Hydraulic motor constant torque self-adaptive PID control system

Abstract

The invention relates to the technical field of hydraulic control, and discloses a hydraulic motor constant torque self-adaptive PID (Proportion Integration Differentiation) control system which comprises a controller and a hydraulic driving unit, the controller performs frequency domain separation on the pressure signal by using a signal preprocessing module, and extracts an average pressure difference representing the driving force and a ripple amplitude representing the fluid rigidity; the state observation module estimates an instantaneous volume elastic modulus based on the ripple amplitude, corrects a compression item in a flow continuity model by using the elastic modulus, and calculates an instantaneous leakage coefficient of the motor in real time; the self-adaptive control module establishes dynamic mapping of PID gain and physical parameters, the proportional gain is adjusted by using a leakage coefficient to match system damping, the integral gain is adjusted by using a volume elastic modulus to adapt to inherent frequency, and a control instruction is synthesized by combining feedforward compensation. According to the method, the problem of model mismatch caused by oil characteristic change and motor abrasion is effectively solved, and the whole-life-cycle control precision of the system is improved.

Description

Technical Field

[0001] This invention relates to the field of hydraulic control technology, specifically to a constant torque adaptive PID control system for hydraulic motors. Background Technology

[0002] Hydraulic motor constant torque control systems are widely used in winches of construction machinery, rotary drive mechanisms, and industrial manufacturing equipment. Their control performance directly affects the smoothness and safety of operation. These systems typically employ a closed-loop pressure control strategy, maintaining a constant pressure difference between the motor inlet and outlet by adjusting the opening of the electro-hydraulic servo valve, thereby achieving precise control of the output torque.

[0003] However, in actual working conditions, the physical parameters of a hydraulic system are not constant. The bulk modulus of hydraulic oil (i.e., fluid stiffness) changes with the increase of oil temperature or the introduction of air. Existing control system designs simplify this to a fixed constant, or can only detect it offline by adding expensive dedicated oil quality sensors, lacking low-cost online monitoring methods. This leads to a mismatch in the system's preset control model when fluid characteristics change.

[0004] Furthermore, during long-term operation, the wear of internal moving parts in a hydraulic motor leads to a gradual increase in the leakage coefficient. Although existing technologies attempt to estimate leakage using flow observers, they neglect the influence of fluid compressibility on transient flow balance during calculations, simply attributing all flow differences to leakage. Under unsteady operating conditions with rapidly changing system pressure, the flow rate used to compress fluid volume is not negligible, and this simplification can lead to significant deviations in the identification of the leakage coefficient.

[0005] Due to a lack of accurate perception of the physical states such as fluid stiffness and leakage coefficient, traditional PID controllers use fixed gain parameters or make superficial adjustments based solely on error statistics, failing to adapt to changes in system damping characteristics and natural frequency at the physical mechanism level. This causes the control system to experience problems such as decreased response bandwidth, increased overshoot, or deteriorated steady-state accuracy when faced with motor wear or fluctuations in oil conditions, making it difficult to maintain consistent control performance throughout the entire lifespan of the equipment. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a constant torque adaptive PID control system for hydraulic motors. This system solves the problems in existing technologies where the inability to monitor changes in the bulk modulus of fluid at low cost and the difficulty in eliminating the interference of fluid compressibility on leakage identification lead to control parameters that cannot adapt to changes in the physical characteristics of the system, resulting in decreased control accuracy and unstable dynamic response throughout the system's lifespan.

[0007] To achieve the above objectives, the present invention provides the following technical solution: This invention provides a constant torque adaptive PID control system for a hydraulic motor, comprising a hydraulic drive hardware unit and a controller. The hydraulic drive hardware unit includes a hydraulic pump, an electro-hydraulic servo valve, a hydraulic motor, a load, and inlet pressure sensors, outlet pressure sensors, a speed sensor, and a valve core position sensor for acquiring system state quantities. The controller is logically divided into a signal preprocessing module, a state observation and identification module, and an adaptive control law calculation module.

[0008] The signal preprocessing module performs signal feature decoupling. It calculates the raw differential pressure signal based on the acquired pressure signal and performs frequency domain separation on the raw differential pressure signal, outputting the average differential pressure signal representing the driving force and the ripple amplitude representing the fluid stiffness, respectively. The state observation and identification module performs cascaded observation of multi-physics parameters. It estimates the instantaneous bulk modulus of the fluid based on the ripple amplitude and uses the instantaneous bulk modulus to correct the fluid compressibility term in the flow continuity model. Then, it combines the average differential pressure signal to observe the instantaneous leakage coefficient of the hydraulic motor in real time. The adaptive control law calculation module establishes a dynamic mapping relationship between the PID control gain and the physical state parameters. It adjusts the proportional gain using the instantaneous leakage coefficient, adjusts the integral gain using the instantaneous bulk modulus, and performs closed-loop feedback calculation on the deviation between the target differential pressure and the average differential pressure signal using the adjusted proportional gain and integral gain. Combined with feedforward compensation, it synthesizes control commands to drive the electro-hydraulic servo valve.

[0009] Further, the signal preprocessing module calculates the difference between the inlet pressure and the outlet pressure to obtain the original differential pressure signal; the signal preprocessing module is configured with a low-frequency control channel and a high-frequency feature extraction channel. In the low-frequency control channel, the system uses a low-pass filter with a cutoff frequency lower than the minimum fundamental frequency of the hydraulic pump to filter out pulsation interference and extract the average differential pressure signal used for feedback control. In the high-frequency feature extraction channel, the system uses the rotational speed signal to calculate the flow pulsation fundamental frequency and uses this to set the center frequency of the bandpass filter, extracts the pressure ripple component from the original signal, and calculates the ripple amplitude.

[0010] Furthermore, the state observation and identification module includes a bulk modulus correction unit. This unit normalizes the ripple amplitude using the rotational speed signal to eliminate the influence of rotational speed changes on the pressure pulsation amplitude. The unit pre-stores a reference ripple amplitude and calculates the instantaneous bulk modulus based on the ratio mapping between the normalized ripple amplitude and the reference ripple amplitude. In addition, this unit can update the reference ripple amplitude based on measured data during system steady-state operation to compensate for pulsation characteristic drift caused by pump source wear.

