Electric connector assembly method and system under point cloud estimation and geometric constraint search

Abstract

The invention belongs to the technical field of automatic control, and particularly discloses an electric connector assembly method and system under point cloud estimation and geometric constraint search. Comprising the following steps: collecting electric connector socket side wall point clouds, extracting plane features, constructing a coordinate system and determining a conversion matrix of robot base coordinates and sockets; the tail end of the robot is controlled to grasp the plug to move towards the socket, so that front angle-edge contact is formed between the plug and the socket; controlling the plug to move along the x direction of the coordinate system so as to carry out first-step search, and determining whether the plug and the socket form line contact or not; controlling the plug to move along the y direction of the coordinate system so as to carry out second-step search, and meanwhile, forming motion constraint through the joint of a plug pin and a socket groove and a guide groove and a chamfer structure, so that the plug and the socket form attached complete surface contact; active compliant control is applied to the robot such that the plug pins are inserted into the socket recesses with a constant force that does not exceed a threshold. According to the invention, the accuracy and reliability of the assembly process are ensured.

Description

Technical Field

[0001] The present invention belongs to the technical field of automatic control, and more specifically, relates to an electric connector assembly method and system under point cloud estimation and geometric constraint search. Background Art

[0002] In a space environment, manual operation is limited by factors such as space, gravity, and temperature, which is difficult and has a high risk. Space robots can perform complex tasks in narrow and extreme environments, avoiding astronauts being exposed to dangerous environments, and at the same time can effectively expand the boundaries of human exploration of the universe. They are becoming the mainstream choice for major space powers to further develop the space industry. Currently, existing space robots mainly focus on carrying large objects and grasping objects with simple geometric shapes, with a certain degree of operation flexibility. However, in complex and delicate tasks (such as assembling precision electric connectors in a microgravity environment), the operation accuracy and flexibility are still limited. The J30J type square electric connector has high reliability and high tolerance, and has become a common choice for power connection, data transmission, and signal transmission in the aerospace field. The robot assembly involving this type of connector is a complex and delicate space operation integrating action sequences such as guiding, positioning, alignment, pressing, and locking. It is of great significance to realize the automatic assembly of square electric connectors by robots under visual-force coordination.

[0003] To solve the problem of screwing assembly of electric connectors, patent document CN114571456A discloses an electric connector assembly method and system based on robot skill learning. The electric connector to be assembled is adjusted to an initial pose based on image information, and the robot is controlled to carry the electric connector to contact the assembly hole position and perform trajectory search; the pose and contact force of the robot end carrying the electric connector to be assembled are used as the input values of the constructed robot assembly skill learning network, and the joint angle of the next action of the robot is used as the output value; based on the reward function in the robot assembly skill learning network, the network is iteratively converged, and the assembly completion situation of the electric connector is judged according to the assembly depth and contact force falling into the assembly hole.

[0004] Patent document CN118721193A discloses a method for machine force perception assembly of a space electric connector in any pose. After the plug and the socket are in single-point contact, an inverted cone diffusion motion is combined with the mutation of the contact moment to identify the deflection angle range of the plug and the socket. In the case of small deflection angle contact, the plug and socket corresponding to the mutation are recorded as a double-point contact state according to the mutation direction of the contact moment. In the case of large deflection angle contact, the single-point contact is judged as bottom contact or side contact according to the tracking error of the spiral motion trajectory. In the double-point contact state, the expected contact force along the end is set to guide the plug to move along the surface of the socket to achieve the Z-axis alignment of the plug and the socket; the expected contact moment along the Z-axis of the plug is set to drive the alignment of the protection grooves of the plug and the socket.

[0005] However, the methods and systems disclosed in the above patent documents are all for circular electrical connectors. During the assembly process of J30J type rectangular electrical connectors, it is not suitable to use a spiral motion trajectory for hole search, and the corresponding assembly strategies and processes need to be changed. At the same time, considering the geometric anisotropy of rectangular connectors, this feature can be fully utilized for the geometric search alignment process. Summary of the Invention

[0006] In view of the above defects or improvement requirements of the prior art, the present invention provides an electrical connector assembly method and system under point cloud estimation and geometric constraint search. By combining the characteristics of robot active compliance control and the characteristics of rectangular electrical connectors, the coordinate system is constructed by collecting the point cloud on the side wall of the electrical connector socket and extracting the plane features, and at the same time, the transformation matrix between the robot base coordinate and the socket is determined, providing an accurate spatial positioning basis for subsequent assembly operations, enabling the robot to accurately move the plug to the specified position and improving the assembly accuracy. During the assembly process, the front angle-edge contact, the line contact search along the x direction, and the surface contact search along the y direction are carried out in sequence. Through the judgment of the contact state conversion conditions and corresponding adjustment strategies, such as expanding the search range, introducing dynamic centering compensation, etc., the relative position and posture of the plug and the socket are continuously optimized, ensuring the accuracy and reliability of the assembly process, and effectively avoiding problems such as assembly failure or poor contact caused by position deviation.

