Solution adding control method for solution preparation and solution preparation system

Abstract

The invention relates to a solution adding control method for solution preparation and a solution preparation system. According to the method, the liquid adding process is divided into a constant-speed liquid adding stage and a decelerating liquid adding stage, liquid adding is conducted at a constant speed in the constant-speed liquid adding stage, when liquid adding stage conversion conditions are met, the decelerating liquid adding stage is started, and the liquid adding rate of the decelerating liquid adding stage is calculated and determined according to a set decelerating control formula. And controlling the liquid adding rate by adopting the calculated and determined liquid adding rate. The system comprises a container, a speed regulating pump, a liquid guide pipe and a control module, a liquid outlet of the speed regulating pump is connected with the container through the liquid guide pipe, and the control module adopts the method to control the flow of the speed regulating pump. According to the invention, the optimal control of the whole liquid adding process can be realized, and the stability of the liquid adding process and the liquid adding accuracy are improved.

Description

Technical Field

[0001] The present invention relates to a solution preparation liquid addition control method and a solution preparation system adopting this liquid addition control method, belonging to the technical field of solution preparation. Background Art

[0002] Liquid quantitative filling technology is widely used in various current production and living fields, such as food processing, petroleum, pesticides, pharmacology, biochemistry, materials, medicine, environmental protection and other industries. Especially in the fields of pharmacology, biochemistry, medicine, and environmental protection, due to the strict requirements for the proportion of substance components, new challenges are posed to the automation, accuracy, and robustness of the filling process.

[0003] Traditional filling and solution preparation technologies, the filling or solution preparation process mainly focuses on the start and end times and results of filling or solution preparation. The control mode usually uses the signal stop control of reaching the liquid addition amount or the running time control to complete the quantitative liquid addition of the solvent. For example, the invention patent with the publication number CN115869842A discloses a liquid addition control method, system, medium, control device and wire cutting machine. The liquid addition control method includes: controlling the water addition component to add water to the mixing container; controlling the stock solution supply component to add the stock solution to the stock solution weighing component, and the stock solution weighing component to add the stock solution to the mixing container, and determining the actual liquid addition amount in the stock solution weighing component. When the actual water addition amount reaches the target water addition amount and the actual liquid addition amount reaches the target liquid addition amount, obtain the stock solution concentration, and finish the liquid addition when the stock solution concentration is within the preset concentration range. The above liquid addition control method realizes the automatic liquid addition and preparation of the cutting fluid, reduces the labor cost, improves the automation degree of liquid addition, and solves the problems of high labor cost and large concentration deviation in manual preparation of cutting fluid in the prior art. Another example, the utility model patent with the publication number CN217006602U discloses a high-precision standard solution preparation device applicable to water quality monitoring, including a high-standard mother liquor weighing system. The high-standard mother liquor weighing system includes a peristaltic pump, a liquid storage ring, a first liquid level gauge and a first three-way valve. The multi-port of the first three-way valve is connected to the liquid inlet of the first liquid level gauge. The liquid outlet of the first liquid level gauge is connected to the liquid inlet of the liquid storage ring. The liquid outlet of the liquid storage ring is connected to the pump head of the peristaltic pump. The first single-port of the first three-way valve is connected to the high-standard mother liquor bottle. The second single-port of the first three-way valve is connected to the standard solution reagent bottle. The high-precision standard solution preparation device applicable to water quality monitoring also includes a distilled water weighing system. The distilled water weighing system includes a diaphragm pump, a pulse flowmeter and a second three-way valve. This preparation device can accurately quantify the high-standard mother liquor and the distilled water required for diluting the high-standard mother liquor, so as to realize the rapid and accurate automatic preparation of standard solutions with any concentration. The repeatability and accuracy of standard solution preparation are good. The above technologies have their own characteristics and are respectively applicable to their respective suitable occasions. However, the above technologies are all prone to large errors between the actual liquid addition amount and the expectation due to uneven flow rate or large cut-off point flow rate during the liquid addition process. Due to the lack of effective control of the intermediate process of liquid addition, it is easy to cause the filling or solution preparation process to end too early or too late, resulting in inaccurate quantitative results. Summary of the Invention

[0004] To overcome the above defects of the prior art, the present invention provides a solution preparation liquid addition control method and a solution preparation system to realize the optimized control of the whole liquid addition process.

