A method and system for in-situ detection and compensation processing of a cubic mirror

Abstract

This invention relates to an in-situ detection and compensation machining method and system for cubic mirrors. During the ultra-precision machining stage of a cubic mirror, the influence of various machining error sources on the machining accuracy is controlled through pre-compensation of machining errors, ensuring the ultra-precision machining accuracy of the outer right angles of the cubic mirror. An in-situ measurement system for the outer right angles of the cubic mirror is established to measure the outer right angles of the machined cubic mirror. Based on the measurement data, the spatial dihedral angle of the outer right angle of the cubic mirror is calculated, and a three-dimensional spatial position model of the cubic mirror is reconstructed. Based on the deviation characteristics of the outer right angle of the cubic mirror and the influence of machining error sources, a compensation machining scheme for the outer right angle of the cubic mirror is formulated and fed back to the ultra-precision machining tool for compensation machining. Through iterative compensation machining and changing the reference surface, the accuracy of all outer right angles of the cubic mirror meets the requirements, solving the problems of poor compensation accuracy and low machining accuracy in the ultra-precision machining process of cubic mirrors.

Description

Technical Field

[0001] This invention relates to the field of optical processing and inspection technology, and in particular to an in-situ inspection and compensation processing method and an in-situ inspection system for a cubic mirror. Background Technology

[0002] A cube mirror is a regular hexahedron machined with ultra-precision precision. All six faces are highly flat mirror surfaces, and the perpendicularity between any two adjacent faces must be extremely high. Cube mirrors have a wide range of applications. In spacecraft development, they are used to reflect the spatial position of the product. By calibrating, measuring, and transferring the cube mirror coordinate system, precise measurements and adjustments of the product or its components can be achieved, making it an indispensable process benchmark in spacecraft manufacturing. In space gravitational wave detection, the cube mirror's quality is a core component of inertial sensors. Together with the capacitor plate frame, it forms a sensitive probe for detecting gravitational wave signals, serving as the measurement benchmark for space gravitational wave detection.

[0003] Depending on the material of the cube mirror, the manufacturing process includes turning, milling, planing, grinding, and polishing. To ensure extremely high flatness and perpendicularity, the right-angle accuracy of the cube mirror needs to be measured with high precision during manufacturing. For cube mirrors made of optical glass, the right-angle accuracy is usually measured using interior angle measurement methods. For cube mirrors made of non-transparent materials or with reflective coatings on the surface, the measuring beam cannot be directly incident on the interior, and the right-angle accuracy cannot be measured using interior angle measurement methods; therefore, external right-angle measurement methods are typically used.

[0004] Traditional methods for measuring external right angles include coordinate measuring machine (CMM), autocollimator method, and external angle interferometry. The CMM is a contact method; its basic principle is to use a CMM to uniformly sample points on the surface of a cubic mirror according to a certain pattern, fit the measurement points of each face to a plane, and thus calculate the accuracy of the angle between adjacent faces. The autocollimator method is a non-contact method; its basic principle is to use the principle of light autocollimation to measure the tilt angle between the plane of the cubic mirror and the plane perpendicular to the optical axis, and combine this with the rotation of a turntable to measure the tilt angle between adjacent planes and the plane perpendicular to the optical axis, ultimately calculating the accuracy of the angle between adjacent faces. Exterior angle interferometry is also a non-contact measurement method. The basic principle is to place a cubic mirror in a parallel cavity composed of two parallel plane mirrors. The included angle edges of the two adjacent measured surfaces are pointed towards the interferometer. A beam of parallel light emitted from the interferometer passes through the two measured surfaces and the parallel plane mirrors and returns, interfering with the reference light in the interferometer. The interference fringes reflect the tilt information of the measured surfaces of the cubic mirror, thereby calculating the accuracy of the included angle between adjacent planes of the cubic mirror.

[0005] The commonly used external right-angle measurement methods mentioned above are all off-site measurement methods, requiring the cubic mirror to be removed from the machine tool and installed on the measuring device for measurement. In-situ measurement refers to measuring the workpiece directly on the machine tool after machining is completed, without removing it from the machine tool. In ultra-precision machining stages, if the external right-angle accuracy measurement results of the cubic mirror do not meet the accuracy requirements, the cubic mirror needs to be reinstalled on the machine tool for repeated machining. However, the above three traditional methods for measuring the external right angle of a cubic mirror have the following drawbacks:

[0006] Firstly, the machining datum and measurement datum of traditional measurement methods do not coincide: Existing methods for measuring the external right angle of a cubic mirror, including coordinate measuring machine (CMM), autocollimator, and external angle interferometry, are all off-site measurement methods. Because these methods require removing the cubic mirror from the machine tool and then mounting it on the measuring device, the original machining datum of the cubic mirror on the machine tool is destroyed. After measurement, it is difficult to restore the original machining datum by repeated installation. Furthermore, repeated disassembly and reassembly introduce installation errors, resulting in the measurement results not being accurately fed back into the iterative machining process, significantly affecting the accuracy of subsequent compensation machining.

[0007] Secondly, the compensation process of traditional measurement methods is a non-closed-loop control: In the ultra-precision cutting stage, in order to ensure the extremely high flatness and perpendicularity accuracy requirements of the cubic mirror, it is necessary to repeatedly perform closed-loop control iterative compensation based on the measurement results of the external right angle of the cubic mirror until the flatness and perpendicularity accuracy requirements are met. Currently, for the ultra-precision cutting technology of cubic mirrors, precise process parameter control and adjustment are usually adopted, which cannot provide targeted compensation for external right angle deviations and cannot achieve precise closed-loop control processing. This limits the iterative compensation effect of the external right angle of the cubic mirror.