[0007] To achieve the above object, according to one aspect of the present invention, an electrical connector assembly method under point cloud estimation and geometric constraint search is proposed, including the following steps:

[0008] Step 1, collect the point cloud on the side wall of the electrical connector socket, extract the plane features, construct the coordinate system and determine the transformation matrix between the robot base coordinate and the socket;

[0009] Step 2, according to the transformation matrix, control the robot end to grasp the plug and move it towards the socket, so that the plug and the socket form a front angle-edge contact;

[0010] Step 3, control the plug to move along the x direction of the coordinate system to perform the first search, and determine whether the plug and the socket form a line contact. If so, terminate the movement in the x direction and enter Step 4. Otherwise, expand the search range until a line contact is formed;

[0011] Step 4, control the plug to move along the y direction of the coordinate system to perform the second search, and at the same time, form a motion constraint through the engagement of the plug pins and the socket grooves and the guide grooves and chamfer structures, so that the plug and the socket form a complete surface contact in a fitting manner;

[0012] Step 5: Apply active compliance control to the robot under the condition of full-surface contact, insert the plug pin into the socket groove with a constant force not exceeding the threshold until the propulsion termination condition is met, and the rectangular electrical connector assembly is completed.

[0013] As a further preference, Step 1 includes the following steps:

[0014] Mount a camera at the end of the robot, collect the point cloud of the electrical connector socket part fixed on the surface of the work platform, preprocess the point cloud data, extract the plane feature of the connector point cloud, that is, the side wall of the connector, establish the target object coordinate system based on this side wall plane, the direction pointed by the normal vector of the side wall plane is the y direction, the length direction of the rectangular plane is the x direction, and the z direction is obtained by vector cross product, so as to establish the transformation matrix between the camera coordinate system and the target object coordinate system.

[0015] As a further preference, in Step 1, through calibration work, complete the transformation from the base coordinate system of the robotic arm to the camera coordinate system, and finally obtain the spatial 6D pose relationship from the base coordinate system of the robotic arm to the socket, including three-dimensional translation and rotation information.

[0016] As a further preference, in Step 2, guide the movement of the end of the robotic arm according to the spatial 6D pose relationship from the base coordinate system of the robotic arm to the socket. During the movement of the robot, according to the prior information of the z-direction dimension of the connector, add an offset on the basis of the established coordinate system to form the front corner point contact in the search stage.

[0017] As a further preference, in Step 3, if the following conditions are met:

[0018]

[0019] Then, the contact state changes from angular contact to line contact;

[0020]

[0021] In the formula, is the variance of the contact moment, is the variance of the normal force, λ1 is the upper limit value of the variance of the normal force, γ1 is the upper limit value of the variance of the contact moment, M(t) is the contact moment, F n (t) is the normal force in the x direction during the contact process, w i is the weight factor, which controls the influence of historical data on the current calculation. is the mean value of the contact moment, is the mean value of the normal force.

[0022] As a further preference, in step four, the plug contacts the edge of the socket at an inclination angle θ to form a front angle contact, restricting the translation in the z direction and the rotation around the x / y directions. Translating along the x direction causes the plug to slide along the edge of the socket. During the sliding process, due to the geometric guidance of the contact edge, the plug is forced to rotate in the z direction to automatically align with the socket, thereby converting the line contact between the plug and the socket into a surface contact.

[0023] As a further preference, in step five, if the following conditions are met:

[0024]

[0025] Then, the contact state changes from a line contact to a surface contact state;

[0026] Wherein,

[0027] In the formula, is the variance of the contact moment, is the variance of the normal force, the same as above here is the variance of the tangential force, λ2 is the lower limit value of the variance of the normal force, γ2 is the lower limit value of the variance of the contact moment, M(t) is the contact moment, F n (t) is the normal force during the contact process in the x direction, w i is the weight factor, controlling the influence of historical data on the current calculation. is the mean value of the contact moment, is the mean value of the normal force, is the mean value of the tangential force.

