A metal foreign body positioning device and positioning method for a material conveyor belt based on a grid search method

Abstract

The present invention discloses a method for locating metal foreign bodies on a material conveyor belt based on a grid search method. Step 1: Calculate the magnetic anomaly characteristic signal S(t) generated by the metal foreign body in the X-axis direction under the background magnetic field excitation; Step 2: Based on the magnetic anomaly characteristic signal S(t) in step 1, after matching filtering with the filter function H(t), calculate the magnetic field energy ratio E of the metal foreign body detected by each sensor. r Step 3: Use the magnetic field energy ratio E of the metal foreign body detected in step 2 r , that is, the grid search method is used to locate the metal foreign body. The present invention is used to solve the problem that the existing method has low positioning accuracy and causes material waste.

Description

Technical Field

[0001] The present invention belongs to the field of metal foreign body detection and positioning; in particular, it relates to a metal foreign body positioning device for a material conveyor belt based on a grid search method and a positioning method thereof. Background Art

[0002] Existing methods for detecting and locating foreign metal objects on conveyor belts primarily rely on parallel coils, consisting of a transmitting coil and a receiving coil. The transmitting coil generates an alternating electromagnetic field, also known as the primary field. When a foreign metal object is present within the primary field, it generates a magnetizing field or eddy current field, also known as the secondary field. The receiving coil is used to capture changes in this secondary field.

[0003] There are two main types of existing detection and positioning devices. The first type uses a transmitting coil and a receiving coil. This device can only determine whether there is a metal foreign object within the coverage area of ​​the coil, but cannot confirm the specific location of the metal foreign object. When a metal foreign object is present, all materials within the coverage area of ​​the coil must be removed, resulting in great waste; the second type is a detection and positioning device that uses a transmitting coil and multiple receiving coil arrays. The resolution of this device for locating metal foreign objects is affected by the coil spacing. Although it can roughly locate the metal foreign object, the positioning accuracy is not high. Therefore, both types of monitoring and positioning devices will cause material waste. Summary of the Invention

[0004] The present invention provides a material conveyor belt metal foreign body positioning device and positioning method based on a grid search method. Existing methods have low positioning accuracy and cause material waste.

[0005] The present invention is achieved through the following technical solutions:

[0006] A material conveyor belt metal foreign body positioning device based on a grid search method, the positioning device includes a conveyor belt 1, an excitation coil 2 and a receiving array of magnetoresistive sensors 3. The excitation coil 2 is arranged above the conveyor belt 1, and the height between the conveyor belt 1 and the excitation coil 2 is H. A plurality of magnetoresistive sensors 3 are placed at equal intervals on the bottom surface of the excitation coil 2.

[0007] A method for locating a metal foreign body in a material conveyor belt based on a grid search method, the method comprising the following steps:

[0008] Step 1: Calculate the magnetic anomaly characteristic signal S(t) generated by the metal foreign body in the X-axis direction under the background magnetic field excitation;

[0009] Step 2: Based on the magnetic anomaly characteristic signal S(t) in step 1, after matching filtering with the filter function H(t), calculate the magnetic field energy ratio E of the metal foreign body detected by each sensor. r

[0010] Step 3: Use the magnetic field energy ratio E of the metal foreign body detected in step 2 r , that is, the grid search method is used to locate the metal foreign body.

[0011] Furthermore, the step 1 is specifically as follows: for the rectangular excitation coil, after a stable excitation current is passed through, a uniform excitation magnetic field will be generated at the bottom center of the coil, that is, a primary background field B P (t), the expression is as follows,

[0012]

[0013] Where A is the excitation field amplitude, f0 is the excitation frequency, The excitation frequency is selected according to the material of the foreign body. The excitation frequency of ferromagnetic metal is 100-200Hz, and the excitation frequency of non-ferromagnetic metal is 10-20KHz. After the background magnetic field is applied, the metal foreign body can be regarded as a magnetic dipole, and its secondary field B S (t) is expressed as

[0014]

