WO2021103502A1

WO2021103502A1 - Multi-channel 3d printing method and 3d printing system

Info

Publication number: WO2021103502A1
Application number: PCT/CN2020/097101
Authority: WO
Inventors: 夏春光
Original assignee: 深圳摩方新材科技有限公司
Priority date: 2020-06-19
Filing date: 2020-06-19
Publication date: 2021-06-03

Abstract

A method and a system for multi-channel 3D printing, comprising: generating a 3D digital model of a sample to be printed, and cutting the 3D digital model into an image sequence; a microdisplay (50), by means of a projection lens (40), projecting an image onto the interface of a transparent window (304) of a printhead (30) with a photosensitive resin; an image collection unit (55) collecting an image reflected from a beam splitter (60) and measuring the quality of the projected image; exposing and printing, the printhead (30) having a plurality of transport channels (306), and controlling a printing material to be extruded from a transport channel and be scraped onto the surface of a substrate (90) or a sample by a hard edge on the end of the printhead (30); and when one layer of printing is complete, returning to position and switching to a transport channel (306) of a material required for a next layer, carrying same to a subsequent printing region by means of the printhead (30), completely printing the resin required for the next layer between the sample and the transparent window (304) of the printhead (30), and printing a next layer, until printing is complete. In the method and the system for multi-channel 3D printing, by means of a plurality of transport channels loading different printing resins, printing of different materials and flexible switching between the different printing materials is achieved, while also improving printing efficiency.

Description

Multi-channel 3D printing method and 3D printing system

Technical field

The present invention relates to 3D printing technology, in particular to a multi-channel 3D printing method and a 3D printing system.

Background technique

Stereo lithography was initially considered a rapid prototyping technology. Rapid prototyping includes a series of technologies that can be used to create real scale models of production components directly from computer aided design (computer aided design CAD) in a fast (faster than before) way. Since its disclosure in US Patent 4,575,330, stereolithography technology has greatly helped engineers visualize complex 3D part geometries, detect errors in prototype schematics, test key components, and verify at a relatively low cost and faster than before. Theoretical design.

In the past few decades, continuous investment in the field of micro-electro-mechanical systems (MEMS) led to the emergence of micro-stereolithography (μSL), which inherited the basic principles of traditional stereo lithography , But with higher spatial resolution. For example, K Ikuta and K. Hirowatari, "Using Stereo Lithography and Metal Molding for Real Three-Dimensional Micromanufacturing", the 6th IEEE Symposium on Microelectronics and Mechanical Systems in 1993, with the aid of single-photon polymerization and two-photon polymerization technology , The resolution of micro-stereolithography has been further enhanced to less than 200nm; for example, S.Maruo and K.Ikuta, "Three-dimensional micromachining by polymerization using single photon absorption", Appl.Phys.Lett.,vol.76,2000; S.Maruo and S.Kawata, "Two-photon absorption near-infrared photopolymerization for three-dimensional microfabrication", J.MEMS, vol. 7, pp.411, 1998; S. Kawata, HBSun, T. Tanaka and K.Takada, "Refined Features of Functional Microdevices", "Nature", Volume 412, Page 697, 2001.

The invention of projection micro-stereolithography (PμSL) by Bertsch et al. has greatly increased the speed. "Micro-stereolithography technology using liquid crystal display as a dynamic mask generator", Microsystem Technologies, p42-47, 1997; Beluze et al., "Micro-stereolithography technology: a new process for constructing complex 3D objects, MEM/MOEM Symposium on the design, testing and micromachining of ", SPIE Conference Proceedings, v3680, n2, p808-817, 1999. The core of this technology is a high-resolution spatial light modulator, which can be a liquid crystal display (LCD) panel or a digital light processing (DLP) panel, both of which can be obtained from the microdisplay industry.

Although projection micro-stereolithography technology has successfully achieved rapid manufacturing speed with good resolution, further improvements are still needed.

The display size of the DLP chip is currently limited to about 13mm. Therefore, when the projected pixel size is the same as the physical pixel size (5 to 8 microns), a single exposure area will be limited to half an inch. In order to print on a larger area with a single projection, the size of the projected pixels needs to be increased, thereby reducing the printing resolution (that is, the size of the projected pixels). PμSL (projection micro-stereolithography) has no significant advantage in multi-material manufacturing, because switching materials in the PμSL process will greatly reduce the speed. Therefore, based on the new technology of coating and spray cleaning (Kavin Kowsari, 3D Printing and Additive Manufacturing. Sep 2018.185-193) or the method of printing and then washing (Han D.et al, Additive Manufacturing, 2019.27: p(606-615) ) Was introduced to increase the speed, but the application of these technologies was impaired by bubble problems or a large amount of consumed resin. Therefore, there is still a need for a projection micro-stereolithography (PμSL) technology capable of multi-material manufacturing and large-area fast printing.

In projection micro-stereolithography (PμSL), there are three types of resin layer definition methods: the first uses a free surface, and the layer thickness is defined by the distance between the resin free surface and the sample stage. Due to the slow viscous movement of the resin, it takes more than half an hour to define a 10um thick resin layer with a viscosity of 50cPs when the printing area is larger than 1cm x 1cm. The second and third methods use transparent films or hard windows. Similarly, for these two cases, there is currently no good way to define a resin layer of 10um or less on an area of 5cm X 5cm or larger, especially for the film case, even if it is faster than the free surface case , It is still unimaginably slow. In the case of hard windows, the fluid force generated when the two surfaces of the sample and the print head are close and separated before or after exposure to define the thin layer is large enough to damage the sample.

In all 3D printing technologies, the accuracy and efficiency of size reproduction are very important. For example, in the immersion multi-material projection micro-stereolithography (PμSL) system (Figure 1), it is very important to have high precision and high efficiency in the dimensional control of all layers, so that the actual CAD model can be replicated within a period of time come out.

Summary of the invention

Based on this, it is necessary to provide a multi-channel 3D printing method that can improve printing efficiency.

