A camera measurement field establishing method and a target

Abstract

The application relates to a camera measurement field establishment method and a target, which comprises the following steps: determining the theoretical coordinates of a measured point according to the digital model of a measured object; adjusting the size of a target mark according to an actual working distance; installing a target base on the measured point of the measured object; manually adjusting the angle of the target mark according to the image quality of the mark in the camera field of view, so that the target mark plane is parallel to the camera view plane; taking a photo to calculate the three-dimensional coordinates of the mark center point in the camera coordinate system; calculating the three-dimensional coordinates of the measured point in the camera coordinate system according to the size information of the base and the target and the conversion relationship formula of the target mark center and the measured point; repeating the above steps to record the three-dimensional coordinates of the measured point in the camera coordinate system and the known coordinates of the measured point; calculating the relationship between the measured point coordinates in the camera coordinate system and the known coordinates of the measured point by adopting an optimal fitting algorithm according to the recorded measured point coordinates, and then establishing the measurement field of the camera; and finally realizing the rapid establishment of the measurement field of the camera.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of visual measurement, and particularly relates to a camera measurement field establishing method and a target. BACKGROUND

[0002] Camera measurement technology has been widely applied in the pose measurement and docking of large-size aircraft parts in aviation manufacturing, visual guidance of industrial robots, augmented reality assisted assembly information projection and other applications due to its high speed and high precision, but the relative position of the measured object in the measurement field needs to be determined through tedious steps, which limits the application of camera measurement technology in the field of aviation manufacturing.

[0003] The camera measurement system is usually established by pasting coded markers, reflective markers and ArUco markers on the measured object, and the position relationship between the actual measured three-dimensional coordinates and the theoretical marker points is used to calculate the pose information of the measured object relative to the camera coordinate system. For markers without size information such as reflective markers, it is usually necessary to increase the number of cameras or use a structured light device to make the visual measurement system complex; for markers with size information such as ArUco markers, the three-dimensional coordinates of the marker center can be directly solved by using a monocular camera, which simplifies the tedious measurement field construction steps. However, the detection accuracy is greatly affected by the angle between the marker and the camera view plane, and there is no special fixing and clamping tool, which greatly limits the application of such markers in visual measurement systems.

[0004] Although the current markers with size information can simplify the tedious measurement field construction steps and reduce the complexity of the system, the placement method of the markers greatly affects the visual detection accuracy, and it is difficult to make the marker plane parallel to the camera plane in actual application, which leads to unstable detection accuracy; and the marker does not have a special fixing and clamping tool, so it is difficult to establish the position relationship between the marker and the theoretical measured point. SUMMARY

[0005] The present application mainly aims at the above problems, and provides a camera measurement field establishing method and a target to solve the problem of tedious traditional measurement field establishing steps when the camera is used for measurement, and to solve the problems of low traditional measurement accuracy and slow speed.

[0006] To achieve the above purpose, the present application provides a target for camera measurement field establishment, which comprises:

[0007] A base, the base comprises a target ball socket and a positioning pin, the positioning pin is used for inserting into the positioning hole of the measured object tool or the measured object;

[0008] A target body comprises a positioning ball rotatably arranged in a target ball socket and a marking plate having a marking plane with a center normal passing through the ball center of the positioning ball.

[0009] Further, the marking plate comprises a base plate at a lower end and an alumina film arranged on the base plate, wherein a marking pattern is drawn on the alumina film.

[0010] Further, the target ball socket is magnetically connected with the positioning ball.

[0011] To achieve the above object, the application provides a camera measurement field establishment method using the above target, comprising the following steps:

[0012] installing the target with known size parameters and marking parameters on a measured point of a measured object and making the marking plane of the target parallel to the camera view plane;

[0013] constructing a conversion relationship between the three-dimensional coordinates of the target marking center points and the three-dimensional coordinates of the measured points on the measured object according to the known size parameters and marking parameters of the target;

[0014] taking a photo and calculating the three-dimensional coordinates of the target marking center points in the camera coordinate system, and calculating the three-dimensional coordinates of the measured points in the camera coordinate system according to the conversion relationship between the three-dimensional coordinates of the target marking center points and the three-dimensional coordinates of the measured points on the measured object;

[0015] repeating the above steps to record not less than six groups of three-dimensional coordinates of the measured points in the camera coordinate system, and recording the known coordinates of the measured points and the three-dimensional coordinates of the measured points in the camera coordinate system at the same time for each group;

[0016] calculating the relationship between the three-dimensional coordinates of the measured points in the camera coordinate system and the known coordinates of the measured points by using the best fitting algorithm according to the recorded known coordinates of the measured points and the three-dimensional coordinates of the measured points in the camera coordinate system, and establishing a camera measurement field.