[0015] Where μ0 represents the vacuum permeability, which is 4π×10 -7 H / m, r = [xyz] T =r0+vt=[vt d -h] T represents the position vector pointing from the target to the sensor position, where is the distance between the metal foreign body and the closest point of the sensor;

[0016] Since the exciting coil plane is parallel to the detection plane, the exciting magnetic field directly below the coil is approximately a vertical magnetic field, which can be expressed as m(t) = [0 0 m z (t)] represents the target magnetization moment,

[0017]

[0018] Where a represents the diameter of the target object, and L represents the material-related parameters of the target object;

[0019] Let w(t) = vt / r0, then the secondary field signal of the metal foreign body in the X direction is expressed as

[0020]

[0021] The above secondary field signal is After mixing and low-pass filtering, the magnetic anomaly characteristic signal can be obtained.

[0022]

[0023] Furthermore, the step 2 is specifically as follows: when a metal foreign body passes through any position below the excitation coil, the magnetic anomaly characteristic signal of the metal foreign body detected by the i-th sensor in the magnetoresistive sensor array is expressed as S i (t), the magnetic field energy of the metal foreign body detected by the i-th sensor is expressed as E i (t), E i (t) is the characteristic signal S of the magnetic anomaly of the metal foreign body i (t) is obtained after the matched filtering of the filter function H(t), which is expressed as

[0024]

[0025] in And ∫H(t) 2 dt=1, α0 is the filter normalization coefficient, and the energy peak is output at time t=0 when the metal foreign body passes directly under the sensor.

[0026] Furthermore, when the target passes under the coil, the three sensors with the largest target magnetic field energy output are selected as positioning sensors. They are named sensors 1, 2, and 3 in descending order of output magnetic field energy values. d is used to represent the lateral offset distance between the metal target and sensor 1. The lateral offset distances between the target and sensors 2 and 3 can be expressed as Dd and 2D-d, respectively. The matched filter output values ​​of the three sensors are recorded as E1(t), E2(t), and E3(t), respectively. Then,

[0027]

[0028]

[0029]

[0030] in

[0031]

[0032]

[0033]

[0034] Then the peak energy of each sensor output after matched filtering is

[0035]

[0036]

[0037]

[0038] The peak energy ratio of the filtered output of sensor No. 2 to sensor No. 1 is

[0039]

[0040] The above expression eliminates the influence of the metal foreign body size and material, and obtains a function only related to the metal foreign body position parameters h and d; similarly, the peak energy ratio of the filtered output of sensor No. 2 and sensor No. 3 is

[0041]

[0042] Furthermore, the step 3 is specifically to combine E r21 (h,d) and E r23 The two equations (h, d) can be used to obtain a set of two-variable high-order equations about the position parameters h and d of the metal foreign body, thereby obtaining the position parameters h and d of the metal foreign body;

[0043] The location of the metal foreign body is realized by solving the binary high-order equations through the grid search method:

[0044]

[0045] The beneficial effects of the present invention are:

[0046] The present invention improves the positioning accuracy of metal foreign matter, can accurately locate the specific position of the impurities on the conveyor belt, facilitates the removal device to accurately remove the metal foreign matter, and ensures the continuity of industrial production and the automation of metal foreign matter removal;

[0047] The present invention can accurately locate the target area when the size and material of the target object are unknown;

[0048] The present invention uses a MEMS magnetoresistive sensor array to replace a traditional receiving coil, which has the advantages of miniaturization and high precision.

[0049] The present invention can save costs and does not cause a large amount of material waste. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Attachment Figure 1 Schematic diagram of the metal foreign body target detection device of the present invention.

[0051] Attachment Figure 2 The peak energy ratio surface of the present invention, wherein (a) the peak energy ratio E 21 Surface diagram, (b) peak energy ratio E 23 Surface plot of .

[0052] Attachment Figure 3 Flowchart of the method of the present invention.

