A microlens array printing system and method for pneumatic microdroplet on-demand dispensing

Abstract

The present application relates to the technical fields of micro-nano additive manufacturing and precision manufacturing of optical elements, and discloses a kind of microlens array printing system and method of pneumatic microdroplet on-demand dispensing, through the linkage of pipetting unit and three-axis moving platform, liquid droplet can be printed on demand without mask or mold, flexible construction arbitrary specification microlens array, significantly reduce manufacturing cost and cycle, solve the problem of lack of flexibility of traditional method;Adopt low-cost, plug-and-play replaceable glass nozzle, effectively inhibit liquid droplet residue after super-hydrophobic treatment, avoid cross-contamination and expensive consumable expenses, break through the limitations of inkjet printing equipment nozzle fixed, easy to block;At the same time, based on the principle of pneumatic on-demand dispensing, the basic liquid droplet unit of nanoliter is realized through collaborative control, and the error level is significantly better than that of traditional pipette, so as to systematically solve the core contradiction of flexibility, economy and precision in flexible manufacturing of microlens array.

Description

Technical Field

[0001] This invention relates to the fields of micro-nano additive manufacturing and precision fabrication of optical components, and particularly to a microlens array printing system and method for on-demand distribution of pneumatic microdroplets. Background Technology

[0002] Microlens arrays (MLAS) are optical elements composed of a series of tiny lenses with diameters ranging from tens of micrometers to several millimeters arranged in a specific geometric pattern. Due to their small size, high integration, and unique convex lens optical properties, they have extremely wide applications in optics and modern manufacturing, such as beam integration, beam homogenization, 3D display, wavefront sensing, and holographic imaging. They are expected to find even deeper applications in future optical communications, high-precision manufacturing, and automotive displays.

[0003] like Figure 6 As shown, traditional mask-based microlens array fabrication methods typically include three steps: mask design, pattern transfer, and thermal reflow molding. Figure 6 As shown in (a), a fixed photomask with a specific light-transmitting / light-blocking pattern is pre-designed and fabricated according to the arrangement, unit size, and spacing requirements of the target microlens array. Since the mask pattern is difficult to change after fabrication, a new mask template usually needs to be fabricated when the array specifications need to be adjusted or the lens arrangement changed. Therefore, this method has certain limitations in terms of structural flexibility, fabrication cycle, and cost control. Figure 6 As shown in (b), a photomask is aligned with a substrate coated with photoresist or other photosensitive materials, and the pattern on the mask is transferred to the substrate surface through photolithography processes such as ultraviolet exposure and development. After development, a regularly arranged array of photoresist micropillars is formed on the substrate. The diameter, height, and spacing of these micropillar structures are mainly determined by the mask pattern and photolithography process parameters. Figure 6 As shown in (c), the photoresist micropillar array is subjected to thermal reflow treatment. When the temperature rises above the softening or glass transition temperature of the photoresist, the micropillar structure melts and rounds under the action of surface tension. Its top gradually shrinks and forms a smooth spherical crown structure, eventually resulting in a regularly arranged hemispherical microlens array.

[0004] Therefore, it is evident that the number of array rows and columns, lens spacing, and overall arrangement in traditional methods are entirely determined by the pattern of a fixed mask. Once the actual application requirements change, such as needing to adjust the lens spacing to match different optical sensor pixel pitches, or needing to increase or decrease the number of array rows and columns to adapt to chips of different sizes, the mask must be redesigned and re-fabricated. This not only results in a process cycle that can take several days or even weeks but also incurs significant additional costs, severely limiting the application of microlens arrays in customized and rapidly iterating scenarios.

[0005] To overcome the limitations of traditional photolithography, researchers have recently explored using microfluidic dispensing or printing techniques to flexibly assemble microlens arrays by directly manipulating tiny volumes of optical liquid monomers. In this application context, precise control of the liquid manipulation volume becomes a key factor determining the optical performance of the microlens array.

