Calibration method for indication error of non-contact optical thickness gauge

Abstract

The present invention provides a calibration method for the indication error of a non-contact optical thickness gauge, which uses a group of glass blocks with known accurate values ​​to perform calibration by a pairing method, and within the measuring range of the calibrated thickness gauge, a calibration point is set at intervals of 10 mm; the calibration point is calibrated, and during calibration, the first glass block is aligned to zero, and the second glass block is calibrated to the indication error of the calibration point, and then the second glass block is aligned to zero, and the third glass block is calibrated to the indication error of the calibration point, and so on, until the last glass block is paired. The present invention has high calibration accuracy, and the calibration method for the repeatability of the measurement result is more perfect than the original evaluation system. The uncertainty evaluation of the indication error measurement result in the calibration method adopts uncertainty component analysis and synthetic standard uncertainty respectively, and finally the evaluation result is analyzed to judge whether the calibrated thickness gauge meets the technical requirements.

Description

Technical Field

[0001] The invention belongs to the technical field of instrument verification and calibration, and in particular relates to a calibration method for indication error of a non-contact optical thickness gauge. Background Art

[0002] The traditional center thickness measurement method is to use contact measurement methods, such as mechanical measurement methods using dial gauges and micrometers; projection optical measurement methods; photoelectric measurement methods with grating digital display readings, etc. The above methods are all due to low detection accuracy, long time consumption, easy scratches on the lens, and inability to achieve real-time online measurement. In addition, when measuring convex lenses and concave lenses, the probe must be replaced, and the maximum point or minimum point must be determined according to the measurement object, and multiple searches must be performed, which also causes damage to the surface of the optical parts being measured, resulting in the possible scrapping of the parts. Therefore, non-contact optical thickness gauges are currently used for measurement.

[0003] The testing principle of the test instrument used for the center thickness of high-precision optical parts is double-beam interferometry or phase interferometry, etc., both of which use two beams of light emitted by the same light source (visible light or laser, etc.) to achieve light interference. The basic conditions for light interference are two beams of light with the same frequency, constant period or constant phase difference and the same vibration direction. The non-contact optical thickness gauge uses the laser double-beam interference non-contact method to solve the problem of high-precision optical parts testing. However, there are currently no corresponding verification procedures / calibration specifications and other technical documents based on verification / calibration. Most of them use the so-called standard lens (generally a standard lens provided by the manufacturer) for comparison testing, which cannot achieve accurate calibration, value traceability and instrument range coverage. Summary of the invention

[0004] The object of the present invention is to provide a method for calibrating the indication error of a non-contact optical thickness gauge, so as to overcome the above-mentioned technical problems existing in the prior art.

[0005] To this end, the technical solution provided by the present invention is as follows: The calibration method of the indication error of the non-contact optical thickness gauge is to use a set of glass blocks with known accurate values ​​for calibration by the pairing method. Within the measuring range of the calibrated thickness gauge, a calibration point is set at intervals of 10mm. Calibrate the first calibrated point. During calibration, align the first glass block to zero position, calibrate the indication error of the calibrated point with the second glass block, align the second glass block to zero position, calibrate the indication error of the calibrated point with the third glass block, and so on, until the last glass block is matched; Repeat the above steps to calibrate the remaining calibration points. When calibrating the positive indication error, the size of the glass block is increased in sequence; when calibrating the negative indication error, the size of the glass block is decreased in sequence.

[0006] It also includes the calibration of the repeatability of the measurement results. During the calibration, a glass block with a known accurate value is randomly placed on the thickness gauge to be calibrated for testing. The measured result value is recorded as d 1. Repeat the above steps 10 times, and the measurement results are recorded as d i ( i =1,2, ...... ,10), and the repeatability of the measurement results is calculated using the following formula s :

[0007] In the formula, s is the measurement repeatability of the calibrated thickness gauge ( ); The arithmetic mean of the measurement results is calculated by repeating the measurement 10 times ( ); is the single measurement result value ( ).

