High-precision full-field tilt deformation calibration system and method for shearing speckle interference system

Abstract

The invention discloses a high-precision full-field inclination calibration system and method for shearing speckle interference. The system comprises an integrated composite calibration target mirror, a two-dimensional piezoelectric deflection driving module, a photoelectric auto-collimation measurement module and a control and data processing unit, the measuring surface of the composite calibration target mirror is divided into a central rough scattering surface and an annular smooth reflecting surface. In the calibration process, the piezoelectric deflection driving module is used for inducing the target mirror to generate high-precision two-dimensional inclination deformation, the photoelectric auto-collimation measurement module is used for obtaining the absolute inclination angle of the target mirror in real time through the smooth reflecting surface to serve as a reference, and meanwhile the shearing speckle interferometer to be calibrated is used for collecting interference data of the rough scattering surface. And the control unit is used for carrying out full-field comparison and calculation on the two data to realize error correction. Physical space alignment of benchmark measurement and speckle measurement is achieved through the double-function area target mirror, the problems that traditional calibration precision is low, and full-field coverage cannot be achieved are solved, and the device has the advantages of being compact in structure, high in repeatability and high in adaptability.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of optical precision measurement and instrument calibration, and particularly relates to a high-precision full-field tilt deformation calibration system and method for shear speckle interferometry. BACKGROUND

[0002] Shearography is a non-contact, full-field optical measurement method, which has high detection sensitivity to object deformation derivatives (such as strain and slope) and is not sensitive to environmental vibration. It is widely used in composite material defect detection, structure health monitoring and material mechanical property evaluation in aerospace. In shear speckle interferometry, the calibration accuracy of system parameters (such as shear amount, object distance, magnification, etc.) directly determines the accuracy of the final deformation quantitative calculation.

[0003] Tilt is the most basic and core calibration mode of shear speckle interferometer. By applying a known full-field tilt deformation to the measured object, the measurement sensitivity matrix of the system can be effectively obtained, and the deflection error of the shear mirror and the geometric distortion of the camera can be calibrated.

[0004] However, the existing calibration systems and methods still have the following limitations in actual engineering applications: 1. Lack of reference and limited precision: Traditional calibration devices usually use piezoelectric ceramics or precision displacement stages to drive ordinary scattering plates to produce tilt. The true value of the deformation often depends on the nominal displacement of the driving element, and lacks an independent, high-precision third-party measurement reference for real-time monitoring, making it difficult to eliminate errors caused by mechanical backlash and nonlinear motion.

[0005] 2. Inconsistent measurement field: Shear speckle interferometer requires a rough surface to produce speckle, while high-precision angle measurement instruments (such as autocollimators) require an optically smooth mirror surface. Existing technologies cannot simultaneously meet the measurement needs of both instruments at the same spatial location, resulting in physical space mismatch between the calibration reference and the system to be calibrated, introducing additional alignment errors.

[0006] 3. Insufficient full-field calibration capability: Traditional point measurement references cannot cover the entire camera field of view, making it difficult to accurately correct the distortion and non-uniformity at the edge of the field of view, and unable to achieve true full-field high-precision calibration.

[0007] 4. Clamping and stability problems: When inducing high-order or large-angle tilt, uneven stress distribution of the clamping of the calibration piece can cause unintended parasitic deformation, affecting the reliability of the calibration field as a "standard value".

[0008] Therefore, how to construct a calibration system that can provide a high-precision absolute angular reference, perfectly align with the shear speckle interferometric measurement field, and achieve real-time monitoring of the entire field is a technical challenge that urgently needs to be solved in the field of optical measurement. Summary of the Invention

[0009] (a) Technical problems to be solved To address the problems in the calibration of shear speckle interferometer systems mentioned above, such as spatial mismatch between reference measurement and speckle measurement, inability to achieve full-field synchronous monitoring, large mechanical backlash, and difficulty in correcting edge distortion, this invention provides a high-precision full-field tilt calibration system and its calibration method for shear speckle interferometers. It aims to provide a high-precision, full-field coverage, and real-time feedback calibration solution by combining an integrated composite target mirror with a high-precision tilting mechanism.

[0010] (II) Technical Solution This invention is achieved through the following technical solution: A high-precision full-field tilt deformation calibration system for shear speckle interferometry includes: Integrated composite calibration target mirror: It is a calibration carrier with a single substrate. Its measurement surface is divided into two concentric functional regions: the central region is a circular rough scattering surface, which is used to generate a speckle field and to perform calibration with a shear speckle interferometer; the outer peripheral region surrounding the rough scattering surface is an annular smooth reflecting surface, which is used to perform angular reference measurement with a photoelectric autocollimator.