[0006] However, existing liquid handling instruments and dispensing technologies have the following significant limitations in practical applications: When handling submicron liquids, traditional micropipettes are constrained by physical properties such as surface tension, resulting in a coefficient of variation (CV) that is often as high as 6% to 12%, making it difficult to guarantee the high consistency of the morphology of each unit in the microlens array; even with high-resolution microfluidic impact printing technology, when faced with the high-viscosity polymer matrix (such as polydimethylsiloxane, PDMS) required for microlens array manufacturing, there is still a lack of a complete solution that combines high precision and low cost integration. Summary of the Invention

[0007] The core of this invention lies in linking a nanoliter liquid transfer unit with a three-axis moving platform, which can print droplets to designated positions on demand according to program settings without any masks or molds. This allows for the flexible construction of microlens array structures with arbitrary row and column specifications and spacing. Compared to traditional photolithography or molding methods that require the pre-fabrication of specific pattern templates, this invention allows for real-time adjustment of array dimensions and arrangement according to actual needs, significantly reducing the process threshold and manufacturing cycle. This solves the technical problems of existing methods that lack flexibility and are difficult to customize and rapidly iterate due to reliance on fixed masks.

[0008] To solve the above problems, the present invention adopts the following technical solution.

[0009] A pneumatic microdroplet on-demand microlens array printing system includes an electronic control unit, a pneumatic control unit, a pipetting unit, a 3D printing platform, and a host computer command control system. The electronic control unit includes a controller and dual solenoid valves, which are a first solenoid valve and a second solenoid valve. The motion controller receives commands from the host computer and drives the 3D printing platform to move, while simultaneously outputting pulse signals to control the opening and closing sequence of the high-speed solenoid valves. The pneumatic control unit includes a high-pressure air source, a pressure regulating valve, and a micro air pump. The high-pressure air source is regulated by the pressure regulating valve and then output to the liquid storage chamber of the pipetting unit. The micro air pump is used to assist in maintaining a stable air supply. The pipetting unit includes a liquid storage device and a replaceable glass nozzle. The glass nozzle is formed by drawing a capillary glass tube, and the outer surface of the nozzle orifice is treated with superhydrophobicity. The 3D printing platform includes an operating platform and two X-axis linear screw modules, one Y-axis linear screw module, and one Z-axis linear screw module mounted on the operating platform. The pipetting unit is installed at the output end of the Z-axis linear screw module.

[0010] Furthermore, the pneumatic control unit controls the pneumatic path through the coordinated control of two solenoid valves. Both the first and second solenoid valves have a first interface, a second interface, and a third interface. The three interfaces of the first solenoid valve are denoted as interface 1-1, interface 1-2, and interface 1-3, respectively; the three interfaces of the second solenoid valve are denoted as interface 2-1, interface 2-2, and interface 2-3, respectively. Interface 1-3 is connected to the high-pressure gas source, interface 1-2 is connected to the liquid storage chamber, and interface 1-1 is connected to interface 2-2; interface 2-3 is connected to the micro air pump, and interface 2-1 is open to the outside atmosphere.

[0011] Furthermore, the electronic control unit controls the opening and closing time of the solenoid valve, the number of high-level pulses, and the gas pressure. Using 3nL, 4nL, and 5nL as basic discrete droplet units, it achieves combined output of liquids of any target volume in the range of 3nL to 500nL by accumulating and superimposing individual droplets, with a minimum dispensing accuracy of 1nL.

[0012] Optionally, the operating platform is equipped with a fixed-position carrier, on which the substrate is placed. The printing system also includes a calibration unit, which includes calibration mark points set on the carrier and a laser and a high-definition camera installed at the output end of the Z-axis linear lead screw module. The high-definition camera, laser and glass nozzle are arranged side by side, and the central axes of the three are parallel to each other. The calibration mark points are fixed in position and their three-dimensional coordinates are marked as (a, b, c).

