CN114353695B - Full-band aberration detection system and detection method for large-gradient convex optical free-form surface - Google Patents
Full-band aberration detection system and detection method for large-gradient convex optical free-form surface Download PDFInfo
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Abstract
The invention discloses a full-band aberration detection system and a detection method for a large-steepness convex optical free-form surface, relates to the technical field of optical free-form surface detection, and aims to provide a full-band aberration detection system and a full-band aberration detection method for a large-steepness convex optical free-form surface so as to solve the problem that the dynamic range and the detection precision cannot be compatible in the full-band aberration detection of the large-steepness convex optical free-form surface and further solve the detection problem of the large-steepness convex optical free-form surface; according to the invention, the full-band aberration detection of the large-gradient convex optical free-form surface is finally carried out by adopting a Zernike polynomial fitting mode through a computer processing system, so that the defects of the existing full-band aberration detection method of the large-gradient convex optical free-form surface are overcome.
Description
Technical Field
The invention relates to the technical field of optical free-form surface detection, in particular to a full-band aberration detection system and a full-band aberration detection method for a large-gradient convex optical free-form surface.
Background
The optical free-form surface has strong capability of correcting aberration and optimizing a system structure, and gradually becomes an indispensable key optical element in the fields of national defense, aerospace, military and the like, and the application range and the production development speed of the optical free-form surface become one of important marks for measuring the state technological level. However, the requirement of high precision and high performance of the optical free-form surface increases the difficulty of processing and detecting the optical free-form surface, especially the difficulty of detection in the processing and manufacturing process, which is far more complicated and difficult than the processing and detection of a spherical mirror: the successful manufacture of the optical key element of the high-precision free-form surface does not depend on the precision, advanced optical design and processing technology of a numerical control machine tool, but also depends on the comprehensive consideration of the free-form surface optical detection technology, huge and complex data calculation and verification of a large amount of test data, so that the processing and detection quality of the optical free-form surface can be improved; in addition, the optical free-form surface is a non-axisymmetric, irregular and randomly-structured surface, the shape is complex, the precision requirement is high, and no definite reference surface exists, so that the problem of whether the optimal matching between the reference surface and the measuring surface of the free-form surface can be realized is the key of free-form surface detection.
The requirement for high precision and high performance of the optical free-form surface increases the difficulty of processing and detecting the optical free-form surface, which is far more complicated and difficult than the processing and detecting of a spherical mirror. The detection in particular in the grinding stage and in the transition stage from grinding to polishing has more limitations: insufficient measurement precision, immature technology, overlong detection period, undersized dynamic range, incapability of carrying out full-aperture in-situ detection and the like. As the prior art: (1) The three-coordinate measuring machine adopts a point-by-point scanning mode to carry out measurement, the measuring speed is low, and the full-field surface shape data of the element to be measured cannot be obtained at one time; the contourgraph can only measure the free-form surface with small deviation degree between the surface shape and the spherical base or the aspheric base (the deviation between the local gradient and the global gradient is less than 5 degrees). (2) The swing arm type contour scanning method also faces the problems of low measurement efficiency, errors in the whole surface shape splicing process and the like, only off-axis aspheric surface type free-form surfaces can be measured at present, and researches on high-freedom-degree free-form surfaces which are complex in measurement shape, large in local gradient change and difficult in surface shape mathematical expression are not reported. (3) The shack-Hartmann wavefront detection method has the advantages of high measurement speed, high measurement precision, large dynamic measurement range and the like, but is influenced by the limitation of the size of a lens and the overlapping of light spots during the measurement of a large-gradient free-form surface. (4) problems faced by computational holography are: the one-to-one compensation measurement mode causes poor measurement universality, so that the detection cost is high; for curved surface elements with large gradients, the CGH used as a compensator needs to realize the output of large gradient wave surface through a diffraction structure with high density, so the groove density of the computed hologram is limited by the current microstructure processing technology level. (5) the partial zero compensation technique faces the problems that: the more the test optical path deviates from the zero-position condition optical path, the larger the return error is, which brings great difficulty to the high-precision recovery of the detected surface shape; in the process of detecting the free-form surface by a partial zero compensation method, the alignment of the to-be-detected piece is difficult, and the surface shape detection precision is influenced; the non-rotational symmetry of the free-form surface can cause the non-rotational symmetric deformation of the interference pattern, and the surface shape recovery precision is influenced. At present, the more complex free-form surface with large gradient change has fewer successful application cases. (6) When the inclined wave surface technology is used for measuring the large-caliber free curved surface, a large-caliber standard compensation lens is needed, the large-caliber standard compensation lens is very difficult to process, and the measuring caliber of the system is limited.
In summary, the precise detection of the free-form surface shape is still a major obstacle, some key scientific problems and technical bottlenecks are still not well solved, and a detection technology for uniform forming is still unavailable so far. Therefore, optical free-form surface processing and detection technology becomes the most important factor restricting the application and development thereof.
In a patent (ZL 201911155752.4) which has been granted by the applicant, although some of the above problems are solved, the problem of high-precision detection of the full frequency band of a free-form surface with a large steepness and a large convex surface class is still not solved. The invention aims to solve the problem of detection of a large-steepness large-convex-surface optical free-form surface, combines a computer-assisted reverse Hartmann detection method with more accurate high-frequency-band aberration measurement and a transverse translation difference phase recovery method with more accurate low-frequency-band aberration measurement, and performs full-band aberration detection of the large-steepness convex-surface optical free-form surface in a Zernike polynomial fitting manner, so as to make up the defects of the conventional full-band aberration detection method of the large-steepness convex-surface optical free-form surface.
