A three-degree-of-freedom autocollimation angle measurement device and method based on a crosshair reticle.

Abstract

This invention discloses a three-degree-of-freedom autocollimation angle measurement device and method based on a crosshair reticle, comprising a probe system, a target mirror system, and a calculation system. The probe system emits a collimated beam containing crosshair image information into the target mirror system. The target mirror system separates the collimated beam containing crosshair image information into two reflected beams parallel to the optical axis, each reflecting beam containing crosshair image information. The probe system also receives the two reflected beams parallel to the optical axis and images the crosshair images corresponding to the two reflected beams. The calculation system calculates the pitch and yaw angles of the target based on the initial and current coordinates of the crosshair image corresponding to one reflected beam parallel to the optical axis, and calculates the roll angle of the target based on the initial and current tilt angles of the crosshair image corresponding to the other reflected beam parallel to the optical axis. This invention enables rapid and high-precision three-degree-of-freedom angle measurement of distant targets.

Description

Technical Field

[0001] This invention belongs to the field of precision measurement technology, specifically relating to a three-degree-of-freedom autocollimation angle measuring device and method based on a crosshair reticle. Background Technology

[0002] Measuring the three degrees of freedom (pitch, yaw, and roll) of an object rotating around the three axes of a Cartesian coordinate system is a crucial task in industrial production and precision measurement. For example, to eliminate the impact of ship hull bending on the aiming performance of shipborne gun systems, and to remotely monitor the deformation of large structures such as oil pipelines, bridges, and buildings, it is often necessary to measure the three degrees of freedom angles between two relatively distant components. Among numerous photoelectric angle measurement methods, the autocollimation method is widely used due to its non-contact nature, simple structure, and high accuracy. An autocollimator is an angle measuring instrument based on the autocollimation method. During measurement, the collimated beam emitted by the autocollimator illuminates a plane mirror rigidly connected to the target. After reflection by the plane mirror, the beam returns to the autocollimator and is imaged on a photodetector located at the focal plane of the objective lens. When the plane mirror produces a pitch or yaw angle, the image on the photodetector shifts; based on geometric relationships, the pitch and yaw angles can be calculated from the shift. However, this method cannot measure the roll angle caused by the plane mirror rotating around the optical axis because the image on the photodetector does not shift or rotate. Therefore, this traditional autocollimation method cannot simultaneously measure three degrees of freedom angles.

[0003] To address the aforementioned problems, researchers have proposed several solutions, which can be categorized into two types based on whether the reflected beam generated by the target mirror is parallel to the optical axis. In the first type, the reflected beam generated by a specially designed target mirror (diffraction grating, polyhedral prism) is not parallel to the optical axis, which significantly shortens the movement distance of the target and severely limits its application. In the second type, the reflected beam generated by the target mirror is parallel to the optical axis and forms moiré fringes on a photodetector. The roll angle is calculated based on the width variation of the moiré fringes, but this method suffers from complex image processing, slow measurement speed, and low measurement accuracy. Overall, while both types of methods possess the ability to simultaneously measure three degrees of freedom angles, they suffer from short target movement distances, slow measurement speeds, and low measurement accuracy. Therefore, how to achieve rapid and high-precision three-degree-of-freedom angle measurement of distant targets based on the self-collimation principle is a problem urgently needing to be solved by those skilled in the art. Summary of the Invention

[0004] To address the problems existing in the prior art, the present invention provides a three-degree-of-freedom autocollimation angle measurement device and method based on a crosshair reticle, which can realize rapid and high-precision three-degree-of-freedom angle measurement of distant targets.

[0005] To solve the above-mentioned technical problems, the present invention is achieved through the following technical solution:

[0006] A three-degree-of-freedom autocollimation angle measurement device based on a crosshair reticle includes a probe system, a target mirror system, and a calculation system. The probe system emits a collimated beam containing crosshair image information into the target mirror system. The target mirror system separates the collimated beam containing crosshair image information into two reflected beams parallel to the optical axis, each reflecting beam containing the crosshair image information. The probe system also receives the two reflected beams parallel to the optical axis and images the crosshair images corresponding to the two reflected beams. The calculation system calculates the pitch and yaw angles of the target based on the initial and current coordinates of the crosshair image corresponding to one reflected beam parallel to the optical axis, and calculates the roll angle of the target based on the initial and current tilt angles of the crosshair image corresponding to the other reflected beam parallel to the optical axis.

