A centering and localizing method for large-aperture spherical optical elements under the manipulation of a robotic arm

Abstract

The present invention discloses a centering and localization method for large-aperture spherical optical elements under the manipulation of a robotic arm. An automatic centering and localization device is adopted, 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 the feedback from the data analysis and processing unit and controlling the movement of the robotic arm. For large-aperture spherical optical elements, automatic centering is achieved by collecting three points on a certain concentric circle on the sphere, and then automatic localization is achieved by collecting edge points. The present invention is simple and easy to implement, without the need to calibrate the sensor. It only requires a robotic arm to carry an optical precision probe for three-dimensional movement, reducing the mechanical design and assembly difficulty, and realizing non-contact, fast, and automatic centering and localization of optical elements, which is suitable for mass production and detection of large-aperture optical elements.

Description

Technical Field

[0001] The present invention belongs to the technical field of optics, and in particular relates to a method for centering and localizing a large-aperture spherical optical element under the manipulation of a robotic arm. Background Art

[0002] Industrial robotic arms are automated mechanical devices that find the most extensive practical applications in various fields. Although they come in different forms, they all share a common feature, that is, they can accept instructions and accurately position to a certain point in three-dimensional (or two-dimensional) space for operation. In the field of surface defect detection of optical elements, a microscopic imaging system is mainly used to scan and image the surface of the sample to be inspected, so as to obtain the morphology and distribution of surface defects. When detecting a large-aperture optical element, it is necessary to first complete the centering of the element, and use the axis position as a reference point to plan the scanning path. If the surface defect detection of the optical element can be combined with the industrial robotic arm, it is of great significance for the pipeline production and processing of precision optical elements.

[0003] Existing methods for automatically centering and localizing large-aperture spherical optical elements, such as the Chinese patent document with the publication number CN105157617A discloses a spherical automatic centering method applied to the surface defect detection of spherical optical elements. It uses spherical reflection crosshair imaging, drives the measured spherical optical element to rotate by a self-rotating table, observes the change in the position of the crosshairs, and fits the center of the crosshair movement trajectory, thereby realizing the centering of the spherical optical element. However, the above method has high requirements for the mechanical structure, and it is necessary to design a self-rotating table structure to drive the sample to rotate, which increases the complexity of design, processing and alignment.

[0004] The Chinese patent document with the publication number CN111288933A discloses an automatic centering method applied to spherical or rotationally symmetric aspherical optical elements. When using an automatic centering device for automatic centering, three laser displacement sensors simultaneously provide the relative distances of three sampling points on the measured optical element. When the relative distances of the three sampling points are 0 or less than the allowable error threshold, it can be considered that the cross-section formed by the three sampling points is a circular cross-section perpendicular to the optical axis, and the center of the circle is the axis position of the optical element. However, the above method has relatively high requirements for the alignment of the laser displacement sensors, and it is necessary to calibrate the initial positions of the three laser displacement sensors. When calibrating, the interval size of the scanning cross-section will affect the calibration accuracy.

[0005] Therefore, it is necessary to design a simple and efficient device and method to realize the centering and localizing of large-aperture spherical optical elements. Summary of the Invention

[0006] To solve the above problems existing in the prior art, the present invention provides a method for centering and localizing a large-aperture spherical optical element under the manipulation of a robotic arm, realizing non-contact, fast, and automatic centering and localizing of the large-aperture spherical optical element.

[0007] A method for centering and localizing a large-aperture spherical optical element under the manipulation of a robotic arm, which adopts an automatic centering and localizing device. The automatic centering and localizing device includes a sample stage, a robotic arm, a probe mounted on the robotic arm 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 the feedback of the data analysis and processing unit and controlling the movement of the robotic arm.

[0008] The method for centering and localizing the large-aperture spherical optical element includes the following steps:

[0009] (1) Fix the spherical optical element to be centered and localized on the sample stage in a horizontally placed posture.

[0010] (2) Under the original tool coordinate system of the robotic arm, control the robotic arm to approach the sample stage so that the sampling point of the spectral confocal sensor is located on the surface of the optical element. Control the robotic arm 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 range. At this time, the coordinates of the original tool coordinate system are recorded as Q1(x1, y1, z1).

[0011] (3) Control the robotic arm to move along the positive X-axis direction. The reading of the spectral confocal sensor changes until the reading of the spectral confocal sensor returns to the center point of the range. At this time, the coordinates of the original tool coordinate system are recorded as Q2(x2, y2, z1).

[0012] (4) Control the robotic arm to move along the positive Y-axis direction. The reading of the spectral confocal sensor changes until the reading of the spectral confocal sensor returns to the center point of the range. At this time, the coordinates of the original tool coordinate system are recorded as Q3(x3, y3, z1).

