A 3D printing system and detection method based on surface defect and focus shift detection

Abstract

The application discloses a kind of 3D printing system and detection method based on surface defect and focal point shift detection, belong to 3D printing technical field, the system is configured with detection module to scanning module, detection module includes: detection laser, for emitting detection laser;Collimating lens, for adjusting detection laser into parallel light;Splitting prism, for reflecting detection laser into scanning module, detection laser is reflected after printing work surface and transmits through splitting prism;Convex lens, for the first focusing of detection laser that transmits through splitting prism;Cylindrical mirror, for the second focusing of one axis of detection laser that is first focused, so that its focus point in X and Y axis is not in the same position;Receiving sensor, for receiving detection laser, and detecting surface defect and focal point shift according to the spot shape of detection laser.The application can improve the precision of printing work surface surface defect detection, and realizes the purpose of real-time monitoring focal point offset.

Description

Technical Field

[0001] This invention belongs to the field of 3D printing technology, and particularly relates to a 3D printing system and detection method based on surface defect and focus drift detection. Background Technology

[0002] 3D printing technology is a technique that uses digital model files as a basis to form objects by printing layers of bondable materials such as metal, plastic, ceramics, and sand. It breaks through the processing limitations of traditional processes and can rapidly create parts with complex structures. Depending on the type of consumables and feeding method, 3D printing equipment employs different technologies, including: Stereolithography (SLA), Selective Laser Melting (SLM), and Selective Laser Sintering (SLS). SLS and SLM processes both involve layering powder and then using a laser or other heat source to sinter or fuse the powder. However, existing 3D printing equipment has the following drawbacks:

[0003] The powder spreading device in existing 3D printing equipment mainly consists of a scraper, a powder feeding chamber, and a recovery chamber. The specific printing process is as follows: the scraper spreads a layer of powder material evenly on the upper surface of the already formed part. A laser beam scans the cross-sectional contour of the part, sintering this layer of powder. The sintered layer automatically bonds to the already formed part below. After one cross-section is sintered, the worktable descends by one layer thickness, and the scraper continues to spread another layer of powder material on top, sintering a new cross-section until the entire model is completed. During the printing process, scanning anomalies may occur. Accumulated anomalies can easily damage the part. Real-time detection and identification of the printed surface of each layer during the printing process allows for timely understanding of the part's printing quality and facilitates the timely identification of the location of abnormal areas, enabling remedial action. Currently, real-time surface defect identification in the printing process all uses camera photography and makes judgments based on the captured images, such as in application publication number CN114372958A. Using cameras to identify printed surface defects has the problem of low detection accuracy. For example, for a standard 500*500mm image size device, a camera with 2000W (4000*5000) pixels needs to cover at least 0.125mm per pixel. If a clear image is required and it can be used for image analysis, the defects that can be identified are close to the 10mm level. Defects of 1mm level or even smaller cannot be identified. These defects are more numerous in probability and have a huge impact on printed parts. Surface defect detection has a huge loophole.

[0004] Furthermore, in order to print parts with high precision, the laser beam must be imaged at the printing surface with the optimal focal length. If the focal point shifts, it will greatly affect the printing quality. Therefore, the detection and positioning of the optimal focal point becomes particularly important. In the initial stage of equipment debugging, various equipment manufacturers will use various methods to adjust the focal position of the laser beam. However, during the 3D printing process, when the laser is turned on, the temperature of the lens and related mechanical parts will change, resulting in problems such as thermal expansion deformation and lens refractive index drift. Under the influence of these factors, the focal point of the optical path system in 3D printing will drift. Currently, there is no feasible method to monitor whether the focal point of the optical path system has drifted in real time during the printing process. We can only infer whether the focal point has drifted by judging from the printing quality of the part after it has been printed. Summary of the Invention

[0005] This invention provides a 3D printing system and detection method based on surface defect and focus drift detection, in order to solve the problems of low recognition accuracy of surface defect detection in existing 3D printing systems and the inability to measure whether focus drift occurs in real time during the printing process.

