Method for detecting inner diameter and depth of micropore with large depth-diameter ratio based on Fraunhofer diffraction

Abstract

The invention discloses a method for detecting the inner diameter and depth of a micropore with a large depth-diameter ratio based on Fraunhofer diffraction, and the method comprises the steps: constructing an optical system, taking laser as a light source, and generating a clear diffraction pattern through a micropore (circular hole) diffraction device. Firstly, light paths are adjusted to be coaxial, and the inner diameter of the round hole is calculated by analyzing the change of diffraction fringes and combining a Fraunhofer diffraction formula. And then, inclining the micropore sample by rotating the high-precision rotating platform at high precision, observing the change of a diffraction pattern, and further calculating the depth of the micropore. In the process, accurate measurement of the depth of the micropore is realized by utilizing the geometrical relationship between the long axis and the short axis and combining a measurement error formula. The method has the advantages of high precision and non-contact measurement, can be effectively applied to detection of micropores with large depth-diameter ratio, and is particularly suitable for micropore structure detection in the fields of oil nozzles, medical instruments, precise instruments and the like. According to the method, accurate inner diameter and depth data can be provided, and a new technical scheme is provided for micropore measurement.

Description

Technical Field

[0001] The invention belongs to the technical field of optical non-contact measurement, and in particular relates to a method for detecting the inner diameter and depth of a micropore with a large aspect ratio based on Fraunhofer diffraction. Background Art

[0002] Micropores or deep micro-holes are widely used in inkjet printing, medical treatment, chemical engineering, aerospace, precision instrumentation, and other fields, such as nozzles, microneedles, and injection holes. Their apertures typically range from micrometers to millimeters. The dimensional accuracy of these micropores directly affects product performance and may even lead to waste of fuel and ink. Therefore, relying on high-precision molds to produce micropores has become a common method. High-precision measurement of micropores with large aspect ratios is critical to ensuring product quality.

[0003] Like other geometric measurements, micropore size measurement is categorized as contact or non-contact, depending on whether or not contact is established with the object being measured. The primary difficulty with contact measurement lies in probe design. For small inner diameter holes, penetrating deeply into the pore can be challenging, so high-precision probe design is crucial. Non-contact measurement primarily relies on electrical and optical methods to measure micropore size. The following introduces some key measurement methods and their current research status.

[0004] Three-dimensional coordinate measurement: This method uses probe displacement on a three-dimensional coordinate measuring machine to determine the aperture diameter, achieving a measurement accuracy of 1μm. However, it is not suitable for small holes with large aspect ratios and is susceptible to probe damage. The oscillation scanning method uses the change in the electrical signal when the probe microvibrates and contacts the hole wall to determine the profile. This method offers high accuracy and does not damage the hole wall, but is only suitable for conductive materials and suffers from system drift. The dual atomic force microscope method uses two atomic force microscopes to measure aperture diameter. This method offers high accuracy but is expensive, complex, and difficult to implement. The fiber optic probe method uses an optical fiber and a CCD system to locate the position of a microsphere probe. This method is suitable for small holes but not for deep holes, and image quality degrades when the light scattering angle is large. The dual fiber coupling method uses a combination of input and output optical fibers for detection, improving accuracy and being suitable for apertures of 10-20μm. However, the system is complex. The computer vision method uses image processing to calculate the aperture diameter. This method is only suitable for end-face measurement, not for deep holes, and is susceptible to burr interference. The pneumatic measurement method uses pressure changes in the airflow within the hole to determine the aperture diameter. This method offers high accuracy but is only suitable for through holes and cannot measure local variations. Capacitance method: This method uses capacitance changes to measure aperture diameter. It can measure both through-holes and blind vias and is suitable for apertures >1.5mm, but can suffer from large eccentricity errors. Inductance method: This method uses a calibration comparison method to measure aperture diameter. It is suitable for apertures 1–5mm and depths exceeding 40mm, with an accuracy below 0.6μm. Optical scanning method: This method uses laser and CCD imaging for measurement, with a resolution of up to 0.1μm and a wide measurement range, suitable for micron-level apertures. Laser differential confocal method: This method achieves ultra-high-resolution measurement through 3D confocal imaging, making it suitable for fine scanning and reconstruction of micropore topography.

