Capacitive sensor for particle filling rate in spiral tube

Abstract

The invention discloses a particle filling rate capacitance sensor in a spiral tube, wherein a screw shaft is coaxially arranged in the spiral tube, spiral blades are evenly arranged on the screw shaft, the screw shaft is grounded, and a first capacitor plate, a second capacitor plate, a third capacitor plate and a fourth capacitor plate are arranged in sequence at equal intervals along the outer wall of the spiral tube, an outer shielding cover is arranged on the outer wall of the first capacitor plate, the second capacitor plate, the third capacitor plate and the fourth capacitor plate, and four radial shielding plates are arranged at equal intervals on the inner wall of the outer shielding cover, each radial shielding plate is located in the middle of the gap between two adjacent capacitor plates, the first capacitor plate, the second capacitor plate, the third capacitor plate, the fourth capacitor plate, the outer shielding cover and the spiral tube are concentrically arranged, and the outer shielding cover and the radial shielding plate are grounded. By re-dividing the cylindrical Gaussian surface, the sensitivity uniformity of different detection areas is improved, the capacitance detection value range is improved, and the difficulty of small capacitance detection is reduced.

Description

Technical Field

[0001] The invention relates to a capacitance sensor for particle filling rate in a spiral tube. Background Art

[0002] As a continuous feeding and conveying equipment, the spiral feeding device has been recognized and widely used in many industries since its launch due to its advantages such as low cost, reliable operation, simple structure, good sealing, and convenient feeding amount control. In terms of implementation mechanism, the device uses continuously rotating spiral blades to achieve continuous and efficient transportation of materials, and has now been applied to many related fields such as chemical industry, building materials, and agriculture. Solving the quantitative problem of discontinuous feeding of powder and granular materials through spirals not only minimizes the impact of the external environment, but also improves the production level and ensures production efficiency. Therefore, it has attracted widespread attention and has become a key direction for the innovation and development of quantitative feeding technology. The future market prospects are very broad.

[0003] However, spiral discontinuous feeding is a time-varying process with a large lag. The movement of particles in the spiral tube belongs to gas-solid two-phase flow. The fluid movement of solid-phase particle materials is complex and is easily affected by factors such as particle material characteristics (particle shape and size and its uniformity, particle density, moisture content), material state distribution, and device operation status (screw rotation start and stop position, speed), resulting in serious uneven density of particles in the spiral tube and incomplete and variable space filling, which seriously affects the discontinuous feeding results. In addition, there are many uncertain influencing factors in the discontinuous feeding process, and some of the influencing factors have complex cross-coupling effects, which leads to poor accuracy and stability of the feeding amount, restricting its application and promotion in actual production.

[0004] Since the particle filling rate in the spiral tube is unstable, the feeding amount is discrete and nonlinear, and the controllability of the feeding amount is poor. Therefore, online detection of the particle filling rate in the spiral tube is very necessary, which is the basis and one of the key problems to improve the quantitative performance of spiral discontinuous feeding. In recent years, thanks to the innovation and application development of particle detection technology, scholars have proposed many particle filling rate detection methods with wide application range and strong operability, such as ultrasonic method, radiation method, laser method, microwave resonance method, electrostatic method, capacitance tomography method and capacitance method, etc. Among them, combined with the actual situation of spiral discontinuous feeding, the capacitance method should be used: the dielectric constant of the material in the pipeline usually has different performances due to different media. If the fluid passes through the detection field, when the filling rate changes, the equivalent dielectric constant will also change accordingly, thereby causing the output capacitance value to change. The capacitance value is a relatively important measurement parameter. It can intuitively and accurately reflect the change of particle filling rate, eliminating the image reconstruction link of capacitance tomography, and has the advantages of convenient installation, low production cost, and fast response speed.

[0005] In the prior art, there are four main types of commonly used pipe outer capacitive sensor structures, such as Figure 1As shown in (a), 1(b), 1(c) and 1(d), they are: a pair of (two-electrode plates s and d) surface plate capacitors, two pairs of (four-electrode plates s1, d1, s2 and d2) cross-surface plate capacitors, four pairs of (eight-electrode plates s1, d1, s2, d2, s3, d3, s4 and d4) surface plate capacitors and spiral (spiral plates s, g and radial plates d) surface plate capacitors. However, the problem of capacitance measurement sensitivity being affected by the uneven distribution of the measured material has always existed. The "soft field" (that is, when the position of the medium changes, the capacitance value of the same plate will be disturbed and affected to varying degrees) characteristic problem makes the measurement results related to multiple factors, including material filling rate, material spatial distribution and flow pattern affected by the position of the spiral blades of the conveying pipe, etc., resulting in a large measurement error, which cannot meet the requirements of real-time online detection of particle filling rate for spiral discontinuous quantitative feeding. Summary of the invention

[0006] In view of the above problems, the present invention provides a capacitance sensor for the particle filling rate in a spiral tube. In view of the problems of poor uniformity in the sensitivity distribution in the detection area and difficulty in detecting tiny capacitance in the capacitance sensor, the structure of the capacitance sensor on the outer surface of the spiral pipe is improved to solve the core problem of weak capacitance detection of the spiral pipe capacitance sensor. By redividing the cylindrical Gaussian surface, the sensitivity uniformity of different detection areas is improved; further, the capacitance detection value range is increased and the difficulty of detecting tiny capacitance is reduced.

