CN111873431A

CN111873431A - Multi-channel 3D printing method and 3D printing system

Info

Publication number: CN111873431A
Application number: CN202010565816.4A
Authority: CN
Inventors: 夏春光
Original assignee: Bmf Material Technology Inc
Current assignee: Bmf Material Technology Inc
Priority date: 2020-06-19
Filing date: 2020-06-19
Publication date: 2020-11-03
Anticipated expiration: 2040-06-19
Also published as: CN111873431B

Abstract

A multi-channel 3D printing method and system comprises the following steps: generating a 3D digital model of a sample to be printed, and cutting the 3D digital model into an image sequence; the micro display device projects an image to an interface between a transparent window of the printing head and the photosensitive resin through the projection lens; the image acquisition unit acquires an image reflected by the beam splitter and detects the quality of a projected image; exposing and printing, wherein the printing head is provided with a plurality of conveying channels, and printing materials are controlled to be extruded from the conveying channels and scraped to the surface of a substrate or a sample by the hard edge at the end part of the printing head; after one layer is printed, returning, using a conveying channel of the material required by the next layer, carrying the material to a subsequent printing area through a printing head, filling resin required for printing the next layer between the sample and a transparent window of the printing head, and printing the next layer until printing is finished; according to the multichannel 3D printing method and system, different printing resins are loaded through the plurality of conveying channels, printing of different materials is achieved, different printing materials are flexibly switched, and meanwhile printing efficiency is improved.

Description

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

Technical Field

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

Background

Stereolithography was originally identified as a rapid prototyping technique. Rapid prototyping comprises a series of techniques that can be used to create a true scale model of a production component directly from computer aided design (cad) in a fast (faster than before) manner. Since its disclosure in U.S. Pat. No. 4,575,330, stereolithography has greatly helped engineers visualize complex three-dimensional part geometries, detect errors in prototype schematics, test critical components, and validate theoretical designs at relatively lower cost and faster time limits than before.

Over the last decades, the constant investment in the field of micro-electro-mechanical systems (MEMS) has led to the emergence of micro-stereolithography (μ SL), which inherits the basic principles of conventional stereolithography, but with higher spatial resolution. For example, K Ikuta and K. hirowatari, "true three-dimensional microfabrication using stereolithography and metal molding", the sixth IEEE mems seminar of 1993, with the aid of single-photon polymerization and two-photon polymerization techniques, the resolution of micro-stereolithography is further enhanced to less than 200 nm; 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 polymerization for three-dimensional microfabrication", j.mems, vol.7, pp.411, 1998; s.kawata, h.b.sun, t.tanaka and k.takada, "refinement features of functional micro devices", nature, volume 412, page 697, 2001.

The invention of Bertsch et al's projection microstereolithography (P μ SL) greatly increased speed. "micro stereolithography using liquid crystal displays as dynamic mask generators", Microsystem Technologies, p42-47, 1997; belize et al, "micro stereolithography: new processes for building complex 3D objects, design of MEM/MOEM, test and micro-machining monograph ", SPIE conference discourse, v3680, n2, p808-817, 1999. At the heart 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, all available from the microdisplay industry.

Although projection micro-stereolithography has successfully achieved fast manufacturing speeds with good resolution, further improvements are still needed.

The display size of DLP chips is currently limited to about 13mm, so when the projected pixel size is the same as the physical pixel size (5 to 8 microns), the single exposure area will be limited to half an inch. In order to print on a larger area in a single projection, the size of the projected pixels needs to be increased, thereby decreasing the printing resolution (i.e., the size of the projected pixels). P μ SL (projection micro-stereolithography) is not a significant advantage in multi-material fabrication because switching materials during P μ SL greatly reduces the speed. Therefore, a new technology based on coating-before-spray cleaning (Kavin Kowsari, 3D Printing and Additive Manufacturing. Sep 2018.185-193) or print-before-rinse method (Han D.et al, Additive Manufacturing, 2019.27: P (606-.

In projection micro-stereolithography (P μ SL), there are three types of resin layer definition methods: the first uses a free surface, the layer thickness of which is defined by the distance between the free surface of the resin 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 print area is larger than 1cm X1 cm. The second and third methods use transparent films or hard windows. Also, for both cases, there is currently no good way to define a resin layer of 10um or less over an area of 5cm X5 cm or more, particularly for the film case, which is still unexpectedly slow even if it is faster than the free surface case. In the case of a hard window, the fluid forces generated when the two surfaces of the sample and the print head are brought into close proximity and separated to define a thin layer before or after exposure are large enough to damage the sample.

In all 3D printing technologies, accuracy and efficiency of size replication are very important. For example, in an immersion multi-material projection micro-stereolithography (P μ SL) system (fig. 1), it is important to have high accuracy and efficiency in dimensional control of all layers so that the actual CAD model can be replicated over time.

Disclosure of Invention

Based on this, there is a need for a multi-channel 3D printing method that can improve printing efficiency.

Meanwhile, the 3D printing system capable of improving printing efficiency is provided.

