An SLA and DLP Additive Manufacturing Optical Alignment and Liquid Surface Monitoring Method

Abstract

The present invention relates to the field of additive manufacturing, and more specifically to an SLA and DLP additive manufacturing optical alignment and liquid surface monitoring method. S1: Use an ultraviolet light CMOS camera to focus the SLA laser of the SLA laser galvanometer system on the forming plane; S2: Project three SLA laser spots within the visible range of the ultraviolet light CMOS camera, record the corresponding deflection angles, and calculate the coordinate reference of the scanning working area of the SLA laser galvanometer system; S3: Use image processing technology to record the SLA spot images in S2; S4: Use an ultraviolet light CMOS camera to focus the projection of the DLP optical engine projection system on the forming plane; S5: Adjust the pixels under the projection of the DLP optical engine projection system so that the projection pixels coincide with the center of the SLA spot image, realizing the coincidence of the coordinate systems of the forming plane, the SLA scanning working area, and the DLP projection working area; S6: Read the slice data to start forming and cure a single-layer slice; it can solve the problems of different working references of the optical path systems of the DLP and SLA hybrid process forming equipment and low printing layer thickness accuracy.

Description

Technical Field

[0001] The present invention relates to the field of additive manufacturing, and more specifically to an optical alignment and liquid surface monitoring method for SLA and DLP additive manufacturing. Background Art

[0002] In additive manufacturing technology, stereolithography manufacturing technology has been widely used due to its advantages such as high precision, high forming efficiency, and high material utilization rate. Its working principle is to irradiate ultraviolet light on photosensitive resin to cause a curing reaction to complete the curing of a single layer, and then gradually complete the curing of each layer through the lifting of a displacement platform to form a three-dimensional model entity. Currently, the main stereolithography additive manufacturing technologies include SLA stereolithography technology and DLP surface forming rapid prototyping technology. Among them, the optical system of SLA stereolithography technology is a laser galvanometer system, and the laser is scanned through the deflection of the galvanometer; the optical system of DLP surface forming technology is a DMD digital micromirror device, and curing and forming are achieved through DLP optical machine projection.

[0003] Currently, it is difficult for large-format stereolithography manufacturing technology to balance the process requirements of large format and high precision. The stitching projection technology of a movable DLP optical machine can expand the forming area, but the printing accuracy of a single optical machine is insufficient; SLA obtains higher printing accuracy by reducing the spot diameter, but it will sacrifice the forming efficiency. Therefore, the hybrid stereolithography technology combining DLP and SLA technologies has become a research hotspot. Among them, the DLP optical machine projection has a large working area, and the SLA laser spot diameter is small. The two are installed on a displacement mechanical mechanism and move synchronously to meet the process requirements of a large-size working area and high-precision curing and forming. Due to the different working principles of the two optical systems, it is difficult to align the optical paths of the hybrid stereolithography forming system. At the same time, for ensuring the consistency of the forming layer thickness, there is a lack of a monitoring and compensation method for the liquid surface of the photosensitive resin. Summary of the Invention

[0004] The purpose of the present invention is to provide an optical alignment and liquid surface monitoring method for SLA and DLP additive manufacturing, which can solve the problems of different working benchmarks of the optical path systems of DLP and SLA hybrid process forming equipment and low printing layer thickness accuracy.

[0005] The purpose of the present invention is achieved through the following technical solutions:

[0006] An optical alignment and liquid surface monitoring method for SLA and DLP additive manufacturing, the method includes the following steps:

[0007] S1: Drive the SLA laser galvanometer system to move along the X-axis direction and the Y-axis direction, and make the SLA laser of the SLA laser galvanometer system focus on the forming plane through an ultraviolet light CMOS camera;

[0008] S2: Project three SLA laser spots within the visible range of the ultraviolet CMOS camera, record the corresponding deflection angles, and calculate the coordinate reference of the scanning working area of the SLA laser galvanometer system;

[0009] S3: Use image processing technology to record the SLA spot images in S2;

[0010] S4: Drive the DLP optical engine projection system to move along the X-axis and Y-axis directions, and through the ultraviolet CMOS camera, make the projection of the DLP optical engine projection system focus on the forming plane;

[0011] S5: Based on the SLA spot images recorded in S3, adjust the pixels under the projection of the DLP optical engine projection system so that the projected pixels coincide with the center of the SLA spot images, realizing the coincidence of the coordinate systems of the forming plane, the SLA scanning working area, and the DLP projection working area;

[0012] S6: Read the slice data to start forming and cure a single-layer slice;

[0013] S7: Lower the forming platform by the thickness of a single-layer slice, and with the help of the visible light CMOS camera, judge whether the liquid level of the photosensitive resin in the resin pool changes, and finely adjust the height of the forming platform;

