Borescope calibration method and matched portable calibration device

Abstract

The invention discloses a borescope calibration method and a matched portable calibration device, and belongs to the technical field of nondestructive testing and metering testing. The device comprises a base, a sliding block, a sliding base, a transmission mechanism, a line pattern standard ruler, a test line locking device and a standard block set (a two-dimensional resolution plate and a height and depth step gauge), can realize precise control of relative positions of a probe and a standard block, and supports field and outfield use. The calibration method comprises the steps of preparation before calibration, implementation of ten calibration items and data recording and analysis, and coverage of core parameters such as X / Y / Z three-axis indication error, depth of field, probe illumination and field angle through standardized processes such as environment quantitative control and multi-point repeated measurement. The borescope calibration method fills the blank of borescope calibration standards in China, reduces manual operation errors, improves the comprehensiveness, repeatability and traceability of calibration, is compatible with various borescopes, is suitable for the industries of aerospace, precision machinery and the like, and also can be referenced and implemented in the medical field.

Description

Technical Field

[0001] This invention belongs to the field of nondestructive testing and metrology technology, specifically relating to a calibration method for a borescope (industrial endoscope) and a matching portable calibration device. It is particularly suitable for the calibration of precision testing equipment in industries such as aerospace, engines, and precision machinery, and can also be used as a reference in other fields such as medicine. Background Technology

[0002] As a core tool for non-destructive testing, borescopes play an irreplaceable role in detecting hidden defects and identifying unwanted materials in assemblies in fields such as aviation, energy, and power. Their measurement accuracy directly affects the accuracy of quantitative analysis of cracks in critical components such as aero-engine blades and various pipes, thus influencing the safety of equipment maintenance decisions.

[0003] Currently, borescopes lack dedicated calibration methods and supporting devices. Most test or calibration reports fail to meet the basic dimensional error requirement of ≤0.2%, and do not cover calibration of key items such as depth of field, field of view, and probe bending angle. Existing performance testing methods have significant limitations: the testing process relies on manual calibration using manufacturer-issued calibration blocks, adjusting parameters only based on qualitative requirements such as "adjusting the lens to make the image clear," without quantitative constraints on key parameters such as the relative distance and angle between the probe and the calibration block, and light intensity. This heavily relies on the operator's subjective judgment, easily leading to measurement deviations. Variables such as illumination, temperature, and vibration in the testing environment are not strictly controlled, further amplifying dimensional measurement errors. While existing solutions provide quantitative evaluation of some geometric parameters, they lack a systematic analysis of optical characteristics, do not establish a complete error tracing model, and do not cover Z-axis (depth direction) measurement errors. Furthermore, existing calibration devices are mostly designed for medical endoscopes, which do not support comprehensive borescope calibration and are too large to meet the needs of various scenarios such as test sites and outdoor environments.

[0004] To address the aforementioned issues, it is necessary to design a set of borehole probe calibration specifications and supporting hardware calibration devices based on quantitative control and system modeling, and to overcome the shortcomings of existing methods through standardized procedures and precision tooling. Summary of the Invention

[0005] The purpose of this invention is to provide a borehole probe calibration method, filling a gap in domestic standards in related fields; at the same time, it provides a portable borehole probe calibration device and standard block kit, enabling high-precision calibration of core performance parameters of industrial borehole probes such as three-dimensional measurement dimensions, depth of field, probe illuminance, field of view, and bending angle, compatible with various borehole probes, and supporting calibration needs in multiple scenarios.

[0006] The technical solution of this invention: To achieve the above-mentioned objectives, this invention provides a portable calibration device for a borescope, comprising a base, a sliding block, a sliding base, a test line lock, a sliding base lock, a gear handle, a gear, a rack, and a linear scale. The base is provided with a guide slot, and the sliding base is slidably connected to the base through the guide slot. The sliding block is fastened to the sliding base by a sliding block fixing screw. The sliding block has a test line guide hole, and the test line lock is located in the Z-direction threaded hole at the front end of the sliding block. The rack is fixed to the bottom surface of the sliding base and meshes with the gear. The gear, gear handle, and gear shaft are fixedly connected. The linear scale is fixed to the surface of the base, and the 0 initial scale line is located on the same ZY plane as the front surface of the base.

[0007] Furthermore, the base has screw holes at the bottom, the flatness of the bottom surface is better than level 3, and the surface roughness of the guide slot is better than Ra0.8μm; the surface roughness of the guide slot of the sliding base is better than Ra0.8μm, and it can slide smoothly along the X direction of the base.

[0008] Furthermore, the sliding block is made of high-definition transparent acrylic, and multiple test line guide holes of different sizes are arranged in parallel. The front end of the lens is flush with the front end face of the sliding block. The test line locker achieves stepless adjustment of the fixed position of the test line through a threaded connection.

