Active-passive compliant combined floating end and force control cooperative large threaded shaft section docking system and method

Abstract

The application discloses a large threaded shaft section docking system and method with floating end and force control cooperation in combination of active and passive compliance, and belongs to the technical field of automatic assembly. The system aims to solve the problem of thread jamming and damage of large heavy threaded workpieces (such as oil drilling rods and wind power tower flanges) in automatic assembly due to the interference of great weight, positioning deviation and rigid impact. The system comprises a six-dimensional force sensor, a passive floating mechanism integrating radial and angular units, and an independent large torque servo rotation unit. The method of the application covers three stages of dynamic gravity compensation, active force control compliant search and active and passive cooperative screwing. By establishing a load centroid identification model, the gravity component of the end is removed, so that the sensor only feeds back pure contact force; in the initial stage of screwing, the physical compliance of the passive mechanism is used to absorb the phase difference of the thread, and then the active axial force cooperation algorithm is used to realize accurate screwing. The application solves the docking difficulty problem of large threaded workpieces caused by weight and positioning error in combination of active and passive compliance, and improves the assembly success rate and quality.

Description

Technical Field

[0001] This invention belongs to the field of automated assembly technology, specifically relating to a system and method for automatic docking and screwing assembly of large threaded shaft components (such as oil pipelines, wind turbine towers, large drive shafts, etc.). Background Technology

[0002] In the field of large equipment manufacturing, there are numerous large threaded shaft segments that require butt joint assembly, such as large pipeline connections, wind turbine tower flange connections, and large drive shaft installations. These components are typically characterized by their large weight, large size, large thread specifications, and high precision requirements for butt joints. Currently, such assembly operations largely rely on manual labor or large specialized tooling.

[0003] Manual operation is the most common traditional method. Workers use hoisting equipment to roughly position the workpiece, then use high-torque wrenches or specialized rotating equipment to tighten it. However, this method is extremely labor-intensive. For workpieces weighing several tons, manual fine-tuning is extremely difficult and time-consuming; it is inefficient and cannot meet the needs of large-scale production; it also poses significant safety risks, as unstable workpiece hoisting or thread jamming can lead to accidents; furthermore, it is difficult to maintain a constant axial tightening force, which can easily cause thread seizing or damage, affecting assembly quality. Currently, the relevant technologies mainly include the following solutions: First, a purely passive floating thread assembly device, such as CN115816042A, which uses elastic elements to passively float the clamp radially and angularly to adapt to the initial deviation of the thread. However, this solution lacks active force sensing and adjustment capabilities, cannot actively control the clamping force, and is difficult to cope with complex positional deviations. Second, a shaft assembly device that combines a force sensor and a floating mechanism, such as CN119910419A, which has a floating clamping mechanism to avoid thread jamming. However, its floating mechanism is mainly used to compensate for coaxiality deviations and does not combine a six-dimensional force sensor to achieve active force control and gravity compensation, and cannot eliminate the interference of the weight of large workpieces on the force control signal. Third, a shaft hole assembly method based on a force control sensor, such as CN113878323A, which uses a force sensor to monitor pressure changes during the assembly process. However, its focus is on pressure detection during the shaft hole insertion stage and does not involve the active-passive collaborative strategy during the thread screwing-in stage.

[0004] 004. In summary, existing technologies have not yet effectively solved the core challenge of automated assembly of large threaded workpieces: how to achieve compliant alignment through active force control while compensating for the interference of enormous self-weight, and how to safely eliminate initial deviations using passive compliance characteristics during the critical thread introduction stage, ultimately achieving high-quality screwing assembly. Therefore, developing a docking system that integrates the advantages of active sensing and passive compliance, and possesses high-precision dynamic gravity compensation capabilities, has become a technological bottleneck in the field of automated assembly of large equipment. Summary of the Invention

[0005] In response to the technical problems of difficult and easily damaged large threaded components in the prior art, such as severe interference with force control, this invention proposes a large threaded shaft segment docking system and method that combines active and passive compliance with floating end and force control coordination. It aims to achieve high-quality compliant screwing assembly through instantaneous response at the physical level and precise compensation at the algorithm level.

