A pressure and flow high-precision control method based on electromagnetic on-off valve

Abstract

The application discloses a pressure and flow high-precision control method based on an electromagnetic switch valve and belongs to the field of electromagnetic switch valve control. The application combines the advantages of high-frequency and low-frequency control strategies. When the difference between the system measurement value and the target value is greater than delta, a PID controller controls the electromagnetic switch valve to work in a lower frequency range, PID closed-loop control is performed on the electromagnetic switch valve, and the actual flow or pressure of the valve path can quickly approach the target value. When the difference between the measurement value and the target value is less than delta for the first time, the working frequency of the electromagnetic switch valve is increased, PID closed-loop control is performed on the electromagnetic switch valve, and finally, pressure and flow high-precision control is realized. According to the method, the response time for the actual flow value to reach the target flow value is shorter, and the control precision is higher after the system is stable.

Description

Technical Field

[0001] This invention belongs to the field of high-precision control of electromagnetic switching valves, specifically relating to a high-precision pressure and flow control method based on electromagnetic switching valves. Background Technology

[0002] The rapid development of electronic and computer technologies has profoundly impacted hydraulic control technology, and mechatronics integration is an inevitable trend in the future development of the mechanical hydraulic field. Electro-hydraulic control valves and their digital control technology are being used more and more widely. Electro-hydraulic control valves can be broadly classified into three categories: servo valves, proportional valves, and high-speed solenoid valves. Among them, high-speed solenoid valves have attracted much research and attention due to their advantages such as low price, strong anti-pollution ability, simple structure, reliable operation, and easy computer interface. The combination of high-speed solenoid valve electro-hydraulic control systems and computer digital control is a hot topic in the development of hydraulic control systems today.

[0003] Currently, among the various solutions for pressure and flow control in hydraulic systems using high-speed electromagnetic switching valves, closed-loop control using PID controllers is frequently employed. The execution flow of a PID controller is very simple: it uses feedback to detect deviation signals and then controls the controlled variable based on these signals. The controller itself is simply the sum of proportional, integral, and derivative components. However, in hydraulic system control, besides the core PID controller, the design of the controllers for input and output signal processing is also crucial. Only by designing both of these controller components effectively can precise hydraulic control be achieved.

[0004] To improve system control performance, existing electromagnetic switching valve flow and pressure control models mostly focus on innovation in control structure or principle to achieve better control effects. Furthermore, in current examples of control methods based on PID controllers for controlling the pressure and flow of hydraulic systems, it is difficult to guarantee both fast response and high control accuracy simultaneously. Often, low-frequency strategies result in fast response but low accuracy, while high-frequency strategies offer high accuracy but slow response. Summary of the Invention

[0005] To address the problems in the existing technology, this invention proposes a high-precision pressure and flow control method based on an electromagnetic switching valve. This method is based on the principle of PID control and adds a part for frequency control of the switching valve, which enables the oil system to quickly and accurately reach the target pressure or target flow value.

[0006] The technical solution of the present invention is as follows:

[0007] This invention provides a high-precision pressure and flow control method based on an electromagnetic switching valve. It provides real-time acquisition of pressure or flow signals from the electromagnetic switching valve circuit as measured values, compares these values ​​with preset pressure or flow target values, and employs a PID controller for closed-loop control of the electromagnetic switching valve's pressure or flow. The high-precision pressure and flow control method includes the following steps:

[0008] S1, set the target value T for pressure or flow control in the PID controller, and set a pressure or flow difference △; obtain the pressure or flow signal on the electromagnetic switch valve line in real time as the measurement value through the sensor;

[0009] S2, when the difference between the measured value and the target value T is greater than △, the PID controller controls the solenoid valve to work within the first frequency range, and performs PID closed-loop control on the pressure or flow of the solenoid valve; within the first frequency range, the actual flow or pressure of the valve will quickly approach the target value.

[0010] When the difference between the measured value and the target value T is less than Δ for the first time, the operating frequency of the solenoid valve is increased to the second frequency range, and PID closed-loop control is performed on the pressure or flow of the solenoid valve. The solenoid valve operating in the second frequency range is used to ultimately achieve high-precision control of pressure and flow. The frequency of the second frequency range is higher than that of the first frequency range.

[0011] According to a preferred embodiment of the present invention, the difference Δ is 5%-10% of the target value.

[0012] According to a preferred embodiment of the present invention, the first frequency range is the normal operating frequency range of the electromagnetic switching valve, which is less than the critical frequency of the electromagnetic switching valve.

[0013] According to a preferred embodiment of the present invention, the second frequency range is greater than the critical frequency of the electromagnetic switching valve, but less than the limiting frequency of the electromagnetic switching valve.

[0014] According to a preferred embodiment of the present invention, the electromagnetic switch valve is a two-position three-way electromagnetic switch valve.

[0015] According to a preferred embodiment of the present invention, the working medium in the electromagnetic switch valve circuit is hydraulic oil.

