CN111366099A - Pre-analysis-based interference weighted sampling dephasing analysis method and measurement system under any cavity length - Google Patents
Pre-analysis-based interference weighted sampling dephasing analysis method and measurement system under any cavity length Download PDFInfo
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Abstract
The invention discloses an interference weighting sampling dephasing analysis method and a measurement system under any cavity length based on pre-analysis, aiming at a multi-surface transparent measured piece which is a transparent parallel flat plate, analyzing a weighting multi-step dephasing algorithm in advance, and storing available parameters, corresponding cavity length coefficients and phase-shifting reference coefficients necessary for the algorithm in a pre-analysis matrix of an algorithm library; when the algorithm is used for resolving the phase, corresponding parameter values in an algorithm library are directly called, and the cavity length value is measured automatically through the distance measurement sensor to the distance value from the measured piece to the front surface of the reference mirror, so that the problem that the fixed algorithm can only be applied to measurement limitation under the fixed cavity length is solved, and the convenient design of the algorithm is realized; the measuring system mainly comprises a laser ranging sensor, a clamp combination and a guide rail matching device, wherein the clamp combination comprises a clamp and a guide rail frame. The guide rail bracket can assist the laser ranging sensor to realize automatic measurement of the distance of the measured piece, and is easy to operate and high in measurement precision.
Description
Technical Field
The invention relates to an optical interference measurement method and device, in particular to an interference weighted sampling dephasing analysis method and a measurement device, which are applied to the technical field of optical measurement.
Background
The optical interference measurement technology is a measurement method which is based on the fluctuation principle of light and can realize the measurement of the precision reaching nano-meter and sub-nano-meter magnitude, and is one of the most accurate and most effective non-contact measurement modes for detecting relevant parameters of optical elements and optical systems. In interferometry, the currently mainstream measurement method is a PZT (Piezoelectric ceramic based PZT) phase shift technology, which has a long application time and a mature technology. However, this technique cannot meet the measurement requirement of higher precision (such as nanometer scale) because the PZT phase shift process will generate hardware error and mechanical stress error. Particularly for the multi-surface interference measurement of the transparent parallel flat crystal, the measurement requirement of the sample is very high, and the existing measurement method generally needs to separate the multi-surface interference signals according to the difference of phase shift frequencies (by setting a cavity length coefficient, namely the ratio of the interference cavity length to the product of the thickness and the refractive index), so that the separation and the measurement of the transparent multi-surface sample cannot be completed simultaneously if the error is large. Meanwhile, when measuring multi-surface transparent elements such as a parallel transmission sheet, a semiconductor substrate coating film and the like, a group of self-interference fringes are formed on the front surface and the rear surface, and the front surface and the rear surface of the element are respectively interfered with the reference mirror to generate two groups of fringes. The three groups of interference fringes finally form superposed cross interference fringes, and if a traditional phase shifting algorithm is used for calculating the multi-surface interference fringes, a large error is generated. The commonly used technologies at present include ellipsometry based on polarized light to perform point-by-point scanning measurement and white light interference. The current method commonly used in industrial application is to coat the back surface of a flat plate with matting paint or vaseline matched with the refractive index of the material to measure each surface one by one, so as to eliminate the influence of the reflection of the back surface on the measurement, but the method can damage the surface of an element, and cannot measure the appearance of multiple surfaces at the same time.
The measuring method based on the wavelength phase shift interference technology is a typical high-precision non-contact measuring technology developed in recent years. This measurement technique is to change the phase value, i.e., phase shift operation, by dynamically changing the voltage applied to the laser, thereby changing the output wavelength of the laser. After the phase shifting operation is carried out, an interference light intensity distribution graph with aliasing interference information on each surface of the measured piece under different phase shifting values is acquired by a CCD camera, then an algorithm is used for calculation, the aliasing interference information is separated, the independent component information of each part of signal is further obtained, the initial phase value of the measured surface can be obtained after the phase is resolved, the surface shape change information of the measured surface can be obtained, and the principle is the principle of the wavelength phase shifting interference measurement technology.
The light intensity change frequency of the interference fringe signal in the wavelength tuning phase shifting process is related to the optical path difference of the coherent light which is interfered. Since the optical path differences of the interference fringe signals to be measured are different, even if the wavelength tuning amount is constant, the variation frequencies corresponding to the respective interference fringes are different, and the interference frequency of each interference information is a function of the optical path difference, in other words, the interference frequency is a function of the cavity length and the thickness and refractive index of the measured object. By utilizing Fourier transform and signal analysis theory, a plurality of groups of interference fringes with different frequency changes can be separated through time domain windowing Fourier transform. Meanwhile, by utilizing the wavelength tuning phase-shifting algorithm interference technology, the detection of the three-dimensional profile of the front surface and the rear surface of the object to be detected can be realized, and the thickness change can be measured.
Because the optical path differences between different surfaces and the reference surface are different, interference information can be actually distinguished according to frequency, namely, through a sample with given thickness and refractive index, when phase demodulation and measurement are carried out by utilizing a weighted multi-phase shift algorithm, cavity length meeting the algorithm requirement is selected, separation and sampling conditions are met, and then the interference information is separated. However, when the object to be measured is placed at some position of the interferometer, interference frequencies determined by the optical path difference may overlap or be close to each other, and the extraction of interference information cannot be performed. Furthermore, many of the existing phase-shifting algorithms adopt a multi-step phase-shifting algorithm, and for the algorithm, the form of a frequency domain sampling window is strongly related to the setting rule of a cavity length coefficient and a phase-shifting value, so that when each reference frequency can be separated theoretically, the result cannot necessarily achieve the purpose of phase-shifting. In other words, the signals are different in frequency, and are not necessarily separated directly, and the cavity length coefficient and the phase shift value are set. Therefore, when a multi-step long phase-shifting algorithm is used for multi-surface interference measurement, the setting of the cavity length coefficient and the phase-shifting value needs to be limited, one algorithm is usually designed to only cope with one or limited situations, and when the cavity length coefficient is changed, the phase-shifting and signal separation cannot be performed, which is one of the main difficulties of the multi-surface phase-shifting technology based on the multi-step phase shifting at present.
Meanwhile, the traditional algorithm design method does not pre-evaluate and analyze the algorithm, so that the specific application range of a designer to a multi-step dephasing algorithm is generally unknown, and only one or a limited plurality of schemes are tested to design the algorithm and make experiments, thereby greatly limiting the application range of the algorithm.
Moreover, most of the traditional design methods are based on discrete parameter design, and generally cannot strictly meet ideal conditions due to the limitation of experimental conditions in the actual process, so that the algorithm needs to be finely adjusted according to known conditions during measurement instead of fundamentally performing comprehensive analysis and prediction and storage of effective data.
