Evaluation method

Abstract

To provide a method for evaluating the shape of a long cylindrical structure while restricting a workload by an operator.SOLUTION: Provided is a method having the following steps: (a) acquiring first point group data by scanning an inner part of a structure with a 3D laser scanner; (b) acquiring second point group data by fitting a cylinder on the first point group data; (c) setting a reference coordinate system including a reference direction substantially parallel to a longitudinal direction of the structure; (d) fitting the cylinder on each of third point group data obtained by dividing the second point group data into a plurality of sections along the reference direction, and determining an expression under the reference coordinate system of a center axis of the cylinder; (e) calculating a clearance between the center axis of the cylinder for each of the plurality of third point group data and each point included in the third point group data; and (f) detecting a surface condition of the inner part of the structure on the basis of a clearance distribution calculated in (e).SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for evaluating the shape of a long, cylindrical structure. [Background technology]

[0002] Rotary kilns, capable of high-temperature firing, are used to produce clinker, the raw material for cement. A rotary kiln has a cylindrical kiln shell. The temperature inside the kiln shell can reach up to 1300°C to 1400°C, so the inner walls of the kiln shell are typically lined with firebricks.

[0003] Raw materials are introduced into the kiln shell from one side (the tail end) of the rotary kiln and fired while rotating with the rotation of the kiln shell, moving toward the other side (the front end) where the burner is installed, thereby producing clinker. As a result, the raw materials or clinker (hereinafter referred to as "raw materials, etc.") are fired while rotating in contact with the surface of the refractory bricks and falling toward the bottom according to the slope of the wall.

[0004] In other words, the refractory bricks lining the inner walls of the kiln shell come into physical contact with the raw materials, and in some places, they collide with the materials with momentum. As a result, the refractory bricks wear down with use of a rotary kiln, and in some cases, parts of the refractory bricks may collapse. In addition, vaporized components from the firing process of the raw materials can adhere to and grow on the surface of the refractory bricks (coating), and the peeling off of this coating can also cause wear and collapse of the refractory bricks.

[0005] Understanding the degree of wear on refractory bricks and replacing them at the appropriate time is important to prevent refractory brick collapse and plastic deformation of the kiln shell caused by increased heat transfer to the kiln shell through refractory bricks with insufficient remaining thickness.

[0006] From this perspective, inspection work has traditionally been carried out periodically to check the wear condition of the refractory bricks. Typically, considering the large number of rotary kilns to be inspected and the manpower required for each inspection, inspection work is carried out about twice a year.

[0007] Traditionally, to assess the wear condition of firebricks, workers have entered the kiln shell and directly measured the wear using measuring instruments such as scales.

[0008] The following patent documents 1 to 3 are known as methods for measuring the amount of material loss or remaining thickness of an object.

[0009] Patent Document 1 discloses a technique for measuring the amount of corrosion and thinning of heat exchanger tubes installed in oil refineries, petrochemical plants, etc. According to the technique disclosed in Patent Document 1, a portion of the target heat exchanger tubes is removed, cut in half lengthwise, and then the amount of thinning is calculated from the three-dimensional shape data obtained by scanning the inner and outer surfaces of the tubes exposed by the cutting process with a 3D scanner.

[0010] According to the technology disclosed in Patent Document 2, a laser beam is shone parallel to the central axis of the kiln shell, and the distance from the laser beam to the refractory material is measured, thereby determining the thickness of the refractory material.

[0011] According to the technology disclosed in Patent Document 3, a measuring device is attached to a movable trolley, and the remaining thickness of the refractory coating inside the furnace body is determined from the amount of movement of the scattered laser beam, and the remaining thickness is represented in a distribution diagram using two-dimensional isobars. [Prior art documents] [Patent Documents]

[0012] [Patent Document 1] Japanese Patent Publication No. 2020-003420 [Patent Document 2] Japanese Patent Publication No. 2005-195380 [Patent Document 3] Japanese Patent Application Publication No. 1-114705 [Overview of the Initiative] [Problems that the invention aims to solve]

[0013] The method described in Patent Document 1 is difficult to apply when the object to be measured is large or when it is not possible to extract a portion of it, such as in the case of a rotary kiln. Furthermore, the methods described in Patent Document 2 or Patent Document 3 are cumbersome and require an enormous amount of work to measure the thickness of all parts of a large object.

[0014] In addition to situations where the thickness of refractory bricks laid inside a kiln shell needs to be measured, there are also situations where it is necessary to inspect the deformation and wear condition of the inner surface of large cylindrical structures such as tunnels, sewer pipes, and water conduits for power plants. However, for the reasons mentioned above, the methods described in Patent Documents 1 to 3 are not easily applicable to such inspections.