[0014] Drive the SLA laser galvanometer system and the DLP optical engine projection system to move along the X-axis and Y-axis directions through the gantry displacement mechanism;

[0015] In the above S1, drive the SLA laser galvanometer system to move along the X-axis and Y-axis directions above the beam splitter. The SLA laser enters and penetrates the beam splitter, irradiates onto the forming platform and is reflected back to the beam splitter. Due to the beam splitting effect of the beam splitter, a part of the light is refracted into the ultraviolet CMOS camera. Observe the spot image displayed on the ultraviolet CMOS camera and finely adjust the up and down position of the SLA laser galvanometer system for focusing;

[0016] The spot diameter of the laser galvanometer in the SLA laser galvanometer system is 10 μm;

[0017] In the above S2, within the visible range of the ultraviolet CMOS camera and without interference between the SLA laser spots, by changing the deflection angle of the laser galvanometer in the SLA laser galvanometer system, drop any three non-collinear SLA laser spots three times, record the deflection angle information at this time, establish the mapping relationship from the deflection angle information to the projection position of the working surface, so as to obtain the reference coordinate system of the SLA scanning working area and complete the coincidence of the coordinate systems of the SLA scanning working area and the forming surface;

[0018] In S3, using OpenCV, record the SLA spot image in S2, process the grayscale of the SLA spot image, and find the central pixel point of the SLA spot image.

[0019] In S4, drive the DLP light engine projection system to move directly above the beam splitter. The calibration slice test image used is a test slice image with a single pixel at the center of the DLP light engine projection system. The DLP light engine projection system projects and penetrates the beam splitter, irradiates the forming platform, and is reflected back to the beam splitter. Due to the beam splitting effect of the beam splitter, a part of the light is refracted into the ultraviolet CMOS camera, so as to focus the DLP light engine projection system according to the image in the ultraviolet CMOS camera.

[0020] The pixel size of the projection of the DLP light engine projection system is 78μm×78μm.

[0021] In S6, read the slice data to start forming, cure a single-layer slice. The slice data divides the SLA working area and the DLP working area. Due to the coincidence of the coordinate systems of the forming plane, the SLA scanning area, and the DLP projection area in step S5, according to the slice data, the SLA laser galvanometer system and the DLP light engine projection system cooperate with each other to complete single-layer curing.

[0022] The working area of the ultraviolet CMOS camera is 6.4mm×6.4mm, and the pixel size is 4.65μm×4.65μm.

[0023] The beneficial effects of the present invention are as follows:

[0024] Based on the ultraviolet CMOS camera, the problem of different working reference coordinate systems in the hybrid process forming is solved, ensuring high-precision cooperation in the hybrid forming process of different optical paths to meet the process requirements of high precision and cross-scale; based on the visible light CMOS camera, the liquid level of the photosensitive resin in the resin pool is monitored. By ensuring the constant height of the forming reference surface, the curing layer thickness is precisely controlled, further meeting the requirements of cross-scale and high-precision hybrid process forming. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The following further elaborates on the present invention in detail in conjunction with the drawings and specific implementation methods.

[0026] Figure 1 It is a schematic diagram of the SLA and DLP additive manufacturing optical alignment and liquid level monitoring method of the present invention;

[0027] Figure 2 It is a schematic diagram of the structure of the SLA and DLP additive manufacturing optical alignment system of the present invention.

[0028] In the figure: SLA galvanometer scanning system 1; DLP optical engine projection system 2; ultraviolet light CMOS camera 3; visible light CMOS camera 4; forming platform 5; resin tank 6; gantry displacement mechanism 7; beam splitter 8. Detailed implementation manners

[0029] The present invention will be further described in detail below with reference to the accompanying drawings.

[0030] As Figures 1 to 2 shown, the steps and functions of an SLA and DLP additive manufacturing optical alignment and liquid level monitoring method will be described in detail below;

[0031] Step S1: In the SLA and DLP additive manufacturing optical alignment system structure as Figure 2 shown, the gantry displacement mechanism 7 drives the SLA galvanometer scanning system 1 and the DLP optical engine projection system 2 to move along the X-axis direction and the Y-axis direction, so that the SLA galvanometer scanning system 1 moves directly above the beam splitter 8; the SLA laser is incident and penetrates the beam splitter 8, irradiates the forming platform 5 and is reflected back to the beam splitter 8, and part of the light is refracted into the ultraviolet light CMOS camera 3 by the beam splitting effect of the beam splitter 8. Observe the spot image displayed on the ultraviolet light CMOS camera 3, and finely adjust the vertical position of the SLA galvanometer scanning system 1 for focusing; wherein, the spot diameter of the laser galvanometer in the SLA galvanometer scanning system 1 is 10 μm, the working area of the ultraviolet light CMOS camera 3 is 6.4 mm × 6.4 mm, and the pixel size is 4.65 μm × 4.65 μm;

[0032] Using the beam splitter 8 as a key component for optical alignment, on the one hand, it avoids the interference between the installation position of the ultraviolet light CMOS camera 3 and the working range of the forming mechanism, thereby reducing the working area size; on the other hand, because it can calibrate the optical system at any time, it reduces the equipment maintenance cost and avoids the problem that the optical system of the equipment needs to be reinstalled and debugged under the condition of misalignment.

