A portable automatic measuring method and device for mirror / mirror-like surface topography

Abstract

The application relates to a portable mirror surface / mirror surface-like appearance automatic measurement method and device, and belongs to the technical field of optical detection. A telescopic frame is composed of three groups of upper, middle and lower parallel guide rails, telescopic rods and telescopic adjusting mechanisms; display modules and image acquisition modules are respectively arranged on the parallel guide rails of the telescopic frame through linear motors; and embedded development boards are wirelessly connected with computers through Wi-Fi modules to control the movement of the linear motors and the telescopic adjusting mechanisms, and automatically adjust the positions and angles of the display modules and the image acquisition modules, so that the measurement accuracy is ensured, and portability and flexibility are considered at the same time; a display screen displays concentric circular ring sinusoidal stripes based on time domain frequency conversion phase shift; a camera collects deformed stripe images reflected by a measured object surface; and three-dimensional appearance of the measured object is obtained through computer processing. The measurement device provided by the application is compact in structure, high in portability and high in automation degree, and the provided measurement method can effectively improve measurement precision and efficiency.

Description

TECHNICAL FIELD

[0001] The present application relates to a kind of mirror surface / mirror surface-like topography measurement method and device, belong to optical detection technical field. BACKGROUND

[0002] Freeform optical element can correct system aberration more significantly, improve system design performance, realize the compactness and high transmittance of optical system, so it has caused intense interest in the research and realization process of photoelectric system such as laser nuclear fusion system, micro-light night vision instrument, photoetching machine, imaging spectrometer etc.. However, due to the existence of surface shape description freedom, gradient change complex characteristics and problems, its surface topography profile high-precision forming difficulty is much greater than traditional optical element. Processing and detection as important and inseparable two parts in the process of optical element manufacturing, the level of detection accuracy often directly determines the pros and cons of processing forming effect.

[0003] With the continuous development of science and technology, high-precision aspherical surface / freeform surface processing schemes such as particle flow processing technology, modern numerical control and controllable flexible polishing technology have appeared in succession, and the corresponding detection means develops slowly. In the process of processing optical elements, the traditional and direct detection means is contact / non-contact three-coordinate machine. However, its point scanning mode makes the whole test process longer, the detection efficiency is not high, and the precision is limited (sub-micron level). Although aspherical surface interferometry based on compensator (such as computer generated hologram element) can achieve nanometer level detection accuracy, but for different surface shape of the measured object needs to design and prepare the corresponding wave surface compensation element, there is weak detection universality problem. Phase retrieval method as a kind of non-interference detection technology has been successfully applied to in-situ detection of optical aspherical mirror. However, the acquisition of several defocus plane light field required in the iterative recovery process relies on precise translation guide rail equipment, and the larger aspherical degree of the measured object further aggravates the requirement of high spatial resolution of detector.

[0004] With the development of the technologies of computational geometry, digital image display and processing, another free-form surface shape detection technology, phase deflectometry (PMD), is developing rapidly, and its measurement accuracy can even be comparable to that of interferometry. PMD is a measurement technology that modulates and demodulates the normal vector of a measured object surface by phase change, using a cosine or sine fringe signal as a medium, and recovers the surface shape of the object by gradient integration or stereo vision. For mirror objects, PMD simplifies the system structure, greatly expands the dynamic measurement range (up to tens of millimeters), while maintaining a similar measurement resolution level to interferometry. However, the existing PMD measurement device is not portable enough, and the automation level of adjustment and detection is not high enough. During the measurement process, two sets of anisotropic horizontal and vertical sine straight fringe patterns are usually displayed in sequence, and the detection efficiency needs to be improved. Therefore, it is a research hotspot and trend in this field to propose a mirror / quasi-mirror shape measurement device and method based on the PMD principle, which is compact in structure, portable, high in automation level and detection efficiency. SUMMARY

[0005] The present application provides a mirror / quasi-mirror shape automatic measurement method and device which is convenient to use / carry, has a high automation level, and can effectively improve the measurement accuracy and efficiency.

[0006] To achieve the above-mentioned purpose, the technical solution adopted by the present application is a portable mirror / quasi-mirror shape automatic measurement device, which comprises a display module, an image acquisition module, a telescopic frame, a stage, an embedded development board and a computer.

[0007] The embedded development board is wirelessly connected to the computer through a Wi-Fi module.

[0008] The telescopic frame comprises three groups of upper, middle and lower parallel guide rails, telescopic rods and a telescopic adjusting mechanism for adjusting the telescopic rods, the guide rails are perpendicular to the telescopic rods, and the two ends of each guide rail are fixed to the telescopic rods, and the telescopic adjusting mechanism is connected to the embedded development board through a data transmission control line.

