Data processing device, measurement system, data processing method, and program

Abstract

To improve the accuracy with which the shape of a circular arc included in a measurement object is measured.SOLUTION: A data processing device 2 comprises: a data acquisition unit 241 for acquiring edge data that indicates the positions of a plurality of points indicating edges of a circular arc included in a measurement object W; an estimation unit 242 for estimating the temporary center coordinate of a circle where the circular arc is included, taking a prescribed position of the measurement object W as a point of reference, by finding a condition for the arithmetic value based on a first evaluation function becoming minimal on the basis of the edge data; and an identification unit 243 for identifying the center coordinate of the circle and the radius of the circle by finding a condition for the arithmetic value based on a second evaluation function different from a first evaluation function becoming minimal, under a constraint condition that the center coordinate of the circle exists within a prescribed range from the temporary center coordinate.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a data processing device, a measurement system, a data processing method, and a program for measuring the shape of an object. [Background technology]

[0002] Conventionally, a technique for measuring the roundness of a workpiece by using point cloud data obtained by irradiating the workpiece with light and identifying the minimum and maximum circles using the least squares method or the minimum area method has been known (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 7301570 Summary of the Invention [Problem to be solved by the invention]

[0004] In order to measure the shape of a circular arc on a workpiece, it may be necessary to specify the center coordinates and radius of a circle that includes the circular arc. When specifying the center coordinates and radius of a circle that includes the circular arc using point cloud data of the circular arc, there is a problem in that large variations in the positions of the point cloud result in large measurement errors.

[0005] The present invention has been made in view of these points, and has as its object to improve the accuracy of measuring the shape of an arc included in an object to be measured. [Means for solving the problem]

[0006] A data processing device according to a first aspect of the present invention includes a data acquisition unit that acquires edge data indicating the positions of multiple points that indicate the edges of an arc included in an object to be measured; an estimation unit that estimates provisional center coordinates of a circle that includes the arc, based on a predetermined position of the object to be measured, by searching for conditions under which a calculated value based on a first evaluation function is minimized based on the edge data; and an identification unit that identifies the center coordinates of the circle and the radius of the circle by searching for conditions under which a calculated value based on a second evaluation function, different from the first evaluation function, is minimized, under the constraint that the center coordinates of the circle are included within a predetermined range from the provisional center coordinates.

[0007] The estimation unit may estimate the provisional center coordinates of the circle by using a minimum area method with the first evaluation function, and the identification unit may search for a condition under which the calculated value based on the second evaluation function is minimized under the constraint that the center coordinates of the circle are included within a predetermined range from the provisional center coordinates.

[0008] The estimation unit may estimate the provisional center coordinates by using the first evaluation function that indicates the difference between the area of ​​a circle that has a common center coordinate and that may include the arc and the area of ​​a circle that may not include the arc.

[0009] The specifying unit is configured to, under a constraint condition that the center coordinates (a, b) are included within a predetermined range from the provisional center coordinates, when the radius of the object to be measured is r and the number of the plurality of points is i, It is also possible to specify a, b, and r that minimize JPEG2025132723000002.jpg1360.

[0010] A measurement system according to a second aspect of the present invention comprises an imaging device that generates captured image data by photographing an object to be measured, and a data processing device that identifies the shape of the object to be measured based on the captured image data. The data processing device has a data acquisition unit that acquires edge data indicating the positions of multiple points that indicate the edges of an arc included in the object to be measured, an estimation unit that estimates provisional center coordinates of a circle that includes the arc, based on a predetermined position of the object to be measured, by searching for conditions under which a calculated value based on a first evaluation function is minimized based on the edge data, and an identification unit that identifies the center coordinates of the circle and the radius of the circle by searching for conditions under which a calculated value based on a second evaluation function, different from the first evaluation function, is minimized, under the constraint that the center coordinates of the circle are included within a predetermined range from the provisional center coordinates.

[0011] A data processing method according to a third aspect of the present invention includes the steps of: acquiring edge data indicating the positions of a plurality of points indicating the edges of an arc included in an object to be measured, executed by a computer; estimating, based on the edge data, a provisional center coordinate of a circle including the arc, with a predetermined position of the object to be measured as a reference, by searching for a condition under which a calculated value based on a first evaluation function is minimized; and identifying the center coordinate of the circle and the radius of the circle by searching for a condition under which a calculated value based on a second evaluation function different from the first evaluation function is minimized, under the constraint that the center coordinate of the circle is included within a predetermined range from the provisional center coordinate.

