Multi-cylinder synchronous control method and system for hydraulic forging press

Abstract

The invention discloses a multi-cylinder synchronous control method and system for a hydraulic forging press, particularly relates to the technical field of manufacturing of large aluminum forgings, and is used for solving the problem that the forming quality of the forgings is influenced due to load mismatch of hydraulic cylinders caused by non-uniform cooling of the forgings in a pressure maintaining stage in the prior art. A mold heat dissipation heat flow signal and a hydraulic cylinder output mechanical work signal are monitored in real time in the pressure maintaining stage, and the inter-cylinder load cooperation state is evaluated based on the piston rod side pressure change rate to generate the dynamic load unbalance amount; calculating a heat flow and mechanical power spectrum entropy ratio to identify a load mismatch stage; after mismatch is recognized, the output work quantity difference of all cylinders is counted and analyzed, and the displacement synchronization reference value is dynamically optimized with the purpose of maintaining load balance; and finally, performing high-precision displacement closed-loop control on each hydraulic cylinder according to the optimized reference value. The device can actively adapt to heat-force coupling changes in the pressure maintaining process, and the multi-cylinder synchronization precision and the internal quality of forgings are effectively improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of large aluminum forging manufacturing, and particularly relates to a multi-cylinder synchronous control method and system of a forging hydraulic press. BACKGROUND

[0002] The large multi-cylinder forging hydraulic press is key equipment for manufacturing aluminum forgings for aerospace, such as integral frames, beams and thin-walled curved structural parts. Such forgings have extremely high requirements for internal organization uniformity, dimensional accuracy and residual stress distribution. In the forging process, the synchronization accuracy of multiple hydraulic cylinders directly determines the forming quality of the forgings. In the prior art, multi-cylinder synchronous control mainly focuses on displacement or force synchronization in the active pressurization phase, and reduces the trajectory deviation of each cylinder actuator in the dynamic process through a feedback control strategy. In the pressure maintaining phase, the control system usually maintains the displacement or pressure parameters of each cylinder constant, and is regarded as a static maintaining process.

[0003] However, in the actual production of large aluminum forgings for aerospace, the cooling and setting of the high-temperature blank under the pressure maintaining pressure in the mold cavity is a complex process involving thermodynamics and structural mechanics coupling. Due to the differences in thermal physical properties between the forging material and the mold material, and the non-uniform heat dissipation caused by the geometric characteristics of the forgings, the system will produce a continuously changing non-uniform thermal stress in the pressure maintaining phase. This stress field acts on the mold, causing the load borne by the multiple hydraulic cylinders driving the upper die to be mismatched in time-varying deformation, which destroys the mechanical balance established in the initial pressure maintaining stage, making it difficult for the synchronous control strategy based on the static assumption to maintain true synchronization between the cylinders, and further affecting the stress state and final quality of the forgings in the critical setting stage. SUMMARY

[0004] The present application provides a multi-cylinder synchronous control method and system of a forging hydraulic press to solve the technical problems in the prior art.

[0005] The technical solution of the present application to solve the above technical problems is as follows: A multi-cylinder synchronous control method of a forging hydraulic press, comprising: S1, monitoring the piston rod side pressure values of the multiple hydraulic cylinders acting on the upper die in real time in the pressure maintaining phase, and synchronously acquiring the heat flow signal and mechanical work signal of the mold heat dissipation; S2, evaluating the discrete coordination degree between the piston rod side pressure change rates of each hydraulic cylinder based on the piston rod side pressure values, and generating a dynamic load imbalance quantity; S3, calculating the ratio of the heat flow power spectrum entropy of the mold heat dissipation to the mechanical power spectrum entropy of the hydraulic cylinder output based on the heat flow signal and the mechanical work signal, and identifying whether the pressure maintaining process enters the load mismatch stage; S4, when it is identified that the load mismatch stage is entered, calculating the output work amount of each hydraulic cylinder for maintaining the displacement synchronization reference within a set time period, and evaluating the relative difference of the output work amount of each hydraulic cylinder. S5、with the goal of maintaining dynamic load imbalance, and based on the relative difference in the output power of each hydraulic cylinder, dynamically adjusting the displacement synchronization reference value of each hydraulic cylinder; S6、based on the dynamically adjusted displacement synchronization reference value, performing displacement closed-loop control on each hydraulic cylinder.

[0006] Further, in the pressure maintaining phase, the piston rod side pressure value of each hydraulic cylinder acting on the upper die is monitored in real time, and the heat flow signal and mechanical work signal of the mold heat dissipation are synchronously obtained, including: Real-time monitoring of the temperature value of at least two predetermined points in the mold cavity, calculating the temperature change per unit time based on the temperature value, and taking the change as the heat flow signal representing the heat dissipation intensity of the mold; Synchronously, the piston rod side pressure value and the piston rod displacement value of each hydraulic cylinder are monitored in real time, and the rate of change of the piston rod displacement with time is calculated, and the piston rod side pressure value is multiplied by the displacement rate of change to obtain the mechanical work signal representing the real-time output power of the hydraulic cylinder.

[0007] Further, based on the piston rod side pressure value, the degree of dispersion and cooperation between the piston rod side pressure change rates of each hydraulic cylinder is evaluated, and a dynamic load imbalance is generated, including: Based on the real-time monitored piston rod side pressure value, the piston rod side pressure change rate of each hydraulic cylinder with time is calculated; Analyze the fluctuation trend of the piston rod side pressure change rate of each hydraulic cylinder in the time domain, and identify whether there is a hydraulic cylinder with a persistent differentiation in the trend of the change rate; Calculate the arithmetic mean of the piston rod side pressure change rates of all hydraulic cylinders at the same time, and calculate the instantaneous deviation of the piston rod side pressure change rate of each hydraulic cylinder from the arithmetic mean; Introduce a sliding time window, and calculate the cumulative effect intensity of the instantaneous deviation of each hydraulic cylinder within the window; Normalize the cumulative effect intensity of each hydraulic cylinder, and combine the indicators representing the deterioration degree of each cylinder after normalization to generate a dynamic load imbalance.

[0008] Further, analyze the fluctuation trend of the piston rod side pressure change rate of each hydraulic cylinder in the time domain, and identify whether there is a hydraulic cylinder with a persistent differentiation in the trend of the change rate, which is achieved by the following way: Segmented linear fitting is performed on the piston rod side pressure change rate sequence of each hydraulic cylinder, and the average slope of the change rate in each time period is calculated; Compare the slope direction and size of different hydraulic cylinders in the same time period; When the slope direction of a certain hydraulic cylinder is continuously opposite to that of the majority of other hydraulic cylinders, or the difference between the absolute value of the slope and the average value continuously exceeds a certain threshold, it is determined that the corresponding cylinder has a trend differentiation.

[0009] Further, a ratio of heat flow power spectrum entropy of mold heat dissipation and mechanical power spectrum entropy of hydraulic cylinder output is calculated based on heat flow signal and mechanical work signal, whether the holding pressure process enters the load mismatch stage is identified, comprising: The heat flow signal and the mechanical work signal are intercepted by synchronous time windows, and the ratio sequence of the heat flow signal power spectrum entropy and the mechanical work signal power spectrum entropy in each time window is calculated; The change trend of the ratio sequence with time is analyzed, when it is detected that the ratio sequence presents a monotonic change trend of continuously deviating from the initial reference value in one direction, and the change amplitude exceeds the set tolerance, it is verified that the monotonic change trend lasts for a preset minimum duration; When the amplitude condition and the duration condition are met at the same time, it is determined that the holding pressure process enters the load mismatch stage.

[0010] Further, the heat flow signal and the mechanical work signal are intercepted by synchronous time windows, and the ratio sequence of the heat flow signal power spectrum entropy and the mechanical work signal power spectrum entropy in each time window is calculated, which is realized by the following way: The synchronous time window is intercepted in a fixed time length and overlapping sliding manner; The power spectrum entropy value of the heat flow signal and the power spectrum entropy value of the mechanical work signal are calculated in each window respectively: the signal data in the window is subjected to Fourier transform to obtain power spectrum density estimation; the power spectrum density is normalized on all frequency components, so that the sum of the power values on each frequency component is 1, thereby forming a probability distribution; the Shannon entropy is calculated based on the probability distribution, and the obtained entropy value is the power spectrum entropy value of the corresponding signal; the power spectrum entropy values of the heat flow signal and the mechanical work signal are independently calculated according to the same process; The heat flow power spectrum entropy value and the mechanical power spectrum entropy value calculated in the same window are divided to obtain the instantaneous ratio value corresponding to the time window; The instantaneous ratio values of each window are arranged in time sequence to form a ratio sequence.

[0011] Further, when the load mismatch stage is identified, the output work amount of each hydraulic cylinder for maintaining the displacement synchronization reference in a set time period is calculated, and the relative difference of the output work amount of each hydraulic cylinder is evaluated, comprising: When the load mismatch stage is identified, the timing is started and the statistical time period is set; In the statistical time period, the mechanical work signal of each hydraulic cylinder is time-integrated to obtain the output work amount of each hydraulic cylinder in the process of maintaining the displacement synchronization reference; The average value of the output work amount of all hydraulic cylinders is calculated; The deviation of the output work amount of each hydraulic cylinder from the average value is calculated respectively based on the average value; Based on the deviation degree of the output power of each hydraulic cylinder, the relative difference distribution characteristics of the output power of the hydraulic cylinder group are evaluated.