At the same time, a 3D printing system that can improve printing efficiency is provided.

A multi-channel 3D printing method, including:

Slice: Generate a 3D digital model of the sample to be printed. The 3D digital model is a combination of different printing materials. The 3D digital model is sliced into an image sequence. Each image in the image sequence represents a layer of the 3D digital model. The slicing direction of the model controls the printing direction of the print head;

Projection: Send the image to the micro display device, the micro display device projects the image to the interface between the transparent window on the print head and the resin through the projection lens, and illuminates the projected image with light;

Image detection: The image acquisition unit collects the image reflected by the spectroscope to detect the quality of the projected image, and prints according to the quality control of the detection;

Exposure printing: exposure to produce a cured layer, the print head has multiple conveying channels for conveying printing materials, so that the substrate and the printing head move relative to each other, so that the printing heads move relatively to cover the printing area, and control the printing material to squeeze from the conveying channel Out, the hard edge of the end of the print head is scraped onto the surface of the substrate or sample for printing;

Continue to expose and print: After one layer is printed, control the print head to move away from the printing area, move the print head away from the sample, adjust the print head or sample stage to return, adjust the distance between the print head and the sample to print the thickness of the next layer, Change to the conveying channel of the material required for the next layer, bring it to the subsequent printing area through the print head, traverse the substrate or sample, and the gap between the sample and the transparent window of the print head is filled with the resin required to print the next layer, and expose Print, print the next layer, until the printing is completed, the model is copied in the resin tank.

In a preferred embodiment, different conveying channels of the print head convey different printing materials, and each conveying channel is correspondingly provided with a liquid flow controller and a shut-off valve, and the flow rate of the printing material is controlled by the liquid flow controller.

In a preferred embodiment, the conveying channel is provided with four on the four sides of the print head, the print head is a trapezoid with a large top and a small bottom, and the print head is formed with a large top and a small bottom. The inner cavity of the trapezoidal cross-section forms a flat conveying channel on the outside of the inner cavity. The inner cavity of the print head forms a tapered end close to the base, and the tapered end covers the non-stick film and forms a transparent window.

In a preferred embodiment, the substrate is set on a printing platform, and the printing platform drives the substrate to move in the X, Y, and Z directions according to printing. When exposing printing or continuing to expose printing, control according to P=P ₀ +P ₁ The pressure of the print head is to compensate for the deformation of the transparent window caused by its contact with the printing resin. P ₀ is the pressure of the non-stick mold of the print head to the atmospheric pressure of air, P ₁ =ρ ₁ gh, ρ ₁ is the resin density, g acceleration of gravity, h It is the depth of the non-stick film of the print head under the resin; during printing, the pressure in the print head is controlled by the flow of gas. If the pressure sensor detects that the pressure of the print head is different from the set pressure, the mass flow controller is controlled according to PID Set the adjustment flow until the pressure in the print head reaches the set value.

In a preferred embodiment, it further includes a restrictor arranged at the downstream outlet of the print head, the restrictor is in a flow blocking state, and the flow of the restrictor is proportional to the pressure of the print head.

In a preferred embodiment, if the printed image is larger than a single exposure size, stitch printing is performed, the image is divided into layer parts, the layer parts are printed step by step, and the edges are stitched together to form a whole layer, and each layer part overlaps on the stitching edge. -20 microns.

In a preferred embodiment, when printing, error compensation is performed on the X/Y direction movement coordinates of the printing platform (X ₀ +XError(X ₀ ,Y ₀ ),Y ₀ +YError(X ₀ ,Y ₀ )), (X ₀ ,Y ₀ ) are theoretical coordinates,

XError(X ₀ ,Y ₀ )=C ₁ +C ₂ +C ₃ Y ₀ +C ₄ X ₀ Y ₀ +C ₅ X ₀ ² +C ₆ Y ₀ ²

YError(X ₀ ,Y ₀ )=D ₁ +D ₂ +D ₃ Y ₀ +D ₄ X ₀ Y ₀ +D ₅ X ₀ ² +D ₆ Y ₀ ²

C ₁ -C ₆ polynomial coefficients, based on the stitching and printing, the measurement error of the stitching point in the X direction is calculated by the quadratic least squares method.

The D ₁ -D ₆ polynomial coefficients are calculated based on the measurement error of the splicing points in the Y direction during splicing printing using the quadratic least squares method.

In a preferred embodiment, when the print head is moved and stopped for exposure, the micro display device is controlled to project a picture on the center of the non-stick film of the print head, and the image acquisition unit captures and analyzes the imaging quality, and compares the imaging with the set theoretical value Compare, if the non-stick mold of the print head is deformed, according to the deformation formula

Adjust the flow to adjust the pressure in the print head. The deformation of the non-stick film set at the cone end of the print head is proportional to the pressure difference, υ Poisson coefficient, a is the radius of the non-stick mold of the print head, E Young's modulus, h is The thickness of the non-stick mold of the print head, p is the pressure difference between the two sides of the non-stick mold of the print head.

A 3D printing system, including: an image system that establishes a 3D digital model and cuts the 3D digital model into an image sequence, a control system, and a micro-display of the interface between the non-stick mold and the resin that is controlled to receive the series of pictures and project them to the print head A device, a projection lens set corresponding to the micro display device and controlled to perform projection, an image acquisition unit that collects and detects the quality of the projected image, and is set corresponding to the image acquisition unit and reflects the projected image to the image acquisition The unit receives and collects the spectroscope, the printing platform, the substrate arranged on the printing platform, the resin tank arranged under the substrate or the sample, and the printing head of the bucket structure corresponding to the printing platform. The printing head Including: the inner cavity of a hollow trapezoid, a transparent window formed by a non-stick film covering one end of the inner cavity, a plurality of conveying channels arranged on the side, and a device corresponding to the conveying channel and controlling the flow rate of the printing material in the conveying channel A liquid flow controller, a mass flow controller arranged corresponding to the inner cavity and controlled to control the pressure of the input gas flow to the non-stick film, and a flow restrictor arranged at the downstream outlet of the print head.