A multi-channel 3D printing method, comprising:

slicing: generating a 3D digital model of a sample to be printed, the 3D digital model being a combination of different printing materials, cutting the 3D digital model into a sequence of images, each image in the sequence of images representing a layer of the 3D digital model, controlling a printing direction of a printing head according to a slicing direction of the model;

projection: sending the image to a microdisplay device, projecting the image to an interface between a transparent window and resin on a print head through a projection lens, and irradiating the projected image with light;

image detection: the image acquisition unit acquires an image reflected by the beam splitter to detect the quality of a projected image, and printing is performed according to the detected quality control;

exposure printing: exposing to generate a solidified layer, wherein the printing head is provided with a plurality of conveying channels for conveying printing materials, the printing head is relatively moved between the substrate and the printing head so as to relatively move the printing head to cover a printing area, the printing materials are controlled to be extruded from the conveying channels, and the printing materials are scraped onto the surface of the substrate or the sample by the end hard edges of the printing head to be printed;

and (3) continuing exposure printing: after printing of one layer, the printing head is controlled to move away from the printing area, the printing head is separated from the sample in a translation mode, the printing head or the sample stage is adjusted to return, the distance between the printing head and the sample is adjusted to be the thickness of the next layer to be printed, a conveying channel of materials required by the next layer is used instead, the printing head is brought to a subsequent printing area, the printing head traverses the substrate or the sample, a gap between the sample and a transparent window of the printing head is filled with resin required by printing of the next layer, exposure printing is carried out, the next layer is printed, and the model is copied in a resin groove.

In a preferred embodiment, different delivery channels of the printhead deliver different printing materials, each delivery channel being provided with a liquid flow controller and a shut-off valve, the flow rate of the printing material being controlled by the liquid flow controller.

In a preferred embodiment, the four side parts of the printing head are provided with four conveying channels, the printing head is a trapezoid body with a large upper part and a small lower part, an inner cavity with a trapezoid section with a large upper part and a small lower part is formed in the printing head, a flat conveying channel is formed outside the inner cavity, one end, close to the substrate, of the inner cavity of the printing head is provided with a conical end, and the conical end covers the non-adhesive film and forms a transparent window.

In a preferred embodiment, the substrate is arranged on a printing platform, the printing platform drives the substrate to move in the direction X, Y, Z according to printing, and when exposure printing or continuous exposure printing is carried out, the substrate is printed according to the formula P₀+P₁Controlling the pressure of the print head to compensate for the deformation of the transparent window caused by its contact with the printing resin, P₀Pressure of non-stick mold of print head to atmospheric air pressure, P₁＝ρ₁gh,ρ₁Resin density, g acceleration of gravity, h is the depth of the non-stick film of the print head under the resin; when printing, the pressure in the printing head is controlled by the flow of the gas, and if the pressure sensor detects that the pressure of the printing 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 printing head reaches the set value.

In a preferred embodiment, the device further comprises a flow restrictor arranged at a downstream outlet of the printing head, wherein the flow restrictor is in a choked flow state, and the flow of the flow restrictor is proportional to the pressure of the printing head.

In a preferred embodiment, the stitching printing is performed if the printed image is larger than a single exposure size, the image is divided into ply portions, the ply portions are printed step by step and stitched into a full ply on top of each other, each ply portion overlapping by 5-20 microns on the stitching edge.

In a preferred embodiment, the X/Y direction motion coordinates of the printing platform are error compensated (X) during printing₀+XError(X₀,Y₀),Y₀+YError(X₀,Y₀))，(X₀,Y₀) In order to be a theoretical coordinate, the method comprises the following steps of,

XError(X₀,Y₀)＝C₁+C₂+C₃Y₀+C₄X₀Y₀+C₅X₀ ²+C₆Y₀ ²

YError(X₀,Y₀)＝D₁+D₂+D₃Y₀+D₄X₀Y₀+D₅X₀ ²+D₆Y₀ ²

C₁-C₆polynomial coefficients are calculated by fitting in a quadratic least square method based on the measurement errors of the splicing points in the X direction during splicing printing,

D₁-D₆and the polynomial coefficient is calculated by fitting in a quadratic least square method based on the measurement error of the splicing point in the Y direction during splicing printing.

In a preferred embodiment, when the printing head stops after moving to prepare for exposure, the micro display device is controlled to project a picture in the center of the non-stick film of the printing head, the image acquisition unit captures and analyzes the imaging quality, the imaging is compared with a set theoretical value, and if the non-stick film of the printing head deforms, the deformation formula is used for calculating the deformation of the non-stick film of the printing head

And adjusting the flow to adjust the pressure in the printing head, wherein the deformation of the non-adhesive film arranged at the conical end of the printing head is in direct proportion to the pressure difference, upsilon Poisson coefficient, a is the radius of the non-adhesive die of the printing head, E Young modulus, h is the thickness of the non-adhesive die of the printing head, and p is the pressure difference of two sides of the non-adhesive die of the printing head.

