A non-contact measurement method and device for round tube thickness

Abstract

The present invention discloses a non-contact measurement method for the thickness of a circular tube, which uses a non-contact sensor assembly to obliquely measure the inner wall and outer wall of the circular tube. The non-contact sensor assembly includes at least five distance measuring sensors distributed on the same circumference, and the detection directions of the distance measuring sensors all point to the center of the circumference. The angles between the detection directions of two adjacent distance measuring sensors are equal and do not exceed 45°. The first distance data of five consecutive distance measuring sensors when measuring the inner wall of the circular tube and the second distance data when measuring the outer wall of the circular tube are selected and converted into the first coordinate and the second coordinate. The first ellipse equation and the second ellipse equation are obtained according to the coordinate fitting, and the difference between the short semi-axis lengths of the first ellipse and the second ellipse is calculated to obtain the thickness of the circular tube. The present invention also discloses a device for implementing the measurement method. The present invention can avoid contacting the circular tube for measurement, and can provide accurate and highly repeatable measurement results.

Description

Technical Field

[0001] The invention relates to a method and a device for measuring the thickness of a round tube, belonging to the technical field of thickness measurement. Background Art

[0002] Paper tubes are widely used in packaging, printing, cables and wires and other industries. The thickness of paper tubes, as one of the key indicators to measure the quality of products, is directly related to factors such as the paper tube's load-bearing capacity, pressure resistance, loading requirements and production costs.

[0003] At present, the detection of paper tube thickness mainly relies on manual measurement using a vernier caliper, which leads to the introduction of a large number of human errors. On the one hand, when the operator is measuring, there may be errors in the relative position of the vernier caliper, the measurement direction may not be accurately aligned with the center of the circle, and the vernier caliper may not be kept level with the cross section of the paper tube. On the other hand, during the measurement process, there are significant differences in the force applied by the operator, which may cause different degrees of compression deformation on the wall of the paper tube. This leads to significant differences in the measurement results of different operators when detecting the thickness of a specific paper tube, and poor repeatability.

[0004] Using non-contact measurement technologies such as laser ranging can effectively prevent deformation errors caused by stress on paper tubes. However, the main problem with non-contact measurement methods is that the measurement angle is difficult to control accurately, that is, the measurement angle is not perpendicular to the axis of the paper tube, which makes the measurement result significantly different from the actual thickness of the paper tube. In addition, due to errors in cutting and other operations, the cut surface of the paper tube is usually not completely perpendicular to the central axis of the cylinder, which also poses a challenge to accurately measuring the thickness of the paper tube. Summary of the invention

[0005] In view of the above-mentioned defects of the prior art, the task of the present invention is to provide a non-contact method for measuring the thickness of a round tube, realize non-contact measurement of the thickness of a round tube, and solve the measurement error problem caused by measurement angle deviation. The task of the present invention is to provide a non-contact device for measuring the thickness of a round tube.

[0006] The technical solution of the present invention is as follows: A non-contact measurement method for the thickness of a round tube comprises the following steps:

[0007] The inner wall and the outer wall of the circular tube are measured using a non-contact sensor assembly, wherein the non-contact sensor assembly includes at least five distance measuring sensors distributed on the same circumference, and the detection directions of the distance measuring sensors are all directed to the center of the circumference, and the angles between the detection directions of two adjacent distance measuring sensors are equal and do not exceed 45°. During measurement, the plane formed by the detection directions of the distance measuring sensors is non-perpendicular to the axial direction of the circular tube;

[0008] Selecting five consecutive first distance data of the distance measuring sensor when measuring the inner wall of the circular tube, and selecting five consecutive second distance data of the distance measuring sensor when measuring the outer wall of the circular tube;

[0009] converting the first distance data and the second distance data into first coordinates and second coordinates of a plane where a circumference of a distance measuring sensor is distributed;

[0010] Fitting the five first coordinates to obtain a first ellipse equation, and fitting the five second coordinates to obtain a second ellipse equation;

[0011] The thickness of the circular tube is obtained by calculating the difference between the lengths of the minor semi-axes of the first ellipse and the second ellipse.

[0012] Furthermore, the angle between the detection directions of two adjacent distance measuring sensors is greater than 10°.

[0013] Furthermore, any one of the first distance data and the second distance data is greater than the radius of the circle+d, and d is not less than 5 mm.

