A six-degree-of-freedom laser measurement system
By designing a six-degree-of-freedom laser measurement system, and utilizing oblique laser triangulation, autocollimation measurement, and visual imaging technology, the system achieves individual measurement of each degree of freedom, solves the degree-of-freedom coupling problem, and achieves miniaturization, integration, and cost reduction, thereby improving measurement accuracy and real-time performance.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- NORTHEAST FORESTRY UNIV
- Filing Date
- 2025-09-17
- Publication Date
- 2026-06-19
AI Technical Summary
In existing six-degree-of-freedom measurement systems, there is a coupling relationship between the degrees of freedom, which affects the measurement accuracy. Furthermore, traditional equipment is large in size, expensive, and difficult to integrate.
Using oblique laser triangulation, autocollimation measurement, and visual imaging technology, three optical systems were designed to share a portion of the optical path and a single laser source. The Z-axis displacement and X and Y-axis rotation angles were measured separately, and the X and Y-axis displacement and Z-axis rotation angle were measured separately. A cross-shaped circular reflective target was used to achieve individual measurement of each degree of freedom.
It achieves six-degree-of-freedom non-contact measurement, avoids coupling between degrees of freedom, and enables system miniaturization, integration, and cost reduction, while improving measurement accuracy and real-time performance.
Smart Images
Figure CN121185181B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to a six-degree-of-freedom laser measurement system, belonging to the field of precision measurement technology, specifically involving oblique laser triangulation, laser autocollimation measurement, and visual measurement technology. Background Technology
[0002] Six-degree-of-freedom (6DOF) measurement technology enables comprehensive analysis and measurement of an object's motion state by simultaneously measuring its translational and rotational parameters in three-dimensional space. This technology plays an irreplaceable role in fields such as intelligent manufacturing, drone navigation, and aerospace.
[0003] Traditional mechanical measurement methods are limited by contact measurement errors, insufficient resolution, and the inability to monitor in real time, making it difficult to meet the demands of modern industry for real-time, non-contact, high-precision measurement. The design of six-degree-of-freedom (6DOF) measurement systems is still relatively lacking. In traditional measurement equipment, the structure of 6DOF measurements is more complex. In optical measurements, the optical path structure is complex, requiring more optical measurement components, resulting in relatively large sizes that are difficult to integrate or have high integration costs. Therefore, developing novel 6DOF measurement technologies that combine high resolution, high integration, and low cost has become an important research direction for improving the motion control accuracy of equipment.
[0004] In the prior art, technologies represented by the invention patent "A Six-Degree-of-Freedom Optical Measurement Method and Integrated System" (application number 202310568066X) and a Japanese invention patent (patent number JP202067372A) both utilize diffraction gratings as targets and achieve six-degree-of-freedom measurement using their diffracted light. However, the diffracted beams at each level change synchronously when the grating pose changes, resulting in complex coupling relationships between the degrees of freedom. This leads to the problem of multiple degrees of freedom being mutually coupled. For example, in the invention patent "A Six-Degree-of-Freedom Optical Measurement Method and Integrated System" (application number 202310568066X), there is coupling between the X-axis and Z-axis measurements, and between the X-axis rotation angle and Z-axis rotation angle measurements, which affects the accuracy of the measurement results, thus necessitating complex decoupling.
[0005] In addition, the invention patent application No. 2024110131879, entitled "A heterodyne six-degree-of-freedom measurement grating interferometer and a six-degree-of-freedom measurement method", also suffers from the problem that the multi-probe combination method cannot separate and decouple the degrees of freedom, resulting in the coupling of multiple results.
[0006] It is evident that designing measurement methods that enable individual measurement of each degree of freedom in optical structure design, thereby avoiding the problem of mutual coupling between degrees of freedom, is a key technical issue that urgently needs to be addressed in the field of six-degree-of-freedom measurement. Summary of the Invention
[0007] To address the aforementioned problems, this invention designs a six-degree-of-freedom laser measurement system. This system integrates oblique laser triangulation, autocollimation measurement, and visual imaging technology. A first optical system measures displacement along the Z-axis, a second optical system measures rotation angles along the X and Y axes, and a third optical system measures displacement along the X and Y axes and rotation angle along the Z-axis, thus comprehensively acquiring the six-degree-of-freedom motion state. Compared to existing technologies, this invention employs an optical path multiplexing mechanism, where the three optical systems share a portion of the optical path and a single laser source, significantly reducing the number of components and achieving system miniaturization, integration, and cost reduction. The six degrees of freedom are measured independently, avoiding coupling relationships between them.
