CN108507492A - The high-precision wide-dynamic-range measurement method and measuring system on a kind of plane surface transmissive element surface - Google Patents

Abstract

The invention provides a high-precision and large dynamic range measurement method and a measurement system for the surface of a plane-curved transmission element, and relates to the field of measurement technology. The interferometer measures the flat surface of the component to obtain the surface shape data; the three-coordinate measuring equipment is calibrated to obtain the structural position parameters of the deflection optical path system; the ideal optical path system is established by ray tracing to obtain the theoretical coordinate position value; the display projection screen displays multi-step phase-shifted sinusoidal gray levels Straight stripes, the computer solves the actual coordinate position value corresponding to the stripes captured by the CCD camera; the corresponding coordinate error is obtained from the theoretical coordinate position value and the actual coordinate position value, and the slope distribution of the surface shape error of the surface to be measured is calculated, and the component to be tested is obtained after integration Surface shape error. The invention solves the technical problems in the prior art that the measurement dynamic range of the surface measurement of the high-precision planar and curved surface transmission element is small and the equipment is expensive. The invention has the beneficial effects of providing a non-contact measuring method with high precision and large dynamic range, and realizing generalization of detection equipment. The operation is simple and efficient.

Description

A high-precision and large dynamic range measurement method and measurement method for the surface of a plane-curved transmission element volume system

technical field

The invention relates to the field of measurement technology, in particular to a measurement system and method for measuring the surface of a transmission element based on optical deflection.

Background technique

Flat-curved transmissive elements, that is, elements that have a flat surface and the rest of the surface are curved. Plane-curved transmission element is an important optical element, which is indispensable in optical elements and industrial products. It is widely used in optical systems and industrial systems, and is also widely used in imaging optics, lighting optics, and transparent glass. . With the advancement of technology, the quality requirements for flat and curved transmission elements are also increasing. This also requires continuous improvement of measurement methods. At present, the commonly used methods for surface measurement of planar and curved transmission elements are mainly divided into interferometry and geometric light detection. Interferometry provides a non-contact high-precision measurement method for the surface measurement of flat and curved transmission elements. Chinese patent application publication number CN106643548A, the application publication date is May 10, 2017, and the invention patent application document named "aspherical optical element surface shape detection device" discloses a device for measuring the aspheric surface shape by interferometry. It is used to detect the surface information of aspheric optical elements. It includes an interferometer and mirrors, phase shifters, standard mirrors, compensating mirrors and aspheric optical elements arranged in sequence from bottom to top in the vertical direction; the interferometer is used to emit the measuring beam in the horizontal direction; the mirror is used to convert the horizontal direction The measuring beam is converted into a vertically upward measuring beam; the phase shifter is used to adjust the phase of the vertically upward measuring beam; the standard mirror is used to provide a reference surface to reflect the vertically upward measuring beam; the compensation mirror is used to compensate The surface shape of the aspheric optical element; the measurement beam reflected by the aspheric optical element and the measurement beam reflected by the reference surface of the standard mirror form interference fringes in the interferometer. The structure realizes the high-precision measurement of the surface shape of the aspheric optical element. However, the dynamic range of interferometry measurement is small, and it has high requirements for the design, manufacture and calibration of the system. When using interferometry to measure the surface of flat and curved transmission elements, the measurement process is relatively complicated, and the measurement of a large dynamic range cannot be completed. Chinese patent application publication number CN107560564A, the application publication date is January 9, 2018, and the invention patent application document named "a free-form surface detection method and system" discloses a method of measuring free-form surfaces using the reverse Hartmann detection method The method and system are used for detecting the surface shape information of a reflective free-form surface. This structure is a kind of geometric light detection method, which realizes the high-precision measurement of the reflective free-form surface shape, but it is difficult to detect the transmission surface shape.

Contents of the invention

In order to solve the technical problems of the non-contact high-precision planar and curved surface transmission element surface measurement in the prior art, the measurement process is complicated, the measurement dynamic range is small, and the measurement equipment is expensive. The dynamic range measurement method and measurement system realize high-precision measurement for a single curved surface of a flat-curved transmission element.