[0017] Further, the conversion relationship between the three-dimensional coordinates of the target marking center points and the three-dimensional coordinates of the measured points on the measured object is constructed as follows:

[0018]

[0019] wherein t x , t y , t z represent correction parameters of target positioning; t d represents the thickness of the base plate of the target; t r represents the radius of the positioning ball of the target; X m, Y m , Z m is the three-dimensional coordinate of the target mark center point; R, T are the external parameters of the camera detecting the mark; X c , Y c , Z c is the three-dimensional coordinate of the measured point.

[0020] Further, the step of making the mark plane of the target parallel to the camera view plane comprises manually adjusting the angle of the target according to the image quality of the mark in the camera view, so that the mark plane of the target is parallel to the camera view plane.

[0021] Further, in the process of quickly establishing the camera measurement field, different sizes of targets can be replaced according to the size of the target mark in the camera view in the measurement field.

[0022] Further, when using single camera measurement, the single camera covers all the mark areas of the targets, the single camera is controlled to take a picture to obtain the current image, and the three-dimensional coordinates of the measured points in the camera coordinate system are calculated, and the pose information of the measured object in the single camera coordinate system is determined through fitting calculation with the known coordinates of the measured points.

[0023] Further, when using multi-camera measurement, the multi-camera covers all the mark areas of the targets, the angle of the target is adjusted so that the mark plane of the target is parallel to the view plane of one of the cameras, the camera is controlled to take a picture to obtain the current image, and the three-dimensional coordinates of the measured points in the camera coordinate system at the fixed position of the target are calculated; the angle of the target is adjusted again so that the mark plane of the target is parallel to the view plane of another camera, the camera is controlled to take a picture to obtain the current image, and the three-dimensional coordinates of the measured points in the camera coordinate system at the fixed position of the target are calculated, the spatial conversion relationship between the multi-cameras is determined according to the three-dimensional coordinate relationship of the measured points in the multi-camera coordinate system, and the camera measurement field is established.

[0024] Further, the known coordinates of the measured points are determined according to the numerical model of the measured object or measured by a laser tracker.

[0025] The above technical scheme of the present application has the following advantages: by using the target of the present application as a special fixed clamping tool for such marks, the marks can be rotated within a certain angle, and the positional relationship between the mark center point and the theoretical measured point can be easily established, thereby realizing the quick establishment of the camera measurement field. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 is a schematic diagram of the exploded structure of the target for establishing a camera measurement field disclosed by the present application.

[0027] Figure 2 This is a schematic diagram of a combined target structure for establishing a camera measurement field, as disclosed in this invention.

[0028] Figure 3 This is a schematic diagram of the conversion relationship between the target marker center point and the measured point disclosed in this invention.

[0029] Figure 4 This is a schematic diagram of a single-camera / multi-camera measurement field establishment method for a target disclosed in this invention.

[0030] In the diagram: 1. Workpiece; 2. Target; 3 and 4. Camera; 5. Tripod; 6. Control computer; 20. Base; 20-1. Target ball socket; 20-2. Positioning pin; 21. Target body; 21-1. Positioning ball; 21-2. Marking plate. Detailed Implementation

[0031] The following is in conjunction with the appendix Figures 1 to 4 The camera measurement field establishment method and target proposed in this invention will be further described in detail below with specific embodiments. The advantages and features of this invention will become clearer from the following description. It should be noted that the accompanying drawings are in a very simplified form and use non-precise proportions, only for the purpose of conveniently and clearly illustrating the embodiments of this invention. Please refer to the accompanying drawings to make the objectives, features, and advantages of this invention more apparent and understandable. It should be understood that the structures, proportions, sizes, etc., depicted in the accompanying drawings are only for the purpose of assisting those skilled in the art in understanding and reading the content disclosed in the specification, and are not intended to limit the implementation conditions of this invention. Therefore, they have no substantial technical significance. Any modifications to the structure, changes in the proportional relationships, or adjustments to the size, without affecting the effects and objectives achieved by this invention, should still fall within the scope of the technical content disclosed in this invention.

[0032] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0033] The main purpose of the present application is to provide a camera measurement field establishment method and a target, by adjusting the position of the target, the relative position of the measured object in the measurement field can be quickly determined, so that the target and the method can be widely applied to large-size aircraft part pose measurement and docking in aviation manufacturing, industrial robot visual guidance, augmented reality assisted assembly information projection and other applications.