[0008] Third, the measurement results of traditional measurement methods are coupled with turntable errors: When measuring the external right angle accuracy of a cubic mirror using the autocollimator method, a turntable needs to be rotated to measure the tilt angle between adjacent planes and the plane perpendicular to the optical axis. Therefore, the rotation error of the turntable will be coupled into the measurement results. In order to improve the measurement accuracy of the autocollimator method, complex and tedious turntable error calibration is usually required.

[0009] Fourth, traditional measurement methods have high processing costs and low processing efficiency: Because the existing ultra-precision cutting technology for cubic mirrors uses off-site measurement methods and process parameter adjustment methods, changes in the processing datum cause the external right angle measurement results of the cubic mirror to be unable to be accurately fed back into the iterative processing process. At the same time, the precise control and adjustment of process parameters require a large amount of time-consuming repeated cutting, resulting in high ultra-precision machining costs and low processing efficiency for cubic mirrors. Summary of the Invention

[0010] One objective of this invention is to address the problem of low machining accuracy in existing cubic mirror ultra-precision cutting and machining technology due to the inability to perform accurate compensation caused by off-site measurement. This invention provides a high-precision measurement method and an ultra-precision compensation machining method that can achieve on-site measurement of the external right angle of a cubic mirror, thereby solving the problems of poor compensation accuracy and low machining accuracy in the ultra-precision cutting and machining process of cubic mirrors.

[0011] This invention provides, in one aspect, a method for in-situ detection and compensation processing of a cubic mirror, comprising the following steps:

[0012] S1. Analyze the various machining error sources existing in the ultra-precision cutting process, and pre-compensate the machining errors caused by each machining error source according to the influence of each machining error source on the machining accuracy of the outer right angle of the cubic mirror.

[0013] S2. After pre-compensation for machining errors, the cubic mirror is subjected to ultra-precision cutting.

[0014] S3. Construct an in-situ detection system for the external right angle of a cubic mirror to measure the external right angle of the finished cubic mirror in place;

[0015] S4. Based on the in-situ measurement data of the external right angle of the cube mirror, calculate the spatial dihedral angle of the external right angle of the cube mirror and reconstruct the three-dimensional spatial position model of the cube mirror plane.

[0016] S5. Based on the three-dimensional spatial position model of the cubic mirror plane, analyze the characteristics of the external right angle deviation of the cubic mirror, and combine the influence of the machining error source to formulate a machining scheme for external right angle compensation of the cubic mirror, and perform targeted compensation cutting on the machined surface of the cubic mirror.

[0017] In one embodiment of the present invention, in step S1, the error source includes one or more of machine tool error, machining process error and detection error, and the machining error is pre-compensated by adjusting the machine tool parameter settings or modifying the machining program.

[0018] In one embodiment of the present invention, step S2 includes the following steps:

[0019] S21. Select one face of the cubic mirror as the reference surface for cutting, and install the cubic mirror on the machine tool turntable, wherein the RMS of the reference surface is better than 1 / 10λ, λ=632.8nm;

[0020] S22. Rotate the machine tool turntable to align the first surface of the cubic mirror to be machined with the tool mounted on the machine tool spindle; start the machining program, and the tool moves along the machine tool to cut the first surface of the cubic mirror to be machined;

[0021] S23. After the cutting is completed, rotate the machine tool turntable 90° to process another surface to be processed;

[0022] S24. Repeat step S3 until the cubic mirror rotates one full revolution to complete the cutting of the four surfaces to be machined.

[0023] In one embodiment of the present invention, in step S21, the cubic mirror is mounted on the machine tool turntable by any one of the following methods: vacuum suction cup connection, adhesive bonding, or bolt connection.

[0024] In one embodiment of the present invention, step S3 includes the following steps:

[0025] S31. Place the cubic mirror on the machine tool turntable, and place two autocollimators with their optical axes facing the two adjacent faces of the cubic mirror respectively, so as to build the cubic mirror external right angle in-situ detection system.

[0026] S32. Use two autocollimators to measure the angle between the emitted light from the cube mirror and the reflected light from the measured surface. This angle is decomposed into components in the X and Y directions to complete the in-situ measurement of the external right angle of the cube mirror.

[0027] In one embodiment of the present invention, step S32 includes the following steps:

[0028] S321. In absolute measurement mode, adjust the two autocollimators in the X and Y dimensions respectively, so that the readings of the two autocollimators in the X and Y dimensions are close to zero.

[0029] S322. Adjust the two autocollimators to relative measurement mode, fix the autocollimators and record the readings of the two autocollimators in the X and Y dimensions;

[0030] S323. Rotate the machine tool turntable by 90° so that the two adjacent faces of the other outer right angle of the cubic mirror face the two autocollimators respectively, and record the readings of the two autocollimators in the X and Y dimensions.

[0031] S324. Repeat the process of rotating the machine tool turntable 90° in the same direction to measure the other two external right angles of the cubic mirror, and record the readings of the two autocollimators in the X and Y dimensions.

