A surface defect scanning method for large-aperture planar optical elements based on a robotic arm

Abstract

The present invention discloses a method for scanning surface defects of large-aperture planar optical components based on a robotic arm. The method employs an automatic centering and localization device, which includes a sample stage, a robotic arm, a probe mounted on the robotic arm and equipped with a spectral confocal sensor and a camera, a data acquisition unit electrically connected to the spectral confocal sensor, a data analysis and processing unit electrically connected to the data acquisition unit, and a control unit for receiving feedback from the data analysis and processing unit and controlling the movement of the robotic arm. After leveling, the method automatically performs centering and localization by collecting the coordinates of three edge points, and then scans the surface according to the parameters of the optical component. The method is simple and easy to implement, requiring no sensor calibration or customization of high-precision guide rails and sample spin stages for specific samples. This reduces the difficulty of mechanical design and assembly, and enables non-contact, rapid, automatic centering and localization scanning of optical components. The method is suitable for streamlined production and testing of large-aperture planar optical components.

Description

Technical Field

[0001] The present invention belongs to the field of optical technology, and in particular relates to a surface defect scanning method for a large-aperture planar optical element based on a robotic arm. Background Art

[0002] With the advancement and development of the aerospace field, large-scale optical remote sensing systems used in space optics and aerospace research, such as space telescopes and remote sensing reconnaissance cameras, require optical systems with sufficiently large apertures to achieve sufficiently high resolution. In the field of surface defect detection for optical components, microscopic imaging systems are primarily used to scan and image the surface of the sample under inspection, thereby determining the morphology and distribution of surface defects. When inspecting large-aperture optical components, scanning efficiency must be considered. If the scanning range for large-aperture optical components is not determined in advance, redundancy or omissions may occur during the scanning process, negatively impacting defect detection in subsequent processes. Therefore, for large-aperture optical components, component centering is first required, followed by scanning path planning using the axis centerline as a reference point. Industrial robotic arms are the most widely used automated mechanical devices in various fields. Despite their diverse forms, they all share a common characteristic: the ability to receive instructions and precisely locate a point in three-dimensional (or two-dimensional) space to perform operations. If the surface defect detection of optical components can be combined with industrial robotic arms, it will be of great significance to the assembly line production and processing of precision optical components.

[0003] Chinese patent publication CN116149037A discloses an ultrafast large-scale scanning system and method. The system includes a sample stage, motion control components, a light source assembly, an objective lens, a reflector, a high-resolution camera, a height sensor, a light intensity sensor, and a control and processing unit. The system automatically controls the sample stage and enables automatic, rapid, and reliable scanning of large areas. However, this method places high demands on the mechanical structure and involves the calibration of multiple sensors, increasing the complexity of design, processing, and assembly.

[0004] Chinese patent publication CN110006905A discloses a large-aperture, ultra-clean, smooth surface defect detection device that combines a line and area array camera. The device first uses a low-magnification line array camera to rapidly scan the entire aperture and capture a dark-field image of the sample surface, extracting defect location information. An area array camera equipped with a high-magnification optical system then locates each defect and performs further data processing and analysis on the image to obtain highly accurate detection results. However, this method increases system complexity and cost due to the scanning motion and corresponding position feedback. Furthermore, image accuracy may be affected by the accuracy of the scanning motion, which in turn affects the final measurement accuracy.

[0005] Therefore, it is necessary to design simple and efficient devices and methods to scan surface defects of large-aperture planar optical elements. Summary of the Invention

[0006] In order to solve the above problems existing in the prior art, the present invention provides a surface defect scanning method for large-aperture planar optical components based on a robotic arm, which realizes non-contact, high-efficiency and automated scanning of surface defects of large-aperture planar optical components.

[0007] A method for scanning surface defects of large-aperture planar optical elements based on a robotic arm employs an automatic centering and localization device. The automatic centering and localization device comprises a sample stage, a robotic arm, a probe mounted on the robotic arm and equipped with a spectral confocal sensor and a camera, a data acquisition unit electrically connected to the spectral confocal sensor, a data analysis and processing unit electrically connected to the data acquisition unit, and a control unit for receiving feedback from the data analysis and processing unit and controlling the movement of the robotic arm.

