A hydraulic machine down speed closed loop control system for angle steel bending forming

Abstract

The present application relates to the technical field of hydraulic machine pressing control, and discloses a hydraulic machine pressing speed closed-loop control system for angle steel bending forming, which comprises the following steps: collecting real-time pressing displacement data of the end of a pressing oil cylinder, analyzing and calculating the plastic strain rate of the instantaneous deformation zone and the initial valve opening of loading, identifying the stick-slip precursor through strain rate fluctuation variance and superimposing a micro compensation amount; identifying the effective deformation time interval with the strain rate higher than the preset plastic starting value, deducing the real-time matching pressing speed in combination with the real-time winding radius and the die wrap angle; selecting a preset uniform speed stroke segment to inversely calculate the current actual eccentric load friction coefficient, combining the elastic deformation amount of the piston rod to correct the displacement and generate the numerical value of the eccentric load action accumulation; combining the friction temperature coefficient of the sealing element to calculate the friction coefficient temperature correction factor, analyzing to obtain the strain rate temperature micro correction amount, and combining the oil temperature change rate to predict the average oil temperature of the pressed part and set the temperature interval boundary linear transition rule.

Description

Technical Field

[0001] This invention relates to the field of hydraulic press pressing control technology, specifically to a closed-loop control system for the pressing speed of a hydraulic press used for bending and forming angle steel. Background Technology

[0002] Existing hydraulic presses for bending and forming dry angle steel mostly adopt fixed speed open-loop or simple displacement closed-loop control, which is difficult to adapt to the complex working conditions of cold bending and rolling of asymmetric cross sections. They have multi-dimensional control defects. There is no pre-matching transition in the idle to loading stage, and load impact and strain rate jump are easily generated at the moment of contact. Conventional closed-loop correction without gradient constraint is prone to control overshoot and cannot identify stick-slip precursors. Stick-slip vibration caused by static and dynamic friction switching will degrade the forming surface quality and dimensional accuracy. In existing technologies, the cumulative effect of material work hardening across multiple passes is not considered. A fixed strain rate target leads to deformation resistance mismatch with increasing passes. Furthermore, the pressing speed is not dynamically adjusted in conjunction with the real-time rolling radius, resulting in significant fluctuations in the strain rate per unit arc length during the rolling radius contraction process, making it impossible to guarantee a uniform plastic deformation rate throughout the entire stroke. During asymmetric section pressing, the friction difference between the two cylinders under eccentric load is significant. Conventional synchronous control only detects the upper displacement of the cylinders, failing to compensate for the lower displacement deviation caused by the elastic deformation of the piston rod, and also failing to accumulate the eccentric load to compensate for unilateral mold wear. After long-term production, the consistency of forming on both sides continuously declines. The comprehensive impact of oil temperature fluctuations on valve flow capacity, sealing friction coefficient, and material deformation resistance is not systematically considered. Fixed parameter control easily leads to speed drift, while real-time adjustment of the compensation coefficient during the pressing process easily induces control oscillations, ultimately restricting the dimensional accuracy and mass production stability of the angle steel rolling process. Therefore, there is a need to provide a closed-loop control system for the pressing speed of a hydraulic press for bending angle steel. Summary of the Invention

[0003] The purpose of this invention is to provide a closed-loop control system for the downward pressing speed of a hydraulic press for bending angle steel. This system constructs a strain rate fluctuation variance stick-slip precursor identification and compensation mechanism, integrating hardening follow-up speed regulation, off-center load synchronous correction, and oil temperature prediction temperature compensation. This addresses the problems of impact vibration, accuracy drift, and poor batch consistency during the bending process. To solve the aforementioned problems in the prior art, this invention achieves this through the following technical solution: In a first aspect, the embodiments of the present invention provide a closed-loop control system for the downward pressing speed of a hydraulic press for bending angle steel, which specifically includes the following modules: Stick-slip speed control module: Collects real-time downward displacement data of the end of the downward cylinder, analyzes and calculates the plastic strain rate of the instantaneous deformation zone and the initial valve opening, constrains the single-cycle valve opening correction increment with the maximum correction gradient, identifies stick-slip precursors through strain rate fluctuation variance and superimposes micro-compensation amount; Hardening follow-up module: Combines the instantaneous deformation zone plastic strain rate sequence to identify the effective deformation time interval where the strain rate is higher than the preset plastic initial value, accumulates and recursively calculates the current pass material work hardening degree and corrects the benchmark target strain rate, and combines the real-time rolling radius and die wrap angle to derive the real-time matching pressing speed. Off-center load synchronization module: Using the real-time matching pressing speed as the initial control reference for both cylinders, the module selects a preset uniform stroke segment to back-calculate the current actual off-center load friction coefficient, calculates the off-center load friction difference to generate the corresponding valve opening compensation amount, and combines the piston rod elastic deformation amount to correct the displacement and generate the cumulative off-center load value. Temperature compensation module: Collects real-time oil temperature data at the hydraulic station outlet, calculates the friction coefficient temperature correction factor based on the friction temperature coefficient of the seal, analyzes and obtains the strain rate temperature micro-correction amount, predicts the average oil temperature of the next part pressing based on the oil temperature change rate, and sets the linear transition rule of the temperature range boundary.

