A method and system for multi-cylinder synchronization control of a forging hydraulic press

Abstract

The application discloses a kind of forging hydraulic press multi-cylinder synchronous control method and system, specifically relates to large aluminum forging manufacturing technical field, for solving the problem that existing technology is caused by uneven cooling of forging in pressure maintaining phase, and then the load mismatch of hydraulic cylinder, further influence forging forming quality;It is through real-time monitoring mold heat dissipation heat flow signal and hydraulic cylinder output mechanical work signal in pressure maintaining phase, based on the evaluation of load coordination state between cylinders generation dynamic load imbalance by piston rod side pressure change rate;Calculate heat flow and mechanical power spectrum entropy ratio to identify load mismatch phase;After identifying mismatch, statistical analysis the output power difference of each cylinder, and dynamic optimization displacement synchronization reference value is taken as the goal of maintaining load balance;Finally, according to the reference value of optimization to each hydraulic cylinder is carried out high-precision displacement closed-loop control to realize;It can actively adapt to the thermal-mechanical coupling change of pressure maintaining process, effectively improve the multi-cylinder synchronization precision and forging internal quality.

Description

A method and system for synchronous control of multiple cylinders in a forging hydraulic press Technical Field

[0001] This invention relates to the field of large aluminum forging manufacturing technology, and in particular to a multi-cylinder synchronous control method and system for a forging hydraulic press. Background Technology

[0002] Large multi-cylinder forging hydraulic presses are key equipment for manufacturing aluminum forgings for aerospace applications, such as integral frames, beams, and thin-walled curved structural components. These forgings have extremely high requirements for internal microstructure uniformity, dimensional accuracy, and residual stress distribution. During the forging process, the synchronization accuracy of multiple hydraulic cylinders directly determines the forming quality of the forging. In existing technologies, multi-cylinder synchronous control mainly focuses on displacement or force synchronization during the active pressurization phase. Feedback control strategies are used to reduce the trajectory deviation of each cylinder actuator during the dynamic process. During the pressure holding phase, the control system typically maintains the displacement or pressure parameters of each cylinder constant, treating it as a static holding process.

[0003] However, in the actual production of large aluminum forgings for aerospace applications, the cooling and shaping of high-temperature billets under holding pressure within the mold cavity is a complex process involving the coupling of thermodynamics and structural mechanics. Due to the differences in thermophysical properties between the forging material and the mold material, as well as the non-uniform heat dissipation caused by the geometric characteristics of the forging itself, the system will generate continuously changing non-uniform thermal stress during the holding pressure stage. This stress field acts on the mold, causing a time-varying mismatch in the load borne by the multiple hydraulic cylinders driving the upper mold, which disrupts the mechanical balance established in the early stage of holding pressure. This makes it difficult for the synchronous control strategy based on static assumptions to maintain true cylinder synchronization, thereby affecting the stress state and final quality of the forging during the critical shaping stage. Summary of the Invention

[0004] This invention addresses the technical problems existing in the prior art by providing a method and system for synchronous control of multiple cylinders in a forging hydraulic press.

[0005] The technical solution of the present invention to solve the above-mentioned technical problems is as follows:

[0006] A method for synchronous control of multiple cylinders in a forging hydraulic press includes:

[0007] S1. During the pressure holding stage, monitor the piston rod side pressure values ​​of multiple hydraulic cylinders acting on the upper mold in real time, and simultaneously acquire the heat flow signal and mechanical work signal of the mold for heat dissipation.

[0008] S2. Evaluate the degree of discrete coordination among the rate of change of piston rod side pressure of each hydraulic cylinder based on the piston rod side pressure value, and generate a dynamic load loss measure.

[0009] S3. 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 mechanical work signal, and identify whether the pressure holding process has entered the load mismatch stage.

[0010] S4. When the load mismatch stage is identified, calculate the output power of each hydraulic cylinder in maintaining the displacement synchronization reference within the set time period, and evaluate the relative difference of the output power of each hydraulic cylinder.

[0011] S5. With the goal of maintaining the stability of dynamic load loss, 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.

[0012] S6. Based on the dynamically adjusted displacement synchronization reference value, perform closed-loop displacement control on each hydraulic cylinder.

[0013] Furthermore, during the pressure holding stage, the piston rod side pressure values ​​of multiple hydraulic cylinders acting on the upper mold are monitored in real time, and the heat flow signal and mechanical work signal of the mold for heat dissipation are acquired simultaneously, including:

[0014] The temperature values ​​at at least two predetermined points inside the mold cavity are monitored in real time. The temperature change per unit time is calculated based on the temperature values, and the change is used as a heat flow signal characterizing the heat dissipation intensity of the mold.

[0015] Simultaneously, the piston rod side pressure value and piston rod displacement value of each hydraulic cylinder are monitored in real time. The rate of change of piston rod displacement with time is calculated. The piston rod side pressure value is multiplied by the rate of change of displacement to obtain the mechanical work signal characterizing the real-time output power of the hydraulic cylinder.

[0016] Furthermore, based on the piston rod side pressure value, the degree of discrete coordination among the rate of change of piston rod side pressure of each hydraulic cylinder is evaluated to generate a dynamic load loss measure, including:

[0017] Based on the piston rod side pressure value obtained from real-time monitoring, the rate of change of piston rod side pressure over time for each hydraulic cylinder is calculated.

[0018] Analyze the fluctuation trend of the rate of change of piston rod side pressure of each hydraulic cylinder in the time domain, and identify whether there are hydraulic cylinders where the rate of change trend shows a continuous divergence;

[0019] Calculate the arithmetic mean of the rate of change of piston rod side pressure of all hydraulic cylinders at the same moment, and calculate the instantaneous deviation of the rate of change of piston rod side pressure of each hydraulic cylinder from the arithmetic mean;

[0020] Introducing a sliding time window, the cumulative effect intensity of the instantaneous deviation of each hydraulic cylinder within the window is calculated;

[0021] The cumulative effect intensity of each hydraulic cylinder is normalized, and the normalized index characterizing the degree of synergistic deterioration of each cylinder is synthesized into a dynamic load loss measure.

[0022] Furthermore, the fluctuation trend of the rate of change of piston rod side pressure in each hydraulic cylinder in the time domain is analyzed to identify whether there are hydraulic cylinders where the rate of change trend shows a continuous divergence. This is achieved through the following methods:

[0023] Piecewise linear fitting was performed on the sequence of piston rod side pressure change rate for each hydraulic cylinder, and the average slope of the change rate within each time period was calculated.

[0024] Compare the slope direction and magnitude of different hydraulic cylinders within the same time period;

[0025] When the slope direction of a certain hydraulic cylinder is continuously opposite to that of most other hydraulic cylinders, or when the difference between the absolute value of its slope and the average value continuously exceeds a set threshold, it is determined that the corresponding cylinder exhibits a trend divergence.

[0026] Furthermore, based on the heat flux signal and mechanical work signal, the ratio of the heat flux power spectral entropy of the mold heat dissipation to the mechanical power spectral entropy of the hydraulic cylinder output is calculated to identify whether the pressure holding process has entered the load mismatch stage, including:

[0027] Synchronous time windows are extracted for heat flow signals and mechanical work signals, and the ratio sequence of power spectral entropy of heat flow signals to power spectral entropy of mechanical work signals within each time window is calculated.

[0028] Analyze the trend of the ratio sequence over time. When the ratio sequence is detected to show a monotonic change trend that continuously deviates from the initial baseline value in one direction and the change amplitude exceeds the set tolerance, at the same time verify that the duration of the monotonic change trend reaches the preset minimum duration.

[0029] When both the amplitude and duration conditions are met, the pressure holding process is determined to have entered the load mismatch stage.

[0030] Furthermore, the heat flux signal and mechanical work signal are synchronously truncated within time windows, and the ratio sequence of the power spectral entropy of the heat flux signal to that of the mechanical work signal within each time window is calculated. This is achieved through the following method:

[0031] The synchronization time window is captured using a fixed duration and overlapping sliding method;

[0032] Within each window, the power spectral entropy values ​​of the heat flow signal and the mechanical work signal are calculated separately: Fourier transform is performed on the signal data within the window to obtain a power spectral density estimate; the power spectral density is normalized across all frequency components so that the sum of the power values ​​of each frequency component is 1, thus forming a probability distribution; Shannon entropy is calculated based on the probability distribution, and the resulting entropy value is the power spectral entropy value of the corresponding signal; the power spectral entropy values ​​of the heat flow signal and the mechanical work signal are calculated independently according to this same process.

[0033] Divide the heat flux power spectrum entropy value calculated within the same window by the mechanical power spectrum entropy value to obtain the instantaneous ratio corresponding to the time window;

[0034] The instantaneous ratios of each window are arranged in chronological order to form a ratio sequence.

