Method and system for electrical connector assembly under point cloud estimation and geometric constraint search

Abstract

The application belongs to the technical field of automatic control, and particularly discloses a kind of point cloud estimation and geometric constraint search under electric connector assembly method and system. Including: collecting electric connector socket side wall point cloud, extracting plane feature, constructing coordinate system and determining the conversion matrix of robot base coordinate and socket;Control robot end to grasp plug to move to socket, so that plug and socket form front angle-edge contact;Control plug to move along the x direction of coordinate system to carry out first step search, and determine whether plug and socket form line contact;Control plug to move along the y direction of coordinate system to carry out second step search, simultaneously through the engagement of plug pin and socket groove and guide groove, chamfer structure forms movement constraint, so that plug and socket form complete face contact of fit;Active compliant control is applied to robot, so that plug pin is inserted into socket groove with constant force not exceeding threshold value.The application ensures the accuracy and reliability of the assembly process.

Description

Technical Field

[0001] This invention belongs to the field of automatic control technology, and more specifically, relates to an electrical connector assembly method and system under point cloud estimation and geometric constraint search. Background Technology

[0002] In the space environment, manual operation is limited by factors such as space, gravity, and temperature, making it difficult and risky. Space robots can perform complex tasks in confined and extreme environments, avoiding astronauts' exposure to dangerous conditions and effectively expanding the boundaries of human space exploration. They are becoming the mainstream choice for major spacefaring nations to further develop their space programs. Currently, existing space robots are mainly used for handling larger objects and grasping objects with simple geometric shapes, possessing a certain degree of operational flexibility. However, in complex and delicate tasks (such as assembling precision electrical connectors in microgravity environments), their operational precision and flexibility remain limited. The J30J square electrical connector has high reliability and high durability, making it a common choice for power connection, data transmission, and signal transmission in the aerospace field. Robotic assembly of this type of connector involves complex and delicate space operations that integrate a sequence of actions such as guidance, positioning, alignment, pressing, and locking. Achieving automated robotic assembly of square electrical connectors under vision-force coordination is of great significance.

[0003] To address the problem of screwing and assembling electrical connectors, patent document CN114571456A discloses an electrical connector assembly method and system based on robot skill learning. The method adjusts the electrical connector to be assembled in an initial pose based on image information, controls a robot to carry the connector to contact the assembly hole, and performs trajectory search. The pose and contact force of the robot's end effector carrying the connector are used as input values ​​to a pre-constructed robot assembly skill learning network, and the joint angle of the robot's next action 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 status of the electrical connector is determined based on the assembly depth and contact force within the assembly hole.

[0004] Patent document CN118721193A discloses a robot force-sensing assembly method for spatial electrical connectors in arbitrary postures. After the plug and socket make single-point contact, the angular range of the plug and socket is identified by combining the inverted conical diffusion motion with the sudden change in contact torque. For small-angle contact, the direction of the sudden change in contact torque is recorded as the corresponding plug and socket as a two-point contact state. For large-angle contact, the tracking error of the spiral motion trajectory is used to determine whether the single-point contact is a bottom contact or a side contact. In the two-point contact state, a desired contact force is set along the end to guide the plug to move along the surface of the socket to achieve Z-axis alignment of the plug and socket. A desired contact torque is set along the Z-axis of the plug to drive the protective grooves of the plug and socket to align.

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

[0006] To address the aforementioned deficiencies or improvement needs of existing technologies, this invention provides an electrical connector assembly method and system based on point cloud estimation and geometric constraint search. Combining the characteristics of active compliant robot control with the features of rectangular electrical connectors, a coordinate system is constructed by acquiring point clouds of the connector socket sidewalls and extracting planar features. Simultaneously, the transformation matrix between the robot's base coordinates and the socket is determined, providing a precise spatial positioning basis for subsequent assembly operations. This enables the robot to accurately move the plug to the designated position, improving assembly accuracy. During the assembly process, front corner-edge contact, line contact search along the x-direction, and surface contact search along the y-direction are performed sequentially. By judging contact state transition conditions and implementing corresponding adjustment strategies, such as expanding the search range and introducing dynamic centering compensation, the relative position and attitude of the plug and socket are continuously optimized, ensuring the accuracy and reliability of the assembly process and effectively avoiding assembly failures or poor contact caused by positional deviations.

