Three degree of freedom optical measurement system and method thereof

Abstract

The application belongs to the field of precise manufacturing detection and industrial automation positioning technology in the new generation of information technology, and particularly relates to a three-degree-of-freedom optical measurement system and a use method thereof. In view of the technical problems of low integration and insufficient synchronous measurement accuracy in the three-degree-of-freedom measurement of objects in the existing precise manufacturing scene, the system comprises a point light source, a light splitting prism, a mirror with an included angle, an imaging optical system, a photoelectric detector and a data processing system, and through coupling calculation of the change of the reflected image information and the mirror included angle, integrated high-precision measurement of three-degree-of-freedom parameters is realized. The application relies on the fusion of optical imaging and data algorithm, breaks through the traditional measurement bottleneck, is suitable for high-precision positioning scenes such as semiconductor packaging detection, aerospace component assembly, industrial robot posture calibration and the like, and provides key technical support for the intelligent upgrading of the new generation of information technology supporting precise manufacturing.

Description

Technical Field

[0001] This invention belongs to the field of optical precision measurement technology, specifically relating to a three-degree-of-freedom optical measurement system for high-precision measurement of the displacement and angle parameters of the target object. Background Technology

[0002] In high-end technology fields such as precision manufacturing, aerospace, robotics maintenance, and precision instrument calibration, the precise measurement of the three-degree-of-freedom motion parameters (DOF) of an object's deflection around the x, y, and z axes is crucial for ensuring equipment operational stability, product processing accuracy, and the reliability of experimental data. For example, in industrial robot joint motion control, real-time acquisition of the three-degree-of-freedom attitude information of joint components is necessary to achieve high-precision positioning of the end effector. In aerospace scenarios such as spacecraft docking and dynamic engine blade inspection, accurate capture of the three-degree-of-freedom displacement and angular changes of moving components is required to mitigate operational risks. In precision instrument calibration, the measurement accuracy of the three-degree-of-freedom parameters of moving components directly determines the instrument's metrological level and reliability. Therefore, developing high-precision, high-stability, and highly adaptable three-degree-of-freedom measurement technology has become one of the core requirements for industry development.

[0003] Currently, three-degree-of-freedom measurement technologies are mainly divided into two categories: contact and non-contact. Contact measurement technologies (such as mechanical probes and dial indicators) are prone to scratching and abrasion of the measured surface due to direct contact with the object during measurement. Furthermore, the measuring force can interfere with the object's motion, making them unsuitable for measuring delicate or high-speed dynamic components. At the same time, these technologies typically only achieve step-by-step measurement of a single or a few degrees of freedom, resulting in low measurement efficiency and the inability to simultaneously acquire complete motion parameters, thus gradually failing to meet the precision measurement needs of high-end fields.

[0004] Non-contact measurement technology, with its advantages of being non-destructive, having a fast response speed, and strong anti-interference capabilities, has become the mainstream direction in the field of three-degree-of-freedom measurement. Among them, optical measurement technology, due to its high measurement accuracy and wide measurement range, is widely used in various precision scenarios. Existing optical three-degree-of-freedom measurement technologies mainly include laser interferometry, multi-camera vision measurement, and grating measurement, but these technologies still have many problems that need to be solved in practical applications.

[0005] While laser interferometry can achieve high-precision measurements, the system's optical path is complex to construct and has stringent requirements for the measurement environment (temperature, humidity, airflow fluctuations). Furthermore, a single optical path can typically only measure 1-2 degrees of freedom. To achieve simultaneous detection of three degrees of freedom (such as angle measurements around the x, y, and z axes), three independent optical paths need to be constructed, resulting in a large system size, high cost, and the potential for mutual interference between the three optical paths, which reduces measurement accuracy and makes it difficult to adapt to measurement scenarios in confined spaces.

[0006] Multi-camera vision measurement technology captures feature points of the object being measured from different angles using multiple cameras, and then calculates the three-degree-of-freedom parameters. However, this technology is significantly affected by ambient lighting conditions, and the accuracy of feature point recognition is prone to fluctuation. At the same time, the installation and calibration process of three cameras is cumbersome, requires a large installation space, and the measurement accuracy depends on camera resolution and algorithm optimization. In measurement scenarios for small reflective mirror-like components fixed to objects, it has poor adaptability and is difficult to accurately capture the attitude changes corresponding to the reflected light signals.

