Method and device for detecting internal thread of water heating valve pipe fitting

Abstract

The application discloses a water heating valve pipe fitting inner thread detection method and device. In view of the problems that liquid remaining in the inner thread hole is easy to cause reflection misjudgment, and conventional blowing is easy to cause water mist to blind the lens, the method adopts a coaxial detection probe comprising a central optical lens, a middle layer negative pressure suction channel and an outer layer positive pressure channel. During detection, the probe is inserted into the pipe fitting inner hole and is tightly sealed; the outer layer channel sprays periodic high-frequency pulse airflow, which strips and atomizes the liquid remaining in the tooth root into droplets; the middle layer negative pressure channel is synchronously opened, and a suction air vortex is formed in front of the lens to discharge the droplets outside the pipe; in addition, a phase locking relationship between lens exposure and pulse airflow is established, the lens stroboscopic exposure is controlled in a trough phase window of the airflow cycle to collect images, and then profile parameters are extracted for quality determination. The application can effectively eliminate liquid reflection and water mist shielding interference, and then realize high-precision detection of the inner thread.

Description

Technical Field

[0001] This invention belongs to the field of valve testing technology, specifically a method and device for testing the internal threads of plumbing valves and fittings. Background Technology

[0002] After machining processes (such as tapping) are completed, plumbing valves and fittings must undergo rigorous inspection to ensure the sealing reliability of subsequent assembly. This inspection must cover key dimensions such as the thread profile, pitch diameter, and thread length of the internal threads, as well as the presence of defects such as broken threads and burrs. In recent years, with the development of industrial automation, non-contact visual inspection technology that utilizes optical probes to penetrate deep into pipe fittings is gradually replacing traditional manual inspection and becoming the industry mainstream.

[0003] However, due to the unavoidable use of cutting and cleaning fluids during the cutting or cleaning processes, and the fact that the internal threads of plumbing fittings are mostly narrow, continuous V-shaped or trapezoidal grooves, liquid easily remains in the dead corners at the bottom of the threads under the combined effects of fluid surface tension and capillary action, forming stubborn micro-liquid pools. When conventional optical probes acquire images, residual droplets against a brass or stainless steel background will produce strong specular reflections, severely obscuring the true thread bottom contour and causing visual algorithms to misidentify them as metal burrs or machining foreign objects.

[0004] Therefore, how to achieve more accurate quality inspection and analysis of the internal threads of water heating valves and fittings is a technical problem that needs to be solved. Summary of the Invention

[0005] In order to solve at least one of the technical defects mentioned in the background art, the present invention aims to provide a method and device for detecting the internal threads of water heating valves and fittings.

[0006] The first aspect of the present invention provides a method for detecting the internal threads of plumbing valves and fittings, comprising: The coaxial testing probe is inserted into the internal threaded hole of the plumbing fitting to be tested to a set depth, so that the root of the coaxial testing probe fits and seals with the port of the plumbing fitting; wherein, the coaxial testing probe includes a central optical lens, a middle negative pressure suction channel and an outer positive pressure channel; High-frequency pulsed airflow, which is periodically varied, is injected into the internal threaded hole through the outer positive pressure channel. The high-frequency pulsed airflow swirls and flows along the spiral groove of the internal threaded hole to peel off the residual liquid in the internal threaded hole and atomize it into droplets. Simultaneously open the middle layer negative pressure suction channel to form an inward suction vortex in front of the central optical lens, suck the droplets into the middle layer negative pressure suction channel and discharge them to the outside of the water heating pipe fitting to be tested; A phase-locked relationship is established between the exposure trigger signal of the central optical lens and the pulse control signal of the high-frequency pulsed airflow. Within a single pulse cycle of the high-frequency pulsed airflow, a preset trough phase window is extracted as a trigger condition. The central optical lens is controlled to perform stroboscopic exposure within the trough phase window to acquire an internal thread image, and the contour parameters of the internal thread image are extracted for quality judgment.

[0007] A second aspect of the present invention provides a device for detecting the internal threads of plumbing valves and fittings, comprising: The probe positioning module is used to insert the coaxial detection probe into the internal threaded hole of the plumbing fitting to be tested to a set depth, so that the root of the coaxial detection probe fits and seals with the port of the plumbing fitting to be tested; wherein, the coaxial detection probe includes a central optical lens, a middle negative pressure suction channel and an outer positive pressure channel. The positive pressure injection module is used to inject a periodically changing high-frequency pulsed airflow into the internal threaded hole through the outer positive pressure channel, so that the high-frequency pulsed airflow flows along the spiral groove of the internal threaded hole and swirls against the wall to strip off the residual liquid in the internal threaded hole and atomize it into droplets. The negative pressure suction module is used to simultaneously open the middle layer negative pressure suction channel, forming an inward suction vortex in front of the central optical lens, sucking the droplets into the middle layer negative pressure suction channel and discharging them to the outside of the water heating pipe fitting to be tested. The phase-locked analysis module is used to establish a phase-locked relationship between the exposure trigger signal of the central optical lens and the pulse control signal of the high-frequency pulsed airflow. Within a single pulse cycle of the high-frequency pulsed airflow, a preset trough phase window is extracted as a trigger condition. The central optical lens is controlled to perform stroboscopic exposure within the trough phase window to acquire an internal thread image, and the contour parameters of the internal thread image are extracted for quality judgment.