[0011] Two-dimensional piezoelectric oscillation drive module: includes a piezoelectric oscillation stage base, a support frame set on it, and a movable platform suspended within the frame by a flexible hinge mechanism; four clamping mechanisms are symmetrically arranged on the movable platform, and the integrated composite calibration target mirror is rigidly fixed to the center of the platform by the clamping mechanisms.

[0012] Control and measurement components: These include a piezoelectric ceramic component installed inside the drive module, a photoelectric autocollimation measurement module aligned with the optical path of the annular smooth reflective surface, and a control unit; the control unit drives the movable platform to oscillate according to a preset step size, and simultaneously acquires the true angle value of the photoelectric autocollimation measurement module and the image data of the shear speckle interferometer to be calibrated.

[0013] Furthermore, the rough scattering surface in the central region is formed by sandblasting or coating a diffuse reflection layer on a microcrystalline glass substrate, and the annular smooth reflective surface is formed by optical coating. Both surfaces are in the same physical plane to ensure the consistency of the tilt angle in spatial distribution.

[0014] Furthermore, the four clamping mechanisms are distributed at the four corners of the movable platform. Each clamping mechanism includes a positioning block and a fine-tuning fastener, which locks the composite calibration target mirror by applying radial force to eliminate centrifugal offset and vibration effects during large-angle swing.

[0015] A method for full-field tilt calibration of shear speckle interferometry using the above system includes the following steps: 1. System alignment: Install the composite calibration target mirror into the clamping mechanism, adjust the optical path so that the field of view of the shear speckle interferometer covers the central rough scattering surface, and the field of view of the photoelectric autocollimator covers the outer peripheral smooth annular reflecting surface; 2. Synchronous Trigger Drive: The control unit sends a command to cause the piezoelectric yaw drive module to generate a preset two-dimensional tilt trajectory; 3. Reference and Data Acquisition: Under each yaw pose, the photoelectric autocollimator measures the absolute tilt angle of the target mirror in real time. θ The shear speckle interferometer synchronously acquires the corresponding speckle interferometric images; 4. Error field mapping: Mapping the angle reference. θ The displacement field is transformed into a full-field theoretical displacement field L(x,y) and then compared with the actual deformation field L'(x,y) calculated by the shear speckle interferometer at the full-field pixel level. 5. Parameter Correction: Based on the full-field comparison results, the shearing error, nonlinear coefficient and lens distortion factor of the system are calculated to generate a calibration correction matrix.

[0016] (III) Beneficial Effects Compared with the prior art, the beneficial effects of the present invention are as follows: 1. Achieved physical integration of the measurement field and the reference field: The design of a central circular rough surface and an outer ring smooth surface cleverly solves the contradiction between the different requirements of speckle measurement and angle reference measurement on the properties of the measured surface, and eliminates spatial alignment errors between different measurement areas.

[0017] 2. Full-field coverage calibration: With the absolute angular reference provided by the annular reflector, tilt response calibration can be performed on every pixel in the entire field of view of the camera, which greatly improves the ability of the shear speckle interferometer to correct complex deformations and lens edge distortions.

[0018] 3. High precision and stability: Combining a piezoelectric drive module with closed-loop feedback and a four-point symmetrical clamping structure ensures high repeatability and minimal hysteresis in tilt deformation, providing mechanical assurance for sub-micron level calibration accuracy.

[0019] 4. Easy to operate and highly efficient: The system achieves synchronous and automated execution of drive, measurement and data calculation through the control unit, eliminating the need for manual replacement of standard parts and shortening the calibration cycle of precision optical instruments. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the high-precision full-field tilt deformation calibration system of the present invention; Figure 2 This is a schematic diagram of the two-dimensional piezoelectric oscillation drive module in this invention; Figure 3 This is a schematic diagram of a shear speckle interferometer; Figure 4 This is a schematic diagram of a microcrystalline deformable part; Figure 5 The tilting assembly was calibrated using a shear speckle interferometer.

[0021] The components in the diagram represent: 1. Photoelectric sensor; 2. Beam splitter; 3. Reticle; 4. Light source; 5. Objective lens; 6. Deformable part reflecting surface; 7. Deformable part scattering surface; 8. Piezoelectric deflector stage moving platform; 9. Piezoelectric deflector stage component; 10. Piezoelectric deflector stage base; 11. Piezoelectric ceramic assembly; 12. Piezoelectric closed-loop sensing assembly; 13. Flexible hinge parallel mechanism; 14. Deformable part clamping mechanism; 15. Microcrystalline deformable part; 16. Piezoelectric controller. Detailed Implementation

[0022] The embodiments of the present invention will be described in detail below with reference to the accompanying drawings. These embodiments are implemented based on the technical solution of the present invention, and provide detailed implementation methods and specific operation processes. However, the scope of protection of the present invention is not limited to the following implementation examples.