[0013] A printing method for a pneumatic microdroplet on-demand dispensing microlens array printing system includes the following steps: S1: The capillary glass tube is fixed in the drawing equipment and drawn into shape. The outer surface of the nozzle is modified with superhydrophobicity to obtain a glass nozzle with an inner diameter of 10μm to 200μm. S2: Install the glass nozzle into the pipetting unit, and achieve on-demand distribution of nano-level droplets by coordinating the gas path through dual solenoid valves, specifically including:  Liquid suction stage: The second solenoid valve is switched to a high-level pulse signal, connecting the liquid storage chamber to a micro air pump via the air path. The micro air pump draws out gas, creating a negative pressure in the liquid storage chamber, drawing the liquid in. Liquid spraying stage: A high-level pulse signal is applied to the first solenoid valve, connecting the high-pressure air source to the liquid storage chamber. The pressure in the liquid storage chamber increases, driving the liquid to be extruded from the nozzle, forming suspended droplets. Afterwards, the high-level pulse signal is removed, connecting the liquid storage chamber to the atmosphere. The chamber pressure drops sharply, creating a transient negative pressure. Under the combined action of surface tension and negative pressure, the droplets separate and shrink into their final shape. S3: Install the pipetting unit on a three-axis precision moving 3D printing platform, and set the number of rows, columns, lens spacing, and droplet volume parameters of the array on the host computer; S4: The 3D printing platform drives the pipetting unit to move sequentially to each target printing position according to the array coordinate sequence set by the program. Each time a target coordinate point is reached, a droplet of a preset volume is sprayed onto the substrate surface according to the method in step S2. S5: After the droplet printing of all array coordinate points is completed, the substrate is solidified to obtain a microlens array.

[0014] Furthermore, the inner diameter of the glass nozzle is 10μm-200μm; the superhydrophobic treatment involves immersing the nozzle in a 1% (w / w) trichlorooctadecylsilane isooctane solution for 10 to 30 minutes, while continuously introducing dry inert gas into the inner cavity of the glass nozzle during the immersion process, so that a superhydrophobic modified layer is formed on the outer surface of the glass nozzle while the inner surface retains hydrophilic properties.

[0015] Furthermore, the spraying stage in step S2 specifically includes three consecutive physical stages: droplet extrusion stage, droplet separation stage, and droplet forming stage. Droplet extrusion stage: The first solenoid valve receives a high-level pulse signal, and high-pressure gas enters the liquid storage chamber through the first solenoid valve. The gas pressure in the liquid storage chamber increases, driving the liquid to be extruded from the nozzle and forming suspended droplets on the outside of the nozzle. Droplet separation stage: The high-level pulse signal is removed, the first solenoid valve switches to low level, the liquid storage chamber is connected to the atmosphere through the cascaded gas path of the first and second solenoid valves, the high-pressure gas in the chamber is released and a transient negative pressure is generated, and the droplet neck contracts and breaks under the combined action of surface tension and negative pressure. Droplet formation stage: The separated droplets shrink into a spherical shape under the combined action of gravity and surface tension.

[0016] Furthermore, in step S4, the volume of each printed droplet is controlled collaboratively by three parameters: driving air pressure P, high-level pulse duration tp, and nozzle inner diameter. In addition, for different liquid media, calibration tests are performed before the formal liquid separation operation to obtain the corresponding air pressure-volume relationship curve for the liquid, and the calibration results are entered into the control system as the parameter basis for the liquid separation operation.

[0017] Furthermore, in step S5, the curing method can be selected from any one of ultraviolet light curing, heat curing, or natural air drying curing, depending on the characteristics of the droplet material.

[0018] Optionally, in step S2, after the glass nozzle is installed and before dispensing the droplets as needed, a calibration step is added. The calibration step is as follows: S21: The electronic control unit controls the 3D printing platform to move in three degrees of freedom according to the three-dimensional coordinates of the calibration mark point, so that the laser moves to directly above the calibration mark point; S22: Then, the electronic control unit controls the laser to turn on, the laser emits laser towards the calibration mark point, and at the same time controls the high-definition camera to capture high-definition images of the laser landing point and the calibration mark point and feeds them back to the electronic control unit. S23: The electronic control unit magnifies the high-definition image at a specific magnification and calculates the offset between the laser landing point and the center point of the calibration mark. When the offset distance exceeds the set threshold, the electronic control unit controls the 3D printing platform to stop working and issues a maintenance alarm. Subsequent operations will continue after the deviation is corrected.