[0006] To solve the above-mentioned technical problems, the technical solution provided by the present invention is as follows:

[0007] This invention relates to a 3D printing system based on surface defect and focus drift detection, comprising a detection module and a scanning module. The scanning module includes a dielectric reflector, a focusing lens, a scanning galvanometer, and a printing working surface disposed on the printing laser optical path; the detection module includes:

[0008] A probe laser, used to emit a probe laser;

[0009] Collimating lens is used to adjust the probe laser into parallel light;

[0010] A beam splitter is used to reflect the probe laser to the scanning module. The probe laser is reflected by the printing surface and then passes through the beam splitter.

[0011] A convex lens is used to focus the probe laser light that has passed through the beam splitter for the first time.

[0012] A cylindrical mirror is used to refocus one axis of the probe laser after the first focusing, so that the focal points on the X and Y axes are not at the same position.

[0013] A receiving sensor is used to receive the probe laser and detect surface defects and focus drift based on the shape of the received probe laser spot.

[0014] Preferably, the beam splitter is tilted so that there is an angle between the probe laser and the printing laser after the probe laser passes through the medium reflector. This causes the reflection point of the probe laser on the printing surface to be misaligned and not coincident with the imaging point of the printing laser, reducing the influence of the printing laser spot on the measurement position error.

[0015] The minimum angle must ensure that the reflection point of the probe laser and the imaging point of the printing laser are misaligned and do not coincide, while the maximum angle must ensure that the probe laser is not blocked by mechanical parts of the optical path system.

[0016] Preferably, the receiving sensor is positioned between the focal points of the X-axis and Y-axis, so that the spot of the detection laser light received by the receiving sensor is circular.

[0017] Preferably, the receiving sensor is a four-quadrant sensor, and the center of the four-quadrant sensor overlaps with the axis of the detection laser.

[0018] Preferably, the focusing lens is an imaging lens disposed between the medium reflector and the scanning galvanometer, or a field lens disposed between the scanning galvanometer and the printing working surface.

[0019] This invention also relates to a detection method for a 3D printing system based on surface defect and focus drift detection, which includes the following steps:

[0020] S1. The detector laser emits a detector laser, which is collimated by a collimating lens and reflected by a beam splitter. It then enters the scanning module through a medium mirror and is projected onto the printing surface along with the printing laser. After being reflected by the printing surface, it passes through a medium mirror and a beam splitter, and then through a convex lens and a cylindrical mirror for secondary focusing, thus forming two different focal points in the X and Y axes. Finally, it is received by the receiving sensor.

[0021] S2. During the printing process, the receiving sensor detects the shape of the received probe laser spot in real time. When the spot shape changes, it is determined that there is a defect on the printed surface or the focus of the focusing lens has drifted.

[0022] Preferably, in step S1, the receiving sensor is positioned between the focal points of the X-axis and Y-axis, such that the spot of the detection laser received by the receiving sensor is circular.

[0023] Preferably, in step S2, if the shape of the light spot changes and is immediately restored, it is determined that there is a defect on the printed surface; if the shape of the light spot changes and cannot be restored, it is determined that the focal point of the focusing lens has drifted.

[0024] Preferably, the receiving sensor is a four-quadrant sensor, with its center overlapping the axis of the detection laser. In step S2, the light intensity values ​​received by the four-quadrant sensor are I1, I2, I3, and I4 in clockwise order. A light intensity ratio parameter P is set. When the light intensity ratio parameter P changes, it is determined that there is a defect on the printed surface or that the focal point of the focusing lens has drifted. The value of the surface defect or the value of the focal point drift are determined based on the change in the light intensity ratio parameter P. The expression for the light intensity ratio parameter P is:

[0025]

[0026] Preferably, the S1 probe laser has an angle between itself and the printing laser after penetrating the medium reflector, so that the reflection point of the probe laser on the printing surface and the imaging point of the printing laser will be misaligned and not coincident, reducing the influence of the printing laser spot on the measurement position error.

