Electro-hydraulic servo control method and electro-hydraulic servo control system

Abstract

This disclosure relates to an electro-hydraulic servo control method and system. The method includes: an FPGA performing quadrature demodulation on a first digital signal and a second digital signal, respectively, and calculating a digital displacement based on the demodulation results; an MCU performing integral separation PID adjustment based on the relationship between the error between the desired displacement and the digital displacement and a threshold, obtaining a basic control quantity, and adjusting the basic control quantity according to the state of the electro-hydraulic servo system. According to this disclosure, the degree of hardware and software synergy is improved, fully utilizing the characteristics of both the FPGA and the MCU, which helps to shorten the control loop cycle and improve the control speed of the electro-hydraulic servo valve. It facilitates synchronous demodulation in the digital domain, thereby eliminating the temperature drift problem of analog devices. The basic control quantity can be adjusted according to the state of the electro-hydraulic servo system, thereby achieving dynamic adjustment of the basic control quantity.

Description

Technical Field

[0001] This disclosure relates to the field of hydraulic control technology, and in particular to electro-hydraulic servo control methods and electro-hydraulic servo control systems. Background Technology

[0002] As the core actuator of a hydraulic system, the control accuracy of an electro-hydraulic servo valve directly depends on the demodulation quality of the position feedback signal and the robustness of the control algorithm. However, existing control technologies have some shortcomings, such as components being easily affected by temperature deviations, difficulty in implementing precise compensation using analog circuits, weak adaptability of specific control algorithms, insufficient software and hardware coordination, and weak automatic adjustment capabilities. Summary of the Invention

[0003] This disclosure provides an electro-hydraulic servo control method and an electro-hydraulic servo control system to address the shortcomings of related technologies.

[0004] According to a first aspect of the present disclosure, an electro-hydraulic servo control method is proposed, executed by an electro-hydraulic servo control system, the electro-hydraulic servo control system including a field-programmable gate array (FPGA) and a microcontroller unit (MCU). The method includes: the FPGA generating a sinusoidal digital sequence according to a preset carrier frequency; a digital-to-analog converter (DAC) outputting an analog sinusoidal excitation signal according to the sinusoidal digital sequence; the analog sinusoidal excitation signal driving the primary coil of a linear variable differential transformer (LVDT); the secondary coil of the LVDT outputting a first differential analog signal and a second differential analog signal; the DAC outputting a first digital signal according to the first differential analog signal and a second digital signal according to the second differential analog signal; and the FPGA processing the first digital signal and the second digital signal respectively. Quadrature demodulation is performed to obtain the first in-phase branch signal and the first quadrature branch signal corresponding to the first digital signal, and the second in-phase branch signal and the second quadrature branch signal corresponding to the second digital signal. A digital displacement is calculated based on the first in-phase branch signal, the first quadrature branch signal, the first in-phase branch signal, and the first quadrature branch signal, and the digital displacement is sent to the MCU. The MCU calculates the error between the desired displacement and the digital displacement, and performs integral separation proportional-integral-derivative (PID) adjustment based on the relationship between the error and n thresholds to obtain a basic control quantity, where n is an integer greater than 1. The MCU determines the state of the electro-hydraulic servo system based on the error and the rate of change of the error, adjusts the basic control quantity based on the state of the electro-hydraulic servo system, and controls the electro-hydraulic servo valve based on the adjusted basic control quantity.

[0005] Optionally, the FPGA performs quadrature demodulation on the first digital signal and the second digital signal respectively, including: the digital filter in the FPGA filters the first digital signal and the second digital signal respectively to remove DC bias and high-frequency noise; and performs quadrature demodulation on the filtered first digital signal and the second digital signal respectively.

[0006] Optionally, the FPGA calculates the digital displacement based on the first in-phase branch signal, the first quadrature branch signal, the first in-phase branch signal, and the first quadrature branch signal, including: performing low-pass filtering on the first in-phase branch signal, the first quadrature branch signal, the first in-phase branch signal, and the first quadrature branch signal; calculating the first square root of the low-pass filtered first in-phase branch signal and the first quadrature branch signal, and the second square root of the low-pass filtered second in-phase branch signal and the second quadrature branch signal; calculating the quotient of the first square root and the first in-phase branch signal as the first displacement amplitude, and calculating the quotient of the second square root and the second in-phase branch signal as the second displacement amplitude; calculating the difference between the first displacement amplitude and the second displacement amplitude, and the sum of the first displacement amplitude and the second displacement amplitude; and calculating the ratio of the difference to the sum as the digital displacement.

