3D measurement device using multi-viewpoint line sensing method

Abstract

To provide a three-dimensional measuring device that measures the three-dimensional shape of an object to be measured with higher precision than before.SOLUTION: A device that measures the three-dimensional shape of a measured object 1 by irradiating the measured object 1 with a laser beam from a laser oscillator 10 as single spot light L and receiving reflected light reflected from the measured object 1, includes: an optical system 20 that receives the reflected light from the measured object 1 on a one-dimensional axis using three or more line CCD (charge coupled device) cameras; and analysis means 40 for calculating the three-dimensional position of the reflected light from a detection signal representing the reflected light brightness distribution on the one-dimensional axis received by the optical system 20. In the analysis of a perspective projection model that analyzes the measured object 1 by projecting it onto a two-dimensional plane, the analysis means 40 converts the world coordinate system into a camera coordinate system by combining three or more line CCD cameras 30, and further calculates the three-dimensional coordinates of a measurement point P from the camera coordinate system.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a three-dimensional measuring apparatus using a multi-viewpoint line sensing method for measuring the three-dimensional shape of a measured object by providing a plurality of line CCD (charge coupled device) cameras.

Background Art

[0002] Techniques for measuring the three-dimensional shape of an object using a line CCD camera (line CCD sensor) are known. For example, Patent Document 1 discloses an optical system arranged at different positions and focusing the reflected light of a single spot light on different regions on the X-axis, and line sensors arranged at different positions and respectively receiving the reflected light of the single spot light focused on different regions on the X-axis by the optical system, and outputting first and second detection signals representing the luminance distribution on the X-axis, an optical system for focusing the reflected light of the single spot light on the Y-axis, a line sensor for receiving the reflected light focused on the Y-axis by the optical system and outputting a third detection signal representing the luminance distribution on the Y-axis, and an arithmetic processing unit for obtaining information on the irradiation position of the single spot light in the detection target based on the first to third detection signals. Claim 3 describes that the line sensor may be a line CCD sensor. Further, Patent Document 2 discloses an image measuring apparatus having imaging means and arithmetic means for calculating coordinate information of a measurement target from image information obtained by imaging the measurement target by the imaging means. The arithmetic means includes error correction means for correcting the image information obtained by imaging the measurement target by the imaging means with error information specific to the imaging means to obtain corrected image information, and coordinate calculation means for calculating coordinate information of the measurement target from the corrected image information. Paragraph 0024 describes that the camera of the imaging means has a line CCD sensor. Furthermore, Patent Document 3 discloses a three-dimensional measurement system comprising a point light source for measurement that can be moved to any position, and a position detection device that receives light from the point light source for measurement and detects the position of the point light source for measurement. A transparent calibration substrate having at least two reference lines spaced apart in the pixel arrangement direction of each line sensor is placed between the first optical system and the first line sensor, and between the second optical system and the second line sensor, which constitute the position detection device. In the probe calculation unit, the amount of shift due to thermal expansion or movement of the line sensor is calculated from the reference position signal and the pixel position of the line sensor corresponding to the reference position signal, among the brightness distribution signal detected by each line sensor and the reference position signal based on the two reference lines, and this amount of shift is corrected to calculate the coordinates of the point light source for measurement. Paragraph 0019 describes a configuration in which CCDs are arranged in a single line as the configuration of the line sensor. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2005-233759 [Patent Document 2] Japanese Patent Publication No. 2012-57996 [Patent Document 3] Japanese Patent Publication No. 2014-202691 [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] Patent documents 1 to 3 describe using three line CCD cameras (line CCD sensors) for measurement, but with only three cameras, there may be areas that are obscured by shadows and cannot be measured depending on the object being measured. Furthermore, 3D measurement using stereo measurement with two or more cameras is also known, but in general stereo measurement, matching multiple images is required, making image processing difficult. Therefore, the present invention aims to provide a three-dimensional measuring device that measures the three-dimensional shape of an object to be measured with greater accuracy than conventional devices. [Means for solving the problem]