[0012] Further, the displacement synchronization reference value of each hydraulic cylinder is dynamically adjusted based on the relative difference of the output power of each hydraulic cylinder, aiming to maintain the stability of the dynamic load imbalance, including: Establish a corresponding relationship between the dynamic load imbalance and the adjustment amount of the displacement synchronization reference value; According to the relative difference distribution characteristics of the output power of each hydraulic cylinder, the adjustment priority of the displacement synchronization reference value of each hydraulic cylinder is determined; For the hydraulic cylinders ranked high in the adjustment priority order, the displacement synchronization reference value is adjusted preferentially; Combined with the real-time change trend of the dynamic load imbalance, the displacement synchronization reference value of each hydraulic cylinder is compensated and corrected; Through iterative adjustment, the dynamic load imbalance gradually returns to the stable interval range.

[0013] Further, based on the dynamically adjusted displacement synchronization reference value, the displacement of each hydraulic cylinder is closed-loop controlled, including: The piston rod displacement value of each hydraulic cylinder is compared with the corresponding dynamically adjusted displacement synchronization reference value, and the displacement deviation value of each hydraulic cylinder is obtained; According to the size and direction of the displacement deviation value, the corresponding control signal is generated; The control signal is output to the servo valve group of each hydraulic cylinder to adjust the flow entering the hydraulic cylinder; Through continuous feedback adjustment, the actual displacement value of the piston rod of each hydraulic cylinder is tracked to the dynamically adjusted displacement synchronization reference value; The closed-loop control of the displacement of each hydraulic cylinder is maintained throughout the pressure maintaining stage until the pressure maintaining process is completed.

[0014] On the other hand, the present application provides a multi-cylinder synchronous control system for a forging hydraulic press, comprising: An information acquisition module is used to monitor the piston rod side pressure value of the plurality of hydraulic cylinders acting on the upper die in real time during the pressure maintaining stage, and to synchronously acquire the heat flow signal and mechanical work signal of the mold heat dissipation; An imbalance analysis module is used to evaluate the discrete coordination degree between the piston rod side pressure change rates of each hydraulic cylinder based on the piston rod side pressure value, and to generate a dynamic load imbalance; A mismatch judgment module is used to calculate the ratio of the heat flow power spectrum entropy of the mold heat dissipation to the mechanical power spectrum entropy of the hydraulic cylinder output based on the heat flow signal and the mechanical work signal, and to identify whether the pressure maintaining process enters the load mismatch stage; a mismatch analysis module, configured to calculate the output work amount of each hydraulic cylinder for maintaining the displacement synchronization reference within a set time period when identifying that the load mismatch stage is entered, and evaluate the relative difference of the output work amount of each hydraulic cylinder; a target adjustment module, configured to take the target of maintaining the dynamic load imbalance stable, and dynamically adjust the displacement synchronization reference value of each hydraulic cylinder based on the relative difference of the output work amount of each hydraulic cylinder; a closed-loop control module, configured to perform displacement closed-loop control on each hydraulic cylinder based on the dynamically adjusted displacement synchronization reference value.

[0015] The present application has the following beneficial effects: 1. By monitoring the mold heat dissipation heat flow and the hydraulic cylinder output mechanical work in real time during the pressure maintaining stage, and introducing the power spectrum entropy ratio as the criterion for identifying the load mismatch, the dynamic influence of the thermal stress change caused by the non-uniform cooling of the forged piece on the load distribution of the hydraulic cylinder can be sensitively captured, the limitation of regarding the process as static in the traditional pressure maintaining control is broken, the focus of the synchronization control is extended from the simple geometric displacement tracking to the energy level of the thermal-mechanical coupling, so that the system can perceive and respond to the load imbalance trend caused by the thermodynamic factors in advance, and a solid foundation is laid for realizing the active and predictive synchronization control in the pressure maintaining stage.

[0016] 2. By quantitatively evaluating the relative difference of the output work amount of each cylinder, and dynamically optimizing the displacement synchronization reference based thereon, the core problem of keeping the multi-cylinder system working cooperatively under the time-varying non-uniform load is effectively solved. This method not only ensures that the upper die always maintains accurate parallelism during the key stage of pressure maintaining, but more importantly, it actively balances the load of each cylinder, promotes the stress distribution inside the forged piece to be more uniform, thereby significantly improves the internal organization consistency, size and appearance accuracy, and residual stress control level of large aluminum forged pieces in the aerospace field, and meets the harsh requirements of such high-end components on forming quality. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 a flow chart of the multi-cylinder synchronization control method of the forging hydraulic press according to the present application; Figure 2 a structural schematic diagram of the multi-cylinder synchronization control system of the forging hydraulic press according to the present application. DETAILED DESCRIPTION

[0018] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative labor fall within the scope of the present application.

[0019] Embodiment 1: Figure 1The application discloses a multi-cylinder synchronous control method for a forging hydraulic press, and relates to the technical field of hydraulic press control. S1, real-time monitoring of the piston rod side pressure values of the plurality of hydraulic cylinders acting on the upper die in the pressure maintaining stage, synchronous acquisition of the heat flow signals and mechanical work signals of the die heat dissipation; S2, based on the piston rod side pressure values, evaluating the discrete coordination degree between the piston rod side pressure change rates of the hydraulic cylinders, and generating a dynamic load imbalance quantity; S3, based on the heat flow signals and the mechanical work signals, calculating the ratio of the heat flow power spectrum entropy of the die heat dissipation to the mechanical power spectrum entropy of the hydraulic cylinder output, and identifying whether the pressure maintaining process enters a load mismatch stage; S4, when it is identified that the load mismatch stage is entered, calculating the output work amounts of the hydraulic cylinders for maintaining the displacement synchronization reference within a set time period, and evaluating the relative differences of the output work amounts of the hydraulic cylinders; S5, taking maintaining the stability of the dynamic load imbalance quantity as a target, and dynamically adjusting the displacement synchronization reference values of the hydraulic cylinders based on the relative differences of the output work amounts of the hydraulic cylinders; S6, based on the dynamically adjusted displacement synchronization reference values, performing displacement closed-loop control on the hydraulic cylinders.

[0020] S1, real-time monitoring of the piston rod side pressure values of the plurality of hydraulic cylinders acting on the upper die in the pressure maintaining stage, synchronous acquisition of the heat flow signals and mechanical work signals of the die heat dissipation, and the specific implementation is as follows: In the pressure maintaining stage, in order to real-time monitor the piston rod side pressure values of the plurality of hydraulic cylinders acting on the upper die, and synchronously acquire the heat flow signals and mechanical work signals of the die heat dissipation, firstly, a corresponding sensor system needs to be configured. Specifically, at least two temperature monitoring points are pre-set in the die cavity, and the selection of the points is based on the analysis of the geometric features of the forged piece and the expected heat dissipation path, for example, one point is located in the center region of the forged piece, and the other point is located in the edge region, so as to capture the non-uniform heat dissipation effect that may exist. The temperature monitoring points are realized by using K-type thermocouples, and the installation of the thermocouples ensures that the temperature measuring ends of the thermocouples are in good thermal contact with the surface of the die cavity, so as to reduce the measurement lag and error. The temperature values are collected in real time at a set sampling frequency, for example, the sampling frequency is 10 hertz, that is, 10 temperature data are collected per second. After the collected temperature analog signals are converted into digital signals by an analog-digital converter, the digital signals are transmitted to a processing unit. Based on the continuously collected temperature values, the temperature change amount per unit time is calculated, and the change amount is defined as the heat flow signal. The unit time is usually set as the time interval of adjacent sampling points, for example, 0.1 second. The calculation of the temperature change rate is realized by using a backward difference method, that is, the temperature value at the current sampling time is subtracted from the temperature value at the immediately preceding sampling time, and the difference value is divided by the sampling time interval (0.1 second), so that the temperature change rate is calculated, and the unit of the temperature change rate is degree Celsius per second. The value directly represents the heat dissipation intensity of the die per unit time, because the heat dissipation rate is proportional to the temperature drop rate.

[0021] Synchronously, the piston rod side pressure value and the piston rod displacement value of each hydraulic cylinder are monitored in real time. The piston rod side pressure value is obtained by a pressure sensor installed on the oil circuit on the piston rod side of the hydraulic cylinder. The range of the pressure sensor is selected according to the maximum working pressure of the hydraulic system, for example, a pressure sensor with a range of 0 to 100 MPa can be selected, and its output signal is a standard current signal (such as 4-20 mA). After the current signal is converted into a standard voltage signal by a signal conditioning circuit, it is read into the processing unit. The piston rod displacement value is measured by a linear variable differential transformer displacement sensor. The accuracy of the displacement sensor is selected according to the control requirements, for example, 0.01 mm. The installation position ensures that the linear motion of the piston rod can be detected in real time and accurately. The displacement value is collected synchronously at the same sampling frequency as the temperature collection, for example, 10 Hz, to ensure the consistency of all signal time series. When calculating the rate of change of the piston rod displacement with time, the backward difference method is also used, that is, the difference between the displacement value at the current sampling time and the displacement value at the previous sampling time is divided by the sampling time interval (0.1 s) to obtain the displacement rate, which is in units of mm / s. Then, the piston rod side pressure value is multiplied by the calculated displacement rate. Before performing the multiplication operation, unit conversion is required: the original unit of the piston rod side pressure value is MPa, which needs to be converted to the International System of Units, Pascal; the original unit of the displacement rate is mm / s, which needs to be converted to m / s (1 mm is equal to 0.001 m). The result of the multiplication operation is the product of pressure (Pascal) and speed (m / s), which has the physical meaning of power, and the unit is watt. The calculated power value is the mechanical work signal representing the real-time output power of the hydraulic cylinder.