[0009] The display module comprises a display screen and a linear motor, the linear motor is fixed to the display module, the linear motor is arranged on the middle and lower two groups of parallel guide rails of the telescopic frame, and the display screen faces the stage; the display screen and the linear motor are connected to the embedded development board through a data transmission control line, respectively.

[0010] The image acquisition module comprises a camera with an automatic focusing function, a sensor for determining the distance between the measured object and the camera, and a linear motor; the linear motor is fixed with the image acquisition module, and the linear motor is arranged on the middle and upper two groups of parallel rails of the telescopic frame respectively; the object table is located at the front focal plane of the camera, the display screen, the object table and the camera are placed in a triangular structure, and the measured object on the object table and its reflected display screen image are located within the depth of field range of the camera; the sensor and the linear motor are connected with the embedded development board through data transmission control lines respectively;

[0011] The display screen displays the concentric ring sinusoidal fringe based on time domain variable frequency phase shift output by the computer received through the embedded development board, the camera acquires the deformed fringe pattern reflected by the measured object surface modulation, and the computer is input through the embedded development board.

[0012] The application provides a kind of portable mirror surface / quasi mirror surface topography automatic measuring device, the sensor is one of laser displacement sensor, ultrasonic distance sensor, infrared distance sensor.

[0013] The application provides a kind of portable mirror surface / quasi mirror surface topography automatic measuring device, the computer controls the movement of linear motor and telescopic adjusting mechanism through embedded development board, and the position and angle of display module and image acquisition module are automatically adjusted.

[0014] The technical scheme of the application includes a kind of portable mirror surface / quasi mirror surface topography automatic measuring method, and the steps are as follows:

[0015] Step one, the installation of measuring device

[0016] The object table and the measured object are placed on the bottom surface of the telescopic frame, and the display module and the image acquisition module are initially installed on the middle parallel rail, the parallel rail below and the middle parallel rail, the upper parallel rail of the telescopic frame respectively; the display screen of the display module and the camera of the image acquisition module are directed to the object table, and the display screen, the object table and the camera are in a triangular structure; the Wi-Fi module of the embedded development board is wirelessly connected with the computer, and the computer controls the distance sensor in the image acquisition module, controls the linear motor in the display module and the image acquisition module, controls the state of the telescopic adjusting mechanism in the telescopic frame and the focusing amount of the camera, so that the measured object on the object table and its reflected display screen image are located within the depth of field range of the camera;

[0017] Step two, display and acquisition of fringe image

[0018] The encoding parameters of concentric circle ring sinusoidal fringe based on time domain variable frequency phase shift are obtained by software design, and the computer transmits the encoding parameters to the display module through Wi-Fi; the embedded development board in the display module generates the isotropic concentric circle ring sinusoidal fringe image for measurement according to the parameter encoding, and transmits the image to the display screen through the data transmission control line, and then the image is reflected by the surface of the object to be measured, and is collected and acquired by the camera in the image acquisition module, and is input into the computer through the Wi-Fi module of the embedded development board;

[0019] Step three, demodulation of fringe image and surface profile reconstruction

[0020] The least square N-step phase shift demodulation algorithm is used to process the single frequency deformation fringe images obtained by the camera in the image acquisition module, and the single frequency truncated phase is calculated; the time domain phase unwrapping method is used for processing, and the absolute phase distribution related to the three-dimensional profile of the object to be measured under the highest frequency is obtained; under the constraint of the law of light reflection, combined with the geometric structure parameters of the system and the distance parameters fed back by the distance sensor in the image acquisition module, the surface profile slope of the object to be measured in each direction is calculated from the absolute phase distribution; the surface profile gradient distribution of the best orthogonal direction of the object to be measured is obtained according to the slope gradient evaluation function; and the three-dimensional surface profile distribution of the object to be measured is reconstructed by using the gradient integration algorithm.

[0021] In step two of the above measurement method, the concentric circle ring sinusoidal fringe image based on time domain variable frequency phase shift has a fringe frequency which is one of a natural number sequence, a multiple sequence, a power function sequence and an exponential sequence. In step three, the slope gradient evaluation function takes the slope square sum in the orthogonal direction as the evaluation index to calculate the surface profile gradient distribution in the best orthogonal direction.

[0022] The present application provides a kind of portable mirror surface / mirror surface profile automatic measurement method, and its fringe frequency uses multiple sequence variation method;Fringe pattern is equal step phase shift, and each phase shift amount θ is , N is total phase shift number, .

