High-precision PCB hole inspection machine and hole inspection method

Abstract

The invention relates to a high-precision PCB hole inspection machine and a hole inspection method, the hole inspection machine comprises a mechanical conveying system and an optical detection system, the optical detection system is arranged in the Z-axis direction of the mechanical conveying system and can move in the Y-axis direction, the resolution of the optical detection system is 12.5 microns, the depth of field is 6 mm, and the optical detection system is arranged in the Z-axis direction of the mechanical conveying system and can move in the Y-axis direction. The optical detection system comprises a line scanning camera, a prime lens and a backlight source, the line scanning camera and the prime lens are coaxially arranged, the backlight source is arranged on the side face of a scanning line and below a workpiece to be detected, the pixel size of the line scanning camera is 5 micrometers, the number of transverse pixels is 16k, the multiplying power of the prime lens is 0.398 X, and the backlight source is blue parallel backlight or white parallel backlight. The optical parameter collaborative design of the specific line scanning camera, the prime lens and the double-color parallel backlight and the prism corner lens structure are adopted, it is guaranteed that the hole edge is clear under the resolution of 12.5 micrometers, and tiny through holes and burrs in the holes can be accurately recognized.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of PCB detection, in particular to a high-precision PCB hole inspection machine and hole inspection method. BACKGROUND

[0002] In the PCB (Printed Circuit Board) manufacturing process, the quality of the through hole is crucial. The tiny through hole thereon is the key channel connecting different layers of circuits. The diameter, roundness and burr on the inner wall of the hole are directly related to the stability of the circuit connection and the quality of signal transmission.

[0003] The existing hole inspection technology mainly includes contact type and non-contact type, but both have obvious limitations. The contact type hole inspection technology mainly uses internal diameter micrometer, plug gauge and three-coordinate measuring machine for hole inspection. Although it can achieve a theoretical accuracy of 1 μm in some scenarios, it generally has low detection efficiency, high skill requirement for operators, is not suitable for blind holes and complex hole structures, and is costly in mass production scenarios. More importantly, contact measurement has large deviation when measuring a tiny hole diameter of 0.13 mm, and cannot effectively identify micron-level burrs in the hole.

[0004] Non-contact optical hole inspection technology, such as visual inspection based on industrial cameras, laser triangulation, CCD camera method, etc., avoids contact, but the traditional optical solution has a contradiction between resolution and edge sharpness: using a small pixel camera and a high magnification lens can obtain high theoretical resolution (such as 7.1 μm), but the imaging edge is easy to blur, resulting in the virtualization of the hole burr and the missed detection. In addition, the depth of field of the existing optical technology is generally small (mostly ≤3 mm), which can only adapt to thin plate detection. When facing thick plates of 4 mm and above, the deep part of the hole is out of the depth of field range and the image is virtualized, which cannot detect the burrs in the deep part. In terms of mechanical structure, the existing equipment has insufficient precision of the conveying system, poor adaptability to the optical system, which leads to the deviation of the workpiece during the conveying process, and the misalignment of the optical acquisition area, which seriously damages the detection accuracy and stability.

[0005] Moreover, most hole inspection equipment has low mechanical structure precision and poor adaptability to the optical system, resulting in insufficient detection stability. The complex structure leads to low space utilization and low detection efficiency, which is difficult to meet the batch production demand.

[0006] Therefore, there is an urgent need for a hole inspection equipment and method that can simultaneously consider high precision, large depth of field, high stability, high efficiency and good environmental adaptability. SUMMARY

[0007] Therefore, it is necessary to provide a high-precision PCB hole inspection machine and hole inspection method to overcome the defects mentioned in the background technology.

[0008] A high-precision PCB hole inspection machine, comprising A mechanical conveying system extending along the X-axis direction for conveying workpieces to be detected; An optical detection system arranged in the Z-axis direction of the mechanical conveying system and movable along the Y-axis direction, the optical detection system having a resolution of 12.5 μm and a depth of field of 6 mm, the optical detection system comprising a line-scan camera, a fixed-focus lens, and a backlight light source, the line-scan camera and the fixed-focus lens being coaxially arranged, the backlight light source being arranged on the side of the scanning line and below the workpiece to be detected, the line-scan camera having a pixel size of 5 μm and a horizontal pixel number of 16k, the fixed-focus lens having a magnification of 0.398X, and the backlight light source being a blue parallel backlight or a white parallel backlight.

