Semi-active variable stiffness compliant assembly end effector and control method

Abstract

The application discloses a semi-active variable stiffness compliant assembly end effector, which comprises a static platform and a dynamic platform, a constraint branch and a plurality of connecting branches located between the static platform and the dynamic platform, one end of the constraint branch is connected to the center point of the static platform, and the other end of the constraint branch is connected to the center point of the dynamic platform; each connecting branch is arranged along the circumference of the constraint branch axis; the constraint branch and each connecting branch is respectively provided with a displacement sensor; and the constraint branch and each connecting branch is connected to the dynamic platform through a force sensor. The anisotropic stiffness of the application is adjustable online, the current of the magneto-rheological damper in the constraint branch and the connecting branches is independently and quickly adjusted, the assembly state can be intelligently identified based on real-time torque information feedback and shaft hole contact mechanics model, the application has the advantages of compact structure and high integration, and the success rate and reliability of assembly are significantly improved.

Description

Technical Field

[0001] This invention relates to the field of precision assembly technology for robots, and in particular to a semi-active variable stiffness compliant assembly end effector and control method. Background Technology

[0002] In the field of precision robotic assembly, shaft-hole assembly tasks require extremely high tolerances. However, the absolute positioning error of industrial robots and workpiece clamping deviations result in millimeter-level positional deviations and degree-level angular deviations between shafts and holes. If a rigid assembly strategy is adopted, even a small alignment error will immediately translate into severe rigid contact forces, leading to part damage, assembly process stagnation, or even failure.

[0003] Currently, the main technologies that give robots compliance include: Active power control (such as impedance control): The output is adjusted in real time through sensor feedback. It has excellent performance, but the system is complex, costly and has limited control bandwidth.

[0004] Passive compliant mechanisms (such as telecentric compliant mechanisms RCC): rely on fixed mechanical structures to provide compliance, are simple and reliable, but their stiffness is not adjustable, cannot adapt to the different requirements of impedance characteristics at different stages of the assembly process, and have poor generalization ability.

[0005] Semi-active variable stiffness mechanisms utilize smart materials such as magnetorheological (MR) or electrorheological (ER) materials to rapidly adjust damping or stiffness through an external field, achieving a balance between response speed and energy consumption. However, most existing semi-active mechanisms still have shortcomings in achieving online reconstruction of multi-degree-of-freedom, anisotropic stiffness fields, and deep integration with macroscopic pose actuation capabilities. Summary of the Invention

[0006] The main objective of this invention is to provide a semi-active variable stiffness compliant assembly end effector and control method, which aims to solve the problems of the current robot compliance technology.

[0007] To achieve the above objectives, the present invention proposes a semi-active variable stiffness compliant assembly end effector, comprising a static platform and a dynamic platform, and a constraint branch and several connecting branches located between the static platform and the dynamic platform. One end of the constraint branch is connected to the center point of the static platform, and the other end of the constraint branch is connected to the center point of the dynamic platform. The connecting branches are arranged sequentially at intervals along the circumferential direction of the constraint branch axis. Displacement sensors are respectively provided on the constraint branches and each of the connecting branches. The constraint branches and each of the connecting branches are respectively connected to the dynamic platform through force sensors.

[0008] Preferably, the constraint branch includes a first elastic spring, a first magnetorheological damper, and two first universal joints. One end of the first magnetorheological damper is detachably connected to the static platform via one of the first universal joints, and the other end of the first magnetorheological damper is detachably connected to the moving platform via the other first universal joint and one of the force sensors. The first elastic spring is sleeved on the outside of the first magnetorheological damper, and both ends of the first elastic spring are respectively connected to the ends of the adjacent first magnetorheological dampers. One of the displacement sensors is respectively connected to both ends of the first magnetorheological damper.

[0009] Preferably, the connecting chain includes a first ball joint, a second spring, a second magnetorheological damper, and a second universal joint. One end of the second magnetorheological damper is detachably connected to the static platform via one of the first ball joints, and the other end of the second magnetorheological damper is detachably connected to the moving platform via another second universal joint and one of the force sensors. The second spring is sleeved on the outside of the second magnetorheological damper, and both ends of the second spring are respectively connected to the adjacent ends of the second magnetorheological damper. One of the displacement sensors is respectively connected to both ends of the second magnetorheological damper.

[0010] To achieve the above objectives, a semi-active variable stiffness compliant assembly end effector control method is also provided, characterized in that, for any of the semi-active variable stiffness compliant assembly end effectors described above, the control method includes: The axial force vector and length vector of the constraint branch and the connecting branch are obtained by each of the displacement sensors and force sensors respectively. Based on the length vectors described, the pose of the moving platform and the tilt angle in the assembly plane are solved in real time using numerical methods. Based on the Jacobian matrix of the moving platform's pose, determine the torque information at the end of the moving platform; The torque information is converted into the contact coordinate system of the shaft connection, and then the dimensionless state point and assembly process state used for jamming determination are calculated. Obtain the friction coefficient, and based on the friction coefficient and the tilt angle, determine the dynamic safety zone using a pin-hole contact mechanics model; Based on the dimensionless state point, the assembly process state, and the dynamic safety region, the control commands for the constraint branches and each connecting branch are determined.