[0007] Optionally, the MCU performs integral separation PID adjustment based on the relationship between the error and n thresholds to obtain the basic control quantity, including: the MCU comparing the error with each of the n thresholds, where the i-th threshold is greater than the (i+1)-th threshold, and i is an integer less than n and greater than 1; if the error is greater than the first threshold, the integral component in the PID is turned off; if the error is less than or equal to the i-th threshold and greater than the (i+1)-th threshold, the integral component in the PID is turned on, and the gain of the proportional component in the PID is adjusted to the gain corresponding to the i-th threshold; if the error is less than or equal to the n-th threshold, the integral component in the PID is turned on, and the gain of the proportional component in the PID is adjusted to a preset gain.

[0008] Optionally, the method further includes: the MCU inputting the basic control quantity into the digital-to-analog converter to output an analog control quantity; and displaying the analog control quantity via an oscilloscope.

[0009] Optionally, the MCU adjusts the basic control quantity according to the state of the electro-hydraulic servo system, including at least one of the following: when the electro-hydraulic servo system is in a stable state, the MCU adjusts the cutoff frequency of the digital filter in the FPGA to improve the signal-to-noise ratio; when the electro-hydraulic servo system is in a dynamic response state, the MCU determines a compensation amount according to the dead-zone model and compensates the basic control quantity according to the compensation amount.

[0010] According to a second aspect of the present disclosure, an electro-hydraulic servo control system is provided, the control system comprising a field-programmable gate array (FPGA) and a microcontroller unit (MCU): the FPGA is used to generate a sinusoidal digital sequence according to a preset carrier frequency, wherein a digital-to-analog converter (DAC) outputs an analog sinusoidal excitation signal according to the sinusoidal digital sequence, the analog sinusoidal excitation signal being used to drive the primary coil of a linear variable differential transformer (LVDT), the secondary coil of the LVDT outputs a first differential analog signal and a second differential analog signal, the DAC outputs a first digital signal according to the first differential analog signal, and outputs a second digital signal according to the second differential analog signal; the FPGA is used to perform quadrature demodulation on the first digital signal and the second digital signal respectively to obtain the first digital signal... The digital signal corresponds to the first in-phase branch signal and the first quadrature branch signal, and the second in-phase branch signal and the second quadrature branch signal correspond to the second digital signal. A digital displacement is calculated based on the first in-phase branch signal, the first quadrature branch signal, the first in-phase branch signal, and the first quadrature branch signal, and the digital displacement is sent to the MCU. The MCU calculates the error between the desired displacement and the digital displacement, and performs integral separation proportional-integral-derivative (PID) adjustment based on the relationship between the error and n thresholds to obtain a basic control quantity, where n is an integer greater than 1. The MCU determines the state of the electro-hydraulic servo system based on the error and the rate of change of the error, adjusts the basic control quantity based on the state of the electro-hydraulic servo system, and controls the electro-hydraulic servo valve based on the adjusted basic control quantity.

[0011] Optionally, the FPGA is used to perform low-pass filtering on the first in-phase branch signal, the first quadrature branch signal, the first in-phase branch signal, and the first quadrature branch signal; calculate the first square root of the low-pass filtered first in-phase branch signal and the first quadrature branch signal, and the second square root of the low-pass filtered second in-phase branch signal and the second quadrature branch signal; calculate the quotient of the first square root and the first in-phase branch signal as the first displacement amplitude, calculate the quotient of the second square root and the second in-phase branch signal as the second displacement amplitude; calculate the difference between the first displacement amplitude and the second displacement amplitude, and the sum of the first displacement amplitude and the second displacement amplitude; calculate the ratio of the difference to the sum as the digital displacement.

[0012] Optionally, the MCU is configured to compare the error with each of the n thresholds, wherein the i-th threshold is greater than the (i+1)-th threshold, and i is an integer less than n and greater than 1; if the error is greater than the first threshold, the integral term in the PID is turned off; if the error is less than or equal to the i-th threshold and greater than the (i+1)-th threshold, the integral term in the PID is turned on, and the gain of the proportional term in the PID is adjusted to the gain corresponding to the i-th threshold; if the error is less than or equal to the n-th threshold, the integral term in the PID is turned on, and the gain of the proportional term in the PID is adjusted to a preset gain.

[0013] Optionally, the MCU is used to adjust the cutoff frequency of the digital filter in the FPGA to improve the signal-to-noise ratio when the electro-hydraulic servo system is in a stable state; and to determine the compensation amount according to the dead-zone model when the electro-hydraulic servo system is in a dynamic response state, and to compensate the basic control quantity according to the compensation amount.