A 3D printing system, comprising: the image system for establishing a 3D digital model and cutting the 3D digital model into an image sequence, a control system, a micro display device which is controlled to receive a series of pictures and projects the pictures to an interface of a non-stick film and resin of a printing head, a projection lens which is arranged corresponding to the micro display device and is controlled to project the pictures, an image acquisition unit which acquires and detects the quality of a projected image, a spectroscope which is arranged corresponding to the image acquisition unit and reflects the projected image to the image acquisition unit for receiving and acquiring, a printing platform, a substrate arranged on the printing platform, a resin tank arranged below the substrate or a sample, and the printing head which is arranged corresponding to the printing platform and has a bucket structure, wherein the printing head comprises: the printing head comprises a hollow trapezoid body, a transparent window, a plurality of conveying channels, a liquid flow controller, a mass flow controller and a flow restrictor, wherein the inner cavity of the hollow trapezoid body, the transparent window is covered at one end of the inner cavity and is formed by a non-stick film, the plurality of conveying channels are arranged on the side portion, the liquid flow controller is arranged corresponding to the conveying channels and controls the flow rate of printing materials in the conveying channels, the mass flow controller is arranged corresponding to the inner cavity and controls the pressure of input gas flow to non-stick films in a.

In a preferred embodiment, the delivery channels are arranged in four directions on four sides of the printhead, the four delivery channels are formed by trapezoidal side walls of the inner cavity and side walls of the outer cavity arranged in parallel, the four delivery channels are arranged at intervals and deliver different printing materials, and each delivery channel is provided with a liquid flow controller for respectively controlling the flow rate of the printing material of each delivery channel

According to the multichannel 3D printing method and the multichannel 3D printing system, the printing heads with the multiple conveying channels are adopted, different printing resins are loaded through the multiple conveying channels, printing of different materials is achieved, different printing materials are flexibly switched, meanwhile, the printing efficiency is improved, and the printing time is saved.

In addition, the method of unique splicing multi-exposure printing is adopted to solve the problem, the image (lens) can be moved, and the sample can also be moved. Meanwhile, the hard edge of the printing head is also a coating scraper, and the splicing movement and the coating step are carried out simultaneously, so that the time is saved, and the efficiency is improved.

In addition, non-adhesive films are utilized, so that the films and the samples are separated in a tangential and staggered manner, and the acting force on the samples during separation is reduced by orders of magnitude.

Also for resins with high viscosity (>500cPs), it is almost impossible to apply a very thin layer of resin (10 microns) at a time when using a single film covering the entire printed format (>50mmX50mm) size, because at that large format the resin drive pressure gradient that the film tension can provide is very small, making the resin flow extremely slow. The invention uses a film much smaller than the printing format, thus under the same film deformation, the driving pressure gradient of the resin is increased by orders of magnitude, and the printing speed and precision are improved.

Drawings

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

FIG. 2a is a cross-sectional view of a portion of a printhead according to one embodiment of the present invention;

FIG. 2b is a top view of a portion of a printhead according to an embodiment of the present invention;

FIG. 3 is a schematic diagram of a trajectory error in x and y directions of a 3D printing system during stitching printing according to an embodiment of the present invention;

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

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

fig. 6 is a schematic view of an exposure printing process of the 3D printing system according to an embodiment of the invention.

Detailed Description

The multichannel 3D printing method provided by the embodiment of the invention comprises the following steps:

and (3) continuing exposure printing: after printing of one layer, the printing head is controlled to move away from the printing area, the printing head is separated from the sample in a translation mode, the printing head or the sample platform is adjusted to return, the distance between the printing head and the sample is adjusted to print the thickness of the next layer, a conveying channel of the material required by the next layer is used instead, the printing head is brought to a subsequent printing area through the printing head and traverses the substrate or the sample, a gap between the sample and a transparent window of the printing head is filled with the resin required by printing of the next layer, exposure printing is carried out, the next layer is printed, and the model is copied in a resin.

Printing of the present invention begins with the creation of a geometric model from a computer or imaging system, which may be a combination of multiple entities, each representing a material. The 3D digital model is sliced into two-dimensional pictures in one direction, and if there are multiple entities in a layer, an equal number of layer segments, typically black and white, may be in grayscale. Each slice represents a thin layer in the 3D digital model. The slice direction of the model will be the print direction of the printer. The series of pictures produced are sequentially read by a printer and projected to the interface of the non-adhesive film and the photosensitive resin arranged at the end of the printing head through the DLP with the 405 nanometer light source, and simultaneously, a graphic image acquisition unit such as a CCD camera can judge the quality of the projected image from the image reflected by the spectroscope. During a certain exposure time, a certain thickness of the solidified layer is generated where light is present, which represents a corresponding layer in the model represented by the projected picture. When the previous layer is exposed and printed, the printing head can be separated from the sample in a translation mode. The printing material may be a simple photosensitive resin or a paste in which a photosensitive resin is mixed with solid particles.

The sample platform can return according to different printing forms, after returning, the distance between the printing head and the sample is the thickness of the next layer to be printed, and a gap between the sample and the printing head film can be filled with a resin layer required by printing the next layer. The exposure is repeated in sequence, and the model is copied in the resin groove as the sample stage descends layer by layer.