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

[0008] Step 1: Collect point cloud data of the side wall of the electrical connector socket, extract planar features, construct a coordinate system, and determine the transformation matrix between the robot's base coordinates and the socket;

[0009] Step 2: According to the transformation matrix, control the robot end effector to move the gripper plug toward the socket, so that the plug and socket form front corner-edge contact;

[0010] Step 3: Control the plug to move along the x-direction of the coordinate system to perform the first step of the search and determine whether the plug and socket form a line contact. If so, stop moving in the x-direction and proceed to 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 step of the search. At the same time, the engagement of the plug pins with the socket groove, as well as the guide groove and chamfer structure, form motion constraints, so that the plug and socket form a complete surface contact.

[0012] Step 5: Under the condition of complete surface contact, apply active compliant control to the robot and use a constant force not exceeding the threshold to insert the plug pins into the socket groove until the push termination condition is met, and the rectangular electrical connector assembly is completed.

[0013] As a further preferred option, step one includes the following steps:

[0014] A camera is mounted on the end effector of the robot to collect point clouds of the electrical connector socket portion fixed on the surface of the work platform. The point cloud data is preprocessed to extract the planar features of the connector point cloud, namely the connector sidewall. Based on the sidewall plane, a target object coordinate system is established. The direction pointed to by the normal vector of the sidewall plane is the y-direction, the length direction of the rectangular plane is the x-direction, and the cross product of the vectors is the z-direction, thereby establishing the transformation matrix between the camera coordinate system and the target object coordinate system.

[0015] As a further preferred option, in step one, the transformation from the robot arm base coordinate system to the camera coordinate system is completed through calibration, and finally the spatial 6D pose relationship between the robot arm base coordinate system and the socket is obtained, including three-dimensional translation and rotation information.

[0016] As a further preferred option, in step two, the movement of the robotic arm end effector is guided according to the spatial 6D pose relationship between the robotic arm base coordinate system and the socket. During the robot's movement, an offset needs to be added based on the prior information of the connector's z-axis dimension to form the front corner contact during the search phase.

[0017] As a further preferred option, in step three, if the following conditions are met:

[0018]

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

[0020]

[0021] In the formula, For the contact torque variance, λ1 is the upper limit of the normal force variance, γ1 is the upper limit of the contact moment variance, M(t) is the contact moment, and F is the contact moment. n (t) represents the normal force in the x-direction during the contact process, and w i This is a weighting factor that controls the impact of historical data on the current calculation. The average contact torque. This represents the mean normal force.

[0022] As a further preferred embodiment, in step four, the plug contacts the edge of the socket at an angle θ to form a front angular contact, restricting translation in the z direction and rotation around the x / y directions. Translation in 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 changing the contact between the plug and the socket from line contact to surface contact.

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

[0024]

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

[0026] in,

[0027] In the formula, For the contact torque variance, The variance of the normal force is the same as above. λ2 is the variance of tangential force, λ2 is the lower limit of the variance of normal force, γ2 is the lower limit of the variance of contact moment, M(t) is the contact moment, and F n (t) represents the normal force during the contact process in the x-direction, w i This is a weighting factor that controls the impact of historical data on the current calculation. The average contact torque. The mean normal force, This represents the average tangential force.

[0028] As a further preferred option, in step five, dynamic centering compensation is introduced. The lateral force offset is monitored in real time by the six-axis force sensor built into the gripper. At the same time, active compliant control is adopted to control the robot end effector. When the lateral contact force of the gripper exceeds the threshold, the stiffness is automatically reduced.

[0029] As a further preferred embodiment, in step five, the stability of the contact state between the plug and the socket is determined by constructing a contact state transition index, wherein the contact state transition index includes:

[0030]

[0031] In the formula, CSI is the contact state transition index. For the variance of the normal force, Let K be the variance of the contact torque. n For normal contact stiffness, K t This refers to the tangential contact stiffness.