[0007] Grating measurement technology is mainly suitable for linear translation or single-angle measurement, and it is difficult to achieve synchronous measurement of three-degree-of-freedom parameters. Moreover, the installation accuracy of grating components is extremely high, and they are easily affected by external factors such as vibration and impact, resulting in insufficient measurement stability and failing to meet the real-time measurement requirements of three-degree-of-freedom dynamic moving parts.

[0008] Furthermore, some existing optical measurement systems employ redundant optical structure designs to achieve three-degree-of-freedom measurements, resulting in high system debugging difficulty, poor versatility, and difficulty in accurately calculating the three-degree-of-freedom angles (deflection and roll) of objects fixed to mirrors using simple structures. Existing technologies lack a simple solution for calculating attitude parameters by adjusting the position of the mirror light source and utilizing the differences in reflection signals from the three reflecting surfaces, thus failing to balance system compactness and measurement accuracy. Summary of the Invention

[0009] To address the aforementioned problems, this invention provides a three-degree-of-freedom optical measurement system and its usage method, which solves the problems of existing optical measurement systems having complex optical paths, requiring multiple optical paths for multiple degrees of freedom resulting in large size, cumbersome installation and calibration, and difficulty in simultaneously achieving high-precision measurement of the deflection angle of a mirror-fixed object around the x / y / z axes in a compact structure.

[0010] To address the aforementioned problems, this invention provides a three-degree-of-freedom optical measurement system, comprising a point light source, a beam splitter prism, a mirror with a included angle, an imaging optical system, a photodetector, and a data processing system.

[0011] The positioning image emitted by the point light source is reflected by the beam splitter and the reflective surface with the included angle mirror, and then transmitted through the imaging optical system to be imaged onto the photosensitive surface of the photodetector.

[0012] The data processing system is used to receive the detection imaging data signal output by the photodetector, and to analyze and process the data to calculate the three-degree-of-freedom parameters.

[0013] This invention also provides a calculation method for a three-degree-of-freedom optical measurement system. Using the three-degree-of-freedom optical measurement system described above, the method measures three degrees of freedom of a mirror with an included angle (fixed to the target, its motion state being equivalent to that of the target). The method includes the following steps:

[0014] A point light source, a beam splitter, a mirror with an angled reflector, an imaging optical system, and a photodetector are installed in the initial position, such that the mirror image of the point light source after reflection by the beam splitter is located at the object-side node of the imaging optical system; the positioning image emitted by the point light source is reflected by different reflective surfaces of the mirror with an angled reflector, and then passes through the imaging optical system to form a clear image on the photodetector.

[0015] The data processing system analyzes the detection image and obtains the detection imaging positioning positions corresponding to different reflective surfaces of the angled mirror. Based on the distance between different positioning positions and the preset angle of the reflective surfaces of the angled mirror, the image distance from the photosensitive surface of the photodetector to the main plane of the imaging optical system is calculated.

[0016] When the angled reflector deflects around the x-axis and y-axis, the positioning position of the detection image will be translated. The data processing system calculates the deflection angle of the angled reflector (deflection angle around the x-axis and deflection angle around the y-axis) based on the displacement of the positioning position of the detection image and the calculated image distance.

[0017] When the angled mirror rolls along the optical axis (z-axis), the detection imaging positioning positions corresponding to different reflective surfaces will roll synchronously along the optical axis direction; the data processing system calculates the roll angle (roll angle around the z-axis) of the angled mirror based on the slope change of the line connecting the centroid positions of the detection imaging of different reflective surfaces.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] With high integration and adaptability to miniaturized scenarios, it adopts an integrated structure of "single light source - single reflector - single detector", eliminating the need for multiple devices to work together and significantly reducing the system size compared to discrete solutions.

[0020] Optimized real-time performance and ease of operation, eliminating the need for pre-calibration of the relative positions of multiple cameras. Core components (CMOS sensor, lens group, and angled mirror) are all mass-produced devices, resulting in a lower overall cost compared to multi-camera collaborative solutions and facilitating industrial-scale deployment.

[0021] When measuring rotation angles along the x and y axes, unlike traditional angle measuring instruments (such as autocollimators), this method utilizes the same optical system area, CCD optical array area, and mirror area for any measurement angle within the measurement range. This significantly reduces angle measurement errors introduced by optical system aberrations, manufacturing errors, installation errors, CCD pixel manufacturing errors, photoelectric efficiency errors, and mirror manufacturing errors, making it easier to achieve high-precision angle measurements along the x and y axes. (See attached diagram.)