[0053] Attachment Figure 4 Schematic diagram of the positioning grid of the present invention. DETAILED DESCRIPTION

[0054] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0055] Example 1

[0056] A material conveyor belt metal foreign body positioning device based on a grid search method, the positioning device includes a conveyor belt 1, an excitation coil 2 and a receiving array of magnetoresistive sensors 3. The excitation coil 2 is arranged above the conveyor belt 1, and the height between the conveyor belt 1 and the excitation coil 2 is H. A plurality of magnetoresistive sensors 3 are placed at equal intervals on the bottom surface of the excitation coil 2.

[0057] A method for locating a metal foreign body in a material conveyor belt based on a grid search method, the method comprising the following steps:

[0058] Step 1: Calculate the magnetic anomaly characteristic signal S(t) generated by the metal foreign body in the X-axis direction under the background magnetic field excitation;

[0059] Step 2: Based on the magnetic anomaly characteristic signal S(t) in step 1, after matching filtering with the filter function H(t), calculate the magnetic field energy ratio E of the metal foreign body detected by each sensor. r

[0060] Step 3: Use the magnetic field energy ratio E of the metal foreign body detected in step 2 r , that is, the grid search method is used to locate the metal foreign body.

[0061] Furthermore, the step 1 is specifically as follows: for the rectangular excitation coil, after a stable excitation current is passed through, a uniform excitation magnetic field will be generated at the bottom center of the coil, that is, a primary background field B P (t), the expression is as follows,

[0062]

[0063] Where A is the excitation field amplitude, f0 is the excitation frequency, The excitation frequency is selected according to the material of the foreign body. The excitation frequency of ferromagnetic metal is 100-200Hz, and the excitation frequency of non-ferromagnetic metal is 10-20KHz. After the background magnetic field is applied, the metal foreign body can be regarded as a magnetic dipole, and its secondary field B S (t) is expressed as

[0064]

[0065] Where μ0 represents the vacuum permeability, which is 4π×10 -7 H / m, r = [xyz] T =r0+vt=[vt d -h] T represents the position vector pointing from the target object to the sensor position (the metal foreign body passes directly under the sensor at time t = 0), where is the distance between the metal foreign body and the closest point of the sensor;

[0066] Since the exciting coil plane is parallel to the detection plane, the exciting magnetic field directly below the coil is approximately a vertical magnetic field, which can be expressed as m(t) = [0 0 m z (t)] represents the target magnetization moment,

[0067]

[0068] Where a represents the diameter of the target object, and L represents the material-related parameters of the target object;

[0069] Let w(t) = vt / r0, then the secondary field signal of the metal foreign body in the X direction is expressed as

[0070]

[0071] The above secondary field signal is After mixing and low-pass filtering, the magnetic anomaly characteristic signal can be obtained.

[0072]

[0073] Furthermore, the step 2 is specifically as follows: when a metal foreign body passes through any position below the excitation coil, the magnetic anomaly characteristic signal of the metal foreign body detected by the i-th sensor in the magnetoresistive sensor array is expressed as S i (t), the magnetic field energy of the metal foreign body detected by the i-th sensor is expressed as E i (t), E i (t) is the characteristic signal S of the magnetic anomaly of the metal foreign body i (t) is obtained after the matched filtering of the filter function H(t), which is expressed as

[0074]

[0075] in And ∫H(t) 2 dt=1, α0 is the filter normalization coefficient, and the energy peak is output at time t=0 when the metal foreign body passes directly under the sensor.

[0076] Furthermore, when the target passes under the coil, the three sensors that output the largest target magnetic field energy are selected as positioning sensors. They are named No. 1, No. 2, and No. 3 in descending order of output magnetic field energy values, such as Figure 1 As shown, S1, S2, and S3 are magnetoresistive sensors No. 1, No. 2, and No. 3 respectively; D is the distance between the two sensors, 27 mm; v is the direction of movement and speed; d is the lateral offset distance between the target and sensor No. 1, 0 ≤ d ≤ 54 mm; h is the vertical detection height from the sensor to the target, 10 ≤ h ≤ 30 mm; H is the distance from the sensor to the conveyor plane, 30 mm. d is used to represent the lateral offset distance between the metal target and sensor No. 1, then the lateral offset distances between the target and sensors No. 2 and No. 3 can be expressed as Dd and 2D-d respectively. The matched filter output values ​​of the three sensors are recorded as E1(t), E2(t), and E3(t) respectively, then

