Laser volumetric direct writing optical lens additive manufacturing system and method

Abstract

The invention discloses a laser volume direct writing optical lens additive manufacturing system and method.The method comprises the steps that firstly, a single-point printing experiment is conducted on photosensitive resin to obtain the relation between irradiation time and curing shape and depth, and a curing growth function model is obtained through fitting and correction; secondly, dwell time required by a design surface is calculated through linear convolution and a nonlinear algorithm; and the residence time is processed through two-dimensional Gaussian filtering, finally, the residence time and laser irradiation energy are correspondingly converted through 3D printing equipment, and additive manufacturing of precise optical parts is achieved. According to the laser direct-writing volume forming 3D printing method, the growth function and the 3D printing technology are combined, and the brand-new laser direct-writing volume forming 3D printing method with high customizability is provided. The forming speed, precision and optical performance of the optical lens printed through the method are far higher than those of optical lenses machined by other additive manufacturing equipment with the same price, and additive manufacturing is further broken through in the field of precision optical manufacturing.

Description

Technical Field

[0001] The present invention relates to the technical field of additive manufacturing, and in particular to a laser volume direct writing optical lens additive manufacturing system and method. Background Art

[0002] Additive manufacturing technology and 3D printing technology are a manufacturing process of continuous superposition from point to surface and then from surface to body. Combined with computer-aided design, complex computer models can be materialized. 3D printing technology can freely manipulate geometric shapes. Compared with traditional manufacturing, 3D printing does not require customized molds or masks, and has a very high material utilization rate, so it has brought revolutionary changes in the customized structure level. With the rapid development of various fields such as military defense, aerospace, and biomedical equipment, the size and precision requirements for customized microstructures are also getting higher and higher. The above characteristics of 3D printing can meet the size and precision requirements for customized parts, and are gradually being more widely used in the above fields.

[0003] Fused Deposition Modeling (FDM) uses ABS and PLA as printing materials. The printing materials are molten through a heating device, and the nozzle will spray and stack them along the specified path. According to the G code movement of the slice file, by controlling the XYZ three-axis movement, layers of processed model sections are formed and stacked until the entire model is printed. In recent years, FDM printing technology has developed rapidly in China. Thanks to its open source program, developers can make corresponding changes according to their needs. FDM printing technology has high utilization rate of printing materials, low cost, and rich material variety, but it has defects such as difficulty in printing complex models, low printing accuracy, low strength of molded parts, and not suitable for the production of large workpieces.

[0004] Selective laser sintering (SLS) uses solid powder as the printing material. The solid powder is spread on the printing platform using a powder spreading device, and a high-energy-density laser is used to selectively sinter the solid powder according to the planned path of the slice, so that the material selectively melts and solidifies. After printing a layer, the sintered solidified layer moves downward through the movement of the Z axis, and the solid powder material is re-laid on top of the printed layer. The above operation is repeated until the entire printing is completed. SLS has a wide range of printing materials, with a utilization rate of nearly 100%, and is suitable for metal parts obtained by polymers and laser sintering metal powders. By controlling the process parameters of SLS, the microstructure of the porous structure and the bracket can be controlled.

[0005] Laminated object manufacturing (LOM) is to cut a metal film or plastic film of a certain thickness into the slice cross-sectional shape of a three-dimensional model with a laser cutter above, then apply hot melt glue on the surface of the film, stick it to the upper layer of the picture, and then cut it according to the interface shape of the next layer of the model. The cut film is then glued to the upper layer of the cut body with hot melt glue. The entire processing is a process of cutting and sticking layer by layer until the printing is completed. Layered object manufacturing technology does not require additional support structures, borrowing money sheets, small manufacturing deformation, and low cost. However, its processing surface quality is poor, there is a lot of waste, there are few types of printing raw materials, and post-processing is difficult.

[0006] Stereolithography Apparatus (SLA) is the earliest developed rapid prototyping process. Hull et al. invented the first 3D printing device based on stereolithography in 1984. Stereolithography is also one of the most in-depth, mature and widely used rapid prototyping processes. SLA uses photosensitive materials as printing raw materials and uses its ultraviolet light curing reaction for processing. The photosensitive resin curing area is controlled by related technologies to solidify according to the specified shape, and the Z-axis movement is used to perform layer-by-layer curing until the printing is completed. In the past few years, photocuring 3D printing has made great progress. It has high printing accuracy, fast speed, low cost, and is suitable for mass production. However, there are still some problems that need to be solved. Its printing materials are limited and support beams are required during the printing process. In addition, there are changes in ultraviolet light intensity, interference in the printing environment, and poor mixing and aging of the printing resin.