[0005] Existing measurement methods each have their own advantages and disadvantages, and it is difficult to simultaneously meet the multiple requirements of high precision, large aspect ratio, and small aperture. Improving measurement accuracy, expanding the measurement range, and eliminating impurity interference remain important research directions in the field of micropore measurement. Summary of the Invention

[0006] To address the technical problems presented in the prior art, the present invention provides a Fraunhofer diffraction-based method for measuring the inner diameter and depth of high-aspect-ratio microapertures. This method utilizes Fraunhofer diffraction technology to measure the physical dimensions of the diffraction fringes of a circular aperture, thereby calculating the inner diameter of the aperture. Furthermore, a high-precision rotating platform is used to measure the fringe order of the aperture at different inclination angles, thereby calculating the aperture depth. This method offers the advantages of simple setup, rapid measurement speed, and low cost.

[0007] In order to solve the technical problem, the technical solution of the present invention is:

[0008] A device based on Fraunhofer circular aperture diffraction, comprising a laser and a first lens, an aperture stop, a second lens, a high aspect ratio circular aperture, a converging lens, and a camera sensor sequentially arranged along the optical axis of the laser;

[0009] A high-precision rotating platform (existing technology) is installed at the lower end of the large aspect ratio circular hole. The high-precision rotating platform controls the measured element to be in different tilt postures. The first lens and the second lens are combined to form a Kepler telescope structure.

[0010] Furthermore, the laser is used to generate Fraunhofer diffraction as a structured light source; the aperture stop is used to perform spatial filtering; the first lens and the second lens are located in front of the circular hole to form a Kepler telescope structure for laser beam expansion; the converging lens is located behind the circular hole to converge parallel light and form an image on the camera sensor; the measured element is fixed on the platform by a clamping device, and a high-precision rotating platform is used to place the measured element in different tilt postures during the measurement process; the camera sensor is used to directly capture the diffraction image.

[0011] A method for detecting the inner diameter and depth of a large aspect ratio microhole based on Fraunhofer diffraction, the method being applied to any of the above-mentioned devices, the method comprising:

[0012] Step 1: Adjust the optical path to be coaxial

[0013] After fixing the laser, adjust the components in the optical path until the optical path is coaxial. Place the circular hole to be measured perpendicular to the optical axis and fix it on a high-precision rotating platform to form a clear concentric diffraction image distributed in the radial direction on the camera sensor. Ensure that the image clarity is high enough.

[0014] Step 2: Calculate the inner diameter of the circular hole

[0015] The distance x between the first-order dark fringe and the central bright spot on the camera sensor at this time is obtained according to the Fraunhofer circular aperture diffraction calculation formula:

[0016]

[0017] Where a is the radius of the circular hole with aspect ratio, Indicates the angle between the main light reaching the first-order dark fringe and the optical axis. λ represents the wavelength of the incident light, and the inner diameter of the circular hole is calculated from this formula;

[0018] Step 3: Tilt the hole

[0019] After measuring the inner diameter of the circular aperture, use a high-precision rotating platform to tilt the aperture at a certain angle β. The diffraction fringes displayed on the camera sensor will become elliptical. At this time, projecting the circular aperture along the optical axis will produce an elliptical distribution. The length of the major axis remains unchanged and is still the diameter a of the circular aperture. However, the minor axis will change due to the tilt angle. The length of the minor axis is recorded as b. Calculate the minor axis length b again through step 1. The calculation formula is:

[0020]

[0021] where x b is the distance between the first-order dark pattern and the central bright spot on the camera sensor in the direction of the minor axis of the ellipse; then, based on the geometric relationship between the major axis and the minor axis, we get:

[0022]

[0023] And through the following formula and the accuracy of the high-precision rotating platform, the measurement error of the circular hole depth is obtained:

[0024]

[0025] Compared with the prior art, the advantages of the present invention are:

[0026] First, it uses non-contact measurement, avoiding physical damage to micropores, making it particularly suitable for delicate and fragile micropore structures. Second, by utilizing variations in the diffraction pattern for precise calculations, it can provide highly accurate measurement results, particularly effective in detecting micropores with large aspect ratios. Furthermore, the system's relatively simple structure, ease of operation, and strong applicability make it suitable for a wide range of applications in areas such as fuel injectors, medical devices, and microfluidic devices. Finally, this method effectively reduces the impact of environmental factors on measurement results, ensuring consistent and reliable measurements. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 , a diagram of the device for detecting the inner diameter and depth of a large aspect ratio micropore based on Fraunhofer diffraction of the present invention;

[0028] Figure 2 , a schematic diagram showing the principle of the method for detecting the inner diameter and depth of a micropore with a large aspect ratio based on Fraunhofer diffraction according to the present invention;

[0029] Figure 3 , the concentric ring diffraction fringe pattern displayed by the display of the present invention. DETAILED DESCRIPTION

[0030] The specific implementation of the present invention is described below in conjunction with examples:

[0031] It should be noted that the structures, proportions, sizes, etc. shown in this specification are only used to match the contents disclosed in the specification for people familiar with this technology to understand and read, and are not used to limit the conditions under which the present invention can be implemented. Any structural modification, change in proportional relationship or adjustment of size should still fall within the scope of the technical content disclosed in the present invention without affecting the efficacy and purpose that can be achieved by the present invention.

[0032] At the same time, the terms such as "upper", "lower", "left", "right", "middle" and "one" quoted in this specification are only for the convenience of description and are not used to limit the scope of implementation of the present invention. Changes or adjustments to their relative relationships should be regarded as the scope of implementation of the present invention without substantially changing the technical content.

[0033] Example 1:

[0034] See Figures 1 to 3 A device for detecting the inner diameter and depth of a large aspect ratio microhole based on Fraunhofer diffraction includes a laser 1 for generating Fraunhofer diffraction as a structured light source; an aperture stop 2 for spatial filtering; two lenses 3 for forming a Kepler telescope structure to convert the light source into a far-field light source for laser beam expansion, a large aspect ratio circular hole 4 to be detected, and an observation object; a high-precision rotating platform 5 for placing the measured component in different tilt postures during the measurement process; a converging lens 6 for converging parallel light; and a camera sensor 7 for displaying the diffraction fringe pattern.

[0035] The aspect ratio is the ratio of a hole's depth to its diameter. This ratio describes the hole's geometric characteristics. For example, if a microhole has a diameter of 1 mm and a depth of 10 mm, its aspect ratio is 10:1. This type of microhole is called a high aspect ratio microhole because the depth is much greater than the diameter.

[0036] Fraunhofer diffraction, a phenomenon described by Fraunhofer optics, occurs when light waves encounter obstacles or pass through apertures during propagation. As a form of diffraction, Fraunhofer diffraction primarily focuses on the behavior of light waves in the near field, where the distance between the light source and the observation point is relatively close.

[0037] An aperture stop is an optical element that limits the propagation of light at a specific position in an optical system. Its main function is to control the size and shape of the light beam entering the optical system.

[0038] This embodiment provides a method for detecting the inner diameter and depth of a microhole with a large aspect ratio based on Fraunhofer diffraction, including:

[0039] Step 1: Adjust the optical path to be coaxial

[0040] After fixing the laser, adjust the components in the optical path until the optical path is coaxial. Place the circular hole to be measured perpendicular to the optical axis and fix it on a high-precision rotating platform to form a clear concentric diffraction image distributed in the radial direction on the camera sensor. Ensure that the image clarity is high enough.