[0077]

[0078]

[0079]

[0080] in

[0081]

[0082]

[0083]

[0084] Then the peak energy of each sensor output after matched filtering is

[0085]

[0086]

[0087]

[0088] The peak energy ratio of the filtered output of sensor No. 2 to sensor No. 1 is

[0089]

[0090] The above expression eliminates the influence of the metal foreign body size and material, and obtains a function only related to the metal foreign body position parameters h and d; similarly, the peak energy ratio of the filtered output of sensor No. 2 and sensor No. 3 is

[0091]

[0092] Furthermore, the step 3 is specifically to combine E r21 (h,d) and E r23 The two equations (h, d) can be used to obtain a set of two-variable high-order equations about the position parameters h and d of the metal foreign body, thereby obtaining the position parameters h and d of the metal foreign body;

[0093] The location of the metal foreign body is realized by solving the binary high-order equations through the grid search method:

[0094]

[0095] The present invention uses miniaturized, high-precision MEMS magnetoresistive sensors to replace traditional receiving coils and designs a sensor array. First, the rough position of metal foreign objects on the conveyor belt is determined through the detection output of the sensor. Then, a grid search algorithm is applied to accurately locate the position of the metal foreign objects, realizing the functions of detecting and locating the metal foreign objects. The positioning accuracy and resolution are improved, making it easier for the rejection device to accurately remove metal foreign objects, ensuring the continuity of industrial production and the automation of metal foreign object rejection.

[0096] Example 2

[0097] First, according to Figure 1 The value range of the setting parameter h of the equipment shown is Set the value range of d to Set the search step size Δh = 1mm, Δd = 1mm. In the selected h and d interval, search E according to the selected step size. r21 (h,d),E r23 (h, d) is traversed to draw E r21 (h,d) and E r23 The distribution surface of (h, d) with position parameters h and d, such as Figure 2 As shown;

[0098] Assume that the actual measured peak energy ratio is expressed as and Let the error function

[0099]

[0100] Then when E Δ When (h, d) takes the minimum, that is, 1 / E Δ The maximum value of (h, d), the corresponding h, d is the positioning result, the positioning calculation formula is as follows

[0101]

[0102] Example 3

[0103] A metal ball with a diameter of 5 mm passes through the position 27 mm away from sensor 1. At this time, the actual position coordinates of the target object are approximately [h, d] = [25, 27] mm. The proposed positioning method is used for positioning. The positioning grid is as follows: Figure 4 shown.

[0104] from Figure 4 As can be seen in the figure, the positioning grid has a peak at [h, d] = [25, 27] mm. The position of the metal ball after positioning according to the algorithm is [h, d] = [25, 27] mm, and the positioning result is accurate.

[0105] The present invention uses a MEMS magnetoresistive sensor array to replace the traditional receiving coil, which has the advantages of miniaturization and high precision. When the size and material of the target object are unknown, the specific position of the metal foreign body on the conveyor belt can be accurately located, thereby improving the positioning accuracy of the metal foreign body, facilitating the removal device to accurately remove the metal foreign body, ensuring the continuity of industrial production and the automation of the removal of metal foreign bodies. It also overcomes the disadvantage that the presence of metal foreign bodies in the current detection device will result in the discard of materials and cause a lot of waste.

