CN110806181A - High-precision optical extensometer and measuring method based on color camera - Google Patents
High-precision optical extensometer and measuring method based on color camera Download PDFInfo
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Abstract
本发明公开了一种基于彩色相机的高精度光学引伸计及测量方法，所涉及的设备包括一台彩色数字相机、一个分光棱镜、一个蓝色滤色片、一个红色滤色片、三个反射镜以及数据处理装置。本测量方法使用了一台彩色数字相机和相应的光学元件对目标点进行追踪，能够消除因样品表面的离面位移和单相机针孔成像模型造成的虚假位移和虚假应变，从而大幅提高了样品的面内位移和应变测量精度。
The invention discloses a high-precision optical extensometer based on a color camera and a measuring method. The involved equipment includes a color digital camera, a light splitting prism, a blue color filter, a red color filter, three reflectors mirror and data processing device. This measurement method uses a color digital camera and corresponding optical components to track the target point, which can eliminate the false displacement and false strain caused by the out-of-plane displacement of the sample surface and the single-camera pinhole imaging model, thereby greatly improving the sample size. The in-plane displacement and strain measurement accuracy.
Description
技术领域technical field
本发明涉及一种基于彩色相机的高精度光学引伸计及测量方法，属于光学测量及无损检测领域。The invention relates to a high-precision optical extensometer based on a color camera and a measurement method, belonging to the fields of optical measurement and nondestructive testing.
背景技术Background technique
应变测量一向是材料性能检测、结构失效分析、工业变形监测等领域的重要目标之一，传统的应变测量技术主要包括接触式和非接触式测量技术。Strain measurement has always been one of the important goals in the fields of material performance testing, structural failure analysis, and industrial deformation monitoring. Traditional strain measurement techniques mainly include contact and non-contact measurement techniques.
接触式测量技术如电阻应变片、光纤应变计或机械式引伸计等方法不仅给被测样品添加了附加质量，还有可能由于粘结剂的使用在一定程度上对样品起到了强化作用，使得这些测量方式在快速发展的生物材料、薄膜材料等样品的检测方面难以被接受。Contact measurement techniques such as resistance strain gauges, fiber optic strain gauges or mechanical extensometers not only add additional mass to the sample to be measured, but may also strengthen the sample to a certain extent due to the use of binders, making the These measurement methods are difficult to accept in the detection of rapidly developing samples such as biological materials and thin film materials.
非接触测量技术中，全场测量的二维和三维数字图像相关技术对于应变的检测精度还有待提高，目前也已经出现了越来越多基于光学方法的视频引伸计，如Instron公司已商品化的视频引伸计，应变测量精度也不能满足实际应用的需要。更重要的是，实际实验条件下样品必然会由于各种原因产生一定的离面位移，在常规针孔成像模型条件下离面位移会在成像系统的像面上产生虚假位移和虚假应变，极大地干扰应变测量结果的精度和分辨率。In the non-contact measurement technology, the 2D and 3D digital image-related technologies for full-field measurement still need to improve the detection accuracy of strain. At present, more and more video extensometers based on optical methods have appeared. For example, Instron has commercialized it. The strain measurement accuracy of the video extensometer cannot meet the needs of practical applications. More importantly, under the actual experimental conditions, the sample will inevitably have a certain out-of-plane displacement due to various reasons. Under the condition of the conventional pinhole imaging model, the out-of-plane displacement will produce false displacement and false strain on the image plane of the imaging system. Accuracy and resolution of geodetic disturbance strain measurements.
针对该问题白鹏翔等人在2015年提出了一种应变修正方法，需要额外附加修正片来保证较高的精度，有学者提出使用远心镜头或者多个相机来规避针孔成像模型，高昂的成本限制了其在实际工程中的应用。In response to this problem, Bai Pengxiang et al. proposed a strain correction method in 2015, which requires additional correction sheets to ensure higher accuracy. Some scholars propose to use telecentric lenses or multiple cameras to avoid the pinhole imaging model, which is expensive. It limits its application in practical engineering.
