Liquid drop quality control method based on coil current and distribution equipment

Abstract

The invention relates to a liquid drop quality control method based on coil current and distribution equipment. The method comprises the following steps: establishing a direct mapping function from target liquid drop mass m to control variable coil current I; according to the direct mapping function, converting a set target droplet mass m into a target coil current; and driving a current source to apply current to a proportional valve coil by taking the target coil current as a control instruction so as to control and output a liquid drop with the quality consistent with that of the target liquid drop. The method has the beneficial effects that the coil current in direct proportion to the electromagnetic force is directly controlled, and a direct model of the coil current and the droplet quality is established, so that the control logic is simplified, and the response speed is increased.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of high-precision fluid control, and particularly relates to a droplet mass control method based on coil current and a dispensing device. BACKGROUND

[0002] In many high-precision fields such as biological medicine, inkjet printing and precision chemical industry, accurate dispensing and control of trace liquid are crucial. Existing droplet injection technologies mostly adopt open-loop control mode, that is, injection is performed according to preset parameters, but it is difficult to cope with errors caused by fluctuations in physical properties of liquid (such as liquid density, viscosity and surface tension), changes in environmental temperature and equipment wear, etc., resulting in poor consistency of the mass of a single droplet and difficulty in ensuring precision. SUMMARY

[0003] The application aims to overcome the deficiencies in the prior art and provide a droplet mass control method based on coil current and a dispensing device.

[0004] In a first aspect, a droplet mass control method based on coil current is provided, comprising:

[0005] S1, a direct mapping function from a target droplet mass m to a control variable coil current I is established;

[0006] S2, according to the direct mapping function, a set target droplet mass m is converted into a target coil current;

[0007] S3, the target coil current is taken as a control instruction to drive a current source to apply current to a proportional valve coil, so as to control and output a droplet consistent with the target droplet mass.

[0008] Preferably, S1 comprises:

[0009] S101, a first theoretical model between a valve core displacement x and a coil current I is established, and the first theoretical model is used to describe coil current I required to drive a valve core to generate a specific displacement x under a given valve port pressure difference ΔP and liquid parameters;

[0010] S102, a second theoretical model between the valve core displacement x and the droplet mass m is established, and the second theoretical model is used to describe droplet mass m corresponding to a specific valve core displacement x under the conditions of a given valve port pressure difference ΔP, liquid density ρ and valve working frequency f;

[0011] S103, based on the first theoretical model and the second theoretical model, the direct mapping function is established by eliminating the intermediate variable valve core displacement x.

[0012] Preferably, in S103, the data pairs of droplet mass m and coil current I are obtained by the first theoretical model and the second theoretical model, and the direct mapping function is generated by using a curve fitting method.

[0013] Preferably, in S103, the curve fitting method is a rational cubic Bezier curve fitting.

[0014] Preferably, in S3, the fuzzy PID control algorithm is used to control the actual current applied to the solenoid valve coil by taking the target coil current as input.

[0015] Preferably, the fuzzy PID control algorithm adjusts the proportional, integral and differential parameters of the PID controller in real time according to the current error e and the current error change rate Δe.

[0016] In a second aspect, a droplet mass dispensing device based on coil current is provided, comprising:

[0017] A reservoir for containing a liquid to be dispensed;

[0018] A gas pressure source connected to the reservoir for applying a predetermined pressure to the liquid in the reservoir;

[0019] A proportional valve with an inlet connected to the outlet of the reservoir for ejecting the liquid;

[0020] A control module configured to perform the method of any one of the first aspect.

[0021] Preferably, the control module comprises an industrial computer and an industrial PLC;

[0022] The industrial computer is configured to provide a human-computer interaction interface, receive a target droplet mass set value, calculate a target coil current based on the direct mapping function, generate a target coil current instruction, and send the target coil current instruction to the industrial PLC;

[0023] The industrial PLC is configured to receive the target coil current instruction from the industrial computer, execute a fuzzy PID control algorithm, and adjust the actual current applied to the proportional valve coil in real time to reach the target coil current.