[0032] In one embodiment of the present invention, step S4 includes the following steps:

[0033] S41. Ignoring the Y-direction deflection component, calculate the out-of-plane right-angle deviation of the cubic mirror using the following formula:

[0034] Δθ i =a xi -b xi +Δ0 (1)

[0035] In equation (1), Δθ iFor the right-angle deviation outside the reference plane, a xi and b xi These are the correction values ​​for the X-direction readings of the two autocollimators, respectively, and Δ0 is the angular deviation between the ideal orthogonal optical axes of the two autocollimators on the measurement reference plane; where i represents the outer right angle number, and the value range is [1,4], i∈N;

[0036] S42. Combining the Y-direction deflection component, calculate the normal vector of the measured plane of the cubic mirror and the spatial dihedral angle deviation of the outer right angle. Use 3D modeling software to construct a spatial 3D model of the measured plane of the cubic mirror. The formula for calculating the spatial dihedral angle deviation of the outer right angle of the cubic mirror is as follows:

[0037] Δφ i =arccos(Δθ) i +Δ i (2)

[0038] In equation (2), ΔΦ i Δθ is the spatial dihedral angle deviation of the outer right angle of the cubic mirror. i The right-angle deviation outside the reference plane, Δ i is the deviation correction value; where i represents the outer right angle number, and the value range is [1,4], i∈N.

[0039] In one embodiment of the present invention, in step S42, the three-dimensional modeling software used is either UG or SolidWorks.

[0040] In one embodiment of the present invention, step S3 includes the following steps:

[0041] S31. Place a cubic mirror on a machine tool turntable, place an interferometer with its standard mirror facing one corner of the cubic mirror on one side of the cubic mirror, and set two plane mirrors and their reflecting surfaces facing the two adjacent corners of the corner on both sides of the cubic mirror. Place a calibrator on the side of any plane mirror away from the cubic mirror, thereby constructing the cubic mirror external right angle in-situ detection system.

[0042] S32. Use the interferometer to measure the included angle between two adjacent planes corresponding to the four edges of the cube mirror, thereby completing the in-situ measurement of the external right angle of the cube mirror.

[0043] In one embodiment of the present invention, step S3 includes the following steps:

[0044] S321. Adjust the position of the cubic mirror so that one corner of the cubic mirror points to the standard mirror of the interferometer, and find the four light spots returned by the two planes adjacent to the corner on the display of the interferometer.

[0045] S322. In the Align mode of the interferometer, adjust the pitch and torsional degrees of freedom of the cubic mirror so that the two brightest spots on the display are close to the central crosshair and are symmetrically distributed.

[0046] S323. In the View mode of the interferometer, adjust the focusing center of the interferometer until the fringes are clear and sharp, and adjust the position of the cubic mirror so that the fringes on the display are sparse.

[0047] S324. The angle between two adjacent planes corresponding to the edge is measured by the interferometer's own software.

[0048] S325. Repeat steps S321 to S324 until the included angle measurement results of two adjacent planes corresponding to the four edges of the cubic mirror are obtained.

[0049] In one embodiment of the present invention, in step S5, the formulated cubic mirror external right angle compensation machining scheme is as follows: based on the three-dimensional spatial positional relationship of the cubic mirror plane and the magnitude of the right angle deviation, the compensation cutting sequence of each plane of the cubic mirror is determined, the corresponding machining tool deflection angle is adjusted, and targeted compensation cutting is performed on the external right angle of a specific cubic mirror.

[0050] In one embodiment of the present invention, the in-situ detection and compensation processing method of the cubic mirror further includes the step: S6, by iterative compensation processing and changing the reference surface, so that all external right angle accuracies of the cubic mirror meet the index requirements.

[0051] In another aspect, the present invention also provides an in-situ detection system for a cubic mirror, which is used for in-situ detection and compensation processing of the cubic mirror. The in-situ detection system for the cubic mirror includes a machine tool turntable for placing and processing the cubic mirror, and two autocollimators placed with their optical axes facing two adjacent faces of the cubic mirror respectively. The autocollimators are used to measure the deflection angle between the outgoing light of the cubic mirror and the reflected light of the measured surface. The deflection angle is decomposed into components in two dimensions, X and Y.

[0052] Alternatively, the in-situ detection system for the cubic mirror includes a machine tool turntable for placing and processing the cubic mirror, an interferometer disposed on one side of the machine tool turntable with a standard mirror facing one corner of the cubic mirror, two plane mirrors disposed on both sides of the machine tool turntable with their reflecting surfaces facing two adjacent corners of the corner, and a calibrator disposed on the side of any plane mirror away from the cubic mirror, wherein the interferometer is used to measure the included angle between two adjacent planes of the corresponding prism of the cubic mirror, and the calibrator is a second interferometer or an autocollimator used to calibrate the parallel cavity composed of the two plane mirrors.

[0053] This invention proposes an in-situ detection and compensation machining method and an in-situ detection system for cubic mirrors. During the ultra-precision cutting machining stage of the cubic mirror, the influence of various machining error sources on the cutting accuracy is controlled through machining error pre-compensation, ensuring the ultra-precision cutting accuracy of the cubic mirror's outer right angles. An in-situ measurement system for the cubic mirror's outer right angles is established to measure the machined outer right angles. Based on the measurement data, the spatial dihedral angle of the cubic mirror's outer right angles is calculated, and a three-dimensional spatial position model of the cubic mirror's plane is reconstructed. Based on the deviation characteristics of the cubic mirror's outer right angles and the influence of machining error sources, a compensation machining scheme for the cubic mirror's outer right angles is formulated and fed back to the ultra-precision cutting machine tool for compensation cutting. Through iterative compensation machining and changing the reference surface, the accuracy of all outer right angles of the cubic mirror ultimately meets the requirements, solving the problems of poor compensation accuracy and low machining accuracy in the ultra-precision cutting machining process of cubic mirrors.