[0007] Furthermore, the target mirror system includes a beam splitter, a first plane mirror, and a second plane mirror. The beam splitter is obliquely disposed on the propagation path of the collimated beam containing crosshair image information. The first plane mirror is perpendicularly disposed on the propagation path of the collimated beam containing crosshair image information and is located behind the beam splitter. The second plane mirror is perpendicular to the normal of the beam splitter and is arranged symmetrically.

[0008] Furthermore, the probe system includes a laser diode, a crosshair reticle, a condenser lens, a beam splitter, a first objective lens, a first photodetector, a second objective lens, and a second photodetector. The crosshair reticle, the condenser lens, and the beam splitter are arranged sequentially along the propagation path of the emitted beam of the laser diode. The beam splitter is used to change the emitted beam of the laser diode into a beam that is perpendicular to the first plane mirror. The first objective lens is arranged between the beam splitter and the first plane mirror. The first photodetector is arranged on the propagation path of the reflected beam of the first plane mirror and is located on the side of the beam splitter away from the first objective lens. The second objective lens and the second photodetector are arranged sequentially on the propagation path of the reflected beam of the second plane mirror.

[0009] Furthermore, the probe system also includes a 45° tilted reflector. The crosshair reticle, the condenser lens, the 45° tilted reflector, and the beam splitter are arranged sequentially along the propagation path of the emitted beam of the laser diode. The laser diode is configured to emit a beam along the z-axis direction. The 45° tilted reflector is used to change the beam emitted by the laser diode into a beam directed towards the beam splitter.

[0010] Furthermore, the roll angle of the target under test is calculated based on the initial and current tilt angles of the crosshair image corresponding to another reflected beam parallel to the optical axis, as detailed below:

[0011]

[0012] In the formula, γ is the roll angle; θ i1 Let θ be the initial tilt angle of the i-th straight line in the crosshair image; i2 is the current tilt angle of the i-th line in the crosshair image; n is the number of lines in the crosshair image.

[0013] A three-degree-of-freedom autocollimation angle measurement method based on a crosshair reticle, employing the aforementioned three-degree-of-freedom autocollimation angle measurement device based on a crosshair reticle, comprising:

[0014] Connect the target mirror system to the target to be tested;

[0015] The probe system emits a collimated beam containing crosshair image information into the target mirror system;

[0016] The target mirror system separates the collimated beam containing crosshair image information into two reflected beams parallel to the optical axis, each of the reflected beams containing the crosshair image information;

[0017] The probe system receives the two reflected beams parallel to the optical axis and images the crosshair images corresponding to the two reflected beams parallel to the optical axis.

[0018] Determine the initial coordinates of the crosshair image corresponding to a reflected beam parallel to the optical axis, and determine the initial tilt angle of the crosshair image corresponding to another reflected beam parallel to the optical axis.

[0019] Control the target under test to perform three-degree-of-freedom angular rotation;

[0020] Determine the current coordinates of the crosshair image corresponding to a reflected beam parallel to the optical axis, and determine the current tilt angle of the crosshair image corresponding to another reflected beam parallel to the optical axis.

[0021] The calculation system calculates the pitch and yaw angles of the target under test based on the initial and current coordinates of the crosshair image corresponding to a reflected beam parallel to the optical axis, and calculates the roll angle of the target under test based on the initial and current tilt angles of the crosshair image corresponding to another reflected beam parallel to the optical axis.

[0022] Further, determining the initial tilt angle of the crosshair image corresponding to the other reflected beam parallel to the optical axis includes:

[0023] Before the target under test is rotated in three degrees of freedom, the gray values ​​of all pixels of the second photodetector are extracted, the equations of all straight lines in the crosshair image on the second photodetector are determined, the arctangent of the slope of all straight line equations is taken to obtain the tilt angle of all straight lines, and the tilt angle of the straight lines is used as the initial tilt angle of the crosshair image on the second photodetector.