[0007] 3D printing has made great progress and brought great changes to the manufacturing industry and innovative design fields. Unlike traditional subtractive manufacturing technology, additive manufacturing can achieve higher economy and sustainability. However, traditional 3D printing methods still have some limitations when generating complex structures. Among them, the manufacturing accuracy of the two-photon polymerization 3D printer is the highest, but its price is also extremely expensive, ranging from hundreds of thousands of dollars. Although the dimensional accuracy of the optical lens manufactured by the two-photon polymerization 3D printer can reach the submicron level of about 100nm, its surface roughness can only reach a maximum of about 3nm, which cannot reach the sub-nanometer roughness. So far, there has been no manufacturing method in the field of additive manufacturing of optical lenses that can simultaneously meet the sub-micron level of dimensional accuracy and the sub-nanometer level of surface roughness. Summary of the invention

[0008] The purpose of the present invention is to combine the growth function with 3D printing technology to propose a new, highly customizable laser volume direct writing optical lens additive manufacturing system and method.

[0009] The technical solution adopted by the present invention is: a laser volume direct writing optical lens additive manufacturing system, including a laser module, an XY two-axis motion platform, two-way stepper motors and a control system, the laser module, the XY two-axis motion platform and the two-way stepper motors are respectively connected to the digital signal output port of the control system.

[0010] Furthermore, it also includes a base, and the laser module, the XY two-axis motion platform and the two-way stepper motors are arranged on the base.

[0011] Furthermore, the laser module is a 405nm laser module.

[0012] Furthermore, the control system is a PCIe multi-function data acquisition card.

[0013] According to the above-mentioned laser volume direct writing optical lens additive manufacturing system, the additive manufacturing method comprises the following steps:

[0014] Step 1: Fitting the time-varying growth function model c(x, y, t): The control system outputs PWM signals with different duty cycles to the laser module, and the marginal relationship between the curing depth, half-peak width and dwell time of the photosensitive resin is obtained by controlling the irradiation time and energy of the laser module. After the fitting and correction process of the Gaussian-like function, the time-varying curing growth function model c(x, y, t) is obtained, where x and y are the coordinates of the XY two-axis motion platform, respectively, and t is the dwell time;

[0015] Step 2: Calculate the linear residence time: Select the growth function c(x, y, t1) at a certain time t1 in the time-varying solidification growth function model c(x, y, t), and calculate the linear residence time based on the given pre-designed surface Z(x, y). The pre-designed surface Z(x, y) is expressed by the convolution of the growth function and the residence time, as shown in the following formula:

[0016]

[0017] Wherein the linear residence time t const Through the non-negative least squares algorithm, we get:

[0018] min ||c(x,y,t1)t const -Z(x,y)||

[0019] subject to const >=0;

[0020] Step 3: Calculate the nonlinear dwell time: Based on the obtained linear dwell time t const The linear volume is found by the following expression:

[0021] V desired (x, y) = t const (x,y)·∫∫c(u,v,t1)dudv

[0022] Then, the time-varying solidification volume model V(t) is established based on the time-varying solidification growth function model c(x, y, t):

[0023]

[0024] Finally, the residence time obtained when the time-varying solidification volume is equal to the linear solidification volume is the nonlinear residence time t':

[0025] V(t')=V desired (x, y)

[0026] Step 4: Gaussian filtering: Smooth the obtained nonlinear dwell time t' through two-dimensional Gaussian filtering to obtain the final dwell time t". The expression of two-dimensional Gaussian filtering is as follows:

[0027]

[0028] t"(x,y)=∑(G(x,y)·t'(x,y));

[0029] Where G(x,y) is a two-dimensional Gaussian kernel function, which is used to weight adjacent values, x0 and y0 are the coordinates of the center point of the printed model, and sigma is the standard deviation of the Gaussian filter;

[0030] Step 5: Convert the final dwell time t" into a corresponding duty cycle of the PWM signal, and transmit it to the laser module (1) via the control system via the TTL interface to achieve the curing process of the resin.