[0015] In view of the above problems, the present invention aims to provide a method for evaluating the shape of a long cylindrical structure while suppressing the amount of work required from the worker. [Means for solving the problem]

[0016] The present invention relates to a method for evaluating the shape of a long cylindrical structure, (a) A step of obtaining first point cloud data by scanning the inside of the structure over the entire area of ​​the measurement target region of the structure using a 3D laser scanner, (b) A step of fitting a cylinder to the first point cloud data to obtain second point cloud data, (c) A step of setting a reference coordinate system that includes a reference plane formed by a portion of the second point cloud data, and a reference direction that is perpendicular to the reference plane and substantially parallel to the longitudinal direction of the structure, For each of the third point cloud data obtained by dividing the second point cloud data into a plurality of sections along the reference direction, perform a fitting process of a cylinder, and determine an equation in the reference coordinate system of the second point cloud data for the central axis of the fitted cylinder in step (d); For each of the plurality of third point cloud data, calculate the separation distance between the central axis of the cylinder fitted in step (d) and each point included in the third point cloud data based on the coordinate information based on the reference coordinate system of the second point cloud data in step (e); Based on the distribution of the separation distances calculated in step (e), detect the surface state of the inner part over the measurement target area of the structure in step (f).

[0017] According to the above method, the inner part of the structure is scanned using a 3D laser scanner over the entire measurement target area of the structure. By using a 3D laser scanner, the actual state on site can be obtained as a huge amount of point cloud data (first point cloud data). By fitting a cylinder corresponding to the shape of the inner part of the structure to this first point cloud data, point cloud data (second point cloud data) based on a new coordinate system can be obtained.

[0018] By the way, in a long structure, over time after being constructed on site, a part may bend due to its own weight. Also, depending on the site, it cannot be denied that ground settlement, fault displacement, etc. may occur. That is, the central axis of the cylinder simulated by the second point cloud data may be different from the central axis of the actual inner part of the structure.

[0019] In particular, when the structure is large, although the central axis of the structure may seem to be straight at first glance to the operator, it cannot be denied that there may be minute inclinations or deflections in the structure. In such a case, when evaluating the surface state of the inner part of the structure based on the second point cloud data, there is a risk of judging that the surface is flat when there are actually irregularities on the surface, or conversely, judging that there are irregularities on the surface when the surface is actually flat. That is, there is a possibility that the shape of the structure cannot be accurately evaluated.

[0020] In contrast, according to the above method, the first point cloud data obtained by scanning with a 3D laser scanner is divided into a plurality of sections along a direction (reference direction) substantially parallel to the longitudinal direction of the structure, and a cylinder is re-fitted to each of the divided point cloud data (third point cloud data). Each cylinder simulated by each of the third point cloud data obtained by this fitting process corresponds to a small section obtained by virtually dividing the structure in the longitudinal direction.

[0021] In other words, each of the third point cloud data is data simulating a small section obtained by virtually dividing a long structure in the longitudinal direction. As described above, when the structure is long, the central axis may deviate depending on the position. However, the third point cloud data obtained by the above method is fitted for each small section obtained by substantially dividing the structure in the longitudinal direction. Therefore, even if the central axis of the long structure is deviated, there is almost no deviation of the central axis in the unit of the small section. In other words, it is possible to set the central axis of one small section and the central axis of another small section at different positions.

[0022]

[0023] Therefore, by calculating the separation distance between the central axis of the cylinder fitted to each of the third point cloud data and each point included in the third point cloud data for each of the cylinders, it is possible to evaluate the surface state of the inner part of the structure for each small section obtained by dividing the long structure in the longitudinal direction.Furthermore, in step (b), the second point cloud data is obtained by fitting the cylinder to the first point cloud data obtained by scanning the entire measurement area of ​​the structure in advance. Therefore, the coordinate information of each point cloud data included in this second point cloud data is identified based on the reference coordinate system. Thus, the coordinates of each point in the third point cloud data fitted in small sections can also be defined by the coordinate information based on the reference coordinate system. In other words, even if the central axes of each cylinder fitted to the third point cloud data are different, the central axis and the position of each point cloud data can be defined by the information based on the reference coordinate system, so the distance between the central axis of each cylinder and each point included in the third point cloud data can be easily calculated, for example, by calculations based on general geometric methods.

[0024] Steps (b) and (d) may be performed by a processing unit executing a predetermined software program using the data obtained by the 3D laser scanner in step (a). Similarly, steps (c), (e), and (f) may also be performed by a processing unit executing a software program.

[0025] The reference direction set in step (c) can be used to define the direction in which the first point cloud data is divided. This division direction follows the longitudinal direction of a long structure, but does not need to be perfectly parallel. In other words, for the reference direction to be "substantially parallel to the longitudinal direction" means that it is close enough to the longitudinal direction to be considered to follow the longitudinal direction of the structure. Typically, the absolute value of the angle between the reference direction and the longitudinal direction is 15° or less, preferably 10° or less, and more preferably 5° or less.