[0054] The present invention has the following beneficial effects:

[0055] (1) The in-situ detection and compensation machining method for cubic mirrors proposed in this invention directly measures the machining accuracy of the outer right angle of the cubic mirror on the machine tool, without destroying the original machining datum of the cubic mirror on the machine tool, thus avoiding installation errors introduced by repeated disassembly and installation. The machining datum of the cubic mirror coincides with the measurement datum, and the measurement results can be accurately fed back to the iterative machining process, improving the subsequent compensation machining accuracy.

[0056] (2) The in-situ detection and compensation processing method for cubic mirror proposed in this invention analyzes and pre-compensates the sources of processing errors before processing, performs in-situ measurement after processing, analyzes the external right angle deviation characteristics of the cubic mirror based on the in-situ measurement results, and then performs targeted compensation cutting on the processed surface of the cubic mirror. This realizes the iterative compensation processing process of "processing-measurement-reprocessing" closed-loop control, which can effectively control the influence of processing error sources on cutting accuracy and improve the iterative compensation effect of external right angle deviation of the cubic mirror.

[0057] (3) The in-situ detection and compensation processing method for cubic mirror proposed in this invention decouples the turntable rotation error from the measurement result through an improved algorithm, avoiding the complex and cumbersome turntable error calibration and improving the measurement accuracy of the in-situ measurement method.

[0058] (4) For the ultra-precision cutting of cubic mirrors, the present invention accurately feeds back the in-situ measurement of the outer right angle to the iterative processing process, and combined with the closed-loop compensation processing method, ensures the extremely high flatness and perpendicularity requirements of the cubic mirror, thereby improving processing efficiency and reducing processing costs.

[0059] The further objects and advantages of the invention will become fully apparent from the following description and accompanying drawings. Attached Figure Description

[0060] Figure 1 This is a flowchart of the in-situ detection and compensation processing method for the cubic mirror of the present invention.

[0061] Figure 2 This is a schematic diagram of the in-situ detection system for the cubic mirror described in this invention.

[0062] Figure 3 This is a flowchart illustrating the in-situ detection process of the external right angle of the cubic mirror according to the present invention.

[0063] Figure 4 This is another structural schematic diagram of the in-situ detection system for the cubic mirror described in this invention.

[0064] Explanation of reference numerals in the attached diagram: 1. Machine tool rotary table; 2. Cube mirror; 3. First autocollimator; 4. Second autocollimator; 5. Interferometer; 6. Plane mirror; 61. First plane mirror; 62. Second plane mirror; 7. Calibration instrument. Detailed Implementation

[0065] The following description is intended to disclose the present invention and enable those skilled in the art to implement it. The preferred embodiments described below are merely examples, and other obvious variations will occur to those skilled in the art. The basic principles of the invention defined in the following description can be applied to other embodiments, modifications, improvements, equivalents, and other technical solutions that do not depart from the spirit and scope of the invention.

[0066] Those skilled in the art should understand that, in the disclosure of this invention, the terms "vertical," "horizontal," "up," "down," "front," "back," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, the above terms should not be construed as limiting this invention.

[0067] It is understood that the term "a" should be understood as "at least one" or "one or more", that is, in one embodiment, the number of an element can be one, while in another embodiment, the number of the element can be multiple, and the term "a" should not be understood as a limitation on the number.

[0068] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection, an electrical connection, or a connection that allows for communication; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0069] like Figures 1 to 3 As shown, the specific process of the in-situ detection and compensation processing method for the cubic mirror according to a preferred embodiment of the present invention and the specific structure of the in-situ detection system are explained.

[0070] The in-situ measurement system is a device for measuring the external right angle accuracy of a cubic mirror during the ultra-precision machining stage. The ultra-precision compensation machining method ensures the machining accuracy of the external right angle of the cubic mirror. The technical solution of this invention, focusing on the machining, measurement, and compensation of the external right angle of a cubic mirror, is divided into the following six parts:

[0071] ① Machining Error Source Analysis and Pre-compensation. To ensure the extremely high flatness and perpendicularity accuracy requirements of the cubic mirror, before ultra-precision cutting, various potential machining error sources during the cutting process are analyzed, and their impact on the machining accuracy of the cubic mirror is controlled. For each machining error source in the ultra-precision cutting process, corresponding measurement methods are adopted for error calibration. Based on the way each machining error affects the machining accuracy of the cubic mirror's outer right angle, methods including but not limited to adjusting machine tool parameter settings and modifying the machining program are used to pre-compensate for the machining errors caused by each machining error source.

[0072] Specifically, the error sources in the cutting process include one or more of the following: machine tool error, machining process error, and inspection error. Specific error items include spindle error, thermal error, tool error, fixture error, elastic deformation error, operation error, installation error, and uncertainty error.

