CN103900495A - Large-diameter mirror plane shape detecting method and device based on stripe reflection - Google Patents

Abstract

The invention discloses a method for detecting the surface shape of a large-diameter mirror surface based on fringe reflection. A projector projects standard fringes to a flat plate, and a first camera images the flat plate to calibrate the phase of the standard fringe pattern; at the same time, the standard fringes on the flat plate The image is reflected by the mirror surface under test to obtain a deformed fringe image, which is captured by the second camera, and the phase of the deformed fringe image is calculated, combined with the calibration results of the phase of the standard fringe image, the gradient distribution of the measured mirror surface can be obtained, and then obtained by integration The measured mirror surface shape. The invention also discloses a detection device based on the detection method. The invention is suitable for detecting large-diameter mirrors, solves the problem of limited measurement aperture due to the limited size of projection displays in existing stripe reflective mirror measurement devices, and can avoid oblique photography at the same time, improving the measurement resolution of the system.

Description

A large-aperture mirror surface shape detection method and device based on fringe reflection

technical field

The invention belongs to the field of optical measurement, in particular to a large-diameter mirror surface shape detection method and device based on fringe reflection.

Background technique

In the fields of astronomical observation, space exploration and energy, mirrors with a diameter of more than 0.5 meters are often used. These large-diameter mirrors are required to be processed into special surface shapes, including spherical surfaces, quadric surfaces and more complex free-form surfaces. During the processing of the mirror surface, the surface shape must be continuously detected to ensure the correct processing. For free-form surfaces, traditional interference detection methods cannot be used.

In today's industrial field, for the detection of free-form mirrors, three-coordinate machines, profilers or computational holographic interferometry are usually used. Among them, the measuring range of the profiler is limited and cannot be used for the detection of large-diameter mirrors; the measuring speed of the three-coordinate machine is extremely slow, which affects the processing efficiency, and the number of measurement sampling points is very small; although the calculation holography method has high precision, it is difficult to test each piece of mirror. A holographic sheet needs to be processed separately, resulting in insufficient flexibility and high cost.

The fringe reflectance method has high efficiency and flexibility in detecting the shape of mirror surfaces, and is suitable for detecting various types of mirror surfaces. However, the existing fringe reflection detection technology generally uses an LCD display to project standard fringes, which is difficult to measure large-diameter mirrors due to the limitation of the size of the display. At the same time, the display and the camera must be located on both sides of the normal of the mirror, that is, oblique projection is adopted, so the fringe image captured by the camera is compressed in one direction, which reduces the measurement resolution in that direction.

Contents of the invention

The object of the present invention is to address the deficiencies in the prior art, and provide a method and device for detecting the surface shape of a large-diameter mirror surface based on fringe reflection, which solves the problem of limited measurement aperture and improves the measurement resolution of the system.

In order to achieve the above-mentioned purpose of the invention, the technical solution adopted in the present invention is a large-diameter mirror surface shape detection method based on fringe reflection, comprising the following steps:

Step 1: Use a projector to project a standard fringe image on the plate, including a horizontal standard fringe image and a vertical standard fringe image. There is a hole in the center of the plate, and the size of the hole in the plate is just enough to accommodate the camera lens. Take the lower left corner of the plate as The origin establishes a flat coordinate system;

Step 2: The projector projects a horizontal standard fringe image on the panel, which is captured by the first camera, and the phase shifting method is used to calculate the fringe image to obtain the horizontal phase on the panel

Step 3: Place a standard length object on the plate along the x direction, and shoot it with the first camera. The horizontal scale factor can be obtained from the length of the standard length object:

分别表示本步骤中标准长度物一端和另一端的相位值，二者根据第一摄像机拍摄的图像中标准长度物一端和另一端所处的位置直接从平板上的横向相位

的对应位置读取，L为标准长度物的长度；where x _p represents the horizontal scale factor,

Represent the phase values of one end and the other end of the standard-length object in this step, and the two are directly obtained from the horizontal phase on the plate according to the positions of the one end and the other end of the standard-length object in the image captured by the first camera.