[0035] Furthermore, when the load mismatch stage is identified, the output power of each hydraulic cylinder in maintaining the displacement synchronization reference within a set time period is calculated, and the relative differences in the output power of each hydraulic cylinder are evaluated, including:

[0036] When the load mismatch phase is detected, start timing and set the statistical time period;

[0037] Within the statistical time period, the mechanical work signal of each hydraulic cylinder is integrated over time to obtain the output work done by each hydraulic cylinder in maintaining the displacement synchronization reference.

[0038] Calculate the average output power of all hydraulic cylinders;

[0039] Using the average value as a benchmark, calculate the degree of deviation of the output power of each hydraulic cylinder from the average value;

[0040] Based on the degree of deviation of the output power of each hydraulic cylinder, the relative difference distribution characteristics of the output power of the hydraulic cylinder group are evaluated.

[0041] Furthermore, with the goal of maintaining dynamic load imbalance stability, and based on the relative differences in the output power of each hydraulic cylinder, the displacement synchronization reference value of each hydraulic cylinder is dynamically adjusted, including:

[0042] Establish the correspondence between dynamic load loss and displacement synchronization benchmark adjustment;

[0043] Based on the relative differences in the output power of each hydraulic cylinder, determine the adjustment priority of the displacement synchronization reference value of each hydraulic cylinder;

[0044] For hydraulic cylinders that rank higher in the adjustment priority order, their displacement synchronization reference value should be adjusted first.

[0045] Based on the real-time changing trend of dynamic load measurement, the synchronous reference value of displacement of each hydraulic cylinder is compensated and corrected.

[0046] Through iterative adjustments, the dynamic load imbalance is gradually brought back to a stable range.

[0047] Furthermore, based on the dynamically adjusted displacement synchronization reference value, closed-loop displacement control is performed on each hydraulic cylinder, including:

[0048] The displacement value of the piston rod monitored in real time for each hydraulic cylinder is compared with the corresponding dynamically adjusted displacement synchronization reference value to obtain the displacement deviation value of each hydraulic cylinder.

[0049] Generate corresponding control signals based on the magnitude and direction of the displacement deviation;

[0050] The control signal is output to the servo valve group of each hydraulic cylinder to regulate the flow rate into the hydraulic cylinder;

[0051] Continuous feedback adjustment enables the actual displacement value of the piston rod of each hydraulic cylinder to track the dynamically adjusted displacement synchronization reference value.

[0052] Closed-loop control of the displacement of each hydraulic cylinder is maintained throughout the pressure holding phase until the pressure holding process ends.

[0053] On the other hand, the present invention provides a multi-cylinder synchronous control system for a forging hydraulic press, comprising:

[0054] The information acquisition module is used to monitor the piston rod side pressure value of multiple hydraulic cylinders acting on the upper mold in real time during the pressure holding stage, and simultaneously acquire the heat flow signal and mechanical work signal of the mold heat dissipation.

[0055] The imbalance analysis module is used to evaluate the degree of discrete coordination between the rate of change of piston rod side pressure of each hydraulic cylinder based on the piston rod side pressure value, and generate a dynamic load imbalance measure.

[0056] The 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 holding process has entered the load mismatch stage.

[0057] The mismatch analysis module is used to calculate the output power of each hydraulic cylinder in maintaining the displacement synchronization reference within a set time period when the load mismatch stage is identified, and to evaluate the relative difference in the output power of each hydraulic cylinder.

[0058] The target adjustment module is used to dynamically adjust the displacement synchronization reference value of each hydraulic cylinder based on the relative difference in the output power of each hydraulic cylinder, with the goal of maintaining the stability of dynamic load loss.

[0059] The closed-loop control module is used to perform closed-loop displacement control on each hydraulic cylinder based on the dynamically adjusted displacement synchronization reference value.

[0060] The beneficial effects of this invention are:

[0061] 1. By real-time monitoring of the heat flow from the mold and the mechanical work output by the hydraulic cylinder during the pressure holding stage, and by introducing the power spectral entropy ratio as a criterion for identifying load mismatch, the system can keenly capture the dynamic impact of thermal stress changes caused by non-uniform cooling of the forging on the load distribution of the hydraulic cylinder. This breaks through the limitation of treating the process as static in traditional pressure holding control, and extends the focus of synchronous control from simple geometric displacement tracking to the energy level of thermo-mechanical coupling. This enables the system to detect and respond to load imbalance trends caused by thermodynamic factors in advance, laying a solid foundation for achieving proactive and predictive synchronous control during the pressure holding stage.

[0062] 2. By quantitatively assessing the relative differences in output power of each cylinder and dynamically optimizing the displacement synchronization benchmark based on this, the core challenge of maintaining coordinated operation of multi-cylinder systems under time-varying non-uniform loads is effectively solved. This method not only ensures that the upper die maintains precise parallelism throughout the critical pressure-holding stage, but more importantly, by actively balancing the load of each cylinder, it promotes a more uniform stress distribution within the forging, thereby significantly improving the internal microstructure consistency, dimensional accuracy, and residual stress control level of large aerospace aluminum forgings, meeting the stringent requirements for forming quality of such high-end components. Attached Figure Description

[0063] Figure 1 is a flowchart of a multi-cylinder synchronous control method for a forging hydraulic press according to the present invention;

[0064] Figure 2 is a schematic diagram of the structure of a multi-cylinder synchronous control system for a forging hydraulic press according to the present invention. Detailed Implementation

[0065] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0066] Example 1: Figure 1 illustrates a multi-cylinder synchronous control method for a forging hydraulic press according to the present invention, comprising:

[0067] S1. During the pressure holding stage, monitor the piston rod side pressure values ​​of multiple hydraulic cylinders acting on the upper mold in real time, and simultaneously acquire the heat flow signal and mechanical work signal of the mold for heat dissipation.

[0068] S2. Evaluate the degree of discrete coordination among the rate of change of piston rod side pressure of each hydraulic cylinder based on the piston rod side pressure value, and generate a dynamic load loss measure.

[0069] S3. 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 mechanical work signal, and identify whether the pressure holding process has entered the load mismatch stage.

[0070] S4. When the load mismatch stage is identified, calculate the output power of each hydraulic cylinder in maintaining the displacement synchronization reference within the set time period, and evaluate the relative difference of the output power of each hydraulic cylinder.

[0071] S5. With the goal of maintaining the stability of dynamic load loss, 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.

[0072] S6. Based on the dynamically adjusted displacement synchronization reference value, perform closed-loop displacement control on each hydraulic cylinder.

[0073] S1. During the pressure holding stage, monitor the piston rod side pressure values ​​of multiple hydraulic cylinders acting on the upper mold in real time, and simultaneously acquire the heat flow signal and mechanical work signal of the mold for heat dissipation. The specific implementation is as follows:

[0074] During the pressure holding stage, to monitor the piston rod side pressure values ​​of multiple hydraulic cylinders acting on the upper die in real time, and to simultaneously acquire the heat flow signal and mechanical work signal of the die, a corresponding sensor system is first required. Specifically, at least two temperature monitoring points are pre-set within the die cavity. The selection of these points is based on the analysis of the forging geometry and the expected heat dissipation path; for example, one point is located in the central region of the forging, and another point is located in the edge region, to capture any potential non-uniform heat dissipation effects. K-type thermocouples are used for temperature monitoring. The thermocouple installation ensures good thermal contact between its measuring end and the die cavity surface to reduce measurement lag and errors. Temperature values ​​are acquired in real time at a set sampling frequency, for example, 10 Hz, meaning 10 temperature data points are collected per second. The acquired analog temperature signal is converted into a digital signal by an analog-to-digital converter and then transmitted to the processing unit. Based on these continuously acquired temperature values, the change in temperature per unit time is calculated, and this change is defined as the heat flow signal. The unit time is typically set to the time interval between adjacent sampling points, for example, 0.1 seconds. The temperature change rate is calculated using the backward difference method, which involves subtracting the temperature value at the current sampling moment from the temperature value at the immediately preceding sampling moment, and then dividing the difference by the sampling time interval (0.1 seconds). The calculated temperature change rate is expressed in degrees Celsius per second. This value directly represents the heat dissipation intensity of the mold per unit time, because the heat dissipation rate is directly proportional to the temperature drop rate.