[0023] Compared with the prior art, the present application has the following advantages:

[0024] 1. The measurement device provided by the present application has compact structure, high portability, high automation degree and high detection efficiency, and is very suitable for automatic and wireless measurement and control of mirror surface / mirror surface element surface profile.

[0025] 2. The measurement device provided by this invention only requires displaying a set of isotropic time-domain frequency-shifted phase-shifted concentric circular sinusoidal fringe images on the display screen. This effectively avoids the need to sequentially display two sets of anisotropic frequency-shifted phase-shifted sinusoidal straight fringe images in the horizontal and vertical directions, as required by existing technical solutions. This significantly reduces the number of images required for measurement and improves measurement efficiency. The use of a distance sensor avoids the ambiguity of slope gradient calculation. The proposed slope gradient evaluation function can obtain the surface gradient distribution of the object under test in the optimal orthogonal direction, thereby improving measurement accuracy. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the structure of a portable automatic measurement device for mirror / mirror-like surface morphology provided in an embodiment of the present invention;

[0027] Figure 2 This is a schematic diagram of the display module in a portable automatic measurement device for mirror / mirror-like surface morphology provided in an embodiment of the present invention;

[0028] Figure 3 This is a schematic diagram of the image acquisition module in a portable automatic measurement device for mirror / mirror-like surface morphology provided in an embodiment of the invention.

[0029] The components include: 1. Display module; 2. Image acquisition module; 3. Telescopic frame; 4. Stage; 5. Computer; 6. Object under test; 11. Embedded development board; 12. Display screen; 13. Linear motor; 21. Camera; 22. Distance sensor; 23. Linear motor; 31. Upper parallel guide rail; 32. Middle parallel guide rail; 33. Lower parallel guide rail; 34. Telescopic rod control motor. Detailed Implementation

[0030] The specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings and examples.

[0031] Example 1

[0032] See appendix Figure 1 This is a schematic diagram of the structure of a portable mirror / mirror-like surface morphology measuring device provided in this embodiment; the measuring device includes: a display module 1, an image acquisition module 2, a retractable frame 3, a stage 4, a computer 5, and the object to be measured 6; see attached diagram. Figure 2 This is a schematic diagram of the display module in this embodiment. The display module 1 includes an embedded development board 11, a display screen 12, and four linear motors 13; see attached diagram. Figure 3 This is a schematic diagram of the image acquisition module in this embodiment. The image acquisition module 2 includes a camera 21 with autofocus, a distance sensor 22, and four linear motors 23. Figure 1It can be seen that the telescopic frame 3 includes three groups of parallel guide rails, i.e., the upper parallel guide rail 31, the middle parallel guide rail 32 and the lower parallel guide rail 33, and eight telescopic motors 34, the guide rails are horizontally arranged and perpendicular to the telescopic rods, and the two ends of each guide rail are fixed with the telescopic rods. The output port of the distance sensor, the control port of the linear motor and the telescopic motor are connected with the embedded development board 11 respectively. The embedded development board 11 is wirelessly connected with the computer 5 through the Wi-Fi module.

[0033] The display module 1 is placed on the middle parallel guide rail 32 and the lower parallel guide rail 33 of the telescopic frame 3 by the linear motor 13, and the display screen 12 of the display module 1 faces the object table 4.

[0034] The image acquisition module 2 is placed on the middle parallel guide rail 32 and the upper parallel guide rail 21 of the telescopic frame 3 by the linear motor 23, and the camera 21 of the image acquisition module 2 faces the object table 4; the display module 1 and the image acquisition module 2 adjust their positions and angles by the linear motor 13, the linear motor 23 and the telescopic motor 34, so as to realize automatic adjustment.

[0035] The object table 4 is located at the front focal plane of the camera, the display screen 12, the object table 4 and the camera 21 are placed in a triangular structure, so that the camera 21 can clearly observe the measured object 6 on the object table 4 and the mirror image of the display screen 12 reflected by the measured object 6; the embedded development board 11 is wirelessly connected with the computer 5 through Wi-Fi, which guarantees the accuracy of the measurement results while taking into account the portability and flexibility; the concentric circular ring sinusoidal fringe based on time domain variable frequency phase shift input by the computer is displayed on the display screen 12, is modulated and reflected by the surface of the measured object 6, a deformed fringe pattern is obtained, and is acquired by the camera 21; the camera 21 transmits the collected pictures to the computer 5, and after data processing, the three-dimensional topography of the measured object 6 is obtained.

[0036] The distance sensor 22 is one of a laser displacement sensor, an ultrasonic distance sensor and an infrared distance sensor, and is used to determine the distance between the measured object 6 and the camera 21.