[0008] This invention utilizes a pulsed airflow injected through an outer positive pressure channel, which swirls along the thread groove wall to effectively remove residual liquid from the dead corners at the bottom of the thread, thereby effectively eliminating image misjudgment caused by liquid specular reflection. Simultaneously, the middle negative pressure suction cyclone promptly discharges atomized droplets outside the tube. Combined with phase-locked stroboscopic exposure technology using a trough phase window, it also overcomes the problem of conventional airflow purging causing water mist to diffuse inside the hole, resulting in optical blindness of the lens. It accurately captures images while maintaining a high level of cleanliness in the inspection environment, significantly improving the image clarity and quality inspection accuracy of visual inspection of narrow inner holes in plumbing valves and fittings. Attached Figure Description

[0009] Figure 1 This is a schematic diagram of the structure of the coaxial detection probe disclosed in an embodiment of the present invention; Figure 2 This is a schematic diagram of the main process of a method for detecting the internal threads of plumbing valves and fittings disclosed in an embodiment of the present invention; Figure 3This is a schematic diagram of the structure of a plumbing valve and pipe fitting internal thread detection device disclosed in an embodiment of the present invention; Figure 4 This is another structural schematic diagram of a water valve fitting internal thread detection device disclosed in an embodiment of the present invention. Detailed Implementation

[0010] The specific embodiments of this disclosure will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are for illustration and explanation only and are not intended to limit this disclosure.

[0011] This invention provides a method for detecting the internal threads of plumbing valves and fittings. This method can be applied to the quality inspection of plumbing valves and fittings after machining (such as tapping) is completed. It is especially suitable for automated inspection scenarios of fittings with narrow inner diameters, deep and fine thread grooves, and residual cutting fluid or cleaning fluid due to previous cutting or cleaning processes.

[0012] To address the technical problems mentioned in the background section, the method for detecting internal threads of plumbing valves and fittings provided in this embodiment achieves effective removal of residual liquid and stable acquisition of high-quality images by integrating a coaxial detection probe with both air and optical paths, and employing a specific air-optical timing coordination strategy. Please refer to... Figure 2 The method includes the following steps: Step 1: Insert the coaxial testing probe into the internal threaded hole of the plumbing fitting to be tested to a set depth, so that the root of the coaxial testing probe fits and seals with the port of the plumbing fitting; wherein, the coaxial testing probe includes a central optical lens, a middle negative pressure suction channel and an outer positive pressure channel; In this embodiment, the probe is first positioned and sealed. Specifically, the coaxial detection probe is slowly inserted into the internal threaded hole of the plumbing fitting under test along the axial direction until a pre-calibrated depth is reached. It should be noted that this set depth is predetermined based on the total depth of the internal threaded hole of the plumbing fitting under test and the axial distribution range of the thread segment to be tested. For example, when the total depth of the internal threaded hole of the fitting under test is 50 mm, and the effective length of the thread to be tested is concentrated in the axial range of 10 mm to 40 mm from the hole opening, the set depth can be calibrated to a value that allows the focal plane of the central optical lens to precisely cover the midpoint of this detection range. It is understood that by accurately positioning the probe to this set depth, it ensures that the subsequent high-frequency pulsed airflow starts its purging effect from the effective detection start point of the threaded hole, thereby avoiding detection blind spots in the entire thread segment that cannot be reached by the airflow; simultaneously, this positioning method also prevents the probe tip from hitting the bottom of the hole or scratching the inner wall due to excessive insertion, protecting the equipment and the workpiece.

[0013] After the probe reaches the set depth, the root of the coaxial testing probe is brought into close contact with the port of the plumbing fitting to be tested, creating a seal. Specifically, an elastic sealing ring or an expandable flexible sealing airbag can be installed at the root of the probe. Once the probe is in place, axial compression or radial expansion is used to make the sealing element make tight contact with the inner wall or end face of the fitting port, thereby effectively isolating the inside of the internal threaded hole from the external atmospheric environment.

[0014] Through the aforementioned sealing and bonding operation, a controlled micro-closed flow field with stable boundary conditions is constructed within the internally threaded hole. On one hand, the sealing and bonding prevents the high-frequency pulsed airflow ejected from the outer positive pressure channel from directly escaping from the orifice, ensuring that the kinetic energy of the pulsed airflow is directionally transmitted along the extension direction of the spiral groove and maintaining sufficient shear force. This avoids insufficient purging force in the bottom area of ​​the hole due to airflow leakage, which would prevent the effective removal of residual liquid. On the other hand, this sealed boundary also isolates the possibility of dust, fibers, or turbulent air from the external environment entering the flow field within the hole, thereby providing a stable and repeatable controlled environment for subsequent gas-liquid separation, droplet extraction, and optical imaging. It should be understood that without this sealing condition, random disturbances in the external airflow will mix with the purging airflow within the hole, which will not only reduce the effective range of the pulsed airflow but may also introduce external contaminants into the field of view, affecting imaging quality and the reliability of detection results.