[0024] Determining the current tilt angle of the crosshair image corresponding to the other reflected beam parallel to the optical axis includes:

[0025] After the target under test is rotated in three degrees of freedom, the gray values ​​of all pixels of the second photodetector are extracted, the equations of all straight lines in the crosshair image on the second photodetector are determined, the arctangent of the slope of all straight line equations is taken to obtain the tilt angle of all straight lines, and the tilt angle of the straight lines is taken as the current tilt angle of the crosshair image on the second photodetector.

[0026] Furthermore, determine the equations of all straight lines in the crosshair image, including:

[0027] To determine whether the inclination angle of the straight line is greater than 45°, the method is as follows: rotate the straight line clockwise until it coincides with the x-axis, and observe whether the rotation angle is greater than 45°.

[0028] If not, sum the products of the row coordinates of the pixels in a column that runs through the line and the corresponding pixel gray values, and then divide by the sum of the corresponding pixel gray values ​​to obtain the gray centroid of the line in that column of pixels; repeat the above process to obtain the gray centroid of the line in each column of pixels; use the least squares method to fit the equation of the line based on all the obtained gray centroids.

[0029] If so, sum the products of the column coordinates of the row of pixels passing through the straight line and the corresponding pixel gray values, and then divide by the sum of the corresponding pixel gray values ​​to obtain the gray centroid of the straight line in that row of pixels; repeat the above process to obtain the gray centroid of the straight line in each row of pixels; use the least squares method to fit the equation of the straight line based on all the obtained gray centroids.

[0030] Compared with the prior art, the present invention has at least the following beneficial effects:

[0031] This invention provides a three-degree-of-freedom autocollimation angle measurement device based on a crosshair reticle. First, the probe system can emit a collimated beam containing crosshair image information to the target mirror system. Then, the target mirror system can separate the collimated beam containing crosshair image information into two reflected beams parallel to the optical axis, each reflecting beam containing crosshair image information. Second, the probe system can also receive the two reflected beams parallel to the optical axis and image the crosshair images corresponding to the two reflected beams parallel to the optical axis. Finally, the calculation system calculates the pitch angle and yaw angle of the target based on the initial and current coordinates of the crosshair image corresponding to one reflected beam parallel to the optical axis, and calculates the roll angle of the target based on the initial and current tilt angles of the crosshair image corresponding to the other reflected beam parallel to the optical axis. In other words, the target mirror system designed in this invention generates two reflected beams parallel to the optical axis that return to the probe system. This characteristic allows the target to move a considerable distance along the optical axis. Furthermore, since the probe system receives two reflected beams parallel to the optical axis and images the crosshair images corresponding to these two beams, beam overlap is avoided, improving measurement accuracy. This invention calculates the pitch and yaw angles of the target based on the initial and current coordinates of the crosshair image corresponding to one reflected beam parallel to the optical axis, i.e., calculating the pitch and yaw angles based on the coordinate changes of the intersection points of the straight lines. Similarly, it calculates the roll angle of the target based on the initial and current tilt angles of the crosshair image corresponding to the other reflected beam parallel to the optical axis, i.e., calculating the roll angle based on the rotation angle of the straight line. Compared to extracting the width changes of moiré fringes, this method offers advantages such as simpler image processing, faster measurement speed, and higher measurement accuracy. In summary, this invention enables rapid and high-precision three-degree-of-freedom angle measurement of distant targets.

[0032] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, preferred embodiments are described below in detail with reference to the accompanying drawings. Attached Figure Description

[0033] To more clearly illustrate the technical solutions in the specific embodiments of the present invention, the drawings used in the description of the specific embodiments will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0034] Figure 1 A schematic diagram of a three-degree-of-freedom autocollimation angle measuring device based on a crosshair reticle provided in an embodiment of the present invention;

[0035] Figure 2 The flowchart illustrates a three-degree-of-freedom autocollimation angle measurement method based on a crosshair reticle, as provided in an embodiment of the present invention.