[0011] Furthermore, the state observation and identification module includes a leakage coefficient observation unit. This unit calculates the estimated flow rate through the electro-hydraulic servo valve based on the valve core position, and, according to the principle of flow continuity, subtracts the theoretical volumetric flow rate of the hydraulic motor and the fluid compression flow rate determined by the instantaneous bulk modulus from the estimated flow rate to obtain the flow rate difference. This unit calculates the instantaneous leakage coefficient by dividing the flow rate difference by the average differential pressure signal. To prevent numerical calculation errors, this unit sets an effective observation threshold, outputting the real-time calculation result only when the absolute value of the average differential pressure signal is higher than the threshold; otherwise, it retains the observation value from the previous moment.

[0012] Furthermore, the adaptive control law calculation module includes a feedforward calculation unit. This unit uses the instantaneous leakage coefficient to calculate the theoretical target flow rate including leakage compensation, and converts the theoretical target flow rate into feedforward control commands based on the inverse model of the electro-hydraulic servo valve. In the inverse model calculation, the system is equipped with minimum differential pressure protection logic to prevent numerical overflow caused by excessively small differential pressure at the valve orifice.

[0013] Furthermore, the adaptive control law calculation module includes an adaptive PID feedback unit. The specific logic of this unit in performing gain scheduling is as follows: the proportional gain is configured to be positively correlated with the instantaneous leakage coefficient to enhance the system's resistance to damping changes; the integral gain is configured to be positively correlated with the instantaneous bulk modulus to match changes in the system's natural frequency. This unit uses the adjusted gain parameters to calculate the deviation between the target differential pressure and the average differential pressure signal, generating feedback control commands.

[0014] Furthermore, the adaptive control law calculation module linearly superimposes the feedforward control command and the feedback control command, and performs amplitude limiting processing according to the rated input range of the electro-hydraulic servo valve to generate the final control command.

[0015] Furthermore, the controller synchronously triggers sampling of each sensor through a hardware timer and an analog-to-digital converter, and a hardware low-pass filter is configured at the front end of the analog-to-digital converter. The cutoff frequency of the hardware low-pass filter is set to be higher than the flow pulsation frequency generated by the hydraulic pump at its highest operating speed, to ensure that the ripple amplitude characteristics are fully preserved in the analog signal stage.

[0016] This invention provides a constant torque adaptive PID control system for hydraulic motors. It offers the following advantages: 1. This invention performs dual-channel frequency domain separation on the pressure signal through a signal preprocessing module, and calculates the instantaneous bulk modulus of elasticity that characterizes the fluid stiffness by utilizing the inherent flow pulsation characteristics of the hydraulic pump. This method eliminates the need for a dedicated oil quality sensor and can achieve online monitoring of fluid stiffness changes using only a conventional pressure sensor. While simplifying the system hardware architecture, it also solves the control model mismatch problem caused by changes in fluid characteristics due to oil temperature rise or air mixing.

[0017] 2. In the state observation stage, this invention adopts a parameter coupling identification mechanism, which uses the instantaneous bulk elastic modulus to correct the fluid compressibility flow term in the flow continuity model in real time, and sets an effective observation threshold to avoid numerical singularities. This eliminates the interference of fluid compressibility on leakage calculation, realizes high-precision observation of the instantaneous leakage coefficient of the hydraulic motor, and improves the accuracy of the system in identifying time-varying leakage parameters under non-steady-state conditions.

[0018] 3. This invention establishes an adaptive PID gain scheduling strategy based on physical state parameters, which maps the instantaneous leakage coefficient to the proportional gain to compensate for changes in system damping, and maps the instantaneous bulk elastic modulus to the integral gain to match the system's natural frequency. Combined with feedforward control that includes leakage compensation, the system can automatically adapt to hydraulic motor wear and oil state fluctuations, ensuring that the system maintains a constant torque response bandwidth and steady-state control accuracy throughout its entire life cycle. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the overall structure of the hydraulic motor constant torque adaptive PID control system of the present invention; Figure 2 This is a data interaction logic block diagram of the various functional modules within the controller of this invention; Figure 3 This is a block diagram of the parameter estimation logic for the state observation and identification module in this invention; Figure 4 This is a comparison chart of the differential pressure response of the present invention and a traditional PID under time-varying leakage conditions; Figure 5 This is a diagram showing the system dynamic response under online observation of bulk modulus and sudden stiffness changes in accordance with the present invention.

[0020] Among them, 10 is a hydraulic pump; 20 is an electro-hydraulic servo valve; 30 is a hydraulic motor; 40 is a load; 50 is an inlet pressure sensor; 60 is an outlet pressure sensor; 70 is a speed sensor; 80 is a valve core position sensor; 100 is a controller; 110 is a signal preprocessing module; 120 is a state observation and identification module; 121 is a bulk modulus correction unit; 122 is a leakage coefficient observation unit; 130 is an adaptive control law calculation module; 131 is a feedforward calculation unit; and 132 is an adaptive PID feedback unit. Detailed Implementation

[0021] The technical solutions in 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.

[0022] See attached document Figure 1 and attached Figure 2 The present invention provides a constant torque adaptive PID control system for a hydraulic motor, which includes a hydraulic drive hardware unit and a control calculation unit.

[0023] The hydraulic drive hardware unit includes a hydraulic pump 10, an electro-hydraulic servo valve 20, a hydraulic motor 30, a load 40, an inlet pressure sensor 50, an outlet pressure sensor 60, a speed sensor 70, and a valve core position sensor 80.

[0024] Hydraulic pump 10 is a positive displacement pump, and its outlet is connected to the inlet of electro-hydraulic servo valve 20 via a hydraulic line to provide a pressure oil source with inherent flow pulsation. Ports A and B of electro-hydraulic servo valve 20 are connected to the inlet and outlet of hydraulic motor 30 via pipelines, respectively. The output shaft of hydraulic motor 30 is mechanically connected to load 40 to drive load 40 to rotate.

[0025] An inlet pressure sensor 50 is installed at the inlet of the hydraulic motor 30 to detect the instantaneous inlet pressure. An outlet pressure sensor 60 is installed at the outlet of the hydraulic motor 30 to detect the instantaneous outlet pressure. Both inlet and outlet pressure sensors are high-frequency response pressure sensors, with their response frequencies covering the flow pulsation fundamental frequency of the hydraulic pump 10. A speed sensor 70 is installed on the output shaft of the hydraulic motor 30 to detect the motor speed. A valve spool position sensor 80 is integrated inside the electro-hydraulic servo valve 20 to detect the actual displacement of the valve spool.