[0028] As a further preference, in step five, dynamic centering compensation is introduced. The lateral force offset is monitored in real time through a six-axis force sensor built into the gripper, and at the same time, the robot end is actively compliant controlled. When the lateral contact force of the gripper exceeds the threshold, the stiffness is automatically reduced.

[0029] As a further preference, in step five, the contact state of the plug and the socket is judged by constructing a contact state conversion index. The contact state conversion index includes:

[0030]

[0031] In the formula, CSI is the contact state conversion index, is the variance of the normal force, is the variance of the contact moment, K n is the normal contact stiffness, K t is the tangential contact stiffness.

[0032] According to another aspect of the present invention, an electric connector robot assembly system under point cloud and geometric constraint search is also provided, including:

[0033] The first main control module is used to collect the point cloud of the side wall of the electrical connector socket, extract the plane features, construct a coordinate system and determine the transformation matrix between the robot base coordinate and the socket;

[0034] The second main control module is used to control the movement of the end of the robot to grasp the plug towards the socket according to the transformation matrix, so that the plug and the socket form a front angle-edge contact;

[0035] The third main control module is used to control the plug to move along the x direction of the coordinate system for the first step of searching, and determine whether the plug and the socket form a line contact. If so, terminate the movement in the x direction and trigger the fourth main control module. Otherwise, expand the search range until the plug and the socket form a line contact;

[0036] The fourth main control module is used to control the plug to move along the y direction of the coordinate system for the second step of searching. At the same time, through the engagement of the plug pins and the socket grooves and the formation of movement constraints by the guide grooves and chamfer structures, the plug and the socket form a complete surface contact in a fitting manner;

[0037] The fifth main control module is used to apply active compliance control to the robot during the complete surface contact, so that the plug pins are inserted into the socket grooves with a constant force not exceeding the threshold until the propulsion termination condition is met, and the rectangular electrical connector assembly is completed.

[0038] Generally speaking, compared with the prior art through the above technical solutions conceived by the present invention, the following technical advantages are mainly possessed:

[0039] 1. The method of the present invention realizes the automation of the electrical connector assembly. The robot can automatically complete the whole process from plug grasping, motion planning to assembly with the socket according to the preset program and transformation matrix, reducing manual intervention and improving the assembly efficiency. It is especially suitable for large-scale production and repetitive assembly tasks. By constructing methods such as the contact state conversion index, it can quickly and accurately judge whether the contact state between the plug and the socket is stable and whether the conversion conditions are met, enabling the robot to adjust the assembly strategy in a timely manner, avoiding unnecessary waiting and repeated adjustments, accelerating the assembly process, and improving the overall production efficiency.

[0040] 2. The present invention introduces active compliance control during the assembly process. The six-axis force sensor built in the gripper is used to monitor the lateral force offset in real time, and the stiffness and actions of the robot are automatically adjusted according to the force feedback information. When the lateral contact force of the gripper exceeds the threshold, the stiffness is automatically reduced, and the plug pins are pushed into the socket grooves with a constant force not exceeding the threshold, effectively avoiding damage to the plug or socket caused by excessive force and improving the reliability of the assembly and the product quality.

[0041] 3. The present invention utilizes the engagement of the plug pins and the socket grooves, as well as the motion constraints formed by the guiding grooves and chamfer structures, enabling the plug and the socket to automatically align and form a complete surface contact in a fitting manner, enhancing the stability and reliability of the assembly process, reducing assembly deviations caused by factors such as human operation errors or mechanical vibrations, and ensuring good electrical connection performance and mechanical strength of the electrical connector.

