WO2022088596A1 - 一种偏折测量中实现屏幕和工件同时对焦的装置和方法 - Google Patents

一种偏折测量中实现屏幕和工件同时对焦的装置和方法 Download PDF

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WO2022088596A1
WO2022088596A1 PCT/CN2021/082640 CN2021082640W WO2022088596A1 WO 2022088596 A1 WO2022088596 A1 WO 2022088596A1 CN 2021082640 W CN2021082640 W CN 2021082640W WO 2022088596 A1 WO2022088596 A1 WO 2022088596A1
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workpiece
camera
screen
focusing mirror
image
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张祥朝
朱睿
陈雨诺
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Fudan University
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    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B7/00—Mountings, adjusting means, or light-tight connections, for optical elements
    • G02B7/18—Mountings, adjusting means, or light-tight connections, for optical elements for prisms; for mirrors
    • G02B7/182—Mountings, adjusting means, or light-tight connections, for optical elements for prisms; for mirrors for mirrors
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/01—Arrangements or apparatus for facilitating the optical investigation
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/84—Systems specially adapted for particular applications
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/01—Arrangements or apparatus for facilitating the optical investigation
    • G01N2021/0187—Mechanical sequence of operations

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  • the invention relates to the technical field of precision manufacturing, in particular to a device and method for realizing simultaneous focusing of a screen and a workpiece in deflection measurement.
  • Deflectometry is a mirror measurement technology developed in recent years [XU X, ZHANG X, NIU Z, et al. Self-calibration of in situ monoscopic deflectometric measurement in precision optical manufacturing. Optics Express, 2019, 27(5): 7523 -7536.], the principle is to generate regular stripes on the display screen, and the stripes are deformed after being reflected by the measured surface. The deformation pattern is captured by a CCD camera, and then the surface gradient distribution of the measured surface can be calculated by deriving the geometric relationship. Then the surface height is obtained by integrating.
  • Deflection measurement is generally performed by multi-step phase shifting of the screen stripes, and the corresponding relationship between the object and the screen pixel is established according to the demodulation phase of each pixel in the captured image. Therefore, the demodulation accuracy of each pixel in the image directly determines the measurement accuracy.
  • the captured image is generally focused on the workpiece under test, but this will cause the screen pattern to be out of focus relative to the camera. Therefore, the convolution effect introduced by the point spread function in the blurred imaging will cause the grayscale of the captured image to change, resulting in Phase demodulation error, as shown in Figure 1; on the contrary, if the screen is clearly imaged in the camera, it will cause the measured workpiece to be out of focus, and the detection uncertainty of the measurement position will increase.
  • This measurement uncertainty problem It is the core factor that restricts the measurement accuracy of the phase measurement deflection technique on complex surfaces [Pavlicek P and Hausler G.Int J Optomech 2014; 8: 292-303].
  • the object of the present invention is to provide a device and method for realizing the simultaneous focusing of the screen and the workpiece in the deflectometry measurement .
  • the technical scheme of the present invention is:
  • the present invention provides a device for achieving simultaneous focusing of a screen and a workpiece in deflection measurement, including a camera, a screen and a workpiece to be measured, and a focusing mirror, wherein the focusing mirror is a concave mirror, and the focusing mirror is used for
  • the screen is imaged at the workpiece to be tested, and the positions of the camera, the workpiece to be tested, the focusing mirror and the screen are suitable for the screen to be reflected on the tested workpiece through the focusing mirror
  • the second image on the workpiece can reflect the first image through the workpiece to be tested again, and the first image is coincident with the workpiece to be tested, so that the camera can focus on the screen and the workpiece to be tested at the same time .
  • the present invention also provides a method for realizing simultaneous focusing of a screen and a workpiece in deflection measurement.
  • the method is realized based on a focusing mirror, and the method includes the following steps:
  • the image matches the target size of the camera.
