Automatic Control Method and System for Outlet Moisture of a Stem Washing Machine Based on Bulk Density

Abstract

This invention discloses an automatic control method and system for the moisture content at the outlet of a tobacco stem washing machine based on bulk density. It effectively overcomes the industry's bias that bulk density parameters fluctuate greatly and are unsuitable as feedback for online control. By detecting the bulk density of tobacco stems at the outlet of the washing machine, it indirectly and accurately characterizes the true overall moisture content of the tobacco stems. The method includes: establishing a model of the correspondence between tobacco stem moisture content and bulk density and determining a setpoint for bulk density; collecting weight and volume data in real time using an electronic belt scale and a 3D scanner and calculating the real-time bulk density; calculating the deviation between the real-time bulk density and the setpoint; adjusting the opening of the dehumidification damper based on the deviation as a fine-tuning means to quickly remove surface moisture, and adjusting the operating frequency of the scraper conveyor as a coarse-tuning means to change the soaking time, forming a closed-loop control. The system includes a detection unit, a control unit, and an execution unit. This invention achieves accurate online detection and automatic coordinated control of the moisture content at the outlet of the tobacco stem washing machine, significantly improving the timeliness, stability, and accuracy of moisture control, and ensuring the processing quality of subsequent stem storage, shredding, and other processes.

Description

Technical Field

[0001] This invention relates to the field of automatic control technology for tobacco processing equipment, and more specifically, to a method and system for automatically controlling the moisture content at the outlet of a tobacco stalk washing machine based on online bulk density detection during the tobacco stalk pretreatment process. Background Technology

[0002] In the production of tobacco stems, the stem washing machine is the first step in the pretreatment of tobacco stems. Its core task is to heat and humidify the tobacco stems to increase their moisture content by 15% to 20% and remove impurities such as stones and mud. To promote uniform water absorption by the tobacco stems, the process requires the washing water temperature to typically reach above 60℃.

[0003] However, two main technical challenges exist in production: firstly, the water absorption characteristics of tobacco stems from different origins and batches vary significantly; secondly, a large amount of free water usually adheres to the surface of the tobacco stems at the outlet of the washing machine, resulting in a severe uneven distribution of moisture between the internal and surface of the stems. Traditional online infrared moisture meters can only detect surface moisture and cannot effectively penetrate the surface water layer to accurately reflect the true, overall moisture content of the tobacco stems.

[0004] For a long time, those skilled in the art have been dedicated to finding more direct methods for moisture detection, such as near-infrared and microwave technologies for control. However, due to interference from surface free water, accurate online detection has not been achieved. Although theoretically, changes in the moisture content of tobacco stems will cause changes in their bulk density (i.e., bulk specific gravity), due to factors such as the highly irregular shape of the tobacco stems at the outlet of the washing machine, the large amount of surface water, and the difficulty in real-time online volume measurement, there is a general technical bias in the field that the bulk specific gravity parameter fluctuates greatly and is subject to a lot of interference, making it unsuitable as the core feedback quantity of an online closed-loop control system.

[0005] Although an industry-provided control method for tobacco stem washing machines has been proposed, which uses a water turbidity sensor to determine whether the water quality exceeds the standard and controls water replacement accordingly, this solution only focuses on the water quality itself and does not involve the detection and control of moisture content at the tobacco stem outlet. In addition, existing technologies have also attempted to stabilize the water temperature of the stem washing machine by adding a compensating steam branch to the water supply pipeline and optimizing PID parameters, but these improvements have not solved the problem of online detection of the true moisture content at the tobacco stem outlet.

[0006] This has resulted in the tobacco stem washing machine being unable to automatically control the output moisture content of the tobacco stems based on key process indicators for a long time. Operators can only rely on experience to manually adjust the equipment parameters, resulting in low control accuracy and large lag, which seriously affects the processing quality and stability of subsequent processes such as stem storage and shredding.