Disclosure of Invention
The invention aims to provide a system and a method for detecting full-band aberration of a large-gradient convex optical free-form surface, which are used for solving the problem that the dynamic range and the detection precision cannot be compatible in the full-band aberration detection of the large-gradient convex optical free-form surface and the problem of detection of the optical free-form surface.
The full-band aberration detection system for the large-gradient convex optical free-form surface comprises a middle-low frequency band aberration detection system, a high-frequency band aberration detection system, a computer processing system and a light path clamping and adjusting system; the optical path clamping and adjusting system is used for adjusting the middle-low frequency band aberration detection system and the high frequency band aberration detection system; firstly, adjusting the high-frequency-band aberration detection system, and then adjusting the middle-low-frequency-band aberration detection system according to the adjusted convex free-form surface to be detected;
in the assembling and adjusting process, the light-emitting screen, the third camera and the convex free-form surface to be measured are aligned, so that the optical axis of the third camera is superposed with the optical axis of the convex free-form surface to be measured, the optical axis of the convex free-form surface to be measured is parallel to the screen of the light-emitting screen, and the third camera is focused on the surface of the convex free-form surface to be measured;
the middle and low frequency range aberration detection system comprises a middle and low frequency information acquisition system and a pupil image monitoring system;
the medium and low frequency information acquisition system comprises a laser, a collimation and beam expansion system, a beam splitter, an imaging mirror and a second camera;
the high-frequency-band aberration detection system comprises a convex free-form surface to be detected, a light-emitting screen and a third camera;
the light beam emitted by the laser is expanded into parallel light beams by the collimation and expansion system, and the parallel light beams are reflected and transmitted by the beam splitter; the transmitted light passes through the pupil image monitoring system, and the wavefront returned by the pupil image monitoring system enters the medium and low frequency information acquisition system again and is imaged at a second camera through the imaging mirror, so that medium and low frequency band surface shape information of the convex free-form surface to be detected is obtained;
the light beam collected by the medium and low frequency information collecting system is imaged at a first camera through a pupil image monitoring system, and a laser galvanometer in the pupil image monitoring system is adjusted through analyzing the light spot image to enable the reflected light beam to be parallel;
the light rays emitted by the light-emitting screen are reflected by the convex free-form surface to be detected and then received by a third camera, and the third camera processes the obtained image by adopting a computer processing system to obtain high-frequency section surface shape information of the convex free-form surface to be detected;
the computer processing system carries out full-band fusion detection on the high-band surface shape information of the to-be-detected convex free-form surface obtained by the calibrated high-band aberration detection system and the low-band surface shape information of the to-be-detected convex free-form surface obtained by the detection low-band aberration detection system; namely: decomposing the data through a Zernike polynomial fitting mode, arranging the Zernike polynomials from low to high according to orders, setting fusion weights according to the variance of the measurement prior precision of different orders of aberration by adopting a statistical data fusion method based on measurement error prior and combining the statistical data fusion method based on the measurement error prior and according to a TTDPR method with high measurement precision of middle and low frequency band aberration and a SCOTS method with high measurement precision of high frequency band aberration, and finally obtaining the full-band surface shape information of the convex free-form surface to be measured.
The full-band aberration detection method for the large-gradient convex optical free-form surface is realized by the following steps:
step 1, constructing and adjusting a high-frequency-band aberration detection system and a medium-low frequency-band aberration detection system;
step 2, acquiring image information of the convex free-form surface to be detected by adopting the adjusted high-frequency aberration detection system and the middle-low frequency aberration detection system respectively;
and 3, respectively processing the high-frequency-band aberration and the medium-low frequency-band aberration of the acquired image information by adopting a computer to obtain the surface shape information of the convex free-form surface to be detected.
The invention has the beneficial effects that: the invention breaks through the traditional aspheric surface detection method, adopts the full-band aberration detection method for cooperatively measuring the large-gradient convex optical free-form surface by adopting the Transverse Translation Difference Phase Recovery (TTDPR) based on the Phase recovery algorithm (PR) and the Sub-aperture Stitching Algorithm (SAS) and the computer-aided inverse Hartmann method, explores a new fusion measurement method, establishes a theoretical model and develops numerical simulation research, realizes the experimental verification of a detection system for cooperatively measuring the optical free-form surface based on two measurement methods, solves the technical problem of high-precision detection of the full-band large-gradient convex optical free-form surface, and guides the surface shape processing of a free-form surface optical element in the grinding stage; the method has the advantages that the surface shape residual error is removed as much as possible in the fine grinding stage, the processing convergence efficiency of the optical free-form surface is improved, the technical support is finally provided for the processing and detection of the optical free-form surface with high precision and high performance, and the method has very important scientific significance. In addition, the scholars in China draw the national requirements, and the processed high-precision and high-performance optical free-form surface elements are widely applied to the fields of aerospace, military affairs and the like, so that a good foundation is laid for improving the international status of processing and detecting the precision optical instruments in China.