[0005] A three-dimensional measurement device using a multi-viewpoint line sensing method corresponding to claim 1, wherein the device measures the three-dimensional shape of an object to be measured by irradiating the object to be measured with laser light from a laser oscillator as a single spot beam and receiving the reflected light reflected from the object to be measured, N(N≧4) units Line CCD (charge-overlapping device) camera And, line CCD camera The system comprises an optical system that receives reflected light from an object to be measured on a one-dimensional axis, and an analysis means that calculates the three-dimensional position of the reflected light from a detection signal representing the reflected light brightness distribution on the one-dimensional axis received by the optical system, wherein the analysis means performs analysis of a perspective projection model in which the object to be measured is projected onto a two-dimensional plane, N units By combining line CCD cameras, the system converts from the world coordinate system to the camera coordinate system, and then calculates the 3D coordinates of the measurement points from the camera coordinate system. In this process, the analysis method calculates the 3D coordinates of the measurement points by determining the camera rays using two of the plane equations from each of the N line CCD cameras, finding the intersection point between the other plane equation and the camera rays, and calculating the 3D coordinates of the measurement points multiple times by changing the combination of plane equations and accumulating this information as measurement point data. Finally, the 3D shape is measured by applying statistical processing to the accumulated measurement point data to determine the 3D coordinates of the measurement points. It is characterized by the following: According to the present invention as described in claim 1, the three-dimensional shape of an object to be measured can be accurately measured by analyzing a perspective projection model using three or more line CCD cameras. Furthermore, according to the present invention as described in claim 1, the accuracy and robustness of measurement can be improved.

[0006] The present invention as described in claim 2 is characterized by comprising an analysis means that uses the DLT (Direct Linear Translation) algorithm as the analysis of a perspective projection model. According to the present invention as described in claim 2, the three-dimensional coordinates of the measurement point can be calculated by the DLT method.

[0009] The present invention as described in claim 3 is N The system is characterized by capturing images of the object to be measured from at least two directions using a line CCD camera on a platform. Claim 3 According to the present invention described herein, it is possible to measure areas that were previously obscured and could not be measured, thereby improving the accuracy and robustness of the measurement.

[0010] The present invention as described in claim 6 is characterized by comprising scanning means for moving a single spot of light across the surface of an object to be measured. According to the present invention as described in claim 6, measurement efficiency can be increased by scanning a single spot of light.

[0011] The present invention as described in claim 7 is characterized by generating the overall three-dimensional shape of an object to be measured by using a scanning means for single-spot light. According to the present invention as described in claim 7, the overall three-dimensional shape of the object to be measured can be obtained in a short time. [Effects of the Invention]

[0012] According to the 3D measurement device using the multi-viewpoint line sensing method of the present invention, the 3D shape of an object to be measured can be accurately measured by analyzing a perspective projection model using three or more line CCD cameras.

[0013] Furthermore, if the analysis method is equipped with an algorithm that uses the DLT (Direct Linear Translation) method for analyzing the perspective projection model, the three-dimensional coordinates of the measurement points can be calculated using the DLT method.

[0014] Furthermore, if the system is equipped with N (N≧4) line CCD cameras, and the analysis means uses the equations of two of the planes of each of the N line CCD cameras to determine the camera rays, and then calculates the 3D coordinates of the measurement points by finding the intersection point between the equation of the other plane and the camera rays, the accuracy and robustness of the measurement can be improved.

[0015] Furthermore, if the analysis method involves calculating the 3D coordinates of the measurement points multiple times by changing the combination of plane equations, and then applying statistical processing to the accumulated information of the measurement points to determine the 3D coordinates of the measurement points, the accuracy and robustness of the measurement can be further improved.

[0016] In addition, when N (N ≥ 4) line CCD cameras are provided and the object to be measured is photographed from at least two directions by the N line CCD cameras, it is possible to measure even the portions that could not be measured because they were in the shade in the past, so that the measurement accuracy and robustness can be improved.

[0017] In addition, when a scanning means for moving a single spot light on the surface of the object to be measured is provided, the measurement efficiency can be increased by scanning the single spot light.