[0016] Compared to existing technologies, this invention combines the advantages of both high-frequency and low-frequency control strategies. The electromagnetic high-speed switching valve initially operates with a low-frequency control strategy, bringing the actual flow rate close to the predetermined flow rate. When the difference between the actual and target flow rates first falls below Δ, the operating frequency of the electromagnetic switching valve is immediately switched to a high frequency, allowing the high-speed switching valve to achieve precise flow control. This invention balances the switching valve's response speed with the accuracy of flow control, combining control methods without altering their fundamental control principles. It employs control strategies with different advantages at different control stages. Compared to fundamental innovations, this invention significantly improves experimental operability and greatly reduces research costs while achieving ideal control requirements. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of an oil system as an example of an embodiment.

[0018] Figure 2 A schematic diagram showing the actual response of the valve core lagging behind the PWM control signal due to factors such as mechanical viscous damping.

[0019] Figure 3 This is a schematic diagram illustrating the control accuracy at a fixed low frequency.

[0020] Figure 4 This is a schematic diagram illustrating the control accuracy at a fixed high frequency.

[0021] Figure 5 This is a schematic diagram showing the relationship between the valve core displacement curve and the PWM control signal at a fixed high frequency.

[0022] Figure 6 This is a schematic diagram of the control principle under the control method of the present invention.

[0023] Figure 7 This is a schematic diagram illustrating the control accuracy of the control method of the present invention. Detailed Implementation

[0024] The present invention will be further described and illustrated below with reference to specific embodiments. The embodiments described are merely examples of the content of this disclosure and do not limit the scope of the invention. The technical features of each embodiment in the present invention can be combined accordingly, provided that there is no mutual conflict.

[0025] by Figure 1 The control strategy of the present invention and the prior art are illustrated using a typical oil system model as an example. Figure 1In the attached diagram, reference numerals 1 and 2 represent two identical two-position three-way high-speed solenoid valves; 3 is the main controller, whose input signals are the real-time data signal and the target value signal measured by the sensor, and whose output signal is the corresponding duty cycle signal obtained by the PWM pulse width modulation part. This duty cycle signal is transmitted to high-speed solenoid valve 1 and high-speed solenoid valve 2 respectively; 4 is a sensor, such as a flow sensor or a pressure sensor, whose function is to measure the flow or pressure of the oil inlet in real time and input the real-time signal to the main controller 3; 5 is a hydraulic cylinder, which is the actuator.

[0026] The method for achieving closed-loop control of the inlet flow of the high-speed solenoid valve in this hydraulic system is as follows: First, a target flow value is preset. When the valve is operating, the pressure / flow sensor detects real-time data and inputs it to the main controller. The main controller compares the target value with the measured value, performs PID negative feedback adjustment on the difference between the target value and the measured value, and then processes it through the PWM pulse width modulation section to output a duty cycle signal for controlling the solenoid valve, thereby achieving real-time flow control of the hydraulic cylinder.

[0027] For various control systems similar to the two-position three-way valve oil flow control model, ideally, within one PWM pulse width modulation cycle, the valve core displacement response waveform should be consistent with the input PWM signal waveform; that is, the valve core should remain open during the high-level phase of the PWM signal and closed during the low-level phase. However, due to practical factors such as the physical response characteristics of the oil itself, the hysteresis of the electromagnetic response, and the mechanical viscous damping between control system hardware components, the actual response of the valve core always lags behind the PWM control signal. Figure 2 As shown.

[0028] Therefore, this invention conducted a series of studies on the kinematic relationship between the PWM control signal and the valve core displacement. This invention found that the experimental results obtained when the high-speed electromagnetic switching valve operates at different frequencies to control the pressure / flow of the hydraulic cylinder are different.

[0029] When the pressure / flow of the hydraulic system is controlled at a fixed low frequency (e.g., 50Hz) with the switching valve, the following may occur: Figure 3 The control results shown are as follows: Because the PWM signal control frequency is low, the valve core of the high-speed solenoid switching valve will inevitably experience periods of complete opening and closing. Therefore, the hydraulic output flow rate of the switching valve within a single control cycle will be relatively large. Although the system response time is fast, once the system stabilizes, due to poor control accuracy, the difference between the actual flow rate and the target flow rate will not meet the expected requirements. Figure 3 As shown.

[0030] When the pressure / flow of the hydraulic system is controlled at a fixed high frequency (e.g., 130Hz) using the switching valve, the following may occur: Figure 4The control results shown are as follows: Although the actual flow rate will reach the range close to the target flow rate at a slower response time, once the system stabilizes, the steady-state error between the actual flow rate and the target flow rate will be smaller under the high-frequency control strategy compared to the low-frequency control strategy.

[0031] This is because the control frequency of the PWM control strategy is too high. Within one motion cycle, the valve receives an open signal but before its opening motion is complete, it receives a close signal, preventing the valve from fully opening or closing. Figure 5 As shown, the oil flow rate within a single cycle is smaller, resulting in more precise control. However, due to the incomplete opening and closing, under the same duty cycle, the oil output of the high-frequency control strategy per unit time will be less than that of the low-frequency control strategy. This is why the high-frequency control strategy has a slower response speed.