发明内容SUMMARY OF THE INVENTION
为了克服现有技术的不足，本发明目的在于提供一种基于彩色相机的高精度光学引伸计及测量方法。使用该光学引伸计和测量方法进行均匀应变检测，可以在较低成本的基础上有效消除由于被测样品离面位移而导致的虚假位移和虚假应变，提高均匀应变测量的精度和分辨率。In order to overcome the deficiencies of the prior art, the present invention aims to provide a high-precision optical extensometer and a measurement method based on a color camera. Using the optical extensometer and measuring method for uniform strain detection can effectively eliminate false displacement and false strain caused by the out-of-plane displacement of the measured sample on the basis of lower cost, and improve the accuracy and resolution of uniform strain measurement.
本发明为解决上述技术问题采用以下技术方案：The present invention adopts the following technical solutions for solving the above-mentioned technical problems:
本发明提供一种基于彩色相机的高精度光学引伸计，包括一台彩色数字相机、一个长焦距镜头、一个分光棱镜、一个蓝色滤色片、一个红色滤色片、第一至第三反射镜以及数据处理装置；其中：The invention provides a high-precision optical extensometer based on a color camera, comprising a color digital camera, a long focal length lens, a beam splitting prism, a blue color filter, a red color filter, first to third reflections mirrors, and data processing means; wherein:
蓝色滤色片和红色滤色片分别覆盖在分光棱镜的两个相邻表面，蓝色滤色片和红色滤色片对从两个方向入射到分光棱镜的光场分别进行蓝色和红色的颜色过滤，经过颜色过滤的两个光场通过分光棱镜合成为一个红蓝两色叠加的光场；The blue color filter and the red color filter cover the two adjacent surfaces of the beam splitting prism, respectively. The two light fields that have been filtered by the color filter are synthesized into a light field with superimposed red and blue colors through the beam splitting prism;
第一反射镜对应于被测样品表面的第一目标点，将第一目标点的漫射光场反射到分光棱镜中覆盖了滤色片的其中一个表面；第二和第三反射镜均对应于被测样品的第二目标点，将第二目标点的漫射光场反射到分光棱镜中覆盖了滤色片的另外一个表面；The first mirror corresponds to the first target point on the surface of the sample to be tested, and reflects the diffuse light field of the first target point to one of the surfaces of the beam splitting prism that covers the color filter; the second and third mirrors both correspond to The second target point of the sample to be tested reflects the diffuse light field of the second target point into the beam splitter prism and covers another surface of the color filter;
彩色数字相机通过长焦距镜头接收从分光棱镜出射的红蓝两色叠加的光场，并进行成像，形成彩色数字图像传输至数据处理装置；The color digital camera receives the superimposed light field of red and blue emitted from the beam splitting prism through the long focal length lens, and performs imaging to form a color digital image and transmit it to the data processing device;
数据处理装置包括颜色通道分离模块、相关运算模块和后处理模块，颜色通道分离模块对接收到的彩色数字图像进行红绿蓝三通道分离，分离出红色和蓝色通道的数字图像；相关运算模块根据颜色通道分离模块分离出的红色和蓝色通道的数字图像，获取第一和第二目标点沿着测量方向的位移信息；后处理模块利用相关运算模块获取的位移信息，结合第一和第二目标点的间距信息，获得被测样本表面的均匀应变信息。The data processing device includes a color channel separation module, a correlation operation module and a post-processing module. The color channel separation module separates the red, green and blue channels of the received color digital image, and separates the red and blue channel digital images; the correlation operation module According to the digital images of the red and blue channels separated by the color channel separation module, the displacement information of the first and second target points along the measurement direction is obtained; the post-processing module uses the displacement information obtained by the correlation operation module to combine the first and second target points. The distance information of the two target points can obtain the uniform strain information of the surface of the tested sample.
