A method for measuring the inner and outer surface topography of a hemispherical resonator based on spectral confocal principle

Abstract

The present application relates to a kind of based on spectral confocal hemispherical harmonic resonator inner and outer surface topography measurement method.The present application includes: adjusting displacement motion platform and attitude adjustment platform makes spectral confocal measuring head optical axis and hemispherical harmonic resonator rotation shaft intersection;Divide scanning measurement interval and carry out curved surface parallel plate approximation at measurement point, record the theoretical angle between plate and spectral confocal measuring head vertical plane;Spectral confocal measuring head and hemispherical harmonic resonator carry out linear scanning motion and rotation motion respectively, collect the spectral peak position data of each measurement point on the surface of hemispherical harmonic resonator;Establish inclined plate compensation model to calculate the distance position information of the inner and outer surface of hemispherical harmonic resonator at each measurement point, and generate inner and outer surface topography after converting measurement result into point cloud.The method provided by the present application can effectively reduce the measurement error introduced by curved surface, and the whole appearance of hemispherical harmonic resonator inner and outer surface can be obtained by once scanning motion, and online measurement can be realized on processing equipment after simple debugging.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of precision measurement, and in particular to a method for measuring the inner and outer surface topography of a hemispherical resonator based on spectral confocal technology. BACKGROUND

[0002] As an important component of the hemispherical resonator gyro, the hemispherical resonator has a transparent hemispherical shell shape, is light and thin, and the thickness is usually less than 1 mm. The geometric topography accuracy of the hemispherical resonator determines the final working performance of the product to a great extent. However, due to the existence of processing errors, the surface topography of the hemispherical resonator produced and manufactured is often different from the theoretical design value, which greatly restricts the development of the hemispherical resonator gyro in the military and civil inertial navigation fields.

[0003] Chinese patent application CN112344865A discloses a system and method for in-situ measuring the wall thickness and wall thickness uniformity of a hemispherical resonator. The hemispherical resonator is clamped on the main shaft C-axis of a machine tool, and a color confocal sensor arranged on the B-axis of the machine tool can measure the wall thickness and the circumferential wall thickness uniformity of the hemispherical resonator. However, the outgoing light of the color confocal sensor must be perpendicular to the axis of the hemispherical resonator and pass through the center of the sphere during the measurement process. This requirement is difficult to achieve in actual operation, and often introduces measurement errors of tens of microns. In addition, the reflected light intensity of the color confocal sensor is weak under large-angle inclined measurement conditions, which makes the method unable to measure the wall thickness of the surface far from the lip edge of the hemispherical resonator, resulting in incomplete measurement data. Some scholars have proposed using a Fizeau interferometer to measure part of the surface of the hemispherical resonator multiple times, and obtaining the surface topography and wall thickness information of the entire surface by surface splicing. However, the operation process of the Fizeau interferometer is extremely complex, and it needs to go through a very tedious debugging process before measurement. It is very difficult to integrate it into the hemispherical resonator processing equipment for online measurement. Therefore, there is an urgent need to develop an online topography measurement technology that can be applied to the processing of hemispherical resonators to guide the processing and ensure the production yield of hemispherical resonators. SUMMARY

[0004] The present application aims to overcome the shortcomings of the prior art and provides a method for measuring the inner and outer surface topography of a hemispherical resonator based on spectral confocal technology.

[0005] The technical solution adopted by the present application to solve its technical problems is as follows:

[0006] Step 1, adjust the position and attitude between the spectral confocal probe and the hemispherical resonator, so that the optical axis of the spectral confocal probe intersects with the rotation axis of the hemispherical resonator and forms a certain angle to complete the initial calibration of the system;

[0007] Step 2, according to the theoretical design value of the inner and outer hemisphere surface radius of the hemispherical resonator, with half of the lateral resolution of the spectral confocal probe as the scanning measurement interval, the curved surface is approximated to a parallel plate at all measurement points, and the theoretical angle value between the plate and the vertical plane of the spectral confocal probe is recorded, that is, the corresponding equivalent inclination angle at the measurement point.

[0008] Step 3, the spectral confocal probe is moved along a straight line, and the hemispherical resonator is rotated around its axis, and the spectral peak position data of each measurement point on the surface of the hemispherical resonator is collected and extracted.