In terms of hardware, the distance of a measured piece is measured by using a graduated scale or a slide rail with a graduation mostly in the traditional method, the accuracy of the measurement method is low, and when the outer edge of a clamp cannot be in the same plane with the measured piece, a large measurement error is necessarily included.
Disclosure of Invention
In order to solve the problems of the prior art, the invention aims to overcome the defects of the prior art, and provides a method and a system for analyzing the dephasing of interference weighted sampling under any cavity length based on pre-analysis. The multi-surface transparent tested piece is a transparent parallel flat plate. The principle mainly comprises the following steps: when the weighted multi-step sampling algorithm is adopted for phase-resolving calculation, not only can the aliasing interference frequencies be separated, but also the interference frequencies are independent from each other, and a certain distance is required between frequency components so that a sampling function can function, meanwhile, a weighted sampling window function is required to accurately sample a signal of a target frequency in a frequency domain and not bring information except the target signal into sampling, and when the three conditions are met, the target information can be extracted by using the multi-step weighted sampling algorithm, so that the phase-resolving operation is completed. However, in practical applications, a weighted sampling algorithm is generally designed to be unchangeable, only one or a few discrete values with a fixed cavity length coefficient range can be processed, and the designed algorithm cannot be dynamically adjusted to cope with different cavity length conditions. However, for the actual measurement process, it cannot be guaranteed that the cavity length well meets the conditions required by the algorithm, because: changing the cavity length changes the distance of the measured object from the front surface of the reference mirror, and this distance may not be too large or too small: if the test condition is too small, the test condition cannot be met, the reference mirror and the tested piece are fixed on the clamp, and the clamp occupies a certain space; if the size of the anti-vibration experiment table is too large, the size of the anti-vibration experiment table on which the interferometer is positioned may not meet the preset cavity length condition and errors are introduced. And if a designed algorithm only meets a plurality of discrete cavity length values, the cavity length needs to be adjusted in the measuring process, namely the distance between the measured piece and the reference mirror needs to be adjusted through a graduated scale or a guide rail with a graduation, and errors are inevitably introduced in the adjusting process, so that the current actual cavity length value can not strictly meet the ideal cavity length condition required by the algorithm. Resulting in large measurement errors or even no measurement. The method provided by the invention is designed aiming at different cavity length coefficients based on a pre-designed algorithm adaptive coefficient library form, and the distance of the measured piece is measured with high precision by using the distance measuring sensor, so that the problems can be well avoided.
In order to achieve the purpose of the invention, the invention adopts the following technical scheme:
a pre-analysis-based interference weighted sampling dephasing analysis method under any cavity length comprises the following processes and steps:
a. according to the characteristics of the weighted multi-step sampling algorithm, performing double iteration on the phase-shifting reference coefficient and the cavity length coefficient within a certain range;
b. judging the mean square error of the maximum error of the algorithm result based on Zernike polynomial interference simulation and multi-step weighted discrete sampling, judging that the algorithm is usable when the separation error of each piece of information is less than 1.2um, otherwise, judging that the algorithm is unusable, and then storing the information in a pre-analysis matrix;
c. measuring the distance of a measured piece by using a laser ranging sensor, setting the thickness and reflectivity information of the measured piece, calling a pre-analysis matrix, selecting and designing specific parameters in an algorithm, and selecting available values from an algorithm library to perform weighted multi-step sampling calculation;
d. after the algorithm parameters are selected, acquiring an interferogram of the interferometer, wherein the acquisition frame number and the phase shift value are related to a phase shift reference coefficient, setting the thickness value and the refractive index of the measured piece during measurement, and measuring the information of each surface of the measured piece.
As a preferred technical scheme, in the process of preparing an iteration and value judgment method, for each cavity length coefficient, a phase-shift reference coefficient value corresponding to a right scale within 1 step of the cavity length coefficient simultaneously meets the conditions of the current phase-shift reference coefficient and a right adjacent phase-shift reference coefficient, a right scale value of a scale range where the actual cavity length coefficient is located is taken as a pre-estimated value, and the phase-shift reference coefficient is selected through the pre-estimated value; after the positioning and selection of the phase-shifting reference coefficient and the cavity length coefficient, the calculation of the sampling function is carried out, and the preparation process of algorithm design is completed.
As a preferred technical scheme of the invention, the aliasing interferometry of the multi-surface transparent measured piece is carried out, the phase-shift reference coefficient is iterated by carrying out double iteration on different cavity length coefficients and phase-shift reference coefficients, the iteration of the cavity length coefficients is taken into the calculation process in the iteration process, so that the unwrapped phase results solved by the surfaces under different cavity length coefficients and different phase-shift reference coefficients are obtained, the surface shape results of the surfaces are further solved, and three pieces of information of the front surface, the rear surface and the thickness change of the measured piece are mainly considered.
A pre-analysis-based measuring system for interference weighted sampling under any cavity length is adopted, the pre-analysis-based method for interference weighted sampling dephasing analysis under any cavity length is adopted, the measuring system mainly comprises a laser ranging sensor, a clamp combination and a guide rail matching device, and the clamp combination comprises a clamp and a guide rail bracket; adjustable reference arms are arranged at two ends of the guide rail frame, and racks are arranged on the inner sides of the adjustable reference arms and are in matched transmission with toothed knobs; the bottom end of the knob is provided with a screw rod which is in threaded connection with a threaded hole at the bottom end inside the guide rail frame, and the knob and the adjustable reference arm are respectively arranged at two ends of the guide rail frame; a high-reflectivity coating is coated on the adjustable reference arm according to the wavelength of the laser so as to be matched with the work of the laser ranging sensor; the tested lens is clamped by the clamp combination; after the tested lens is clamped by the clamp, the clamp is combined with the guide rail frame through the clamp assembling threaded hole; the guide rail frame consists of an upper hollow cavity and a lower hollow cavity, and a groove is formed in the lower part of the guide rail frame, so that the guide rail frame is clamped on the guide rail and performs matched motion; a guide rail frame assembling threaded hole is formed above the guide rail frame, and the upper structure and the lower structure of the guide rail frame are assembled through bolts; the adjustable reference arm is clamped in the grooves at the two sides of the guide rail frame through the reference arm guide grooves at the two ends and moves; the adjustable reference arm is controlled to move back and forth by rotating the knob, so that the front surface of the measured mirror is corrected and the distance measurement of the laser distance measuring sensor is realized; the laser ranging sensors are arranged on the front side and the rear side of the bottom of the interferometer respectively, the outer surface of the reference mirror is used as a standard, and the distance average value of the calibrated adjustable reference arm is measured and used as the absolute distance value between the measured mirror and the reference mirror, so that the cavity length value is obtained; the laser ranging sensor is in signal connection with an upper computer, and the computer reads the average value of the measured distance values to serve as data information for calculating the cavity length coefficient.