[0026] The aforementioned structure is a kiln shell with firebricks attached to its inner wall surface. The aforementioned step (f) may include a step of detecting the degree of wear of the refractory bricks over the measurement target area.

[0027] As mentioned above, conventionally, the amount of wear on the refractory bricks inside the kiln shell was measured directly by workers who entered the kiln shell using measuring instruments such as scales. Therefore, the upper part of the kiln shell near the ceiling and areas that were out of reach could only be judged visually to determine if there were any abnormalities. As a result, there was a risk that the evaluation results would depend on the skill level of the workers.

[0028] In contrast, the above method utilizes a 3D laser scanner, allowing for the creation of point cloud data that accurately represents the internal conditions of the kiln shell. Therefore, evaluating the degree of wear on the refractory bricks based on this point cloud data eliminates discrepancies in measurement results by different workers. Furthermore, this method is expected to significantly reduce the time and personnel required for on-site work, ensure safety during operations, and enable measurements in locations that are inaccessible to humans.

[0029] Furthermore, according to the above method, even if a long kiln shell is bending under its own weight, third-point cloud data, which consists of cylinders fitted to each small section obtained by dividing the kiln shell in the longitudinal direction, is used. Therefore, as described above, a central axis can be set for each cylinder to which each third-point cloud data is fitted, and by calculating the distance between the central axis and the point cloud data for each cylinder, the surface condition of the inside of the kiln shell can be detected for each small section obtained by dividing the kiln shell in the longitudinal direction. More specifically, in areas where the distance between the central axis and the point cloud data is relatively long, it can be evaluated that wear of the refractory bricks is progressing.

[0030] Step (f) may also be a method of detecting the distribution of the remaining thickness of the refractory bricks over the measurement target area by calculating the difference in the separation distance calculated in step (e) from the value of the inner diameter of the kiln shell that has been measured or designed in advance.

[0031] The reference surface set in step (c) may be the end face of the cylinder fitted in step (b). [Effects of the Invention]

[0032] According to the present invention, the shape of a long cylindrical structure can be evaluated while suppressing the amount of work required from the worker. [Brief explanation of the drawing]

[0033] [Figure 1] This is a flowchart schematically illustrating the procedure of one embodiment of the method for evaluating the shape of a structure according to the present invention. [Figure 2] This diagram schematically illustrates the process of scanning the inner surface of a kiln shell. [Figure 3] This is a photograph showing an example of the scanning process, viewed along the longitudinal direction of the kiln shell. [Figure 4] This is a block diagram schematically showing an example of the configuration of an arithmetic processing unit. [Figure 5] This is an example of point cloud data (second point cloud data) whose coordinate space has been transformed. [Figure 6] Figure 5 shows the second point cloud data with the reference coordinate system superimposed. [Figure 7] This is a schematic diagram illustrating a situation where the central axis of the fitted cylinder is misaligned with the central axis of the actual kiln shell. [Figure 8] This is a schematic diagram illustrating the process of fitting point cloud data to a cylinder for each section. [Figure 9] This is a schematic diagram illustrating the process of fitting point cloud data to a cylinder for each section. [Figure 10] This is a schematic diagram illustrating a method for calculating the remaining thickness of firebricks. [Figure 11] This is an example of a 3D contour map that shows the distribution of the remaining thickness of firebricks in 3D format. [Figure 12]This diagram schematically illustrates a method for generating a kiln development diagram from a 3D contour map. [Figure 13] This is an example of a kiln unfolding diagram, with comparative examples and embodiments illustrated separately. [Modes for carrying out the invention]

[0034] In the following, embodiments of the method for evaluating the shape of a structure according to the present invention will be described with reference to the drawings as appropriate. However, the following drawings are schematic representations, and the dimensional ratios shown in the drawings do not necessarily match the actual dimensional ratios. Furthermore, the dimensional ratios do not necessarily match between the drawings.

[0035] This method can be used to evaluate the shape of long, cylindrical structures, and more typically, is suitable for evaluating large structures. A typical example of such a structure is the kiln shell of a rotary kiln. Other examples of structures include tunnels, sewer pipes, factory piping, and water conduits in power plants.

[0036] This method allows for the evaluation of the shape of the long cylindrical structure exemplified above, and more specifically, the surface condition of the inside of the cylinder. The surface condition here refers to whether or not there are irregularities on the surface, and in what manner the irregularities exist. More specifically, the manner of existence of irregularities refers to the location of the irregularities, the size (area, depth) of the irregularities, and the distribution of the irregularities. For example, if a part of the inner wall of the cylinder has peeled off, the peeled-off area will be recessed compared to the surrounding area, and therefore irregularities will exist in that region.

