequence, and a liquid phase camera 73 and a liquid phase marker 74 are provided on the liquid phase V hard tube 29; the gas phase arm 3 includes a gas phase I joint 31, a gas phase I hard tube 32, a gas phase II joint 35, a gas phase II hard tube 36, a gas phase III joint 37, a gas phase III hard tube 33, a gas phase IV joint 34, a gas phase IV hard tube 310, a gas phase V joint 38, a gas phase V hard tube 39 and a gas phase actuator 5 connected in sequence, and a gas phase camera 71 and a gas phase marker 72 are provided on the gas phase V hard tube 39.

[0070] like Figure 4 As shown, the liquid phase actuator 4 connects the liquid phase arm flange 41 with the tank truck liquid phase flange 6 by rotating the joints of the liquid phase arm 2. Similarly, the gas phase actuator 5 connects the gas phase arm flange with the tank truck gas phase flange by rotating the joints of the gas phase arm 3.

[0071] Example 2:

[0072] A land-based LNG double-loading vehicle arm precise positioning docking method is implemented using the land-based LNG double-loading vehicle arm precise positioning docking system in Example 1, such as Figure 6 As shown, the following steps are included:

[0073] For the liquid phase arm:

[0074] Step 1: Determine four virtual flanges between the end of the liquid phase arm and the tank truck's liquid phase flange 6 along the central axis of the tank truck's liquid phase flange. The position of the first virtual flange is the end point of the rough positioning, and the remaining three virtual flanges and the tank truck's liquid phase flange are the target positions of the liquid phase arm's fine positioning step-by-step movement.

[0075] Specifically, in step 1, the pose matrix of the first virtual flange is The first virtual flange position is a position 250 mm away from the tank truck's liquid phase flange plane along the center axis of the tank truck's liquid phase flange;

[0076] Specifically, in step 1, the pose matrix of the second virtual flange is The second virtual flange position is a position 150 mm away from the tank truck's liquid phase flange plane along the center axis of the tank truck's liquid phase flange;

[0077] Specifically, in step 1, the pose matrix of the third virtual flange is The third virtual flange position is a position 100 mm away from the tank truck's liquid phase flange plane along the center axis of the tank truck's liquid phase flange;

[0078] Specifically, in step 1, the pose matrix of the fourth virtual flange is The fourth virtual flange position is a position 50 mm away from the tank truck's liquid phase flange plane along the center axis of the tank truck's liquid phase flange;

[0079] Specifically, in step 1, the pose matrix of the tank truck liquid phase flange 6 is

[0080] In this application, the first virtual flange position is used as the rough positioning end point, and three virtual flanges are set along the central axis of the tank truck's liquid phase flange after the first virtual flange as transition positions for fine positioning step-by-step docking. The step-by-step positioning docking realizes multi-step control and gradual docking in the fine positioning process, thereby improving the docking accuracy.

[0081] In addition, the method of providing a virtual flange along the central axis of the tank truck's liquid phase flange allows the liquid phase arm 2 and the tank truck's liquid phase flange 6 to be aligned first during the step-by-step docking process. During the final docking, if alignment is not performed first, the guide rod 42 may first touch the tank truck's liquid phase flange 6. When the guide rod 42 first touches the tank truck's liquid phase flange 6, the liquid phase arm 2 can no longer move, ultimately leading to docking failure. However, the method of providing a virtual flange along the central axis of the tank truck's liquid phase flange in the present application avoids the situation where the guide rod 42 first touches the tank truck's liquid phase flange 6 by performing alignment first, thereby improving the success rate of docking.

[0082] Step 2: Control the end of the liquid phase arm to move to the first virtual flange position through the PLC, that is, complete the rough positioning. The specific implementation method of controlling the end of the liquid phase arm to move to the first virtual flange position through the PLC is prior art and will not be described in detail here.

[0083] Step 3: The liquid phase arm remains stationary, and the column camera 75 photographs the liquid phase marker 74. Simultaneously, the liquid phase camera 73 photographs the tank truck liquid phase flange 6. The column camera 75 locates the tank truck liquid phase flange 6 based on the two simultaneously taken photos.

[0084] In this application, the first virtual flange position satisfies the requirement that the liquid phase camera 73 can capture the tank truck liquid phase flange 6 and the column camera 75 can capture the liquid phase marker 74;

[0085] During the shooting process of each camera at the first virtual flange position, the liquid phase arm 2 is in a stationary state, and the two images collected by the two cameras are images at the same time, which avoids the time asynchrony during dynamic acquisition and enables more accurate positioning;

[0086] Step 4, establishing the liquid phase arm coordinate system based on the DH method;

