A high-temperature clamping adaptive control method and system based on motor current sensing

Abstract

The application discloses a high-temperature clamping self-adaptive control method and system based on motor current sensing, and the motor current and rotor position are collected, the electromagnetic torque is estimated based on a motor model, and the real-time clamping force is mapped through a lead screw transmission and a connecting rod mechanism; meanwhile, the friction coefficient is thermally corrected according to the temperature, the upper limit of damage prevention is calculated based on the Hertz contact theory under different working conditions, and the safety interval is constructed in combination with the lower limit of anti-slip; the force increasing, force limiting or steady-state force reducing control is executed according to the comparison between the clamping force and the safety interval; and the anti-slip is preferentially ensured and a warning is given when the safety interval is inverted. The application can realize the real-time sensing of the clamping force without the end force sensor, realizes the adaptive safe clamping in the high-temperature environment, and can effectively avoid the workpiece sliding or surface damage.

Description

Technical Field

[0001] This invention belongs to the field of precision control and monitoring technology for robots, specifically relating to a high-temperature gripping adaptive control method and system based on motor current sensing. This method specifically targets the composite transmission gripping mechanism at the end effector of a robotic arm. Through nonlinear torque-force mapping, thermal correction of the friction coefficient under high-temperature service conditions, a bidirectional gripping stability quantification criterion, and an adaptive control strategy, it achieves quantitative assessment and correction of gripping stability, providing technical support for ensuring gripping reliability. Background Technology

[0002] In the production and processing of metal billets, it is often necessary to clamp the billets in an ultra-high temperature environment (≥300℃) to complete the material handling and feeding operations. This ultra-high temperature environment not only causes conventional clamping status monitoring sensors in engineering to fail, but also changes the surface properties of the workpiece material, significantly increasing the difficulty of stable control of the clamping jaws on the billets, and easily causing problems such as billet slippage and dropping. Existing technologies cannot accurately characterize the force transmission law of electric cylinder-linkage type variable Yar-comparable characteristic mechanisms through linear models, resulting in insufficient accuracy in clamping status estimation; conventional force sensors (such as resistance strain gauges and piezoelectric sensors) fail due to their inability to withstand high temperatures or severe signal drift, making it difficult for robotic arms to accurately sense the end-effector clamping force.

[0003] While there are some existing technologies that use current to estimate torque, they have the following shortcomings.

[0004] First, most existing technologies are based on linear transmission models, which lack specificity and ignore the variable Jacobian characteristics of the mechanism. However, for a robotic arm employing a "electric cylinder-rotary gripper" composite transmission, the force transmission changes drastically with the gripper's opening and closing angle, exhibiting variable Jacobian characteristics. Continuing to use linear models would lead to significant deviations in force estimation.

[0005] Secondly, while existing technologies mention calculating the minimum clamping force based on the coefficient of friction, they typically assume the coefficient of friction to be constant and are difficult to obtain accurately. Generally, sensors are needed to detect slippage for prediction, or a very small coefficient of friction is set to ensure sufficient clamping force and stable clamping. However, excessive clamping force can cause significant residual stress or damage to the workpiece / end tool, affecting tool life over long-term use, and the residual stress in the workpiece directly impacts the final machining quality.

[0006] To address these issues, existing technologies use soft material buffers or simple force threshold limits to prevent workpiece damage. However, especially in high-temperature environments, the coefficient of friction often shifts significantly, sensors often malfunction, and soft material buffers are difficult to apply. The clamping problem is generally solved by ensuring a sufficiently large clamping force. Therefore, the residual stress on the workpiece under the combined effects of high temperature and clamping force becomes a significant factor reducing its machining quality. Summary of the Invention

[0007] To address the problems in the existing technology, this invention provides a high-temperature clamping adaptive control method and system based on motor current sensing. The aim is to achieve stable and non-destructive control of billet clamping under high-temperature conditions by utilizing only the three-phase current signal of the servo drive motor and the opening and closing angle signal of the robotic gripper, without relying on feedback from the end force sensor.

[0008] A high-temperature clamping adaptive control method based on motor current sensing includes the following steps: Step 1: Real-time estimation of clamping force based on motor current decoupling Constructing a nonlinear variable Jacobian mapping model from motor torque to end clamping force: using the lead screw drive formula Calculate the thrust of the electric cylinder ,in For the reduction ratio, For lead screw drive efficiency. For the lead screw, The motor outputs torque; then, through the torque balance principle of the linkage mechanism, a clamping force is established. With electric cylinder thrust geometric mapping relationship ,in, For power boom, For resistance arm, The grippers open at a half angle, thus obtaining a real-time estimated clamping force. ; Step 2: Thermal correction of high-temperature friction coefficient Read the current operating temperature The correction coefficient is obtained based on the temperature-friction correction curve determined and fitted in advance through high-temperature friction and wear experiments. Calculate the corrected effective static friction coefficient : ;in, The static friction coefficient between the gripper and the workpiece at room temperature; Step 3: Determining the stability of bidirectional clamping Calculate the lower limit of anti-slip safety : ;in, For anti-slip safety margin coefficient, For workpiece quality, The acceleration is gravitational; based on the dynamic switching stress constraint criterion during the operation phase, the upper limit of the damage prevention safety is calculated. ; Step 4: Adaptive Feedback Control Real-time estimated clamping force and safe interval [ , Comparison: when At that time, increase the motor torque command until the clamping force is reached. Entering a safe zone; when At that time, the motor output torque is limited to reduce the clamping force. Keep within the upper limit of damage prevention safety; When the robotic arm is in a stable handling state, the clamping force is... Reduced to the lower limit of anti-slip safety ; when At that time, the clamping force is forcibly applied. Adjusted to the lower limit of anti-slip safety And trigger an abnormal warning signal.