[0037] In the following embodiments, the case in which the structure to be evaluated is a kiln shell of a cement kiln will be used as an example for explanation.

[0038] Figure 1 is a flowchart schematically showing the procedure of one embodiment of the method for evaluating the shape of a structure according to the present invention. The evaluation method of this embodiment will be described below with reference to the flowchart shown in Figure 1.

[0039] (Step #1) First, the inner portion of the cylindrical structure to be scanned by a 3D laser scanner. In this embodiment, the inside of the kiln shell 1 of the cement kiln is scanned by the 3D laser scanner. Figure 2 is a schematic diagram of the scanning process. Figure 3 is a photograph showing an example of the scanning process in action, viewed along the longitudinal direction of the kiln shell 1.

[0040] Kiln shell 1 is a long, cylindrical structure with firebricks laid on its interior. For example, the longitudinal length of kiln shell 1 is 100m, and the inner diameter (radius) is 2.75m according to the design specifications. An example of the size of a single firebrick inside kiln shell 1 is 10cm (length) x 20cm (width) x 25cm (height) at the initial construction stage (before wear).

[0041] In this embodiment, the 3D laser scanner 11 irradiates the object to be measured (in this case, the inner wall of the kiln shell 1) with laser light and receives the light reflected from the object. The 3D laser scanner 11 calculates the distance between the light emission window and the object to be measured by detecting the phase difference between the emitted light and the reflected light. This method is generally called the "phase difference method".

[0042] Typically, the 3D laser scanner 11 has a main body that can rotate 180° along a horizontal plane, and a measurement unit including a laser light emission window and a light receiving unit that can rotate 360° vertically along a plane formed by one axis constituting the horizontal plane and a vertical axis. In this way, the measurement unit can be rotated 360° while the entire main body can be rotated horizontally by 180°, making it possible to acquire high-precision, all-around data in a short time. Specifically, the 3D laser scanner 11 can measure coordinates at a rate of 40 million points per 3 minutes.

[0043] When the length of the object to be evaluated is long, as in the case of kiln shell 1, if the 3D laser scanner 11 is installed in one location and the coordinates of all point clouds are measured, the accuracy of the measurement results for distant locations will be low. In such cases, it is acceptable to move the installation location of the 3D laser scanner 11 and perform measurements multiple times.

[0044] Specifically, as shown in Figure 2, after scanning is performed using the 3D laser scanner 11 at installation location a1, the 3D laser scanner 11 is moved to installation location a2 and scanning is performed in the same manner. The movement of the installation location of the 3D laser scanner 11 and scanning are repeated according to the longitudinal length of the kiln shell 1.

[0045] When employing such a method, it is preferable to place a reference ball 13 at an arbitrary position, from the viewpoint of synthesizing the point cloud data obtained by scanning at each installation location. By also scanning the reference ball 13, the point cloud data obtained under adjacent installation locations can be accurately synthesized. From this viewpoint, the reference ball 13 is placed at a position that is included in both the area scannable by the 3D laser scanner 11 from the rearward adjacent installation location and the area scannable by the 3D laser scanner 11 from the frontward adjacent installation location.

[0046] For example, the installation locations (a1, a2, a3, ...) of the 3D laser scanners 11 can be spaced 10m to 20m apart. While the above describes scanning while moving the installation location of the 3D laser scanner 11, it is also possible to prepare multiple 3D laser scanners 11 and install each 3D laser scanner 11 at different locations (a1, a2, a3, ...). In this case, the point cloud data obtained from each 3D laser scanner 11 can be output to a separate processing unit, where the processing unit performs the synthesis.

[0047] The interval (measurement pitch) of the point cloud data may be set appropriately according to the dimensions of the kiln shell 1. For example, when scanning over a longitudinal distance of 10m to 20m, the measurement pitch of the point cloud data is preferably 5 to 15mm, and more preferably around 12mm.

[0048] Step #1 yields a large number of point cloud data that simulates the conditions of the inner wall surface of kiln shell 1. This point cloud data is referred to as the "first point cloud data".

[0049] Step #1 corresponds to process (a).

[0050] (Step #2, Step #3) Next, the first point cloud data dc1 (see Figure 4) obtained in step #1 is fitted with a cylinder. In detail, step #2 includes the steps of transforming the coordinate space of the first point cloud data dc1 into a coordinate space that is easier to compare with the cylindrical shape, and fitting a cylinder whose central axis coincides with the Z axis and whose radius is d in the transformed coordinate space. The function for performing the fitting process may be installed in the 3D laser scanner 11 itself, or it may be installed in a different processing unit than the 3D laser scanner 11. Here, the first point cloud data whose coordinates have been transformed is referred to as the "second point cloud data dc2". In the second point cloud data dc2 (see Figure 4), the coordinates of each point change due to the transformation of the coordinate space, but their relative positions remain the same as in the first point cloud data dc1. When the coordinate space is not distinguished, it is simply referred to as "point cloud data".