[0008] After calibrating the indication error, the uncertainty of the indication error measurement result is evaluated.

[0009] Indication error of each calibration point Calculate according to the following formula:

[0010] In the formula, r i The value obtained by calibrating each calibrated point with the corresponding glass block ( ); I n The actual size of the last glass block used to calibrate the indication error of the calibration point (mm); I 1 is the actual size of the glass block used for initial zero alignment (mm); n The number of glass blocks used for each calibration point.

[0011] The uncertainty assessment of the indication error measurement result includes the following steps: Step 1) Uncertainty components u i analyze; Step 2) Based on the uncertainty components obtained by analysis u i Combined standard uncertainty u c , and obtain the expanded uncertainty of the measurement result U ; Step 3) Analyze the evaluation results based on the relationship between the expanded uncertainty of the measurement results and the maximum allowable error of the thickness gauge. When the expanded uncertainty of the measurement results is less than the maximum allowable error of the thickness gauge, the calibrated thickness gauge meets the technical requirements.

[0012] Step 1) Uncertainty components u i Analysis includes uncertainty components introduced by metrological standards u 1 and the uncertainty components introduced by the measurement u 2.

[0013] Uncertainty components introduced by measurement standards u 1= U / 3, where U is the measurement uncertainty of the glass block, , where the confidence factor k =2, d is the size of the glass block.

[0014] Uncertainty components introduced by measurement u 2 Take the uncertainty component introduced by the instrument measurement repeatability rate u 21 and the uncertainty component introduced by the digital resolution of the instrument u 22 The larger of the two; ; ; In the formula, The arithmetic mean of the measurement results is calculated by repeating the measurement 10 times ( ); is the single measurement result value ( ); px is the digital resolution of the instrument.

[0015] Combined standard uncertainty , the expanded uncertainty of the measurement result U=ku c , k= 2 。

[0016] The beneficial effects of the present invention are: The method for calibrating the indication error of the non-contact optical thickness gauge provided by the present invention utilizes a "glass gauge block" to calibrate the non-contact thickness gauge, which can not only realize accurate measurement of the instrument, but also perform traceability, actual verification and measurement uncertainty analysis.

[0017] The indication error of the non-contact optical thickness gauge is calibrated by the "pairing method" using a "glass block". Within the measuring range of the instrument, one point is calibrated every 10mm, which has higher calibration accuracy.

[0018] The calibration method for the repeatability of the measurement results is more complete than the original evaluation system. The uncertainty evaluation of the indication error measurement results in the calibration method uses the uncertainty components Analytical and combined standard uncertainties ,Finally, the evaluation results are analyzed to determine whether the calibrated thickness gauge meets the technical requirements. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Picture 1 It is the value traceability diagram of the present invention. DETAILED DESCRIPTION

[0020] The following describes the implementation of the present invention through specific embodiments. Those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification.

[0021] The exemplary embodiments of the present invention are now described with reference to the accompanying drawings. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. These embodiments are provided to disclose the present invention in detail and completely and to fully convey the scope of the present invention to those skilled in the art. The terms used in the exemplary embodiments shown in the accompanying drawings are not intended to limit the present invention.

[0022] Unless otherwise specified, the terms (including technical terms) used herein have the commonly understood meanings to those skilled in the art. In addition, it is understood that the terms defined in commonly used dictionaries should be understood to have the same meanings as those in the context of the relevant fields, and should not be understood as idealized or overly formal meanings.

[0023] Example 1 The present invention provides a calibration method for the indication error of a non-contact optical thickness gauge, which uses a group of glass blocks with known accurate values ​​to perform calibration by a pairing method, and sets a calibration point at intervals of 10 mm within the measuring range of the calibrated thickness gauge; Calibrate the first calibrated point. During calibration, align the first glass block to zero position, calibrate the indication error of the calibrated point with the second glass block, align the second glass block to zero position, calibrate the indication error of the calibrated point with the third glass block, and so on, until the last glass block is matched; Repeat the above steps to calibrate the remaining calibration points. The present invention formulates a block diagram of a metrology calibration system, such as Picture 1 As shown, using a "glass block" (parallel flat crystal, focal length The lens calibration method is to calibrate the instrument according to the test range of the instrument being calibrated and follow the principle of uniform distribution, using a group of glass blocks (parallel flat glass crystals with known accurate values) to calibrate the instrument.