[0026] The control unit includes a controller 100. The controller 100 is electrically connected to the inlet pressure sensor 50, the outlet pressure sensor 60, the speed sensor 70, the valve core position sensor 80, and the electro-hydraulic servo valve 20 via signal lines. The controller 100 is configured to acquire sensor signals and output control commands to the electro-hydraulic servo valve 20.

[0027] The controller 100 is logically divided into: a signal preprocessing module 110, a state observation and identification module 120, and an adaptive control law calculation module 130.

[0028] The signal preprocessing module 110 is configured to receive raw signals collected by the inlet pressure sensor 50, the outlet pressure sensor 60, the speed sensor 70, and the valve core position sensor 80. The signal preprocessing module 110 performs differential calculations on the instantaneous inlet and outlet pressures to obtain a differential pressure signal, and performs frequency domain separation processing on this differential pressure signal to output an average differential pressure signal for feedback control. and the pressure ripple component used for feature extraction and ripple amplitude .

[0029] The state observation and identification module 120 is connected to the signal preprocessing module 110. The state observation and identification module 120 is configured to utilize ripple amplitude based on the fluid impedance principle and flow continuity model. Real-time estimation of the instantaneous bulk modulus of hydraulic oil And utilize this instantaneous bulk elastic modulus Instantaneous leakage coefficient of hydraulic motor 30 Conduct observations.

[0030] The adaptive control law calculation module 130 is connected to the state observation and identification module 120. The adaptive control law calculation module 130 is configured to calculate based on the instantaneous leakage coefficient. and instantaneous bulk modulus The proportional gain and integral gain of the PID controller are adjusted in real time, and the feedforward control quantity is calculated to finally synthesize the total control command. Output to electro-hydraulic servo valve 20.

[0031] The controller 100 performs parameter observation and control calculations based on the flow continuity model of the hydraulic motor 30. This flow continuity model is described as follows: ; in, This indicates the instantaneous flow rate entering the high-pressure chamber of the hydraulic motor 30; This represents the theoretical displacement of hydraulic motor 30, which is a constant. This indicates the motor angular velocity (i.e., speed signal) measured by the speed sensor 70. This represents the instantaneous leakage coefficient of the hydraulic motor 30; This indicates the pressure difference between the inlet and outlet of the hydraulic motor 30; The total volume of the controlled cavity is a constant. This represents the instantaneous bulk modulus of the fluid, estimated in real time by the controller 100. This represents the rate of change of pressure difference; Indicates the current moment.

[0032] The condition observation and identification module 120 includes a bulk modulus correction unit 121 and a leakage coefficient observation unit 122.

[0033] The bulk modulus correction unit 121 is configured to store the reference ripple amplitude value. and nominal bulk modulus And based on the real-time input ripple amplitude value Calculate the instantaneous bulk modulus The bulk modulus correction unit 121 is also configured to, when a preset steady-state condition is met, adjust the reference ripple amplitude. An update is performed to compensate for the wear of hydraulic pump 10.

[0034] Leakage coefficient observation unit 122 is configured to receive instantaneous bulk modulus. And combined with the average differential pressure signal Motor angular velocity The estimated flow rate corresponding to the valve core displacement is used to inversely solve the flow continuity model to obtain the instantaneous leakage coefficient. The leakage coefficient observation unit 122 is also configured to monitor the average differential pressure signal. When the value is below a preset threshold, the leakage coefficient of the previous moment is locked.

[0035] The adaptive control law calculation module 130 includes a feedforward calculation unit 131 and an adaptive PID feedback unit 132.

[0036] The feedforward calculation unit 131 is configured to calculate based on the target pressure difference and the instantaneous leakage coefficient. Calculate the theoretical equilibrium flow rate and generate the feedforward control quantity.

[0037] The adaptive PID feedback unit 132 is configured to establish a proportional gain. With instantaneous leakage coefficient The positive correlation mapping relationship and integral gain With instantaneous bulk elastic modulus The positive correlation mapping relationship is used to calculate the PID gain of the current control cycle in real time based on the mapping relationship.

[0038] Those skilled in the art will understand that the controller 100 can be a PLC (Programmable Logic Controller), DSP (Digital Signal Processor), FPGA (Field Programmable Gate Array), or industrial PC, and its internal modules are implemented through software code, hardware logic circuits, or a combination of both. Common signal acquisition circuits, AD conversion circuits, and drive amplifier circuits are well-known technologies in the field and will not be described in detail here.

[0039] See attached document Figure 2The signal preprocessing module 110 is configured to perform high-frequency data acquisition and multi-channel signal synchronization tasks to ensure that the physical quantities entering the subsequent observation algorithm are strictly aligned in the time dimension. This process mainly includes: synchronous trigger sampling, anti-aliasing filtering, analog-to-digital conversion, and physical quantity mapping.

[0040] The controller 100 is internally equipped with a high-precision timer and a multi-channel analog-to-digital converter. To capture the high-frequency flow pulsation characteristics generated by the hydraulic pump 10, the controller 100's sampling frequency... The value is set to satisfy the Nyquist sampling theorem and be able to reconstruct the ripple envelope. Specifically, the sampling frequency... The settings are based on the following relationship: ; in, Indicates the maximum permissible operating speed of hydraulic pump 10 (unit: rpm); This indicates the number of pistons in hydraulic pump 10 (i.e., the fundamental frequency multiple of the pump). The oversampling coefficient is used in this embodiment to ensure the accuracy of subsequent ripple amplitude analysis. The value range is set to 10 to 20; This is the conversion factor for rotational speed units.

[0041] Controller 100 uses a hardware timer to generate a period of The interrupt signal. At the current moment determined by the sampling trigger signal. The controller 100 simultaneously triggers the sampling of analog signals from the inlet pressure sensor 50, the outlet pressure sensor 60, the speed sensor 70, and the valve core position sensor 80.

[0042] For the analog voltage or current signals transmitted by the inlet pressure sensor 50 and the outlet pressure sensor 60, a cutoff frequency of [frequency value missing] is used before they enter the analog-to-digital converter. The hardware low-pass filter is used for anti-aliasing. Cutoff frequency. Set to less than the sampling frequency Half of, and higher than the flow pulsation frequency generated by hydraulic pump 10 at its highest operating speed (i.e., This method filters out high-frequency noise interference above the Nyquist frequency while fully preserving the fundamental frequency component of the flow pulsation used for subsequent feature extraction. The specific topology of the hardware filtering circuit (such as a Butterworth filter or a Chebyshev filter) can be designed by those skilled in the art based on signal-to-noise ratio requirements; such designs are well-known in the field and will not be elaborated upon here.