[0051] Figure 4 is a schematic block diagram showing the configuration of a processing unit when fitting is performed by the processing unit. In this embodiment, an example is shown in which the processing unit 20 has a function to evaluate the inner surface state of the kiln shell 1 in addition to the fitting process.

[0052] The arithmetic processing unit 20 shown in Figure 4 comprises a fitting processing unit 21, a division processing unit 24, a surface condition evaluation unit 25, a storage unit 27, and an output unit 29. The fitting processing unit 21, the division processing unit 24, and the surface condition evaluation unit 25 are all composed of software or dedicated hardware capable of performing predetermined arithmetic processing. Details of the division processing unit 24 and the surface condition evaluation unit 25 will be described later in step #3 and beyond.

[0053] The memory unit 27 is an area for temporarily recording calculation results and is composed of a storage medium such as a hard disk or flash memory. The output unit 29 is a functional means for outputting calculation results. The output unit 29 consists of a monitor for outputting information to the arithmetic processing unit 20 itself, an interface for outputting information to other devices via wireless or wired means, etc.

[0054] The fitting processing unit 21 performs a fitting process to the first point cloud data dc1 obtained in step #1 using the 3D laser scanner 11. However, the fitting method is not limited in this invention.

[0055] As described above, when performing the fitting process to a cylinder, a coordinate space transformation process is first performed to facilitate comparison with the cylindrical shape. Specifically, the fitting processing unit 21 performs a coordinate transformation by performing calculations on the first point cloud data dc1 obtained by the 3D laser scanner 11 to calculate the second point cloud data dc2.

[0056] The Z-axis is defined parallel to the direction of the central axis of the cylinder to be fitted to the first point cloud data dc1, and the X and Y axes are defined perpendicular to it.

[0057] First, in order to tentatively determine the direction of the Z axis, we place a point A(x) in the 3D coordinate space, which is xyz space. A , y A , z A ), point B(x B , y B , zB ) Assume two points. The separation distance between an arbitrary measurement point and the line segment AB connecting point A and point B is geometrically calculated. Hereinafter, the distance between the i-th measurement point and the line segment AB is denoted as Di.

[0058] Next, the radius d of the cylinder that fits the first point group data dc1 is determined such that the sum of squared errors ε defined by the following formula (1) is minimized. As an example of a specific calculation method, in the following formula (1), the value of ε is calculated while gradually changing the value of d, and a method of searching for d at which the value of ε is minimized can be adopted. The minimum value of ε derived through such calculations is hereinafter denoted as ε AB and described as.

[0059]

Number

[0060] Next, while changing the coordinates of point A and point B, the above-described calculation process is repeatedly performed. By this calculation, for each combination of points A and B, the sum of squared errors ε AB is obtained.

[0061] The obtained sums of squared errors ε AB are compared with each other, and the combination of points A and B for which the value of ε AB shows the minimum value, and the value of d at this time is specified. The direction of the line segment AB connecting points A and B specified in this way is defined as the direction of the Z axis. Also, the value of d at this time becomes the radius of the cylinder that fits the first point group data dc1.

[0062] The directions of the X axis and the Y axis can be arbitrarily determined. As an example, it may be determined that the direction orthogonal to both the z axis in the original x - y - z space and the newly defined Z axis is the X axis, and the direction orthogonal to both the Z axis and the X axis is the Y axis.

[0063] The above process determines the orientation of the new Z, X, and Y axes. As described above, the cylinder fitted to the first point cloud data dc1 has its central axis coincide with the Z axis in this coordinate system and its radius coincide with d. The origin is set at any position on line segment AB. The origin can be arbitrarily determined as long as it is on line segment AB. For example, the origin of the XYZ coordinate system is set such that the origin of the xyz coordinate system lies on the XY plane under the condition Z=0 in the newly established reference coordinate system (XYZ coordinate system). In this way, a new XYZ coordinate system can be defined.

[0064] Based on the above, the cylinder to be fitted to the second point cloud data dc2, obtained by transforming the first point cloud data dc1 into data in a different coordinate space, has a side surface defined by equation X. 2 +Y 2 =d 2 The end face is represented as Z=0. Figure 5 is a diagram showing an example of the second point cloud data dc2 transformed through this process, and Figure 6 is a diagram of Figure 5 with the XYZ coordinate system added.

[0065] As described above, the fitting processing unit 21 performs calculations to fit the cylinder to the first point cloud data dc1 (corresponding to step (b)), and further, the reference coordinate system (XYZ coordinate system) is identified (corresponding to step (c)). Information regarding the central axis of the fitted cylinder (in this case, the Z axis), i.e., information regarding the reference direction, may be recorded in the storage unit 27. Also, as shown in Figure 6, the surface at the end position of the cylinder fitted to the first point cloud data dc1 may be used as the reference surface 18.