[0022] The whole data acquisition, transmission and processing process is implemented in the processing unit, which adopts an operating system with real-time task scheduling capability to ensure that the sampling time of each sensor signal is strictly synchronized, and the alignment accuracy of the signal timestamp is controlled within a certain range, for example, better than 1 millisecond, thereby avoiding introducing additional errors due to asynchronous signals. The acquisition of heat flow signals and mechanical work signals is performed synchronously, which means that the collection of temperature, piston rod side pressure and piston rod displacement data triggers a signal from the same high-precision clock source inside the processing unit. When calculating the temperature change rate and displacement change rate, the selected sampling time interval (e.g. 0.1 seconds) is set based on a comprehensive consideration of the dynamic response characteristics of the pressure maintaining process system and the process control accuracy. This interval should effectively capture meaningful dynamic changes in the process, while also taking into account the computational load of the processing unit. For heat flow signals, the original temperature data can be preprocessed before calculating the temperature change rate, such as using a moving average filtering algorithm to smooth the temperature values of consecutive multiple sampling points (e.g. 5 points) to suppress the adverse effects of measurement noise on the stability of the differential calculation. Similarly, in the displacement change rate calculation, the original displacement data can also be preprocessed by filtering. The calculation of the mechanical work signal involves multiplication, which is completed by floating point operation instructions in the processing unit. The whole monitoring system runs continuously during the pressure maintaining stage until the end of the pressure maintaining process instruction is issued, ensuring the continuity and integrity of the data record, and providing a reliable data basis for subsequent analysis.

[0023] S2, based on the piston rod side pressure value, evaluate the degree of dispersion coordination between the piston rod side pressure change rates of each hydraulic cylinder, generate a dynamic load imbalance quantity, the specific implementation is as follows: Based on the real-time monitored piston rod side pressure value, the piston rod side pressure change rate of each hydraulic cylinder with time is calculated. The piston rod side pressure value is a continuous time series data obtained by real-time acquisition through the pressure sensor according to the method described above, and its sampling frequency is set to a fixed value, for example, 10 Hz. The calculation of the piston rod side pressure change rate is realized by using numerical differentiation method in the processing unit, and the backward difference method is used. For each sampling time, the processing unit performs the following operations: take the piston rod side pressure value at the current time, subtract the piston rod side pressure value at the previous sampling time, divide the obtained difference by the sampling time interval (e.g. 0.1 seconds), and the calculation result is the piston rod side pressure change rate at that time, whose unit is pressure unit divided by time, for example, megapascal per second. This calculation process is independent and parallel for each hydraulic cylinder in the hydraulic machine system, thereby generating an independent and continuous changing piston rod side pressure change rate data sequence for each hydraulic cylinder with time.

[0024] The fluctuation trend of the pressure rate of change on the piston rod side of each hydraulic cylinder in the time domain is analyzed to identify whether there is a hydraulic cylinder with persistent differentiation in the trend of the rate of change. This analysis process is achieved by piecewise linear fitting of the rate of change sequence of the pressure on the piston rod side of each hydraulic cylinder. First, the continuous time sequence of the pressure rate of change on the piston rod side is divided into multiple continuous time periods, which can be continuous and non-overlapping or partially overlapping. The length of each time period is pre-set according to the dynamic characteristics of the pressure maintaining process, for example, it can be set to a window containing 50 consecutive sampling points (corresponding to a time length of 5 seconds). In each specific time period, the set of pressure rate of change data points of a certain hydraulic cylinder is linearly fitted using the least squares method to obtain a best fitting straight line. The slope of the fitting straight line is defined as the average slope of the pressure rate of change on the piston rod side of the hydraulic cylinder in this time period. The sign (positive or negative) of the average slope represents the main trend direction (up or down) of the rate of change in the time period, and the size of the absolute value represents the strength or steepness of the trend. Next, the average slopes calculated in the same time period for different hydraulic cylinders are compared. The comparison includes two aspects: one is the direction of the average slope (i.e. the sign), and the other is the size of the average slope (i.e. the absolute value). The criterion for identifying whether a hydraulic cylinder has trend differentiation is set to meet one of the following conditions: condition one, the average slope direction of the hydraulic cylinder is continuously opposite to the average slope direction of most hydraulic cylinders (for example, more than two-thirds of the total number of hydraulic cylinders) in the system for a continuous number of time periods (for example, 3 consecutive time periods); condition two, the difference between the absolute value of the average slope of the hydraulic cylinder and the arithmetic mean of the absolute values of the average slopes of all hydraulic cylinders in the time period exceeds a pre-set threshold value for a continuous number of time periods (for example, 3 consecutive time periods). The determination of the threshold value can be based on historical normal operation data statistics, for example, calculating the standard deviation of the difference between the absolute value of the slope and the average value of each cylinder under historical normal working conditions, and setting the threshold value to be 2 times the standard deviation. When a certain hydraulic cylinder meets any of the above conditions, the processing unit determines that the hydraulic cylinder has trend differentiation. This determination result indicates that the load dynamic response characteristics of the hydraulic cylinder have deviated significantly from the overall coordinated state of the hydraulic cylinder group.

[0025] The arithmetic mean of the pressure rate of change of all hydraulic cylinders at the same time is calculated, and the instantaneous deviation of the pressure rate of change of each hydraulic cylinder from the arithmetic mean is calculated. For each sampling time, the processing unit performs the following calculation: first, the pressure rate of change values of the piston rod side of all N hydraulic cylinders at that time are summed, and then the sum is divided by the total number N of hydraulic cylinders, and the quotient is the arithmetic mean of the pressure rate of change of all hydraulic cylinders at that time. Next, for each hydraulic cylinder in the system, the specific value of the pressure rate of change of the piston rod side at that sampling time is subtracted from the arithmetic mean calculated in the previous step, and the difference obtained is the instantaneous deviation of the hydraulic cylinder at the current time. The instantaneous deviation is an algebraic value with positive and negative signs, and the positive and negative signs represent the direction of deviation (higher or lower than the average), and the absolute value represents the degree of instantaneous deviation from the average level.

[0026] A sliding time window is introduced to calculate the cumulative effect intensity of the instantaneous deviation of each hydraulic cylinder within the window. The length of the sliding time window needs to be set to effectively reflect the persistence of the trend, for example, the window length is set to 30 seconds, which means that the window contains 300 consecutive sampling points (based on a sampling frequency of 10 Hz). The window slides along the time axis, and the step size of each slide is one sampling interval (0.1 seconds). For each hydraulic cylinder, within the time interval covered by each sliding window, the processing unit performs the following calculation: first, take the absolute value of the instantaneous deviation value of the hydraulic cylinder at each sampling time within the window, and then accumulate and sum all the absolute values corresponding to the sampling points within the window. This cumulative sum is the cumulative effect intensity of the instantaneous deviation of the hydraulic cylinder within this specific time window. The cumulative effect intensity is a non-negative scalar value, and the larger the value, the longer the duration of the hydraulic cylinder deviating from the overall average state and the larger the deviation, i.e. the stronger the cumulative misalignment effect.

[0027] The cumulative effect intensity of each hydraulic cylinder is normalized. The purpose of normalization is to eliminate the influence of the absolute value magnitude, so that the collaborative degradation of different hydraulic cylinders is comparable. A specific and feasible normalization method is as follows: in the processing unit, first find the maximum value of the cumulative effect intensity of all hydraulic cylinders in the current sliding window. Then, divide the cumulative effect intensity of each hydraulic cylinder by this maximum value. After such processing, each hydraulic cylinder obtains a normalized index value between 0 and 1. This normalized index value directly quantitatively represents the collaborative degradation of the hydraulic cylinder relative to the worst-performing hydraulic cylinder within the current window period, and the closer the value is to 1, the more serious the collaborative degradation of the cylinder. Other normalization bases can also be used, such as dividing by the arithmetic mean of all hydraulic cylinder cumulative effect intensities.

[0028] The synthesized index of the normalized index representing the degree of deterioration of the cylinder cooperation is the dynamic load imbalance. The synthesis process is completed in the processing unit, and the purpose is to generate a single index that can comprehensively reflect the load synchronization state of the entire multi-cylinder system. There are many choices for the synthesis method, for example, taking the maximum value of all the normalized index values of the hydraulic cylinders as the dynamic load imbalance, this method focuses on the state of the least coordinated hydraulic cylinder; or calculating the standard deviation of all the normalized index values of the hydraulic cylinders, this method reflects the dispersion degree of the cooperation of the entire hydraulic cylinder group; or calculating the arithmetic mean of all the normalized index values, this method reflects the average deterioration level of the whole. The dynamic load imbalance is a comprehensive scalar index, and its numerical value directly represents the synchronization or out-of-step degree of the entire multi-cylinder system in the dynamic distribution of the load, and the higher the value, the more serious the load imbalance of the system. This dynamic load imbalance will be output, providing a key quantitative basis for subsequent judgment whether to enter the load mismatch stage and control decision of synchronous reference adjustment. The entire process from calculating the change rate to generating the dynamic load imbalance is repeated once every time the sliding window is updated (i.e. every sliding sampling interval), thereby generating a dynamic load imbalance sequence that is constantly updated over time, which reflects the change of the load cooperation state in the pressure maintaining process in real time.