[0007] In order to achieve the above technical objectives and the above technical effects, the present invention is implemented through the following technical solutions:

[0008] A particle filling rate capacitive sensor in a spiral tube, wherein a screw shaft is coaxially arranged in the spiral tube, spiral blades are evenly arranged on the screw shaft, the screw shaft is grounded, and a first capacitor plate, a second capacitor plate, a third capacitor plate and a fourth capacitor plate are arranged in sequence at equal intervals along the outer wall of the spiral tube, an outer shielding cover is arranged on the outer walls of the first capacitor plate, the second capacitor plate, the third capacitor plate and the fourth capacitor plate, and four radial shielding plates are arranged at equal intervals on the inner wall of the outer shielding cover, each radial shielding plate is located in the middle of the gap between two adjacent capacitor plates, the first capacitor plate, the second capacitor plate, the third capacitor plate, the fourth capacitor plate, and the outer shielding cover are arranged concentrically with the spiral tube, and the outer shielding cover and the radial shielding plates are grounded.

[0009] Preferably, the first capacitor plate, the second capacitor plate, the third capacitor plate and the fourth capacitor plate are attached to the outer wall of the spiral tube, one end of the radial shielding plate is integrally formed with the outer shielding cover and the other end of the radial shielding plate is inserted into the spiral tube by a set distance.

[0010] Preferably, the spiral tube is made of acrylic, the screw shaft is made of steel, and the first capacitor plate, the second capacitor plate, the third capacitor plate, the fourth capacitor plate, the outer shielding cover and the radial shielding plate are all made of copper foil.

[0011] Preferably, the first capacitor plate, the second capacitor plate, the third capacitor plate and the fourth capacitor plate have the same shape and an opening angle of 80°.

[0012] Preferably, the axial length of the first capacitor plate is equal to the pitch of the spiral blade and equal to the inner diameter of the spiral tube.

[0013] Preferably, the distance that the radial shielding electrode is inserted into the spiral tube is 10% of the thickness of the spiral tube.

[0014] Preferably, the first capacitor plate, the second capacitor plate, the third capacitor plate and the fourth capacitor plate divide the capacitive sensor into four coaxial capacitors, which correspond to the four regions of the spiral tube respectively. The capacitance values ​​between the four capacitor plates and the spiral axis are the capacitance values ​​to be measured and are recorded as C edci (i=1,2,3,4):

[0015] C edci =C oi h(ε g ,ε o ,β(x,y,z))

[0016] In the formula, C oi is the equivalent capacitance of the empty tube; ε g is the relative dielectric constant of the material, ε o is the relative dielectric constant of vacuum, x, y and z are the spatial distribution of particle volume, β(x, y, z) is the volume filling rate distribution of solid medium, and h function is the fitting function obtained by experimental fitting;

[0017] The total capacitance of the capacitive sensor is recorded as C avg :

[0018]

[0019] The beneficial effects of the present invention are:

[0020] First, the present invention designs an array capacitor consisting of four capacitor plates laid on the outer surface of an insulating spiral tube, and uses the screw shaft as the inner capacitor plate to form an irregular dynamic capacitance sensor, which divides the spiral tube into four regions. The gas phase and solid phase media of the gas-solid two-phase flow have different dielectric constants. When the gas-solid mixed fluid flows through each sensitive field, the floating change of the equivalent dielectric constant will change the capacitance value. Therefore, the medium distribution in the pipeline is reconstructed through the change of the capacitance value of the four regions, thereby realizing the detection of the particle flow filling rate. By detecting the capacitance of different regions, the traditional cylindrical capacitance sensor structure is improved to solve the core problem of the detection of tiny capacitance of the spiral pipeline capacitance sensor. The present invention re-divides the cylindrical Gaussian surface to improve the uniformity of the detection sensitivity of different detection areas.

[0021] Second, in order to accurately reflect the capacitance value of the particle filling rate in the spiral tube and reduce the stray capacitance value of the four detection electrodes outside the spiral pipe, radial shielding plates are added between the detection electrodes and evenly distributed on the outside of the pipe. Through scientific control of the insertion depth of the radial shielding plates, the coupling effect and edge effect of adjacent plates can be blocked to affect the capacitance value measurement, and the potential field is concentrated within the range to be detected. In order to avoid electrostatic interference and ensure the reliability and accuracy of the operation of the capacitive sensor, an outer shielding cover is set on the outside of the capacitive sensor, and it is grounded with the radial shielding plate to increase the capacitance detection value range and reduce the difficulty of detecting tiny capacitance.