[0014] According to embodiments of this disclosure, control of an electro-hydraulic servo valve is implemented based on an FPGA and an MCU. The FPGA is used to perform high-frequency tasks (e.g., tasks with a cycle in the hundreds of microseconds), such as outputting sinusoidal excitation signals, performing quadrature demodulation of digital signals, and calculating digital displacement. This frees up MCU resources for complex nonlinear control algorithms (e.g., tasks with a time consumption in the milliseconds), such as integral separation PID adjustment based on the relationship between error and threshold, and adjusting basic control quantities based on the state of the electro-hydraulic servo system. This improves the coordination between hardware and software, fully utilizes the characteristics of both the FPGA and the MCU, and helps to shorten the control loop cycle (e.g., it can be optimized to within 1 millisecond, or even reach 500 microseconds), thus increasing the control speed of the electro-hydraulic servo valve.

[0015] Furthermore, FPGAs claim to send two digital signals, and the signal sent to the MCU is also a digital shift, which facilitates synchronous demodulation in the digital domain, thereby eliminating the temperature drift problem of analog devices. Moreover, through quadrature demodulation, FPGAs can automatically compensate for phase errors caused by circuit transmission delays, and the demodulation accuracy can be greater than or equal to 0.1%FS (Full Scale).

[0016] Furthermore, the MCU can adjust the basic control quantity according to the status of the electro-hydraulic servo system, thereby achieving dynamic adjustment of the basic control quantity. This allows it to adapt to changes in working conditions such as oil temperature and valve core wear in the hydraulic system, extending the system's service life and maintenance cycle.

[0017] It should be understood that the above general description and the following detailed description are exemplary and explanatory only, and are not intended to limit this disclosure. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of this disclosure, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this disclosure. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 This is a schematic flowchart illustrating an electro-hydraulic servo control method according to an embodiment of the present disclosure.

[0020] Figure 2 This is a schematic flowchart illustrating a calculation of digital displacement according to an embodiment of the present disclosure.

[0021] Figure 3 This is a schematic diagram illustrating an orthogonal demodulation according to an embodiment of the present disclosure.

[0022] Figure 4 This is a schematic flowchart illustrating an integral separation PID according to an embodiment of the present disclosure.

[0023] Figure 5 This is a schematic diagram illustrating the collaborative operation of an MCU and an FPGA according to an embodiment of the present disclosure. Detailed Implementation

[0024] The technical solutions of the embodiments of this disclosure will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this disclosure, and not all embodiments. Based on the embodiments of this disclosure, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this disclosure.

[0025] The terminology used in this disclosure is for the purpose of describing particular embodiments only and is not intended to be limiting of the present disclosure. The singular forms “a” and “the” as used in this disclosure and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise. It should also be understood that the term “and / or” as used herein refers to and includes any and all possible combinations of one or more of the associated listed items.

[0026] It should be understood that although the terms first, second, third, etc., may be used to describe various information in embodiments of this disclosure, such information should not be limited to these terms. These terms are only used to distinguish information of the same type from one another. For example, first information may also be referred to as second information without departing from the scope of embodiments of this disclosure, and similarly, second information may also be referred to as first information. Depending on the context, the word "if" as used herein may be interpreted as "when," "when," or "in response to a determination."

[0027] For the sake of brevity and ease of understanding, this document uses the terms "greater than" or "less than", "higher than" or "lower than" to describe size relationships. However, it will be understood by those skilled in the art that the term "greater than" also includes the meaning of "greater than or equal to", and "less than" also includes the meaning of "less than or equal to"; the term "higher than" also includes the meaning of "higher than or equal to", and "lower than" also includes the meaning of "lower than or equal to".

[0028] In some embodiments, the electro-hydraulic servo valve, as the core actuator of the hydraulic system, directly depends on the demodulation quality of the position feedback signal and the robustness of the control algorithm in terms of control accuracy. However, existing control technologies have some technical shortcomings that urgently need to be addressed.

[0029] For example, analog demodulation has inherent drawbacks: traditional LVDT (Linear Variable Displacement Transducer) signal demodulation often uses analog multipliers or dedicated demodulation chips (such as AD598 / 698). These solutions are greatly affected by component temperature drift, and the zero point is prone to drift after long-term operation; moreover, analog circuits cannot accurately compensate for the phase delay between the excitation signal and the feedback signal, which easily leads to fluctuations in demodulation error with frequency changes.

[0030] For example, the control algorithm has poor adaptability: when using a PID (Proportion Integration Differential) control algorithm, the control parameters are fixed, making it difficult to adapt to the nonlinear characteristics of the hydraulic system under different operating conditions (such as dead zone, saturation, and frictional changes). It is also prone to overshoot under start-up or large-scale commands, and sluggish response under small signals.

[0031] For example, there is insufficient hardware-software coordination: digital control schemes often load all tasks onto a single processor, such as a DSP (Digital Signal Processor) or MCU (Microcontroller Unit). High-speed demodulation operations consume a lot of resources, resulting in longer control loop cycles and reduced real-time performance; or they rely solely on FPGA (Field Programmable Gate Array) for logic control, lacking support for complex adaptive algorithms.