[0029] S3, calculate the ratio of the heat flow power spectrum entropy of the mold heat dissipation and the mechanical power spectrum entropy of the hydraulic cylinder output based on the heat flow signal and the mechanical work signal, identify whether the pressure maintaining process enters the load mismatch stage, and the specific implementation is as follows: The ratio of the heat flow power spectrum entropy of the mold heat dissipation and the mechanical power spectrum entropy of the hydraulic cylinder output is calculated based on the heat flow signal and the mechanical work signal to identify whether the pressure maintaining process enters the load mismatch stage. First, the heat flow signal and the mechanical work signal are intercepted by synchronous time windows. The heat flow signal is a continuous time sequence signal obtained by monitoring the temperature change rate of the predetermined point in the mold cavity according to the foregoing method, and the mechanical work signal is a continuous time sequence signal obtained by multiplying the piston rod side pressure value and the piston rod displacement change rate according to the foregoing method. Synchronous time window interception is performed in a fixed length and overlapping sliding manner. The fixed length of the time window is dynamically set according to the signal characteristics and the process, for example, the length of a time window can be set to 10 seconds. Overlapping sliding means that the starting point of the next time window lags behind the starting point of the previous time window by a fixed time interval, which is less than the window length, for example, lagging behind by 1 second, thereby forming continuous overlapping analysis windows. The heat flow signal data segment and the mechanical work signal data segment contained in each time window are strictly aligned in time, ensuring that both reflect the physical process in the same time period. The selection of the time window length needs to consider the lowest frequency component of the signal spectrum characteristics, for example, a 10-second window length can analyze frequency components as low as 0.1 Hz, which covers the main thermodynamic dynamic characteristics of the pressure maintaining process.

[0030] In each synchronization time window, the power spectrum entropy value of the heat flow signal and the power spectrum entropy value of the mechanical work signal are calculated independently. The calculation process starts with Fourier transform of the signal data in the window to obtain the power spectrum density estimate. Specifically, for a discrete signal data sequence (e.g. containing 100 sampling points, corresponding to a 10-second window length and a 10-Hz sampling frequency) in each time window, a fast Fourier transform algorithm is applied to convert it from the time domain to the frequency domain. The number of points of the fast Fourier transform can be set to be equal to or greater than the number of sampling points in the window, for example, 128 points, and the data less than 128 points is zero-processed. After the transformation, the complex representation of the signal at the discrete frequency points is obtained. Then, the square operation is performed on the complex amplitude value of each frequency component to obtain the power estimate value of the frequency component. The power estimate values of all frequency components are combined to form the power spectrum density estimate of the signal in this time window. The frequency resolution of the power spectrum density estimate is determined by the window length, for example, the frequency resolution corresponding to a 10-second window length is 0.1 Hz. Next, the power spectrum density is normalized over all frequency components, the purpose of which is to convert the power spectrum density into a probability distribution. The specific operation is to first calculate the sum of the power estimate values of all frequency components, and then divide the power estimate value of each frequency component by the sum. In this way, the normalized power value corresponding to each frequency component is between 0 and 1, and the sum of the normalized power values of all frequency components is equal to 1, thereby meeting the axiomatic requirements of the probability distribution. Based on this probability distribution, the Shannon entropy is calculated. The calculation method of the Shannon entropy is: for each frequency component, calculate its corresponding normalized power value multiplied by the logarithm of the normalized power value to the base 2; then sum all these products; finally, take the inverse of the sum. The calculated entropy value is the power spectrum entropy value of the signal in the current time window. The power spectrum entropy values of the heat flow signal and the mechanical work signal are strictly calculated independently according to the same process described above, i.e. the whole process of Fourier transform, power spectrum estimation, normalization and Shannon entropy calculation is independently completed for the heat flow signal data segment and the mechanical work signal data segment respectively. The power spectrum entropy is a dimensionless scalar, and the larger the value, the more uniform and disordered the energy distribution of the signal in the frequency domain.

[0031] The heat flow power spectrum entropy value and the mechanical power spectrum entropy value calculated in the same time window are divided to obtain the instantaneous ratio corresponding to the time window. Specifically, the calculated heat flow power spectrum entropy value is taken as the numerator, and the mechanical power spectrum entropy value is taken as the denominator to perform the division operation, and the quotient obtained is the instantaneous ratio. The ratio is a dimensionless value, which reflects the relative relationship between the energy distribution disorder degree of the mold heat dissipation process and the energy distribution disorder degree of the hydraulic cylinder mechanical output in a specific time window. Before performing the division operation, a very small constant (e.g. 1e-10) can be added to the denominator to prevent numerical calculation errors caused by a zero denominator.

[0032] The instantaneous ratio values calculated by each sliding time window are arranged in time sequence to form a continuous ratio sequence. This ratio sequence is sorted in ascending order according to the center timestamp or the start timestamp of the time window, which constitutes a new signal evolving over time. The sequence is plotted with time as the horizontal coordinate and the ratio as the vertical coordinate, which characterizes the dynamic change characteristics of the heat-engine power spectrum entropy ratio during the pressure maintaining process. The time interval between adjacent data points in the sequence is determined by the sliding step, for example, a sliding step of 1 second means that a new ratio data point is generated every second.

[0033] The trend of the ratio sequence over time is analyzed to identify whether the pressure maintaining process enters the load mismatch stage. The analysis process first needs to determine a stable initial reference value. The initial reference value is obtained by calculating the arithmetic mean of the ratio sequence during a period considered to be relatively stable after the start of the pressure maintaining stage. The length of this stable period needs to be long enough to obtain a reliable statistical reference, for example, taking the average of all instantaneous ratio values calculated within the first 30 seconds after the start of the pressure maintaining as the initial reference value. Then, the subsequent values of the ratio sequence are continuously monitored relative to the initial reference value. When a monotonic change trend is detected in which the ratio sequence continuously deviates from the initial reference value in a single direction, i.e., the ratio sequence continuously rises or continuously falls for multiple consecutive data points, further judgment is triggered. Two conditions need to be verified simultaneously: condition one is that the change amplitude exceeds a set tolerance, i.e., the absolute difference between the current value of the ratio sequence and the initial reference value divided by the initial reference value exceeds a pre-set threshold, which is, for example, 15% of the initial reference value. The setting of this percentage threshold is based on the analysis of the fluctuation range of the ratio in a large number of historical normal pressure maintaining process data, for example, taking 1.5 times the upper limit of the normal fluctuation range as the tolerance; condition two is that the duration of the above monotonic change trend reaches a pre-set minimum duration, which is, for example, 20 seconds. The setting of the minimum duration needs to consider the thermal inertia time constant of the process to ensure that the identified trend has statistical significance and is not random fluctuation, which can be based on prior knowledge or experimental data analysis of the dynamic characteristics of the process. Only when the change of the ratio sequence meets both the amplitude condition (change amplitude exceeds the set tolerance) and the duration condition (monotonic change trend duration reaches the pre-set minimum duration) at the same time, the processing unit finally determines that the pressure maintaining process enters the load mismatch stage. The determination result will be used as the basis for decision-making to trigger subsequent control actions (such as calculating the output work of each cylinder). The entire identification process is repeated when each new time window data arrives, achieving real-time state monitoring and judgment. If there is a short-term abnormality in the signal during the identification process (such as transient sensor interference), simple data filtering or outlier rejection logic can be introduced, for example, ignoring dramatic fluctuations with a duration of less than 2 seconds, to improve the robustness of the judgment.

[0034] S4, when the load mismatch stage is identified, the output work done by each hydraulic cylinder to maintain the displacement synchronization reference within a set time period is calculated, and the relative difference of the output work of each hydraulic cylinder is evaluated, which is implemented as follows: When the load mismatch stage is identified, a timer is started and a statistical time period is set. The identification of the load mismatch stage is based on the analysis results of the ratio sequence of thermal power spectrum entropy and mechanical power spectrum entropy in the previous steps. Once the processing unit determines that the load mismatch stage is entered, it immediately starts an internal timer and starts counting from zero. At the same time, a statistical time period is set, the length of which is determined comprehensively according to the response characteristics of the hydraulic system, the dynamic time scale of the load mismatch process, and the real-time requirements of the control system. For example, the statistical time period can be set to 10 seconds. The basis of this setting is that it needs to be long enough to cover the main dynamic response period of the hydraulic system, so as to capture the stable statistical characteristics of the output work of each hydraulic cylinder, and avoid false judgment caused by temporary fluctuations of pressure or flow; at the same time, it needs to be short enough to ensure that the control system can respond to the load mismatch state in time, and prevent the disorder from further aggravating. The setting of the statistical time period can be a fixed value based on a large number of process tests, or it can be fine-tuned according to the dynamic characteristics of the system monitored in the stable stage of the previous pressure maintaining process (such as the dominant frequency of the main pressure fluctuation), but the core principle is to cover a typical period that can reliably reflect the characteristics of the work difference of each cylinder.