[0073] Taking spindle axial runout error as an example, it can be measured using a dial indicator in conjunction with a spindle inspection bar. The main steps are as follows: 1) Install the spindle inspection bar in the spindle taper hole; 2) Install the dial indicator on the machine tool rotary table, ensuring the dial indicator tip is perpendicular to the lower end of the inspection bar; 3) Rotate the spindle at a constant speed and observe the swing value of the indicator pointer. The maximum difference in the dial indicator readings is the spindle axial runout error; 4) Remove the inspection bar, rotate it 180 degrees, and reinstall it in the spindle taper hole. Repeat the above steps to perform another measurement; 5) Take the average of the two measurements as the measured value of the spindle axial runout. The pre-compensation method for spindle axial runout error mainly involves adjusting the relevant settings of the spindle bearings to minimize the impact of runout error on the cutting surface shape.

[0074] It should be understood that for other sources of machining error, the corresponding commonly used measurement methods in the field can be used for error calibration, and the machining error can be pre-compensated by adjusting the machine tool parameter settings, modifying the machining program, etc. This invention will not describe them in detail one by one.

[0075] ② Ultra-precision cutting. After pre-compensation for machining errors, cutting is performed according to the ultra-precision cutting process for cubic mirrors.

[0076] The basic process of ultra-precision machining of cubic mirrors is as follows:

[0077] Step 1: Select one face of the cubic mirror as the reference plane for machining, requiring the RMS (root mean square) of the reference plane to be better than 1 / 10λ (λ = 632.8nm); mount the cubic mirror on the machine tool rotary table, the mounting method including but not limited to vacuum chuck connection, bonding, bolt connection, etc.; Step 2: along Figure 2 Rotate the machine tool turntable in direction B as shown to align the first surface of the cubic mirror to be machined with the tool mounted on the machine tool spindle; start the machining program, and the tool moves along the X-axis of the machine tool to cut the first surface of the cubic mirror to be machined;

[0078] Step 3: After the cutting is completed, rotate the machine tool turntable 90° along direction B to process the other surface of the cubic mirror;

[0079] Step 4: Repeat Step 3 above until the cubic mirror has rotated one full circle and completed the cutting of the four surfaces to be processed.

[0080] It is worth mentioning that the cubic mirror has extremely high requirements for dimensional and geometrical accuracy. As a reference surface for cutting, its surface accuracy must not affect the cutting accuracy of other machined surfaces. RMS 1 / 10λ is the initial surface accuracy index of the reference surface, used to ensure that the final dimensions and geometrical accuracy of the remaining machined surfaces meet the tolerance requirements.

[0081] In addition, it is worth mentioning that only four faces can be cut in one clamping, and the remaining faces of the cubic mirror need to be clamped twice for cutting.

[0082] ③ In-situ measurement. A square mirror external right-angle in-situ measurement system is installed on an ultra-precision cutting machine tool, such as... Figure 2 As shown, the system consists of two autocollimators (including a first autocollimator 3 and a second autocollimator 4) and a machine tool turntable 1. The finished cubic mirror 2 remains in its original position on the machine tool turntable 1, and the two autocollimators are positioned with their optical axes facing the two adjacent surfaces of the cubic mirror 2, respectively. The autocollimators are used to measure the angle between the emitted light and the reflected light from the measured surface. This angle is decomposed into components in the X and Y directions, and the readings are obtained from the autocollimator readings.

[0083] The flowchart for measuring the external right angle of a cubic mirror in place is as follows: Figure 3 As shown, the in-situ measurement steps are as follows:

[0084] Step 1: In absolute measurement mode, adjust the two autocollimators in the X and Y dimensions respectively, so that the readings of the two autocollimators in the X and Y dimensions are close to zero;

[0085] Step 2: Adjust both autocollimators to relative measurement mode, fix the autocollimators and record the readings of the two autocollimators in the X and Y dimensions;

[0086] Step 3: Rotate the machine tool turntable 90° so that the two adjacent faces of the other outer right angle of the cubic mirror face the two autocollimators respectively, and record the readings of the two autocollimators in the X and Y dimensions;

[0087] Step 4: Repeatedly rotate the machine tool turntable 90° in the same direction, measure the other two external right angles of the cubic mirror, and record the readings of the two autocollimators in the X and Y dimensions.

[0088] It should be understood that the X and Y dimensions are two dimensions in an autocollimator, which are different from the X and Y axes of a machine tool rotary table.

[0089] In another embodiment of the present invention, an interferometer can also be used to construct an in-situ measurement system for the external right angle of a square mirror, specifically, as shown below. Figure 4As shown, the cubic mirror external right angle in-situ measurement system includes a machine tool turntable 1 for placing and processing the cubic mirror 2, an interferometer 5 disposed on one side of the machine tool turntable 1 with the standard mirror facing one corner of the cubic mirror 2, two plane mirrors 6 disposed on both sides of the machine tool turntable 1 with their reflecting surfaces facing the two adjacent corners of the corner, and a calibrator 7 disposed on the side of any plane mirror 6 away from the cubic mirror 2. The interferometer 5 is used to measure the included angle between two adjacent planes of the corresponding prism of the cubic mirror 2, and the calibrator 7 is a second interferometer or autocollimator used to calibrate the parallel cavity composed of the two plane mirrors.

[0090] Specifically, the two plane mirrors 6 include a first plane mirror 61 and a second plane mirror 62. In this specific embodiment, the calibrator 7 is disposed on the side of the second plane mirror 62 that is away from the cubic mirror 2.