Since microdisplay devices such as LCD or DLP chips are of a certain size, such as 1920X1080 pixel DLP, with an optical accuracy of ten microns, the print area covered by one chip is only 19.2mm X10.8mm. When the sample size exceeds the range covered by one chip, the invention adopts a spliced printing mode. In the stitching mode, the picture representing one layer of the model is further cut into a plurality of pictures, i.e. layer portions, which are smaller than the resolution of a single DLP. For example, a 3800X2000 pixel picture may be sliced into four 1900X1000 sub-pictures, each of which will represent a quarter of the area in a layer. For each layer in the model, it will be done by multiple exposures, projecting all sub-pictures, i.e. layer parts, of the current layer in turn. The boundaries between adjacent regions/pictures are typically given an amount of overlap, typically 5-20 microns, to improve mechanical properties. The position and overlap of the exposures for each region are precisely controlled by the XY axis combination. The system has two coordinate systems, one is a DLP/LCD vertical coordinate system, and the other is a motion coordinate system consisting of XY axes. If the two coordinate systems are not perfectly parallel due to errors in mechanical assembly, misalignment errors can occur in adjacent areas in the stitching print. For this purpose, the measured errors are compensated in the stitching printing mode. Because of the presence of the axis of printing platform X, Y, multiple identical samples can be printed repeatedly across the entire swath for samples smaller than the swath printed by the printer, which can increase throughput speed, which is a matrix printing mode.

Further, different conveying channels of the printing head of the embodiment convey different printing materials, each conveying channel is correspondingly provided with a liquid flow controller (LFC liquid controllers) and a stop valve, and the flow rate of the printing materials is controlled by the liquid flow controllers.

Further, four conveying channels are arranged on four side portions of the printing head, the printing head is a trapezoid body with a large upper portion and a small lower portion, an inner cavity with a trapezoid cross section is formed in the printing head, and the outer side of the inner cavity forms a flat conveying channel. The inner cavity of the printing head is provided with a taper end near one end of the substrate, and the taper end covers the non-adhesive film and forms a transparent window.

Further, the base setting of this embodiment is on print platform, and print platform drives the base and moves in X, Y, Z orientation according to printing, when exposure printing or continued exposure printing, according to P become P₀+P₁The print head pressure is controlled to compensate for deformation of the transparent window caused by its contact with the printing resin. P₀Pressure of non-stick mold of print head to atmospheric air pressure, P₁＝ρ₁gh,ρ₁Resin density, g acceleration of gravity, h is the depth of the non-stick film of the print head under the resin; when printing, the pressure in the printing head is controlled by the flow of the gas, and if the pressure sensor detects that the pressure of the printing 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 printing head reaches the set value.

Further, the print head 30 of the present embodiment further includes: a flow restrictor 312 disposed at a downstream outlet of the printhead 30. The orifice of the restrictor 312 at the downstream outlet is small enough (<50 microns) to be choked, with its flow rate only proportional to the upstream, i.e., pressure in the printhead.

When the actual pressure measured by the pressure sensor of the printhead 30 is lower than the set pressure, a mass flow controller (MFC mass flow controller) disposed upstream increases the flow rate appropriately according to the PID (proportional-integral-derivative) setting until the pressure in the printhead reaches the set value. And vice versa.

Further, in this embodiment, if the printed image is larger than a single exposure size, stitching printing is performed to divide the image into layer sections, the layer sections are printed step by step and stitched into a whole layer by overlapping edges, and each layer section is overlapped by 5 to 20 micrometers on the stitched edge.

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, each representing a layer (e.g., 5 to 20 microns) of the model. The control computer or image system sends an image to a microdisplay device (e.g., a DLP (digital light processing) or LCD (liquid crystal display panel)), and the image is projected through a projection lens onto the bottom surface (wet surface) of the print head. The bright areas polymerize while the dark areas remain liquid. Due to size limitations of LCD or DLP chips, such as DLP chips with 1920X1080 pixels at 10um printing optical resolution, a single exposure covers only 19.2mm X10.8mm area. Therefore, if the cross section of the sample is larger than 19.2mmx10.8mm, printing cannot be performed using a single exposure method. The invention provides a splicing printing method for multiple exposure. In this way, the image representing the 3D model layer is further divided into a plurality of smaller images, i.e., layer segments, each image being no larger than the DLP pixel resolution. For example, an image with a pixel resolution of 3800X2000 may be divided into four 1900X1000 sub-images, each sub-image representing a quarter of the layer. As a result, the entire layer of the model will be printed section by section based on the sub-images. In order to improve the mechanical strength of the common edge of adjacent sections, there is typically an overlap of about 5-20 microns on the edge.

The XY print stage assembly can precisely control the precise position and amount of overlap. There are two coordinate systems: one is a coordinate system vertical to the DLP/LCD panel, and the other is a motion coordinate system formed by the printing platform on XY axes. When the two coordinate systems are not parallel due to assembly tolerances, there will be an offset error on the shared edges of adjacent cross-sections. As shown in fig. 3, a is the size of a single exposure; b is the result of the precise alignment in the x direction; c is the result of an error offset in the x direction; b' is the result of the precise alignment in the y-direction; c' is the result of the error shifting in the y direction. In precision printing, the error requirement is less than 10um, and the stage assembly tolerance is usually within the allowable range; and the offset is not linear with the distance the print platform moves. Thus, in the present invention, the offset is measured at 5 or more evenly distributed points in the x and y directions of the full range printed square sample. An offset error curve of at least a second order polynomial interpolation will be introduced into the translation in the XY direction to compensate for the offset to ensure that the accuracy of the stitched printed sample is within specification.