[0032] According to another aspect of the present invention, an electrical connector robot assembly system based on point cloud and geometric constraint search is also provided, comprising:

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

[0034] The second main control module is used to control the robot end effector to move the gripper plug toward the socket according to the transformation matrix, so that the plug and the socket form front corner-edge contact;

[0035] 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 of the search and determine whether the plug and socket have formed a line contact. If so, the movement in the x-direction is terminated and the fourth main control module is triggered. Otherwise, the search range is expanded until the plug and 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 to perform the second step of the search. At the same time, the engagement of the plug pins and the socket groove, as well as the guide groove and chamfer structure, form motion constraints to make the plug and socket form a complete surface contact.

[0037] The fifth main control module is used to apply active compliant control to the robot when it is in contact with the complete surface of the contact bar, so that the plug pins are inserted into the socket groove with a constant force not exceeding the threshold until the push termination condition is met, and the rectangular electrical connector assembly is completed.

[0038] In summary, compared with the prior art, the above-described technical solutions conceived by this invention mainly possess the following technical advantages:

[0039] 1. This invention automates the assembly of electrical connectors. A robot can automatically complete the entire process from plug gripping and motion planning to socket assembly based on a pre-set program and transition matrix. This reduces manual intervention, improves assembly efficiency, and is particularly suitable for large-scale production and repetitive assembly tasks. By constructing contact state transition indices and other methods, the robot can quickly and accurately determine whether the contact state of the plug and socket is stable and whether the transition conditions are met. This allows the robot to adjust its assembly strategy in a timely manner, avoiding unnecessary waiting and repeated adjustments, accelerating the assembly process, and improving overall production efficiency.

[0040] 2. This invention introduces active compliance control during the assembly process. The six-axis force sensor built into the gripper monitors the lateral force deviation in real time and automatically adjusts the robot's stiffness and movement based on 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 groove with a constant force that does not exceed the threshold. This effectively avoids damage to the plug or socket caused by excessive force, and improves the reliability of assembly and product quality.

[0041] 3. This invention utilizes the engagement of the plug pins and the socket groove, as well as the motion constraints formed by the guide groove and chamfer structure, to enable the plug and socket to automatically align and form a complete, close-fitting surface contact. This enhances the stability and reliability of the assembly process, reduces assembly deviations caused by human error or mechanical vibration, and ensures the good electrical connection performance and mechanical strength of the electrical connector.

[0042] 4. This invention establishes a transformation matrix between the socket and the robot base coordinate system, achieving coordinate system unification and providing excellent guidance for the robot to efficiently approach the target and perform subsequent search and insertion processes. The 6-DOF constraint is decomposed into a three-stage geometric alignment (axial alignment → planar fit → vertical insertion). By guiding the constraint step-by-step through geometric features, the 6-DOF coupled problem is decoupled into a serial single-DOF operation, significantly reducing assembly complexity and demonstrating good adaptability to rectangular electrical connectors of different sizes. Attached Figure Description

[0043] Figure 1 This 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 In this embodiment of the invention, the target object coordinate system is established on the side wall of the socket based on planar features in real point cloud data.

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

[0046] Figure 4 This is the first step of the search in the x-direction sliding of the plug involved in the embodiment of the present invention;

[0047] Figure 5 This is a schematic diagram of the second step of searching to form a sidewall fit as the plug is advanced along the y-direction, according to an embodiment of the present invention. Detailed Implementation

[0048] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0049] like Figure 1 As shown in the figure, the robot force-sensing assembly method for a space electrical connector in any posture provided by the embodiment of the present invention is characterized by including the following steps:

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

[0051] Based on any of the above embodiments or combinations of embodiments, in this step, a camera is mounted on the end of the robot to collect point clouds of the electrical connector socket portion fixed on the surface of the work platform. The point cloud data is preprocessed to extract the planar features of the connector point cloud, namely the connector sidewall. A target object coordinate system is established based on the sidewall plane. The direction pointed to by the normal vector of the sidewall plane is the y direction, the length direction of the rectangular plane is the x direction, and the cross product of the vectors is the z direction, thereby establishing the transformation matrix between the camera coordinate system and the target object coordinate system.

