Active dual-chamber cylindrical piston gas flow standard device and test method

Abstract

This invention relates to an active dual-chamber cylindrical piston gas flow standard device and testing method. The device includes a fixed base, a balance cylinder fixedly installed on one side of the fixed base, a metering cylinder installed on the other side of the fixed base, a piston metering rod disposed in the balance cylinder and the metering cylinder, and a drive assembly disposed on the piston metering rod; the drive assembly is located between the balance cylinder and the metering cylinder. The testing method involves the following steps: This invention solves the thrust imbalance problem caused by uneven force distribution under high pressure conditions in traditional single-chamber piston structures by adopting a dual-chamber cylindrical piston structure with symmetrically arranged balance and metering chambers. This invention integrates a genetic algorithm optimization, LSTM state recognition, and fuzzy control intelligent PID control strategy to construct a closed-loop regulation mechanism with parameter self-tuning, state self-judgment, and disturbance self-adaptation. The three mechanisms work together to improve the system's adaptability, stability, and intelligent regulation capability in scenarios involving small flow rates and high-pressure gas flow control.

Claims

1. An active dual-chamber cylindrical piston gas flow standard device, characterized in that, It includes a fixed base (8), a balance cylinder (1) fixedly installed on one side of the fixed base (8), a metering cylinder (2) installed on the other side of the fixed base (8), a piston metering rod (3) passing through the balance cylinder (1) and the metering cylinder (2), and a drive assembly installed on the piston metering rod (3) and driving the piston metering rod (3) to perform reciprocating linear motion; the drive assembly is located between the balance cylinder (1) and the metering cylinder (2); Piston rod sealing assemblies are provided between the corresponding ends of the balance cylinder (1) and the metering cylinder (2) and the piston metering rod (3), and sealing caps (4) are installed on the outer ends of the balance cylinder (1) and the metering cylinder (2). An air guide pipe (9) connecting the two chambers is installed on the side wall of the balance cylinder (1) and the metering cylinder (2). The piston rod sealing assembly includes a piston rod sealing assembly A (5) disposed between the balance cylinder (1) and the piston metering rod (3) and a piston rod sealing assembly B (6) disposed between the metering cylinder (2) and the piston metering rod (3). The piston rod sealing assembly B (6) includes a sealing ring cover (61) with its end embedded in the port of the metering cylinder (2), a first sealing sleeve (62) nested in the inner port groove of the sealing ring cover (61), a second sealing sleeve (63) nested in the other port groove of the first sealing sleeve (62), and a third sealing sleeve (64) nested in the other port groove of the second sealing sleeve (63); a cap-shaped sealing ring (65) is provided between the sealing ring cover (61) and the metering cylinder (2), between the first sealing sleeve (62) and the metering cylinder (2), and between the second sealing sleeve (63) and the metering cylinder (2). A first piston rod guide ring (66) is provided in the inner cavity of the sealing ring cover (61), and a second piston rod guide ring (67) is provided in the inner cavity of the third sealing sleeve (64); a lip-shaped dustproof ring (70) is provided on the inner wall of the sealing ring cover (61). A first O-ring (68) and a second O-ring (69) are sequentially arranged between the sealing ring cover (61) and the inner wall of the metering cylinder (2), and a third O-ring (71) is arranged between the second sealing sleeve (63) and the third sealing sleeve (64). The drive assembly includes a servo motor (10), a reducer (11) connected to the drive shaft of the servo motor (10), a ball screw (13) connected to the reducer (11) via a coupling (12), and a T-shaped connecting block (14); the ball screw (13) is parallel to the piston metering rod (3); A grating ruler connecting block (15) is installed on the upper side of the T-shaped connecting block (14), and the upper side of the grating ruler connecting block (15) is connected to the grating ruler (16).

2. The active dual-chamber cylindrical piston gas flow standard device according to claim 1, characterized in that, Pressure tapping holes (72) are provided on both the first sealing sleeve (62) and the second sealing sleeve (63). Pressure tapping connectors (73) communicating with the corresponding pressure tapping holes (72) are provided on the metering cylinder body (2). The two pressure tapping connectors (73) are connected to the external pressure gauge and differential pressure gauge respectively.

3. The active dual-chamber cylindrical piston gas flow standard device according to claim 1, characterized in that, The lower side of the T-shaped connecting block (14) is connected to the ball screw (13) through a precision nut, and the upper side of the T-shaped connecting block (14) is engaged with the piston measuring rod (3) through the guide hole inside it; the servo motor (10) drives the ball screw (13) to rotate through the reducer (11), and the rotational power of the ball screw (13) is transmitted to the piston measuring rod (3) through the T-shaped connecting block (14). The piston measuring rod (3) moves precisely along a predetermined trajectory under the guidance of the T-shaped connecting block (14).

4. The active dual-chamber cylindrical piston gas flow standard device according to claim 3, characterized in that, The piston measuring rod (3) is parallel to the grating ruler (16).