[0022] Third, in the actual discontinuous feeding process of the spiral, the frequent start and stop of the screw shaft, the rotation and the acceleration and deceleration of the motor affect the distribution of the material state in the tube, resulting in serious uneven density of particles in the spiral tube, incomplete and variable space filling, etc., which seriously affect the quantitative feeding results. The four detection areas cannot make the particles evenly distributed, and the distribution of materials of different volumes aggravates the degree of influence on the measurement results. Therefore, the present invention minimizes the influence of particle distribution under different volumes on the filling rate through strict size limitation, so as to accurately obtain the capacitance detection value under different areas and improve the detection sensitivity of the sensor. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a schematic diagram of the structure of a commonly used pipe outer side capacitance sensor;

[0024] Figure 2 Schematic diagram of the structure of the particle filling rate capacitance sensor in the spiral tube of the present invention;

[0025] Figure 3 is a schematic cross-sectional view of a capacitance sensor for particle filling rate in a spiral tube according to an embodiment of the present invention;

[0026] Figure 4 It is a schematic diagram of the structure of the spiral discontinuous feeding device for particulate materials of the present invention;

[0027] Figure 5 This is a model diagram of the spiral discontinuous feeding device for particulate materials of the present invention;

[0028] Figure 6 It is a physical picture of two types of small yellow rice of the present invention;

[0029] Figure 7 It is a schematic diagram of the feed test operation interface of the present invention;

[0030] Figure 8 It is a schematic diagram of quantitative error of two materials of the present invention;

[0031] Fig. 9 It is a schematic diagram of the definition of R1 and R2 of the present invention;

[0032] The meanings of the marks in the accompanying drawings are as follows: 1: screw shaft; 2: spiral tube; 3: first capacitor plate; 4: second capacitor plate; 5: third capacitor plate; 6: fourth capacitor plate; 7: outer shielding cover; 8: radial shielding plate; 9: host computer; 10: data acquisition card; 11: weighing sensor; 12: material tray; 13: bracket; 14: stepping motor; 15: storage bin; 16: capacitive sensor; 17: discharge port; 18: spiral blade; 19: proximity switch. DETAILED DESCRIPTION

[0033] The technical solution of the present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments so that those skilled in the art can better understand the present invention and implement it, but the embodiments are not intended to limit the present invention.

[0034] In industrial and agricultural production, a large number of loose granular materials need to be fed discontinuously to achieve quantitative batching or quantitative packaging, such as food, powder metallurgy, ceramic building materials, fertilizers, pesticides and agricultural and sideline products. For granular materials with very small particle size, it is easy to have problems such as adsorption and splashing in quantitative feeding production. With the continuous increase of error fluctuations, it will not only affect production efficiency and make it difficult to meet quality requirements, but also generate additional production costs and increase power consumption losses, so it is not conducive to the stable, efficient and sustainable development of production enterprises. According to relevant data, for the quantitative packaging production of agricultural fertilizers alone, the annual loss generated by each 1% increase in loss is as much as tens of billions of yuan. In addition, for dust materials represented by pesticides and fertilizers, if there is no quantitative production with safety protection, the dust splash will damage the working environment at the least, and induce poisoning, pneumoconiosis and other diseases in operators at the worst, which will cause great harm to human health; and for powder and granular materials such as food and medicine, if the quantitative feeding production is completely open, direct human participation will also have adverse effects on the hygienic quality of the product.

[0035] Therefore, it is urgent to study and solve the quantitative problem of discontinuous feeding of granular materials, improve the quantitative production speed of granular materials, optimize the on-site environment, reduce energy consumption, improve resource utilization, and promote safe and efficient production of granular materials. The structural design of a capacitive sensor suitable for online detection of the particle filling rate in a spiral tube is the key to the next step of research. Therefore, the present invention combines the structure of a spiral feeder to design a capacitive sensor for the particle filling rate in a spiral tube, which can detect the particle filling rate in a spiral tube online.

[0036] like Figure 2-Figure 3 As shown, a capacitive sensor for particle filling rate in a spiral tube, wherein a screw shaft 1 is coaxially arranged in the spiral tube 2, spiral blades 18 are evenly arranged on the screw shaft 1, the screw shaft 1 is grounded as an inner plate of the capacitor, the spiral tube is made of insulating material, and a first capacitor plate 3, a second capacitor plate 4, a third capacitor plate 5 and a fourth capacitor plate 6 are evenly arranged along the outer wall of the spiral tube 2, wherein the first capacitor plate 3, the second capacitor plate 4, the third capacitor plate 5 and the fourth capacitor plate 6 are arranged in sequence and in parallel.

