Search

CN-122015650-A - Multi-class round special-shaped target for resisting centroid deviation and binocular vision positioning method thereof

CN122015650ACN 122015650 ACN122015650 ACN 122015650ACN-122015650-A

Abstract

The invention discloses a multi-class circle special-shaped target for resisting centroid deviation and a binocular vision positioning method thereof, which belong to the technical field of industrial vision measurement and precise positioning, wherein the target comprises a white background substrate and seven black circles which are symmetrically distributed, wherein the center of the target is provided with a large circle, the right upper part and the right lower part of the target are respectively provided with a standard perfect circle small circle, and the four corners of the target are respectively provided with a special class circle small circle which is designed according to a cylindrical surface nonlinear projection formula. The positioning method comprises the steps of collecting target images by a binocular camera, extracting two-dimensional center coordinates, resolving three-dimensional point clouds through three-dimensional matching, extracting cylindrical space axial vectors, constructing a normal plane, orthogonally projecting three-dimensional feature points to the normal plane to conduct two-dimensional circle fitting, and resolving inner anchoring column centers and surface highest axis reference point coordinates through inverse coordinate transformation. The invention effectively overcomes the positioning errors caused by cylindrical curvature deformation, spatial inclination and rotation around the shaft, and obviously improves the positioning robustness and universality under complex working conditions.

Inventors

  • ZHANG JIANWEI
  • YANG QINGHUA

Assignees

  • 成都大学

Dates

Publication Date
20260512
Application Date
20260413

Claims (8)

  1. 1. The multi-class round special-shaped target capable of resisting centroid offset is characterized by comprising a white background substrate and seven black circles arranged on the white background substrate, wherein the seven black circles are symmetrically distributed with respect to the center position of the white background substrate, and the seven black circles are formed by the following steps: A center big circle is arranged at the center of the white background substrate and is used as a datum reference of a multi-class circle special-shaped target; Setting a standard perfect circle in the right upper direction and the right lower direction of the white background substrate respectively; A special round-like small circle is respectively arranged in the left upper, left lower, right upper and right lower directions of the white background substrate; the outline of the special round-like small circle is determined by the following nonlinear projection formula: , wherein, For the horizontal coordinate of any point of the unfolding plane, v is the vertical coordinate of any point of the unfolding plane, R is the radius of a standard perfect circle, alpha is the offset angle of the target relative to the surface of the cylinder or cylinder-like tool, and R is the cylinder radius of the cylinder or cylinder-like tool.
  2. 2. The multi-class circle special-shaped target for resisting centroid deflection according to claim 1, wherein the white background substrate is made of polyethylene terephthalate, has a thickness of 0.1mm-0.2mm, a size of 75 mm-100 mm multiplied by 90 mm-120 mm and a gray value of more than or equal to 230, wherein all seven black circles are printed by UV, the gray value of less than or equal to 20 and the gray difference of the white background substrate is more than or equal to 210.
  3. 3. The multi-class circle shaped target with centroid deviation resistance according to claim 1, wherein the diameter of the center major circle is 12mm-18mm, the diameters of the standard perfect circle minor circle and the special class circle minor circle are 10mm-15mm, the value range of the deviation angle alpha is 0 DEG-20 DEG, and the value range of the cylinder radius R is 50mm-100mm.
  4. 4. A method for binocular vision positioning of a cylinder or cylinder-like tool based on a multi-class circular shaped target according to any one of claims 1-3, comprising the steps of: S1, synchronously collecting left and right views of a plurality of round special-shaped targets on the cylindrical surface of a cylinder or a cylinder-like tool through a binocular camera; S2, respectively performing self-adaptive threshold segmentation and circular contour screening on the left view and the right view, and extracting two-dimensional center coordinates of seven black circles; S3, numbering seven black circles by taking a center large circle as a reference, matching circles with the same numbers of left and right views, and understanding three-dimensional space coordinates of each circle through binocular vision polar constraint and triangulation source; s4, calculating an initial axial direction vector of the cylinder in space according to three-dimensional space coordinates of the large center circle and the standard perfect circle small right above and below, and constructing a space normal plane perpendicular to the initial axial direction vector; S5, uniformly projecting three-dimensional space coordinates of seven black circles into the space normal plane, and performing two-dimensional circle curve fitting or vector difference operation on projection points in the space normal plane to obtain circle center two-dimensional coordinates of a cylindrical section and a cylindrical actual fitting radius; S6, combining the two-dimensional coordinates of the circle center of the cylindrical section with the coordinates of the normal vector and the reference point of the space normal plane, and solving the three-dimensional anchoring column center coordinates of the corresponding section position on the real central axis inside the cylinder through inverse coordinate transformation; S7, carrying out normal extension of a radius R to the surface of the cylinder based on the three-dimensional anchoring cylindrical center coordinates and the set binocular camera observation direction, solving the three-dimensional space coordinates of the highest axis relative to the fixed reference point, which are free from the rotation interference of the cylinder, and taking the three-dimensional space coordinates as a reference for continuous positioning and moving distance measurement.
  5. 5. The binocular vision positioning method of cylindrical or cylindrical-like tools according to claim 4, wherein in the step S2, the threshold range of the adaptive threshold segmentation is 120-180, and the circularity threshold of the circular contour screening is not less than 0.85.
  6. 6. The binocular vision positioning method of the cylindrical or cylindrical-like tool according to claim 4, wherein in the step S3, the triangulation principle is based on an internal reference of a binocular camera, the internal reference comprises a focal length and principal point coordinates, the external reference comprises a base line distance, an optical axis parallelism, a rotation matrix and a translation vector, and the resolution of the binocular camera is larger than or equal to 2048×1536, and the base line distance is 100mm-120mm.
  7. 7. The binocular vision positioning method of the cylindrical or cylindrical-like tool according to claim 4, wherein in the step S5, a least square method is adopted when fitting a two-dimensional circular curve of projection points in the space normal plane, and a two-dimensional coordinate of a circle center of a cylindrical section in the space normal plane and an actual fitting radius of the cylindrical are calculated by minimizing a sum of squares of distances from the projection points corresponding to seven black circles to the fitting circle center.
  8. 8. The binocular vision positioning method of a cylinder or cylinder-like tool according to claim 4, wherein the repetition precision of the three-dimensional space coordinates of the highest axis of the cylinder or cylinder-like tool with respect to a fixed reference point is less than or equal to 1mm and the movement precision is less than or equal to 3mm in a depth range of 1.2m-3.2 m.