[0013] (5) Let the radius of curvature of the spherical optical element be R, then the coordinates of the center of the sphere

[0014] (6) Under the original tool coordinate system, control the robotic arm to approach the sample stage so that the sampling point of the spectral confocal sensor is located on the surface of the optical element. Control the robotic arm 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 range.

[0015] (7) Control the robotic arm to move along the negative X-axis until the reading of the spectral confocal sensor changes abruptly. At the critical value position, control the robotic arm to move along the Z-axis so that the reading of the spectral confocal sensor is at the center point of the range. At this time, the coordinates of the original tool coordinate system are recorded as A(a1, b1, c1); control the robotic arm to move along the positive X-axis until the reading of the spectral confocal sensor changes abruptly. At the critical value position, control the robotic arm to move along the Z-axis so that the reading of the spectral confocal sensor is at the center point of the range. At this time, the coordinates of the original tool coordinate system are recorded as B(a2, b2, c2); control the robotic arm to move along the positive Y-axis until the reading of the spectral confocal sensor changes abruptly. At the critical value position, control the robotic arm to move along the Z-axis so that the reading of the spectral confocal sensor is at the center point of the range. At this time, the coordinates of the robotic arm are recorded as C(a3, b3, c3);

[0016] (8) Let the normal vector of the edge surface of the spherical optical element be Then its vertex coordinates

[0017] (9) Let the coordinates of point P be (x′, y′, z′), the calibration distance between the spectral confocal sensor and the camera be L, the projection length of L on the X-axis be α, and the projection length on the Y-axis be β. From P′(x′ - α, y′ - β, z′), Using these three points, reconstruct the robotic arm tool coordinate system according to the three-point method, denoted as coordinate system S; the origin of the S coordinate system corresponds to the vertex of the spherical optical element;

[0018] (10) In the S coordinate system, localize according to the size of the spherical optical element and scan the spherical optical element along the path planned by the algorithm.

[0019] Preferably, the robotic arm is an industrial high-precision robotic arm that can communicate with the control unit and realize the functions of automatic centering and localization of the robotic arm for the spherical optical element through the algorithm of the control unit.

[0020] There are six coordinate systems on the industrial high-precision robotic arm: the world coordinate system, the base coordinate system, the joint coordinate system, the tool coordinate system, the workpiece coordinate system, and the 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.

[0021] Preferably, the end of the industrial robotic arm is equipped with an optically precise probe with a well-integrated design, which can achieve functions such as high-precision distance detection, optical imaging, autofocus, and defect detection.

[0022] Further, the localization is to determine the function of the boundary of the spherical optical element on the robotic arm tool coordinate system.

[0023] Further, the optical precision probe is equipped with a variety of devices such as a spectral confocal sensor, a light source, a camera, and an objective lens driver. Moreover, the camera spindle on the robotic arm is parallel to the optical axis of the spectral confocal sensor.

[0024] The spectral confocal sensor is a non-contact measurement sensor. In spectral confocal measurement, by using a special lens, the focal halo range of different color lights is extended to form a special magnified chromatic aberration, so that according to the distance from different measured objects to the lens, a light of an exact wavelength will be focused on the measured object. By measuring the wavelength of the reflected light, the exact distance from the measured object to the lens can be obtained.

[0025] Further, the large-aperture spherical optical element is fixed on the sample stage through a clamping mechanism.

[0026] The horizontally placed posture means that the optical axis of the large-aperture spherical optical element is perpendicular to the horizontal plane.

[0027] The large-aperture spherical optical element does not need to be pre-leveled before centering and localization.

[0028] Further, the centering and localization accuracy of the large-aperture spherical optical element is jointly determined by the end positioning accuracy of the industrial robotic arm and the measurement accuracy of the spectral confocal sensor.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] The present invention provides a new device and method for centering and localization of large-aperture spherical optical elements. For large-aperture spherical optical elements, only the optical precision probe needs to be carried by an industrial robotic arm for three-dimensional movement, and there is no need to customize high-precision guide rails and sample spin tables for specific samples, which greatly reduces the mechanical design, assembly and adjustment difficulty and production cost; the spectral confocal sensor is used, which has strong anti-tilt ability and is convenient for assembly and adjustment, and one sensor can reduce various calibration works caused by the differences of multiple sensors, improving the production efficiency. The centering method is simple to operate, has few steps, is fast, and has high efficiency, and has great engineering application value, laying a foundation for high-efficiency, fast and high-precision surface defect detection of large-aperture spherical optical elements. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 It is a diagram of the centering process of the circular-aperture concave spherical optical element in the embodiment of the present invention;

[0032] Figure 2 It is a schematic diagram of the edge point acquisition of the circular-aperture concave spherical optical element in the embodiment of the present invention;

[0033] Figure 3Schematic diagram for solving the vertex of the circular-aperture concave spherical optical element in the embodiment of the present invention;

[0034] Figure 4 Schematic diagram of the S coordinate system in the embodiment of the present invention. Detailed implementation manners

[0035] The present invention will be further described in detail below with reference to the drawings and embodiments. It should be noted that the following embodiments are intended to facilitate the understanding of the present invention and do not impose any limitations on it.

