Handheld combined optical target and calibration method

Abstract

A handheld combined optical target and a calibration method. The handheld combined optical target comprises a positioning target body, a surface scanning head, a handle and a hinge rotating mechanism, wherein one side of the surface scanning head is connected to a bottom end of the positioning target body by means of the hinge rotating mechanism, and the handle is arranged at the side of the positioning target body. A target surface is scanned by means of the surface scanning head, thereby improving the three-dimensional scanning efficiency; and the positioning target body of the optical target can be easily positioned by means of a visual system, so as to provide a new low-cost space tracking method for large-view-of-field stitch scanning. The switching between two fixing and fastening modes improves the flexibility of measurement.

Description

A handheld combined optical target and calibration method Technical Field

[0001] The embodiments of the present invention relate to the field of visual measurement technology, and in particular to a handheld combined optical target and a calibration method. Background Art

[0002] The portable optical target 3D measurement system can track and locate the 3D coordinate information of spatial points and is widely used in various industries, such as the detection of geometric information such as the inner cavity and outer shape of large special-shaped workpieces in industry, and the tracking and positioning of position information such as joints and spines during medical surgery.

[0003] Existing portable optical target measurement systems typically consist of a vision system, an optical target, a computer, and related software. The optical target's surface features several markings, and a contact probe is attached to its base. During use, the optical target is held and positioned so that the probe contacts a specific point on the surface of the object being measured. The markings are then captured by the vision system. Image processing methods and visual measurement techniques are then used to obtain the three-dimensional coordinates of the markings, allowing the measured point's position to be inferred and calculated.

[0004] Traditional optical targets typically use a probe to contact the surface for single-point measurement, resulting in sparse point clouds. Furthermore, the optical target and the probe at the bottom are fixedly connected. For some invisible surfaces, multiple adjustments or even movement of the vision system are required to observe them. However, moving the vision system requires additional calibration objects to calibrate its position relative to the world coordinate system, resulting in limited flexibility and ultimately low measurement efficiency for large targets.

[0005] Summary of the Invention

[0006] In view of this, embodiments of the present invention provide a handheld combined optical target and calibration method to at least partially solve the above problems.

[0007] According to a first aspect of an embodiment of the present invention, a handheld combined optical target is provided, comprising a positioning target body, an area scanning head, a handle and a hinge rotation mechanism, wherein one side of the area scanning head is connected to the bottom end of the positioning target body through the hinge rotation mechanism, and the handle is arranged on the side of the positioning target body.

[0008] In one implementation, the positioning target includes a plurality of optical feature points, and the plurality of optical feature points are arranged on the surface of the positioning target.

[0009] In another implementation, an optical projection module and an image acquisition module are provided on the other side of the area scanning head; wherein, the optical projection module and the image acquisition module are located in the same horizontal plane, the optical projection module is used to project a specific coding pattern onto the target surface, and the image acquisition module is used to acquire the specific coding pattern modulated by the target surface, so as to realize the contour reconstruction of the target surface and obtain high-density three-dimensional point cloud data through decoding.

[0010] In another implementation, the number of the plurality of optical feature points is at least three.

[0011] In another implementation, there are two fixed positioning modes between the area scanning head and the positioning target, and the hinge rotation mechanism is rotated up and down to achieve switching between the two fixed positioning modes.

[0012] In another implementation, the two fixed positioning methods include the surface scanning head and the positioning target being parallel to each other, which is used to scan radial measurement targets such as the end face of the workpiece during measurement; or the surface scanning head and the positioning target being perpendicular to each other, which is used to scan the axial contour data of the workpiece during measurement.

[0013] According to a second aspect of an embodiment of the present invention, a handheld combined optical target calibration method is provided, comprising a binocular stereo vision system and a dot calibration plate, the method comprising the following steps:

[0014] Step 1: Place the dot calibration plate at a specific position observable by the binocular stereo vision system. After adjusting the posture of the optical target to the preset position, use the binocular stereo vision system to collect and locate multiple optical feature points of the target.

