A large-aperture workbench phase-shifting interference surface shape measurement device and method

Abstract

The present invention relates to a large-aperture workbench phase-shifting interference surface shape measurement device and method, aiming to solve the problem that the existing large-aperture interferometer is difficult to accurately shift phase or even cannot shift phase. The device uses a single piezoelectric ceramic to drive a low-friction heavy-load workbench to move along a linear guide rail with a small thrust, thereby driving a large-aperture optical element fixed on the workbench to complete phase shifting; three displacement sensors are used to monitor the pitch and yaw of the workbench in real time and highly dynamically, thereby calculating the translation and tilt phase shift errors of the optical element, and bringing them into the tilt elimination phase shift algorithm, and finally accurately extracting the surface shape result to be measured from the phase-shifting interference diagram. The device and method not only have a simple mechanical structure and low cost, but also the measurement accuracy is not affected by factors such as 1) the diameter and weight of the element, 2) motion errors such as the pitch and yaw of the workbench, 3) chromatic aberration caused by wavelength tuning, and 4) the length of the interference cavity. The device and method provide a simple and feasible way with high precision and low cost for large-aperture phase-shifting interference measurement.

Description

Technical Field

[0001] The invention relates to a large-caliber workbench phase-shift interference surface shape measuring device and method, belonging to the field of precision optical detection. Technical Background

[0002] Large-aperture optical components are widely used in large optical systems or major national projects such as astronomical telescopes, inertial confinement fusion devices, and high-energy laser weapons. The quality of the surface morphology of large-aperture optical components is one of the key parameters that determine the overall performance indicators of these systems. Therefore, it is of great significance to accurately measure the surface morphology of large-aperture optical components. In addition, the surface shape detection capability and detection accuracy of large-aperture optical components are also important indicators for measuring the development level of a country's precision measurement and manufacturing fields.

[0003] Phase-shift interferometry (PSI) is widely used in the field of optical surface detection as an extremely important detection method due to its unique anti-background interference ability and high-precision measurement ability in the field of optical interferometry. The basic principle of PSI is to introduce a phase shift in the interference pattern, and then calculate the phase and surface distribution through the collected multi-frame phase-shift interferogram. Phase shifting is the most critical step in PSI, and the accuracy of phase shifting directly determines the measurement accuracy. At present, the most classic and widely used phase shifting method is the mechanical phase shifting of the reference mirror, that is, the reference mirror is driven to step by the elongation of three piezoelectric ceramics (PZT), thereby introducing a phase shift in the reference light. This phase shifting method is not only relatively simple, but also can compensate for the tilt phase shift error caused by the cantilever fixed structure of the reference mirror by individually controlling each PZT. For example, Zhu Yu et al. proposed a three-piezoelectric ceramic phase shifter (Zhu Yu, Chen Jinbang, Zhu Rihong, Gao Zhishan. Correction and calibration of interferometer phase shifter composed of three piezoelectric ceramic stacks [J]. Acta Optica Sinica, 2001, 21(4): 468-471), which not only performs nonlinear correction on the three piezoelectric ceramic stacks, but also comprehensively analyzes the inconsistency between the piezoelectric ceramic stacks, thereby realizing the tilt calibration in small-aperture phase-shifting interferometry. The load of this phase shifter is only about 10KG, which can meet the general needs of small-aperture phase-shifting interferometry.

[0004] However, the surface shape detection of large-aperture optical components generally requires a large-aperture reference mirror. When the PZT is used, its weight is usually tens of kilograms or even hundreds of kilograms. In this case, if the 3-PZT mechanical phase shifter is used to drive the large-aperture reference mirror for phase shifting, the heavy weight of the reference mirror will inevitably seriously hinder the extension of one or more PZTs, resulting in an increase in the phase shift error or even the inability to drive the phase shift. Dr. Wu Xuhua of Nanjing University of Science and Technology wrote in his dissertation (Wu Xuhua. Research on Key Technologies of Phase-Shifting Interferometer [D]. Nanjing University of Science and Technology, 2007.) studied a three-piezoelectric ceramic phase shifter used in a 300mm aperture phase-shifting interferometer. This phase shifter already requires complex tilt correction and nonlinear correction due to the heavy weight of the reference mirror. In fact, when the aperture of the interferometer continues to increase, even up to 600mm or more, the reference mirror phase shifting method is difficult to achieve accurate phase shifting, and even PZT cannot drive the reference mirror to complete phase shifting and measurement. It can be seen that the reference mirror mechanical phase shifting method (three-piezoelectric ceramic phase shifting method) is difficult to achieve high-precision large-aperture phase-shifting interferometry.