[0012] A fourth aspect of the present invention provides a program for causing a computer to execute the following steps: acquiring edge data indicating the positions of multiple points that indicate the edges of an arc included in an object to be measured; estimating, based on the edge data, a provisional center coordinate of a circle that includes the arc, with a predetermined position of the object to be measured as a reference, by searching for a condition that minimizes a calculated value based on a first evaluation function based on the edge data; and identifying the center coordinate of the circle and the radius of the circle by searching for a condition that minimizes a calculated value based on a second evaluation function, different from the first evaluation function, under the constraint that the center coordinate of the circle is included within a predetermined range from the provisional center coordinate. [Effects of the Invention]

[0013] The present invention provides an advantage in that the accuracy of measuring the shape of an arc included in an object to be measured is improved. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 1 is a diagram for explaining an overview of a measurement system S. [Figure 2] 1 is a diagram showing an example of a measurement target W including an arc-shaped portion. FIG. [Figure 3] FIG. 2 is a diagram showing the configuration of a data processing device 2. [Figure 4] 10 is a first example of a flowchart showing the flow of processing in the data processing device 2. [Figure 5] FIG. 10 is a diagram for explaining a minimum area method. [Figure 6] 10 is a second example of a flowchart showing the flow of processing in the data processing device 2. DETAILED DESCRIPTION OF THE INVENTION

[0015] [Overview of Measurement System S] FIG. 1 is a diagram illustrating an overview of a measurement system S. The measurement system S is an image measurement system for non-contact measurement of the dimensions of a workpiece W that includes an arc-shaped portion. The measurement system S includes an imaging device 1 and a data processing device 2. In the measurement system S, the imaging device 1 and the data processing device 2 may be configured as an integrated unit.

[0016] The imaging device 1 is a camera that generates captured image data by capturing an image of the workpiece W through an optical lens. Some workpieces W, the shape of which is to be measured, have edges that are circular or part of a sphere (i.e., arc-shaped). The workpiece W is, for example, a member that has a plate-like portion with an arc-shaped corner, or a member that has a cylindrical or cylindrical portion.

[0017] The data processing device 2 analyzes the captured image data to measure the radius and center coordinates of circles, including arcs, on the object to be measured W. The data processing device 2 identifies the edges (i.e., contour lines) of the object to be measured W in the captured image data, and estimates the shape of the object to be measured W by the least squares method using a function representing a straight line or a curve for the identified edges.

[0018] 2A and 2B are diagrams showing examples of a workpiece W including an arc. The workpiece W1 shown in FIG. 2A is a rectangle with four arc-shaped corners. The workpiece W2 shown in FIG. 2B is an oval rectangle with two opposing sides formed into arcs. In addition to the shapes shown in FIG. 2A, the workpiece W may have other shapes including an arc, such as a cylindrical, cylindrical, or spherical shape.

[0019] When inspecting whether such a workpiece W has been manufactured to a shape that meets a predetermined standard, the pass / fail is determined based on whether the center coordinates and radius of the circle that contains the arc (shown by the dashed line in Figure 2) are within a standard range. To improve the accuracy of such inspections, it is necessary to fit the arc to an appropriate circular function.

[0020] Conventionally, when a vision measuring system fits an arc-shaped edge to a circular function, if there is a large variation (disturbance) in the positions of the point cloud representing the edge and the magnitude of the variation deviates from a normal distribution, it has been difficult to properly estimate the center coordinates of the circle containing the arc edge. As a result, the vision measuring system has been unable to properly measure the shape of the arc edge.

[0021] In response to this, the data processing device 2 first estimates the provisional center coordinates of the circle containing the arc, using a predetermined position on the object to be measured as a reference, by searching for a condition that minimizes the calculated value based on the first evaluation function. Next, the data processing device 2 identifies the radius R of the circle and the center coordinates (a, b) of the circle by searching for a condition that minimizes the calculated value based on a second evaluation function, which is different from the first evaluation function, under the constraint that the center coordinates of the circle are included within a predetermined range from the provisional center coordinates. In the example shown in FIG. 2, the predetermined position is the intersection (0, 0) of the extension lines of the two sides, but the predetermined position may be another position. By performing processing in this manner, the data processing device 2 can improve the accuracy of estimating the center coordinates and radius of the arc contained in the object to be measured W when the positions of the point cloud representing the edge vary greatly and the variation deviates from a normal distribution.

[0022] [Configuration of data processing device 2] 3 is a diagram showing the configuration of the data processing device 2. The data processing device 2 has a communication unit 21, a display unit 22, a storage unit 23, and a control unit 24. The control unit 24 has a data acquisition unit 241, an estimation unit 242, and an identification unit 243.