[0066] (Step #4) Next, the second point cloud data dc2 obtained in step #2 is divided into multiple sections along the reference direction (in this case, the Z-axis direction) set in step #3. For convenience, this divided point cloud data is referred to as the "third point cloud data dc3".

[0067] The second point cloud data dc2 obtained in step #2 may be recorded in the storage unit 27. In this step #4, the partitioning processing unit 24 may read information about the first point cloud data dc1 from the storage unit 27 and perform the processing described later.

[0068] The division processing unit 24 divides the second point cloud data dc2 into multiple sections based on the reference direction (i.e., the direction of the central axis 17) determined in step #2 and a predetermined number of divisions. As a result, the second point cloud data dc2 is converted into multiple third point cloud data dc3, each divided into sections. In this division process, the width of each section may be uniform or different.

[0069] Next, the multiple third point cloud data dc3 obtained in this way are fitted to cylinders in the fitting processing unit 21. The fitting process is performed in the same manner as in step #2. In other words, this process defines the central axis of the cylinder fitted to each third point cloud data dc3 by an equation under the reference coordinate system of the second point cloud data.

[0070] Because Kiln Shell 1 is a long structure, over time after its construction on site, it may partially sag due to its own weight. Therefore, the first point cloud data dc1, based on the inner surface of Kiln Shell 1, may differ significantly from the cylindrical shape fitted to the first point cloud data dc1 in step #2.

[0071] Figure 7 is a diagram that exaggerates the points mentioned above. In reality, the position of the central axis of the second point cloud data dc2 should change according to the position in the Z-axis direction (the longitudinal direction of the kiln shell 1). In other words, the central axis 17 of the cylinder to which the second point cloud data dc2 is fitted, as determined by the processing in step #2, may not accurately simulate the central axis of the inner space of the kiln shell 1.

[0072] In contrast, in step #4, the cylinder is fitted to the third point cloud data dc3, which is obtained by dividing the second point cloud data dc2 into small sections in the Z direction. As a result, as shown in Figure 8, multiple third point cloud data dc3 are obtained, each fitted to a different cylindrical shape at different positions in the Z direction.

[0073] As a result, even if the position of the central axis of the kiln shell 1 in the X direction changes according to the position of the Z coordinate, as shown in Figure 7, it is possible to fit cylinders with different central axes to each sub-section (see Figure 9). Figure 9 schematically shows the case where one third-point cloud data dc3 is fitted to a cylinder 31a having a central axis 35a, another third-point cloud data dc3 is fitted to a cylinder 31b having a central axis 35b, and yet another third-point cloud data dc3 is fitted to a cylinder 31c having a central axis 35c.

[0074] (Step #5) The same processing as in step #3 is performed on each of the third point cloud data dc3 obtained in step #4 to determine the equations for the central axes (35a, 35b, 35c, ...) of each cylinder (31a, 31b, 31c, ...) under the reference coordinate system XYZ.

[0075] Then, in the surface condition evaluation unit 25, for each third point cloud data dc3, the separation distance between the corresponding cylinder (31a, 31b, 31c, ...) and its central axis (35a, 35b, 35c, ...) is calculated, for example, by a calculation based on a geometric method.

[0076] Let's take the third point cloud data dc3, fitted by cylinder 31a, as an example. This third point cloud data dc3 reproduces the surface state of small regions that are virtually divided along the longitudinal direction of the kiln shell 1 within the space inside the kiln shell 1. In other words, regarding the distance between each point shown in this third point cloud data dc3 and the central axis of cylinder 31a, locations where this value is longer than the surrounding area indicate that the position of the inner wall is in a direction away from the central axis.

[0077] (Step #6) The surface condition evaluation unit 25 evaluates the surface condition inside the kiln shell 1 based on the distance between each point indicated by the third point group data dc3 calculated in step #5 and the central axis of the cylinder 31a.

[0078] For example, the design value of the inner diameter (radius) R of the kiln shell 1 may be known in advance from the specifications, design documents, etc., of the cement kiln including the kiln shell 1. Therefore, as shown in Figure 10, by calculating the difference value Bi between the distance ri between the cylinder 31b and the central axis 35b and the inner diameter R of the kiln shell 1 at a certain point i included in the third point cloud data dc3, information regarding the thickness of the refractory bricks remaining inside the kiln shell 1 at the location corresponding to that point i can be obtained. By performing a similar calculation process for all points belonging to the third point cloud data dc3 fitted by the same cylinder 31b, the distribution of the thickness of the remaining refractory bricks in the small section of the inner wall surface of the kiln shell 1 simulated by this cylinder 31b can be calculated.