[0035] The mechanical work signal of each hydraulic cylinder is time-integrated over the set statistical time period to obtain the output work done by each hydraulic cylinder in maintaining the displacement synchronization reference. The mechanical work signal is the real-time output power value of the hydraulic cylinder calculated in real time by multiplying the piston rod side pressure value by the piston rod displacement rate of change according to the aforementioned method, and its unit is watt. The time integration operation is performed in the processing unit, and its physical meaning is to calculate the cumulative effect of power in time, i.e. energy. In specific implementation, for each hydraulic cylinder in the system, from the continuously recorded time series of the mechanical work signal, a segment of discrete data is intercepted from the start time of the timer, with a duration of the set statistical time period (e.g. 10 seconds). Since the mechanical work signal is a discrete data sequence collected at a fixed sampling frequency (e.g. 10 Hz), the integral operation is realized by numerical integration method. The trapezoidal method with high precision is used for numerical integration, and the calculation process is as follows: the power values corresponding to the adjacent two sampling time points (with an interval of 0.1 seconds) are added, and then divided by 2 to obtain the average power estimate in this small time interval; then multiply this average power estimate by the sampling time interval (0.1 seconds) to obtain the work done in this small time interval; finally, the work done in all continuous time intervals within the statistical time period is accumulated and summed. The output work calculated is in joules, which quantitatively represents the total energy consumed by the hydraulic cylinder to overcome the load it bears and maintain its piston rod displacement consistent with the initially set displacement synchronization reference within the specific statistical time period. The output work of each hydraulic cylinder is independently calculated according to the same numerical integration method.

[0036] The average value of the output work of all hydraulic cylinders is calculated. After the statistical time period ends, the processing unit has obtained the output work values of all hydraulic cylinders within that period. All these work values are algebraically added to obtain the total output work of the entire hydraulic cylinder group within that time period. Then the total output work is divided by the total number N of hydraulic cylinders, and the quotient obtained is the arithmetic mean of the output work of all hydraulic cylinders. This average value represents the average level of energy paid by the hydraulic cylinder group as a whole to maintain the displacement synchronization reference during the identified load mismatch stage, which provides an objective and quantitative reference point for the next step of evaluating the difference of individual hydraulic cylinders relative to the overall level.

[0037] With the calculated average value as the benchmark, the deviation of the output power of each hydraulic cylinder from the average value is calculated. For each hydraulic cylinder in the system, the absolute deviation of the output power of the hydraulic cylinder from the average value is obtained by subtracting the average value of the output power of all hydraulic cylinders calculated in the previous step from the specific value of the output power of the hydraulic cylinder calculated in the statistical time period. In order to eliminate the influence of the absolute power value difference caused by the different total loads of the system and make the deviation degrees in different pressure maintaining processes or under different working conditions comparable, it is usually necessary to further calculate the relative deviation degree. The calculation method of the relative deviation degree is to divide the absolute deviation calculated above by the average value of the output power of all hydraulic cylinders, and then multiply by 100%, thereby obtaining a percentage value. This percentage value is the deviation degree of the output power of each hydraulic cylinder from the average value, which can be positive or negative. A positive value indicates that the output power of the cylinder is higher than the average level in the group, which usually means that it bears a relatively larger load or there is an efficiency loss. A negative value indicates that the output power of the cylinder is lower than the average level in the group. The absolute value of the deviation degree indicates the degree of deviation from the average level.

[0038] Based on the deviation degree of the output power of each hydraulic cylinder, the relative difference distribution characteristics of the output power of the hydraulic cylinder group are evaluated. The purpose of the evaluation is to quantitatively grasp the inconsistency of the output power of all hydraulic cylinders as a whole, and to provide a basis for subsequent control decisions. A commonly used and effective evaluation method is to calculate the sample standard deviation of the relative deviation degrees of all hydraulic cylinders. The calculation process of the standard deviation is as follows: first, the arithmetic mean of all relative deviation degrees is calculated (theoretically close to zero under a large number of samples, but a small value in a single calculation); then, the difference between the relative deviation degree of each hydraulic cylinder and the average value (or directly with zero) is calculated, and the square of the difference is calculated; then, the arithmetic mean of all these square values is calculated; finally, the square root of the average value is taken. The standard deviation value calculated is a dimensionless value, and its size directly reflects the dispersion degree of the output power of the hydraulic cylinder group. The larger the standard deviation, the greater the difference between the output power of each cylinder, and the worse the synchronization coordination. In addition to the standard deviation, the maximum absolute value of the relative deviation degree among all hydraulic cylinders can be found, that is, the maximum deviation absolute value, which reflects how large the difference between the most extreme hydraulic cylinder and the average level is. Further, the distribution form of the relative deviation degree can be analyzed, for example, whether the deviation degree value is obviously concentrated in the positive value area or the negative value area, which may indicate that there is a systematic deviation in the load distribution; or check whether there are a few obvious outliers in the distribution, which may indicate that individual hydraulic cylinders have abnormalities. The comprehensive evaluation results of these distribution characteristics (such as standard deviation, maximum deviation absolute value, distribution skewness, etc.) constitute a complete quantitative description of the energy output coordination state of the hydraulic cylinder group in the load mismatch stage. The evaluation results provide direct and quantitative decision-making basis for determining which hydraulic cylinders need to be adjusted first, the direction and amplitude of the adjustment in the subsequent step of dynamically adjusting the displacement synchronization reference value. After the processing unit completes the evaluation, the key input information for guiding the adjustment of the synchronization reference is generated.

[0039] S5, with the goal of maintaining the stability of the dynamic load imbalance, and dynamically adjusting the displacement synchronization reference value of each hydraulic cylinder based on the relative difference of the output power of each hydraulic cylinder, which is implemented as follows: The target is to maintain the dynamic load imbalance and adjust the displacement synchronization reference value of each hydraulic cylinder based on the relative difference of the output power of each hydraulic cylinder. First, the corresponding relationship between the dynamic load imbalance and the displacement synchronization reference value adjustment amount is established. The dynamic load imbalance is a comprehensive quantitative index generated by analyzing the discrete coordination degree of the pressure change rate of each hydraulic cylinder piston rod side according to the foregoing steps, which represents the load coordination state of the hydraulic cylinder group in real time. The corresponding relationship is usually represented by a control function or a rule-based mapping relationship, and the core is to convert the change of the dynamic load imbalance into the adjustment instruction of the displacement synchronization reference value. For example, a proportional control relationship can be established, that is, the overall adjustment amplitude of the displacement synchronization reference value is proportional to the degree of deviation of the current dynamic load imbalance from the target stable interval. The target stable interval is obtained by analyzing a large amount of historical normal pressure maintaining process data, for example, it can be set to the range of plus or minus 5% of the average value of the dynamic load imbalance under historical normal working conditions. The determination of the proportional coefficient, that is, the control gain, needs to be combined with the dynamic characteristics of the hydraulic system, which can be obtained by system identification experiment; for example, during the equipment debugging stage, a small known load disturbance is actively applied, and the response amplitude of the dynamic load imbalance and the minimum displacement reference adjustment amount required to restore balance are accurately measured, and the ratio of the two can be used as the estimated value of the initial gain, usually the gain coefficient is a dimensionless decimal, for example, 0.05. Another more robust way is to establish a query table based on fuzzy rules or piecewise linear interpolation, which maps different value intervals of the dynamic load imbalance to the preset and verified displacement reference adjustment amount. The basic principle of establishing the corresponding relationship is: when the dynamic load imbalance increases (indicating that the coordination between hydraulic cylinders deteriorates), the overall adjustment direction of the displacement synchronization reference value should aim to reduce the load difference between the cylinders and make the dynamic load imbalance fall back; vice versa.

[0040] According to the relative difference distribution characteristics of the output work amounts of the hydraulic cylinders, adjustment priorities of the displacement synchronization reference values of the hydraulic cylinders are determined. The relative difference distribution characteristics of the output work amounts are derived from the evaluation results of the foregoing step, and specifically include a deviation degree (expressed in percentage) of the output work amount of each hydraulic cylinder from an average value of the output work amounts of all the hydraulic cylinders, and a statistical quantity such as a standard deviation reflecting an overall dispersion degree. The determination rule of the adjustment priorities is based on a core logic that the hydraulic cylinder having the greatest contribution to the current load imbalance should be given the highest adjustment priority. In specific implementation, the hydraulic cylinders are sorted according to the absolute values of the deviation degrees of the output work amounts from the average value. The greater the absolute value of the deviation degree of the hydraulic cylinder, the more significant the difference between the current working state of the hydraulic cylinder and the group average state, and the greater the influence on the overall load imbalance, so the displacement synchronization reference value of the hydraulic cylinder needs to be adjusted in priority to correct the main imbalance source quickly. For example, all the hydraulic cylinders can be arranged in descending order according to the absolute values of the deviation degrees from large to small, and the hydraulic cylinder arranged in the first place has the highest adjustment priority. Another more refined strategy is to introduce priority threshold partitions, for example, the hydraulic cylinder with the absolute value of the deviation degree exceeding 15% is set as a high-priority adjustment object, the hydraulic cylinder with the deviation degree between 8% and 15% is set as a medium-priority adjustment object, and the hydraulic cylinder with the deviation degree less than 8% is set as a low-priority adjustment object or is not adjusted in the current control cycle. The priority threshold can be determined according to the standard deviation multiple of the normal fluctuation range in the historical data.