[0043] Controller 100 performs synchronous sampling and holding operation to ensure the instantaneous pressure at the oil inlet. Instantaneous pressure at the oil outlet Motor angular velocity and valve core displacement All reflect the same current moment. The system state. This synchronization mechanism eliminates phase errors caused by channel scanning delays, preventing them from occurring in subsequent use. Numerical oscillations caused by timing misalignment are introduced when calculating the leakage coefficient.

[0044] After completing the analog-to-digital conversion, the signal preprocessing module 110 maps the digital quantity to a value with physical units based on the calibration curves of each sensor. Subsequently, the signal preprocessing module 110 calculates the pressure difference between the inlet and outlet, generating the raw differential pressure signal. ; in, and These are the calibrated instantaneous pressures at the inlet and outlet, respectively.

[0045] The original differential pressure signal Along with the synchronously acquired motor angular velocity and valve core displacement It is temporarily stored in the high-speed buffer of the controller 100 as the input data source for subsequent frequency domain separation and parameter identification.

[0046] The signal preprocessing module 110 is configured to buffer the raw differential pressure signal The signal is split into two parallel processing channels: a low-frequency control channel for acquiring steady-state control feedback and a high-frequency feature extraction channel for acquiring fluid stiffness characteristics.

[0047] In the low-frequency control channel, the signal preprocessing module 110 uses a digital low-pass filter to process the raw differential pressure signal. Filtering is performed. The cutoff frequency of this digital low-pass filter. It is set to a minimum fundamental frequency lower than that of the hydraulic pump 10 to completely filter out flow pulsation components and high-frequency measurement noise.

[0048] After processing by the low-frequency control channel, the signal preprocessing module 110 outputs the average differential pressure signal. The average differential pressure signal It represents the current moment. The effective hydraulic driving force required to drive the load 40 is transmitted to the subsequent state observation and identification module 120 and adaptive control law calculation module 130 for observing the leakage coefficient and calculating the error of PID feedback control. The specific algorithm implementation of the digital low-pass filter (such as a first-order hysteresis filter or a finite impulse response filter) is well-known in the art and will not be elaborated here.

[0049] In the high-frequency feature extraction channel, the signal preprocessing module 110 first uses the synchronously acquired motor angular velocity... Real-time calculation of the instantaneous flow pulsation fundamental frequency of hydraulic pump 10 The calculation process follows the kinematic relationship below: ; in, Indicates the current time The instantaneous flow pulsation fundamental frequency; Indicates the current time The absolute value of the motor's angular velocity (unit: rad / s); This indicates the transmission ratio between a 30-liter hydraulic motor and a 10-liter hydraulic pump (assuming the pump and motor are directly connected or connected through a fixed speed ratio; if it is an independent pump source, the pump speed is used directly for calculation). Indicates the number of plungers in hydraulic pump 10; This is the conversion constant between angles and radians.

[0050] The signal preprocessing module 110 is equipped with a digital bandpass filter with a variable center frequency. The signal preprocessing module 110 processes the calculated instantaneous flow pulsation fundamental frequency. The center frequency of the digital bandpass filter is set in real time. The signal preprocessing module 110 uses the digital bandpass filter to process the raw differential pressure signal. Filtering is performed to remove DC components and non-fundamental frequency noise, extracting only the pressure ripple component containing pump source pulsation characteristics. .

[0051] Subsequently, the signal preprocessing module 110 processes the pressure ripple component. Amplitude calculations are performed to obtain the ripple amplitude that reflects the fluid stiffness characteristics. To improve computational robustness, this embodiment employs the sliding window root mean square algorithm for solution, and its discretization calculation formula is described below: ; in, Indicates the current time ripple amplitude; This indicates the number of sampling points contained in the sliding window, and the corresponding window time length covers at least one complete pulsation cycle; Indicates moving forward from the current moment. Each sampling period Historical values ​​of pressure ripple components; The summation operator is used to represent summation operations. from Increment to Add up all the items.

[0052] The signal preprocessing module 110 calculates the average pressure difference signal. Pressure ripple component and ripple amplitude The data is synchronously output to the internal data bus of the controller 100 for use by the state observation and identification module 120. Through the above dual-channel processing, the system achieves decoupled extraction of control signals and feature signals from a single physical sensor data source.

[0053] See attached document Figure 3 The bulk modulus correction unit 121 is configured to extract the ripple amplitude of the channel output based on the fluid impedance characteristics using high-frequency features. Instantaneous bulk modulus of hydraulic oil Real-time estimation is performed. The bulk modulus correction unit 121 adopts a dual-time-scale processing logic, that is, it responds to the transient changes in oil stiffness on a short time scale, and learns and compensates for the reference drift caused by the wear of the hydraulic pump 10 on a long time scale.

[0054] The bulk modulus correction unit 121 first performs speed normalization. Since the flow rate pulsation amplitude output by the hydraulic pump 10 has an inherent coupling relationship with the speed (typically exhibiting nonlinear decay or fluctuation as the speed increases), in order to eliminate the interference of speed changes on stiffness observation, the bulk modulus correction unit 121 performs speed normalization based on the current time... motor angular velocity Calculate the normalized ripple amplitude The calculation is based on a pre-calibrated pump source impedance characteristic curve, and its linearized approximation is described as follows: ; in, This represents the normalized ripple amplitude after eliminating the influence of rotational speed; This represents the ripple amplitude value input by the signal preprocessing module 110; This represents the reference angular velocity during system calibration, and is a constant. This represents the absolute value of the motor's angular velocity at the current moment; To prevent tiny positive numbers with a denominator of zero.

[0055] The bulk modulus correction unit 121 internally maintains a reference ripple amplitude value. The reference ripple amplitude This characterizes the theoretical ripple level that the hydraulic pump 10 should produce in its current healthy state under the nominal bulk modulus. To distinguish between the two physical phenomena of decreased oil stiffness and increased internal leakage of the pump source, the bulk modulus correction unit 121 is equipped with a benchmark self-learning mechanism based on a forgetting factor.

