CN107121095B - A method and device for accurately measuring a super large radius of curvature - Google Patents

Abstract

The invention discloses a device and method for accurately measuring a super large radius of curvature. The device comprises: a measured element, a light source; The surface of the measured element reflects the reflected light reflected by the measured element onto the first grating and the second grating; the first grating and the second grating; used to produce the first grating at the second grating under the irradiation of reflected parallel light The Talbot image and the second grating form moiré fringes; imaging system; used to collect moiré fringe images and transmit them to a computer; computer; used to process moiré fringe images to determine the angle of moiré fringes, and then calculate The radius of curvature of the component under test. The device has a simple structure and can realize accurate measurement of the ultra-large curvature radius of the optical element.

Description

A method and device for accurately measuring a super large radius of curvature

technical field

The invention belongs to the field of measuring the radius of curvature of an optical element, in particular to a method and a device for accurately measuring a super large radius of curvature.

Background technique

The large-aperture optical component system is a large-scale high-power laser system, such as the domestic ICF laser driver, the US National Ignition Facility (NIF) and the French Mega-Joule Laser Project (Mega-Joule Project). Thousands of various optical components must be used. There are only 8,000 optical components of various apertures above 400×500, of which there are about 1,000 long-focus lens systems for spatial filtering and focusing. Therefore, effective parameter testing must be carried out for these large-aperture long-focus optical systems. Large-aperture optical components are also widely used in the LIGO (laser interferometer Gravitational Wave Observatory) system in the United States.

Due to large aperture (above 250mm), large radius of curvature (greater than 10 meters), and interference factors such as air disturbance, large-aperture optical components seriously affect the accuracy of the test. Existing methods for measuring the radius of curvature, such as a contact spherometer, a self-imaging radius of curvature measuring instrument, and a radius of curvature measuring instrument using the interference principle, can achieve high-precision measurement of a small radius of curvature (less than 10 meters). However, for ultra-large curvature radii (greater than 5000 meters), it is difficult to obtain high-precision measurement using traditional radius measurement methods. How to achieve high-precision measurement of such a large number of components is of great significance to these major projects.

Therefore, it is necessary to develop a detection instrument capable of precision ultra-large radius of curvature, which can be used as an accurate measurement instrument for optical components in major national engineering projects such as laser nuclear fusion and gravitational wave measurement, as a detection of the lens from each process to the final acceptance. Basis and standards to meet the quality requirements for these optical components.

Contents of the invention

In order to solve the problem that it is difficult to measure the ultra-large radius of curvature of the optical element in the prior art, the present invention proposes a method and device for accurately measuring the ultra-large radius of curvature. The device has a simple structure and can realize accurate measurement of the ultra-large curvature radius of the optical element.

The first aspect of the present invention proposes a device for accurately measuring the ultra-large radius of curvature, including;

DUT, light source;

The beam splitter is placed obliquely between the measured element and the light source, and is used to irradiate the light emitted by the light source onto the surface of the measured element, and reflect the reflected light reflected by the measured element onto the first grating and the second grating;

The first grating and the second grating; under the irradiation of reflected parallel light, the Taber image generated by the first grating at the second grating and the second grating form Moiré fringes;

Imaging system; used to collect Moiré fringe images and transmit them to a computer;

A computer; used to process the moiré fringe image to determine the angle of the moiré fringe, and then calculate the radius of curvature of the measured element.

Preferably, the device provided by the first aspect of the present invention further includes: a collimating lens arranged between the beam splitter and the light source and used to convert the emitted light from the light source into parallel light. When the light source is close to the component under test, the collimator lens can be placed between the light source and the beam splitter to change the divergent light into parallel light.

Preferably, the device provided by the first aspect of the present invention further includes: a pinhole for adjusting the propagation direction of the light source, a first high-precision displacement platform for fixing the laser and the pinhole, and a first high-precision displacement platform for fixing the second grating and the imaging system. Two high-precision displacement platforms and a high-precision displacement driver for driving the movement of the first high-precision displacement platform and the second high-precision displacement platform.

