Shape measurement method

Abstract

To provide a shape measurement method that can measure the cross-sectional shape of a required region with high precision while suppressing an increase in measurement time.SOLUTION: A method includes: obtaining a polygon image, having a plurality of triangular surfaces Ts each formed of each point of a three-dimensional point group and other two points nearby it in a required region Rn of a three-dimensional point group image of a surface of a work W after obtaining the three-dimensional point group image through three-dimensional measurement; and obtaining the cross-sectional shape of the required region Rn after increasing the number of the three-dimensional point group by setting a new point within each triangular surface Ts of the polygon image.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a shape measuring method capable of accurately measuring the cross-sectional shape of a required portion of an object to be measured. [Background technology]

[0002] In order to measure the three-dimensional shape of an object to be measured, for example, in Patent Document 1, the object to be measured is placed on a precision XYZ stage, and the object is moved so that its outer surface is brought into contact with a stylus, and the three-dimensional coordinate data at the time of contact is obtained as coordinate data on the measuring instrument side. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2000-28350 Summary of the Invention [Problem to be solved by the invention]

[0004] In order to measure the three-dimensional shape of an object more compactly and simply, a method is adopted in which the object is placed on a three-dimensional tilting stage that can tilt about two mutually perpendicular axes, the posture of the object is tilted, a line laser beam from a three-dimensional shape detection sensor is projected onto the outer surface of the object, and this is photographed with a stereo camera. In this case, the photographed outer surface of the object is sequentially imported into a computing device as a three-dimensional point cloud, but measuring the entire outer surface of the object with high precision, i.e., increasing the density of the three-dimensional point cloud overall, requires a long measurement time.

[0005] Therefore, the present invention aims to solve this problem by providing a shape measurement method that can increase the density of the three-dimensional point cloud only in the necessary areas of the outer surface of the object to be measured, thereby enabling high-precision cross-sectional shape measurement of the necessary areas while suppressing increases in measurement time. [Means for solving the problem]

[0006] In order to achieve the above object, in the first invention, a three-dimensional point cloud image of the surface of the object to be measured (W) is obtained by three-dimensional measurement, and then a polygon image is obtained in a necessary region (Rn) of the three-dimensional point cloud image, in which each point of the three-dimensional point cloud and two other points nearby form multiple triangular surfaces (Ts).The number of three-dimensional point clouds is increased by setting new points within each triangular surface (Ts) of the polygon image, and then a cross-sectional shape in the necessary region (Rn) is obtained.

[0007] In the first invention, the density of the point cloud can be increased only in the necessary area, so that the quantization error of the cross-sectional shape measured in the necessary area can be reduced, and a more accurate cross-sectional shape can be obtained.

[0008] In the second invention, a new triangular surface is formed from the new point and a plurality of points in its vicinity, and a new point is further set within the new triangular surface to increase the number of the three-dimensional point group.

[0009] According to the second invention, the density of the point cloud can be further increased only in the necessary region, and a more accurate cross-sectional shape can be obtained in the necessary region.

[0010] The symbols in parentheses above indicate, for reference, the correspondence with specific means described in the embodiments to be described later. [Effects of the Invention]

[0011] As described above, according to the shape measurement method of the present invention, the density of the three-dimensional point cloud can be increased only in the necessary areas of the outer surface of the object to be measured, making it possible to perform high-precision cross-sectional shape measurement of the necessary areas while suppressing increases in measurement time. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a diagram showing an equipment configuration for carrying out a measurement method of the present invention. [Figure 2] FIG. 2 is a partially enlarged perspective view of a workpiece to be measured, including a chipping region. [Figure 3] This is a three-dimensional point cloud image including a chipping area of ​​a workpiece to be measured. [Figure 4] This is a polygon image of the required area. [Figure 5] FIG. 1 is a two-dimensional schematic diagram illustrating the effect of upsampling. [Figure 6] FIG. 10 is a diagram showing an example of a point cloud distribution in one cross section of a three-dimensional point cloud image of a necessary area. [Figure 7] FIG. 10 is a two-dimensional schematic diagram illustrating another effect of upsampling. DETAILED DESCRIPTION OF THE INVENTION

[0013] The embodiments described below are merely examples, and various design improvements made by those skilled in the art without departing from the gist of the present invention are also included in the scope of the present invention.

[0014] An example of a three-dimensional tilting stage is shown in Figure 1. The tilting stage 1 is equipped with a circular, plate-like table 11 that can tilt around two mutually perpendicular axes, X and Y, at its center, allowing the posture of the workpiece to be measured, placed on the table 11, to be changed in three dimensions.