作为本发明的进一步技术方案，红色滤色片和蓝色滤色片的位置能够互换。As a further technical solution of the present invention, the positions of the red color filter and the blue color filter can be interchanged.
作为本发明的进一步技术方案，被测表面的均匀应变大小为(x2-x1)/s，x1和x2分别为第一和第二目标点沿着测量方向的位移，s为第一和第二目标点的间距。As a further technical solution of the present invention, the uniform strain of the measured surface is (x 2 -x 1 )/s, where x 1 and x 2 are the displacements of the first and second target points along the measurement direction, respectively, and s is the first The distance between the first and second target points.
本发明还提供一种基于如上任一所述的基于彩色相机的高精度光学引伸计的均匀应变测量方法，包括如下步骤：The present invention also provides a method for measuring uniform strain based on the color camera-based high-precision optical extensometer as described above, comprising the following steps:
(1)在被测样品表面选取两个目标点作为测量点，两目标点的连线方向为测量方向，在目标点人工生成随机散斑或利用被测样品表面纹理，作为变形信息的载体；(1) Select two target points on the surface of the tested sample as measurement points, and the direction of the line connecting the two target points is the measurement direction, and artificially generate random speckles at the target points or use the surface texture of the tested sample as the carrier of deformation information;
(2)固定安装长焦距镜头和彩色数字相机，使长焦距镜头的光轴与被测样品表面垂直；(2) The long focal length lens and the color digital camera are fixedly installed, so that the optical axis of the long focal length lens is perpendicular to the surface of the tested sample;
(3)在长焦距镜头与被测样品之间放置分光棱镜，使分光棱镜对准长焦距镜头且其中一个表面与长焦距镜头的光轴垂直；(3) Place a beam splitter prism between the long focal length lens and the sample to be tested, so that the beam splitter prism is aligned with the long focal length lens and one of its surfaces is perpendicular to the optical axis of the long focal length lens;
(4)在分光棱镜的相邻两个表面分别覆盖上蓝色和红色滤色片，使这两个表面分别能够对各自的入射光线进行滤色处理；(4) The two adjacent surfaces of the beam splitting prism are covered with blue and red color filters respectively, so that the two surfaces can filter the respective incident light rays;
(5)安装第一个反射镜，使被测样品表面的第一个目标点能够通过第一个反射镜入射到覆盖有滤色片的分光棱镜其中一个表面；安装剩余两个反射镜，使被测样品表面的第二个目标点能够通过剩余两个反射镜入射到覆盖有滤色片的分光棱镜另外一个表面；调整三个反光镜的位置，使两个目标点上的漫射光场经过反射进入长焦距镜头的光程相等；(5) Install the first reflector so that the first target point on the surface of the sample to be tested can be incident on one of the surfaces of the beam splitter prism covered with the color filter through the first reflector; install the remaining two reflectors so that the The second target point on the surface of the tested sample can be incident on the other surface of the beam splitter prism covered with the color filter through the remaining two mirrors; adjust the positions of the three mirrors so that the diffuse light fields on the two target points pass through The optical path of reflection into a long focal length lens is equal;
(6)利用彩色数字相机通过长焦距镜头采集彩色数字图像，并对采集到的彩色数字图像进行颜色通道分离，分离出红色和蓝色通道的数字图像；(6) Using a color digital camera to collect a color digital image through a long focal length lens, and performing color channel separation on the collected color digital image to separate the red and blue channel digital images;
(7)根据分离出的红色和蓝色通道的数字图像，分别得到两个目标点沿着测量方向产生的位移为x1和x2，结合两个目标点的间距s，计算被测表面的均匀应变大小为(x2-x1)/s。(7) According to the separated digital images of the red and blue channels, the displacements of the two target points along the measurement direction are obtained as x 1 and x 2 respectively, and the distance s of the two target points is combined to calculate the measured surface The uniform strain magnitude is (x 2 -x 1 )/s.