[0009] Step 4, a tilted plate compensation model is established to calculate the distance D of the outer surface of the hemispherical resonator and the distance ΔD between the inner and outer surfaces, and finally the measurement results are converted into point cloud to generate the inner and outer surface topography of the hemispherical resonator.

[0010] Further, the specific method of the curved surface parallel plate approximation in step 2 is:

[0011] A parallel tangent plane is made at any measurement point on the surface of the hemispherical resonator, and a limited plane is obtained by taking the two tangent planes, which is the curved surface approximation parallel plate at the measurement point.

[0012] Further, the specific content of the tilted plate compensation model in step 4 includes:

[0013] 4-1. By integrating the inclination angle values of the approximate parallel plate of each measurement point and the spectral peak position data, the influence of the tilted plate on the spectral peak position offset collected by the spectral confocal probe is compensated by the method of ray tracing, and the distance ΔD between the inner and outer surfaces of the hemispherical resonator at the measurement point (i.e. the distance between the inner and outer surfaces of the hemispherical resonator at the measurement point) is obtained:

[0014]

[0015] Where δ is the measured original spectral peak position difference, θ1 is the incident angle of the light focused on the lower surface of the plate, α is the inclination angle of the plate, n1 is the refractive index of the plate material, and ω is the rotation angle around the optical axis of the spectral confocal probe.

[0016] 4-2. Select a plurality of plates with different thicknesses at different inclination angles to perform calibration measurement experiments using the spectral confocal probe, compare the difference between the actual nominal value ΔD a and the model measurement value ΔD m , introduce an inclination correction factor k to modify the plate inclination angle α in the above formula to kα, and substitute it into the model to make the model measurement correction value ΔD m and the actual nominal value ΔD a as small as possible, so as to improve the measurement accuracy of the model.

[0017] Further, the wall thickness and various size and shape error values at any position of the hemispherical resonator can be obtained through data processing according to the inner and outer surface topography of the hemispherical resonator.

[0018] Compared with the prior art, the present application has the following beneficial effects:

[0019] 1. The relative position relationship between the spectral confocal measuring head and the hemispherical resonator during measurement is low, the system is easy to adjust and simple to operate, and can be integrated on the hemispherical resonator processing equipment to realize online measurement after simple installation and adjustment.

[0020] 2. Based on the curved surface parallel plate approximation scheme, an inclined plate compensation model is established to compensate the measurement results of the spectral confocal measuring head, so that the measurement error is improved to the sub-micron level, and the measurement error introduced by the surface curvature when the spectral confocal sensor measures the curved surface of the hemispherical resonator is effectively reduced.

[0021] 3. The spectral confocal measuring head with a large working inclination angle is used, and the full appearance measurement of the inner and outer surfaces of the hemispherical resonator can be realized through one straight line scanning movement of the measuring head and the rotation movement of the hemispherical resonator around the axis, the measurement data is complete, and the measured appearance result can also be used for further calculation of the wall thickness and various size and shape error values at any position of the hemispherical resonator. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 It is a flow chart of the hemispherical resonator inner and outer surface topography measurement method of the present application.

[0023] Figure 2 It is a hemispherical resonator surface topography measurement schematic diagram of the present application.

[0024] Figure 3 It is a schematic diagram of the curved surface parallel plate approximation of the present application.

[0025] Figure 4 It is a principle diagram of the inclined plate compensation model of the present application. DETAILED DESCRIPTION

[0026] In order to make the purpose, technical scheme and advantages of the present application clearer, the following will be further described in detail in combination with the drawings and examples.

[0027] The present application discloses a hemispherical resonator inner and outer surface topography measurement method based on spectral confocal, as shown in Figure 1 The steps include:

[0028] Step 1, as shown in Figure 2As shown, adjusting the displacement stage and attitude adjustment stage changes the position and attitude between the spectral confocal probe and the hemispherical harmonic oscillator, so that the optical axis of the spectral confocal probe intersects the rotation axis of the hemispherical harmonic oscillator and forms a certain angle θ. Since the signal-to-noise ratio of the spectral signal obtained by the spectral confocal probe is greatly reduced under large tilt angle measurement conditions, the angle θ is set to a maximum measurable tilt angle of 40° to maximize the effective measurement area of ​​the spectral confocal probe. In this embodiment, the measurable tilt angle range of the spectral confocal probe reaches 80°, basically covering the entire inner and outer surfaces of the hemispherical harmonic oscillator. However, the maximum measurable tilt angle here is not limited to the above value, and its specific value can be selected differently depending on the design range and accuracy of the spectral confocal probe. This completes the initial calibration of the system.