[0009] As a preferred embodiment of the high-precision PCB hole inspection machine, the mechanical conveying system comprises: A base; A conveying system arranged on the upper surface of the base for transporting workpieces to be detected.

[0010] As a preferred embodiment of the high-precision PCB hole inspection machine, the conveying system comprises: A whole-board portion comprising a first mounting seat, the upper surface of the first mounting seat being provided with plate feeding rollers, the ends of the plate feeding rollers being provided with driving mechanisms, a plurality of the plate feeding rollers being arranged side by side and inclined in the X-axis direction, and the ends of the plate feeding rollers being further provided with side belt blocking edge assemblies extending in the X-axis direction; A lower belt line portion comprising a second mounting seat, the upper surface of the second mounting seat being provided with a first lower belt line and a second lower belt line arranged at intervals in the X-axis direction, the upper surface of the first lower belt line and the second lower belt line being provided with a belt pressure roller assembly connected with the second mounting seat, and the interval between the first lower belt line and the second lower belt line being provided with a collection trigger sensor.

[0011] As a preferred embodiment of the high-precision PCB hole inspection machine, the first mounting seat is further provided with bearing lifting assemblies at both ends, the upper surfaces of the bearing lifting assemblies being provided with rollers rolling thereon, and the upper surfaces of the rollers being flush with the upper surfaces of the plate feeding rollers.

[0012] As a preferred embodiment of the high-precision PCB hole inspection machine, the conveying system further comprises a plate discharging portion, the plate discharging portion comprising a third mounting seat, the upper surface of the third mounting seat being provided with plate discharging rollers, and one side of the plate discharging rollers being provided with a code spraying portion.

[0013] As a preferred embodiment of the high-precision PCB hole inspection machine, the optical detection system is arranged in the Y-axis direction at the interval between the first lower belt line and the second lower belt line, and further comprises: Gantry frame Z-axis movement assembly, which is in sliding connection with the gantry frame, drives the line-scan camera and the fixed-focus lens to move along the Z-axis direction, and forms an optical acquisition area between the line-scan camera and the fixed-focus lens and the backlight light source.

[0014] As a preferred high-precision PCB hole inspection machine in the application, the optical detection system is connected with a processing and monitoring computer, and the processing and monitoring computer is configured to perform image analysis, including: Image preprocessing, enhancing the contrast of hole edges and removing noise; Feature extraction, calculating the number of pixels occupied by the through hole and converting the actual aperture size, and detecting the abnormal gray area in the hole; Defect judgment, comparing the feature data with the preset standard, and outputting the qualified or unqualified result.

[0015] A hole inspection method of a high-precision PCB hole inspection machine, comprising the following steps: Place the workpiece to be detected on the whole board part, limit the lateral displacement through the side belt edge component, and convey the workpiece to be detected through the inboard roller; The workpiece to be detected triggers the acquisition trigger sensor, starts the first lower belt line and the second lower belt line to convey synchronously, and conveys the workpiece to the optical acquisition area; The optical detection system is initialized, the line-scan camera, the acquisition card and the backlight light source are turned on, the exposure time and the resolution are set; The optical detection system acquires images in one scanning mode, the backlight light source emits light which penetrates the through hole, the lens receives the light transmission signal, and the line-scan camera captures the image; The processing and monitoring computer analyzes the image and judges the through hole defect; The workpiece is output through the outboard part, and the detection result is printed.

[0016] As a preferred hole inspection method in the application, in the optical acquisition step, the color of the backlight light source is selected according to the thickness of the board, and blue parallel backlight is used for boards with a thickness of 4mm or more.

[0017] As a preferred hole inspection method in the application, the image analysis step specifically includes: Image preprocessing: enhancing the contrast of hole edges and removing noise caused by uneven backlight through algorithm; Feature extraction: identifying the through hole area in the image, calculating the number of pixels occupied by the through hole and converting the actual aperture size, and detecting the abnormal gray area in the hole to determine whether there is an oversize burr; Defect judgment: comparing the extracted feature data with the preset standard, outputting the judgment result and marking the defect position.