[0008] The objective of this invention is achieved as follows:
[0009] A six-degree-of-freedom laser measurement system is divided into a first optical system, a second optical system, and a third optical system according to the different degrees of freedom being measured. The first optical system uses the oblique-shot laser triangulation principle to measure the displacement of the object in the Z-axis direction. The second optical system uses the autocollimation measurement principle to measure the rotation angle of the object in the X-axis and Y-axis directions. The third optical system uses the visual imaging measurement principle to measure the displacement of the object in the X-axis and Y-axis directions and the rotation angle in the Z-axis direction.
[0010] The first optical system, the second optical system, and the third optical system together include: a laser source, a collimating and beam-expanding lens, and a cross-shaped circular reflective target;
[0011] The first optical system also includes a first beam splitter, a reflector, a first focusing lens, and a first CCD camera;
[0012] The second optical system also includes a second beam splitter, a second focusing lens, and a second CCD camera;
[0013] The third optical system also includes a third beam splitter, a telecentric lens, and a third CCD camera;
[0014] The laser beam output from the laser source becomes a parallel beam after passing through a collimating and beam-expanding lens, and then illuminates the cross-shaped circular reflective target, producing reflected light.
[0015] In the first optical system, the laser source expands the laser beam through a collimating and beam-expanding lens, and then reflects it sequentially through the first beam-splitting prism and the mirror before obliquely incident on the cross-shaped circular reflective target. The reflected beam enters the first CCD camera after passing through the first focusing lens. The displacement of the object under test in the Z-axis direction is measured by the change in the position of the light spot in the first CCD camera.
[0016] In the second optical system, the laser source expands the laser beam through a collimating and beam-expanding lens and then incident it perpendicularly onto the cross-shaped circular reflective target. The reflected beam is then focused by the second focusing lens after being reflected by the second beam splitter and enters the second CCD camera. The rotation angle of the object under test in the X and Y axes is measured by the change in the position of the light spot in the second CCD camera.
[0017] In the third optical system, the laser source expands the laser beam through a collimating and expanding lens, and then incident it perpendicularly onto the cross-shaped circular reflective target. The reflected beam is reflected sequentially by the second and third beam-splitting prisms, and then enters the third CCD camera through the telecentric lens. The displacement of the object under test in the X and Y axes is measured by the change in the position of the light spot in the third CCD camera, and the rotation angle of the object under test in the Z axis is measured by the rotation angle of the cross-shaped circular pattern in the third CCD camera.
[0018] In the aforementioned six-degree-of-freedom laser measurement system, the cross-shaped circular reflective target is a circular reflector with high reflectivity and high precision placed on the surface of the object being measured, and a cross-shaped circular pattern is machined on it.
[0019] In the aforementioned six-degree-of-freedom laser measurement system, the placement of the laser source, collimating and expanding lens, first beam splitter, reflector, cross-shaped circular reflective target, first focusing lens, and first CCD camera in the first optical system satisfies the conditions of Scherm's law.
[0020] The above-mentioned six-degree-of-freedom laser measurement system also includes a computer. Images acquired by the first CCD camera, the second CCD camera, and the third CCD camera are transmitted to the computer. The computer uses the images obtained by the first CCD camera, the second CCD camera, and the third CCD camera to determine the six-degree-of-freedom motion state of the object being measured.
[0021] The beneficial effects of the six-degree-of-freedom laser measurement system of this invention are as follows:
[0022] The first and sixth degrees of freedom measurements are both non-contact optical measurements, which can avoid the problem of damaging the object being measured by contact with its surface.
[0023] The second, first, second, and third optical systems together include a laser source, a collimating and beam-expanding lens, and a cross-shaped circular reflective target. The shared mechanism significantly reduces the number of optical components, improves the efficiency of optical path utilization, and is conducive to achieving system miniaturization, integration, and low cost, with obvious advantages in space-constrained application scenarios.
[0024] Third, the cross-ring reflective target is a circular reflector with high reflectivity and high precision, with a cross-ring pattern machined on it. When placed on the surface of the object being measured, this design lays the technical foundation for six-degree-of-freedom individual measurement.
[0025] Fourth, the first, second, and third optical systems can measure each degree of freedom individually, thereby avoiding the problem of mutual coupling between the degrees of freedom. Attached Figure Description
[0026] Figure 1 This is a schematic diagram of the overall six-degree-of-freedom laser measurement system of the present invention.