[0006] The technical solution provided by this invention is as follows: an industrial robot end effector integrating six-dimensional force sensing and an active-passive composite compliant structure, coupled with a high-torque independent rotating unit. The core of the active-passive compliant floating end effector and the force-controlled coordinated docking system for large threaded shaft segments lies in: using a six-dimensional force sensor to construct an "active sensing layer" and using a passive floating mechanism integrating crossed roller guides and spherical pairs to construct a "physical compliance layer".

[0007] The large threaded shaft docking system, which combines active and passive compliant floating end effectors with force control coordination, includes an industrial robot end effector unit and an independent workpiece clamping and rotation unit.

[0008] The industrial robot end effector unit includes a six-dimensional force sensor, a passive floating mechanism, and a clamping mechanism.

[0009] 009. A six-dimensional force sensor, with a first flange face on its top, is fixedly connected to the end flange of an industrial robot via a first connecting plate. This sensor is used to detect the forces and torques in six degrees of freedom of the docking system in real time. Its readings will be used for subsequent gravity compensation and contact force control, and it is a core component for realizing active force control.

[0010] The passive floating mechanism, connected to the output of a six-dimensional force sensor, integrates a radial floating unit and an angular swing unit. The radial floating unit, composed of crossed roller guides and a first elastic reset element, provides translational displacement compensation in the X, Y, and Z axes. The angular swing unit, composed of a spherical pair and a second elastic reset element, provides attitude compliance capability around each coordinate axis. The passive floating mechanism is a purely mechanical structure, requiring no external power source. The stiffness of the first and second elastic reset elements is preset according to the mass distribution of the first workpiece to ensure that the mechanism is in a central zero position in a non-contact state.

[0011] The clamping mechanism, fixed to the passive floating mechanism via a third connecting plate, is used to grip and secure a first workpiece with internal or external threads. The clamping mechanism includes an upper V-block and a lower V-block, which are connected by a first threaded rod and a second threaded rod, and a fastening nut is used to achieve flexible locking of shaft segments with different diameters.

[0012] In addition, the clamping mechanism can also be a pneumatic gripper.

[0013] The end effector unit may also integrate a vision guidance subsystem, which includes an industrial camera and an image processor mounted on the end of the industrial robot; the industrial camera is used to identify the axial position, end face height and phase information of the thread start point of the second workpiece in real time.

[0014] The independent workpiece clamping and rotating unit includes the following components: Mounting base: A high-rigidity base that is firmly fixed to the ground or workbench with anchor bolts, providing stable support for the entire rotating unit.

[0015] Servo rotary mechanism: Its housing is fixedly connected to the mounting base. The mechanism contains a servo motor and a reducer to provide precise, controllable, high-torque rotational power.

[0016] Chuck: Its back is coaxially fixed to the output flange of the servo rotary mechanism via bolts. This chuck has a self-centering structure and a large clamping force, used to firmly clamp a second workpiece with internal or external threads. When the servo rotary mechanism is started, it will drive the second workpiece to rotate precisely in a fixed position.

[0017] The system integration method described above includes the following three stages: Phase 1: Gravity compensation and force control initialization.

[0018] The industrial robot controller drives the industrial robot to sequentially change the first workpiece into at least 5 different spatial poses, synchronously recording the robot joint angles and the original force and torque readings of the six-dimensional force sensor in each pose. Based on the collected data, the mass m and centroid coordinates (x, y, z) of the overall load formed by the end effector unit and the first workpiece are identified by the least squares algorithm. A dynamic gravity compensation model is established. In the subsequent docking process, the gravity components of each axis of the industrial robot's arm are calculated in real time according to the real-time attitude angle of the industrial robot. The gravity and the zero-position offset of the six-dimensional force sensor are subtracted from the readings of the six-dimensional force sensor to obtain the pure external contact force signal.