[0011] Preferably, the formula for calculating the torque information is as follows: ; in, This refers to the torque information acting on the end of the moving platform; The Jacobian matrix is ​​the mapping from the length change rate of the constraint branch and each of the connecting branches to the generalized velocity of the moving platform. The axial force vector is composed of the axial forces of the constraint branches and each of the connecting branches; superscript Indicates matrix transpose; superscript This represents the Moore-Penrose generalized inverse.

[0012] Preferably, the formula for calculating the dimensionless state point is as follows: in, This refers to the dimensionless state point; Along the contact coordinate system The radial contact force component in the direction; Along the contact coordinate system The axial contact force component in the direction; For contact coordinate system The contact torque component of the shaft; The radius of the inserted axis; and These are used to normalize the radial contact force component and the contact torque component, respectively.

[0013] Preferably, the step of determining the control commands for the constraint branches and each connecting branch based on the dimensionless state point, the assembly process state, and the dynamic safety region includes: Based on the dimensionless state point, the assembly process state, and the dynamic safety zone, determine the desired torque adjustment amount; The torque adjustment is solved and mapped to the axial damping force change of the constraint branch and each of the connecting branches; The control command is determined based on the change in damping force.

[0014] Preferably, the optimal damping distribution mapping formula for the torque adjustment amount is as follows: ; in, The decision vector is controlled by the excitation current (i.e., the dissipation force amplitude of the constraint branch 3 and each connecting branch 4). The active mapping submatrix (generally the first 5 columns of the Jacobian transpose matrix are taken); It is a diagonal matrix of the transiently driveable quadrant; The desired operating space torque adjustment amount; This is the spatial dimension weight matrix, used to prioritize approximation convergence in higher-dimensional directions under rank deficiency conditions; This represents the regularization coefficient, used to smooth out control chattering caused by the velocity crossing zero point; It is a decision vector composed of the target damping force amplitudes of the magnetorheological dampers in each connected branch of the previous control cycle.

[0015] To achieve the above objectives, [the following is provided].

[0016] Compared with the prior art, the present invention has at least the following beneficial effects: 1. Anisotropic stiffness is adjustable online. By independently and quickly adjusting the current of the magnetorheological dampers in the constraint branches and several connecting branches, the overall stiffness matrix of the end effector in the operating space can be reshaped online and dynamically, realizing the anisotropic distribution of stiffness and breaking through the limitation of fixed stiffness in traditional passive compliant mechanisms.

[0017] 2. Intelligent compliance and proactive anti-jamming: Based on real-time torque feedback and shaft-hole contact mechanics model, it can intelligently identify assembly states (single-point contact and two-point contact risks, etc.). Through state machine decision-making, it exhibits low stiffness to absorb errors when "compliant alignment" is needed, and enhances stiffness in specific directions to stabilize the posture when facing "jamming risks," thus achieving adaptive impedance adjustment.

[0018] 3. The structure is compact and highly integrated. The variable stiffness module (damper and spring) is directly integrated into the sliding pair of each branch, and highly integrated with the force sensor and displacement sensor, forming a compact unit that integrates sensing and execution, which is convenient to connect with industrial robots as a standard module.

[0019] 4. Significantly improves assembly performance. Experiments show that in shaft and hole assembly tasks with ±2mm positional deviation and ±1° angular deviation, this solution can effectively reduce the peak contact force by more than 60% and stabilize the contact force fluctuation within ±5%, significantly improving the success rate and reliability of assembly. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0021] Figure 1 A schematic diagram of a semi-active variable stiffness compliant assembly end effector; Figure 2 This is a schematic diagram of the structure connecting the branches; Figure 3 A structural diagram showing another perspective of the connecting branch; Figure 4 A flowchart illustrating the end-effector control method for semi-active variable stiffness compliant assembly.

[0022] Explanation of icon numbers: 1. Static platform; 2. Dynamic platform; 3. Constraint chain; 31. First elastic spring; 32. First magnetorheological damper; 33. First universal joint; 4. Connecting branch; 41. Second elastic spring; 42. Second magnetorheological damper; 43. Second universal joint; 44. First ball joint; 5. Displacement sensor; 6. Force sensor; The realization of the objective, functional features and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0023] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0024] like Figures 1 to 3 The semi-active variable stiffness compliant assembly end effector shown includes a static platform 1 and a moving platform 2, as well as a constraint branch 3 and several connecting branches 4 located between the static platform 1 and the moving platform 2. One end of the constraint branch 3 is connected to the center point of the static platform 1, and the other end of the constraint branch 3 is connected to the center point of the moving platform 2. Each connecting branch 4 is arranged circumferentially along the axis of the constraint branch 3. Displacement sensors 5 are respectively installed on the constraint branch 3 and each connecting branch 4. The constraint branch 3 and each connecting branch 4 are respectively connected to the moving platform 2 through force sensors 6.

