Helical blade grading positioning method based on position characteristic quantity threshold value method

Abstract

The invention provides a helical blade grading positioning method based on a position characteristic quantity threshold value method, which adopts a capacitive sensor, uniformly arranges n electrodes on the periphery of an insulating pipeline, and comprises the following steps of: dividing the circumference into n rotational symmetry periods at equal intervals; obtaining the numerical relationship between the position of the helical blade and the capacitance measurement value of each electrode through simulation or test; primary positioning: determining which rotational symmetry period the helical blade is in, and judging the partition of the helical blade in the rotational symmetry period; performing secondary positioning; third-stage positioning: according to the second-stage positioning result, determining the number of the measured value of the adjacent electrode pair closest to the helical blade and the number of the measured value of the adjacent electrode pair closer to the helical blade; taking the ratio M of the normalized measured values of the nearest and second nearest adjacent electrode pairs as a third-level positioning characteristic quantity; and a third-level positioning threshold value is determined, and the angle of the spiral blade is determined according to the relation between M and the third-level positioning threshold value.

Description

A hierarchical positioning method for spiral blades based on position feature thresholding. Technical Field

[0001] This invention belongs to the field of detection related to spiral conveying processes. It utilizes capacitance tomography to monitor spiral conveying processes and relates to a spiral blade hierarchical positioning method based on the spiral blade position feature threshold method. Background Technology

[0002] Electrical Capacitance Tomography (ECT) is a non-invasive imaging technique that uses an array of electrodes to measure changes in dielectric constant. By applying an excitation signal to the excitation electrode, the induced voltage or charge at the remaining electrodes is measured to obtain the corresponding capacitance value. The sensitivity matrix of ECT quantifies the influence of the unit change in dielectric constant of each discrete unit in the measured area on the capacitance measurement value of each electrode by matrix elements, and establishes a quantitative mapping relationship between dielectric constant distribution and capacitance measurement data. In ECT, the perturbation method to solve the sensitivity matrix is ​​a direct and intuitive numerical method. Its core idea is to apply a small perturbation to the dielectric constant of the discrete unit in the measured area, calculate the change in the corresponding capacitance measurement value, and thus approximate the elements of the sensitivity matrix. Based on the capacitance measurement value and the sensitivity matrix, the change in dielectric constant distribution can be inferred [1]. ECT is particularly suitable for detecting the internal structure of non-conductive multiphase flow. However, recent studies have found that ECT technology can detect metals in sensitive fields [2][3][4]. At the same time, this technology has also been tried to be applied to the monitoring of spiral conveying process [5], showing the application value of ECT in the field of dielectric detection in the background of grounded metal.

[0003] The central spiral structure of the screw conveyor is a spiral blade, as shown in Figure 1(a), which is made of metal and grounded. Currently, our team has achieved static imaging of the screw conveyor based on effective data and prior flow pattern information using ECT, under the premise of knowing the position of the spiral blade [5]. That is, imaging when the spiral blade is not rotating, where the effective data is the measurement value of the non-adjacent electrode pairs on both sides of the spiral blade, and the prior flow pattern information is the inherent characteristic information of the flow pattern during the screw conveyor process. However, ECT still faces the problem of difficulty in achieving dynamic imaging in the actual process of detecting the screw conveyor. Its key technical bottleneck is the unknown position of the spiral blade. Affected by the change in the speed of the screw conveyor, it is difficult to determine the real-time position of the spiral blade based on the initial position, speed and other initial information of the spiral blade. This seriously restricts the real-time performance and reliability of ECT detection of the screw conveyor process.

[0004] Therefore, determining the position of the helical blades during the helical transport process based on ECT detection is a technical challenge that urgently needs to be solved in realizing dynamic imaging of helical transport in ECT detection.