[0042] 4. The present invention establishes a transformation matrix between the socket coordinate system and the robot base coordinate system to achieve coordinate system unification, providing good guidance for the robot to approach the target efficiently and perform subsequent search and insertion processes. The six-degree-of-freedom constraint is decomposed into three-stage geometric alignment (axial alignment → planar fitting → vertical insertion). Through step-by-step guiding constraints of geometric features, the six-degree-of-freedom coupling problem is decoupled into serial single-degree-of-freedom operations, significantly reducing the assembly complexity and having good adaptability for rectangular electrical connectors of different sizes. Description of the Drawings

[0043] Figure 1 is a flowchart of an electrical connector assembly method under point cloud estimation and geometric constraint search according to an embodiment of the present invention;

[0044] Figure 2 is the target object coordinate system established on the side wall of the socket based on the plane features in the real point cloud data in an embodiment of the present invention;

[0045] Figure 3 is a schematic diagram of the initial inclined contact formed by the plug corner points and the socket edge according to an embodiment of the present invention;

[0046] Figure 4 is the first-step search for the plug to slide along the x direction according to an embodiment of the present invention;

[0047] Figure 5 is a schematic diagram of the second-step search for the plug to advance along the y direction to form side wall fitting according to an embodiment of the present invention. Detailed Embodiments

[0048] In order to make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below with reference to the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0049] As Figure 1 shown, a machine force perception assembly method for a spatial electrical connector in any posture provided by an embodiment of the present invention is characterized by including the following steps:

[0050] Step 1: Collect the point cloud of the side wall of the electrical connector socket, extract the plane features, construct a coordinate system, and determine the transformation matrix between the robot base coordinate and the socket.

[0051] Based on any one of the above embodiments or a combination of multiple embodiments, in this step, a camera is mounted at the end of the robot to collect the point cloud of part of the electrical connector socket fixed on the surface of the working platform, preprocess the point cloud data, and extract the plane features of the connector point cloud, that is, the side wall of the connector. Based on this side wall plane, a target object coordinate system is established. The direction indicated by the normal vector of the side wall plane is the y - direction, the length direction of the rectangular plane is the x - direction, and the z - direction is obtained by vector cross - product, thereby establishing the transformation matrix between the camera coordinate system and the target object coordinate system.

[0052] In addition, in this step, through calibration work, the transformation from the robot arm base coordinate system to the camera coordinate system is completed, and finally the 6D spatial pose relationship from the robot arm base coordinate system to the socket is obtained, including three - dimensional translation and rotation information.

[0053] More specifically, in this step, a camera is mounted at the end of the robot. The camera collects the point cloud of part of the electrical connector socket fixed on the surface of the working platform, and preprocesses the point cloud data, including filtering, sampling, and segmentation. The plane features of the connector point cloud (i.e., the side wall of the connector) are extracted. Based on this plane, a target object coordinate system is established. The direction indicated by the normal vector of the plane is the y - direction, the length direction of the rectangular plane is the x - direction, and the z - direction is obtained by vector cross - product, thereby establishing the transformation matrix between the camera coordinate system and the target object coordinate system. In this embodiment, preprocessing the point cloud data, including filtering, sampling, and segmentation, and extracting the plane features of the connector point cloud can adopt the conventional methods of point cloud data processing and plane feature extraction in the prior art, which will not be elaborated in this invention one by one.

[0054] According to the transformation matrix, control the end of the robot to grasp the plug and move it towards the socket. During the movement process, control the movement of the end of the robot by constructing a search strategy. Starting from the initial position, first replace the end - effector of the robot arm from the 3D camera to the two - finger gripper, and grasp the electrical connector plug to be assembled. That is, under the condition of knowing the target socket pose (but with a certain error), perform subsequent operations. Specifically:

[0055] Step 2: According to the transformation matrix, control the end of the robot to grasp the plug and move it towards the socket so that the plug and the socket form a front - angle - edge contact; in this step, guide the movement of the end of the robot arm according to the 6D spatial pose relationship from the robot arm base coordinate system to the socket. During the movement of the robot, based on the prior information of the z - direction dimension of the connector, add a bias on the basis of the established coordinate system to form a front - angle point contact in the search stage.

[0056] Step 3: Control the plug to move along the x-axis of the coordinate system for the first search, and determine whether a line contact is formed between the plug and the socket. If so, terminate the movement in the x-direction and proceed to Step 4. Otherwise, expand the search range until a line contact is formed. In this step, if the following conditions are met:

[0057]

[0058] Then, the contact state changes from angular contact to line contact;

[0059] Among them,

[0060] In the formula, is the variance of the contact torque, is the variance of the normal force, λ1 is the upper limit value of the normal force variance, γ1 is the upper limit value of the contact torque variance, M(t) is the contact torque, F n (t) is the normal force during the contact process in the x-direction, w i is the weight factor, which controls the influence of historical data on the current calculation. is the mean value of the contact torque, is the mean value of the normal force.