[0032] For example, it lacks online self-tuning capability: electro-hydraulic servo systems are generally set with fixed parameters at the factory and cannot be corrected online based on environmental factors such as aging of the servo valve and changes in oil viscosity.

[0033] Figure 1 This is a schematic flowchart illustrating an electro-hydraulic servo control method according to an embodiment of the present disclosure. The electro-hydraulic servo control method shown in this embodiment can be executed by an electro-hydraulic servo control system, which includes an FPGA and an MCU.

[0034] like Figure 1 As shown, the electro-hydraulic servo control method may include the following steps:

[0035] In step S101, the FPGA generates a sinusoidal digital sequence according to a preset carrier frequency. The digital-to-analog converter (DAC) outputs an analog sinusoidal excitation signal according to the sinusoidal digital sequence. The analog sinusoidal excitation signal is used to drive the primary coil of the linear variable differential transformer (LVDT). The secondary coil of the LVDT outputs a first differential analog signal and a second differential analog signal. The digital-to-digital converter (ADC) outputs a first digital signal according to the first differential analog signal and a second digital signal according to the second differential analog signal.

[0036] For example, the preset carrier wave can be generated based on a preset program inside the electro-hydraulic servo control system. One of its functions is to generate a sine sequence through a digital dot matrix and then convert it into an excitation signal. The excitation signal can be transmitted back as a differential signal via an LVDT, and then demodulated to obtain digital displacement.

[0037] For example, an FPGA generates a sinusoidal digital sequence based on a preset carrier frequency. Specifically, it can use DSS (Direct Digital Synthesizer) technology to generate a high-resolution (e.g., resolution greater than a threshold) sinusoidal digital sequence. Then, a low-noise, low-distortion analog sinusoidal excitation signal is output through a high-precision DAC.

[0038] In step S102, the FPGA performs quadrature demodulation on the first digital signal and the second digital signal to obtain the first in-phase branch signal and the first quadrature branch signal corresponding to the first digital signal, and the second in-phase branch signal and the second quadrature branch signal corresponding to the second digital signal. The FPGA calculates the digital displacement based on the first in-phase branch signal, the first quadrature branch signal, the first in-phase branch signal, and the first quadrature branch signal, and sends the digital displacement to the MCU.

[0039] In step S103, the MCU calculates the error between the desired displacement (e.g., input by the user) and the digital displacement (e.g., which can be used as input for subsequent PID control), performs integral separation PID adjustment based on the relationship between the error and n thresholds, and obtains the basic control quantity, where n is an integer greater than 1.

[0040] In step S104, the MCU determines the state of the electro-hydraulic servo system based on the error and the rate of change of the error, adjusts the basic control quantity based on the state of the electro-hydraulic servo system, and controls the electro-hydraulic servo valve based on the adjusted basic control quantity.

[0041] According to embodiments of this disclosure, control of an electro-hydraulic servo valve is implemented based on an FPGA and an MCU. The FPGA is used to perform high-frequency tasks (e.g., tasks with a cycle in the hundreds of microseconds), such as outputting sinusoidal excitation signals, performing quadrature demodulation of digital signals, and calculating digital displacement. This frees up MCU resources for complex nonlinear control algorithms (e.g., tasks with a time consumption in the milliseconds), such as integral separation PID adjustment based on the relationship between error and threshold, and adjusting basic control quantities based on the state of the electro-hydraulic servo system. This improves the coordination between hardware and software, fully utilizes the characteristics of both the FPGA and the MCU, and helps to shorten the control loop cycle (e.g., it can be optimized to within 1 millisecond, or even reach 500 microseconds), thus increasing the control speed of the electro-hydraulic servo valve.

[0042] Furthermore, FPGAs claim to send two digital signals, and the signal sent to the MCU is also a digital shift, which facilitates synchronous demodulation in the digital domain, thereby eliminating the temperature drift problem of analog devices. Moreover, through quadrature demodulation, FPGAs can automatically compensate for phase errors caused by circuit transmission delays, and the demodulation accuracy can be greater than or equal to 0.1%FS (Full Scale).

[0043] Furthermore, the MCU can adjust the basic control quantity according to the status of the electro-hydraulic servo system, thereby achieving dynamic adjustment of the basic control quantity. This allows it to adapt to changes in working conditions such as oil temperature and valve core wear in the hydraulic system, extending the system's service life and maintenance cycle.

[0044] In some embodiments, the FPGA performs quadrature demodulation on the first digital signal and the second digital signal respectively, including: the digital filter in the FPGA filters the first digital signal and the second digital signal respectively to remove DC bias and high-frequency noise; and performs quadrature demodulation on the filtered first digital signal and the second digital signal respectively.

[0045] Figure 2 This is a schematic flowchart illustrating a calculation of digital displacement according to an embodiment of the present disclosure.