[0009] Furthermore, the motor output torque The calculation process is as follows: Collect the three-phase stator current of the servo motor. and rotor mechanical position The Clark and Park transformations are used to decouple the current in the three-phase stationary coordinate system into a direct-axis current in the rotating coordinate system. and cross-axis current Calculate the motor output torque based on the electromagnetic torque formula for permanent magnet synchronous motors: ;in, This represents the number of pole pairs of the motor. It is a permanent magnet flux chain. , These are the d-axis and q-axis inductances, respectively.

[0010] Furthermore, in step 3, calculating the upper limit of damage prevention safety specifically involves using the material's yield strength during the contact and lifting stages. 90% of the maximum allowable contact stress is used; during the steady-state transport phase, the material's high-temperature creep threshold is used. The maximum permissible contact stress is used as the reference point; based on the inverse solution of Hertzian contact theory, the upper limit of the maximum clamping force, i.e., the upper limit of damage prevention safety, is obtained. .

[0011] Further, based on Hertzian contact theory, the upper limit of damage prevention safety is determined by inverse solution. The formula is: in, This is the effective contact length between the gripper and the workpiece. The equivalent radius of the workpiece. It is a V-shaped jaw half-angle. The combined elastic modulus of the workpiece and gripper materials must meet the following requirements. , This represents the maximum permissible contact stress under the current operating conditions. The elastic modulus of the workpiece. Let be the elastic modulus of the gripper. Let Poisson's ratio be the workpiece. is the Poisson's ratio of the gripper material.

[0012] Furthermore, the three-phase stator current in step 1 is acquired in real time by a current sensor, and the rotor mechanical position is obtained through encoder feedback, eliminating the need to install additional force sensors at the end of the grippers.

[0013] Further, the temperature-friction correction curve in step 2. The friction coefficients were determined by conducting high-temperature friction and wear experiments beforehand and then obtained using curve fitting.

[0014] Furthermore, the gripper adopts a V-shaped jaw structure, and the included angle of the V-shaped jaw is... When clamping a cylindrical workpiece, two parallel lines of contact are formed.

[0015] Furthermore, the grippers open at a half angle. The rotor position is obtained in real time by combining the feedback from the encoder with the kinematic relationship of the transmission mechanism.

[0016] A high-temperature clamping adaptive control system based on motor current sensing, employing the aforementioned high-temperature clamping adaptive control method based on motor current sensing, includes: a current sensor, a position encoder, a servo driver, and a controller; the controller is configured to execute steps 1 to 4, estimate the clamping force in real time, and output adaptive control commands. The beneficial effects of this invention are: overcoming the problem of sensor failure at high temperatures: This invention abandons the traditional end force sensor feedback path and innovatively uses only the internal current signal of the servo motor and the opening and closing angle signal of the gripper to indirectly estimate and control the clamping force, effectively solving the industry pain point that conventional electronic sensors are easily damaged and have serious temperature drift in ultra-high temperature and strong radiation environments.

[0017] This invention solves the problem of nonlinear force estimation for variable Jacobian mechanisms: For mechanisms with variable Jacobian characteristics, such as electric cylinder-rotary grippers, this invention establishes a nonlinear dynamic model based on the Jacobian matrix, which can compensate for mechanical gain fluctuations caused by changes in the opening and closing angle of the gripper in real time, and significantly improve the clamping force estimation accuracy in the entire workspace.

[0018] High-temperature environment adaptability: By introducing a temperature-friction correction coefficient, this system can compensate for the thermal drift of the contact surface friction coefficient under high-temperature conditions, ensuring that the workpiece will not slip even when friction conditions deteriorate.