[0005] Related literature [1]. X. Li et al., "A strategy to screen capacitances of adverse effects on image reconstruction for ECT sensors mounted outside thick pipe wall," Measurement, vol. 245, 2025, Art. no. 116645. [2]. M. A. Abdelrahman, A. Gupta, and W. A. Deabes, "A feature-based solution to forward problem in electrical capacitance tomography of conductive materials," IEEE Trans. Instrum. Meas., vol. 60, no. 2, pp. 430-441, 2011. [3]. M. Zhang, Y. Xu, and M. Soleimani, "Quantitative reconstruction of the exterior boundary shape of metallic inclusions using electrical capacitance tomography," IEEE Sens. J., vol. 17, no. 24, pp. 8263-8270, 2017. [4]. E. Al Hosani, M. Zhang, J. Abascal, and M. Soleimani, "Imaging metallic samples using electrical capacitance tomography: forward modelling and reconstruction algorithms," Meas. Sci. Technol., vol. 27, no. 11, 2016, Art. no. 115402. [5]. J. Ye, X. Ji, J. Wang, Y. She, C. Wang and W.Yang, "ECT ImageReconstruction With Selection of Valid Data and Prior Flow Information," IEEETrans. Instrum. Meas., vol. 74, pp. 1-12, Art no. 4515012, 2025. Summary of the Invention

[0006] The purpose of this invention is to propose a hierarchical positioning method for helical blades based on a threshold method for helical blade position feature quantities. This method first analyzes the measurements between electrode pairs and extracts primary positioning feature quantities based on the measurements from a single-frame ECT (Electronic Tolerance) image to achieve primary positioning of the helical blade. Then, based on the primary positioning results, electrodes near the helical blade are identified, and secondary positioning feature quantities are extracted to achieve secondary positioning of the helical blade. Finally, based on the secondary positioning results, the nearest and second-nearest adjacent electrode pairs to the helical blade are determined, and tertiary positioning feature quantities are extracted to achieve the final positioning of the helical blade.

[0007] To achieve the above objectives, this invention employs the following technical solution: a hierarchical positioning method for spiral blades based on a position feature threshold method. This method utilizes a capacitance sensor, with n electrodes evenly arranged around the outer circumference of an insulated pipe. The insulated pipe is located inside a spiral conveying pipe, and the spiral blade is grounded and positioned at the center of the conveying pipe. Capacitance measurement between electrode pairs is achieved through a capacitance measurement circuit. The hierarchical positioning of the spiral blade includes the following steps: dividing the circumference into n rotationally symmetric periods at equal intervals; determining the positioning scale of the spiral blade considering the spiral blade rotation speed; obtaining the numerical relationship between the position of the spiral blade and the capacitance measurement values ​​of each electrode through simulation or experiment; and a first-level positioning step: extracting the electrode numbers of each adjacent electrode pair whose capacitance measurement values ​​are less than their overall average; determining, based on the prior correspondence between the electrode numbers and the spiral blade position, which rotationally symmetric period the spiral blade is in, and determining its partition within this corresponding rotational period—whether it is in the upper or lower partition. Secondary positioning steps: Further subdivide the rotationally symmetric period into the first interval, second interval, third interval and fourth interval. Determine the adjacent electrode pairs for secondary positioning according to the partition where the helical blade is located. Use the ratio of normalized measurement values ​​of adjacent electrode pairs for secondary positioning, P, as the secondary positioning feature. According to the numerical relationship obtained in step (2), find the secondary positioning threshold of each subdivision corresponding to the measurement value P of each adjacent electrode pair for secondary positioning. Determine the subdivision of the helical blade based on the primary positioning result according to the relationship between P and the corresponding secondary positioning threshold. Tertiary positioning steps: Based on the secondary positioning result, determine the measurement value number of the adjacent electrode pair closest to the helical blade and the measurement value number of the adjacent electrode pair second closest to the helical blade. Use the ratio of normalized measurement values ​​of the closest and second closest adjacent electrode pairs, M, as the tertiary positioning feature. Determine the tertiary positioning threshold and determine the helical blade angle according to the relationship between M and the tertiary positioning threshold.

[0008] Furthermore, n=12, the electrode duty cycle is 70%; the further subdivision is into four sections: the first section, the second section, the third section, and the fourth section.

[0009] The advantages of this invention are: (1) It positions the helical blade based on single-frame measurement values, making the helical blade positioning data independent and enabling positioning based on measurement data under different working conditions. This improves the real-time performance and versatility of helical blade positioning.