[0046] like Figure 2 As shown, in some embodiments, the FPGA calculates the digital displacement based on the first in-phase branch signal, the first quadrature branch signal, the first in-phase branch signal, and the first quadrature branch signal, including:

[0047] In step S201, the first in-phase branch signal, the first quadrature branch signal, the first in-phase branch signal, and the first quadrature branch signal are subjected to low-pass filtering.

[0048] In step S202, the first square root of the first in-phase branch signal and the first quadrature branch signal after low-pass filtering, and the second square root of the second in-phase branch signal and the second quadrature branch signal after low-pass filtering are calculated.

[0049] In step S203, the quotient of the first square root and the first in-phase branch signal is calculated as the first displacement amplitude, and the quotient of the second square root and the second in-phase branch signal is calculated as the second displacement amplitude.

[0050] In step S204, the difference between the first displacement amplitude and the second displacement amplitude, and the sum of the first displacement amplitude and the second displacement amplitude are calculated.

[0051] In step S205, the ratio of the difference to the sum is calculated as the digital displacement.

[0052] Figure 3This is a schematic diagram illustrating an orthogonal demodulation according to an embodiment of the present disclosure.

[0053] For example, the first digital signal is denoted as digital signal A, the second digital signal is denoted as digital signal B, and the first in-phase branch signal is denoted as I. A The signal of the first orthogonal branch is denoted as Q. A The second in-phase branch signal is denoted as I. B The signal of the second orthogonal branch is denoted as Q. B .

[0054] like Figure 3 As shown, digital signals A and B can be input to a BPF (Band Pass Filter). For example, a BPF has the characteristics of FIR (Finite Impulse Response), which can filter out DC bias and high-frequency noise in the signal and retain only the effective carrier signal.

[0055] Then, orthogonal decomposition can be performed on the filtered A-channel digital signal to obtain I. A and Q A The filtered B-channel digital signal is orthogonally decomposed to obtain I. B and Q B The signal obtained by orthogonal decomposition contains low-frequency displacement information and double excitation signal.

[0056] The digital displacement is calculated based on the first in-phase branch signal, the first quadrature branch signal, the first in-phase branch signal, and the first quadrature branch signal. Specifically, this may include:

[0057] Will I A Q A I B Q B Input the LPF (Lower Pass Filter) separately to filter out high-frequency components. For the obtained low-frequency I... A and Q A It can calculate the square root. ,For example For the obtained low-frequency I B and Q B It can calculate the square root. ,For example .

[0058] Then, normalization is performed, for example, to calculate the displacement amplitude of path A. and displacement amplitude of road B Then calculate As a digital displacement, the subtraction of the numerators in digital displacement is to obtain the true displacement difference, while the division of the denominators helps to automatically offset the overall signal gain error caused by temperature changes, device aging, or fluctuations in the excitation source.

[0059] In some embodiments, the MCU performs integral separation PID adjustment based on the relationship between the error and the n threshold to obtain the basic control quantity, including:

[0060] The MCU compares the error with each of the n thresholds, wherein the i-th threshold is greater than the (i+1)-th threshold, and i is an integer less than n and greater than 1;

[0061] If the error is greater than the first threshold, the integral term in the PID controller is turned off; if the error is less than or equal to the i-th threshold and greater than the (i+1)-th threshold, the integral term in the PID controller is turned on, and the gain of the proportional term in the PID controller is adjusted to the gain corresponding to the i-th threshold; if the error is less than or equal to the n-th threshold, the integral term in the PID controller is turned on, and the gain of the proportional term in the PID controller is adjusted to a preset gain.

[0062] Figure 4 This is a schematic flowchart illustrating an integral separation PID according to an embodiment of the present disclosure.

[0063] Taking n=2 as an example, that is, n thresholds including threshold #1 and threshold #2.

[0064] like Figure 4 As shown, after obtaining the desired displacement and the digital displacement, the MCU can calculate the error between the desired displacement and the digital displacement, for example, denoted as e(t), that is, the error is the amount that changes with time t. It can also calculate the rate of change of the error, for example, by taking the derivative of e(t).

[0065] The MCU can determine whether the error is greater than threshold #1. If the error is greater than threshold #1, it means that the error is extremely large. In this case, the integration stage needs to be turned off to achieve integration separation in order to prevent oscillation. If the error is less than or equal to threshold #1, it means that the error is not too large. The integration stage can be turned on, and it can be determined whether the error is greater than threshold #2.

[0066] If the error is greater than threshold #2 (and less than or equal to threshold #1), the gain of the proportional element can be adjusted, for example, to Kp1. If the error is less than or equal to threshold #2, the gain of the proportional element can be a preset gain, for example, Kp2. It should be noted that Kp1 and Kp2 can be determined based on the system state, and there is no necessary relationship between them.