[0075] Simultaneously, the piston rod side pressure and piston rod displacement values ​​of each hydraulic cylinder are monitored in real time. The piston rod side pressure value is acquired by a pressure sensor installed on the hydraulic cylinder piston rod side oil circuit. The range of the pressure sensor is selected based on the maximum working pressure of the hydraulic press system; for example, a pressure sensor with a range of 0 to 100 MPa can be selected. Its output signal is a standard current signal (e.g., 4-20 mA), which is converted into a standard voltage signal by a signal conditioning circuit before being read by 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 control requirements, for example, 0.01 mm. Its installation position ensures that the linear movement of the piston rod can be detected accurately and in real time. The displacement value is synchronously acquired using the same sampling frequency as the temperature acquisition, for example, 10 Hz, to ensure the consistency of all signal time series. When calculating the rate of change of piston rod displacement over time, the backward difference method is also used. That is, the difference between the displacement value at the current sampling moment and the displacement value at the previous sampling moment is divided by the sampling time interval (0.1 seconds) to obtain the rate of change of displacement, with the unit being millimeters per second. Subsequently, the piston rod side pressure value is multiplied by the calculated displacement change rate. Before performing the multiplication, unit conversion is required: the original unit of the piston rod side pressure value is megapascals, which needs to be converted to pascals (SI); the original unit of the displacement change rate is millimeters per second, which needs to be converted to meters per second (1 millimeter equals 0.001 meters). The result of the multiplication is the product of pressure (Pascals) and velocity (meters per second), which physically represents power, measured in watts. The calculated power value is the mechanical work signal characterizing the real-time output power of the hydraulic cylinder.

[0076] The entire data acquisition, transmission, and processing process is implemented within the processing unit. This unit employs an operating system with real-time task scheduling capabilities to ensure strict synchronization of the sampling times of all sensor signals. The alignment accuracy of the signal timestamps is controlled within a certain range, for example, better than 1 millisecond, thus avoiding additional errors introduced by signal asynchrony. The acquisition of heat flux and mechanical work signals is synchronized, meaning that the trigger signals for acquiring temperature, piston rod side pressure, and piston rod displacement data originate from the same high-precision clock source within the processing unit. When calculating the rate of change of temperature and displacement, 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 holding process system and the accuracy of process control. This interval must effectively capture meaningful dynamic changes during the process while also taking into account the computational load of the processing unit. For heat flux signals, the raw temperature data can be preprocessed before calculating the rate of change of temperature. For example, a moving average filtering algorithm can be used to smooth the temperature values ​​of multiple consecutive sampling points (e.g., 5 points) to suppress the adverse effects of measurement noise on the stability of differential calculations. Similarly, the raw displacement data can also be filtered and preprocessed in the calculation of the rate of change of displacement. The calculation of mechanical work signals involves multiplication operations, which are performed using floating-point instructions in the processing unit. The entire monitoring system operates continuously during the pressure holding phase until the end-of-pressure instruction is issued, ensuring the continuity and integrity of data recording and providing a reliable data foundation for subsequent analysis.

[0077] S2. Evaluate the degree of discrete coordination among the rate of change of piston rod side pressure of each hydraulic cylinder based on the piston rod side pressure value, and generate a dynamic load loss measure. The specific implementation is as follows:

[0078] Based on the real-time monitored piston rod side pressure values, the rate of change of piston rod side pressure over time for each hydraulic cylinder is calculated. The piston rod side pressure values ​​are continuous time-series data acquired in real-time by a pressure sensor using the aforementioned method, with a sampling frequency set to a fixed value, such as 10 Hz. The calculation of the rate of change of piston rod side pressure is implemented in the processing unit using a numerical differentiation method, specifically applying the backward difference method. For each sampling moment, the processing unit performs the following operations: taking the piston rod side pressure value at the current moment, subtracting the piston rod side pressure value at the previous sampling moment, and dividing the resulting difference by the sampling time interval (e.g., 0.1 seconds). The result is the rate of change of piston rod side pressure at that moment, expressed in pressure units divided by time, for example, megapascals per second. This calculation process is performed independently and in parallel for each hydraulic cylinder in the hydraulic press system, thereby generating an independent, continuously changing data sequence of piston rod side pressure rate of change over time for each hydraulic cylinder.

[0079] This study analyzes the fluctuation trend of the piston rod side pressure change rate of each hydraulic cylinder in the time domain to identify hydraulic cylinders exhibiting persistent divergence in their change rate trends. This analysis is achieved through piecewise linear fitting of the piston rod side pressure change rate sequence for each hydraulic cylinder. First, the continuous piston rod side pressure change rate time series is divided into multiple consecutive time periods. These time periods can be continuous and non-overlapping or partially overlapping. The length of each time period is pre-set based on the dynamic characteristics of the pressure holding process; for example, it can be set to a window containing 50 consecutive sampling points (corresponding to a 5-second duration). Within each specific time period, the least squares method is used to perform linear fitting on the set of piston rod side pressure change rate data points for a specific hydraulic cylinder, obtaining an optimally fitted straight line. The slope of this fitted line is defined as the average slope of the piston rod side pressure change rate for that hydraulic cylinder within this time period. The sign (positive or negative) of the average slope indicates the main trend direction (increasing or decreasing) of the change rate within that time period, while its absolute value indicates the strength or steepness of the trend. Next, the average slopes calculated for different hydraulic cylinders within the same time period are compared. The comparison includes two aspects: the direction of the average slope (i.e., the sign) and the magnitude of the average slope (i.e., the absolute value). The criterion for identifying whether a hydraulic cylinder exhibits trend differentiation is set to meet one of the following conditions: Condition 1, the average slope direction of this hydraulic cylinder is consistently opposite to the average slope direction of most hydraulic cylinders in the system (e.g., hydraulic cylinders representing more than two-thirds of the total number of cylinders) for multiple consecutive time periods (e.g., three consecutive time periods); Condition 2, the difference between the absolute value of the average slope of this hydraulic cylinder and the arithmetic mean of the absolute values ​​of the average slopes of all hydraulic cylinders within that time period exceeds a preset threshold for multiple consecutive time periods (e.g., three consecutive time periods). This threshold can be determined based on historical normal operation data statistics, for example, by calculating the standard deviation of the difference between the absolute value of the slope of each cylinder and the average value under historical normal operating conditions, and setting the threshold to twice this standard deviation. When a hydraulic cylinder meets either of the above conditions, the processing unit determines that the hydraulic cylinder exhibits trend differentiation. This determination indicates that the load dynamic response characteristics of this hydraulic cylinder have begun to significantly deviate from the overall cooperative state of the hydraulic cylinder group.

[0080] Calculate the arithmetic mean of the piston rod side pressure change rate 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 this arithmetic mean. For each sampling time, the processing unit performs the following calculations: First, sum the piston rod side pressure change rate values ​​of all N hydraulic cylinders at that time, then divide the sum by the total number of hydraulic cylinders N. The quotient is the arithmetic mean of the piston rod side pressure change rate of all hydraulic cylinders at that time. Next, for each hydraulic cylinder in the system, subtract the arithmetic mean calculated in the previous step from its specific piston rod side pressure change rate value at that sampling time. The difference is the instantaneous deviation of that hydraulic cylinder at the current time. The instantaneous deviation is a signed algebraic value, where the sign indicates the direction of deviation (above or below the average), and the absolute value indicates the degree of instantaneous deviation from the average level.

[0081] 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, a window length of 30 seconds means that the window contains 300 consecutive sampling points (based on a 10 Hz sampling frequency). The window slides along the time axis, with each slide step being a 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, the absolute value of the instantaneous deviation of the hydraulic cylinder at each sampling moment within this window is taken, and then the absolute values ​​corresponding to all sampling points within the window are summed. This 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. The larger the value, the longer the duration and the greater the magnitude of the deviation of the hydraulic cylinder from the overall average state within this time period, i.e., the stronger the cumulative misalignment effect.

[0082] The cumulative effect intensity of each hydraulic cylinder is normalized. The purpose of normalization is to eliminate the influence of absolute numerical magnitudes, making the degree of synergistic degradation between different hydraulic cylinders comparable. A specific and feasible normalization method is as follows: In the processing unit, first, find the maximum value among the cumulative effect intensities of all hydraulic cylinders within the current sliding window. Then, divide the cumulative effect intensity of each hydraulic cylinder by this maximum value. After this processing, each hydraulic cylinder obtains a normalized index value between 0 and 1. This normalized index value directly and quantitatively characterizes the degree of synergistic degradation of that hydraulic cylinder relative to the worst-performing hydraulic cylinder within the current window period; the closer the value is to 1, the more severe the synergistic degradation problem of that cylinder. Other normalization benchmarks can also be used, such as dividing by the arithmetic mean of the cumulative effect intensities of all hydraulic cylinders.