Description

Multi-class round special-shaped target for resisting centroid deviation and binocular vision positioning method thereof Technical Field The invention relates to the technical field of industrial vision measurement and precise positioning, in particular to a multi-class round special-shaped target for resisting centroid deviation and a binocular vision positioning method thereof. Background In applications such as industrial automation assembly, precision machining, end effector guidance, and measurement system precision calibration, cylindrical or cylinder-like structures of industrial tools are widely used, such as tubular tools, assembly effectors, and various types of cylindrical end members. In order to realize the spatial position detection, motion track tracking and assembly accuracy control of the tool in the operation process, an industrial site generally adopts a stereoscopic vision measurement scheme based on a vision target and a binocular camera, and a target image is acquired and three-dimensional spatial coordinates of the target image are calculated by pasting the vision target on the surface of a cylinder or a cylinder-like tool, so that the tool position measurement and system calibration are realized. However, due to the structural characteristics of the measured object, the complexity of imaging conditions and the interference of the multi-degree-of-freedom posture change in the actual operation, the conventional vision measurement scheme still faces a plurality of key problems affecting the measurement precision and stability in the actual application, and the key problems are mainly represented in the following aspects: 1. Target projection deformation problem caused by cylindrical curved surface attachment The existing visual targets are in the form of flat perfect circles or checkerboards and the like, when the visual targets are adhered to the surfaces of cylindrical or cylindrical-like curved surfaces, the visual targets are affected by curvature, obvious nonlinear projection deformation can be generated in a camera imaging plane, originally regular geometric structures are in an elliptical-like shape or an irregular contour in imaging, geometric characteristics of the visual targets are degraded, and further extraction precision of two-dimensional characteristic points or circle centers is reduced. 2. Centroid systematic shift problem caused by tool tiny posture change In the actual industrial operation or system calibration process, the cylinder or cylinder-like tool inevitably generates small-angle rotation or posture disturbance, and is usually within a range of +/-5 degrees. When the tool rotates, the gray distribution and the outline morphology of the visual target attached to the surface of the tool change in imaging, so that the centroid of the target calculated based on gray or geometric features is systematically shifted towards the rotation direction, and the offset increases with the increase of the rotation angle, so that a significant error is generated between the extracted two-dimensional centroid and the real geometric center of the target. 3. Problem of positioning reference point slippage caused by rotation interference around axis During tool movement or continuous machining operations, there is often accompanied by slight spin (Roll) about its own central axis. Such rotation can result in physical slippage of the spatial location of a visual target attached to the tool surface. If the characteristic points on the surface target are directly used as absolute reference points for continuous positioning or displacement measurement, surface slip caused by rotation can be seriously misjudged by a system as spatial translation of the whole tool, so that distance measurement and positioning references are lost, and the existing algorithm generally lacks a mechanism for extracting an absolute motionless point which is not interfered by rotation. 4. Error superposition problem caused by lens distortion and field-of-view edge effect In binocular vision measurement systems with large working distances and field of view ranges, the effects of lens radial distortion and tangential distortion are significantly enhanced as the target imaging location approaches the camera field of view edge. Under the combined action of cylindrical curved surface attachment and attitude change, the distortion effect can further amplify the irregularity of the target outline, so that the extraction error of the two-dimensional circle center or the characteristic point is obviously increased, and the subsequent three-dimensional space coordinate calculation and the system calibration precision are adversely affected. 5. The existing target structure is difficult to meet the requirements of high-precision measurement and calibration With the continuous improvement of industrial assembly precision and calibration requirements of a measuring system, the tolerance range of the three-dimensional spa