As a preferred technical scheme of the invention, the tested piece is clamped by a clamp of the clamp combination, so that the tested transparent parallel flat plate can be perpendicular to the workbench, the tested parallel flat plate is parallel to the outer surface of the reference mirror of the interferometer, and interference is respectively generated between the front surface and the rear surface of the tested piece and the outer edge surface of the reference mirror by adjusting the position of the clamp.
As a preferred technical scheme of the invention, the bottom end of the guide rail frame is matched with a guide rail on the workbench to move, and the vertical height center of the clamp is aligned with the center of a circle on the outer surface of the interferometer.
Preferably, a wavelength phase-shifting interferometer is used for acquiring the interferogram, and the acquisition frame number and the phase-shifting value are respectively related to the phase-shifting reference coefficient.
Preferably, the interferometer is connected with a computer by using a data connecting line, and the computer directly reads the acquired interferogram acquired by a CCD camera in the interferometer.
Preferably, a high-precision laser ranging sensor is used, preferably a German JENOPTIK high-precision laser ranging sensor, model JGS-70, the sensor is arranged on a workbench parallel to the outer surface of a reference mirror of an interferometer, two ends of the interferometer are respectively provided with one sensor, signals measured by the high-precision laser ranging sensor are transmitted to a computer through a data transmission line for reading, and the average value of the two measured distance values is used as an actual distance value. And calibrating the sensor by taking the outer surface of the reference mirror as a benchmark, wherein the measured distance of the measured piece is an absolute distance.
As a preferable technical scheme of the invention, the clamp is divided into two parts, one part is a part for clamping the measured piece, a vacuum self-centering mirror frame can be selected, the clamp is selected according to different calibers of the measured piece, and when the calibers of the measured piece are between 30 and 200mm, the type of the clamp is preferably selected: FPSTA-4SCML-8V, the fixture needs to be mounted on the rail mount. The other part is a guide rail frame matched with the clamp, and a threaded hole is drilled at the bottom of the clamp and is connected with the guide rail frame through a bolt. The bottom end of the guide rail frame is matched with the guide rail and can be embedded on the guide rail. The two ends of the guide rail frame are provided with threaded holes to be matched with the clamp. The adjustable reference arms are arranged at two ends of the guide rail frame, racks are arranged on the inner sides of the adjustable reference arms and can be matched with the knobs, the knobs are toothed cylinders, the bottom ends of the knobs are studs and are in threaded connection with threaded holes in the bottom end inside the guide rail frame, and the knobs and the adjustable reference arms are respectively arranged at two ends of the guide rail frame. The reference arm is coated with a high reflectivity coating, preferably 1030-i0 coating material, depending on the laser wavelength, to match the operation of the laser range sensor.
Preferably, the multi-surface dephasing algorithm comprises 6 algorithms, which respectively correspond to different phase-shifting reference coefficients and can correspond to different cavity length coefficient distribution situations.
The guide rail is preferably a high-precision measuring guide rail, and a GCM-720205M type guide rail is preferably adopted.
Preferably a CCD camera, preferably DFK37AUX273 model and its associated data link.
Preferably a wavelength tunable laser, preferably a Newfocus TLB-6804 series wavelength tunable laser.
The principle of the invention is as follows:
the design process of the algorithm provided by the invention comprises the following steps: firstly, a main following function is set based on experience, a multi-surface interference phase shift measurement algorithm is accurately designed, a Zernike fitting mode is used for completely simulating a multi-surface interference acquisition process and an algorithm processing process, phase results after unpacking of all surface solutions under different cavity length coefficients and different phase shift reference coefficients are obtained through double iteration of different cavity length coefficients and phase shift reference coefficients, and then all surface shape results are solved, wherein three information of the front surface, the rear surface and the thickness change of a measured piece are mainly considered. And (4) performing inclination elimination treatment on the surface shape results of all the surfaces, and then respectively solving residual errors with respective mean values. The residual here is the peak value of the distance of each data from the mean, i.e., the maximum value of the average difference. The residual data is stored and a decision is made. The judgment conditions are selected as follows: during double iteration, under the conditions of the current cavity length coefficient and the phase-shifting reference coefficient, the residual error results of three interference information, namely the current surface, the back surface and the thickness change, are simultaneously less than 1.2nm, and the algorithm under the conditions is judged to be applicable. And solving the double iteration results of the cavity length coefficient and the phase-shifting reference coefficient, and then placing the solution in a pre-analysis matrix. When the algorithm is used, the distance from a measured piece to a reference mirror is measured by a high-precision laser ranging sensor, the value is read into the phase-shifting algorithm designed by the invention, and then the cavity length coefficient and the phase-shifting reference coefficient can be automatically calculated only by inputting the values of the thickness and the refractive index. In the solving process of the pre-analysis matrix, because the calculation process under different cavity length coefficients is inevitably discrete data, the data processing mode designed by the invention is as follows: the position search is carried out on the actual cavity length coefficient, two discrete values always exist to enable the actual cavity length coefficient to be between the two discrete values, so that the adjacent larger value is selected as a pre-estimated value, and the phase shift reference coefficient is searched for the pre-estimated value to complete the preparation process of the algorithm.
The next step is that the current adaptable phase-shifting reference coefficient and the actual cavity length value searched from the pre-analysis matrix are brought into a phase-solving algorithm, the phase-shifting value, the interferogram acquisition frame number and the weighted sampling function are designed through different phase-shifting reference coefficients, the data are subjected to arc tangent calculation to obtain a wrapping phase, the surface shape of the corresponding measured surface can be obtained after de-wrapping and de-tilting, and the multi-surface interference measurement process is completed.
When a pre-analysis matrix is constructed, the iteration step of the phase-shifting reference coefficient is 1, the iteration step of the cavity length coefficient is 0.1, and the parameters of the double iteration are discrete, so that the conditions of all the cavity length coefficients cannot be satisfied certainly. The judging method comprises the following steps: for each cavity length coefficient, the phase-shift reference coefficient value corresponding to the right scale within 1 step must satisfy the conditions of the current phase-shift reference coefficient and the right adjacent phase-shift reference coefficient, so the processing method adopted here is to take the right scale value of the scale range where the actual cavity length coefficient is located as the pre-estimated value, and then select the phase-shift reference coefficient through the pre-estimated value. The calculation of the sampling function can be carried out after the positioning and the selection of the phase-shifting reference coefficient and the cavity length coefficient, the design process of the algorithm is completed at the moment, and the algorithm can be automatically and specifically designed only by inputting the thickness and the reflectivity of a measured piece when in use.