[0067] The aforementioned gain can then be substituted into the PID formula (refer to relevant techniques, which will not be elaborated here) to calculate the basic control quantity, for example, denoted as U. base .

[0068] According to this embodiment, robust intelligent control is achieved. By introducing integral separation and variable gain (e.g., adjusting the gain of the proportional element) strategies, the overshoot problem of the hydraulic system under large signals and the dead zone stagnation problem under small signals are effectively solved, thereby improving the dynamic response speed and steady-state accuracy of the system.

[0069] In some embodiments, the MCU adjusts the basic control quantities according to the state of the electro-hydraulic servo system, including at least one of the following:

[0070] When the electro-hydraulic servo system is in a stable state, the MCU adjusts the cutoff frequency of the digital filter in the FPGA to improve the signal-to-noise ratio.

[0071] When the electro-hydraulic servo system is in a dynamic response state, the MCU determines the compensation amount based on the dead-time model (refer to relevant technologies, which will not be elaborated here), and compensates the basic control quantity based on the compensation amount.

[0072] like Figure 4 As shown, for example, the MCU can determine the state of the electro-hydraulic servo system based on the rate of change of the error. When the electro-hydraulic servo system is in a stable state, the MCU adjusts the cutoff frequency of the digital filter in the FPGA to improve the signal-to-noise ratio, thereby adjusting the basic control quantity. When the electro-hydraulic servo system is in a dynamic response state, the MCU determines the compensation amount (e.g., denoted as U) based on the dead-zone model. comp The basic control quantity is compensated based on the compensation amount, for example, the result after compensation is denoted as U. out .

[0073] The MCU can convert the compensated result into U out Output to a DAC or FPGA, for example, a DAC or FPGA can output U out (The position corresponding to the electro-hydraulic servo valve control) is converted into an analog output, thereby realizing U-based... out Control of electro-hydraulic servo valves.

[0074] In some embodiments, the method further includes: the MCU inputting the basic control quantity into the digital-to-analog converter to output an analog control quantity; and displaying the analog control quantity via an oscilloscope.

[0075] For example, after the MCU inputs the basic control quantity to the DAC, it can obtain the analog control quantity, which can then be displayed on the oscilloscope for subsequent debugging and monitoring.

[0076] Figure 5 This is a schematic diagram illustrating the collaborative operation of an MCU and an FPGA according to an embodiment of the present disclosure.

[0077] like Figure 5 As shown, the FPGA is responsible for sensor excitation and demodulation. Real-time PID control can be implemented in the MCU (or the FPGA). The FPGA and MCU can exchange information through registers. For example, the FPGA demodulates the position and sends it to the position register. After the MCU performs the calculation, it writes the DAC control information out of the register. The FPGA will send the register result to the DAC in real time to convert it into an analog output.

[0078] Embodiments of this disclosure also propose an electro-hydraulic servo control system, including an FPGA and an MCU. The FPGA is used to generate a sinusoidal digital sequence according to a preset carrier frequency. A digital-to-analog converter (DAC) outputs an analog sinusoidal excitation signal based on the sinusoidal digital sequence. The analog sinusoidal excitation signal drives the primary coil of a linear variable differential transformer (LVDT). The secondary coil of the LVDT outputs a first differential analog signal and a second differential analog signal. The DAC outputs a first digital signal based on the first differential analog signal and a second digital signal based on the second differential analog signal. The first and second digital signals are quadrature demodulated to obtain a first in-phase branch corresponding to the first digital signal. The system receives the first in-phase branch signal, the first quadrature branch signal, and the second in-phase branch signal corresponding to the second digital signal. Based on these signals, a digital displacement is calculated and sent to the MCU. The MCU calculates the error between the desired displacement and the digital displacement, performs integral-separation proportional-integral-derivative (PID) adjustment based on the relationship between the error and n thresholds to obtain a basic control quantity, where n is an integer greater than 1. The electro-hydraulic servo system state is determined based on the error and its rate of change. The basic control quantity is adjusted according to the electro-hydraulic servo system state, and the electro-hydraulic servo valve is controlled based on the adjusted basic control quantity.

[0079] In some embodiments, the digital filter in the FPGA is used to filter the first digital signal and the second digital signal respectively to remove DC bias and high-frequency noise; and to perform quadrature demodulation on the filtered first digital signal and the second digital signal respectively.

[0080] In some embodiments, the FPGA is used to perform low-pass filtering on the first in-phase branch signal, the first quadrature branch signal, the first in-phase branch signal, and the first quadrature branch signal; calculate the first square root of the low-pass filtered first in-phase branch signal and the first quadrature branch signal, and the second square root of the low-pass filtered second in-phase branch signal and the second quadrature branch signal; calculate the quotient of the first square root and the first in-phase branch signal as the first displacement amplitude, and calculate the quotient of the second square root and the second in-phase branch signal as the second displacement amplitude; calculate the difference between the first displacement amplitude and the second displacement amplitude, and the sum of the first displacement amplitude and the second displacement amplitude; calculate the ratio of the difference to the sum as the digital displacement.