[0022] Figure 1Schematic diagram of the basic principle and structure of a three-optical-degree-of-freedom measurement system

[0023] Figure 2 A schematic diagram of the mirror image of a point light source after it has passed through a beam splitter.

[0024] Figure 3 The included angle of the reflecting mirror is Schematic diagram of images acquired by CCD.

[0025] Figure 4 Angle-angled mirror deflects around the y-axis Time system structure diagram

[0026] Figure 5 Angle-angled mirror deflects around the y-axis Schematic diagram of images acquired by CCD.

[0027] Figure 6 Rotation of the angled mirror around the z-axis Schematic diagram of images acquired by CCD. Detailed Implementation

[0028] The specific embodiments of the present invention will be further described in detail below with reference to the accompanying drawings.

[0029] The structure of the three-optical-degree-of-freedom measurement system in this embodiment is as follows: Figure 1 As shown, it includes: a point light source 1, a beam splitter 2, a mirror with a included angle 3, an imaging optical system 4, a photodetector 5, and a data processing system 6 (not shown in Figure 1, but electrically connected to the photodetector 5).

[0030] 3. Angle-set reflector: It has a double-reflective structure, and the fixed angle between the two reflective surfaces is preset to be... (Unit: °), it is rigidly connected to the target being measured, and its motion state (deflection, rolling) is completely consistent with that of the target being measured.

[0031] Imaging Optical System 4: It adopts a single lens structure with a preset lens focal length of f (unit: mm, using an achromatic lens to reduce aberrations); it can automatically adjust the image distance based on sharpness recognition.

[0032] Photodetector 5: Employs a CCD image sensor to receive the positioning image after reflection by the angled mirror 3 and refraction by the imaging optical system 4. Its pixel size is [missing information]. (Unit: mm)

[0033] Data Processing System 6: It has a built-in custom subpixel positioning algorithm and data calculation module, which can receive image data transmitted by photodetector 5 and complete centroid coordinate extraction and angle calculation.

[0034] Determine the initial state: Displace the angled mirror along the z-axis. The change in the centroid position of the positioning image corresponding to the two reflecting surfaces on the CCD is less than a certain value, ensuring that the position of the mirrored point light source after passing through the beam splitter is at the center of the single lens. At this point, the small displacement of the mirror does not affect the centroid position of the light spot. This is the initial state, which can be found in [reference needed]. Figure 2 As shown.

[0035] When the reflector has an angle At this time, the light beam emitted from point light source 1 is reflected by the two reflecting surfaces of beam splitter prism 2 and angled reflector 3, forming two beams; both beams pass through imaging optical system 4 and are finally imaged on the photosensitive surface of photodetector 5. At this time, two positioning images are formed on the CCD (corresponding to the two reflecting surfaces of angled reflector 3, respectively), as shown below. Figure 3 As shown.

[0036] Photodetector 5 acquires two positioning images in the initial state and transmits the data to data processing system 6 to complete the following basic parameter calculations:

[0037] Image distance v calculation: Data processing system 6 extracts the centroid coordinates of the two positioning images (denoted as centroid 1: (x2, y2) and centroid 2: (x2, y2) respectively), and calculates the center coordinates of the centroids of the two light spots. , ; Calculate the linear distance D (unit: mm) between the centroids of the two light spots on photodetector 4, using the formula for distance between two points. (obtained); combined with the fixed angle of the included reflector 2. , by geometric relations ( The image distance v (unit: mm, i.e., the distance from the photosensitive surface of photodetector 4 to the principal plane of imaging optical system 3) is derived and calculated using the following formula: .

[0038] The target under test is driven by an external worktable, which causes the angled reflector 2 to deflect synchronously around the x-axis (or y-axis). The deflection angle is denoted as . (To be measured), the system structure diagram at this time can be found here. Figure 4 .

[0039] Photodetector 4 acquires the positioning image after deflection and transmits the data to data processing system 5. Please refer to the image acquired by the CCD at this time. Figure 5 .

[0040] This step involves measuring the displacement of the positioning center after the angled reflector 2 deflects, and calculating its deflection angle around the x-axis or y-axis. (Unit: °), the specific operation is as follows:

[0041] Coordinate extraction: Data processing system 5 extracts the new coordinates (x3, y3) of centroid 1 and the new coordinates (x4, y4) of centroid 2 after deflection using a sub-pixel algorithm, and then calculates the new coordinates (x5, y5) of the center of the two spot centroids.