[0004] Secondly, the present invention provides a closed-loop control method for the pressing speed of a hydraulic press for bending angle steel, which specifically includes the following steps: Step 1: Collect real-time downward displacement data of the end of the downward cylinder, analyze and calculate the plastic strain rate of the instantaneous deformation zone and the initial valve opening, use the maximum correction gradient to constrain the single-cycle valve opening correction increment, identify stick-slip precursors through strain rate fluctuation variance and superimpose micro-compensation amount; Step 2: Combine the instantaneous deformation zone plastic strain rate sequence to identify the effective deformation time interval where the strain rate is higher than the preset plastic initial value, accumulate and recursively calculate the current pass material work hardening degree and correct the benchmark target strain rate, and deduce the real-time matching pressing speed by combining the real-time rolling radius and the die wrap angle. Step 3: Using the real-time matching pressing speed as the initial control reference for both cylinders, select the preset uniform stroke segment to back-calculate the current actual off-center load friction coefficient, calculate the off-center load friction difference to generate the corresponding valve opening compensation amount, and combine the piston rod elastic deformation amount to correct the displacement and generate the off-center load cumulative amount value. Step 4: Collect real-time oil temperature data at the hydraulic station outlet, calculate the friction coefficient temperature correction factor based on the friction temperature coefficient of the seal, analyze and obtain the strain rate temperature micro-correction amount, predict the average oil temperature of the next part pressing based on the oil temperature change rate, and set the linear transition rule for the temperature range boundary.

[0005] The beneficial effects of this invention are: 1. Construct a valve-closed-loop mechanism with plastic strain rate as the direct control target, introduce single-cycle maximum correction gradient constraint to suppress control overshoot, use continuous three-cycle strain rate fluctuation variance to identify stick-slip precursors, generate a small positive compensation amount by linking interval proportion to break the stick-slip critical state in advance, and match the contact prediction position valve and speed with dual pre-matching to solve the defects of large impact of idle transition load, significant strain rate jump, and inability to intervene in stick-slip vibration in advance; establish a work hardening degree calculation model for cross-pass cumulative plastic deformation amount recursively, link hardening degree to reverse correct the benchmark target strain rate to offset the increase in yield strength, combine real-time rolling radius and die wrap angle to derive contact arc length and dynamically match pressing speed to ensure constant plastic deformation rate per unit arc length, and solve the defects of deformation resistance mismatch and uneven strain rate fluctuation of rolling radius shrinkage after multi-pass hardening under fixed strain rate control; 2. A method for calculating the friction coefficient of off-center load using dynamic identification in the uniform speed segment is adopted. The valve opening compensation amount is generated in real time to offset the difference in off-center load friction. The axial elastic deformation of the piston rod is introduced to correct the displacement feedback and ensure the synchronization of the lower end of the cylinder. The cumulative off-center load amount is used to derive the wear correction factor and offset the speed benchmark in the opposite direction. This solves the defects of low synchronization accuracy of dual cylinders under asymmetrical section, deformation deviation in displacement detection, and lack of compensation for wear on one side of the mold. An integrated correction system of valve flow, sealing friction, and strain rate linked to oil temperature is constructed. The average oil temperature of the lower part is predicted by the oil temperature change rate and the compensation coefficient is pre-assigned. A linear transition rule for the temperature range boundary is provided to solve the defects of speed drift caused by oil temperature fluctuation and control oscillation easily induced by adjustment during the pressing process. Attached Figure Description

[0006] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0007] Figure 1 This is a schematic diagram of the structure of a closed-loop control system for the downward pressing speed of a hydraulic press for bending angle steel, provided in Embodiment 1 of the present invention. Figure 2 This is a flowchart of the steps of a closed-loop control method for the downward pressing speed of a hydraulic press for bending angle steel, provided in Embodiment 2 of the present invention. Detailed Implementation