[0015] In addition, please see Figure 1 The coaxial detection probe used in this embodiment comprises, from the inside out, a central optical lens, a middle negative pressure suction channel, and an outer positive pressure channel. Due to the narrow diameter and limited axial space of the internal threaded holes in plumbing valves and fittings, a compact coaxial nested layout of these three channels integrates pneumatic cleaning and optical detection functions within a minimal radial dimension. Specifically, the outer positive pressure channel, located at the outermost edge of the probe and having the largest radial dimension, delivers a high-speed pulsed airflow towards the hole wall to perform the stripping and atomization of residual liquid. The middle negative pressure suction channel, situated between the outer positive pressure channel and the central optical lens, creates a backflow vortex in front of the lens to promptly remove atomized products from the field of view. The central optical lens, located at the core of the probe, utilizes the clean medium channel formed in front of the lens by the outer and middle air paths to achieve unobstructed image acquisition.

[0016] Step 2: A periodically varying high-frequency pulsed airflow is injected into the internal threaded hole through the outer positive pressure channel, causing the high-frequency pulsed airflow to swirl and flow along the spiral groove of the internal threaded hole to peel off the residual liquid in the internal threaded hole and atomize it into droplets. After the probe is positioned and sealed, this embodiment further performs a pneumatic stripping operation to remove residual liquid.

[0017] Specifically, a periodically varying high-frequency pulsed airflow is injected into the internally threaded hole through an outer positive pressure channel. Upon entering the hole, this high-frequency pulsed airflow, guided by the channel structure and the hole wall, spirals and flows along the spiral groove of the internally threaded hole, forming a rotating air curtain that propagates forward along a spiral path. It should be noted that, compared to continuous constant-pressure airflow, the high-frequency pulsed airflow used in this invention has a higher peak velocity and peak dynamic pressure at the instant of the rising edge of each cycle, generating a stronger impact shearing effect than continuous constant-pressure airflow. This is particularly crucial for overcoming the surface tension of residual liquid within the microgroove at the tooth root. Simultaneously, the periodic intervals provide the necessary timing window for subsequent negative pressure suction and stroboscopic imaging steps, enabling the entire gas-light synergistic process to be executed in a time-division and orderly manner.

[0018] In this embodiment, after being sheared against the wall by a high-frequency pulsed airflow, the micro-liquid pool remaining in the dead corner of the thread root is stripped into a large number of micron-sized droplets, which then migrate towards the orifice along the direction of the airflow. It is understood that if only a direct-blowing airflow is used, the gas will travel in a straight line along the orifice axis, making it difficult to reach the dead corner area located at the junction of the spiral groove sidewall and the thread root. However, by making the airflow swirl and flow along the spiral groove wall, the airflow path is basically consistent with the extension direction of the thread, thereby enabling thorough sweeping of the inner surface of each thread groove, improving the comprehensiveness and efficiency of liquid stripping.

[0019] Furthermore, to ensure that the high-frequency pulsed airflow can efficiently penetrate the spiral groove rather than generate ineffective rebound at the tooth crest, this embodiment adopts the following preferred configuration for the end structure of the outer positive pressure channel of the probe: Optionally, the outer positive pressure channel has multiple tangential micro-nozzles at its end along the circumferential direction, and the axial tilt angle of the tangential micro-nozzles is adapted to the tooth profile angle of the internal thread hole, so as to guide the high-frequency pulse airflow to smoothly cut into the spiral groove.

[0020] Multiple tangential micro-nozzles are evenly distributed along the circumference at the end of the outer positive pressure channel. "Tangential" means that the jetting direction of each micro-nozzle is obliquely ejected along the tangent of the outer channel circumference, causing the multiple airflows ejected from the nozzles to merge into a single annular airflow rotating around the probe axis within the hole. Simultaneously, each tangential micro-nozzle also has a preset tilt angle in the axial direction, which is adapted to the tooth profile angle of the internal thread hole to be tested. Specifically, the tooth profile angle of the internal thread is typically 55° (Whitworth thread) or 60° (metric thread), and the inclination angle of its tooth flank relative to the pipe axis is called the tooth profile half-angle; the axial tilt angle of the tangential micro-nozzle is set to be approximately consistent with this tooth profile half-angle, making the airflow direction ejected from the nozzle nearly parallel to the tooth flank surface of the spiral groove.

[0021] Through the above structural design, when the high-frequency pulsed airflow is ejected from the tangential micro-nozzle, its tangential component in the circumferential direction drives the airflow to rotate along the orifice wall, while the axial component guides the airflow forward along the spiral groove's direction of rotation. This allows the airflow to enter the spiral groove through a cutting rather than impacting motion. It is understandable that if the axial tilt angle of the tangential micro-nozzle does not match the tooth profile angle—for example, if the tilt angle is too large or too small—a large impact angle will be formed between the airflow and the tooth lateral surface. Some kinetic energy will be wasted in the direction perpendicular to the tooth surface, not only failing to effectively enter the tooth root region but also potentially generating turbulence due to airflow rebound, exacerbating the disordered scattering of droplets. Only when the tilt angle matches the tooth profile angle can the airflow slide into the spiral groove at a smaller incident angle, flowing along the tooth lateral surface towards the tooth root, thereby maximizing the conversion efficiency of airflow kinetic energy into liquid stripping work. This allows even stubborn micro-liquid pools at the bottom of deep and narrow V-grooves to be effectively sheared and carried away by the high-speed airflow.