In a preferred embodiment, the four conveying channels are arranged on the four sides of the print head. The four conveying channels are formed by the trapezoidal side walls of the inner cavity and the side walls of the outer cavity arranged in parallel. The four conveying channels are separated from each other. Set up and deliver different printing materials, and each conveying channel is equipped with a liquid flow controller to control the flow rate of the printing material in each conveying channel separately

The above-mentioned multi-channel 3D printing method and 3D printing system adopt a multi-conveying channel print head and load different printing resins through multiple conveying channels to realize printing of different materials and flexible switching between different printing materials, while improving printing efficiency and saving printing time .

In addition, a unique method of splicing multiple exposure printing is adopted to solve the problem, which can move the image (lens) or the sample. The present invention moves the sample. At the same time, the hard edge of the print head is actually a coating squeegee, and the splicing movement and coating steps are performed at the same time, saving time and improving efficiency.

In addition, the non-stick membrane is used to make the membrane and the sample stagger and separate, which reduces the force on the sample during separation by an order of magnitude.

On the other hand, for resins with high viscosity (>500cPs), it is almost impossible to apply a very thin (~10 microns) resin layer every time when a film covering the entire print format (>50mmX50mm) is used. In large format, the resin driving pressure gradient provided by the tension of the film is very small, making the resin flow extremely slow. The invention adopts a film much smaller than the printing width, so that under the same film deformation, the driving pressure gradient of the resin is increased by an order of magnitude to increase the printing speed and accuracy.

Description of the drawings

FIG. 1 is a schematic diagram of a part of the structure of a 3D printing system according to an embodiment of the present invention;

Figure 2a is a cross-sectional view of a partial structure of a print head according to an embodiment of the present invention;

Figure 2b is a top view of a partial structure of a print head according to an embodiment of the present invention;

3 is a schematic diagram of track errors in the x and y directions of the 3D printing system during splicing printing according to an embodiment of the present invention;

4 is a schematic diagram of three exposure modes according to an embodiment of the present invention;

FIG. 5 is a schematic diagram of a process of printing and switching material printing by a 3D printing system according to an embodiment of the present invention;

FIG. 6 is a schematic diagram of an exposure printing process of a 3D printing system according to an embodiment of the present invention.

Detailed ways

The multi-channel 3D printing method according to an embodiment of the present invention includes:

Continue to expose and print: After one layer is printed, control the print head to move away from the printing area, move the print head away from the sample, adjust the print head or sample stage to return, adjust the distance between the print head and the sample, and print the thickness of the next layer. Use the conveying channel of the material required for the next layer to pass through the print head to the subsequent printing area, traverse the substrate or sample, and the gap between the sample and the transparent window of the print head is filled with the resin required to print the next layer, and expose and print , Print the next layer, until the printing is completed, the model is copied in the resin tank.

The printing of the present invention starts from the establishment of a geometric model by a computer or an image system. The model can be a combination of multiple entities, and each entity represents a material. The 3D digital model is sliced into two-dimensional pictures in one direction. If there are multiple entities in a layer, the same number of layer partial pictures will be generated, which are generally black and white, and may have grayscale. Each layer picture represents a thin layer in the 3D digital model. The slicing direction of the model will be the printing direction of the printer. The resulting series of pictures will be read by the printer in turn and projected onto the interface between the non-stick film and photosensitive resin at the end of the print head through the DLP with a 405-nanometer light source. At the same time, a graphic image acquisition unit such as a CCD camera will split the light The image reflected by the mirror judges the quality of the projected image. Within a certain exposure time, a certain thickness of cured layer will be produced where there is light, which represents the corresponding layer in the model represented by the projected picture. When the upper layer is exposed and printed, the print head will move away from the sample. The printing material here may be a simple photosensitive resin, or a paste formed by mixing photosensitive resin and solid particles.

The sample stage will return according to different printing forms. After returning, the distance between the print head and the sample is the thickness of the next layer to be printed, and the gap between the sample and the print head film will be filled with the resin needed to print the next layer Floor. The exposure is repeated in sequence, and the model is copied in the resin tank as the sample stage descends layer by layer.

Since micro display devices such as LCD or DLP chips have a certain size, such as 1920X1080 pixel DLP, with an optical precision of ten microns, the printing area covered by a chip is only 19.2mmX10.8mm. Therefore, when the size of the sample is smaller than a chip When covering an area, we call it single projection mode. When the sample size exceeds the range covered by a chip, the present invention adopts the splicing printing mode. In splicing printing mode, the picture representing one layer of the model will be further cut into multiple pictures that are smaller than a single DLP resolution, that is, the layer part. For example, a 3800X2000 pixel picture can be cut into four 1900X1000 sub-pictures, and each sub-picture will represent a quarter of the area in a layer. For each layer in the model, it will be completed through multiple exposures, and all sub-pictures of the current layer are projected in turn, that is, the layer part. In order to improve the mechanical properties at the junction of adjacent areas/pictures, a certain amount of overlap is usually given, usually 5-20 microns. The position and overlap of the exposure of each area are precisely controlled by the XY axis combination. There are two coordinate systems in the system, one is a DLP/LCD vertical coordinate system, and the other is a motion coordinate system composed of XY axes. If the two coordinate systems are not completely parallel due to mechanical assembly errors, there will be misalignment errors in adjacent areas during stitching and printing. For this reason, the measured error is compensated in the stitching printing mode. Due to the existence of the X and Y axes of the printing platform, for samples smaller than the printer's print format, multiple identical samples can be printed repeatedly in the entire format, which can increase the speed of mass production. This is the matrix printing mode.

Furthermore, the different conveying channels of the print head of this embodiment convey different printing materials, and each conveying channel is correspondingly provided with a liquid flow controller (LFC) and a shut-off valve, and the flow rate of the printing material is controlled by the liquid flow controller.