[0037] The measurement device provided in the embodiment is wirelessly connected with the computer 5 through Wi-Fi, and remote control is completed.

[0038] The embedded development board can be one of an FPGA, a DSP, a Raspberry Pi, and a single-chip microcomputer development board. The embedded development board used in the embodiment is an embedded Raspberry Pi development board, and runs a Raspberry Pi operating system. The embedded development board is wirelessly connected to the computer through a Wi-Fi module. The telescopic motor in the telescopic frame involved in the measuring device is connected to the Raspberry Pi development board through a general-purpose input / output port (GPIO) on the Raspberry Pi development board. The display screen in the display module and the linear motor are connected to the Raspberry Pi development board through the GPIO port on the Raspberry Pi development board. The camera in the image acquisition module is connected to the Raspberry Pi development board through a camera serial interface (CSI) on the Raspberry Pi development board. The distance sensor and the linear motor are connected to the Raspberry Pi development board through the GPIO port on the Raspberry Pi development board.

[0039] The portable mirror / mirror-like surface topography measuring device provided in the embodiment has a measuring method including the following steps.

[0040] Step 1: Adjustment of the measuring device

[0041] The structure of the measuring device is shown in the accompanying drawings Figure 1 The object table 4 and the measured object 6 are placed on the bottom surface of the telescopic frame 3. The display module 1 and the image acquisition module 2 are connected through data transmission control lines, and are preliminarily installed on the two groups of parallel rails, i.e., the middle parallel rail 32, the lower parallel rail 33, and the middle parallel rail 32, the upper parallel rail 31 of the telescopic frame 3, respectively. The display screen 12 of the display module 1 and the camera 21 of the image acquisition module 2 are both directed towards the object table 4, so that the display screen 12, the object table 4, and the camera 21 form a triangular structure. The Wi-Fi module of the embedded development board 11 is wirelessly connected to the computer 5. The computer controls the states of the linear motors 13 and 23 in the display module 1 and the image acquisition module 2, the state of the telescopic motor 34 in the telescopic frame 3, and the focusing amount of the camera 21, in combination with the distance sensor 22 in the image acquisition module 2, so that the measured object on the object table and its reflected display screen image are located within the depth of field of the camera.

[0042] Step 2: Display and acquisition of the fringe image

[0043] The coding parameters of the concentric circular ring sinusoidal fringe based on time domain frequency shifting phase shift are set on the computer using the GUI software developed in conjunction, and the relevant parameters are transmitted to the display module 1 through Wi-Fi. The isotropic concentric circular ring sinusoidal fringe image for measurement is generated by the embedded development board 11 in the display module 1 according to the parameters, transmitted to the display screen 12 through the data transmission control line, and then acquired by the camera 21 in the image acquisition module 2 through the reflection of the surface of the measured object 6.

[0044] Step three, demodulation of fringe pattern and surface profile reconstruction

[0045] Each single frequency deformed fringe pattern obtained by camera 21 in image acquisition module 2 is processed by least square N-step phase shift demodulation algorithm to calculate each single frequency truncated phase; absolute phase distribution related to three-dimensional profile of object 6 to be measured under the highest frequency is obtained by temporal phase unwrapping technology; under the constraint of law of light reflection, combined with system geometric structure parameters and distance parameters fed back by distance sensor 22 in image acquisition module 2, surface profile slope in each direction of object 6 to be measured is unambiguously calculated from absolute phase distribution; surface profile gradient distribution in the best orthogonal direction of object 6 to be measured is obtained according to slope gradient evaluation function; finally, three-dimensional surface profile distribution of object 6 to be measured is reconstructed by gradient integration algorithm.

[0046] In step two, fringe frequency of concentric circular ring sinusoidal fringe pattern based on time domain frequency conversion phase shift can vary according to one of natural number sequence, multiple sequence, power function sequence and exponential sequence, and varies according to multiple sequence (4 multiple values) in the present application; fringe pattern is equal step phase shift, and each step phase shift amount is , and total phase shift step number is .

[0047] In step three, slope gradient evaluation function takes slope square sum in orthogonal direction as evaluation index to calculate surface profile gradient distribution in the best orthogonal direction.