[0005] Because of this, large-aperture phase-shifting interferometers currently have to use wavelength-tuned phase-shifting, which uses a tunable laser as the interferometer light source and introduces the phase shift by tuning the laser wavelength. The advantage of wavelength-tuned phase-shifting is that both the reference mirror and the measured mirror remain stationary during the phase-shift measurement, which greatly increases the mechanical stability of the instrument system, and the phase-shifting accuracy is independent of the measurement aperture or component weight.

[0006] For example, in 2005, Chengdu Precision Optical Engineering Research Center successfully developed Wavelength tuning phase-shifting interferometer (L.Chai, Q.Xu, Y.Deng, G.Cheng, J.Xu, and Q.Shi, "500-mm aperture wavelength-tuning phase-shifting interferometer," in 2nd International Symposium on Advanced Optical Manufacturing and Testing Technologies (SPIE, 2006), p.6.), which uses the tunable semiconductor laser of New Focus Company of the United States as the light source. When the cavity length is 21cm, the PV value measurement accuracy can reach 1 / 20λ. In 2011, Dr. Liu Zhaodong of Nanjing University of Science and Technology wrote his dissertation (Liu Zhaodong. Near-infrared phase-shifting Fizeau interferometer calibration and test technology research [D]. Nanjing University of Science and Technology, 2011.) introduced in detail the 600mm aperture wavelength phase-shifting interferometer he studied, which also used the tunable semiconductor laser of New Focus Company in the United States as the light source. ZYGO Company is currently one of the leaders in the world's interferometric measurement industry. Its 24-inch Large-aperture phase-shifting interferometers also use wavelength-tuned phase-shifting to perform phase-shifting interferometry ( https: / / zygo.com.cn / ).

[0007] However, the wavelength tuning phase shifting method has its inherent defects in principle. First, the change of wavelength will introduce chromatic aberration, which brings difficult-to-analyze errors to high-precision surface measurement. Secondly, the phase shift introduced by wavelength tuning is related to the length of the interference cavity. In the case of a long interference cavity, high-resolution wavelength tuning is required, and in the case of a short interference cavity, phase shifting requires a wide range of wavelength tuning. The existing wavelength tuning lasers cannot meet both high resolution and large tuning range requirements at the same time. Therefore, the scope of application of wavelength tuning phase shifting is limited, and the phase shifting accuracy needs to be improved. Not only that, due to the limitation of process level, the wavelength tuning lasers with good performance currently mainly rely on foreign imports. This seriously limits my country's independent research on high-precision large-aperture phase shifting interferometers. This in turn restricts the research and construction of major scientific research projects in my country such as laser nuclear fusion and extreme ultraviolet lithography.

[0008] In summary, in principle, mechanical phase shifting is the first choice for phase-shifting interferometry. However, in large-aperture phase-shifting interferometers, the aperture of the phase-shifted optical element is as high as 800mm and the mass is about 100KG, which makes it impossible to achieve phase shifting using traditional mechanical phase shifting methods, that is, "unable to move". Therefore, large-aperture interferometers have to use wavelength phase shifting. However, there are many problems with the wavelength phase shifting method, which also makes it difficult to improve the phase shifting accuracy and measurement accuracy, that is, "unable to shift accurately" or "unable to measure accurately".