[0014] Furthermore, when using a non-contact sensor assembly to measure the inner and outer walls of a circular tube, an alarm signal is generated when the number of first distance data greater than the circumferential radius + d is less than 5 or the number of second distance data greater than the circumferential radius + d is less than 5, and d is not less than 5 mm.

[0015] Furthermore, the alarm signal is at least one of a vibration, video and audio signal.

[0016] Another technical solution of the present invention is a non-contact measuring device for the thickness of a round tube, comprising a gripping portion, a non-contact sensor assembly and a calculating portion, wherein the non-contact sensor assembly comprises at least five distance measuring sensors distributed on the same circumference and the detection directions of the distance measuring sensors all point to the center of the circumference, and the angles between the detection directions of two adjacent distance measuring sensors are equal and do not exceed 45°, the gripping portion is connected to the non-contact sensor assembly, and the calculating portion is electrically connected to the non-contact sensor assembly;

[0017] The calculation unit is used to obtain the first distance data of five consecutive ranging sensors when measuring the inner wall of the circular tube, and the second distance data of five consecutive ranging sensors when measuring the outer wall of the circular tube; convert the first distance data and the second distance data into the first coordinate and the second coordinate of the plane where the circumference of the distance measuring sensors are distributed; fit the five first coordinates to obtain the first ellipse equation, and fit the five second coordinates to obtain the second ellipse equation; calculate the difference between the short semi-axis lengths of the first ellipse and the second ellipse to obtain the thickness of the circular tube.

[0018] Furthermore, the angle between the detection directions of two adjacent distance measuring sensors is greater than 10°.

[0019] Furthermore, the holding portion is provided with a display screen, and the display screen is used to display the thickness of the round tube.

[0020] Furthermore, the calculation unit generates an alarm signal when the number of first distance data greater than the circumferential radius + d is less than 5 or the number of second distance data greater than the circumferential radius + d is less than 5, and d is not less than 5 mm, and the holding unit is used to output the alarm signal.

[0021] Furthermore, it comprises a telescopic rod, and the telescopic rod is connected between the gripping portion and the non-contact sensor assembly.

[0022] The advantages of the present invention compared with the prior art are:

[0023] The present invention avoids direct contact with the round tube, and the measurement result is independent of the measurement personnel and the measurement angle. The present invention can provide accurate and highly repeatable measurement results. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 Schematic diagram of the structure of the non-contact measurement device for round tube thickness.

[0025] Figure 2 Schematic diagram of the non-contact measurement device for round tube thickness and the relative position of the round tube during testing.

[0026] Figure 3 This is the geometric relationship diagram between the ellipse intersection line and the distance sensor when measuring the inner diameter.

[0027] Figure 4 This is the geometric relationship diagram between the ellipse intersection line and the distance sensor when measuring the outer diameter. DETAILED DESCRIPTION

[0028] The present invention will be further described below in conjunction with the embodiments, but are not intended to limit the present invention.

[0029] Please combine Figure 1 As shown, the non-contact measuring device for the thickness of a round tube comprises a gripping portion 1, a telescopic rod 2 and a non-contact sensor assembly 3. The gripping portion 1 is provided with a display screen for displaying the measurement results and possible alarm information. The gripping portion 1 is connected to the non-contact sensor assembly 3 through the telescopic rod 2, and the distance of the non-contact sensor assembly 3 can be controlled by the extension and retraction of the telescopic rod 2, so that the measurement personnel can measure at a suitable position from the round tube. It should be pointed out that the gripping portion 1 and the telescopic rod 2 can be connected by a rotatable structure of the prior art, thereby changing the angle between the gripping portion 1 and the telescopic rod 2, thereby facilitating operation.

[0030] The non-contact sensor assembly 3 includes at least five ranging sensors 3a distributed on the same circumference, and the detection directions of the ranging sensors 3a are all directed to the center of the circumference. The angles between the detection directions of two adjacent ranging sensors 3a are equal and do not exceed 45°. The angles between the detection directions of two adjacent ranging sensors 3a should not be too small, and generally the angle is not less than 10°. In this embodiment, the non-contact sensor assembly 3 has an arc-shaped back plate 3b, and five laser ranging sensors 3a are arranged on the arc-shaped back plate 3b according to the above requirements, and the angle between two adjacent laser ranging sensors 3a is 30°.