[0019] Achieving damage protection for high-temperature billets: This invention is the first to introduce Hertzian contact theory and material properties at high temperatures (yield strength, creep threshold) into the control closed loop, dynamically adjusting the upper limit of force for different operation stages, effectively preventing workpiece surface indentation or internal residual stress damage caused by excessive clamping force. Attached Figure Description

[0020] Figure 1 This is a flowchart of the present invention; Figure 2 This is a block diagram of the control structure of the present invention; Figure 3 This is a schematic diagram of the mechanical analysis of the robotic arm used in this invention; Figure 4 This is a schematic diagram of the V-shaped jaws clamping a cylindrical blank in this invention; Figure 5 The simulation results are shown in the figure comparing the variable Jacobian model and the fixed-scale linear model. Figure 6 For Hertzian contact back-calculation Simulation results of the high-temperature clamping stability range; Figure 7 The simulation results are shown in the diagram. Detailed Implementation

[0021] The present invention will now be described in detail with reference to the accompanying drawings. Embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention. The directional terms such as left, center, right, top, and bottom in the embodiments of the present invention are only relative concepts or referenced to the normal use state of the product, and should not be considered restrictive.

[0022] A high-temperature clamping adaptive control method based on motor current sensing, such as Figure 1 and Figure 2 As shown, it includes the following steps: Step 1: Real-time estimation of clamping force based on motor current decoupling The servo driver acquires the three-phase stator current of the motor in real time via a current sensor. The rotor mechanical position fed back by the encoder. No additional force sensor needs to be installed at the end of the gripper; The currents in the three-phase stationary coordinate system are decoupled into direct-axis currents in the rotating coordinate system using Clark and Park transformations. and cross-axis current ; Calculate the motor output torque using the electromagnetic torque formula for a permanent magnet synchronous motor: in, This represents the number of pole pairs of the motor. It is a permanent magnet flux chain. , These are the d-axis and q-axis inductances, respectively. , These are the d-axis and q-axis currents, respectively. like Figure 3 As shown, in view of the nonlinear transmission characteristics of the "electric cylinder-connecting rod" mechanism, a nonlinear variable Jacobian mapping model from motor torque to end clamping force is constructed to accurately map the motor torque into end clamping force.