[0009] To this end, the present invention proposes a large-aperture workbench phase-shifting interference surface shape measurement device and method. The phase shifting method is mechanical phase shifting, but unlike the traditional mechanical phase shifting method, the device and method fix the large-aperture, heavy-weight optical element on a low-friction heavy-load workbench. Even under heavy load conditions, the friction resistance of the low-friction heavy-load workbench is close to zero, so the very small thrust output by a single piezoelectric ceramic can push it to move along the linear guide rail, thereby effectively solving the key problem of "immovable" large-aperture optical elements. Three displacement sensors are used to accurately monitor the pitch and yaw of the low-friction heavy-load workbench during the phase shifting process, and then the translation and tilt phase shift errors are accurately calculated, and brought into the tilt elimination phase shifting algorithm to accurately calculate the surface shape to be measured, thereby solving the problem of "inaccurate movement / inaccurate measurement" from the side. The present invention effectively solves the problems of "cannot move" and "cannot move / measure accurately" commonly existing in existing large-aperture interferometers, and does not require expensive, imported wavelength-tuned lasers, thereby providing a high-precision, low-cost, autonomous and controllable detection approach for the research of many major scientific research or engineering projects in my country. Summary of the invention

[0010] The purpose of the present invention is to solve the problems of "cannot move" and "cannot move accurately" in the current large-aperture interferometer, and to propose a large-aperture workbench phase-shifting interference surface shape measurement device and method.

[0011] The present invention fixes large-caliber and heavy-weight optical elements on a low-friction heavy-load workbench. Even under heavy load, the friction resistance of the low-friction heavy-load workbench is close to zero, so the small thrust output by a single piezoelectric ceramic can push it to move along the linear guide rail, thereby effectively solving the key problem of "immovable" large-caliber optical elements. On this basis, three displacement sensors are used to accurately monitor the pitch and yaw of the low-friction heavy-load workbench during the phase shifting process, and then accurately calculate the translation and tilt phase shift errors, and bring them into the tilt-eliminating phase shifting algorithm to accurately calculate the surface shape to be measured, thereby solving the problem of "improper shifting" from the side.

[0012] The purpose of the present invention is achieved through the following technical solutions.

[0013] A large-aperture workbench phase-shifting interference surface shape measuring device includes a small-aperture interferometer host, a beam expansion system, a large-aperture collimator, a transmission flat crystal, a measured flat crystal, a large-aperture adjustment frame, a low-friction heavy-load workbench, a sensor monitoring plate, a linear guide rail, piezoelectric ceramics, a sensor workbench, a sensor fixing frame, displacement sensor A, displacement sensor B and displacement sensor C; the collimated light beam emitted by the small-aperture interferometer host is expanded by the beam expansion system into a large-aperture measuring light, the transmission flat crystal is fixed on the beam expansion system, and the measured flat crystal is fixed on the low-friction heavy-load workbench through the large-aperture adjustment frame. The large-aperture measuring light passes through the transmission flat crystal and is reflected by the measured flat crystal along the original path, and enters the beam expansion system and the small-aperture interferometer host after passing through the transmission flat crystal again. Both the low-friction heavy-load workbench and the sensor workbench can move along the linear guide rail, and the sensor workbench can be locked and fixed with the linear guide rail; the piezoelectric ceramic is fixed on the sensor workbench, and it contacts and is pre-tightened with the low-friction heavy-load workbench through a ball head. During the phase shift measurement, the sensor table is locked and fixed with the linear guide rail, and the low-friction heavy-load table is driven by the piezoelectric ceramic to move along the linear guide rail without creeping, thereby driving the measured flat crystal to complete the phase shift. The sensor monitoring plate is fixed on the low-friction heavy-load table, and the sensor bracket is fixed on the sensor table. Three displacement sensors are configured on it to monitor the displacement of three local positions on the sensor monitoring plate in real time and highly dynamically during the phase shift process, and then the translation and tilt phase shift errors of the measured flat crystal are calculated, and the surface shape to be measured is accurately solved.

[0014] The displacement sensor includes a contact displacement sensor and a non-contact displacement sensor.

[0015] The low-friction heavy-load workbench includes a hydraulic workbench, an air-floating workbench, a precision ball workbench, a magnetic suspension workbench, and the like.