[0022] Step 3: Simultaneously open the middle layer negative pressure suction channel to form an inward suction vortex in front of the central optical lens, sucking the droplets into the middle layer negative pressure suction channel and discharging them to the outside of the water heating pipe fitting to be tested. While the outer positive pressure channel jets a high-frequency pulsed airflow to strip and atomize the residual liquid, this embodiment simultaneously activates the middle negative pressure suction channel. "Simultaneous activation" means that the negative pressure suction and positive pressure jetting actions begin almost simultaneously, rather than waiting until the atomized droplets have diffused to the front of the lens before suction begins. It is understandable that, due to the extremely small space within the internal threaded hole, once the micron-sized droplets generated by atomization are formed, their diffusion speed is extremely fast. If the suction action lags behind the jetting action, the droplets will rapidly disperse throughout the hole space, with some forming a high-concentration aerosol layer at the front of the lens, severely interfering with the subsequent imaging optical path. Therefore, this embodiment employs a control strategy of simultaneously activating positive pressure jetting and negative pressure suction, tightly coupling the formation and capture of droplets in time, thereby effectively suppressing droplet accumulation within the field of view.

[0023] Once the intermediate negative pressure suction channel is opened, a negative pressure zone lower than the ambient pressure inside the channel is formed, creating a directional pressure difference in front of the central optical lens, pointing towards the suction channel inlet. Driven by this pressure difference, the gas in front of the lens, carrying atomized droplets suspended within it, accelerates its flow along converging streamlines towards the suction channel inlet, forming a suction flow field similar to a micro-cyclone. It should be noted that this cyclone is an axisymmetric converging flow pattern determined by the coaxial annular gap structure of the probe and the negative pressure source. Its streamlines converge centripetally in front of the lens, ensuring that the droplets must pass through the leading edge region of the lens's field of view before being sucked into the channel, thus achieving continuous cleaning of the optical window in front of the lens along the suction path.

[0024] During the aforementioned suction process, the droplets drawn into the middle negative pressure suction channel move with the airflow along the channel's interior away from the lens, and are finally discharged to the outside of the tested plumbing fitting via the exhaust pipe connected to the probe root. It is understood that this discharge path is spatially separate from the airflow inlet path: clean outside air enters the orifice through the outer positive pressure channel, carries the atomized products, and returns through the middle negative pressure suction channel, forming a directional circulation path of outer layer air supply and middle layer exhaust. This path arrangement avoids disordered airflow reversal within the orifice, ensuring that the stripped droplets are always transported in the same direction (i.e., from the bottom of the orifice to the orifice opening), preventing repeated swirling within the orifice due to turbulent flow, thus significantly improving droplet removal efficiency.

[0025] Step 4: Establish the phase-locked relationship between the exposure trigger signal of the central optical lens and the pulse control signal of the high-frequency pulsed airflow; within a single pulse cycle of the high-frequency pulsed airflow, extract the preset trough phase window as the trigger condition, control the central optical lens to perform stroboscopic exposure within the trough phase window to acquire the internal thread image, and extract the contour parameters of the internal thread image for quality judgment.

[0026] It should be noted that although the aforementioned combined positive pressure jetting and negative pressure suction can expel most of the residual liquid inside the orifice as atomized droplets, the periodic intermittent nature of the high-frequency pulsed airflow means that the airflow velocity, pressure, and turbulence intensity inside the orifice are undergoing drastic changes during the rising edge and peak phase of each pulse cycle. If image exposure is performed during such a highly turbulent phase, even if no droplets remain in the field of view, the change in the density gradient of the airflow itself will lead to uneven light refractive index, resulting in image distortion or local blurring. Therefore, it is necessary to select a time window with minimal airflow disturbance and the most uniform medium from the pulsed airflow sequence for exposure to ensure image quality.

[0027] To address the aforementioned issues, this embodiment establishes a phase-locked relationship between the exposure trigger signal of the central optical lens and the pulse control signal of the high-frequency pulsed airflow. Specifically, the pulse control signal is an electrical signal used to drive the outer positive pressure channel solenoid valve or pneumatic component to generate periodic airflow. Its waveform is a periodic square wave or square wave-like wave, including a high-level phase (corresponding to the airflow injection phase) and a low-level phase (corresponding to the airflow intermittent phase). The exposure trigger signal is a trigger pulse sent to the central optical lens or the camera connected to it, used to control the exposure start time and exposure duration of the image sensor. Phase locking means that the exposure trigger signal is synchronously triggered with a specific phase point of the pulse control signal as a reference, ensuring that each exposure occurs at the same preset phase position in the pulse control signal waveform. Through this phase-locked relationship, the airflow state corresponding to each image acquisition can be ensured to have good consistency, thereby avoiding uncontrollable image quality fluctuations introduced by the random drift of the exposure time relative to the airflow phase.

[0028] Based on the established phase-locked relationship, this embodiment extracts a preset trough phase window as a trigger condition within a single pulse cycle of the high-frequency pulsed airflow. The control center optical lens performs stroboscopic exposure within the trough phase window to acquire images of the internal thread. The trough phase window refers to a specific time interval within a single pulse cycle where the airflow energy is lowest and the flow field is most stable. It can be understood that exposing within the trough phase window is equivalent to embedding the image acquisition action into the most favorable imaging period of the airflow cycle, thereby ensuring that each acquisition has optimal medium transparency conditions. After exposure, image processing algorithms such as edge detection and contour extraction are performed on the acquired internal thread image to extract contour parameters such as tooth angle, pitch, and tooth height. These parameters are then compared with a preset standard template to complete the quality assessment.