[0024] Features of this calibration method: 1. Use two beams of light emitted by the same light source to achieve light interference. If it is polychromatic light, the interference fringes are colored fringes; if it is monochromatic light, the interference fringes are equally spaced fringes of light and dark. By point Two beams of monochromatic light of the same frequency are emitted from the optical part and reflected twice by the upper and lower surfaces. Due to the refractive index of the glass Refractive index with air Different, so there is a certain optical path difference between the two beams, at point When the two particles meet, interference fringes of alternating light and dark are produced.

[0025] The optical path difference between the two beams is

[0026] Where: is the thickness of the glass, is the refractive index of glass, is the incident angle of the light wave.

[0027] 2. The measuring instrument used is a "glass block". The block itself can be calibrated, and the measurement value can be traced.

[0028] The number of pairs of glass blocks and the thickness intervals used in this calibration method may vary according to the actual conditions of the instrument being calibrated.

[0029] The present invention can perform periodic verification and calibration on the non-contact optical thickness gauge, which not only realizes accurate measurement of the instrument, but also can trace the value, thus realizing periodic verification and factory-entry and post-repair verification of the non-contact optical thickness gauge.

[0030] Example 2 On the basis of Example 1, this example provides a method for calibrating the indication error of a non-contact optical thickness gauge. When calibrating the positive indication error, the size of the glass block is increased in sequence; when calibrating the negative indication error, the size of the glass block is decreased in sequence.

[0031] This method ensures that the calibration process is accurate, thereby improving the accuracy and reliability of the measurement.

[0032] Example 3 Based on Example 1, this example provides a method for calibrating the indication error of a non-contact optical thickness gauge, which also includes calibrating the repeatability of the measurement result. During the calibration, a glass block with a known accurate value is randomly placed on the thickness gauge to be calibrated for testing. The obtained measurement result is recorded as d 1. Repeat the above steps 10 times, and the measurement results are recorded as d i ( i =1,2, ...... ,10), and the repeatability of the measurement results is calculated using the following formula s :

[0033] In the formula, s is the measurement repeatability of the calibrated thickness gauge ( ); The arithmetic mean of the measurement results is calculated by repeating the measurement 10 times ( ); is the single measurement result value ( ).

[0034] The repeatability of the measurement results can be used to determine the stability and reliability of the measurement system under different conditions. High repeatability means small errors and high measurement accuracy.

[0035] Example 4 On the basis of Example 1, this example provides a method for calibrating the indication error of a non-contact optical thickness gauge. After the indication error is calibrated, the uncertainty of the indication error measurement result is evaluated.

[0036] Indication error of each calibration point Calculate according to the following formula:

[0037] In the formula, r i The value obtained by calibrating each calibrated point with the corresponding glass block ( ); I n The actual size of the last glass block used to calibrate the indication error of the calibration point (mm); I 1 is the actual size of the glass block used for initial zero alignment (mm); n The number of glass blocks used for each calibration point.

[0038] Example 5 Based on Example 4, this embodiment provides a method for calibrating the indication error of a non-contact optical thickness gauge, and the uncertainty assessment of the indication error measurement result includes the following steps: Step 1) Uncertainty components u i analyze; Step 2) Based on the uncertainty components obtained by analysis u i Combined standard uncertainty u c , and obtain the expanded uncertainty of the measurement result U ; Step 3) Analyze the evaluation results based on the relationship between the expanded uncertainty of the measurement results and the maximum allowable error of the thickness gauge. When the expanded uncertainty of the measurement results is less than the maximum allowable error of the thickness gauge, the calibrated thickness gauge meets the technical requirements.