[0009] Furthermore, the line pattern of the standard ruler has a line pattern range of 0-100mm, a resolution of 1mm, and an error between the initial 0 mark and the front surface of the base ≤0.1mm; the gear and rack mesh to drive the sliding base, and the travel error is ≤0.02mm / 10mm.

[0010] Furthermore, it also includes a standard block set, which consists of a two-dimensional resolution plate and a height and depth step gauge. The two-dimensional resolution plate is a national standard A1 resolution plate, which is etched with straight line segments with a line width of 0.005-0.5mm and circles with a diameter of 0.01-5mm. The height and depth step gauge has five levels of steps with a width of ±0.1mm, ±0.5mm, ±1mm, ±2mm, and ±5mm.

[0011] In another aspect, the present invention also proposes a borescope calibration method, employing a portable calibration device designed as described above, comprising the following steps: Preparation before calibration: Assemble the portable calibration device, fix the standard block set, and control the calibration environment temperature to 15℃-35℃ and humidity ≤85%; The calibration items include: calibration of optimal working distance range, X / Y axis indication error, Z axis indication error, probe illuminance, lens diopter, field of view, bending angle, working length, working outer diameter, and resolution; Data recording and analysis: Record environmental parameters, measured values, and error values, and perform uncertainty analysis.

[0012] Furthermore, for the X / Y axis indication error calibration, five different line width measurement points are selected, and each point is measured three times and the average value is taken; for the Z axis indication error calibration, five different height / depth measurement points are selected, and each point is measured three times and the average value is taken.

[0013] Furthermore, the probe illumination calibration requires turning off the ambient light source, with the ambient illumination below 80 lx, adjusting the borehole probe light source to maximum brightness, and taking the average value after three measurements; the field of view is measured using the distance method or the goniometer method, and the average value is taken after three measurements.

[0014] Furthermore, the resolution calibration is performed using a 220V / 15W incandescent lamp for illumination. The center of the field of view is observed through a monitor, and the values ​​of the best stripes in the same group of four directions on the A1 resolution plate that can be clearly distinguished are recorded.

[0015] Furthermore, the uncertainty includes Type A repeatability standard deviation and Type B line gauge accuracy, slider positioning error, and gear rack transmission error, with an expanded uncertainty (k=2) of ±0.12 mm.

[0016] The beneficial effects of this invention are: Portability of the device: The integrated structural design can be stored in a customized box, supporting on-site and field use, and solving the problems of large size and inconvenience of moving traditional devices.

[0017] Comprehensive calibration: Through a set of three-dimensional multi-parameter standard blocks, it achieves X / Y / Z three-axis indication error calibration, covering multiple dimensions such as optical characteristics, geometric parameters, and working performance, filling the gap that traditional tools only support two-dimensional calibration.

[0018] Standardized operation: By using quantitative environmental control, precision transmission and positioning mechanisms, and multi-point repetitive measurement processes, subjective operations are transformed into standardized steps, reducing X / Y axis measurement errors by more than 50% and improving calibration traceability and repeatability.

[0019] Wide compatibility: Compatible with various borescopes such as fiber, optical, and electrical ones. The test line guide holes can be designed in multiple sizes to meet the calibration requirements of different models of equipment.

[0020] Filling the standard gap: Establishing a complete calibration standard for borescopes will provide a unified technical basis for metrology institutions, manufacturers, and third-party testing organizations, and promote the mutual recognition of test results within the industry. Attached Figure Description Figure 1 This is a schematic diagram (front view) of the overall structure of the calibration device. The components include: test lock 1, sliding block 2, sliding block fixing screw 3, base 4, sliding base 5, rack 6, gear 7, gear shaft 8, gear handle 9, sliding base lock 10, guide slot 11, line standard ruler 12, and test line guide hole 13.

[0021] Figure 2 This is a schematic diagram (3D view) of the overall structure of the calibration device. Figure 3 Schematic diagram of the Z-axis dimension calibration standard block; Figure 4 This is a schematic diagram of a light shield; Figure 5 Schematic diagram of field of view measurement using the distance method Among them, A-pattern plate, B-hole probe lens, β-field of view, D-pattern plate diameter, L-distance from lens to pattern plate; Figure 6 This is a schematic diagram of measuring the field of view using the goniometer method. Detailed Implementation

[0022] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0023] The technical solution of the invention comprises two parts: a hardware system and a calibration method, as detailed below: (a) Hardware System The hardware system includes a portable borescope calibration device and a set of standard blocks. The portable borescope calibration device consists of a test locker 1, a sliding block 2, a sliding block fixing screw 3, a base 4, a sliding base 5, a rack 6, a gear 7, a gear shaft 8, a gear handle 9, a sliding base locker 10, a guide slot 11, a line standard ruler 12, and a test line guide hole 13. The set of standard blocks consists of a two-dimensional resolution plate (XY axis dimension calibration standard block) and a height and depth step gauge (Z axis dimension calibration standard block).