[0016] The present invention discloses a large-aperture workbench phase-shifting interference surface shape measurement method, and the measurement steps are as follows:

[0017] Step 1: Turn on the small-aperture interferometer host, install the transmission flat crystal and the measured flat crystal in sequence, and adjust the posture of each flat crystal until interference fringes are observed in the main control computer;

[0018] Step 2: The main control computer outputs a nonlinear increasing analog voltage signal to control the piezoelectric ceramic to extend at equal intervals, thereby driving the low-friction heavy-load workbench and the flat crystal to be measured to achieve fixed-step phase shifting;

[0019] Step 3: The main control computer collects the phase-shifting interference pattern and simultaneously collects the measurement data of the three displacement sensors at high speed;

[0020] Step 4: Calculate the magnitude and direction of the translation and tilt phase shift errors from the measurement data of the three displacement sensors, bring them into the tilt elimination phase shift interference algorithm and finally calculate the surface measurement results.

[0021] The formula for calculating the translation and tilt phase errors from the measurement data of the three displacement sensors described in the method of the present invention is as follows:

[0022]

[0023]

[0024]

[0025] The subscript n represents the number of phase shift steps, δ(n) represents the translation phase shift amount, α(n) and β(n) represent the tilt phase shift coefficients, and a n b n c n are the displacements measured by the three displacement sensors, λ is the wavelength of the interferometer light source, D is the effective measurement aperture, and l is the distance between displacement sensors A and B, and between B and C.

[0026] The phase shift described in the method of the present invention can also adopt a random phase shift mode, that is, the main control computer outputs analog voltage in equal steps to make the piezoelectric ceramics stretch nonlinearly; or arbitrarily give an output analog voltage to make the piezoelectric ceramics stretch randomly.

[0027] When the surface morphology of a large-aperture spherical measured component is measured in the method of the present invention, the measured flat crystal is replaced with a measured spherical mirror, and a large-aperture lens or a large-aperture computerized holographic plate is placed between the measured spherical mirror and the transmission flat crystal to achieve convergence or divergence of the measurement light beam, and the center of the measured spherical mirror coincides with the convergence point of the measurement light beam.

[0028] The calculation steps of the de-tilting phase-shifting interference algorithm described in the method of the present invention are as follows:

[0029] Step (1), calculate the background a(i,j) and modulation b(i,j) from all interference patterns I(i,j,n), where (i,j) represents the pixel coordinates, max[I(i,j,n)] and min[I(i,j,n)] represent the maximum grayscale value and the minimum grayscale value of the pixel point (i,j) in all interference patterns, respectively;

[0030] a(i,j)={max[I(i,j,n)]+min[I(i,j,n)]} / 2

[0031] b(i,j)={max[I(i,j,n)]-min[I(i,j,n)]} / 2

[0032] Step (2), taking the calculated translation and tilt phase shifts as known values, and calculating the phase distribution using the least squares method; writing the light intensity model of the interference pattern as I(i,j,n)=a(i,j)+C(i,j)cos[Δ(i,j,n)]+S(i,j)sin[Δ(i,j,n)],

[0033] Among them, Δ(i,j,n) is the tilt phase shift, C(i,j) and S(i,j) are two intermediate parameters introduced for the convenience of writing, which are:

[0034] Δ(i,j,n)=δ n +α n i+β n j,

[0035] C(i,j)=b(i,j)cos[W(i,j)4π / λ],

[0036] S(i,j)=b(i,j)sin[W(i,j)4π / λ],

[0037] Substitute all known quantities and use the least squares method to find C(i,j) and S(i,j), and then use the inverse tangent formula to find the surface shape W(i,j);

[0038] Step (3), taking the surface shape W(i, j) obtained in step (2) as a known value, recalculate the new translation phase shift and tilt phase shift parameters; rewrite the light intensity expression as

[0039]

[0040] G S (i,j,n)=b(i,j)sin[Φ(i,j,n)]

[0041] Φ(i,j,n)=W(i,j)4π / λ+Δ(i,j,n)

[0042] in, represents the light intensity model, are the correction values ​​of α(n), β(n) and δ(n), G s (i, j, n) is an intermediate parameter introduced for the sake of writing convenience. Φ(i, j, n) represents the total phase, which includes the phase distribution and tilt phase shift caused by the measured surface shape. Substitute all known quantities and calculate it by the least squares method. Substitute the following formula to obtain the new tilt phase shift parameters and translation phase shift quantities α′(n), β′(n), δ′(n):

[0043]

[0044] Step (4), given the convergence threshold ε, As a criterion to determine whether the iterative calculation converges; if If the calculation is successful, it is considered convergent and the measured surface shape result is obtained directly. Otherwise, repeat steps (2), (3), (4) until the calculation converges.