[0061] Step 4: Control the plug to move along the Y-axis of the coordinate system for the second search. At the same time, form a motion constraint through the engagement of the plug pins and the socket grooves and the guiding grooves and chamfer structures, so that the plug and the socket form a complete surface contact in a fitting manner. In this step, the plug contacts the edge of the socket at an inclination angle θ to form a front angular contact, restricting the translation in the z-direction and the rotation around the x / y axes, and translating along the x-axis, causing the plug to slide along the edge of the socket. During the sliding process, due to the geometric guidance of the contact edge, the plug is forced to rotate automatically in the z-direction to align with the socket, thereby converting the line contact between the plug and the socket into a surface contact.

[0062] In this step, if the following conditions are met:

[0063]

[0064] Then, the contact state changes from line contact to surface contact state;

[0065] Among them,

[0066] In the formula, is the variance of the contact torque, is the variance of the normal force, λ1 is the upper limit value of the normal force variance, γ1 is the upper limit value of the contact torque variance, M(t) is the contact torque, F n (t) is the normal force during the contact process in the x-direction, w i is the weight factor, which controls the influence of historical data on the current calculation. is the mean contact moment, is the mean normal force.

[0067] Step Five, under the condition of full surface contact, apply active compliance control to the robot so that the plug pins are pushed into the socket grooves with a constant force not exceeding the threshold until the propulsion termination condition is met, and the rectangular electrical connector assembly is completed. In this step, the contact state of the plug and the socket is judged by constructing a contact state transition index, and the contact state transition index includes:

[0068]

[0069] In the formula, CSI is the contact state transition index, is the variance of the normal force, is the variance of the contact moment, K n is the normal contact stiffness, K t is the tangential contact stiffness.

[0070] In addition, in Step Five, dynamic centering compensation is introduced. The lateral force offset is monitored in real time through a six-axis force sensor built into the gripper, and at the same time, the movement of the robot end is controlled by active compliance. When the lateral contact force of the gripper exceeds the threshold, the stiffness is automatically reduced.

[0071] In an embodiment of the present invention, an electrical connector assembly method under point cloud estimation and geometric constraint search includes the following steps:

[0072] (1) Mount a 3D camera at the end of the UR5 robotic arm, as Figure 2 shown, collect the point cloud of the electrical connector socket part fixed on the surface of the work platform, preprocess the point cloud data, including filtering, sampling and segmentation, extract the plane feature (i.e., the side wall of the connector) of the connector point cloud, establish a target object coordinate system based on this plane, the direction pointed by the plane normal vector is the y direction, the length direction of the rectangular plane is the x direction, and the z direction is obtained by vector cross product, so as to establish the transformation matrix between the camera coordinate system and the target object coordinate system. In addition, through calibration work, the transformation from the robotic arm base coordinate system to the camera coordinate system is completed, and finally the 6D pose relationship between the robotic arm base coordinate system and the electrical connector socket is obtained, including three-dimensional translation and rotation information. When using the pose information to guide the movement of the robotic arm end, consider providing the prior information of the z-direction dimension of the electrical connector, and add an offset on the basis of establishing the coordinate system to form the front corner point contact in the search stage.

[0073] (2) After visually assisting in determining the pose relationship, enter the subsequent assembly stage. The two-finger gripper is planned to be used to control the plug in the assembly stage.

[0074] The entire assembly process is divided into three stages: ① grasping; ② searching; ③ inserting. Starting from the initial position, first replace the end effector of the robotic arm from the 3D camera to the two-finger gripper to grasp the electrical connector plug to be assembled. We perform subsequent operations under the condition that the pose of the target socket is known (but with a certain error).

[0075] There is a certain error in the pose relationship determined by the point cloud information. Considering the initial position relationship between the robot and the plug, based on the above obtained through the point cloud, a certain margin is added in the z direction as the motion instruction of the robot to raise the height of the hole-searching plane to avoid rigid collision at the end.

[0076] (3) Since the geometric size of the electrical connector plug to be assembled is small, to achieve reliable grasping without affecting the assembly joint, the grasping strategy mainly needs to consider the following points: ① The contact area between the plug and the fingers can be used. Multiple grasping strategies can be adopted here, such as clamping contact or parallel grasping of the wire or joint; ② The free space that must be maintained around the connector; ③ Whether a positioning function is required to provide a repeatable position or sufficient assembly force. Adopt a grasping method where the two fingers closely fit the side wall of the electrical connector to ensure that the pose of the plug is relatively stable during the assembly process, and the space near the lower part of the connected plug is free, so that the insertion process is not affected.