[0018] The application has the following advantages: The application adopts the optical parameter collaborative design of a specific line scan camera + a fixed focus lens + a double-color parallel backlight and a prism corner lens structure to ensure clear hole edges at 12.5 μm resolution, accurately identify 0.13 mm tiny through holes and 15 μm burrs in the holes, solve the defects of the contradiction between high resolution and edge definition and the missing detection of tiny defects in the traditional optical scheme, and through the combination scheme of lens magnification adjustment and blue parallel backlight optimization, the depth of field of the optical detection system is improved to 6 mm, the hole imaging edge is still clear at the depth of field, the burrs in the deep part of the hole of the 4 mm and above thick plate can be stably detected, the overall volume of the mechanical conveying system is significantly reduced compared with the existing equipment, the assembly process is simplified, the space utilization is improved, and the adaptability, detection stability of the optical system are effectively improved. BRIEF DESCRIPTION OF DRAWINGS

[0019] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments or the prior art description will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creating laborious work.

[0020] Figure 1 It is a structure schematic diagram of the hole inspection machine of the embodiment of the present application; Figure 2 It is a structure schematic diagram of the whole plate part of the embodiment of the present application; Figure 3 It is a structure schematic diagram of the lower belt line part of the embodiment of the present application; Figure 4 It is a structure schematic diagram of the plate ejection part of the embodiment of the present application; Figure 5 It is a structure schematic diagram of the optical detection system of the embodiment of the present application; Explanation of reference signs: 1000, base; 2000, conveying system; 2100, whole plate part; 2110, first mounting seat; 2120, plate feeding roller; 2130, driving mechanism; 2140, side belt edge blocking assembly; 2150, bearing lifting assembly; 2160, roller; 2200, lower belt line part; 2210, second mounting seat; 2220, first lower belt line; 2230, second lower belt line; 2300, plate ejection part; 2310, third mounting seat; 2320, plate ejection roller; 3000, optical detection system; 3100, line scan camera; 3200, fixed focus lens; 3300, backlight light source; 3400, gantry; 3500, Z-axis motion assembly. DETAILED DESCRIPTION

[0021] In order to make the above objectives, features and advantages of the present application more clear and easily understood, the detailed description of the specific embodiments of the present application is made below with reference to the accompanying drawings. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present application. However, the present application can be practiced in a number of different ways without the specific details described herein, and it is understood that similar improvements can be made without departing from the spirit and scope of the present application, and therefore the present application is not limited to the following disclosed specific embodiments.

[0022] In the description of the present application, it should be understood that the terms "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the purpose of facilitating the description of the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the present application.

[0023] In addition, the terms "first", "second" are only for descriptive purpose, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the technical features indicated. Therefore, the features defined with "first", "second" can explicitly or implicitly include at least one of the features. In the description of the present application, the meaning of "a plurality of" is at least two, such as two, three, etc., unless otherwise explicitly specified and limited.

[0024] In the present application, unless otherwise explicitly specified and limited, the terms "mounting", "connecting", "connecting", "fixing" and the like should be understood in a broad sense, for example, can be fixedly connected, or can be detachably connected, or can be integrated; can be mechanically connected, or can be electrically connected; can be directly connected, or can be indirectly connected through an intermediate medium; can be the internal communication of two elements or the interaction relationship between two elements, unless otherwise explicitly limited. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0025] In the present application, unless specifically stated and limited otherwise, a first feature is "on" or "under" a second feature can be that the first and second features are in direct contact, or the first and second features are in indirect contact through an intermediate medium. Moreover, the first feature is "over", "above" and "on top of" the second feature can be that the first feature is directly above or obliquely above the second feature, or only indicates that the first feature is higher in horizontal height than the second feature. The first feature is "under", "below" and "underneath" the second feature can be that the first feature is directly below or obliquely below the second feature, or only indicates that the first feature is lower in horizontal height than the second feature.