  • the distance between the screen and the focusing mirror relative to the workpiece to be measured is adjusted so that the second image reflected by the screen on the workpiece to be measured through the focusing mirror can be reflected into the first image through the workpiece to be measured again, and the first image is
  • the steps of matching the image in the camera to the target size of the camera include,
  • the step of adjusting the focal length of the camera and the distance between the workpiece to be tested and the camera so that the workpiece to be tested is clearly imaged on the image plane of the camera includes:
  • the camera does not directly focus and image the screen, but reflects the screen onto the workpiece to be tested through the focusing mirror, so that the camera can realize the focus on the screen when focusing on the workpiece to be tested.
  • the second image reflected by the screen on the workpiece to be tested through the focusing mirror can reflect the first image through the workpiece to be tested again, and it is ensured that the first image coincides with the workpiece to be tested. Based on this, it can be ensured that when the camera is focusing on the workpiece to be tested, the image of the screen in the camera can truly reflect the original appearance of the screen, ensuring the authenticity of the image.
  • 1 is a schematic diagram of the point spread function of each point of an off-axis measurement screen in the prior art
  • Embodiment 1 of the present invention is a schematic structural diagram of Embodiment 1 of the present invention.
  • Fig. 3 is the method flow chart of the second embodiment of the present invention.
  • FIG. 4 is a schematic diagram of the point spread function of the simultaneous focusing and measuring of each point of the optical path screen according to the present invention.
  • connection may be a fixed connection, a detachable connection, or an integral connection; it may be a mechanical connection, or a connection. It can be an electrical connection; it can be a direct connection, or an indirect connection through an intermediate medium, or the internal connection of the two structures.
  • connection may be a fixed connection, a detachable connection, or an integral connection; it may be a mechanical connection, or a connection. It can be an electrical connection; it can be a direct connection, or an indirect connection through an intermediate medium, or the internal connection of the two structures.
  • FIG. 1 Provided is a device for realizing simultaneous focusing of a screen and a workpiece in deflection measurement, as shown in FIG.
  • the focusing mirror 4 is used to image the screen 2 at the workpiece 3 to be tested.
  • the positions of the camera 1, the workpiece to be tested 3, the focusing mirror 4 and the screen 2 are adapted so that the second image (ie, the image 2) reflected by the screen 2 on the workpiece 3 to be tested through the focusing mirror 4 can be
  • the first image (ie, image 1) is reflected by the workpiece 3 under test again, and the first image is overlapped with the workpiece 3 under test, so that the camera 1 can focus on the screen 2 and the workpiece under test 3 at the same time, that is, the camera 1 is focusing on the workpiece 3.
  • the image 1 reflected by the screen 2 through the focusing mirror 4 and the workpiece 3 to be tested can also be synchronously focused by the camera 1, thus solving the problem in the prior art that the camera 1 cannot simultaneously focus on the screen 2 and the image 1.
  • the focusing mirror 4 is set to be a concave mirror, and the workpiece 3 to be tested is also concave.
  • configure the angle between the line connecting the center of the screen 2 and the center of the focusing mirror 4 and the normal at the center of the focusing mirror 4, and the connecting line between the center of the focusing mirror 4 and the center of the workpiece 3 to be tested and the focusing mirror 4 The angle between the normal at the center, the angle between the line connecting the center of the focusing mirror 4 and the center of the workpiece 3 to be tested and the normal at the center of the workpiece 3 to be tested, and the center of the workpiece 3 to be tested and the center of the camera 1
  • the angle between the line connecting the center and the normal line at the center of the workpiece 3 to be tested is equal, as shown by the angle ⁇ in Figure 1; on the other hand, the distance L 1 , The radius of curvature R of the focusing mirror 4 and the distance L 2 from the workpiece 3 to the focusing mirror 4 along the optical axi
  • the parameters of the camera 1, the shape and size of the workpiece 3 to be measured, the ⁇ value, one of L 1 and L 2 , and one of S 1 and S 2 can be determined when in use.
  • the configuration arranges the apparatus provided by this embodiment.
  • the second image reflected by the screen on the workpiece to be tested through the focusing mirror can reflect the first image through the workpiece to be tested again.
  • the first image can be focused by the camera at the same time, and there is no error between the imaging of the first image in the camera and the direct imaging of the screen in the camera, so that the camera can simultaneously focus on the screen and the workpiece to be tested.