The invention has higher precision for measuring the middle and low order aberration according to TTDPR, and lower precision for measuring the high order aberration. The computer-aided reverse Hartmann measurement method has higher precision for the measurement of high-order aberration and lower precision for low-order measurement. The invention solves the detection problem in the prior art, not only increases the detection dynamic range, but also ensures the detection precision of high-order aberration, and can carry out full-order aberration detection.
The invention combines a computer-assisted reverse Hartmann detection method with more accurate high-frequency band aberration measurement with a transverse translation difference phase recovery method with more accurate medium-low frequency band aberration measurement, and performs full-band aberration detection on the large-steepness convex optical free-form surface in a Zernike polynomial fitting mode, thereby overcoming the defects of the existing full-band aberration detection method of the large-steepness convex optical free-form surface.
The detection system provided by the invention has the advantages of simple structure and low manufacturing cost, solves the problem of measuring the wavefront aberration of the surface shape of the large-gradient convex optical free-form surface, has high measurement precision, large dynamic range of measurement slope and high spatial resolution, and can be used for measuring the large numerical slope which cannot be measured by an interferometer and Hartmann detection.
Drawings
FIG. 1 is a schematic diagram of the full-band aberration detection method for a large-steepness convex optical free-form surface according to the present invention;
FIG. 2 is a schematic diagram of a full-band aberration detection system for a large-steepness convex optical free-form surface;
fig. 3 is a schematic diagram of a hardware structure in a large-steepness convex optical free-form surface full-band aberration detection system.
In the figure: 1. the device comprises a laser, 2, a collimation and beam expansion system, 3, a beam splitter, 4, a beam splitting prism, 5, an adjustable aperture diaphragm, 6, a laser galvanometer, 7, a collimation and beam contraction system, 8, a first camera, 9, an imaging mirror, 10, a second camera, 11, a convex free-form surface to be measured, 12, a light-emitting screen, 13, a third camera, 14, a pinhole, 15, a camera lens, 16, a target surface, 17, a mounting plate, 18 and a Y-direction guide rail, 19 and a Z-direction guide rail, 20, a tooling part, 21, an X-axis, Y-axis and Z-axis rotating table, 22, an air floatation vibration isolation platform, M1, a high-precision small displacement table, M2 and five-degree-of-freedom displacement tables, D1, an adjusting frame, D2, a deflection and pitching two-dimensional adjusting frames.
Detailed Description
In a first embodiment, the present embodiment is described with reference to fig. 1 to 3, and a high-steepness convex optical free-form surface full-band aberration detection system includes a medium-low frequency aberration detection system A1, a high-band aberration detection system A2, a computer processing system A3, and an optical path clamping and adjusting system A4;
the medium and low frequency aberration detection system A1 comprises a medium and low frequency information acquisition system A11 and a pupil image monitoring system A12.
In the medium-low frequency information acquisition system a11, a thin beam emitted from the He-Ne laser 1 is expanded into a wide beam of parallel light (about 20 mm) by the collimation and expansion system 2, and the parallel light is transmitted forward to the beam splitter 3 and is divided into two paths of reflected light and transmitted light. One path of transmitted light propagates forward to the pupil image monitoring system A12, and the wavefront returning through the pupil image monitoring system A12 reenters the medium and low frequency information acquisition system A11 and is imaged at the camera 10 through the imaging mirror 9. The laser 1 is placed on a mini-adjustable frame D1 (four-dimensional compound adjustable frame), and the mini-adjustable frame D1 can provide the laser 1 with angular degrees of freedom in two directions of pitching and yawing. The laser 1 is adjusted back and forth, and the emergent light rays are made parallel light (the quality of the light beams is measured by using a shearing interferometer) by precisely adjusting the adjusting frame D1. The second camera 10 is fixed on the high-precision small displacement table M2 through a switching element, the switching element is connected with the second camera 10 and the five-degree-of-freedom displacement table M2 through screws, and fine adjustment of the pose of the second camera 10 can be achieved through adjusting the prestress of the screws. The five-degree-of-freedom displacement table M2 is moved back and forth, focus searching and defocusing image acquisition can be achieved in a large range, the acquired in-focus and defocusing images are sent to a computer processing TTDPR program, and the surface shape of the free curved surface to be measured is obtained through solving.
The pupil image monitoring system A12 is composed of a beam splitting prism 4, an adjustable aperture diaphragm 5, a laser galvanometer 6, a collimation and beam reduction optical system 7 and a first camera 8. Parallel light emitted from the medium-low frequency aberration detection system A1 enters the high-precision two-dimensional laser galvanometer 6 after passing through the beam splitter prism 4, light beams emitted from the high-precision two-dimensional laser galvanometer 6 are reflected by the surface of the convex free-form surface 11 to be detected and then return to the two-dimensional laser galvanometer 6, the light beams enter the beam splitter prism for splitting through the adjustable aperture diaphragm 5, one path of the light beams returns as original, the other path of the light beams enters the collimation and beam reduction optical system 7 and is imaged at the first camera 8, and the laser galvanometer is finely adjusted through image analysis, so that reflected light beams are parallel as much as possible. The collimating and beam-reducing optical system 7 is fixed on the deflection and pitching two-dimensional adjusting frame D2 through threaded connection, the first camera 8 performs high-precision light spot analysis by adopting a large pixel number and a small pixel size to realize the collimation of a light path, and the first camera 8 is fixed on the five-degree-of-freedom displacement table M1 through the adapter plate to conveniently adjust the light path.