During printing, the X/Y direction motion coordinate of the printing platform is subjected to error compensation (X)₀+XError(X₀,Y₀),Y₀+YError(X₀,Y₀))，(X₀,Y₀) In order to be a theoretical coordinate, the method comprises the following steps of,

XError(X₀,Y₀)＝C₁+C₂+C₃Y₀+C₄X₀Y₀+C₅X₀ ²+C₆Y₀ ²

YError(X₀,Y₀)＝D₁+D₂+D₃Y₀+D₄X₀Y₀+D₅X₀ ²+D₆Y₀ ²

Specifically, for accurate (<10 micron error) stitching printing, 20X10 connected rectangles 19.2X10.8X0.1 mm thick are first stitched and printed on a full-width sample stage, and if there is a theoretical 100 micron overlap of the squares around, the squares will provide 19X9 pieces of stitching point data and their coordinates. The printed sample is taken off from the sample table, the actual overlapping amount in the X direction and the Y direction is measured, for example, the splicing overlapping in the X direction is 80, the error in the X direction at the coordinate point is xeror (X, Y) is 100-80-20 micrometers, and the repeated measurement results in the error in the X direction of 19X 9-171 points and the error in the Y direction of 171 points.

Assume that the quadratic error function of the XY telemechanical system at the entire printing platform is:

XError(x,y)＝C₁+C₂x+C₃y+C₄xy+C₅x^2+C₆y^2，

YError(x,y)＝D₁+D₂x+D₃y+D₄xy+D₅x^2+D₆y^2，

where x, y are coordinates and C and D are polynomial coefficients. C_1～6And D_1～6It can be calculated by a quadratic least square fitting based on the measurement errors in the X and Y directions at 171 points. This results in a distribution of the axis movement errors over the entire printing area. These two error equations will be used to correct the motion error of the axis, such as when the axis is going to the theoretical value (X)₀，Y₀) Where, according to the error formula, the control command for the axis requires the axis to go (X)₀+XError(X₀,Y₀),Y₀+YError(X₀,Y₀))。

When the printing head stops after moving and is ready for exposure, the micro display device is controlled to project a picture at the center of the non-stick film of the printing head, the image acquisition unit captures and analyzes the imaging quality, the imaging quality is compared with a set theoretical value, and if the non-stick film of the printing head deforms, the deformation formula is used for calculating the deformation of the non-stick film of the printing head

The flow is adjusted to adjust the pressure in the printing head, the deformation of the non-stick film arranged at the conical end of the printing head is in direct proportion to the pressure difference, the upsilon Poisson coefficient is a half of the radius or the diagonal length of the non-stick film of the printing head, the E Young modulus is h is the thickness of the non-stick film of the printing head, and p is the pressure difference of two sides of the non-stick film of the printing head.

As shown in fig. 1, fig. 2a and fig. 2b, a 3D printing system 100 according to an embodiment of the present invention includes: the image system comprises an image system, a control system, a micro display device 50, a projection lens 40, an image acquisition unit 55, a spectroscope 60, a printing platform 80, a substrate 90, a resin tank 70 and a printing head 30, wherein the image system is used for establishing a 3D digital model and cutting the 3D digital model into an image sequence, the micro display device 50 is controlled to receive images and project the images to an interface of a non-stick mold and resin of the printing head, the projection lens 40 is arranged corresponding to the micro display device and is controlled to project the images, the image acquisition unit 55 is used for acquiring and detecting the quality of projected images, the spectroscope 60 is arranged corresponding to the image acquisition unit 55 and reflects the projected images to the image acquisition unit 55 to receive and acquire the images, the printing platform 80.

The print head 30 of the present embodiment includes: an inner cavity 302 of the hollow trapezoid body, a transparent window 304 formed by a non-stick film covering one end of the inner cavity 302, a plurality of delivery channels 306 arranged at the side, a liquid flow controller 308 arranged corresponding to the delivery channels and controlling the flow rate of the printing material in the delivery channels, a mass flow controller 310 arranged corresponding to the inner cavity 302 and controlling the flow of the input gas to generate pressure on the non-stick film, and a flow restrictor 312 arranged at the downstream outlet of the print head. A doctor blade 301 is formed at an end portion of the outer wall of the print head 30 to scrape the resin.

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

Further, the microdisplay device of the present embodiment is a DLP or LCD chip. Of course, other chips may be used as desired.

Preferably, the image capturing unit of the present embodiment can be implemented by using a CCD. Of course, other devices with image capture processing capabilities, such as CMOS, may be used.

Further, the base 90 of the present embodiment is connected to the printing platform 80 by a base arm 92.

The four feed channels 306 are provided on four sides of the printhead, the four feed channels 306 are formed by trapezoidal sidewalls of the internal chamber and outer chamber sidewalls arranged in parallel, the four feed channels are arranged spaced apart from each other and feed different printing materials, and each feed channel is provided with a liquid flow controller 308 to control the flow rate of the printing material of each feed channel 306, respectively.

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

The non-stick film-formed transparent window of the cone end of the print head of the present embodiment is preferably a 130um thick film of dupont teflon AF2400, which is air permeable and has excellent optical clarity. The permeability of gases, in particular oxygen, makes the film non-tacky during photopolymerization, since oxygen is a photo-crosslinking inhibitor. Other films such as Polydimethylsiloxane (PDMS) films or surface-coated rigid windows may of course also be used. When the print head is in contact with the resin, the tip of the print head is liquid-tightly sealed.