[0036] The method of the present invention uses an automatic centering and localization device. The automatic centering and localization device includes a sample stage, a robotic arm, a probe mounted on the robotic arm and equipped with devices such as 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 the feedback from the data analysis and processing unit and controlling the movement of the robotic arm.

[0037] In terms of large-aperture spherical optical elements, considering that square-aperture spherical optical elements are not common in daily life, only the centering and localization methods for circular-aperture spherical optical elements are listed here. Taking a large-aperture concave spherical optical element as an example, the specific steps are as follows:

[0038] Step 1: Fix the optical element to be centered and localized on the sample stage in a horizontal placement posture.

[0039] Step 2: As shown in, in the original tool coordinate system, control the robotic arm to approach the sample stage so that the sampling point of the spectral confocal sensor is located on the surface of the optical element. Control the robotic arm 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 range. At this time, the coordinates of the original tool coordinate system are recorded as Q1(x1, y1, z1). Figure 1

[0040] Step 3: Control the robotic arm to move along the positive X-axis direction. The reading of the spectral confocal sensor will change until the reading of the spectral confocal sensor returns to the center point of the range. At this time, the coordinates of the original tool coordinate system are recorded as Q2(x2, y2, z1).

[0041] Step 4: Control the robotic arm to move along the positive Y-axis direction. The reading of the spectral confocal sensor will change until the reading of the spectral confocal sensor returns to the center point of the range. At this time, the coordinates of the original tool coordinate system are recorded as Q3(x3, y3, z1).

[0042] Step 5: Assume that the coordinates of the center Q of the optical element are (x0, y0, z0), the radius of curvature is R, and the distance from the center Q to the concentric circle plane of Q1, Q2, and Q3 is h. Then, we can obtain

[0043]

[0044] Therefore, the coordinates of the center of the sphere

[0045] Step 6: Under the original tool coordinate system, control the robotic arm to approach the sample stage so that the sampling point of the spectral confocal sensor is located on the surface of the optical element. Control the robotic arm 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 range.

[0046] Step 7: As Figure 2 shown, control the robotic arm to move along the negative X-axis direction until the reading of the spectral confocal sensor changes abruptly (edge point). At the critical value position, 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 range. At this time, the coordinates of the original tool coordinate system are recorded as A(a1, b1, c1); control the robotic arm to move along the positive X-axis direction until the reading of the spectral confocal sensor changes abruptly (edge point). At the critical value position, 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 range. At this time, the coordinates of the original tool coordinate system are recorded as B(a2, b2, c2); control the robotic arm to move along the positive Y-axis direction until the reading of the spectral confocal sensor changes abruptly (edge point). At the critical value position, 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 range. At this time, the coordinates of the robotic arm are recorded as C(a3, b3, c3).

[0047] Step 8: As Figure 3 shown, assume that the normal vector of the edge surface of the optical element is The coordinates of point P are (x′, y′, z′). Flip the sample and its corresponding coordinate system so that it becomes a part of the sphere, and we can obtain

[0048]

[0049] As can be seen from the figure, the vertex coordinates where

[0050] Then

[0051]

[0052] Step 9: The three points required for the boundary conditions for localizing the optical element are P(x′, y′, z′),

[0053] Step 10: Considering the distance between the spectral confocal sensor and the camera, assuming 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. From P′(x′ - α, y′ - β, z′),

[0054] Using these three points, the robotic arm tool coordinate system is reconstructed according to the three-point method, denoted as coordinate system S. The origin of the S coordinate system corresponds to the vertex of the spherical optical element.

[0055] Step 11: As shown in (a) or (b) of Figure 4 , in the S coordinate system, localize according to the size of the spherical optical element and scan the spherical optical element along the path planned by the algorithm.

[0056] The above embodiments have detailed 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 used to limit the present invention. Any modifications, supplements, and equivalent replacements made within the principle scope of the present invention should be included within the protection scope of the present invention.