[0005] The technical solution of the present invention to achieve the above object is: for the solution preparation liquid addition control method, when approaching the expected value of the liquid addition amount, gradually reduce the liquid addition rate.

[0006] Preferably, the liquid addition process is divided into a constant-speed liquid addition stage and a decelerating liquid addition stage. During the constant-speed liquid addition stage, liquid is added at a constant speed. When the liquid addition stage conversion condition is reached, the decelerating liquid addition stage is entered. During the decelerating liquid addition stage, the liquid addition rate is gradually decreased.

[0007] Preferably, the liquid addition stage conversion condition is that the liquid addition amount reaches 70% of the expected liquid addition value.

[0008] Preferably, the liquid addition rate in the decelerating liquid addition stage is calculated and determined according to the following deceleration control formula, and the liquid addition rate control is implemented using the calculated liquid addition rate:

[0009]

[0010] where is the liquid addition rate at time t; x0 is the initial value of the remaining liquid addition amount; is the initial liquid addition rate; k is a constant parameter; t is the time, with an initial value of 0.

[0011] Preferably, the value range of k is [0.3, 0.4].

[0012] Preferably, during the decelerating liquid addition stage, at regular intervals, taking this moment as the initial moment, according to the real-time remaining liquid addition amount and real-time liquid addition rate at this moment, the subsequent real-time liquid addition rate is recalculated and determined according to the deceleration control formula.

[0013] The liquid addition rate can be controlled by controlling a speed-regulating pump (or regulating pump) so that its output rate is the required liquid addition rate, and the specific control method is based on the setting of the speed-regulating pump.

[0014] Preferably, the following model is used to predict the control quantity of the speed-regulating pump:

[0015]

[0016] where J is the objective function, used to describe the heuristic value that the system needs to minimize; β is the weight factor, used to characterize the influence degree of the state residual and input quantity on the system during the system optimization process; r(t) is the input value of the controlled quantity at time t; y(t) is the feedback signal; u(t) is the control signal;

[0017] Taking the prediction result as the control signal, control the liquid addition of the speed-regulating pump.

[0018] Preferably, during the liquid addition process, the liquid addition amount is measured in real time. The liquid addition amount can also be indirectly measured by measuring the amount of solution in the preparation container.

[0019] The solution preparation system includes a container, a speed control pump, a liquid guiding pipe, and a control module. The liquid outlet of the speed control pump is connected to the container through the liquid guiding pipe, and the control module controls the flow rate of the speed control pump by implementing any one of the solution preparation liquid addition control methods disclosed in the present invention.

[0020] Preferably, the solution preparation system further includes a detection module and a cut-off valve. The detection module is used to continuously detect the liquid addition amount during the entire liquid addition process or the amount of solution in the container. The detection module can adopt a monocular vision system or a weighing system. The cut-off valve is used to control the start and stop of the liquid addition process, usually controlling the start and stop of the speed control pump. The cut-off valve can adopt an electromagnetic valve.

[0021] Preferably, the liquid guiding pipe adopts an elastic hose, such as a rubber hose.

[0022] The beneficial effects of the present invention are as follows: By changing the liquid addition rate in the later stage of liquid addition, the present invention can slow down the liquid addition rate in the final stage of liquid addition (when the liquid addition amount is close to the expected value) to near zero speed, avoiding errors caused by the activation delay (activation delay of the cut-off valve) when the speed control pump shuts down, and realizing the optimized control of the liquid addition rate and the liquid addition rate change rate in the entire liquid addition process. The liquid addition rate and the rate change rate gradually decrease according to the set optimized curve, improving the smoothness of the liquid addition process and the accuracy of liquid addition. Description of the Drawings

[0023] Figure 1 is a schematic diagram of the control flow in the decelerated liquid addition stage of the present invention;