[0042] Angle calculation: If deflected about the x-axis: the displacement of the centroids of the two light spots in the y-direction. ,but If deflected about the y-axis: the displacement of the centroids of the two light spots in the x-direction. ,but .

[0043] Motion control: The target under test is driven by an external worktable, which in turn drives the angled reflector 2 to roll synchronously around the z-axis (optical axis). The roll angle is denoted as . (To be measured).

[0044] Image Acquisition: Photodetector 4 acquires the positioning image after the roll and transmits the data to data processing system 5; the image acquired by the CCD at this time can be found in [reference needed]. Figure 6 .

[0045] This step calculates the roll angle around the z-axis by measuring the change in the slope of the line connecting the two positioning centers after the angled mirror 2 rolls. The specific steps are as follows:

[0046] Coordinate extraction: Data processing system 5 extracts the new coordinates (x6, y6) of positioning center 1 and the new coordinates (x7, y7) of positioning center 2 after the roll using a sub-pixel algorithm.

[0047] Slope calculation: The slope of the line connecting the two positioning centers before roll. (x2 ≠ x1, when x2=x1, one rotation); after rolling, the slope of the line connecting the two positioning centers. (x2≠x1, when x2=x1, it rotates one revolution).

[0048] Roll angle calculation: Based on the formula for the angle between two lines, the roll angle is calculated. satisfy .

[0049] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A three-degree-of-freedom optical measurement system, comprising a point light source, a beam splitter prism, a mirror with a included angle, an imaging optical system, a photodetector, and a data processing system, characterized in that, Includes: point light sources, used to provide positioning images; A beam splitter is used to adjust the position of the mirror point light source; an angled reflector is used to reflect the positioning image; an imaging optical system is used to image the positioning image reflected by the reflector onto a photodetector; a photodetector is used to receive the imaged positioning image; and a data processing system, electrically connected to the photodetector, is used to receive positioning image signal data, identify signal reading areas in the positioning image, calculate the positioning positions of different reflectors corresponding to the positioning image, and then calculate the deflection angles of the angled reflector around the x, y, and z axes.

2. The three-degree-of-freedom optical measurement system according to claim 1, characterized in that, The point light source can be implemented in two forms, including but not limited to the following two types: one is single-mode optical fiber, and the other is LED micro lamp beads.

3. The three-degree-of-freedom optical measurement system according to claim 1, characterized in that, The beam splitter consists of a beam splitting surface and an optical glass substrate, such as a cubic beam splitter and a wedge beam splitter.

4. The three-degree-of-freedom optical measurement system according to claim 1, characterized in that, The angled reflector consists of multiple reflective surfaces with angles, such as a reflector composed of two reflective surfaces with a known fixed angle.

5. The three-degree-of-freedom optical measurement system according to claim 1, characterized in that, The imaging optical system can automatically adjust the focal length so that the positioning image reflected by the angled mirror is clearly imaged on the photodetector.

6. The three-degree-of-freedom optical measurement system according to claim 1, characterized in that, The photodetector is a device capable of receiving image light signals, such as a CMOS image sensor or a CCD image sensor.

7. The three-degree-of-freedom optical measurement system according to claim 1, characterized in that, The data processing system is a system capable of receiving data signals from photodetectors and possessing a certain computing power, such as a computer.

8. A measurement method for a three-degree-of-freedom optical measurement system, characterized in that, The three-degree-of-freedom optical measurement system as described in any one of claims 1-7 is used to measure three degrees of freedom of an object fixed to a mirror with an included angle, comprising the following steps: A point light source, a beam splitter, a mirror with an angle, an imaging optical system, and a photodetector are installed in the initial position; the image formed by the point light source after passing through the beam splitter is located at the object-side node of the imaging optical system; the positioning image emitted by the point light source is reflected by different reflective surfaces of the beam splitter and the mirror with an angle, and then clearly imaged on the photodetector after passing through the imaging optical system. Based on the distance between the positioning positions of the positioning images reflected by different reflective surfaces on the angled mirror, and the angle between the different reflective surfaces on the angled mirror, the image distance from the photodetector to the principal plane of the imaging optical system can be calculated; based on the image distance and the position change of the center of the positioning position in the positioning image acquired by the photodetector, the deflection angle of the angled mirror can be calculated; based on the slope change of the line connecting the centroids of the light spots in the positioning image acquired by the photodetector, the roll angle of the angled mirror can be calculated.

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