[0010] (2) The positioning scheme based on the threshold method of helical blade position feature quantity can quickly determine the position of helical blade through hierarchical positioning, which greatly shortens the positioning time. Attached Figure Description

[0011] Figure 1 is a structural diagram of the ECT sensor. Figure 2 is a schematic diagram of the primary positioning partition of the spiral blade. Figure 3 is a schematic diagram of the secondary positioning partition of the spiral blade. Figure 4 is a flowchart of the present invention. Figure 5 is a single-frame measurement value distribution diagram. Detailed Implementation

[0012] The specific implementation scheme of the present invention is described with reference to FIG4.

[0013] Step 1: Obtain ECT measurement values ​​under full-excitation and full-detection mode, and calculate sensitivity based on the perturbation method.

[0014] The ECT sensor used in this study consists of a set of electrodes, a shield, and an acrylic insulated tube, as shown in Figure 1. The sensor tube diameter is 100 mm. The simulation model uses a 64×64 grid. Due to the reduced capacitance caused by the helical blades, and the improved measurement accuracy due to wider electrodes, 12 electrodes, namely E1-E12, were selected. The electrode duty cycle is 70%, therefore each electrode has a radius of 21°. The helical blade positioning angle... In a clockwise direction, as shown in Figure 1.

[0015] The measurement system features high sensitivity and noise immunity, and employs dual bandpass filters to reduce noise generated by the grounding helical blades. A programmable gain amplifier (PGA) provides a wide measurement range and high resolution. The data acquisition system operates at an average speed of 900 frames per second, achieved by applying an excitation signal to one electrode and acquiring measurements from the other electrodes; the excitation-detection mode is full excitation and full detection. Therefore, a single frame of acquired data contains 132 independent measurements.

[0016] (1) where This is the capacitance measurement value. is the dielectric constant. When a metal helical blade is present in the ECT detection area, the perturbation method is suitable for calculating the sensitivity matrix, as shown in formula (2).

[0017] (2) where It represents the change in capacitance, and Δε represents the change in dielectric constant. It is a sensitivity matrix.

[0018] Step 2: Analysis of the positioning interval of the helical blades.

[0019] Since the position and manifold distribution of the helical blades are fixed in each frame of the ECT-reconstructed image, meaning each frame is static, the helical blade localization result in a single frame should be a single location from an image perspective. Therefore, this invention uses the single-frame capacitance measurement values ​​obtained by ECT detection to locate the helical blades. Assuming the helical blades rotate clockwise, ECT collects 132 capacitance measurements. Within time t, the helical blade rotates for 100 seconds. Angle. Because the spiral blades in a single frame image need to be positioned in one location, It should be a tiny rotation, and The two reconstructed images before and after the interval are very similar.

[0020] The value is related to the acquisition rate and screw rotation speed of the ECT hardware system. When the screw rotation speed is fixed, the higher the acquisition rate, the better. The larger the value, the greater the spiral rotation speed when the acquisition rate is fixed. The larger the value, the better. The experimental platform's spiral rotation speed is between 200 and 300 revolutions per minute, and the hardware system's data acquisition rate is 900 frames per second. Therefore, the data acquired per single frame... The helical blade can rotate a maximum of 2° in time t. Therefore, at maximum speed, The two reconstructed images before and after the interval are very similar, provided that their similarity is acceptable. The smaller the better. Based on a maximum rotation speed of 300 rpm and a sampling rate of 900 frames per second, we can obtain... 2°.

[0021] The smallest unit for positioning a spiral blade is the positioning interval. The angle through which the helical blade rotates within the time frame of data acquisition. This is relevant. Since the positioning of the helical blade is based on a single frame measurement, the blade has already rotated a certain distance within the time frame of acquiring a single positioning data point. Since a smaller positioning interval between the spiral blades results in higher positioning accuracy and higher reconstructed image quality, therefore, [the following is taken as an example]. That is, the positioning interval of the imaging helical blade. 2°.

[0022] Step 3: Setting the positioning and indexing of the helical blades.

[0023] The inventors' previous work (i.e., related reference 5) has already achieved static imaging of ECT detection of helical conveyors based on effective data selection and prior flow pattern information, given the known helical blade positions. Therefore, to achieve dynamic imaging of the ECT detection of helical conveyors, it is necessary to first have a basic dataset at different helical blade positions, and secondly, to know the helical blade positions in a single frame of measurement data. The basic dataset consists of empty-field measurements, full-field measurements, and sensitivity matrices at different helical blade positions. Based on the helical blade positions, the corresponding empty-field measurements, full-field measurements, and sensitivity matrices from the basic dataset are selected, and then imaging is performed based on the effective data and prior flow pattern information at that helical blade position.