[0091] Correspondingly, the steps for measuring the external right angle of the cube mirror using the interferometer 5 are as follows:

[0092] Step 1: Adjust the position of the cubic mirror so that one corner of the cubic mirror points to the standard mirror of the interferometer, and find the four light spots returned by the two planes adjacent to the corner on the display of the interferometer.

[0093] Step 2: In alignment mode, adjust the pitch and torsional degrees of freedom of the cube mirror so that the two brightest points on the display are close to the central crosshair and are symmetrically distributed.

[0094] Step 3: In the field of view mode, adjust the focusing center of the interferometer until the fringes are clear and sharp, and adjust the position of the cubic mirror to make the fringes on the display sparse.

[0095] Step 4: Measure the included angle between the two adjacent planes corresponding to the edge using the interferometer's own software;

[0096] Step 5: Repeat Step 1 to Step 5 until the included angle measurement results of two adjacent planes corresponding to the four edges of the cube mirror are obtained.

[0097] It should be understood that existing autocollimator measurement methods include single autocollimator measurement and dual autocollimator measurement: the measurement results of a single autocollimator are coupled with turntable rotation errors, and its measurement accuracy is heavily dependent on the rotational accuracy of the turntable. Commercial goniometers typically integrate the autocollimator and turntable into one unit, improving measurement accuracy by calibrating the turntable error. Dual autocollimator measurement requires a complex calibration process to orthogonalize the optical axes of the two autocollimators, and the calibration accuracy directly affects the measurement accuracy and uncertainty. The measurement steps of the exterior angle interferometry method require adjusting the pitch and torsional degrees of freedom of the cubic mirror, which cannot be adjusted for a cubic mirror clamped on a machine tool.

[0098] In other words, the existing autocollimator measurement method, if directly combined with the machine tool turntable for measurement, has a complex and cumbersome calibration process and low measurement accuracy. The existing exterior angle interferometry method cannot be combined with the machine tool for in-situ measurement. Therefore, the cubic mirror exterior right angle in-situ measurement system built in this invention is not obtained by simply combining the existing autocollimator measurement method or the existing exterior angle interferometry method with the machine tool turntable, but rather is a new in-situ measurement system.

[0099] The main purpose of in-situ measurement in this invention is to eliminate the installation error introduced by secondary clamping in order to improve the accuracy of compensation cutting. Under the premise of in-situ measurement, the technical solution of this invention does not require a complicated calibration process, the measurement results are decoupled from the turntable error, and the measurement method is highly accurate and simple to implement.

[0100] ④ Solving the spatial dihedral angle and reconstructing the three-dimensional spatial position model of the cube mirror. Based on in-situ measurement data, the spatial dihedral angle deviation of the external right angle of the cube mirror is calculated. The calculation steps are as follows:

[0101] nnbStep1: Ignoring the Y-direction deflection component, calculate the out-of-plane right angle deviation of the cubic mirror using the following formula:

[0102] Δθ i =a xi -b xi +Δ0 (1)

[0103] In equation (1), Δθ i For the right-angle deviation outside the reference plane, a xi b is the correction value for the X-direction reading of the first autocollimator 3. xi Δ0 is the correction value for the X-direction reading of the second autocollimator 4, and Δ0 is the angular deviation between the ideal orthogonal optical axes of the two autocollimators on the measurement reference plane. Here, i represents the outer right angle number, with a value range of [1,4], i∈N.

[0104] Step 2: Combining the Y-direction deflection component, calculate the normal vector of the measured plane of the cubic mirror and the spatial dihedral angle deviation of the outer right angle. Use 3D modeling software, including but not limited to UG and SolidWorks, to construct a spatial 3D model of the measured plane of the cubic mirror. The formula for calculating the spatial dihedral angle deviation of the outer right angle of the cubic mirror is as follows:

[0105] Δφ i =arccos(Δθ) i +Δ i (2)

[0106] In equation (2), ΔΦ i Δθ is the spatial dihedral angle deviation of the outer right angle of the cubic mirror. i The right-angle deviation outside the reference plane, Δ i This is the deviation correction value. Where i represents the outer right angle number, and its value ranges from [1,4], i∈N.

[0107] It should be understood that, based on the above description of the steps, the cube mirror external right angle deviation algorithm of the present invention can be summarized into two steps: Step 1, calculate the cube mirror external right angle deviation without considering the Y-direction deflection component; Step 2, correct the cube mirror external right angle deviation value by combining the Y-direction deflection component. The purpose of dividing the present invention into two steps is mainly to make the algorithm flow more organized and clear.

[0108] ⑤ Ultra-precision compensation machining. Based on the spatial three-dimensional model of the measured plane of the cubic mirror, analyze the characteristics of the external right angle deviation of the cubic mirror. Combined with the influencing factors such as machining error sources, analyze the causes of the external right angle deviation. Prioritize the two surfaces with the worst parallelism accuracy for compensation, formulate an external right angle compensation machining plan, and perform targeted compensation cutting on the machined surface of the cubic mirror.

[0109] It is worth mentioning that the cubic mirror external right angle compensation machining scheme is a direct compensation cutting method formulated for the existing external right angle deviation characteristics. Based on the existing three-dimensional spatial position relationship of the cubic mirror plane and the magnitude of the right angle deviation, the compensation cutting sequence of each plane is determined, the corresponding machining tool deflection angle is adjusted, and targeted compensation cutting is performed on the specific cubic mirror external right angle.