[0031] Compared with the prior art, the beneficial effects of the present invention are as follows: the present invention opens up another scheme for photocuring additive manufacturing by combining the fitting of the growth function and the calculation of the dwell time in the process of computer-controlled optical surface treatment with laser volume direct writing curing additive manufacturing; the 3D printer has a simple structure and only requires an XY two-axis motion platform and a laser module; the processing cost is low, and the ultraviolet laser used in the present invention is a traditional wire-cut laser unit of the hundred-yuan level. As long as the corresponding growth function of the laser-cured resin can be fitted, additive manufacturing can be carried out without any other requirements for the laser; a wide range of processable materials can be used, as long as photocurable resin materials can be processed by this method; the processing speed is fast; it only takes 366 seconds to process a 4mm-diameter optical lens; the surface accuracy and surface roughness of the finished product have significant advantages over 3D printing equipment of the same price.

[0032] In addition to the above-described purposes, features and advantages, the present invention has other purposes, features and advantages. The present invention will be further described in detail with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 It is a structural schematic diagram of a laser volume direct writing 3D printer.

[0034] Figure 2 This is a schematic diagram of the control system of a 3D printer.

[0035] Figure 3 It is a schematic diagram of the processing process.

[0036] Figure 4 It is a function diagram of the resin curing height and half-peak width obtained through the laser unit irradiation experiment and the curing growth model.

[0037] Figure 1 Among them, 1. Laser module, 2. XY two-axis motion platform and two-way stepper motors, 3. Base. DETAILED DESCRIPTION

[0038] The specific implementation modes of the present invention are described in detail below with reference to the accompanying drawings.

[0039] The embodiments of the present invention can be seen Figure 1 and Figure 2 A laser volume direct writing optical lens additive manufacturing system includes a laser module 1, an XY two-axis motion platform, two-way stepper motors 2 and a PCIe multi-function data acquisition card (control system). The laser module 1, the XY two-axis motion platform and the two-way stepper motors 2 are respectively connected to the digital signal output port of the PCIe multi-function data acquisition card, and the computer outputs the signal to the PCIe multi-function data acquisition card, and transmits the corresponding PWM output signal through the digital output port of the data acquisition card to control the printing process in real time. The specific principle of laser direct writing volume forming 3D printing can be seen in Figure 3 The present invention is based on the idea of ​​growth function. It adjusts the solidification amount of different dwelling points by controlling the dwelling time of different dwelling points, and finally obtains the designed surface through the cumulative forming of each solidification point.

[0040] In the process of obtaining the final residence time, it is necessary to first establish a growth function model, and then establish a residence time solution model by combining linear and nonlinear algorithms. In the process of single-point curing experiment of photosensitive resin, by controlling the irradiation time and energy of the laser module, the marginal relationship between the curing depth of photosensitive resin, half-peak width and residence time is obtained. After the fitting and correction process of the Gaussian function, the time-varying curing growth function model c(x, y, t) is obtained as follows Figure 4 Select Figure 4In the time-varying solidification growth function, the growth function c(x, y, t1) at a certain time t1 is obtained, and the pre-designed surface Z(x, y) is given.

[0041] The additive manufacturing method of the laser volume direct writing optical lens additive manufacturing system comprises the following steps:

[0042] Step 1: Fitting the time-varying growth function model c(x, y, t): The control system outputs PWM signals with different duty cycles to the laser module 1, and the marginal relationship between the curing depth, half-peak width and dwell time of the photosensitive resin is obtained by controlling the irradiation time and energy of the laser module 1. After the fitting and correction process of the Gaussian-like function, the time-varying curing growth function model c(x, y, t) is obtained, where x and y are the coordinates of the XY two-axis motion platform, respectively, and t is the dwell time;

[0043] Step 2: Calculate the linear residence time: Select the growth function c(x, y, t1) at a certain time t1 in the time-varying solidification growth function model c(x, y, t), and calculate the linear residence time based on the given pre-designed surface Z(x, y). The pre-designed surface Z(x, y) is expressed by the convolution of the growth function and the residence time, as shown in the following formula:

[0044]

[0045] Wherein the linear residence time t const Through the non-negative least squares algorithm, we get:

[0046] min ||c(x,y,t1)t const -Z(x,∑)||

[0047] subject to const >=0;

[0048] Step 3: Calculate the nonlinear dwell time: Based on the obtained linear dwell time t const The linear volume is found by the following expression:

[0049] V desired (x, y) = t const (x,y)·∫∫c(u,v,t1)dudv

[0050] Then, the time-varying solidification volume model V(t) is established based on the time-varying solidification growth function model c(x, y, t):

[0051]

[0052] Finally, the residence time obtained when the time-varying solidification volume is equal to the linear solidification volume is the nonlinear residence time t':