[0077] (4) The purpose of the search strategy is to align the plug and the socket. When using mechanical search, the design of the search strategy should consider the following points: ① The change in the covered pose; ② The initial contact between the plug and the socket, which is divided into three categories according to the presentation method of the plug: point contact, line contact, or plane contact - specifically, point contact means that the tip edges of the plug and the socket cross each other, line contact means that the tip edges are aligned but the plug is not contained by the socket, and plane contact means that the outer wall of the plug partially fits the inner or outer wall of the socket; ③ The height of the pins, which may bend if contacted by the tip of the plug; ④ Verify whether the plug has successfully slid into the socket after alignment.

[0078] Based on the above purposes, the mechanical search strategy used here is as follows Figure 3 、 Figure 4 、 Figure 5 as shown (the plug and socket of the assembly model shown in the figure are not the actual electrical connectors used, only for illustrating the search strategy).

[0079] Use an inclined plug for the initial contact, gently pressing the corner of the plug on the edge of the connector, as Figure 2 shown. The movement in the x direction allows the plug to slide into the socket when aligned, as Figure 3 shown. Next, establish contact with the sides of the plug and the socket through the movement in the y direction, as Figure 4 shown.

[0080] At this time, the front corner of the plug should be gently inserted and placed on the edge of the socket. To quickly cover the position uncertainty between the plug and the socket, an open-loop position control is used for searching without using force feedback. After physical contact, based on the guiding groove or chamfer structure of the rectangular connector, the position deviation can be self-corrected, reducing the necessity of real-time force control.

[0081] Explanation of the principle of the search strategy: The above strategy is actually a geometric alignment process of restricting degrees of freedom in stages, achieving alignment by gradually restricting the relative movement degrees of freedom between the plug and the socket: In the first step, the plug contacts the socket edge at an inclination angle θ, forming a point / line contact (the front corner contacts the edge), restricting the translation in the z direction and the rotation around the x / y directions; In the second step, translate in the x direction to make the plug slide along the socket edge. During the sliding process, due to the geometric guidance of the contact edge, the plug is forced to rotate automatically in the z direction to align with the socket (similar to the "guide rail effect"), and then the line contact is converted into a surface contact; In the third step, move along the y-axis to make multiple plug pins fully engage with the socket grooves, restricting two degrees of freedom, the translation in the y direction and the rotation around the z direction, due to geometric interference. Since the plug is contained within the socket, there is a translation degree of freedom in the x direction. However, at this time, the contact relationship changes, and the initial inclined angle point contact has become a fit between planes, so the translation degree of freedom constraint in the z direction is released, and only a single degree of freedom along the insertion direction of the z-axis remains.

[0082] The x direction is the tangential direction during the contact process, and the y direction is the normal direction. Define the normal force F n (t) and the tangential force F t (t) as the measured values at time t, and also consider the contact moment M(t) (to avoid relying only on the change of force). Record and calculate the weighted sliding variance of the sensor data respectively:

[0083]

[0084] where ω i is the weight factor, controlling the influence of historical data on the current calculation. The data closer to the current moment has a higher weight; α controls the attenuation rate of historical data (taking an empirical value of 0.1 - 0.5).

[0085] When the contact state changes from point contact to line contact and finally to surface contact: gradually decreases (contact is stable); decreases to nearly 0 (no slip); first increases and then decreases because line contact is more likely to cause moment changes than point contact, while surface contact tends to be stable. Based on the above points, the determination conditions for the conversion of the contact state can be determined:

[0086] 1. It shows that the contact area becomes larger and the point contact begins to transform into line contact.

[0087] 2. It indicates that the contact area is stable and enters the surface contact state.

[0088] To determine the convergence state, the contact stiffness is estimated by further combining the force-displacement relationship, and the definitions of normal and tangential stiffness are introduced: Construct a contact state index (CSI) to comprehensively judge:

[0089]

[0090] 3. When the CSI drops to a certain threshold, it indicates that the contact is stable. CSI < δ indicates that the contact moment and stiffness of the system have converged and the contact state is stable.