[0079] By performing this process for all the cylinders (31a, 31b, 31c, ...) shown in Figure 9, the distribution of the thickness of the refractory bricks remaining on the inner wall surface can be calculated over the entire longitudinal direction of the kiln shell 1.

[0080] In the above explanation, it was assumed that for each cylinder (31a, 31b, 31c, ...), the difference between the distance from the central axis and the inner diameter was calculated for all points belonging to the third point cloud data dc3 fitted by that cylinder. However, from the perspective of reducing the computational load, it is also acceptable to extract points to be calculated from multiple points belonging to the third point cloud data dc3 at predetermined intervals, and perform the above difference calculation only on these extracted points.

[0081] The information on the distribution of refractory brick thickness across the entire longitudinal direction of the kiln shell 1, calculated using the method described above, may be represented as a 3D contour map, as exemplified in Figure 11, for easier visual recognition. The calculation process for this representation may also be performed in the surface condition evaluation unit 25.

[0082] As described above, multiple refractory bricks are laid inside the kiln shell 1. Therefore, it is preferable that the information be output in a manner that allows for easy identification of the location and number of refractory bricks that need to be replaced after calculating the remaining thickness of the refractory bricks. From this viewpoint, the surface condition evaluation unit 25 may have a function to create a planar unfolded drawing (hereinafter referred to as the "kiln unfolded drawing") obtained by unfolding the above 3D contour drawing into a planar drawing.

[0083] Figure 12 is a schematic diagram illustrating the method for generating a kiln unfolded diagram from a 3D contour drawing. As shown in Figure 12, the kiln unfolded diagram is created by unfolding the 3D contour drawing into a plane with the circumferential direction of the cross-section perpendicular to the central axis as one axis and the direction of the central axis as the other axis. In this process, each region is color-coded according to the range of remaining thickness, making it immediately clear where the remaining thickness of the refractory bricks is thin on the inner wall of the kiln shell 1, which can be used to plan repair work such as replacement and to predict the amount of wear.

[0084] Figure 13 shows an example of a kiln unfolded diagram generated according to the procedure described above. The comparative example shows the distribution of refractory brick thickness calculated from the spacing between cylinders fitted to the entire kiln shell 1, based on the second point cloud data dc2 obtained in step #2, and is represented as a kiln unfolded diagram. As described above, in step #4, fitting is performed for each small section divided in the longitudinal direction of the kiln shell 1, and the distribution of refractory brick thickness calculated from the spacing between each of the multiple cylinders used in this fitting is represented as a kiln unfolded diagram.

[0085] In a rotary kiln, the kiln shell rotates circumferentially, transporting the raw materials to the front of the kiln while firing. Therefore, if the position of the kiln shell in the longitudinal direction is the same, the degree of wear on the refractory bricks in the circumferential direction is usually expected to be about the same.

[0086] However, according to the comparative example in Figure 13, for example, within region A1, it can be confirmed that a large displacement occurs in the remaining thickness of the refractory bricks in the circumferential direction, even though the position in the central axis direction (longitudinal direction) is the same. The reason for this is thought to be that, as described above with reference to Figure 7, the first point cloud data dc1 obtained by measuring the kiln shell 1 is significantly different from the shape of the single cylinder that is fitted to the first point cloud data dc1. In detail, although the central axis of the kiln shell 1 is displaced to some extent depending on the position in the longitudinal direction, the second point cloud data dc2 is fitted to a cylinder having the same central axis. Therefore, when the remaining thickness of the refractory bricks is calculated based on the distance between the central axis and the inner wall surface of the kiln shell 1, it is inferred that in the longitudinal direction, there is a large difference in the remaining thickness of the refractory bricks in the circumferential direction at locations where there is a discrepancy between the central axis of the fitted cylinder and the central axis of the actual kiln shell 1.

[0087] In contrast, according to the results of the embodiment shown in Figure 13, the remaining thickness of the refractory bricks is almost uniform in the circumferential direction within the same region A1. This is thought to be because, as described above with reference to Figures 8 to 9, the central axes of the multiple virtual cylindrical bodies are able to almost perfectly reproduce the position of the central axis corresponding to the position of the kiln shell 1 in the longitudinal direction.

[0088] Verification revealed that, due to its own weight, the central axis of the cross-section of Kiln Shell 1 may shift by approximately 5mm to 10mm when advanced 10m in the longitudinal direction. The initial thickness of a standard refractory brick is approximately 20cm to 30cm. Therefore, for example, if the remaining thickness of the refractory brick is to be measured in 5mm increments, setting the division unit in step #4 to 5m or less makes it possible to limit the central axis shift to 5mm or less, thus keeping the estimation error of the remaining thickness of the refractory brick due to the central axis shift within an acceptable range. Furthermore, setting the division unit in step #4 to 2m or less makes it possible to limit the central axis shift to 3mm or less, effectively eliminating the estimation error of the remaining thickness of the refractory brick due to the central axis shift.