[0024] In a third aspect, a computer storage medium is provided, and the computer storage medium stores a computer program; when the computer program runs on a computer, the computer program causes the computer to execute the method of any one of the first aspect.

[0025] In a fourth aspect, an electronic device is provided, comprising:

[0026] A memory for storing a computer program;

[0027] a processor for executing the computer program to implement the method of any of the first aspect.

[0028] The present application has the following advantages:

[0029] 1. The present application simplifies the control logic and improves the response speed by directly controlling the coil current proportional to the electromagnetic force and establishing a direct model of the droplet mass.

[0030] 2. The present application uses closed-loop control of the coil current, which can effectively overcome the disturbance caused by external factors such as supply voltage fluctuations, liquid viscosity temperature changes, etc. The application of fuzzy PID further enhances the robustness of the system, ensuring high stability and consistency of the droplet mass under continuous working conditions.

[0031] 3. Based on the direct calculation of the model and the high-speed closed-loop control algorithm, the absolute error and repeatability error of the droplet mass can be stably controlled within 0.4mg, which has very high industrial application value. BRIEF DESCRIPTION OF DRAWINGS

[0032] Figure 1 The device provided by the present application is shown in the schematic diagram of the overall structure;

[0033] Figure 2 The structure parameter schematic diagram of the proportional valve provided by the present application is shown in the schematic diagram of the overall structure;

[0034] Figure 3 The Bezier curve fitting schematic diagram of the coil current-droplet mass model provided by the present application is shown in the schematic diagram of the overall structure;

[0035] Figure 4 The liquid material and error diagram of the actual test provided by the present application is shown in the schematic diagram of the overall structure;

[0036] Figure 5 The membership function diagram of the fuzzy PID control algorithm provided by the present application is shown in the schematic diagram of the overall structure;

[0037] The figure mark explanation: storage tank 1, air pressure source 2, proportional valve 3, coil 31, valve core 32, spring 33, inlet 34, outlet 35, control module 4, industrial PLC 41, industrial computer 42, electronic balance 43, current sensor 5, pressure sensor 6. DETAILED DESCRIPTION

[0038] The present application will be further described below in conjunction with the embodiments. The following description of the embodiments is only for the purpose of helping to understand the present application. It should be noted that for ordinary people in the technical field, some modifications can be made to the present application without departing from the principles of the present application, and these improvements and modifications also fall within the scope of protection of the claims of the present application.

[0039] Embodiment 1

[0040] To solve the problems of the prior art, Embodiment 1 of the present application provides a droplet mass dispensing device based on coil current, as shown in Figure 1 , comprising:

[0041] a reservoir 1 for containing a liquid to be dispensed, such as a biological reagent or a precision chemical material.

[0042] a gas pressure source 2 connected to the reservoir 1 for applying a stable, pre-set pressure to the liquid in the reservoir as a power source for liquid injection.

[0043] a proportional valve 3, the inlet 34 of which is connected to the outlet of the reservoir 1 for injecting the liquid. The proportional valve 3 comprises a coil 31, a valve core 32, a spring 33, an inlet 34 and an outlet 35.

[0044] Specifically, in combination with Figure 2 , which shows the structural parameters of the proportional valve 3 used in this embodiment. These parameters are the basis for establishing the mathematical model later, including the half-cone angle β of the valve core, the injection angle θ, the small end diameter , the large end diameter and the minimum valve core diameter . Other key parameters, such as the flow coefficient , the pressure difference ΔP between the inlet and outlet, the spring coefficient , etc., are all pre-input into the industrial computer 41 of the control module 4 as known parameters. Among them, "closed state" refers to the default state of the proportional valve when it is not powered or the coil current is zero. "Open state" refers to the working state of the proportional valve when the coil is applied with sufficient control current I.