[0110] Understandably, if the external right angle accuracy measurement results do not meet the requirements, an external right angle compensation machining scheme will be formulated based on the external right angle deviation characteristics and the influence of machining error sources, and fed back to the ultra-precision cutting machine tool for compensation cutting machining; if the measurement results meet the requirements, the machining reference surface will be replaced.

[0111] ⑥ Replace the machining reference surface. After the external right angle accuracy of the cubic mirror under the current reference surface meets the requirements, take one of the machined surfaces as the new reference surface and repeat the above steps to machine the other two surfaces until all external right angle accuracy of the cubic mirror meets the requirements.

[0112] It is worth mentioning that, in this specific embodiment of the present invention, the required index is that the perpendicularity between any two adjacent planes is better than 2 arcseconds. It should be understood that, in some embodiments of the present invention, corresponding index requirements can be set according to specific needs, and the present invention does not impose any limitations on this.

[0113] Compared with the traditional method of measuring the external right angle of a cubic mirror, the present invention has the following advantages:

[0114] (1) Alignment of Machining and Measurement References: Existing methods for measuring the external right angle of a cubic mirror, including coordinate measuring machine (CMM), autocollimator, and external angle interferometry, are all off-site measurement methods. These methods result in the machining and measurement references of the cubic mirror not aligning, making it impossible to accurately feed the measurement results back into the iterative machining process. The on-site measurement method for the external right angle of a cubic mirror proposed in this invention directly measures the machining accuracy of the external right angle on the machine tool, without disrupting the original machining reference of the cubic mirror on the machine tool, thus avoiding installation errors introduced by repeated disassembly and reassembly. With the machining and measurement references aligning, the measurement results can be accurately fed back into the iterative machining process, improving the accuracy of subsequent compensation machining.

[0115] (2) Closed-loop compensation machining: Existing ultra-precision cutting technology for cubic mirrors requires precise process parameter control and adjustment, necessitating repeated cutting of each plane of the cubic mirror, making it impossible to specifically compensate for external right-angle deviations. The cubic mirror external right-angle compensation machining method proposed in this invention analyzes and pre-compensates machining error sources before machining, performs in-situ measurements after machining, analyzes the characteristics of external right-angle deviations of the cubic mirror based on the in-situ measurement results, and then performs targeted compensation cutting on the machined surface of the cubic mirror. This realizes an iterative compensation machining process with closed-loop control of "machining-measurement-remachining", which can effectively control the influence of machining error sources on cutting accuracy and improve the iterative compensation effect of external right-angle deviations of the cubic mirror.

[0116] (3) Measurement results are not affected by turntable rotation error: The measurement results of the autocollimator measurement method are coupled with turntable rotation error, which affects the accuracy of the final measurement results. The cubic mirror external right angle in-situ measurement method proposed in this invention decouples the turntable rotation error from the measurement results through an improved algorithm, avoiding the complex and cumbersome turntable error calibration and improving the measurement accuracy of the in-situ measurement method.

[0117] (4) For the ultra-precision cutting of cubic mirrors, the present invention accurately feeds back the in-situ measurement of the outer right angle to the iterative processing process, and combined with the closed-loop compensation processing method, ensures the extremely high flatness and perpendicularity requirements of the cubic mirror, thereby improving processing efficiency and reducing processing costs.

[0118] In summary, this invention proposes an in-situ measurement and ultra-precision compensation machining method for the external right angle of a cubic mirror. During the ultra-precision cutting stage of the cubic mirror, an in-situ measurement system is established to measure the machining accuracy of the external right angle. An ultra-precision compensation machining method is then used in conjunction with the in-situ measurement results to perform targeted compensation machining on the cubic mirror. This invention solves the problem of poor compensation accuracy and low machining precision caused by off-site measurement in the ultra-precision cutting machining of cubic mirrors, ensuring extremely high flatness and perpendicularity accuracy requirements for the cubic mirror.

[0119] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0120] The above embodiments merely illustrate preferred implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention should be determined by the appended claims.