本发明采用以上技术方案与现有技术相比，具有以下技术效果：Compared with the prior art, the present invention adopts the above technical scheme, and has the following technical effects:
(1)被测样品表面无损：与工业领域中以应变片为代表的传统接触式测量技术相比，本发明采用了光学测量技术，不需要与样品表面直接接触，无附加质量，对样品没有损伤，不会限制样品变形；(1) The surface of the sample to be tested is non-destructive: compared with the traditional contact measurement technology represented by strain gauges in the industrial field, the present invention adopts optical measurement technology, which does not require direct contact with the surface of the sample, has no additional mass, and has no effect on the sample. damage, will not limit the deformation of the sample;
(2)消除了样品表面离面位移的影响：分光棱镜和反射镜的使用使两个目标点均能够以垂直入射的方式在图像芯片中心成像，而且数字相机采用的是长焦距镜头，使得目标点一定程度的离面位移并不会在数字相机的像面上产生虚假位移，根据位移计算的应变也不包含虚假应变，因而消除了测量过程中由于样品不可避免产生的离面位移而导致的虚假位移和虚假应变，为测量精度的提高提供了基础；(2) The influence of the off-plane displacement of the sample surface is eliminated: the use of beam splitting prisms and mirrors enables both target points to be imaged at the center of the image chip in a way of normal incidence, and the digital camera uses a long focal length lens, so that the target A certain degree of out-of-plane displacement of the point will not produce false displacement on the image plane of the digital camera, and the strain calculated from the displacement does not include false strain, thus eliminating the inevitable out-of-plane displacement of the sample during the measurement process. False displacement and false strain provide a basis for the improvement of measurement accuracy;
(3)应变测量精度提高：相对于基于针孔成像模型单相机的均匀应变测量来说测量精度有了极大的提高；单相机测量中视场和分辨率是一对矛盾的因素，浪费了视场范围，限制了测量标距，使得均匀应变测量精度有限，而彩色相机和分光棱镜以及反光镜的采用使目标点的选取更加灵活，同时每个目标点都能在满画幅的图像芯片上成像，增加了空间分辨率，在保证位移测量精度的同时，测量标距也不再受到限制，因而极大提升了均匀应变的测量精度；(3) Improvement of strain measurement accuracy: Compared with the uniform strain measurement based on the single camera of the pinhole imaging model, the measurement accuracy has been greatly improved; the field of view and resolution in the single camera measurement are a pair of contradictory factors, wasting the visual field. The field range limits the measurement gauge length, making the uniform strain measurement accuracy limited, and the use of color cameras, beam splitting prisms and mirrors makes the selection of target points more flexible, and each target point can be imaged on a full-frame image chip , increasing the spatial resolution, while ensuring the displacement measurement accuracy, the measurement gauge length is no longer limited, thus greatly improving the measurement accuracy of uniform strain;
(4)成本较低：仅使用一个彩色相机，避免了多个相机之间软件和硬件的同步步骤，降低了成本；与基于远心镜头的单相机应变测量相比，增加棱镜和反射镜的代价远比不上昂贵的远心镜头，且能够得到更高的测量精度，既降低了成本又提高了测量效果。(4) Lower cost: only one color camera is used, which avoids the synchronization steps of software and hardware among multiple cameras and reduces the cost; compared with the single-camera strain measurement based on telecentric lens, it increases the The cost is far less than the expensive telecentric lens, and higher measurement accuracy can be obtained, which not only reduces the cost but also improves the measurement effect.
附图说明Description of drawings
图1是本发明涉及的光学引伸计测量示意图。FIG. 1 is a schematic diagram of the measurement of the optical extensometer involved in the present invention.
图中：1-被测样品，2-第一个目标点，3-第二个目标点，4-第一个反射镜，5-第二个反射镜，6-第三个反射镜，7-分光棱镜，8-蓝色滤色片，9-红色滤色片，10-长焦距镜头，11-彩色数字相机。In the figure: 1- the sample to be tested, 2- the first target point, 3- the second target point, 4- the first mirror, 5- the second mirror, 6- the third mirror, 7 - Beam splitting prism, 8- blue color filter, 9- red color filter, 10- telephoto lens, 11- color digital camera.