[0091] The above search strategy decouples the 6-degree-of-freedom coupling problem into serial single-degree-of-freedom operations by guiding constraints step by step through geometric features, significantly reducing the assembly complexity. At the same time, according to relevant literature, this staged constraint strategy can reduce the insertion and extraction force by 30-40% and increase the assembly success rate by 5 times.

[0092] (5) For the insertion stage, the following aspects should be considered: ① The control of the double-finger gripper should be able to avoid jamming of the connector - introduce dynamic centering compensation, and monitor the lateral force offset in real time through the six-axis force sensor built into the gripper; at the same time, adopt active compliance control to automatically reduce the stiffness when the lateral contact force exceeds the threshold; ② The assembly force should not exceed a certain threshold to avoid damaging the parts, which can be achieved through the compliance of the fingers. For this purpose, the method in the present invention uses an impedance + position hybrid control mode to keep the pushing force in the z-direction for insertion constant. When the plug part is fully inserted into the socket, a sudden drop in force or the stop of the velocity-displacement curve is detected as the termination condition for the end of assembly.

[0093] The present invention also provides an electrical connector assembly system under point cloud estimation and geometric constraint search for performing the method of any one of the above embodiments or a combination of multiple embodiments, including:

[0094] A first main control module for collecting the point cloud of the side wall of the electrical connector socket, extracting plane features, constructing a coordinate system, and determining the transformation matrix between the robot base coordinate and the socket;

[0095] A second main control module for controlling the robot end to grasp the plug and move it towards the socket according to the transformation matrix, so that the plug and the socket form a front angle-edge contact;

[0096] A third main control module for controlling the plug to move along the X direction of the coordinate system for the first step of search and determining whether the plug and the socket form a line contact. If so, terminate the movement in the X direction and trigger the fourth main control module; otherwise, expand the search range until the plug and the socket form a line contact;

[0097] The fourth main control module is used to control the plug to move along the Y direction of the coordinate system for the second-step search. At the same time, through the engagement of the plug pins and the socket grooves and the formation of motion constraints by the guiding grooves and chamfer structures, the plug and the socket form a complete surface contact in a fitting manner.

[0098] The fifth main control module is used to apply active compliance control to the robot during the complete surface contact, so that the plug pins push into the socket grooves with a constant force not exceeding the threshold until the propulsion termination condition is met, and the rectangular electrical connector assembly is completed.

[0099] Based on any of the above embodiments, the present invention establishes a transformation matrix between the socket and the robot base coordinate system to realize the unification of the coordinate system, providing good guidance for the robot to approach the target efficiently and perform subsequent search and insertion processes.

[0100] Those skilled in the art can easily understand that the above are only the preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. An electrical connector assembly method under point cloud estimation and geometric constraint search, characterized in that It includes the following steps: Step 1: Collect the point cloud of the side wall of the electrical connector socket, extract the planar features, construct a coordinate system, and determine the transformation matrix between the robot base coordinate and the socket. Step 2: According to the transformation matrix, control the end of the robot to grasp the plug and move it towards the socket, so that the plug and the socket form a front angle-edge contact. Step 3: Control the plug to move along the x-direction of the coordinate system for the first search, and determine whether the plug and the socket form a line contact. If so, terminate the movement in the x-direction and enter Step 4. Otherwise, expand the search range until a line contact is formed. Step 4: Control the plug to move along the y-direction of the coordinate system for the second search. At the same time, through the engagement of the plug pins and the socket grooves and the formation of motion constraints by the guide grooves and chamfer structures, the plug and the socket form a conforming full-surface contact. Step 5: Under the condition of full-surface contact, apply active compliance control to the robot, and insert the plug pins into the socket grooves with a constant force not exceeding the threshold until the propulsion termination condition is met, and the rectangular electrical connector assembly is completed.

2. The electrical connector assembly method under point cloud estimation and geometric constraint search according to claim 1, wherein Step 1 includes the following steps: Mount a camera at the end of the robot, collect the point cloud of part of the electrical connector socket fixed on the surface of the work platform, preprocess the point cloud data, extract the planar features of the connector point cloud, that is, the side wall of the connector socket. Based on this side wall plane, establish a target object coordinate system. The direction pointed by the normal vector of the side wall plane is the y-direction, the length direction of the rectangular plane is the x-direction, and the z-direction is obtained by vector cross product, so as to establish the transformation matrix between the camera coordinate system and the target object coordinate system.