[0081] In some embodiments, the MCU is configured to compare the error with each of the n thresholds, wherein the i-th threshold is greater than the (i+1)-th threshold, and i is an integer less than n and greater than 1; if the error is greater than the first threshold, the integral term in the PID is turned off; if the error is less than or equal to the i-th threshold and greater than the (i+1)-th threshold, the integral term in the PID is turned on, and the gain of the proportional term in the PID is adjusted to the gain corresponding to the i-th threshold; if the error is less than or equal to the n-th threshold, the integral term in the PID is turned on, and the gain of the proportional term in the PID is adjusted to a preset gain.

[0082] In some embodiments, the MCU also inputs the basic control quantity into the digital-to-analog converter to output an analog control quantity; the analog control quantity is then displayed on an oscilloscope.

[0083] In some embodiments, the MCU is used to adjust the cutoff frequency of the digital filter in the FPGA to improve the signal-to-noise ratio when the electro-hydraulic servo system is in a stable state; and when the electro-hydraulic servo system is in a dynamic response state, the MCU determines a compensation amount based on the dead-zone model and compensates the basic control quantity based on the compensation amount.

[0084] Other embodiments of this disclosure will readily occur to those skilled in the art upon consideration of the specification and practice of the disclosure herein. This application is intended to cover any variations, uses, or adaptations of this disclosure that follow the general principles of this disclosure and include common knowledge or customary techniques in the art not disclosed herein. The specification and examples are to be considered exemplary only, and the true scope and spirit of this disclosure are indicated by the following claims.

[0085] It should be understood that this disclosure is not limited to the precise structures described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope. The scope of this disclosure is limited only by the appended claims.

Claims

1. An electro-hydraulic servo control method, characterized in that, The method is executed by an electro-hydraulic servo control system, which includes a field-programmable gate array (FPGA) and a microcontroller unit (MCU). The FPGA generates a sinusoidal digital sequence according to a preset carrier frequency. The digital-to-analog converter outputs an analog sinusoidal excitation signal according to the sinusoidal digital sequence. The analog sinusoidal excitation signal is used to drive the primary coil of the linear variable differential transformer (LVDT). The secondary coil of the LVDT outputs a first differential analog signal and a second differential analog signal. The analog-to-digital converter outputs a first digital signal according to the first differential analog signal and a second digital signal according to the second differential analog signal. The FPGA performs quadrature demodulation on the first digital signal and the second digital signal to obtain the first in-phase branch signal and the first quadrature branch signal corresponding to the first digital signal, and the second in-phase branch signal and the second quadrature branch signal corresponding to the second digital signal. The FPGA calculates the digital displacement based on the first in-phase branch signal, the first quadrature branch signal, the first in-phase branch signal, and the first quadrature branch signal, and sends the digital displacement to the MCU. The MCU calculates the error between the desired displacement and the digital displacement, and performs integral separation proportional-integral-derivative PID adjustment based on the relationship between the error and n thresholds to obtain the basic control quantity, where n is an integer greater than 1. The MCU determines the state of the electro-hydraulic servo system based on the error and the rate of change of the error, adjusts the basic control quantity based on the state of the electro-hydraulic servo system, and controls the electro-hydraulic servo valve based on the adjusted basic control quantity.

2. The method according to claim 1, characterized in that, The FPGA performs quadrature demodulation on the first digital signal and the second digital signal, respectively, including: The digital filter in the FPGA filters the first digital signal and the second digital signal respectively to remove DC bias and high-frequency noise; and performs quadrature demodulation on the filtered first digital signal and the second digital signal respectively.

3. The method according to claim 1, characterized in that, The FPGA calculates the digital displacement based on the first in-phase branch signal, the first quadrature branch signal, the first in-phase branch signal, and the first quadrature branch signal, including: The FPGA performs low-pass filtering on the first in-phase branch signal, the first quadrature branch signal, the first in-phase branch signal, and the first quadrature branch signal; Calculate the first square root of the first in-phase branch signal and the first quadrature branch signal after low-pass filtering, and the second square root of the second in-phase branch signal and the second quadrature branch signal after low-pass filtering; The quotient of the first square root and the first in-phase branch signal is used as the first displacement amplitude, and the quotient of the second square root and the second in-phase branch signal is used as the second displacement amplitude. Calculate the difference between the first displacement amplitude and the second displacement amplitude, and the sum of the first displacement amplitude and the second displacement amplitude; The ratio of the difference to the sum is calculated as the digital displacement.