图2为本发明方法中消除离面位移原理示意图。FIG. 2 is a schematic diagram of the principle of eliminating out-of-plane displacement in the method of the present invention.
具体实施方式Detailed ways
下面结合附图对本发明的技术方案做进一步的详细说明：Below in conjunction with accompanying drawing, the technical scheme of the present invention is described in further detail:
如图1所示，本发明实施例公开的一种基于彩色相机的高精度光学引伸计，包括一台彩色数字相机11、一个长焦距镜头10、一个分光棱镜7、一个蓝色滤色片8、一个红色滤色片9、第一个反射镜4、第二个反射镜5、第三个反射镜6及数据处理装置。As shown in FIG. 1 , a high-precision optical extensometer based on a color camera disclosed in an embodiment of the present invention includes a color digital camera 11 , a long focal length lens 10 , a beam splitting prism 7 , and a blue color filter 8 , a red color filter 9, a first reflector 4, a second reflector 5, a third reflector 6 and a data processing device.
蓝色滤色片8和红色滤色片9分别覆盖在分光棱镜7的两个相邻表面上，具体来说，分光棱镜7包含四个表面(两个与长焦距镜头10的光轴平行的表面，两个与长焦距镜头10的光轴垂直的表面)，红色滤色片9则位于与长焦距镜头10的光轴垂直的两表面中距离长焦距镜头10较远的一个表面上，蓝色滤色片8所在的表面则与红色滤色片9和分光棱镜的内部反射面相交于一点。The blue color filter 8 and the red color filter 9 are respectively covered on two adjacent surfaces of the dichroic prism 7. Specifically, the dichroic prism 7 includes four surfaces (two parallel to the optical axis of the telephoto lens 10). surface, two surfaces perpendicular to the optical axis of the telephoto lens 10), the red color filter 9 is located on the one surface farther from the telephoto lens 10 among the two surfaces perpendicular to the optical axis of the telephoto lens 10, the blue The surface on which the color filter 8 is located intersects with the red color filter 9 and the internal reflection surface of the beam splitting prism at one point.
被测样品1的第一个目标点2的光场经过反射镜4射向蓝色滤色片8，经过滤色之后仅保留蓝色分量进入分光棱镜7，通过分光棱镜7的内部反射面射向长焦距镜头10；被测样品1的第二个目标点3的光场经过反射镜6和反射镜5的两次反射，射向红色滤色片9，经过滤色后仅保留红色分量进入分光棱镜7，透射过分光棱镜7的内部反射面后直接射向长焦距镜头10；此时，目标点2的蓝色光场和目标点3的红色光场离开分光棱镜7后产生叠加，生成了彩色光场共同射向长焦距镜头10，并在彩色数字相机11的像面上成像，生成彩色的数字图像。The light field of the first target point 2 of the sample to be tested 1 is emitted to the blue color filter 8 through the reflector 4. After filtering, only the blue component is retained and enters the beam splitter prism 7, and is emitted through the internal reflection surface of the beam splitter prism 7. To the long focal length lens 10; the light field of the second target point 3 of the sample under test 1 is reflected twice by the mirror 6 and the mirror 5, and then shoots towards the red color filter 9. After filtering, only the red component is retained to enter The beam splitting prism 7 transmits through the internal reflection surface of the beam splitting prism 7 and then directly shoots toward the long focal length lens 10; at this time, the blue light field of the target point 2 and the red light field of the target point 3 are superimposed after leaving the beam splitting prism 7, generating a The color light fields are jointly emitted to the long focal length lens 10 and imaged on the image plane of the color digital camera 11 to generate a color digital image.
蓝色滤色片8和红色滤色片9可以交换位置，交换位置后对测量结果不产生任何影响。The positions of the blue color filter 8 and the red color filter 9 can be exchanged, and the exchange of positions will not have any effect on the measurement results.