[0083] The normalized indices characterizing the degree of coordination degradation of each cylinder are synthesized into a dynamic load misalignment measure. This synthesis process is completed in the processing unit, aiming to generate a single index that comprehensively reflects the load synchronization state of the entire multi-cylinder system. Several synthesis methods can be chosen. For example, the maximum value among the normalized indices of all hydraulic cylinders can be used as the dynamic load misalignment measure; this method focuses on the state of the least coordinated hydraulic cylinder. Alternatively, the standard deviation of the normalized indices of all hydraulic cylinders can be calculated; this method reflects the dispersion of the coordination of the entire hydraulic cylinder group. Another method is to calculate the arithmetic mean of all normalized indices; this method reflects the overall average degradation level. The dynamic load misalignment measure is a comprehensive scalar index; its value directly characterizes the degree of synchronization or desynchronization of the entire multi-cylinder system in the dynamic load distribution. A higher value indicates a more severe load imbalance in the system. This dynamic load misalignment measure will be output, providing crucial quantitative basis for subsequent control decisions to determine whether the system has entered the load misalignment stage and to adjust the synchronization benchmark. The entire process, from calculating the rate of change to generating dynamic load imbalance measures, is repeated once every time a sliding window is updated (i.e., every time a sampling interval is slid), thus generating a dynamic load imbalance measure sequence that is constantly updated over time, reflecting the changes in load coordination status during the pressure holding process in real time.

[0084] S3. Calculate the ratio of the heat flux power spectral entropy of the mold heat dissipation to the mechanical power spectral entropy of the hydraulic cylinder output based on the heat flux signal and mechanical work signal. Identify whether the pressure holding process has entered the load mismatch stage. The specific implementation is as follows:

[0085] The ratio of the heat flux power spectrum entropy of the mold to the mechanical power spectrum entropy of the hydraulic cylinder output is calculated based on the heat flux signal and the mechanical work signal to identify whether the pressure holding process has entered the load mismatch stage. First, synchronous time windows are extracted for the heat flux signal and the mechanical work signal. The heat flux signal is a continuous time series signal obtained by monitoring the temperature change rate at a predetermined point within the mold cavity using the aforementioned method. The mechanical work signal is a continuous time series signal obtained by multiplying the piston rod side pressure value by the piston rod displacement change rate using the aforementioned method. Synchronous time window extraction is performed using a fixed duration and overlapping sliding method. The fixed duration of the time window is dynamically set according to the signal characteristics and process; for example, the length of a time window can be set to 10 seconds. Overlapping sliding means that the starting point of the subsequent 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, 1 second, thus forming continuously overlapping analysis windows. The heat flux signal data segments and mechanical work signal data segments contained within each time window are strictly aligned in time to ensure that both reflect the physical process within the same time period. The selection of the time window length needs to take into account 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 holding process.

[0086] Within each synchronization time window, the power spectral entropy values ​​of the heat flow signal and the mechanical work signal are calculated independently. The calculation process begins with performing a Fourier transform on the signal data within the window to obtain a power spectral density estimate. Specifically, for the discrete signal data sequence within each time window (e.g., containing 100 sampling points, corresponding to a 10-second window length and a 10 Hz sampling frequency), a Fast Fourier Transform (FFT) algorithm is applied to transform it from the time domain to the frequency domain. The number of points in the FFT can be set to be equal to or greater than the number of sampling points within the window, for example, 128 points, with zero-padding applied to data with fewer than 128 points. The transformed signal is then represented by complex numbers at discrete frequency points. Next, the complex amplitude value of each frequency component is squared to obtain the power estimate for that frequency component. The power estimates of all frequency components are combined to form the power spectral density estimate of the signal within this time window. The frequency resolution of the power spectral density estimate is determined by the window length; for example, a 10-second window length corresponds to a frequency resolution of 0.1 Hz. Next, the power spectral density is normalized across all frequency components to transform it into a probability distribution. Specifically, the sum of the power estimates for all frequency components is calculated first, and then the power estimate for each frequency component is divided by this sum. This results in a normalized power value for each frequency component between 0 and 1, and the sum of the normalized power values ​​for all frequency components equals 1, thus satisfying the axioms of probability distribution. Based on this probability distribution, the Shannon entropy is calculated. The Shannon entropy is calculated as follows: for each frequency component, its corresponding normalized power value is multiplied by the base-2 logarithm of that normalized power value; then all these products are summed; finally, the negative of the sum is taken. The calculated entropy value is the power spectral entropy value of the signal within the current time window. The power spectral entropy values ​​of the heat flow signal and the mechanical work signal are calculated independently, strictly following the same process described above. That is, the entire process of Fourier transform, power spectral estimation, normalization, and Shannon entropy calculation is performed independently for the heat flow signal data segment and the mechanical work signal data segment, respectively. Power spectral entropy is a dimensionless scalar; the larger its value, the more uniform and disordered the distribution of signal energy in the frequency domain.

[0087] The instantaneous ratio is obtained by dividing the calculated heat flux power spectrum entropy value by the mechanical power spectrum entropy value within the same time window. Specifically, the calculated heat flux power spectrum entropy value is used as the numerator, and the mechanical power spectrum entropy value is used as the denominator. The quotient is the instantaneous ratio. This ratio is a dimensionless value that reflects the relative relationship between the disorder of energy distribution during the mold's heat dissipation process and the disorder of energy distribution during the hydraulic cylinder's mechanical output within a specific time window. Before performing the division, a very small constant (e.g., 1e-10) can be added to the denominator to prevent numerical calculation errors caused by a denominator of zero.

[0088] The instantaneous ratios calculated from each sliding time window are arranged chronologically to form a continuous ratio sequence. This sequence is sorted in ascending order according to the center or start timestamp of the time window, constituting a new signal that evolves over time. Plotting time on the x-axis and the ratio on the y-axis, this sequence characterizes the dynamic changes in the thermo-mechanical power spectral entropy ratio during the pressure holding process. The time interval between adjacent data points in the sequence is determined by the sliding step size; for example, a 1-second sliding step size means a new ratio data point is generated every second.

[0089] Analyzing the trend of the ratio sequence over time helps identify whether the pressure holding process has entered the load mismatch stage. The analysis first requires determining a stable initial baseline value. This initial baseline value is obtained by calculating the arithmetic mean of the ratio sequence during a period considered relatively stable under load after the start of the pressure holding phase. This stable period needs to be long enough to obtain a reliable statistical baseline; for example, the average of all calculated instantaneous ratios within the first 30 seconds after the start of pressure holding can be used as the initial baseline value. Then, the changes in subsequent values ​​of the ratio sequence relative to this initial baseline value are continuously monitored. When a monotonic change in the ratio sequence is detected, indicating a continuous unidirectional deviation from the initial baseline value (i.e., multiple consecutive data points showing a continuous upward or downward trend), further judgment is triggered. Two conditions need to be verified simultaneously: the first condition is that the change exceeds a set tolerance; that is, the percentage change obtained by dividing the absolute difference between the current value of the ratio sequence and the initial baseline value by the initial baseline value exceeds a preset threshold. This threshold (i.e., the set tolerance) can be set, for example, to 15% of the initial baseline value. The percentage threshold is set based on the analysis of the ratio fluctuation range in a large amount of historical normal pressure holding process data. For example, 1.5 times the upper limit of the normal fluctuation range is taken as the tolerance. The second condition is that the duration of the above monotonic change trend reaches the preset minimum duration, which can be set to 20 seconds for example. The setting of the minimum duration needs to take into account the thermal inertia time constant of the process to ensure that the identified trend is statistically significant rather than random fluctuation. The basis can be prior knowledge of the process dynamic characteristics or experimental data analysis. Only when the change of the ratio sequence simultaneously meets the amplitude condition (the change amplitude exceeds the set tolerance) and the duration condition (the duration of the monotonic change trend reaches the preset minimum duration) will the processing unit finally determine that the pressure holding process has entered the load mismatch stage. This determination result will serve as the decision basis for triggering subsequent control actions (such as calculating the output power of each cylinder). The entire identification process is repeated when new time window data arrives to achieve real-time status monitoring and judgment. If a brief anomaly occurs in the signal during the identification process (such as momentary sensor interference), simple data filtering or outlier removal logic can be introduced, such as ignoring drastic fluctuations lasting less than 2 seconds, to improve the robustness of the judgment.