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

[0053] More specifically, in this step, a camera is mounted on the robot's end effector. This camera acquires point clouds of the electrical connector socket portion fixed to the surface of the work platform. The point cloud data is preprocessed, including filtering, sampling, and segmentation, to extract the planar features of the connector point cloud (i.e., the connector sidewalls). Based on this plane, a target object coordinate system is established, with the plane normal vector pointing in the y-direction, the rectangular plane length direction in the x-direction, and the vector cross product yielding the z-direction, thereby establishing a transformation matrix between the camera coordinate system and the target object coordinate system. In this embodiment, the preprocessing of the point cloud data, including filtering, sampling, and segmentation, and the extraction of planar features from the connector point cloud, can employ conventional methods of point cloud data processing and planar feature extraction in existing technologies, which will not be elaborated upon in detail here.

[0054] Based on the transformation matrix, the robot's end effector is controlled to move from the plug to the socket. During the movement, a search strategy is constructed to control the robot's end effector movement. Starting from the initial position, the end effector is first replaced by a two-finger gripper, which grasps the electrical connector plug to be assembled. That is, subsequent operations are performed with the target socket pose known (but with some error). Specifically:

[0055] Step 2: According to the transformation matrix, control the robot end effector to move the gripper plug toward the socket so that the plug and socket form front corner-edge contact. In this step, the robot end effector is guided to move according to the spatial 6D pose relationship from the robot base coordinate system to the socket. During the robot's movement, an offset needs to be added to the coordinate system based on the prior information of the connector's z-axis dimension in order to form front corner contact during the search phase.

[0056] Step 3: Control the plug to move along the x-axis of the coordinate system to perform the first step of the search and determine whether the plug and socket form line contact. If so, terminate the movement in the x-axis and proceed to step 4; otherwise, expand the search range until 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] in,

[0060] In the formula, For the contact torque variance, λ1 is the upper limit of the normal force variance, γ1 is the upper limit of the contact moment variance, M(t) is the contact moment, and F is the contact moment. n (t) represents the normal force in the x-direction during the contact process, and w i This is a weighting factor that controls the impact of historical data on the current calculation. The average contact torque. This represents the mean normal force.

[0061] Step four involves controlling the plug to move along the Y-axis of the coordinate system for the second-step search. Simultaneously, the engagement of the plug pins with the socket groove, along with the guide groove and chamfered structure, creates motion constraints, ensuring a complete, close-fitting surface contact between the plug and socket. In this step, the plug contacts the socket edge at an angle θ, forming a front angular contact. This restricts translation in the z-direction and rotation around the x / y directions. Translation along the x-direction allows the plug to slide along the socket edge. During this sliding process, the geometric guidance of the contact edge forces the plug to rotate in the z-direction to automatically align with the socket, thus transforming the plug and socket from line contact to 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.

[0065] in,

[0066] In the formula, For the contact torque variance, λ1 is the upper limit of the normal force variance, γ1 is the upper limit of the contact moment variance, M(t) is the contact moment, and F is the contact moment. n (t) represents the normal force in the x-direction during the contact process, and w i This is a weighting factor that controls the impact of historical data on the current calculation. The average contact torque. This represents the mean normal force.

[0067] Step 5: Under complete surface contact conditions, apply active compliant control to the robot, causing the plug pins to advance into the socket groove with a constant force not exceeding a threshold until the advancement termination condition is met, thus completing the assembly of the rectangular electrical connector. In this step, a contact state transition index is constructed to determine whether the contact state between the plug and socket is stable. The contact state transition index includes:

[0068]

[0069] In the formula, CSI is the contact state transition index. For the variance of the normal force, Let K be the variance of the contact torque. n For normal contact stiffness, K t This refers to the tangential contact stiffness.

[0070] In addition, in step five, dynamic centering compensation is introduced. The lateral force offset is monitored in real time by the built-in six-axis force sensor of the gripper. At the same time, active compliant control is adopted to control the robot end effector. When the lateral contact force of the gripper exceeds the threshold, the stiffness is automatically reduced.