[0024] Base: Used to fix the entire device. It has a bottom counterweight and screw holes, which can be fixed to the workbench with M4 or M6 screws. The flatness of the bottom surface is better than grade 3. It is equipped with a guide slot with a surface roughness better than Ra0.8μm, so that the sliding base can slide smoothly in the X direction.

[0025] Sliding base: It is equipped with a guide slot corresponding to the base. The surface roughness of the slot is better than Ra0.8μm. It is installed on the base through the guide slot and can slide along the X direction, driving the sliding block to move.

[0026] Sliding block: It is fastened to the sliding base by the sliding block fixing screw (2 pairs recommended). It has a smooth test line guide hole along the X direction to adapt to the commonly used test lines of the borehole probe. Multiple different sizes can be set in parallel to improve compatibility. The sliding block is made of high-definition transparent acrylic. The front end of the lens is flush with the front end of the sliding block. The test line is fixed by the test line locker.

[0027] Test lead locker: The sliding block has a threaded hole along the Z direction near the front end face. The lower half of the test lead locker is machined with a corresponding external thread. The test lead is fixed by tightening downward through the threaded hole, which can achieve stepless adjustment of the fixed position.

[0028] Sliding base locking device: The front end is flat, and the axial surface is machined with external threads to match the threaded hole on the base. After tightening, the front end face contacts the sliding base to apply pressure and fix the position of the sliding base relative to the base.

[0029] Transmission mechanism: The rack is bonded or mechanically fixed to the bottom surface of the sliding base and meshes with the gear; the gear, gear handle and gear shaft are fixed and do not rotate relative to each other, rotating the gear handle can drive the rack, sliding base and sliding block to move in the X direction.

[0030] Linear standard ruler: Fixed to the base surface, with etched or printed 0-100mm range and 1mm resolution line standard. The initial 0 mark on the side is located on the same ZY plane as the front surface of the base, with an error ≤0.1mm.

[0031] Standard block set: Two-dimensional resolution board: The national standard A1 resolution board is selected. The center distance deviation of the bright (dark) lines of each unit is ±5%, the difference in the distance deviation between adjacent units is within ±5%, the line width deviation is 10%, and multiple sets of straight line segments with line width of 0.005-0.5mm and circles with diameter of 0.01-5mm are etched for XY axis dimension calibration.

[0032] Height and Depth Step Gauge: It is machined with five levels of raised steps (0.1mm, 0.5mm, 1mm, 2mm, 5mm) and five levels of recessed steps (-0.1mm, -0.5mm, -1mm, -2mm, -5mm). The shape is round or square, and it is used for Z-axis dimension calibration.

[0033] (II) Calibration Method Before calibration, the following equipment is required: a Class I or Class II illuminance meter with a measurement range of 0–200 klx, a goniometer with a measurement range of 0–25 m⁻¹ and a maximum permissible error of ±0.01 m⁻¹, a goniometer with a measurement range of 0–360° and a maximum permissible error of ±0.2°, a vernier caliper with a graduation of 0.05 mm, a Class II steel tape measure with a measurement range of 0–5 m, and a light shield customized according to the shape of the sliding block.

[0034] Preparation before calibration Hardware assembly: Place the base on a workbench with a flatness better than level 3, and fix it with screws if necessary; insert the sliding base into the base guide slot, and fasten the sliding block to the sliding base with fixing screws; insert the borescope test lead (including lens) into the test lead guide hole, with the front end of the lens flush with the front end of the sliding block, and fix it with the test lead locker; fix the standard block set to the ZY plane at the front end of the base, ensuring that it is flush with the front surface of the base.

[0035] Environmental and equipment checks: The calibration environment temperature is controlled between 15℃ and 35℃, the humidity is ≤85%, and there is no strong direct light or electromagnetic interference; turn off the ambient light source, check the appearance of the borescope, the cleanliness of the lens, the illumination spot, the direction markings of the field of view, etc., and ensure that there are no abnormalities, and that the image storage and other functions are normal.

[0036] Calibration Project Implementation Steps Optimal working distance range (depth of field range): Set the lens illumination to medium level, fix a special ruler or resolution board at the 0 mark of the slider, adjust the distance between the lens and the ruler using the gear handle, and record the shortest depth of field where lines can be clearly distinguished and the longest depth of field where they are about to become blurred. The two constitute the optimal working distance range.

[0037] X / Y axis indication error calibration: Fix the resolution plate to the front face of the base, select 5 measurement points with different line widths in each direction, and record the theoretical value Ls; move the slider to the shortest depth of field distance and lock it, fine-tune the standard block so that the measurement point is located in the center of the monitor, record the value displayed by the device, repeat the measurement 3 times and take the average value Li, and calculate the error.