[0045] The control module 4 is the core of the device and is used to implement the droplet mass control method described below in the present application. In this embodiment, the control module 4 is specifically composed of an industrial PLC 41 and an industrial computer 42 working in cooperation, and in addition, an electronic balance 43 is connected for real-time monitoring of the total amount of droplets.

[0046] The industrial computer 42 is configured to provide a human-computer interaction interface, receive a target droplet mass set value, calculate a target coil current based on the direct mapping function, generate a target coil current instruction, and send the target coil current instruction to the industrial PLC 41.

[0047] The industrial PLC 41 is configured to receive the target coil current instruction from the industrial computer 42, collect the actual current value fed back by the current sensor 5, perform a fuzzy PID control algorithm, and precisely close-loop control the actual current applied to the proportional valve coil, so that the target coil current is quickly and stably tracked.

[0048] A current sensor 5 is arranged between the proportional valve 3 and the control module 4 for real-time detection and feedback of the current. A pressure sensor 6 is arranged between the storage cylinder 1 and the air pressure source 2, and is installed on the pipeline for accurately measuring the valve port pressure difference ΔP when the system is stably working. During the operation of the device, the pressure sensor continuously monitors the liquid pressure.

[0049] Embodiment 2

[0050] Based on the embodiment 1, the embodiment 2 of the present application provides a droplet mass control method based on coil current, comprising:

[0051] S1, a direct mapping function from the target droplet mass m to the control variable coil current I is established.

[0052] S1 includes:

[0053] S101, a first theoretical model between the valve core displacement x and the coil current I is established, and the first theoretical model is used to describe the coil current I required to drive the valve core to generate a specific displacement x under a given valve port pressure difference ΔP and liquid parameters.

[0054] Specifically, when the valve core reaches the working position, there is a balance between the electromagnetic force, the spring force and the hydraulic pressure. The kinematics equation of the valve core can be represented by the Newton dynamic balance equation:

[0055]

[0056] Where x is the displacement of the valve core, F m is the electromagnetic force, is the hydraulic pressure, is the spring coefficient.

[0057] The electromagnetic force F m can be expressed as:

[0058]

[0059] Where μ0 is the magnetic permittivity of air, S is the cross-sectional area of the armature, I is the coil current, and N is the number of turns of the coil. When the valve piston is working, the hydraulic pressure is composed of a static part and a transient part. Assuming that the fluid is static, the transient force of the transient part can be ignored, and the hydraulic pressure The equation can be expressed as:

[0060]

[0061] where p is the liquid density, Q is the flow rate at the valve port, v is the flow velocity, and 0 is the spray angle. The flow rate Q can be expressed as:

[0062]

[0063] where C d is the flow coefficient, A is the flow area, and AP is the pressure difference between the inlet and outlet. The flow area A is defined as:

[0064] where b is the half-cone angle of the valve piston, D m is the average diameter of the valve seat, which is given by:

[0065]

[0066] where D1 is the small end diameter of the valve seat and D2 is the large end diameter of the valve seat. The flow velocity v can be determined by the Bernoulli equation:

[0067] According to the above formula, the relationship between the spool displacement and the coil current can be derived as follows:

[0068]

[0069] S102, a second theoretical model between the spool displacement x and the droplet mass m is established, and the second theoretical model is used to describe the droplet mass m corresponding to a specific spool displacement x under the conditions of a given valve port pressure difference AP, liquid density p, and valve working frequency f.

[0070] Specifically, the mass of the droplet is the flow rate in the working cycle, which can be described as:

[0071]

[0072] where T is the cycle time. The maximum working frequency f of the valve can be expressed as .

[0073] According to the above formula, the relationship between the spool displacement and the droplet mass can be derived as follows:

[0074]

[0075] S103, based on the first theoretical model and the second theoretical model, a direct mapping function is established by eliminating the intermediate variable spool displacement x.

[0076] In S103, a plurality of data pairs of droplet mass m and coil current I are obtained by the first theoretical model and the second theoretical model, and a direct mapping function is generated by using a curve fitting method.