3. The electrical connector assembly method under point cloud estimation and geometric constraint search according to claim 2, characterized in that In Step 1, through calibration work, complete the transformation from the mechanical arm base coordinate system to the camera coordinate system, and finally obtain the spatial 6D pose relationship from the mechanical arm base coordinate system to the socket, including three-dimensional translation and rotation information.

4. A method for assembling an electrical connector under point cloud estimation and geometric constraint search according to claim 1, characterized in that In Step 2, guide the movement of the end of the mechanical arm according to the spatial 6D pose relationship from the mechanical arm base coordinate system to the socket. During the movement of the robot, based on the prior information of the z-direction dimension of the connector, add an offset on the basis of the established coordinate system to form a front angle point contact in the search stage.

5. A method for assembling an electrical connector under point cloud estimation and geometric constraint search according to claim 1, characterized in that, In Step 3, if it satisfies: Then, the contact state changes from angular contact to line contact; Among them, In the formula, is the variance of the contact moment, is the variance of the normal force, λ1 is the upper limit value of the variance of the normal force, γ1 is the upper limit value of the variance of the contact moment, M(t) is the contact moment, F n (t) is the normal force in the x - direction during the contact process, w i is the weight factor, which controls the influence of historical data on the current calculation. is the mean value of the contact moment, is the mean value of the normal force.

6. The electrical connector assembly method under point cloud estimation and geometric constraint search according to claim 1, characterized in that In Step 4, the plug contacts the edge of the socket at an inclination angle θ to form a front angle contact, restricting the translation in the z-direction and the rotation around the x / y directions. Translate along the x-direction, so that the plug slides along the edge of the socket. During the sliding process, due to the geometric guidance of the contact edge, the plug is forced to rotate automatically in the z-direction to align with the socket, and then the plug and the socket are converted from line contact to surface contact.

7. A method for assembling an electrical connector under point cloud estimation and geometric constraint search according to claim 1, characterized in that In Step 4, if it satisfies: Then, the contact state enters the surface contact state from the line contact state; Among them, Wherein, is the variance of the contact moment, is the variance of the normal force, which is the same as above here is the variance of the tangential force, λ2 is the lower limit value of the normal force variance, γ2 is the lower limit value of the contact moment variance, M(t) is the contact moment, F n (t) is the normal force during the contact process in the x direction, w i is the weight factor, which controls the influence of historical data on the current calculation. is the mean value of the contact moment, is the mean value of the normal force, is the mean value of the tangential force.

8. A method for assembling an electrical connector under point cloud estimation and geometric constraint search according to claim 1, characterized in that, In Step 5, introduce dynamic centering compensation, monitor the lateral force offset in real time through the six-axis force sensor built in the gripper, and at the same time use active compliance to control the movement of the end of the robot. When the lateral contact force of the gripper exceeds the threshold, automatically reduce the stiffness.

9. The electrical connector assembly method under point cloud estimation and geometric constraint search according to claim 1, characterized in that In Step 5, judge whether the contact state between the plug and the socket is stable by constructing a contact state conversion index. The contact state conversion index includes: Wherein, CSI is the contact state conversion index, is the variance of the normal force, is the variance of the contact moment, K n is the normal contact stiffness, K t is the tangential contact stiffness.

10. An electrical connector assembly system under point cloud estimation and geometric constraint search, characterized in that, It includes: The first main control module is used to collect the point cloud of the side wall of the electrical connector socket, extract the planar features, construct a coordinate system, and determine the transformation matrix between the robot base coordinate and the socket. The second main control module is used to control the end of the robot to grasp the plug and move it towards the socket according to the conversion matrix, so that the plug and the socket form a front angle-edge contact; The third main control module is used to control the plug to move along the x direction of the coordinate system to perform the first-step search, and determine whether the plug and the socket form a line contact. If so, terminate the movement in the x direction and trigger the fourth main control module. Otherwise, expand the search range until the plug and the socket form a line contact; The fourth main control module is used to control the plug to move along the y direction of the coordinate system to perform the second-step search. At the same time, through the engagement of the plug pins and the socket grooves and the formation of motion constraints by the guide grooves and chamfer structures, the plug and the socket form a complete surface contact that fits together; The fifth main control module is used to apply active compliance control to the robot during the complete surface contact, so that the plug pins are inserted into the socket grooves with a constant force not exceeding the threshold until the propulsion termination condition is met, and the rectangular electrical connector assembly is completed.

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