[0026] It should be noted that when an element is referred to as being "fixed" or "set" on another element, it can be directly on the other element or there can be an intermediate element. When an element is considered to be "connected" to another element, it can be directly connected to the other element or there can be an intermediate element. The terms "vertical", "horizontal", "up", "down", "left", "right" and similar expressions used herein are only for illustrative purposes and are not indicative of the only implementation.

[0027] According to one aspect of the present application, the embodiments of the present application provide a high-precision PCB hole inspection machine, please refer to Figures 1 to 5 The high-precision PCB hole inspection machine includes a mechanical conveying system and an optical detection system 3000, the mechanical conveying system extends along the X-axis direction and is used for conveying a workpiece to be detected, the optical detection system 3000 is arranged in the Z-axis direction of the mechanical conveying system and is movable along the Y-axis direction, the resolution of the optical detection system 3000 is 12.5 μm, and the depth of field is 6 mm. The optical detection system 3000 includes a line-scan camera 3100, a fixed-focus lens 3200 and a backlight light source 3300. The line-scan camera 3100 and the fixed-focus lens 3200 are coaxially arranged, and the backlight light source 3300 is arranged on the side of the scanning line and below the workpiece to be detected. The pixel size of the line-scan camera 3100 is 5 μm, the number of transverse pixels is 16k, the magnification of the fixed-focus lens 3200 is 0.398X, and the backlight light source 3300 is a blue parallel backlight or a white parallel backlight.

[0028] In one embodiment, please refer to Figure 1 The mechanical conveying system extends along the X-axis direction and is used for conveying a workpiece to be detected. The mechanical conveying system includes a base 1000 and a conveying system 2000 arranged on the base 1000. The conveying system 2000 is provided with a feeding station and a discharging station in the X-axis direction. The workpiece to be detected enters from the feeding station, is detected by the optical detection system 3000, and is then taken out from the discharging station.

[0029] In one embodiment, the conveying system 2000 includes a whole board portion 2100 and a lower belt line portion arranged in sequence from the feeding station to the discharging station.

[0030] Please see Figure 2 As shown, the whole plate part 2100 includes a first mounting base 2110. The bottom of the first mounting base 2110 is connected to the base 1000. The upper surface of the first mounting base 2110 is provided with a feeding roller 2120. Multiple feeding rollers 2120 are arranged side by side at an inclination in the X-axis direction to form a whole plate roller. The end of the feeding roller 2120 is provided with a driving mechanism 2130. The whole plate roller is driven by the driving mechanism 2130 to uniformly convey the workpiece to be inspected. The end of the feeding roller 2120 is also provided with a side belt guard assembly 2140 extending in the X-axis direction to prevent the workpiece to be inspected from being displaced in the Y-axis direction during the conveying process.

[0031] Please see Figure 3 As shown, the lower belt conveyor section 2200 includes a second mounting base 2210. The bottom of the second mounting base 2210 is connected to the base 1000. A first lower belt conveyor 2220 and a second lower belt conveyor 2230 are spaced apart along the X-axis on its upper surface. These two conveyors are driven by a steel wheel with a drive device, which drives the covered belt to rotate synchronously at a uniform speed. The runout of the steel wheel should not exceed 0.05mm, ensuring that the upper surfaces of the first lower belt conveyor 2220 and the second lower belt conveyor 2230 are on the same horizontal plane. A belt pressure roller assembly is provided above the first lower belt conveyor 2220 and the second lower belt conveyor 2230 to prevent the workpiece to be inspected from floating during transport, which could lead to errors in the inspection results. The first lower belt conveyor 2220... A data acquisition trigger sensor is installed between the first and second lower conveyor belts 2220 and 2230. The workpiece to be tested is conveyed from the plate section 2100 to the lower conveyor belt section 2200. During the conveying process from the first lower conveyor belt 2220 to the second lower conveyor belt 2230, the data acquisition trigger sensor installed between the first lower conveyor belt 2220 and the second lower conveyor belt 2230 is triggered. The data acquisition trigger sensor sends a signal to the control system to start the synchronous conveying of the first lower conveyor belt 2220 and the second lower conveyor belt 2230, accurately conveying the workpiece to be tested to the optical acquisition area directly below the fixed-focus lens 3200. This structure realizes the timing synchronization of mechanical conveying and optical acquisition, avoiding misalignment of the acquisition area caused by the conveying deviation of the workpiece to be tested.