Claims

1. A portable automatic measuring device for mirror / mirror-like surface morphology, characterized in that: It includes a display module (1), an image acquisition module (2), a retractable frame (3), a stage (4), an embedded development board (11), and a computer (5); The embedded development board is wirelessly connected to the computer via a Wi-Fi module; The retractable frame includes three sets of parallel guide rails (upper, middle, and lower), a telescopic rod, and a telescopic adjustment mechanism for adjusting the telescopic rod. The guide rails are perpendicular to the telescopic rod, and both ends of each guide rail are fixed to the telescopic rod. The telescopic adjustment mechanism is connected to the embedded development board via a data transmission control line. The display module includes a display screen and a linear motor. The linear motor is fixed to the display module and is placed on the middle and lower sets of parallel guide rails of the telescopic frame. The display screen faces the stage. The display screen and the linear motor are connected to the embedded development board through data transmission control lines. The image acquisition module includes a camera with autofocus, a sensor for determining the distance between the object being measured and the camera, and a linear motor. The linear motor is fixed to the image acquisition module and is placed on two sets of parallel guide rails in the middle and upper parts of the telescopic frame. The stage is located at the front focal plane of the camera. The display screen, stage, and camera are arranged in a triangular structure. The object being measured on the stage and its reflected image on the display screen are within the depth of field of the camera. The sensor and linear motor are connected to the embedded development board via data transmission control lines. The display screen shows concentric circular sinusoidal fringes based on time-domain frequency conversion phase shift, which are received from the computer via the embedded development board. The camera acquires the deformed fringe pattern modulated and reflected by the surface of the object under test, and inputs it into the computer via the embedded development board.

2. The portable automatic measuring device for mirror / mirror-like surface morphology according to claim 1, characterized in that: The sensor is one of a laser displacement sensor, an ultrasonic distance sensor, or an infrared distance sensor.

3. The portable automatic measuring device for mirror / mirror-like surface morphology according to claim 1, characterized in that: The computer controls the movement of the linear motor and telescopic adjustment mechanism through an embedded development board, automatically adjusting the position and angle of the display module and image acquisition module.

4. A portable automatic measurement method for the morphology of mirrors / mirror-like surfaces, characterized in that... Includes the following steps: Step 1: Assembly and adjustment of the measuring device Place the stage and the object under test on the bottom of the telescopic frame. Initially install the display module and the image acquisition module onto the two sets of parallel rails of the telescopic frame: the middle parallel rail, the lower parallel rail, and the middle and upper parallel rails, respectively. The display screen of the display module and the camera of the image acquisition module face the stage, forming a triangular structure between the display screen, the stage, and the camera. Wirelessly connect the Wi-Fi module of the embedded development board to the computer. The computer controls the distance sensor in the image acquisition module, the linear motors in the display module and the image acquisition module, the telescopic adjustment mechanism in the telescopic frame, and the focus of the camera to ensure that the object under test on the stage and its reflected image on the display screen are within the depth of field of the camera. Step 2: Display and Acquisition of the Stripe Image The computer obtains the encoding parameters of the concentric ring sinusoidal fringes based on time-domain frequency conversion phase shift through software design, and transmits the encoding parameters to the display module via Wi-Fi; the embedded development board in the display module generates an isotropic concentric ring sinusoidal fringe image for measurement according to the parameter encoding, transmits it to the display screen through the data transmission control line, and then, after reflection from the surface of the object under test, is acquired by the camera in the image acquisition module and input into the computer via the Wi-Fi module of the embedded development board; Step 3: Demodulation and surface reconstruction of the striped image The least squares N-step phase-shift demodulation algorithm is used to process the single-frequency deformable stripe images obtained by the camera in the image acquisition module, and the truncated phase of each single frequency is calculated. The temporal phase expansion method is used to obtain the absolute phase distribution related to the three-dimensional shape of the object under test at the highest frequency. Under the constraint of the law of light reflection, combined with the system's geometric parameters and the distance parameters fed back by the distance sensor in the image acquisition module, the surface slope of the object under test in each direction is calculated from the absolute phase distribution. The surface gradient distribution of the object under test in the best orthogonal direction is obtained according to the slope gradient evaluation function. Then, the three-dimensional surface distribution of the object under test is reconstructed using the gradient integral algorithm.

5. The portable automatic measurement method for mirror / mirror-like surface morphology according to claim 4, characterized in that: The concentric circular sinusoidal fringe image based on time-domain frequency conversion phase shift described in step two has a fringe frequency that is a variation of one of the following: natural number sequence, multiple sequence, power function sequence, or exponential sequence.

6. The portable automatic measurement method for mirror / mirror-like surface morphology according to claim 4, characterized in that: The slope gradient evaluation function described in step three uses the sum of squares of the slopes in the orthogonal directions as the evaluation index to calculate the optimal orthogonal surface gradient distribution.

7. The portable automatic measurement method for mirror / mirror-like surface morphology according to claim 5, characterized in that: The fringe frequency is achieved using a multiple sequence variation method; the fringe pattern is a constant-step phase shift, with each step's phase shift θ being... , N This represents the total number of phase shift steps. N ≥4.

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