[0025] By employing a parallel mechanism configuration consisting of a static platform 1, a moving platform 2, constraint branches 3, and several connecting branches 4, the end effector achieves multi-degree-of-freedom motion capabilities within the operating space. The constraint branches 3 are located at the center point, and the connecting branches 4 are spaced circumferentially, giving the mechanism a defined five degrees of freedom. This provides a stable mechanical topology foundation for subsequent online reconstruction of the anisotropic stiffness field. The comprehensive deployment of displacement sensors 5 and force sensors 6 (each constraining branch 3 and each connecting branch 4) enables real-time acquisition of the axial force vector and length force vector of each branch. This provides a complete and redundant sensing data source for high-precision forward kinematics and static mapping, avoiding the risk of control failure due to the failure of a single sensor.

[0026] Specifically, the static platform 1 is used to connect to the external robotic arm; the moving platform 2 is used to connect to the external workpiece. Both the static platform 1 and the moving platform 2 are circular plates; the constraint branches 3 and the connecting branches 4 are respectively connected to the edges of the moving platform 2 and the static platform 1.

[0027] Specifically, there are five connecting branches.

[0028] The constraint branch 3 includes a first elastic spring 31, a first magnetorheological damper 32, and two first universal joints 33. One end of the first magnetorheological damper 32 is detachably connected to the static platform 1 through one of the first universal joints 33, and the other end of the first magnetorheological damper 32 is detachably connected to the moving platform 2 through the other first universal joint 33 and one of the force sensors 6. The first elastic spring 31 is sleeved on the outside of the first magnetorheological damper 32, and the two ends of the first elastic spring 31 are respectively connected to the ends of the adjacent first magnetorheological damper 32. One of the displacement sensors 5 is respectively connected to the two ends of the first magnetorheological damper 32.

[0029] The first universal joint 33 allows for detachable connection of the two ends of the constraint branch 3 to the static platform 1 and the moving platform 2, respectively, ensuring the universal rotational freedom of the constraint branch 3 in space. This allows the moving platform 2 to complete the expected pose adjustment under constraint conditions. The series combination of the first magnetorheological damper 32 and the first elastic spring 31 enables the branch to provide semi-active variable stiffness capability while providing mechanical constraints. The first magnetorheological damper 32 provides controllable damping force through current adjustment, while the spring provides basic elastic support. Together, they can achieve continuous adjustment of the axial equivalent stiffness of the constraint branch 3. The displacement sensor 5 is connected to both ends of the first magnetorheological damper 32 to monitor the change in the length of the branch in real time, providing key input data for the forward kinematics solution. The detachable connection method facilitates maintenance and replacement.

[0030] The connecting chain 4 includes a first ball joint 44, a second elastic spring 41, a second magnetorheological damper 42, and a second universal joint 43. One end of the second magnetorheological damper 42 is detachably connected to the static platform 1 through one of the first ball joints 44, and the other end of the second magnetorheological damper 42 is detachably connected to the moving platform 2 through another second universal joint 43 and one of the force sensors 6. The second elastic spring 41 is sleeved on the outside of the second magnetorheological damper 42, and the two ends of the second elastic spring 41 are respectively connected to the ends of the adjacent second magnetorheological damper 42. One of the displacement sensors 5 is respectively connected to the two ends of the second magnetorheological damper 42.

[0031] The stationary platform 1 is connected via a first ball joint 44 (S-joint), and the moving platform 2 (after modification) is connected via a second universal joint 43 (U-joint). This gives the connecting branch 4 the standard configuration of a UPS branch, where the upper second universal joint 43 provides two rotational degrees of freedom, and the lower first ball joint 44 provides three rotational degrees of freedom. Together with the intermediate sliding pair (the second magnetorheological damper 42 and the second spring 41), they constitute a five-degree-of-freedom branch motion capability in space. The series combination of the second magnetorheological damper 42 and the second spring 41 gives each connecting branch 4 independent semi-active variable stiffness capability. By independently adjusting the current of each connecting branch 4, anisotropic stiffness ellipsoids can be reconstructed online within the operating space, achieving differentiated impedance characteristics such as "lateral compliance and rotational stiffness," which is impossible with traditional passive compliant mechanisms (such as RCC). The displacement sensor 5 allows the length of each connecting branch 4 to be monitored in real time, providing data support for real-time updates of the Jacobian matrix and force-displacement closed-loop control.