[0087] Taking the liquid phase arm as an example, the loading arm coordinate system is established based on the DH method. Figure 3 It can be seen that the end of the liquid phase V hard tube 29 of the present invention is fixedly connected to the liquid phase actuator 4, and the liquid phase arm flange 41 is fixedly connected to the liquid phase actuator 4. The present invention adds a virtual rotary joint between the liquid phase actuator 4 and the liquid phase arm flange 41, so that the liquid phase arm flange 41 can be virtually rotated around the axis of the liquid phase actuator 4, and further virtualizes the liquid phase arm flange 41 as an independent liquid phase arm flange joint, and establishes an independent liquid phase arm flange joint coordinate system, and the Z axis of the liquid phase arm flange joint coordinate system is collinear with the axis of the liquid phase actuator 4; in this application, the liquid phase arm 2 is a serial open-chain robotic arm, and the three-dimensional model of the liquid phase arm 2 is simplified. The liquid phase arm joint is replaced by a pie column, and the liquid phase arm hard tube is replaced by a cylindrical connecting rod, so as to facilitate the study of the actual liquid phase arm 2. The coordinate system established by the present invention is as follows Figure 5 As shown, it includes the 0-link coordinate system, the 1-link coordinate system, the 2-link coordinate system, the 3-link coordinate system, the 4-link coordinate system, the 5-link coordinate system, and the 6-link coordinate system, which are established in sequence from the end of the support column 1 to the end of the liquid phase arm.

[0088] Step 5, use i to represent the sequence number, let i = 2;

[0089] Step 6: Read the current angle value of each joint of the liquid phase arm and calculate the pose matrix of the liquid phase arm end coordinate system relative to the earth coordinate system.

[0090] Specifically, read the current angle value of each joint of the liquid phase arm 2 and calculate the homogeneous transformation matrix of each joint Then calculate the pose matrix of the liquid phase arm end coordinate system relative to the earth coordinate system As shown in formula (1):

[0091]

[0092] in is the homogeneous transformation matrix between the 1-link coordinate system and the 0-link coordinate system, is the homogeneous transformation matrix between the 2-link coordinate system and the 1-link coordinate system, is the homogeneous transformation matrix between the 3-link coordinate system and the 2-link coordinate system, is the homogeneous transformation matrix between the 4-link coordinate system and the 3-link coordinate system, is the homogeneous transformation matrix between the 5-link coordinate system and the 4-link coordinate system, is the homogeneous transformation matrix between the 6-link coordinate system and the 5-link coordinate system;

[0093] Step 7: Using the column camera 75, the position matrix of the tank truck liquid phase flange 6 relative to the liquid phase arm end coordinate system is collected.

[0094] Step 8: According to the pose matrix of the liquid phase arm end coordinate system relative to the earth coordinate system Combined with the position matrix of the tank truck liquid phase flange 6 relative to the liquid phase arm end coordinate system Calculate the position matrix of the tank truck liquid phase flange 6 relative to the geodetic coordinate system As shown in formula (2);

[0095]

[0096] Step 9: Pose matrix based on target position i Calculate the pose matrix of the target position i with respect to the earth coordinate system As shown in formula (3);

[0097]

[0098] Step 10: Inversely solve to obtain the joint angles when the end of the liquid phase arm reaches the target position i;

[0099] Specifically, step 10 uses the Newton iteration method to solve the inverse kinematics; the specific inverse solution method is a prior art and will not be repeated here;

[0100] Step 11, controlling the end of the liquid phase arm to move from the current position to the target position i through PLC;

[0101] Specifically, step 11 includes the following sub-steps:

[0102] Step 11.1, calculate the difference between the current joint angle and the corresponding joint angle at the target position i, and record it as the joint angle difference;

[0103] Step 11.2: Set the ratio of the joint speeds to the ratio of the joint angle differences to be consistent, and determine the speed of the corresponding servo motor based on the ratio of the joint speeds.

[0104] Step 11.3, driving the liquid phase arm to move for a time t according to the rotation speed of each servo motor;

[0105] Specifically, in step 11.3, t is 0.5s;

[0106] Step 12: Obtain the distance between the current end of the liquid phase arm and the target position i through the column camera 75;

[0107] If the distance between the end of the current liquid phase arm and the target position i is less than the error setting value, the liquid phase arm reaches the target position i, and then proceeds to step 13;

[0108] Otherwise, repeat steps 6 to 12;

[0109] Specifically, in step 12, the error setting value is 0.1 mm.

[0110] Step 13: When i < 5, set i = i + 1, take the position of the end of the liquid phase arm as the current position, and repeat steps 6 to 12;

[0111] Otherwise, the docking operation is terminated.

[0112] For the gas phase arm, the process is the same as above.

[0113] In this application, three virtual flanges are set along the central axis of the liquid phase flange of the tank truck after the first virtual flange at the end point of rough positioning as transition positions for fine positioning and step-by-step docking. When controlling from the current position to the target position, the current angle of each joint and the angle of each joint at the corresponding target position are determined, and the planned trajectory is realized by controlling the speed of each joint. This control method will make the loading arm movement smoother, avoid jamming during the movement process and frequent starting and stopping of the motor, increase the service life of the motor, and avoid energy loss.

[0114] Although the above describes the specific embodiments of the present invention in conjunction with the accompanying drawings, it is not a limitation of the present invention. Those skilled in the art should understand that various modifications or variations that can be made by those skilled in the art on the basis of the technical solution of the present invention without any creative work are still within the scope of protection of the present invention.