[0019] Phase Two: Active Force Control for Smooth Insertion.

[0020] The industrial robot switches to a force / position hybrid control mode, setting the axial direction to force control mode with a desired contact force of a small, constant value; the radial and torsional directions are set to zero-force control mode; the robot performs hole-searching operations based on the gravity-compensated cleaning signal; when the first workpiece contacts the chamfered edge of the second workpiece and generates radial force, the robot actively corrects its posture to reduce the force to zero, achieving automatic alignment of the axis; as the axial insertion depth increases, when the insertion displacement reaches the preset contact threshold, it is determined that the axis and hole are initially aligned, and the robot stops active axial feeding.

[0021] Phase 3: Active and passive coordinated thread insertion.

[0022] The locking release device of the passive floating mechanism is activated, placing it in a fully free-compensated state. The industrial robot applies a preset clamping force along the axial direction, ensuring the threaded end faces of the two workpieces are tightly fitted until the gap of the passive floating mechanism in the negative axial direction is completely eliminated. The servo rotary mechanism is activated, driving the second workpiece to rotate at an extremely low speed. In the initial 1-2 rotations, the passive floating mechanism spontaneously absorbs the radial force and deflection torque generated by the phase difference at the thread starting point using its mechanical compliance, guiding the thread to naturally slide into the meshing track. After successful thread insertion, the system enters the active collaborative mode. Based on the axial traction force detected by the sensor, the industrial robot actively adjusts the axial feed speed, ensuring that the feed amount and rotation amount are matched in real time based on the thread lead.

[0023] The conditions for successful thread insertion are that the axial force detected by the six-dimensional force sensor changes abruptly and enters a stable traction force range, while the torque value is within the preset normal fluctuation range of twisting.

[0024] During the tightening process, the system monitors abnormal fluctuations in torque and axial force in real time. If the values ​​exceed the preset safety threshold, it is determined that the thread is stuck, and the system immediately triggers the automatic retraction program: the servo rotary mechanism rotates in the opposite direction 1-2 times, and the industrial robot synchronously returns to its original position to release stress. After the stress is released, the system attempts to re-execute the import step.

[0025] With a vision camera installed, after the threads are initially engaged, the robot temporarily releases the clamping mechanism, uses the reset element of the passive floating mechanism to return the mechanical center to zero, then clamps it again and adjusts it to the ideal coaxiality based on visual feedback, and then continues to perform deep screwing.

[0026] Compared with the prior art, the present invention has the following significant advantages: (1) Significantly improves the system's fault tolerance and assembly success rate. By combining active force control search insertion and passive compliant guidance, the system effectively solves the docking problems caused by factors such as workpiece machining errors, positioning deviations, and hoisting deformation. Even with certain initial deviations, the system can achieve smooth thread engagement, avoiding thread jamming and damage.

[0027] (2) Protect the threads and improve assembly quality. In the critical thread introduction stage, a passive floating mechanism is used to absorb harmful radial forces instead of using a robot to rigidly correct the deviation, which fundamentally avoids thread scraping and damage caused by delays or inaccuracies in active control.

[0028] (3) To achieve compliant assembly of large and heavy workpieces, dynamic gravity compensation technology eliminates the interference of the end effector and workpiece weight on force control, making fine operation based on micro-contact force possible, which is suitable for assembling large workpieces weighing several tons.