  • the method is based on the device of the above-mentioned first embodiment, and the optical path suitable for use can be designed through the steps provided by the method, so that the screen and the workpiece to be measured can be The cameras focus at the same time.
  • the method includes step S202, step S204 and step S206.
  • Step S202 adjust the focal length of the camera and the distance between the workpiece to be tested and the camera, so that the workpiece to be tested is clearly imaged on the image plane of the camera, and the entire aperture of the workpiece to be tested can be seen from the image plane of the camera.
  • a conspicuous label can be affixed to the workpiece under test; then adjust the focal length of the camera and the distance between the workpiece under test and the camera, so that the label of the workpiece under test can be clearly imaged on the image surface of the camera.
  • the camera The relative positional relationship with the measured workpiece is determined, and the camera completes the focusing on the measured workpiece.
  • Step S204 select a concave mirror with a known radius of curvature R as the focusing mirror, and set the center points of the screen, the focusing mirror, the workpiece to be measured, and the camera as A, B, C, and O, respectively, and adjust the positions of the screen and the focusing mirror. , make the angle between the line connecting point AB and the normal line at point B of the focusing mirror, the angle between the line connecting point BC and the normal line at point B of the focusing mirror, and the angle between the line connecting point BC and the normal line at point C of the measured workpiece And the angle between the line connecting point OC and the normal line at point C of the workpiece to be tested is equal.
  • the workpiece to be tested is usually a concave surface with a certain curvature, those skilled in the art can ensure that the above four included angles are all equal by placing the focusing mirror and the screen reasonably.
  • Step S206 adjust the distance between the screen and the focusing mirror relative to the workpiece under test, so that the second image reflected by the screen on the workpiece under test through the focusing mirror can reflect the first image through the workpiece again, and make the first image in the workpiece.
  • the image in the camera matches the target size of the camera.
  • the distance L 2 from the measured workpiece to the focusing mirror along the optical axis can be determined; or, in one embodiment, L 2 can be determined first, and then L 1 can be obtained by calculating according to R and the above formula.
  • center point of the workpiece to be tested is made to coincide with the center of the first image.
  • the distance S 1 from the center of the workpiece to be tested to the focusing mirror along the direction of the optical axis can be determined; thus, the positions of the camera 1, the screen 2, the workpiece 3 to be tested and the focusing mirror 4 are completely determined.
  • S 1 may also be determined first, and then S 2 is obtained by calculation according to f and the above formula.
  • the diameter of image 1 obtained through the lens is 600mm.
  • the camera, the workpiece to be tested, the focusing mirror and the screen are arranged according to the above-mentioned coordinates.
  • the obtained point spread function is shown in Fig. 4.
  • the screen can be clearly imaged in the At the camera target surface, the blurring effect caused by the defocusing effect is significantly reduced.