[0023] The communication unit 21 has a communication interface for receiving captured image data from the imaging device 1. The communication unit 21 is, for example, a USB (Universal Serial Bus) or LAN (Local Area Network) interface. When the imaging device 1 and the data processing device 2 are housed in a single housing, the communication unit 21 may be a serial communication interface such as an SPI (Serial Peripheral Interface) or an I2C (Inter-Integrated Circuit).

[0024] The display unit 22 is a display that displays the measurement results, including the center coordinates and radius of the object to be measured W identified by the identification unit 243.

[0025] The storage unit 23 has storage media such as a ROM (Read Only Memory), a RAM (Random Access Memory), and an SSD (Solid State Drive). The storage unit 23 stores programs executed by the control unit 24. The storage unit 23 also temporarily stores captured image data received by the communication unit 21. The storage unit 23 may also store measurement data used to measure the shape of the workpiece W. The measurement data is, for example, design data indicating the shape of the edge of the workpiece W.

[0026] The control unit 24 includes, for example, a CPU (Central Processing Unit). The control unit 24 executes the programs stored in the storage unit 23 to function as a data acquisition unit 241, an estimation unit 242, and an identification unit 243.

[0027] The data acquisition unit 241 acquires edge data indicating the positions of multiple points indicating the edge of an arc included in the object to be measured W. The data acquisition unit 241 may acquire captured image data and acquire edge data based on the acquired captured image data. In this case, the data acquisition unit 241 estimates pixels in which the degree of change in luminance in a specified pixel range in the captured image data is equal to or greater than a threshold as pixels indicating an edge. For example, the data acquisition unit 241 detects multiple pixels in which the difference in pixel value between adjacent pixels in the captured image data is equal to or greater than a threshold as pixels indicating an edge.

[0028] The data acquisition unit 241 identifies an edge area of ​​the object W to be measured in a range corresponding to the arc in the measurement data by matching an area including a plurality of pixels indicating an edge with the edge of the object W indicated by the measurement data. The data acquisition unit 241 acquires edge data by identifying the position of a point cloud made up of a plurality of pixels included in the identified edge area. The data acquisition unit 241 may acquire the edge data generated in this manner from the imaging device 1.

[0029] The estimation unit 242 estimates the provisional center coordinates of the circle containing the arc, with a predetermined position of the object to be measured as a reference, by searching for a condition that minimizes a calculated value based on the first evaluation function based on the edge data. The first evaluation function will be described in detail later, but it is a function that indicates the difference between the radius of the circumscribing circle and the radius of the inscribing circle of the point group included in the edge data, or a function that indicates the difference between the area of ​​the circumscribing circle and the area of ​​the inscribing circle of the point group included in the edge data. The estimation unit 242 notifies the identification unit 243 of the estimated provisional center coordinates.

[0030] The identification unit 243 identifies the radius and center coordinates of the circle by searching for a condition under which a calculated value based on a second evaluation function, which is different from the first evaluation function, is minimized under the constraint that the center coordinates of the circle are included within a predetermined range from the provisional center coordinates. If the predetermined range is set to be the same regardless of the radius or inclination angle of the arc, the constraint may be too strict depending on the shape of the arc, which may result in a problem that the condition under which the calculated value based on the second evaluation function is minimized cannot be found. Alternatively, the constraint may be too loose, which may result in a problem that it takes a long time to find the condition under which the calculated value based on the second evaluation function is minimized.

[0031] Therefore, the specifying unit 243 may set the predetermined range so that it increases as the radius of the arc in the object to be measured W increases. Also, the specifying unit 243 may set the predetermined range so that it increases as the inclination angle of the arc decreases.

[0032] The second evaluation function is a function used in, for example, the nonlinear least squares method. For example, under the constraint that the center coordinates (a, b) are included within a predetermined range from the provisional center coordinates (a1, b1), the radius of the object to be measured is R, and the number of points is i, the second evaluation function Identify a, b, and R that minimize JPEG2025132723000003.jpg1185.

[0033] [Processing flow in data processing device 2] (Minimum area method) 4 is a first example of a flowchart showing the flow of processing in the data processing device 2. In the first example, the estimation unit 242 estimates the provisional center coordinates of the identified set of circles by a minimum area method that identifies a set of circles with common center coordinates that minimizes the difference between the radius of the circumscribing circle and the radius of the inscribing circle of the point cloud.

[0034] When the data acquisition unit 241 acquires captured image data (S11), it acquires edge data based on the acquired captured image data (S12). The estimation unit 242 estimates the provisional center coordinates of the circle by using a minimum area method that uses a first evaluation function (S13). Specifically, the provisional center coordinates are estimated by using a first evaluation function that indicates the difference between the radius of a circle that may contain an arc (for example, a circumscribing circle of a point cloud) and the radius of a circle that may not contain an arc (for example, an inscribing circle of a point cloud), both of which have common center coordinates.