[0019] Compared with the prior art, the advantages of this invention are: (1) This solution links the nanoliter liquid transfer unit with the three-axis moving platform, which can print droplets to the designated position as needed according to the program settings without any mask or mold, and flexibly construct microlens array structures with arbitrary row and column specifications and arbitrary spacing. Compared with the traditional photolithography or molding method, which requires the pre-made specific pattern template, the array dimension and arrangement can be adjusted in real time according to actual needs, which significantly reduces the process threshold and manufacturing cycle, thereby solving the technical problems of existing methods that lack flexibility due to reliance on fixed masks and are difficult to achieve customized and rapid iterative manufacturing.

[0020] (2) A replaceable glass nozzle design is adopted. The nozzle is formed by drawing ordinary capillary glass tubes using a microelectrode drawing instrument, and the outer surface of the nozzle is treated with superhydrophobicity by immersion in trichlorooctadecylsilane solution. It has the advantages of low cost, plug-and-play, good biocompatibility, and corrosion resistance. Different batches of nozzles can be replaced as needed, which effectively avoids the risk of cross-contamination and eliminates the need to bear the continuous expenses of high-priced consumables. This solves the technical problem that existing inkjet printing equipment is difficult to develop towards miniaturization and portability due to fixed nozzle structure, easy clogging, cumbersome cleaning, or high replacement cost.

[0021] (3) Based on the principle of pneumatic microdroplet on-demand distribution, 3 nL, 4 nL and 5 nL are used as basic discrete droplet units. By precisely controlling the opening and closing time of the solenoid valve, the number of high-level pulses and the gas pressure, the precise combination output of the target distribution volume can be achieved, and the minimum liquid distribution accuracy can reach 1 nL. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the overall system layout of the present invention; Figure 2 This is a schematic diagram of the manufacturing process of the replaceable superhydrophobic glass nozzle of the present invention; Figure 3 This is a schematic diagram illustrating the working principle of the pneumatic nanopipette of the present invention. Figure 4 This is a schematic diagram illustrating the working principle of the pneumatic nanopipette of the present invention. Figure 5 This is a schematic diagram of the printing method of the present invention; Figure 6 This is a schematic diagram of the traditional mask-mode microlens array fabrication process in the prior art; Figure 7 This is a schematic diagram of the direct-write fabrication process of the maskless microlens array of the present invention; Figure 8 This is a calibration schematic diagram of the calibration unit of the present invention.

[0023] Explanation of the labels in the diagram: 1 Y-axis linear screw module, 2 X-axis linear screw module, 3 base, 4 glass nozzle, first solenoid valve, 6 micro air pump, 7 second solenoid valve, 8 Z-axis linear screw module, 9 liquid storage chamber, 10 calibration mark point, 11 pressure regulating valve, 12 high pressure air source, 13 support frame, 15 liquid storage device. Detailed Implementation

[0024] The technical solution will now be clearly and completely described with reference to the accompanying drawings in the embodiments of the present invention.

[0025] First implementation method: This embodiment provides a replaceable superhydrophobic capillary glass nozzle suitable for pneumatic precision liquid dispensing equipment and its preparation method. Please refer to [link to relevant documentation]. Figure 2 It illustrates the fabrication process of the replaceable superhydrophobic capillary glass nozzle of this embodiment, which mainly includes the following steps: Step 1: Selection and Fixing of the Capillary Substrate: In this embodiment, a capillary glass tube is used as the nozzle substrate. The capillary glass tube is fixedly installed in the clamping mechanism of the microelectrode drawing instrument. Preferably, the drawing instrument has an automatic softening point testing function to ensure that the drawing parameters are accurately matched with the material properties of a specific batch of glass tubes. After fixing, a softening point test is performed on the capillary glass tube. The test confirms that the preferred range of the softening point system parameters of the capillary glass tube used in this embodiment is 650 to 750, and more preferably 700.

[0026] In addition, the capillary substrate is not limited to glass, but can also be replaced by quartz capillary tube, borosilicate glass tube or other microtube structures with hot stretching and forming capabilities; the hot stretching equipment is not limited to microelectrode stretching instrument, and those skilled in the art can also select laser tapering equipment or flame stretching equipment, etc., which can achieve capillary stretching and forming, according to actual needs.