[0032] Both the first magnetorheological damper 32 and the second magnetorheological damper 42 adopt a shear valve operating mode. The piston and cylinder are made of 20 steel, and the damping medium is Lord's MRF-122ED magnetorheological fluid. By changing the current (0-2A) of the input coil, the damping force can be quickly and continuously adjusted, thereby changing the axial equivalent dynamic stiffness of the branch.

[0033] The following describes a semi-active variable stiffness compliant assembly end-effector control method according to an embodiment of the present invention with reference to the accompanying drawings.

[0034] Figure 4 This is a flowchart illustrating a semi-active variable stiffness compliant assembly end-effector control method.

[0035] Please see Figure 4 To achieve the above objectives, a semi-active variable stiffness compliant assembly end effector control method is provided in the fourth embodiment of the present invention, such as any of the aforementioned semi-active variable stiffness compliant assembly end effectors. The control method includes: Step S10: Obtain the axial force vector and length vector of the constraint branch 3 and the connecting branch 4 respectively through each displacement sensor 5 and each force sensor 6. Step S20: Based on each length vector, the pose of the moving platform 2 and the tilt angle in the assembly plane are solved in real time using numerical methods; wherein, the assembly plane is the plane in which the end effector deflects when subjected to force, and is generally assumed to be the XZ plane in space.

[0036] Step S30: Determine the torque information at the end of the moving platform 2 based on the Jacobian matrix of the pose of the moving platform 2; Step S40: The torque information is converted into the contact coordinate system of the shaft connection, and then the dimensionless state point and assembly process state used for jamming determination are calculated; wherein, the shaft connection is to establish the origin of the contact coordinate system on the end of the inserted shaft (i.e. the end face of the shaft), so that the contact coordinate system can accurately reflect the force state on the contact interface.

[0037] Step S50: Obtain the friction coefficient. Based on the friction coefficient and tilt angle, determine the dynamic safety zone using a pin-hole contact mechanics model. The friction coefficient is obtained through preliminary quasi-static sliding friction experiments at the material interface.

[0038] Step S60: Based on the dimensionless state point, assembly process state, and dynamic safety area, determine the control commands for constraint branch 3 and each connecting branch 4.

[0039] Specifically, the numerical method used is the Newton-Raphson method. Based on the constraint branches and the closed-loop vector chains of each connecting branch, a nonlinear equation system is constructed regarding the spatial pose of the moving platform (including the spatial deflection angle). The Newton-Raphson numerical iteration method is used to solve the nonlinear equation system online, thereby obtaining high-precision pose feedback data containing transient insertion depth and spatial deflection angle, where the spatial deflection angle represents the tilt angle.

[0040] The length constraint equation for the i-th branch in the nonlinear equation system is: in, The pose vector of the moving platform is a five-degree-of-freedom vector. Let be the translational position vector of the center of the moving platform relative to the fixed coordinate system of the static platform; and These are the rotation angles of the moving platform around the two attitude axes, respectively. This is the rotation matrix used to transform the moving platform's fixed coordinate system to the static platform's fixed coordinate system. For the first The position vector of the connection point between the branch and the moving platform in the fixed coordinate system of the moving platform; For the first The position vector of the connection point between the branch and the static platform in the fixed coordinate system of the static platform; For the first The length of each branch is measured in real time by a displacement sensor; For the first Length constraint residuals of branch chains; Each corresponds to one constraint branch and five connection branches.

[0041] The formula for calculating the residual vector, which combines the length constraint equations of the six branches, is as follows: Based on the branch lengths measured in real time by each displacement sensor, the nonlinear equations are solved using the Newton-Raphson iteration method in the least squares sense, thereby obtaining the real-time position and attitude information of the moving platform, and further determining the tilt angle during the shaft hole assembly process.

[0042] Specifically, the dynamic security zone is represented as a dynamic parallelogram-shaped security zone.

[0043] Specifically, the dynamic safety zone is determined based on the shaft-hole contact state. The contact coordinate system is... The origin of the contact coordinate system is set at the end of the insertion axis. The shaft is along the axial direction of the inserted shaft. The shaft is located within the contact plane where the shaft hole is relatively inclined. The axis is determined according to the right-hand rule. This is achieved by converting the torque information at the end of the moving platform to the contact coordinate system. Obtain the contact force component , and contact torque components .

[0044] The force and moment balance relationship of the pin-hole contact mechanics model in the contact coordinate system is as follows: ; in, Contact coordinate system Middle The radial contact resultant force component in the direction; Contact coordinate system Middle The axial contact resultant force component in the direction; For shaft hole contact action around The resultant torque generated by the shaft; and These are the normal contact forces at the first and second contact points, respectively; The coefficient of friction between the contact surfaces of the shaft and the hole; The relative inclination angle between the insertion shaft axis and the hole axis within the contact plane; The radius of the inserted shaft; The second contact point is relative to the origin of the contact coordinate system along... The axial distance in the direction, that is, the lever arm parameter of the normal contact force at the second contact point relative to the origin of the contact coordinate system.