[0029] (4) The system has high reliability. The passive floating mechanism is a purely mechanical structure, requiring no additional sensors or control algorithms, resulting in low cost and high reliability. The active force control algorithm is mature and easy to implement on existing industrial robots. Attached Figure Description

[0030] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0031] Figure 1 This is a schematic diagram of the structure of the present invention. Figure 2 This is a schematic diagram of the structure of an end effector for an industrial robot. Figure 3 Schematic diagram of the independent workpiece clamping and rotating unit; Figure 4 Flowchart of active and passive collaborative docking assembly method for large threaded shaft segments; Figure 5 Schematic diagram of a pneumatic clamping mechanism equipped with a vision system Figure 6 This is a schematic diagram of a pneumatic chuck. In the diagram: 1. Industrial robot; 2. First connecting plate; 3. Six-dimensional force sensor; 4. Second connecting plate; 5. Passive floating mechanism; 6. Third connecting plate; 7. Upper V-block; 8. Lower V-block; 9. First threaded rod; 10. Second threaded rod; 11. First fastening nut; 12. Second fastening nut; 13. Chuck; 14. Servo rotary mechanism; 15. Reducer connecting plate; 16. Reducer; 17. Servo motor; 18. First workpiece; 19. Second workpiece; 20. Worktable; 21. Pneumatic gripper; 22. Vision camera; 23. Pneumatic chuck. Detailed Implementation

[0032] Example 1 A large threaded shaft segment docking system combining active and passive compliant floating end caps with force control coordination, such as... Figure 1 As shown, it includes an end effector unit mounted on the industrial robot 1 and an independent workpiece clamping and rotating unit mounted on the worktable 20.

[0033] like Figure 2 The industrial robot end effector unit shown includes a six-dimensional force sensor 3, a passive floating mechanism 5, and a clamping mechanism.

[0034] The six-dimensional force sensor 3 has a first flange face on its top, which is fixedly connected to the end flange of the industrial robot 1 via a first connecting plate 2. This sensor is used to detect the forces and torques in six degrees of freedom of the docking system in real time. Its readings will be used for subsequent gravity compensation and contact force control, and it is a core component for realizing active force control. The six-dimensional force sensor 3 has a digital filtering module with a frequency greater than 500Hz.

[0035] The passive floating mechanism 5 has a second flange face on its top, which is fixedly connected to the bottom second connecting plate 4 of the six-dimensional force sensor by bolts. This mechanism is a non-powered, purely mechanical structure, integrating a radial floating unit and an angular swing unit, giving it the ability to float radially and swing angularly. This mechanism is used to passively absorb and accommodate the radial force and deflection torque generated by the axial misalignment or angular deviation between the first and second workpieces during the initial thread engagement stage, guiding the thread to naturally engage and avoiding jamming caused by rigid contact.

[0036] The clamping mechanism, designed according to the shaft segment structure, is used to rigidly grip and fix the first workpiece 18 with internal threads, and is connected to the passive floating mechanism 5 through the third connecting plate 6.

[0037] The clamping mechanism uses upper V-block 7 and lower V-block 8 to grip the first workpiece 18 and locks it in place via first screw 9, second threaded rod 10, first fastening nut 11, and second fastening nut 12. Figure 3 The servo rotary mechanism 14 shown drives the chuck 13 to grip the second workpiece 19, which rotates under the drive of the servo motor 17 and the reducer 16. Based on the above system, the docking of the externally threaded workpiece 19 and the internally threaded workpiece 18 is performed as follows: Figure 5 As shown, the specific method is as follows: Phase 1: Gravity Compensation and Force Control Preparation (1) Industrial robot 1 grabs internal thread workpiece 18, moves it to the vicinity of the assembly station, and records the current angles of each joint of industrial robot 1.

[0038] (2) The controller of the industrial robot 1 collects the readings of the six-dimensional force sensor 3 in the current pose.

[0039] (3) The industrial robot 1 changes to 5 different postures in sequence, and records the readings of the six-dimensional force sensor 3 and the kinematic parameters of the industrial robot 1 in each posture.

[0040] (4) Identify the center of mass and mass of the end effector unit, and establish a gravity compensation model to compensate for the gravity components of the six axes. After compensation, the reading of the six-dimensional force sensor 3 returns to zero, and only outputs the external contact force.