[0015] Step 2: reconstructing the multiple optical feature points through a binocular stereo vision system to generate three-dimensional coordinates of the multiple optical feature points in a binocular stereo vision coordinate system;

[0016] The dot calibration plate is scanned by an area scanning head to reconstruct the dot calibration plate, and the three-dimensional coordinates of the centers of all dots on the dot calibration plate are generated in the coordinate system of the area scanning head;

[0017] Establishing a positioning target coordinate system through the three-dimensional coordinates of multiple optical feature points;

[0018] Step 3: Calculate the motion relationship between the positioning target coordinate system and the binocular stereo vision coordinate system;

[0019] Step 4: Establish a calibration plate coordinate system based on the three-dimensional coordinates of the centers of all the dots on the dot calibration plate;

[0020] Step 5: Calculate the motion relationship between the coordinate system of the surface scanning head and the coordinate system of the calibration plate;

[0021] Step 6: Calculate the motion relationship between the binocular stereo vision coordinate system and the calibration plate coordinate system;

[0022] Step 7. According to the motion relationship between the positioning target coordinate system and the binocular stereo vision coordinate system, the motion relationship between the area scanning head coordinate system and the calibration plate coordinate system, and the motion relationship between the binocular stereo vision coordinate system and the calibration plate coordinate system, the motion relationship between the area scanning head coordinate system and the positioning target coordinate system is determined to achieve self-calibration of the handheld combined optical target.

[0023] In summary, this solution has the following effects:

[0024] 1) By replacing the light pen probe end with a surface scanning head, the efficiency of 3D scanning is improved, and rich, high-density 3D contour data of the target surface can be obtained.

[0025] 2) Traditional large-field-of-view stitching measurements often require the use of expensive positioning equipment such as total stations and theodolites. However, the positioning target part of the optical target in the solution of the present invention can be easily positioned by the visual system, providing a new low-cost spatial tracking method for large-field-of-view stitching scanning.

[0026] 3) The orientation of the surface scanning head in the present invention can be adjusted to be parallel or perpendicular to the target body through a hinge, which has significant advantages in contour measurement tasks that require simultaneous measurement of axial and radial data, can effectively avoid measurement blind spots, and has strong flexibility. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments recorded in the embodiments of the present invention. For ordinary technicians in this field, other drawings can also be obtained based on these drawings.

[0028] FIG1 is a schematic structural diagram of a handheld combined optical target in an embodiment of the present invention.

[0029] FIG2A is a front view of a handheld combined optical target according to an embodiment of the present invention.

[0030] FIG. 2B is a side view of a handheld combined optical target according to another embodiment of the present invention.

[0031] FIG3 is a schematic diagram of a scenario of a handheld combined optical target calibration method according to an embodiment of the present invention.

[0032] FIG4 is a schematic diagram of establishing a positioning target coordinate system in the handheld combined optical target calibration method according to an embodiment of the present invention.

[0033] FIG5A is a schematic diagram of establishing a calibration plate coordinate system in a handheld combined optical target calibration method according to an embodiment of the present invention.

[0034] FIG5B is a schematic diagram of establishing a calibration plate coordinate system in a handheld combined optical target calibration method according to another embodiment of the present invention. DETAILED DESCRIPTION

[0035] In order to have a clearer understanding of the technical features, purposes and effects of the embodiments of the present application, the specific implementation methods of the embodiments of the present application are now described with reference to the accompanying drawings.

[0036] In this document, “illustrative” means “serving as an example, instance or illustration”, and any diagram or implementation described in this document as “illustrative” should not be interpreted as a more preferred or more advantageous technical solution.

[0037] To simplify the drawings, only the parts related to the present application are schematically shown in each figure, and they do not represent the actual structure of the product. In addition, to simplify the drawings and facilitate understanding, in some figures, only one or more components with the same structure or function are schematically shown, or only one or more are labeled.

[0038] In order to enable those skilled in the art to better understand the technical solutions in the embodiments of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. All other embodiments obtained by those skilled in the art based on the embodiments in the embodiments of the present invention should fall within the scope of protection of the embodiments of the present invention.

[0039] The specific implementation of the embodiment of the present invention is further described below with reference to the accompanying drawings of the embodiment of the present invention.

[0040] According to a first aspect of an embodiment of the present invention, a handheld modular optical target is provided. Referring to FIG1 , FIG1 is a schematic structural diagram of a handheld modular optical target 100 according to an embodiment of the present invention, which mainly includes:

[0041] Positioning target 101;

[0042] Area scanning head 102;

[0043] handle 103;

[0044] Hinge rotation mechanism 104 .

[0045] One side of the area scanning head is connected to the bottom end of the positioning target through a hinge rotation mechanism, and a handle is arranged on the side of the positioning target.

[0046] It should be understood that the area scanning head is used to obtain high-density three-dimensional surface data of the target surface, thereby improving the three-dimensional scanning efficiency.