[0038] Z-axis indication error calibration: Fix the height and depth step gauge to the front end of the base, select 5 measurement points with different heights / depths, and record the theoretical value Zs; move the sliding block to the shortest depth of field distance and lock it, use the 3D measurement function to record the displayed value Zi, repeat the measurement 3 times and take the average value, and calculate the error.

[0039] Probe illuminance: Fix the light shield, turn off the ambient light source (ambient illuminance is below 80 lx), place the illuminance meter probe at the shortest depth of field position, adjust the borehole probe light source to the maximum brightness, record the illuminance count value after it stabilizes, and repeat 3 times to take the average value.

[0040] Lens diopter: Place the diopter tube over the lens, rotate the diopter adjustment ring, check the adjustment function, and record the diopter value.

[0041] Field of view: The distance method or the goniometer method is used, and the average value is taken after 3 measurements. The distance method calculates the field of view β by measuring the diameter D of the pattern board A and the distance L from the lens to the pattern board. The goniometer method takes the center of the lens end face as the center and reads the goniometer scale value on the diagonal of the monitor.

[0042] Bending angle: With the main hose of the borehole probe in a straight position, operate the bending handwheel to bend the angle up, down, left, and right to the maximum angle, and use a protractor to measure the maximum angle value in four directions.

[0043] Working length: The total length from the main (flexible) tube to the probe is measured using a steel tape measure.

[0044] Working outer diameter: Measure the maximum outer diameter of each component from the main (flexible) tube to the probe using a vernier caliper.

[0045] Resolution: Fix the resolution plate to the front end of the base, move the sliding block to the specified working distance, illuminate with a 220V / 15W incandescent lamp, observe the center of the field of view through the monitor, and record the values ​​of the best stripes in the same group of four directions of the A1 resolution plate that can be clearly distinguished.

[0046] Data recording and uncertainty analysis: The calibration record sheet includes environmental parameters, measured values ​​of each item, error values, and pass / fail criteria, and can be accompanied by image records; the uncertainty includes Type A (standard deviation of repeated measurements ≤ 0.02 mm) and Type B (accuracy of line standard ruler ± 0.1 mm, sliding block positioning error ± 0.05 mm, gear and rack transmission error ≤ 0.02 mm / 10 mm stroke). The combined uncertainty is calculated according to the formula, and the expanded uncertainty (k=2) is ± 0.12 mm.

[0047] Example 1: The hardware of the present invention includes a portable calibration device for a borescope and a set of standard blocks.

[0048] The portable calibration device for borescopes consists of a base, a sliding block, a sliding base, a test line lock, a sliding base lock, a gear handle, a gear, a rack, a line gauge, and a sliding block fixing screw.

[0049] The base is used to fix the entire device. The base has a counterweight at the bottom and, if necessary, screw holes can be provided to fix it to the worktable surface with screws, preventing device displacement and measurement errors. The flatness of the bottom surface is better than grade 3; it should be placed on a worktable with good flatness during operation to avoid affecting the measurement results. The base has a guide slot structure; the surface roughness of the slot should be better than Ra0.8μm, allowing the sliding base to slide smoothly along the X direction within the base.

[0050] The sliding block is fixed to the sliding base by sliding block fixing screws. Multiple pairs of sliding screws can be set to increase the tightness of the connection. The sliding base is provided with a guide slot corresponding to the base. The surface roughness of the slot should be better than Ra0.8μm. It is installed on the base through the guide slot and can slide smoothly on the base in the X direction along the guide slot, thereby driving the sliding block to move.

[0051] The sliding block has a smooth test line guide hole along the X direction, with the hole diameter adapted to the test lines of commonly used borescopes. The test line and the lens at the end of the test line are placed in the test line guide hole, with the front end of the lens aligned with the front face of the sliding block and fixed by the test line locker. The lens slides along with the sliding block as it slides. The sliding block is made of high-definition transparent acrylic, allowing users to easily observe the position and status of the test line and lens.

[0052] It should be noted that if the test lead guide hole is too large relative to the diameter of the test lead, it may affect the fixation of the test lead. To expand the scope of application, multiple test lead guide holes of different sizes can be set in parallel to improve compatibility.

[0053] The test lead lock is used to fix the test lead. The sliding block has a threaded hole in the Z direction near the front end face. The lower half of the test lead lock is machined with a corresponding external thread. By tightening downward through the threaded hole, the test lead in the test lead guide hole can be fixed, and the fixed position can be infinitely adjusted.

[0054] The sliding base lock is used to fix the position of the sliding base relative to the base. The front end of the sliding base lock is flat, and the axial surface is machined with external threads to cooperate with the threaded hole on the base. During calibration, the sliding block needs to be moved along the X-axis to several calibration points. When it is moved to a certain calibration point, the sliding base lock is rotated to tighten it, so that the front end face contacts the sliding base to apply pressure and fix it.