[0018] In addition, when generating the entire three-dimensional shape of the object to be measured by using the scanning means of the single spot light, the entire three-dimensional shape of the object to be measured can be obtained in a short time.

Brief Description of Drawings

[0019] [Figure 1] Configuration diagram of a three-dimensional measurement device by a multi-viewpoint type line sensing method according to an embodiment of the present invention [Figure 2] Configuration diagram of the same laser oscillator [Figure 3] Diagram showing the difference between an area CCD camera and a line CCD camera [Figure 4] Diagram showing the difference between light collection by a spherical lens and light collection by a semi-cylindrical lens [Figure 5] Diagram showing the luminance distribution received by the line CCD camera [Figure 6] Flowchart showing the operation of a three-dimensional measurement device by a multi-viewpoint type line sensing method according to an embodiment of the present invention [Figure 7] Diagram showing a generalized perspective projection model used for calculating the three-dimensional coordinates of the same measurement point [Figure 8] Image diagram for calculating the three-dimensional coordinates of the measurement point using the equation of the same plane [Figure 9] Schematic diagram showing the state where the same three-dimensional measurement device is installed in a water tank [Figure 10] Diagram showing the 3D model of the three-dimensional measurement device actually used in the same actual measurement [Figure 11]A photograph of the 3D measuring device used in the actual measurement. [Figure 12] Comparison diagram of the wing shape measurement results of the same propeller. [Figure 13] Comparison diagram of cavitation shape measurement results near the wingtips of the same propeller. [Figure 14] This figure shows the shape measurement results of propeller wingtip vortex cavitation using the same 3D measurement device. [Modes for carrying out the invention]

[0020] This document describes a three-dimensional measurement device using a multi-viewpoint line sensing method according to an embodiment of the present invention. Figure 1 is a diagram of the configuration of a 3D measurement device using the multi-viewline sensing method according to this embodiment, and Figure 2 is a diagram of the configuration of a laser oscillator. A three-dimensional measurement device using the multi-viewpoint line sensing method (hereinafter sometimes simply referred to as "three-dimensional measurement device") comprises a laser oscillator 10, a plurality of optical systems 20, a plurality of line CCD cameras 30, an analysis means (analysis device) 40, a control means 50, and a scanning means (laser scanning device) 51. For example, a computer can be used for the analysis means 40 and the control means 50.

[0021] The laser oscillator 10 generates laser light as a single spot beam L and irradiates the object to be measured 1, such as a propeller, with the single spot beam L. The control means 50 transmits a control signal to the scanning means 51 to control the scanning of the single-spot light L across the surface of the object to be measured 1. By scanning the object to be measured 1 with the single-spot light L, the measurement efficiency can be increased. Furthermore, by using the scanning means 51 to scan the object to be measured 1 thoroughly with a single spot light L, the overall three-dimensional shape of the object to be measured 1 can be generated in a short time. As shown in Figure 2, the laser oscillator 10 comprises a laser oscillation unit 11, a first mirror 12, and a second mirror 13. The laser oscillator 11 generates a laser beam of a predetermined diameter. The laser oscillation wavelength is appropriately selected according to the operating environment and the physical properties of the object to be measured 1. The first mirror 12 deflects the laser beam emitted from the laser oscillator 11 on the XZ plane by, for example, reciprocating rotational motion around the Y axis. The second mirror 13 deflects the laser beam reflected from the first mirror 12 on the YZ plane by, for example, reciprocating rotational motion around the X axis. As a result, the laser beam is irradiated onto the object to be measured 1. Furthermore, electrically controllable mirrors are used for the first mirror 12 and the second mirror 13. Examples of electrically controllable mirrors include galvanometer mirrors, polygon mirrors, and MEMS (Micro Electro Mechanical Systems) mirrors.

[0022] Each optical system 20 has a semi-cylindrical lens that focuses the reflected light of a single spot of light L onto a one-dimensional axis. Each line CCD camera 30 receives reflected light focused by the optical system 20 and outputs a detection signal representing the reflected light brightness distribution on a one-dimensional axis. The analysis means 40 calculates the three-dimensional position of the measurement point P (the irradiation position of the single spot light L) from the detection signal output by the line CCD camera 30 using an analysis algorithm.