[0045] A complete closed-loop control chain was established, from physical sensing (force sensor 6 and displacement sensor 5) to mathematical model solving (i.e., kinematic forward kinematics for pose calculation, Jacobian kinematics for torque calculation, and coordinate system transformation for state points), and then to control decision-making (i.e., safe zone determination and control command generation). The introduction of the "dynamic safe zone" transforms the anti-jamming problem of shaft-hole assembly into a region constraint problem in state space—changing the control objective from "fuzzy compliance" to "definite geometric boundary constraints," significantly improving the determinism and interpretability of the control. The conversion of torque information to the contact coordinate system directly reduces the control quantity from the final six-dimensional force / torque to key components (FCx, FCz, MCy) directly related to the jamming physical mechanism, achieving physical dimensionality reduction of the control quantity and lowering decision complexity.

[0046] In the fifth embodiment of the present invention, based on the fourth embodiment, the torque information acting on the end of the moving platform is determined according to the axial force of each connecting branch and the Jacobian matrix corresponding to the current pose of the moving platform. The calculation formula for the torque information at the end of the moving platform is as follows: ; in, This refers to the torque information acting on the end of the moving platform; The Jacobian matrix is ​​the mapping from the length change rate of the constraint branch and each of the connecting branches to the generalized velocity of the moving platform. The axial force vector is composed of the axial forces of the constraint branches and each of the connecting branches; superscript Indicates matrix transpose; superscript This represents the Moore-Penrose generalized inverse.

[0047] Furthermore, the base coordinate system The torque information is converted to the contact coordinate system fixed to the insertion shaft. The torque information in the contact coordinate system is obtained: in, and Contact coordinate system and base coordinate system The six-dimensional generalized force / torque vector; For the base coordinate system To contact coordinate system The force / torque coordinate transformation matrix is ​​expressed as follows: in, For the base coordinate system To contact coordinate system rotation matrix; This is the position vector pointing from the origin of the base coordinate system to the origin of the contact coordinate system; It is its antisymmetric matrix.

[0048] Based on the torque information in the contact coordinate system, the radial contact force is extracted. Axial contact force and anti-overturning contact moment It is used for subsequent calculations of dimensionless state points and assembly jamming states.

[0049] Through static mapping, under redundant driving conditions of the degrees of freedom at the ends of constrained branch 3 and each connecting branch 4, the optimal estimate of the six-dimensional torque information acting on the end of the moving platform 2 can be obtained in the least squares sense. This mapping does not depend on the external force model and is entirely based on the Jacobian matrix of the pose of the moving platform 2 and the axial force vector measured in real time. It realizes end-effector force sensing without external force sensor 6, reduces hardware costs, and ensures the real-time nature of the information.

[0050] In the sixth embodiment of the present invention, based on the fourth embodiment, the calculation formula for the dimensionless state point is as follows: ; in, and Represents dimensionless force and dimensionless torque (i.e., dimensionless state point). , , and These are the contact force and torque components mapped to each dimension within the contact coordinate system. The radius of the inserted axis.

[0051] Specifically, the calculation formula for the critical boundary mapping relationship for anti-jamming is as follows: ; in, is the slope coefficient of the stagnation critical boundary in the dimensionless state plane; It is a dimensionless radial contact force; It is a dimensionless anti-overturning moment; A dimensionless intermediate parameter related to the relative tilt angle between the shaft and the hole and the coefficient of contact friction; symbol " "These represent two stuck critical boundaries in the dimensionless state plane."

[0052] The calculation formula for the intermediate parameters is as follows: ; in, The coefficient of friction between the insertion shaft and the contact surface of the hole wall; The relative inclination angle between the insertion shaft axis and the hole axis within the contact plane; This is the axial distance between the second contact point and the origin of the contact coordinate system. The radius of the inserted axis; The coefficient of friction and relative tilt angle Commonly determined contact state parameters; The dimensionless geometric parameters are determined by the location of the second contact point, the coefficient of friction, and the radius of the insertion shaft. The slope coefficient of the stuck critical boundary is determined by the contact state parameters and the dimensionless geometric parameters.

[0053] The original force and torque physical quantities are transformed into dimensionless state points, achieving normalization and physical decoupling. Normalization eliminates the influence of the assembly load size (i.e., the magnitude of FCz) on the decision result, enabling the control strategy to generalize to workpieces of different sizes and weights. Physical decoupling characterizes the horizontal coordinates FCx and FCz as the degree of lateral pushing, and the vertical coordinates MCy and (rFCz) as the degree of overturning tilt. These correspond to the two main jamming modes of single-point contact and two-point contact, respectively, facilitating differentiated control by the FSM decision-maker based on the different modes.