[0035] FIG. 5 is a diagram for explaining the minimum area method. The multiple small circles indicated by solid lines in FIG. 5 are multiple points (point cloud) included in the edge data. The estimation unit 242 executes estimation processing using the minimum area method, using parameters (center coordinates and radius) obtained from the edge data by, for example, the linear least squares method as initial values. The estimation unit 242 estimates (a1, b1) as the provisional center coordinates, where the radius of a circle that may contain an arc is R1, and the radius of a circle that may not contain an arc is R2, under the following constraints, to find the coordinates of the provisional center that minimize the difference between R1 and R2. <Restrictions> JPEG2025132723000004.jpg9119, and R1-R2 is the smallest

[0036] 4, the identification unit 243 searches for optimal conditions that minimize the calculated value based on the second evaluation function such as that shown in equation (1) under the constraint that the center coordinates of the circle are included within a predetermined range from the provisional center coordinates estimated by the estimation unit 242 (S14). The identification unit 243 identifies (a, b) when the calculated value based on the second evaluation function is minimized as the center coordinates of the circle including the arc, and identifies R when the calculated value based on the second evaluation function is minimized as the radius of the circle including the arc (S15).

[0037] (Minimum area method) When the estimation unit 242 estimates the provisional center coordinates using the minimum area method, the range of the center coordinates identified using the second evaluation function is limited, so the search time can be shortened and the accuracy of the identified center coordinates and radius is increased compared to when the provisional center coordinates are not used. However, because the evaluation function used in the minimum area method is nonlinear and the calculations performed in the minimum area method are processes similar to nonlinear programming, the amount of calculation is large and it is possible that the calculation will converge to an incorrect value.

[0038] Therefore, the estimation unit 242 may estimate the provisional center coordinates by using a first evaluation function that indicates the difference between the area of ​​a circle that may contain an arc and the area of ​​a circle that may not contain an arc, both of which have the same center coordinates. The estimation unit 242 estimates R1 under the following constraints, where (a1, b1) is the provisional center coordinate, R1 is the radius of the circle that may contain an arc, and R2 is the radius of the circle that may not contain an arc. 2 and R2 2 The coordinates (a1, b1) that minimize the difference between the coordinates are estimated as the provisional center coordinates. In this specification, this estimation method is referred to as the minimum area method to distinguish it from the minimum region method. <Restrictions> JPEG2025132723000005.jpg8119, R1 2 -R2 2 is minimum

[0039] 6 is a second example of a flowchart showing the flow of processing in the data processing device 2. In the second example, the estimation unit 242 estimates the provisional center coordinates by a method using the area difference between multiple circles as described above. In the flowchart shown in FIG. 6, S21, S22, S24, and S25 are the same as S11, S12, S14, and S15 in the flowchart of FIG. 4, but S23 differs from S13 in the flowchart of FIG. 4. Instead of the processing of S13 in the flowchart shown in FIG. 4, the estimation unit 242 estimates the provisional center coordinates based on the area difference between the circles (S23).

[0040] In this way, the estimation unit 242 calculates R1, which is the difference between the area of ​​a circle that may contain an arc and the area of ​​a circle that may not contain an arc. 2 -R2 2 Select two circles with the same center coordinates that minimize the distance, and set the center coordinates of those circles as the temporary center coordinates. Here, tn=a 2 +b 2 -Rn 2 (n=1,2) and R1 2 -R2 2 The condition that is minimum is equivalent to the condition that t1-t2 is minimum, and the constraint can be expressed as a linear function.

[0041] Therefore, the process of minimizing the difference between the area of ​​a circle that may contain an arc and the area of ​​a circle that may not contain an arc is based on linear programming, which requires less computation than the minimum area method. Also, since the evaluation function can be expressed as a linear function, this method does not require initial values ​​and converges to a unique solution, further improving the reliability of the identified center coordinates and radius.

[0042] [Variations] In the above explanation, an example has been shown in which the data processing device 2 identifies the radius and center coordinates of a circle that includes an arc included in the flat plate-like object to be measured W. However, the object to be measured W may include a part of a spherical surface, and the data processing device 2 may identify the radius and center coordinates of a circle that includes an arc included in the part of the spherical surface. In this case, the center coordinates may be coordinates in three-dimensional space.