Further, the conveying channel of this embodiment is provided with four on the four sides of the print head. The print head is a trapezoidal body with a large upper and a small bottom. The print head is formed with an inner section of a trapezoidal cross-section with a large upper and a lower bottom. A flat conveying channel is formed on the outside of the cavity and the inner cavity. The inner cavity of the print head forms a tapered end at one end close to the substrate, and the tapered end covers the non-stick film and forms a transparent window.

Further, the substrate of this embodiment is set on a printing platform, and the printing platform drives the substrate to move in the X, Y, and Z directions according to printing. When exposure printing or continuing exposure printing, the pressure of the print head is controlled _{according to P=P 0} +P ₁ To compensate for the deformation of the transparent window caused by contact with the printing resin. P ₀ is the pressure of the non-stick mold of the print head to the atmospheric pressure of air, P ₁ =ρ ₁ gh, ρ ₁ is the resin density, g acceleration of gravity, and h is the depth of the non-stick film of the print head under the resin; when printing, air is passed through The flow rate controls the pressure in the print head. If the pressure sensor detects that the pressure of the print head is different from the set pressure, the mass flow controller is controlled to adjust the flow according to the PID setting until the pressure in the print head reaches the set value.

Furthermore, the print head 30 of this embodiment further includes a flow restrictor 312 provided at the downstream outlet of the print head 30. The orifice of the orifice at the downstream outlet of the restrictor 312 is small enough (<50 microns) to be in a flow-blocking state, and its flow rate is only proportional to the upstream pressure in the print head.

When the actual pressure measured by the pressure sensor of the print head 30 is lower than the set pressure, the upstream mass flow controller (MFC mass flow controller) will increase the flow appropriately according to the PID (Proportion Integration Differentiation) setting , Until the pressure in the print head reaches the set value. vice versa.

Further, in this embodiment, if the printed image is larger than a single exposure size, stitch printing is performed, the image is divided into layer parts, the layer parts are printed step by step, and the edges are stitched together to form a whole layer, and each layer part overlaps on the stitching edge 5- 20 microns.

The printing process first generates a 3D model in a computer or image system, and then cuts the digital model into a series of images, where each image represents a layer of the model (such as 5 to 20 microns). The control computer or imaging system sends the image to the micro display device (such as DLP (digital light processing) or LCD (liquid crystal display)), and the image is projected onto the bottom surface of the print head (wet surface) through the projection lens )on. The bright areas converge, while the dark areas remain liquid. Due to the size limitation of LCD or DLP chips, such as a DLP chip with 1920X1080 pixels at 10um printing optical resolution, a single exposure only covers an area of 19.2mmX10.8mm. Therefore, if the cross section of the sample is larger than 19.2mmX10.8mm, it cannot be printed using a single exposure method. The invention provides a multi-exposure splicing printing method. In this way, the image representing the layer of the 3D model is further divided into multiple smaller images or layer parts, each of which is not larger than the DLP pixel resolution. For example, an image with a pixel resolution of 3800X2000 can be divided into four 1900X1000 sub-images, and each sub-image represents a quarter of the layer. As a result, the entire layer of the model will be printed section by section based on the sub-image. In order to improve the mechanical strength of the shared edge of adjacent parts, there is usually an overlap of about 5-20 microns on the edge.

XY printing platform components can precisely control the precise position and overlap amount. There are two coordinate systems: one is the vertical coordinate system with the DLP/LCD panel, and the other is the movement coordinate system composed of the XY axis of the printing platform. When the two coordinate systems are not parallel due to assembly tolerances, there will be offset errors on the shared edges of adjacent sections. As shown in Figure 3, A is the size of a single exposure; B is the result of accurate alignment in the x direction; C is the result of an error offset in the x direction; B'is the result of accurate alignment in the y direction; C' It is the result of the error offset in the y direction. In precision printing, the error requirement is less than 10um, and the assembly tolerance of the stage is usually within the allowable range; and the offset is not linear with the moving distance of the printing platform. Therefore, in the present invention, the offset is measured at 5 or more uniformly distributed points in the x and y directions of the square sample printed in the full range. The offset error curve of at least second-order polynomial interpolation will be introduced into the translation in the XY direction to compensate for the offset, so as to ensure that the accuracy of the spliced printed samples is within the specification range.

_{When printing, perform error compensation (X 0} +XError(X ₀ ,Y ₀ ),Y ₀ +YError(X ₀ ,Y ₀ )) on the X/Y direction movement coordinates of the printing platform, (X ₀ ,Y ₀ ) is Theoretical coordinates,

Specifically, for precise splicing and printing (<10 microns error), first splicing and printing 20X10 pieces of connected rectangles with a size of 19.2X10.8X0.1 mm thick on the full-frame sample table, if there are theoretically 100 With a micron overlap, these squares will provide 19X9 splicing point data and their coordinates. Measure the actual overlap amount in the X direction and Y direction before the printed sample is taken off the sample stage. For example, the actual stitching overlap in the X direction is 80, and the error in the X direction at this coordinate point is XError(x,y) =100-80=20 microns, repeated measurement will get 19X9=171 points of error in the X direction, and also get the same 171 points of error in the Y direction.

Assume that the quadratic error function of the XY telecontrol system on the entire printing platform is:

XError(x,y)=C ₁ +C ₂ x+C ₃ y+C ₄ xy+C ₅ x^2+C ₆ y^2,

YError(x,y)=D ₁ +D ₂ x+D ₃ y+D ₄ xy+D ₅ x^2+D ₆ y^2,

Here x, y are coordinates, and C and D are polynomial coefficients. C _1～6 and D _1～6 can be calculated by the quadratic least squares fitting calculation based on the measurement errors in the X direction and the Y direction at 171 points. In this way, the axis motion error distribution in the entire printing area is obtained. These two error formulas will be used to correct the movement error of the axis. For example, the axis should go to the theoretical value (X ₀ , Y ₀ ). According to the error formula, the control command of the axis requires the axis to go to (X ₀ +XError (X ₀ ,Y ₀ ),Y ₀ +YError(X ₀ ,Y ₀ )).