It is assumed that the center of the non-stick film in the resin is deflected, i.e., deformed, by pressure due to the linear elasticity of the film

Where υ is the poisson ratio of the membrane, a is the radius of the circular membrane tip, E is the young's modulus, h is the thickness, and p is the pressure differential across the membrane. It indicates that the deformation of the tip is proportional to the pressure difference; thus, non-adhesive flexing can be eliminated by controlling the pressure in the print head and the pressure difference across it

Liquid pressure on the wet surface of the transparent window of the print head (i.e., the surface in contact with the uncured resin or other printing material) may be caused by excess resin under the non-stick film. Therefore, the pressure inside the print head should be controlled to compensate for the liquid pressure to eliminate deformation of the non-adhesive transparent window.

The combination of a Mass Flow Controller (MFC), a flow restrictor disposed at the downstream outlet of the printhead, and a pressure sensor on the printhead controls the pressure P in the printhead.

The thickness of the non-stick oxygen inhibiting layer can be improved by increasing the oxygen concentration in the printhead; thus, MFCs can use flow rates of various oxygen concentration mixtures to control pressure. The membrane together with the seal forms part of the internal cone of the print head.

The delivery channel is arranged outside the lumen cone. The four channels in turn form a hollow inner cone shape and are flat. These channels (i.e., four channels) are connected to a Liquid Flow Controller (LFC) and a 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 transfer channel and flow can be controlled and stopped immediately. This minimizes the amount of resin used during printing.

As shown in fig. 4, three printing modes are provided on the 3D printing of the present embodiment by means of the XY stage.

When printing a single sample smaller than a single exposure size, the print platform will not move during printing if only one printing material is needed in the exposure area. However, where multiple materials are used, the printing platform moves to apply the selected resin. This is referred to as a single exposure mode.

If multiple identical samples are required, the print platform is moved incrementally X, Y and prints the identical samples in an array. This is referred to as the array exposure mode. For small volume production this pattern is certainly faster than a repeated single exposure pattern. When the sample size increases beyond the size of a single exposure, the system will further divide a layer into multiple portions by overlapping 5um to 20um on the shared edge and stitch the adjacent portions into a whole layer. This is the stitching exposure mode.

When multiple identical samples are required for one sample, 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 positioned on top of the sample or substrate (if the first layer) at a distance from the sample or substrate (when the first layer) equal to the thickness of the current layer (fig. 5). Taking two opposing resin feed channels a and C as an example (fig. 5), in order to coat the resin C on the substrate, the feed channel that feeds the resin C is placed in the direction of movement of the print head 30 relative to the substrate during printing. The substrate is moved and the printhead is moved for the same purpose. As the substrate moves, resin C is extruded from the slit exit of the flat delivery channel and immediately scraped to the substrate surface (if the first layer or top) by a hard edge on the inner cone of the print head. As shown in

steps

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

The DLP then projects a layer image onto the wet surface of the film in step 4. To change the material of the adjacent area to a, the print head is moved to ensure that the conveying path for conveying the resin a is 2 to 3mm away from the designated printing area, and then compression of the resin a is started in step 5, and moved and scraped as in step 6. After the DLP projects an image onto the resin a in step 7, the substrate adjusts the position of the conveying path that conveys the resin C to print the next layer in

steps

8 and 9. To scrape off the resin, it is important to control the rate of resin flow from the LFC to ensure that the thickness of the new layer is correct. A lower than desired resin flow rate will result in a thinner layer than designed because the vacuum effect due to less resin will pull the film towards the sample or substrate.

The minimum flow rate of the resin depends on the conservation of volume 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 velocity 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 zone.

As shown in fig. 6, the

numbers

1 and 2 represent the sequence of platform movements. For example, in resin a or C printing, the substrate first moves the transport path transporting a or resin C away from the new area by 2 to 3mm, but remains facing the new area, and then the print head 30 presses and coats fresh resin on the new area in a scraping motion.

The operation of printing resins B and D is similar, but the substrate needs to move around to align the designated channels with the new areas. The movement of the print head relative to the sample is always a shearing movement during printing. After the entire layer has been printed, the print head will move beyond the boundary of the sample before the sample stage moves down one layer thickness to define the next layer of fresh resin. By maintaining a shear motion between the print head and the sample, the only interaction between the print head and the sample is a fluid shear force.

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

σ＝-pI+2μ

σ is the fluid stress tensor, p is the pressure, I is the deterministic tensor, μ is the fluid viscosity, and is the velocity gradient tensor (or fluid strain tensor). For two surfaces that are almost in contact with each other, separated at a rate of 10mm/s in a resin with a viscosity of 50cPs, the vacuum effect is typically about 1e5 Pas. However, if the two surfaces are bisected by each other with a gap of 20um, the force is about 1e2 Pas. Thus, the method greatly reduces the possibility of damage or deformation to the sample.

After a new layer space by moving the substrate down, the print head will move in and start scanning and printing the next layer step by step.

In the present invention, the print head can also be moved while holding the sample stationary by moving the sample in direction X, Y, Z.

The method of the present invention not only provides more precise control over a larger print area (e.g., a 10cm x10 cm print area of 10um layer thickness) at higher speeds and desired layer thicknesses, but also allows for switching of the printing materials, e.g., switching the use of at least 4 resins during printing.

The present invention scans the sample step by step using a print head that can be as large as one exposure of the entire DLP chip or a portion of the DLP chip. This method greatly improves the dimensional accuracy of samples printed using a projection micro-stereolithography (P μ SL) system, and by combining the switching of printing materials (e.g., switching of resins) and coating processes, the printing speed is significantly improved.