[0090] S4. When the load mismatch stage is detected, calculate the output power of each hydraulic cylinder in maintaining the displacement synchronization reference within a set time period, and evaluate the relative difference in the output power of each hydraulic cylinder. The specific implementation is as follows:

[0091] When the load mismatch stage is detected, a timer is started and a statistical time period is set. The detection of the load mismatch stage is based on the analysis results of the ratio sequence of thermal power spectrum entropy to mechanical power spectrum entropy from the preceding steps. Once the processing unit determines that the load mismatch stage has been entered, it immediately starts an internal timer, beginning the count from zero. Simultaneously, a statistical time period is set, the length of which is predetermined based on the response characteristics of the hydraulic system, the dynamic timescale 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. This setting is based on the premise that it needs to be long enough to cover the main dynamic response cycles of multiple hydraulic systems, thereby capturing the stable statistical characteristics of the output power of each hydraulic cylinder and avoiding misjudgments caused by short-term fluctuations in pressure or flow; at the same time, it needs to be short enough to ensure that the control system can respond promptly to the load mismatch state and prevent further aggravation of the mismatch. The statistical time period can be set as a fixed value based on a large number of process experiments, or it can be finely adjusted according to the dynamic characteristics of the system monitored in the early stable stage of the pressure holding process (such as the dominant frequency of main pressure fluctuations). However, the core principle is that it must cover a typical period of time that can reliably reflect the power difference characteristics of each cylinder.

[0092] Within a set statistical time period, the mechanical work signal of each hydraulic cylinder is integrated over time to obtain the output power of 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 change rate using the aforementioned method, and its unit is watts. The time integration operation is performed in the processing unit, and its physical meaning is to calculate the cumulative effect of power over time, i.e., energy. In specific implementation, for each hydraulic cylinder in the system, a discrete data segment is extracted from its continuously recorded mechanical work signal time sequence, starting from the timer start time and lasting for a 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 integration operation is implemented using a numerical integration method. Numerical integration using the trapezoidal rule, which offers higher accuracy, is performed as follows: The power values ​​corresponding to two adjacent sampling time points (0.1 seconds apart) are added together and then divided by 2 to obtain the average power estimate for that small time interval. This average power estimate is then multiplied by the sampling time interval (0.1 seconds) to obtain the elementary work performed within this small time interval. Finally, the elementary work calculated for all consecutive time intervals within the statistical time period is summed. The calculated output power is expressed in joules, quantitatively representing the total energy consumed by the hydraulic cylinder within that specific statistical time period to overcome its own load and maintain the piston rod displacement in line with the initially set displacement synchronization reference. The output power of each hydraulic cylinder is calculated independently using the same numerical integration method.

[0093] Calculate the average output power of all hydraulic cylinders. After the statistical time period ends, the processing unit has obtained the output power values ​​of all hydraulic cylinders during that period. These power values ​​are algebraically summed to obtain the total output power of the entire hydraulic cylinder group during that time period. Then, the total output power is divided by the total number of hydraulic cylinders, N; the quotient is the arithmetic mean of the output power of all hydraulic cylinders. This average value represents the average energy exerted by the entire hydraulic cylinder group to maintain displacement synchronization during the identified load mismatch phase. It provides an objective and quantitative benchmark for further evaluation of the differences between individual hydraulic cylinders and the overall level.

[0094] Using the calculated average value as a benchmark, the deviation of each hydraulic cylinder's output power from the average value is calculated. For each hydraulic cylinder in the system, the specific value of its output power calculated within the statistical time period is subtracted from the average value of all hydraulic cylinders' output power calculated in the previous step. The difference is the absolute deviation of that hydraulic cylinder's output power from the average value. To eliminate the influence of differences in absolute power values ​​caused by different total system loads and to make the deviations in different pressure holding processes or under different operating conditions comparable, it is usually necessary to further calculate the relative deviation. The method for calculating the relative deviation is as follows: divide the absolute deviation obtained above by the average value of all hydraulic cylinders' output power, and then multiply by 100% to obtain a percentage value. This percentage value is the deviation of each hydraulic cylinder's output power from the average value. The value can be positive or negative. A positive value indicates that the cylinder's output power is higher than the average level within the group, usually meaning that it is under a relatively larger load or there is an efficiency loss; a negative value indicates that the cylinder's output power is lower than the average level within the group. The absolute value of the deviation indicates the degree of deviation from the average level.

[0095] Based on the deviation 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, providing a basis for subsequent control decisions. A commonly used and effective evaluation method is to calculate the sample standard deviation of the relative deviation of all hydraulic cylinders. The calculation process of the standard deviation is as follows: First, calculate the arithmetic mean of all relative deviations (theoretically close to zero with a large number of samples, but may be a small value in a single calculation); then, calculate the difference between the relative deviation of each hydraulic cylinder and this mean (or directly with zero), and square this difference; next, calculate the arithmetic mean of all these squared values; finally, take the square root of the mean. The calculated standard deviation is a dimensionless value, and its magnitude directly reflects the dispersion of the output power of the hydraulic cylinder group. The larger the standard deviation, the greater the difference in output power between the cylinders, and the worse the synchronization coordination. In addition to the standard deviation, the value with the largest absolute value of relative deviation among all hydraulic cylinders can also be found, i.e., the maximum absolute value of deviation. This value reflects how much the hydraulic cylinder with the most extreme performance deviates from the average level. Furthermore, the distribution pattern of the relative deviation can be analyzed. For example, observe whether the deviation values ​​are significantly concentrated in positive or negative regions, which may indicate a systematic deviation in the load distribution; or check whether there are a few obvious outliers in the distribution, which may indicate an anomaly in individual hydraulic cylinders. The comprehensive evaluation results of these distribution characteristics (such as standard deviation, maximum absolute deviation, distribution skewness, etc.) constitute a complete quantitative description of the energy output coordination state of the hydraulic cylinder group during the load mismatch stage. This evaluation result provides a direct and quantitative decision-making basis for determining which hydraulic cylinders need to be adjusted first, and the direction and magnitude of adjustment, when dynamically adjusting the displacement synchronization reference value in subsequent steps. After the processing unit completes this evaluation, it generates key input information to guide the adjustment of the synchronization reference.

[0096] S5. With the goal of maintaining the stability of dynamic load imbalance, and based on the relative differences in the output power of each hydraulic cylinder, the displacement synchronization reference value of each hydraulic cylinder is dynamically adjusted. The specific implementation is as follows:

[0097] The goal is to maintain the stability of dynamic load imbalance, and the displacement synchronization reference value of each hydraulic cylinder is dynamically adjusted based on the relative differences in the output power of each hydraulic cylinder. First, a correspondence is established between the dynamic load imbalance and the adjustment amount of the displacement synchronization reference value. The dynamic load imbalance is a comprehensive quantitative index that characterizes the load coordination state of the hydraulic cylinder group in real time, generated by analyzing the discrete coordination degree of the rate of change of piston rod side pressure of each hydraulic cylinder in the aforementioned steps. This correspondence is usually expressed as a control function or a rule-based mapping relationship, the core of which is to convert the change of dynamic load imbalance into an adjustment command for the displacement synchronization reference value. For example, a proportional control relationship can be established, that is, the overall adjustment range of the displacement synchronization reference value is proportional to the degree to which the current dynamic load imbalance deviates from its target stable range. The target stable range is obtained by analyzing a large amount of historical normal pressure holding process data, for example, it can be set as ±5% of the average value of the dynamic load imbalance under historical normal operating conditions. The determination of the proportional gain, or control gain, needs to be considered in conjunction with the dynamic characteristics of the hydraulic system and can be obtained through system identification experiments. For example, during equipment commissioning, a known small load disturbance is actively applied, and the response amplitude of the dynamic load imbalance and the minimum displacement reference adjustment required to restore balance are accurately measured. The ratio of these two can be used as an estimate of the initial gain. Typically, this gain coefficient is a dimensionless decimal, such as 0.05. Another more robust approach is to establish a lookup table based on fuzzy rules or piecewise linear interpolation, mapping different numerical ranges of the dynamic load imbalance to preset, validated displacement reference adjustments. The basic principle for establishing this correspondence is: when the dynamic load imbalance increases (indicating deterioration in the coordination between hydraulic cylinders), the overall adjustment direction of the displacement synchronization reference value should aim to reduce the load difference between cylinders, causing the dynamic load imbalance to decrease; conversely, the opposite is also true.

[0098] Based on the relative differences in the output power of each hydraulic cylinder, the adjustment priority of the displacement synchronization reference value for each hydraulic cylinder is determined. The relative differences in output power are derived from the evaluation results of the preceding steps, specifically including the deviation of each hydraulic cylinder's output power from the average output power of all hydraulic cylinders (expressed as a percentage), and statistical measures reflecting the overall dispersion, such as standard deviation. The rule for determining the adjustment priority is based on a core logic: the hydraulic cylinder that contributes the most to the current load imbalance should receive the highest priority for adjustment. In practice, the cylinders are ranked according to the absolute value of their deviation from the average value. The larger the absolute value of the deviation, the more significant the difference between the current working state and the group average state, and the greater the impact on the overall load imbalance. Therefore, their displacement synchronization reference values ​​need to be adjusted first to quickly correct the main source of imbalance. For example, all hydraulic cylinders can be arranged in descending order of their absolute deviation values, with the cylinder ranked first having the highest adjustment priority. Another more refined strategy is to introduce priority threshold partitioning. For example, hydraulic cylinders with an absolute deviation exceeding 15% are designated as high-priority adjustment targets, those with a deviation between 8% and 15% are medium-priority, and those below 8% are low-priority or will not be adjusted within the current control cycle. The priority threshold can be determined based on the standard deviation multiple of the normal fluctuation range in historical data.