[0027] The minimum angle must ensure that the reflection point of the probe laser and the imaging point of the printing laser are misaligned and do not coincide, while the maximum angle must ensure that the probe laser is not blocked by mechanical parts of the optical path system.

[0028] Compared with the prior art, the technical solution provided by this invention has the following advantages:

[0029] The 3D printing system based on surface defect and focus drift detection disclosed in this invention is equipped with a detection module. This detection module emits a probe laser, which is collimated by a collimating lens and reflected by a beam splitter. The probe laser then passes through a medium mirror and enters the scanning module, where it is projected onto the printing surface along with the printing laser. After being reflected by the printing surface, the laser passes through the medium mirror and beam splitter, and is then refocused by a convex lens and a cylindrical mirror, forming two different focal points in the X and Y axes. Finally, the laser beam is received by a receiving sensor. During the printing process, the receiving sensor detects the shape of the received probe laser spot in real time. When the spot shape changes, it indicates that there is a defect on the printing surface or that the focus of the focusing lens has drifted. The system has high accuracy in detecting surface defects on the printing surface and can monitor focus drift in real time. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of a 3D printing system based on surface defect and focus drift detection;

[0031] Figure 2 This is a schematic diagram of another 3D printing system based on surface defect and focus drift detection;

[0032] Figure 3 It is the equivalent optical path diagram of the detection laser when the detection optical path and the printing optical path are parallel;

[0033] Figure 4 It is the equivalent optical path diagram of the detection laser when the focal length is shortened due to the protrusion of the printed surface or the focus shift.

[0034] Figure 5 It is the equivalent optical path diagram of the detection laser when the focal length increases due to printing surface concavity or focus drift;

[0035] Figure 6 This is a schematic diagram of the shape of the detection laser spot received by the receiving sensor when a defect exists;

[0036] Figure 7 It is the equivalent optical path diagram of the detection laser when the detection optical path and the printing optical path are tilted.

[0037] Reference numerals: 1-Printing laser, 2-Medium reflector, 3-Focusing lens, 4-Scanning galvanometer, 5-Printing working surface, 6-Detector laser, 7-Detector laser, 8-Collimating lens, 9-Beam splitter prism, 10-Convex lens, 11-Cylindrical mirror, 12-Receiving sensor. Detailed Implementation

[0038] To further understand the content of this invention, the invention will be described in detail with reference to the embodiments. The following embodiments are used to illustrate the invention, but are not intended to limit the scope of the invention.

[0039] See attached document Figure 1 and 2 As shown, this invention relates to a 3D printing system based on surface defect and focus drift detection, comprising a detection module and a scanning module. The scanning module includes a medium reflector 2, a focusing lens 3, a scanning galvanometer 4, and a printing working surface 5 disposed on the optical path of the printing laser 1. The focusing lens 2 is an imaging lens disposed between the medium reflector 2 and the scanning galvanometer 4, such as... Figure 1 As shown, or it could be a field lens positioned between the scanning galvanometer 4 and the printing surface 5, such as... Figure 2 As shown.

[0040] The detection module includes:

[0041] Detection laser 6, used to emit detection laser 7;

[0042] Collimating lens 8 is used to collimate the probe laser 7 and adjust the probe laser 7 into parallel light.

[0043] The beam splitter 9 is used to reflect a portion of the power of the probe laser 7 into the scanning module. This portion of the power of the probe laser 7 is projected onto the printing surface 5 through the medium reflector 2, the focusing lens 3, and the scanning galvanometer 4 to form a probe spot. It is then reflected by the printing surface 5, passes through the scanning galvanometer 4, the focusing lens 3, and the medium reflector 2, and then passes through the beam splitter 9.

[0044] The convex lens 10 is used to focus the probe laser 7 that passes through the beam splitter 9 for the first time.