When the print head stops and prepares for exposure after moving, control the micro display device to project a picture on the center of the non-stick film of the print head. The image acquisition unit captures and analyzes the imaging quality, and compares the imaging with the set theoretical value. If the print head is not sticky Mold deformation, according to the deformation formula

Adjust the flow rate to adjust the pressure in the print head. The deformation of the non-stick film set at the cone end of the print head is proportional to the pressure difference, υ Poisson coefficient, a is the radius of the non-stick mold of the print head or half of the diagonal length, E Yang The modulus, h is the thickness of the non-stick mold of the print head, and p is the pressure difference between the two sides of the non-stick mold of the print head.

As shown in Figures 1, 2a and 2b, a 3D printing system 100 according to an embodiment of the present invention includes: an image system that establishes a 3D digital model and cuts the 3D digital model into an image sequence, a control system, and a controlled receiving image and projecting it onto The micro display device 50 of the interface between the non-stick mold of the print head and the resin, the projection lens 40 that is set corresponding to the micro display device and controlled to perform projection, the image acquisition unit 55 that collects and detects the quality of the projected image, and the image acquisition unit 55 correspondingly set and reflect the projected image to the image acquisition unit 55 to receive the collected spectroscope 60, the printing platform 80, the substrate 90 arranged on the printing platform 80, the resin tank 70 arranged under the substrate or the sample, corresponding to the printing platform Set the print head 30 of the bucket-shaped structure.

The print head 30 of this embodiment includes: a hollow trapezoidal inner cavity 302, a transparent window 304 formed by a non-stick film covering one end of the inner cavity 302, a plurality of conveying channels 306 arranged on the side, corresponding to the conveying channels A liquid flow controller 308 that sets and controls the flow rate of the printing material in the conveying channel, a mass flow controller 310 that is set corresponding to the inner cavity 302 and controls the input gas flow to generate pressure on the non-mucosal film, and is set at the downstream outlet of the print head The restrictor 312. A scraper 301 is formed at the end of the outer wall of the print head 30 to scrape the resin.

The image system and control system of this embodiment can be implemented by using the computer 20, or can be implemented by using a graphics processing chip and a control chip, respectively.

Further, the micro display device of this embodiment is a DLP or LCD chip. Of course, other chips can also be used as needed.

Preferably, the image acquisition unit of this embodiment can be implemented by using a CCD. Of course, other devices with image acquisition and processing functions, such as CMOS, can also be used.

Furthermore, the substrate 90 of this embodiment is connected to the printing platform 80 through the substrate arm 92.

There are four conveying channels 306 on the four sides of the print head. The four conveying channels 306 are formed by the trapezoidal side walls of the inner cavity and the side walls of the outer cavity arranged in parallel. The four conveying channels are spaced apart from each other and convey different printing materials. Each conveying channel is provided with a liquid flow controller 308 to control the flow rate of the printing material in each conveying channel 306 respectively.

In an embodiment of the present invention, the size of the transparent window of the print head should be set to cover the projection size of a single DLP/LCD chip. For example, if the projection of a 17mm chip is 20mm and the pixel resolution is 10μm, the rectangular window can be set to a diagonal of about 24mm.

The transparent window formed by the non-stick film of the tapered end of the print head of this embodiment is preferably a 130um thick film of DuPont Teflon AF2400, which is breathable and has excellent optical clarity. Gas permeability, especially oxygen permeability, makes the film non-sticky during photopolymerization, because oxygen is a photocrosslinking inhibitor. Of course, other films such as polydimethylsiloxane (PDMS) films or surface-coated hard windows can also be used. When the print head is in contact with the resin, the tip of the print head is liquid-tightly sealed.

Assuming that the film has linear elasticity, the deflection in the center of the non-stick film in the resin due to pressure is deformation

Where υ is the Poisson's ratio of the membrane, ɑ is the radius of the circular membrane tip, E is the Young's modulus, h is the thickness, and p is the pressure difference between the two sides of the membrane. It shows that the deformation of the tip is proportional to the pressure difference; therefore, the deflection of the non-mucosal membrane can be eliminated by controlling the pressure in the print head and the pressure difference on both sides

The liquid pressure on the wet surface of the transparent window of the print head (that is, the surface in contact with uncured resin or other printing materials) may be caused by too much resin under the non-stick film. Therefore, the pressure inside the print head should be controlled to compensate for the liquid pressure to eliminate the deformation of the non-sticky transparent window.

A mass flow controller (MFC), a combination of a flow restrictor at the downstream outlet of the print head and a pressure sensor on the print head controls the pressure P in the print head.

The thickness of the non-stick oxygen suppression layer can be improved by increasing the oxygen concentration in the print head; therefore, MFC can use the flow rate of various oxygen concentration mixtures to control the pressure. The membrane and the seal together form part of the inner cone of the print head.

The conveying channel is arranged on the outer side of the inner cavity cone. The four channels sequentially form a hollow inner cone shape and are flat. These channels (ie four channels) are connected to the liquid flow controller (LFC) and the shut-off valve. Each LFC controls the flow rate of one resin. The resin is incompressible, so the LFC and shut-off valve are located upstream of the outlet of the conveying channel, and the flow can be controlled and stopped immediately. This can minimize the amount of resin used in the printing process.

As shown in FIG. 4, with the aid of the XY platform, the 3D printing of this embodiment provides three printing modes.

When printing a single sample smaller than a single exposure size, if only one printing material is required in the exposed area, the printing platform will not move during the printing process. However, in the case of using multiple materials, the printing platform moves to apply the selected resin. This is called a single exposure mode.

If multiple identical samples are needed, the printing platform moves gradually along X and Y and prints the same samples in an array. This is called the array exposure mode. For small batch production, this mode is definitely faster than repeated single exposure mode. When the sample size increases beyond the size of a single exposure, the system will further divide one layer into multiple parts by overlapping 5um to 20um on the shared edge, and stitch adjacent parts into a whole layer. This is the stitching exposure mode.