[0099] For hydraulic cylinders that rank high in the adjustment priority order, their displacement synchronization reference values ​​are adjusted first. Once the adjustment priority order is determined, the displacement synchronization reference values ​​of the hydraulic cylinders are calculated and adjusted sequentially according to this order. The direction of the adjustment (increase or decrease) is determined by the sign of the deviation in output power, and its physical meaning is to guide the redistribution of load through the adjustment of the displacement reference. For a hydraulic cylinder with a positive deviation in output power (i.e., its output power is higher than the average), this usually indicates that it is currently under a relatively excessive load or has additional energy loss. To balance the load of each cylinder, its displacement synchronization reference value should be appropriately reduced, causing its piston rod to retract slightly, thereby prompting some load to be transferred to the hydraulic cylinder with lower output power. Therefore, the adjustment amount of the displacement synchronization reference value for this cylinder should be negative (decrease). Conversely, for a hydraulic cylinder with a negative deviation in output power, its displacement synchronization reference value should be appropriately increased, with a positive adjustment amount (increase). The magnitude of the adjustment amount is positively correlated with the absolute value of the cylinder's deviation, generally following the quantitative principle of "the greater the deviation, the greater the adjustment." For example, the reference adjustment amount ΔSi for a single hydraulic cylinder can be estimated using the following formula:

[0100] ΔSi=Kp*|Di|*sign(Di)*ΔStotalweighted;

[0101] Where Di is the deviation degree of the cylinder, Kp is a proportionality coefficient (0 < Kp ≤ 1) used to prevent excessive single adjustment, and ΔStotalweighted is the weighted total adjustment amount calculated based on the dynamic load imbalance measurement. The adjustment process is progressive and only one round of adjustment is performed within a control cycle (such as 2 seconds), rather than a large one-time change, to avoid excessive impact on the hydraulic system or causing instability.

[0102] Combined with the real-time change trend of the dynamic load imbalance measurement, the displacement synchronization reference value of each hydraulic cylinder is compensatorily corrected. While performing the preliminary adjustment calculation based on the output power difference, the control system continuously monitors the latest value and its change trend of the dynamic load imbalance measurement. The change trend can be obtained by calculating the difference or the linear regression slope of the dynamic load imbalance measurement within the recent several control cycles (such as three consecutive cycles). The purpose of this compensatorily correction is to introduce a differential control effect, enhance the damping of the system, improve the response quality, and prevent overshoot or continuous oscillation. The compensation rule can be: If the dynamic load imbalance measurement still shows a rapid growth trend (a large positive change rate) within the current control cycle, then based on the preliminary adjustment amount for each cylinder, an additional compensation correction amount proportional to the change rate is added, and the direction is the same as the preliminary adjustment amount to strengthen the deviation correction force. On the contrary, if the dynamic load imbalance measurement has started to decline but the decline speed is too fast (the absolute value of the negative change rate is too large), then a compensation amount proportional to the change rate should be subtracted from the preliminary adjustment amount to play a "braking" effect and 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 change rate of the dynamic load imbalance measurement. This compensation amount will be superimposed on the preliminary adjustment amount of each hydraulic cylinder according to the priority weight.

[0103] The dynamic load imbalance is gradually brought back to a stable range through iterative adjustments. The entire dynamic adjustment process of the displacement synchronization reference value is a typical closed-loop feedback control iterative process. Within each iteration cycle (e.g., 2 seconds), the processing unit executes the following sequence: acquiring the latest sensor data, calculating the current dynamic load imbalance and the relative difference in output power of each cylinder, calculating the adjustment amount (including compensation correction) of the displacement synchronization reference value of each cylinder in this round according to the above rules, and sending the new displacement synchronization reference value to the displacement controller of each cylinder. After the system runs for the next cycle with the new reference value, data is collected again to evaluate the effect. Each iteration does not expect the dynamic load imbalance to immediately and completely recover to the ideal state, but rather to gradually approach the target through multiple iterations. The iteration process continues, and the dynamic load imbalance will be gradually guided to decrease under control, eventually stabilizing within a preset stable range (e.g., within ±5% of the target value). The termination condition for iterative adjustment can be set as follows: within several consecutive control cycles (e.g., 3 to 5 cycles), the dynamic load imbalance remains within the stable range, and the relative difference distribution characteristic index (e.g., standard deviation) of the output power of each cylinder is continuously lower than a certain preset threshold (e.g., 5%). Once the termination conditions are met, the system is considered to have returned to a satisfactory state of synchronous equilibrium. Large-scale baseline adjustments can then be paused, transitioning to a more refined maintenance mode or awaiting the next load mismatch trigger. The entire iterative process ensures the gradual, stable, and robust nature of control actions.

[0104] S6. Based on the dynamically adjusted displacement synchronization reference value, perform closed-loop displacement control on each hydraulic cylinder, as follows:

[0105] Based on the dynamically adjusted displacement synchronization reference value, closed-loop displacement control is performed on each hydraulic cylinder. First, the real-time monitored piston rod displacement value of each hydraulic cylinder 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. This sensor has a measurement accuracy of up to 0.01 mm, and its sampling frequency is synchronized with the control system cycle, for example, set to 100 Hz. The dynamically adjusted displacement synchronization reference value is the latest command value generated by the aforementioned control logic after iterative optimization based on the real-time calculated dynamic load loss and the relative differences in the output power of each hydraulic cylinder. The comparison operation is executed in the digital logic of the processing unit. For each hydraulic cylinder in the system, within each control cycle (e.g., 10 milliseconds), the actual piston rod displacement value measured by the displacement sensor at the current sampling time is subtracted from the latest dynamically adjusted displacement synchronization reference value independently set for that hydraulic cylinder. The resulting algebraic difference is the displacement deviation value of that hydraulic cylinder within the current control cycle. The displacement deviation value is an algebraic quantity with a positive or negative sign, and the unit is the same as the displacement value, which is millimeters; a positive value indicates that the actual displacement exceeds the currently set reference value, and a negative value indicates that the actual displacement has not yet reached the currently set reference value.

[0106] The control signal is generated based on the magnitude and direction of the displacement deviation. The generation of the control signal employs a classic proportional-integral-derivative (PI-DE) control algorithm. The processing unit maintains an independent control algorithm instance for each hydraulic cylinder. The output signal of the proportional control element is proportional to the displacement deviation value calculated in the current control cycle, i.e., proportional term output = Kp × 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 rapid response proportional to the instantaneous magnitude of the deviation.

[0107] The output signal of the integral control element is proportional to the cumulative value of the displacement deviation over time (i.e., the integral), specifically, the integral term output = Ki × ∫e(τ)dτ. The integral interval extends from the current control cycle back a specific time or from the start of the deviation, where Ki is the integral gain coefficient. The function of the integral term is to eliminate the steady-state error of the system and ensure long-term accuracy. The output signal of the derivative control element is proportional to the rate of change of the displacement deviation (i.e., the derivative), specifically, the derivative term output = Kd × de(t) / dt, where Kd is the derivative gain coefficient. The function of the derivative term is to provide a damping effect, predict the trend of deviation changes, and suppress overshoot and oscillations.

[0108] The output values ​​of the proportional, integral, and derivative terms are algebraically added to obtain the final comprehensive control signal U(t) for this control cycle of the hydraulic cylinder: U(t) = Kp × e(t) + Ki × ∫e(τ)dτ + Kd × de(t) / dt. The key parameters Kp, Ki, and Kd (or equivalent integral time Ti and derivative time Td) in the control algorithm need to be engineered based on the dynamic characteristics of the specific hydraulic actuator (such as response speed, inertia, and damping). This can be achieved, for example, through on-site debugging using the Ziegler-Nichols critical proportional method or other trial-and-error methods to ensure the stability, speed, and accuracy of the closed-loop system. The generated control signal is typically normalized to a standard range of voltage (e.g., -10V to +10V) or current (e.g., 4mA to 20mA). Its magnitude represents the strength of the control action, and its sign (positive or negative) represents the direction of the control action (causing the piston rod to extend or retract).