[0007] Therefore, how to overcome the above-mentioned technical biases, achieve accurate online detection of the overall moisture content of tobacco stems at the outlet of the stem washing machine, and realize stable and reliable automatic control based on this is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0008] The purpose of this invention is to overcome the shortcomings of the prior art and provide an automatic control method and system for the moisture content of tobacco stems at the outlet of a tobacco stem washing machine based on bulk density. By detecting the bulk density of tobacco stems at the outlet of the tobacco stem washing machine online, and using this as an effective characterization parameter of the true moisture content of the tobacco stems, the soaking time and dehumidification intensity of the tobacco stem washing machine can be automatically and synergistically adjusted, thereby significantly improving the accuracy and stability of tobacco stem moisture control.

[0009] To achieve the above objectives, the present invention adopts the following technical solution:

[0010] The technical solution adopted in this invention is as follows:

[0011] This invention provides an automatic control method for outlet moisture of a straw washing machine based on bulk density, comprising the following steps:

[0012] Step 1: Before mass production, collect historical production data from multiple batches of tobacco stems for a specific brand. Install a high-precision online moisture meter at the outlet of the stem storage tank to detect the true moisture content of the tobacco stems after storage and equalization. Through data analysis, establish a model relating the true moisture content M of the tobacco stems for that brand to the bulk density ρ. Calculate the corresponding bulk density setpoint ρ based on the target moisture content required by the process standard. set .

[0013] Step Two: The weight data W of the tobacco stems on the conveyor belt is collected in real time using an electronic belt scale. The volume data V of the tobacco stem pile is obtained using a 3D scanner. The 3D scanner is installed directly above the electronic belt scale to scan the 3D outline of the tobacco stem pile passing through the scale and calculate its volume. The control system calculates the real-time pile density ρ = W / V based on the weight and volume data.

[0014] Step 3: The control unit compares the real-time bulk density ρ with the set value ρ set Compare and calculate the deviation Δρ = ρ - ρ set If Δρ>0, it indicates that the tobacco stem has absorbed too much water (overall moisture content is too high); if Δρ<0, it indicates that the tobacco stem has not absorbed enough water (overall moisture content is too low).

[0015] Step 4: The control unit generates the adjustment amount of the dehumidification damper opening and the adjustment amount of the scraper motor frequency based on the bulk density deviation Δρ. The two work together but have different functions:

[0016] When Δρ>0, it indicates that the overall moisture content of the tobacco stem is too high. Therefore, a coordinated instruction is generated to increase the opening of the dehumidification damper to enhance the surface moisture extraction (fine adjustment) and to increase the frequency of the scraper motor to shorten the soaking time, thereby reducing the amount of water absorbed from the source (coarse adjustment).

[0017] When Δρ < 0, a coordinated command is generated to reduce the opening of the exhaust damper and the frequency of the scraper motor.

[0018] Step 5: The execution unit adjusts the opening of the exhaust damper and the operating frequency of the scraper according to the instructions. Steps 2 to 4 are repeated to form a dynamic closed-loop control.

[0019] The principle behind the above control method is that the overall moisture content of tobacco stems is determined by two factors: soaking time (coarse adjustment) and the intensity of surface moisture removal (fine adjustment). The scraper speed determines the soaking time of the tobacco stems in the washing machine; the faster the speed, the shorter the dwell time and the less water absorbed. This is a coarse adjustment method to control the moisture content from the source. The dehumidification damper removes the moisture adhering to the surface of the tobacco stems through a strong airflow, which is a fine adjustment method to quickly correct instantaneous deviations. The two work together to ensure control accuracy and keep the dehumidification damper stable within its optimal operating range.

[0020] Furthermore, the present invention also provides an automatic control system for outlet moisture of a straw washing machine based on bulk density, comprising:

[0021] A detection unit, located at the outlet conveyor belt of the tobacco stem washing machine, is used to detect and output the bulk density value of the tobacco stems in real time. The detection unit includes an electronic belt scale for measuring the weight of the tobacco stems and a 3D scanner for measuring the volume of the tobacco stems. The 3D scanner is mounted directly above the electronic belt scale. The control unit calculates the real-time bulk density based on the weight and volume data.

[0022] The control unit is connected to the detection unit, receives the bulk density value, and generates control commands for the dehumidification damper and the scraper conveyor based on the preset bulk density setting value.