[0023] First stage transmission (rotation to linear): The motor drives the electric cylinder lead screw through a reducer, with a reduction ratio of 1. The lead of the lead screw is Ignoring internal friction losses in the lead screw, the output thrust of the electric cylinder lead screw is... for: in, For lead screw drive efficiency; Second-stage transmission (linear to clamping – variable yappa link): Establish the kinematic geometry model of the linkage mechanism and calculate it using the torque balance principle; the gripper opening angle is... The grippers open at a half angle The rotor position, fed back by the encoder, is calculated in real time based on the kinematic relationship of the transmission mechanism; it is known that the electric cylinder provides the thrust. Institutions such as Figure 3 and Figure 4 As shown, the derivation is based on geometric relationships; Power boom: Resistance arm: in, Indicates the length of input link 1, Indicates the length of intermediate link 2, Indicates the length of output link 3, Indicates the height from point C to the center line of the gripper. This indicates the angle between segment BC in the integrated connecting rod BCD and the center line of symmetry of the gripper. Indicates the angle between the extension of link AB and segment BC. The angle between segment CD of the integrated connecting rod BCD and the center line of symmetry of the gripper is indicated. This indicates the included angle between the intermediate connecting rod 2 and the output connecting rod 3, and is a fixed value; the claw head 4 contacts and clamps the cylindrical blank 5; Based on the principle of torque balance: , yes According to the method of forces acting at nodules, the component force on the connecting rod is: , It is the clamping force output by the mechanical gripper; get: This allows for the real-time estimation of clamping force. In this embodiment, the Jacobian mapping relationship between the motor output torque and the equivalent clamping force of the single-sided gripper is as follows: in: The angle parameters in the above trigonometric functions are in degrees. Step 2: Thermal correction of high-temperature friction coefficient Read the current operating temperature from the system Considering the changes in the friction coefficient caused by lubrication failure and surface oxidation of the gripper mechanism at high temperatures, a temperature-friction correction coefficient is introduced. The temperature-friction correction coefficient is obtained based on the temperature-friction correction curve determined and fitted in advance through high-temperature friction and wear experiments. Simultaneously, the coefficient of friction between the grippers and the workpiece (blank) under normal temperature conditions was measured. ; Calculate the corrected effective static friction coefficient : ; Among them, the temperature-friction correction curve The friction coefficient was determined by conducting high-temperature friction and wear experiments in advance and then obtained by curve fitting method. Step 3: Determining the stability of bidirectional clamping Lower limit anti-slip judgment critical algorithm: Based on the mass m of the workpiece (blank) being clamped, and incorporating the anti-slip safety margin factor. Calculate the lower limit of anti-slip safety. : in, The acceleration is due to gravity; friction is provided by the left and right grippers respectively, therefore the lower limit of the anti-slip safety limit is calculated. When using this method, the minimum required unilateral friction force should be taken as the benchmark, and the unilateral friction force = total friction force / 2. Upper limit damage prevention judgment critical algorithm: The system dynamically switches stress constraint criteria based on the work phase (condition A and condition B) and calculates the upper limit of damage prevention safety. Operating Condition A: Contact and Lifting Phase (Prevention of Instantaneous Damage) At this stage, the main focus is on preventing macroscopic indentations on the workpiece surface caused by impact, based on the material's yield strength at the current temperature. 90% of the maximum allowable contact stress; Based on the inverse solution of Hertzian contact theory, the upper limit of damage prevention safety is obtained as follows: ; Operating Condition B: Steady-state transport stage (preventing high-temperature creep) During this stage, the workpiece is under prolonged stress; to prevent time-dependent deformation of the material, the high-temperature creep threshold of the material at the current temperature is used. As the maximum permissible contact stress; Based on the inverse solution of Hertzian contact theory, the upper limit of damage prevention safety is obtained as follows: ; Among them, the estimated clamping force described in this invention Specifically, it refers to the resultant force output by the single-sided gripper at the end of a robotic arm along the closing direction; for V-shaped jaws, the clamping force... Decomposed into normal components acting on the contact generatrix , The included angle of the V-jaws is ; This embodiment uses V-shaped jaws to clamp the cylindrical blank, simplifying the contact form to two parallel lines. According to Hertzian contact theory, the maximum pressure on a single-sided contact line is... The calculation formula is: Normal force acting in the direction normal to the contact surface; The comprehensive elastic modulus is derived from the elastic modulus of the workpiece. And the elastic modulus of the gripper Decide: in, The effective contact length between the gripper and the workpiece (i.e., gripper width, for example, 50mm); This is the equivalent contact radius (here, the equivalent radius of the workpiece, for example, 100mm). Let Poisson's ratio be the workpiece. The Poisson's ratio of the gripper material; Based on Hertzian contact theory, the upper limit of damage prevention safety is determined by inverse solution. The formula is: ; Step 4: Adaptive Feedback Control Real-time estimated clamping force and safe interval [ , Comparison: when At that time, increase the motor torque command until the clamping force is reached. Entering a safe zone; when At that time, the motor output torque is limited to reduce the clamping force. Keep within the upper limit of damage prevention safety; When the robotic arm is in a stable handling state, the clamping force is... Reduced to the lower limit of anti-slip safety ; when At that time, the clamping force is forcibly applied. Adjusted to the lower limit of anti-slip safety And trigger an abnormal warning signal (1) Anti-slip force enhancement strategy Judgment condition: When the real-time estimated clamping force is less than the lower limit of the anti-slip safety limit ( )hour; Action Execution: The system determines that the clamping force is insufficient and there is a risk of slippage. At this time, the controller automatically increases the torque command of the motor, driving the gripper to apply greater force until the real-time estimated clamping force rises back to the anti-slip safety lower limit. The above ensures a firm grasp; (2) Damage prevention and force limiting strategy Judgment condition: When the real-time estimated clamping force exceeds the damage prevention safety limit ( )hour; Action Execution: If the system determines that the clamping force is too large, potentially damaging the workpiece or causing plastic deformation, the controller immediately limits the motor's output torque to prevent further increase, thus "locking" the real-time estimated clamping force at the safe upper limit to prevent damage. Within this range, ensure it is not damaged by pinching; (3) Steady-state shape preservation strategy (anti-creep) Judgment condition: When the robotic arm completes the lifting action and is in a stable handling state; Action: Considering that high-temperature workpieces (blanks) are prone to indentation when subjected to force for a long time, the system no longer maintains the strong force at the time of gripping, but automatically reduces the real-time estimated clamping force; Specific steps: The system first switches the damage prevention safety upper limit to the damage prevention safety upper limit calculated based on the high-temperature creep threshold. Subsequently, in order to minimize stress, the controller performs a force reduction operation, linearly reducing the real-time estimated clamping force to near the lower limit of the anti-slip safety limit. The minimum maintenance level; this is intended to ensure that during long-term handling, the actual contact stress is always well below the material's creep threshold, thereby eliminating the risk of indentation creep from a physical source; (4) Safety priority and alarm strategy under extreme working conditions Judgment condition: When the minimum theoretical clamping force required to prevent the workpiece from slipping, calculated by the system in step 3, is greater than the upper limit of the damage prevention safety that allows the workpiece to remain undamaged, the condition is determined based on the following condition. When (i.e., the extreme condition in which the clamping stability safety range is reversed); Action Execution: Considering that the slippage and detachment of heavy workpieces at high temperatures in industrial settings constitutes a major production safety accident, while surface indentations or creep on the workpiece are considered product quality defects; the control system adheres to the principle of "absolute priority for slippage prevention and safety." Specific methods: ① Forced force increase and load protection: The controller automatically disables the damage prevention force limiting strategy and the steady-state shape preservation strategy, and forcibly sets the real-time estimated clamping force to the currently calculated lower limit threshold for anti-slip safety (i.e., the lower limit for anti-slip safety). ① The system prioritizes controlling the servo motor to ensure that the high-temperature workpiece does not slip during handling; ② It triggers anomaly warnings: Instead of outputting the usual "clamping ready" status, the system simultaneously sends a "workpiece damage warning / severe working condition alarm" signal (i.e., anomaly warning signal) to the host computer and the field interface. This signal is used to remind process personnel that the load-bearing capacity of the workpiece material at the current temperature can no longer meet the safety clamping requirements, which will inevitably lead to plastic deformation or creep damage. Manual intervention is required to adjust the front-end heating process, shorten the handling time, or replace the clamping jaw surface, thereby eliminating potential defects from a physical source.