[0032] Before the workpiece to be inspected reaches the optical acquisition area, the optical inspection system 3000 completes pre-start and parameter calibration. The hardware is then activated, turning on the line scan camera 3100, the acquisition card, and the blue backlight for thick plate inspection. Exposure time and resolution are set to ensure the optical inspection system 3000 is in optimal inspection condition, eliminating the impact of hardware errors on image quality.

[0033] When the workpiece to be detected is conveyed to the optical detection collection, the mechanical conveying system needs to be paused or run at a uniform low speed to prevent shaking interference, and then the optical detection system 3000 starts the collection process in a one-time scanning manner: first, according to the thickness of the workpiece to be detected and the size of the through hole, a white or blue type backlight is selected; then the parallel backlight source 3300 emits uniform light, which penetrates through the through hole of the workpiece to be detected, forming a bright-dark contrast of the hole-plate, with the through hole area transmitting light and the plate area blocking light; then, the minimum distance between the front and back is 13mm by using the prism corner design, the focusing lens 3200 receives the transmitted light signal, and the optical signal of the through hole profile and the small burr details is converted into an optical image; finally, the line scan camera 3100 captures the optical image to obtain a high-definition and non-virtual through hole image, which can accurately identify the hole edge and burr details, and the image data is transmitted to the processing and monitoring computer in real time through the collection card to complete the acquisition of single-frame or multi-frame images.

[0034] In one embodiment, the first mounting seat 2110 is also provided with a bearing lifting assembly 2150 at both ends close to and away from the feeding station, and the bearing lifting assemblies 2150 at both ends are diagonally arranged. The upper surface of the bearing lifting assembly 2150 is provided with a steel ball roller 2160 which is flush with the upper surface of the plate feeding roller 2120, so as to avoid the inclination of the workpiece to be detected during conveying and ensure the stability of the workpiece to be detected. The height of the steel ball roller 2160 can be adjusted by the bearing lifting assembly 2150.

[0035] In one embodiment, the conveying system 2000 further comprises a plate discharging part 2300 which is arranged between the lower belt line part 2200 and the discharging station. Please refer to Figure 4 which comprises a third mounting seat 2310, and the upper surface of the third mounting seat 2310 is provided with a plate discharging roller 2320. One side of the plate discharging roller 2320 is provided with a code spraying part. After the processing and monitoring computer judges the through hole, the second lower belt line 2230 conveys the detected workpiece to the plate discharging part 2300, and the plate discharging roller 2320 uniformly discharges the detected workpiece. If marking is needed, the code spraying part sprays the detection results, such as the qualified number and the defect type, at the specified position of the detected workpiece, and the industrial computer automatically stores the detection data.

[0036] In one embodiment, the optical detection system 3000 is arranged in the Y-axis direction between the first lower belt line 2220 and the second lower belt line 2230. Please refer to Figure 5 which further comprises a gantry 3400 and a Z-axis motion assembly 3500.

[0037] The gantry 3400 uses a marble gantry as a high-precision support reference to fix the linear guide rail and Z-axis motion assembly 3600, ensuring the parallelism and perpendicularity of optical components such as the line scan camera 3100 and fixed-focus lens 3200 during movement and acquisition, and preventing vibration or displacement from affecting the accuracy of hole inspection. The linear guide rail is set on the gantry 3400 and extends along the Z-axis direction. The Z-axis motion assembly 3500 is slidably connected to the linear guide rail. The line scan camera 3100 and fixed-focus lens 3200 are mounted on the Z-axis motion assembly. The component 3600 and the backlight source 3300 are installed on both sides below the gap between the first lower belt conveyor 2220 and the second lower belt conveyor 2230 and are connected to the base 1000. The line scan camera 3100 and the fixed-focus lens 3200 form an optical acquisition area with the backlight source 3300. The Z-axis motion component 3600 drives the line scan camera 3100 and the fixed-focus lens 3200 to move along the Z-axis direction, so as to realize the full field of view coverage and precise alignment of the line scan lens on the optical acquisition area, and adapt to the single scan acquisition requirements.