[0036] In the diagram: 1—Laser diode; 2—Forked reticle; 3—Condenser lens; 4—45° tilting mirror; 5—Beam splitter prism; 6—First objective lens; 7—First photodetector; 8—Beam splitter plate; 9—First plane mirror; 10—Second plane mirror; 11—Second objective lens; 12—Second photodetector; 100—Probe system; 200—Target mirror system; 300—Computing system. Detailed Implementation

[0037] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0038] As a specific embodiment of the present invention, such as Figure 1 As shown, a three-degree-of-freedom autocollimation angle measurement device based on a crosshair reticle includes a probe system 100, a target mirror system 200, and a computing system 300. The probe system 100 emits a collimated beam containing crosshair image information into the target mirror system 200. The target mirror system 200 separates the collimated beam containing crosshair image information into two reflected beams parallel to the optical axis, each reflecting beam containing crosshair image information. The probe system 100 also receives the two reflected beams parallel to the optical axis and images the crosshair images corresponding to the two reflected beams parallel to the optical axis. The computing system 300 calculates the pitch and yaw angles of the target based on the initial and current coordinates of the crosshair image corresponding to one reflected beam parallel to the optical axis, and calculates the roll angle of the target based on the initial and current tilt angles of the crosshair image corresponding to the other reflected beam parallel to the optical axis.

[0039] Specifically, based on the initial and current tilt angles of the crosshair image corresponding to another reflected beam parallel to the optical axis, the roll angle of the target under test is calculated as follows:

[0040]

[0041] In the formula, γ is the roll angle; θ i1 Let θ be the initial tilt angle of the i-th straight line in the crosshair image; i2 is the current tilt angle of the i-th line in the crosshair image; n is the number of lines in the crosshair image.

[0042] Based on the above implementation methods, as a more preferred implementation method, such as... Figure 1As shown, the target mirror system 200 includes a beam splitter 8, a first plane mirror 9, and a second plane mirror 10. The beam splitter 8 is tilted along the propagation path of the collimated beam containing crosshair image information; for example, the tilt angle of the beam splitter 8 is 45°. The first plane mirror 9 is vertically positioned along the propagation path of the collimated beam containing crosshair image information and is located behind the beam splitter 8. The second plane mirror 10 is perpendicular to the normal of the beam splitter 8 and is arranged symmetrically. Preferably, the distance between the second plane mirror 10 and the beam splitter 8 is adjustable. Furthermore, to facilitate installation on the target, the target mirror system 200 may have a base plate to which the beam splitter 8, the first plane mirror 9, and the second plane mirror 10 are rigidly connected.

[0043] Specifically, such as Figure 1 As shown, the beam splitter 8 separates the collimated beam containing crosshair image information into two beams. One beam passes through the beam splitter 8 and is directed towards the first plane mirror 9, and is reflected by the first plane mirror 9 before being directed towards the probe system 100. The other beam is reflected and directed towards the second plane mirror 10, and is reflected by the second plane mirror 10 before being directed towards the probe system 100.

[0044] Based on the above implementation methods, as a more preferred implementation method, such as... Figure 1 As shown, the probe system 100 includes a laser diode 1, a crosshair reticle 2, a condenser lens 3, a beam splitter 5, a first objective lens 6, a first photodetector 7, a second objective lens 11, and a second photodetector 12. The crosshair reticle 2, the condenser lens 3, and the beam splitter 5 are arranged sequentially along the propagation path of the emitted beam of the laser diode 1. The beam splitter 5 is used to change the emitted beam of the laser diode 1 into a beam that is perpendicular to the first plane mirror 9. The first objective lens 6 is arranged between the beam splitter 5 and the first plane mirror 9. The first photodetector 7 is arranged on the propagation path of the reflected beam of the first plane mirror 9 and is located on the side of the beam splitter 5 away from the first objective lens 6. The second objective lens 11 and the second photodetector 12 are arranged sequentially on the propagation path of the reflected beam of the second plane mirror 10.

[0045] Specifically, the laser emitted by laser diode 1 passes through crosshair reticle 2 to form a beam containing crosshair image information. This beam then passes sequentially through condenser lens 3 and beam splitter prism 5 before being reflected to first objective lens 6. After passing through first objective lens 6, the beam containing crosshair image information forms a collimated beam, which is then directed towards beam splitter 8. First photodetector 7 receives the reflected beam parallel to the optical axis from first plane mirror 9 and images the corresponding crosshair image. Second photodetector 12 receives the reflected beam parallel to the optical axis from second plane mirror 10 and images the corresponding crosshair image.