[0037] Preferably, the first capacitor plate 3, the second capacitor plate 4, the third capacitor plate 5 and the fourth capacitor plate 6 have the same shape and an angle of 80°. The present invention designs an array capacitor consisting of four capacitor plates laid on the outer surface of an insulating spiral tube, and uses the screw shaft as the inner capacitor plate to form an irregular dynamic capacitance sensor, dividing the spiral tube into four regions. The gas phase and solid phase media of the gas-solid two-phase flow have different dielectric constants. When the gas-solid mixed fluid flows through each sensitive field, the floating change of the equivalent dielectric constant will cause the capacitance value to change. Therefore, the medium distribution in the pipeline is reconstructed by the change of the capacitance value of the four regions, thereby realizing the detection of the particle flow filling rate. By detecting the capacitance of different regions, the traditional cylindrical capacitance sensor structure is improved to solve the core problem of the detection of tiny capacitance of the spiral pipeline capacitance sensor. The present invention re-divides the cylindrical Gaussian surface to improve the uniformity of the detection sensitivity of different detection areas.

[0038] The outer side walls of the first capacitor plate 3, the second capacitor plate 4, the third capacitor plate 5 and the fourth capacitor plate 6 are provided with an outer shielding cover 7, and the inner side wall of the outer shielding cover 7 is provided with four radial shielding plates 8 at equal intervals, and each radial shielding plate 8 is located in the middle of the gap between two adjacent capacitor plates. The first capacitor plate 3, the second capacitor plate 4, the third capacitor plate 5, the fourth capacitor plate 6, the outer shielding cover 7 and the spiral tube 2 are concentrically arranged, and the outer shielding cover 7 and the radial shielding plates 8 are grounded.

[0039] In order to accurately reflect the capacitance value of the particle filling rate in the spiral tube and reduce the stray capacitance value of the four detection electrodes outside the spiral pipe, radial shielding plates are added between the detection electrodes and evenly distributed on the outer periphery of the pipe. Through scientific control of the insertion depth of the radial shielding plates, the coupling effect and edge effect of adjacent plates can be blocked to affect the capacitance value measurement, and the potential field is concentrated within the range to be detected. In order to avoid electrostatic interference and ensure the reliability and accuracy of the operation of the capacitive sensor, an outer shielding cover is set on the outside of the capacitive sensor, and it is grounded with the radial shielding plate to increase the capacitance detection value range and reduce the difficulty of detecting tiny capacitance.

[0040] The first capacitor plate 3, the second capacitor plate 4, the third capacitor plate 5 and the fourth capacitor plate 6 are attached to the outer wall of the spiral tube 2, one end of the radial shielding plate 8 is integrally formed with the outer shielding cover 7 and the other end of the radial shielding plate 8 is inserted into the spiral tube 2 by a set distance.

[0041] The spiral tube 2 is made of acrylic, the screw shaft 1 is made of steel, and the first capacitor plate 3, the second capacitor plate 4, the third capacitor plate 5, the fourth capacitor plate 6, the outer shielding cover 7 and the radial shielding plate 8 are all made of copper foil.

[0042] The axial length of the first capacitor plate 3 is equal to the pitch of the spiral blade 18 and equal to the inner diameter of the spiral tube 2 .

[0043] The distance that the radial shielding plate 8 is inserted into the spiral tube 2 is 10% of the thickness of the spiral tube 2 .

[0044] In the actual discontinuous feeding process of the spiral, the frequent start and stop of the screw shaft, the rotation and the acceleration and deceleration of the motor affect the distribution of the material state in the tube, resulting in serious uneven density of particles in the spiral tube, incomplete and variable space filling, etc., which seriously affect the quantitative feeding results. The four detection areas cannot make the particles evenly distributed, and the distribution of materials of different volumes aggravates the degree of influence on the measurement results. Therefore, the present invention minimizes the influence of particle distribution under different volumes on the filling rate through strict size limitation, so as to accurately obtain the capacitance detection value under different areas and improve the detection sensitivity of the sensor.

[0045] The first capacitor plate 3, the second capacitor plate 4, the third capacitor plate 5 and the fourth capacitor plate 6 divide the capacitive sensor 16 into four coaxial capacitors, which correspond to the four regions of the spiral tube 2 respectively. The capacitance values ​​between the four capacitor plates and the spiral axis are the capacitance values ​​to be measured and are recorded as C edci (i=1,2,3,4):

[0046] C edci =C oi h(ε g ,ε o ,β(x,y,z))

[0047] In the formula, C oi is the equivalent capacitance of the empty tube; ε g is the relative dielectric constant of the material, ε o is the relative dielectric constant of vacuum, x, y and z are the spatial distribution of particle volume, β(x, y, z) is the volume filling rate distribution of solid phase medium, and h function is the fitting function obtained through experimental fitting. Because different materials, different spiral tube sizes, and different volume filling rates of materials all affect the final capacitance value, it is necessary to obtain the calculation formula of each capacitor through a large number of experiments.