[0055] The gear and rack, along with a handle connected to the gear shaft, work together to provide displacement for the sliding block. The rack is bonded or mechanically fixed to the sliding base and engages with the gear; the gear, the dimensional rotating handle, and the gear shaft are fixed without relative rotation. When the sliding block needs to slide to a certain calibration point on the base, the gear handle is manually rotated, causing the rack to move along the X-axis, thereby moving the sliding base and the sliding block to the designated position along the X-axis.

[0056] The linear scale is used to provide a standard dimension in the X-axis direction during calibration. The linear scale has etched or printed linear markings ranging from 0-100 mm with a resolution of 1 mm. It is fixed to the base surface, with the initial 0-degree mark on its side aligned with the front surface of the base (ZY plane). When the calibration point needs to be changed, the test line lock secures the test line of the borescope being calibrated and its front lens. Rotating the gear handle moves the sliding block (front face) to align with the corresponding calibration point on the linear scale, ensuring the distance between the lens and the standard block is the required distance for the standard calibration point. The front plane (ZY plane) of the sliding base is in close contact with the standard block, guaranteeing an initial distance of zero.

[0057] The standard block set consists of a two-dimensional resolution plate (XY axis dimension calibration standard block) and a customized height and depth step gauge (Z axis dimension calibration standard block). The XY axis dimension calibration standard block is used to calibrate the length measurement error in the XY direction of the borehole probe. Several sets of straight line segments with standard line width and depth are etched on the XY axis dimension calibration standard block. The line width can be set to (0.005-0.5) mm, and the resolution and accuracy can refer to the relevant national standards for resolution plates. Several sets of circles are etched using the same process, and the diameter range can be (0.01-5) mm as needed.

[0058] The Z-axis dimension calibration standard block is used to calibrate the length measurement error in the Z direction of the borehole probe. The Z-axis dimension calibration standard block is machined with five levels of raised steps with heights of 0.1mm, 0.5mm, 1mm, 2mm, and 5mm, and five levels of recessed steps with depths of -0.1mm, -0.5mm, -1mm, -2mm, and -5mm. The shape can be set to round or square as needed.

[0059] This invention includes a borehole probe calibration method, which, in conjunction with the hardware of this invention, enables the calibration of the borehole probe. In addition to the portable borehole probe calibration device and the standard block kit, the following products are also required: illuminometer, angle meter, goniometer, vernier caliper, and steel tape measure.

[0060] I. Preparations before calibration 1. Hardware and Equipment Preparation Once assembled, the portable borescope calibration device can be stored in a custom case for portable use without further disassembly.

[0061] First, place the base on a workbench with a flatness better than grade 3, ensuring complete contact between the bottom surface and the workbench. If additional fixation is required, screw holes are provided at the bottom of the base; use M4 or M6 screws to lock the base to the workbench. Check the surface roughness of the guide slot (Ra≤0.8μm) to ensure smooth sliding of the sliding base. Insert the sliding base into the guide slot of the base, ensuring no wobble along the ZY axis. Secure the sliding block to the sliding base using the sliding block fixing screws (two pairs of screws are recommended). Align the test lead (including lens) of the borescope with the test lead guide hole of the sliding block, with the tip of the lens flush with the front face of the sliding block. Screw in the lower half of the test lead lock. Adjust the height of the test line locker by opening the Z-axis threaded hole at the front end of the sliding block, ensuring the bottom of the locker contacts the test line. Tighten the locker to prevent the test line from moving or rotating. Check if the lens is centered to avoid measurement deviation. Fix the rack to the bottom surface of the sliding base, with the gear meshing with the rack. Secure the rack, gear shaft, and gear handle in sequence without relative rotation. Confirm that the rack and gear mesh without jamming, and that the sliding base moves smoothly when the gear handle is rotated. Fix the line scale to the base surface, ensuring that the initial 0-degree mark on the side is on the same plane (ZY plane) as the front surface of the base, with an error ≤0.1mm. Check the clarity of the line scale, ensuring a resolution of 1mm.

[0062] Next, prepare a set of standard blocks. The resolution board should be an A1 resolution board as specified in the national standard. The center-to-center distance deviation of the light (or dark) lines in each unit should be ±5%, and the difference in the center-to-center distance deviation between two adjacent light (or dark) lines should be within ±5%. The line width deviation of the light (or dark) lines should be 10%. Place the height and depth step gauge or resolution board at the front end of the base (ZY plane), flush with the front surface of the base. Use a magnetic base or clamp to fix the standard blocks to prevent movement.

[0063] Finally, prepare the other equipment required for calibration: Illuminance meter: Measurement range (0~200) klx, Class I or Class II; Angle gauge: measuring range (0~25) m⁻¹, maximum permissible error: ±0.01 m⁻¹; Goniometer: Measurement range 0~360°, maximum permissible error: ±0.2°; Vernier calipers: graduation value 0.05mm; Steel tape measure: measuring range (0~5)m, Class II; Light shield: Customized according to the shape and size of the sliding block, and should not affect the placement of the standard block.