[0008] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0009] Example 1: As Figure 1 As shown in the figure, the hydraulic press pressing speed closed-loop control system for angle steel bending and forming provided by the present invention specifically includes the following modules: Stick-slip speed control module: Collects real-time downward displacement data of the end of the downward cylinder, analyzes and calculates the plastic strain rate of the instantaneous deformation zone and the initial valve opening, constrains the single-cycle valve opening correction increment with the maximum correction gradient, identifies stick-slip precursors through strain rate fluctuation variance and superimposes micro-compensation amount; In a specific embodiment, the closed-loop control unit for the downward pressing speed of the dry angle steel bending and forming hydraulic press collects real-time downward pressing displacement through a stroke detection device installed at the end of the downward pressing cylinder. The collection interval follows a preset displacement sampling period. The closed-loop control unit for the downward pressing speed of the dry angle steel bending and forming hydraulic press stores basic system configuration parameters. The system's basic configuration parameters include: the inner radius of the rolling target, the die surface parameters, the initial clamping position parameters of the dry angle steel, the hydraulic valve structure parameters, the hydraulic system pressure parameters, the lower limit threshold of the preset stick-slip precursor interval, the width of the preset stick-slip precursor interval, the maximum amplitude ratio of the preset stick-slip compensation, the maximum increment of the preset single-cycle stick-slip compensation, and the conversion coefficient of the preset strain rate deviation valve opening. Multiply the initial set pressing speed value by the web thickness value of the angle steel to obtain the numerator value; take the inner radius value of the rolled target, square it and multiply it by two to obtain the denominator value; divide the numerator value by the denominator value to obtain the plastic strain rate value of the target deformation zone. Calculate the theoretical contact displacement point between the angle steel and the mold based on the mold surface parameters and the initial clamping position parameters of the angle steel. Subtract the preset prediction distance value from the theoretical contact displacement point value to obtain the contact prediction position value. Take the displacement point corresponding to the contact prediction position value as the contact prediction position. Multiply the target downward pressing speed value of the deformation zone with the effective working area value of the rodless chamber of the downward pressing cylinder to obtain the target flow rate value. Multiply the pressure difference across the valve port by two and divide by the hydraulic oil density. Take the square root of the result to obtain the pressure difference flow rate conversion value. Multiply the valve port flow coefficient value by the valve port area gradient value and then multiply by the pressure difference flow rate conversion value to obtain the valve port unit opening flow capacity value. Divide the target flow rate value by the valve port unit opening flow capacity value to obtain the initial valve port opening value. Within each displacement sampling period, the instantaneous downward velocity is calculated based on the difference between two adjacent displacement sampling values. Following the same calculation logic as the plastic strain rate of the target deformation zone, the instantaneous plastic strain rate value of the deformation zone is obtained. Calculate the deviation between the instantaneous deformation zone plastic strain rate value and the target deformation zone plastic strain rate value, multiply the deviation value by the preset strain rate deviation valve opening conversion coefficient value, and generate the valve opening basic correction value. The valve opening correction increment within a single period is compared with the preset maximum correction gradient value. The valve opening correction increment is the difference between the current valve opening basic correction value and the previous sampling period final correction value. If the correction increment exceeds the maximum correction gradient value, the current correction value is output according to the maximum correction gradient value to avoid excessive correction range causing control overshoot. Extract the plastic strain rate values ​​of the instantaneous deformation zone for three consecutive sampling periods, calculate the fluctuation variance values ​​of the strain rate data for three consecutive sampling periods, and when the fluctuation variance values ​​enter the preset stick-slip precursor interval, extract the current fluctuation variance values ​​and the preset lower limit threshold values ​​of the stick-slip precursor interval, and calculate the difference between the two values; divide the difference values ​​by the preset stick-slip precursor interval width values ​​to obtain the interval proportion coefficient values. Multiply the interval proportion coefficient value by the preset stick-slip compensation maximum amplitude proportion value, and then multiply by the current cycle reference valve opening value. The current cycle reference valve opening value is the final valve opening command value output in the previous sampling cycle, thus obtaining the initial micro-amplitude positive compensation value. The initial micro-amplitude positive compensation value is compared with the preset maximum increment value of single-cycle stick-slip compensation. If the initial micro-amplitude positive compensation value exceeds the preset maximum increment value of single-cycle stick-slip compensation, the final micro-amplitude positive compensation value is output according to the preset maximum increment value of single-cycle stick-slip compensation. If it does not exceed the limit, the initial micro-amplitude positive compensation value is directly output as the final micro-amplitude positive compensation value to offset the sudden change in resistance during the switching process from static friction to dynamic friction. Specifically, when the pressing displacement of the hydraulic press for bending and forming dry angle steel reaches the contact prediction position, the closed-loop control unit adjusts the valve opening to the initial valve opening value before loading, and at the same time smoothly reduces the idle pressing speed to the target pressing speed in the deformation zone, ensuring that there is no load impact and strain rate jump when the dry angle steel contacts the mold. During the pressing process, the oil flow rate is adjusted in real time according to the valve opening correction amount after gradient constraint, so that the plastic strain rate of the instantaneous deformation zone gradually matches the plastic strain rate of the target deformation zone; when the characteristics of stick-slip precursor are identified, a small positive compensation amount is superimposed on the current valve opening command to break the stick-slip critical state in advance. For example, the preset displacement sampling period is 1 millisecond, the preset prediction distance is 5 millimeters, the preset maximum correction gradient corresponds to a strain rate adjustment amplitude of no more than 0.5% of the target value per cycle, the thickness of the angle steel web is 16 millimeters, the target inner radius is 1516 millimeters, the initial pressing speed is set to 0.015 meters per second, and the corresponding plastic strain rate of the target deformation zone is 5.2 × 10⁻⁶. -4 per second; Hardening follow-up module: Combines the instantaneous deformation zone plastic strain rate sequence to identify the effective deformation time interval where the strain rate is higher than the preset plastic initial value, accumulates and recursively calculates the current pass material work hardening degree and corrects the benchmark target strain rate, and combines the real-time rolling radius and die wrap angle to derive the real-time matching pressing speed. In a specific embodiment, the closed-loop control unit for the downward pressing speed of the dry angle steel bending and forming hydraulic press stores the actual deformation zone strain rate sequence for each pass, the effective deformation time interval, the real-time rolling radius sequence, and the pre-stored material and mold process parameters through the pass recording unit. The material and mold process parameters include material hardening curve parameters, preset mold wrap angle parameters, preset plasticity initiation value, material hardening strengthening coefficient value, and raw material initial hardness value; The instantaneous plastic strain rate values ​​of the deformation zone at each moment within a single pass are compared with the preset plastic starting value in the sampling time sequence. The moment when the strain rate value first exceeds the preset plastic starting value is marked as the start time of the interval, and the moment when the strain rate value first falls below the preset plastic starting value is marked as the end time of the interval. The effective deformation time interval value is obtained by subtracting the interval start time value from the interval end time value. Within the effective deformation time interval, the strain rate values ​​of the actual deformation zone at each moment are integrated. The integration operation adopts the trapezoidal numerical integration method, which multiplies the average strain rate of two adjacent sampling moments by the sampling period duration, and accumulates the calculation results of all time periods segment by segment to obtain the cumulative plastic deformation value of a single pass. The calculation process for the total cumulative plastic deformation and the work hardening degree of the material is as follows: the cumulative plastic deformation values ​​of all completed passes are summed to obtain the current total cumulative plastic deformation value; the total cumulative plastic deformation value is multiplied by the material hardening coefficient value to obtain the hardening increment value; the initial hardening degree of the raw material is added to the hardening increment value to obtain the work hardening degree value of the material at the beginning of the current pass. Based on the current material work hardening value, the reference target strain rate value for the current pass is adjusted. When the material work hardening is higher than the initial hardening, the reference target strain rate value is reduced accordingly to offset the increase in material yield strength caused by hardening. During the pressing process, the contact point coordinates between the angle steel and the die are determined based on the real-time pressing displacement and die surface parameters. The current deformation arc is then fitted by combining the die surface arc parameters to calculate the current inner radius of the roll. Multiply the current inner radius of the roll by the radian value of the preset mold wrap angle to obtain the contact arc length of the deformation zone; multiply the reference target strain rate by the square of twice the current inner radius of the roll to obtain the numerator value; divide the numerator value by the web thickness of the dry angle steel to obtain the real-time matching pressing speed value. The closed-loop control unit of the hydraulic press for bending and forming dry angle steel uses the corrected reference target strain rate value as the control reference for the current pass, replacing the initially set fixed strain rate parameter. The calculated real-time matching pressing speed value is input into the contact pre-matching and strain rate full-segment smoothing calibration link to dynamically update the speed target value, so that the plastic deformation rate per unit arc length remains constant during the process of reducing the rolling radius and increasing the contact arc length. For example, the preset plasticity initial value is 0.9 times the material yield strain, the preset die wrap angle is 20 degrees, the cumulative plastic deformation per pass is 0.003, and the total cumulative plastic deformation after 8 passes is 0.024, corresponding to a 12% increase in the material work hardening degree compared to the initial value, and a corresponding decrease of about 8% in the benchmark target strain rate; during the process of reducing the rolling radius from 1600 mm to 1500 mm, the real-time matching pressing speed is dynamically adjusted from 0.0164 m / s to 0.0144 m / s. Off-center load synchronization module: Using the real-time matching pressing speed as the initial control reference for both cylinders, the module selects a preset uniform stroke segment to back-calculate the current actual off-center load friction coefficient, calculates the off-center load friction difference to generate the corresponding valve opening compensation amount, and combines the piston rod elastic deformation amount to correct the displacement and generate the cumulative off-center load value. In a specific embodiment, the hydraulic press for bending and forming dry angle steel is equipped with a left-side pressing cylinder and a right-side pressing cylinder, with the two pressing cylinders acting on the two flanges of the dry angle steel section respectively; The closed-loop control unit for the downward pressing speed of the hydraulic press for bending and forming dry angle steel collects real-time displacement data of the left cylinder through the stroke detection device matched with the left cylinder, and collects real-time pressure data of the rodless chamber of the left cylinder through the pressure detection device matched with the left cylinder. The closed-loop control unit for the downward pressing