[0045] Beneficial Effects

[0046] Compared with the prior art, the present invention has the following advantages:

[0047] 1. It adopts low-friction heavy-load workbench phase shifting technology, with large load-bearing capacity, high motion accuracy, no influence of chromatic aberration or cavity length, and is suitable for large-aperture phase shifting interferometry;

[0048] 2. Three displacement sensors are used to monitor the translation and tilt phase errors of the components at the same time, and are brought into the algorithm for solution. Without any phase shift calibration, the measurement accuracy can be effectively guaranteed not to be affected by the phase shift error;

[0049] 3. The use of the de-tilt phase-shifting interferometry iterative algorithm further suppresses the influence of the tilt phase-shifting error on the measurement accuracy, greatly improving the accuracy of large-aperture phase-shifting interferometry measurement;

[0050] 4. There is no need for the complex mechanical structure required for three-piezoelectric ceramic phase shifting, and there is no need to use imported, expensive wavelength-tuned lasers, which greatly reduces system costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Figure 1 It is a schematic diagram of the principle of the present invention;

[0052] Figure 2 is a schematic diagram of the distribution of three displacement sensors of the present invention;

[0053] Figure 3 It is the algorithm calculation flow chart of the present invention;

[0054] Figure 4 is a schematic diagram of an air-floating workbench and a capacitive sensor used in Embodiment 1 of the present invention;

[0055] Figure 5 is a schematic diagram of a hydraulic workbench and an optical sensor used in Embodiment 2 of the present invention;

[0056] Figure 6 Schematic diagram of embodiment 3 of the present invention using a dense bead workbench and an inductive sensor to measure the measured mirror shape of a spherical surface;

[0057] Figure 7 is a schematic diagram of the distribution of displacement sensors according to Embodiment 3 of the present invention;

[0058] Among them: 1- small-aperture interferometer host, 2- beam expansion system, 3- large-aperture collimator, 4- transmission flat crystal, 5- measured flat crystal, 6- large-aperture adjustment frame, 7- low-friction heavy-load workbench, 8- sensor monitoring plate, 9- linear guide, 10- piezoelectric ceramic (PZT), 11- sensor workbench, 12- sensor fixing frame, 13- displacement sensor A, 14- displacement sensor B, 15- displacement sensor C, 16- air floating workbench, 17- capacitive sensor, 1 8-high pressure air pump, 19-intake pipe, 20-exhaust pipe, 21-main control computer, 22-optical sensor, 23-corner cone prism, 24-hydraulic workbench, 25-hydraulic pump, 26-oil drain pipe, 27-oil suction pipe, 28-large-diameter converging mirror, 29-converging mirror tooling, 30-converging mirror workbench, 31-measured spherical mirror, 32-dense bead workbench, 33-precision ball, 34-inductive sensor, 35-stepping motor, 36-screw, 37-translation stage. DETAILED DESCRIPTION

[0059] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0060] A large-aperture workbench phase-shifting interference surface shape measuring device comprises a small-aperture interferometer host, a beam expansion system, a large-aperture collimator, a transmission flat crystal, a measured flat crystal, a large-aperture adjustment frame, a low-friction heavy-load workbench, a sensor monitoring plate, a linear guide rail, a piezoelectric ceramic, a sensor workbench, a sensor fixing frame, a displacement sensor A, a displacement sensor B and a displacement sensor C; Figure 1 Figure 2 and Figure 3 shown.

[0061] Example 1

[0062] When an air-floating workbench is used as a low-friction heavy-load workbench, and a capacitive sensor is used as a displacement sensor to detect the surface shape of a large-diameter flat crystal, the measuring device is as follows: Figure 4 shown.