[0024] (5) Adaptive control logic The control system compares and estimates the clamping force in real time. With dynamic safety interval [ , It outputs control actions based on different situations: A high-temperature clamping adaptive control system based on motor current sensing, employing the aforementioned high-temperature clamping adaptive control method based on motor current sensing, includes: a current sensor, a position encoder, a servo driver, and a controller; the current sensor (installed at the output of the servo driver) is used to collect three-phase current; the position encoder (installed at the motor shaft end) is used to provide feedback on the rotor's mechanical position; and the servo driver receives commands from the controller to drive the motor. The controller (which can be a PLC, embedded industrial computer, or dedicated motion control card) executes steps one through four above. The controller communicates with the central main controller via fieldbus, receiving operation stage instructions (such as "lifting" and "transporting") and workpiece quality and material parameters, and outputs clamping force estimation, alarm signals and motor torque instructions; the entire system can achieve high-precision and high-reliability high-temperature clamping adaptive control without installing force sensors at the end of the grippers.

[0025] Verification example: To verify the effectiveness of the technical solution of the present invention, three simulation verifications were carried out for the variable Yarcosian force mapping model, the method for determining the stable range of high temperature clamping, and the adaptive clamping control strategy.

[0026] I. Simulation 1: Verification of the Influence of Gripper Angle on Force Transmission Characteristics 1. Simulation Purpose This simulation verifies the nonlinear force transmission characteristics of an electric cylinder-linkage-rotary gripper mechanism under different gripper opening and closing angles. Since the power arm, resistance arm, and force direction of the linkage mechanism all change at different opening and closing angles, the end-grip clamping force is not a fixed-proportion amplification of the motor output torque, but rather depends on the current gripper opening and closing angle. This simulation verifies the necessity of using a variable Jacobian force mapping model by comparing the "variable Jacobian model" and the "fixed-proportion linear model."

[0027] 2. Simulation Model According to the clamping force-motor output torque relationship in the instruction manual, the variable Jacobian model can be expressed as: In the formula, The variable Yarable force transmission coefficient is determined by the geometric parameters of the gripper mechanism, the lead screw, the reduction ratio, the transmission efficiency, and the gripper opening and closing angle. For comparison, a fixed-scale linear model is set up: in, To calibrate the angle, this model ignores the effect of changes in the gripper angle on the force transmission process.

[0028] 3. Simulation parameters 4. Simulation data 5. Simulation Results Based on the above parameters, the clamping force at different jaw opening and closing angles is calculated and compared with a fixed-proportion linear model.

[0029] Simulation results are as follows Figure 5 As shown, the fixed-proportion linear model... The position serves as the calibration point, thus intersecting with the variable Jacobian model at that angle. When the gripper angle deviates... Subsequently, the fixed-scale linear model maintained a constant clamping force, while the clamping force calculated by the variable Jacobian model varied with the opening and closing angle of the grippers. Within the simulation range, the clamping force calculated by the variable Jacobian model was approximately... Increase to The fixed-proportion linear model always remains at approximately Nearby. This result shows that if a fixed proportionality coefficient is used to describe the mapping relationship between push rod force or motor torque and clamping force, a significant estimation deviation will occur at non-calibrated angles.

[0030] 6. Results Analysis Simulation results show that, under the condition that the motor output torque remains constant, the clamping force at the end of the gripper changes significantly with the opening and closing angle of the gripper. This indicates that the force transmission process of the electric cylinder-connecting rod-rotary gripper mechanism is angle-dependent.

[0031] Although Within the operating range, the clamping force curve generally exhibits a relatively smooth, monotonically increasing trend. However, this trend does not indicate that the force transmission of the mechanism follows a fixed proportional linear relationship. This is due to the variable Availability coefficient in the formula provided in the instruction manual. It includes trigonometric and inverse trigonometric function terms, specifically related to the input link angle, the effort arm, the resistance arm, and the output link attitude. Therefore, Essentially, it is a nonlinear function that varies with the opening and closing angle of the grippers.

[0032] Compared to a fixed-proportion linear model, a variable Jacobian model can reflect the impact of changes in the mechanism's geometry on the clamping force during the opening and closing of the grippers. When the gripper angle is less than the calibrated angle, the fixed-proportion model will overestimate the actual clamping force; when the gripper angle is greater than the calibrated angle, the fixed-proportion model will underestimate the actual clamping force. The former may lead the control system to misjudge the clamping stability, increasing the risk of workpiece slippage; the latter may lead the control system to continue increasing the current or torque, increasing the risk of workpiece crushing, plastic deformation, or high-temperature creep.