Claims

1. A centering and localization method for large-aperture spherical optical elements under the manipulation of a robotic arm, characterized in that, An automatic centering and localization device is adopted. The automatic centering and localization device 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; The method for centering and localizing a large-aperture spherical optical element includes the following steps: (1) Fix the spherical optical element to be centered and localized on the sample stage in a horizontally placed posture; (2) Under the original tool coordinate system of the robotic arm, control the robotic arm to approach the sample stage so that the sampling point of the spectral confocal sensor is located on the surface of the optical element. Control the robotic arm 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 measurement range. At this time, the coordinates of the original tool coordinate system are denoted as Q1(x1, y1, z1); (3) Control the robotic arm to move along the positive X-axis direction. The reading of the spectral confocal sensor changes until the reading of the spectral confocal sensor returns to the center point of the measurement range. At this time, the coordinates of the original tool coordinate system are denoted as Q2(x2, y2, z1); (4) Control the robotic arm to move along the positive Y-axis direction. The reading of the spectral confocal sensor changes until the reading of the spectral confocal sensor returns to the center point of the measurement range. At this time, the coordinates of the original tool coordinate system are denoted as Q3(x3, y3, z1); (5) If the radius of curvature of the spherical optical element is R, then the coordinates of the center of the sphere (6) Under the original tool coordinate system, control the robotic arm to approach the sample stage so that the sampling point of the spectral confocal sensor is located on the surface of the optical element. Control the robotic arm 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 measurement range; (7) Control the robotic arm to move along the negative X-axis direction until the reading of the spectral confocal sensor changes suddenly. At the critical value position, 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 measurement range. At this time, the coordinates of the original tool coordinate system are denoted as A(a1, b1, c1); Control the robotic arm to move along the positive X-axis direction until the reading of the spectral confocal sensor changes suddenly. At the critical value position, 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 measurement range. At this time, the coordinates of the original tool coordinate system are denoted as B(a2, b2, c2); Control the robotic arm to move along the positive Y-axis direction until the reading of the spectral confocal sensor changes suddenly. At the critical value position, 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 measurement range. At this time, the coordinates of the robotic arm are denoted as C(a3, b3, c3); (8) Let the normal vector of the edge surface of the spherical optical element be Then its vertex coordinates (9) Let the coordinates of point P be (x′, y′, z′), the calibration distance between the spectral confocal sensor and the camera be L, the projection length of L on the X-axis be α, and the projection length on the Y-axis be β. From P′(x′ - α, y′ - β, z′), Using these three points, the robotic arm tool coordinate system is reconstructed according to the three-point method, denoted as coordinate system S; The origin of the S coordinate system corresponds to the vertex of the spherical optical element; (10) Under the S coordinate system, localize according to the size of the spherical optical element and scan the spherical optical element according to the path planned by the algorithm.

2. The centering and localization method of a large-aperture spherical optical element under the manipulation of a robotic arm according to claim 1, characterized in that, The robotic arm is an industrial high-precision robotic arm, communicates with the control unit, and realizes the automatic centering and localization functions of the robotic arm for the spherical optical element through the algorithm of the control unit.

3. The centering and localization method for large-aperture spherical optical elements under the manipulation of a robotic arm according to claim 2, characterized in that, There are six coordinate systems on the industrial high-precision robotic arm: the earth coordinate system, the base coordinate system, the joint coordinate system, the tool coordinate system, the workpiece coordinate system, and the 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, and is composed of the tool center point and the coordinate position.

4. The centering and localization method of a large-aperture spherical optical element under the manipulation of a robotic arm according to claim 1, characterized in that, The localization described is a function for determining the boundary of the spherical optical element on the robotic arm tool coordinate system.

5. The centering and localization method for a large-aperture spherical optical element under the manipulation of a robotic arm according to claim 1, characterized in that, The camera spindle on the robotic arm is parallel to the optical axis of the spectral confocal sensor.

6. The centering and localization method of a large-aperture spherical optical element under the manipulation of a robotic arm according to claim 1, characterized in that, The large-aperture spherical optical element is fixed on the sample stage through a clamping mechanism.

7. The centering and localizing method for a large-aperture spherical optical element under the manipulation of a robotic arm according to claim 1, wherein The centering and localization accuracy of the large-aperture spherical optical element are jointly determined by the end positioning accuracy of the industrial robotic arm and the measurement accuracy of the spectral confocal sensor.

8. The centering and localization method for a large-aperture spherical optical element under the manipulation of a robotic arm according to claim 1, characterized in that, The spectral confocal sensor focuses light of an exact wavelength onto the object to be measured according to the distance from the different objects to be measured to the lens, and obtains the exact distance from the object to be measured to the lens by measuring the wavelength of the reflected light.

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