[0041] For the hydraulic cylinders ranked high in the adjustment priority order, the displacement synchronization reference values thereof are adjusted in priority. After the adjustment priority order is determined, the displacement synchronization reference values of the hydraulic cylinders are calculated and adjusted in sequence according to the order. The direction (increase or decrease) of the adjustment amount is determined according to the positive or negative sign of the output work amount deviation degree, and the physical meaning thereof is to guide the redistribution of the load through the adjustment of the displacement reference. For a hydraulic cylinder with a positive output work amount deviation degree (i.e., the output work amount thereof is higher than the average value), this usually implies that the current load borne by the hydraulic cylinder is relatively large or there is additional energy loss, and in order to balance the loads of the cylinders, the displacement synchronization reference value of the hydraulic cylinder should be appropriately reduced to slightly retract the piston rod, so as to promote the transfer of part of the load to the hydraulic cylinders with lower output work amounts. Therefore, the adjustment amount of the displacement synchronization reference value of the cylinder should be negative (decrease). Conversely, for a hydraulic cylinder with a negative output work amount deviation degree, the displacement synchronization reference value thereof should be appropriately increased, and the adjustment amount is positive (increase). The size of the adjustment amount is positively correlated with the absolute value of the deviation degree of the cylinder, and generally follows the quantitative principle that “the greater the deviation, the greater the adjustment amplitude”. For example, the reference adjustment amount ΔSi of a single hydraulic cylinder can be estimated as follows: ΔSi=Kp*|Di|*sign(Di)*ΔStotalweighted; where Di is the deviation of the cylinder, Kp is a proportional coefficient (0 < Kp < 1) to prevent excessive adjustment at one time, and ΔStotalweighted is the weighted total adjustment calculated according to the dynamic load imbalance. The adjustment process is gradual, and only one round of adjustment is performed in a control cycle (for example, 2 seconds), rather than a one-time large change, to avoid excessive impact on the hydraulic system or cause instability.

[0042] In combination with the real-time change trend of the dynamic load imbalance, the displacement synchronization reference value of each hydraulic cylinder is compensated and corrected. While the preliminary adjustment calculation is made according to the output power difference, the control system continuously monitors the latest value and change trend of the dynamic load imbalance. The change trend can be obtained by calculating the difference or linear regression slope of the dynamic load imbalance in the last few control cycles (for example, 3 consecutive cycles). The purpose of this compensatory correction is to introduce a differential control effect, enhance the damping of the system, improve the response quality, and prevent overshoot or sustained oscillation. The compensation rule can be: if the dynamic load imbalance still shows a rapid growth trend (a large positive change rate) in the current control cycle, an additional compensation correction amount proportional to the change rate is added to the preliminary adjustment amount of each cylinder, and the direction is consistent with the preliminary adjustment amount, to strengthen the correction strength. On the contrary, if the dynamic load imbalance has begun to decline but the decline is too fast (the absolute value of the negative change rate is too large), a compensation amount proportional to the change rate should be subtracted from the preliminary adjustment amount, which has a "braking" effect to prevent overcorrection. The compensation correction amount ΔC can be expressed as: ΔC = Kd * (dDLI / dt), where Kd is the differential gain coefficient, and dDLI / dt is the estimated value of the change rate of the dynamic load imbalance. The compensation amount will be distributed and superimposed on the preliminary adjustment amount of each hydraulic cylinder according to the priority weight.

[0043] The dynamic load imbalance is gradually returned to the stable interval range through iterative adjustment. The dynamic adjustment process of the entire displacement synchronization reference value is a typical closed-loop feedback control iterative process. Within each iteration period (for example, 2 seconds), the processing unit performs the following sequence: collects the latest sensor data, calculates the current dynamic load imbalance and the relative difference of the output power of each cylinder, calculates the adjustment amount (including compensation correction) of the displacement synchronization reference value of each cylinder in this round according to the above rules, and issues the new displacement synchronization reference value to the displacement controller of each cylinder. After the system runs under the new reference value for one cycle, the data is collected again to evaluate the effect. Each iteration does not expect the dynamic load imbalance to immediately return to the ideal state, but gradually approaches the target through multiple iterations. The iterative process continues, and the dynamic load imbalance will be gradually reduced under the control and finally stabilized within the preset stable interval range (for example, within the interval of ±5% of the target value). The termination condition of iterative adjustment can be set as that the dynamic load imbalance remains within the stable interval for a plurality of control cycles (for example, 3 to 5 cycles), and the relative difference distribution characteristic index (such as standard deviation) of the output power of each cylinder also continuously falls below a certain preset threshold (for example, 5%). Once the termination condition is met, it is considered that the system has reached a satisfactory synchronous balance state, and large-scale reference adjustment can be suspended, and a more fine maintenance mode or waiting for the next load mismatch trigger is entered. The entire iterative process ensures the progressiveness, stability and robustness of the control action.

[0044] S6, based on the displacement synchronization reference value adjusted dynamically, performing displacement closed-loop control on each hydraulic cylinder, and the implementation is as follows: Based on the dynamically adjusted displacement synchronization reference value, displacement closed-loop control is performed on each hydraulic cylinder. First, the piston rod displacement value monitored by each hydraulic cylinder in real time is compared with the corresponding dynamically adjusted displacement synchronization reference value to obtain the displacement deviation value of each hydraulic cylinder. The piston rod displacement value is measured in real time by a linear variable differential transformer displacement sensor installed on each hydraulic cylinder, and the measurement accuracy of the sensor can reach 0.01 millimeters. The sampling frequency is synchronized with the control system period, for example, set to 100 Hz. The dynamically adjusted displacement synchronization reference value is the latest instruction value generated after iteration optimization by the aforementioned control logic according to the dynamically calculated dynamic load imbalance and the relative difference between the output work amounts of each hydraulic cylinder. The comparison operation is performed in the digital logic of the processing unit. For each hydraulic cylinder in the system, the actual value of the piston rod displacement measured by the displacement sensor at the current sampling time is subtracted from the current latest dynamically adjusted displacement synchronization reference value set independently for the hydraulic cylinder in each control period (for example, 10 milliseconds), and the resulting algebraic difference is the displacement deviation value of the hydraulic cylinder in the current control period. The displacement deviation value is an algebraic quantity with positive and negative signs, and the unit is the same as the displacement value, that is, millimeters; a positive value indicates that the actual displacement exceeds the current set reference value, and a negative value indicates that the actual displacement has not reached the current set reference value.

[0045] According to the size and direction of the displacement deviation value, a corresponding control signal is generated. The generation of the control signal is realized by using the classical proportional-integral-derivative control algorithm. The processing unit independently maintains a set of control algorithm instances for each hydraulic cylinder. The output signal of the proportional control link is proportional to the displacement deviation value calculated in the current control period, that is, the proportional term output = Kp x e(t), where Kp is the proportional gain coefficient and e(t) is the current displacement deviation value. The role of the proportional term is to provide a fast response proportional to the instantaneous size of the deviation.

[0046] The output signal of the integral control link is proportional to the cumulative value of the displacement deviation value over time (i.e., the integral), that is, the integral term output = Ki x ∫e(τ)dτ, the integral interval is backtracked from a certain time in the current control period or from the beginning of the deviation, and Ki is the integral gain coefficient. The role of the integral term is to eliminate the steady-state error of the system and ensure long-term accuracy. The output signal of the differential control link is proportional to the rate of change of the displacement deviation value (i.e., the differential), that is, the differential term output = Kd x de(t) / dt, and Kd is the differential gain coefficient. The role of the differential term is to provide damping effect, predict the trend of the deviation, and suppress overshoot and oscillation.

[0047] The output values of the proportional, integral, and derivative terms are algebraically added to obtain the final comprehensive control signal U(t) = Kp x e(t) + Ki x ∫e(τ)dτ + Kd x de(t) / dt for this control cycle of the hydraulic cylinder. The key parameters Kp, Ki, Kd (or equivalent integral time Ti, derivative time Td) in the control algorithm need to be engineered according to the dynamic characteristics (such as response speed, inertia, damping) of the specific hydraulic actuator, for example, determined by on-site debugging through the Ziegler-Nichols critical proportional degree method or other trial-and-error methods, to ensure the stability, speed, and accuracy of the closed-loop system. The generated control signal is usually normalized to a standard range of voltage signal (e.g. -10 volts to +10 volts) or current signal (e.g. 4 milliamps to 20 milliamps), with the magnitude representing the strength of the control action and the sign (positive or negative) representing the direction of the control action (to extend or retract the piston rod).

[0048] The control signal is output to the servo valve group of each hydraulic cylinder to adjust the flow into the hydraulic cylinder. The digital quantity of the control signal generated by the processing unit is converted to an analog voltage or current signal through its integrated digital-to-analog conversion channel. After signal amplification and driving capacity improvement by the power amplification circuit, the analog signal is transmitted to the servo valve group of the corresponding hydraulic cylinder through a shielded cable. The servo valve group is usually composed of high dynamic response electro-hydraulic servo valves or high precision proportional valves and their matching amplifiers. The core components of the servo valve are the torque motor and the spool valve, which can accurately and quickly adjust the displacement and opening direction of the main valve core according to the polarity and magnitude of the input electric signal. When the control signal is negative (corresponding to the need to reduce the displacement deviation, i.e. to extend the piston rod), the servo valve group adjusts the valve port so that the pressure oil enters the piston rod side (rod cavity) of the hydraulic cylinder in a flow proportional to the absolute value of the control signal, while connecting the piston side (rodless cavity) to the oil return line, thereby generating a force to retract the piston rod. The flow into the hydraulic cylinder is directly proportional to the size of the control signal within a certain linear range, thereby achieving precise control of the movement speed of the hydraulic cylinder. The adjustment of the flow directly changes the movement state of the piston rod, and the purpose is to generate the necessary hydraulic thrust to correct the current displacement deviation.