[0048] The total capacitance of the capacitive sensor is recorded as C avg :

[0049]

[0050] Subsequently, the rotation angle of the spiral blade 18 can be calculated and determined based on the material filling rate value and speed detected in real time, and the material can be pushed forward along the pipeline for feeding.

[0051] Among them, due to the soft field effect during actual capacitance sensor detection, there is a higher sensitivity near the electrode in the detection field, and a lower sensitivity far away from the electrode. When the solid phase distribution in the spiral pipe is uneven and the flow pattern changes, the above formula can be used for filling rate detection under different sensor output capacitance values ​​to improve the soft field effect of capacitance detection.

[0052] The total material filling rate β and the capacitance value C between each detection electrode in the detection electrode array edci The relationship between (i=1,2,3,4) is:

[0053]

[0054] Where l is the length of the capacitor plate, and θ is the angle between the tangent lines of the cross sections of two adjacent capacitor plates. Fig. 9 As shown in the cross-section, R1 is the distance from the intersection of the axial extension line of the capacitor plate and the spiral blade angle θ to the closer point of the capacitor plate, and R1 is less than or equal to the pitch of the spiral blade. R2 is the distance from the intersection of the axial extension line of the capacitor plate and the spiral blade angle θ to the farther point of the capacitor plate, and R2=R1+l.

[0055] Correspondingly, the spiral discontinuous feeding device for granular materials can refer to Figure 4 As shown, it should be noted that: Figure 4 and Figure 5This is a physical model diagram of the present invention. Therefore, a material tray 12 and a weighing sensor 11 are designed to verify the error of feeding. In actual industrial applications, the discharge port 17 is directly connected to the quantitative packaging device to achieve quantitative packaging of granular materials. It can effectively isolate the influence of the external environment on the feeding, help to improve the quantitative production efficiency and safety, avoid waste of resources, and make production more environmentally friendly.

[0056] The spiral discontinuous feeding device for particulate materials includes a host computer 9 (with data processing function) and a bracket 13, on which a spiral tube 2 is arranged, and a screw shaft 1 is coaxially arranged inside the spiral tube 2, and spiral blades 18 are evenly arranged on the screw shaft 1. A storage bin 15 is arranged on the top of one end of the spiral tube 2 and a discharge port 17 is arranged on the bottom of the other end. A stepper motor 14 and a proximity switch 19 are arranged on the end of the spiral tube 2 close to the storage bin 15, and also include a data acquisition card 10 and a capacitive sensor 16. The screw shaft 1 is grounded, and the capacitive sensor 16 is wrapped on the outer wall of the spiral tube 2 and close to the discharge port 17.

[0057] The capacitive sensor 16 includes a first capacitor plate 3, a second capacitor plate 4, a third capacitor plate 5 and a fourth capacitor plate 6 which are arranged in sequence at equal intervals along the outer wall of the spiral tube 2, an outer shielding cover 7 is arranged on the outer walls of the first capacitor plate 3, the second capacitor plate 4, the third capacitor plate 5 and the fourth capacitor plate 6, and four radial shielding plates 8 are arranged at equal intervals on the inner wall of the outer shielding cover 7, each radial shielding plate 8 is located in the middle of the gap between two adjacent capacitor plates, the first capacitor plate 3, the second capacitor plate 4, the third capacitor plate 5, the fourth capacitor plate 6, the outer shielding cover 7 and the spiral tube 2 are concentrically arranged, and the outer shielding cover 7 and the radial shielding plates 8 are grounded.

[0058] The first capacitor plate 3, the second capacitor plate 4, the third capacitor plate 5 and the fourth capacitor plate 6 are respectively connected to the host computer 9 through the data acquisition card 10. The host computer 9 controls the discharge of the storage bin 15 and the start and stop of the screw shaft 1 by controlling the stepper motor 14 (the host computer controls the motor angle and speed) and the proximity switch 19.

[0059] The first capacitor plate 3, the second capacitor plate 4, the third capacitor plate 5 and the fourth capacitor plate 6 are attached to the outer wall of the spiral tube 2, one end of the radial shielding plate 8 is integrally formed with the outer shielding cover 7 and the other end of the radial shielding plate 8 is inserted into the spiral tube 2 by a set distance.

[0060] The spiral tube 2 is made of acrylic, the screw shaft 1 is made of steel, and the first capacitor plate 3, the second capacitor plate 4, the third capacitor plate 5, the fourth capacitor plate 6, the outer shielding cover 7 and the radial shielding plate 8 are all made of copper foil.