调整彩色数字相机11、长焦距镜头10和分光棱镜7的位置，使长焦距镜头10的光轴与分光棱镜7的四个表面成平行或垂直的姿态；微调反射镜4、5、6和分光棱镜7的位置，使目标点2和3经过多次反射进入长焦距镜头10的光程相等；微调反射镜4、5、6，使目标点2和3入射到反射镜4和6的光线与被测样品1的表面垂直。Adjust the positions of the color digital camera 11, the telephoto lens 10 and the beam splitting prism 7 so that the optical axis of the telephoto lens 10 is parallel or perpendicular to the four surfaces of the beam splitting prism 7; fine-tune the mirrors 4, 5, 6 and beam splitting The position of the prism 7 makes the optical paths of the target points 2 and 3 into the long focal length lens 10 after multiple reflections equal; fine-tune the mirrors 4, 5, 6, so that the light incident from the target points 2 and 3 to the mirrors 4 and 6 is the same as that of the mirrors 4 and 6. The surface of the sample 1 to be tested is vertical.
利用彩色数字相机11分别采集被测样品1变形前后的数字图像，首先利用数据处理装置中的颜色通道分离模块对采集到的彩色数字图像进行红绿蓝三通道分离，将分离出红色和蓝色通道的数字图像，其中蓝色通道字图像仅包含目标点2变形前后的光场信息，红色通道数字图像仅包含目标点3变形前后的光场信息；然后利用数据处理装置的相关运算模块处理分离出来的蓝色和红色通道数字图像，分别获取目标点2和3沿着测量方向的位移信息；最后利用数据处理装置的后处理模块对位移信息进行处理，结合两目标点2和3的间距信息，获得被测样品1表面的均匀应变信息。The digital images before and after deformation of the sample 1 under test are collected by the color digital camera 11. First, the collected color digital images are separated by three channels of red, green and blue by using the color channel separation module in the data processing device, and the red and blue are separated. The digital image of the channel, in which the blue channel word image only contains the light field information before and after the deformation of the target point 2, and the red channel digital image only contains the light field information before and after the deformation of the target point 3; Then use the relevant operation module of the data processing device to process the separation The blue and red channel digital images obtained, respectively obtain the displacement information of the target points 2 and 3 along the measurement direction; finally, use the post-processing module of the data processing device to process the displacement information, and combine the distance information of the two target points 2 and 3 , to obtain the uniform strain information on the surface of the tested sample 1.
本发明实施例公开的一种基于彩色相机的高精度光学引伸计及测量方法，能够消除由于被测样品表面产生离面位移而导致测量结果中包含的虚假位移和虚假应变，虚假位移和应变产生原理如图2所示。不使用远心镜头的普通相机和镜头在成像时普遍遵循针孔成像模型，如图2中如果将目标点设定为被测样品表面上远离光轴的一点A，经过镜头会在像面上的a点成像。当被测样品表面产生一定程度的离面位移使A点移动到了B点，根据针孔成像模型将会在像面上与a点存在一定距离的b点成像。在被测样品并未产生变形的条件下，仅仅由于被测样品表面产生离面位移而使同一个点在像面上所成的像点产生了位移，位移的大小为a点和b点的间距，根据位移数据能够计算出相应的应变数据，这就是由离面位移导致的虚假位移和虚假应变。当把目标点设定在被测样品表面与光轴的交点C，在像面上的c点成像。随着被测样品表面的离面位移C点移动到了D点，此时在像面上d点成像。不难发现，c点和d点其实是重合的，即目标点在像面上并未产生位移，也就意味着离面位移并不会导致虚假位移以及后续的虚假应变。如图1中目标点2和3的光场由于垂直射向反射镜4和6，且大致通过长焦距镜头10的光心进行成像，因而目标点2和3轻微的离面位移并不会引起虚假位移和虚假应变，测量精度自然能够得到提高。The embodiment of the present invention discloses a high-precision optical extensometer based on a color camera and a measurement method, which can eliminate the false displacement and false strain contained in the measurement result caused by the off-plane displacement of the sample surface to be measured, and the false displacement and strain generated The principle is shown in Figure 2. Ordinary cameras and lenses that do not use telecentric lenses generally follow the pinhole imaging model when imaging. As shown in Figure 2, if the target point is set to a point A on the surface of the tested sample that is far from the optical axis, it will pass through the lens on the image plane. point a imaging. When a certain degree of off-plane displacement occurs on the surface of the sample to be tested, point A