The high-frequency-band aberration detection system A2 comprises a convex free-form surface 11 to be detected, a luminescent screen 12 and a third camera 13; the light emitted by the light-emitting screen 12 is received by the camera 13 through the reflector of the convex free-form surface 11 to be measured, and the third camera 13 processes the obtained image by the computer to obtain the surface shape information of the convex free-form surface 11 to be measured.
In this embodiment, since the difficulty of the high-band aberration detection system A2 lies in the calibration of the system, the high-band aberration detection system A2 with the large-steepness convex free-form surface is installed and adjusted first, and then the low-and-medium-frequency aberration detection system A1 is installed and adjusted according to the adjusted measured convex free-form surface 11. The specific implementation processes of the high-frequency-band aberration detection system A2 of the large-steepness convex free-form surface and the low-frequency aberration detection system A1 of the large-steepness convex free-form surface are explained according to the sequence of installation and adjustment:
the high-frequency aberration detection system A2 of the large-gradient convex free-form surface uses a luminescent screen as a light source, a phase shift fringe pattern with light intensity coding is displayed on the luminescent screen 12, and the phase shift fringe pattern passes through the convex free-form surface 11 to be detected and then is projected onto a corresponding camera focal plane 16 through a camera pinhole 14, so that the position of corresponding light is obtained, the wavefront slope is calculated according to the geometric relation of an optical system, the wavefront surface shape is reconstructed, and the wavefront aberration is calculated.
Due to the off-axis configuration in the detection system, it has high requirements for the calibration of the system geometry, so the process of calibration by the calculation-assisted optimization module has specific processes in the issued patent (ZL 201911155752.4): 1. constructing an experimental system for detecting the aberration of the middle and high frequency bands, and performing pre-calibration on geometrical parameters of the system; 2. establishing a system model in the optical track tracking software; 3. obtaining a wavefront aberration W1 in a reverse Hartmann measurement system; 4. optimizing geometrical parameters of the system; 5. performing ray tracing in the system model to obtain updated wavefront aberration W2; 6. fitting W1 and W2 by using orthogonal polynomials, and updating the target function; 7. and if the target function is smaller than the threshold epsilon, outputting the measured surface shape error Wsurf, otherwise, continuously optimizing the geometric parameters of the system, and repeating the steps 4 to 7.
The specific installation and adjustment process of the high-frequency-band aberration detection system A2 with the large-gradient convex free-form surface is as follows:
first, a set of horizontal and vertical sinusoidal phase-shifted fringe patterns is generated on the luminescent screen 12;
since the corresponding relationship between the pixel position on the luminescent screen 12 and the position of the convex free-form surface 11 to be measured illuminated by the luminescent screen needs to be determined, the pixel position on the screen needs to be encoded by the light intensity, and a sine stripe pattern is selected for display. The number of pixels of one period of the sine stripes is selected according to the screen size and the resolution of the luminescent screen 12, and the actual size (unit millimeter) corresponding to the stripes of one period is determined. By using the phase shift technology, the phase shift step number N (adopting four-step phase shift) of the phase shift fringe is selected, and the phase shift fringe pattern modulated by the light intensity is obtained by using Matlab programming.
Secondly, collimating and calibrating a system consisting of the luminescent screen 12, the third camera 13 and the convex free-form surface 11 to be measured to obtain the spatial coordinate positions of the luminescent screen and the third camera;
because this patent is for solving big steepness convex surface free-form surface shape detection problem, and is different with luminescent screen 12 and third camera 13 in the patent of having granted (ZL 201911155752.4) and the convex surface free-form surface position relation that awaits measuring, leads to the calibration installation and transfers the degree of difficulty and increase.
The third camera 13 is composed of a focal plane 16, a camera lens 15 and a pinhole 14, the pinhole 14 is installed outside the lens close to the CCD camera to eliminate the effect of pupil aberration on the system (the light rays of different fields will pass through the center of the adjustable diaphragm of the lens, because of the pupil aberration, the chief ray of each field will not converge at a point at the pupil entrance position, which will affect the calculation of slope), the light-emitting screen 12, the third camera 13 with the external pinhole and the convex free-form surface 11 to be measured are collimated, so that the optical axes of the third camera 13 and the convex free-form surface 11 to be measured coincide, and the optical axis of the convex free-form surface 11 to be measured is parallel to the screen of the light-emitting screen 12 (the position is that the convex free-form surface to be measured is perpendicular to the light-emitting screen 12). The third camera 13 is focused on the surface of the convex free-form surface 11 to be measured. On the basis of preliminary calibration of structural parameters of a measurement system, a computer-aided ray tracing measurement method is utilized to carry out reverse optimization on system element deviation and inclination parameters including a surface to be measured, and further effective correction of calibration errors is realized. And calibrating and measuring to obtain the distance between the luminescent screen 12, the pinhole 14 and the convex free-form surface 11 to be measured.