[0063] The collimated light beam emitted by the small-aperture interferometer host 1 (aperture 100mm) is expanded by the beam expansion system 2 into a large-aperture measuring light (aperture 800mm). The transmission flat crystal 4 is fixed on the beam expansion system 2, and the measured flat crystal 5 is fixed on the air-floating workbench 16 through the large-aperture adjustment frame 6. The total weight of the measured flat crystal 5 and the large-aperture adjustment frame 6 is as high as 200Kg. After passing through the transmission flat crystal 4, the large-aperture measuring light is reflected by the measured flat crystal 5 along the original path, and then passes through the transmission flat crystal 4 again before entering the beam expansion system 2 and the small-aperture interferometer host 1. The air-floating workbench 16 and the sensor workbench 11 can both move along the linear guide rail 9, and the sensor workbench 11 can be locked and fixed with the linear guide rail 9. The piezoelectric ceramic 10 is fixed on the sensor workbench 11, and it is in contact with the air-floating workbench 16 through a ball head and is pre-tightened. The high-pressure air pump 18 delivers high-pressure air into the gap between the air-floating workbench 16 and the linear guide 9 through the air inlet pipe 19, thereby forming a layer of high-pressure air film and ensuring that the air-floating workbench 16 and the linear guide 9 are not in direct contact, thereby ensuring low-friction heavy-load characteristics. The exhaust gas is uniformly collected and discharged by the exhaust pipe 20. During the phase shift measurement process, the sensor workbench 11 is locked and fixed with the linear guide, and the air-floating workbench 16 is driven by the piezoelectric ceramic 10 to move along the linear guide 9 without creeping, thereby driving the measured flat crystal 5 to complete the phase shift. The sensor monitoring plate 8 is fixed on the air-floating workbench 16, and the sensor fixing frame 12 is fixed on the sensor workbench 11. Three capacitive sensors 17 are configured on it to monitor the displacement of three local positions on the sensor monitoring plate 8 during the phase shift process in real time and with high dynamics, and then the translation and tilt phase shift errors of the measured flat crystal 5 are calculated, and the surface shape to be measured is accurately solved by this.

[0064] The steps to achieve the five-faceted measurement of the flat crystal are as follows:

[0065] Step 1: Open the small-aperture interferometer host 1, install the transmission flat crystal 4 and the measured flat crystal 5 in sequence, and adjust the posture of each flat crystal until interference fringes are observed in the main control computer 21;

[0066] Step 2: The main control computer 21 outputs a nonlinear increasing analog voltage signal to control the piezoelectric ceramic 10 to extend at equal intervals, thereby driving the air-floating workbench 16 and the measured flat crystal 5 to achieve fixed-step phase shifting;

[0067] Step 3: The main control computer 21 collects the phase-shifting interference pattern and simultaneously collects the measurement data of the three capacitance sensors 17 at high speed;

[0068] Step 4: Calculate the magnitude and direction of the translation and tilt phase shift errors from the measurement data of the three capacitive sensors 17, bring them into the tilt elimination phase shift interference algorithm and finally calculate the surface measurement result.

[0069] Example 2

[0070] When a hydraulic workbench is used as a low-friction heavy-load workbench and an optical sensor is used as a displacement sensor to detect the surface shape of a large-diameter flat crystal, the measuring device is as follows: Figure 5 shown.

[0071] The difference between this embodiment and embodiment 1 is that a hydraulic workbench 24 is used as a low-friction heavy-load workbench, and a hydraulic pump 25 is used to provide high-pressure lubricating oil to the hydraulic workbench 24 through an oil drain pipe 26, so that the hydraulic workbench 24 is not in direct contact with the linear guide rail 9, thereby achieving low-friction heavy-load characteristics. Three optical sensors 22 are used as displacement sensors, and three corner cube prisms 23 are correspondingly fixed on the sensor monitoring plate 8 to reflect the outgoing measurement light of the optical sensor 22 along the original path.

[0072] Example 3

[0073] When using a dense bead workbench as a low-friction heavy-load workbench and an inductive sensor as a displacement sensor to detect the surface shape of a large-aperture spherical mirror, the measuring device is as follows: Figure 6 and Figure 7 shown.