[0023] The execution unit includes a dehumidification damper actuator and a scraper conveyor motor frequency converter connected to the control unit. The dehumidification damper actuator adjusts the opening of the dehumidification damper according to the dehumidification control command to change the intensity of moisture removal from the surface of the tobacco stems; the scraper motor frequency converter adjusts the operating frequency of the conveying scraper according to the scraper control command to change the soaking time of the tobacco stems in the stem washing machine.

[0024] Preferably, the suction port corresponding to the dehumidification damper is installed between the inner layers of the outlet conveyor belt, close to the electronic belt scale, with the port facing the upper layer of the conveyor belt. Through gravity and airflow, it quickly removes moisture adhering to the surface of the tobacco stems on the conveyor belt. This configuration allows for the rapid removal of surface moisture by a strong airflow before the tobacco stems fall into the electronic belt scale for weighing and volume scanning, thereby improving the accuracy of subsequent bulk density detection.

[0025] Preferably, the scraper conveyor speed is adjusted using a proportional coefficient: F = k × F o Where F is the actual operating frequency, Fo The reference frequency is denoted by k, and the adjustment coefficient is denoted by k. The optimal coefficient is determined through analysis of historical batch data to maintain the average opening of the exhaust damper between approximately 40% and 60%, thus reserving sufficient adjustment margin to cope with sudden disturbances.

[0026] Preferably, the adjustment of the exhaust damper adopts an incremental PID control algorithm to achieve a fast and accurate response to instantaneous deviations.

[0027] Compared with existing technologies, the main design concept of this invention lies in overcoming the traditional technical prejudice that bulk density is unsuitable for online control. Through the coordinated operation of an electronic belt scale and a 3D scanner, accurate online measurement of the bulk density of tobacco stems at the outlet of a stalk washing machine with irregular shapes is achieved. Replacing traditional surface moisture detection with bulk density more accurately reflects the overall water absorption state of the tobacco stems, overcoming the fundamental limitation of infrared moisture meters, which can only detect surface moisture. In implementation, a dual-channel collaborative control architecture of scraper speed and exhaust damper is adopted. Specifically, the scraper speed is coarsely adjusted according to the deviation trend, changing the overall water absorption environment of the tobacco stems from the source; the exhaust damper is quickly and finely adjusted for instantaneous deviations, eliminating residual fluctuations. The two have clear division of labor and work together, ensuring control accuracy while keeping the actuators consistently within their optimal operating range. Furthermore, by establishing a correspondence between bulk density and moisture content through historical batch data, the system can automatically adapt to the differences in water absorption characteristics of different brands and batches of tobacco stems, without frequent manual intervention. Therefore, the precise control of the moisture content at the outlet of the tobacco stem washing machine is directly related to the processing quality of subsequent stem storage, shredding, and other processes. This invention can significantly improve the uniformity and stability of tobacco stem moisture content. Attached Figure Description

[0028] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described below with reference to the accompanying drawings, wherein:

[0029] Figure 1 A schematic diagram of the automatic control system for outlet moisture of a straw washing machine based on bulk density provided in an embodiment of the present invention;

[0030] Figure 2 This is a flowchart illustrating an automatic moisture control method for the outlet of a straw washing machine based on bulk density, provided in an embodiment of the present invention.

[0031] Explanation of reference numerals in the attached figures:

[0032] 100—Stalk washing machine; 101—Outlet conveyor belt; 201—Electronic belt scale; 202—3D scanner; 300—Control unit (PLC); 401—Damp exhaust damper; 402—Damp exhaust damper actuator; 403—Air intake; 501—Scraper conveyor; 502—Scraper motor frequency converter. Detailed Implementation

[0033] Embodiments of the present invention are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0034] In conjunction with the foregoing invention content, such as Figure 1 As shown, this embodiment provides an automatic control system for the outlet moisture of a tobacco stem washing machine based on bulk density. The tobacco stem washing machine 100 is used to heat and humidify tobacco stems. A detection unit is installed at the next stage after the outlet conveyor belt 101 of the tobacco stem washing machine 100. In this embodiment, the detection unit includes an electronic belt scale 201 for measuring the weight of the tobacco stems and a three-dimensional scanner 202 for measuring the volume of the tobacco stems. Specifically, the three-dimensional scanner 202 is installed directly above the electronic belt scale 201 and is used to scan the three-dimensional outline of the tobacco stem pile passing through the electronic belt scale 201 and calculate its volume. In actual operation, the three-dimensional scanner 202 can be a laser three-dimensional scanner or a structured light three-dimensional scanner, with the scanning frequency synchronized with the sampling frequency of the electronic belt scale 201 to ensure the consistency of weight and volume data over time.