[0056] When the system is in steady-state operation (i.e., the rate of change of the average pressure difference is less than the first threshold and the rate of change of the motor angular velocity is less than the second threshold), the bulk modulus correction unit 121 activates the reference update logic and uses the recursive least squares principle to update the reference ripple amplitude. Perform iterative updates. The update formula is as follows: ; in, Indicates the current update cycle The baseline ripple amplitude after completion; This represents the baseline ripple amplitude value from the previous update cycle; The forgetting factor, which ranges from 0.95 to 0.999, is used to set the update inertia of the baseline value, ensuring that the baseline value only reflects the pump source wear trend over a long time scale, and is not affected by changes in the oil state over a short time scale. This represents the normalized ripple amplitude at the current moment.

[0057] After maintaining the baseline value, the bulk modulus correction unit 121 calculates the instantaneous bulk modulus at the current moment based on the principle of positive correlation between fluid stiffness and pressure fluctuation amplitude. The calculation uses the ratio mapping method, and the specific formula is as follows: ; in, This represents the instantaneous bulk modulus of elasticity output to the leakage coefficient observation unit 122; This represents the nominal bulk modulus of elasticity of hydraulic oil under standard operating conditions, and is a preset constant. This indicates the currently effective reference ripple amplitude. The fluid resistance correction index is determined by the frequency response characteristics of the hydraulic pipeline. In this embodiment... The value ranges from 1.0 to 1.2.

[0058] Through the above processing, the bulk modulus correction unit 121 can automatically reduce the reference ripple amplitude value when the hydraulic pump 10 experiences wear, resulting in a decrease in output pulsation capability. This avoids incorrectly identifying pump source wear as instantaneous bulk modulus. The decrease ensured the accuracy of subsequent leakage coefficient observations.

[0059] Leakage coefficient observation unit 122 is configured to receive the instantaneous bulk modulus output by bulk modulus correction unit 121. Combined with the average differential pressure signal output by the signal preprocessing module 110 Motor angular velocity and valve core displacement The instantaneous leakage coefficient of hydraulic motor 30 Perform a reverse solution.

[0060] To calculate the leakage coefficient, the leakage coefficient observation unit 122 first calculates the estimated flow rate entering the high-pressure chamber of the hydraulic motor 30 based on the flow characteristic equation of the electro-hydraulic servo valve 20. The calculation process is based on the following formula: ; in, Indicates the current time The estimated flow rate through the electro-hydraulic servo valve 20 to the hydraulic motor 30; The flow gain coefficient of the electro-hydraulic servo valve 20 is a preset constant. This indicates the valve core displacement measured by the valve core position sensor 80; This indicates the oil supply pressure of the hydraulic system, which is a known constant or a real-time measured value. This represents the load pressure at the current moment, numerically corresponding to the instantaneous pressure at the oil inlet. .

[0061] Obtain estimated flow Subsequently, the leakage coefficient observation unit 122 calculates the original leakage coefficient based on the inverse operation model of the flow continuity equation. To improve the calculation accuracy, the inverse operation model introduces the instantaneous bulk elastic modulus. This is used to correct the fluid compressibility term, thereby isolating the coupling effect of fluid compressibility on leakage calculations. Original leakage coefficient. The calculation formula is as follows: ; in, This represents the original leakage coefficient calculated at the current moment; This indicates the theoretical displacement of hydraulic motor 30; Indicates the angular velocity of the motor; Indicates the total volume of the controlled cavity; This represents the instantaneous bulk modulus input by the bulk modulus correction unit 121; Indicates average differential pressure signal The first-order time derivative is obtained through difference operations; This represents the average differential pressure signal; Represents the theoretical volumetric flow rate; This indicates the fluid compression flow rate.

[0062] Given the average pressure difference signal in the above formula Located in the denominator, when the system is in startup, braking, or low-load condition, The value may approach zero, leading to divergence in the calculation results or the generation of numerical singularities. To address this issue, the leakage coefficient observation unit 122 is equipped with singularity avoidance logic.

[0063] The leakage coefficient observation unit 122 monitors the absolute value of the average differential pressure signal in real time. .when Greater than the preset effective observation threshold At that time, the leakage coefficient observation unit 122 determines that it is currently in the effective observation range and directly calculates the original leakage coefficient. The instantaneous leakage coefficient at the current moment Output.

[0064] when Less than or equal to the preset effective observation threshold At this time, the leakage coefficient observation unit 122 determines that it is currently in the numerical singularity domain. At this point, the leakage coefficient observation unit 122 executes a zero-order hold strategy, suspends the inverse solution operation, and locks the leakage coefficient of the previous valid observation time as the instantaneous leakage coefficient of the current time. The logic is described as follows: ; in, This represents the instantaneous leakage coefficient that is ultimately output to the adaptive control law calculation module 130; This represents the effective observation threshold to prevent the denominator from approaching zero; Indicates the previous sampling period The instantaneous leakage coefficient of the output; This indicates a conditional judgment logic, used to indicate that the system will execute the calculation rules or assignment operations before the comma in this line only if the mathematical inequality following the operator is true.

[0065] Through the above-mentioned singularity avoidance logic, the system can maintain the numerical stability of the leakage coefficient observation value across the entire operating range, prevent sudden changes in control parameters due to excessively small pressure differences, and ensure the continuity of the adaptive control process.

[0066] The feedforward calculation unit 131 is configured to perform open-loop control calculations based on an inverse dynamics model. Its purpose is to generate reference control commands for the target operating conditions of the hydraulic motor 30, thereby undertaking the main control energy output and reducing the adjustment burden on the subsequent PID feedback controller. This feedforward calculation unit 131 utilizes the instantaneous leakage coefficient output by the leakage coefficient observation unit 122 in real time. This enables dynamic compensation for the time-varying leakage characteristics of the system.

[0067] Feedforward calculation unit 131 receives the target pressure difference command input from the outside. This command corresponds to the target torque required to be output by the hydraulic motor 30. Simultaneously, the feedforward calculation unit 131 receives the current motor angular velocity. and the oil supply pressure of the hydraulic system and the instantaneous pressure at the oil inlet .