[0047] In one implementation, the positioning target includes a plurality of optical feature points 1011 , and the plurality of optical feature points are arranged on the surface of the positioning target.

[0048] Exemplarily, the multiple optical feature points are multiple light-emitting LED points, which can be clearly imaged in the visual system for spatial positioning of the optical target.

[0049] In another implementation, an optical projection module 1021 and an image acquisition module 1022 are provided on the other side of the area scanning head; wherein the optical projection module and the image acquisition module are located on the same horizontal plane.

[0050] It should be understood that the optical projection module is used to project a specific coding pattern onto the target surface, and the image acquisition module is used to acquire the specific coding pattern modulated by the target surface, so as to reconstruct the contour of the target surface and obtain high-density three-dimensional point cloud data through decoding.

[0051] In another implementation, the number of the plurality of optical feature points is at least three.

[0052] In another implementation, there are two fixed positioning modes between the area scanning head and the positioning target, and the hinge rotation mechanism is rotated up and down to achieve switching between the two fixed positioning modes.

[0053] For example, the orientation of the area scanning head can be adjusted to be parallel or perpendicular to the positioning target through a hinge rotation mechanism. When contour measurement requires simultaneous measurement of axial and radial data, it can effectively avoid measurement blind spots and has high flexibility.

[0054] In another implementation, the two fixed positioning methods include the surface scanning head and the positioning target being parallel to each other, which is used to scan radial measurement targets such as the end face of the workpiece during measurement; or the surface scanning head and the positioning target being perpendicular to each other, which is used to scan the axial contour data of the workpiece during measurement.

[0055] For example, taking the parallel state of the surface scanning head and the positioning target as an example, referring to Figures 2A and 2B, the optical projection module projects a specific coding pattern to the target surface, and the image acquisition module captures the coding pattern modulated by the target surface, and reconstructs the contour of the target surface through decoding to obtain high-density three-dimensional point cloud data.

[0056] In summary, the present invention improves the efficiency of 3D scanning by scanning the target surface with an area scanner. The positioning portion of the optical target can be easily located using a visual system, providing a new, low-cost spatial tracking method for large-field-of-view stitching scanning. The ability to switch between two fixed positioning modes enhances measurement flexibility.

[0057] Because the handheld modular optical target of the present invention has two fixed positioning modes, that is, two different relative positions between the area scanner head and the positioning target, the overall structure of the optical target changes when the area scanner head is adjusted to different positions. Therefore, pre-calibration is crucial. The main task of calibration is to determine the kinematic relationship between the coordinate system of the area scanner head and the coordinate system of the positioning target.

[0058] 3 is a schematic diagram of a handheld combined optical target calibration method according to an embodiment of the present invention. The entire calibration process is described by taking the positioning when the surface scanning head is parallel to the positioning target as an example. The calibration process for another positioning is similar and will not be repeated here.

[0059] The handheld combined optical target calibration method shown in FIG3 includes a binocular stereo vision system 301 and a dot calibration plate 302. The method mainly includes the following steps:

[0060] Step 1: Place the dot calibration plate at a specific position observable by the binocular stereo vision system. After adjusting the posture of the optical target 100 to a preset position, collect and locate multiple optical feature points of the target through the binocular stereo vision system.

[0061] It should be understood that the system parameters of the binocular stereo vision system and the area scanning head have been calibrated in advance by default.

[0062] It should also be understood that the calibration plate is placed at a specific position observable by the binocular stereo vision system and remains stationary throughout the calibration process, and the specific position can be adjusted according to actual conditions.

[0063] It should also be understood that before collecting multiple optical feature points of the positioning target through the binocular stereo vision system, the operator is required to hold the handle of the optical target and adjust the target posture so that the area scanning head can scan and reconstruct the entire dot calibration plate, and the optical feature points on the positioning target can be captured and reconstructed by the binocular stereo vision system.

[0064] Step 2: reconstructing the multiple optical feature points through a binocular stereo vision system to generate three-dimensional coordinates of the multiple optical feature points in a binocular stereo vision coordinate system;

[0065] It should be understood that the binocular stereo vision system collects and locates the optical feature points on the target and reconstructs the optical feature points to generate the three-dimensional coordinates P of the multiple optical feature points. V Based on binocular stereo vision coordinate system O V middle.