[0035] The electronic belt scale 201 and the 3D scanner 202 transmit the real-time detected weight and volume signals to the control unit 300, such as a programmable logic controller (PLC), respectively.

[0036] The PLC internally stores the set value ρ of the bulk density of the tobacco stems for the current processing grade. set The PLC calculates the bulk density ρ=W / V in real time based on the received weight W and volume V, and then compares it with ρ set Compare them.

[0037] Based on the comparison results, the PLC sends instructions to the execution unit, which includes a dehumidification damper actuator 402 connected to the dehumidification damper 401 and a scraper motor frequency converter 502 connected to the motor of the scraper conveyor 501. The air intake 403 of the dehumidification damper 401 is preferably installed between the inner layers of the outlet conveyor belt 101, close to the electronic belt scale 201, with the air intake facing upwards, directly opposite the upper layer of the conveyor belt. This arrangement allows for the rapid removal of a large amount of free moisture adhering to the surface of the tobacco stems on the conveyor belt using gravity and strong airflow before the tobacco stems fall into the electronic belt scale 201 for weighing and volume scanning, thereby improving the accuracy of subsequent bulk density detection. Furthermore, the scraper conveyor 501 is located below the outlet conveyor belt 101, and its operating speed directly determines the soaking time of the tobacco stems in the stem washing machine 100: the faster the speed, the shorter the residence time, and the less water absorbed.

[0038] This embodiment, based on the aforementioned system, describes in detail its control method, which embodies the principle of coordinated control between scraper speed (coarse adjustment / feedforward) and exhaust damper (fine adjustment / feedback). Combined with... Figure 2 As shown, the method includes the following steps:

[0039] Step S1: Establish the model and calibrate the set values.

[0040] Before mass production, process engineers collected historical production data from 20 batches of tobacco stems for a specific brand (e.g., "Brand A"). Simultaneously, a high-precision online moisture meter was installed at the outlet of the stem storage tank to detect the true moisture content of the tobacco stems after storage and equalization. Data analysis revealed that when the moisture meter at the stem storage tank outlet showed a qualified moisture content of 38%, the corresponding bulk density at the stem washing machine outlet remained stable between 400 and 600 kg / m³. Through linear regression fitting, a model was established to correlate the true moisture content M of this brand of tobacco stems with the bulk density ρ: M = 0.06ρ + 8 (this is only an exemplary model; the actual model coefficients will vary depending on the raw materials). Based on the target moisture content of 38% required by the process standard, the corresponding bulk density setpoint ρ was calculated. set =500kg / m³, and input it into the PLC.

[0041] Step S2: Data acquisition and real-time heap weight calculation.

[0042] After the system is started, the PLC collects the weight signal W(t) of the electronic belt scale and the volume signal V(t) of the 3D scanner in real time at a frequency of 1 second / time, and calculates the real-time bulk density ρ(t) according to the formula ρ(t)=W(t) / V(t).

[0043] Step S3: Deviation judgment.

[0044] PLC calculation deviation Δρ=ρ(t)-500.

[0045] Step S4: Generation of collaborative control instructions (core logic).

[0046] The PLC takes the deviation Δρ as input and feeds it into two parallel but logically coordinated control branches, as detailed below:

[0047] Branch A: Scraper speed feedforward-feedback composite control (coarse adjustment)

[0048] First, based on historical data of the tobacco stems of this brand, a basic adjustment coefficient k is determined using an optimization algorithm (such as the least squares method). base The goal of this coefficient is to ensure that the average opening of the exhaust damper remains stable at around 50% under steady-state conditions, providing sufficient adjustment margin to cope with sudden disturbances. In this embodiment, k is calculated... base =1.0.

[0049] Then, feedback fine-tuning is performed based on the real-time deviation Δρ to obtain the final adjustment coefficient k=k base +α×Δρ. Where α is the fine-tuning gain coefficient, which is set to 0.01 in this embodiment.