The printing material used in the present invention is generally referred to as a resin. Such as light curable resins that are used industrially to print and cure when building 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 a gas permeable material, in particular an oxygen permeable material, for example Polydimethylsiloxane (PDMS) or Teflon AF from dupont. The outer individual delivery channels are flat and are connected to the tapered outer wall of the lumen. The 4 resin channels extrude different resins and coat the top of the sample as desired.

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

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

The 3D printing system of the present invention includes: a microdisplay device such as an LCD or DLP microdisplay chip that displays a digital image from an imaging system or computer using a light source, a projection lens having an optical axis, a print head with a flat head that is sealed and optically transparent and air permeable, an image capture unit such as a Charge Coupled Device (CCD) that can monitor the projection onto the print head, a printing platform that can control the movement of the sample substrate or print head in the X, Y and Z directions, a resin bath. The resin tank is used to collect excess resin dripping from the print head 30.

The 3D printing system is arranged relative to the surface of the substrate, the projection lens is positioned between the surface of the substrate and the CCD and above the substrate, the optical axis of the projection lens is intersected with the surface of the substrate, and the CCD can be focused through the lens along the optical axis of the projection lens.

The present invention provides three printing modes. When only one sample is required that is smaller than a single exposure size, it is referred to as a single exposure mode. If multiple samples are required, the XY printing stage will move in steps and print the same samples in the array, which is referred to as the array exposure mode. When the sample size increases beyond the size of a single exposure, the system will further divide a layer into multiple portions by overlapping 5um to 20um on the adjacent or common edge and stitch adjacent portions into a whole layer, which is a stitched exposure mode. A stitching pattern may also be used in combination with an array pattern.

The present invention compensates for mechanical tolerances in the translation of the printing platform in the XY direction based on interpolated offset error curves from measured data of actual samples to ensure that the accuracy of the stitched printed samples is within specification.

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

The distance between one end of the print head to the top of the sample or substrate (if 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, wherein the hard edge on the tip of the inner cone acts as a resin coating blade. The coating thickness is determined by the gap between the flat head of the print head and the top layer of the sample. In the present invention, the sample may be moved in XYZ directions by the print stage, or the print head may be moved while the sample remains stationary.

The print head is positioned so that the side carrying the transport path for transporting the layer of printing material first follows a line across the substrate or sample which specifies the direction in which the print head is brought to the print zone. Moving the print head relative to the substrate by moving the substrate, the print head or both the substrate and the print head to cause the print head to cover the print zone, wherein as the print head moves to cover the print zone, printing material is extruded from the outlet of the flat transport path carrying the layer of printing material which is immediately scraped onto the surface of the substrate or sample by the hard edge of the flat tip, then the movement of the print head relative to the dimensions of the substrate is stopped and the printing material is squeezed once the print head has covered the print zone. An image is sent from the control computer to the LCD micro display chip or the DLP micro display chip, the image is projected from the LCD or DLP chip through the lens onto the flat head surface of the print head, and then the projected image is irradiated with light. The printing material for printing the next layer or the part of the next layer is modified by moving the print head away from the printing area, placing the print head so that the side with the transport path transporting the material to be printed, first specifies the direction in which the print head is brought to the subsequent printing area along a line crossing the subsequent printing area, which is located in the layer just printed in the new layer on top of the print head, the part of the layer adjacent to the part of the layer already printed, and then printing and scraping.

After printing the entire layer, the print head will move beyond the periphery of the sample after which the sample stage will move down a distance equal to the thickness of the next layer of printing material before printing the next layer. The printing material is composed of a light-curable resin or may be a mixture of a photosensitive resin and solid particles. The transparent window material of the printing head is 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 due to contact with the printing material. The pressure within the printhead is controlled by controlling the flow of gas introduced into the printhead. The gas introduced into the printhead comprises oxygen. The pressure P in the printhead is controlled by a combination of a Mass Flow Controller (MFC), a downstream flow restrictor and a pressure sensor on the printhead controller. The outer surface of the inner cone of the printhead is attached to at least four delivery channels, each delivery channel attached to a different surface on a different side of the inner cone. The delivery passage is connected to liquid flow controllers each of which controls the flow rate of one of the photocurable resins and to shut-off valves. The movement of the print head is controlled by three levels of precision in the X, Y and Z directions. Three precision stages of movement of the substrate in the X, Y and Z directions may also be used to control the motion. The print platform controls the movement of the printhead and/or the substrate in at least the X and Y directions.

In light of the foregoing description of the preferred embodiments according to the present application, it is to be understood that various changes and modifications may be made without departing from the spirit and scope of the invention. The technical scope of the present application is not limited to the contents of the specification, and must be determined according to the scope of the claims.

As will be appreciated by one skilled in the art, embodiments of the present application may be provided as a method, system, or computer program product. Accordingly, the present application may take the form of an entirely hardware embodiment, an entirely software embodiment or an embodiment combining software and hardware aspects. Furthermore, the present application may take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, and the like) having computer-usable program code embodied therein.

The present application is described with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the application. It will be understood that each flow and/or block of the flow diagrams and/or block diagrams, and combinations of flows and/or blocks in the flow diagrams and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.