[0033] Therefore, this simulation verifies the necessity and rationality of replacing the fixed-proportion linear model with a variable Jacobian force mapping model in this invention.

[0034] II. Simulation 2: Verification of the Stable Range Changes in High-Temperature Clamping 1. Simulation Purpose This simulation is used to verify the impact of high temperature environment on the gripping stability of robotic arm. It focuses on analyzing the impact of temperature change on effective friction coefficient, lower limit of anti-slip safety, upper limit of anti-damage safety, and gripping stability safety range.

[0035] In high-temperature clamping operations, the friction state between the gripper and the workpiece contact surface changes with temperature, leading to variations in the minimum clamping force required to prevent workpiece slippage. Simultaneously, the yield strength and creep resistance of the workpiece material decrease at high temperatures, resulting in a reduction in its maximum withstandable contact load. Therefore, robotic gripping control cannot rely solely on a fixed friction coefficient or a fixed clamping force threshold at room temperature; instead, the stable clamping range should be dynamically determined based on the current temperature.

[0036] This simulation verifies the rationality of the high-temperature friction correction and bidirectional clamping stability determination method in this invention by establishing a temperature-friction coefficient correction model, an anti-slip safety lower limit model, and a damage prevention safety upper limit model based on Hertzian contact theory.

[0037] 2. Simulation Model 2.1 High-Temperature Friction Coefficient Correction Model Let the static friction coefficient between the gripper and the billet at room temperature be... The effective static friction coefficient at the current temperature is ,but: In the formula, This is the temperature-friction correction factor. In this simulation, a piecewise interpolation method is used to simulate the variation of the effective static friction coefficient with temperature.

[0038] 2.2 Anti-slip safety lower limit model To prevent slippage of the workpiece during clamping and handling, the lower limit of the anti-slip safety margin is calculated based on the workpiece weight, effective friction coefficient, and anti-slip safety margin coefficient: Take the anti-slip safety margin coefficient workpiece quality .

[0039] 2.3 Damage Prevention Safety Upper Limit Model The cylindrical blank is held by a V-shaped jaw, with a half-angle V-groove. , Effective contact length, workpiece equivalent radius The overall elastic modulus is calculated from the material parameters of the workpiece and the gripper, and the allowable contact stress is the smaller of the yield strength and the creep threshold. The upper limit of damage protection safety is obtained based on the inverse solution of Hertzian contact theory: 3. Simulation parameters The following parameters are used in this simulation: The effective friction coefficient is set as follows based on temperature: Temperature—The performance settings for high-temperature materials are as follows: Note: The above parameters are used for numerical simulation verification during the R&D stage. In actual engineering applications, they can be replaced or calibrated according to the specific workpiece material manual, gripper material parameters and high-temperature friction test data.

[0040] 4. Simulation data 5. Simulation Results Based on the above model and parameters, the changes in the effective friction coefficient, lower limit of anti-slip safety, upper limit of damage prevention safety, and width of the safety range were calculated as the temperature increased from 25℃ to 900℃. The results were then plotted as a four-in-one simulation result graph, as shown below. Figure 6 As shown. Figure 6 includes four parts of the results: (1) Curve of effective static friction coefficient as a function of temperature; (2) Lower limit of anti-slip safety Damage prevention safety limit Temperature variation curve; (3) Width of safe interval Temperature variation curve; (4) Schematic diagram of the clamping stability interval filling.

[0041] 6. Simulation Result Analysis As shown in the simulation results of the four-in-one model, the increase in temperature will affect both the lower and upper limits of the clamping stability.

[0042] First, as temperature increases, the effective static friction coefficient between the grippers and the workpiece gradually decreases. Since the lower limit of anti-slip safety is inversely proportional to the effective friction coefficient, a greater clamping force is required to prevent the workpiece from slipping when the effective friction coefficient decreases. Therefore, the lower limit of anti-slip safety... It increases with increasing temperature.

[0043] Secondly, as the temperature increases, the high-temperature yield strength and creep resistance of the billet material decrease, and the maximum allowable contact stress decreases. It decreases with increasing temperature. According to the Hertzian contact inverse formula: It is known that the upper limit of damage protection safety is directly proportional to the square of the maximum permissible contact stress. Therefore, when the permissible contact stress of a material decreases at high temperatures, the permissible upper limit of damage protection safety increases. It will decrease significantly.

[0044] Furthermore, the curve showing the change in the safe range width indicates that as the temperature increases, the lower limit of the anti-slip safety gradually rises, while the upper limit of the damage prevention safety gradually decreases. The combined effect of these two factors causes the clamping stability range to gradually shrink. This demonstrates that the feasible range for clamping control under high-temperature conditions is not fixed but is closely related to temperature, friction state, and the high-temperature properties of the material.