[0043] [Effects of Data Processing Device 2] As described above, the data processing device 2 first estimates the provisional center coordinates of a circle containing an arc, with a predetermined position of the workpiece W as a reference, by searching for a condition that minimizes the calculated value based on the first evaluation function based on the edge data of the workpiece W. Then, under the constraint that the center coordinates of the circle are included within a predetermined range from the provisional center coordinates, the data processing device 2 identifies the center coordinates of the circle and its radius by searching for a condition that minimizes the calculated value based on a second evaluation function different from the first evaluation function. By configuring the data processing device 2 in this way, the amount of calculation required to calculate a solution to the optimization problem using the second evaluation function is reduced, and the accuracy of measuring the shape of the arc is improved.

[0044] The present invention has been described above using embodiments, but the technical scope of the present invention is not limited to the scope described in the above embodiments, and various modifications and changes are possible within the scope of the gist of the present invention. For example, all or part of the device can be configured by functionally or physically distributing or integrating any unit. Furthermore, new embodiments resulting from any combination of multiple embodiments are also included in the embodiments of the present invention. The effects of the new embodiments resulting from the combination also have the effects of the original embodiments. [Explanation of symbols]

[0045] 1. Imaging device 2. Data Processing Device 21 Communications Department 22 Display section 23 Memory section 24 Control Unit 241 Data Acquisition Unit 242 Estimation Department 243 Specific part

Claims

1. a data acquisition unit that acquires edge data indicating the positions of a plurality of points that indicate the edge of an arc included in the object to be measured; an estimation unit that estimates provisional center coordinates of a circle that includes the arc, based on a predetermined position of the object to be measured, by searching for a condition that minimizes a calculated value based on a first evaluation function, based on the edge data; an identification unit that identifies the center coordinates of the circle and the radius of the circle by searching for a condition that minimizes a calculated value based on a second evaluation function different from the first evaluation function under a constraint that the center coordinates of the circle are included within a predetermined range from the provisional center coordinates; A data processing device having:

2. the estimation unit estimates temporary center coordinates of the circle by using a minimum area method using the first evaluation function; the specifying unit searches for a condition under which a calculation value based on the second evaluation function is minimized under the constraint condition that the center coordinates of the circle are included within a predetermined range from the provisional center coordinates.

2. The data processing device according to claim 1.

3. the estimation unit estimates the tentative center coordinates by using the first evaluation function indicating a difference between an area of ​​a circle that has a common center coordinate and that may include the arc and an area of ​​a circle that may not include the arc.

2. The data processing device according to claim 1.

4. The specifying unit is configured to, under a constraint condition that the center coordinates (a, b) are included within a predetermined range from the provisional center coordinates, when the radius of the object to be measured is r and the number of the plurality of points is i, Identify a, b, and r such that 2. The data processing device according to claim 1.

5. an imaging device that generates captured image data by capturing an image of an object to be measured; a data processing device that identifies the shape of the object to be measured based on the captured image data; Equipped with The data processing device includes: a data acquisition unit that acquires edge data indicating the positions of a plurality of points that indicate the edge of an arc included in the object to be measured; an estimation unit that estimates provisional center coordinates of a circle that includes the arc, based on a predetermined position of the object to be measured, by searching for a condition that minimizes a calculated value based on a first evaluation function, based on the edge data; an identification unit that identifies the center coordinates of the circle and the radius of the circle by searching for a condition that minimizes a calculated value based on a second evaluation function different from the first evaluation function under a constraint that the center coordinates of the circle are included within a predetermined range from the provisional center coordinates; A measurement system having:

6. The computer executes acquiring edge data indicating the positions of a plurality of points indicating the edge of a circular arc included in the object to be measured; a step of estimating provisional center coordinates of a circle including the arc, based on a predetermined position of the object to be measured, by searching for a condition that minimizes a calculated value based on a first evaluation function, based on the edge data; a step of identifying the center coordinates of the circle and the radius of the circle by searching for a condition that minimizes a calculated value based on a second evaluation function different from the first evaluation function under a constraint that the center coordinates of the circle are included within a predetermined range from the provisional center coordinates; A data processing method comprising:

7. On the computer, acquiring edge data indicating the positions of a plurality of points indicating the edge of a circular arc included in the object to be measured; a step of estimating provisional center coordinates of a circle including the arc, based on a predetermined position of the object to be measured, by searching for a condition that minimizes a calculated value based on a first evaluation function, based on the edge data; a step of identifying the center coordinates of the circle and the radius of the circle by searching for a condition that minimizes a calculated value based on a second evaluation function different from the first evaluation function under a constraint that the center coordinates of the circle are included within a predetermined range from the provisional center coordinates; A program to execute.

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