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

[0072] (1) A 3D camera is mounted on the end effector of the UR5 robotic arm, such as Figure 2 As shown, point clouds of the electrical connector socket portion fixed on the surface of the work platform are collected. The point cloud data undergoes preprocessing, including filtering, sampling, and segmentation, to extract the planar features of the connector point cloud (i.e., the connector sidewalls). Based on this plane, a target object coordinate system is established, with the plane normal vector pointing in the y-direction, the rectangular plane length direction in the x-direction, and the vector cross product yielding the z-direction, thus establishing a transformation matrix between the camera coordinate system and the target object coordinate system. Furthermore, through calibration, the transformation from the robotic arm base coordinate system to the camera coordinate system is completed, ultimately obtaining the 6D spatial pose relationship between the robotic arm base coordinate system and the electrical connector socket, including 3D translation and rotation information. When using the pose information to guide the robotic arm's end effector movement, prior information on the z-axis dimension of the electrical connector is considered, and an offset is added to the established coordinate system to form the front corner contact during the search phase.

[0073] (2) After the pose relationship is determined with visual assistance, the subsequent assembly stage will begin. A two-finger gripper will be used to control the plug during the assembly stage.

[0074] The entire assembly process is divided into three stages: ① gripping; ② searching; ③ insertion. Starting from the initial position, the end effector of the robotic arm is first replaced from a 3D camera to a two-finger gripper to grasp the electrical connector plug to be assembled. Subsequent operations are performed with the target socket pose known (but with some margin of error).

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

[0076] (3) Due to the small geometric dimensions of the connector plug to be assembled, to achieve reliable gripping without affecting the assembly joint, the gripping strategy mainly needs to consider the following points: ① The contact area between the plug and the fingers can be used. Various gripping strategies can be adopted here, such as clamping contact or parallel gripping of the wire or connector; ② The necessary free space around the connector; ③ Whether a positioning function is needed to provide repeatable positioning or sufficient assembly force. A gripping method using two fingers tightly pressed against the sidewall of the connector ensures the relatively stable posture of the plug during assembly and allows for free space near the lower part of the plug, thus preventing interference with the insertion process.

[0077] (4) The purpose of the search strategy is to achieve alignment between the plug and the socket. When using mechanical search, the design of the search strategy should consider the following points: ① Strategy coverage of changes in posture; ② Initial contact between the plug and the socket, which is divided into three categories according to the way the plug is presented: point contact, which means that the tips of the plug and the socket intersect; line contact, which means that the tips of the two are aligned but the plug is not contained by the socket; and planar contact, which means that the outer wall of the plug is in contact with the inner wall or part of the outer wall of the socket; ③ The height of the pins, which may bend if they are in contact with the tip of the plug; ④ Verify whether the plug has successfully slid into the socket after alignment.

[0078] Based on the above objectives, 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 actual electrical connectors used, but are only used to illustrate the search strategy).

[0079] Use the angled plug for initial contact, gently pressing the corner of the plug against the edge of the connector, such as... Figure 2 As shown. Movement in the x-direction allows the plug to slide into the socket during alignment, as... Figure 3 As shown. Next, by moving along the y-direction, contact is established with the sides of the plug and socket, as... Figure 4 As shown.

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

[0081] The principle behind the search strategy is explained as follows: The strategy described above is actually a phased geometric alignment process that restricts the degrees of freedom of the plug and socket. Alignment is achieved by gradually restricting the relative motion degrees of freedom of the plug and socket: First, the plug contacts the edge of the socket at an angle θ, forming a point / line contact (front corner contacts the edge), restricting translation in the z-direction and rotation around the x / y directions. Second, the plug translates along the x-direction, causing it 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 (similar to the "guide rail effect"), thus changing from line contact to surface contact. Third, the plug moves along the y-axis, causing multiple plug pins to fully engage with the socket groove. Geometric interference restricts two degrees of freedom: translation in the y-direction and rotation around the z-direction. Since the plug is contained within the socket, the translational degree of freedom in the x-direction remains. However, at this point, the contact relationship changes; the initial tilted corner point contact has become a planar fit. Therefore, the constraint on the translational degree of freedom in the z-direction is released, leaving only the single degree of freedom along the z-axis insertion direction.