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Abstract

一种偏折测量中实现屏幕和工件同时对焦的装置和方法，属于精密制造领域，其中装置包括相机（1）、屏幕（2）、被测工件（3）和对焦镜（4），对焦镜（4）为凹面反射镜，对焦镜（4）用于将屏幕（2）成像在被测工件（3）处，相机（1）、被测工件（3）、对焦镜（4）和屏幕（2）的位置适于使屏幕（2）经过对焦镜（4）反射在被测工件（3）上的第二像（像2）能够再次经过被测工件（3）反射出第一像（像1），且第一像（像1）与被测工件（3）重合以便于相机（1）同时对屏幕（2）和被测工件（3）对焦。这种装置结构简单且使用方便，能够克服偏折测量的角度-位置不确定度难题、克服屏幕离焦造成的相位解析误差，从而显著提高相位测量偏折术对复杂光学曲面的测量精度。

Description

一种偏折测量中实现屏幕和工件同时对焦的装置和方法 技术领域
本发明涉及精密制造技术领域，特别涉及一种偏折测量中实现屏幕和工件同时对焦的装置和方法。
背景技术
在现代精密制造中，复杂的非球面和自由曲面光学元件得到了广泛的应用，但是其面形质量测量给精密工程领域提出了巨大的难题。
偏折术是近年来发展的反射镜面测量技术[XU X，ZHANG X，NIU Z，et al.Self-calibration of in situ monoscopic deflectometric measurement in precision optical manufacturing.Optics Express，2019，27(5)：7523-7536.]，其原理是在显示器屏幕上产生规则条纹，经被测表面反射后条纹发生变形，采用CCD相机拍摄变形图样，再由几何关系推导可以计算出被测面形的表面梯度分布，再通过积分得到面形高度。因其测量系统结构简单、精度可达纳米级、量程达到毫米级、动态范围比干涉仪高1000倍、可用于复杂曲面的测量的优点，近年来得到广泛关注[Maldonado AV.High resolution optical surface metrology with the slope measuring portable test system.MSc Thesis，The University of Arizona，2015]。
偏折测量一般是通过屏幕条纹的多步移相，根据采集图像中各像素的解调相位来建立其与屏幕像素之间的物像对应关系，因此图像中各像素的解调精度直接决定了测量精度。当前一般是将采集图像清晰对焦于被测工件上，但是这会导致屏幕图样相对于相机离焦，因此模糊成像中点扩散函数引入的卷积效应将导致采集图像的灰度发生变换，于是造成相位解调误差，如图1所示；反之，如果使屏幕在相机中清晰成像，则会导致被测工件离焦，对测量的位置的探测不确定度会增大，该测量不确定度问题是制约相位测量偏折术对复杂曲面测量精度的核心因素[Pavlicek P and Hausler G.Int J Optomech 2014；8：292-303]。
因此，如何使屏幕和被测工件都能够清晰地成像，以克服测量角度和位置不确定度之间的矛盾，从而提高对复杂曲面的测量精度正成为亟待解决的技术问题。
发明内容
针对现有技术存在的偏折术测量中被测工件和屏幕在相机中的成像无法同时保持清晰的问题，本发明的目的在于提供一种偏折测量中实现屏幕和工件同时对焦的装置和方法。
为实现上述目的，本发明的技术方案为：
一方面，本发明提供一种偏折测量中实现屏幕和工件同时对焦的装置，包括相机、屏幕 和被测工件，还包括对焦镜，所述对焦镜为凹面反射镜，所述对焦镜用于将所述屏幕成像在所述被测工件处，所述相机、所述被测工件、所述对焦镜和所述屏幕的位置适于使所述屏幕经过所述对焦镜反射在所述被测工件上的第二像能够再次经过所述被测工件反射出第一像，且所述第一像与所述被测工件重合以便于所述相机同时对所述屏幕和所述被测工件对焦。
另一方面，本发明还提供一种偏折测量中实现屏幕和工件同时对焦的方法，所述方法基于对焦镜实现，所述方法包括以下步骤，