5. A test method for an active dual-chamber cylindrical piston gas flow standard device according to any one of claims 1-4, characterized in that, The following steps are used: S1. Supply air to the flow controller under test and set the target flow value; S2. Start the servo motor (10) to reset the piston metering rod (3) to the starting position; S3. Calculate the target piston speed based on the target flow rate and piston cross-sectional area, and set it as the initial setpoint for the PID controller; S4. Close the balance valve between the piston balance chamber and the metering chamber. The servo motor (10) drives the ball screw (13) to rotate through the reducer (11). The rotational power of the ball screw (13) is transmitted to the piston metering rod (3) through the T-shaped connecting block (14). Under the guidance of the T-shaped connecting block (14), the piston metering rod (3) moves into the metering cylinder (2) along a predetermined trajectory. S5. Measure the displacement and time of the piston metering rod (3) in real time, calculate the actual gas flow rate and compare it with the target gas flow rate to obtain the flow error ΔQ, and input it into the PID controller for closed-loop regulation; S6. The control system monitors the pressure, temperature and flow rate of the gas in the metering chamber in real time, calculates the error and determines whether the dual-chamber cylindrical piston gas flow standard device is in a stable or disturbed state. S7. When the dual-chamber cylindrical piston gas flow standard device is in a disturbed state, the fuzzy controller is automatically activated to adjust the output of the PID controller. S8. Once the pressure difference and flow rate error have stabilized, the dual-chamber cylindrical piston gas flow standard device begins the formal flow rate calibration process.

6. The test method for an active dual-chamber cylindrical piston gas flow standard device according to claim 5, characterized in that, The initial settings for the PID controller in S3 are as follows: The initial setpoints are designed using a PID parameter design method based on a genetic algorithm (GA). This method is based on the parameters of the piston metering rod (3) and the flow control data from the historical calibration process. It constructs a multi-objective fitness function and sets the proportional coefficient K of the PID controller accordingly. p Integral coefficient K i Differential coefficient K d Encoded as genetic individuals, global optimization of parameter sets is achieved through an iterative evolutionary process; The optimization objectives include: minimizing the system's steady-state error, minimizing differential pressure fluctuations, and minimizing the settling time; Genetic algorithms (GA) iteratively obtain PID parameter combinations through population initialization, fitness evaluation, selection, crossover, and mutation operations, and use them as the initial controller configuration for the control system.

7. The test method for an active dual-chamber cylindrical piston gas flow standard device according to claim 6, characterized in that, The specific operation of closed-loop regulation in S5 is as follows: S51. Compare the measured actual flow rate with the target flow rate, and automatically adjust the servo motor speed according to the error to minimize the error; S52. Error Calculation: Real-time acquisition of the displacement and movement time of the piston metering rod, calculation of the current instantaneous flow rate Q1, and comparison with the set target flow rate Q2 to obtain the error: ΔQ=Q2-Q1; unit: ml / min; S53. The flow error ΔQ is used as the input to the PID controller and enters the adjustment algorithm. The PID controller adjusts according to the following formula. In the formula, K p K i K d The proportional, integral, and differential coefficients are obtained from the genetic algorithm optimization; u(t) is the controller output; To integrate the flow error Δt along the time axis; It is the first derivative of the flow error Δr with respect to time; S54, Output Used to adjust the speed of the servo motor in real time, thereby changing the pushing speed of the piston metering rod driven by the ball screw; S55. After adjustment, measure the displacement and time in real time, recalculate the flow rate, and form a continuous feedback loop until the flow error ΔQ approaches 0.

8. The test method for an active dual-chamber cylindrical piston gas flow standard device according to claim 5, characterized in that, The specific steps in S6 for determining whether the dual-chamber cylindrical piston gas flow standard device is in a stable or disturbed state are as follows: A state recognition model based on Long Short-Term Memory (LSTM) neural network is used to learn and classify continuously collected data to determine the current state of the system. When the pressure difference ΔP < 5Pa, the continuous stabilization time is 60s, and the flow error ΔQ enters the ±1% target value range, the system is determined to be in a stable state and enters an effective metering cycle. When the pressure difference ΔP and the flow error ΔQ are still in the process of convergence, the parameter fluctuations gradually slow down, the system is judged to be in a transition state, and the system continues to adjust but does not perform metering. If a sudden change in pressure difference, a sharp deviation in error, or a large jump in temperature occurs, the system determines it to be in a disturbance state and immediately activates the fuzzy control intervention module to correct the output of the PID controller.

9. The test method for an active dual-chamber cylindrical piston gas flow standard device according to claim 5, characterized in that... The fuzzy controller in S7 has a dual-input, three-output structure. Its input variables include: the pressure difference ΔP between the balance chamber and the metering chamber; and the flow error ΔQ between the piston output flow rate and the set flow rate of the flowmeter under test. The pressure difference ΔP and the flow error ΔQ are each divided into seven fuzzy linguistic variables: NB, NM, NS, ZO, PS, PM, and PB. The membership function type is a symmetric triangular function. The pressure difference ΔP and the flow error ΔQ are adapted to the input space of the fuzzy controller, and a linear normalization method is used to map the physical quantities to the range [-3, +3]. The typical variation range of the pressure difference ΔP is ±5 Pa, and the normalization function is: The baseline setting for the flow error ΔQ is ±1% of the target flow value, and the corresponding normalization function is: ; The output variables are the adjustments to three parameters of the current PID controller: the proportional coefficient K. p Integral coefficient K i and differential coefficient K d The fuzzy control rules consist of 49 rules. The fuzzy inference uses the Mamdani model, and the centroid method is used for defuzzification. The final output correction value is combined with the original PID parameters to control the speed of the servo motor.

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