[0050] The final frequency command output to the inverter is F = k × F o F o The reference frequency is 30Hz. For example, when Δρ=+5, k=1.0+0.01×5=1.05, F=1.05×30=31.5Hz, the scraper speed increases, the soaking time of the tobacco stem is shortened, thus reducing the amount of water absorbed from the source.

[0051] Branch B: PID feedback control of the exhaust damper (fine-tuning)

[0052] For the control of the exhaust damper, an incremental PID control algorithm is used. The target opening increment ΔV target =K_p×(Δρ(t)-Δρ(t-1))+K i ×Δρ(t)+K d ×(Δρ(t)-2Δρ(t-1)+Δρ(t-2)). In this embodiment, K is taken through engineering tuning. p =2.0, K i =0.5, K d =0.1. Final target opening V target =V current +ΔV target .

[0053] For example, when Δρ=+5, the PID controller calculates a positive opening increment, and the PLC opens the exhaust damper through the actuator to enhance the suction of surface moisture and quickly reduce the surface moisture of the tobacco stem to correct the instantaneous deviation.

[0054] Step S5: Execution and closed-loop feedback.

[0055] The frequency converter adjusts the speed of the scraper conveyor according to the frequency command F. The actuator adjusts the speed according to the target opening V. target Adjust the opening of the exhaust damper.

[0056] After the system completes one round of adjustment, it returns to step S2 to continue collecting new data, thereby achieving dynamic and continuous closed-loop automatic control.

[0057] Through the aforementioned collaborative control method, the scraper speed is coarsely adjusted based on the deviation trend, altering the overall water absorption environment of the tobacco stem (feedforward effect); while the dehumidification damper performs rapid fine-tuning of the instantaneous deviation, eliminating residual fluctuations (feedback effect). The combined action of these two mechanisms not only ensures control accuracy but also keeps the dehumidification damper consistently within its optimal operating range of approximately 50%, preserving ample adjustment margin to handle sudden disturbances. This is precisely where the non-obviousness and inventiveness of the control logic of this invention lie.

[0058] In this invention, when directional terms are mentioned, they are relative concepts based on the embodiments. Furthermore, "at least one" refers to one or more, and "more than one" refers to two or more. "And / or" describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent the existence of A alone, A and B simultaneously, or B alone. A and B can be singular or plural. The character " / " generally indicates that the preceding and following related objects have an "or" relationship. "At least one of the following" and similar expressions refer to any combination of these items, including any combination of single or plural items. For example, at least one of a, b, and c can represent: a, b, c, a and b, a and c, b and c, or a and b and c, where a, b, and c can be single or multiple.

[0059] The above description of the structure, features, and effects of the present invention is based on the embodiments shown in the figures. However, the above are only preferred embodiments of the present invention. It should be noted that the technical features involved in the above embodiments and their preferred methods can be reasonably combined and matched by those skilled in the art to form a variety of equivalent solutions without departing from or changing the design concept and technical effects of the present invention. Therefore, the present invention is not limited to the scope of implementation shown in the figures. Any changes made in accordance with the concept of the present invention, or modifications to equivalent embodiments, that do not exceed the spirit covered by the specification and figures, should be within the protection scope of the present invention.

Claims

1. A method for automatic control of outlet moisture content of a straw washing machine based on bulk density, characterized in that, include: Step 1: Establish a model relating tobacco stem moisture content to bulk density, and determine the setpoint ρ for bulk density based on the standard moisture content. set ; Step 2: Collect real-time data on the weight W and accumulated volume V of the tobacco stems on the conveyor belt at the outlet of the tobacco stem washing machine; Step 3: Calculate the real-time bulk density ρ = W / V based on the weight data W and volume data V; Step 4: Calculate the real-time bulk density ρ and the set bulk density ρ. set The deviation Δρ=ρ-ρ set ; Step 5: Generate coordinated control commands based on the deviation Δρ: When Δρ > 0, increase the opening of the exhaust damper to enhance surface moisture extraction, and at the same time increase the operating frequency of the scraper conveyor to shorten the soaking time of the tobacco stems; when Δρ < 0, decrease the opening of the exhaust damper, and at the same time decrease the operating frequency of the scraper conveyor. Step 6: Execute the cooperative control command and repeat steps 2 to 5 to form a dynamic closed-loop control.