The corresponding position is read, and L is the length of the standard length object;

和步骤3获得的横向比例因子x_p，得到被测镜面的水平方向梯度为：Step 4: The horizontal standard fringe image on the plate is reflected by the measured mirror surface and becomes a horizontal deformed fringe image, which is captured by the second camera, and the phase θ _x of the horizontal deformed fringe image is obtained by the phase shifting method. transverse phase

and the horizontal scale factor x _p obtained in step 3, the horizontal gradient of the measured mirror is obtained as:

Among them, ω _x represents the horizontal gradient of the measured mirror surface, and D is the distance from the flat panel to the measured mirror surface;

Step 5: The projector projects a longitudinal standard fringe image on the panel, and the first camera captures the longitudinal standard fringe image on the panel, and uses the phase shifting method to calculate the fringe image to obtain the longitudinal phase on the panel

Step 6: Place a standard length object on the plate along the y direction, and shoot it with the first camera to obtain the vertical scale factor:

where y _p represents the vertical scaling factor, Represent the phase values of one end and the other end of the standard-length object in this step, which are directly obtained from the longitudinal phase on the plate according to the positions of the one end and the other end of the standard-length object in the image captured by the first camera The corresponding position reads;

和步骤6获得的纵向比例因子yp，得到被测镜面的竖直方向梯度为：Step 7: The projector projects a longitudinal standard fringe image on the flat panel, which becomes a longitudinally deformed fringe image after being reflected by the measured mirror surface, and is captured by the second camera. The phase θy of the longitudinally deformed fringe image is obtained by the phase shifting method, and the flat panel obtained according to step 5 vertical phase on

and the vertical scale factor yp obtained in step 6, the vertical direction gradient of the measured mirror surface is obtained as:

Where ωy represents the vertical direction gradient of the measured mirror surface;

Step 8: numerically integrate the horizontal direction gradient ωx of the measured mirror surface and the vertical direction gradient ω _y of the measured mirror surface to obtain the surface shape of the measured mirror surface.

The invention also discloses a detection device based on the detection method, including a projector, a first camera, a flat panel, and a second video camera; the flat panel is provided with a middle hole for placing the second video camera, and the projector and the first video camera are located at Below the plate, and located on both sides of the middle hole respectively, the central axis of the two forms an included angle of 40°-50° with the plate.

Preferably, the central axes of the projector and the first camera form an included angle of 45°±5° with the flat panel.

The most preferred solution is: the central axis of the projector and the first camera forms an included angle of 45° with the flat panel.

Beneficial effects: the present invention is suitable for detecting large-diameter mirrors, and solves the problem of limited measurement aperture due to the limited size of projection displays in existing stripe reflective mirror measurement devices, and can avoid oblique photography and improve the measurement resolution of the system.

Description of drawings

Fig. 1 is the schematic diagram of detection optical path of the present invention;

Fig. 2 is horizontal standard fringe image and vertical standard fringe image;

Fig. 3 is a schematic diagram of using a measuring rod to calibrate the horizontal scale factor;

Fig. 4 is a schematic diagram of using a measuring rod to calibrate the longitudinal scale factor;

Fig. 5 is the transverse phase on the flat plate and the vertical phase on the flat plate;

Fig. 6 is the deformed fringe image in the horizontal direction and the deformed fringe image in the vertical direction;

Fig. 7 is the horizontal direction gradient of measured mirror surface and the vertical direction gradient of measured mirror surface;

Figure 8 shows the surface shape of the tested mirror.

Detailed ways

The present invention will be further illustrated below in conjunction with the accompanying drawings and specific embodiments. This embodiment is implemented on the premise of the technical solution of the present invention. It should be understood that these embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention.

As shown in Figure 1, a kind of large-diameter mirror surface shape detection device based on fringe reflection, comprises projector 1, first video camera 2, flat panel 3, second video camera 4; Said flat panel 3 is provided with and places second video camera 4 The center hole 5, the projector 1 and the first camera 2 are located below the plate 3, and are respectively located on both sides of the center hole 5, and the central axis of the two forms an angle of 45° with the plate.

The detection method is to arrange the optical path in the following order: the projector projects the standard fringe image (including the horizontal standard fringe image and the vertical standard fringe image) onto the surface of the plate, and the standard fringe image on the surface of the plate is captured by the first camera, and at the same time passes through the mirror surface under test. The deformed fringe image obtained after reflection is captured by the second camera. The standard fringe image is a sinusoidal parallel straight fringe, where the horizontal standard fringe image can be written as:

And the vertical standard stripe image can be written as:

为条纹初始相位，根据移相法的需要设置为0、π/2、π、3π/2四个数值，错误！未找到引用源。中显示了M和N等于10、

为0的横向标准条纹图像和纵向标准条纹图像；以平板左下角为原点建立坐标系。Where I represents the grayscale of the fringe image, x and y are the abscissa in the fringe image and the ordinate in the fringe image, M and N are the fringe frequency in the x direction and the fringe frequency in the y direction, respectively, which are used to control the standard fringe The density of stripes in the image should be 10 to 20 in general measurement, and it is set to 10 in this example;

It is the initial phase of the fringe, and it is set to four values of 0, π/2, π, 3π/2 according to the needs of the phase shifting method, wrong! Reference source not found. shows M and N equal to 10,

The horizontal standard fringe image and the vertical standard fringe image are 0; the coordinate system is established with the lower left corner of the plate as the origin.