[0082] The x-direction is the tangential direction during the contact process, and the y-direction is the normal direction. The normal force F is defined as follows: n (t) and tangential force F t (t) represents the measured value at time t, taking into account the contact torque M(t) (to avoid relying solely on force changes). The weighted sliding variance of the sensor data is recorded and calculated separately:

[0083]

[0084] Where ω i It is a weighting factor that controls the influence of historical data on the current calculation. The closer the data is to the current moment, the higher the weight. α controls the decay rate of historical data (based on empirical values ​​of 0.1-0.5).

[0085] When the contact state changes from point contact to line contact, and finally to surface contact: Gradually decreasing (contact stabilized); It drops to near 0 (no slip); The torque increases first and then decreases because line contact is more prone to torque changes than point contact, while surface contact tends to be stable. Based on the above points, the criteria for determining the contact state transition can be determined as follows:

[0086] 1. This indicates that the contact area has increased, and the point contact has begun to change into a line contact.

[0087] 2. This indicates that the contact area is stable and has entered a surface contact state.

[0088] To determine the convergence state, contact stiffness is further estimated by combining the force-displacement relationship, and definitions of normal and tangential stiffness are introduced: Construct a Contact State Index (CSI) to make a comprehensive judgment:

[0089]

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

[0091] The aforementioned search strategy decouples the 6-DOF coupled problem into a series of single-DOF operations by guiding constraints step by step using geometric features, significantly reducing assembly complexity. Furthermore, according to relevant literature, this phased constraint strategy can reduce insertion and extraction forces by 30-40% while increasing the assembly success rate by 5 times.

[0092] (5) For the insertion stage, the following aspects should be considered: ① The control of the two-finger gripper should be able to avoid connector jamming—introduce dynamic centering compensation, and monitor lateral force deviation in real time through the built-in six-axis force sensor of the gripper; at the same time, adopt active compliance control, and automatically reduce stiffness when the lateral contact force exceeds the threshold; ② The assembly force should not exceed a certain threshold to avoid damage to the parts, which can be achieved through the compliance of the fingers. To this end, the method in this invention uses an impedance + position hybrid control mode to keep the pushing force of the z-axis 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 based on point cloud estimation and geometric constraint search, for performing the method of any of the above embodiments or a combination of embodiments, including:

[0094] The first main control module is used to collect point clouds of the side wall of the electrical connector socket, extract planar features, construct a coordinate system, and determine the transformation matrix between the robot base coordinates and the socket;

[0095] The second main control module is used to control the robot end effector to move the gripper plug toward the socket according to the transformation matrix, so that the plug and the socket form front corner-edge contact;

[0096] 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 of the search and determine whether the plug and socket have formed a line contact. If so, the movement in the X direction is terminated and the fourth main control module is triggered. Otherwise, the search range is expanded until the plug and 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 to perform the second step of the search. At the same time, the engagement of the plug pins and the socket groove, as well as the guide groove and chamfer structure, form motion constraints to make the plug and socket form a complete surface contact.

[0098] The fifth main control module is used to apply active compliance control to the robot when the contact strip is fully connected, so that the plug pins are pushed into the socket groove with a constant force not exceeding the threshold until the pushing 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, realizing coordinate system unification, and providing good guidance for the robot to efficiently approach the target and perform subsequent search and insertion processes.

[0100] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for assembling electrical connectors under point cloud estimation and geometric constraint search, characterized in that, Includes the following steps: Step 1: Collect point cloud data of the side wall of the electrical connector socket, extract planar features, construct a coordinate system, and determine the transformation matrix between the robot's base coordinates and the socket; Step 2: According to the transformation matrix, control the robot end effector to move the gripper plug toward the socket, so that the plug and the socket form a front corner-edge contact; Step 3: Control the plug to move along the x-direction of the coordinate system to perform the first step of the search and determine whether the plug and socket form a line contact. If so, stop moving in the x-direction and proceed to 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 to perform the second step of the search. At the same time, the engagement of the plug pins with the socket groove, as well as the guide groove and chamfer structure, form motion constraints, so that the plug and socket form a complete surface contact. In step four, if the following conditions are met: ； Then, the contact state changes from line contact to surface contact. in, , , , In the formula, For the contact torque variance, The variance of the normal force is the same as above. For the variance of tangential force, This represents the lower limit of the variance of the normal force. Let F be the lower limit of the contact torque variance, where 𝑀(𝑡) is the contact torque. n (x) represents the normal force during the contact process in the x-direction. As a weighting factor, it controls the impact of historical data on the current calculation. The average contact torque. The mean normal force, The average tangential force; Step 5: Under the condition of complete surface contact, apply active compliant control to the robot and use a constant force not exceeding the threshold to insert the plug pins into the socket groove until the push termination condition is met, and the rectangular electrical connector assembly is completed. In step five, a contact state transition index is constructed to determine whether the contact state between the plug and the socket is stable. The contact state transition index includes: ； In the formula, CSI is the contact state transition index. For the variance of the normal force, For the contact torque variance, For normal contact stiffness, This refers to the tangential contact stiffness.