[0053] V(t')=V desired (x,y)

[0054] Step 4: Gaussian filtering: Smooth the obtained nonlinear dwell time t' through two-dimensional Gaussian filtering to obtain the final dwell time t". The expression of two-dimensional Gaussian filtering is as follows:

[0055]

[0056] t"(x,y)=∑(G(x,y)·t'(x,y));

[0057] Where G(x,y) is a two-dimensional Gaussian kernel function, which is used to weight adjacent values, x0 and y0 are the coordinates of the center point of the printed model, and sigma is the standard deviation of the Gaussian filter;

[0058] Step 5: Convert the final dwell time t" into a corresponding duty cycle of the PWM signal, and transmit it to the laser module 1 via the control system via the TTL interface to realize the curing process of the resin.

[0059] Through the above method, a 4mm diameter high-precision optical lens with a sub-micron surface error and a sub-nanometer surface error can be obtained in a few minutes by only using the laser module 1, the XY two-axis motion platform and the two-way stepper motor 2. This not only greatly reduces the manufacturing cost of additive manufacturing, but also greatly increases the upper limit of additive manufacturing capabilities.

[0060] The present invention adds a numerical calculation method on the basis of traditional additive manufacturing, thereby reducing the equipment manufacturing cost and improving the printing effect, while meeting the sub-micron level of dimensional accuracy and sub-nanometer level of surface roughness.

[0061] The above description is only an advantageous embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A laser volume direct writing optical lens additive manufacturing system, characterized in that: It comprises a laser module (1), an XY two-axis motion platform, two-way stepping motors (2) and a control system. The laser module (1), the XY two-axis motion platform and the two-way stepping motors (2) are respectively connected to the digital signal output port of the control system.

2. The laser volume direct writing optical lens additive manufacturing system according to claim 1, characterized in that: It also comprises a base (3), on which the laser module (1), the XY two-axis motion platform and the two-way stepping motors (2) are arranged.

3. The laser volume direct writing optical lens additive manufacturing system according to claim 1, characterized in that: The laser module (1) is a 405 nm laser module.

4. The laser volume direct writing optical lens additive manufacturing system according to claim 1, characterized in that: The control system is a PCIe multi-function data acquisition card.

5. The additive manufacturing method of the laser volume direct writing optical lens additive manufacturing system according to any one of claims 1 to 4, characterized in that: The following steps are involved: Step 1: Fitting the time-varying growth function model c(x, y, t): The control system outputs PWM signals with different duty cycles to the laser module (1), and the irradiation time and energy of the laser module (1) are controlled to obtain the marginal relationship between the curing depth, half-peak width and dwell time of the photosensitive resin. After a Gaussian-like function fitting and correction process, the time-varying curing growth function model c(x, y, t) is obtained, wherein x and y are the coordinates of the XY two-axis motion platform, respectively, and t is the dwell time; Step 2: Calculate the linear residence time: Select the growth function c(x, y, t1) at a certain time t1 in the time-varying solidification growth function model c(x, y, t), and calculate the linear residence time based on the given pre-designed surface Z(x, y). The pre-designed surface Z(x, y) is expressed by the convolution of the growth function and the residence time, as shown in the following formula: Wherein the linear residence time t const Through the non-negative least squares algorithm, we get: min||c(x,y,t1)t const -Z(x,y)|| subject to t const >=0; Step 3: Calculate the nonlinear dwell time: Based on the obtained linear dwell time t const The linear volume is found by the following expression: V desired (x,y)=t const (x,y)·∫∫c(u,v,t1)dudv Then, the time-varying solidification volume model V(t) is established based on the time-varying solidification growth function model c(x,y,t): Finally, the residence time obtained when the time-varying solidification volume is equal to the linear solidification volume is the nonlinear residence time t': V(t’)=V desired (x,y) Step 4: Gaussian filtering: Smooth the obtained nonlinear dwell time t' through two-dimensional Gaussian filtering to obtain the final dwell time t". The expression of two-dimensional Gaussian filtering is as follows: t"(x,y)=∑(G(x,y)·t'(x,y)); Where G(x,y) is a two-dimensional Gaussian kernel function, which is used to weight adjacent values, x0 and y0 are the coordinates of the center point of the printed model, and sigma is the standard deviation of the Gaussian filter; Step 5: Convert the final dwell time t" into a corresponding duty cycle of the PWM signal, and transmit it to the laser module (1) via the control system via the TTL interface to achieve the curing process of the resin.

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