The technical solution of the present invention is: a high-precision and large dynamic range measurement method for the surface of a plane-curved transmission element: comprising: an optical deflection optical path system composed of a display projection screen, an element to be measured, a CCD camera, and a computer. The element under test has a plane. The method includes the following steps: Step 1, use an interferometer to measure the surface shape of the component to be measured to obtain surface shape data W _flat ; Step 2, use a three-coordinate measuring device to calibrate the structural position parameters of each device in the optical deflection optical path system ; Step 3, use the surface shape data W _flat and the structural position parameters to establish an ideal optical path system with the same structural position parameters in the ray tracing software of the computer, and obtain the theoretical coordinate position values (x _ideal , y _ideal ) on the display projection screen ; Step 4, the display projection screen displays multi-step phase-shifted sinusoidal gray-scale straight stripes in the x and y directions respectively, the light emitted by the stripes is captured by the CCD camera through the transmission of the component to be tested, and the computer solves the phase corresponding to the stripes taken by the CCD camera distribution, and calculate the actual coordinate position value (x _meas , y _meas ) of the sinusoidal grayscale straight stripe projection on the display projection screen; step 5, combine the theoretical coordinate position value (x _ideal , y _ideal ) and the actual coordinate position value (x _meas , y _meas ) into The local slope of the surface shape error of the component under test is calculated, and the surface shape error of the component under test is obtained after integration.

Preferably, the surface shape data W _flat measured in step 1 is the plane surface data of the component under test in the ideal optical path system.

Preferably, in step 4, the multi-step phase-shifted sinusoidal gray-scale straight stripes in the x and y directions are pre-stored in the computer, and the computer controls the display projection screen to display the multi-step phase-shifted sinusoidal gray-scale straight stripes in the x and y directions in sequence.

Preferably, in step 5, the geometric relationship of each point on the curved surface of the component to be tested is converted into the slope of the tangent plane of each point, and the slope of the tangent plane is integrated to obtain the surface shape parameters.

A measurement system for high-precision and large dynamic range measurement of the surface of a planar and curved transmission element: the display projection screen and the CCD camera are arranged face to face, the element to be measured is located between the display projection screen and the CCD camera, and the plane of the element to be measured is connected to the display projection The screen is tightly attached, the central axis of the CCD camera lens is perpendicular to the display projection screen, and the CCD camera obtains a complete and clear image of the component under test. The display projection screen and the CCD camera are electrically connected to the computer respectively.

Compared with the prior art, the beneficial effect of the present invention is that the generalization of detection equipment is realized by using the principle of optical deflection. The small number of equipment reduces the difficulty of system construction and use, and the operation is simple and efficient. No need for other compensating optical components and standard optical components, the calibration of the measurement system is simplified, and the detection cost is reduced under the conditions of high precision and large dynamic range. It provides a non-contact, high-precision, and large dynamic range measurement method for the measurement of the surface of the planar and curved transmission element.

Description of drawings

Accompanying drawing 1 is the schematic diagram of optical deflection optical path system of the present invention;

Accompanying drawing 2 is the relationship diagram of the deflection angle of the ray passing through point D in Fig. 1 and the inclination angle of the tangent plane where point D is located;

Accompanying drawing 3 is the result figure of the plane shape of the component to be measured measured with interferometer in the embodiment of the present invention;

Accompanying drawing 4 is the result graph of the curved surface error of the component under test measured in the embodiment of the present invention.

In the figure: 1-display projection screen; 2-component to be tested; 3-CCD camera; 4-computer.

Detailed ways

The technical solutions of the present invention will be further specifically described below through the embodiments and in conjunction with the accompanying drawings.

Example 1:

As shown in FIG. 1 , a measurement system for high-precision and large dynamic range measurement of the surface of a plane-curved transmission element: it includes a display projection screen 1 , an element to be measured 2 , a CCD camera 3 and a computer 4 . The element under test 2 has one flat surface, and the rest are curved surfaces. The CCD camera 3 is provided with a filter, and the filter is provided with a filter aperture. The optical filter is closely attached to the lens end face of the CCD camera 3 . The display projection screen 1 and the CCD camera 3 are arranged face to face. The device under test 2 is located between the display projection screen 1 and the CCD camera 3 . In order to avoid deflection of the light emitted from the display projection screen 1 entering the DUT 2 , the plane of the DUT 2 is closely attached to the display projection screen 1 , and the curved surface faces the CCD camera 3 . The central axis of the lens of the CCD camera 3 is perpendicular to the display projection screen 1 . The distance between the CCD camera 3 and the display projection screen 1 depends on whether the CCD camera 3 can obtain a complete and clear image of the DUT 2 . The display projection screen 1, the component under test 2, and the CCD camera 3 form an optical deflection optical path system (the optical path is represented by a thin solid line with arrows in FIG. 1). The display projection screen 1 and the CCD camera 3 are respectively electrically connected to the computer 4 (indicated by a thin solid line in FIG. 1 ).

A method for measuring the surface of a plane-curved transmission element with high precision and large dynamic range, comprising the following steps: Step 1: Using an interferometer to measure the surface shape of the plane of the element 2 to be measured to obtain surface shape data W _flat . Since the measurement error of the interferometer can be ignored, the surface shape data W _flat measured by the interferometer is set to be the plane surface data of the component under test 2 in the ideal optical path system.