[0033] Step S2: Within the visible range of the ultraviolet light CMOS camera 3, and when the SLA laser spots do not interfere with each other, by changing the deflection angle of the laser galvanometer in the SLA galvanometer scanning system 1, three arbitrarily non-collinear SLA laser spots are cast three times, record the deflection angle information at this time, establish the mapping relationship from the deflection angle information to the projection position on the working surface, so as to obtain the reference coordinate system of the SLA scanning working area, and complete the coincidence of the SLA scanning working area coordinate system and the forming surface coordinate system; on the basis of ensuring the parallelism of the installation of the forming platform 5, three-point calibration of the SLA galvanometer scanning system 1 is beneficial to the accurate coincidence of the SSLA scanning working area coordinate system and the forming coordinate system;

[0034] Step S3: Using OpenCV, record the spot image in the above Step S2, process the grayscale of the spot image, find the center pixel point of the spot, and lay a foundation for subsequent optical path calibration; process the grayscale of the spot image, and take the absolute value of the difference between its grayscale value and 255 as the new grayscale of the spot image, which is beneficial to the alignment of the center pixel points of the DLP projection and the SLA spot in the subsequent process, and avoids the overlapping problem caused by similar grayscales and inconsistent sizes of the two projection spots;

[0035] Step S4: In the SLA and DLP additive manufacturing optical alignment system structure shown in Figure 2 , the gantry displacement mechanism 7 drives the SLA laser galvanometer system 1 and the DLP optical machine projection system 2 to move along the X-axis direction and the Y-axis direction, so that the DLP optical machine projection system 2 moves directly above the beam splitter 8; the slice test image used for calibration is a test slice image with a single pixel located at the center of the DLP optical machine projection system 2; the DLP optical machine projection system 2 projects and penetrates the beam splitter 8, irradiates the forming platform 5 and is reflected back to the beam splitter 8, and a part of the light is refracted into the ultraviolet CMOS camera 3 by the beam splitting effect of the beam splitter 8, so as to focus the DLP optical machine projection system 2 according to the image in the ultraviolet CMOS camera 3. Among them, the pixel size of the DLP optical machine projection system 2 is 78μm×78μm;

[0036] Step S5: Based on the SLA spot image recorded in S3, fine-tune through the gantry displacement mechanism 7 in the SLA and DLP additive manufacturing optical alignment system shown in Figure 2 to make the pixels of the DLP projection coincide with the center of the SLA spot, so that the projection pixels coincide with the center of the SLA spot image, and realize the coincidence of the coordinate systems of the forming plane, the SLA scanning working area, and the DLP projection working area;

[0037] Step S6: Read the slice data to start forming, cure a single-layer slice, and the slice data divides the SLA working area and the DLP working area. Due to the coincidence of the coordinate systems of the forming plane, the SLA scanning area, and the DLP projection area in the above Step S5, according to the slice data, the SLA laser galvanometer system and the DLP optical machine projection system cooperate with each other to complete the single-layer curing;

[0038] Step S7: The forming platform 5 descends by a single-layer slicing layer thickness, and with the help of the visible light CMOS camera 4, it judges whether the liquid level height of the photosensitive resin in the resin tank 6 changes, and finely adjusts the height of the forming platform 5; Since the accuracy of a single pixel of the visible light CMOS camera 4 is high, the liquid level height can be monitored at the micron level, so as to ensure the consistency of the single-layer curing height, and further ensure the high-precision control of the forming layer thickness; Using the visible light CMOS camera 4 to replace the commonly used laser rangefinder, on the one hand, it avoids the curing pollution caused by the laser irradiating on the resin, and on the other hand, it realizes the liquid level control with pixel accuracy (≤5μm), and the forming layer thickness is more accurately guaranteed.

[0039] In this article, specific examples are used to elaborate on the principle and implementation manner of the present invention. The description of the above embodiments is only used to help understand the method of the present invention and its core idea; at the same time, for those of ordinary skill in the art, according to the idea of the present invention, there will be changes in the specific implementation manner and application scope. To sum up, the content of this specification should not be construed as a limitation to the present invention.