[0054] In the seventh embodiment of the present invention, based on the fourth embodiment, step S60 includes: Step S61: Determine the desired torque adjustment amount based on the dimensionless state point, assembly process state, and dynamic safety zone; Step S62: Solve for the torque adjustment amount and map it to the axial damping force change of the constraint branch 3 and each connecting branch 4. Step S63: Determine the control command based on the change in damping force.

[0055] Specifically, the dynamic safety zone forms a parallelogram envelope to prevent jamming. Its actual function is as an inequality constraint: the real-time contact state point must strictly fall within the parallelogram envelope to be judged as a safe and damage-free assembly.

[0056] The formula for calculating the envelope of a parallelogram is as follows: ; in, It is a dimensionless radial contact force; It is a dimensionless anti-overturning moment; To prevent the slope coefficient of the critical boundary from being stuck in the dimensionless state plane; The dimensionless contact state parameter is determined by the relative tilt angle between the shaft and the hole and the friction coefficient of the contact surface. relative to the center boundary The safety boundary width. When the real-time dimensionless state point satisfies the above inequality, it is determined that the current shaft-hole contact state is within the dynamic safety zone; when the real-time dimensionless state point approaches or exceeds the dynamic safety zone, it is determined that there is a risk of jamming in the assembly process, and a corresponding torque information adjustment amount is generated.

[0057] Generate the desired adjustment amount based on the current assembly state: When facing the lateral error compliance zone, the radial impedance is actively reduced to accommodate and absorb the translation error. The formula for calculating the adjustment amount is as follows: .

[0058] When facing the critical wedging region, the anti-overturning resistance is enhanced to maintain axial stability and forcibly eliminate parasitic torque. The formula for calculating the adjustment amount is as follows: .

[0059] in, Contact coordinate system The desired torque information adjustment amount generated below; Contact coordinate system Middle The radial contact force component in the direction; Contact coordinate system Middle winding The anti-overturning contact moment of the shaft; This is the radial contact force adjustment coefficient, used to determine the adjustment range of the radial damping force under lateral error compliance conditions; This is the anti-overturning moment adjustment coefficient, used to determine the adjustment range of anti-overturning damping under the critical wedging state; the negative sign indicates that the direction of the generated adjustment is opposite to the direction of the current radial contact force or anti-overturning contact moment, so as to reduce the lateral extrusion force and anti-overturning moment between the shaft and the hole.

[0060] A hierarchical mapping architecture was established, from high-level decision-making (generating the desired torque adjustment) to low-level execution (mapping to changes in branch damping forces and then generating control commands). The high-level decision maker (FSM) is responsible for generating strategic torque adjustments based on the current state and safe zone, while the low-level mapper is responsible for accurately decomposing the objective into the axial damping forces of each branch according to the Jacobian transpose.

[0061] This layered architecture decouples strategy from execution. The decision-making layer does not need to concern itself with the physical characteristics of specific actuators, and the execution layer does not need to concern itself with the strategy logic, which facilitates system maintenance, debugging, and functional expansion. At the same time, the Jacobi transpose mapping ensures the consistency of the force domain between the torque adjustment and the branch damping force change, that is, the force requirements of the operating space and the force output of the joint space remain equivalent at the energy level.

[0062] In the eighth embodiment of the present invention, based on the seventh embodiment, the optimal damping distribution mapping formula for the torque adjustment amount is as follows: ; in, The decision vector is controlled by the excitation current (i.e., the dissipation force amplitude of the constraint branch 3 and each connecting branch 4). The active mapping submatrix (generally the first 5 columns of the Jacobian transpose matrix are taken); It is a diagonal matrix of the transiently driveable quadrant; The desired operating space torque adjustment amount; This is the spatial dimension weight matrix, used to prioritize approximation convergence in higher-dimensional directions under rank deficiency conditions; This represents the regularization coefficient, used to smooth out control chattering caused by the velocity crossing zero point; It is a decision vector composed of the target damping force amplitudes of the magnetorheological dampers in each connected branch of the previous control cycle.

[0063] By using the Jacobian transpose mapping, the desired adjustment amount in the operating space (i.e., the six-dimensional force / torque information at the end point) is precisely converted into the damping force adjustment amount in the joint space (i.e., the constraint branch 3 and each connecting branch 4). The physical meaning of this mapping is that any torque adjustment amount in the operating space corresponds to a unique combination of axial forces of each branch in the parallel mechanism (under non-singular poses). This ensures that the reshaping of the end impedance can be precisely achieved through the independent current adjustment of each MR damper, realizing the lossless transmission of "operating space pointing to branch space execution".