[0064] See attached diagram for a schematic of the sunshade. Figure 4 It is installed at the front end of the sliding block to eliminate the influence of ambient light on lens illumination.

[0065] 2. Environmental and equipment inspection Calibration ambient temperature requirements: 15℃-35℃; humidity requirements: ≤85%; Check that the hardware and equipment are installed correctly and are working properly; Check the following items in order of need: Appearance of borescope: It should be flat, smooth, and free of scratches and burrs. Electroplated parts should have a uniform color and should not have obvious scratches, burn marks, visible cracks, pinholes, pits, spots, or burrs. Painted or powder-coated parts should have a flat, smooth surface with a uniform color and should not have exposed substrate, blistering, peeling, cracking, or other defects.

[0066] Lens cleanliness: Under good lighting, the lens surface is free of obvious stains, scratches, water stains or residues when observed with the naked eye.

[0067] Illumination spot: At the normal working distance, place a white board at the end being measured and illuminate it with immersion transmitted light or the endoscope's built-in light source. Observe it with the naked eye through the eyepiece or monitor. The illumination spot should fill the field of view without obvious bright or dark areas.

[0068] Field aperture direction mark (applicable to fiber optic endoscopes): At the normal working distance, place a whiteboard at the end being measured and illuminate it with immersion light or the endoscope's own light source. When viewed through the eyepiece, the direction of the field aperture arrow indicating the direction mark should be upward.

[0069] Delamination or mold: At the normal working distance, place a white board at the end to be tested, illuminate it with immersion light or the light source of the endoscope, and observe it with the naked eye through the eyepiece or monitor. There should be no obvious delamination or mold.

[0070] Image storage and other functions: All functions work normally.

[0071] II. Calibration Project Implementation Steps The calibration items for different types of industrial endoscopes are shown in Table 1.

[0072] Table 1

[0073] 1. Optimal working distance range (depth of field range) Set the borescope lens illumination to the medium setting (or the commonly used setting). All subsequent calibration items, except for 4. Probe Illumination and the exception notes, should be set to this setting.

[0074] Fix a dedicated ruler or resolution plate (with lines 1.2mm or 0.8mm wide) at the 0 mark of the slider. Adjust the distance between the dedicated ruler and the lens by adjusting the slider using the gear handle, so that the outline of the lines on the dedicated ruler can be distinguished on the borescope monitor. Record the mark that can just be clearly seen as the shortest depth of field. Continue to slide the lens backward, and record the blurred mark as the longest depth of field. Record the two extreme distances of the longest and shortest depth of field as the optimal working distance range (depth of field range).

[0075] 2. X / Y axis indication error calibration Standard block installation: Place the resolution plate on the front face of the base, ensuring that its surface is flush with the front surface of the base, i.e., the 0 mark of the line scale. Select 5 measurement points in each direction on the standard block (e.g., line widths of 0.1mm, 0.2mm, 0.5mm, 1mm, and 2mm) and record their theoretical values ​​Ls. Move the sliding block to the shortest depth of field distance (the calibration data) using the gear handle, tighten the sliding base lock, and fine-tune the position of the standard block so that the measurement point image is located in the center area of ​​the borescope monitor. Record the measurement value displayed by the device, repeat the measurement 3 times, take the average of the three points as the calibration value Li, and calculate the error in this direction according to the following formula. or

[0076] Repeat the above steps to calibrate the error in the other direction.

[0077] 3. Z-axis indication error calibration Standard block installation: Fix the height and depth step gauge to the front end of the base to ensure that its initial surface is flush with the front surface of the base; Select 5 measuring points on the step gauge (e.g., +0.1mm, -0.1mm, +0.5mm, -0.5mm, +2mm) and record their theoretical values ​​Zs; Move the slider to the shortest depth-of-field distance (calibrated for this time) using the gear handle, and tighten the sliding base lock. Using the borescope's 3D measurement function, fine-tune the position of the standard block so that the measurement point image is located in the center area of ​​the borescope monitor. For concave borehole steps (negative depth), ensure that the lens can clearly identify the edge of the concave borehole. Record the displayed depth or height (Zi). Each point is measured three times, and the average value is used as the calibration value Zi. The error in this direction is calculated using the following formula.

[0078] 4. Probe illumination Turn off the ambient light source, ensure the light shield is fixed, place the illuminance meter probe, and move the slider to the shortest depth of field distance (the calibration data) using the gear handle. Tighten the sliding base lock. With the ambient light illuminance below 80 lx, adjust the borescope light source brightness to its maximum value, ensuring the illumination light fills the illuminance meter probe. After the illuminance meter reading stabilizes, record the value. Repeat this method three times and take the average as the measurement value.