Compared with the prior art, the invention has the following obvious and prominent substantive characteristics and remarkable advantages:
1. the method comprises the steps of analyzing a weighted multi-step dephasing algorithm in advance, and storing available parameters, corresponding cavity length coefficients and phase-shifting reference coefficients required by the algorithm in a pre-analysis matrix of an algorithm library; when the algorithm is used for resolving the phase, corresponding parameter values in an algorithm library are directly called, and the distance value from a measured piece to the front surface of the reference mirror is automatically measured through the distance measuring sensor, namely, the cavity length value is measured, so that the problem that the fixed algorithm can only be applied to measurement limitation under the fixed cavity length is solved, and the convenient design of the algorithm is realized;
2. based on the characteristics of the weighted multi-step sampling algorithm, the invention also realizes the weighted multi-step interferometry technique under any cavity length, breaks through the technical bottleneck and widens the range for the application of the weighted sampling wavelength phase-shifting and phase-resolving algorithm;
3. the invention constructs an algorithm parameter available database by analyzing the characteristics of the algorithm in advance, can automatically search a parameter database for automatic design of the algorithm by inputting the thickness value and the reflectivity value only when actually measuring, and can measure the non-contact multi-surface information at the same time, and the algorithm has high calculation speed, low calculation cost and good measurement effect, and can solve the problem of algorithm adaptability under any cavity length; the guide rail bracket designed by the invention can assist the laser ranging sensor to realize automatic measurement of the distance of the measured piece, so that the technology is more convenient to realize; the invention carries out pre-analysis and processing from the angle of algorithm adaptability, and reversely carries out algorithm design and measurement scheme formulation on the basis of the characteristics of a comprehensive and meticulous analysis dephasing algorithm; the innovative technology provided by the invention is beneficial to the application of the interferometric technology and the development of the multi-surface measurement technology, and develops a design idea of the measurement technology for technicians in the field;
4. the invention reversely designs the algorithm and makes the experimental acquisition scheme and automatically designs the algorithm after pre-analyzing and obtaining the phase-shift value suitable for the current working condition; the method can well solve the problem of phase-shifting bottleneck under any cavity length, reduces the technical application cost and the design cost because the algorithm is automatically designed, widens the application range of the wavelength phase-shifting interference technology, is simple and easy to implement, has low cost, and is suitable for popularization and use.
Drawings
Fig. 1 is a schematic structural diagram of a reference arm of a measuring system according to a preferred embodiment of the present invention.
Fig. 2 is a schematic view of a knob structure of a measuring system according to a preferred embodiment of the present invention.
Fig. 3 is a front view of a rail frame structure of a measuring system according to a preferred embodiment of the present invention.
Fig. 4 is a top view of a rail frame structure of a measuring system according to a preferred embodiment of the present invention.
Fig. 5 is a left side view of a rail frame structure of a measuring system according to a preferred embodiment of the present invention.
Fig. 6 is a schematic diagram of the overall system structure of the measuring system according to the preferred embodiment of the present invention.
FIG. 7 is a flow chart of the algorithm employed by the measurement system in accordance with the preferred embodiment of the present invention.
FIG. 8 is an aliased interferogram acquired by the interference weighted sampling dephasing analysis method in accordance with the preferred embodiment of the present invention.
FIG. 9 is a diagram of the phase-resolved result obtained by the interference weighted sampling phase-resolved analysis method according to the preferred embodiment of the present invention.
FIG. 10 is a residual error diagram of the results of the interference weighted sampling dephasing analysis method according to the preferred embodiment of the present invention.
FIG. 11 is a diagram of a pre-analysis parameter library used in the interferometric weighted sampling dephasing analysis method according to the preferred embodiment of the invention.
Detailed Description
The above-described scheme is further illustrated below with reference to specific embodiments, which are detailed below:
in the present embodiment, referring to fig. 7, a method for resolving phase by interference weighted sampling at any cavity length based on pre-analysis includes the following procedures and steps:
a. according to the characteristics of the weighted multi-step sampling algorithm, performing double iteration on the phase-shifting reference coefficient and the cavity length coefficient within a certain range;
b. judging the mean square error of the maximum error of the algorithm result based on Zernike polynomial interference simulation and multi-step weighted discrete sampling, judging that the algorithm is usable when the separation error of each piece of information is less than 1.2um, otherwise, judging that the algorithm is unusable, and then storing the information in a pre-analysis matrix;
c. measuring the distance of a measured piece by using a laser ranging sensor, setting the thickness and reflectivity information of the measured piece, calling a pre-analysis matrix, selecting and designing specific parameters in an algorithm, and selecting available values from an algorithm library to perform weighted multi-step sampling calculation; when the method is actually used, the hardware design part uses the laser ranging sensor to realize automatic measurement of the distance of the measured piece, so that only the thickness and reflectivity information of the measured piece needs to be input during operation, specific parameters in the algorithm can be automatically selected and designed after the preanalysis matrix is called, and available values are selected from 6 standby algorithms to carry out weighted multi-step sampling calculation;
d. after the algorithm parameters are selected, the establishment of an experimental scheme and the acquisition of an interferogram of an interferometer are carried out, wherein the acquisition frame number and the phase shift value are related to a phase shift reference coefficient, the thickness value and the refractive index of the measured piece are set during measurement, and the measurement of the information of each surface of the measured piece is carried out. The embodiment is based on a pre-analysis interference weighting sampling dephasing analysis method under any cavity length, and is in the aspect of automatic design of an algorithm.
In this embodiment, referring to fig. 7, in the process of making the iteration and value determination method, for each cavity length coefficient, the phase shift reference coefficient value corresponding to the right scale within 1 step of the cavity length coefficient simultaneously satisfies the condition of the current phase shift reference coefficient and the adjacent phase shift reference coefficient on the right side of the current phase shift reference coefficient, the right scale value of the scale range where the actual cavity length coefficient is located is taken as a pre-estimated value, and the phase shift reference coefficient is selected according to the pre-estimated value; after the positioning and selection of the phase-shifting reference coefficient and the cavity length coefficient, the calculation of the sampling function is carried out, and the preparation process of algorithm design is completed.
In this embodiment, referring to fig. 7, performing aliasing interferometry on a multi-surface transparent measured object, performing double iteration on different cavity length coefficients and phase-shift reference coefficients, performing iteration on the phase-shift reference coefficients, and incorporating the iteration of the cavity length coefficients into a calculation process in the iteration process, thereby obtaining unwrapped phase results solved for each surface under different cavity length coefficients and different phase-shift reference coefficients, further solving each surface shape result, and mainly considering three information of the front surface, the rear surface, and the thickness variation of the measured object.
In the embodiment, in terms of hardware, the laser ranging sensor 20, the clamp combination and the guide rail are used for realizing high-precision realization of an automatic algorithm.