[0074] The difference between this embodiment and embodiment 1 is that a large-aperture converging mirror 28 is placed between the transmission flat crystal 4 and the spherical mirror 31 to be measured, and is fixed on the converging mirror workbench 30 through the converging mirror fixture 29. The translation stage 37 is locked and connected to the sensor workbench 11. The main control computer 21 controls the rotation of the stepper motor 35 and the lead screw 36, and drives the translation stage 37 to drive the sensor workbench 11 and the dense bead workbench 32 to move axially, so that the center of the spherical mirror 31 to be measured coincides with the converging center of the measuring light beam. The dense bead workbench 32 is used as a low-friction heavy-load workbench, and the gap between it and the linear guide 9 is filled with precision balls 33, so that the sliding friction during movement is converted into rolling friction, thereby realizing low-friction heavy-load characteristics. Three inductive sensors 34 are used as displacement sensors, and the 34 are distributed in an inverted "T" shape, so as to reduce the height of the sensor fixing frame 12 and the sensing detection plate 8, thereby increasing the mechanical stability of the system.

[0075] The specific implementation modes of the present invention are described above in conjunction with the accompanying drawings, but these descriptions cannot be understood as limiting the scope of the present invention. The protection scope of the present invention is defined by the attached claims, and any changes made on the basis of the claims of the present invention are within the protection scope of the present invention.

Claims

1. A large-aperture workbench phase-shift interferometry surface shape measurement method, characterized in that: The measuring method is realized by a large-aperture workbench phase-shifting interference surface shape measuring device, which includes a small-aperture interferometer host, a beam expansion system, a large-aperture collimator, a transmission flat crystal, a measured flat crystal, a large-aperture adjustment frame, a low-friction heavy-load workbench, a sensor monitoring plate, a linear guide rail, piezoelectric ceramics, a sensor workbench, a sensor fixing frame, a displacement sensor A, a displacement sensor B and a displacement sensor C; The collimated light beam emitted by the small-aperture interferometer host is expanded by the beam expansion system into a large-aperture measuring light. The transmission flat crystal is fixed on the beam expansion system, and the measured flat crystal is fixed on the low-friction heavy-load workbench through the large-aperture adjustment frame; the large-aperture measuring light passes through the transmission flat crystal and is reflected by the measured flat crystal along the original path, and then passes through the transmission flat crystal again before entering the beam expansion system and the small-aperture interferometer host; the low-friction heavy-load workbench and the sensor workbench can both move along the linear guide rail, and the sensor workbench can be locked and fixed with the linear guide rail; the piezoelectric ceramic is fixed on the sensor workbench, and there is a connection between it and the low-friction heavy-load workbench. The sensor is contacted and pre-tightened through the ball head; during the phase shift measurement process, the sensor workbench is locked and fixed with the linear guide rail, and the low-friction heavy-load workbench is driven by the piezoelectric ceramic to move along the linear guide rail without creeping, thereby driving the measured flat crystal to complete the phase shift; the sensor monitoring plate is fixed on the low-friction heavy-load workbench, and the sensor bracket is fixed on the sensor workbench, on which three displacement sensors are configured to monitor the displacement of three local positions on the sensor monitoring plate in real time and highly dynamically during the phase shift process, thereby calculating the translation and tilt phase shift errors of the measured flat crystal, and using this to accurately solve the surface shape to be measured; The displacement sensor includes a contact displacement sensor and a non-contact displacement sensor; The low-friction heavy-load workbench includes a hydraulic workbench, an air-floating workbench, a precision ball workbench and a magnetic suspension workbench; The measuring steps of the large-aperture workbench phase-shifting interference surface shape measuring method are as follows: Step 1: Turn on the small-aperture interferometer host, install the transmission flat crystal and the measured flat crystal in sequence, and adjust the posture of each flat crystal until interference fringes are observed in the main control computer; Step 2: The main control computer outputs a nonlinear increasing analog voltage signal to control the piezoelectric ceramic to extend at equal intervals, thereby driving the low-friction heavy-load workbench and the flat crystal to be measured to achieve fixed-step phase shifting; Step 3: The main control computer collects the phase-shifting interference pattern and simultaneously collects the measurement data of the three displacement sensors at high speed; Step 4: Calculate the magnitude and direction of the translation and tilt phase shift errors from the measurement data of the three displacement sensors, bring them into the tilt elimination phase shift interference algorithm and finally calculate the surface measurement results.