的值分别为0、π/2、π、3π/2的情况下，分别由第一摄像机拍摄到平板上的四幅横向标准条纹图像，其灰度依次为I₁、I₂、I₃、I₄，可得平板上的横向相位为：According to the content of step 2 of the claim, the projector projects a horizontal standard fringe image on the flat panel, and sets the initial phase of the fringe according to the phase shifting method

When the values of are 0, π/2, π, 3π/2, respectively, the four horizontal standard stripe images on the flat panel are captured by the first camera, and their gray levels are I ₁ , I ₂ , I ₃ , I ₄ , the transverse phase on the plate can be obtained as:

的计算结果如错误！未找到引用源。所示。Lateral phase on the plate

The calculation result of is wrong! Reference source not found. shown.

According to the content of step 3 of the claim, the combination error! Reference source not found. , place a standard length object on the flat plate along the x direction. The standard length object used in this embodiment is a measuring rod, which is photographed by the first camera. Since the measuring rod and the flat plate are in the same plane, the length of the measuring rod can be obtained Horizontal scale factor:

分别表示测量杆一端和另一端的相位值，二者根据第一摄像机拍摄的图像中测量杆左端和右端所处的位置直接从平板上的横向相位的对应位置读取，本例中分别为-7.5rad和7.5rad；测量杆长度L已通过量具(游标卡尺等)事先进行测量，其值为1米；因此横向比例因子x_p的值为-1/15。where x _p represents the horizontal scale factor,

respectively represent the phase values of one end and the other end of the measuring rod, and the two are directly obtained from the lateral phase on the plate according to the positions of the left end and the right end of the measuring rod in the image captured by the first camera The corresponding position readings of , in this example are -7.5rad and 7.5rad respectively; the length L of the measuring rod has been measured in advance by a measuring tool (vernier caliper, etc.), and its value is 1 meter; therefore, the value of the horizontal scale factor x _p is -1 /15.

和步骤3获得的横向比例因子x_p，得到被测镜面的水平方向梯度为：According to the content of step 4 of the claim, the horizontal standard fringe image on the flat plate becomes a horizontal deformed fringe image after being reflected by the measured mirror surface, and is captured by the second camera, such as error! Reference source not found. As shown, the phase θ _x of the laterally deformed fringe image is obtained by the same phase-shifting method as the above step 2, and the lateral phase on the flat plate obtained according to step 2

and the horizontal scale factor x _p obtained in step 3, the horizontal gradient of the measured mirror is obtained as:

Among them, ω _x represents the horizontal direction gradient of the measured mirror surface, and D is the distance from the plate to the measured mirror surface, which can be obtained by various measuring tools or laser range finders. The measurement result in this example is 0.5 meters, so the calculated measured The horizontal direction gradient ω _x of the mirror surface is wrong! Reference source not found. shown.

According to the content of step 5 of the claim, the projector projects a longitudinal standard fringe image on the flat panel, and the vertical standard fringe image on the flat panel is captured by the first camera, and the image is calculated using the same phase-shifting method as in step 2 above to obtain the vertical standard fringe image on the flat panel. longitudinal phase

According to the content of step 6 of the claims, the combination error! Reference source not found. , place a measuring rod on the plate along the y direction, and shoot it with the first camera to obtain the vertical scale factor:

的对应位置读取，本例中分别为-9rad和9rad，因此纵向比例因子y_p的值为-1/18。where y _p represents the vertical scaling factor, respectively represent the phase values of one end and the other end of the measuring rod in this step, and the two are directly obtained from the longitudinal phase on the plate according to the positions of the upper end and the lower end of the measuring rod in the image captured by the first camera

The corresponding positions of , in this example are -9rad and 9rad respectively, so the value of the vertical scale factor y _p is -1/18.