[0029] Furthermore, to ensure accurate positioning of the trough phase window under different operating conditions, this embodiment employs the following configuration: Optionally, the trough phase window is: the time interval during which the jet pressure value of the outer positive pressure channel drops below a preset pressure threshold within a single cycle of the high-frequency pulse airflow; within the trough phase window, the atomization action of the residual liquid is periodically paused, and the generated droplets are emptied by the middle negative pressure suction channel.

[0030] Specifically, the trough phase window is defined as the time interval within a single cycle of the high-frequency pulsed airflow when the jet pressure in the outer positive pressure channel drops below a preset pressure threshold. In practice, a pressure sensor can be installed in the outer positive pressure channel to monitor the instantaneous value of the jet pressure in real time; or, in a sensorless solution, the starting time and duration of the pressure drop below the threshold can be determined directly based on the waveform parameters of the pulse control signal (such as duty cycle and frequency) and the supply pressure and pipeline response characteristics through time-series calculations. The preset pressure threshold can be calibrated as a value below the effective atomization critical pressure, for example, set to 15% to 25% of the peak pressure. When the jet pressure is below this threshold, the shear force of the airflow on the residual liquid is insufficient to overcome the liquid surface tension, thus the new atomization action is periodically paused. Simultaneously, droplets generated and suspended in the orifice during the first half of the pulse cycle continue to be continuously emptied by the middle negative pressure suction channel during this pressure trough period.

[0031] By pausing atomization and continuously removing newly generated droplets, the latter half of the trough phase window can achieve a clean state where there are no new fog sources and existing droplets are removed. It should be noted that this clean state is achieved by periodically modulating the jet pressure to stagger the atomization and suction processes in time, thereby creating an optimal window for imaging without sacrificing production efficiency (i.e., without extending the total duration of a single detection cycle).

[0032] Furthermore, to ensure that the flow field conditions within the trough phase window reach the optimal state for imaging, this embodiment further refines and configures the negative pressure control strategy within the window: Optionally, the suction negative pressure value of the middle layer negative pressure suction channel and the jet gas pressure value of the outer layer positive pressure channel are in a asynchronous alternating control state, and the trough phase window is divided into a dynamic evacuation stage and a steady-state exposure stage on the time axis. During the dynamic evacuation phase, i.e., the initial period when the injection pressure value just drops below the preset pressure threshold, the suction negative pressure value is controlled to rise to the maximum peak value in order to force the inertial rebound gas-liquid mixture generated at the bottom of the internal threaded hole due to the sudden drop in positive pressure. During the steady-state exposure phase, the suction negative pressure value is controlled to fall back to the reference negative pressure value in order to establish a stable laminar flow state in front of the central optical lens before triggering the stroboscopic exposure.

[0033] Specifically, the jet pressure of the outer positive pressure channel and the suction negative pressure of the middle negative pressure suction channel are set to an asynchronous alternating control state. Specifically, during the rising edge and peak phase of the pulse cycle, when the jet pressure is high, the suction negative pressure can be maintained at a lower reference value; when the jet pressure drops sharply and enters the trough phase window, the suction negative pressure is dynamically adjusted according to the time progression within the window. By decoupling the control of the jet pressure and the suction negative pressure, the suction channel can provide the strongest suction capacity at the most needed time (i.e., the instant of the sharp drop in positive pressure), while actively reducing the suction intensity at times when a stable flow field is required to avoid introducing additional disturbances.

[0034] Based on this, the trough phase window is further subdivided on the time axis into a dynamic emptying stage and a steady-state exposure stage: During the dynamic evacuation phase, specifically the initial period when the jet pressure drops below the preset pressure threshold, the suction negative pressure is rapidly increased to its maximum peak value. It should be noted that when the high-pressure airflow in the outer positive pressure channel suddenly stops, the pressure gradient of the flow field, which was previously continuously pushed towards the bottom of the orifice by the high-pressure gas, reverses. The gas-liquid mixture accumulated near the bottom of the orifice undergoes a reverse expansion and rebound due to inertia, forming a gas-liquid cloud that rushes back towards the orifice opening. This inertial rebound mixture contains both droplets that failed to be discharged in time and water vapor that has escaped from the liquid surface due to the sudden pressure drop. If a low suction negative pressure is maintained during this phase, the rebound mixture will have sufficient time to diffuse towards the front of the lens. Therefore, this invention sets the suction negative pressure to its maximum peak value at the initial moment of the sudden drop in positive pressure, forming a powerful intercepting suction to capture and quickly remove the inertial rebound mixture head-on, thereby eliminating the most likely source of disturbance to contaminate the field of view at its inception.