When a sample requires multiple identical samples, but stitching is required because the sample is larger than a single exposure, the stitching mode can be used in combination with the array mode.

The print head 30 of this embodiment is located on the upper part of the sample or the substrate (if it is the first layer), and the distance between the print head and the sample or the substrate (when it is the first layer) is equal to the thickness of the current layer ( Figure 5). Taking two opposite resin conveying channels A and C as an example (Figure 5), in order to coat resin C on the substrate, the conveying channel for conveying resin C is placed in the moving direction of the print head 30 relative to the substrate during the printing process. Coating. The same can be achieved by moving the substrate and moving the print head. When the substrate moves, the resin C is extruded from the slit outlet of the flat conveying channel, and is immediately scraped to the substrate surface (if it is the first layer or the top) by the hard edges on the inner cone of the print head. As shown in

steps

2 and 3, when resin C is coated on a substrate or sample, it may take several seconds for the new resin layer in contact with the film to settle.

Then, DLP projects the layer image onto the wet surface of the film in step 4. To change the material of the adjacent area to A, move the print head to ensure that the conveying path for conveying resin A is 2 to 3 mm away from the designated printing area, and then start compressing resin A in step 5 and move it as in step 6. And scratch. After the DLP projects the image on the resin A in step 7, the substrate adjusts the position of the conveying channel for conveying the resin C in

steps

8 and 9 to print the next layer. In order to scrape the resin, it is important to control the resin flow rate from the LFC to ensure that the thickness of the new layer is correct. A resin flow rate lower than required will cause the layer to be thinner than designed because the vacuum effect due to less resin will pull the film toward the sample or substrate.

The minimum flow rate of the resin depends on the volume conservation during the coating process:

R=H*t*V

R is the volume flow, H is the width of the print head, t is the thickness of the current layer, and V is the relative speed between the print head and the substrate. The flow rate must be higher than this value and further optimized according to the viscosity of the resin. Thinner resin tends to flow and drip into the resin tank below, so the flow rate needs to be higher. The movement of the print head depends on which resin is to be used in the next area.

As shown in Figure 6, the

numbers

1 and 2 represent the sequence of platform movement. For example, in resin A or C printing, the substrate first moves the conveying path for conveying A or resin C away from the new area by 2 to 3 mm, but keeps facing the new area, and then the print head 30 squeezes and coats the new area Fresh resin is in the scraping motion.

The operation of printing resins B and D is similar, but the substrate needs to be moved in a roundabout way to align the designated channel with the new area. During the printing process, the movement of the print head relative to the sample is always shearing. After printing a complete layer, the print head will move beyond the boundary of the sample before the sample stage moves down to a thickness to define the next layer of fresh resin. By maintaining the shear movement between the print head and the sample, the interaction force between the print head and the sample is only the fluid shear force.

The fluid shear force is much smaller than the vertical or normal separation of the two surfaces in the typical resin in existing projection micro-stereolithography. As shown in the following formula:

σ=-pI+2με

σ is the fluid stress tensor, p is the pressure, I is the definite tensor, μ is the fluid viscosity, and ε is the velocity gradient tensor (or fluid strain tensor). For two surfaces that are almost in contact with each other, they are separated in a resin with a viscosity of 50 cPs at a speed of 10 mm/s, and the vacuum effect is usually about 1e5Pas. However, if the two surfaces cut each other with a gap of 20um, the force is about 1e2Pas. Therefore, this method greatly reduces the possibility of damage or deformation of the sample.

After moving the substrate down to a new layer space, the print head will move in and begin to scan and print the next layer step by step.

In the present invention, the sample can be moved in the X, Y, and Z directions, or the print head can be moved while keeping the sample fixed.

The method of the present invention not only provides more precise control in a larger printing area (for example, a 10cm×10cm printing area with a layer thickness of 10um) at a higher speed and a desired layer thickness, but also allows switching printing materials, such as Switch to use at least 4 resins during printing.

The invention uses a print head to scan the sample step by step, and the print head can be as large as one exposure of the entire DLP chip or part of the DLP chip. This method greatly improves the dimensional accuracy of samples printed using the projection micro-stereolithography (PμSL) system, and by combining the switching of printing materials (for example, the switching of resin) and the coating process, the printing speed is significantly improved .

The printing material used in the present invention generally refers to resin. For example, light-curable resins used in the industry for printing and curing when constructing layers in 3D printing operations.

The print head of the present invention has a hard flat tip at one end. The end of the trapezoidal internal cavity of the print head is covered and sealed by a non-stick film. The non-stick film may comprise gas permeable materials, especially oxygen permeable materials, such as polydimethylsiloxane (PDMS) or Teflon AF from DuPont. The outer conveying channels are flat and connected to the tapered outer wall of the inner cavity. The 4 resin channels extrude different resins and coat the top of the sample as needed.

Further, the print head 30 of this embodiment may be provided with an ultrasonic source with a frequency exceeding 10 kHz to increase the flow speed of the resin, for example, a piezoelectric ceramic vibrator is bonded to the print head housing.

Further, the print head 30 of the present embodiment has pressure control to compensate for the deformation of the film or the hard window due to contact with the printing material. The pressure control gas may be a gas that prevents the sample from adhering to the film or hard window during the polymerization process, such as oxygen or a mixture thereof.

The 3D printing system of the present invention includes: a micro display device such as LCD or DLP micro display chip that uses a light source to display digital images from an image system or computer, a projection lens with an optical axis, and a printing with a sealed, optically transparent and air-permeable flat head Head, image acquisition unit capable of monitoring the projection on the print head, such as a charge-coupled device (CCD), a printing platform that can control the movement of the sample substrate or the print head in the X, Y, and Z directions, and a resin tank. The resin tank is used to collect excessive resin dripping from the print head 30.

The 3D printing system of the present invention is arranged relative to the surface of the substrate, the projection lens is located between the substrate surface and the CCD and above the substrate, the optical axis of the projection lens intersects the substrate surface, and the CCD can be focused by the lens along the optical axis of the projection lens .