[0049] The actual displacement values of the piston rods of each hydraulic cylinder are continuously adjusted to track the dynamically adjusted displacement synchronization reference values. The above process constitutes a complete negative feedback control loop through real-time monitoring of the piston rod displacement, comparison with the dynamically adjusted displacement synchronization reference value to calculate the deviation, use of a control algorithm to generate a control signal, and driving of the servo valve group to adjust the flow. This closed-loop control system continuously and cyclically operates at a fixed, short control period (for example, 10 milliseconds, corresponding to a control frequency of 100 Hz). At the beginning of each control period, the system collects the latest data from all displacement sensors; in the middle of the period, the processing unit completes all calculations and outputs the control signal; and before the end of the period, the control signal has already acted on the servo valve. Through this high-frequency, continuous, and timely feedback adjustment mechanism, as soon as the actual displacement value of any hydraulic cylinder deviates from its current displacement synchronization reference value, whether due to load fluctuations or active adjustment of the reference value itself, the control system can detect the deviation within milliseconds and immediately take corrective action. This enables the actual displacement values of the piston rods of each hydraulic cylinder to dynamically and accurately track their respective independent and possibly continuously optimized displacement synchronization reference values, thereby achieving high-precision synchronous movement in a multi-cylinder system, even in the face of time-varying and asymmetric load disturbances.

[0050] The closed-loop control of displacement of each hydraulic cylinder is maintained throughout the entire pressure maintaining phase until the end of the pressure maintaining process. As a basic control loop at the execution level, the displacement closed-loop control is continuously put into operation from the moment the pressure maintaining phase begins. In the early stage of pressure maintaining, if no significant load mismatch is detected, the displacement synchronization reference value usually remains the initial set synchronization value, and the role of closed-loop control is to suppress random disturbances and maintain the initial synchronization accuracy. After the aforementioned monitoring logic identifies that the system enters the load mismatch phase and dynamically adjusts the displacement synchronization reference value, the displacement closed-loop control system seamlessly switches to tracking the new, optimized reference value. This continuous feedback control based on deviation is carried out throughout every moment of the entire pressure maintaining phase, regardless of whether the displacement synchronization reference value is dynamically adjusted or not. The end of the pressure maintaining process is usually triggered by the process controller according to the preset pressure maintaining time (for example, the timer reaching the set value) or other process completion conditions (such as the pressure in the mold cavity dropping to a certain threshold). Once the processing unit receives the pressure maintaining end instruction from the upper-level process controller, the displacement closed-loop control stops running, and the control system will then perform subsequent process steps such as pressure relief, main cylinder return, and ejection cylinder action. During the entire pressure maintaining period, maintaining high-precision displacement synchronization control is crucial for ensuring the internal organization uniformity, geometric size accuracy, and residual stress distribution of large forgings, especially aluminum alloy forgings required in the aerospace field.

[0051] Example 2: Figure 2A structure schematic diagram of a multi-cylinder synchronous control system of a forging hydraulic press is given, a multi-cylinder synchronous control system of a forging hydraulic press, comprising: An information acquisition module is configured to monitor the piston rod side pressure values of the plurality of hydraulic cylinders acting on the upper die in real time during the pressure maintaining stage, and synchronously acquire heat flow signals and mechanical work signals of die heat dissipation; An imbalance analysis module is configured to evaluate the discrete coordination degree between the piston rod side pressure change rates of the hydraulic cylinders based on the piston rod side pressure values, and generate a dynamic load imbalance quantity; A mismatch judgment module is configured to calculate the ratio of the heat flow power spectrum entropy of die heat dissipation to the mechanical power spectrum entropy of hydraulic cylinder output based on the heat flow signals and the mechanical work signals, and identify whether the pressure maintaining process enters a load mismatch stage; A mismatch analysis module is configured to calculate the output work amounts of the hydraulic cylinders for maintaining the displacement synchronization reference within a set time period when it is identified that the load mismatch stage is entered, and evaluate the relative differences of the output work amounts of the hydraulic cylinders; A target adjustment module is configured to take maintaining the stability of the dynamic load imbalance quantity as a target, and dynamically adjust the displacement synchronization reference values of the hydraulic cylinders based on the relative differences of the output work amounts of the hydraulic cylinders; A closed-loop control module is configured to perform displacement closed-loop control on the hydraulic cylinders based on the dynamically adjusted displacement synchronization reference values.

[0052] The calculations involved in the embodiments are all dimensionless numerical calculations, and the preset parameters and threshold values in the calculations are set by a person skilled in the art according to actual conditions.

[0053] It should be noted that the present application can be deployed on the device itself to realize embedded applications, or can be run on a PC or other terminal with a user interface, thereby meeting various hardware environments and use requirements.

[0054] The above-described embodiments can be implemented in whole or in part by software, hardware, firmware, or any combination thereof. When implemented by software, the above-described embodiments can be implemented in whole or in part in the form of a computer program product. The computer program product includes one or more computer instructions or computer programs. When the computer instructions or computer programs are loaded or executed on a computer, the processes or functions according to the embodiments of the present application are wholly or partially generated. The computer can be a general-purpose computer, a special-purpose computer, a computer network, or other programmable devices. The computer instructions can be stored in a computer-readable storage medium or transmitted from one computer-readable storage medium to another computer-readable storage medium, for example, the computer instructions can be transmitted from one website, computer, server, or data center to another website, computer, server, or data center in a wireless or wired manner. The wired transmission manner includes optical fiber, twisted pair, coaxial cable, etc. The wireless transmission includes infrared rays, microwaves, etc. The computer-readable storage medium can be any available medium accessible by a computer or a data storage device such as a server, data center, etc. containing one or more available medium collections. The available medium can be a magnetic medium (for example, a floppy disk, a hard disk, a magnetic tape), an optical medium (for example, a DVD), or a semiconductor medium. The semiconductor medium can be a solid-state disk.

[0055] Those skilled in the art can clearly understand that, for the convenience and brevity of description, the specific working processes of the above-described system, device, and module can refer to the corresponding processes in the foregoing method embodiments, which will not be described here.

[0056] In several embodiments provided in the present application, it should be understood that the disclosed system, device, and method can be implemented in other ways. For example, the above-described device embodiments are only schematic, for example, the division of the modules is only a logical function division, and actual implementation can have another division manner, for example, a plurality of modules or components can be combined or integrated into another system, or some features can be ignored or not executed. In addition, the coupling or direct coupling or communication connection between the displayed or discussed ones can be indirect coupling or communication connection through some interfaces, devices, or modules, and can be electrical, mechanical, or other forms.

[0057] The modules illustrated as separate components can or can not be physically separate, and the components illustrated as modules can or can not be physical modules, which can be located in one place or distributed on a plurality of network modules. Part or all of the modules can be selected according to actual needs to achieve the purpose of the embodiments.

[0058] In addition, each functional module in each embodiment of the present application can be integrated in one processing module, or each module can exist physically independently, or two or more modules can be integrated in one module.

[0059] If the functions are implemented in the form of software function modules and sold or used as independent products, the functions can be stored in a computer readable storage medium. Based on this understanding, the technical solutions of the present application or the part of the technical solutions that essentially contribute to the prior art can be embodied in the form of a software product. The computer software product is stored in a storage medium and includes a plurality of instructions for causing a computer device (which can be a personal computer, a server or a network device, etc.) to execute all or part of the steps of the embodiments of the present application. The aforementioned storage medium includes a U disk, a mobile hard disk, a read-only memory (ROM), a random access memory (RAM), a magnetic disk or an optical disk, and various media that can store program codes.

[0060] The above is only a specific embodiment of the present application, but the protection scope of the present application is not limited thereto. Any person skilled in the art can easily think of changes or replacements within the technical scope disclosed in the present application, which should be included in the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

[0061] Finally, the above is only a preferred embodiment of the present application and is not used to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application should be included in the protection scope of the present application.

Claims

1. A method for synchronizing control of a plurality of cylinders of a forging hydraulic press, characterized by, The method comprises the following steps: S1. Real-time monitoring of the piston rod side pressure values of the plurality of hydraulic cylinders acting on the upper die during the pressure maintaining stage, and synchronous acquisition of the heat flow signal and mechanical work signal of the mold heat dissipation; S2. Based on the piston rod side pressure values, evaluating the discrete coordination degree between the piston rod side pressure change rates of each hydraulic cylinder, and generating a dynamic load imbalance quantity; S3. Based on the heat flow signal and the mechanical work signal, calculating the ratio of the heat flow power spectrum entropy of the mold heat dissipation to the mechanical power spectrum entropy of the hydraulic cylinder output, and identifying whether the pressure maintaining process enters the load mismatch stage; S4. When it is identified that the load mismatch stage is entered, calculating the output work amount of each hydraulic cylinder for maintaining the displacement synchronization reference within a set time period, and evaluating the relative difference of the output work amount of each hydraulic cylinder; S5. Taking maintaining the stability of the dynamic load imbalance quantity as the target, and dynamically adjusting the displacement synchronization reference value of each hydraulic cylinder based on the relative difference of the output work amount of each hydraulic cylinder; S6. Based on the dynamically adjusted displacement synchronization reference value, performing displacement closed-loop control on each hydraulic cylinder.