Step 2: Use a three-coordinate measuring device to calibrate the structural position parameters of each device in the optical deflection optical path system. Including the structural position parameter calibration of the component under test 2, the display projection screen 1, and the CCD camera 3. The structural location parameters are represented by F={xi _, y _i , _zi ;T _i,x ,T _i,y ,T _i,z ,d _m2screen } _i=1,2,3 . Among them: (xi _, y _i , zi ₎ is the spatial coordinate value position of the i-th element, (T _i,x , T _i,y , T _i,z ) represents the inclination angle of the i-th element with respect to each coordinate axis , d _m2screen is the distance between a point on the surface to be measured and its corresponding luminous pixel on the display projection screen 1 .

Step 3: The computer 4 is equipped with ray tracing software. Using the surface shape data W _flat obtained in step 1 and the structural position parameters obtained in step 2, an ideal optical path system with structural position parameters corresponding to the actual optical deflection optical path system is established in the ray tracing software of computer 4. The computer 4 performs ray tracing to obtain the theoretical coordinate position value corresponding to the projected coordinate value of the phase of the actual component under test 2 on the display projection screen 1 , which is (x _ideal , y _ideal ).

Step 4: Multi-step phase-shifted sinusoidal gray-scale straight stripes in the x and y directions are pre-existed in the computer 4 . The computer 4 controls and displays the projection screen 1 to sequentially display multi-step phase-shifted sinusoidal gray-scale straight stripes in the x and y directions. The display projection screen 1 respectively displays multi-step phase-shifted sinusoidal gray-scale straight stripes in the x and y directions. The light rays sequentially emitted by the fringes in the x and y directions in the display projection screen 1 pass through the plane and curved surface of the component under test 2 , and the corresponding images are collected by the CCD camera 3 . The image collected by the CCD camera 3 is the deformed fringe after passing through the device under test 2 . The computer 4 uses a multi-step phase unwrapping algorithm to solve the phase distributions Φ _x and Φ _y corresponding to the deformed fringes, and calculates the actual coordinate position value (x _meas ,y _meas ).

Step 5: As shown in FIG. 2 , the light emitted from the light-emitting pixels of the display projection screen 1 passes through the curved surface of the device under test 2 and is deflected, and then received by the CCD camera 3 . According to the principle of optical deflection, in the optical deflection optical path system, the geometric relationship of each point on the curved surface of the component under test 2 is (wherein: n is the refractive index of the component to be measured 2; A is the angle between a certain point incident light and the horizontal line on the curved surface of the component to be measured 2, and B is the angle between the outgoing light of this point and the horizontal line; Angle of inclination), the slope of the tangent plane at this point on the curved surface of the component 2 to be measured can be obtained as Convert the geometric relationship of the optical deflection optical path system into the slope of the tangent plane at each point on the curved surface of the component under test 2, and substitute the coordinate values of each point in the optical deflection optical path system to obtain:

Among them: (x _m , y _m ) is the coordinate value of the point on the surface of the component under test 2; (x _screen , y _screen ) is the coordinate value of the light-emitting pixel on the display projection screen 1; (x _camera , y _camera ) is the CCD The center coordinate value of the filter hole on the filter of the camera 3; d _m2screen is the distance between the point on the surface to be measured and its corresponding display pixel on the projection screen 1; d _m2camera is the point and The distance from the center of the filter hole on the CCD camera 3 filter. The surface shape error Δw of the curved surface of the component under test 2 is the deviation between the actual surface shape w _{actual of} the curved surface of the component under test 2 and the ideal component surface shape w _ideal in the ideal optical path system. The local slope corresponding to the surface shape error Δw is:

In the formula: n is the refractive index of the component under test 2, and _cosθz is the cosine value of the angle between the light refracted by the component under test 2 and the central axis of the lens of the CCD camera 3. Using the integral method, the surface shape error of the component under test 2 is obtained. .

A specific measurement example is used to further illustrate:

Display projection screen 1 has a pixel resolution of 1920×1080, a diagonal length of the projection screen of 58.4 cm, and a screen aspect ratio of 16:9. For the convenience of description, the element 2 to be tested is selected as a plane-curved transmission element whose bottom surface is a plane and whose curved surface is a concave spherical surface. The diameter of the concave spherical surface is 25.4mm, the radius of curvature is 100mm, the refractive index is 1.51, and the distance from the center of the curved surface to the plane is 3mm. The component to be tested 2 is placed between the display projection screen 1 and the CCD camera 3 , and the bottom surface is in close contact with the display projection screen 1 . The front of the CCD camera 3 is equipped with a small filter hole, and the CCD camera 3 can obtain a complete and clear image of the component under test 2 . The display projection screen 1, the component under test 2 and the CCD camera 3 constitute an optical deflection optical path system.