[0031] A calculation unit is provided in the gripping part 1, and the calculation unit is electrically connected to the non-contact sensor assembly 3, that is, receiving the detection data of the distance measuring sensor 3a and calculating the measurement result (tube thickness), and then sending the measurement result to the display screen for display. The specific calculation unit is used to obtain the first distance data of five consecutive distance measuring sensors 3a when measuring the inner wall of the tube, and the second distance data of five consecutive distance measuring sensors 3a when measuring the outer wall of the tube; converting the first distance data and the first distance data into the first coordinate and the second coordinate of the plane where the circumference of the distance measuring sensor 3a is distributed; fitting the five first coordinates to obtain the first ellipse equation, fitting the five second coordinates to obtain the second ellipse equation; calculating the difference between the short semi-axis lengths of the first ellipse and the second ellipse to obtain the tube thickness.

[0032] When acquiring the first distance data and the second distance data, the calculation unit also determines the size of the first distance data and the second distance data. When any of the first distance data values ​​in the first distance data is smaller than the radius of the circumference of the distance sensor 3a or when any of the second distance data values ​​in the second distance data is smaller than the radius of the circumference of the distance sensor 3a, an alarm signal is generated. The alarm signal may be a vibration signal that causes the grip 1 to vibrate, a video signal that displays a prompt message on a display screen, or an audio signal that generates a sound prompt. The alarm signal is used to remind the measurement personnel to change the measurement position. In this process, the radius of the circumference of the distance sensor is used as the threshold for judgment. As a preferred embodiment, in order to further improve the accuracy, the radius of the circumference of the distance sensor 3a + 10mm is used as the threshold for judgment in this embodiment. That is, when any of the first distance data values ​​in the first distance data is < (the radius of the circumference of the distance sensor 3a + 10mm) or when any of the second distance data values ​​in the second distance data is < (the radius of the circumference of the distance sensor 3a + 10mm), an alarm signal is generated.

[0033] In an embodiment where more than five distance measuring sensors 3a are arranged, the calculation unit determines whether there are five distance measuring sensors 3a in consecutive positions that obtain first distance data greater than the circumferential radius + 10 mm (threshold), and whether there are five distance measuring sensors 3a in consecutive positions that obtain second distance data greater than the circumferential radius + 10 mm (threshold), and generates the aforementioned alarm signal when the adjustment is not satisfied.

[0034] The specific method of performing non-contact measurement of the thickness of a round tube using the aforementioned non-contact measurement device for the thickness of a round tube is described below.

[0035] Please combine Figures 2 to 4 As shown, the measurement personnel align the non-contact sensor assembly with the inner wall and the outer wall of the circular tube 4 in an inclined manner to obtain the first distance data and the second distance data. The inclination mentioned here means that the plane A formed by the detection direction of the distance measuring sensor 3a is not perpendicular to the axial direction of the circular tube 4 during measurement.

[0036] Assume that the plane formed by the detection direction of the ranging sensor is A, the intersection line between plane A and the cylindrical surface of the inner wall of the circular tube is an ellipse, and the five measuring points are evenly distributed on a certain arc of the ellipse.

[0037] When measuring the inner diameter, the geometric relationship between the ellipse intersection line and the distance sensor is shown in Figure 3 The distance sensor is located on a specific arc, and the radius of the arc is known, with the center of the circle being O and the radius being s 0 The distance sensor measures the first distance between it and the wall of the circular tube, which is recorded as l i .

[0038] In the actual measurement process, the position of the non-contact sensor assembly relative to the inner cylindrical surface of the tube is random. Therefore, there may be a situation where the center O is on the cylindrical surface or outside the cylindrical surface. To ensure that the center O is inside the cylindrical surface of the tube, it is necessary to meet l i - s 0 >10mm.

[0039] When the measured geometric relationship corresponds to Figure 4 In this case, the origin of plane A is set at the position of the center of circle O, and x The negative direction of the axis points to the distance sensor at the edge, and this distance sensor is used as the starting point, and is numbered from 1 to 5 in sequence.

[0040] Due to the angle between adjacent distance sensors α is known, then the line connecting each distance sensor and the origin is x The angle in the negative direction of the axis can be expressed as

[0041]

[0042] in, θ i Should be less than 180°. Then the measurement point corresponds to the first two-dimensional coordinate ( x s,i , y s,i ) can be expressed as:

[0043]

[0044] When measuring the outer diameter, the intersection of plane A and the cylindrical surface of the inner wall of the tube also presents an ellipse, such as Figure 4 As shown, the coordinate axis setting is the same as that when measuring the inner diameter, and the two-dimensional second coordinate corresponding to the measuring point can also be described by equations (1) and (2).