The laser and the pinhole fixed on the first high-precision displacement platform can be accurately moved to different positions under the drive of the high-precision displacement driver, and the combined optical power value under different light source positions is measured many times, and then The radius of curvature of the component under test is calculated, which can effectively eliminate the influence of the collimation of the illumination beam.

In order to prevent the influence of air flow on the measurement, it is preferable to seal the whole device with a cover.

The second aspect of the present invention provides a method for accurately measuring the ultra-large radius of curvature using the system provided by the first aspect, which specifically includes:

(1) Calibrate the system for accurate measurement of ultra-large curvature radius Since the measured focal length is the distance from the first grating to the focal point, by accurately moving the measured lens along the optical axis, multiple groups of standard mirrors with precise focal lengths can be obtained to realize Accurate calibration of multiple systems;

(2) Using a high-precision displacement driver to drive the first high-precision displacement platform to move to a corresponding position, avoiding the influence of the collimation of the illumination beam;

(3) Utilize the high-precision displacement driver to drive the second high-precision displacement platform to move to the corresponding position, and record the distance z between the first grating and the second grating, and the grid line angle θ between the first grating and the second grating;

(4) Utilize the imaging system to collect moiré fringe images, and transmit the moiré fringe images to the computer;

(5) The computer processes the received moiré fringe image, determines the angle α of the moiré fringe, and calculates the radius of curvature Δr of the measured element;

Among them, s is the distance between the first grating and the optical axis of the tested component, r is the radius of the tested component, and its value is:

is the ratio of the period P ₁ of the first grating to the period P ₂ of the second grating;

The formula for calculating the angle α of Moiré fringes is:

P′ ₁ is the period of the Taber image, according to the magnification relationship of the Taber image get;

Δz is the uncertainty of z, Δs is the uncertainty of s, Δθ is the uncertainty of θ, Δα is the uncertainty of α, and Δβ is the uncertainty of β.

Preferably, the uncertainty Δz and the uncertainty Δs are measured by a high-precision grating ruler, and their values reach 0.1mm and 0.01mm respectively.

As a preference, the method for obtaining the uncertainty Δα is as follows: Since α is the angle of the Moiré fringe calculated by the computer, an accurately printed black and white fringe pattern with a precise and determined angle is used to pass through the image acquisition system of the multiple measurement system The image of the pattern is obtained and calculated by the method of calculating the moiré fringe angle, and the uncertainty Δα of α is obtained, and its value reaches 0.003°.

The method of obtaining the uncertainty Δθ is as follows: when the reflective surface to be measured is a plane, and the angle between the grid lines of the two gratings is 0 degrees, the theoretical moiré fringe period is infinite (the collected image is a uniform gray scale Fig. 1), taking this as a starting point, the angle between the grid lines between the two gratings is controlled by a precise rotary table, and the uncertainty of the grid line angle is determined by the precision rotary table, so that the uncertainty Δθ of θ can be obtained, Its value reaches 0.003°.

Preferably, the method for obtaining the uncertainty Δβ is as follows: since β is the ratio of the period of two gratings, the uncertainty Δβ of β can be accurately obtained through the accurate measurement of the scanning electron microscope, and its value is 0.00001.

The device for accurately measuring the ultra-large curvature radius of the present invention combines the most basic optical measuring instruments, has simple structure, low cost, and is easy to operate during the measurement process, and can realize accurate measurement of the ultra-large curvature radius of the optical element.

Description of drawings

Fig. 1 is the first schematic structural view of the device for accurately measuring the super large radius of curvature applied in embodiment 1;

Fig. 2 is the second structural representation of the device for accurately measuring the ultra-large radius of curvature applied in embodiment 1;

Fig. 3 is the schematic diagram of applying the device shown in Fig. 1 in embodiment 2 to solve the measured radius through multiple measurements of the precise moving light source;

Fig. 4 is a schematic diagram of applying the device shown in Fig. 2 in Embodiment 2 to calculate the measured radius through multiple measurements of a precise moving light source.