Referring to fig. 1 to 7, a pre-analysis-based measurement system for interference weighted sampling at any cavity length mainly includes a laser ranging sensor 20, a device for matching a clamp assembly 18 with a guide rail 19, and the clamp assembly 18 includes a clamp and a guide rail frame 7;
two ends of the guide rail bracket 7 are provided with adjustable reference arms 1, and racks 3 are arranged on the inner sides of the adjustable reference arms 1 and are in matched transmission with knobs 4 with teeth 5; the bottom end of the knob 4 is provided with a screw rod 6 which is in threaded connection with a threaded hole 8 at the bottom end inside the guide rail frame 7, and the knob 4 and the adjustable reference arm 1 are respectively arranged at two ends of the guide rail frame 7; the adjustable reference arm 1 is coated with a high-reflectivity coating 2 according to the wavelength of a laser so as to be matched with the work of the laser ranging sensor 20;
the tested lens 17 is clamped by a clamp assembly 18; after the tested lens 16 is clamped by the clamp, the clamp is combined with the guide rail bracket 7 through the clamp assembly threaded hole 11; the guide rail frame 7 consists of an upper hollow cavity and a lower hollow cavity, and a groove is formed in the lower part of the guide rail frame to enable the guide rail frame 7 to be clamped on the guide rail 19 and to move in a matching manner; a guide rail frame assembling threaded hole 10 is formed above the guide rail frame 7, and the upper structure and the lower structure of the guide rail frame are assembled through a bolt 9; the adjustable reference arm 1 is clamped in the grooves at the two sides of the guide rail bracket 7 through the reference arm guide grooves 25 at the two ends and moves;
the adjustable reference arm 1 is controlled to move back and forth by rotating the knob 4, so that the correction of the front surface of the measured mirror 17 and the distance measurement of the laser distance measuring sensor 20 are realized; the laser ranging sensors 20 are respectively arranged on the front side and the rear side of the bottom of the interferometer, the outer surface of the reference mirror 16 is used as a reference, and the distance average value of the calibrated adjustable reference arm 1 is measured to be used as the absolute distance value between the measured mirror 17 and the reference mirror 16, so that the cavity length value is obtained; the laser distance measuring sensor 20 is in signal connection with an upper computer, and the computer reads the average value of the measured distance values as data information for calculating the cavity length coefficient.
In the present embodiment, referring to fig. 3-6, the tested object is clamped by the clamps of the clamp assembly 18, so that the tested transparent parallel plate can be perpendicular to the worktable, so that the tested parallel plate is parallel to the outer surface of the reference mirror 16 of the interferometer, and by adjusting the position of the clamps, interference is generated between the front and rear surfaces of the tested object and the outer edge surface of the reference mirror 16, respectively.
In this embodiment, referring to fig. 3-6, the bottom end of the rail frame 7 moves in cooperation with the rail 19 on the table, and the vertical height center of the fixture is aligned with the center of the outer surface circle of the interferometer.
The detailed description of the specific parts in the figures and the accompanying drawings is:
the wavelength phase-shifting interferometer can separate each independent component of the aliasing interference signal according to the acquired interference image by setting different phase-shifting values and acquisition frame numbers according to a weighted multi-step sampling algorithm. The phase of the wavelength tunable phase-shifting initial interference signal is expressed as:
θ0is the initial phase of the surface of the element, and h (x, y) is the geometric change of the surface topography of the element, i.e. the distribution of the optical path difference, and it can be seen from the above formula that the initial phase value is measuredThe profile of the sample surface can be obtained, and when the wavelength is changed, the phase value θ (x, y) and the taylor series expansion thereof can be expressed as:
wherein λ is0The initial wavelength of the laser, k is the number of phase shift steps, i.e. the number of acquired images, and Δ λ is the single wavelength change tuning amount corresponding to one phase shift. Here, three main signals are mainly considered, namely a front surface signal, a back surface signal and a thickness variation signal. T is the average thickness of the element to be measured, and the signal frequency v of each group of interference fringes formed by reflection of the measuring beamp,q(x, y) may be represented by the general formula:
wherein p and q are integers reflecting the paths of the two beams, n is the refractive index of the element to be measured,
is the rate of change of refractive index with wavelength. The light intensity signal of each surface interference is a periodic signal in a time domain, so that the light intensity signal can be transformed into a frequency domain through an Euler formula and Fourier transform, and is expressed as:
where w (v) is a fourier transform version of the window function w (t) and is required to satisfy the condition of 0 at one and two multiples. The solution for the phase distribution to be measured can be expressed as:
in the actual measurement process, the phase-shifting interference technology can be regarded as based on the dispersion of a small number of variables which are smoothly arranged to the whole bodyAnd (6) sampling. In the case of discrete sampling, the window function w (t) is associated with the phase shift value σkThe relationship between them is:
where k denotes the number of phase shifts and δ [ ] denotes the dirac delta function. The light intensity interference signal can be rewritten into a Fourier transform form, and the phase to be measured can be expressed as:
wherein,
called the characteristic coefficient of the phase shift algorithm, the constant const is the complex phase of the transmission window when v is 0. The above is the theoretical basis for the weighted multi-step sampling measurement technique.
When the technology is used for actual measurement, the solution of a pre-analysis matrix needs to be carried out firstly. The solved pre-analysis matrix can be stored for direct use in subsequent measurement without solving the matrix for each measurement. The solving process of the algorithm pre-analysis matrix is very simple, as shown in the algorithm flow chart of fig. 7:
the first step is to set a main following function based on experience, wherein 6 groups of sampling weight functions are adopted based on different cavity length coefficients and phase shift reference coefficients, and a multi-surface interference acquisition process and an algorithm processing process are completely simulated by accurately designing a multi-surface interference phase shift measurement algorithm and using a Zernike fitting mode. The phase-shifting reference coefficient is iterated through double iteration of different cavity length coefficients and phase-shifting reference coefficients, iteration of the cavity length coefficients is brought into a calculation process in the iteration process, namely double iteration, phase results obtained after unwrapping and solved by the surfaces under different cavity length coefficients and different phase-shifting reference coefficients are obtained, and then surface shape results of the surfaces are solved, wherein three pieces of information, namely the front surface, the rear surface and thickness change of the measured piece are mainly considered. And solving a residual error after the surface shape results are subjected to inclination elimination, wherein the residual error is obtained by the peak distance of each data deviating from the mean value and is the maximum average difference value. The residual data is stored in a pre-analysis matrix and decisions and magnitudes are made. The judgment conditions are selected as follows: during double iteration, under the conditions of the current cavity length coefficient and the phase-shifting reference coefficient, the residual error results of three interference information, namely the current surface, the back surface and the thickness change, are simultaneously less than 1.2nm, and the algorithm under the conditions is judged to be applicable. The double iteration results of the cavity length coefficient and the phase shift reference coefficient are solved and then placed in the pre-analysis matrix again to cover the old parameters, so that the pre-analysis parameter library shown in fig. 11 can be obtained.