moves to point B, and according to the pinhole imaging model, point b, which is at a certain distance from point a, will be imaged on the image plane. Under the condition that the sample to be tested is not deformed, the image point formed by the same point on the image plane is displaced only due to the off-plane displacement of the surface of the sample to be tested. The magnitude of the displacement is the difference between points a and b. According to the displacement data, the corresponding strain data can be calculated, which is the false displacement and false strain caused by the out-of-plane displacement. When the target point is set at the intersection C of the sample surface and the optical axis, the image will be imaged at point c on the image plane. With the out-of-plane displacement of the sample surface to be measured, the point C moves to the point D, and the image is imaged at the point d on the image plane. It is not difficult to find that point c and point d are actually coincident, that is, the target point does not have displacement on the image plane, which means that the off-plane displacement will not cause false displacement and subsequent false strain. Since the light fields of target points 2 and 3 in Fig. 1 are perpendicular to the mirrors 4 and 6, and are imaged through the optical center of the long focal length lens 10, the slight out-of-plane displacement of the target points 2 and 3 will not cause False displacement and false strain, the measurement accuracy can naturally be improved.
本发明实施例公开的一种基于彩色相机的高精度光学引伸计及测量方法，目标点2和3及其附近区域均能够在彩色数字相机11的整个图像芯片上进行成像而不是仅占据图像芯片的一部分，增大了目标点2和3成像的放大倍数，有利于提高位移和应变测量精度。A high-precision optical extensometer and measurement method based on a color camera disclosed in the embodiment of the present invention, the target points 2 and 3 and their adjacent areas can be imaged on the entire image chip of the color digital camera 11 instead of occupying only the image chip part of the target point 2 and 3, the imaging magnification is increased, which is beneficial to improve the displacement and strain measurement accuracy.
本发明实施例公开的一种基于上述光学引伸计的均匀应变测量方法，包括以下步骤：A method for measuring uniform strain based on the above-mentioned optical extensometer disclosed in the embodiment of the present invention includes the following steps:
步骤1、在被测样品表面选取两个目标点作为测量点，两目标点的连线方向为测量方向，在目标点人工生成随机散斑或利用样品表面纹理，作为变形信息的载体；Step 1. Select two target points on the surface of the sample to be measured as measurement points, and the direction of the line connecting the two target points is the measurement direction, and artificially generate random speckles at the target points or use the surface texture of the sample as the carrier of deformation information;
步骤2、固定安装长焦距镜头和彩色数字相机，使长焦距镜头的光轴尽量与被测样品表面垂直；Step 2. Fix the long focal length lens and the color digital camera, so that the optical axis of the long focal length lens is as perpendicular to the surface of the tested sample as possible;
步骤3、在长焦距镜头与被测样品之间放置分光棱镜，使分光棱镜对准镜头且其中一个侧面与长焦距镜头的光轴垂直；Step 3. Place a beam-splitting prism between the telephoto lens and the sample to be tested, so that the beam-splitting prism is aligned with the lens and one of its sides is perpendicular to the optical axis of the telephoto lens;
步骤4、在分光棱镜的相邻两个侧面分别覆盖上蓝色和红色滤色片，使两个侧面分别能够对各自的入射光线进行滤色处理；Step 4. Cover the two adjacent sides of the beam splitting prism with blue and red color filters respectively, so that the two sides can filter the respective incident light;