[0008] The method for scanning surface defects of a large-aperture planar optical element comprises the following steps:

[0009] (1) Fix the planar optical element to be centered and localized on the sample stage in a horizontal position;

[0010] (2) In the original tool coordinate system of the robotic arm, the robotic arm is controlled to approach the sample stage so that the sampling point of the spectral confocal sensor is located on the surface of the planar optical element, and the robotic arm is controlled to move along the Z-axis so that the spectral confocal sensor is located within the working distance;

[0011] (3) Randomly locate three non-collinear points on the surface of the planar optical element, and make the reading of the spectral confocal sensor at the center of the range. Reconstruct the robot tool coordinate system according to the three-point method, which is recorded as coordinate system T1. At this time, the surface of the planar optical element is parallel to the xoy plane of the T1 coordinate system;

[0012] (4) In the T1 coordinate system, control the robotic arm to move along the Z axis so that the spectral confocal sensor is within the working distance and the reading of the spectral confocal sensor is at the center of the range;

[0013] (5) Control the robotic arm to move along the negative direction of the X-axis until the reading of the spectral confocal sensor changes suddenly (edge ​​point). At this time, the coordinate of the T1 coordinate system is marked as P1 (x1, y1, 0); Control the robotic arm to move along the positive direction of the X-axis until the reading of the spectral confocal sensor changes suddenly (edge ​​point). At this time, the coordinate of the T1 coordinate system is marked as P2 (x2, y2, 0); Control the robotic arm to move along the positive direction of the Y-axis until the reading of the spectral confocal sensor changes suddenly (edge ​​point). At this time, the coordinate of the T1 coordinate system is marked as P3 (x3, y3, 0);

[0014] (6) In the xoy plane of the T1 coordinate system, the x0 coordinate of the center of the circle is obtained from the horizontal coordinate of the midpoint of P1 and P2, and the y0 coordinate of the center of the circle is obtained from the vertical coordinate of the midpoint of P2 and P3. Therefore, the coordinates of the center of the circle are

[0015] (7) Assume that the calibration distance between the spectral confocal sensor and the camera is L, the projection length of L on the X axis is α, and the projection length on the Y axis is β, Three points, according to the three-point method, the robot tool coordinate system is reconstructed and recorded as coordinate system T2; the origin of the T2 coordinate system corresponds to the center of the plane optical element;

[0016] (8) In the T2 coordinate system, the plane optical element is localized according to its size and scanned according to the path planned by the algorithm.

[0017] Furthermore, the robotic arm is an industrial high-precision robotic arm that communicates with a control unit. By setting an algorithm in the control unit, the robotic arm can automatically perform centering, localization and scanning functions on planar optical elements.

[0018] Furthermore, the robotic arm is an industrial high-precision robotic arm. There are six coordinate systems on the industrial high-precision robotic arm, namely: geodetic coordinate system, base coordinate system, joint coordinate system, tool coordinate system, workpiece coordinate system and user coordinate system. Among them, the tool coordinate system is used to determine the position of the tool, that is, the position of the optical precision probe, which consists of the tool center point (TCP) and the coordinate position.

[0019] The end of the industrial robot arm is equipped with a fully integrated optical precision probe that can achieve high-precision distance detection, optical imaging, autofocus, defect detection and other functions.

[0020] Furthermore, the localization is a function for determining the boundary of the optical plane element on the robot tool coordinate system.

[0021] Furthermore, the optical precision probe is equipped with multiple devices such as a spectral confocal sensor, a light source, a camera, and an objective lens driver, and the main axis of the camera on the robotic arm is parallel to the optical axis of the spectral confocal sensor.

[0022] The spectral confocal sensor is a non-contact measurement sensor. Spectral confocal measurement uses a special lens to extend the focal halo range of different colors of light, forming a special amplified chromatic aberration. This allows light of a precise wavelength to be focused on the object being measured according to the distance between the object being measured and the lens. By measuring the wavelength of the reflected light, the precise distance from the object being measured to the lens can be obtained.