调整相机焦距以及被测工件与相机之间的距离，使被测工件在相机的像面上清晰成像，且从相机的像面上能够看到被测工件的整个口径；
选择已知曲率半径为R的凹面反射镜作为对焦镜，并设屏幕、对焦镜、被测工件以及相机的中心点分别为A、B、C和O，调整屏幕和对焦镜的位置，使AB点连线与对焦镜B点处法线的夹角、BC点连线与对焦镜B点处法线的夹角、BC点连线与被测工件C点处法线的夹角以及OC点连线与被测工件C点处法线的夹角相等。
调整屏幕和对焦镜相对被测工件的距离，使屏幕经过对焦镜反射在被测工件上的第二像能够再次经过被测工件反射出第一像，并且使得所述第一像在相机中的像与相机的靶面尺寸相匹配。
进一步的，所述调整屏幕和对焦镜相对被测工件的距离，使屏幕经过对焦镜反射在被测工件上的第二像能够再次经过被测工件反射成第一像，并且使得所述第一像在相机中的像与相机的靶面尺寸相匹配的步骤包括，
确定屏幕到对焦镜沿光轴方向的距离L 1；
根据对焦镜的曲率半径R以及公式
Figure PCTCN2021082640-appb-000001
确定被测工件到对焦镜沿光轴方向的距离L 2；
确定相机靶面中心到相机光心沿光轴的距离S 2，根据相机镜头焦距f以及公式
Figure PCTCN2021082640-appb-000002
确定被测工件中心到对焦镜沿光轴方向的距离S 1。
优选的，所述调整相机焦距以及被测工件与相机之间的距离，使被测工件在相机的像面上清晰成像的步骤包括，
在被测工件上设置标签；
调整相机焦距以及被测工件与相机之间的距离，使被测工件的标签在相机的像面上清晰成像。
采用上述技术方案，由于对焦镜的设置，使得相机不直接对屏幕进行对焦成像，而是通过对焦镜将屏幕反射到被测工件上，使相机在对被测工件对焦时即可实现对屏幕的对焦；另外，由于通过对位置的调整，保证屏幕经过对焦镜反射在被测工件上的第二像能够再次经过被测工件反射出第一像，且在确保第一像与被测工件重合的基础上，能够保证相机在对被测 工件对焦时，屏幕在相机中的成像能够真实的反映出屏幕原本的样子，保证成像的真实性。
附图说明
图1为现有技术中离轴测量屏幕各点的点扩散函数示意图；
图2为本发明实施例一的结构示意图；
图3为本发明实施例二的方法流程图；
图4为本发明同时对焦测量光路屏幕各点的点扩散函数示意图。
图中：1-相机、2-屏幕、3-被测工件、4-对焦镜。
具体实施方式
下面结合附图对本发明的具体实施方式作进一步说明。在此需要说明的是，对于这些实施方式的说明用于帮助理解本发明，但并不构成对本发明的限定。此外，下面所描述的本发明各个实施方式中所涉及的技术特征只要彼此之间未构成冲突就可以相互组合。
需要说明的是，在本发明的描述中，术语“上”、“下”、“左”、“右”、“前”、“后”等指示的方位或位置关系为基于附图所示对本发明结构的说明，仅是为了便于描述本发明的简便，而不是指示或暗示所指的装置或元件必须具有特定的方位、以特定的方位构造和操作，因此不能理解为对本发明的限制。
对于本技术方案中的“第一”和“第二”，仅为对相同或相似结构，或者起相似功能的对应结构的称谓区分，不是对这些结构重要性的排列，也没有排序、或比较大小、或其他含义。
另外，除非另有明确的规定和限定，术语“安装”、“连接”应做广义理解，例如，连接可以是固定连接，也可以是可拆卸连接，或一体地连接；可以是机械连接，也可以是电连接；可以是直接相连，也可以通过中间媒介间接相连，可以是两个结构内部的连通。对于本领域的普通技术人员而言，可以根据本发明的总体思路，联系本方案上下文具体情况理解上述术语在本发明中的具体含义。
实施例一
提供一种偏折测量中实现屏幕和工件同时对焦的装置，如图2所示，其包括相机1、屏幕2和被测工件3，还包括对焦镜4。
其中，对焦镜4用于将屏幕2成像在被测工件3处。并且本实施例中，配置相机1、被测工件3、对焦镜4和屏幕2的位置适于：使屏幕2经过对焦镜4反射在被测工件3上的第二像(即像2)能够再次经过被测工件3反射出第一像(即像1)，并且使第一像与被测工件3重合，以便于相机1同时对屏幕2和被测工件3对焦，即，相机1在对被测工件3进行对焦时，屏幕2经过对焦镜4和被测工件3反射出的像1，也能够同步的被相机1对焦，从而解决了现有技术中，相机1无法同时对屏幕2和被测工件3进行对焦的问题。