speed of the dry angle steel bending and forming hydraulic press collects real-time displacement data of the right-side cylinder through the stroke detection device matched with the right-side cylinder, and collects real-time pressure data of the rodless chamber of the right-side cylinder through the pressure detection device matched with the right-side cylinder. The data acquisition intervals on both sides are consistent with the preset displacement sampling period. The closed-loop control unit of the hydraulic press for bending and forming dry angle steel stores the cylinder and structural correction parameters. The cylinder and structural modification parameters include: cylinder structural parameters, piston rod elastic modulus parameters, mold wear correction benchmark parameters, preset opening resistance conversion coefficient value, piston rod effective length value, piston rod cross-sectional area value, and preset wear accumulation coefficient value. The corresponding instantaneous downward speed is calculated based on the real-time displacement data of the left and right cylinders. The reference target downward speed value is used as the initial value to generate the valve opening command of the left and right cylinders respectively, thus constructing a dual-sided independent speed closed loop foundation. A preset constant speed travel segment is selected within each pass. The preset constant speed travel segment is determined by a combination of dynamic judgment and fixed interval fallback. The dynamic judgment rule is to extract the instantaneous downward speed value within a consecutive preset number of sampling periods, calculate the fluctuation range of the speed value, and when the fluctuation range is less than the preset speed fluctuation threshold value, the interval is determined to be a constant speed travel segment. If the dynamic judgment does not identify a valid constant speed interval, the middle 30% travel interval of each pass is selected as the constant speed travel segment by default. Extract the average pressure difference and the average speed deviation of the two cylinders within the constant speed stroke segment; take the average speed deviation value within the constant speed stroke segment, multiply it by the effective working area value of the rodless chamber of the lower pressure cylinder, and obtain the flow deviation value; Divide the flow deviation value by the flow capacity value per unit opening of the valve to obtain the valve opening deviation value. Multiply the valve opening deviation value by the preset opening resistance conversion coefficient value to obtain the resistance difference value. Multiply the average pressure difference between the two sides by the effective working area of ​​the rodless chamber of a single cylinder to obtain the value of the eccentric load positive pressure. Divide the resistance difference value by the eccentric load normal pressure value to obtain the current actual eccentric load friction coefficient value. Update the fixed friction coefficient benchmark in the compensation model with the current actual eccentric load friction coefficient value. The initial value of the fixed friction coefficient benchmark in the compensation model is taken as the preset standard friction coefficient value. The preset standard friction coefficient value is determined by the factory friction characteristic parameters of the cylinder seal. Multiply the real-time pressure difference between the rodless chambers of the two cylinders by the effective working area of ​​the rodless chamber of the lower cylinder, and then multiply by the current actual eccentric load friction coefficient to obtain the eccentric load friction difference value. Divide the value of the difference in friction force due to eccentric load by the value of the effective working area of ​​the rodless chamber of the lower pressure cylinder to obtain the value of the compensation pressure difference. Substitute the value of the compensation pressure difference into the valve port flow characteristic formula to obtain the value of the valve port opening compensation of the cylinder on the side with greater pressure. The compensation amount is to offset the speed reduction caused by the additional friction force; based on the real-time rodless chamber pressure values ​​of the two cylinders, the real-time pressure value of the rodless chamber of the cylinder is multiplied by the effective working area value of the rodless chamber of the lower cylinder to obtain the axial force value of the piston rod. Multiply the axial force value of the piston rod by the effective length value of the piston rod, divide by the cross-sectional area value of the piston rod, and then divide by the elastic modulus value of the piston rod to obtain the axial elastic deformation value of the piston rod. Calculate the difference in axial elastic deformation values ​​of the piston rods on both sides, and convert the difference in axial elastic deformation values ​​of the piston rods on both sides into displacement compensation; record the difference in eccentric load pressure and the corresponding duration of each pass, and generate the cumulative value of eccentric load. After producing a preset number of workpieces, the cumulative value of the off-center load is multiplied by the preset wear accumulation coefficient value, and then divided by the mold wear correction reference parameter value to obtain the mold wear correction factor value. The closed-loop control unit of the hydraulic press for bending and forming dry angle steel adds the valve opening compensation amount to the basic valve opening command on the side with greater pressure, thereby offsetting the additional friction caused by the off-center load and keeping the actual pressing speed on both sides consistent. The displacement compensation is superimposed on the stroke detection feedback value on the corresponding side to ensure the displacement synchronization accuracy of the actual action point at the lower end of the cylinder, rather than the nominal synchronization of the detection point at the upper end of the cylinder. When the preset production quantity is reached, the closed-loop control unit of the hydraulic press for bending and forming dry angle steel applies a slight reverse offset to the speed reference of the cylinders on both sides according to the mold wear correction factor, so as to offset the difference in surface height caused by the wear of one side of the mold. For example, the preset uniform speed stroke segment is the middle 30% stroke interval of each pass, the effective working area of ​​the rodless chamber of a single cylinder is 0.012 square meters, and the pressure difference between the two cylinders when the asymmetrical section is pressed down is 0.5 MPa. Temperature compensation module: Collects real-time oil temperature data at the hydraulic station outlet, calculates the friction coefficient temperature correction factor based on the friction temperature coefficient of the seal, analyzes and obtains the strain rate temperature micro-correction amount, predicts the average oil temperature of the next part pressing based on the oil temperature change rate, and sets the linear transition rule of the temperature range boundary. In a specific embodiment, the closed-loop control unit for the downward pressing speed of the dry angle steel bending and forming hydraulic press collects real-time hydraulic oil temperature data through an oil temperature detection device installed at the oil outlet of the hydraulic station. The data collection interval follows a preset temperature sampling cycle, and the closed-loop control unit for the downward pressing speed of the dry angle steel bending and forming hydraulic press stores temperature-related characteristic parameters. The closed-loop control unit of the hydraulic press for bending and forming dry angle steel pre-stores parameters corresponding to hydraulic oil viscosity and temperature, friction temperature coefficient of seals, and yield strength temperature coefficient of materials. Temperature-related characteristic parameters include: hydraulic oil viscosity-temperature parameters, seal friction temperature coefficient, material yield strength temperature coefficient, standard oil temperature value, standard kinematic viscosity value, preset temperature range parameters, and estimated pressing time for the next workpiece. Based on the real-time oil temperature value and the preset hydraulic oil viscosity temperature corresponding parameters, the kinematic viscosity value of the hydraulic oil at the current oil temperature is calculated by interpolation; the ratio of the kinematic viscosity value of the hydraulic oil at the standard oil temperature to the kinematic viscosity value of the hydraulic oil at the current oil temperature is taken, and the square root of the ratio of the kinematic viscosity value of the hydraulic oil at the standard oil temperature to the current oil temperature is taken to obtain the valve port flow correction coefficient value. Take the difference between the current oil temperature and the standard oil temperature, multiply it by the preset friction temperature coefficient of the seal to obtain the friction coefficient change rate; add one to the friction coefficient change rate to obtain the friction coefficient temperature correction factor. Based on the difference between the current oil temperature and the standard oil temperature, the difference is multiplied by the preset material yield strength temperature coefficient, and then multiplied by the benchmark target strain rate to obtain the strain rate temperature micro-correction value. When the oil temperature increases, the material deformation temperature increases, and the material yield strength decreases, corresponding to a slight increase in the benchmark target strain rate value; when the oil temperature decreases, the benchmark target strain rate value is slightly decreased to ensure that the deformation resistance matches the loading speed. Extract the oil temperature values ​​at the start and end of the continuous preset duration, subtract the oil temperature value at the start from the end time, and then divide by the continuous preset duration to obtain the oil temperature change rate value. Based on the oil temperature change rate, take the current oil temperature value, add the oil temperature change rate value, multiply by the estimated pressing time of the next workpiece, and then divide by two to obtain the predicted average oil temperature value for pressing the next workpiece. The initial values ​​of the valve orifice flow correction coefficient, friction coefficient temperature correction factor, and strain rate temperature micro-correction amount are calculated in advance based on the predicted average oil temperature. When the oil temperature fluctuates near the boundary of two adjacent preset temperature ranges, and the absolute value of the difference between the oil temperature and the preset temperature range boundary value is less than the preset boundary fluctuation threshold value, it is determined that the oil temperature is fluctuating near the range boundary. Determine the boundary values ​​of the two adjacent preset temperature ranges to which the current oil temperature value belongs, calculate the ratio of the difference between the current oil temperature value and the boundary value of the low temperature range to the total width of the range, take the difference between the compensation coefficient value corresponding to the low temperature range and the compensation coefficient value corresponding to the high temperature range, multiply it by the ratio value, and then add the compensation coefficient value corresponding to the low temperature range to obtain the linear transition value of the compensation coefficient, so that the compensation coefficient does not undergo a step change. The closed-loop control unit of the hydraulic press for bending and forming dry angle steel multiplies the valve port flow correction coefficient with the basic valve port opening command to obtain the valve port opening command after flow compensation, thus offsetting the fluctuation of valve port flow capacity caused by oil temperature changes. The friction coefficient temperature correction factor is applied to the fixed friction coefficient benchmark in the dynamic identification and synchronous compensation of the uneven load friction of the dual-cylinder, correcting the fluctuation of the friction coefficient of the seal caused by oil temperature changes. The strain rate temperature micro-correction value is superimposed on the benchmark target strain rate value of the cross-pass hardening recursion and arc length follow-up strain rate adaptation link to offset the change of material deformation resistance with temperature. Before pressing the next workpiece, the closed-loop control unit of the angle steel bending forming hydraulic press sets the pre-set values ​​of the three compensation coefficients according to the predicted oil temperature. During the pressing of a single workpiece, the three compensation coefficients remain unchanged at the initial values ​​set before pressing and are not adjusted in real time. If the oil temperature changes during pressing and exceeds the preset oil temperature allowable deviation threshold, the compensation coefficient values ​​are updated before the start of the next pass to avoid control oscillation caused by frequent adjustments during pressing. For example, the preset standard oil temperature is 40 degrees Celsius, corresponding to a standard kinematic viscosity of 46 square millimeters per second, and the preset temperature sampling period is 10 seconds. When the oil temperature rises to 60 degrees Celsius, the kinematic viscosity of the hydraulic oil drops to 28 square millimeters per second, corresponding to a valve port flow correction coefficient of 0.78 and a friction coefficient temperature correction factor of 0.92.