[0023] Here, Figure 3 shows the difference between an area CCD camera and a line CCD camera, with Figure 3(a) being an area CCD camera and Figure 3(b) being a line CCD camera. In an area CCD camera, the CCD elements 100 are arranged vertically and horizontally, whereas in a line CCD camera 30, the CCD elements 100 are arranged in a single horizontal row. The line CCD camera 30 has the advantage of being fast and having high resolution because it does not scan a plane. Figure 4 shows the difference between focusing with a spherical lens and focusing with a semi-cylindrical lens, with Figure 4(a) showing a spherical lens and Figure 4(b) showing a semi-cylindrical lens. Figure 5 shows the brightness distribution received by a line CCD camera. A spherical (hemispherical) lens focuses light to a single point, with all points in three-dimensional space as the focal point. On the other hand, a semi-cylindrical lens focuses bright spots on a two-dimensional plane in a certain three-dimensional space onto one axis of the line CCD camera 30, and the brightness distribution of the bright spots received at this time is shown in Figure 5.

[0024] Figure 6 is a flowchart showing the operation of the 3D measurement device using the multi-viewpoint line sensing method according to this embodiment. When measurement is started, the scanning means 51 irradiates the object to be measured 1 with a single spot beam L from the laser oscillator 10 (step S1). Next, the reflected light from the object 1 irradiated with a single-spot light L is focused by each optical system 20 and detected by each line CCD camera 30 (step S2). This obtains a detection signal representing the reflected light brightness distribution on a one-dimensional axis.

[0025] The analysis means 40 calculates the three-dimensional coordinates of the reflected light on the object under measurement 1 based on the perspective projection model (step S3). The method for calculating the three-dimensional coordinates in step S3 will be described later. Next, the analysis means 40 determines whether to measure other points on the object to be measured 1 (step S4). The determination in step S4 is made, for example, by whether or not there are any points remaining that have been pre-inputted as points to be measured. If the analysis means 40 determines that there are still points to measure (Yes) and decides to measure other points, the control means 50 moves the projection position of the single spot light L to the scanning means 51 (step S5) and executes step S1 again. On the other hand, if the analysis means 40 determines that no other points need to be measured (No) because there are no more points to measure, the process proceeds to step S6.

[0026] In step S6, the analysis means 40 calculates the overall three-dimensional coordinate information of the object to be measured 1 based on the three-dimensional coordinates of the collected reflected light and generates image data. The image data generated by the analysis means 40 is transmitted to a display means (not shown), such as a monitor, and an image of the object 1 to be measured is displayed on the display means.

[0027] Figure 7 shows a generalized perspective projection model used to calculate the three-dimensional coordinates of measurement points. The analysis means 40 uses, for example, the DLT (Direct Linear Translation) algorithm as an analysis of a perspective projection model that projects the object to be measured 1 onto a two-dimensional plane for analysis. In this case, the image coordinates of the measurement point P are constructed by combining the images (detection signals) of three line CCD cameras 30, and the three-dimensional coordinates are calculated from these two-dimensional coordinates using the DLT method. The camera coordinate system is a coordinate system fixed to the camera, with the horizontal direction as X, the vertical direction as Y, and the depth direction as Z, with the center of the camera lens as the origin. The world coordinate system is a coordinate system set in the space in which the object being measured 1 exists. The relationship between the camera coordinate system and the world coordinate system is shown in equation (1) below.

number

number

number

[0028] In the DLT method, calibration, which is a camera parameter estimation process, is required before performing the measurement work. At this time, the camera parameters L1~L in equations (2) and (3) are obtained from the correspondence between known world coordinates for calibration called control points and the camera coordinates of the measured control points. 11 Estimate the following camera parameters L1~L 11 The least squares method is used to estimate this. By estimating the camera parameters beforehand, in step S3 above, it is possible to perform a coordinate transformation from the camera coordinate system to the world coordinate system and calculate the 3D coordinates of the measurement point P. In this way, the analysis means 40 combines three or more line CCD cameras 30 based on the perspective projection model to convert from the world coordinate system to the camera coordinate system, and then calculates the 3D coordinates of the measurement point P from the camera coordinate system. By analyzing the perspective projection model using these three or more line CCD cameras 30, the 3D shape of the object to be measured 1 can be measured with high accuracy.