[0061] The first capacitor plate 3 , the second capacitor plate 4 , the third capacitor plate 5 and the fourth capacitor plate 6 have the same shape and an opening angle of 80°.

[0062] In order to facilitate experimental verification or teaching demonstration, the present invention also provides a model demonstration device of a spiral discontinuous feeding device for granular materials, and its result schematic diagram and actual diagram are as follows: Figure 4 and 5 As shown, it includes a host computer 9 and a bracket 13, a spiral tube 2 is arranged on the bracket 13, a screw shaft 1 is coaxially arranged in the spiral tube 2, spiral blades 18 are evenly arranged on the screw shaft 1, a storage bin 15 is arranged on the top of one end of the spiral tube 2 and a discharge port 17 is arranged on the bottom of the other end, a stepper motor 14 and a proximity switch 19 are arranged on the end of the spiral tube 2 close to the storage bin 15, and also includes a data acquisition card 10 and a capacitive sensor 16, the screw shaft 1 is grounded, and the capacitive sensor 16 is wrapped on the outer wall of the spiral tube 2 and close to the discharge port 17.

[0063] A material tray 12 is provided below the discharge port 17, and a weighing sensor 11 is provided at the bottom of the material tray 12. The screw shaft drive motor is driven by a stepper motor 14, the filling rate sensor is detected by the above-mentioned capacitive sensor, and the weighing sensor 11 is a strain force sensor for weighing verification.

[0064] The capacitive sensor 16 includes a first capacitor plate 3, a second capacitor plate 4, a third capacitor plate 5 and a fourth capacitor plate 6 which are arranged in sequence at equal intervals along the outer wall of the spiral tube 2, an outer shielding cover 7 is arranged on the outer walls of the first capacitor plate 3, the second capacitor plate 4, the third capacitor plate 5 and the fourth capacitor plate 6, and four radial shielding plates 8 are arranged at equal intervals on the inner wall of the outer shielding cover 7, each radial shielding plate 8 is located in the middle of the gap between two adjacent capacitor plates, the first capacitor plate 3, the second capacitor plate 4, the third capacitor plate 5, the fourth capacitor plate 6, the outer shielding cover 7 and the spiral tube 2 are concentrically arranged, and the outer shielding cover 7 and the radial shielding plates 8 are grounded.

[0065] The first capacitor plate 3, the second capacitor plate 4, the third capacitor plate 5 and the fourth capacitor plate 6 are respectively connected to the host computer 9 through the data acquisition card 10, and the host computer 9 controls the discharge of the storage bin 15 and the start and stop of the screw shaft 1 by controlling the stepper motor 14 and the proximity switch 19.

[0066] The first capacitor plate 3, the second capacitor plate 4, the third capacitor plate 5 and the fourth capacitor plate 6 are attached to the outer wall of the spiral tube 2, one end of the radial shielding plate 8 is integrally formed with the outer shielding cover 7 and the other end of the radial shielding plate 8 is inserted into the spiral tube 2 by a set distance.

[0067] The spiral tube 2 is made of acrylic, the screw shaft 1 is made of steel, and the first capacitor plate 3, the second capacitor plate 4, the third capacitor plate 5, the fourth capacitor plate 6, the outer shielding cover 7 and the radial shielding plate 8 are all made of copper foil.

[0068] The first capacitor plate 3 , the second capacitor plate 4 , the third capacitor plate 5 and the fourth capacitor plate 6 have the same shape and an opening angle of 80°.

[0069] The inner and outer diameters of the spiral tube 2 are 40 mm and 50 mm respectively, the diameter of the screw shaft 1 is 13 mm, the thickness of the spiral blade 18 is 2 mm, the outer diameter of the spiral blade 18 is 38 mm, and the pitch is 40 mm;

[0070] The first capacitor plate 3 has an axial length of 40 mm, a thickness of 0.5 mm, and a size of 35×40 mm after the curved surface is flattened;

[0071] The radial shielding plate 8 has an axial length of 40 mm, a radial insertion depth of 3 mm, and a thickness of 1 mm;

[0072] The outer shielding cover 7 has an axial length of 40 mm, a diameter of 54 mm and a thickness of 1 mm.

[0073] When measuring tiny capacitance, the capacitor plates are prone to capacitor contact with noise, generating additional contact parasitic capacitance. Parasitic capacitance is a very important influencing factor, which will cause the capacitance of single capacitors and small-capacity sensors to change, not only affecting the sensor measurement accuracy, but also causing serious interference to the sensor during operation. In order to overcome the instability of the parasitic capacitance of the capacitor, the present invention adopts the following shielding measures at the sensor and sensor leads: (1) The wires connected to the capacitor plates, radial shielding plates, and outer shielding covers are special shielding wires to reduce the influence of stray capacitance; (2) The copper foil of the capacitor plates is selected to be 0.5 mm thin to reduce the edge effect between the plates to a certain extent; (3) The metal of the pipe and the outer shell that contacts the external object are grounded to eliminate the interference of external electrostatic fields and alternating electromagnetic fields.