和步骤6获得的纵向比例因子y_p，得到被测镜面的竖直方向梯度为：According to the content of step 7 of the claim, the projector projects a longitudinal standard stripe image on the flat panel, which becomes a longitudinal deformed stripe image after being reflected by the measured mirror surface, and is captured by the second camera, such as error! Reference source not found. As shown, the phase θ _y of the longitudinally deformed fringe image is acquired by the phase shifting method, and the longitudinal phase on the plate obtained according to step 5

and the vertical scale factor y _p obtained in step 6, the vertical gradient of the measured mirror surface is obtained as:

Among them, ω _y represents the vertical direction gradient of the measured mirror surface, and the calculation result is wrong! Reference source not found. shown.

According to the content of step 8 of the claims, the horizontal direction gradient ω _x of the measured mirror surface and the vertical direction gradient ω _y of the measured mirror surface are numerically integrated to obtain the surface shape of the measured mirror surface, and the calculation result is like an error! Reference source not found. shown.

Claims (4)

1. the heavy caliber mirror shape detection method based on streak reflex, its feature comprises the following steps:

Step 1: use projector to flat board projection standing striation image, comprise horizontal standing striation image and longitudinal standing striation image, its middle plateform center is provided with dull and stereotyped mesopore, and the size of dull and stereotyped mesopore just in time can be held camera lens, sets up dull and stereotyped coordinate system taking the dull and stereotyped lower left corner as initial point;

Step 2: projector projects horizontal standing striation image to flat board, is taken by the first video camera, uses phase-shifting method to calculate the horizontal phase place on flat board to stripe pattern

Step 3: place in the x-direction standard length thing on flat board, by the first video camera, it is taken, can obtain the grid scale factor by the length of standard length thing:

Wherein x _prepresent the grid scale factor,

represent respectively the phase value of this step Plays length thing one end and the other end, image Plays length thing one end and the directly horizontal phase place from flat board of the residing position of the other end that the two is taken according to the first video camera

correspondence position read, L is the length of standard length thing;

Step 4: the horizontal standing striation image on flat board becomes transversely deforming stripe pattern after tested mirror-reflection, is taken by the second video camera, obtains the phase theta of transversely deforming stripe pattern by phase-shifting method _x, the horizontal phase place on the flat board obtaining according to step 2

the grid scale factor x obtaining with step 3 _p, the horizontal direction gradient that obtains tested minute surface is:

Wherein ω _xrepresent the horizontal direction gradient of tested minute surface, D is the dull and stereotyped distance to tested minute surface;

Step 5: projector projects longitudinal standing striation image to flat board, takes the longitudinal standing striation image on flat board by the first video camera, uses phase-shifting method to calculate the longitudinal phase place on flat board to stripe pattern

Step 6: place in the y-direction standard length thing on flat board, by the first video camera, it is taken, obtain longitudinal scale factor:

Wherein y _prepresent longitudinal scale factor,

represent respectively the phase value of this step Plays length thing one end and the other end, image Plays length thing one end and the directly longitudinal phase place from flat board of the residing position of the other end that the two is taken according to the first video camera

correspondence position read;

Step 7: projector projects longitudinal standing striation image to flat board, becomes linear deformation stripe pattern after tested mirror-reflection, is taken by the second video camera, obtains the phase theta of linear deformation stripe pattern by phase-shifting method _y, the longitudinal phase place on the flat board obtaining according to step 5 the longitudinal scale factor y obtaining with step 6 _p, the vertical direction gradient that obtains tested minute surface is:

Wherein ω _yrepresent the vertical direction gradient of tested minute surface;

Step 8: to the horizontal direction gradient ω of tested minute surface _xwith the vertical direction gradient ω to tested minute surface _ycarry out the face shape that numerical integration obtains tested minute surface.

2. the heavy caliber mirror shape pick-up unit based on streak reflex, is characterized in that: comprise projector (1), the first video camera (2), dull and stereotyped (3), the second video camera (4); Described flat board (3) is provided with the mesopore (5) of placing the second video camera (4), described projector (1) and the first video camera (2) are positioned at flat board (3) below, and lay respectively at the both sides of mesopore (5), the axis of the two becomes 40 ° of-50 ° of angles with dull and stereotyped (3).

3. a kind of heavy caliber mirror shape pick-up unit based on streak reflex according to claim 2, is characterized in that: the axis of described projector (1) and the first video camera (2) and dull and stereotyped (3) are at 45 ° ± and 5 ° of angles.

4. according to a kind of heavy caliber mirror shape pick-up unit based on streak reflex described in claim 2 or 3, it is characterized in that: the axis of described projector (1) and the first video camera (2) and dull and stereotyped (3) angle at 45 °.

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