When the algorithm is used, the distance from a measured piece to a reference mirror is measured by a high-precision laser ranging sensor, the value is read into the phase-shifting algorithm designed in the text, and then the cavity length coefficient and the phase-shifting reference coefficient can be automatically calculated only by inputting the values of the thickness and the refractive index. In the process of solving the pre-analysis matrix, because the calculation process under different cavity length coefficients inevitably is discrete data, the processing mode selected by the method of the embodiment is as follows: the position search is carried out on the actual cavity length coefficient, two discrete values always exist to enable the actual cavity length coefficient to be between the two discrete values, so that the adjacent larger value is selected as a pre-estimated value, and the phase shift reference coefficient is searched for the pre-estimated value to complete the preparation process of the algorithm. In the notation, N denotes a phase shift reference coefficient and M denotes a cavity length coefficient, which is a ratio of a cavity length from the front surface to the reference mirror to an optical path length of a thickness variation.
Total number of acquisition frames H and sampling basis function V under different N1--V6Appended to the following.
k is 1 … … H, j is an imaginary unit, so the sampling function can be expressed as:
wherein Vi' is the sampling basis function ViNormalized (0-1) result of (a), wherein i ═ 1 … … 6. The next step is to bring the current adaptable phase-shifting reference coefficient and the actual cavity length value searched from the pre-analysis matrix into a phase-resolving algorithm, design the phase-shifting value, the interferogram acquisition frame number and the weighted sampling function through different phase-shifting reference coefficients, then perform arc tangent calculation on the data to obtain a wrapping phase, obtain the surface shape of the corresponding measured surface through simple calculation after the wrapping and the obliquity are taken, and complete the multi-surface interference measurement process. In the searching process, because the iteration parameters are discrete when the pre-analysis matrix is constructed, the iteration step pitch of N is 1, and the iteration step pitch of M is 0.1, the situation of all cavity length coefficients cannot be satisfied certainly. As can be seen from the schematic diagram of the pre-analysis parameter library in fig. 11, for a certain cavity length coefficient, the value N corresponding to the right scale within 1 step must satisfy the conditions of N and N +1, so the processing method adopted here is to take the right scale value of the scale range where the actual cavity length coefficient is located as the pre-estimated value, and then select N according to the pre-estimated value. After the phase-shifting reference coefficient N and the cavity length coefficient M are positioned and selected, the calculation of a sampling function can be carried out, at the moment, the algorithm design process is completed, and the formulation of a specific measurement scheme and the design of an acquisition scheme of an interference pattern are carried out next.
The total collection frame number, the phase shift value of each frame and the corresponding collection total frame number H set based on experience can be determined through the selected N value, and the phase shift value is 2 pi/N.
As can be seen from fig. 6, a thin line frame in the drawing indicates the inside of the interferometer, when the interferometer works, a tunable light beam is emitted by the wavelength tunable laser 12, and is split into two light beams by the beam splitter prism 13, one light beam enters the observation system CCD camera 24 after passing through the second lens 21, the diaphragm 22 and the third lens 23, after a part of the first lens 14 and the collimating lens 15 are collimated, the light beam passes through the reference mirror 16 and is transmitted to the measured mirror 17, and is reflected, and then enters the observation system through a reverse light path, and interference occurs between the light beams, at this time, the observation system can acquire an interference light intensity cross fringe with aliasing of multi-surface interference information, as shown in fig. 8. The interference pattern collected by the CCD camera 24 is connected with a computer through a data line for data transmission and reading and writing, so that the algorithm in the computer can directly act on the interference pattern.
The measured lens 17 is held by a clamp assembly 18, wherein the clamp assembly 18 comprises a clamp and the guide rail frame 7. As shown in fig. 4, after the test lens 16 is held by the jig, the jig is combined with the rail holder 7 through the jig fitting screw hole 11. The structure of the guide rail frame 7 can be seen from fig. 3, 4 and 5, and the guide rail frame 7 is composed of an upper hollow cavity and a lower hollow cavity with a certain thickness, and the lower hollow cavity is provided with a groove and can be clamped on the guide rail 19 and perform matching movement. And a guide rail frame assembling threaded hole 10 is formed above the guide rail frame 7, and the upper structure and the lower structure of the guide rail frame are assembled through a bolt 9. As can be seen from fig. 5, the reference arm 1 can be caught in the grooves on both sides of the rail holder 7 by the reference arm guide grooves 25 on both ends and can move. The left side and the right side inside the guide rail frame 7 are respectively provided with a knob 4, and the lower part of the knob is assembled in a matching way through a screw rod 6 of the knob and a threaded hole 8 on the frame body.
And as can be seen from fig. 2, the knob 4 is provided with teeth 5, as can be seen from fig. 1, the knob 4 can be matched with the racks 3 on the reference arms 1 arranged at the two ends of the frame body, and the part of the reference arm 1 facing the interferometer is coated with a coating material 2, and the coating can improve the reflectivity of the material so as to match laser ranging. The reference arm 1 can be moved back and forth by rotating the knob 4, and thus the calibration with the front surface of the test mirror 17 and the ranging with the laser ranging sensor 20 can be achieved. The laser ranging sensors 20 can be adhered to the front side and the rear side of the bottom of the interferometer respectively, the outer surface of the reference mirror 16 is used as a reference, the distance average value of the calibrated reference arm 1 is measured and used as the absolute distance value of the measured mirror 17 and the reference mirror 16, and the cavity length value can be obtained, so that the algorithm design process is substituted. Meanwhile, the laser ranging sensor 20 is connected with a computer through a data line, and the computer reads the average value of the measured distance values to be used as necessary data for calculating the cavity length coefficient.
After the above processes are completed, algorithm pre-analysis and data acquisition are completed, and the next step is that during measurement, the thickness and refractive index values of the measured element are directly input in calculation, the current actual cavity length value is read and measured by a distance measuring sensor, the acquired interferogram is calculated through a weighting sampling function matched with the current cavity length value, a phase resolving result can be obtained, and the shape distribution of each surface of the measured element can be obtained after simple calculation. As shown in fig. 9 and 10, the residual error unit in fig. 10 is um, and it can be seen from the results that the technology provided by the present invention can well implement the multi-surface interference solution and measurement process for the transparent parallel flat plate, the residual error is at sub-nanometer level, and the measurement accuracy is very high.