[0034] To achieve the above-mentioned purpose, the present application provides a target for camera measurement field establishment, which is a special fixed clamping tool for such markers, so that the markers can rotate within a certain angle, and the positional relationship between the markers and the theoretical measured points can be easily established, thereby realizing the rapid establishment of the camera measurement field.

[0035] Specifically, please refer to Figure 1 , Figure 2 which schematically shows the target for camera measurement field establishment provided by an embodiment of the present application, as shown in Figure 1 The target 2 includes a base 20 and a target body 21, wherein the upper part of the base 20 is a target ball socket 20-1, the shape of the target ball socket 20-1 is designed according to the size of the target body 21, and the target ball socket 20-1 can be tightly connected with the lower part of the target body 21, and the target ball socket 20-1 has magnetism and can directly attract the target body 21. The lower part of the base 20 is a positioning pin 20-2, which can be inserted into the positioning hole of the measured object tool or the measured object.

[0036] The upper part of the target body 21 is a marker plate 21-2, which is composed of a base plate and an alumina film arranged on the base plate, and a marker pattern is drawn on the alumina film; the lower part of the target body 21 is a positioning ball 21-1, which is a sphere with smooth surface processed by precision machining, and can be arbitrarily rotated in the target ball socket 20-1 of the base 20, and can be fixed at a certain angle under the action of magnetic attraction, and the marker plate 21-2 has a marker plane, the center normal line of the marker plane passes through the ball center of the positioning ball, so as to build the relationship between the marker center point on the marker plane of the target 2 and the measured point on the measured object.

[0037] In some embodiments, the marker on the target 2 can be an existing augmented reality marker such as ArUco, or a self-defined marker with a known shape; a monocular camera can be used to measure the three-dimensional coordinates of the marker center point of the target.

[0038] In the preparation of the marker on the target 2 in the present embodiment, there is no particular limitation on the use of augmented reality markers such as ArUco or the use of self-defined markers with a known shape.

[0039] When the size parameters and the mark parameters of the target 2 are known, a conversion relationship between the three-dimensional coordinates of the target mark center point and the three-dimensional coordinates of the measured point on the measured object tool or the measured object can be established. Each part of the target is precisely machined, and the target needs to be calibrated before actual use to correct the three-dimensional coordinate calculation parameters of the target.

[0040] In this embodiment, the combination mode of each part of the target for quickly establishing a camera measurement field is as shown in Figure 3 In actual use, the target body 21 is adsorbed in the base 20 of the target to quickly complete the combination of the target, and then the angle of the target is adjusted to make the target mark plane as parallel as possible to the camera view plane, thereby improving the mark detection precision.

[0041] Corresponding to the target 2 described above, the application further provides a camera measurement field establishment method using the target 2 with the above structure to determine the relative position of the measured object in the measurement field. Please refer to Figure 4 which schematically shows a schematic diagram of the camera measurement field establishment method provided by an embodiment of the application, as shown in Figure 4 The camera measurement field establishment method comprises the following steps:

[0042] Step S100: installing the target with known size parameters and mark parameters on the measured point of the measured object and making the mark plane of the target parallel to the camera view plane;

[0043] Wherein, each parameter of the target can be obtained by an auxiliary tool or before the target is machined, and in use, the target is inserted into the positioning hole of the measured object tool or the measured object, the size of the target mark is adjusted according to the actual working distance to meet the visual positioning requirement, and the angle of the target mark is manually adjusted according to the camera view mark image quality to make the target mark plane as parallel as possible to the camera view plane.

[0044] Step S200: constructing the conversion relationship between the three-dimensional coordinates of the target mark center point and the three-dimensional coordinates of the measured point on the measured object according to the size parameters and the mark parameters of the target;

[0045] According to the known size parameters and the mark parameters of the target, the conversion relationship between the three-dimensional coordinates of the target mark center point and the three-dimensional coordinates of the measured point on the measured object tool or the measured object is established. The conversion relationship diagram is as shown in Figure 3 , wherein O m is the target mark coordinate system, O m is the origin coordinate (X m , Y m , Z m ), and O c is the measured point coordinate system, and O c is the measured point coordinate Pc (X c , Y c , Z c ), both of which have the following relationship:

[0046]

[0047] In the formula, t x , t y , t z represent the correction parameters of target positioning; t d represents the substrate thickness of the target; t r represents the positioning ball radius of the target; X m , Y m , Z m are the three-dimensional coordinates of the target mark center point; R, T are the external parameters of the camera detecting the mark, X c , Y c , Z c are the three-dimensional coordinates of the measured point.