[0029] Figure 8 is an illustrative diagram showing how to calculate the 3D coordinates of a measurement point using a plane equation. The calculation method uses a planar equation to analyze the perspective projection model, either as an alternative to or in combination with the DLT method. The camera model of the line CCD camera 30 can be expressed as a planar equation, as shown in equations (4), (5), and (6) below.

number

number

number

[0030] Reflected light from the object to be measured 1 is received by three or more line CCD cameras 30. The camera ray (straight line) is determined by combining the equations of the two planes of two of the line CCD cameras 30, and the intersection point of this camera ray and the equation of the plane of the other line CCD camera 30 is found. This intersection point becomes the 3D coordinate of the measurement point P. Generally, the camera ray is the tracking light from the viewpoint to a certain point when viewed from the viewpoint of the camera (viewpoint). For example, from the camera coordinate system in Figure 7, (X w ,Y w ,Z w The arrow extending from ) becomes the camera beam. Following this principle, the number of line CCD cameras 30 can be increased to N (N≧4) to increase the number of plane equations, and the information about each measurement point P can be increased by calculating the 3D coordinates for each measurement point P multiple times by changing the combination of plane equations. Then, statistical processing is performed on the information about measurement point P accumulated by calculating the 3D coordinates of measurement point P multiple times, and the 3D coordinates of measurement point P are determined based on, for example, the maximum value, minimum value, mean value, or standard deviation. By using four or more line CCD cameras 30 and performing statistical processing on the information from the measurement point P, the accuracy and robustness of the measurement can be further improved.

[0031] Figure 9 is a schematic diagram showing a 3D measurement device using the multi-viewpoint line sensing method installed in a water tank, and shows a view from above of a cavitation tank containing a ship's propeller. There are a total of six line CCD cameras 30, which are positioned with three on one side and three on the other side of tank 2. On one side of the water tank 2, one laser oscillator 10, three optical systems 20, and three line CCD cameras 30 are mounted on a common first mount 60 and installed near the water tank 2. On the other side of the water tank 2, three optical systems 20 and three line CCD cameras 30 are mounted on a common second mount 70 and installed near the water tank 2. A single spot beam L is shone from a laser oscillator 10 onto a rotating propeller (object to be measured 1), and the reflected light is received by six line CCD cameras 30, three on each side of the water tank 2, to reproduce the three-dimensional shape of the propeller and cavitation. At this time, as shown in Figure 9, by using four or more line CCD cameras 30 and photographing the object to be measured 1 from at least two directions with four or more line CCD cameras 30, it becomes possible to photograph from multiple angles compared to when there are three or fewer line CCD cameras 30 or when photographing from one direction, and the areas that are in shadow (blind spots) on the object to be measured 1 can be reduced, so that areas that could not be measured in the past can also be measured, improving the accuracy and robustness of the measurement.

[0032] Next, we will explain the actual measurement results using a 3D measurement device based on the multi-viewpoint line sensing method. Figure 10 shows a 3D model of the 3D measuring device used in the actual measurements; Figure 10(a) is an oblique view, and Figure 10(b) is a front view. Figure 11 is a photograph of the 3D measuring device used in the actual measurements. For the measurement, four line CCD cameras 30 and optical system 20 were arranged as shown in Figure 10, and the shape of a model ship propeller (φ250 mm) and the shape of the cavitation were photographed as the object to be measured 1.