[0027] Figure 2 This is a schematic diagram of the first optical system in the six-degree-of-freedom laser measurement system of the present invention.
[0028] Figure 3 This is a schematic diagram of the second optical system in the six-degree-of-freedom laser measurement system of the present invention.
[0029] Figure 4 This is a schematic diagram of the third optical system in the six-degree-of-freedom laser measurement system of the present invention.
[0030] In the diagram: 1. Laser source, 2. Collimating and expanding lens, 3. First beam splitter, 4. Reflector, 5. Cross-shaped circular reflector target, 6. First focusing lens, 7. First CCD camera, 8. Second beam splitter, 9. Third beam splitter, 10. Second focusing lens, 11. Second CCD camera, 12. Telecentric lens, 13. Third CCD camera, 14. Computer. Detailed Implementation
[0031] The specific embodiments of the present invention will now be described in further detail with reference to the accompanying drawings.
[0032] Method 1
[0033] The following are specific embodiments of the six-degree-of-freedom laser measurement system of the present invention.
[0034] The overall schematic diagram of the six-degree-of-freedom laser measurement system in this specific embodiment is as follows: Figure 1 As shown, based on the different degrees of freedom being measured, the system is divided into a first optical system, a second optical system, and a third optical system. The first optical system uses the principle of oblique laser triangulation to measure the displacement of the object in the Z-axis direction. The second optical system uses the principle of autocollimation to measure the rotation angle of the object in the X-axis and Y-axis directions. The third optical system uses the principle of visual imaging to measure the displacement of the object in the X-axis and Y-axis directions and the rotation angle in the Z-axis direction.
[0035] The first optical system, the second optical system, and the third optical system together include: a laser source 1, a collimating and beam-expanding lens 2, and a cross-shaped circular reflective target 5;
[0036] The first optical system also includes a first beam splitter 3, a reflector 4, a first focusing lens 6, and a first CCD camera 7; as Figure 2 As shown;
[0037] The second optical system also includes a second beam splitter 8, a second focusing lens 10, and a second CCD camera 11; as Figure 3 As shown;
[0038] The third optical system also includes a third beam splitter 9, a telecentric lens 12, and a third CCD camera 13; as shown in the figure. Figure 4 As shown;
[0039] The laser beam output from the laser source 1 becomes a parallel beam after passing through the collimating and beam expanding lens 2, and illuminates the cross-shaped circular reflective target 5, producing reflected light.
[0040] In the first optical system, the laser light source 1 expands the laser beam through the collimating and expanding lens 2, and then reflects it sequentially through the first beam splitter prism 3 and the reflector 4 before obliquely incident on the cross-ring reflector target 5. The reflected beam passes through the first focusing lens 6 and enters the first CCD camera 7. The displacement of the object under test in the Z-axis direction is measured by the change of the position of the light spot in the first CCD camera 7.
[0041] The first optical system utilizes only the specular reflection characteristics of the cross-shaped circular reflective target 5. The displacement changes of the X and Y axes and the rotation angle changes of the Z axis will not affect the position of the light spot on the first CCD camera 7. Within the X and Y axis rotation angle measurement range, the light spot on the first CCD camera 7 will only undergo slight deformation, while its center of mass position will not change. Therefore, there is no coupling relationship between the Z axis measurement and other degrees of freedom.
[0042] In the second optical system, the laser source 1 expands the laser beam through the collimating and beam-expanding lens 2 and then incident it perpendicularly onto the cross-shaped circular reflective target 5. The reflected beam is reflected by the second beam splitter 8 and then focused by the second focusing lens 10 into the second CCD camera 11. The rotation angle of the object under test in the X and Y axes is measured by the change in the position of the light spot in the second CCD camera 11.
[0043] The second optical system also utilizes only the specular reflection characteristics of the cross-shaped ring reflective target 5. Changes in the displacement of the X, Y, and Z axes and changes in the rotation angle of the Z axis will not affect the position of the reflected light. After being focused by the lens, the position of the light spot on the second CCD camera 11 remains unchanged. Therefore, there is no coupling relationship between the X and Y axis rotation angle measurement and other degrees of freedom.