[0039] The uncertainty assessment of the indication error measurement result is an important means to measure the accuracy of the measuring instrument. Therefore, it is necessary to analyze the standard uncertainty of each input quantity, including measurement repeatability, resolution and other factors, synthesize the standard uncertainty of each input quantity, and obtain the combined standard uncertainty. Finally, according to the combined standard uncertainty, multiply it by k , and obtain the expanded uncertainty. ‌‌‌

[0040] Example 6 Based on Example 5, this example provides a method for calibrating the indication error of a non-contact optical thickness gauge, step 1) uncertainty component u i Analysis includes uncertainty components introduced by metrological standards u 1 and the uncertainty components introduced by the measurement u 2.

[0041] The measurement error of the lens center thickness and the integer part of the interference fringe , decimal part and wavelength However, the multi-beam interferometry method is used to measure the center thickness of the lens. When, wavelength The measurement result is only related to the decimal part. It is related to the measurement accuracy, so the uncertainty component of its measurement result only considers the following sources.

[0042] 1. Uncertainty components introduced by measurement standards u 1= U / 3, where U is the measurement uncertainty of the glass block, , d is the size of the glass block.

[0043] 2. Uncertainty components introduced by measurement u 2 Take the uncertainty component introduced by the instrument measurement repeatability rate u 21 and the uncertainty component introduced by the digital resolution of the instrument u 22 The larger of the two; ; ; In the formula, The arithmetic mean of the measurement results is calculated by repeating the measurement 10 times ( ); is the single measurement result value ( ); px is the digital resolution of the instrument.

[0044] In addition, there are other influencing factors, such as wavelength deviation, glass refractive index deviation, etc., but the influence is very small, so they can be ignored.

[0045] Example 7 Based on Example 6, this example provides a method for calibrating the indication error of a non-contact optical thickness gauge, and the synthetic standard uncertainty is , the expanded uncertainty of the measurement result U=ku c , k= 2 。

[0046] This embodiment takes a non-contact lens center thickness gauge produced by a German manufacturer as an example, and after calibrating its indication error using the above calibration method, the measurement uncertainty of the calibration result is evaluated.

[0047] The technical indicators of the instrument are: maximum allowable error no more than ±0.5um, measurement repeatability no more than ±0.25um, and minimum resolution 0.1 um.

[0048] 1. Uncertainty components introduced by measurement standards

[0049] According to the verification results of the superior department (here in accordance with the technical requirements of the third-class gauge block), the measurement uncertainty of the measurement standard (glass gauge block) used is , then the measurement uncertainty component introduced by it is , if the thickness is measured hour, . 2. Uncertainty component introduced by measurement repeatability / digital display resolution

[0050] 1) Uncertainty component introduced by instrument measurement repeatability rate

[0051] Select The glass block was measured 10 times and the experimental standard deviation was calculated. It represents the uncertainty component introduced by the repeatability of the measurement result, that is,

[0052]

[0053] 2) Uncertainty component introduced by the digital resolution of the instrument

[0054] The digital resolution of the calibrated instrument is 0.1 , so according to the uniform distribution treatment, we can get

[0055] Therefore, take .

[0056] 2. Combined standard uncertainty

[0057] The combined uncertainty of the measurement result is

[0058] Get confidence factor , then the expanded uncertainty of the measurement result is

[0059] 3. Analysis of evaluation results According to the measurement uncertainty evaluation results and the technical requirements of the maximum allowable error of the instrument, it can be obtained that:

[0060] Therefore, the uncertainty analysis and evaluation results of the above calibration results indicate that the thickness gauge meets or satisfies the technical requirements after calibration.

[0061] The above examples are merely illustrative of the present invention and do not constitute a limitation on the protection scope of the present invention. All designs that are the same or similar to the present invention fall within the protection scope of the present invention.