2. The electrical connector assembly method under point cloud estimation and geometric constraint search according to claim 1, characterized in that, Step one includes the following steps: A camera is mounted on the end effector of the robot to collect point clouds of the electrical connector socket portion fixed on the surface of the work platform. The point cloud data is preprocessed to extract the planar features of the connector point cloud, namely the sidewall of the connector socket. Based on the sidewall plane, a target object coordinate system is established. The direction pointed to by the normal vector of the sidewall plane is the y-direction, the length direction of the rectangular plane is the x-direction, and the cross product of the vectors is the z-direction, thereby establishing 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 one, the transformation from the robot arm base coordinate system to the camera coordinate system is completed through calibration, and finally the spatial 6D pose relationship between the robot arm base coordinate system and the socket is obtained, including three-dimensional translation and rotation information.

4. The electrical connector assembly method under point cloud estimation and geometric constraint search according to claim 1, characterized in that, In step two, the robot arm end effector is guided to move according to the spatial 6D pose relationship between the robot arm base coordinate system and the socket. During the robot's movement, an offset needs to be added based on the prior information of the connector's z-axis dimension to form the front corner contact during the search phase.

5. The electrical connector assembly method under point cloud estimation and geometric constraint search according to claim 1, characterized in that, In step three, if the following conditions are met: ； Then, the contact state changes from angular contact to line contact; in, , , In the formula, For the contact torque variance, For the variance of the normal force, This represents the upper limit of the variance of the normal force. Let F be the upper limit of the contact torque variance, where 𝑀(𝑡) is the contact torque. n (x) represents the normal force in the x-direction during the contact process. As a weighting factor, it controls the impact of historical data on the current calculation. The average contact torque. This represents the mean 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 four, the plug contacts the edge of the socket at an angle θ, forming a front angular contact, which restricts translation in the z direction and rotation around the x / y directions. Translation in 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 changing the contact between the plug and the socket from line contact to surface contact.

7. The electrical connector assembly method under point cloud estimation and geometric constraint search according to claim 1, characterized in that, In step five, dynamic centering compensation is introduced. The lateral force offset is monitored in real time by the built-in six-axis force sensor of the gripper. At the same time, active compliant control is adopted to control the robot end effector. When the lateral contact force of the gripper exceeds the threshold, the stiffness is automatically reduced.

8. An electrical connector assembly system based on point cloud estimation and geometric constraint search, used to implement the electrical connector assembly method based on point cloud estimation and geometric constraint search as described in any one of claims 1-7, characterized in that, include: The first main control module is used to collect point clouds of the side wall of the electrical connector socket, extract planar features, construct a coordinate system, and determine the transformation matrix between the robot's base coordinates and the socket. The second main control module is used to control the robot end effector to move the gripper plug toward the socket according to the transformation matrix, so that the plug and the socket form front corner-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 of the search and determine whether the plug and socket have formed a line contact. If so, the movement in the x-direction is terminated and the fourth main control module is triggered. Otherwise, the search range is expanded until the plug and 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 of the search. At the same time, the engagement of the plug pins and the socket groove, as well as the guide groove and chamfer structure, form motion constraints to make the plug and socket form a complete surface contact. The fifth main control module is used to apply active compliant control to the robot when it is in contact with the complete surface of the contact bar, so that the plug pins are inserted into the socket groove with a constant force not exceeding the threshold until the push termination condition is met, and the rectangular electrical connector assembly is completed.

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