[0038] In one embodiment, the optical inspection system 3000 is connected to a processing and monitoring computer configured to perform image analysis, including: Image preprocessing enhances hole edge contrast and removes noise.

[0039] Feature extraction is performed to calculate the number of pixels occupied by the through-hole and convert it into the actual hole diameter, and to detect gray-scale abnormal areas within the hole.

[0040] Defect determination involves comparing feature data with preset standards and outputting a pass or fail result.

[0041] According to one aspect of this application, embodiments of this application provide a method for inspecting holes using a high-precision PCB board hole inspection machine, comprising the following steps: Feeding and positioning: The workpiece to be inspected is placed on the feed roller 2120 of the whole plate section 2100. The lateral displacement is restricted by the side belt edge assembly 2140. The feed roller 2120 is driven by the drive mechanism 2130 to convey the workpiece to be inspected.

[0042] Detection triggering and conveying connection: The workpiece to be tested is conveyed from the whole plate section 2100 to the lower belt conveyor section 2200, triggering the acquisition trigger sensor. The acquisition trigger sensor signal starts the synchronous conveying of the first lower belt conveyor 2220 and the second lower belt conveyor 2230, accurately conveying the workpiece to be tested to the optical acquisition area.

[0043] Optical system initialization: Before the workpiece to be inspected arrives at the optical acquisition area, the optical inspection system 3000 completes pre-start and parameter calibration, turns on the line scan camera 3100, the acquisition card and the backlight source 3300, and sets the exposure time and resolution.

[0044] Optical acquisition and image acquisition: when the workpiece to be detected is conveyed to the optical acquisition area, the mechanical conveying system is paused or runs at a uniform low speed to eliminate jitter interference. The backlight light source 3300 emits uniform light, which penetrates through the through hole on the workpiece to be detected, forming a bright-dark contrast of light transmission in the through hole area and light shielding in the plate area. The fixed focus lens 3200 receives the light transmission signal, and the line scan camera 3100 captures the optical image.

[0045] Among them, the color of the backlight light source 3300 is selected according to the thickness of the workpiece to be detected: for 4mm and above thick plates, blue parallel backlight is used, which has the characteristics of short wavelength and strong penetration, ensuring clear imaging of the hole depth of thick plates. For 3mm and below thin plates, white parallel backlight can be used.

[0046] Image analysis and defect judgment: the processing monitoring computer performs algorithm analysis on the acquired image: Image preprocessing: optimize image quality through algorithm, enhance hole edge contrast, and remove noise caused by uneven backlight.

[0047] Feature extraction: identify the through hole area in the image, calculate the number of pixels occupied by the through hole, such as 0.13mm through hole occupying 9 pixels under 12.5μm resolution, and convert the actual hole size, while detecting the abnormal gray area in the hole to determine whether there is an oversized burr, such as a 15μm burr.

[0048] Defect judgment: compare the extracted feature data with the preset standard, output "qualified" or "unqualified" judgment result, and mark the defect position.

[0049] Detection piece output and result record: after the judgment is completed, the PCB is sent out by the plate roller 2320, and the code printing part sprays the detection result at the specified position of the detected workpiece. The industrial computer automatically stores the detection data for subsequent traceability and quality analysis.

[0050] According to one aspect of the present application, embodiments of the present application provide two group comparison tests for determining that the optical parameter combination in the embodiments is the only solution that can simultaneously meet the requirements of clear edge, 0.13mm hole recognition and thick plate hole burr detection.

[0051] Comparison test one is used to determine the related parameters of the line scan camera 3100. Comparison test 1 identifies and detects 0.13mm through holes and 15um burrs by setting different camera parameters. The relevant data is shown in Table 1. Table 1 Recognition effect of different resolutions

[0052] From Table 1 and the figure, it can be concluded that the 12.5 μm resolution avoids the edge blur and burr missed detection problems of Test 1 7.1 μm resolution, and has a larger depth of field than Test 2 10.1 μm resolution, which can adapt to thick plates; and the combination of 0.398X lens and blue backlight is the only parameter combination that can simultaneously satisfy the edge clear 0.13 mm through-hole recognition.