[0074] Preferably, the data acquisition card may be a NET6043-S2XE data acquisition card, the stepper motor may be a Sihong SH-8611A stepper motor driver, and the proximity switch may be a PNP Hall proximity switch.

[0075] The capacitance sensor is installed in the front section of the discharge port on the surface of the pipeline, and the measurement area formed by the electrodes is usually regarded as the positive sensitive area. The capacitance measurement value mainly depends on the medium distribution, and the medium distribution in other areas will not have much impact on its measurement results. Therefore, the measurement of the filling rate of the particle material distribution in the pipeline cross section is realized. Its positive sensitive area can be regarded as a scanning area, and a capacitance measurement value reflects the distribution trend of the material particles at a specific angle or direction.

[0076] Yellow millet, also known as millet or yellow millet, is golden and shiny in appearance. It is a very important cereal crop after rice and wheat. It is popular in both the south and the north. It is small in size, light in weight and hard in texture. Once the equipment shakes during operation or the operating environment changes, it will have a significant impact on the flow of yellow millet particles, thereby adversely affecting the accuracy and stability of discontinuous feeding quantification. Therefore, the present invention uses yellow millet, a typical agricultural granular material, as a material object for specific demonstration.

[0077] The test material used in the present invention is the "Qinzhou Yellow" small yellow rice from Qin County, which has uniform color and full particles. In order to test the adaptability of different materials, two types of small yellow rice are selected. The test material 1# small yellow rice is light yellow in color and 3mm in diameter, and the test material 2# small yellow rice is golden yellow in color and 2mm in diameter. The appearance of the two types of materials is as follows Figure 6 As shown, Figure 6 (a) is 1# small yellow rice, Figure 6 (b) is 2# small yellow rice.

[0078] The first capacitor plate 3, the second capacitor plate 4, the third capacitor plate 5 and the fourth capacitor plate 6 divide the capacitive sensor 16 into four coaxial capacitors, which correspond to the four regions of the spiral tube 2 respectively. The capacitance values ​​between the four capacitor plates and the spiral axis are the capacitance values ​​to be measured and are recorded as C edci (i=1,2,3,4):

[0079] C edci =C oi h(ε g ,ε o ,β(x,y,z))

[0080] In the formula, C oi is the equivalent capacitance of the empty tube; ε g is the relative dielectric constant of millet, ε o is the relative dielectric constant of vacuum, x, y and z are the spatial distribution of particle volume, β(x, y, z) is the volume filling rate distribution of solid medium, and h function is the fitting function obtained by experimental fitting;

[0081] The upper computer 9 calculates and determines the rotation angle of the spiral blade 18 according to the set discharge volume, based on the real-time detection of the material filling rate value and speed (this is the prior art), and controls the material to be pushed forward along the pipeline for feeding.

[0082] Among them, due to the soft field effect during actual capacitance sensor detection, there is a higher sensitivity near the electrode in the detection field, and a lower sensitivity far away from the electrode. The solid phase distribution in the spiral pipe is uneven. When the flow pattern changes, the above formula can be used for filling rate detection under different sensor output capacitance values ​​to improve the soft field effect of capacitance detection.

[0083] The total material filling rate β and the capacitance value C between each detection electrode in the detection electrode array edci The relationship between (i=1,2,3,4) is:

[0084]

[0085] Where l is the length of the capacitor plate, and θ is the angle between the tangent lines of the cross sections of two adjacent capacitor plates. Fig. 9 As shown in the cross-section, R1 is the distance from the intersection of the axial extension line of the capacitor plate and the spiral blade angle θ to the closer point of the capacitor plate, and R1 is less than or equal to the pitch of the spiral blade. R2 is the distance from the intersection of the axial extension line of the capacitor plate and the spiral blade angle θ to the farther point of the capacitor plate, and R2=R1+l.

[0086] According to the feeding amount range, it is divided into small-dose feeding of 25-100g, medium-dose feeding of 125-200g and large-dose feeding of 225-300g, and the spiral discontinuous feeding test data is collected. The collected data is shown in Table 1, where Mean.E is the average absolute error of multiple feeding amounts, Max.E is the maximum absolute error of multiple feeding amounts, Mean.RE is the average relative error of multiple feeding amounts, Max.RE is the maximum relative error of multiple feeding amounts, and RMSE is the root mean square error. The feeding test operation interface is as follows: Figure 7 shown.