[0109] The control signal is output to the servo valve assembly of each hydraulic cylinder to regulate the flow rate entering the hydraulic cylinder. The digital control signal generated by the processing unit is converted into an analog voltage or current signal through its integrated digital-to-analog converter. After the analog signal is amplified and its driving capability is enhanced by the power amplifier circuit, it is transmitted to the corresponding servo valve assembly of the hydraulic cylinder through a shielded cable. The servo valve assembly is usually composed of a high-dynamic-response electro-hydraulic servo valve or a high-precision proportional valve and its matching amplifier. 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 electrical signal. When the control signal is negative (corresponding to the need to reduce the displacement deviation, i.e., the piston rod needs to extend), the servo valve assembly adjusts the valve port, allowing the pressurized oil to enter the piston rod side (rod chamber) of the hydraulic cylinder at a flow rate proportional to the absolute value of the control signal, while simultaneously connecting the piston side (rodless chamber) to the return oil circuit, thereby generating a force that retracts the piston rod. The flow rate into the hydraulic cylinder is directly proportional to the magnitude of the control signal within a certain linear range, thus achieving precise control of the hydraulic cylinder's movement speed. The adjustment of the flow rate directly changes the motion state of the piston rod, with the aim of generating the necessary hydraulic thrust to correct the current displacement deviation.

[0110] Continuous feedback adjustment ensures that the actual displacement value of each hydraulic cylinder's piston rod tracks the dynamically adjusted displacement synchronization reference value. This process, involving real-time monitoring of the piston rod displacement, comparison with the dynamically adjusted displacement synchronization reference value to calculate the deviation, generation of control signals using a control algorithm, and driving the servo valve assembly to adjust the flow rate, constitutes a complete negative feedback control closed loop. This closed-loop control system operates continuously and cyclically with a fixed, short control cycle (e.g., 10 milliseconds, corresponding to a control frequency of 100 Hz). At the beginning of each control cycle, the system collects the latest data from all displacement sensors; midway through the cycle, the processing unit completes all calculations and outputs control signals; before the end of the cycle, the control signals have already been applied to the servo valves. Through this high-frequency, continuous, and timely feedback adjustment mechanism, if the actual displacement value of any hydraulic cylinder's piston rod deviates from its current displacement synchronization reference value, whether due to load fluctuations or active adjustments to the reference value itself, the control system can detect the deviation within milliseconds and immediately generate corresponding corrective actions. This allows the actual displacement value of each hydraulic cylinder piston rod to dynamically and accurately track its own independent and potentially continuously optimized displacement synchronization reference value, thereby achieving high-precision synchronous motion in a multi-cylinder system and maintaining stability even when faced with time-varying and asymmetrical load disturbances.

[0111] Throughout the pressure holding phase, closed-loop control of the displacement of each hydraulic cylinder is maintained until the pressure holding process ends. Displacement closed-loop control, as the fundamental control loop at the execution level, is continuously operational from the start of the pressure holding phase. In the initial stage of pressure holding, if no significant load mismatch is detected, the displacement synchronization reference value typically remains at the initially set synchronization value. The role of closed-loop control is to suppress random disturbances and maintain initial synchronization accuracy. When the aforementioned monitoring logic identifies that the system has entered the load mismatch stage and dynamically adjusts the displacement synchronization reference value, the displacement closed-loop control system seamlessly switches to tracking the new, optimized reference value. This deviation-based continuous feedback control persists at every moment throughout the entire pressure holding phase, regardless of whether the displacement synchronization reference value has been dynamically adjusted. The end of the pressure holding process is typically triggered by the process controller based on a preset pressure holding time (e.g., a timer reaching a set value) or other process completion conditions (e.g., the pressure inside the mold cavity drops to a specific threshold). Once the processing unit receives the pressure holding end command from the upper-level process controller, the displacement closed-loop control stops operating, and the control system subsequently executes subsequent process steps such as pressure relief, main cylinder return, and ejector cylinder action. Maintaining high-precision displacement synchronization control throughout the holding pressure period is crucial for ensuring the internal microstructure uniformity, dimensional accuracy, and residual stress distribution of large forgings, especially aluminum alloy forgings required in the aerospace field.

[0112] Example 2: Figure 2 shows a schematic diagram of the structure of a multi-cylinder synchronous control system for a forging hydraulic press according to the present invention. The multi-cylinder synchronous control system for a forging hydraulic press includes:

[0113] The information acquisition module is used to monitor the piston rod side pressure value of multiple hydraulic cylinders acting on the upper mold in real time during the pressure holding stage, and simultaneously acquire the heat flow signal and mechanical work signal of the mold heat dissipation.

[0114] The imbalance analysis module is used to evaluate the degree of discrete coordination between the rate of change of piston rod side pressure of each hydraulic cylinder based on the piston rod side pressure value, and generate a dynamic load imbalance measure.

[0115] The 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 holding process has entered the load mismatch stage.

[0116] The mismatch analysis module is used to calculate the output power of each hydraulic cylinder in maintaining the displacement synchronization reference within a set time period when the load mismatch stage is identified, and to evaluate the relative difference in the output power of each hydraulic cylinder.

[0117] The target adjustment module is used to dynamically adjust the displacement synchronization reference value of each hydraulic cylinder based on the relative difference in the output power of each hydraulic cylinder, with the goal of maintaining the stability of dynamic load loss.

[0118] The closed-loop control module is used to perform closed-loop displacement control on each hydraulic cylinder based on the dynamically adjusted displacement synchronization reference value.

[0119] All calculations involved in the embodiments are dimensionless numerical calculations, and the preset parameters and thresholds in the calculations are set by those skilled in the art according to the actual situation.

[0120] It should be noted that this invention can be deployed on the device itself to realize embedded applications, or it can run on a PC or other terminal with a user interface, thereby meeting various hardware environments and usage requirements.

[0121] The above embodiments can be implemented, in whole or in part, by software, hardware, firmware, or any other combination thereof. When implemented using software, the above embodiments can be implemented, in whole or in part, as a computer program product. A 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, all or part of the processes or functions according to the embodiments of this application are generated. The computer can be a general-purpose computer, a special-purpose computer, a computer network, or other programmable device. Computer instructions can be stored in a computer-readable storage medium or transmitted from one computer-readable storage medium to another. For example, computer instructions can be transmitted from one website, computer, server, or data center to another website, computer, server, or data center via wireless or wired transmission; wired transmission methods include optical fiber, twisted pair, coaxial cable, etc.; wireless transmission includes infrared, microwave, etc. Computer-readable storage media can be any available medium that a computer can access or a data storage device such as a server or data center that contains one or more sets of available media. Available media can be magnetic media (e.g., floppy disks, hard disks, magnetic tapes), optical media (e.g., DVDs), or semiconductor media. Semiconductor media can be solid-state drives.

[0122] Those skilled in the art will understand that, for the sake of convenience and brevity, the specific working processes of the systems, devices, and modules described above can be referred to the corresponding processes in the foregoing method embodiments, and will not be repeated here.

[0123] In the several embodiments provided in this application, it should be understood that the disclosed systems, apparatuses, and methods can be implemented in other ways. For example, the apparatus embodiments described above are merely illustrative; for instance, the division of modules is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple modules or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the coupling or direct coupling or communication connection shown or discussed may be through some interfaces; the indirect coupling or communication connection between apparatuses or modules may be electrical, mechanical, or other forms.

[0124] The modules described as separate components may or may not be physically separate. The components shown as modules may or may not be physical modules; they may be located in one place or distributed across multiple network modules. Some or all of the modules can be selected to achieve the purpose of this embodiment according to actual needs.

[0125] In addition, the functional modules in the various embodiments of this application can be integrated into one processing module, or each module can exist physically separately, or two or more modules can be integrated into one module.

[0126] If a function is implemented as a software module and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of this application, in essence, or the part that contributes to the prior art, or a portion of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute all or part of the steps of the methods in the various embodiments of this application. The aforementioned storage medium includes various media capable of storing program code, such as USB flash drives, portable hard drives, read-only memory (ROM), random access memory (RAM), magnetic disks, or optical disks.

[0127] The above are merely specific embodiments of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

[0128] In conclusion, the above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for synchronous control of multiple cylinders in a forging hydraulic press, characterized in that, include: S1. During the pressure holding stage, monitor the piston rod side pressure values ​​of multiple hydraulic cylinders acting on the upper mold in real time, and simultaneously acquire the heat flow signal and mechanical work signal of the mold heat dissipation. S2. Based on the piston rod side pressure values, assess the degree of discrete coordination between the rate of change of piston rod side pressure of each hydraulic cylinder, and generate a dynamic load mismatch measure. S3. Based on the heat flow signal and mechanical work signal, calculate the ratio of the heat flow power spectrum entropy of the mold heat dissipation to the mechanical power spectrum entropy output by the hydraulic cylinders, and identify whether the pressure holding process has entered the load mismatch stage. S4. When the load mismatch stage is identified, calculate the output work done by each hydraulic cylinder to maintain the displacement synchronization reference within a set time period, and assess the relative difference in the output work of each hydraulic cylinder. S5. With the goal of maintaining the stability of the dynamic load mismatch measure, dynamically adjust the displacement synchronization reference value of each hydraulic cylinder based on the relative difference in the output work of each hydraulic cylinder. S6. Based on the dynamically adjusted displacement synchronization reference value, perform closed-loop displacement control on each hydraulic cylinder.