[0010] Example 2: Based on the same inventive concept as the closed-loop control system for the downward pressing speed of a hydraulic press for bending angle steel in the foregoing examples, such as... Figure 2 As shown in the figure, the closed-loop control method for the downward pressing speed of a hydraulic press for bending angle steel provided by the present invention specifically includes the following steps: Step 1: Collect real-time downward displacement data of the end of the downward cylinder, analyze and calculate the plastic strain rate of the instantaneous deformation zone and the initial valve opening, use the maximum correction gradient to constrain the single-cycle valve opening correction increment, identify stick-slip precursors through strain rate fluctuation variance and superimpose micro-compensation amount; Step 2: Combine the instantaneous deformation zone plastic strain rate sequence to identify the effective deformation time interval where the strain rate is higher than the preset plastic initial value, accumulate and recursively calculate the current pass material work hardening degree and correct the benchmark target strain rate, and deduce the real-time matching pressing speed by combining the real-time rolling radius and the die wrap angle. Step 3: Using the real-time matching pressing speed as the initial control reference for both cylinders, select the preset uniform stroke segment to back-calculate the current actual off-center load friction coefficient, calculate the off-center load friction difference to generate the corresponding valve opening compensation amount, and combine the piston rod elastic deformation amount to correct the displacement and generate the off-center load cumulative amount value. Step 4: Collect real-time oil temperature data at the hydraulic station outlet, calculate the friction coefficient temperature correction factor based on the friction temperature coefficient of the seal, analyze and obtain the strain rate temperature micro-correction amount, predict the average oil temperature of the next part pressing based on the oil temperature change rate, and set the linear transition rule for the temperature range boundary.