[0046] like Figure 1 As shown, preferably, in order to reduce the size of the probe system 100, the probe system 100 further includes a 45° tilting mirror 4, a crosshair reticle 2, a condenser lens 3, a 45° tilting mirror 4 and a beam splitter 5 arranged sequentially along the propagation path of the emitted beam of the laser diode 1. The laser diode 1 is configured to emit a beam along the z-axis direction, and the 45° tilting mirror 4 is used to change the beam emitted by the laser diode 1 into a beam directed towards the beam splitter 5.

[0047] In addition, for ease of installation and integration, the probe system 100 may have a base plate, and all the aforementioned components in the probe system 100 are rigidly connected to the base plate.

[0048] More specifically, such as Figure 1 As shown, a three-degree-of-freedom self-collimation angle measuring device based on a crosshair reticle operates as follows:

[0049] The laser beam emitted by the laser diode 1 of the probe system 100 passes sequentially through the crosshair reticle 2, condenser lens 3, 45° tilting mirror 4, beam splitter prism 5, and first objective lens 6 to form a collimated beam with a crosshair pattern, which exits along the optical axis. The collimated beam enters the target mirror system 200 and is split into two beams by the beam splitter 8. The transmitted beam a passes through the first plane mirror 9 and returns to the probe system 100 along the optical axis, passing again through the beam splitter 8, first objective lens 6, and beam splitter prism 5, finally forming a crosshair image on the first photodetector 7 located at the focal plane of the first objective lens 6. The reflected beam b passes through the second plane mirror 10 and returns to the probe system 100 parallel to the optical axis, passing through the second objective lens 11 and forming a crosshair image on the second photodetector 12 located at the focal plane of the second objective lens 11. The first photodetector 7 and the second photodetector 12 respectively transmit the crosshair images to the computing system 300 for processing. The calculation system 300 calculates the pitch and yaw angles of the target under test based on the displacement of the crosshair image on the first photodetector 7, using the same calculation method as existing technologies. Furthermore, based on the vector representation of reflection optics, it can be proven that when the target under test generates a roll angle γ, the crosshair image on the second photodetector 12 will rotate by an angle 2γ. Therefore, the roll angle of the target under test can be calculated based on the rotation angle of the crosshair image on the second photodetector 12.

[0050] As another specific embodiment of the present invention, combined with Figure 2 As shown, a three-degree-of-freedom autocollimation angle measurement method based on a crosshair reticle is also provided. This method uses the aforementioned three-degree-of-freedom autocollimation angle measurement device based on a crosshair reticle for measurement, and specifically includes the following steps:

[0051] S1: Rigidly connect the target mirror system to the target to be tested.

[0052] Preferably, bolts are used to mechanically connect the target system to the target under test, so that there is no relative displacement or rotation between the target system and the target under test.

[0053] S2: Adjust the probe system so that the crosshair images on the first and second photodetectors are located in the center region of the image plane.

[0054] Specifically, the pitch, yaw, and roll directions of the probe system are adjusted until the crosshair image is located in the center region of the image plane of the first photodetector and the second photodetector, respectively.

[0055] S3: Determine the initial coordinates of the crosshair image on the first photodetector and determine the initial tilt angle of the crosshair image on the second photodetector.

[0056] It should be noted that this embodiment does not specifically limit the shape and size of the pattern on the crosshair reticle. The pattern can be designed as an M-shape, N-shape, star shape, cross shape, etc. This embodiment uses a cross-shaped pattern on the crosshair reticle for illustration.

[0057] Specifically, the initial coordinates of the crosshair image on the first photodetector are determined as follows:

[0058] Extract the grayscale values ​​of all pixels of the first photodetector, determine the equations of the two straight lines in the crosshair image, calculate the intersection point of the two straight lines, and use the coordinates of the intersection point as the initial coordinates of the crosshair image on the first photodetector.

[0059] It should be noted that in this embodiment, a Cartesian coordinate system is established on the image plane where the crosshair image is located, where the horizontal axis is the x-axis and the vertical axis is the y-axis.