These computer program instructions may also be stored in a computer-readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including instruction means which implement the function specified in the flowchart flow or flows and/or block diagram block or blocks.

These computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.

Claims

1. A multi-channel 3D printing method, comprising:

image detection: the image acquisition unit acquires an image reflected by the beam splitter and detects the quality of a projected image, and printing is performed according to the detected quality control;

exposure printing: exposing to generate a solidified layer, wherein the printing head is provided with at least two conveying channels for conveying printing materials, the relative motion between the substrate and the printing head is realized, so that the printing head moves relatively to cover a printing area, the printing materials are controlled to be extruded from the conveying channels, and the printing materials are scraped onto the surface of the substrate or the sample by the end hard edges of the printing head to be printed;

2. The multi-channel 3D printing method according to claim 1, wherein different transport channels of the print head transport different printing materials, each transport channel is provided with a liquid flow controller and a stop valve, and the flow rate of the printing materials is controlled by the liquid flow controller.

3. The multi-channel 3D printing method according to claim 2, wherein the conveying channels are four on four side portions of a printing head, the printing head is a trapezoid body with a large upper portion and a small lower portion, an inner cavity with a trapezoid cross section is formed in the printing head, the flat conveying channel is formed outside the inner cavity, a tapered end is formed at one end, close to the substrate, of the inner cavity of the printing head, and the tapered end covers the non-adhesive film and forms a transparent window.

4. The multi-channel 3D printing method according to claim 1, wherein the substrate is disposed on a printing platform, the printing platform drives the substrate to move in the direction X, Y, Z according to printing, and when exposure printing or continuous exposure printing is performed, the substrate is printed according to P-P₀+P₁Controlling the pressure of the print head to compensate for the deformation of the transparent window caused by its contact with the printing resin, P₀Pressure of non-stick mold of print head to atmospheric air pressure, P₁＝ρ₁gh,ρ₁Resin density, g acceleration of gravity, h is the depth of the non-stick film of the print head under the resin; when printing, the pressure in the printing head is controlled by the flow of the gas, and if the pressure sensor detects that the pressure of the printing 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 printing head reaches the set value.

5. The multi-channel 3D printing method as claimed in claim 4, further comprising a flow restrictor disposed at a downstream outlet of the print head, the flow restrictor being in a choked flow state, the flow restrictor flow being proportional to the print head pressure.

6. A method for multi-channel 3D printing according to any of claims 1 to 5 wherein if the image is printed to be larger than a single exposure size then stitching printing is performed to divide the image into layer sections, printing the layer sections step by step and stitching together the layers in a full stack, each layer section overlapping 5 to 20 microns on the stitching side.

7. The multi-channel 3D printing method according to claim 6, wherein the X/Y direction motion coordinates of the printing platform are error compensated (X) while printing₀+XError(X₀,Y₀),Y₀+YError(X₀,Y₀))，(X₀,Y₀) In order to be a theoretical coordinate, the method comprises the following steps of,

XError(X₀,Y₀)＝C₁+C₂+C₃Y₀+C₄X₀Y₀+C₅X₀ ²+C₆Y₀ ²

YError(X₀,Y₀)＝D₁+D₂+D₃Y₀+D₄X₀Y₀+D₅X₀ ²+D₆Y₀ ²

8. The multi-channel 3D printing method as claimed in any one of claims 1 to 5, wherein when the print head is stopped after moving for exposure, the micro display device is controlled to project a picture in the center of the non-stick film of the print head, the image acquisition unit captures and analyzes the imaging quality, the imaging is compared with a set theoretical value, and if the non-stick film of the print head is deformed, the deformation formula is used to calculate the image quality

9. A 3D printing system, comprising: the image system for establishing a 3D digital model and cutting the 3D digital model into an image sequence, a control system, a micro display device which is controlled to receive a series of pictures and projects the pictures to an interface of a non-stick film and resin of a printing head, a projection lens which is arranged corresponding to the micro display device and is controlled to project the pictures, an image acquisition unit which acquires and detects the quality of a projected image, a spectroscope which is arranged corresponding to the image acquisition unit and reflects the projected image to the image acquisition unit for receiving and acquiring, a printing platform, a substrate arranged on the printing platform, a resin tank arranged below the substrate or a sample, and the printing head with a bucket-shaped structure which is arranged corresponding to the printing platform are characterized in that the printing head comprises: the printing head comprises a hollow trapezoid body, a transparent window, a plurality of conveying channels, a liquid flow controller, a mass flow controller and a flow restrictor, wherein the inner cavity of the hollow trapezoid body, the transparent window is covered at one end of the inner cavity and is formed by a non-stick film, the plurality of conveying channels are arranged on the side portion, the liquid flow controller is arranged corresponding to the conveying channels and controls the flow rate of printing materials in the conveying channels, the mass flow controller is arranged corresponding to the inner cavity and controls the pressure of input gas flow to non-stick films in a.

10. The 3D printing system of claim 9, wherein the delivery channels are four on four sides of the printhead, the four delivery channels are formed by trapezoidal sidewalls of the internal cavity and parallel sidewalls of the external cavity, the four delivery channels are spaced apart from each other and deliver different printing materials, and each delivery channel is provided with a liquid flow controller to control the flow rate of the printing material of each delivery channel.