[0066] The dot calibration plate is scanned by an area scanning head to reconstruct the dot calibration plate, and the three-dimensional coordinates of the centers of all dots on the dot calibration plate are generated in the coordinate system of the area scanning head;

[0067] It should be understood that the area scanning head scans and reconstructs the entire dot calibration plate to obtain a three-dimensional point cloud, and uses the point cloud feature extraction and segmentation algorithm to obtain the center coordinates of each dot as the main feature point. The three-dimensional coordinates of the center of these dots are X S Established in the surface scanning head coordinate system O S middle.

[0068] Establishing a positioning target coordinate system through the three-dimensional coordinates of multiple optical feature points;

[0069] For example, referring to FIG4 , which is a schematic diagram of establishing a positioning target coordinate system in a handheld combined optical target calibration method according to an embodiment of the present invention, the three-dimensional coordinates P of the plurality of optical feature points obtained by reconstruction are used. V Establish positioning target coordinate system O T , with the three-dimensional coordinates P1 of one of the optical feature points V The origin of the target coordinate system is located at the target coordinate system O T The three coordinate axes The establishment method is shown in formula (1):

[0070] Step 3: Calculate the motion relationship between the positioning target coordinate system and the binocular stereo vision coordinate system;

[0071] Positioning target coordinate system O T With binocular stereo vision coordinate system O V The relationship between the movements It can be obtained by calculation, in,

[0072] Step 4: Establish a calibration plate coordinate system based on the three-dimensional coordinates of the centers of all the dots on the dot calibration plate;

[0073] 5A and 5B are schematic diagrams of establishing a calibration plate coordinate system for a handheld combined optical target calibration method according to an embodiment of the present invention, FIG5A is in a face scanning head coordinate system, and FIG5B is in a binocular stereo vision coordinate system.

[0074] Based on the obtained three-dimensional coordinate X of the circle center S Establish calibration plate coordinate system O P Generally, the center of the circle closest to the triangle mark on the upper left corner of the calibration plate is As the coordinate origin, the two centers of the circle in the upper right corner and the lower left corner of the dot calibration plate as shown in Figure 5A and As the anchor point, establish the calibration plate coordinate system O P , calibration plate coordinate system OP The establishment method is shown in formula (2):

[0075] Step 5: Calculate the motion relationship between the coordinate system of the surface scanning head and the coordinate system of the calibration plate;

[0076] Area scanning head coordinate system O S and calibration plate coordinate system O P The relationship between the movements It can be obtained by calculation, in,

[0077] Step 6: Calculate the motion relationship between the binocular stereo vision coordinate system and the calibration plate coordinate system;

[0078] Calculate binocular stereo vision coordinate system O V and calibration plate coordinate system O P The relationship between the movements Specifically:

[0079] Use binocular stereo vision system based on triangulation principle to reconstruct the center of the circle on the dot plate and obtain the coordinates X of all the circle centers. V , X V Located in the binocular stereo vision coordinate system O V Next. According to the calculation surface scanning head coordinate system O S and calibration plate coordinate system O P The relationship between the movements The same operation as above is performed to calculate the binocular stereo vision coordinate system O V and calibration plate coordinate system O P The relationship between the movements

[0080] Step 7. According to the motion relationship between the positioning target coordinate system and the binocular stereo vision coordinate system, the motion relationship between the area scanning head coordinate system and the calibration plate coordinate system, and the motion relationship between the binocular stereo vision coordinate system and the calibration plate coordinate system, the motion relationship between the area scanning head coordinate system and the positioning target coordinate system is determined to achieve self-calibration of the handheld combined optical target.

[0081] For example, since the physical parameters of the dot distribution on the dot calibration plate are known, the coordinates X of the centers of the circles in the calibration plate coordinate system are P is also a known quantity, where the Z coordinate of the original circle center is 0. According to the coordinate system chain association model, the following formula (3) can be obtained:

[0082] Then the surface scanning head coordinate system OS and the positioning target coordinate system O T The relationship between the movements The calculation is as follows:

[0083] Through the above steps (1-7), we can get Target calibration is complete.

[0084] On this basis, in order to make the calibration results more robust, in practice, the optical target can be adjusted to shoot and scan the calibration plate at different angles to obtain multiple sets of chain correlation equations:

[0085] Among them, i and j represent the serial numbers of optical targets placed at different angles, i≠j.

[0086] By simply transforming formula (5), the multiple sets of equations are converted into the classic AX=XB form, and the optimal solution is obtained by the method in the literature [FC Park, BJ Martin. Robot sensor calibration: solving AX=XB on the Euclidean group [J]. IEEE. T. Robot. 10 (5) (2002) 717-721.] Achieve high-precision calibration of the target.