[0041] In this embodiment, the gravity compensation model is established and executed as follows: The purpose of gravity compensation is to subtract the influence of self-weight and the zero point from the measured value to obtain the pure external contact force. This is achieved by collecting... The zero-point force of the sensor is obtained from sensor data under different orientations. Simultaneously calculate the coordinates of the load's center of mass in the sensor coordinate system. And the tilt angle of the six-dimensional force sensor 3. , When there is no external force, the torque measured by the six-dimensional force sensor 3 satisfies a linear relationship:

[0042] in , , As an intermediate variable, After stacking the data sets, the centroid coordinates are obtained by solving the least squares method. The gravity vector in the world coordinate system The gravity component is obtained by transforming the coordinates to the sensor coordinate system. The force measured by the six-dimensional force sensor 3 satisfies:

[0043] The equation can be rearranged into a linear form. Similarly, the solution is obtained using the least squares method. ,in For inclusion The combination of quantities, solved inversely, yields:

[0044]

[0045]

[0046] At the same time, zero-point force can be obtained. Combined with the already obtained , , The coordinates of the center of mass can be used to calculate the zero-point torque.

[0047] During the actual assembly process, based on the current posture angle of industrial robot 1 and the identified installation tilt angle Calculate the rotation matrix from the world coordinate system to the sensor coordinate system. Transform the gravity vector to the sensor coordinate system:

[0048] The torque generated by gravity can be calculated:

[0049] Calculate the external contact force:

[0050] Calculate the external contact torque:

[0051] income This refers to the external force / torque that actually acts on the end effector unit, and can be used for force-controlled assembly.

[0052] Phase Two: Active Force Controlled Compliant Insertion (1) Industrial robot 1 switches to force / position hybrid control mode. Control settings: axial force control is used, with a desired contact force of 10N; radial force control is used, with a desired force of 0N; attitude angle force control is used, with a desired torque of 0Nm; the robot adjusts its posture in real time based on sensor feedback.

[0053] (2) The industrial robot 1 moves slowly, bringing the shaft end of the internally threaded workpiece 18 close to the opening of the externally threaded workpiece 19. When it contacts the edge of the opening, the six-dimensional force sensor 3 detects the radial force, and the industrial robot 1 responds immediately, adjusting its position to make the radial force zero, while the axial force is maintained at 10N, thus realizing hole searching and automatic centering.

[0054] (3) As the insertion depth increases, when the joint encoder of the industrial robot 1 reports that the insertion depth has reached the preset threshold, it is determined that the initial engagement of the shaft hole is completed and the axial feed is stopped.

[0055] Phase 3: Active and Passive Coordination Threading (1) Axial clamping: Turn off the force control system, but turn on the force monitoring of the six-dimensional force sensor 1, and at the same time turn on the floating end 5. The industrial robot 1 slowly feeds along the axis until the axial (negative) floating amount of the floating mechanism 5 is completely eliminated. In this way, the end effector unit holding the workpiece 18 will be moved axially by the robotic arm until the threads of the workpiece 18 and workpiece 19 are in contact and clamped. The six-dimensional force sensor 3 monitors and stops feeding when the thread clamping force reaches 50N.

[0056] (2) Start rotation: The servo rotary mechanism 14 in the independent unit starts at a very low speed, such as 1 rpm, and drives the internal thread workpiece 19 to rotate through the chuck 13.

[0057] (3) Passive Compliant Introduction: In the initial 1-2 rotations, due to the phase difference between the starting points of the internal and external threads or a slight misalignment of the axis, radial force and deflection torque are generated during contact. These forces / torques act directly on the passive floating mechanism 5 at the end through the internal threaded workpiece 18. This mechanism immediately generates a slight radial slip or angular oscillation, thereby conforming to the helical trajectory of the external thread and allowing the internal threaded workpiece 18 to automatically slide into the correct thread track.