Detailed ways

In order to describe the present invention more specifically, the technical solutions of the present invention will be described in detail below in conjunction with the accompanying drawings and specific embodiments.

Example 1

As shown in Figure 1, the device for accurately measuring the ultra-large radius of curvature used in this embodiment includes: a measured element with a radius of 5,000 meters, an infrared laser, a microscopic objective lens for collimation, an imaging lens for splitting light, and a pinhole , grating 1 and grating 2 with a period ratio of 1.004018, CCD, ground glass sheet supporting grating 2, computer and high-precision displacement driver, infrared laser and pinhole are fixed on high-precision displacement platform 1, grating 2, ground glass sheet and CCD are fixed on the second high-precision displacement platform.

After the calibration of the system for accurately measuring the ultra-large radius of curvature is completed;

Firstly, the high-precision displacement driver is used to drive the first high-precision displacement platform to move to the corresponding position, so as to avoid the influence of the collimation of the illumination beam;

Then, use the high-precision displacement driver to drive the second high-precision displacement platform to move to the corresponding position, record that the distance z between the first grating and the second grating is 10m, and the angle θ between the grid lines between the first grating and the second grating is 0.3°;

Next, use the imaging system to collect the moiré fringe image, and transmit the moiré fringe image to the computer;

Finally, the computer processes the received moiré fringe image, determines that the angle α of the moiré fringe is 37.4813°, and calculates the radius of curvature of the tested component as:

Δr＝2*0.1mm(Δz)+2*0.01mm(Δs)+24.89m(Δz)+3.11m(Δβ)+20.67m(Δθ)+0.135m(Δα)＝48.80522m

The relative measurement error is:

It can be seen from the above analysis that Δz, Δθ, and Δβ have a great influence on the measurement accuracy. If Δz can be reduced (the uncertainty of the measurement distance of 10 meters is less than 0.1mm, and environmental factors such as temperature and humidity are strictly controlled, the accuracy can be further improved by using the Reneshaw grating ruler). According to the radius of the specific measuring element, further optimize the initial parameter settings, such as the angle between the grating lines, the period ratio of the grating and other parameters, and the measurement accuracy can be further improved.

In this embodiment, the structure shown in FIG. 2 can also be used to measure the radius of the device under test. In FIG. 2, there is no collimator lens, and the light splitting function is a beam splitter.

Example 2

Using the system described in Figure 1, by precisely moving the position of the light source, the combined optical power value under different point light source positions is measured multiple times, and the schematic diagram of the principle is shown in Figure 3.

Since the light emitted by the laser always has a certain focal power after passing through the collimation system, it is impossible to achieve ideal parallel light. Suppose this focal power is The focal length of the measured surface with the measured radius R is R/2, then the combined optical power for:

Where d is the distance between the equivalent lens of the collimation system and the lens under test.

Adjust the initial position of the test system, and place the light source near the focal length of the collimator lens. Place the measured lens at the measurement position, collect moiré fringes, measure the angle of the moiré fringes, and calculate the measured value R ₁ at this time; move the light source δ ₁ accurately forward, collect the moiré fringe image, and calculate the current Continue to move the light source δ _{2 precisely} forward, do the same operation, collect moiré fringe images, and calculate the measured value R3 at this time by computer.

According to the collective imaging formula, we have:

u represents the object distance, v ₁ , v ₂ , and v ₃ represent the image distances in the three states, and the radius R of the lens under test can be obtained through the calculation of the above formulas.

In this embodiment, the structure shown in FIG. 2 can also be used to accurately move the position of the light source to perform multiple measurements of combined optical power values at different point light source positions. The schematic diagram of the principle is shown in FIG. 4 .