[0068] The feedforward calculation unit 131 first calculates the theoretical target flow rate required to maintain the hydraulic motor 30 at its current speed and establish the target pressure difference. This calculation not only considers the motor's volumetric displacement requirements but also creatively utilizes real-time observed leakage coefficients to calculate the leakage compensation flow rate. The calculation formula is as follows: ; in, This represents the theoretical target flow rate required to meet the target operating conditions. This indicates the theoretical displacement of hydraulic motor 30; This represents the motor's angular velocity at the current moment; This represents the instantaneous leakage coefficient, which is input in real time by the leakage coefficient observation unit 122. This parameter reflects the actual leakage level at the current moment under the conditions of internal wear and oil viscosity of the motor. This indicates the target differential pressure command at the current moment.

[0069] Subsequently, the feedforward calculation unit 131, based on the reverse flow characteristics of the electro-hydraulic servo valve 20, calculates the theoretical target flow rate. Converted into corresponding feedforward voltage control commands To eliminate the impact of valve port pressure drop variations on flow gain, the feedforward calculation unit 131 incorporates a pressure compensation circuit. This is to prevent pressure fluctuations at the inlet port from affecting the flow gain. Approaching the oil supply pressure The denominator approaches zero, causing numerical calculation overflow. The feedforward calculation unit 131 has a preset minimum differential pressure protection threshold. (e.g., 0.5 MPa). When the real-time monitored valve port pressure difference ( When the value is less than this threshold, use When used in denominator operations, its calculation formula is described as follows: ; in, This indicates the feedforward control command output to the adder (usually normalized to control voltage or current). Indicates the nominal flow gain coefficient of the electro-hydraulic servo valve 20; Indicates the oil supply pressure of the hydraulic system; This indicates the instantaneous pressure at the oil inlet measured at the current moment; This represents the pressure compensation term used to approximate the valve orifice pressure drop.

[0070] The feedforward calculation unit 131 calculates the feedforward control command. The output is sent to the summation node inside controller 100. This is achieved by introducing real-time updates. The feedforward calculation unit 131 can automatically adapt to the increased clearance or leakage caused by the rise in oil temperature of the hydraulic motor 30 due to long-term operation, thereby eliminating most of the steady-state error in the open-loop stage and ensuring that the system maintains high-precision torque response characteristics throughout its entire life cycle. For the nonlinear correction of the flow characteristics of the electro-hydraulic servo valve (such as dead zone compensation or saturation limitation), those skilled in the art can make conventional settings according to the specific valve parameters; this is well-known technology in the field and will not be elaborated further here.

[0071] The adaptive PID feedback unit 132 is configured to perform closed-loop feedback operations based on parameter scheduling, aiming to eliminate residual errors caused by model nonlinearity and external disturbances. By establishing a dynamic mapping relationship between the PID gain and physical state parameters, the adaptive PID feedback unit 132 ensures that the controller 100 maintains a constant damping ratio and response bandwidth when the leakage characteristics of the hydraulic motor 30 change or the stiffness of the hydraulic oil fluctuates.

[0072] The adaptive PID feedback unit 132 first receives the target differential pressure command. and the average differential pressure signal output by the signal preprocessing module 110 The adaptive PID feedback unit 132 calculates the control deviation between the two. The deviation is defined as the target value minus the feedback value.

[0073] To achieve adaptive gain adjustment, the adaptive PID feedback unit 132 receives the instantaneous leakage coefficient output by the leakage coefficient observation unit 122. and the instantaneous bulk modulus output by the bulk modulus correction unit 121 The adaptive PID feedback unit 132 is based on the physical control mechanism that increased leakage requires enhanced proportional action to counteract damping and increased stiffness requires enhanced integral action to match bandwidth. It calculates the current proportional gain in real time. and integral gain The scheduling logic for this parameter follows the calculation formula: ; ; in, Indicates the current time proportional gain; This represents the nominal proportional gain under standard leakage conditions, and is a preset constant. This represents the leakage compensation weighting coefficient, used to adjust the sensitivity of the proportional gain to changes in leakage. In this embodiment, the value ranges from 0.5 to 1.0. Indicates the instantaneous leakage coefficient; This represents the initial leakage coefficient of the hydraulic motor 30 at the factory, which is a preset constant; Indicates the current time Integral gain; This represents the nominal integral gain under the nominal oil stiffness, which is a preset constant. Indicates the instantaneous bulk modulus; This indicates the nominal bulk modulus, which is consistent with the parameters used in the bulk modulus correction unit 121.

[0074] After obtaining the PID gain at the current moment, the adaptive PID feedback unit 132 utilizes the control deviation Calculate feedback control commands To prevent integral saturation, the calculation process includes integral limiting logic. The calculation description of the feedback control command is as follows: ; in, Indicates feedback control commands; Indicates the control deviation at the current moment; Indicates the control deviation from the system startup time. Up to the current moment The time integral term; This represents the integral variable.

[0075] The adaptive PID feedback unit 132 will calculate the feedback control command. and feedforward control commands The output is then sent to the subsequent instruction synthesis node. The specific discretization implementation of the PID algorithm (such as positional or incremental) and the specific code logic for integral separation and anti-integral saturation can be conventionally selected by those skilled in the art based on the microprocessor's computing power; these are well-known technologies in the field and will not be elaborated upon here.

[0076] The adaptive control law calculation module 130 is configured to respond to feedforward control commands. and feedback control commands Superposition and synthesis are performed, and amplitude limiting processing is executed to generate the final physical control signal for the electro-hydraulic servo valve 20. This process aims to ensure that the control commands of the output components include dynamic compensation for system nonlinearity and strictly comply with the rated electrical input specifications of the electro-hydraulic servo valve 20, preventing coil overheating or mechanical impact of the spool valve due to control saturation.

[0077] The adaptive control law calculation module 130 first performs a linear superposition operation, converting the feedforward control command output by the feedforward calculation unit 131 into a linear superposition operation. Feedback control commands output by the adaptive PID feedback unit 132 Add them together to generate the original composition instructions. The original synthesis instruction This represents the total control energy required to achieve the target torque under ideal, unconstrained conditions.

[0078] To ensure system security and hardware compatibility, the adaptive control law calculation module 130 is equipped with a saturation limiting circuit. The adaptive control law calculation module 130 processes the original synthesized instructions... With the preset control saturation threshold Compare and control the saturation threshold. Set according to the rated input voltage or rated input current of the electro-hydraulic servo valve 20 (e.g.) or The adaptive control law calculation module 130 calculates the final restricted control command based on the comparison results. The calculation logic is as follows: ; in, This indicates the restricted control command ultimately used for driving after the amplitude limiting process; This refers to the original composite command obtained by superimposing the feedforward control command and the feedback control command, i.e. ; This indicates the allowable control saturation threshold of the electro-hydraulic servo valve 20, which is the maximum positive control quantity that the system is allowed to output; This represents the negative value of the control saturation threshold allowed by the electro-hydraulic servo valve 20, which is the maximum negative control quantity that the system is allowed to output. This indicates a conditional judgment logic, used to indicate that the system will execute the calculation rules or assignment operations before the comma in this line only if the mathematical inequality following the operator is true.