[0058] (4) Active feed coordinated screwing: After the thread is successfully introduced, the threaded pair itself will generate a forward traction force. Under the action of the traction force, the gripper and the workpiece will feed axially, gradually using up the axial (positive) floating amount of the floating end. When the force sensor monitors that the axial force is greater than 50N, the system enters the active feed coordinated mode: the robot restarts the axial force control, and starts to actively and accurately feed axially according to the traction force of the thread. Through force control, the feed speed is strictly matched with the rotation speed of the servo rotary mechanism 14.

[0059] (5) Tightening process monitoring: Throughout the tightening process, the control system continuously monitors the axial force and torque readings of the six-dimensional force sensor 3. When the real-time monitored torque value reaches the preset target torque, the rotation and feed are stopped, and the assembly is completed. If, during the tightening process, the axial force or torque is detected to fluctuate violently and exceed the safety threshold, it is determined that the thread is stuck. The system immediately stops the rotation and feed and executes the preset retraction program: the servo rotary mechanism 14 rotates in the opposite direction 1-2 times, while the industrial robot 1 retracts slightly according to the lead to release stress. After loosening, try to re-import according to steps (1)-(4) of this stage. If the number of retries exceeds the preset maximum value, the system alarms and prompts manual intervention.

[0060] Compared with traditional methods, this invention improves assembly efficiency and quality. A detailed comparison is shown in the table below: ; Example 2 This embodiment is basically the same as Example 1, except for the type and configuration of the clamping mechanism. For example... Figure 5 and Figure 6 As shown, the clamping mechanism is a pneumatic gripper 21, paired with a vision camera 22. Additionally, the rotary unit uses a pneumatic chuck 23 to clamp the workpiece. This embodiment is suitable for assembly scenarios requiring rapid workpiece switching. The method for docking the second workpiece 19 with the first workpiece 18 based on the above system is as follows: Phase 1: Visual Guidance and Grasping (1) Positioning and clamping of the second workpiece 19: The second workpiece 19 on the worktable is photographed by the camera 22, and the control system identifies its position and posture. The industrial robot 1 grasps the second workpiece 19 and, according to the visual recognition result, accurately places it in the pneumatic chuck 23. The control system sends a signal, the pneumatic chuck 23 clamps, and the clamping status sensor confirms successful clamping.

[0061] (2) Gripping of internal threaded workpiece: Camera 22 identifies the posture of the first workpiece 18 on the worktable. The industrial robot 1 adjusts its own posture according to the visual recognition result and grips the first workpiece 18.

[0062] (3) Identification of the axis of the external threaded workpiece: The camera 22 captures the image of the second workpiece 19, which is fixed on the pneumatic chuck 23, and accurately identifies its axis position and orientation. This information is used for the initial guidance of subsequent force-controlled insertion.

[0063] Phase Two: Gravity Compensation and Force Control Preparation (1) Industrial robot 1 changes to 5 different postures in sequence, and records sensor readings and robot kinematic parameters in each posture.

[0064] (2) The controller identifies the center of mass and mass of the end effector unit and establishes a gravity compensation model to compensate for the gravity components of the six axes. After compensation, the force sensor readings return to zero, and only the external contact force is output.

[0065] Phase Three: Active Force Controlled Compliant Insertion (1) The industrial robot 1 moves the first workpiece 18 to the vicinity of the opening of the second workpiece 19 based on the axis information of the second workpiece 19 recognized by vision, and initially aligns it.

[0066] (2) Industrial robot 1 switches to force / position hybrid control mode, which is the same as stage two of embodiment 1: axial constant force of 10N insertion, radial and angular zero force control to achieve hole search and automatic centering.

[0067] (3) When the encoder feedback of the industrial robot 1 joint reaches the preset threshold, it is determined that the initial engagement of the shaft hole is completed and the axial feed is stopped.