2. The multi-cylinder synchronization control method of a forging hydraulic press according to claim 1, characterized by, Real-time monitoring of the piston rod side pressure values of the plurality of hydraulic cylinders acting on the upper die during the pressure maintaining stage, and synchronous acquisition of the heat flow signal and mechanical work signal of the mold heat dissipation, comprising: Real-time monitoring of the temperature values of at least two predetermined points in the mold cavity, and calculating the temperature change amount per unit time based on the temperature values, which is taken as the heat flow signal representing the mold heat dissipation intensity; Synchronously, real-time monitoring of the piston rod side pressure values and the piston rod displacement values of each hydraulic cylinder, and calculating the change rate of the piston rod displacement with time, and multiplying the piston rod side pressure value by the displacement change rate to obtain the mechanical work signal representing the real-time output power of the hydraulic cylinder.

3. The multi-cylinder synchronization control method of a forging hydraulic press according to claim 1, characterized by, Based on the piston rod side pressure values, evaluating the discrete coordination degree between the piston rod side pressure change rates of each hydraulic cylinder, and generating a dynamic load imbalance quantity, comprising: Based on the real-time monitored piston rod side pressure values, calculating the piston rod side pressure change rate of each hydraulic cylinder with time; Analyzing the fluctuation trend of the piston rod side pressure change rate of each hydraulic cylinder in the time domain, and identifying whether there is a hydraulic cylinder with persistent differentiation in the change rate trend; Calculating the arithmetic mean of the piston rod side pressure change rates of all hydraulic cylinders at the same time, and calculating the instantaneous deviation of the piston rod side pressure change rate of each hydraulic cylinder from the arithmetic mean; Introducing a sliding time window, and calculating the cumulative effect intensity of the instantaneous deviation of each hydraulic cylinder within the window; Normalizing the cumulative effect intensity of each hydraulic cylinder, and synthesizing the index representing the coordination degradation degree of each cylinder after normalization into a dynamic load imbalance quantity.

4. The multi-cylinder synchronization control method of a forging hydraulic press according to claim 3, characterized by, Analyzing the fluctuation trend of the piston rod side pressure change rate of each hydraulic cylinder in the time domain, and identifying whether there is a hydraulic cylinder with persistent differentiation in the change rate trend, which is achieved by the following methods: Segmented linear fitting is performed on the piston rod side pressure change rate sequence of each hydraulic cylinder, and the average slope of the change rate in each time period is calculated; Comparing the slope direction and size of different hydraulic cylinders in the same time period; When the slope direction of a certain hydraulic cylinder is continuously opposite to that of the majority of other hydraulic cylinders, or the difference between the absolute value of the slope and the average value continuously exceeds a set threshold, it is determined that the corresponding cylinder has trend differentiation.

5. The multi-cylinder synchronization control method of a forging hydraulic press according to claim 1, characterized by, The ratio of the heat flow power spectrum entropy of the mold heat dissipation and the mechanical power spectrum entropy of the hydraulic cylinder output is calculated based on the heat flow signal and the mechanical work signal to identify whether the pressure maintaining process enters the load mismatch stage, including: The heat flow signal and the mechanical work signal are synchronously time windowed, and the ratio sequence of the heat flow signal power spectrum entropy and the mechanical work signal power spectrum entropy in each time window is calculated. The trend of the ratio sequence over time is analyzed, and when it is detected that the ratio sequence presents a monotonic change trend of continuously deviating from the initial reference value in one direction, and the change amplitude exceeds the set tolerance, it is verified that the monotonic change trend lasts for a preset minimum duration. When the amplitude condition and the duration condition are met at the same time, it is determined that the pressure maintaining process enters the load mismatch stage.

6. The multi-cylinder synchronization control method of a forging hydraulic press according to claim 5, characterized by, The heat flow signal and the mechanical work signal are synchronously time windowed, and the ratio sequence of the heat flow signal power spectrum entropy and the mechanical work signal power spectrum entropy in each time window is calculated, which is realized by the following methods: Synchronously time windowed in a fixed time length and overlapping sliding manner; The power spectrum entropy value of the heat flow signal and the power spectrum entropy value of the mechanical work signal are calculated in each window: Fourier transform is performed on the signal data in the window to obtain the power spectrum density estimate; the power spectrum density is normalized over all frequency components, so that the sum of the power values at each frequency component is 1, thereby forming a probability distribution; Based on the probability distribution, the Shannon entropy is calculated, and the obtained entropy value is the power spectrum entropy value of the corresponding signal; the power spectrum entropy values of the heat flow signal and the mechanical work signal are independently calculated according to the same process; The heat flow power spectrum entropy value and the mechanical power spectrum entropy value calculated in the same window are divided to obtain the instantaneous ratio corresponding to the time window; The instantaneous ratios of each window are arranged in time sequence to form a ratio sequence.

7. The multi-cylinder synchronization control method of a forging hydraulic press according to claim 1, characterized by, When the load mismatch stage is identified, the output work amount of each hydraulic cylinder for maintaining the displacement synchronization reference within a set time period is calculated, and the relative difference of the output work amount of each hydraulic cylinder is evaluated, including: When the load mismatch stage is identified, the timing is started and the statistical time period is set; In the statistical time period, the mechanical work signal of each hydraulic cylinder is time integrated to obtain the output work amount of each hydraulic cylinder in the process of maintaining the displacement synchronization reference; The average value of the output work amount of all hydraulic cylinders is calculated; The deviation of the output work amount of each hydraulic cylinder relative to the average value is calculated based on the average value; Based on the deviation of the output work amount of each hydraulic cylinder, the relative difference distribution characteristics of the output work amount of the hydraulic cylinder group are evaluated.

8. The multi-cylinder synchronization control method of a forging hydraulic press according to claim 1, characterized by, The dynamic load imbalance is maintained stable, and the displacement synchronization reference value of each hydraulic cylinder is dynamically adjusted based on the relative difference of the output work amount of each hydraulic cylinder, including: Establish the corresponding relationship between the dynamic load imbalance and the displacement synchronization reference value adjustment amount; According to the relative difference distribution characteristics of the output work amount of each hydraulic cylinder, the adjustment priority of the displacement synchronization reference value of each hydraulic cylinder is determined; For the hydraulic cylinders ranked high in the adjustment priority order, the displacement synchronization reference value is adjusted first; Combined with the real-time change trend of the dynamic load imbalance, the displacement synchronization reference value of each hydraulic cylinder is compensated and corrected; Through iterative adjustment, the dynamic load imbalance gradually returns to the stable interval range.

9. The multi-cylinder synchronization control method of a forging hydraulic press according to claim 1, characterized by, Based on the dynamically adjusted displacement synchronization reference value, displacement closed-loop control is performed on each hydraulic cylinder, including: Comparing the piston rod displacement value monitored by each hydraulic cylinder in real time with the corresponding dynamically adjusted displacement synchronization reference value to obtain the displacement deviation value of each hydraulic cylinder; Generating a corresponding control signal according to the size and direction of the displacement deviation value; Outputting the control signal to the servo valve group of each hydraulic cylinder to adjust the flow entering the hydraulic cylinder; Through continuous feedback adjustment, the actual displacement value of the piston rod of each hydraulic cylinder tracks the dynamically adjusted displacement synchronization reference value; Maintain closed-loop control of the displacement of each hydraulic cylinder throughout the pressure maintaining stage until the pressure maintaining process is completed.

10. A multi-cylinder synchronous control system of a forging hydraulic press, used for implementing the multi-cylinder synchronous control method of the forging hydraulic press according to any one of claims 1-9, characterized in that, Including: An information acquisition module for monitoring the piston rod side pressure value of each hydraulic cylinder acting on the upper die in real time during the pressure maintaining stage, and synchronously acquiring the heat flow signal and mechanical work signal of mold heat dissipation; An imbalance analysis module for evaluating the discrete coordination degree between the piston rod side pressure change rates of each hydraulic cylinder based on the piston rod side pressure value, and generating a dynamic load imbalance quantity; A mismatch judgment module for calculating the ratio of the heat flow power spectrum entropy of mold heat dissipation to the mechanical power spectrum entropy of hydraulic cylinder output based on the heat flow signal and mechanical work signal, and identifying whether the pressure maintaining process enters the load mismatch stage; A mismatch analysis module for calculating the output work amount of each hydraulic cylinder for maintaining the displacement synchronization reference within a set time period when it is identified that the load mismatch stage is entered, and evaluating the relative difference of the output work amount of each hydraulic cylinder; A target adjustment module for taking maintaining the stability of the dynamic load imbalance quantity as the target, and dynamically adjusting the displacement synchronization reference value of each hydraulic cylinder based on the relative difference of the output work amount of each hydraulic cylinder; A closed-loop control module for performing displacement closed-loop control on each hydraulic cylinder based on the dynamically adjusted displacement synchronization reference value.

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