The measurement steps are as follows:

Step 1: Using an interferometer, measure the surface shape of the bottom surface of the component 2 to be tested in advance to obtain its surface shape data W _flat , and FIG. 3 shows the measured surface shape data.

Step 2: Calibrate the position parameter F of each device in the optical deflection optical path system with a three-coordinate measuring device with a measurement accuracy of 1.9 μm.

Step 3: Use the structural position parameters of the optical deflection optical path system obtained by the calibration of the three-coordinate equipment and the plane surface data W _flat measured by the interferometer to establish a structure with the same structural position parameters in the ray tracing software of the computer 4 Ideal optical system. The theoretical coordinate position value (x _ideal , y _ideal ) corresponding to the projected coordinate value of the actual phase on the display projection screen 1 is obtained.

Step 4: The computer 4 controls and realizes the multi-step phase-shifting sinusoidal gray-scale straight stripes in the x and y directions to be displayed on the display projection screen 1, and the corresponding gray-scale straight stripes have a width of 8.18 mm. The CCD camera 3 collects in real time the image of the multi-step phase-shifted sinusoidal gray-scale straight stripes transmitted through the component under test 2 . And use the multi-step phase-shifting unwrapping algorithm to solve the phase distribution Φ _x and Φ _y corresponding to the fringes captured by the CCD camera 3 and deformed after passing through the component under test 2, and calculate the sinusoidal grayscale straight fringes projected on the display projection screen Coordinate value (x _meas , ymeas) on 1. x _meas =Φ _x /2π×8.18, y _meas =Φ _y /2π×8.18.

Step 5: According to the principle of optical deflection, calculate the local slope corresponding to the surface shape error of the transmission surface of the component under test 2 as: Integrate the local slope deviation (Δw _x , Δw _y ) to obtain the surface shape error of the component under test 2, as shown in FIG. 4 .

Claims (5)

1. A high-precision and large dynamic range measuring method on the surface of a planar curved transmission element: comprising: an optical deflection optical path system and a computer that display a projection screen, an element to be measured, a CCD camera, and a computer, the element to be measured has a plane, and It is characterized in that the method includes the following steps: Step 1, use an interferometer to measure the surface shape of the plane of the component to be measured to obtain surface shape data W _flat ; Step 2, use a three-coordinate measuring device to measure the structure of each device in the optical deflection optical path system Position parameter calibration; step 3, use the surface shape data W _flat and structure position parameters to establish an ideal optical path system with corresponding same structure position parameters in the computer ray tracing software, and obtain the theoretical coordinate position value (x _ideal , y _ideal ); step 4, the display screen displays multi-step phase-shifted sinusoidal gray-scale straight stripes in the x and y directions respectively, the light emitted by the stripes passes through the component to be tested and is captured by the CCD camera, and the computer solves the results of the stripes captured by the CCD camera The corresponding phase distribution is calculated to obtain the actual coordinate position value (x _meas , y _meas ) of the sinusoidal grayscale straight stripe projection on the display projection screen; step 5, the theoretical coordinate position value (x _ideal , y _ideal ) and the actual coordinate position Value (x _meas , y _meas ) is substituted into The local slope of the surface shape error of the component under test is calculated, and the surface shape error of the component under test is obtained after integration. 2. The high-precision and large dynamic range measuring method of a plane-curved surface transmission element surface according to claim 1, characterized in that: the surface shape data W _flat measured in step 1 is the value of the element to be measured in the ideal optical path system plane data. 3. The method for measuring the surface of a flat and curved transmission element with high precision and large dynamic range according to claim 1, characterized in that: in step 4, the multi-step phase-shifted sinusoidal gray-scale straight stripes in the x and y directions are pre-stored in the computer , the computer-controlled display projection screen sequentially displays multi-step phase-shifted sinusoidal gray-scale straight stripes in the x and y directions. 4. The high-precision and large dynamic range measuring method of a plane-curved surface transmission element surface according to claim 1, characterized in that: in step 5, the geometric relationship of each point on the curved surface of the element to be measured is converted into the slope of the tangent plane of each point , and integrate the slope of the cut surface to obtain the surface shape parameters. 5. The measurement system of a high-precision and large dynamic range measurement method for the surface of a plane-curved transmission element according to claim 1, characterized in that: the display projection screen is arranged face to face with the CCD camera, and the element to be measured is located on the display Between the projection screen and the CCD camera, the plane of the component to be measured is closely attached to the display projection screen, the central axis of the CCD camera lens is perpendicular to the display projection screen, and the CCD camera obtains a complete and clear image of the component to be measured. The display projection screen, The CCD cameras are respectively electrically connected to the computer.