[0027] Step 2: Optimization of nozzle drawing parameters and drawing process: Based on the determination of the softening point, the parameters for nozzle diameter consistency and cone profile stability are optimized by microscopic morphology observation and the controlled variable method. The parameters include at least: heat, pull, velocity, pressure and delay.

[0028] In this embodiment, the preferred range for the nozzle inner diameter of the drawn nozzle is 10 μm to 200 μm. Taking a glass nozzle with a target nozzle inner diameter of approximately 40 ± 3 μm as an example, the preferred combination of parameters for the drawing instrument is as follows: heat: 700 to 710; pulling force: 0 to 10; speed: 0 to 10; air pressure: 450 to 550; delay: 200 to 300.

[0029] It should be noted that the above parameter values ​​are based on the internal scale of a specific model of drawing instrument. The specific values ​​of different devices may vary due to differences in instrument range and calibration method. Those skilled in the art can make adaptive adjustments according to the characteristics of the equipment used.

[0030] After the drawing process is completed, the geometry of the nozzle cone region and the inner diameter of the nozzle are measured and verified using a microscope.

[0031] Step 3: Selection of nozzle geometry and testing of conductivity: After drawing, nozzle samples with uniform and complete conical structures and no obvious deformation defects are selected through visual inspection and microscopic observation. Then, a conductivity test is performed: fluid (preferably deionized water) is introduced into the nozzle cavity to observe whether the liquid can pass smoothly through the nozzle orifice, confirming that there are no blockage defects in the nozzle cavity. Nozzles that simultaneously meet the geometric shape and conductivity requirements are selected and included in the subsequent superhydrophobication treatment process.

[0032] Step 4: Superhydrophobic modification treatment of the nozzle outer surface: To suppress the adhesion and residue of trace amounts of liquid on the outer surface of the nozzle, qualified glass nozzles undergo low surface energy superhydrophobic modification treatment. The specific treatment process is as follows: the nozzle is immersed in an organic solution containing a low surface energy modifying agent for a certain period of time; during the immersion process, a dry inert gas is continuously introduced into the inner cavity of the nozzle to ensure that a superhydrophobic coating does not form on the inner surface of the nozzle, thereby preserving the normal wetting and flow characteristics of the liquid in the inner cavity of the nozzle and effectively avoiding the impact of superhydrophobicity of the inner surface on the stable transport of the liquid in the cavity.

[0033] The organic solution used is a 1% (w / w) trichlorooctadecylsilane isooctane solution, and the soaking time is 10 min to 30 min, more preferably 20 min, so as to form a uniform and dense low surface energy superhydrophobic modified layer on the outer surface of the nozzle.

[0034] It is worth noting that, in this embodiment, the organic solvent used for superhydrophobic modification can also be a silane coupling agent with equivalent surface energy reduction function, such as fluorosilane or perfluoroalkylsilane; and the organic solvent can also be an organic solvent such as ethanol or n-hexane.

[0035] Step 5: Nozzle installation, replacement, and operation process: The superhydrophobic treated individual glass nozzles are directly installed at the nozzle interface of the pneumatic liquid separator, achieving detachable and fixed installation through quick-connect structures such as clamps, clips, or threaded joints. When it is necessary to switch the type of liquid medium or adjust the droplet volume distribution range, the operator only needs to remove the old glass nozzle and install the new glass nozzle of the corresponding specification, effectively avoiding the risk of cross-contamination between different liquids and significantly reducing the continuous operating costs of equipment consumables.

[0036] The glass nozzle, as the core consumable for pneumatic droplet distribution in this invention, has geometric parameters (orifice inner diameter) that directly determine the basic volume range of a single droplet during the droplet distribution process in the second embodiment. Its superhydrophobic outer surface properties effectively suppress droplet residue and ensure clean separation of the droplet from the nozzle, thus providing a basis for the high-precision maskless printing of the microlens array in the third embodiment.

[0037] Second implementation method: This embodiment, based on the replaceable superhydrophobic capillary glass nozzle prepared in the first embodiment, further provides a high-precision quantitative dispensing method for submicroliter-level liquids based on the principle of on-demand pneumatic microdroplet dispensing. It addresses the technical problem of significantly increased operational errors in traditional micropipettes when handling submicroliter-level liquids due to limitations imposed by their working principle and physical effects such as liquid surface tension.