Claims

1. An optical alignment and liquid level monitoring method for SLA and DLP additive manufacturing, characterized in that: The method includes the following steps: S1: Drive the SLA galvanometer scanning system (1) to move in the X-axis direction and the Y-axis direction, and through the ultraviolet CMOS camera (3), make the SLA laser of the SLA galvanometer scanning system (1) focus on the forming plane; S2: Project three SLA laser spots within the visible range of the ultraviolet CMOS camera (3), record the corresponding deflection angles, and calculate the coordinate system reference of the scanning working area of the SLA galvanometer scanning system (1); S3: Use image processing technology to record the SLA spot image in S2; S4: Drive the DLP optical engine projection system (2) to move in the X-axis direction and the Y-axis direction, and through the ultraviolet CMOS camera (3), make the projection of the DLP optical engine projection system (2) focus on the forming plane; S5: Based on the SLA spot image recorded in S3, adjust the pixels under the projection of the DLP optical engine projection system (2) so that the projected pixels coincide with the center of the SLA spot image, and achieve the coincidence of the coordinate systems of the forming plane, the SLA scanning working area, and the DLP projection working area; S6: Read the slice data to start forming and cure a single-layer slice; S7: Lower the forming platform (5) by the thickness of a single-layer slice, and with the help of the visible light CMOS camera (4), judge whether the liquid level of the photosensitive resin in the resin pool (6) changes, and finely adjust the height of the forming platform (5).

2. The SLA and DLP additive manufacturing optical alignment and liquid level monitoring method according to claim 1, characterized in that: Drive the SLA galvanometer scanning system (1) and the DLP optical engine projection system (2) to move in the X-axis direction and the Y-axis direction through the gantry displacement mechanism (7).

3. The SLA and DLP additive manufacturing optical alignment and liquid level monitoring method according to claim 1, characterized in that: In S1, drive the SLA galvanometer scanning system (1) to move above the beam splitter (8) in the X-axis direction and the Y-axis direction. The SLA laser enters and penetrates the beam splitter (8), irradiates onto the forming platform (5) and is reflected back to the beam splitter (8). Due to the beam splitting effect of the beam splitter (8), part of the light is refracted into the ultraviolet CMOS camera (3). Observe the spot image displayed on the ultraviolet CMOS camera (3), and finely adjust the vertical position of the SLA galvanometer scanning system (1) for focusing.

4. A method for optical alignment and liquid level monitoring in SLA and DLP additive manufacturing according to claim 3, characterized in that: The spot diameter of the laser galvanometer in the SLA galvanometer scanning system (1) is 10 μm.

5. A method for optical alignment and liquid level monitoring in SLA and DLP additive manufacturing according to claim 1, characterized in that: In S2, within the visible range of the ultraviolet CMOS camera (3), without interference between the SLA laser spots, by changing the deflection angle of the laser galvanometer in the SLA galvanometer scanning system (1), project three arbitrarily non-collinear SLA laser spots three times, record the deflection angle information at this time, establish the mapping relationship from the deflection angle information to the projection position on the working surface, so as to obtain the reference coordinate system of the SLA scanning working area and complete the coincidence of the coordinate system of the SLA scanning working area and the forming surface coordinate system.

6. A method for optical alignment and liquid level monitoring in SLA and DLP additive manufacturing according to claim 1, characterized in that: In S3, use OpenCV to record the SLA spot image in S2, process the gray level of the SLA spot image, and find the center pixel point of the SLA spot image.

7. A method for optical alignment and liquid level monitoring in SLA and DLP additive manufacturing according to claim 1, characterized in that: In S4, the DLP optical engine projection system (2) is driven to move directly above the beam splitter (8). The slice test image used for calibration is a test slice image with a single pixel located at the center of the DLP optical engine projection system (2). The DLP optical engine projection system (2) projects incident light that penetrates the beam splitter (8), irradiates onto the forming platform (5) and is reflected back to the beam splitter (8). Due to the beam splitting effect of the beam splitter (8), a part of the light is refracted into the ultraviolet CMOS camera (3), so as to focus the DLP optical engine projection system (2) according to the image in the ultraviolet CMOS camera (3).

8. A method for optical alignment and liquid level monitoring in SLA and DLP additive manufacturing according to claim 7, characterized in that: The projection pixel size of the DLP optical engine projection system (2) is 78μm×78μm.

9. A method for optical alignment and liquid level monitoring in SLA and DLP additive manufacturing according to claim 1, characterized in that: In S6, the slice data is read to start forming, and a single layer of slice is cured. The slice data divides the SLA working area and the DLP working area. Due to the coincidence of the coordinate systems of the forming plane, the SLA scanning area and the DLP projection area in step S5, according to the slice data, the SLA galvanometer system (1) and the DLP optical engine projection system (2) cooperate with each other to complete the single-layer curing.

10. A method for optical alignment and liquid level monitoring of SLA and DLP additive manufacturing according to claim 3 or 7, characterized in that: The working area of the ultraviolet CMOS camera (3) is 6.4mm×6.4mm, and the pixel size is 4.65μm×4.65μm.

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