[0053] The parameters of Test 2 are used to determine the relevant parameters of the fixed-focus lens 3200 magnification and the backlight 3300. Table 2 Recognition effect of different lens magnification and backlight color

[0054] From Table 1 and the figure, it can be concluded that only Test 3 0.398X magnification + blue backlight combination can increase the depth of field to 6 mm, and the penetration of blue backlight solves the problem of light attenuation in the deep part of the white backlight thick plate, completely meeting the burr detection requirements in the hole of the 4 mm and above thick plate; while the depth of field of other magnifications or backlight colors is only 3.2 mm at most, which cannot adapt to thick plates.

[0055] The blue backlight 3300 has the following advantages: The detection target and background contrast are more intense, and the edge is clearer. There are glass fibers, resin particles and other small obstacles in the microscopic structure of the PCB, and when the light penetrates, it will be deflected when it encounters these obstacles, resulting in scattering. The amount of scattering is related to the matching degree of the wavelength of the light and the size of the obstacle. The closer the wavelength is to the size of the obstacle, the more likely it is to be deflected. The wavelength is much smaller than the size of the obstacle, and it is easier to bypass the obstacle. Blue light and other short-wavelength light are much smaller than the size of the obstacles such as glass fibers in the PCB, and can easily bypass obstacles when penetrating, and are not easy to be deflected. The long-wavelength light in white light, such as red light and yellow light, is closer to the size of the obstacle, and is more likely to be deflected and scattered. Therefore, the light with shorter wavelength scatters less when penetrating the PCB.

[0056] Increasing the depth of field makes the details in the deep part of the object more clear. The depth of field in the prior art is only 3 mm, and the deep part of the thick plate hole cannot be clearly photographed. The blue parallel backlight can help the lens to pull the clear range. White light contains multiple wavelengths of light, and when penetrating the thick plate 4 mm above the PCB, the light of different wavelengths will disperse, resulting in uneven light in the deep part of the hole, and the imaging will be blurred. Blue light is single-wavelength light, and when penetrating the thick plate, it is more consistent in straight line and is not easy to disperse, and can reach the deepest part of the hole. The hole wall on the back of the plate and the small burr in the deep part can be clearly recorded by the lens, and will not be missed due to light dispersion.

[0057] As shown in the control test 2, with blue backlight and 0.398X lens, the depth of field is directly to 6 mm, and the burr in the deep part of the 4 mm thick plate hole can be clearly recorded, while the white backlight cannot.

[0058] Reduce ambient light interference, make the detection result more stable, there are various stray light in the industrial workshop, these stray light will be reflected to the fixed focus lens 3200, resulting in the image taken has noise, affect the detection accuracy. The wavelength of blue parallel backlight and the wavelength of common white stray light and yellow light in the workshop are different. The fixed focus lens 3200 can receive only blue light by filtering, filter stray light. No matter how the workshop environment light changes, the image taken by the fixed focus lens 3200 will not be disturbed, the details of the hole are always stable, and there is no situation that sometimes it can be seen and sometimes it cannot be seen. The reliability of the detection result is higher.

[0059] The technical features of the above-described embodiments can be combined in any manner. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described, but it should be considered that any combination of the technical features is within the scope of the present disclosure as long as the combination does not contradict.

[0060] The above-described embodiments only express several implementation manners of the present application, and the description is more specific and detailed, but it should not be understood as a limitation on the patent scope of the application. It should be pointed out that for ordinary skilled persons in the art, some modifications and improvements can be made without departing from the concept of the present application, and these are within the protection scope of the present application. Therefore, the patent protection scope of the present application should be subject to the appended claims.

Claims

1. A high-precision PCB hole inspection machine, characterized in that: include A mechanical conveying system, extending along the X-axis, is used to convey workpieces to be inspected; An optical inspection system is positioned along the Z-axis of the mechanical conveying system and can move along the Y-axis. The optical inspection system has a resolution of 12.5 μm and a depth of field of 6 mm. The optical inspection system includes a line scan camera, a fixed-focus lens, and a backlight source. The line scan camera and the fixed-focus lens are coaxially arranged. The backlight source is located on the side of the scan line and below the workpiece to be inspected. The pixel size of the line scan camera is 5 μm, and the number of horizontal pixels is 16k. The magnification of the fixed-focus lens is 0.398X. The backlight source is a blue parallel backlight or a white parallel backlight.