The above-mentioned specific embodiments have described the technical solutions and beneficial effects of the present invention in detail. It should be understood that the above-mentioned are only the most preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, supplements and equivalent replacements made within the scope shall be included in the protection scope of the present invention.

Claims (1)

1. A method for accurately measuring the super large radius of curvature, the device for realizing the accurate measurement of the super large radius of curvature of the method comprises: DUT, light source; The beam splitter is placed obliquely between the measured element and the light source, and is used to irradiate the light emitted by the light source onto the surface of the measured element, and reflect the reflected light reflected by the measured element onto the first grating and the second grating; The first grating and the second grating; under the irradiation of reflected parallel light, the Taber image generated by the first grating at the second grating and the second grating form Moiré fringes; Imaging system; used to collect Moiré fringe images and transmit them to a computer; A computer; used to process the moiré fringe image to determine the angle of the moiré fringe, and then calculate the radius of curvature of the measured element; A collimating lens arranged between the beam splitter and the light source and used to convert the emitted light from the light source into parallel light; The pinhole used to adjust the propagation direction of the light source, the first high-precision displacement platform used to fix the laser and the pinhole, the second high-precision displacement platform used to fix the second grating and imaging system, and the first high-precision displacement platform used to drive the A high-precision displacement driver for the movement of the platform and the second high-precision displacement platform; The method for accurately measuring the super large radius of curvature comprises the following steps: (1) To calibrate the system for accurately measuring the ultra-large radius of curvature, since the measured focal length is the distance from the first grating to the focal point, by accurately moving the measured lens along the optical axis, multiple sets of standard mirrors with precise focal lengths can be obtained, Realize accurate calibration of multiple systems; (2) Using a high-precision displacement driver to drive the first high-precision displacement platform to move to a corresponding position, avoiding the influence of the collimation of the illumination beam; (3) Utilize the high-precision displacement driver to drive the second high-precision displacement platform to move to the corresponding position, and record the distance z between the first grating and the second grating, and the grid line angle θ between the first grating and the second grating; (4) Utilize the imaging system to collect moiré fringe images, and transmit the moiré fringe images to the computer; (5) The computer processes the received moiré fringe image, determines the angle α of the moiré fringe, and calculates the radius of curvature Δr of the measured element; Among them, s is the distance between the first grating and the optical axis of the tested component, r is the radius of the tested component, and its value is: is the ratio of the period P ₁ of the first grating to the period P ₂ of the second grating; The formula for calculating the angle α of Moiré fringes is: P′ ₁ is the period of the Taber image, according to the magnification relationship of the Taber image get; Δz is the uncertainty of z, Δs is the uncertainty of s, Δθ is the uncertainty of θ, Δα is the uncertainty of α, and Δβ is the uncertainty of β; Uncertainty Δz and uncertainty Δs are measured by high-precision grating ruler, and their values reach 0.1mm and 0.01mm respectively; The method of obtaining the uncertainty Δα is: since α is the angle of the moiré fringe calculated by the computer, the image of the pattern is obtained through the image acquisition system of the multiple measurement system and calculated by the method of calculating the angle of the moiré fringe to obtain the indeterminate value of α Certainty Δα, its value reaches 0.003°; The method to obtain the uncertainty Δθ is: when the reflective surface to be measured is a plane and the angle between the grid lines of the two gratings is 0 degrees, the theoretical moiré fringe period is infinite. Using this as a starting point, through precise rotation The table controls the angle between the grid lines between the two gratings, and the uncertainty of the grid line angle is determined by the precision rotary table, thus obtaining the uncertainty Δθ of θ, and its value reaches 0.003°; The method of obtaining the uncertainty Δβ is as follows: since β is the ratio of the periods of the two gratings, the uncertainty Δβ of β is accurately obtained through the precise measurement of the scanning electron microscope, and its value is 0.00001.