[0077] Specifically, according to the first theoretical model and the second theoretical model, a rational cubic Bezier curve is used to interpolate discrete points (I, m , which represents the nonlinear relationship between the coil current and the droplet mass.

[0078] In combination Figure 3 , the k-order rational cubic Bezier curve is defined as:

[0079]

[0080] In order to maintain the C1 continuity of the entire curve, the tangent E is used as a boundary condition to construct the second curve segment:

[0081] First, Figure 3 The first part of the (1) in the formula represents the nonlinear relationship curve between the coil current and the droplet mass which is composed of a curve segment from point to and a curve segment from point to .

[0082] Subsequently, the tangent E of the curve at point is calculated using the above formula. As shown in the (2) part of the formula Figure 3 , the curve segment from point to is retained, and the curve segment from point to is deleted.

[0083] Finally, as shown in the (3) part of the formula Figure 4 , let a=a+1, c=c+1, and select discrete points , and to reconstruct a new curve .

[0084] Repeat the above steps until the last point is selected. As shown in the (4) part of the formula Figure 4 , the control model of the current droplet mass is generated under the C1 continuity condition by following the above steps.

[0085] S2, according to the direct mapping function, the set target droplet mass m is converted into a target coil current.

[0086] Wherein, the target droplet mass m is obtained by theoretical calculation of the maximum working frequency and flow coefficient of the proportional valve.

[0087] S3, taking the target coil current as a control instruction, driving the current source to apply current to the proportional valve coil, thereby controlling and outputting droplets consistent with the target droplet mass.

[0088] It should be noted that the method provided in this embodiment is a corresponding method for the device provided in Embodiment 1, so in this embodiment, the same or similar parts as in Embodiment 1 can be mutually referred to, and will not be repeated in this application.

[0089] Embodiment 3:

[0090] Based on Embodiment 2, the present embodiment 3 provides a more specific droplet mass control method based on coil current, comprising:

[0091] S1, establishing a direct mapping function from the target droplet mass m to the control variable coil current I;

[0092] S2, according to the direct mapping function, converting the set target droplet mass m into a target coil current;

[0093] S3, taking the target coil current as a control instruction, driving the current source to apply current to the proportional valve coil, thereby controlling and outputting droplets consistent with the target droplet mass.

[0094] The control instruction in S3 is to use a fuzzy PID control algorithm, taking the target coil current as input, and controlling the actual current applied to the coil to ensure that the piston of the proportional valve can quickly and stably reach the predetermined position.

[0095] The fuzzy PID control algorithm can adjust the proportional, integral and derivative parameters of the PID controller in real time according to the current error e and the current error change rate Δe, and the fuzzy PID control algorithm can be expressed as:

[0096]

[0097] Wherein, , and represent the proportional, integral and derivative gains respectively. The error e and its change rate Δe are selected as the input of the fuzzy PID controller. At the same time, the adjusted parameters , and are selected as the output, and are expressed as follows:

[0098]

[0099] Next, the crisp values are converted into fuzzy values through a fuzzification process, which is a part of fuzzy logic reasoning. The fuzzification of parameters is shown in Table 1, where NB, NM, NS, ZO, PS, PM and PB represent negative big, negative medium, negative small, zero, positive small, positive medium and positive big, respectively. For each fuzzy domain, seven fuzzy subsets are defined based on different input and output variables, and a Gaussian membership function is applied, as shown in Figure 5

[0100] where the horizontal axis is the universe of discourse, representing the range of all possible values of the input variable, which is normalized. The vertical axis is the membership degree, indicating the credibility of an exact input value (any point on the horizontal axis) belonging to a certain fuzzy linguistic set. The curve in the figure is a Gaussian function curve, which is one of the most commonly used shapes of membership functions.

[0101] Table 1: Determination of the universe of discourse and setting of fuzzy sets

[0102]

[0103] Then, according to the actual valve core characteristics and the desired control target, the fuzzy rule table of ΔKp, ΔKi and ΔKd is established, obtaining 49 fuzzy rules, as shown in Table 2.