The present invention provides three printing modes. When only one sample smaller than the size of a single exposure is needed, it is called a single exposure mode. If multiple samples are needed, the XY printing platform will gradually move and print the same samples in the array, which is called the array exposure mode. When the sample size increases to exceed the size of a single exposure, the system will further divide a layer into multiple parts by overlapping 5um to 20um on the adjacent edge or common edge, and stitch adjacent parts into a whole layer. This is splicing Exposure mode. It is also possible to combine stitching mode and array mode.

The present invention is based on the interpolation offset error curve of the measurement data from the actual sample to compensate the mechanical tolerance in the translation of the printing platform in the XY direction, so as to ensure that the accuracy of the spliced printed sample is within the specification range.

The tapered end of the print head 30 of the present invention is above the sample, or, if used for the first layer, above the substrate.

The distance from the end of the print head to the top of the sample or the substrate (if it is the first layer) is the thickness of the current layer. After one exposure, the print head moves into a new area while squeezing the resin, where the hard edge on the tip of the inner cone serves as a resin coating scraper. The coating thickness is determined by the gap between the flat end of the print head and the top layer of the sample. In the present invention, the sample can be moved in the XYZ direction through the printing platform, or the print head can be moved while the sample remains stationary.

The print head is positioned so that the side carrying the conveying channel for transporting the printing material of this layer first follows a line that traverses the substrate or sample, and this line specifies the direction in which the print head is brought to the printing area. The print head is moved relative to the substrate by moving the substrate, the print head or the substrate and the print head at the same time, so that the print head covers the print area. When the print head moves to cover the print area, the print material is removed from the one that carries the print material of this layer. Extruded from the exit of the flat conveying channel, the printing material is immediately scraped onto the surface of the substrate or sample by the hard edge of the flat tip, and then stops moving the print head relative to the size of the substrate, and squeezes and prints once the print head covers the printing area material. Send the image from the control computer to the LCD micro display chip or DLP micro display chip, project the image from the LCD or DLP chip through the lens onto the flat surface of the print head, and then irradiate the projected image with light. By moving the print head away from the printing area and placing the print head so that the side with the conveying channel for conveying the material to be printed, change the printing material used to print the next layer or the part of the next layer, which is first along the cross The line of the subsequent printing area specifies the direction in which the print head is brought to the subsequent printing area, and then printing and scraping are performed. The subsequent printing area is located in the newly printed layer in the new layer at the top of the print head, which is the same as the printed layer. The adjacent layer part.

After printing the entire layer, the print head will move beyond the periphery of the sample. After that, the sample stage will move down a distance equal to the thickness of the next layer of printing material, and then print the next layer. The printing material is composed of a light-curing resin or a mixture of a photosensitive resin and solid particles. The transparent window material of the print head is an oxygen-permeable material. Preferably, the transparent window material is polydimethylsiloxane or polytetrafluoroethylene AF.

The pressure in the print head is controlled to compensate for the deformation of the transparent window caused by contact with the printing material. The pressure inside the print head is controlled by controlling the flow of gas introduced into the head. The gas introduced into the print head includes oxygen. The pressure P in the print head is controlled by a combination of a mass flow controller (MFC), a downstream restrictor and a pressure sensor on the print head controller. The outer surface of the inner cone of the print head is attached to at least four conveying channels, each conveying channel being attached to a different surface on a different side of the inner cone. The conveying channel is connected to a liquid flow controller and a shut-off valve, wherein each liquid flow controller controls the flow rate of a light-curing resin. The movement of the print head is controlled by three precision levels in the X, Y and Z directions. It is also possible to use the three precision levels of the substrate in the X, Y and Z directions to control the movement. The printing platform controls the movement of the printing head and/or the substrate at least in the X and Y directions.

Taking the above-mentioned ideal embodiment based on this application as enlightenment, through the above description, relevant staff can make various changes and modifications without departing from the scope of the technical idea of this application. The technical scope of this application is not limited to the content in the specification, and its technical scope must be determined according to the scope of the claims.

Those skilled in the art should understand that the embodiments of the present application can be provided as methods, systems, or computer program products. Therefore, this application may adopt the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware. Moreover, this application may adopt the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program codes.

This application is described with reference to flowcharts and/or block diagrams of methods, devices (systems), and computer program products according to embodiments of this application. It should be understood that each process and/or block in the flowchart and/or block diagram, and the combination of processes and/or blocks in the flowchart and/or block diagram can be realized by computer program instructions. These computer program instructions can be provided to the processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing equipment to generate a machine, so that the instructions executed by the processor of the computer or other programmable data processing equipment are used to generate It is a device that realizes the functions specified in one process or multiple processes in the flowchart and/or one block or multiple blocks in the block diagram.

These computer program instructions can also be stored in a computer-readable memory that can direct a computer or other programmable data processing equipment to work in a specific manner, so that the instructions stored in the computer-readable memory produce an article of manufacture including the instruction device. The device implements the functions specified in one process or multiple processes in the flowchart and/or one block or multiple blocks in the block diagram.

These computer program instructions can also be loaded on a computer or other programmable data processing equipment, so that a series of operation steps are executed on the computer or other programmable equipment to produce computer-implemented processing, so as to execute on the computer or other programmable equipment. The instructions provide steps for implementing the functions specified in one process or multiple processes in the flowchart and/or one block or multiple blocks in the block diagram.