Claims

1. A method for calibrating the indication error of a non-contact optical thickness gauge, characterized in that: Use a set of glass blocks with known accurate values ​​to calibrate by pairing method. Set a calibration point every 8-12mm within the measuring range of the thickness gauge to be calibrated. Calibrate the first calibrated point. During calibration, align the first glass block to zero position, calibrate the indication error of the calibrated point with the second glass block, align the second glass block to zero position, calibrate the indication error of the calibrated point with the third glass block, and so on, until the last glass block is matched; Repeat the above steps to calibrate the remaining calibration points.

2. The method for calibrating the indication error of a non-contact optical thickness gauge according to claim 1, characterized in that: When calibrating the positive indication error, the size of the glass block is increased in sequence; when calibrating the negative indication error, the size of the glass block is decreased in sequence.

3. The method for calibrating the indication error of a non-contact optical thickness gauge according to claim 1, characterized in that: It also includes the calibration of the repeatability of the measurement results. During the calibration, a glass block with a known accurate value is randomly placed on the thickness gauge to be calibrated for testing. The measured result value is recorded as d 1. Repeat the above steps 10 times, and the measurement results are recorded as d i ( i =1,2, ...... ,10), and the repeatability of the measurement results is calculated using the following formula s : In the formula, s is the measurement repeatability of the calibrated thickness gauge ( ); The arithmetic mean of the measurement results is calculated by repeating the measurement 10 times ( ); is the single measurement result value ( ); n is the number of measurements.

4. The method for calibrating the indication error of a non-contact optical thickness gauge according to claim 1, characterized in that: After calibrating the indication error, the uncertainty of the indication error measurement result is evaluated.

5. The method for calibrating the indication error of a non-contact optical thickness gauge according to claim 1, characterized in that: Indication error of each calibration point Calculate according to the following formula: In the formula, r i The value obtained by calibrating each calibrated point with the corresponding glass block ( ); I n The actual size of the last glass block used to calibrate the indication error of the calibration point (mm); I 1 is the actual size of the glass block used for initial zero alignment (mm); n The number of glass blocks used for each calibration point.

6. The method for calibrating the indication error of a non-contact optical thickness gauge according to claim 4, characterized in that: The uncertainty assessment of the indication error measurement result includes the following steps: Step 1) Uncertainty components u i analyze; Step 2) Based on the uncertainty components obtained by analysis u i Combined standard uncertainty u c , and obtain the expanded uncertainty of the measurement result U ; Step 3) Analyze the evaluation results based on the relationship between the expanded uncertainty of the measurement results and the maximum allowable error of the thickness gauge. When the expanded uncertainty of the measurement results is less than the maximum allowable error of the thickness gauge, the calibrated thickness gauge meets the technical requirements.

7. The method for calibrating the indication error of a non-contact optical thickness gauge according to claim 6, characterized in that: Step 1) Uncertainty components u i Analysis includes uncertainty components introduced by metrological standards u 1 and the uncertainty components introduced by the measurement u 2.

8. The method for calibrating the indication error of a non-contact optical thickness gauge according to claim 7, characterized in that: Uncertainty components introduced by measurement standards u 1= U / 3, where U is the measurement uncertainty of the glass block, , where the confidence factor k =2, d is the size of the glass block.

9. The method for calibrating the indication error of a non-contact optical thickness gauge according to claim 7, characterized in that: Uncertainty components introduced by measurement u 2 Take the uncertainty component introduced by the instrument measurement repeatability rate u 21 and the uncertainty component introduced by the digital resolution of the instrument u 22 The larger of the two; ； In the formula, The arithmetic mean of the measurement results is calculated by repeating the measurement 10 times ( ); is the single measurement result value ( ); px is the digital resolution of the instrument; n is the number of measurements.

10. The method for calibrating the indication error of a non-contact optical thickness gauge according to claim 7, characterized in that: Combined standard uncertainty , the expanded uncertainty of the measurement result U=ku c , k= 2.

Images