[0035] During the steady-state exposure phase, the suction negative pressure is controlled to decrease from its maximum peak value back to the reference negative pressure value. It should be noted that if high negative pressure suction continues after the dynamic evacuation phase, excessive suction force will generate a continuous, non-uniform accelerated flow field in front of the lens, leading to localized turbulence or vortices. This non-uniformity of the microscopic flow field will also adversely affect image quality by altering local air density and refractive index. Therefore, after the inertial rebound mixture has been effectively evacuated, the suction negative pressure is actively reduced to a lower reference level, allowing the gas medium inside the aperture to gradually transition from high-intensity directional flow to a slow, uniform laminar flow state. In this stable laminar flow state, the density distribution of the medium in front of the lens tends to be uniform, and the refractive index field is stable. Triggering stroboscopic exposure at this point yields the original image with minimal distortion and the highest clarity. Subsequently, the contour parameters of the internal thread image are extracted for quality assessment.

[0036] Furthermore, although the precise timing coordination between the dynamic evacuation stage and the steady-state exposure stage achieves a high degree of cleanliness and stability at the macroscopic flow field level, a very small amount of residual micro-aerosols with extremely small particle sizes (e.g., submicron scale), invisible to the naked eye but capable of generating Mie scattering under strong light, may still exist in actual physical processes. Due to their extremely small particle size, these aerosols settle very slowly, can remain suspended in a gravitational field for extended periods, and their motion is primarily dominated by Brownian motion, exhibiting randomness and unpredictability, making them impossible to completely eliminate through gas path design. To further eliminate these residual optical interference factors, this embodiment further employs an aerosol suppression strategy based on multi-frame image difference during the steady-state exposure stage: Optionally, when the strobe exposure is triggered during the steady-state exposure phase, the central optical lens is specifically controlled to continuously perform at least two short exposures with microsecond intervals to obtain at least two consecutive initial internal thread images; The pixel-level differential comparison is performed on the at least two consecutive initial internal thread images. The pixel region with a differential value greater than the dynamic threshold is determined to be a residual micro aerosol that is still slowly drifting in the stable laminar flow state, and the pixel region is marked as a dynamic noise mask. The initial internal thread image is filtered and culled using the dynamic noise mask, and then fused with static pixels to output the final internal thread image for extracting the contour parameters.

[0037] Specifically, when triggering stroboscopic exposure during the steady-state exposure phase, the optical lens at the control center continuously performs at least two short exposures with microsecond intervals. A microsecond interval refers to the time interval between two adjacent exposures being on the order of microseconds (e.g., 10 to 100 microseconds). This timescale is much smaller than the macroscopic convection migration time of aerosol particles, but sufficient to cause them to produce pixel-level displacements recognizable by an image sensor under Brownian motion. Through these short, continuous exposures, at least two consecutive initial internal thread images are acquired.

[0038] Furthermore, pixel-level differential comparison is performed on at least two consecutive initial internal thread images. Specifically, the grayscale values ​​of corresponding pixels in the two images are subtracted point by point, and the absolute value is used to obtain a differential image. In this differential image, pixel regions with grayscale values ​​greater than a certain preset dynamic threshold are identified as regions whose positions have changed during the time interval between the two exposures. Since the physical contour of the metal internal thread remains absolutely stationary between the two images, its differential value should be zero or close to zero; however, suspended micro-aerosols, due to Brownian motion or slow drift, have different imaging positions in the two images, appearing as high-value regions in the differential image. Pixel regions with differential values ​​greater than the dynamic threshold are identified as residual micro-aerosols, and these regions are marked as dynamic noise masks. It should be noted that this dynamic threshold can be adaptively adjusted according to the image noise level to balance detection sensitivity and false detection rate.

[0039] A dynamic noise mask is used to filter and remove noise from the initial internal thread image, and then static pixels are fused together. Specifically, pixel regions marked as dynamic noise masks are identified as invalid information by the algorithm, and their grayscale values ​​are set to zero or filled by neighborhood interpolation to achieve filtering and removal. Static pixels that remain unchanged during multiple exposures (i.e., the real thread contour information) are preserved, and weighted fusion of static pixels from multiple frames can be performed to further improve the signal-to-noise ratio.

[0040] Through the dual processing of physical pneumatic cleaning and algorithmic differential noise reduction, the final output image of the internal thread used to extract contour parameters can achieve high cleanliness and clarity, providing a reliable data source for subsequent precision quality judgments such as tooth angle measurement, pitch diameter calculation, and pitch detection. This can significantly improve the overall accuracy and stability of visual inspection of the internal threads of plumbing valves and fittings.

[0041] Please see Figure 3 This invention provides a device 200 for detecting the internal threads of plumbing valves and fittings, comprising: The probe positioning module 201 is used to insert the coaxial detection probe into the internal threaded hole of the plumbing fitting to be tested to a set depth, so that the root of the coaxial detection probe fits and seals with the port of the plumbing fitting to be tested; wherein, the coaxial detection probe includes a central optical lens, a middle negative pressure suction channel and an outer positive pressure channel. The positive pressure injection module 202 is used to inject a periodically changing high-frequency pulsed airflow into the internal threaded hole through the outer positive pressure channel, so that the high-frequency pulsed airflow flows along the spiral groove of the internal threaded hole and swirls against the wall to peel off the residual liquid in the internal threaded hole and atomize it into droplets. The negative pressure suction module 203 is used to simultaneously open the middle layer negative pressure suction channel, forming an inward suction cyclone in front of the central optical lens, sucking the droplets into the middle layer negative pressure suction channel and discharging them to the outside of the water heating pipe fitting to be tested. Phase-locked analysis module 204 is used to establish a phase-locked relationship between the exposure trigger signal of the central optical lens and the pulse control signal of the high-frequency pulsed airflow; within a single pulse cycle of the high-frequency pulsed airflow, a preset trough phase window is extracted as a trigger condition, and the central optical lens is controlled to perform stroboscopic exposure within the trough phase window to acquire an internal thread image, and the contour parameters of the internal thread image are extracted for quality judgment.