[0104] Table 2: Fuzzy rules

[0105]

[0106] Finally, the PID controller effectively improves the response speed and positioning accuracy of the valve core by real-time correction of the three parameters, thereby ensuring the stable output of the droplet mass.

[0107] In order to verify the actual effect of the present application, the following experiments are carried out using 8 different types of raw materials, and the measured droplet mass obtained is shown in Figure 4 and Table 3. The results obtained all meet the set requirements, indicating that the present application can achieve the requirement of precisely controlling the droplet mass.

[0108] Table 3: Liquid materials and errors

[0109]

[0110] It should be noted that the parts in this embodiment that are the same as or similar to those in Embodiment 2 can be mutually referenced, and will not be described again in this application.​

Claims

1. A method for droplet mass control based on coil current, characterized in that, include: S1. Establish a direct mapping function from the target droplet mass m to the control variable coil current I; S2. Based on the direct mapping function, convert the set target droplet mass m into the target coil current; S3. Using the target coil current as a control command, drive the current source to apply current to the proportional valve coil, thereby controlling and outputting a droplet with the same mass as the target droplet.

2. The droplet mass control method based on coil current according to claim 1, characterized in that, S1 includes: S101. Establish a first theoretical model between valve core displacement x and coil current I. The first theoretical model is used to describe the coil current I required to drive the valve core to generate a specific displacement x under a given valve orifice pressure difference ΔP and liquid parameters. S102. Establish a second theoretical model between valve core displacement x and droplet mass m. The second theoretical model is used to describe the droplet mass m corresponding to a specific valve core displacement x under the given valve orifice pressure difference ΔP, liquid density ρ and valve operating frequency f. S103. Based on the first theoretical model and the second theoretical model, the direct mapping function is established by eliminating the intermediate variable valve core displacement x.

3. The droplet mass control method based on coil current according to claim 2, characterized in that, In S103, multiple sets of data pairs of droplet mass m and coil current I are obtained through the first theoretical model and the second theoretical model, and the direct mapping function is generated by curve fitting method.

4. The droplet mass control method based on coil current according to claim 3, characterized in that, In S103, the curve fitting method is rational cubic Bézier curve fitting.

5. The droplet mass control method based on coil current according to claim 4, characterized in that, In S3, a fuzzy PID control algorithm is used, taking the target coil current as input to control the actual current applied to the solenoid valve coil.

6. The droplet mass control method based on coil current according to claim 5, characterized in that, The fuzzy PID control algorithm adjusts the proportional, integral, and derivative parameters of the PID controller in real time based on the current error e and the rate of change of the current error Δe.

7. A droplet mass distribution device based on coil current, characterized in that, include: Storage cylinder, used to hold liquid to be dispensed; A pressure source, connected to the storage cylinder, is used to apply a preset pressure to the liquid inside the storage cylinder; A proportional valve, the inlet of which is connected to the outlet of the storage cylinder, is used for spraying liquid; The control module is configured to perform the method as described in any one of claims 1 to 6.

8. The droplet mass distribution device based on coil current according to claim 7, characterized in that, The control module includes an industrial computer and an industrial PLC; The industrial computer is configured to: provide a human-machine interface, receive a target droplet mass setting value, calculate the target coil current based on the direct mapping function, generate a target coil current command, and send the target coil current command to the industrial PLC; The industrial PLC is configured to receive the target coil current command from the industrial computer. The fuzzy PID control algorithm is executed to adjust the actual current applied to the proportional valve coil in real time so that it reaches the target coil current.

9. A computer storage medium, characterized in that, The computer storage medium stores a computer program; when the computer program is run on the computer, it causes the computer to perform the method described in any one of claims 1 to 6.

10. An electronic device, characterized in that, include: Memory, used to store computer programs; A processor for executing the computer program to implement the method as described in any one of claims 1 to 6.

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