步骤5、安装第一个反射镜，使被测样品表面第一个目标点能够通过第一个反射镜入射到覆盖有滤色片的分光棱镜其中一个侧面，安装剩余两个反射镜，使被测样品表面第二个目标点能够通过剩余两个反射镜入射到覆盖有滤色片的分光棱镜另外一个侧面；调整反光镜的位置，使两路光线的光程相等；Step 5. Install the first reflector so that the first target point on the surface of the sample to be tested can be incident on one of the sides of the beam splitter prism covered with the color filter through the first reflector, and install the remaining two reflectors so that the The second target point on the surface of the test sample can be incident on the other side of the beam splitter prism covered with the color filter through the remaining two mirrors; adjust the position of the mirror to make the optical paths of the two rays equal;
步骤6、利用彩色数字相机采集彩色数字图像，并对采集到的图像进行颜色通道分离，分离出蓝色分量数字图像和红色分量数字图像；Step 6, using a color digital camera to collect a color digital image, and performing color channel separation on the collected image to separate a blue component digital image and a red component digital image;
步骤7、利用数字图像相关技术对分离出的数字图像进行相关运算，追踪两目标点的位移，分别得到两目标点沿着测量方向产生的位移为x1和x2，结合两目标点的间距s，可以计算被测表面的均匀应变大小为(x2-x1)/s。Step 7. Use digital image correlation technology to perform correlation operation on the separated digital image, track the displacement of the two target points, and obtain the displacements of the two target points along the measurement direction as x 1 and x 2 respectively, combined with the distance between the two target points. s, the uniform strain of the measured surface can be calculated as (x 2 -x 1 )/s.
在步骤7中，数字图像相关算法为现有技术。例如，期刊名称为《光学学报》，2013年04期，公开了名称为《使用双远心镜头的高精度二维数字图像相关测量系统》的文章中公开了数字图像相关算法。In step 7, the digital image correlation algorithm is the prior art. For example, the journal titled "Optical Acta Sinica", 2013-04, published the digital image correlation algorithm in the article titled "High-precision two-dimensional digital image correlation measurement system using bi-telecentric lens".
本发明使用彩色相机和分光棱镜以及反射镜作为图像采集设备，与传统的单相机相比，两个目标点的间距即应变测量标距是根据实际需求可调的，具有更高的灵活性。两目标点间距与应变测量精度有着直接的联系，间距的增大可以扩大应变测量标距，在相对位移精度固定不变的情况下，也能极大增加应变测量的精度和分辨率。Compared with the traditional single camera, the distance between the two target points, that is, the strain measurement gauge length, is adjustable according to actual needs, and has higher flexibility. The distance between the two target points is directly related to the strain measurement accuracy. The increase of the distance can expand the gauge length of the strain measurement, and can greatly increase the accuracy and resolution of the strain measurement when the relative displacement accuracy is fixed.
本发明使用彩色相机以不同颜色通道的方式同时满画幅记录了两个目标点的光场信息，提高了两个目标点数字图像的空间分辨率，间接提高了位移和应变的测量精度和分辨率。The invention uses a color camera to simultaneously record the light field information of two target points in a full-frame manner with different color channels, improves the spatial resolution of the digital images of the two target points, and indirectly improves the measurement accuracy and resolution of displacement and strain. .
以上内容是结合具体的优选实施方式对本发明所作的进一步详细说明，不能认定本发明的具体实施只局限于这些说明。对于本发明所属技术领域的普通技术人员来说，在不脱离本发明构思的前提下，还可以做出若干简单推演或替代，都应当视为属于本发明的保护范围。The above content is a further detailed description of the present invention in combination with specific preferred embodiments, and it cannot be considered that the specific implementation of the present invention is limited to these descriptions. For those of ordinary skill in the technical field of the present invention, without departing from the concept of the present invention, some simple deductions or substitutions can be made, which should be regarded as belonging to the protection scope of the present invention.
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