[0042] Optionally, the outer positive pressure channel has multiple tangential micro-nozzles at its end along the circumferential direction, and the axial tilt angle of the tangential micro-nozzles is adapted to the tooth profile angle of the internal thread hole, so as to guide the high-frequency pulse airflow to smoothly cut into the spiral groove.

[0043] Optionally, the trough phase window is: the time interval during which the jet pressure value of the outer positive pressure channel drops below a preset pressure threshold within a single cycle of the high-frequency pulse airflow; within the trough phase window, the atomization action of the residual liquid is periodically paused, and the generated droplets are emptied by the middle negative pressure suction channel.

[0044] Optionally, such as Figure 4 As shown, the device further includes: The alternating control module 205 is used to make the suction negative pressure value of the middle layer negative pressure suction channel and the injection air pressure value of the outer layer positive pressure channel in an asynchronous alternating control state, and to divide the trough phase window into a dynamic evacuation stage and a steady-state exposure stage on the time axis. During the dynamic evacuation phase, i.e., the initial period when the injection pressure value just drops below the preset pressure threshold, the suction negative pressure value is controlled to rise to the maximum peak value in order to force the inertial rebound gas-liquid mixture generated at the bottom of the internal threaded hole due to the sudden drop in positive pressure. During the steady-state exposure phase, the suction negative pressure value is controlled to fall back to the reference negative pressure value in order to establish a stable laminar flow state in front of the central optical lens before triggering the stroboscopic exposure.

[0045] Optionally, the phase-locked analysis module 204 is specifically used for: The central optical lens is controlled to continuously perform at least two short exposures with microsecond intervals to obtain at least two consecutive initial internal thread images; Perform pixel-level differential comparison on the at least two consecutive initial internal thread images; determine the pixel region with a differential value greater than the dynamic threshold as a residual micro aerosol that is still slowly drifting in the stable laminar flow state, and mark the pixel region as a dynamic noise mask. The initial internal thread image is filtered and culled using the dynamic noise mask, and then fused with static pixels to output the final internal thread image for extracting the contour parameters.

[0046] It should be noted that the implementation principle and technical effects of the apparatus provided in the embodiments of the present invention are highly consistent with those of the aforementioned methods and apparatus embodiments. For the sake of brevity, for any technical details not covered in the above embodiments, please refer directly to the detailed descriptions of the corresponding sections above, and they will not be repeated here.

[0047] Finally, it should be noted that the differentiated technical features disclosed in the foregoing embodiments and claims of this invention can be mutually referenced, combined, or substituted in any form according to actual engineering needs, provided there are no technical conflicts or logical contradictions. New technical solutions formed through the recombination or substitution of the above features all fall within the scope fully disclosed in this specification, do not depart from the core technical concept of this invention, and are protected by law under this invention.

Claims

1. A method for detecting the internal threads of plumbing valves and fittings, characterized in that, include: The coaxial testing probe is inserted into the internal threaded hole of the plumbing fitting to be tested to a set depth, so that the root of the coaxial testing probe fits and seals with the port of the plumbing fitting; wherein, the coaxial testing probe includes a central optical lens, a middle negative pressure suction channel and an outer positive pressure channel; High-frequency pulsed airflow, which is periodically varied, is injected into the internal threaded hole through the outer positive pressure channel. The high-frequency pulsed airflow swirls and flows along the spiral groove of the internal threaded hole to peel off the residual liquid in the internal threaded hole and atomize it into droplets. Simultaneously open the middle layer negative pressure suction channel to form an inward suction vortex in front of the central optical lens, suck the droplets into the middle layer negative pressure suction channel and discharge them to the outside of the water heating pipe fitting to be tested; A phase-locked relationship is established between the exposure trigger signal of the central optical lens and the pulse control signal of the high-frequency pulsed airflow. Within a single pulse cycle of the high-frequency pulsed airflow, a preset trough phase window is extracted as a trigger condition. The central optical lens is controlled to perform stroboscopic exposure within the trough phase window to acquire an internal thread image, and the contour parameters of the internal thread image are extracted for quality judgment.

2. The method for detecting the internal threads of plumbing valves and fittings according to claim 1, characterized in that, The outer positive pressure channel has multiple tangential micro-nozzles at its end along the circumferential direction, and the axial tilt angle of the tangential micro-nozzles is adapted to the tooth profile angle of the internal thread hole to guide the high-frequency pulse airflow to smoothly cut into the spiral groove.

3. The method for detecting the internal threads of plumbing valves and fittings according to claim 1 or 2, characterized in that, The trough phase window is the time interval during which the jet pressure of the outer positive pressure channel drops below a preset pressure threshold within a single cycle of the high-frequency pulse airflow; within the trough phase window, the atomization of the residual liquid is periodically paused, and the generated droplets are emptied by the middle negative pressure suction channel.