2. A large-aperture worktable phase-shift interferometry surface measurement method as claimed in claim 1, characterized in that: The formula for calculating the translation and tilt phase errors from the measurement data of the three displacement sensors is as follows: The subscript n represents the number of phase shift steps, δ(n) represents the translation phase shift amount, α(n) and β(n) represent the tilt phase shift coefficients, and a n b n c n are the displacements measured by the three displacement sensors, λ is the wavelength of the interferometer light source, D is the effective measurement aperture, and l is the distance between displacement sensors A and B, and between B and C.

3. A large-aperture worktable phase-shift interferometry surface measurement method as claimed in claim 1, characterized in that: Phase shifting can also be performed in a random phase shifting manner, that is, the host computer outputs analog voltage in equal steps to make the piezoelectric ceramics stretch nonlinearly; or an arbitrary given output analog voltage can be used to make the piezoelectric ceramics stretch randomly.

4. A large-aperture worktable phase-shift interferometry surface measurement method as claimed in claim 1, characterized in that: When measuring the surface morphology of a large-aperture spherical component under test, the measured flat crystal is replaced with the measured spherical mirror, and a large-aperture lens or a large-aperture computerized holographic plate is placed between the measured spherical mirror and the transmission flat crystal to achieve convergence or divergence of the measurement beam, and the center of the measured spherical mirror coincides with the convergence point of the measurement beam.

5. A large-aperture, high-precision phase-shifting interferometry measurement method based on phase shifting of a low-friction, heavy-loaded workbench as claimed in claim 1, characterized in that: The calculation steps of the de-tilting phase-shifting interferometry algorithm are as follows: Step (1), calculate the background a(i,j) and modulation b(i,j) from all interference patterns I(i,j,n), where (i,j) represents the pixel coordinates, max[I(i,j,n)] and min[I(i,j,n)] represent the maximum grayscale value and the minimum grayscale value of the pixel point (i,j) in all interference patterns, respectively; a(i,j)={max[I(i,j,n)]+min[I(i,j,n)]} / 2 b(i,j)={max[I(i,j,n)]-min[I(i,j,n)]} / 2 Step (2), taking the calculated translation and tilt phase shifts as known values, and calculating the phase distribution using the least squares method; the light intensity model of the interference pattern is written as I(i,j,n)=a(i,j)+C(i,j)cos[Δ(i,j,n)]+S(i,j)sin[Δ(i,j,n)], where Δ(i,j,n) is the tilt phase shift, and C(i,j) and S(i,j) are two intermediate parameters introduced for the convenience of writing, as follows: Δ(i,j,n)=δ n +a n i+b n j, C(i,j)=b(i,j)cos[W(i,j)4π / λ], S(i,j)=b(i,j)sin[W(i,j)4π / λ], Substitute all known quantities and use the least squares method to find C(i,j) and S(i,j), and then use the inverse tangent formula to find the surface shape W(i,j); Step (3), taking the surface shape W(i, j) obtained in step (2) as a known value, recalculate the new translation phase shift and tilt phase shift parameters; rewrite the light intensity expression as G S (i,j,n)=b(i,j)sin[Φ(i,j,n)] Φ(i,j,n)=W(i,j)4π / λ+Δ(i,j,n) in, represents the light intensity model, are the correction values ​​of α(n), β(n) and δ(n), G s (i, j, n) is an intermediate parameter introduced for the sake of writing convenience. Φ(i, j, n) represents the total phase, which includes the phase distribution and tilt phase shift caused by the measured surface shape. Substitute all known quantities and calculate it by the least squares method. Substitute the following formula to obtain the new tilt phase shift parameters and translation phase shift quantities α′(n), β′(n), δ′(n): Step (4), given the convergence threshold ε, As a criterion to determine whether the iterative calculation converges; if If the calculation is successful, it is considered convergent and the measured surface shape result is obtained directly. Otherwise, repeat steps (2), (3), (4) until the calculation converges.

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