[0011] 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 closed-loop control system for the downward pressing speed of a hydraulic press for bending angle steel, characterized in that, Includes the following modules: Stick-slip speed control module: Collects real-time downward displacement data of the end of the downward cylinder, analyzes and calculates the plastic strain rate of the instantaneous deformation zone and the initial valve opening, constrains the single-cycle valve opening correction increment with the maximum correction gradient, identifies stick-slip precursors through strain rate fluctuation variance and superimposes micro-compensation amount; The method for identifying early signs of stickiness is as follows: Extract the plastic strain rate values ​​of the instantaneous deformation zone for three consecutive sampling periods, calculate the fluctuation variance values ​​of the strain rate data for three consecutive sampling periods, and when the fluctuation variance values ​​enter the preset stick-slip precursor interval, extract the current fluctuation variance values ​​and calculate the difference between the current fluctuation variance values ​​and the preset lower limit threshold values ​​of the stick-slip precursor interval, and divide the difference values ​​by the preset stick-slip precursor interval width values ​​to obtain the interval proportion coefficient. The initial micro-amplitude positive compensation amount is obtained by multiplying the interval proportion coefficient by the preset maximum stick-slip compensation value and then multiplying it by the current cycle reference valve opening value. The initial micro-positive compensation amount is compared with the preset maximum increment value of single-cycle stick-slip compensation. If it exceeds the preset maximum increment value of single-cycle stick-slip compensation, the final micro-positive compensation amount is output according to the preset maximum increment value of single-cycle stick-slip compensation. If it does not exceed the preset maximum increment value of stick-slip compensation, the initial micro-positive compensation amount is output directly. Hardening follow-up module: Combines the instantaneous deformation zone plastic strain rate sequence to identify the effective deformation time interval where the strain rate is higher than the preset plastic initial value, accumulates and recursively calculates the current pass material work hardening degree and corrects the benchmark target strain rate, and combines the real-time rolling radius and die wrap angle to derive the real-time matching pressing speed. The method for recursively calculating the work hardening degree of the material in the current pass is as follows: Within the effective deformation time interval, the trapezoidal numerical integration method is used to multiply the average strain rate of two adjacent sampling times by the sampling period duration and accumulate them segment by segment to obtain the cumulative plastic deformation value of a single pass. The total cumulative plastic deformation value is obtained by summing the cumulative plastic deformation values ​​of all completed passes. The total cumulative plastic deformation value is multiplied by the material hardening coefficient to obtain the hardening increment value. The initial hardness value of the raw material is added to the hardening increment value to obtain the material work hardness value at the start of the current pass. Off-center load synchronization module: Using the real-time matching pressing speed as the initial control reference for both cylinders, the module selects a preset uniform stroke segment to back-calculate the current actual off-center load friction coefficient, calculates the off-center load friction difference to generate the corresponding valve opening compensation amount, and combines the piston rod elastic deformation amount to correct the displacement and generate the cumulative off-center load value. Temperature compensation module: Collects real-time oil temperature data at the hydraulic station outlet, calculates the friction coefficient temperature correction factor based on the friction temperature coefficient of the seal, analyzes and obtains the strain rate temperature micro-correction amount, predicts the average oil temperature of the next part pressing based on the oil temperature change rate, and sets the linear transition rule of the temperature range boundary. The method for predicting the average oil temperature during pressing of the lower part is as follows: Extract the oil temperature values ​​at the start and end of the continuous preset duration, subtract the oil temperature value at the start from the oil temperature value at the end, and then divide by the continuous preset duration to obtain the oil temperature change rate value. Take the current oil temperature value, add the oil temperature change rate value, multiply by the estimated pressing time of the next workpiece, and then divide by two to obtain the predicted average oil temperature value for the next workpiece pressing. Combine the predicted average oil temperature to calculate the initial values ​​of the corresponding valve flow correction coefficient, friction coefficient temperature correction factor, and strain rate temperature micro-correction amount in advance.