[0087] Table 1 Data collected from the feeding test

[0088]

[0089] It can be seen from Table 1 that as the amount of feed increases, the feeding performance becomes better, but the RMSE shows an opposite trend. Large-dose feed leads to increased material dispersion. From the perspective of Mean.RE, 2# material 1.3%~1% and 1# material 1.6%~1.1% both reach the preset feeding performance target. Even for small-dose feed, a good feeding effect is shown. Affected by the particle size, the performance of 2# material is better than that of 1# material. From the perspective of Mean.E and Max.E, the performance of 2# material is better than that of 1# material. The quantitative errors of the two materials are shown in Figure 8 As shown, they are all below 2%. For material 2# with better particle characteristics, the quantitative error is between -1.13% and 1.65%, which is basically consistent with the simulation analysis results.

[0090] The present invention aims at the technical difficulties such as poor quantitative accuracy of discontinuous feeding of granular materials. According to the actual structure of the spiral feeder, an array capacitance sensor structure composed of 4 capacitance plates on the outer surface of the spiral is designed, the main performance of particle filling rate capacitance detection and its influencing factors are analyzed, a filling rate detection mathematical model is established, the relationship between the sensor output capacitance and the filling rate is established, and the particle filling rate capacitance detection mechanism in the spiral tube is revealed, providing a theoretical basis for particle filling rate detection. That is, the present invention analyzes the complex nonlinear relationship between the spiral discontinuous feeding amount and the influencing factors, and establishes a theoretical estimation model for the spiral discontinuous feeding amount. The above results show that the stability and accuracy of the discharge amount of the present invention have reached the preset feeding performance target. It has important theoretical value and guiding significance for perfecting the theory of spiral discontinuous feeding theorem, improving the quantitative performance of spiral discontinuous feeding, and promoting its application and promotion in industrial and agricultural production.

[0091] The above are only preferred embodiments of the present invention, and are not intended to limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made using the contents of the present invention specification and drawings, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. Capacitive sensor for particle filling rate in spiral tube, where: A screw shaft (1) is coaxially arranged inside a spiral tube (2), and spiral blades (18) are evenly arranged on the screw shaft (1), characterized in that the screw shaft (1) is grounded, and a first capacitor plate (3), a second capacitor plate (4), a third capacitor plate (5) and a fourth capacitor plate (6) are arranged in sequence at equal intervals along the outer wall of the spiral tube (2), an outer shielding cover (7) is arranged on the outer walls of the first capacitor plate (3), the second capacitor plate (4), the third capacitor plate (5) and the fourth capacitor plate (6), and an inner wall of the outer shielding cover (7) is provided with four radial shielding plates (8) at equal intervals, and each radial shielding plate (8) is located in the middle of a gap between two adjacent capacitor plates, and the first capacitor plate (3), the second capacitor plate (4), the third capacitor plate (5), the fourth capacitor plate (6) and the outer shielding cover (7) are arranged concentrically with the spiral tube (2), and the outer shielding cover (7) and the radial shielding plates (8) are grounded; The first capacitor plate (3), the second capacitor plate (4), the third capacitor plate (5) and the fourth capacitor plate (6) are attached to the outer wall of the spiral tube (2), one end of the radial shielding plate (8) is integrally formed with the outer shielding cover (7) and the other end of the radial shielding plate (8) is inserted into the spiral tube (2) by a set distance; The spiral tube (2) is made of acrylic material, the screw shaft (1) is made of steel material, and the first capacitor plate (3), the second capacitor plate (4), the third capacitor plate (5), the fourth capacitor plate (6), the outer shielding cover (7) and the radial shielding plate (8) are all made of copper foil; The first capacitor plate (3), the second capacitor plate (4), the third capacitor plate (5) and the fourth capacitor plate (6) have the same shape and an opening angle of 80°; The axial length of the first capacitor plate (3) is equal to the pitch of the spiral blade (18) and equal to the inner diameter of the spiral tube (2); The distance that the radial shielding plate (8) is inserted into the spiral tube (2) is 10% of the thickness of the spiral tube (2); The first capacitor plate (3), the second capacitor plate (4), the third capacitor plate (5) and the fourth capacitor plate (6) divide the capacitive sensor (16) into four coaxial capacitors, which respectively correspond to the four regions of the spiral tube (2). The capacitance values ​​between the four capacitor plates and the spiral axis are the capacitance values ​​to be measured and are respectively recorded as C edci (i=1,2,3,4): C edci =C oi h(e g ,he o ,β(x,y,z)) In the formula, C oi is the equivalent capacitance of the empty tube; ε g is the relative dielectric constant of the material, ε o is the relative dielectric constant of vacuum, x, y and z are the spatial distribution of particle volume, β(x, y, z) is the volume filling rate distribution of solid medium, and h function is the fitting function obtained by experimental fitting; The total capacitance of the capacitive sensor is recorded as C avg :

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