具体在本实施例中，设置对焦镜4为凹面反射镜，被测工件3也为凹面。一方面，配置 屏幕2的中心和对焦镜4的中心的连线与对焦镜4中心处法线之间的夹角、对焦镜4的中心和被测工件3的中心的连线与对焦镜4中心处法线之间的夹角、对焦镜4的中心和被测工件3的中心的连线与被测工件3中心处法线之间的夹角以及被测工件3的中心和相机1的中心的连线与被测工件3中心处法线之间的夹角相等，如图1中的角度θ所示；另一方面，配置屏幕2到对焦镜4沿光轴方向的距离L 1、对焦镜4的曲率半径R以及被测工件3到对焦镜4沿光轴方向的距离L 2满足公式
Figure PCTCN2021082640-appb-000003
最后，配置好相机靶面中心到相机光心沿光轴的距离为S 2和被测工件中心到对焦镜沿光轴方向的距离S 1中的任一个参数数值，再根据公式
Figure PCTCN2021082640-appb-000004
由于相机镜头焦距f已知，因此即可计算出另一个参数数值，从而确定各个构件的位置。
通过以上三个方面的配置，使用时，确定相机1参数、被测工件3的形状尺寸、θ数值、L 1和L 2其中一个、S 1和S 2其中一个的基础上，即可按照上述配置布置出本实施例提供的装置。
即，相机在对被测工件对焦时，屏幕经过对焦镜反射在被测工件上的第二像能够再次经过被测工件反射出第一像，在第一像与被测工件重合的基础上，该第一像能够同时被相机所对焦，并且第一像在相机中的成像与屏幕在相机中直接成像无误差，从而实现相机能够同时对屏幕和被测工件进行对焦。
实施例二
提供一种偏折测量中实现屏幕和工件同时对焦的方法，该方法基于上述实施例一的装置，通过该方法提供的步骤即可设计出适于使用的光路，使屏幕和被测工件能够被相机同时对焦，具体而言，该方法包括步骤S202、步骤S204和步骤S206。
步骤S202，调整相机焦距以及被测工件与相机之间的距离，使被测工件在相机的像面上清晰成像，且从相机的像面上能够看到被测工件的整个口径。
具体操作时，可在被测工件上贴醒目的标签；之后再调整相机焦距以及被测工件与相机之间的距离，使被测工件的标签在相机的像面上清晰成像，此时，相机与被测工件之间的相对位置关系确定，并且相机完成对被测工件的对焦。
步骤S204，选择已知曲率半径为R的凹面反射镜作为对焦镜，并设屏幕、对焦镜、被测工件以及相机的中心点分别为A、B、C和O，调整屏幕和对焦镜的位置，使AB点连线与对焦镜B点处法线的夹角、BC点连线与对焦镜B点处法线的夹角、BC点连线与被测工件C点处法线的夹角以及OC点连线与被测工件C点处法线的夹角相等。
由于被测工件通常为具有一定曲率的凹面，因此本领域技术人员，通过合理的摆放对焦镜以及屏幕的位置，即可确保上述的四个夹角全部相等。
步骤S206，调整屏幕和对焦镜相对被测工件的距离，使屏幕经过对焦镜反射在被测工件上的第二像能够再次经过被测工件反射出第一像，并且使得所述第一像在相机中的像与相机 的靶面尺寸相匹配。
具体操作时，首先，确定屏幕到对焦镜沿光轴方向的距离L 1；
其次，根据对焦镜的曲率半径R以及公式
Figure PCTCN2021082640-appb-000005
即可确定被测工件到对焦镜沿光轴方向的距离L 2；或者，在一个实施例中，还可以先确定L 2，再根据R和上述公式计算获得L 1。
最后，使被测工件的中心点与所述第一像的中心重合。
具体操作时，先确定相机靶面中心到相机光心沿光轴的距离S 2；
其次，根据已知的相机镜头焦距f以及公式
Figure PCTCN2021082640-appb-000006
即可确定被测工件中心到对焦镜沿光轴方向的距离S 1；从而完全确定相机1、屏幕2、被测工件3和对焦镜4的位置。或者，在一个实施例中，还可以先确定S 1，再根据f和上述公式计算获得S 2。