2. The automatic control method for outlet moisture of a straw washing machine based on bulk density according to claim 1, characterized in that, In step five, the operating frequency of the scraper conveyor is adjusted using a proportional coefficient: F = k × F o Where F is the actual operating frequency, F o The reference frequency is k, and the adjustment coefficient is k = k base +α×Δρ, where k base α is the base adjustment coefficient, and α is the fine-tuning gain coefficient.

3. The automatic control method for outlet moisture of a straw washing machine based on bulk density according to claim 1, characterized in that, The method for establishing the correspondence model between the moisture content of tobacco stems and the bulk density in step one is as follows: statistically analyze the historical production data of tobacco stems of the same brand from multiple batches, install an online moisture meter at the outlet of the tobacco stem storage cabinet to obtain the true moisture content of the tobacco stems after storage and equalization, and establish the correspondence between the true moisture content and the bulk density at the outlet of the tobacco washing machine.

4. The automatic control method for outlet moisture of a straw washing machine based on bulk density according to claim 1, characterized in that, The adjustment of the exhaust damper in step five adopts an incremental PID control algorithm, with a target opening increment ΔV. target =K p × (Δρ(t) - Δρ(t-1)) + K i × Δρ(t) + K d × (Δρ(t) - 2Δρ(t-1) + Δρ(t-2)).

5. The automatic control method for outlet moisture of a straw washing machine based on bulk density according to claim 1, characterized in that, The accumulated volume data mentioned in step two is obtained by a 3D scanner, which is installed directly above the electronic belt scale and is used to scan the 3D outline of the tobacco stalk pile on the conveyor belt and calculate its volume.

6. An automatic control system for the outlet moisture of a stem washing machine based on bulk density, implementing the automatic control method for outlet moisture of a stem washing machine according to any one of claims 1 to 5, characterized in that, include: The detection unit, located at the outlet conveyor belt of the tobacco stem washing machine, includes an electronic belt scale for measuring the weight of tobacco stems and a three-dimensional scanner for measuring the volume of tobacco stem accumulation. The control unit is connected to the detection unit, receives weight signals and volume signals and calculates real-time bulk density, and generates dehumidification damper control commands and scraper conveyor control commands based on the preset bulk density setting value. The execution unit includes a dehumidification damper actuator and a scraper conveyor motor frequency converter connected to the control unit. The dehumidification damper actuator adjusts the opening of the dehumidification damper according to the dehumidification control command, and the scraper motor frequency converter adjusts the operating frequency of the conveying scraper according to the scraper control command.

7. The automatic control system for outlet moisture of a straw washing machine based on bulk density according to claim 6, characterized in that, The air intake corresponding to the dehumidification damper is installed between the inner layers of the outlet conveyor belt, close to the electronic belt scale, with the air intake facing the upper layer of the conveyor belt. It quickly removes the moisture adhering to the surface of the tobacco stems on the conveyor belt through gravity and airflow.

8. The automatic control system for outlet moisture of a straw washing machine based on bulk density according to claim 6, characterized in that, The 3D scanner is a laser 3D scanner or a structured light 3D scanner, installed directly above the electronic belt scale, with a scanning frequency synchronized with the sampling frequency of the electronic belt scale.

9. The automatic control system for outlet moisture of a straw washing machine based on bulk density according to claim 6, characterized in that, The control unit is a programmable logic controller, which internally stores the set value of the bulk density corresponding to the current grade of tobacco stems being processed, and runs a proportional regulation algorithm and a PID regulation algorithm to control the frequency of the scraper conveyor and the opening of the dehumidification damper, respectively.

10. The automatic control system for outlet moisture of a straw washing machine based on bulk density according to claim 9, characterized in that, The frequency control of the scraper conveyor adopts a feedforward-feedback composite control method, wherein the basic adjustment coefficient k base Based on historical data, the average opening of the exhaust damper is optimized to maintain it between 40% and 60%, and the feedback fine-tuning gain α is corrected according to the real-time deviation.

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