[0015] A three-dimensional shape detection sensor 2 is installed above the tilting stage 1 facing downward. Cameras 21 and 22 are provided on the left and right sides of the shape detection sensor 2, facing the table 11 located at the center below. A line laser emitter 23 is installed between the left and right cameras 21 and 22 facing the table 11, and a line laser beam L of a fixed length extending left and right is scanned in the front-to-back direction. The left and right cameras 21 and 22 are connected to a processing device 3, and images with parallax captured by each camera 21 and 22 are sequentially imported into the processing device 3. The three-dimensional shape of the workpiece surface scanned with the line laser beam L is then obtained as a discrete point cloud in three-dimensional space by known calculations within the processing device 3. The processing device 3 may be built into the three-dimensional detection sensor 2.

[0016] For example, when determining the quality of processing by measuring the size, depth, cross-sectional area, etc. of chipping W2 (chips or cracks) that has occurred on the cut surface W1 of the workpiece W as shown in Figure 2, in order to accurately measure the size, etc. of the chipping W2, it is necessary to increase the density of the three-dimensional point cloud (Figure 3) of the workpiece surface obtained in the processing device 3. However, obtaining a high-density three-dimensional point cloud increases the measurement time.

[0017] Therefore, in this embodiment, in order to increase the density of only the point cloud in the necessary region Rn including the chipping region Rw2 of the above three-dimensional point cloud, a polygon image (FIG. 4) is generated in which each point of the three-dimensional point cloud in the necessary region Rn and two other points nearby form multiple triangular surfaces Ts. A new point is then set at the center of gravity of each triangular surface Ts. By performing upsampling in this way to set a new point at the center of gravity of each triangular surface Ts, it is possible to increase the density of only the point cloud in the necessary region Rn.

[0018] The effect of the above upsampling will be explained using the two-dimensional schematic diagram shown in Figure 5. When measuring the cross-sectional shape shown by the point cloud in Figure 5(1), in order to reduce the computational burden, the value of each point in the Z-axis (height) direction is measured using a rectangular cross-sectional shape that maintains a constant width in the Y-axis direction (quantization), but this causes so-called quantization errors.

[0019] Therefore, by upsampling, new points (white circles) are set between each point as shown in Figure 5(2) to increase the density of the point cloud, which reduces the quantization error of the cross-sectional shape measured by quantization, making it possible to obtain a more accurate cross-sectional shape.

[0020] Figure 6(1) shows an example of the point cloud distribution in a cross section parallel to the YZ plane in the three-dimensional point cloud image (Figure 3) of the necessary region Rn obtained by the processing device 3. If the point cloud density is low enough to accurately obtain the cross-sectional shape of the shaded chipping region Rw2, obtaining a polygon image as described above and setting new points at the centers of gravity of each triangular surface increases the number of points in the necessary region Rn and their density, as shown in Figure 3(2). Therefore, by measuring the cross-sectional shape of the chipping region Rw2 with the increased point cloud, an accurate cross-sectional shape (or cross-sectional area) can be obtained. Then, by overlaying this cross-sectional shape in the X-axis direction (perpendicular to the paper surface), where the point cloud density is higher, the three-dimensional shape (or volume) of the chipping region Rw2 can be accurately measured.

[0021] As shown in the two-dimensional schematic diagram of Figure 7(1), noise removal when obtaining the point cloud may result in some of the point cloud being missing. In this case, the above-mentioned upsampling can be used to set new points (white circles) to compensate for the missing points, as shown in Figure 7(2), thereby avoiding a decrease in the density of the point cloud in the required region Rn.

[0022] In the above embodiment, the new point is set at the center of gravity of the triangular surface of the polygon image, but it may be set at another position such as the incenter or circumcenter. It is also possible to further increase the point cloud density by forming a new triangular surface using the new point and a number of points in its vicinity, and setting additional new points within the triangular surface. [Explanation of symbols]

[0023] 1...tilting stage, 2...shape detection sensor, 21, 22...camera, 23...line laser emitter, 3...processing device, Rn...required area, Ts...triangular surface, W...workpiece (object to be measured).

Claims

1. A shape measurement method in which a three-dimensional point cloud image of the surface of a measured object is obtained by three-dimensional measurement, a polygon image is obtained in a required area of ​​the three-dimensional point cloud image, in which each point of the three-dimensional point cloud and two other points nearby form multiple triangular surfaces, and the number of three-dimensional point clouds is increased by setting new points within each triangular surface of the polygon image, and then a cross-sectional shape in the required area is obtained.

2. 2. The shape measurement method according to claim 1, wherein a new triangular surface is formed by the new point and a plurality of points in its vicinity, and a new point is set within the new triangular surface to increase the number of the three-dimensional point cloud.

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