[0024] Figure 2 is a curve graph of the rate change at different k values in the decelerated liquid addition stage of the present invention;

[0025] Figure 3 is a curve graph of the rate change rate change at different k values in the decelerated liquid addition stage of the present invention;

[0026] Figure 4 is a schematic diagram of the control principle of the speed control pump involved in the present invention. Detailed Embodiments

[0027] See Figures 1-4 , the present invention discloses a solution preparation liquid addition control method. When approaching the expected liquid addition amount, the liquid addition rate is gradually reduced so that the liquid addition rate in the final stage of liquid addition (when the liquid addition amount is close to the expected value) is slowed down to near zero speed, avoiding errors caused by the activation delay of the equipment when stopping liquid addition, and realizing the optimized control of the liquid addition rate in the entire liquid addition process. Effectively improving the smoothness of the liquid addition process and the accuracy of liquid addition while taking into account time consumption / time constraints.

[0028] Specifically, it includes the following steps / content:

[0029] 1. Construct a solution preparation system

[0030] The solution preparation system includes a container, a speed regulating pump, a liquid guiding pipe, a control module, a detection module and a stop valve. The liquid outlet of the speed regulating pump is connected to the container through the liquid guiding pipe. Controlling the flow rate (liquid addition rate) during the liquid quantitative filling process or solution preparation process is essentially controlling the actual operating rate of the speed regulating pump. The control module is used to control the liquid addition of the speed regulating pump, mainly execute the processing of detection data and the operation of control algorithms, and generate a speed regulating signal to output to the speed regulating pump. The control module can adopt an ARM control chip. The detection module is used to continuously measure the liquid addition amount during the entire liquid addition process or the solution amount in the container, and output the measurement result to the control module. The detection module can adopt a monocular vision system or a weighing system. The container preferably adopts a transparent / translucent container, which is convenient for detecting and observing the liquid addition amount, and its sealing performance can be set according to the usage requirements and usage scenarios. The liquid guiding pipe usually adopts an elastic hose, such as a rubber hose. The stop valve is used to control the start and stop of the liquid addition process, usually control the start and stop of the speed regulating pump. The stop valve can adopt an electromagnetic valve, and the electromagnetic valve can adopt a multi-way switch type according to actual needs to realize multiple functions such as multi-way liquid inlet and cleaning and draining.

[0031] 2. Define the uniform liquid addition stage and the decelerating liquid addition stage of the liquid addition process, and set the liquid addition stage conversion conditions

[0032] When the liquid addition process starts, the stop valve connects the liquid addition circuit, and the speed regulating pump starts to work until the liquid addition amount reaches the expected value, and then the speed regulating pump stops working.

[0033] In the middle stage of the liquid addition process, since the actual liquid addition volume is far from the expected liquid addition value, the liquid can be added at a constant speed according to the common speed of the speed control pump, which is defined as the constant speed liquid addition stage; in the later stage of the liquid addition process, the flow rate of the speed control pump is gradually reduced, and the actual liquid addition rate is steadily reduced, while taking into account the time constraint to avoid the influence of a long-term low-speed liquid addition process on the solution preparation effect, which is defined as the deceleration liquid addition stage. Assuming that the speed control pump reduces the liquid addition speed with a constant acceleration and a final speed of zero, the time required to introduce an equal amount of reagent (to be added) in the deceleration liquid addition stage is twice that of the constant speed liquid addition strategy. In order to ensure that the additional time loss caused by deceleration liquid addition does not exceed 15% of the original time loss, the liquid addition stage conversion condition is set at the moment when "the liquid addition volume reaches 70% of the expected liquid addition value (total expected liquid addition volume)". It is also possible to set the liquid addition stage conversion condition at the moment when the liquid addition volume reaches other percentages of the expected liquid addition value according to the actual solution preparation situation (for example, fully considering the influence of deceleration liquid addition on the solution preparation effect). Splitting the liquid addition process into a constant speed liquid addition stage and a deceleration liquid addition stage according to the principle of less time loss based on the liquid addition conversion condition can reduce the cut-off liquid addition rate when the liquid addition volume is close to the expected liquid addition value, effectively reduce the liquid addition error, and improve the accuracy of liquid addition.