[0024] Therefore, it is necessary to construct a basic dataset for dynamic imaging, and then determine the positioning scale of the helical blade. Combining the rotation period of 360° and the positioning interval of 2° for a single helical blade, the positioning scale of the helical blade is obtained as 180, namely 0°, 2°, 4°, ..., 360°, or -178°, ..., -1°, 0°, 2°, 4°, ..., 180°. Based on the rotational symmetry of the electrode and helical blade positions, 30° is a rotational symmetry period. Therefore, this paper first describes the positioning method within a 30° rotation of the helical blade, specifically the helical blade positions as -6°, -4°, -2°, 0°, 2°, 4°, 6°, 8°, 10°, 12°, 14°, 16°, 18°, 20°, and 22°.

[0025] Step 4: A hierarchical positioning scheme for helical blades based on the threshold determination method of helical blade position feature quantities.

[0026] A. The shielding effect and tip effect of the grounded metal in the first-stage positioning method of the helical blade result in a smaller capacitance between adjacent electrode pairs closest to the blade tip than others, as shown in Figure 5. Therefore, the first-stage positioning process of the helical blade is as follows: a. Select all the measurement values ​​between adjacent electrode pairs from the single-frame measurement values ​​and calculate the average value of all the measurement values ​​between adjacent electrode pairs. .

[0027] b. When the measured value between adjacent electrode pairs (or pairs of pairs) is less than At that time, the helical blades are located near these electrode pairs.

[0028] c. Based on the ECT electrode pair number near the spiral blade, determine the electrodes near the spiral blade, and then determine the primary positioning result.

[0029] The primary positioning method can quickly locate the propeller blade within a rotationally symmetric 30° period, with this 30° divided into upper and lower parts, such as the upper interval of -6.5° to 6.5° and the lower interval of 6.5° to 23.5° within the range of -6.5° to 23.5°. The primary positioning method can clearly identify which rotationally symmetric 30° period the propeller blade is located in, and simultaneously determine whether it falls within the upper or lower interval of that period.

[0030] Based on the first-level positioning rules of the helical blade, the measured values ​​of the stable coal powder conveying state of the helical blade in the range of -6.5° to 23.5° were used to locate the blade. The results are shown in Table 1.

[0031] Table 1 shows the first-order positioning results of the helical blades within the range of -6.5° to 23.5°.

[0032] B. Two-stage positioning method for helical blades: The distance between adjacent electrode pairs and the tip of the helical blade directly affects the capacitance of that adjacent electrode pair. The smaller the distance, the smaller the capacitance value of the adjacent electrode pair. Therefore, the data of all adjacent electrode pairs are subjected to max-min normalization to obtain C1, C2, ..., C 24 As shown in Table 2, the distance between the tip of the spiral blade and different adjacent electrode pairs can be determined based on the normalized capacitance value.

[0033] Table 2 shows the normalized serial numbers of the measurements between adjacent electrode pairs.

[0034] The secondary localization process is as follows: a. Extract the capacitors of adjacent electrode pairs from random frame data, and then perform max-min normalization on them to obtain C1, C2, ..., C 24 .

[0035] b. Based on the primary positioning results, it can be determined which 30° rotational symmetry cycle the propeller blade is within, thus identifying the two electrode numbers within that cycle. Combining this with an electrode duty cycle of 70% (21° radian for a single electrode), the two electrode numbers within that 30° rotational symmetry cycle can be determined, sequentially named electrode E in a clockwise direction. up and electrode E down Take electrode pair E up -E down C up Take electrode pair E down- E up C down Based on this, the secondary localization feature quantity P is extracted. (3) c. The upper and lower intervals of the 30° rotationally symmetric period are simultaneously divided into two, i.e., the 30° rotationally symmetric period is divided into four. The P value of the helical blade in different four intervals has inherent characteristics. Therefore, the secondary positioning position of the helical blade can be determined based on the P value.