[0068] Phase 4: Active and Passive Coordination Threading (1) Axial clamping and floating preparation: Turn off the force control system, but turn on the force monitoring of the six-dimensional force sensor 3, and simultaneously turn on the passive floating mechanism 5. The industrial robot 1 slowly feeds along the axial direction until the axial (negative) floating amount of the floating mechanism 5 is completely eliminated, so that the first workpiece 18 and the second workpiece 19 are in threaded contact and clamped. The force sensor monitors the axial force, and stops feeding when the clamping force reaches 50N.

[0069] (2) Start rotation: The servo rotary mechanism 14 in the independent unit starts at a very low speed (e.g., 1 rpm) and drives the second workpiece 19 to rotate through the pneumatic chuck 23.

[0070] (3) Passive Compliant Engagement: In the initial 1-2 rotations, due to the phase difference between the starting points of the internal and external threads or a slight misalignment of the shaft, radial force and deflection torque are generated upon contact. These forces / torques act directly on the passive floating mechanism 5 at the end through the first workpiece 18. This mechanism immediately generates a slight radial slide or angular oscillation, causing the first workpiece 18 to automatically slide into the correct thread track, achieving initial engagement.

[0071] (4) Mid-course correction: Release - return to zero - re-grip - adjust After approximately 1-2 turns of tightening and initial thread engagement, the system performs a mid-way correction operation: (4a) Release the pneumatic gripper 21: The industrial robot 1 maintains its current position, and the control system sends a signal to temporarily release the gripper of the first workpiece 18. At this time, the first workpiece 18 is maintained in connection only by the thread engagement with the second workpiece 19.

[0072] (4b) Close the floating end and return to zero: The industrial robot 1 moves away a small distance (e.g., 10mm) and then controls the passive floating mechanism 5 to perform a zero-return operation (e.g., by a cylinder or spring reset mechanism) to return the floating platform to the center zero position and eliminate the displacement and angle deviation caused by the previous floating.

[0073] (4c) Re-grip workpiece 18: The industrial robot 1 moves back to the vicinity of the first workpiece 18 and, guided by the vision system or force, re-aligns and clamps the first workpiece 18. Since the first workpiece 18 has now been partially screwed into the workpiece 19, its posture is constrained by the thread, and re-gripping can eliminate the gripping point deviation caused by the previous floating.

[0074] (4d) Force-controlled pose adjustment: After re-grabbing, industrial robot 1 activates the active force control mode to perform brief pose fine-tuning. The control objectives are: to return the radial force and deflection torque to zero, ensuring that the posture after gripping is ideally aligned with the thread axis.

[0075] (5) Active Feed Coordinated Twisting: After completing the above corrections, the system re-enters the twisting mode. At this time, only one industrial robot activates axial force control, and starts to actively and precisely perform axial feed according to the traction force of the thread. Through force control, the feed speed and the rotation speed of the rotary mechanism are strictly matched. As twisting proceeds, the workpiece will be axially fed under the action of the thread traction force.

[0076] (6) Tightening process monitoring and anomaly handling: Similar to Example 1, continuously monitor the axial force and torque readings, and stop when the target torque is reached; if thread jamming occurs (axial force or torque fluctuates drastically beyond the safety threshold), execute the retraction procedure: the rotary mechanism rotates in the opposite direction 1-2 times, the robotic arm retracts slightly according to the lead, releases stress, and then attempts to reintroduce. If the number of retries exceeds the preset maximum value, the system alarms.