[0044] In the third optical system, the laser light source 1 expands the laser beam through the collimating and beam-expanding lens 2 and then incident it perpendicularly onto the cross-shaped circular reflective target 5. The reflected beam is reflected sequentially by the second beam splitter 8 and the third beam splitter 9, and then enters the third CCD camera 13 through the telecentric lens 12. The displacement of the object under test in the X and Y axes is measured by the change in the position of the light spot in the third CCD camera 13, and the rotation angle of the object under test in the Z axis is measured by the rotation angle of the cross-shaped circular pattern in the third CCD camera 13.
[0045] The third optical system is based on the principle of visual imaging. It uses a telecentric lens 12 to capture the changes in the X and Y axis displacements and Z axis rotation angles of the cross-shaped ring pattern on the target. These changes are independent of each other and do not interfere with each other. Within the measurement range of the X and Y axis rotation angles and Z axis displacements, the imaging characteristics of the telecentric lens 12 ensure that the imaging effect of the cross-shaped ring pattern on the target is not significantly affected. Therefore, the measurement of the X and Y axis displacements and Z axis rotation angles is not coupled with other degrees of freedom.
[0046] Method 2
[0047] The following are specific embodiments of the six-degree-of-freedom laser measurement system of the present invention.
[0048] The six-degree-of-freedom laser measurement system in this specific embodiment is further defined based on the first specific embodiment: the cross-shaped circular reflective target 5 is a circular reflector with high reflectivity and high precision placed on the surface of the object being measured, and a cross-shaped circular pattern is processed on it.
[0049] Method 3
[0050] The following are specific embodiments of the six-degree-of-freedom laser measurement system of the present invention.
[0051] The six-degree-of-freedom laser measurement system under this specific embodiment is further defined based on the first embodiment: in the first optical system, the placement positions of the laser source 1, collimating beam expander lens 2, first beam splitter prism 3, reflector 4, cross-shaped circular reflector target 5, first focusing lens 6 and first CCD camera 7 satisfy the conditions of Scherm's law.
[0052] Method 4
[0053] The following are specific embodiments of the six-degree-of-freedom laser measurement system of the present invention.
[0054] The six-degree-of-freedom laser measurement system under this specific embodiment, based on specific embodiment one, specific embodiment two, or specific embodiment three, is further defined as follows: it also includes a computer 14. The images acquired by the first CCD camera 7, the second CCD camera 11, and the third CCD camera 13 are transmitted to the computer 14. The computer 14 obtains the six-degree-of-freedom motion state of the measured object through the images obtained by the first CCD camera 7, the second CCD camera 11, and the third CCD camera 13.
[0055] Method 5
[0056] The following is a specific implementation of the six-degree-of-freedom laser measurement method of the present invention.
[0057] The six-degree-of-freedom laser measurement method under this specific implementation method includes the following steps:
[0058] The laser beam from laser source 1 is expanded by collimating and expanding lens 2, then reflected sequentially by first beam splitter prism 3 and reflector 4 before being obliquely incident on cross-shaped circular reflective target 5. The reflected beam passes through focusing lens 6 and enters first CCD camera 7. The Z-axis displacement of the measured object is measured using the oblique laser triangulation principle, as shown in the following formula:
[0059]
[0060] In the formula, x is the image displacement of the image point, ΔZ is the displacement of the measured object along the Z-axis, L and L′ are the object distance and image distance at the reference position, α is the angle between the laser beam and the optical axis of the imaging lens, and β is the angle between the photosensitive surface of the linear CCD and the optical axis of the imaging lens. The incident angle of the laser source is 1, thereby realizing the displacement measurement of the object in the Z-axis direction.
[0061] Another reflected beam passes through the second beam splitter 8 and is focused by the focusing lens 10 into the second CCD camera 11. The rotation angles of the object under test in the X and Y axes are measured using the self-collimation measurement principle, as shown in the following formula:
[0062] ΔL x =f tan 2θ x
[0063] ΔL y =f tan 2θ y
[0064] In the formula, ΔL x and ΔL y Both are linear offsets of the target image point relative to the original null position, where f is the focal length of the focusing lens, and θ is the linear offset of the target image point relative to the original null position. x and θ y All of these are the tilt angles of the object being measured.