[0060] Specifically, the initial tilt angle of the crosshair image on the second photodetector is determined as follows:

[0061] Extract the grayscale values ​​of all pixels of the second photodetector, determine the equations of the two straight lines in the crosshair image, take the arctangent of the slope of the two straight line equations to obtain the tilt angles of the two straight lines, and use the tilt angles of the two straight lines as the two initial tilt angles of the crosshair image on the second photodetector.

[0062] Preferably, when determining the equation of a straight line in the crosshair image, first determine whether the inclination angle of the straight line is greater than 45°. The determination method is: rotate the straight line clockwise until it coincides with the x-axis, and observe whether the rotation angle is greater than 45°.

[0063] If not, sum the products of the row coordinates of the pixels in a column passing through the straight line and the corresponding pixel gray values, and then divide by the sum of the corresponding pixel gray values ​​to obtain the gray centroid of the straight line in that column of pixels. Repeat the above process to obtain the gray centroid of the straight line in each column of pixels; use the least squares method to fit the equation of the straight line based on all the obtained gray centroids;

[0064] If so, sum the products of the column coordinates of the pixels in a row passing through the straight line and the corresponding pixel grayscale values, and then divide by the sum of the corresponding pixel grayscale values ​​to obtain the grayscale centroid of the straight line in that row of pixels. Repeat the above process to obtain the grayscale centroid of the straight line in each row of pixels; use the least squares method to fit the equation of the straight line based on all the obtained grayscale centroids.

[0065] Preferably, the length of each column of pixels or each row of pixels that runs through the straight line should be no less than 1.5 times the width of the straight line, so as to ensure that each column of pixels or each row of pixels can completely run through the straight line.

[0066] It should be noted that, in this embodiment, the equations of the straight lines in the crosshair image are all determined using the method described above.

[0067] S4: Control the target under test to perform three-degree-of-freedom angular rotation.

[0068] Specifically, the target to be tested is controlled to rotate simultaneously along the three coordinate axes of the Cartesian coordinate system, causing the crosshair image on the first photodetector to shift and the crosshair image on the second photodetector to rotate.

[0069] S5: Determine the current coordinates of the crosshair image on the first photodetector and determine the current tilt angle of the crosshair image on the second photodetector.

[0070] Specifically, the current coordinates of the crosshair image on the first photodetector are determined as follows:

[0071] Extract the grayscale values ​​of all pixels of the first photodetector, determine the equations of the two straight lines in the crosshair image, calculate the intersection point of the two straight lines, and use the coordinates of the intersection point as the current coordinates of the crosshair image on the first photodetector.

[0072] Specifically, the current tilt angle of the crosshair image on the second photodetector is determined as follows:

[0073] Extract the grayscale values ​​of all pixels of the second photodetector, determine the equations of the two straight lines in the crosshair image, take the arctangent of the slope of the two straight line equations to obtain the tilt angles of the two straight lines, and use the tilt angles of the two straight lines as the two current tilt angles of the crosshair image on the second photodetector.

[0074] S6: Determine the three-degree-of-freedom rotation angle of the target under test based on the initial and current coordinates of the crosshair image on the first photodetector and the initial and current tilt angles of the crosshair image on the second photodetector.

[0075] For example, if the initial coordinates of the crosshair image on the first photodetector in the x-axis direction are x1 and the current coordinates are x2, and the initial coordinates in the y-axis direction are y1 and the current coordinates are y2, then the pitch angle α and yaw angle β of the target to be measured are obtained according to the following formulas:

[0076]

[0077]

[0078] In the formula: f is the focal length of the first objective lens.

[0079] For example, the initial tilt angle of the first straight line in the crosshair image on the second photodetector is θ. 11 The current tilt angle is θ 12The initial inclination angle of the second straight line is θ. 21 The current tilt angle is θ 22 The roll angle γ of the target under test is obtained according to the following formula:

[0080]

[0081] That is, the roll angle of the target under test is equal to the arithmetic average of half the rotation angles of the two straight lines on the second photodetector.

[0082] It should be noted that the more straight lines involved in the roll angle calculation, the smaller the measurement error of the roll angle. Therefore, the number of straight lines in the reticle pattern should be increased as much as possible, for example, by using an M-shaped reticle or a star-shaped reticle containing multiple straight lines. In this embodiment, for ease of calculation, a cross-shaped reticle containing two straight lines is used.