Thirdly, a phase shift fringe pattern displayed on the luminescent screen 12 deflected by the convex free-form surface 11 to be detected is photographed, and a group of horizontal and vertical phase shift fringe patterns are photographed as reference after the convex free-form surface 11 to be detected is removed;
the light-emitting screen 12 displays a set of phase-shift fringe patterns one after another, and the third camera 13 performs shooting in synchronization. And removing the convex free-form surface 11 to be measured, and then shooting a group of horizontal and vertical phase shift fringe patterns. Multiple sets of phase shifted fringe patterns are taken and averaged to eliminate environmental effects.
And finally, combining the shot phase shift fringe pattern with a computer to perform phase expansion, calculating the slope and recovering the wavefront, and analyzing the wavefront aberration according to the recovered surface shape information of the lens to be detected.
The phase value corresponding to each pixel position of the luminescent screen 12 is calculated by a phase shift algorithm. And (4) performing phase expansion on the shot phase shift fringe pattern to obtain screen pixel positions corresponding to each part of the convex free-form surface 11 to be detected and calculating the slope. The resulting slope can be compared to the wavefront slope of an ideal test mirror. And finally, restoring the wavefront by the slope data so as to analyze the aberration. And converting the phase value into a world coordinate value according to the pose condition of the luminescent screen 12 in the world coordinate system and the pixel size of the luminescent screen 12.
When the system is calibrated, the convex free-form surface 11 to be measured and the light-emitting screen 12 are kept vertically placed. A certain point light source S (x) on the luminescent screen 12 s ,y s ,z s ) The emitted light is reflected by the corresponding mirror surface M (x) to be measured m ,y m ,z m ) After point reflection, it passes through the external pinhole C (x) of the third camera 13 c ,y c ,z c ) Finally, an image corresponding to the point is obtained on the target surface 16 of the third camera 13. It can also be considered that the light "emitted" from a certain pixel point on the target surface 16 of the camera passes through the pinhole 14 and is then reflected by the M point on the free-form curved surface 11 to be measured to the S point on the luminescent screen 12. Each M point on the mirror surface to be measured is a sub-aperture or "mirror pixel" formed by dividing the camera pixel.
And (3) establishing a world coordinate system by taking the central position O of the surface to be measured as an original point and taking a tangent plane of the surface to be measured at the point O as an xOy plane (called as a calibration plane). When the surface shape w (x) of the lens to be measured m ,y m ) Much smaller than the distance between the calibration plane and the camera 13 or the luminescent screen 12, i.e. w (x) m ,y m )＜＜z m2s And w (x) m ,y m )＜＜z m2c According to the triangulation principle, the slope of the point M on the convex free-form surface 11 of the lens to be measured can be obtained by the following formula:
in the formula z m2s And z m2c Respectively the z-direction distance of the calibration plane to the pixel point on the luminescent screen 12 and the pinhole 14 of the third camera 13. Since a better initial value is needed in calculating the slope, an ideal surface shape model or a surface shape obtained by other detection methods can be used to provide a better initial surface shape estimate w 0 (x m ,y m ) W is to be 0 (x m ,y m ) In place of w (x) in the formula m ,y m ) Then (x) is obtained m ,y m ) The x and y direction slope data of the point, and the surface shape w obtained by calculating the slope 1 (x m ,y m ) Instead of w (x) in the formula m ,y m ) And then another group of slopes is obtained, and so on, the wavefront shape is reconstructed by repeatedly and iteratively calculating the wavefront slope, and the wavefront aberration is calculated, so that the detected surface shape can be obtained.
The computer processing system A3 comprises a high-steepness convex free-form surface middle-low frequency detection processing and a high-steepness convex free-form surface high-frequency detection processing.
The middle and low frequency detection processing process of the large-gradient convex free-form surface is as follows: inputting system parameters of a medium-low frequency aberration detection system and a pupil image monitoring system into a system modeling module to establish an integral detection system model; inputting in-focus and out-of-focus images received by a camera in a medium and low frequency aberration detection system into an image acquisition processing module to obtain wavefront phase information, inputting the phase information into a wavefront fitting module to obtain fitted discrete parameters, and inputting the parameters into a system modeling module to serve as an optimization target of an optimization function; pupil image information output by a pupil image monitoring system is input into a system modeling module, a pupil image obtained by the pupil image monitoring system is used as a parameter for reference adjustment of a galvanometer and enters a galvanometer adjustment module so as to perform laser galvanometer adjustment in real time, a reflected light beam can be accurately controlled to be completely returned to a camera of a medium and low frequency aberration detection system, the collection of an in-focus image and an out-of-focus image is realized by moving the camera, and a surface shape error of an area to be detected is solved by a transverse translation difference phase recovery algorithm; the above is the process of returning the light beam from a small aperture to the aberration detection system to measure the surface shape error, the Y-guide rail 18 and the Z-guide rail 19 in the optical path clamping and adjusting system A4 are moved to make the light beam point to a new area to be measured and keep the same overlapping rate with the previous area, and the angle of the laser galvanometer 6 is adjusted to realize the light beam collimation, and the above detection process is repeated to realize the measurement of the new area to be measured surface shape error; and moving the Y-direction guide rail and the Z-direction guide rail for multiple times until the whole area to be measured is covered, and obtaining the data of the whole surface shape to be measured by adopting a matching and splicing SAS method for the three-dimensional surface shape error data obtained by measurement.