例如，配置相机的参数为：焦距35mm、靶面尺寸18mm；配置被测工件尺寸参数为：口径596mm、曲率半径为776mm的凹面型被测工件；配置屏幕的尺寸为95mm。
则在布置光路时：如图3所示，首先根据物像放大关系y’/y＝600/18＝33.3，在相机位置固定的情况下，可以得到被测工件所摆放的位置。例如将坐标系原点建立在被测工件底部中心，则相机靶面中心的坐标为(287.7mm，1151.5mm)；
其次从相机靶面逆向追迹，经过镜头所得像1的口径为600mm，采用光线追迹，经过被测工件再次成像得到的像2尺寸为526.4mm，根据其与屏幕之间的尺寸放大关系y’/y＝526.4/95＝5.54，可知屏幕相对于对焦镜的成像关系；
再根据实际光路元件尺寸，调整其位置，得到对焦镜的曲率半径为150mm，其中心坐标为(-161.6mm，638.3mm)，而屏幕的中心坐标为(-247.6mm，561mm)。
按照上述坐标布置相机、被测工件、对焦镜和屏幕，使用时，在采用本发明提供的含有对焦镜的装置后，得到的点扩散函数如图4所示，显然是可以将屏幕清晰成像在相机靶面处，显著减小离焦效应引起的模糊效应。
以上结合附图对本发明的实施方式作了详细说明，但本发明不限于所描述的实施方式。对于本领域的技术人员而言，在不脱离本发明原理和精神的情况下，对这些实施方式进行多种变化、修改、替换和变型，仍落入本发明的保护范围内。

Claims (4)

  1. 一种偏折测量中实现屏幕和工件同时对焦的装置，包括相机、屏幕和被测工件，其特征在于：还包括对焦镜，所述对焦镜为凹面反射镜，所述对焦镜用于将所述屏幕成像在所述被测工件处，所述相机、所述被测工件、所述对焦镜和所述屏幕的位置适于使所述屏幕经过所述对焦镜反射在所述被测工件上的第二像能够再次经过所述被测工件反射出第一像，且所述第一像与所述被测工件重合以便于所述相机同时对所述屏幕和所述被测工件对焦。
  2. 根据权利要求1所述的偏折测量中实现屏幕和工件同时对焦的方法，其特征在于：所述方法基于对焦镜实现，所述方法包括以下步骤，
    调整相机焦距以及被测工件与相机之间的距离，使被测工件在相机的像面上清晰成像，且从相机的像面上能够看到被测工件的整个口径；
    选择已知曲率半径为R的凹面反射镜作为对焦镜，并设屏幕、对焦镜、被测工件以及相机的中心点分别为A、B、C和O，调整屏幕和对焦镜的位置，使AB点连线与对焦镜B点处法线的夹角、BC点连线与对焦镜B点处法线的夹角、BC点连线与被测工件C点处法线的夹角以及OC点连线与被测工件C点处法线的夹角相等。
    调整屏幕和对焦镜相对被测工件的距离，使屏幕经过对焦镜反射在被测工件上的第二像能够再次经过被测工件反射出第一像，并且使得所述第一像在相机中的像与相机的靶面尺寸相匹配。
  3. 根据权利要求2所述的偏折测量中实现屏幕和工件同时对焦的方法，其特征在于：所述调整屏幕和对焦镜相对被测工件的距离，使屏幕经过对焦镜反射在被测工件上的第二像能够再次经过被测工件反射成第一像，并且使得所述第一像在相机中的像与相机的靶面尺寸相匹配的步骤包括，
    确定屏幕到对焦镜沿光轴方向的距离L 1；
    根据对焦镜的曲率半径R以及公式
    Figure PCTCN2021082640-appb-100001
    确定被测工件到对焦镜沿光轴方向的距离L 2；
    确定相机靶面中心到相机光心沿光轴的距离S 2，根据相机镜头焦距f以及公式
    Figure PCTCN2021082640-appb-100002
    确定被测工件中心到对焦镜沿光轴方向的距离S 1。
  4. 根据权利要求2所述的偏折测量中实现屏幕和工件同时对焦的方法，其特征在于：所述调整相机焦距以及被测工件与相机之间的距离，使被测工件在相机的像面上清晰成像的步骤包括，
    在被测工件上设置标签；
    调整相机焦距以及被测工件与相机之间的距离，使被测工件的标签在相机的像面上清晰成像。
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