[0034] During the liquid addition process, the liquid addition volume or the solution volume is measured in real time to determine whether the liquid addition is completed. If the liquid addition is completed, the cut-off valve is closed and the liquid addition ends. If the liquid addition is not completed, it is determined whether the current moment meets the liquid addition stage conversion condition. If the liquid addition stage conversion condition is not met, the constant speed liquid addition is maintained. If the liquid addition stage conversion condition is met, the liquid addition is switched from the constant speed liquid addition stage to the deceleration liquid addition stage, and step three is executed. The determination process can be performed by the control module.

[0035] III. Calculate the expected change process of the liquid addition rate based on the deceleration control formula

[0036] In the later stage of liquid addition (deceleration liquid addition stage), the liquid addition rate (flow rate) is calculated and determined according to the deceleration control formula. The deceleration control formula is:

[0037]

[0038] In the formula, k is a constant parameter; t is time, which can be used to mark the current moment and any other moment. The initial value of t (the value at the initial moment when implementing the rate control according to the deceleration control formula) t0 is set to 0, x(t) is the remaining liquid addition volume, which is the difference between the completed liquid addition volume (or the existing liquid volume in the container) and the target liquid addition volume (completed liquid addition volume - target liquid addition volume). It is negative during the liquid addition process (referring to the deceleration liquid addition stage of the liquid addition process, the same below) and zero at the end of the liquid addition. x0 is the initial value of x(t), x · (t) is the liquid addition rate, which is positive during the liquid addition process and zero at the end of the liquid addition. x · 0 is x· (t) is the initial value, and \(\ddot{x}(t)\) is the time derivative of the liquid addition rate, or the liquid addition acceleration rate, which is negative during the liquid addition process and zero at the end of the liquid addition.

[0039] Based on the deceleration control formula, we can obtain:

[0040]

[0041] Furthermore, we can know that:

[0042] (1) When \(k\leq0\), the system will reach a steady state as \(t\rightarrow\infty\), and at this time

[0043] (2) When \(0 < k < 0.5\), it will reach the final state within a finite time, and the corresponding time is

[0044] (3) When \(0.5\leq k < 1\), the system will reach the final state at time \(T\), at this time \(x(T)=0\) and but is not zero. When \(k = 0.5\), the system corresponds to a uniformly decelerated motion, and the final state acceleration value remains constant; when \(0.5 < k < 1\), a divergent situation will occur, but in practice, it is restricted by the shutdown state of the speed control valve, which does not affect the final state and the final speed returning to zero;

[0045] (4) When \(k\geq1\), the closing speed of the system state will continuously increase, and there will be a large contact speed at the final state.

[0046] Based on the above analysis and according to practical experience, when \(k\) takes values in the range of \(0.3\) to \(0.4\) (including the end values), the system will have a short low-speed operation time, ensuring the time-saving nature of actual liquid addition (as shown in Figure 2 and Figure 3 ), and better realizing the optimization of the control process / liquid addition process.

[0047] In actual use, due to the existence of measurement errors and control errors, during the actual deceleration control process, it should be recalculated every once in a while (preferably at fixed intervals), and this time node should be used as the new starting moment, and the subsequent control rate should be calculated based on the deceleration control formula and the newly established initial values.

[0048] If it is required that the system add liquid at a non-zero low speed through the cut-off point (the moment when the liquid addition amount reaches the expected value), the initial state value \(x_0\) can be appropriately adjusted to place the theoretical cut-off point after the actual cut-off point.

[0049] IV. Calculate the model predictive control quantity of the speed control pump according to the rate tracking expected value

[0050] After calculating and determining x according to the deceleration control formula · (t), the speed parameter at time t is obtained. If the speed control pump can directly implement flow control, this signal can be used as the input to control the working state of the speed control pump; if the speed control pump needs to adjust the outlet speed, the outlet speed to be controlled can also be determined according to x · (t), and the corresponding outlet speed is used as the output to control the working state of the speed control pump. For flow control, the conversion relationship between flow and outlet speed (flow velocity) is:

[0051]

[0052] In the formula, x · (t) is the liquid addition rate, d is the outlet aperture, and v(t) is the outlet speed.