[0023] Furthermore, the large-aperture planar optical element is fixed on the sample stage by a clamping mechanism.

[0024] The horizontal placement posture refers to the placement of the optical axis of the large-aperture planar optical element perpendicular to the horizontal plane.

[0025] Furthermore, the centering and localization accuracy of the large-aperture planar optical element is determined by the end positioning accuracy of the industrial robot arm and the measurement accuracy of the spectral confocal sensor. Compared with the prior art, the present invention has the following advantages:

[0026] The present invention provides a new device and method for scanning surface defects of large-aperture planar optical components. For large-aperture planar optical components, only an industrial robotic arm is required to carry an optical precision probe for three-dimensional movement, eliminating the need for customized high-precision guide rails and sample spin stages for specific samples. This significantly reduces mechanical design, assembly difficulty, and production costs. The use of a spectral confocal sensor offers strong anti-tilt capability and facilitates assembly. Furthermore, a single sensor can reduce the various calibration tasks associated with differences between multiple sensors, improving production efficiency. The centering method is simple to operate, requires few steps, is fast, and is highly efficient. It possesses significant engineering application value and lays the foundation for efficient, rapid, and high-precision surface defect detection of large-aperture planar optical components. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 Schematic diagram of leveling a large-aperture circular planar optical element in an embodiment of the present invention;

[0028] Figure 2 This is a schematic diagram of centering a large-aperture circular planar optical element in an embodiment of the present invention;

[0029] Figure 3 Schematic diagram of the scanning trajectory of a large-aperture circular planar optical element in an embodiment of the present invention;

[0030] Figure 4 Schematic diagram of the simulation of the scanning trajectory of a 150mm aperture circular plane optical element in an embodiment of the present invention;

[0031] Figure 5 This is a 150mm diameter circular planar silicon carbide sample and the scanning and stitching results in an embodiment of the present invention;

[0032] Figure 6 Schematic diagram of the scanning trajectory of a large-aperture square planar optical element in an embodiment of the present invention. DETAILED DESCRIPTION

[0033] The present invention will be described in further detail below with reference to the accompanying drawings and examples. It should be noted that the following examples are intended to facilitate understanding of the present invention and do not have any limiting effect on the present invention.

[0034] The method of the present invention adopts an automatic centering and localization device, which includes a sample stage, a robotic arm, a probe installed on the robotic arm and equipped with a spectral confocal sensor, a camera and other equipment, a data acquisition unit electrically connected to the spectral confocal sensor, a data analysis and processing unit electrically connected to the data acquisition unit, and a control unit for receiving feedback from the data analysis and processing unit and controlling the movement of the robotic arm.

[0035] In terms of large-aperture planar optical elements, square-aperture planar optical elements do not require centering due to their geometric characteristics. After leveling, they can be localized according to the size of the optical element. However, circular-aperture planar optical elements require centering and localization, which specifically includes the following steps:

[0036] Step 1: Fix the planar optical element to be centered and localized on the sample stage in a horizontal position.

[0037] Step 2: Figure 1 As shown in the figure, in the original tool coordinate system, the robotic arm is controlled to approach the sample stage so that the sampling point of the spectral confocal sensor is located on the surface of the optical element. The robotic arm is controlled to move along the Z-axis direction so that the spectral confocal sensor is within the working distance and the reading of the spectral confocal sensor is at the center of the range. At this time, the coordinate of the original tool coordinate system is marked as point A.

[0038] Step 3: Control the robotic arm to move a certain distance along the X-axis direction so that the sampling point of the spectral confocal sensor does not exceed the range of the optical element surface. Control the robotic arm to move along the Z-axis direction so that the reading of the spectral confocal sensor is at the center point of the measuring range. At this time, the coordinate of the original tool coordinate system is marked as point B.

[0039] Step 4: Control the robotic arm to move a certain distance along the Y-axis direction so that the sampling point of the spectral confocal sensor does not exceed the range of the optical element surface. Control the robotic arm to move along the Z-axis direction so that the reading of the spectral confocal sensor is at the center point of the measuring range. At this time, the coordinate of the original tool coordinate system is marked as point C.