[0079] Note: Ambient light intensity values ​​during calibration should be recorded.

[0080] 5. Lens perspective Place the diopter tube over the lens and rotate the diopter adjustment ring back and forth to check if the adjustment function is normal. Measure and record the lens diopter value.

[0081] 6. Field of view Option to use Figure 5 , Figure 6 Any of the methods described herein. Measure the field of view three times and take the average value as the measurement.

[0082] Figure 5 In the diagram, A—pattern plate; B—hole probe lens; β—field of view; D—pattern plate diameter; L—distance from the front edge of the observation optical system to the pattern plate. When the outer edge of the diameter D of the pattern plate A coincides with the circumference of the endoscope's field of view aperture, measure the distance L from the end face of the objective lens probe to the pattern plate, and then proceed according to... Calculate the field of view angle β: like Figure 6 As shown, take the center of the lens end face as the center of the goniometer, adjust the position of the goniometer so that the goniometer scale is imaged on the diagonal of the monitor, and read the scale value of the goniometer from the monitor.

[0083] 7. Bending angle For borehole probes with bending function, straighten the main hose section behind the bending section, operate the bending handwheel to bend the bend upward, downward, left and right to the maximum angle, and use a protractor to measure the maximum angle value in the four directions as the bending angle.

[0084] 8. Working length The working length is the sum of the lengths from the main (flexible) tube to the probe measured with a steel tape measure.

[0085] 9. Working outer diameter Use vernier calipers to measure the maximum outer diameter of each component, from the main (flexible) tube to the probe, to determine the working outer diameter.

[0086] 10. Resolution Fix the resolution plate to the front end of the base, move the sliding block to the specified working distance using the gear handle, illuminate with a 220V / 15W incandescent lamp, and observe the center of the field of view through the monitor. You should be able to clearly distinguish the best stripes in the four directions of the same group on the A1 resolution plate, which is the resolution value.

[0087] III. Data Recording and Uncertainty Analysis The calibration record sheet includes environmental parameters (temperature, humidity, illuminance), measured values ​​of each calibration item, error values, and pass / fail criteria; image records (such as screenshots of Z-axis step measurements) may be attached.

[0088] Uncertainty assessment: Type A uncertainty: Standard deviation of repeated measurements for each item (e.g., standard deviation of 3 measurements of the X / Y axis ≤ 0.02 mm); Type B uncertainty: The accuracy of the line gauge (e.g., ±0.1mm); The sliding block positioning error (e.g., ±0.05mm, originates from the guide slot roughness Ra0.8μm); Gear and rack transmission error (e.g., ≤0.02mm / 10mm stroke).

[0089] Combined uncertainty:

[0090] The expanded uncertainty (k=2) is ±0.12 mm (example).

[0091] Compared with the prior art, the present invention has the following advantages or positive effects. Integrated Portable Calibration Device Structure: A portable calibration device is provided, comprising a base, a sliding block, a sliding base, a test line lock, a sliding base lock, a gear handle, a gear, a rack, a linear scale, and a sliding block fixing screw. Through a precision guide slot and a stepless adjustment mechanism, the relative position of the probe and the standard block or the object being calibrated can be precisely controlled (distance deviation ≤ ±0.1mm), supporting both field and outdoor use.

[0092] 3D Multi-Parameter Calibration Standard Block Set: Includes a 2D resolution plate (for X / Y axis dimension calibration) and a height and depth step gauge (for Z axis depth calibration), covering the 3D measurement error calibration needs of industrial borescopes and overcoming the shortcomings of traditional tools that only support 2D calibration.

[0093] (a) Precision transmission and positioning mechanism: The sliding block moves precisely along the X-axis through a gear-rack transmission system. Combined with the sliding base lock to fix the calibration point position, the relative distance between the probe and the standard block can be precisely adjusted to the preset calibration point (such as the scale position of the line scale).

[0094] (b) Systematic calibration method: Integrates calibration items such as X / Y / Z axis indication error, probe illuminance, field of view, bending angle, and depth of field range, covering optical characteristics (distortion, resolution) and geometric parameters (size, angle), providing a systematic calibration scheme. It is the first to propose a complete calibration process covering optical characteristics (resolution, distortion), geometric parameters (size, angle), and working performance (depth of field, illuminance), filling the gap in domestic standards.

[0095] (c) Standardized procedures in calibration methods: Provide standardized calibration procedures, including environmental checks, hardware installation specifications, multi-point repeated measurements (e.g., taking the average of 3 X / Y axis measurements), error calculation formulas and uncertainty analysis, to reduce human error and improve traceability.

[0096] (d) High adaptability of calibration methods: covering fiber optic, optical, and electrical endoscopes, and can also be used as a reference in medicine.