[0045] Finally, the schematic diagram of the clamping stability interval filling visually demonstrates that the clamping stability determination method proposed in this invention can form a dynamic safe clamping interval at different temperatures. When the real-time estimated clamping force is within this interval, the system can determine that the clamping is reliable; when the clamping force is lower than the lower limit of anti-slip safety, the system should implement force increase control; when the clamping force is higher than the upper limit of anti-damage safety, the system should implement force limit or force reduction control; when the lower limit of anti-slip safety is higher than the upper limit of anti-damage safety, it indicates that the safety interval is reversed under the current working condition, and a safety priority strategy needs to be implemented and an abnormal warning should be output.

[0046] III. Simulation 3: Verification of Adaptive Clamping Control Process 1. Simulation Purpose This simulation is used to verify the feasibility of the adaptive clamping control strategy proposed in this invention under dynamic high-temperature conditions.

[0047] In actual high-temperature billet handling, the clamping state is not constant. On the one hand, the clamping force requirements are different in different operation stages such as clamping, lifting, and handling by the robot; on the other hand, as the operating temperature changes, the effective friction coefficient between the gripper and the billet and the allowable contact stress of the workpiece material will change, resulting in dynamic changes in the lower limit of anti-slip safety and the upper limit of anti-damage safety.

[0048] Therefore, this simulation calculates the lower limit of anti-slip safety by setting temperature conditions that vary over time. Damage prevention safety limit and clamping force The goal is to verify whether the control system can automatically execute strategies such as force increase, load maintenance, force reduction, force limit, or alarm based on the relationship between clamping force and safety range.

[0049] 2. Model Setup 2.1 Dynamic Temperature Condition Model To simulate the effect of temperature changes on clamping stability during high-temperature handling, this simulation sets up a 0–10 s operation process: 2.2 System target clamping force settings at different operation stages: 3. Simulation parameters The main parameters used in this simulation are as follows: The temperature-friction coefficient and temperature-material property parameters are set as in Simulation 2.

[0050] 4. Simulation data 5. Simulation Results Based on the aforementioned dynamic temperature conditions and control logic, the clamping force, lower limit of anti-slip safety, upper limit of anti-damage safety, and changes in the width of the safety interval within 0–10 s are calculated, and a simulation diagram of the adaptive clamping control process is plotted, such as... Figure 7 As shown, the figure includes four parts of the results: (1) Curve of temperature change over time during operation; (2) Curve showing the change of effective friction coefficient over time; (3) Real-time estimated clamping force Compare the curves with the dynamic safety interval; (4) Width of safe interval Curve showing how it changes over time.

[0051] Part (3) is the core result, which is used to demonstrate whether the estimated clamping force can be adaptively adjusted as the dynamic safety range changes.

[0052] 6. Results Analysis Simulation results show that, in the initial clamping stage, the clamping force is... Below the lower limit of anti-slip safety The system determines there is a risk of slippage and therefore executes force-increasing control, causing the clamping force to rise rapidly and enter a safe range. This demonstrates that the control strategy of the present invention can automatically compensate for insufficient clamping force, preventing the billet from slipping.

[0053] When the clamping force enters the... and Once a dynamic safety zone is established, the system no longer blindly increases the clamping force, but instead maintains the clamping force within the safety zone according to the operation stage. During the lifting stage, the control target is located slightly below the middle of the safety zone to ensure sufficient anti-slip margin; during the steady-state handling stage, the control target is lowered towards the lower limit of the anti-slip safety zone to reduce the risk of indentation, plastic deformation, or creep damage to the billet under high temperature and long-term stress.

[0054] As the operating temperature gradually increases from 300℃ to 900℃, the effective static friction coefficient decreases, and the lower limit of the anti-slip safety gradually increases; simultaneously, the allowable contact stress of the material decreases, and the upper limit of the damage prevention safety gradually decreases, causing the dynamic safety range to gradually narrow. Simulation results show that the control system can readjust the estimated clamping force according to the changes in the dynamic safety range, keeping the clamping force within the safety range or close to a reasonable target value.

[0055] If it occurs at a certain moment If the safety range is inverted, it indicates that the anti-slip and anti-damage requirements cannot be simultaneously met under the current temperature and load conditions. In this case, the control system should prioritize anti-slip safety, setting the clamping force to the lower limit of anti-slip safety and simultaneously outputting a workpiece damage risk warning or abnormal working condition alarm. This simulation provides a basis for determining this type of alarm strategy through the safety range width curve.

[0056] IV. Verification Conclusion The above three simulations respectively verified that: (1) the variable Jacobian force mapping model can accurately reflect the nonlinear influence of the gripper angle on force transmission compared with the fixed proportional linear model; (2) the high temperature friction correction and bidirectional clamping stability determination method can dynamically calculate the safe clamping range that changes with temperature; (3) the adaptive control strategy can automatically execute force increase, force limit, force decrease and alarm actions according to the change of the safe range. The comprehensive simulation results fully demonstrate the effectiveness and feasibility of the technical solution of the present invention.