[0079] Obtain restricted control instructions Subsequently, the adaptive control law calculation module 130 transmits it to the analog-to-digital converter interface of the controller 100. The analog-to-digital converter interface converts the discrete constrained control commands... Converted into a continuous analog current signal This analog current signal The torque motor coil, which acts directly on the electro-hydraulic servo valve 20, drives the valve core to generate displacement, thereby controlling the flow rate of high-pressure oil entering the hydraulic motor 30.

[0080] Specific application examples: To verify the effectiveness of the constant torque adaptive PID control system for hydraulic motors provided by this invention, a simulation environment simulating a deep-sea winch hydraulic drive system was constructed. The main physical parameters of the system are set as follows: Hydraulic pump 10:9 piston axial piston pump ( Rated speed 1500rpm, displacement 100mL / r.

[0081] Hydraulic Motor 30: Low-speed, high-torque radial piston motor, theoretical displacement Controlled cavity volume .

[0082] Hydraulic system: oil supply pressure nominal bulk modulus .

[0083] Initial leakage condition: Initial leakage coefficient at the factory .

[0084] Controller 100 settings: Sampling frequency Low-pass filter cutoff frequency .

[0085] To visually demonstrate the technical effects, two sets of control strategies were set up for comparison: Comparison group (traditional method): The traditional feedforward and fixed-gain PID control strategy is adopted. Its PID parameters are tuned based on the initial state of the system (standard oil temperature, no wear) and remain unchanged during operation.

[0086] Experimental group (method of the present invention): The adaptive PID control strategy based on leakage and stiffness observation of the present invention is adopted, which includes complete signal preprocessing, state observation and parameter scheduling logic.

[0087] Operating Condition 1: Time-varying operating condition caused by leakage due to oil temperature rise The simulation depicts the process of a system going from cold start to thermal equilibrium. to During period s, assuming the hydraulic oil temperature gradually increases, leading to a decrease in viscosity, the actual leakage coefficient of the hydraulic motor 30 decreases from... linearly increase to 3 Simultaneously, a step target pressure differential command is given. .

[0088] See attached document Figure 4 Control group: In the initial stage of s, since the leakage has not yet increased significantly, the system can briefly follow the target. However, as time goes on ( As leakage continues to increase and the fixed-gain PID lacks a feedforward compensation mechanism, its integral action is insufficient to offset the flow loss, causing the pressure curve to gradually droop and resulting in a significant steady-state error drift (the error is approximately 0.85 MPa at 10 s).

[0089] Experimental group: The curve exhibits characteristics of simulated real high-frequency sensor noise (micro-spurs). Thanks to the real-time compensation of the leakage coefficient observation unit 122, the experimental group remained close to the 10MPa target line throughout the process without pressure drift, demonstrating the system's robustness to time-varying leakage.

[0090] Operating Condition 2: Sudden Stiffness Change Due to Oil-Gas Mixing This simulates the situation where air is mixed in during a simulated operating condition. At a certain moment, air bubbles suddenly entered the simulated hydraulic oil, causing the instantaneous bulk modulus to... A step drop occurred.

[0091] See attached document Figure 5 Regarding the observation of bulk modulus (top subplot): Steady-state coincidence verification accuracy: In the initial stage, since no sudden changes in operating conditions occurred, the online observations (solid lines) and the actual physical values ​​(dotted lines) remained highly consistent, proving the high accuracy of the observation algorithm under steady-state conditions.

[0092] Dynamic tracking capability: In At the location indicated by the arrow and the text annotation "Air ingress causes a sudden drop in stiffness," the actual bulk modulus of elasticity drops instantaneously from 1.4 GPa. Although the online observations experienced a brief transition, The curve then coincides with the true value curve again, indicating that the algorithm has completed convergence and locking for the new working condition.

[0093] Regarding the dynamic response of differential pressure (see the sub-figure below): Performance consistency under nominal operating conditions: During this phase, because the hydraulic oil stiffness is at its nominal state (without air mixing), the preset parameters of the traditional controller match the system well. Therefore, the comparison group (dashed line) and the experimental group (solid line) in the figure overlap during this time period, indicating that under ideal working conditions, both can stably track the target.

[0094] Differences after mutation: Control group: In After the stiffness of the fluid suddenly drops, the original integral gain decreases as the fluid becomes softer. It appears too large. As indicated by the dashed box and the text annotation "low-frequency oscillation caused by parameter mismatch," the curve separates from the experimental group and falls into a constant-amplitude oscillation with an amplitude of approximately ±0.8 MPa, losing control stability.

[0095] Experimental group: Adaptive PID feedback unit 132 according to the formula Upon sensing a decrease in stiffness, the integral gain was automatically and quickly adjusted downwards. As shown in the figure, the experimental group only... A small fluctuation occurs at point s, which then quickly subsides, effectively suppressing the oscillation and maintaining the smooth operation of the system.

[0096] The table below summarizes the key performance indicators of the two control strategies under the aforementioned combined operating conditions: Experimental results show that the hydraulic motor constant torque adaptive PID control system proposed in this invention effectively extracts the high-frequency ripple characteristics hidden in the pressure signal through the signal preprocessing module 110, and accurately identifies the time-varying parameters (leakage coefficient and bulk modulus) of the system using the state observation and identification module 120.

[0097] Compared with existing technologies, this invention can adjust control parameters in real time through the adaptive control law calculation module 130 when facing complex working conditions such as wear of hydraulic pump 10, oil temperature changes and oil stiffness fluctuations. This completely solves the industry problem of performance degradation of traditional fixed gain controllers after system aging or changes in working conditions, and achieves high-precision constant torque control throughout the entire life cycle.