[0040] Step 5: Based on the coordinates of points A, B, and C, the robot tool coordinate system is reconstructed according to the three-point method and recorded as coordinate system T1. At this time, the surface of the optical element is parallel to the xoy plane of the T1 coordinate system.

[0041] Step 6: Figure 2 As shown, in the T1 coordinate system, the robotic arm is controlled to move along the Z-axis direction so that the spectral confocal sensor is within the working distance and the reading of the spectral confocal sensor is at the center point of the measuring range.

[0042] Step 7. Control the robotic arm to move along the negative direction of the X-axis until the reading of the spectral confocal sensor changes suddenly (edge ​​point). At this time, the coordinate of the T1 coordinate system is marked as P1 (x1, y1, 0); control the robotic arm to move along the positive direction of the X-axis until the reading of the spectral confocal sensor changes suddenly (edge ​​point). At this time, the coordinate of the T1 coordinate system is marked as P2 (x2, y2, 0); control the robotic arm to move along the positive direction of the Y-axis until the reading of the spectral confocal sensor changes suddenly (edge ​​point). At this time, the coordinate of the T1 coordinate system is marked as P3 (x3, y3, 0).

[0043] Step 8. In the xoy plane of the T1 coordinate system, the x0 coordinate of the center of the circle is obtained from the horizontal coordinate of the midpoint of P1 and P2, and the y0 coordinate of the center of the circle is obtained from the vertical coordinate of the midpoint of P2 and P3. Therefore, the coordinates of the center of the circle are

[0044] Step 9. Considering the distance between the spectral confocal sensor and the camera, assume that the calibration distance between the spectral confocal sensor and the camera is L, the projection length of L on the X axis is α, and the projection length on the Y axis is β. The three-point method is used to reconstruct the robot tool coordinate system, which is recorded as coordinate system T2. The origin of the T2 coordinate system corresponds to the center of the plane optical element.

[0045] Step 10: Figure 3 As shown, in the T2 coordinate system, the optical precision probe installed on the end of the robotic arm starts from the upper left corner of the optical element, is carried by the robotic arm and performs serpentine scanning according to the coordinates calculated by the path planning algorithm.

[0046] Step 11: Figure 4 The figure shows a simulation diagram of the scanning trajectory of a 150mm-aperture circular plane optical element. According to the coordinate points given by the control unit, the robotic arm scans along the corresponding path. The scanning range in the figure just fully covers the entire optical element plane.

[0047] Step 12: Figure 5 As shown in (a), a 150mm diameter circular plane silicon carbide sample is fixed on the sample stage. The corresponding parameters are input into the control unit. The robotic arm scans according to the given coordinate points. When acquiring the image of each sub-aperture, the control unit reads the real-time position coordinates from the robotic arm and splices the images according to the feedback real-time position coordinates, as shown in the figure. Figure 5 As shown in (b), it is the scanning and stitching result of a 150mm diameter circular plane silicon carbide sample.

[0048] like Figure 6As shown, for a large-aperture square flat optical element, after leveling, it is localized according to its size. The optical precision probe mounted on the end of the robotic arm starts from the upper left corner of the sample and is carried by the robotic arm and performs a serpentine scan according to the coordinates calculated by the path planning algorithm.