[0057] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A high-temperature clamping adaptive control method based on motor current sensing, characterized in that, Includes the following steps: Step 1: Real-time estimation of clamping force based on motor current decoupling Constructing a nonlinear variable Jacobian mapping model from motor torque to end clamping force: using the lead screw drive formula Calculate the thrust of the electric cylinder ,in For the reduction ratio, For lead screw drive efficiency. For the lead screw, The motor outputs torque; then, through the torque balance principle of the linkage mechanism, a clamping force is established. With electric cylinder thrust geometric mapping relationship ,in, For power boom, For resistance arm, The grippers open at a half angle, thus obtaining a real-time estimated clamping force. ; Step 2: Thermal correction of high-temperature friction coefficient Read the current operating temperature The correction coefficient is obtained based on the temperature-friction correction curve determined and fitted in advance through high-temperature friction and wear experiments. Calculate the corrected effective static friction coefficient : ;in, The static friction coefficient between the gripper and the workpiece at room temperature; Step 3: Determining the stability of bidirectional clamping Calculate the lower limit of anti-slip safety : ;in, For anti-slip safety margin coefficient, For workpiece quality, The acceleration is gravitational; based on the dynamic switching stress constraint criterion during the operation phase, the upper limit of the damage prevention safety is calculated. ; Step 4: Adaptive Feedback Control Real-time estimated clamping force and safe interval [ , Comparison: when At that time, increase the motor torque command until the clamping force is reached. Entering a safe zone; when At that time, the motor output torque is limited to reduce the clamping force. Keep within the upper limit of damage prevention safety; When the robotic arm is in a stable handling state, the clamping force is... Reduced to the lower limit of anti-slip safety ; when At that time, the clamping force is forcibly applied. Adjusted to the lower limit of anti-slip safety And triggers an abnormal warning signal.

2. The high-temperature clamping adaptive control method based on motor current sensing according to claim 1, characterized in that: The motor output torque The calculation process is as follows: Collect the three-phase stator current of the servo motor. and rotor mechanical position The Clark and Park transformations are used to decouple the current in the three-phase stationary coordinate system into a direct-axis current in the rotating coordinate system. and cross-axis current ; Calculate the motor output torque using the electromagnetic torque formula for a permanent magnet synchronous motor: ;in, This represents the number of pole pairs of the motor. It is a permanent magnet flux chain. , These are the d-axis and q-axis inductances, respectively.

3. The high-temperature clamping adaptive control method based on motor current sensing according to claim 1, characterized in that: In step 3, calculating the upper limit of damage prevention safety specifically involves: during the contact and lifting stages, using the material yield strength... 90% of the maximum allowable contact stress is used; during the steady-state transport phase, the material's high-temperature creep threshold is used. The maximum permissible contact stress is used as the reference point; based on the inverse solution of Hertzian contact theory, the upper limit of the maximum clamping force, i.e., the upper limit of damage prevention safety, is obtained. .

4. The high-temperature clamping adaptive control method based on motor current sensing according to claim 3, characterized in that: Based on Hertzian contact theory, the upper limit of damage prevention safety is determined by inverse solution. The formula is: in, This is the effective contact length between the gripper and the workpiece. The equivalent radius of the workpiece. It is a V-shaped jaw half-angle. The combined elastic modulus of the workpiece and gripper materials must meet the following requirements. , This represents the maximum permissible contact stress under the current operating conditions. The elastic modulus of the workpiece. Let be the elastic modulus of the gripper. Let Poisson's ratio be the workpiece. is the Poisson's ratio of the gripper material.

5. The high-temperature clamping adaptive control method based on motor current sensing according to claim 1, characterized in that: In step 1, the three-phase stator current is acquired in real time by a current sensor, and the rotor mechanical position is obtained through encoder feedback, eliminating the need for additional force sensors installed at the end of the grippers.

6. The high-temperature clamping adaptive control method based on motor current sensing according to claim 1, characterized in that: The temperature-friction correction curve in step 2 The friction coefficients were determined by conducting high-temperature friction and wear experiments beforehand and then obtained using curve fitting.

7. The high-temperature clamping adaptive control method based on motor current sensing according to claim 1, characterized in that: The grippers adopt a V-shaped jaw structure, and the included angle of the V-shaped jaws is... When clamping a cylindrical workpiece, two parallel lines of contact are formed.

8. The high-temperature clamping adaptive control method based on motor current sensing according to claim 1, characterized in that: The grippers open at a half angle The rotor position is obtained in real time by combining the feedback from the encoder with the kinematic relationship of the transmission mechanism.

9. A high-temperature clamping adaptive control system based on motor current sensing, characterized in that, The high-temperature clamping adaptive control method based on motor current sensing according to any one of claims 1-8 includes: a current sensor, a position encoder, a servo driver, and a controller; the controller is configured to execute steps 1 to 4, estimate the clamping force in real time, and output adaptive control commands.

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