Claims

1. A constant torque adaptive PID control system for a hydraulic motor, characterized in that, Includes hydraulic drive hardware unit and controller (100); The hydraulic drive hardware unit includes a hydraulic pump (10), an electro-hydraulic servo valve (20), a hydraulic motor (30), a load (40), and a sensor assembly for acquiring system status quantities. The controller (100) is logically divided into: The signal preprocessing module (110) is used to calculate the original differential pressure signal based on the collected pressure signal, and to perform frequency domain separation on the original differential pressure signal, and decouple and output the average differential pressure signal representing the driving force and the ripple amplitude representing the fluid stiffness. The state observation and identification module (120) is used to estimate the instantaneous bulk modulus of the fluid based on the ripple amplitude, and to correct the flow continuity model by combining the average pressure difference signal and the instantaneous bulk modulus, and to observe the instantaneous leakage coefficient of the hydraulic motor (30) in real time. The adaptive control law calculation module (130) is used to establish a dynamic mapping between PID gain and physical state parameters: The proportional gain is adjusted using the instantaneous leakage coefficient, the integral gain is adjusted using the instantaneous bulk modulus, and the adjusted proportional gain and integral gain are used to perform closed-loop feedback calculation on the deviation between the target pressure difference and the average pressure difference signal. The final control command is synthesized by combining the feedforward control command to drive the electro-hydraulic servo valve (20).

2. The hydraulic motor constant torque adaptive PID control system according to claim 1, characterized in that, The sensor assembly includes an inlet pressure sensor (50), an outlet pressure sensor (60), a speed sensor (70), and a valve core position sensor (80). The outlet of the hydraulic pump (10) is connected to the inlet of the electro-hydraulic servo valve (20), the electro-hydraulic servo valve (20) is connected to the inlet and outlet of the hydraulic motor (30), the output shaft of the hydraulic motor (30) is connected to the load (40), the inlet pressure sensor (50) and the outlet pressure sensor (60) are respectively installed at the inlet and outlet of the hydraulic motor (30), the speed sensor (70) is installed on the output shaft of the hydraulic motor (30), and the valve core position sensor (80) is integrated inside the electro-hydraulic servo valve (20).

3. The hydraulic motor constant torque adaptive PID control system according to claim 2, characterized in that, The signal preprocessing module (110) calculates the difference between the inlet pressure and the outlet pressure to obtain the original differential pressure signal; The signal preprocessing module (110) includes a low-frequency control channel and a high-frequency feature extraction channel; In the low-frequency control channel, the signal preprocessing module (110) uses a low-pass filter with a cutoff frequency lower than the minimum fundamental frequency of the hydraulic pump (10) to extract the average differential pressure signal; In the high-frequency feature extraction channel, the signal preprocessing module (110) calculates the flow pulsation fundamental frequency based on the rotational speed measured by the rotational speed sensor (70) and sets it as the center frequency of the bandpass filter, extracts the pressure ripple component from the original differential pressure signal and calculates the ripple amplitude.

4. The hydraulic motor constant torque adaptive PID control system according to claim 3, characterized in that, The state observation and identification module (120) includes a bulk modulus correction unit (121). The bulk modulus correction unit (121) normalizes the ripple amplitude using the rotation speed signal; The bulk modulus correction unit (121) stores a reference ripple amplitude value and calculates the instantaneous bulk modulus according to the mapping relationship between the normalized ripple amplitude value and the reference ripple amplitude value. The bulk modulus correction unit (121) is also used to update the reference ripple amplitude value according to the measured ripple amplitude value when the system is in steady state, in order to compensate for pump source wear.

5. The hydraulic motor constant torque adaptive PID control system according to claim 2, characterized in that, The state observation and identification module (120) also includes a leakage coefficient observation unit (122). The leakage coefficient observation unit (122) calculates the estimated flow rate through the electro-hydraulic servo valve (20) based on the data from the valve core position sensor (80); The leakage coefficient observation unit (122) subtracts the theoretical volumetric flow rate of the hydraulic motor (30) and the fluid compression flow rate determined by the instantaneous bulk modulus from the estimated flow rate to obtain the flow rate difference; The leakage coefficient observation unit (122) divides the flow difference by the average pressure difference signal to calculate the instantaneous leakage coefficient.

6. The hydraulic motor constant torque adaptive PID control system according to claim 5, characterized in that, The leakage coefficient observation unit (122) stores effective observation thresholds; When the absolute value of the average differential pressure signal is higher than the effective observation threshold, the instantaneous leakage coefficient calculated in real time is output. When the absolute value of the average differential pressure signal is lower than or equal to the effective observation threshold, the instantaneous leakage coefficient of the previous moment is locked and output.

7. The hydraulic motor constant torque adaptive PID control system according to claim 1, characterized in that, The adaptive control law calculation module (130) includes a feedforward calculation unit (131). The feedforward calculation unit (131) uses the instantaneous leakage coefficient to calculate the theoretical target flow rate including leakage compensation; The feedforward calculation unit (131) converts the theoretical target flow rate into feedforward control commands based on the inverse model of the electro-hydraulic servo valve; In the inverse model operation, the feedforward calculation unit (131) stores a minimum differential pressure protection threshold. When the valve port differential pressure is less than the minimum differential pressure protection threshold, the minimum differential pressure protection threshold is used to participate in the denominator operation to prevent numerical overflow.

8. The hydraulic motor constant torque adaptive PID control system according to claim 7, characterized in that, The adaptive control law calculation module (130) also includes an adaptive PID feedback unit (132). The specific logic for the adaptive PID feedback unit (132) to execute the dynamic mapping is as follows: The proportional gain is set to be positively correlated with the instantaneous leakage coefficient; The integral gain is set to be positively correlated with the instantaneous bulk modulus; The adaptive PID feedback unit (132) uses the adjusted proportional gain and integral gain to calculate the deviation between the target pressure difference and the average pressure difference signal, and generates a feedback control command.

9. The hydraulic motor constant torque adaptive PID control system according to claim 8, characterized in that, The adaptive control law calculation module (130) superimposes the feedforward control command and the feedback control command, and performs amplitude limiting processing according to the rated input range of the electro-hydraulic servo valve (20) to generate the final control command.

10. The hydraulic motor constant torque adaptive PID control system according to claim 1, characterized in that, The controller (100) includes a hardware timer and an analog-to-digital converter for synchronously triggering sampling of the sensor components; The front end of the analog-to-digital converter is connected to a hardware low-pass filter. The cutoff frequency of the hardware low-pass filter is set to be higher than the flow pulsation frequency generated by the hydraulic pump (10) at its highest operating speed, in order to preserve the ripple amplitude characteristics.

Images