[0049] The embodiments described above provide a detailed description of the technical solutions and beneficial effects of the present invention. It should be understood that the above are only specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, supplements and equivalent substitutions made within the scope of the principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for scanning surface defects of large-aperture planar optical elements based on a robotic arm, characterized in that: An automatic centering and localization device is used, which includes a sample stage, a robotic arm, a probe with a spectral confocal sensor and a camera mounted on the robotic arm, a data acquisition unit electrically connected to the spectral confocal sensor, a data analysis and processing unit electrically connected to the data acquisition unit, and a control unit for receiving feedback from the data analysis and processing unit and controlling the movement of the robotic arm; The method for scanning surface defects of a large-aperture planar optical element comprises the following steps: (1) Fix the planar optical element to be centered and localized on the sample stage in a horizontal position; (2) In the original tool coordinate system of the robotic arm, the robotic arm is controlled to approach the sample stage so that the sampling point of the spectral confocal sensor is located on the surface of the planar optical element, and the robotic arm is controlled to move along the Z-axis so that the spectral confocal sensor is located within the working distance; (3) Randomly locate three non-collinear points on the surface of the planar optical element, and make the reading of the spectral confocal sensor at the center of the range. Reconstruct the robot tool coordinate system according to the three-point method, which is recorded as coordinate system T1. At this time, the surface of the planar optical element is parallel to the xoy plane of the T1 coordinate system; (4) In the T1 coordinate system, control the robotic arm to move along the Z axis so that the spectral confocal sensor is within the working distance and the reading of the spectral confocal sensor is at the center of the range; (5) Control the robotic arm to move along the negative direction of the X-axis until the reading of the spectral confocal sensor changes suddenly. At this time, the coordinate of the T1 coordinate system is marked as P1 (x1, y1, 0); Control the robotic arm to move along the positive direction of the X-axis until the reading of the spectral confocal sensor changes suddenly. At this time, the coordinate of the T1 coordinate system is marked as P2 (x2, y2, 0); Control the robotic arm to move along the positive direction of the Y-axis until the reading of the spectral confocal sensor changes suddenly. At this time, the coordinate of the T1 coordinate system is marked as P3 (x3, y3, 0); (6) In the xoy plane of the T1 coordinate system, the x0 coordinate of the center of the circle is obtained from the horizontal coordinate of the midpoint of P1 and P2, and the y0 coordinate of the center of the circle is obtained from the vertical coordinate of the midpoint of P2 and P3. Therefore, the coordinates of the center of the circle are (7) Assume that the calibration distance between the spectral confocal sensor and the camera is L, the projection length of L on the X axis is α, and the projection length on the Y axis is β, Three points, according to the three-point method, the robot tool coordinate system is reconstructed and recorded as coordinate system T2; the origin of the T2 coordinate system corresponds to the center of the plane optical element; (8) In the T2 coordinate system, the plane optical element is localized according to its size and scanned according to the path planned by the algorithm.

2. The surface defect scanning method of a large-aperture planar optical element based on a robotic arm according to claim 1, characterized in that: The robotic arm is an industrial high-precision robotic arm that communicates with a control unit. By setting an algorithm in the control unit, the robotic arm can automatically perform centering, localization and scanning functions on planar optical elements.

3. The surface defect scanning method of a large-aperture planar optical element based on a robotic arm according to claim 1, characterized in that: The robotic arm is an industrial high-precision robotic arm. There are six coordinate systems on the industrial high-precision robotic arm, namely: geodetic coordinate system, base coordinate system, joint coordinate system, tool coordinate system, workpiece coordinate system and user coordinate system. Among them, the tool coordinate system is used to determine the position of the tool, that is, the position of the optical precision probe, which consists of the tool center point and coordinate position.

4. The surface defect scanning method of a large-aperture planar optical element based on a robotic arm according to claim 1, characterized in that: The localization is a function for determining the boundary of the optical plane element on the robot tool coordinate system.

5. The surface defect scanning method of a large-aperture planar optical element based on a robotic arm according to claim 1, characterized in that: The main axis of the camera on the robotic arm is parallel to the optical axis of the spectral confocal sensor.

6. The surface defect scanning method of a large-aperture planar optical element based on a robotic arm according to claim 1, characterized in that: The large-aperture planar optical element is fixed on the sample stage through a clamping mechanism.

7. The surface defect scanning method of a large-aperture planar optical element based on a robotic arm according to claim 1, characterized in that: The centering and localization accuracy of the large-aperture planar optical element is determined by the end positioning accuracy of the industrial robot arm and the measurement accuracy of the spectral confocal sensor.

8. The surface defect scanning method of a large-aperture planar optical element based on a robotic arm according to claim 1, characterized in that: The spectral confocal sensor focuses light of a precise wavelength onto the object according to the distance between the object and the lens, and obtains the precise distance between the object and the lens by measuring the wavelength of the reflected light.

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