2. The high-precision PCB hole inspection machine according to claim 1, characterized in that, The mechanical transmission system includes: Base; The conveying system, located on the upper surface of the base, is used to transport the workpiece to be inspected.

3. The high-precision PCB hole inspection machine according to claim 2, characterized in that, The conveying system includes: The whole plate part includes a first mounting base, the upper surface of the first mounting base is provided with a feeding roller, the end of the feeding roller is provided with a driving mechanism, a plurality of feeding rollers are arranged side by side inclined in the X-axis direction, and the end of the feeding roller is also provided with a side belt baffle assembly extending in the X-axis direction. The lower belt conveyor section includes a second mounting base. The upper surface of the second mounting base is provided with a first lower belt conveyor and a second lower belt conveyor at intervals along the X-axis. A belt pressure roller assembly connected to the second mounting base is provided above the first lower belt conveyor and the second lower belt conveyor. A data acquisition trigger sensor is provided at the interval between the first lower belt conveyor and the second lower belt conveyor.

4. The high-precision PCB hole inspection machine according to claim 3, characterized in that, The first mounting base is also provided with bearing lifting assemblies at both ends. Rollers are rolled on the upper surface of the bearing lifting assemblies, and the upper surfaces of the rollers and the feed roller are flush.

5. The high-precision PCB hole inspection machine according to claim 3, characterized in that, The conveying system also includes a plate discharge section, which includes a third mounting base. The upper surface of the third mounting base is provided with a plate discharge roller, and one side of the plate discharge roller is provided with a coding section.

6. The high-precision PCB hole inspection machine according to claim 1, characterized in that, The optical detection system is positioned along the Y-axis at the interval between the first and second lower belt lines, and further includes: Gantry frame; The Z-axis motion component is slidably connected to the gantry, driving the line scan camera and fixed-focus lens to move along the Z-axis direction, forming an optical acquisition area between the line scan camera and fixed-focus lens and the backlight source.

7. The high-precision PCB hole inspection machine according to claim 6, characterized in that, The optical detection system is connected to a processing and monitoring computer, which is configured to perform image analysis, including: Image preprocessing, enhancing hole edge contrast and removing noise; Feature extraction, calculation of the number of pixels occupied by the through hole and conversion of the actual hole diameter, detection of gray-scale abnormal areas inside the hole; Defect determination involves comparing feature data with preset standards and outputting a pass or fail result.

8. A method of inspecting holes of a high-precision PCB board according to any one of claims 1 to 7, characterized in that, Includes the following steps: The workpiece to be inspected is placed on the whole plate section, and the lateral displacement is restricted by the side belt edge guard assembly. The feed roller conveys the workpiece to be inspected. The workpiece to be inspected triggers the acquisition sensor, which starts the first and second lower conveyor belts to transport the workpiece to the optical acquisition area. Initialize the optical inspection system, turn on the line scan camera, acquisition card and backlight source, and set the exposure time and resolution; The optical detection system collects images in one scanning mode, a back light source emits light through the through hole, a lens receives the light signal, and a line scanning camera captures the image; The processing monitoring computer analyzes the image and determines the through hole defects; The workpiece is output through the plate output part, and the detection result is sprayed and printed.

9. The method of claim 8, wherein, In the optical acquisition step, the color of the back light source is selected according to the thickness of the plate. For plates with a thickness of 4 mm or more, a blue parallel back light is used.

10. The method of claim 8, wherein, The image analysis step specifically includes: Image preprocessing: enhancing the contrast of the hole edge through algorithm, removing noise caused by uneven back light; Feature extraction: identifying the through hole area in the image, calculating the number of pixels occupied by the through hole and converting the actual aperture size, and detecting the abnormal gray area in the hole to determine whether there is an oversize burr; Defect determination: compare the extracted feature data with the preset standard, output the determination result and mark the defect position.

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