[0036] Secondary positioning refines the positioning based on primary positioning. It can precisely locate the helical blade within a 30° rotationally symmetric periodic division. According to the secondary positioning rules for helical blades, the threshold values ​​and results of the secondary positioning feature quantities of the helical blades when the blades are located between -6.5° and 23.5° are shown in Table 3.

[0037] Table 3 shows the threshold values ​​of the positional characteristics of the second-stage helical blades within the range of -6.5° to 23.5° and the positioning results.

[0038] C. Three-level positioning method for helical blades. The three-level positioning process is as follows: Based on the two-level positioning results, the nearest and second-nearest adjacent electrode pairs to the helical blade are determined, and then the three-level positioning feature quantity M is extracted. The three-level positioning feature quantity is... (4) Based on the secondary positioning results, the capacitor of the nearest adjacent electrode pair to the spiral blade can be determined. And the capacitance of the adjacent electrode pair closest to the helical blade. The capacitance of the adjacent electrode pair closest to the helical blade is most affected by the helical blade. The capacitance of the next closest adjacent electrode pair is affected by the helical blade in the second largest way. Therefore, the value of M has inherent characteristics under different helical blade positions. The three-level positioning position of the helical blade, i.e., the specific angle of the helical blade, can be determined based on the threshold of M.

[0039] The threshold values ​​of the three-level positional characteristic quantities of the helical blade and the positioning results are shown in Table 4 when the helical blade is within the range of -6.5° to 23.5°.

[0040] Table 4 shows the threshold values ​​of the positional characteristics of the third-stage helical blades and the positioning results within the range of -6.5° to 23.5°.

[0041] The Level 3 positioning results should provide the specific position of the helical blades, i.e., the degree of the helical blades. .

[0042] Dynamic imaging of the helical conveyor process based on ECT detection. Utilizing the Landweber method, dynamic imaging of the helical conveyor using ECT detection is achieved based on effective data at the helical blade position and prior flow pattern information.

Claims

1. A hierarchical positioning method for helical blades based on position feature thresholding, employing a capacitance sensor, with n electrodes evenly arranged on the outer circumference of an insulated pipe, the insulated pipe being placed inside a helical conveying pipe, the helical blades being grounded and located at the center of the conveying pipe, and capacitance measurement between electrode pairs achieved through a capacitance measurement circuit; the hierarchical positioning of the helical blades includes the following steps: dividing the circumference into n rotationally symmetric periods at equal intervals, determining the positioning scale of the helical blades considering the rotational speed of the helical blades; obtaining the numerical relationship between the position of the helical blades and the capacitance measurements of each electrode through simulation or experiment; First-level positioning steps: Extract the electrode numbers of each adjacent electrode pair whose capacitance measurement value is less than its overall average value. Based on the prior correspondence between the electrode numbers and the position of the spiral blade, determine which rotational symmetry period the spiral blade is in and determine whether it is in the upper or lower interval of this rotational period. Secondary positioning steps: Further subdivide the rotationally symmetric period into the first, second, third, and fourth intervals. Based on the partition where the helical blade is located, determine the adjacent electrode pairs for secondary positioning. Use the ratio P of the normalized measurement values ​​of the adjacent electrode pairs for secondary positioning as the secondary positioning feature. Based on the numerical relationship obtained in step (2), find the secondary positioning threshold of each subdivision corresponding to the measurement value P of each adjacent electrode pair for secondary positioning. Based on the relationship between P and the corresponding secondary positioning threshold, determine the subdivision of the helical blade based on the primary positioning result. The three-level positioning steps are as follows: Based on the two-level positioning results, determine the measurement value number of the nearest adjacent electrode pair to the spiral blade and the measurement value number of the second nearest adjacent electrode pair to the spiral blade; use the ratio M of the normalized measurement values ​​of the nearest and second nearest adjacent electrode pairs as the three-level positioning feature quantity. Determine the three-level positioning threshold, and then determine the helical blade angle based on the relationship between M and the three-level positioning threshold.

2. The hierarchical positioning method for spiral blades based on the position feature threshold method according to claim 1, characterized in that, n=12, electrode duty cycle is 70%.

3. The hierarchical positioning method for spiral blades based on the position feature threshold method according to claim 2, characterized in that, The area is further subdivided into four sections: the first section, the second section, the third section, and the fourth section.

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