After the computer processing system A3 respectively realizes the high-frequency band and medium-low frequency band detection of the large-gradient convex free-form surface, the method for realizing full-frequency band fusion detection comprises the following steps: the surface shape of the free-form surface can be decomposed in a Zernike polynomial fitting mode, and the Zernike polynomials are arranged from low to high according to the order number. A statistical data fusion method based on measurement error prior is combined with a statistical data fusion method based on measurement error prior, and fusion weight values are set according to the variance of the TTDPR method with high middle-low frequency range aberration measurement precision and the SCOTS method with high frequency range aberration measurement precision on the measurement prior precision of different orders of aberrations, so that the mean square error of measurement results is reduced.
In the embodiment, the full-band fusion measurement characteristic of the large-gradient convex free-form surface is that mutual precision verification and information fusion of different frequency bands are realized through two modes of TTDPR and SCOTS, so that data fusion is realized, and finally, the full-band aberration detection of the convex free-form surface is realized.
In this embodiment, the optical path clamping and adjusting system A4 includes a mounting plate 17, a Y-axis guide rail 18, a Z-axis guide rail 19, an x-axis, Y-axis, and Z-axis rotary table 21, an air-flotation vibration isolation platform 22, a high-precision small displacement platform M1, a five-degree-of-freedom displacement platform M2, an adjusting frame D1, and a yaw and pitch two-dimensional adjusting frame D2;
the middle and low frequency information acquisition system A11 and the pupil image monitoring system A12 are fixed on a mounting plate 17, the mounting plate 17 is fixed on a slide block of the Z-directional guide rail 19 and moves up and down along with the slide block or is locked at a certain position of the Z-directional guide rail 19; the direction of the Z-direction guide rail 19 is parallel to the emergent light direction of the laser 1 of the medium-low frequency information acquisition system A11 and is vertically fixed on the air floatation vibration isolation platform 22; the Z-direction guide rail 19 is vertically fixed on a sliding block of the Y-direction guide rail 18, the Y-direction guide rail 18 is horizontally fixed on an air-floating vibration isolation platform 22, and the Y-direction guide rail 18 is vertical to the emergent light direction of the laser 1 of the medium-low frequency information acquisition system A11;
the X-axis, Y-axis and Z-axis rotating table 21 is fixed on the tool part 20; the tooling part 20 is vertically fixed on an air floatation vibration isolation platform 22, and a clamping mechanism of the convex free-form surface 11 to be measured is fixed on an X-axis, Y-axis and Z-axis rotating platform 21, so that the rotation of the convex free-form surface 11 to be measured around the X direction, the Y direction and the Z direction is realized.
In a second embodiment, the present invention is a method for detecting a full-band aberration of a convex optical free-form surface with large steepness by using the system described in the first embodiment, and the method is implemented by the following steps:
step 1, constructing and adjusting a high-frequency aberration detection system and a medium-low frequency aberration detection system;
step 2, acquiring image information of the convex free-form surface 11 to be detected by adopting the adjusted high-frequency aberration detection system and the middle-low frequency aberration detection system respectively;
and 3, respectively processing the high-frequency-band aberration and the medium-low frequency-band aberration of the acquired image information by using a computer to obtain the surface shape information of the convex free-form surface 11 to be detected.
Claims (10)
1. The full-band aberration detection system for the large-gradient convex optical free-form surface comprises a medium-low frequency band aberration detection system (A1), a high-frequency band aberration detection system (A2), a computer processing system (A3) and a light path clamping and adjusting system (A4); the optical path clamping and adjusting system (A4) is used for adjusting the middle-low frequency range aberration detection system (A1) and the high-frequency range aberration detection system (A2); the method is characterized in that: firstly, the high-frequency-band aberration detection system (A2) is adjusted, and then the medium-low frequency aberration detection system (A1) is adjusted according to the adjusted detected convex free-form surface (11);
in the assembling and adjusting process, the light-emitting screen (12), the third camera (13) and the convex free-form surface (11) to be measured are aligned, so that the optical axis of the third camera (13) is overlapped with the optical axis of the convex free-form surface (11) to be measured, the optical axis of the convex free-form surface (11) to be measured is parallel to the screen of the light-emitting screen (12), and the third camera (13) is focused on the surface of the convex free-form surface (11) to be measured;
the middle and low frequency range aberration detection system (A1) comprises a middle and low frequency information acquisition system (A11) and a pupil image monitoring system (A12);
the medium and low frequency information acquisition system (A11) comprises a laser (1), a collimation and beam expansion system (2), a beam splitter (3), an imaging mirror (9) and a second camera (10);
the high-frequency-band aberration detection system (A2) comprises a convex free-form surface (11) to be detected, a light-emitting screen (12) and a third camera (13);
the light beam emitted by the laser (1) is expanded into parallel light beams by the collimation and expansion system (2), and the parallel light beams are reflected and transmitted by the beam splitter (3); the transmitted light passes through the pupil image monitoring system (A12), the wavefront returned by the pupil image monitoring system (A12) enters the medium and low frequency information acquisition system (A11) again, and is imaged at the second camera (10) through the imaging mirror (9), and medium and low frequency band surface shape information of the convex free-form surface (11) to be detected is obtained;
the light beam collected by the medium and low frequency information collecting system (A11) is imaged at a first camera (8) through a pupil image monitoring system (A12), and a laser galvanometer (6) in the pupil image monitoring system (A12) is adjusted through analyzing the light spot image to enable the reflected light beam to be parallel;
the light emitted by the luminescent screen (12) is reflected by the convex free-form surface (11) to be detected and then received by the third camera (13), and the third camera (13) processes the obtained image by using the computer processing system (A3) to obtain the high-frequency section surface shape information of the convex free-form surface (11) to be detected;
the computer processing system (A3) performs full-band fusion detection on the high-frequency-band surface shape information of the to-be-detected convex free-form surface (11) obtained by the calibrated high-frequency-band aberration detection system (A2) and the low-frequency-band surface shape information of the to-be-detected convex free-form surface (11) obtained by the middle-low frequency-band aberration detection system (A1); namely: decomposing the data by a Zernike polynomial fitting mode, arranging the Zernike polynomials from low to high according to orders, setting fusion weight values according to the variance of the measurement prior precision of different orders of aberration by adopting a statistical data fusion method based on measurement error prior and combining a statistical data fusion method based on measurement error prior, and finally obtaining the full-band surface shape information of the convex free surface (11) to be measured according to the TTDPR method with high measurement precision of the middle-low frequency band aberration and the SCOTS method with high measurement precision of the high frequency band aberration.