[0023] 1. System Overall Structure and Hardware Composition like Figure 1 and Figure 2 As shown, this invention provides a high-precision full-field tilt deformation calibration system for shear speckle interferometry, the core of which lies in the construction of an integrated optical and mechanical co-calibration platform. The system mainly consists of an integrated composite calibration target mirror, a two-dimensional piezoelectric pendulum drive module, a photoelectric self-collimation measurement module, and the shear speckle interferometer to be calibrated.

[0024] Integrated composite calibration target mirror 15: Made of microcrystalline glass material with extremely low thermal expansion coefficient and high mechanical stability. For example... Figure 4 As shown, the target mirror's measured surface is designed with partitions: the central circular region is a rough scattering surface 7, used to generate a random speckle field that meets the requirements of shear speckle measurement; the outer annular region is a smooth reflecting surface 6, with a surface shape accuracy better than λ / 20, used to cooperate with the autocollimator for angle measurement. The target mirror is rigidly fixed to the moving platform by four clamping mechanisms 14 around its perimeter.

[0025] Two-dimensional piezoelectric oscillation drive module: This module consists of a piezoelectric oscillation stage base 10, a support frame 9, and a moving platform 8. The three are connected by an integrated, backlash-free flexible hinge parallel mechanism 13. An internal piezoelectric ceramic component 11 serves as the drive source, and under the control of the piezoelectric controller 16, the moving platform 8 is driven to generate precise oscillations around the X and Y axes through the displacement amplification principle of the flexible hinge.

[0026] Sensing and Control System: The system incorporates a piezoelectric closed-loop sensing component 12 (such as a capacitive or strain gauge sensor) to monitor the platform's angular displacement in real time and feed it back to the controller. This closed-loop system ensures a deflection angle accuracy of ±0.001°, motion hysteresis ≤0.0001°, and long-term angular drift ≤0.0005° / h. The overall structure is constructed using high-precision CNC milling and Invar steel, with a mechanical natural frequency ≥500Hz.

[0027] 2. Measurement Principles and Mathematical Models The calibration reference of this invention is based on geometric optics and displacement conversion logic. The autocollimator module constitutes the angle measurement reference through the light source 4, reticle 3, objective lens 5 and photoelectric sensor 1.

[0028] Angle Measurement: A parallel beam of light emitted from the collimator illuminates the smooth reflective surface 6 of the target mirror and returns, forming an image on the photoelectric sensor 1. When the target mirror deflects by an angle θ with the platform, the image on the photoelectric sensor shifts. satisfy: Where f is the focal length of the objective lens.

[0029] Deformation transformation: As shown in the figure, when the target mirror deflects by θ from its initial position, for a region with a calibration length of D, the height difference (i.e., deformation) L between its two endpoints is defined as: The L value is used as the true value of deformation for calibrating the shear speckle interferometer.

[0030] 3. Characteristics of Shear Speckle Interferometer The shear speckle interferometer to be calibrated employs an integrated design of dual-wavelength orthogonal shear optical paths, enabling electrically controlled adjustment of the shearing amount and synchronous phase shifting of both wavelengths. This system allows for quantitative correction of the interferometer's shearing parameters, full-field phase-to-displacement conversion coefficients, and image distortion at different wavelengths.

[0031] 4. Calibration Implementation Steps and Methods The calibration method provided in this embodiment has the following steps: Step 1: Installation and Initialization. The microcrystalline glass target mirror 15 is rigidly fixed to the center of the moving platform 8 using four clamping mechanisms 14. The optical path of the shear speckle interferometer to be calibrated is aligned with the rough scattering surface 7, and the optical path of the photoelectric autocollimator is aligned with the smooth annular reflecting surface 6.

[0032] Step 2: Reference Alignment and Zero-Position Calibration. Turn on the power and control the piezoelectric yaw module to reset to zero position. Record the initial angle value of the collimator and the initial reference phase of the shear speckle interferometer.

[0033] Step 3: Synchronous Deformation Induction and Data Acquisition. The piezoelectric controller drives the platform to perform two-dimensional stepping yaw within a preset range (e.g., ±1°). At each step position: The real-time absolute tilt angle θ of the target mirror is read using an autocollimator; Interference patterns on rough surfaces are simultaneously acquired using a shear speckle interferometer, and the measured deformation L' is calculated.