Attached: v corresponding to different N1--V6The method specifically comprises the following steps:
n is 9, collecting frame number H is 57, V1：
V1＝[0.2222,1.5556,6.2222,18.6667,46.6667,102.6667,205.3333,381.3333,667.3333,1241.3333,1899.3333,2837.3333,4125.3333,5833.3333,8025.3333,10752,14042,17892,22129.3333,26931.3333,32041.3333,37294.6667,42494.6667,47422.6667,51851.3333,55561.3333,58361.3333,60111.3333,60749.3333,60111.3333,58361.3333,55561.3333,51851.3333,47422.6667,42494.6667,37294.6667,32041.3333,26931.3333,22129.3333,17892,14042,10752,8025.3333,5833.3333,4125.3333,2837.3333,1899.3333,1241.3333,667.3333,381.3333,205.3333,102.6667,46.6667,18.6667,6.2222,1.5556]；
N is 10, collecting frame number H is 64, V2:
V2＝[0.2,1.4,5.6,16.8,42,92.4,184.8,343.2,600.6,1001,1894.2,2759.4,3967.6,5602.8,7752,10500,13923,18081,23009,28707,34839,41905,49476,57372,65373,73227,80661,87395,93159,97713,100870,102522,102522,100870,97713,93159,87395,80661,73227,65373,57372,49476,41905,34839,28707,23009,18081,13923,10500,7752,5602.8,3967.6,2759.4,1894.2,1001,600.6,343.2,184.8,92.4,42,16.8,5.6,1.4,0.2]；
N is 11, collecting frame number H is 71, V3:
V3＝[1.2727,5.0909,15.2727,38.1818,84,168,312,546,910,1456,2836.9091,3954.3636,5485.4545,7528.3636,10186.9091,13566,17766,22876,28966,36078,44216,52750.7273,62767.0909,73534.3636,84859.0909,96500.7273,108178,119578,130368,140210,148778,155778,160970.7273,164197.0909,165406.3636,164197.0909,160970.7273,155778,148778,140210,130368,119578,108178,96500.7273,84859.0909,73534.3636,62767.0909,52750.7273,44216,36078,28966,22876,17766,13566,10186.9091,7528.3636,5485.4545,3954.3636,2836.9091,1456,910,546,312,168,84,38.1818,15.2727,5.0909,1.2727,0.1818]；
N is 12, and the number of acquisition frames H is 78, V4:
V4＝[0.1667,1.1667,4.6667,14,35,77,154,286,500.5,834.1667,1334.6667,2062.6667,4170.8333,5591.8333,7505.3333,10024,13268.5,17363.5,22432.6667,28592.6667,35946.1667,44573.8333,54525.3333,65809.3333,77308,91084,105910,121580.6667,137837.1667,154372.1667,170837.3333,186853.3333,202022.3333,215943,228228,238524,246534.1667,252043.1667,254944.6667,254944.6667,252043.1667,246534.1667,238524,228228,215943,202022.3333,186853.3333,170837.3333,154372.1667,137837.1667,121580.6667,105910,91084,77308,65809.3333,54525.3333,44573.8333,35946.1667,28592.6667,22432.6667,17363.5,13268.5,10024,7505.3333,5591.8333,4170.8333,2062.6667,1334.6667,834.1667,500.5,286,154,77,35,14,4.6667,1.1667,0.1667]；
N is 13, collecting frame number H is 85, V5:
V5＝[0.1538,1.0769,4.3077,12.9231,32.3077,71.0769,142.1538,264,462,770,1232,1904,2856,6021.0769,7803.5385,10166.1538,13236.4615,17152.1538,22057.5385,28099.0769,35420,44154,54418,66304,79870,95130,110198.3077,128676.1538,148560.6154,169635.8462,191626.6154,214202.1538,236982.3077,259546,281442,302202,321356,338450,353066,364844.3077,373508.1538,378890.6154,380963.8462,378890.6154,373508.1538,364844.3077,353066,338450,321356,302202,281442,259546,236982.3077,214202.1538,191626.6154,169635.8462,148560.6154,128676.1538,110198.3077,95130,79870,66304,54418,44154,35420,28099.0769,22057.5385,17152.1538,13236.4615,10166.1538,7803.5385,6021.0769,2856,1904,1232,770,462,264]；
N＝14，The collection frame number H is 92, V6:
V6＝[0.1429,1,4,12,30,66,132,245.1429,429,715,1144,1768,2652,3876,8539.1429,10748,13634,17340,22021,27841,34969,43574.1429,53820,65858,79820,95810,113895,134095,153372.1429,177637,203727,231417,260417,290375,320882,351479.1429,381667,410917,438685,464427,487617,507767,524449.1429,537320,546147,550837,550837,546147,537320,524449.1429,507767,487617,464427,438685,410917,381667,351479.1429,320882,290375,260417,231417,203727,177637,153372.1429,134095,113895,95810,79820,65858,53820,43574.1429,34969,27841,22021,17340,13634,10748,8539.1429]。
The method and the system for analyzing the phase of the interference weighted sampling under any cavity length based on pre-analysis are used for solving the problem of aliasing interference measurement of a multi-surface transparent measured piece, and comprise two parts of algorithm design and hardware realization: in the aspect of automatic design of the algorithm, the method is mainly divided into the following processes. Firstly, performing double iteration on a phase-shifting reference coefficient and a cavity length coefficient within a certain range according to the characteristics of a weighted multi-step sampling algorithm; then, the mean square error of the maximum error is taken for judging the algorithm result based on Zernike polynomial interference simulation and multi-step weighted discrete sampling, when the separation error of each piece of information is less than 1.2um, the algorithm is judged to be available, otherwise, the algorithm is judged to be unavailable, and then the information is stored in a pre-analysis matrix; when the method is actually used, the hardware design part uses the laser ranging sensor to realize the automatic measurement of the distance of the measured piece, so that only the thickness and reflectivity information of the measured piece needs to be input during operation, specific parameters in the algorithm can be automatically selected and designed after the preanalysis matrix is called, and available values are selected from 6 standby algorithms to carry out weighted multi-step sampling calculation; and then, after the algorithm parameters are selected, making an experimental scheme and acquiring an interferogram of the interferometer, wherein the acquisition frame number and the phase shift value are related to a phase shift reference coefficient. When in measurement, the information of each surface can be automatically measured only by inputting the thickness value and the refractive index of the measured piece. In terms of hardware: the high-precision realization of an automatic algorithm is realized by matching a laser ranging sensor, a clamp combination and a guide rail, wherein the clamp combination comprises a clamp and a guide rail frame. And reversely designing an algorithm and an experimental acquisition scheme and automatically designing the algorithm after the phase-shift value which is suitable for the current working condition is obtained through pre-analysis. The technology can well solve the problem of phase-shifting bottleneck under any cavity length, and because the algorithm is automatically designed, the application cost and the design cost of the technology are reduced, and the application range of the wavelength phase-shifting interference technology is widened. The method and the test system solve the problem of phase solving in interferometry, and particularly solve the problem of measurement limitation of the intelligent application of one algorithm in a weighted multi-step sampling algorithm to a narrow-range discrete cavity length condition. The method and the test system automatically design the solution technical scheme of the algorithm parameters by pre-analyzing the solution algorithm, and the method comprises a design method of an algorithm library, an algorithm and an automatic design technology of an experimental scheme; the method can well solve the problem of phase-shifting bottleneck under any cavity length, reduces the technical application cost and the design cost because the algorithm is automatically designed, widens the application range of the wavelength phase-shifting interference technology, is simple and easy to implement, has low cost, and is suitable for popularization and use.