[0083] This allows for the determination of the three degrees of freedom angles of the target under test, enabling rapid and high-precision three-degree-of-freedom angle measurement of distant targets.

[0084] This invention designs a target-mirror system to generate two reflected beams parallel to the optical axis that return to the probe system. By detecting the displacement and rotation of the crosshair images on two photodetectors, it achieves rapid and high-precision three-degree-of-freedom angle measurement of distant targets, thus broadening the application range of the traditional autocollimation method. This invention has the following technical advantages:

[0085] (1) The target mirror system consists of two plane mirrors and a beam splitter, which is simple in structure, small in size, light in weight, and easy to install and debug. It avoids the problems of complex structure, difficult processing, and increased cost caused by using special target mirrors.

[0086] (2) The target mirror system generates two reflected beams parallel to the optical axis and returns to the probe system. This characteristic allows the target to be measured to move a greater distance along the optical axis. Furthermore, since the two reflected beams are received by two photodetectors respectively, beam overlap is avoided.

[0087] (3) According to the vector representation of reflection optics, it can be proved that when the target under test generates pitch and yaw angles, the tilt angle of the crosshair image on the second photodetector remains unchanged; when the target under test generates roll angles, the coordinates of the crosshair image on the first photodetector remain unchanged, indicating that the measurement of pitch angle, yaw angle and roll angle do not affect each other.

[0088] (4) According to the vector representation of reflection optics, it can be proved that when the target under test generates a roll angle γ, the crosshair image on the second photodetector will rotate by 2γ angles, thus doubling the measurement resolution of the roll angle.

[0089] (5) The equations of the straight lines in the crosshair image are extracted using the gray-scale centroid method. The pitch and yaw angles of the target are calculated based on the coordinate changes of the intersection points of the lines, and the roll angle of the target is calculated based on the rotation angle of the lines. Compared with extracting the width changes of moiré fringes, this method has the advantages of simple image processing, fast measurement speed, and high measurement accuracy.

[0090] Finally, it should be noted that the above-described embodiments are merely specific implementations of the present invention, used to illustrate the technical solutions of the present invention, and not to limit it. The scope of protection of the present invention is not limited thereto. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that any person skilled in the art can still modify or easily conceive of changes to the technical solutions described in the foregoing embodiments within the technical scope disclosed in the present invention, or make equivalent substitutions for some of the technical features; and these modifications, changes, or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention, and should all be covered within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of protection of the claims.