[0064] Specifically, step S63 also includes: Step S70: Determine the working state of the end effector based on the radial contact force amplitude, the anti-overturning contact torque amplitude, the axial contact force, and the jamming warning index. The working state includes at least one of the following: free space state, single-point contact dominant state, two-point contact risk state, and steady-state alignment insertion state. Step S71: Determine the corresponding semi-active damping adjustment strategy based on the operating state.

[0065] Specifically, define the radial contact force amplitude. and anti-overturning contact moment amplitude They are respectively: , .

[0066] in, Contact coordinate system The amplitude of the radial contact force; Contact coordinate system The amplitude of the anti-overturning contact moment; For the contact coordinate system The radial contact force component in the direction; For the contact coordinate system The contact torque component of the shaft. Specifically, when the radial resultant force... At the same time, and resists overturning torque It is in free space state; when the radial resultant force And resists overturning torque At this time, the single-point contact is dominant, and translational error is smoothly absorbed; when the anti-overturning torque is... At the same time, the stagnation warning index is calculated. ,like This triggers a two-point contact risk state, which is judged as a high-risk precursor to jamming, and the rotational impedance is quickly adjusted to resist tilting; when and Simultaneously satisfying the axial convergence condition and Triggered at time.

[0067] in, This is the threshold for determining radial contact force, used to determine whether significant radial contact has occurred; The threshold for anti-overturning contact torque is used to determine whether there is obvious shaft-hole overturning contact. Contact coordinate system Middle The axial contact force component in the direction; This is the axial contact force convergence threshold. The coefficient of friction between the insertion shaft and the contact surface of the hole wall; The jamming warning index is used to characterize the degree of radial contact action relative to the axial friction bearing capacity. The preset jamming warning threshold, when This indicates a high risk of wedging or jamming in the current shaft-hole contact state.

[0068] During axial feeding, due to incomplete compensation of spatial angle deviation, an initial transient single-point collision (i.e., the lateral error compliance zone dominated by single-point contact) will occur between the shaft and the hole wall. As insertion deepens, if a secondary collision occurs, the system will enter a two-point contact force mode (i.e., the wedge-cutting critical zone with two-point contact risk), which is the main physical cause of fatal jamming.

[0069] Throughout the assembly process, constraint branch 3 is set to input a constant reference current and is responsible for providing the basic passive axial impedance. Its main function is to directly bear the main downward insertion force along the Z-axis, avoiding the control algorithm from falling into rank deficiency and physical redundancy.

[0070] Connecting branch 4 is responsible for performing high-frequency dynamic impedance reshaping. In the event of a transient impact, the current in each connecting branch 4 drops rapidly to unload kinetic energy. In the insertion zone where jamming is likely to occur, these five independent connecting branches 4 perform high-frequency asynchronous dynamic damping distribution based on the feedback of the contact force. By reshaping the spatial anisotropy matrix, they constrain the attitude and prevent excessive accumulation of destructive anti-overturning internal stress.

[0071] In the description of this specification, references are made to the terms "one embodiment", "another embodiment", "other embodiments" Descriptions such as "example" or "first embodiment to Xth embodiment" refer to descriptions in conjunction with that embodiment or example. Specific features, structures, materials, or characteristics are included in at least one embodiment or example of the present invention.

[0072] In this specification, the illustrative expressions of the terms used above do not necessarily refer to the same embodiments or examples.

[0073] Furthermore, the specific features, structures, materials, method steps, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0074] It should be noted that, in this document, the terms "comprising," "including," or any other variations thereof are intended to... This encompasses non-exclusivity inclusion, thereby allowing a process, method, article, or device to include a range of elements. The setting includes not only those elements, but also other elements not explicitly listed, or may also include... Elements inherent to such a process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising a..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes that element.

[0075] The sequence numbers of the above embodiments of the present invention are merely for descriptive purposes and do not represent the superiority or inferiority of the embodiments. Through the above description of the embodiments, those skilled in the art can clearly understand that the methods of the above embodiments can be implemented by means of software plus necessary general-purpose hardware platforms. Of course, they can also be implemented by hardware, but in many cases, the former is a better implementation method. Based on this understanding, the technical solution of the present invention, in essence, or the part that contributes to the prior art, can be embodied in the form of a software product. This computer software product is stored in a storage medium (such as ROM / RAM, magnetic disk, optical disk), and includes several instructions to cause a terminal (which may be a mobile phone, computer, server, air conditioner, or network device, etc.) to execute the methods described in the various embodiments of the present invention.

[0076] The embodiments of the present invention have been described above with reference to the accompanying drawings, but the present invention is not limited thereto. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art, guided by the teachings of this invention, will apply the principles and claims of this invention without departing from its spirit and scope. Within the scope of protection, many other forms can be made, all of which fall within the protection scope of this invention.