[0089] [Alternative Embodiment] The following describes other embodiments.

[0090] <1> In the embodiments described above, step #1 was described as scanning the inner wall surface of the kiln shell 1 over its entire length. In other words, the entire length of the inner wall surface of the kiln shell 1 was considered to be the measurement target area. However, the present invention does not exclude cases where only a part of the inner wall surface of the kiln shell 1 is used as the measurement target area.

[0091] For example, a portion of the kiln shell 1 in the longitudinal direction may be designated as the measurement area, and the inner wall surface of the kiln shell 1 within this area may be scanned in step #1. Even in this case, if the length of the measurement area in the longitudinal direction is sufficiently long, the position of the central axis of the kiln shell 1 may be displaced depending on the position in the longitudinal direction. Therefore, by following the same procedure as in the above embodiment, the remaining thickness of the refractory bricks lining the kiln shell 1 can be evaluated with accuracy.

[0092] <2> In the embodiments described above, the method was described in the case where the structure to be measured is a kiln shell 1 and the remaining thickness of the refractory bricks laid on its inner wall is to be evaluated. However, the method of the present invention is not limited to a kiln shell 1, but can also be applied to the evaluation of the surface condition of the inner wall (inner part) of other long cylindrical structures.

[0093] In other words, using the method described above, even if the central axis of the structure is displaced to some extent depending on its position in the longitudinal direction, the distribution of the distance between the inner wall of the structure and its central axis can be calculated with high accuracy. For example, if the distance at a certain point is sufficiently longer than the distance at adjacent points or the average distance across the entire area, it can be estimated that a depression has formed at that point. Conversely, if the distance at a certain point is sufficiently shorter than the distance at adjacent points or the average distance across the entire area, it can be estimated that there is a factor (such as foreign matter) that causes the formation of a protrusion at that point.

[0094] Specifically, it can be used to evaluate the surface condition of the inner walls of structures such as road tunnels, water conduits for hydroelectric power generation, and sewer pipes. Furthermore, according to the method of the present invention, even if the structure is a kiln shell 1, it can be used not only to evaluate the remaining thickness of refractory bricks, but also simply to evaluate the surface condition of the inner wall (such as the presence of irregularities).

[0095] (3) The present invention is not limited to the embodiments described above, and includes various modifications. For example, the embodiments described above are described in detail for a better understanding of the present invention and are not necessarily limited to all configurations described. The scope of the present invention is indicated by the claims, and all modifications within the meaning and scope equivalent to the claims are intended to be included. [Explanation of Symbols]

[0096] 1: Kilnshell 11: 3D Laser Scanner 13: Reference ball 17: Central axis 18: Reference plane 20: Arithmetic Processing Unit 21: Fitting Processing Unit 24: Partitioning Processing Unit 25: Surface condition evaluation unit 27: Storage section 29: Output section 31a, 31b, 31c: Cylinder 35a, 35b, 35c: Central axis dc1: First point cloud data dc2: Second point cloud data dc3: Third point cloud data

Claims

1. A method for evaluating the shape of a long cylindrical structure, (a) A step of obtaining first point cloud data by scanning the inside of the structure over the entire area of ​​the measurement target region of the structure using a 3D laser scanner, (b) A step of fitting a cylinder to the first point cloud data to obtain second point cloud data, Step (c) of setting a reference coordinate system that includes a reference plane formed by a portion of the second point cloud data, and a reference direction that is perpendicular to the reference plane and substantially parallel to the longitudinal direction of the structure, (d) A step of fitting a cylinder to each of the third point cloud data obtained by dividing the second point cloud data along the reference direction, and determining the equation of the central axis of the fitted cylinder in the reference coordinate system of the second point cloud data, Step (e) for each of the multiple third point cloud data sets, the distance between the central axis of the cylinder fitted in step (d) and each point included in the third point cloud data set is calculated based on the coordinate information of the second point cloud data set that is based on the reference coordinate system, An evaluation method characterized by comprising: step (e) a step of detecting the surface condition of the inner part of the structure over the measurement target area based on the distribution of the separation distance calculated in step (e);

2. The aforementioned structure is a kiln shell with firebricks attached to its inner wall surface. The evaluation method according to claim 1, characterized in that step (f) includes a step of detecting the degree of wear of the refractory bricks over the measurement target area.

3. The evaluation method according to claim 2, characterized in that step (f) includes a step of detecting the distribution of the remaining thickness of the refractory bricks over the measurement target area by calculating the difference of the separation distance calculated in step (e) from the value of the outer diameter of the kiln shell that has been measured or designed in advance.

4. The evaluation method according to any one of claims 1 to 3, characterized in that the reference surface set in step (c) is the end face of the cylinder fitted in step (b).

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