[0045] therefore, Figure 3 and Figure 4 The general equation of the intersection line of the ellipse can be expressed as

[0046]

[0047] Substituting the coordinates of the measured points into equation (3), the equation group can be expressed as follows:

[0048]

[0049] in:

[0050]

[0051] The standard equation of an ellipse (3) involves five parameters: b 0 , c 0 , d 0 , e 0 ,and f 0 . It can be calculated by A The inverse matrix can be directly solved X

[0052]

[0053] Using the least squares method to obtain the parameters in the basic expression of the ellipse intersection b 0 , c 0 , d 0 , e0 ,and f 0 Corresponding values. According to geometric principles, Figure 3 and Figure 4 The length of the minor semi-axis of the corresponding ellipse intersection line r b Corresponding to the radius of the cross section of the cylinder. From the general equation of the ellipse, the length of the minor semi-axis of the ellipse intersection can be obtained r b

[0054]

[0055] The radius of the cylindrical section corresponding to the ellipse intersection line can be calculated as:

[0056]

[0057] The thickness of the tube is obtained as , is obtained by formula (10) when measuring the outer diameter , is obtained by formula (10) when measuring the inner diameter .

[0058] Theoretically, when the center O is outside the cylindrical surface, formulas similar to equations (1) and (2) can also be obtained to obtain the coordinates corresponding to the measurement points. However, from the perspective of practical application, when the center O is outside the cylindrical surface, the distance between adjacent measurement points will be shorter, which will result in a decrease in the numerical difference of the coordinate points. At the same time, considering factors such as the measurement error of the ranging sensor, this may result in a hyperbolic equation being obtained when solving equation (3) instead of the expected elliptical equation. Therefore, using the radius of the circle where the ranging sensor is distributed + 10 mm as the threshold for the above judgment will improve accuracy.

[0059] The accuracy of the measurement of the present invention depends on the measured value l i The accuracy of the non-contact distance measuring sensor is the same as that of the non-contact distance measuring sensor. The accuracy of the laser distance measuring sensor and the ultrasonic distance measuring sensor can reach the micron level. Therefore, the device of the present invention has high measurement accuracy.

[0060] In order to verify the accuracy of the measurement results of the present invention, a section of hard steel pipe was selected and the thickness of the steel pipe was measured by a vernier caliper to be 8.05 mm.

[0061] The non-contact measuring device of the round tube thickness is adopted s 0 The distance between adjacent laser distance sensors is 100 mm, and the accuracy of the selected laser distance sensor is 0.1 mm. The number of non-contact laser distance sensors is 5, and the angle between adjacent distance sensors is αis 30°.

[0062] First, measure the inner diameter of the steel pipe, and the distance sensor returns the measured distance l i They are 368.96 mm, 355.19 mm, 324.68 mm, 300.68 mm, and 298.83 mm, respectively. The two-dimensional coordinates of the measuring points obtained by equations (1) and (2) are: [268.962, 0], [221.005, -127.597], [112.339, -194.576], [0, -200.684], [-99.416, -172.194]. Using equation (8), we can calculate b 0 = 0.5142, c 0 = 1.1321, d 0 =20.8045, e 0 =-161.1667, f 0 =-77936. The length of the minor semi-axis of the ellipse intersection line is obtained from formula (9): r b = 251.9901 mm, so the inner diameter can be calculated by (10) R Cin = 251.9901 mm.

[0063] Then measure the outer diameter of the steel pipe, and the distance sensor returns the measured distance l i They are 237.06 mm, 160.22 mm, 149.47 mm, 155.87 mm, and 202.33 mm, respectively. Therefore, the two-dimensional coordinates of the measurement points are: [137.06, 0], [52.15, -30.11], [24.74, -42.84], [0, -55.871], [-51.167, -88.624], respectively. It can be calculated from formula (8) a 0 =1, b 0 =-0.5926, c 0 =2.6875, d 0 =-642.3644, e 0 = 1389.7, f 0 = 69256. The length of the minor semi-axis of the ellipse intersection line is obtained from equation (9):r b = 260.0001 mm, so the inner diameter can be calculated by (10) R Cout = 260.0001 mm.

[0064] It can be concluded that the thickness of the steel pipe is 8.01 mm. It can be seen that the method for measuring thickness proposed by the present invention is reliable.