[0033] Figure 12 is a comparison diagram of the propeller wing shape measurement results, where Figure 12(a) shows the measurement results of a conventional 3D measurement device using the combined line CCD method, and Figure 12(b) shows the measurement results of a 3D measurement device using the multi-viewpoint line sensing method of the present invention. The conventional combined line CCD method involves irradiating the object to be measured 1 with a laser, capturing the scattered light from the surface with three line CCD cameras 30, and calculating the three-dimensional position of the measurement point P from the peak positions of each captured image. Table 1 below compares the accuracy of the two 3D measuring devices. [Table 1] Figure 12 and Table 1 show that the 3D measurement device of the present invention has significantly improved shape measurement accuracy compared to conventional 3D measurement devices using the combined line CCD method.

[0034] Figure 13 is a comparative diagram of cavitation shape measurement results near the propeller wingtip. Figure 13(a) shows the measurement results of a conventional 3D measurement device using the combined line CCD method, and Figure 13(b) shows the measurement results of a 3D measurement device using the multi-viewpoint line sensing method of the present invention. Photographs of the cavitation are also shown on the left side of Figures 13(a) and (b). Figure 13 shows that the 3D measurement device of the present invention can accurately capture and measure the shape of cavitation near the wingtip, which cannot be captured by conventional 3D measurement devices using the combined line CCD method.

[0035] Figure 14 shows the shape measurement results of propeller wingtip vortex cavitation using the 3D measurement device based on the multi-viewpoint line sensing method of the present invention. A photograph of the wingtip vortex cavitation is also shown in the upper part of Figure 14. Conventionally, measuring the shape of propeller wingtip vortex cavitation has been difficult, but with the 3D measurement device of the present invention, it is possible to measure the shape of propeller wingtip vortex cavitation, as shown in Figure 14.

[0036] Thus, it has been confirmed that the 3D measuring device of the present invention has improved accuracy and robustness compared to conventional 3D measuring devices. [Industrial applicability]

[0037] This invention can be used for measuring propeller shape and deformation in cavitation tanks, measuring cavitation shape, and as a distance sensor or object recognition sensor for underwater robots. Furthermore, it can be applied to virtually any other 3D measurement application. [Explanation of Symbols]

[0038] 1 Object to be measured 10. Laser Oscillator 20 Optical system 30-line CCD camera 40 Analysis methods 51 Scanning means L Single spot light P measurement point

Claims

1. A device for measuring the three-dimensional shape of an object to be measured by irradiating the object to be measured with laser light from a laser oscillator as a single spot beam and receiving the reflected light reflected from the object to be measured, N (N≧4) line CCD (charge coupled device) cameras, and an optical system that receives the reflected light from the object to be measured on a one-dimensional axis using the line CCD cameras, The optical system comprises an analysis means for calculating the three-dimensional position of the reflected light from a detection signal representing the reflected light intensity distribution on the one-dimensional axis received by the optical system, The analysis means, in analyzing a perspective projection model in which the object to be measured is projected onto a two-dimensional plane for analysis, combines N line CCD cameras to convert from a world coordinate system to a camera coordinate system, and further calculates the three-dimensional coordinates of the measurement points from the camera coordinate system, wherein the analysis means calculates the camera rays using two of the plane equations of each of the N line CCD cameras, calculates the three-dimensional coordinates of the measurement points by finding the intersection point of the other plane equation and the camera rays, calculates the three-dimensional coordinates of the measurement points multiple times by changing the combination of the plane equations and stores the information of the measurement points, and measures the three-dimensional shape by applying statistical processing to the stored information of the measurement points to determine the three-dimensional coordinates of the measurement points.

2. The 3D measurement device using a multi-viewpoint line sensing method according to claim 1, characterized in that it is equipped with the analysis means that uses the DLT (Direct Linear Translation) algorithm as the analysis of the perspective projection model.

3. A three-dimensional measurement device using a multi-view line sensing method according to Claim 1, characterized in that the object to be measured is photographed from at least two directions by N line CCD cameras.

4. A three-dimensional measurement device using a multi-viewline sensing method according to claim 1, characterized by comprising scanning means for moving the single spot light on the surface of the object to be measured.

5. A three-dimensional measurement device using a multi-viewpoint line sensing method according to claim 4, characterized in that the overall three-dimensional shape of the object to be measured is generated by using the scanning means of the single spot light.

Images