[0048] Step S300: photographing and calculating the three-dimensional coordinates of the target mark center point in the camera coordinate system, and calculating the three-dimensional coordinates of the measured point in the camera coordinate system according to the conversion relationship between the three-dimensional coordinates of the target mark center point and the three-dimensional coordinates of the measured point on the measured object.

[0049] Step S400: repeating the above steps to record the three-dimensional coordinates of no less than 6 groups of measured points in the camera coordinate system, and recording the known coordinates of the measured point and the three-dimensional coordinates of the measured point in the camera coordinate system at the same time;

[0050] Step S500: according to the recorded known coordinates of the measured point and the three-dimensional coordinates of the measured point in the camera coordinate system, using the best fitting algorithm to calculate the relationship between the three-dimensional coordinates of the measured point in the camera coordinate system and the known coordinates of the measured point, and establishing the camera measurement field

[0051] In step S400, the number distribution of the target 2 should as far as possible envelope the whole region of the measured object; as shown, the camera 3 is placed on a stable tripod 5, and the field of view of the camera 3 can cover all the positioning marks. The angle of the target 2 is adjusted to make the mark plane of the target 2 and the visual plane of the camera 3 as parallel as possible. Figure 4

[0052] ​In steps S300-S500, camera 3 is connected to control computer 6 via USB 3.0 or GigE. Camera 3 acquires images of fixed target marks on the object under test, calculates the three-dimensional coordinates of the measured point in the camera coordinate system using image processing algorithms, and establishes the transformation relationship between the actual three-dimensional coordinates of the measured point and the known three-dimensional coordinates of the measured point using an optimal fitting algorithm, thus completing the establishment of the camera measurement field. The theoretical coordinates of the measured point can be determined based on the digital model of the object under test, or the accurate coordinates of the measured point can be measured using a laser tracker, serving as the basis for subsequent optimal fitting and registration.

[0053] Preferably, during the rapid establishment of the camera measurement field, targets of different sizes can be replaced according to the size of the target markers in the field of view of the industrial camera.

[0054] In this embodiment of the invention, the camera can be a single camera or multiple cameras for measurement. When using a single camera, the single camera acquires an image of the tooling or target on the object being measured, which can determine the three-dimensional coordinate information of the object being measured within the camera's measurement field. When using multiple cameras, multiple cameras simultaneously acquire images of the tooling or target on the object being measured, which can establish spatial relationships between the multiple cameras and create a multi-camera measurement field.

[0055] The following section will provide a detailed explanation of measurement using a single camera, with specific examples.

[0056] When using a single camera for measurement, target 2 is placed inside the positioning hole of workpiece 1, as shown in the attached figure. Figure 4 As shown, the field of view of camera 3 can cover all the positioning mark areas. The angle of target 2 is adjusted so that the marking plane of target 2 is as parallel as possible to the camera's viewing plane. Computer 6 controls camera 3 to take pictures to acquire the current image and calculates the three-dimensional coordinates of the measured point of target 2 at a fixed position. By fitting the known three-dimensional coordinates of the measured point position of workpiece 1, the pose information of workpiece 1 in the coordinate system of camera 3 is determined.

[0057] When using multi-camera measurement, target 2 is placed inside the positioning hole of workpiece 1, as shown in the attached figure. Figure 4 Figure 4 As shown, cameras 3 and 4 can cover all the positioning marker areas. The target angle is adjusted so that the target marking plane is as parallel as possible to the view plane of camera 3, and the three-dimensional coordinates of the measured point at a fixed position on the target in the coordinate system of camera 3 are calculated. The target positioning sphere angle is then adjusted again so that the target marking plane is as parallel as possible to the view plane of camera 4, and the three-dimensional coordinates of the measured point at a fixed position on the target in the coordinate system of camera 4 are calculated. Based on the relationship between the three-dimensional coordinates of the measured point in the coordinate systems of camera 3 and camera 4, the spatial transformation relationship between camera 3 and camera 4 is determined, thereby establishing a multi-camera measurement field.

[0058] Thus, the application can quickly construct a single-camera / multi-camera vision measurement field by using more than 6 targets, simplifies the traditional measurement field establishment steps, and has good accuracy; in terms of hardware, the camera measurement field does not need additional auxiliary measurement equipment, and only the positional relationship between the three-dimensional coordinates of the targets and the theoretical coordinates is used to establish the camera measurement field, so that the structure is simpler. In actual use, the three-dimensional coordinate measurement value of the measured point is optimized by adjusting the angle between the positioning target mark and the camera visual plane, and the use is more convenient. The relationship between the camera and the measured object only depends on the best fitting result between the actual measured point coordinates and the known measured point coordinates, the data amount is small, and the solving speed is faster. Therefore, it can be widely applied to the pose measurement and docking of large-size aircraft parts in aviation manufacturing, vision guidance of industrial robots, augmented reality auxiliary assembly information projection and other application scenarios.