2. The system according to claim 1, wherein the system comprises:
the pupil image monitoring system (A12) is composed of a beam splitter prism (4), an adjustable aperture diaphragm (5), a laser galvanometer (6), a collimated beam-reducing optical system (7) and a first camera (8);
the light beam collected by the medium and low frequency information collection system (A11) enters the laser galvanometer (6) after passing through the beam splitting prism (4) of the pupil image monitoring system (A12), the light beam emitted by the laser galvanometer returns to the laser galvanometer (6) after being reflected by the surface of the convex free-form surface (11) to be measured, and enters the beam splitting prism (4) for light splitting after passing through the adjustable aperture diaphragm (5), wherein one path returns as the original path, the other path enters the collimation and beam reduction optical system (7) to be imaged at the first camera (8), and the laser galvanometer (6) is adjusted through analyzing the spot image so as to enable the reflected light beams to be parallel.
3. The system according to claim 1, wherein the system comprises: the calibration method further comprises the step of calibrating the high-frequency-band aberration detection system (A2), and the specific calibration process comprises the following steps:
a, generating a group of sinusoidal phase shift fringe patterns in the horizontal and vertical directions on a luminescent screen (12);
step B, a system formed by the luminescent screen (12), the third camera (13) and the convex free-form surface (11) to be detected is collimated and calibrated, so that the optical axis of the third camera (13) is superposed with the optical axis of the convex free-form surface (11) to be detected, the optical axis of the convex free-form surface (11) to be detected is parallel to the screen of the luminescent screen (12), the spatial position coordinates of the luminescent screen (12), the third camera (13) and the convex free-form surface (11) to be detected are obtained, and the third camera (13) is focused on the surface of the convex free-form surface (11) to be detected;
a computer-aided optimization module is adopted to effectively correct the calibration error; obtaining the distance between a light-emitting screen (12), a pinhole (14) and a convex free-form surface (11) to be measured, which are calibrated and measured;
step C, a camera is adopted to shoot a phase shift fringe pattern displayed on the luminescent screen (12) deflected by the convex free-form surface (11) to be detected, and a group of horizontal and vertical phase shift fringe patterns are shot as reference after the convex free-form surface (11) to be detected is removed;
the luminescent screen (12) displays a group of phase shift fringe patterns one by one, and the third camera (13) shoots synchronously; removing the convex free-form surface (11) to be measured, and then shooting a group of horizontal and vertical phase shift fringe patterns; taking multiple groups of phase-shift fringe patterns for averaging to eliminate the influence of the environment;
and D, performing phase expansion on the shot phase shift fringe pattern by adopting a computer processing system (A3), calculating the slope and recovering the wavefront, and analyzing the wavefront aberration according to the recovered surface shape information of the lens to be detected.
4. The system of claim 3, wherein the full-band aberration detection system comprises:
in the step a, the phase shift fringe pattern is obtained in the following manner: selecting a sine stripe image for display, selecting the number of pixels of one period of the sine stripe according to the screen size and the resolution of the luminescent screen (12), determining the actual size corresponding to the stripe of one period, selecting the phase shift step number N of the phase shift stripe by utilizing a phase shift technology, and obtaining the phase shift stripe image modulated by light intensity by utilizing Matlab programming.
5. The system of claim 3, wherein the full-band aberration detection system comprises:
in the step D, the computer processing system (A3) calculates phase values corresponding to pixel positions of the luminescent screen (12) through a phase shift algorithm, performs phase expansion on the shot phase shift fringe pattern to obtain screen pixel positions corresponding to all parts of the convex free-form surface (11) to be detected, calculates a slope, compares the obtained slope with a wave front slope of an ideal mirror to be detected, recovers a wave front from slope data, performs aberration analysis, and converts the phase values into world coordinate values according to the pose condition of the luminescent screen (12) in a world coordinate system and the pixel size of the luminescent screen (12).