[0029] Step 2: Based on the theoretical design values ​​of the radii of the inner and outer hemispheres of the hemispherical harmonic oscillator, in this embodiment, half the lateral resolution of the spectral confocal probe is used as the scanning measurement interval. A curved parallel plate approximation is applied to all measurement points, and the theoretical angle between this plate and the perpendicular plane of the spectral confocal probe (i.e., the equivalent tilt angle at the measurement point) is recorded. It should be noted that although the actual morphology of the inner and outer hemispheres of the hemispherical harmonic oscillator may differ from its theoretical design value, the equivalent tilt angle error caused by this difference can be ignored due to the insensitivity of the spectral confocal probe to small tilt angles.

[0030] like Figure 3 As shown, the specific method for approximating a curved parallel plate is as follows: take any measurement point on the surface of the hemispherical harmonic oscillator (since at extremely small scales, the choice of inner or outer surface measurement point as a parallel tangent has little impact on the final measurement result) as the tangent point and make parallel tangents on the inner and outer surfaces at that point. Take the finite-sized plane between the two tangents to obtain the curved approximating parallel plate at that measurement point. The plate material is the same as the fused silica used in the hemispherical harmonic oscillator in this embodiment.

[0031] Step 3: Move the spectral confocal probe along a straight line and rotate the hemispherical harmonic oscillator around its own axis. Make sure that the hemispherical harmonic oscillator rotates exactly one revolution for every one scanning measurement interval of the spectral confocal probe. At the same time, collect and extract the spectral peak position data at each measurement point on the surface of the hemispherical harmonic oscillator.

[0032] Step 4: Establish an inclined plate compensation model and calculate the distance D between the outer surface of the hemispherical harmonic oscillator and the spacing ΔD between the inner and outer surfaces of the hemispherical harmonic oscillator at each measurement point (i.e., Figure 2 The distance between the measurement points on the inner and outer surfaces of the hemispherical harmonic oscillator is shown. Finally, the measurement results are converted into point clouds to generate the morphology of the inner and outer surfaces of the hemispherical harmonic oscillator.

[0033] The specific contents of the inclined flat plate compensation model include:

[0034] (1) The approximate parallel plate inclination values and spectral peak position data of each measurement point are integrated, and the light ray tracing method is used to compensate the influence of the tilted plate on the spectral peak position offset collected by the spectral confocal probe. As shown in FIG. 1, the light rays with wavelengths λ1 and λ2 are focused on the upper and lower surfaces of the parallel plate, respectively. According to the sine theorem, we have: Figure 4

[0035] n0 sinθ1=n1 sinθ2, (1)

[0036] where θ1 and θ2 are the incident angle and the refraction angle of the light ray focused on the lower surface of the plate, n0 and n1 are the refractive indices of air and the plate material, and n0 = 1. Then, the sine theorem is applied in triangles OO1O2 and OO2O3, and we have:

[0037]

[0038]

[0039] where α is the inclination of the plate, and d is the distance between the upper and lower surfaces of the parallel plate under the measurement section shown in FIG. 1. By combining equations (1) to (3), we have: Figure 4

[0040]

[0041] where δ is the measured original spectral peak position difference, which can be directly read in the spectral confocal sensor, and its essence is the difference between the distances corresponding to the two spectral peaks in the measured signal.