Claims

1. A three-degree-of-freedom autocollimation angle measurement method based on a crosshair reticle, characterized in that, A three-degree-of-freedom autocollimation angle measuring device based on a crosshair reticle is adopted. The measuring device includes a probe system (100), a target mirror system (200), and a computing system (300). The target mirror system (200) includes a beam splitter (8), a first plane mirror (9), and a second plane mirror (10); the probe system (100) includes a laser diode (1), a crosshair reticle (2), a condenser lens (3), a beam splitter (5), a first objective lens (6), a first photodetector (7), a second objective lens (11), and a second photodetector (12). The crosshair reticle (2), the condenser lens (3), and the beam splitter (5) are arranged sequentially along the propagation path of the emitted beam of the laser diode (1). The beam splitter (5) is used for... To change the emitted beam of the laser diode (1) into a beam that is perpendicular to the first plane mirror (9), the first objective lens (6) is arranged between the beam splitter (5) and the first plane mirror (9), and the first photodetector (7) is arranged on the propagation path of the reflected beam of the first plane mirror (9) and is located on the side of the beam splitter (5) away from the first objective lens (6); the second objective lens (11) and the second photodetector (12) are arranged sequentially on the propagation path of the reflected beam of the second plane mirror (10); Measurement methods include: Connect the target mirror system (200) to the target to be tested; The probe system (100) emits a collimated beam containing crosshair image information to the target mirror system (200); The target mirror system (200) separates the collimated beam containing crosshair image information into two reflected beams parallel to the optical axis, each of the reflected beams containing the crosshair image information; The probe system (100) receives the two reflected beams parallel to the optical axis and images the crosshair images corresponding to the two reflected beams parallel to the optical axis. Determine the initial coordinates of the crosshair image corresponding to one reflected beam parallel to the optical axis, and determine the initial tilt angle of the crosshair image corresponding to another reflected beam parallel to the optical axis, including: Before the target under test is rotated in three degrees of freedom, the gray values ​​of all pixels of the second photodetector (12) are extracted, the equations of all straight lines in the crosshair image on the second photodetector (12) are determined, the arctangent of the slope of all straight line equations is taken to obtain the tilt angle of all straight lines, and the tilt angle of the straight lines is used as the initial tilt angle of the crosshair image on the second photodetector (12). Control the target under test to perform three-degree-of-freedom angular rotation; Determine the current coordinates of the crosshair image corresponding to a reflected beam parallel to the optical axis, and determine the current tilt angle of the crosshair image corresponding to another reflected beam parallel to the optical axis, including: After the target under test is rotated in three degrees of freedom, the gray values ​​of all pixels of the second photodetector (12) are extracted, the equations of all straight lines in the crosshair image on the second photodetector (12) are determined, the arctangent of the slope of all straight line equations is taken to obtain the tilt angle of all straight lines, and the tilt angle of the straight lines is taken as the current tilt angle of the crosshair image on the second photodetector (12). The calculation system (300) calculates the pitch angle and yaw angle of the target under test based on the initial and current coordinates of the crosshair image corresponding to a beam of reflected light parallel to the optical axis, and calculates the roll angle of the target under test based on the initial and current tilt angles of the crosshair image corresponding to another beam of reflected light parallel to the optical axis.

2. The three-degree-of-freedom autocollimation angle measurement method based on a crosshair reticle according to claim 1, characterized in that, Determine the equations of all straight lines in the crosshair image, including: To determine whether the inclination angle of the straight line is greater than 45°, the method is as follows: rotate the straight line clockwise until it is parallel to the line. x With the axes aligned, observe whether the rotation angle is greater than 45°. If not, sum the products of the row coordinates of the pixels in a column that runs through the line and the corresponding pixel gray values, and then divide by the sum of the corresponding pixel gray values ​​to obtain the gray centroid of the line in that column of pixels; repeat the above process to obtain the gray centroid of the line in each column of pixels; use the least squares method to fit the equation of the line based on all the obtained gray centroids. If so, sum the products of the column coordinates of the row of pixels passing through the straight line and the corresponding pixel gray values, and then divide by the sum of the corresponding pixel gray values ​​to obtain the gray centroid of the straight line in that row of pixels; repeat the above process to obtain the gray centroid of the straight line in each row of pixels; use the least squares method to fit the equation of the straight line based on all the obtained gray centroids.

3. The three-degree-of-freedom autocollimation angle measurement method based on a crosshair reticle according to claim 1, characterized in that, The beam splitter (8) is tilted on the propagation path of the collimated beam containing crosshair image information; the first plane mirror (9) is vertically disposed on the propagation path of the collimated beam containing crosshair image information and is located behind the beam splitter (8); the second plane mirror (10) is perpendicular to the normal of the beam splitter (8) and is arranged symmetrically.

4. The three-degree-of-freedom autocollimation angle measurement method based on a crosshair reticle according to claim 1, characterized in that, The probe system (100) also includes a 45° tilted mirror (4). The crosshair reticle (2), the condenser (3), the 45° tilted mirror (4) and the beam splitter (5) are arranged sequentially along the propagation path of the emitted beam of the laser diode (1). The laser diode (1) is configured to emit a beam along the z-axis. The 45° tilted mirror (4) is used to change the beam emitted by the laser diode (1) into a beam directed towards the beam splitter (5).

5. The three-degree-of-freedom autocollimation angle measurement method based on a crosshair reticle according to claim 1, characterized in that, The roll angle of the target under test is calculated based on the initial and current tilt angles of the crosshair image corresponding to another reflected beam parallel to the optical axis, as detailed below: In the formula, γ is the roll angle; The first crosshair in the image The initial inclination angle of a straight line; The first crosshair in the image The current tilt angle of the straight line; This represents the number of straight lines in the crosshair image.

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