[0032] Based on the respective advantages of the two control strategies described above, this invention proposes a high-precision pressure and flow control method for a high-speed electromagnetic switching valve. This invention acquires the pressure or flow signal on the electromagnetic switching valve circuit in real time as a measured value, compares it with a preset pressure or flow target value, and uses a PID controller to perform closed-loop control of the pressure or flow of the electromagnetic switching valve. The high-precision pressure and flow control method includes the following steps:

[0033] S1. First, the critical frequency and limiting frequency of the two-position three-way high-speed electromagnetic switch valve must be measured using traditional experimental methods. It should be noted that the valve's normal operating frequency is generally slightly lower than the critical frequency. In this embodiment, the two-position three-way high-speed electromagnetic switch valve has a critical frequency of 125Hz, a limiting frequency of 200Hz, and a normal operating frequency of 50Hz. A target value T for pressure or flow control is set within the PID controller, and a pressure or flow difference Δ is set, with the Δ value between 5% and 10% of the target flow. The pressure or flow signal on the electromagnetic switch valve circuit is acquired in real time by a sensor as a measurement value.

[0034] S2, when the difference between the measured value and the target value T is greater than Δ, the PID controller controls the solenoid valve to work in the first frequency range (the first frequency range is 50-70Hz, which is called the low frequency state) to perform PID closed-loop control on the pressure or flow of the solenoid valve; in the first frequency range, the actual flow or pressure of the valve will quickly approach the target value.

[0035] When the difference between the measured value and the target value T is less than Δ for the first time, the operating frequency of the solenoid valve is increased to the second frequency range (130-150Hz, referred to as the high-frequency state). PID closed-loop control is then applied to the pressure or flow rate of the solenoid valve. This allows for high-precision pressure and flow control to be achieved using the solenoid valve operating within the second frequency range. The result is as follows: Figure 6As shown; the frequencies in the second frequency range are higher than those in the first frequency range.

[0036] The actual control effect of this method is that the response time for the actual flow rate to reach the target flow rate is shorter, and the control accuracy is also high after the system stabilizes. Figure 7 As shown.

[0037] This invention combines the advantages of both high-frequency and low-frequency control strategies, leveraging their strengths and mitigating their weaknesses. The electromagnetic high-speed switching valve initially operates with a low-frequency control strategy, bringing the actual flow rate close to the predetermined flow rate. When the difference between the actual and target flow rates first falls below Δ, the operating frequency of the electromagnetic switching valve is immediately switched to a high frequency, allowing the high-speed switching valve to achieve precise flow control. This balances the valve's response speed with the accuracy of flow control. This invention is innovative in the field of high-speed switching valve control of hydraulic cylinders, achieving both high-speed response and precise flow control of the hydraulic cylinder through a frequency switching strategy. This invention identifies the shortcomings and advantages of each of the two control strategies in principle, combining them without altering their fundamental control principles. Different control strategies with varying advantages are used at different control stages. Compared to fundamental innovation, this invention significantly improves experimental operability and greatly reduces research costs while achieving ideal control requirements.

[0038] The above-described embodiments are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. Those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention.

Claims

1. A high-precision pressure and flow control method based on an electromagnetic switching valve, characterized in that, The pressure or flow signal on the electromagnetic switch valve line is acquired in real time as a measured value and compared with a preset pressure or flow target value. A PID controller is used to perform closed-loop control of the pressure or flow of the electromagnetic switch valve. The high-precision pressure and flow control method includes the following steps: S1, set the target value T for pressure or flow control in the PID controller, and set a pressure or flow difference Δ, wherein the difference Δ is 5%-10% of the target value; The pressure or flow signal on the electromagnetic switch valve line is acquired in real time by the sensor as a measurement value. S2, when the difference between the measured value and the target value T is greater than Δ, the PID controller controls the solenoid valve to work within the first frequency range, and performs PID closed-loop control on the pressure or flow of the solenoid valve; within the first frequency range, the actual flow or pressure of the valve will quickly approach the target value; the first frequency range is the normal design frequency operating range of the solenoid valve, which is less than the critical frequency of the solenoid valve. When the difference between the measured value and the target value T is less than Δ for the first time, the operating frequency of the solenoid valve is increased to the second frequency range, and PID closed-loop control is performed on the pressure or flow of the solenoid valve. The solenoid valve operating in the second frequency range is used to ultimately achieve high-precision control of pressure and flow. The second frequency range is greater than the critical frequency of the solenoid valve, but less than the limit frequency of the solenoid valve. The frequency of the second frequency range is higher than that of the first frequency range.

2. The high-precision pressure and flow control method based on an electromagnetic switching valve according to claim 1, characterized in that, The electromagnetic switch valve is a two-position three-way electromagnetic switch valve.

3. The high-precision pressure and flow control method based on an electromagnetic switching valve according to claim 1, characterized in that, The working medium in the electromagnetic switch valve circuit is hydraulic oil.

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