[0045] Cylindrical mirror 11 is used to focus one of the axes of the probe laser 7 after the first focusing, and to make the focal points of the laser 7 on the X-axis and Y-axis not be at the same position.

[0046] The receiving sensor 12 is used to receive the detection laser 7. The receiving sensor 12 is a four-quadrant sensor. The receiving sensor 12 is set in the middle of the two axis focal points of the X-axis and Y-axis, so that under normal circumstances, the spot of the detection laser received by the receiving sensor 12 is circular, and the center of the four-quadrant sensor overlaps with the axis of the detection laser.

[0047] The detection method for the 3D printing system based on surface defect and focus drift detection includes the following steps:

[0048] S1. The detector laser 6 emits a detector laser 7. The detector laser 7 is first collimated by the collimating lens 8 to form a parallel beam, and then partially reflected by the beam splitter prism 9. The detector laser 7 reflected by the beam splitter prism 9 passes through the medium reflector 2 and enters the scanning module. Together with the printing laser 1, it is focused by the focusing lens 3 and reflected by the scanning galvanometer 4, projected onto the printing surface 5, reflected again by the printing surface 5, passed through the scanning galvanometer 4 and the focusing lens 3, and then through the medium reflector 2 and the beam splitter prism 9. It then passes through the convex lens 10 and the cylindrical mirror 11 for secondary focusing, thus forming two different focal points in the X-axis and Y-axis directions. Finally, it is received by the receiving sensor 12. The equivalent optical path diagram of the detector laser 7 is shown below. Figure 3 As shown.

[0049] S2. During the printing process, the receiving sensor 12 detects the shape of the light spot of the received probe laser 7 in real time. When the shape of the light spot changes, it is determined that there is a defect on the printing surface or the focus of the focusing lens has drifted.

[0050] Since the receiving sensor 12 is located in the middle of the focal points of the X and Y axes, under normal circumstances, the detection laser 7 received by the receiving sensor 12 is a circular spot. The light intensity values ​​in the four quadrants of the receiving sensor 12 are equal. The light intensity values ​​received by the four quadrant sensors in clockwise order are I1, I2, I3, and I4. The light intensity ratio parameter P is set, and the expression for the light intensity ratio parameter P is:

[0051]

[0052] Therefore, under normal circumstances, I1 = I2 = I3 = I4, and thus P = 1.

[0053] If the shape of the light spot changes and immediately returns to its original shape, a defect is determined to exist on the printed surface. When the shape of the light spot changes, the spot becomes elliptical, such as... Figure 6 As shown; and when the light intensity ratio parameter P > 1, defects such as protrusions appear on the printed working surface, as shown. Figure 4 As shown; when the light intensity ratio parameter P < 1, a concave defect appears on the printed working surface, such as... Figure 5 As shown, this allows us to determine whether there are defects on the printed surface based on the magnitude and specific value of P, record the location of surface defects, and judge the quality of the workpiece based on the number of defects and the importance of their location after the entire document is printed.

[0054] When the shape of the light spot changes and cannot be restored, it is determined that the focal point of the focusing lens has drifted, and the shape of the light spot of the probe laser received by the receiving sensor 12 is always elliptical, such as... Figure 6 As shown; and when the light intensity ratio parameter P > 1, the optical path system of the scanning module experiences focus drift and the focal length becomes shorter, as... Figure 4 As shown; when the light intensity ratio parameter P < 1, the optical path system of the scanning module experiences focus drift and the focal length becomes longer, as... Figure 5 As shown, this allows us to determine whether the focal length of the optical system has drifted based on the value of P and its specific value. At this time, the position of the focusing lens is adjusted by the focusing mechanism to change the focal length until the shape of the detection laser spot received by the receiving sensor 12 returns to a circle. If the focusing mechanism still cannot restore the focal length after adjusting it, the system needs to be stopped for maintenance.