6. The system according to claim 1, wherein the system comprises:
the processing process of the computer processing system (A3) for the middle-low frequency range aberration detection system (A1) is as follows:
inputting system parameters of a medium-low frequency information acquisition system (A11) and a pupil image monitoring system (12) into a system modeling module to establish an integral detection system model; inputting in-focus and out-of-focus images received by a second camera (10) in the middle and low frequency band aberration detection system into an image acquisition processing module to obtain wave front phase information, inputting the phase information into a wave front fitting module to obtain fitted discrete parameters, and inputting the parameters into a system modeling module to serve as an optimization target of an optimization function;
pupil image information output by a pupil image monitoring system is input into a system modeling module, a pupil image obtained by the pupil image monitoring system is used as a parameter for reference adjustment of a galvanometer and enters a galvanometer adjustment module so as to perform laser galvanometer adjustment in real time, a reflected light beam is accurately controlled to be completely returned to a second camera (10) of a medium and low frequency information acquisition system (A11), the acquisition of an in-focus image and an out-of-focus image is realized by moving the second camera (10), and the surface shape error of an area to be measured is solved by a transverse translation difference phase recovery algorithm;
moving a Y-guide rail (18) and a Z-guide rail (19) in the optical path clamping and adjusting system (A4), enabling the light beam to point to a new area to be measured and keep the same overlapping rate with the previous area, adjusting the angle of a laser galvanometer (6) to realize light beam collimation, and repeating the detection process to realize the measurement of the new surface shape error of the area to be measured; and moving the Y-direction guide rail and the Z-direction guide rail for multiple times until the whole area to be measured is covered, and obtaining the data of the whole surface shape to be measured by adopting a matching and splicing SAS method for the three-dimensional surface shape error data obtained by measurement.
7. The system according to claim 1, wherein the system comprises: the optical path clamping and adjusting system (A4) comprises a mounting plate (17), a Y-axis guide rail (18), a Z-axis guide rail (19), an X-axis, Y-axis and Z-axis rotating table (21), an air floatation vibration isolation platform (22), a high-precision small displacement platform (M1), a five-degree-of-freedom displacement platform (M2), an adjusting frame (D1) and a deflection and pitching two-dimensional adjusting frame (D2);
the middle and low frequency information acquisition system (A11) and the pupil image monitoring system (A12) are fixedly arranged on a mounting plate (17), the mounting plate (17) is fixed on a slide block of the Z-direction guide rail (19) and moves up and down along with the slide block or is locked at a certain position of the Z-direction guide rail (19); the direction of the Z-direction guide rail (19) is parallel to the emergent light direction of a laser (1) of a medium and low frequency information acquisition system (A11), and the Z-direction guide rail is vertically fixed on an air floatation vibration isolation platform (22); the Z-direction guide rail (19) is vertically fixed on a slide block of the Y-direction guide rail (18), the Y-direction guide rail (18) is horizontally fixed on an air-floating vibration isolation platform (22), and the Y-direction guide rail (18) is vertical to the emergent light direction of a laser (1) of the medium-low frequency information acquisition system (A11);
the X-axis, Y-axis and Z-axis rotating table (21) is fixed on the tooling part (20); the tool piece (20) is vertically fixed on the air floatation vibration isolation platform (22), and the clamping mechanism of the convex free-form surface (11) to be measured is fixed on the X-axis, Y-axis and Z-axis rotating platform (21), so that the rotation of the convex free-form surface (11) to be measured around the X direction, the Y direction and the Z direction is realized.
8. The system according to claim 7, wherein the full-band aberration detection system comprises: the laser (1) is placed on an adjusting frame (D1), and the adjusting frame (D1) provides the laser with angular degrees of freedom in two directions of pitching and deflecting; the front and back adjustment laser (1) is used for precisely adjusting the adjusting frame D1 to enable emergent rays to be parallel light; the second camera (10) is fixed on the five-degree-of-freedom displacement table (M2) through a switching element, the switching element is connected with the second camera (10) and the five-degree-of-freedom displacement table (M2) through screws, and fine adjustment of the pose of the second camera (10) is achieved through adjusting the prestress of the screws; and the five-degree-of-freedom displacement table (M2) is moved back and forth to realize focus search and defocusing image acquisition in a large range, and the acquired in-focus and defocusing images are sent to a computer processing system (A3) to obtain the surface shape of the middle and low frequency band of the convex free curved surface (11) to be detected.
9. The system according to claim 7, wherein the full-band aberration detection system comprises:
the collimation beam-shrinking optical system (7) is fixed on the deflection and pitching two-dimensional adjusting frame (D2) through threaded connection, the first camera (8) adopts the large pixel number and the small pixel size to perform high-precision light spot analysis to realize the collimation of a light path, and the first camera (8) is fixed on the high-precision small displacement table (M1) through the adapter plate to facilitate the adjustment of the light path.
10. The full-band aberration detection method of the large-gradient convex optical free-form surface is characterized by comprising the following steps of: the method is realized on the basis of the full-band aberration detection system of the large-gradient convex optical free-form surface as claimed in any one of claims 1 to 9, and the method is realized by the following steps:
step 1, constructing and adjusting a high-frequency-band aberration detection system and a medium-low frequency-band aberration detection system;
step 2, acquiring image information of the convex free-form surface (11) to be detected by adopting the adjusted high-frequency-band aberration detection system and the middle-low-frequency-band aberration detection system respectively;
and 3, respectively processing the high-frequency-band aberration and the medium-low frequency-band aberration of the acquired image information by adopting a computer to obtain the surface shape information of the convex free-form surface (11) to be detected.
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