[0053] Since the expected flow or speed control process has good local smoothness, model predictive control can be used to calculate the actual control quantity of the speed control pump. For the single-time-point state tracking problem of a single pump, it belongs to a single-input single-output problem. Denote the input value of the controlled quantity at time t as r(t), the feedback signal as y(t), and the control signal as u(t). The control system block diagram is as shown in Figure 4 . Then the optimal control process is equivalent to solving the most suitable u(t) so that the control quantity at the next moment satisfies the optimal tracking of the change trajectory of the control quantity within the local time window of the current moment and the previous moments. The optimization function to be solved can be defined as:

[0054]

[0055] In the formula, J is the objective function, which is used to describe the heuristic value that the system needs to perform minimization search. β is the weight factor, which is used to characterize the influence degree of the state residual and the input quantity on the system during the system optimization process, and the default value is 0.5. For the objective function, this function is optimized and solved by the least square method, that is, the optimized control quantity input at time t + 1 is obtained, and this control quantity is used as the control signal to control the liquid addition of the speed control pump until the liquid addition is completed.

[0056] All the preferred and optional technical means disclosed in the present invention, except as otherwise specified and unless one preferred or optional technical means is a further limitation of another technical means, can be arbitrarily combined to form several different technical solutions.

Claims

1. A solution preparation and liquid addition control method, characterized in that When approaching the expected value of the added liquid amount, gradually reduce the addition rate.

2. The solution preparation and liquid addition control method according to claim 1, characterized in that The liquid adding process is divided into a uniform liquid adding stage and a deceleration liquid adding stage. In the uniform liquid adding stage, liquid adding is performed at a uniform speed. When the liquid adding stage conversion condition is reached, the deceleration liquid adding stage is entered. In the deceleration liquid adding stage, the liquid adding rate is gradually reduced.

3. The solution preparation and liquid addition control method according to claim 2, characterized in that The switching condition of the liquid adding stage is that the liquid adding amount reaches 70% of the expected liquid adding value.

4. The solution preparation and liquid addition control method according to claim 2, characterized in that The liquid adding rate in the deceleration and liquid adding stage is calculated and determined according to the following deceleration control formula, and the liquid adding rate is controlled by using the calculated liquid adding rate: in, is the liquid addition rate at time t; x0 is the initial value of the liquid addition margin; is the initial value of the liquid addition rate; k is a constant parameter; t is the time, and its initial value is 0.

5. The solution preparation and liquid addition control method according to claim 4, characterized in that The value range of k is [0.3,0.4].

6. The solution preparation and liquid addition control method according to claim 5, characterized in that In the deceleration and liquid addition stage, at a certain interval, the moment is taken as the initial moment, and the subsequent real-time liquid addition rate is recalculated and determined according to the deceleration control formula based on the real-time liquid addition surplus and the real-time liquid addition rate at that moment.

7. The solution preparation and liquid addition control method according to claim 6, characterized in that The liquid addition rate is controlled by controlling the speed regulating pump.

8. The solution preparation and liquid addition control method according to claim 7, characterized in that The following model is used to predict the control amount of the speed regulating pump, and the prediction result is used as a control signal to control the speed regulating pump to add liquid: Among them, J is the objective function, which is used to describe the heuristic value that the system needs to minimize and search for; β is the weight factor, which is used to characterize the influence of the state residual and input on the system during the system optimization process; r(t) is the input value of the controlled quantity at time t; y(t) is the feedback signal; and u(t) is the control signal.

9. The solution preparation and liquid addition control method according to claim 1, characterized in that During the liquid adding process, the amount of liquid added is measured in real time.

10. Solution preparation system, characterized in that It comprises a container, a speed regulating pump, a liquid guiding tube and a control module, wherein the liquid outlet of the speed regulating pump is connected to the container via the liquid guiding tube, and the control module implements flow control of the speed regulating pump by using the solution preparation and liquid addition control method according to any one of claims 1 to 9.

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