While the embodiments of the present invention have been described with reference to the accompanying drawings, the present invention is not limited to the above embodiments, and various changes and modifications can be made according to the purpose of the invention, and any changes, modifications, substitutions, combinations or simplifications made according to the spirit and principle of the technical solution of the present invention shall be equivalent substitutions, as long as the purpose of the present invention is met, and the present invention shall fall within the protection scope of the present invention without departing from the technical principle and inventive concept of the interferometric weighted sampling dephasing analysis method and measurement system based on the pre-analysis under any cavity length.
Claims (6)
1. A pre-analysis-based interference weighted sampling dephasing analysis method under any cavity length is characterized by comprising the following processes and steps:
a. according to the characteristics of the weighted multi-step sampling algorithm, performing double iteration on the phase-shifting reference coefficient and the cavity length coefficient within a certain range;
b. judging the mean square error of the maximum error of the algorithm result based on Zernike polynomial interference simulation and multi-step weighted discrete sampling, judging that the algorithm is usable when the separation error of each piece of information is less than 1.2um, otherwise, judging that the algorithm is unusable, and then storing the information in a pre-analysis matrix;
c. measuring the distance of a measured piece by using a laser ranging sensor, setting the thickness and reflectivity information of the measured piece, calling a pre-analysis matrix, selecting and designing specific parameters in an algorithm, and selecting available values from an algorithm library to perform weighted multi-step sampling calculation;
d. after the algorithm parameters are selected, acquiring an interferogram of the interferometer, wherein the acquisition frame number and the phase shift value are related to a phase shift reference coefficient, setting the thickness value and the refractive index of the measured piece during measurement, and measuring the information of each surface of the measured piece.
2. The pre-analysis-based interferometric weighted sampling dephasing analysis method at any cavity length according to claim 1, comprising: in the process of establishing an iteration and value judgment method, for each cavity length coefficient, enabling a phase-shifting reference coefficient value corresponding to right-side scales within 1 step pitch to simultaneously meet the conditions of a current phase-shifting reference coefficient and a right-side adjacent phase-shifting reference coefficient, taking a right-side scale value of a scale range where an actual cavity length coefficient is located as a pre-estimated value, and selecting the phase-shifting reference coefficient through the pre-estimated value; after the positioning and selection of the phase-shifting reference coefficient and the cavity length coefficient, the calculation of the sampling function is carried out, and the preparation process of algorithm design is completed.
3. The pre-analysis-based interferometric weighted sampling dephasing analysis method at any cavity length according to claim 1, comprising: carrying out aliasing interference measurement on a multi-surface transparent measured piece, carrying out double iteration on different cavity length coefficients and phase-shifting reference coefficients, carrying out iteration on the phase-shifting reference coefficients, taking the iteration of the cavity length coefficients into a calculation process in the iteration process, thus obtaining the phase result after unwrapping solved by each surface under different cavity length coefficients and different phase-shifting reference coefficients, further solving the surface shape result of each surface, and mainly considering three information of the front surface, the rear surface and the thickness change of the measured piece.
4. A pre-analysis-based measurement system for interference weighted sampling at any cavity length adopts the pre-analysis-based method for resolving the phase of the interference weighted sampling at any cavity length according to claim 1, and is characterized in that: the measuring system mainly comprises a laser ranging sensor (20), a clamp combination (18) and a matching device of a guide rail (19), wherein the clamp combination (18) comprises a clamp and a guide rail frame (7);
adjustable reference arms (1) are arranged at two ends of the guide rail frame (7), and racks (3) are arranged on the inner sides of the adjustable reference arms (1) and are in matched transmission with knobs (4) with teeth (5); the bottom end of the knob (4) is provided with a screw rod (6) which is in threaded connection with a threaded hole (8) at the bottom end inside the guide rail frame (7), and the knob (4) and the adjustable reference arm (1) are respectively arranged at two ends of the guide rail frame (7); a high-reflectivity coating (2) is coated on the adjustable reference arm (1) according to the wavelength of a laser so as to be matched with the work of the laser ranging sensor (20);
the tested lens (17) is clamped by a clamp combination (18); after the tested lens (16) is clamped by the clamp, the clamp is combined with the guide rail frame (7) through the clamp assembling threaded hole (11); the guide rail bracket (7) consists of an upper hollow cavity and a lower hollow cavity, and a groove is formed in the lower part of the guide rail bracket (7) so that the guide rail bracket (7) is clamped on the guide rail (19) and moves in a matching way; a guide rail frame assembling threaded hole (10) is formed above the guide rail frame (7) to assemble the upper and lower structures of the guide rail frame through a bolt (9); the adjustable reference arm (1) is clamped in grooves at two sides of the guide rail bracket (7) through reference arm guide grooves (25) at two ends and moves;
the adjustable reference arm (1) is controlled to move back and forth by rotating the knob (4), so that the correction of the front surface of the measured mirror (17) and the distance measurement of the laser distance measuring sensor (20) are realized; the laser ranging sensors (20) are arranged on the front side and the rear side of the bottom of the interferometer respectively, the outer surface of the reference mirror (16) is used as a standard, the distance average value of the calibrated adjustable reference arm (1) is measured and used as the absolute distance value between the measured mirror (17) and the reference mirror (16), and therefore a cavity length value is obtained; the laser ranging sensor (20) is in signal connection with an upper computer, and the computer reads the average value of the measured distance values as data information for calculating the cavity length coefficient.
5. The pre-analysis based measurement system for interferometric weighted sampling at arbitrary cavity lengths as set forth in claim 4, wherein: the tested piece is clamped by a clamp of a clamp assembly (18), so that the tested transparent parallel flat plate can be perpendicular to the workbench, the tested parallel flat plate is parallel to the outer surface of a reference mirror (16) of the interferometer, and interference is generated between the front surface and the rear surface of the tested piece and the outer edge surface of the reference mirror (16) respectively by adjusting the position of the clamp.
6. The pre-analysis based measurement system for interferometric weighted sampling at arbitrary cavity lengths as set forth in claim 4, wherein: the bottom end of the guide rail frame (7) is matched with a guide rail (19) on the workbench to move, and the vertical height center of the clamp is aligned with the center of the circle of the outer surface of the interferometer.
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| CN112880569A (en) * | 2021-01-25 | 2021-06-01 | 上海大学 | Multi-surface measurement method based on cavity length correction |
| CN112880981A (en) * | 2021-01-25 | 2021-06-01 | 上海大学 | Multi-surface interference measurement method capable of adaptively adjusting cavity length |
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| CN114636382B (en) * | 2021-10-20 | 2024-03-19 | 上海大学 | Four-surface interferometry method and fixture guide rail system for transparent parallel flat plate at any measuring position |
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