[0059] The above only describes the preferred embodiments of the application, and it should be noted that those skilled in the art can make several improvements and modifications without departing from the technical principles of the application, and these improvements and modifications should also be considered as the protection scope of the application.

Claims

1. A camera measurement field establishing method characterized by, The target is used to establish a camera measurement field, and comprises a base including a target ball socket and a positioning pin for insertion into a positioning hole of a measured object tool or a measured object, and a target body including a positioning ball rotatably arranged in the target ball socket and a mark plate having a mark plane with a center normal line passing through a ball center of the positioning ball. The camera measurement field establishment method comprises the following steps: installing the target with known size parameters and mark parameters on a measured point of the measured object and making the mark plane of the target parallel to a camera visual plane; constructing a conversion relationship between the three-dimensional coordinates of the target mark center points and the three-dimensional coordinates of the measured points on the measured object according to the known size parameters and mark parameters of the target; taking a photo and calculating the three-dimensional coordinates of the target mark center points in a camera coordinate system, and calculating the three-dimensional coordinates of the measured points in the camera coordinate system according to the conversion relationship between the three-dimensional coordinates of the target mark center points and the three-dimensional coordinates of the measured points on the measured object; repeating the above steps to record not less than six groups of three-dimensional coordinates of the measured points in the camera coordinate system, and recording the known coordinates of the measured points and the three-dimensional coordinates of the measured points in the camera coordinate system at the same time for each group; calculating the relationship between the three-dimensional coordinates of the measured points in the camera coordinate system and the known coordinates of the measured points by using a best fitting algorithm according to the recorded known coordinates of the measured points and the three-dimensional coordinates of the measured points in the camera coordinate system, and establishing a camera measurement field.

2. A camera measurement field establishing method according to claim 1, characterized in that, The mark plate comprises a base plate at a lower end and an aluminum oxide film arranged on the base plate, wherein a mark pattern is drawn on the aluminum oxide film.

3. The camera measurement field establishing method of claim 1, wherein, The target ball socket and the positioning ball are magnetically connected.

4. The camera measurement field establishing method of claim 1, wherein, The conversion relationship between the three-dimensional coordinates of the target mark center points and the three-dimensional coordinates of the measured points on the measured object is constructed as follows: In the formula t x , t y , t z represents a correction parameter of target positioning; t d represents the substrate thickness of the target; t r represents the positioning ball radius of the target; X m , Y m , Z m is the three-dimensional coordinates of the target mark center point; R , T is the external parameter of the camera detecting the mark; X c , Y c , Z c is the three-dimensional coordinates of the measured point.

5. The camera measurement field establishing method of claim 1, wherein, The step of making the mark plane of the target parallel to the camera visual plane comprises manually adjusting the angle of the target according to the mark image quality in the camera view, so that the mark plane of the target is parallel to the camera visual plane.

6. The camera measurement field establishing method of claim 1, wherein, In the process of quickly establishing the camera measurement field, different sizes of targets can be replaced according to the size of the target mark in the camera visual field in the measurement field.

7. The camera measurement field establishing method of claim 1, wherein, When a single camera is used for measurement, the single camera covers all the mark areas of the targets, controls the single camera to take a photo to obtain a current image, calculates the three-dimensional coordinates of the measured points in the camera coordinate system, and determines the pose information of the measured object in the single camera coordinate system by fitting calculation with the known coordinates of the measured points.

8. The camera measurement field establishing method of claim 1, wherein, When using multi-camera measurement, the multi-camera covers all the target mark areas, the target angle is adjusted so that the target mark plane is parallel to the view plane of one camera, the camera is controlled to take a picture to obtain a current image, and the three-dimensional coordinates of the measured point at the fixed position of the target in the coordinate system of the camera are calculated; the target angle is adjusted again so that the target mark plane is parallel to the view plane of another camera, the camera is controlled to take a picture to obtain a current image, and the three-dimensional coordinates of the measured point at the fixed position of the target in the coordinate system of the camera are calculated; according to the three-dimensional coordinate relationship of the measured point in the multi-camera coordinate system, the space conversion relationship between the multi-cameras is determined, and a camera measurement field is established.

9. The camera measurement field establishing method of claim 1, wherein, The known coordinates of the measured point are determined according to a measured object numerical model or are measured by a laser tracker.

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