[0041] Step 2: Calculate the inner diameter of the circular hole

[0042] The distance x between the first-order dark fringe and the central bright spot on the camera sensor at this time is obtained according to the Fraunhofer circular aperture diffraction calculation formula:

[0043]

[0044] Where a is the radius of the circular hole with aspect ratio, Indicates the angle between the main light reaching the first-order dark fringe and the optical axis. λ represents the wavelength of the incident light, and the inner diameter of the circular hole is calculated from this formula;

[0045] Step 3: Tilt the microwell

[0046] After measuring the inner diameter of the circular aperture, use a high-precision rotating platform to tilt the aperture at a certain angle β. The diffraction fringes displayed on the camera sensor will become elliptical. At this time, projecting the circular aperture along the optical axis will produce an elliptical distribution. The length of the major axis remains unchanged and is still the diameter a of the circular aperture. However, the minor axis will change due to the tilt angle. The length of the minor axis is recorded as b. Calculate the minor axis length b again through step 1. The calculation formula is:

[0047]

[0048] where x bis the distance between the first-order dark pattern and the central bright spot on the camera sensor in the direction of the minor axis of the ellipse; then, according to the geometric relationship between the major axis and the minor axis, such as Figure 2 As shown, we can get:

[0049]

[0050] And through the following formula and the accuracy of the high-precision rotating platform, the measurement error of the circular hole depth is obtained:

[0051]

[0052] The preferred embodiments of the present invention are described in detail above, but the present invention is not limited to the above embodiments. Various changes can be made within the knowledge of ordinary technicians in this field without departing from the scope of the present invention.

[0053] Many other changes and modifications can be made without departing from the spirit and scope of the present invention. It should be understood that the present invention is not limited to the specific embodiments, and the scope of the present invention is defined by the appended claims.

Claims

1. A device based on Fraunhofer circular aperture diffraction, characterized in that: The device comprises a laser (1), and a first lens (2), an aperture stop (3), a second lens (4), a large aspect ratio circular hole (5), a converging lens (6), and a camera sensor (7) which are sequentially arranged and distributed along the optical axis of the laser (1); A high-precision rotating platform (8) is installed at the lower end of the large aspect ratio circular hole (5), and the high-precision rotating platform (8) controls the measured component to be in different tilt postures. The first lens (2) and the second lens (4) are combined to form a Kepler telescope structure.

2. The device based on Fraunhofer circular aperture diffraction according to claim 1, characterized in that: The laser (1) is used to generate Fraunhofer diffraction as a structured light source; the aperture stop (3) is used to perform spatial filtering; the first lens (2) and the second lens (4) are located in front of the circular hole to form a Kepler telescope structure for laser beam expansion; the converging lens (6) is located behind the circular hole and is used to converge parallel light and form an image on a camera sensor; the measured component is fixed on a platform by a clamping device, and a high-precision rotating platform (8) is used to place the measured component in different tilt postures during the measurement process; the camera sensor (7) is used to directly capture the diffraction image.

3. A method for detecting the inner diameter and depth of a micropore with a large aspect ratio based on Fraunhofer diffraction, characterized in that: The method is applied to the device according to any one of claims 1 to 2, and the method includes: Step 1: Adjust the optical path to be coaxial After fixing the laser, adjust the components in the optical path until the optical path is coaxial. Place the circular hole to be measured perpendicular to the optical axis and fix it on a high-precision rotating platform to form a clear concentric diffraction image distributed in the radial direction on the camera sensor. Ensure that the image clarity is high enough. Step 2: Calculate the inner diameter of the circular hole The distance x between the first-order dark fringe and the central bright spot on the camera sensor at this time is obtained according to the Fraunhofer circular aperture diffraction calculation formula: Where a is the radius of the circular hole with aspect ratio, Indicates the angle between the main light reaching the first-order dark fringe and the optical axis. λ represents the wavelength of the incident light, and the inner diameter of the circular hole is calculated from this formula; Step 3: Tilt the hole After measuring the inner diameter of the circular aperture, use a high-precision rotating platform to tilt the aperture at a certain angle β. The diffraction fringes displayed on the camera sensor will become elliptical. At this time, projecting the circular aperture along the optical axis will produce an elliptical distribution. The length of the major axis remains unchanged and is still the diameter a of the circular aperture. However, the minor axis will change due to the tilt angle. The length of the minor axis is recorded as b. Calculate the minor axis length b again through step 1. The calculation formula is: where x b is the distance between the first-order dark pattern and the central bright spot on the camera sensor in the direction of the minor axis of the ellipse; then, based on the geometric relationship between the major axis and the minor axis, we get: And through the following formula and the accuracy of the high-precision rotating platform, the measurement error of the circular hole depth is obtained:

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