4. The method according to any one of claims 1 to 3, characterized in that, The MCU performs integral separation PID adjustment based on the relationship between the error and the n threshold to obtain the basic control quantities, including: The MCU compares the error with each of the n thresholds, wherein the i-th threshold is greater than the (i+1)-th threshold, and i is an integer less than n and greater than 1; If the error is greater than the first threshold, the integral term in the PID controller is turned off; if the error is less than or equal to the i-th threshold and greater than the (i+1)-th threshold, the integral term in the PID controller is turned on, and the gain of the proportional term in the PID controller is adjusted to the gain corresponding to the i-th threshold; if the error is less than or equal to the n-th threshold, the integral term in the PID controller is turned on, and the gain of the proportional term in the PID controller is adjusted to a preset gain.

5. The method according to any one of claims 1 to 3, characterized in that, The method further includes: The MCU inputs the basic control quantity into the digital-to-analog converter to output an analog control quantity; The analog control quantity is displayed on an oscilloscope.

6. The method according to any one of claims 1 to 3, characterized in that, The MCU adjusts the basic control quantity according to the state of the electro-hydraulic servo system, including at least one of the following: When the electro-hydraulic servo system is in a stable state, the MCU adjusts the cutoff frequency of the digital filter in the FPGA to improve the signal-to-noise ratio; When the electro-hydraulic servo system is in a dynamic response state, the MCU determines the compensation amount based on the dead-zone model and compensates the basic control quantity based on the compensation amount.

7. An electro-hydraulic servo control system, characterized in that, The control system includes a field-programmable gate array (FPGA) and a microcontroller unit (MCU), wherein: The FPGA is used to generate a sinusoidal digital sequence according to a preset carrier frequency. A digital-to-analog converter (DAC) outputs an analog sinusoidal excitation signal based on the sinusoidal digital sequence. This analog sinusoidal excitation signal drives the primary coil of a linear variable differential transformer (LVDT). The secondary coil of the LVDT outputs a first differential analog signal and a second differential analog signal. The DAC outputs a first digital signal based on the first differential analog signal and a second digital signal based on the second differential analog signal. The first and second digital signals are quadrature demodulated to obtain a first in-phase branch signal and a first quadrature branch signal corresponding to the first digital signal, and a second in-phase branch signal and a second quadrature branch signal corresponding to the second digital signal. A digital displacement is calculated based on the first in-phase branch signal, the first quadrature branch signal, the first in-phase branch signal, and the first quadrature branch signal, and the digital displacement is sent to the MCU. The MCU is used to calculate the error between the desired displacement and the digital displacement, and to perform integral separation proportional-integral-derivative PID adjustment based on the relationship between the error and n thresholds to obtain the basic control quantity, where n is an integer greater than 1; the state of the electro-hydraulic servo system is determined based on the error and the rate of change of the error, the basic control quantity is adjusted based on the state of the electro-hydraulic servo system, and the electro-hydraulic servo valve is controlled based on the adjusted basic control quantity.

8. The method according to claim 7, characterized in that, The FPGA is used to perform low-pass filtering on the first in-phase branch signal, the first quadrature branch signal, the first in-phase branch signal, and the first quadrature branch signal; calculate the first square root of the first in-phase branch signal and the first quadrature branch signal after low-pass filtering, and the second square root of the second in-phase branch signal and the second quadrature branch signal after low-pass filtering; calculate the quotient of the first square root and the first in-phase branch signal as the first displacement amplitude, and calculate the quotient of the second square root and the second in-phase branch signal as the second displacement amplitude; Calculate the difference between the first displacement amplitude and the second displacement amplitude, and the sum of the first displacement amplitude and the second displacement amplitude; The ratio of the difference to the sum is calculated as the digital displacement.

9. The method according to any one of claims 7 to 8, characterized in that, The MCU is used to compare the error with each of the n thresholds, wherein the i-th threshold is greater than the (i+1)-th threshold, and i is an integer less than n and greater than 1; if the error is greater than the first threshold, the integral term in the PID is turned off; if the error is less than or equal to the i-th threshold and greater than the (i+1)-th threshold, the integral term in the PID is turned on, and the gain of the proportional term in the PID is adjusted to the gain corresponding to the i-th threshold; if the error is less than or equal to the n-th threshold, the integral term in the PID is turned on, and the gain of the proportional term in the PID is adjusted to a preset gain.

10. The method according to any one of claims 7 to 8, characterized in that, The MCU is used to adjust the cutoff frequency of the digital filter in the FPGA to improve the signal-to-noise ratio when the electro-hydraulic servo system is in a stable state; and to determine the compensation amount according to the dead-zone model when the electro-hydraulic servo system is in a dynamic response state, and to compensate the basic control quantity according to the compensation amount.

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