Claims

1. A land-based LNG dual-carriage arm precise positioning docking method, implemented using a land-based LNG dual-carriage arm precise positioning docking system, characterized in that: An onshore LNG double loading arm precision positioning docking system comprises an LNG double loading arm, which comprises a support column and a liquid phase arm and a gas phase arm mounted on the support column. The liquid phase arm and the gas phase arm respectively comprise five joints and five rigid tubes, each of which is driven by a servo motor. The system is characterized in that a column camera is provided on the upper portion of the support column, a liquid phase camera and a liquid phase marker are provided on the rigid tube at the end of the liquid phase arm, and a gas phase camera and a gas phase marker are provided on the rigid tube at the end of the gas phase arm. The end of the liquid phase arm is provided with a liquid phase arm flange for docking with the liquid phase flange of a tank truck, and the end of the gas phase arm is provided with a gas phase arm flange for docking with the gas phase flange of a tank truck. The docking method comprises the following steps: For the liquid phase arm: Step 1: Determine four virtual flanges between the end of the liquid phase arm and the liquid phase flange of the tank truck along the central axis of the liquid phase flange of the tank truck. The position of the first virtual flange is the end point of the rough positioning, and the positions of the remaining three virtual flanges and the liquid phase flange of the tank truck are the target positions of the liquid phase arm's fine positioning step-by-step movement; Step 2: Control the end of the liquid phase arm to move to the first virtual flange position through PLC; Step 3: The liquid phase arm remains stationary, and the column camera photographs the liquid phase marker and the liquid phase flange of the tank truck. The column camera positions the tank truck liquid phase flange based on the two simultaneously taken photos. Step 4, establishing the liquid phase arm coordinate system based on the DH method; Step 5, use i to represent the sequence number, let i = 2; Step 6: Read the current angle value of each joint of the liquid phase arm and calculate the homogeneous transformation matrix of each joint Get the pose matrix of the liquid phase arm end coordinate system relative to the earth coordinate system As shown in formula (1): Step 7: Collect the pose matrix of the tank truck’s liquid phase flange relative to the liquid phase arm’s end coordinate system based on the column camera Step 8: According to the pose matrix of the liquid phase arm end coordinate system relative to the earth coordinate system Combined with the position matrix of the tank truck liquid phase flange relative to the liquid phase arm end coordinate system Calculate the position matrix of the tank truck liquid phase flange relative to the geodetic coordinate system As shown in formula (2); Step 9: Pose matrix based on target position i Calculate the pose matrix of the target position i with respect to the earth coordinate system As shown in formula (3); Step 10: Inversely solve to obtain the joint angles when the end of the liquid phase arm reaches the target position i; Step 11, controlling the end of the liquid phase arm to move from the current position to the target position i through PLC; Step 12: Obtain the distance between the current end of the liquid phase arm and the target position i through the column camera; If the distance between the end of the current liquid phase arm and the target position i is less than the error setting value, the liquid phase arm reaches the target position i, and then proceeds to step 13; Otherwise, repeat steps 6 to 12; Step 13: When i < 5, set i = i + 1, take the position of the end of the liquid phase arm as the current position, and repeat steps 6 to 12; Otherwise, the docking operation is terminated; The step 11 includes the following sub-steps: Step 11.1, calculate the difference between the current joint angle and the corresponding joint angle at the target position i, and record it as the joint angle difference; Step 11.2: Set the ratio of the joint speeds to the ratio of the joint angle differences to be consistent, and determine the speed of the corresponding servo motor based on the ratio of the joint speeds. Step 11.3, driving the liquid phase arm to move for a time t according to the rotation speed of each servo motor; For the gas phase arm, the process is the same as above.

2. The onshore LNG dual-loading vehicle arm precise positioning docking method according to claim 1, characterized in that: In step 1, the pose matrix of the first virtual flange is The first virtual flange position is a position 250 mm away from the tank truck's liquid phase flange plane along the center axis of the tank truck's liquid phase flange; The pose matrix of the second virtual flange is The second virtual flange position is a position 150 mm away from the tank truck's liquid phase flange plane along the center axis of the tank truck's liquid phase flange; The pose matrix of the third virtual flange is The third virtual flange position is a position 100 mm away from the tank truck's liquid phase flange plane along the center axis of the tank truck's liquid phase flange; The pose matrix of the fourth virtual flange is The fourth virtual flange position is a position 50 mm away from the tank truck's liquid phase flange plane along the center axis of the tank truck's liquid phase flange; The pose matrix of the tank truck liquid phase flange is 3. The onshore LNG dual-loading vehicle arm precise positioning docking method according to claim 2, characterized in that: Step 10 uses Newton's iteration method to solve the inverse kinematics.

4. The onshore LNG dual-loading vehicle arm precise positioning docking method according to claim 3, characterized in that: In step 11.3, t is 0.5s.

5. The onshore LNG dual-loading vehicle arm precise positioning docking method according to claim 1, characterized in that: In step 12, the error setting value is 0.1 mm.

Images