2. The closed-loop control system for the downward pressing speed of a hydraulic press for bending angle steel according to claim 1, characterized in that, The method for constraining the single-cycle valve opening correction increment is as follows: Calculate the deviation between the instantaneous deformation zone plastic strain rate value and the target deformation zone plastic strain rate value, and multiply the deviation value by the preset strain rate deviation valve opening conversion coefficient value to generate the valve opening basic correction value. The difference between the current valve opening basic correction value and the previous sampling period final valve opening correction value is used to calculate the valve opening correction increment. The valve opening correction increment is compared with the preset maximum correction gradient value. If it exceeds the maximum correction gradient value, the current correction value is output according to the maximum correction gradient value. If it does not exceed the maximum correction gradient value, the current correction value is output according to the valve opening basic correction value.

3. The closed-loop control system for the downward pressing speed of a hydraulic press for bending angle steel according to claim 1, characterized in that, The method for obtaining the effective deformation time interval is as follows: The instantaneous plastic strain rate values ​​of the deformation zone at each moment within a single pass are compared with the preset plastic starting value in the order of sampling time. The moment when the strain rate value first exceeds the preset plastic starting value is marked as the start time of the interval. The moment when the marked strain rate value first falls below the preset plasticity initiation value is the interval termination time. The effective deformation time interval value is obtained by subtracting the interval initiation time value from the interval termination time value.