[0087] Use the hinged rotation mechanism to move the area scanner to another position and repeat the above steps (1-7) to calibrate the target in the other position. Record the calibration parameters for the two different positions. In actual measurement, call the corresponding calibration parameters according to the usage situation to complete the measurement.

[0088] In summary, the present invention improves the efficiency of 3D scanning by scanning the target surface with an area scanner. The positioning portion of the optical target can be easily located using a visual system, providing a new, low-cost spatial tracking method for large-field-of-view stitching scanning. The ability to switch between two fixed positioning modes enhances measurement flexibility.

[0089] It should be understood that although this specification is described according to various embodiments, not every embodiment contains only one independent technical solution. This narrative method of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other implementation methods that can be understood by those skilled in the art.

[0090] The above implementation methods are only used to illustrate the embodiments of the present application, and are not intended to limit the embodiments of the present application. Ordinary technicians in the relevant technical field can make various changes and modifications without departing from the spirit and scope of the embodiments of the present application. Therefore, all equivalent technical solutions also fall within the scope of the embodiments of the present application, and the scope of patent protection of the embodiments of the present application should be defined by the claims.

Claims

1. A handheld combined optical target, characterized in that: It comprises a positioning target body, a surface scanning head, a handle and a hinge rotating mechanism, wherein one side of the surface scanning head is connected to the bottom end of the positioning target body through the hinge rotating mechanism, and the handle is arranged on the side of the positioning target body.

2. The handheld combined optical target according to claim 1, characterized in that: The positioning target includes a plurality of optical feature points, and the plurality of optical feature points are arranged on the surface of the positioning target.

3. The handheld combined optical target according to claim 2, characterized in that: An optical projection module and an image acquisition module are provided on the other side of the area scanning head; Among them, the optical projection module and the image acquisition module are located in the same horizontal plane, the optical projection module is used to project a specific coding pattern onto a target surface, and the image acquisition module is used to acquire the specific coding pattern modulated by the target surface, so as to achieve contour reconstruction of the target surface and obtain high-density three-dimensional point cloud data through decoding.

4. The handheld combined optical target according to claim 2, characterized in that: The number of the plurality of optical feature points is at least three.

5. The handheld combined optical target according to claim 1, characterized in that: There are two fixed positioning modes between the surface scanning head and the positioning target body, and the hinge rotating mechanism is rotated up and down to realize the switching of the two fixed positioning modes.

6. The handheld combined optical target according to claim 5, characterized in that: The two fixed positioning methods include: The surface scanning head is parallel to the positioning target body and is used to scan radial measurement targets such as the end face of the workpiece during measurement; or The surface scanning head is in a vertical state with respect to the positioning target body, and is used for scanning the axial profile data of the workpiece during measurement.

7. A handheld combined optical target calibration method according to claim 1, comprising a binocular stereo vision system and a dot calibration plate, the method comprising the following steps: Step 1, placing the dot calibration plate at a specific position observable by the binocular stereo vision system, and after adjusting the posture of the optical target to a preset position, collecting the multiple optical feature points of the positioning target through the binocular stereo vision system; Step 2: reconstructing the plurality of optical feature points through the binocular stereo vision system to generate three-dimensional coordinates of the plurality of optical feature points in a binocular stereo vision coordinate system; Reconstructing the dot calibration plate by scanning the dot calibration plate with the area scanning head, and generating three-dimensional coordinates of the centers of all dots on the dot calibration plate in the area scanning head coordinate system; Establishing a positioning target coordinate system through the three-dimensional coordinates of the plurality of optical feature points; Step 3, calculating the motion relationship between the positioning target coordinate system and the binocular stereo vision coordinate system; Step 4: establishing a calibration plate coordinate system based on the three-dimensional coordinates of the centers of all the dots on the dot calibration plate; Step 5: Calculate the motion relationship between the coordinate system of the surface scanning head and the coordinate system of the calibration plate; Step 6: Calculate the motion relationship between the binocular stereo vision coordinate system and the calibration plate coordinate system; Step 7. Determine the motion relationship between the surface scanning head coordinate system and the positioning target coordinate system according to the motion relationship between the positioning target coordinate system and the binocular stereo vision coordinate system, the motion relationship between the surface scanning head coordinate system and the calibration plate coordinate system, and the motion relationship between the binocular stereo vision coordinate system and the calibration plate coordinate system, so as to realize self-calibration of the handheld combined optical target.

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