2. The multi-cylinder synchronous control method for a forging hydraulic press according to claim 1, characterized in that, During the pressure holding stage, the piston rod side pressure values ​​of multiple hydraulic cylinders acting on the upper mold are monitored in real time, and the heat flow signal and mechanical work signal of mold heat dissipation are acquired simultaneously. This includes: real-time monitoring of the temperature values ​​at at least two predetermined points in the mold cavity, calculating the temperature change per unit time based on the temperature values, and using the change as a heat flow signal characterizing the heat dissipation intensity of the mold; simultaneously, real-time monitoring of the piston rod side pressure value and piston rod displacement value of each hydraulic cylinder, calculating the rate of change of piston rod displacement with time, and multiplying the piston rod side pressure value by the rate of change of displacement to obtain the mechanical work signal characterizing the real-time output power of the hydraulic cylinder.

3. The multi-cylinder synchronous control method for a forging hydraulic press according to claim 1, characterized in that, The discrete coordination degree among the piston rod side pressure change rates of each hydraulic cylinder is evaluated based on the piston rod side pressure value, generating a dynamic load mismatch measure. This includes: calculating the piston rod side pressure change rate of each hydraulic cylinder over time based on the real-time monitored piston rod side pressure value; analyzing the fluctuation trend of the piston rod side pressure change rate of each hydraulic cylinder in the time domain to identify whether there are hydraulic cylinders with a persistent divergence in the change rate trend; calculating the arithmetic mean of the piston rod side pressure change rates of all hydraulic cylinders at the same moment, 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 to calculate 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 normalized index characterizing the degree of coordination degradation of each cylinder into a dynamic load mismatch measure.

4. The multi-cylinder synchronous control method for a forging hydraulic press according to claim 3, characterized in that, To analyze the fluctuation trend of the piston rod side pressure change rate of each hydraulic cylinder in the time domain, and to identify whether there are hydraulic cylinders with a persistent divergence in the change rate trend, the following method is used: perform piecewise linear fitting on the piston rod side pressure change rate sequence of each hydraulic cylinder, and calculate the average slope of the change rate in each time period; compare the slope direction and magnitude of different hydraulic cylinders in the same time period; when the slope direction of a certain hydraulic cylinder is continuously opposite to that of most other hydraulic cylinders, or when the difference between the absolute value of its slope and the average value continuously exceeds a set threshold, it is determined that the corresponding cylinder has a trend divergence.

5. The multi-cylinder synchronous control method for a forging hydraulic press according to claim 1, characterized in that, The ratio of the heat flux power spectral entropy of the mold heat dissipation to the mechanical power spectral entropy of the hydraulic cylinder output is calculated based on the heat flux signal and mechanical work signal to identify whether the pressure holding process has entered the load mismatch stage. This includes: synchronously capturing the heat flux signal and mechanical work signal within a time window, and calculating the ratio sequence of the heat flux signal power spectral entropy to the mechanical work signal power spectral entropy within each time window; analyzing the trend of the ratio sequence over time; when the ratio sequence is detected to show a monotonic change trend that continuously deviates unidirectionally from the initial reference value, and the change amplitude exceeds the set tolerance, the duration of the monotonic change trend is verified to reach the preset minimum duration; when both the amplitude condition and the duration condition are met, it is determined that the pressure holding process has entered the load mismatch stage.

6. The multi-cylinder synchronous control method for a forging hydraulic press according to claim 5, characterized in that, Synchronous time windows are extracted for heat flow signals and mechanical work signals. The ratio sequence of the power spectral entropy of the heat flow signal to that of the mechanical work signal within each time window is calculated. This is achieved by extracting synchronous time windows in a fixed-duration, overlapping sliding manner; calculating the power spectral entropy values ​​of the heat flow signal and the mechanical work signal within each window; performing Fourier transform on the signal data within the window to obtain a power spectral density estimate; and normalizing the power spectral density across all frequency components so that the sum of the power values ​​of each frequency component is 1, thus forming a probability distribution. The Shannon entropy is calculated based on the probability distribution, and the resulting 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 calculated independently 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 chronological order to form a ratio sequence.

7. The multi-cylinder synchronous control method for a forging hydraulic press according to claim 1, characterized in that, When the load mismatch stage is detected, the output power of each hydraulic cylinder in maintaining the displacement synchronization reference within a set time period is calculated, and the relative difference of the output power of each hydraulic cylinder is evaluated. This includes: when the load mismatch stage is detected, starting the timer and setting a statistical time period; within the statistical time period, performing time integration on the mechanical work signal of each hydraulic cylinder to obtain the output power of each hydraulic cylinder in maintaining the displacement synchronization reference; calculating the average value of the output power of all hydraulic cylinders; using the average value as a reference, calculating the degree of deviation of the output power of each hydraulic cylinder from the average value; and evaluating the relative difference distribution characteristics of the output power of the hydraulic cylinder group based on the degree of deviation of the output power of each hydraulic cylinder.

8. The multi-cylinder synchronous control method for a forging hydraulic press according to claim 1, characterized in that, With the goal of maintaining the stability of dynamic load imbalance, the displacement synchronization reference value of each hydraulic cylinder is dynamically adjusted based on the relative differences in the output power of each hydraulic cylinder. This includes: establishing a correspondence between the dynamic load imbalance and the adjustment amount of the displacement synchronization reference value; determining the adjustment priority of the displacement synchronization reference value of each hydraulic cylinder according to the distribution characteristics of the relative differences in the output power of each hydraulic cylinder; prioritizing the adjustment of the displacement synchronization reference value of hydraulic cylinders that rank higher in the adjustment priority order; compensating for the displacement synchronization reference value of each hydraulic cylinder by combining the real-time change trend of the dynamic load imbalance; and gradually returning the dynamic load imbalance to the stable range through iterative adjustment.

9. A multi-cylinder synchronous control method for a forging hydraulic press according to claim 1, characterized in that, Based on the dynamically adjusted displacement synchronization reference value, closed-loop displacement control is performed on each hydraulic cylinder, including: comparing the real-time monitored piston rod displacement value of each hydraulic cylinder with the corresponding dynamically adjusted displacement synchronization reference value to obtain the displacement deviation value of each hydraulic cylinder; generating corresponding control signals according to the magnitude and direction of the displacement deviation value; outputting the control signals to the servo valve group of each hydraulic cylinder to adjust the flow rate entering the hydraulic cylinder; making the actual displacement value of the piston rod of each hydraulic cylinder track the dynamically adjusted displacement synchronization reference value through continuous feedback adjustment; maintaining closed-loop control of the displacement of each hydraulic cylinder throughout the pressure holding phase until the pressure holding process ends.

10. A multi-cylinder synchronous control system for a forging hydraulic press, used to implement the multi-cylinder synchronous control method for a forging hydraulic press as described in any one of claims 1-9, characterized in that, include: The system comprises the following modules: an information acquisition module for real-time monitoring of piston rod side pressure values ​​of multiple hydraulic cylinders acting on the upper mold during the pressure holding phase, and simultaneous acquisition of heat flow and mechanical work signals from mold heat dissipation; an imbalance analysis module for evaluating the degree of discrete coordination among the rate of change of piston rod side pressure of each hydraulic cylinder based on the piston rod side pressure value, generating a dynamic load mismatch measure; a mismatch judgment module for calculating the ratio of heat flow power spectrum entropy of mold heat dissipation to mechanical power spectrum entropy of hydraulic cylinder output based on heat flow and mechanical work signals, identifying whether the pressure holding process has entered the load mismatch phase; a mismatch analysis module for calculating the output work done by each hydraulic cylinder to maintain the displacement synchronization reference within a set time period when the load mismatch phase is identified, and evaluating the relative difference in output work of each hydraulic cylinder; a target adjustment module for dynamically adjusting the displacement synchronization reference value of each hydraulic cylinder based on the relative difference in output work of each hydraulic cylinder, with the goal of maintaining the stability of the dynamic load mismatch measure; and a closed-loop control module for performing closed-loop displacement control of each hydraulic cylinder based on the dynamically adjusted displacement synchronization reference value.

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