Claims

1. A method for locating a metal foreign body in a material conveyor belt based on a grid search method, characterized in that: The positioning device comprises a conveyor belt (1), an excitation coil (2) and a magnetoresistive sensor (3) receiving array, wherein the excitation coil (2) is arranged above the conveyor belt (1), the height between the conveyor belt (1) and the excitation coil (2) is H, and a plurality of magnetoresistive sensors (3) are arranged at equal intervals on the bottom surface of the excitation coil (2); The positioning method comprises the following steps: Step 1: Calculate the magnetic anomaly characteristic signal S(t) generated by the metal foreign body in the X-axis direction under the background magnetic field excitation; Step 2: Based on the magnetic anomaly characteristic signal S(t) in step 1, after matching filtering with the filter function H(t), calculate the magnetic field energy ratio E of the metal foreign body detected by each sensor. r ; When a metal foreign body passes through any position below the excitation coil, the magnetic anomaly characteristic signal of the metal foreign body detected by the i-th sensor in the magnetoresistive sensor array is expressed as S i (t), the magnetic field energy of the metal foreign body detected by the i-th sensor is expressed as E i (t), E i (t) is the characteristic signal S of the magnetic anomaly of the metal foreign body i (t) is obtained after the matched filtering process of the filter function H(t), When the target passes under the coil, the three sensors with the largest target magnetic field energy output are selected as positioning sensors. They are named sensors 1, 2, and 3 in descending order of output magnetic field energy values. d is used to represent the lateral offset distance between the metal target and sensor 1. The lateral offset distances between the target and sensors 2 and 3 can be expressed as Dd and 2D-d, respectively. The matched filter output values ​​of the three sensors are recorded as E1(t), E2(t), and E3(t), respectively. Then, in Where D is the distance between the two sensors, and h is the vertical detection height from the sensor to the target; Then the peak energy of each sensor output after matched filtering is The peak energy ratio of the filtered output of sensor No. 2 to sensor No. 1 is The above expression eliminates the influence of the metal foreign body size and material, and obtains a function only related to the metal foreign body position parameters h and d; similarly, the peak energy ratio of the filtered output of sensor No. 2 and sensor No. 3 is Step 3: Use the metal foreign body magnetic field energy ratio E detected in step 2 r , that is, the grid search method is used to locate the metal foreign body; The step 3 is specifically to combine E r21 (h,d) and E r23 The two equations (h, d) can be used to obtain a set of two-variable high-order equations about the position parameters h and d of the metal foreign body, thereby obtaining the position parameters h and d of the metal foreign body; The location of the metal foreign body is realized by solving the binary high-order equations through the grid search method:

2. The method for locating a metal foreign body on a material conveyor belt based on a grid search method according to claim 1, characterized in that: Specifically, the step 1 is as follows: for a rectangular excitation coil, after a stable excitation current is passed through, a uniform excitation magnetic field is generated at the bottom center of the coil, namely, a primary background field B. P (t), the expression is as follows, Where A is the excitation field amplitude, f0 is the excitation frequency, The excitation frequency is selected according to the material of the foreign body. The excitation frequency of ferromagnetic metal is 100-200Hz, and the excitation frequency of non-ferromagnetic metal is 10-20KHz. After the background magnetic field is applied, the metal foreign body can be regarded as a magnetic dipole, and its secondary field B S (t) is expressed as Where μ0 represents the vacuum permeability, which is 4π×10 -7 H / m, r = [xyz] T =r0+vt=[vt dh] T represents the position vector pointing from the target to the sensor position, where is the distance between the metal foreign body and the closest point of the sensor; Since the exciting coil plane is parallel to the detection plane, the exciting magnetic field directly below the coil is approximately a vertical magnetic field, which can be expressed as m(t) = [0 0m z (t)] represents the target magnetization moment, Where a represents the diameter of the target object, and L represents the material-related parameters of the target object; Let w(t) = vt / r0, where v is the direction and velocity of motion. The secondary field signal of the metal foreign body in the X direction is expressed as follows: The above secondary field signal is After mixing and low-pass filtering, the magnetic anomaly characteristic signal can be obtained.

3. The method for locating metal foreign matter on a material conveyor belt based on a grid search method according to claim 1, characterized in that: The step 2 is expressed as: in And ∫H(t) 2 dt=1, α0 is the filter normalization coefficient, and the energy peak is output at time t=0 when the metal foreign body passes directly under the sensor.

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