4. The closed-loop control system for the downward pressing speed of a hydraulic press for bending angle steel according to claim 1, characterized in that, The method for deriving the real-time matching downward pressure speed is as follows: The coordinates of the contact point between the dry angle steel and the mold are determined based on the real-time downward displacement value. The current deformation arc is fitted by the mold surface arc parameters to calculate the current inner radius value of the roll. The current inner radius value of the roll is multiplied by the arc value of the preset mold wrap angle to obtain the contact arc length value of the deformation zone. The numerator is obtained by multiplying the baseline target strain rate by the square of twice the current inner radius of the roll. The numerator is then divided by the web thickness of the angle steel to obtain the real-time matching pressing speed.

5. A closed-loop control system for the downward pressing speed of a hydraulic press for bending angle steel according to claim 1, characterized in that, The method for obtaining the current actual off-center load friction coefficient is as follows: Select a preset uniform speed stroke segment within each pass, extract the average pressure difference and average speed deviation of the two cylinders within the uniform speed stroke segment, and multiply the average speed deviation by the effective working area of ​​the rodless chamber of the lower pressure cylinder to obtain the flow deviation value. Divide the flow deviation value by the flow capacity value per unit opening of the valve to obtain the valve opening deviation value, and multiply the valve opening deviation value by the preset opening resistance conversion coefficient value to obtain the resistance difference value. Multiply the average pressure difference between the two sides by the effective working area of ​​the rodless chamber of a single cylinder to obtain the eccentric load positive pressure value. Divide the resistance difference value by the eccentric load positive pressure value to obtain the current actual eccentric load friction coefficient value.

6. The closed-loop control system for the downward pressing speed of a hydraulic press for bending angle steel according to claim 1, characterized in that, The method for generating the cumulative value of off-center loading is as follows: Based on the real-time rodless chamber pressure values ​​of both cylinders, the axial force value of the piston rod is obtained by multiplying the real-time pressure value of the rodless chamber of the cylinder by the effective working area value of the rodless chamber of the lower cylinder; the axial force value of the piston rod is multiplied by the effective length value of the piston rod, divided by the cross-sectional area value of the piston rod, and then divided by the elastic modulus value of the piston rod to obtain the axial elastic deformation value of the piston rod. Calculate the difference in axial elastic deformation values ​​of the piston rods on both sides, and convert the difference in axial elastic deformation values ​​of the piston rods on both sides into displacement compensation. The differential pressure value of the eccentric load and the corresponding duration of each cycle are recorded to generate the cumulative value of the eccentric load.

7. A closed-loop control system for the downward pressing speed of a hydraulic press for bending angle steel according to claim 1, characterized in that, The method for setting the linear transition rule for the temperature range boundary is as follows: When the absolute value of the difference between the oil temperature value and the boundary value of the preset temperature range is less than the preset boundary fluctuation threshold value, determine the boundary values ​​of the two adjacent preset temperature ranges to which the current oil temperature value belongs, and calculate the proportion of the difference between the current oil temperature value and the boundary value of the low temperature range to the total width of the range. The difference between the compensation coefficient value corresponding to the low temperature range and the compensation coefficient value corresponding to the high temperature range is multiplied by the proportional value and then superimposed on the compensation coefficient value corresponding to the low temperature range to obtain the linear transition value of the compensation coefficient.

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