[0042] After fully considering the light rays under different rotation angles ω around the optical axis of the spectral confocal probe, the distance ΔD between the upper and lower surfaces of the parallel plate (i.e., the distance between the inner and outer surfaces of the corresponding hemispherical resonator at the measurement point) is finally obtained after normalization:

[0043]

[0044] (2) A plurality of fused quartz glass plates with different thicknesses are selected to perform calibration measurement experiments using the spectral confocal probe at different inclination angles. The difference between the actual nominal value ΔD a and the model measurement value ΔD m is compared, and the inclination correction factor k is introduced to correct the plate inclination α in the above equation to kα. The difference between the corrected model measurement value ΔD m ’ and the actual nominal value ΔD a is minimized to improve the measurement accuracy of the model.

[0045] ​​As a preferred embodiment, the wall thickness and the error values of various dimensions and shapes at any position of the hemispherical resonator can be obtained by data processing according to the inner and outer surface topography of the hemispherical resonator.

[0046] It should be emphasized that the above-mentioned embodiments are only for illustrating the technical concept and characteristics of the present application, and the purpose is to enable those skilled in the art to understand the content of the present application and to implement it, and cannot limit the protection scope of the present application. Any equivalent changes or modifications made in accordance with the spirit and essence of the present application shall be covered within the protection scope of the present application.

Claims

1. A method for measuring the inner and outer surface morphology of a hemispherical harmonic oscillator based on spectral confocality, characterized in that, Includes the following steps: Step 1: Adjust the position and orientation between the spectral confocal probe and the hemispherical harmonic oscillator so that the optical axis of the spectral confocal probe intersects with the rotation axis of the hemispherical harmonic oscillator and forms a certain angle to complete the initial calibration of the system. Step 2: Based on the theoretical design values ​​of the inner and outer hemispherical surfaces of the hemispherical harmonic oscillator, and using half the lateral resolution of the spectral confocal probe as the scanning measurement interval, approximate all measurement points with a curved parallel plate and record the theoretical angle between the plate and the vertical plane of the spectral confocal probe. Step 3: Move the spectral confocal probe along a straight line to scan, and rotate the hemispherical harmonic oscillator around its own axis to collect and extract the spectral peak position data at each measurement point on the surface of the hemispherical harmonic oscillator. Step 4: Establish a tilted plate compensation model, calculate the distance D between the outer surface of the hemispherical harmonic oscillator and the spacing ΔD between the inner and outer surfaces at each measurement point, and finally convert the measurement results into point clouds to generate the morphology of the inner and outer surfaces of the hemispherical harmonic oscillator. The specific content of the inclined plate compensation model in step 4 includes: 4-1. Combining the approximate parallel plate tilt angle values ​​and spectral peak position data at each measurement point, the influence of the tilted plate on the spectral peak position shift acquired by the confocal spectral probe is compensated using ray tracing. The distance ΔD between the inner and outer surfaces of the hemispherical harmonic oscillator at the measurement point is obtained as follows: In the formula, δ is the measured difference in the position of the original spectral peaks, θ1 is the incident angle of the light focused on the lower surface of the plate, α is the tilt angle of the plate, n1 is the refractive index of the plate material, and ω is the rotation angle around the optical axis of the spectral confocal probe. 4-2. Select multiple plates of different thicknesses and conduct calibration measurement experiments using a spectral confocal probe at different tilt angles, comparing the actual nominal value ΔD. a With model measurement value ΔD m The difference between them is addressed by introducing a tilt angle correction factor k to correct the flat plate tilt angle α in the above formula to kα. Substituting this into the model makes the model measurement correction value ΔD corrected. m ’ Compared with the actual nominal value ΔD a To minimize the difference, thereby improving the model's measurement accuracy.

2. The method for measuring the inner and outer surface morphology of a hemispherical harmonic oscillator based on spectral confocality according to claim 1, characterized in that, The specific method for approximating the curved parallel plate in step 2 is as follows: take any measurement point on the surface of the hemispherical harmonic oscillator as the tangent point and make parallel tangents to the inner and outer surfaces at that point. Take the finite-sized plane between the two tangents to obtain the curved approximation parallel plate at that measurement point.

3. The method for measuring the inner and outer surface morphology of a hemispherical harmonic oscillator based on spectral confocality according to claim 1, characterized in that, Based on the morphology of the inner and outer surfaces of the hemispherical harmonic oscillator, the wall thickness and various dimensional and shape error values ​​at any position of the hemispherical harmonic oscillator can also be obtained through data processing.

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