[0097] (e) Multi-level high-precision coverage of height depth step gauge: Through positive and negative depth symmetrical design, it covers depth measurement and error calibration in the Z-axis direction, solving the limitation of traditional testing that can only calibrate two-dimensional dimensions.

[0098] The calibration method and apparatus proposed in this invention transform subjective operations into a standardized process through quantitative control of environment, distance, and angle, significantly reducing human error (e.g., reducing X / Y axis measurement error by more than 50%). Secondly, by comprehensively covering optical characteristics and geometric parameters through multi-dimensional calibration items, it overcomes the limitations of existing solutions. The portable hardware involved greatly facilitates on-site calibration in the field. Finally, the formulation of the standard fills the gap in domestic industrial endoscope calibration standards, providing a unified technical basis for metrology institutions, manufacturing enterprises, and third-party testing institutions, and promoting industry-wide mutual recognition of test results.

[0099] The above description is merely a specific embodiment of the present invention, providing a detailed description of the invention. Parts not covered herein are conventional techniques. However, the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention. The scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A portable calibration device for a borescope, characterized in that, The system includes a base, a sliding block, a sliding base, a test line locker, a sliding base locker, a gear handle, a gear, a rack, and a linear scale. The base has a guide slot, and the sliding base is slidably connected to the base through the guide slot. The sliding block is fastened to the sliding base by a sliding block fixing screw. The sliding block has a test line guide hole, and the test line locker is located in the Z-direction threaded hole at the front end of the sliding block. The rack is fixed to the bottom surface of the sliding base and meshes with the gear. The gear, gear handle, and gear shaft are fixedly connected. The linear scale is fixed to the surface of the base, and the 0 initial scale line is located on the same ZY plane as the front surface of the base.

2. The portable calibration device for borescopes according to claim 1, characterized in that, The base has screw holes at the bottom, the flatness of the bottom surface is better than level 3, and the surface roughness of the guide slot is better than Ra0.8μm; the surface roughness of the guide slot of the sliding base is better than Ra0.8μm, and it can slide smoothly along the X direction of the base.

3. The portable calibration device for borescopes according to claim 1, characterized in that, The sliding block is made of high-definition transparent acrylic, and multiple test line guide holes of different sizes are arranged in parallel. The front end of the lens is flush with the front end face of the sliding block. The test line locker achieves stepless adjustment of the fixed position of the test line through a threaded connection.

4. The portable calibration device for a borescope according to claim 1, characterized in that, The line pattern of the standard ruler has a line pattern range of 0-100mm and a resolution of 1mm. The error between the initial 0 mark and the front surface of the base is ≤0.1mm. The gear and rack mesh to drive the sliding base, and the travel error is ≤0.02mm / 10mm.

5. The portable calibration device for a borescope according to claim 1, characterized in that, It also includes a standard block set, which consists of a two-dimensional resolution plate and a height and depth step gauge. The two-dimensional resolution plate is a national standard A1 resolution plate, which is etched with straight line segments with a line width of 0.005-0.5mm and circles with a diameter of 0.01-5mm. The height and depth step gauge has five steps with a range of ±0.1mm, ±0.5mm, ±1mm, ±2mm and ±5mm.

6. A method for calibrating a borescope, characterized in that, The portable calibration device according to any one of claims 1-5 includes the following steps: Preparation before calibration: Assemble the portable calibration device, fix the standard block set, and control the calibration environment temperature to 15℃-35℃ and humidity ≤85%; The calibration items include: calibration of optimal working distance range, X / Y axis indication error, Z axis indication error, probe illuminance, lens diopter, field of view, bending angle, working length, working outer diameter, and resolution; Data recording and analysis: Record environmental parameters, measured values, and error values, and perform uncertainty analysis.

7. The borescope calibration method according to claim 6, characterized in that, The X / Y axis indication error calibration selects 5 different line width measurement points, and each point is measured 3 times and the average value is taken; the Z axis indication error calibration selects 5 different height / depth measurement points, and each point is measured 3 times and the average value is taken.

8. The borescope calibration method according to claim 6, characterized in that, The probe illumination calibration requires turning off the ambient light source. When the ambient illumination is below 80 lx, adjust the borehole probe light source to the maximum brightness and take three measurements to obtain the average value. The field of view is measured using the distance method or the goniometer method, and the average value is obtained after three measurements.

9. The borescope calibration method according to claim 6, characterized in that, The resolution calibration was performed using a 220V / 15W incandescent lamp for illumination. The center of the field of view was observed through a monitor, and the values ​​of the best stripes in the same group of four directions on the A1 resolution plate that could be clearly distinguished were recorded.

10. The borescope calibration method according to claim 6, characterized in that, The uncertainty includes Type A repeatability standard deviation and Type B accuracy of line gauge, sliding block positioning error, and gear and rack transmission error, with an expanded uncertainty (k=2) of ±0.12 mm.

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