[0065] When the object being measured rotates along the Z-axis, the rotation angle θ in the Z-axis direction... Z The rotation angle Δθ3 of the cross ring is directly determined. When the object being measured moves along the X and Y axes, the cross ring pattern on the cross ring reflective target 5 will also rotate, and the reflected light will move accordingly. After passing through the third beam splitter 9, it will enter the third CCD camera 13 through the telecentric lens 12. The formula is as follows:
[0066] Δθ3=θ Z
[0067] ΔL x ′=βΔx
[0068] ΔL y ′=βΔy
[0069] In the formula, ΔL x ′、ΔL y ′ represents the positional change detected by the third CCD camera 13, Δθ3 is the rotation angle of the cross ring, and θ Z Δx and Δy are the rotation angles along the Z-axis, thus measuring the rotation angle of the object under test in the Z-axis direction; Δx and Δy are the lateral displacements of the object under test in the two directions; and β is the magnification of the lens imaging system, thus measuring the positional changes of the object under test in the X and Y-axis directions.
[0070] The above measurement results are summarized and processed by computer 14 to obtain the six-degree-of-freedom motion state of the measured object, including the displacement in the X, Y, and Z axis directions and the rotation angle in the X, Y, and Z axis directions.
Claims
1. A six degree of freedom laser measurement system characterized by, Based on the different degrees of freedom being measured, the system is divided into a first optical system, a second optical system, and a third optical system. The first optical system uses the principle of oblique laser triangulation to measure the displacement of the object in the Z-axis direction. The second optical system uses the principle of autocollimation to measure the rotation angle of the object in the X-axis and Y-axis directions. The third optical system uses the principle of visual imaging to measure the displacement of the object in the X-axis and Y-axis directions and the rotation angle in the Z-axis direction. The first optical system, the second optical system, and the third optical system together include: a laser source (1), a collimating and beam-expanding lens (2), and a cross-shaped circular reflective target (5); The first optical system also includes a first beam splitter (3), a reflector (4), a first focusing lens (6), and a first CCD camera (7); The second optical system also includes a second beam splitter (8), a second focusing lens (10), and a second CCD camera (11); The third optical system also includes a third beam splitter (9), a telecentric lens (12), and a third CCD camera (13); The laser beam output from the laser source (1) becomes a parallel beam after passing through the collimating and beam expanding lens (2), and illuminates the cross-shaped circular reflective target (5), generating reflected light; In the first optical system, the laser light source (1) expands the laser beam through the collimating and expanding lens (2), and then reflects it in sequence through the first beam splitter (3) and the reflector (4) before obliquely incident on the cross-shaped circular reflector target (5). The reflected beam passes through the first focusing lens (6) and then enters the first CCD camera (7). The displacement of the object under test in the Z-axis direction is measured by the change of the position of the light spot in the first CCD camera (7). In the second optical system, the laser light source (1) expands the laser beam through the collimating and beam-expanding lens (2) and then incident it perpendicularly onto the cross-shaped circular reflective target (5). The reflected beam is reflected by the second beam splitter (8) and then focused by the second focusing lens (10) into the second CCD camera (11). The rotation angle of the X and Y axes of the object under test is measured by the change of the position of the light spot in the second CCD camera (11). In the third optical system, the laser light source (1) expands the laser beam through the collimating and expanding lens (2) and then incident it perpendicularly onto the cross-shaped circular reflective target (5). The reflected beam is reflected sequentially by the second beam splitter (8) and the third beam splitter (9), and then enters the third CCD camera (13) through the telecentric lens (12). The displacement of the object under test in the X and Y axes is measured by the change in the position of the light spot in the third CCD camera (13). The rotation angle of the object under test in the Z axis is measured by the rotation angle of the cross-shaped circular pattern in the third CCD camera (13).
2. A six degree of freedom laser measurement system according to claim 1, wherein, The cross-shaped circular reflective target (5) is a circular reflector with high reflectivity and high precision placed on the surface of the object being tested, and a cross-shaped circular pattern is processed on it.
3. A six degree of freedom laser measurement system according to claim 1, wherein, In the first optical system, the placement of the laser source (1), collimating beam expander (2), first beam splitter (3), reflector (4), cross-shaped ring reflector target (5), first focusing lens (6) and first CCD camera (7) satisfies the conditions of Scham's law.
4. A six degree of freedom laser measurement system according to claim 1, 2 or 3, characterised in that, It also includes a computer (14). The images acquired by the first CCD camera (7), the second CCD camera (11) and the third CCD camera (13) are transmitted to the computer (14). The computer (14) uses the images obtained by the first CCD camera (7), the second CCD camera (11) and the third CCD camera (13) to determine the six-degree-of-freedom motion state of the object under test.