[0034] Step 4: Error Analysis and Closed-Loop Calibration. According to the formula... Calculate the true deformation value at each moment and compare it with the measured value L' of the shear speckle interferometer. Calculate the full-field error distribution: Step 5: Verification and Parameter Derivation. Repeat the experiment multiple times to verify the repeatability of the system under different yaw directions. If the error exceeds the threshold, correct the interferometer's intrinsic parameter matrix based on the comparison results to complete the full-field calibration.

[0035] 5. Summary of Technological Advantages The calibration component designed in this embodiment exhibits a deformation sensitivity of less than 20 nm and a stability deviation of ≤ ±25%, enabling high repeatability of cumulative step deformation for at least 20 cycles. The integrated design of the "mirror-rough surface" ensures strict spatial alignment between the reference and target measurements, significantly improving the quantitative measurement accuracy of shear speckle interferometry in material performance testing and structural health monitoring.

Claims

1. A high-precision full-field tilt deformation calibration system for shear speckle interferometry systems, characterized in that, include: Integrated composite calibration target mirror: It is composed of a microcrystalline glass substrate, and its measurement surface is divided into two concentric functional regions: the central region is a circular rough scattering surface (7) for shear speckle interference calibration; the outer peripheral region surrounding the rough scattering surface is an annular smooth reflecting surface (6) for photoelectric self-collimation angle measurement. Two-dimensional piezoelectric oscillation drive module: includes a piezoelectric oscillation stage base (10), a piezoelectric oscillation stage component (9) disposed on the base (10), and a piezoelectric oscillation stage moving platform (8) located inside the component (9); four deformable component clamping mechanisms (14) are symmetrically arranged on the moving platform (8) for rigidly fixing the composite calibration target mirror to the center of the moving platform (8); Drive and sensing components: including a piezoelectric ceramic component installed between the component (9) and the moving platform (8), a closed-loop sensing component for detecting the yaw angle, and a piezoelectric controller for driving the moving platform (8) to generate a two-dimensional angular yaw relative to the base (10); Photoelectric autocollimation measurement module: Its measurement optical path is directly facing the annular smooth reflective surface (6) around the composite calibration target mirror, and is used to measure the absolute tilt angle generated by the sway of the moving platform (8) in real time.

2. The high-precision full-field tilt deformation calibration system according to claim 1, characterized in that: The four deformable clamping mechanisms (14) are evenly distributed along the circumference of the composite calibration target mirror, and each clamping mechanism is fixed to the four corner areas of the piezoelectric deflection stage moving platform (8) by fasteners, applying radial constraint to the target mirror from the outer periphery to the center.

3. The high-precision full-field tilt deformation calibration system according to claim 1, characterized in that: The rough scattering surface (7) in the central region and the annular smooth reflecting surface (6) in the outer peripheral region are located on the same physical plane, and the junction of the two is seamlessly connected to ensure that the shear speckle interferometer and the photoelectric autocollimator measure the same physical deformation field.

4. The high-precision full-field tilt deformation calibration system according to claim 1, characterized in that: The piezoelectric pendulum stage component (9) has a rectangular frame structure and is connected to the moving platform (8) through an internally embedded flexible hinge mechanism. The piezoelectric pendulum stage base (10) is located at the bottom of the frame to provide overall support.

5. The high-precision full-field tilt deformation calibration system according to any one of claims 1-4, characterized in that, It also includes a control and data processing unit, which is configured to: The drive module is controlled to perform two-dimensional scanning yaw according to a preset angle step size; Synchronously acquire the angle reference value output by the photoelectric self-collimation measurement module θ Phase data acquired by a shear speckle interferometer; Based on angle reference value θ The geometric parameters of the target mirror are used to calculate the theoretical deformation distribution of the entire field, and the results are compared with the measurement results of the shear speckle interferometer to solve the error correction coefficient of the entire field.

6. A method for full-field tilt calibration of shear speckle interferometry using the system described in any one of claims 1 to 5, characterized in that, Includes the following steps: S1. Target mirror installation: The composite calibration target mirror is fixed on the moving platform (8) using four clamping mechanisms (14), and the annular smooth reflecting surface (6) and the central rough scattering surface (7) are respectively aligned with the autocollimator and the speckle interferometer. S2. Reference Alignment: Adjust the piezoelectric drive module to the zero position and record the initial angle reading of the photoelectric autocollimation measurement module; S3. Stepping and Swinging Acquisition: The control drive module executes two-dimensional swinging. At each swinging position, the photoelectric autocollimation measurement module reads the real-time tilt angle as the true value, and the shear speckle interferometer acquires the corresponding full-field interference image. S4. Full-field calibration calculation: Convert the true angle values ​​at each location point into a full-field deformation field, calculate the measurement sensitivity and systematic error distribution of the shear speckle interferometer in the full field, and generate a correction mapping table.

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