4. The method for detecting the internal threads of plumbing valves and fittings according to claim 3, characterized in that, The suction negative pressure value of the middle layer negative pressure suction channel and the jet gas pressure value of the outer layer positive pressure channel are in an asynchronous alternating control state, and the trough phase window is divided into a dynamic evacuation stage and a steady-state exposure stage on the time axis. During the dynamic evacuation phase, i.e., the initial period when the injection pressure value just drops below the preset pressure threshold, the suction negative pressure value is controlled to rise to the maximum peak value in order to force the inertial rebound gas-liquid mixture generated at the bottom of the internal threaded hole due to the sudden drop in positive pressure. During the steady-state exposure phase, the suction negative pressure value is controlled to fall back to the reference negative pressure value in order to establish a stable laminar flow state in front of the central optical lens before triggering the stroboscopic exposure.

5. The method for detecting the internal threads of plumbing valves and fittings according to claim 4, characterized in that, When the strobe exposure is triggered during the steady-state exposure phase, the central optical lens is specifically controlled to continuously perform at least two short exposures with microsecond intervals to obtain at least two consecutive initial internal thread images. The pixel-level differential comparison is performed on the at least two consecutive initial internal thread images. The pixel region with a differential value greater than the dynamic threshold is determined to be a residual micro aerosol that is still slowly drifting in the stable laminar flow state, and the pixel region is marked as a dynamic noise mask. The initial internal thread image is filtered and culled using the dynamic noise mask, and then fused with static pixels to output the final internal thread image for extracting the contour parameters.

6. A device for detecting the internal threads of plumbing valves and fittings, characterized in that, include: The probe positioning module is used to insert the coaxial detection probe into the internal threaded hole of the plumbing fitting to be tested to a set depth, so that the root of the coaxial detection probe fits and seals with the port of the plumbing fitting to be tested; wherein, the coaxial detection probe includes a central optical lens, a middle negative pressure suction channel and an outer positive pressure channel. The positive pressure injection module is used to inject a periodically changing high-frequency pulsed airflow into the internal threaded hole through the outer positive pressure channel, so that the high-frequency pulsed airflow flows along the spiral groove of the internal threaded hole and swirls against the wall to strip off the residual liquid in the internal threaded hole and atomize it into droplets. The negative pressure suction module is used to simultaneously open the middle layer negative pressure suction channel, forming an inward suction vortex in front of the central optical lens, sucking the droplets into the middle layer negative pressure suction channel and discharging them to the outside of the water heating pipe fitting to be tested. The phase-locked analysis module is used to establish a phase-locked relationship between the exposure trigger signal of the central optical lens and the pulse control signal of the high-frequency pulsed airflow. Within a single pulse cycle of the high-frequency pulsed airflow, a preset trough phase window is extracted as a trigger condition. The central optical lens is controlled to perform stroboscopic exposure within the trough phase window to acquire an internal thread image, and the contour parameters of the internal thread image are extracted for quality judgment.

7. The plumbing valve and pipe fitting internal thread detection device according to claim 6, characterized in that, The outer positive pressure channel has multiple tangential micro-nozzles at its end along the circumferential direction, and the axial tilt angle of the tangential micro-nozzles is adapted to the tooth profile angle of the internal thread hole to guide the high-frequency pulse airflow to smoothly cut into the spiral groove.

8. The device for detecting the internal threads of plumbing valves and fittings according to claim 6 or 7, characterized in that, The trough phase window is the time interval during which the jet pressure of the outer positive pressure channel drops below a preset pressure threshold within a single cycle of the high-frequency pulse airflow; within the trough phase window, the atomization of the residual liquid is periodically paused, and the generated droplets are emptied by the middle negative pressure suction channel.

9. The device for detecting internal threads of plumbing valves and fittings according to claim 8, characterized in that, The device further includes: An alternating control module is used to make the suction negative pressure value of the middle layer negative pressure suction channel and the injection air pressure value of the outer layer positive pressure channel in an asynchronous alternating control state, and to divide the trough phase window into a dynamic evacuation stage and a steady-state exposure stage on the time axis. During the dynamic evacuation phase, i.e., the initial period when the injection pressure value just drops below the preset pressure threshold, the suction negative pressure value is controlled to rise to the maximum peak value in order to force the inertial rebound gas-liquid mixture generated at the bottom of the internal threaded hole due to the sudden drop in positive pressure. During the steady-state exposure phase, the suction negative pressure value is controlled to fall back to the reference negative pressure value in order to establish a stable laminar flow state in front of the central optical lens before triggering the stroboscopic exposure.

10. The device for detecting internal threads of plumbing valves and fittings according to claim 9, characterized in that, The phase-locked analysis module is specifically used for: The central optical lens is controlled to continuously perform at least two short exposures with microsecond intervals to obtain at least two consecutive initial internal thread images; The pixel-level differential comparison is performed on the at least two consecutive initial internal thread images. The pixel region with a differential value greater than the dynamic threshold is determined to be a residual micro aerosol that is still slowly drifting in the stable laminar flow state, and the pixel region is marked as a dynamic noise mask. The initial internal thread image is filtered and culled using the dynamic noise mask, and then fused with static pixels to output the final internal thread image for extracting the contour parameters.

Images