Claims

A multi-channel 3D printing method is characterized in that it comprises:

Slice: Generate a 3D digital model of the sample to be printed. The 3D digital model is a combination of different printing materials. The 3D digital model is sliced into an image sequence. Each image in the image sequence represents a layer of the 3D digital model. The slicing direction of the model controls the printing direction of the print head;

Projection: Send the image to the micro display device, the micro display device projects the image to the interface between the transparent window on the print head and the resin through the projection lens, and illuminates the projected image with light;

Image detection: The image acquisition unit collects the image reflected by the spectroscope and detects the quality of the projected image, and prints according to the quality control of the detection;

Exposure printing: exposure to produce a cured layer, the print head has at least two conveying channels for conveying printing materials, so that the substrate and the printing head move relative to each other, so that the printing heads move relatively to cover the printing area, and control the printing materials from the conveying channel Extrusion, the hard edge of the end of the print head is scraped onto the surface of the substrate or sample for printing;

Continue to expose and print: After one layer is printed, control the print head to move away from the printing area, move the print head away from the sample, adjust the print head or sample stage to return, adjust the distance between the print head and the sample to print the thickness of the next layer, Change to the conveying channel of the material required for the next layer, bring it to the subsequent printing area through the print head, traverse the substrate or sample, and the gap between the sample and the transparent window of the print head is filled with the resin required to print the next layer, and expose Print, print the next layer, until the printing is completed, the model is copied in the resin tank.
The multi-channel 3D printing method according to claim 1, wherein the different conveying channels of the print head convey different printing materials, and each conveying channel is correspondingly provided with a liquid flow controller and a shut-off valve, which are controlled by the liquid flow The device controls the flow rate of the printing material.
The multi-channel 3D printing method according to claim 2, wherein the conveying channel is provided with four on the four sides of the printing head, and the printing head is a trapezoidal body with a large upper and a lower one, and the printing An inner cavity with a trapezoidal cross-section is formed in the head, and a flat conveying channel is formed outside the inner cavity. One end of the inner cavity of the printing head close to the base forms a tapered end, and the tapered end covers the non-mucosal membrane and forms a transparent window.
The multi-channel 3D printing method according to claim 1, wherein the substrate is set on a printing platform, and the printing platform drives the substrate to move in the X, Y, and Z directions according to printing. When the exposure printing or the exposure printing continues, According to P=P 0 +P 1, the pressure of the print head is controlled to compensate for the deformation of the transparent window caused by its contact with the printing resin. P 0 is the pressure of the non-stick mold of the print head to the atmospheric pressure of air, P 1 ＝ρ 1 gh,ρ 1 Is the resin density, g acceleration of gravity, h is the depth of the non-stick film of the print head under the resin; during printing, the pressure in the print head is controlled by the flow of gas, if the pressure sensor detects that the pressure of the print head is different from the set pressure When, control the mass flow controller to adjust the flow according to the PID setting until the pressure in the print head reaches the set value.
The multi-channel 3D printing method according to claim 4, further comprising a restrictor arranged at the downstream outlet of the print head, the restrictor is in a flow blocking state, and the flow of the restrictor is proportional to the pressure of the print head.
The multi-channel 3D printing method according to any one of claims 1 to 5, characterized in that if the printed image is larger than a single exposure size, stitching printing is performed, the image is divided into layer parts, the layer parts are printed step by step, and the edges are stitched together In a whole layer, each layer part overlaps 5-20 microns on the splicing edge.
The multi-channel 3D printing method according to claim 6, characterized in that, during printing, error compensation is performed on the X/Y direction movement coordinates of the printing platform (X 0 +XError(X 0 ,Y 0 ),Y 0 +YError (X 0 ,Y 0 )), (X 0 ,Y 0 ) are theoretical coordinates,

XError(X 0 ,Y 0 )=C 1 +C 2 +C 3 Y 0 +C 4 X 0 Y 0 +C 5 X 0 2 +C 6 Y 0 2

YError(X 0 ,Y 0 )=D 1 +D 2 +D 3 Y 0 +D 4 X 0 Y 0 +D 5 X 0 2 +D 6 Y 0 2

C 1 -C 6 polynomial coefficients, based on the stitching and printing, the measurement error of the stitching point in the X direction is calculated by the quadratic least squares method.

The D 1 -D 6 polynomial coefficients are calculated based on the measurement error of the splicing points in the Y direction during splicing printing using the quadratic least squares method.
The multi-channel 3D printing method according to any one of claims 1 to 5, characterized in that, when the print head is moved and then stopped to prepare for exposure, the micro display device is controlled to first project a picture on the center of the non-stick film of the print head, and the image is collected The unit captures and analyzes the imaging quality, and compares the imaging with the set theoretical value. If the non-stick mold of the print head deforms, according to the deformation formula

Adjust the flow to adjust the pressure in the print head. The deformation of the non-stick film set at the cone end of the print head is proportional to the pressure difference, υ Poisson coefficient, a is the radius of the non-stick mold of the print head, E Young's modulus, h is The thickness of the non-stick mold of the print head, p is the pressure difference between the two sides of the non-stick mold of the print head.
A 3D printing system, including: an image system that establishes a 3D digital model and cuts the 3D digital model into an image sequence, a control system, and a micro-display of the interface between the non-stick mold and the resin that is controlled to receive the series of pictures and project them to the print head A device, a projection lens set corresponding to the micro display device and controlled to perform projection, an image acquisition unit that collects and detects the quality of the projected image, and is set corresponding to the image acquisition unit and reflects the projected image to the image acquisition The unit receives and collects the spectroscope, the printing platform, the substrate arranged on the printing platform, the resin tank arranged under the substrate or the sample, and the printing head with a bucket structure corresponding to the printing platform, characterized in that: The print head includes: an inner cavity of a hollow trapezoidal body, a transparent window formed by a non-stick film covering one end of the inner cavity, a plurality of conveying channels arranged on the side, and a conveying channel corresponding to and controlling the conveying channel. A liquid flow controller for the flow rate of the printing material, a mass flow controller arranged corresponding to the inner cavity and controlled to control the pressure of the input gas flow on the non-stick film, and a flow restrictor arranged at the downstream outlet of the printing head.
The 3D printing system according to claim 9, wherein the conveying channels are provided on four sides of the print head, and the four conveying channels are formed by the trapezoidal side walls of the inner cavity and the side walls of the outer cavity arranged in parallel , The four conveying channels are spaced apart from each other and convey different printing materials, and each conveying channel is equipped with a liquid flow controller to separately control the flow rate of the printing material in each conveying channel.