[0065] The non-contact measuring device for the thickness of a round tube is used to measure a paper tube, and the inner diameter of the paper tube is measured. The distance measured by the distance measuring sensor is returned. l i They are 351.17 mm, 355.09 mm, 303.28 mm, 260.96 mm, and 250.11 mm, respectively. The two-dimensional coordinates of the measuring points obtained by equations (1) and (2) are [251.17, 0], [220.91, -127.54], [101.64, -176.04], [0, -160.96], and [-75.05, -129.99], respectively. Using equation (8), we can calculate b 0 = 0.9817, c 0 = 1.2534, d 0 =-16.0050, e 0 =-165.2132, f 0 = -59066. From equation (9), we can get the length of the minor axis of the ellipse intersection line: r b =199.8447 mm, so the inner diameter can be calculated by (10) R Cin = 199.8447 mm.

[0066] Measure the outer diameter of the paper tube and the distance the sensor returns l i They are 237.06 mm, 160.22 mm, 149.47 mm, 155.87 mm, and 202.33 mm, respectively. Therefore, the two-dimensional coordinates of the measurement points are: [137.06, 0], [52.15, -30.11], [24.74, -42.84], [0, -55.871], [-51.167, -88.624], respectively. It can be calculated from formula (8) b 0 =-0.5926, c0 =2.6875, d 0 =-642.3644, e 0 = 1389.7, f 0 = 69256. The length of the minor semi-axis of the ellipse intersection line is obtained from equation (9): r b =250.8125 mm, so the inner diameter can be calculated by (10) R Cout = 250.8125 mm. Therefore, the thickness of the paper tube is 50.97 mm.

[0067] In order to further verify the reliability and repeatability of the device, different personnel were arranged to measure the thickness of the paper tube multiple times. The results are shown in Table 1.

[0068] Table 1 Test results

[0069]

[0070] The measurement results show high accuracy and good repeatability and are not affected by the tester and the measurement method.

Claims

1. A non-contact measuring device for the thickness of a round tube, characterized in that: It comprises a gripping part, a non-contact sensor assembly and a calculating part, wherein the non-contact sensor assembly comprises at least five distance measuring sensors distributed on the same circumference and the detection directions of the distance measuring sensors all point to the center of the circumference, and the angles between the detection directions of two adjacent distance measuring sensors are equal and do not exceed 45°, the gripping part is connected to the non-contact sensor assembly, and the calculating part is electrically connected to the non-contact sensor assembly. When the non-contact sensor assembly is used to measure the inner wall and the outer wall of a circular tube, an alarm signal is generated when the number of first distance data greater than the circumference radius + d is less than 5 or the number of second distance data greater than the circumference radius + d is less than 5, and d is not less than 5 mm, and the gripping part is used to output the alarm signal; The calculation unit is used to obtain the first distance data of five consecutive distance measuring sensors when measuring the inner wall of the circular tube, and the second distance data of five consecutive distance measuring sensors when measuring the outer wall of the circular tube; convert the first distance data and the second distance data into the first coordinate and the second coordinate of the plane where the circumference of the distance measuring sensors is distributed, , , l i When measuring the inner wall of a circular tube, it indicates the first distance data; when measuring the outer wall of a circular tube, it indicates the second distance data. s 0 Indicates the radius of the circle where the ranging sensor is located. α is the angle between adjacent distance measuring sensors ， ( x s,i , y s,i ) represents the first coordinate when measuring the inner wall of a circular tube, and represents the second coordinate when measuring the outer wall of a circular tube; the first ellipse equation is obtained by fitting the five first coordinates, and the second ellipse equation is obtained by fitting the five second coordinates. The specific ellipse equation is expressed as , after substituting the coordinates, it is expressed as AX=Y, where , , , calculate the inverse matrix of A to solve X; calculate the difference between the short semi-axis lengths of the first ellipse and the second ellipse to obtain the thickness of the circular tube.

2. The non-contact measuring device for round tube thickness according to claim 1, characterized in that: The included angle between the detection directions of two adjacent distance measuring sensors is greater than 10°.

3. The non-contact measuring device for round tube thickness according to claim 1, characterized in that: The holding portion is provided with a display screen, and the display screen is used to display the thickness of the round tube.

4. The non-contact measuring device for round tube thickness according to claim 1, characterized in that: It comprises a telescopic rod, which is connected between the gripping part and the non-contact sensor assembly.

5. The non-contact measuring device for round tube thickness according to claim 1, characterized in that: The alarm signal is at least one of a vibration, video and audio signal.

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