Claims

1. A large threaded shaft segment docking system that combines active and passive compliant floating end-effectors with force control coordination, characterized in that, The system includes an execution unit, an actuator unit integrated into the end of an industrial robot (1), and an independent workpiece clamping and rotation unit, used to realize the automated docking and screwing assembly of the first workpiece (18) and the second workpiece (19); the end actuator unit includes a six-dimensional force sensor (3), whose input end is rigidly connected to the end of the industrial robot (1) through a first connecting plate (2), used to detect the force and torque signals of the system in three-dimensional translation and three-dimensional rotational degrees of freedom in real time; a passive floating mechanism (5), connected to the output end of the six-dimensional force sensor (3), which integrates a radial floating unit and an angular swing unit; the radial floating unit is composed of a cross roller guide and a first elastic reset element, providing translational displacement compensation in the X, Y, and Z axis directions; The angular swing unit is composed of a spherical pair and a second elastic reset element, providing attitude compliance capability around each coordinate axis; the clamping mechanism is fixed to the passive floating mechanism (5) through the third connecting plate (6), and is used to grip and fix the first workpiece (18) with internal or external threads; the independent workpiece clamping and rotating unit includes a mounting base, which is fixed on the external worktable (20) to provide high rigidity support for the entire rotation process; the servo rotary mechanism (14) is fixed to the mounting base and integrates a servo motor (17) and a reducer (16) to output controlled constant speed or large torque; the chuck (13) is coaxially mounted on the output shaft of the servo rotary mechanism (14) to clamp and drive the second workpiece (19) to rotate.

2. The large threaded shaft segment docking system with active and passive compliant combined floating end and force control coordination as described in claim 1, characterized in that, The passive floating mechanism (5) is a purely mechanical structure that does not require external energy to drive it. The stiffness of the first elastic reset element and the second elastic reset element is preset according to the mass distribution of the first workpiece (18) to ensure that the mechanism is in the center zero position in a non-contact state.

3. The large threaded shaft segment docking system with active and passive compliant combined floating end and force control coordination as described in claim 1, characterized in that, The clamping mechanism includes an upper V-block (7) and a lower V-block (8). The upper and lower V-blocks are connected by a first threaded rod (9) and a second threaded rod (10), and (12) is used to achieve flexible locking of shaft segments with different diameters.

4. The large threaded shaft segment docking system with active and passive compliant combined floating end and force control coordination as described in claim 1, characterized in that, The clamping mechanism is a pneumatic gripper (21).

5. The large threaded shaft segment docking system with active and passive compliant combined floating end and force control coordination as described in claim 1, characterized in that, It also integrates a vision guidance subsystem, which includes an industrial camera (22) installed at the end of the industrial robot (1) and an image processor; the industrial camera (22) is used to identify the axial position, end face height and phase information of the thread start point of the second workpiece (19) in real time.

6. The large threaded shaft segment docking system with active and passive compliant combined floating end and force control coordination as described in claim 1, characterized in that, The six-dimensional force sensor (3) is equipped with a digital filtering module for filtering out inertial force noise generated by the motion acceleration of the industrial robot (1), and its communication frequency is not lower than 500Hz.

7. A large threaded shaft segment docking system based on the active-passive compliant combined floating end and force control coordination as described in any one of claims 1 to 6, characterized in that, The method comprises the following three collaborative phases.

8. The method for connecting large threaded shaft segments using a combination of active and passive compliant coupling as described in claim 7, characterized in that, The condition for successful thread insertion is that the axial force detected by the six-dimensional force sensor (3) changes abruptly and enters a stable traction force range, while the torque value is within the preset normal twisting fluctuation range.

9. The method for connecting large threaded shaft segments using a combination of active and passive compliant coupling as described in claim 7, characterized in that, During the screwing process in the third stage, the system monitors abnormal fluctuations in torque and axial force in real time. If the value exceeds the preset safety threshold, it is determined that the thread is stuck, and the system immediately triggers the automatic return program: the servo rotary mechanism (14) rotates in the opposite direction for 1-2 turns, and the industrial robot (1) returns to its original position to release stress. After the stress is released, the import step is re-executed.

10. The method for connecting large threaded shaft segments using a combination of active and passive compliant coupling as described in claim 7, characterized in that, The method also includes a vision-based mid-course correction step: after the threads are initially engaged, the robot temporarily releases the clamping mechanism, uses the reset element of the passive floating mechanism (5) to achieve the mechanical center returning to zero, then clamps again and adjusts to the ideal coaxiality according to visual feedback, and then continues to perform deep screwing.

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