Claims

1. A method for in-situ detection and compensation processing of a cubic mirror, characterized in that... The steps include: S1. Analyze the various machining error sources existing in the ultra-precision cutting process, and pre-compensate the machining errors caused by each machining error source according to the influence of each machining error source on the machining accuracy of the outer right angle of the cubic mirror. S2. After pre-compensation for machining errors, the cubic mirror is subjected to ultra-precision cutting. S3. Construct an in-situ detection system for the external right angle of a cubic mirror to measure the external right angle of the finished cubic mirror in place. S4. Based on the in-situ measurement data of the external right angle of the cube mirror, calculate the spatial dihedral angle of the external right angle of the cube mirror and reconstruct the three-dimensional spatial position model of the cube mirror plane. S5. Based on the three-dimensional spatial position model of the cubic mirror plane, analyze the characteristics of the external right angle deviation of the cubic mirror, and combine the influence of the machining error source to formulate a machining scheme for external right angle compensation of the cubic mirror, and perform targeted compensation cutting on the machined surface of the cubic mirror. Wherein: step S3 includes the following steps: S31. Place the cubic mirror on the machine tool turntable, and place two autocollimators with their optical axes facing the two adjacent faces of the cubic mirror respectively, so as to build the cubic mirror external right angle in-situ detection system. S32. Use two autocollimators to measure the angle between the outgoing light from the cube mirror and the reflected light from the measured surface. The angle is decomposed into components in the X and Y directions to complete the in-situ measurement of the external right angle of the cube mirror. Step S32 includes the following steps: S321. In absolute measurement mode, adjust the two autocollimators in the X and Y dimensions respectively, so that the readings of the two autocollimators in the X and Y dimensions are close to zero. S322. Adjust the two autocollimators to relative measurement mode, fix the autocollimators and record the readings of the two autocollimators in the X and Y dimensions; S323. Rotate the machine tool turntable by 90° so that the two adjacent faces of the other outer right angle of the cubic mirror face the two autocollimators respectively, and record the readings of the two autocollimators in the X and Y dimensions. S324. Repeat the process of rotating the machine tool turntable by 90° in the same direction to measure the other two external right angles of the cubic mirror, and record the readings of the two autocollimators in the X and Y dimensions. Step S4 includes the following steps: S41. Ignoring the Y-direction deflection component, calculate the out-of-plane right-angle deviation of the cubic mirror using the following formula: (1) In equation (1), Δ θ i For right angle deviation outside the reference plane, a xi and b xi These are the correction values ​​for the X-direction readings of the two autocollimators, respectively, and Δ0 is the angular deviation between the ideal orthogonal optical axes of the two autocollimators on the measurement reference plane; where, i This represents the outer right angle number, with a value range of [1, 4]. i ∈N; S42. Combining the Y-direction deflection component, calculate the normal vector of the measured plane of the cubic mirror and the spatial dihedral angle deviation of the outer right angle. Use 3D modeling software to construct a spatial 3D model of the measured plane of the cubic mirror. The formula for calculating the spatial dihedral angle deviation of the outer right angle of the cubic mirror is as follows: (2) In equation (2), Δ Φ i Δ is the spatial dihedral angle deviation of the outer right angle of the cubic mirror. θ i Δ represents the right-angle deviation outside the reference plane. i This is the deviation correction value; where, i This represents the outer right angle number, with a value range of [1, 4]. i ∈N; In step S5, the formulated machining scheme for the external right angle compensation of the cubic mirror is as follows: based on the three-dimensional spatial positional relationship of the cubic mirror plane and the magnitude of the right angle deviation, the compensation cutting sequence of each plane of the cubic mirror is determined, the corresponding machining tool deflection angle is adjusted, and targeted compensation cutting is performed on the external right angle of the specific cubic mirror.

2. The method for in-situ detection and compensation processing of a cubic mirror according to claim 1, characterized in that, In step S1, the error sources include one or more of machine tool errors, machining process errors, and detection errors. The machining errors are pre-compensated by adjusting the machine tool parameter settings or modifying the machining program.

3. The method for in-situ detection and compensation processing of a cubic mirror according to claim 1, characterized in that, Step S2 includes the following steps: S21. Select one face of the cubic mirror as the reference surface for cutting, and install the cubic mirror on the machine tool turntable, wherein the RMS of the reference surface is better than 1 / 10 λ, λ = 632.8 nm; S22. Rotate the machine tool turntable to align the first surface of the cubic mirror to be machined with the tool mounted on the machine tool spindle; start the machining program, and the tool moves along the machine tool to cut the first surface of the cubic mirror to be machined; S23. After the cutting is completed, rotate the machine tool turntable 90° to process another surface to be processed; S24. Repeat step S3 until the cubic mirror rotates one full revolution to complete the cutting of the four surfaces to be machined.

4. The method for in-situ detection and compensation processing of a cubic mirror according to claim 3, characterized in that, In step S21, the cubic mirror is mounted on the machine tool turntable by any of the following methods: vacuum suction cup connection, adhesive bonding, or bolt connection.

5. The method for in-situ detection and compensation processing of a cubic mirror according to claim 1, characterized in that, In step S42, the 3D modeling software used is either UG or SolidWorks.

6. The method for in-situ detection and compensation processing of a cubic mirror according to any one of claims 1 to 5, characterized in that, It also includes the following steps: S6, through iterative compensation processing and replacement of the reference surface, to ensure that all external right angles of the cubic mirror meet the required specifications.

7. An in-situ detection system for a cubic mirror, used for in-situ detection and compensation processing of a cubic mirror according to any one of claims 1 to 5, characterized in that, The in-situ detection system for the cubic mirror includes a machine tool turntable for placing and processing the cubic mirror, and two autocollimators placed with their optical axes facing two adjacent faces of the cubic mirror respectively. The autocollimators are used to measure the angle between the outgoing light from the cubic mirror and the reflected light from the measured surface. The angle is decomposed into components in two dimensions, X and Y. Alternatively, the in-situ detection system for the cubic mirror includes a machine tool turntable for placing and processing the cubic mirror, an interferometer disposed on one side of the machine tool turntable with a standard mirror facing one corner of the cubic mirror, two plane mirrors disposed on both sides of the machine tool turntable with their reflecting surfaces facing two adjacent corners of the corner, and a calibrator disposed on the side of any plane mirror away from the cubic mirror, wherein the interferometer is used to measure the included angle between two adjacent planes of the corresponding prism of the cubic mirror, and the calibrator is a second interferometer or an autocollimator used to calibrate the parallel cavity composed of the two plane mirrors.

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