Claims

1. A semi-active variable stiffness compliant assembly end effector, characterized in that, It includes a static platform and a dynamic platform, as well as constraint branches and several connecting branches located between the static platform and the dynamic platform. One end of each constraint branch is connected to the center point of the static platform, and the other end of each constraint branch is connected to the center point of the dynamic platform. Each connecting branch is arranged at intervals along the circumference of the constraint branch axis. Displacement sensors are respectively installed on each constraint branch and each connecting branch. Each constraint branch and each connecting branch is connected to the dynamic platform through a force sensor.

2. The semi-active variable stiffness compliant assembly end effector as described in claim 1, characterized in that, The constraint chain includes a first elastic spring, a first magnetorheological damper, and two first universal joints. One end of the first magnetorheological damper is detachably connected to the static platform via one of the first universal joints, and the other end of the first magnetorheological damper is detachably connected to the moving platform via the other first universal joint and one of the force sensors. The first elastic spring is sleeved on the outside of the first magnetorheological damper, and both ends of the first elastic spring are respectively connected to the ends of the adjacent first magnetorheological dampers. One of the displacement sensors is respectively connected to both ends of the first magnetorheological damper.

3. The semi-active variable stiffness compliant assembly end effector as described in claim 1, characterized in that, The connecting chain includes a first ball joint, a second elastic spring, a second magnetorheological damper, and a second universal joint. One end of the second magnetorheological damper is detachably connected to the static platform via one of the first ball joints, and the other end of the second magnetorheological damper is detachably connected to the moving platform via another second universal joint and one of the force sensors. The second elastic spring is sleeved on the outside of the second magnetorheological damper, and both ends of the second elastic spring are respectively connected to the adjacent ends of the second magnetorheological damper. One of the displacement sensors is respectively connected to both ends of the second magnetorheological damper.

4. A semi-active variable stiffness compliant assembly end-effector control method, characterized in that, A semi-active variable stiffness compliant assembly end effector as described in any one of claims 1-3, wherein the control method includes: The axial force vector and length vector of the constraint branch and the connecting branch are obtained by each of the displacement sensors and force sensors respectively. Based on the length vectors described, the pose of the moving platform and the tilt angle in the assembly plane are solved in real time using numerical methods. Based on the Jacobian matrix of the moving platform's pose, determine the torque information at the end of the moving platform; The torque information is converted into the contact coordinate system of the shaft connection, and then the dimensionless state point and assembly process state used for jamming determination are calculated. Obtain the friction coefficient, and based on the friction coefficient and the tilt angle, determine the dynamic safety zone using a pin-hole contact mechanics model; Based on the dimensionless state point, the assembly process state, and the dynamic safety region, the control commands for the constraint branches and each connecting branch are determined.

5. The semi-active variable stiffness compliant assembly end-effector control method as described in claim 4, characterized in that, The formula for calculating the torque information at the end of the moving platform is as follows: ； in, This refers to the torque information acting on the end of the moving platform; The Jacobian matrix is ​​the mapping from the length change rate of the constraint branch and each of the connecting branches to the generalized velocity of the moving platform. The axial force vector is composed of the axial forces of the constraint branches and each of the connecting branches; superscript Indicates matrix transpose; superscript This represents the Moore-Penrose generalized inverse.

6. The semi-active variable stiffness compliant assembly end-effector control method as described in claim 4, characterized in that, The formula for calculating the dimensionless state point is as follows: in, This refers to the dimensionless state point; Along the contact coordinate system The radial contact force component in the direction; Along the contact coordinate system The axial contact force component in the direction; For contact coordinate system The contact torque component of the shaft; The radius of the inserted axis; and These are used to normalize the radial contact force component and the contact torque component, respectively.

7. The semi-active variable stiffness compliant assembly end-effector control method as described in claim 4, characterized in that, The step of determining the control commands for the constraint branches and each connecting branch based on the dimensionless state point, the assembly process state, and the dynamic safety region includes: Based on the dimensionless state point, the assembly process state, and the dynamic safety zone, determine the desired torque adjustment amount; The torque adjustment is solved and mapped to the axial damping force change of the constraint branch and each of the connecting branches; The control command is determined based on the change in damping force.

8. The semi-active variable stiffness compliant assembly end-effector control method as described in claim 7, characterized in that, The optimal damping distribution mapping formula for the torque adjustment amount is as follows: ； in, The decision vector is controlled by the excitation current (i.e., the dissipation force amplitude of the constraint branch 3 and each connecting branch 4). The active mapping submatrix (generally the first 5 columns of the Jacobian transpose matrix are taken); It is a diagonal matrix of the transiently driveable quadrant; The desired operating space torque adjustment amount; This is the spatial dimension weight matrix, used to prioritize approximation convergence in higher-dimensional directions under rank deficiency conditions; This represents the regularization coefficient, used to smooth out control chattering caused by the velocity crossing zero point; It is a decision vector composed of the target damping force amplitudes of the magnetorheological dampers in each connected branch of the previous control cycle.

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