[0055] The beam splitter of the aforementioned 3D printing system based on surface defect and focus drift detection is preferably tilted, so that there is a tilt angle between the probe laser 7 and the printing laser 1 optical path after the probe laser 7 penetrates the medium reflector 2. Figure 7 As shown, this angle ensures that the reflection point of the probe laser 7 on the printing surface 5 is offset from the imaging point of the printing laser 1, reducing the influence of the printing laser 1's spot on the measurement position error. The minimum angle required to guarantee that the reflection point of the probe laser and the imaging point of the printing laser are offset from each other, and the maximum angle required to ensure that the probe laser is not obstructed by mechanical parts of the optical path system.

[0056] The present invention has been described in detail above with reference to the embodiments, but the content described is only a preferred embodiment of the present invention and should not be considered as limiting the scope of the present invention. All equivalent changes and improvements made in accordance with the scope of the present invention should still fall within the patent coverage of the present invention.

Claims

1. A detection method for a 3D printing system based on surface defect and focus drift detection, characterized in that: It is based on a 3D printing system for surface defect and focus drift detection. The 3D printing system includes a detection module and a scanning module. The scanning module includes a medium reflector, a focusing lens, a scanning galvanometer, and a printing surface arranged on the printing laser path. The detection module includes: A probe laser, used to emit a probe laser; Collimating lens is used to adjust the probe laser into parallel light; A beam splitter is used to reflect the probe laser to the scanning module. The probe laser is reflected by the printing surface and then passes through the beam splitter. A convex lens is used to focus the probe laser light that has passed through the beam splitter for the first time. A cylindrical mirror is used to refocus one axis of the probe laser after the first focusing, so that the focal points on the X and Y axes are not at the same position. A receiving sensor is used to receive the probe laser and detect surface defects and focus drift based on the shape of the received probe laser spot; The detection method includes the following steps: S1. The detector laser emits a detector laser, which is collimated by a collimating lens and reflected by a beam splitter. It then enters the scanning module through a medium mirror and is projected onto the printing surface along with the printing laser. After being reflected by the printing surface, it passes through a medium mirror and a beam splitter, and then through a convex lens and a cylindrical mirror for secondary focusing, thus forming two different focal points in the X and Y axes. Finally, it is received by the receiving sensor. S2. During the printing process, the receiving sensor detects the shape of the received probe laser spot in real time. If the spot shape changes, it immediately recovers and it is determined that there is a defect on the printed surface. If the spot shape changes and cannot be recovered, it is determined that the focus of the focusing lens has drifted.

2. The detection method for a 3D printing system based on surface defect and focus drift detection according to claim 1, characterized in that: The focusing lens is an imaging lens disposed between the medium reflector and the scanning galvanometer, or a field lens disposed between the scanning galvanometer and the printing working surface.

3. The detection method for a 3D printing system based on surface defect and focus drift detection according to claim 1, characterized in that: In step S1, the receiving sensor is positioned between the focal points of the X-axis and Y-axis, so that the spot of the detection laser light received by the receiving sensor is circular.

4. The detection method for a 3D printing system based on surface defect and focus drift detection according to claim 1, characterized in that: The receiving sensor is a four-quadrant sensor, with its center overlapping the axis of the detection laser. In step S2, the light intensity values ​​received by the four-quadrant sensor are, in clockwise order, respectively... I 1. I 2. I 3 and I 4. Set the light intensity ratio parameter P When the light intensity ratio parameter P When changes occur, it is determined that there is a defect on the printed surface or that the focal point of the focusing lens has drifted, and the light intensity ratio parameter is used to determine this. P The change in intensity determines the value of the surface defect or the value of the focus drift; the light intensity ratio parameter... P The expression is: .

5. The detection method for a 3D printing system based on surface defect and focus drift detection according to claim 1, characterized in that: The beam splitter is tilted, and there is a tilt angle between the S1 detection laser and the printing laser optical path after the laser penetrates the medium reflector.

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