[0038] This embodiment adopts a dual-solenoid valve collaborative control architecture, introducing two independent three-port T-shaped solenoid valves, the first solenoid valve 5 and the second solenoid valve 7, to jointly form a complete pneumatic control loop. For ease of description, the interfaces are uniformly defined as follows: the three interfaces of the first solenoid valve 5 are sequentially labeled as interface 1-1, interface 1-2, and interface 1-3; the three interfaces of the second solenoid valve 7 are sequentially labeled as interface 2-1, interface 2-2, and interface 2-3. The physical connection relationships of each interface are as follows: interface 1-3 is connected to the high-pressure gas source 12 and the pressure regulating valve 11, serving as the high-pressure gas input end; interface 1-2 is connected to the liquid storage chamber 9 of the liquid storage device 15, serving as the chamber pressure control end; interface 1-1 and interface 2-2 are interconnected, forming a cascaded pneumatic channel between the two valves; interface 2-3 is connected to the micro air pump 6, serving as the negative pressure generation end; interface 2-1 is directly connected to the outside atmosphere, serving as the pressure relief end.

[0039] The first solenoid valve 5 and the second solenoid valve 7 described above both follow the same level control logic: when in a low-level state, the 1-2 interface of the first solenoid valve 5 is connected to its 1-1 interface, and the 2-2 interface of the second solenoid valve 7 is connected to its 2-1 interface. That is, in the low-level state, their respective interfaces 1 and 2 are connected. Correspondingly, when a high-level pulse trigger signal is received, their respective interfaces 2 and 3 are connected. Figure 5 The entire liquid distribution process is divided into two main steps: the liquid suction stage and the liquid spraying stage. The high and low level states of the two valves switch in tandem during each stage to precisely control the dynamic changes in air pressure within the liquid storage chamber.

[0040] like Figure 3 As shown, the purpose of the aspiration stage is to draw liquid from the syringe into the reservoir to replenish the liquid source for the subsequent droplet ejection operation.

[0041] like Figure 3 As shown in Figure a, when neither of the two solenoid valves receives a high-level trigger signal (i.e., both are in a low-level state), the 1-2 interface of the first solenoid valve 5 (connected to the liquid storage chamber) is connected to the outside atmosphere via the 1-1 interface → 2-2 interface → 2-1 interface of the second solenoid valve 7. The air pressure inside the liquid storage chamber is balanced with the atmospheric pressure, the system is in a stable standby state, the tip of the glass nozzle maintains surface tension sealing, and the liquid does not generate spontaneous flow.

[0042] During the liquid aspiration stage, such as Figure 3As shown in Figure b, the controller sends a high-level trigger signal to the second solenoid valve 7, causing the internal air path of the second solenoid valve 7 to switch, with interface 2-2 now connected to interface 2-3. At this point, the air path connection becomes: liquid storage chamber 9 of the liquid storage device 15 → interface 1-2 → interface 1-1 → interface 2-2 → interface 2-3 → micro air pump 6. The micro air pump 6 continues to operate, drawing gas outwards from the side of the liquid storage chamber 9, creating a continuous negative pressure inside the liquid storage chamber 9. Driven by this negative pressure, the liquid overcomes gravity and pipeline resistance, and is continuously drawn into the liquid storage chamber 9 along the needle until the liquid volume in the liquid storage chamber 9 reaches a predetermined value. At this point, the controller cancels the high-level signal from the second solenoid valve 7, the micro air pump 6 stops operating, the liquid suction phase ends, and preparation is made for the subsequent liquid spraying operation.

[0043] like Figure 4 As shown, the liquid spraying stage is driven by the voltage pulse signal generated by the controller and is divided into three continuous physical stages: droplet extrusion, droplet separation, and droplet formation. In each stage, the level states of the first solenoid valve 5 and the second solenoid valve 7 work together to precisely control the gas pressure changes in the liquid storage chamber.

[0044] During the spraying phase, such as Figure 4 In Figure a, the controller outputs a high-level pulse signal with a duration of tp to the first solenoid valve 5. This signal drives the first solenoid valve 5 to operate via a MOS switch, and its internal gas path switches to a state where interface 1-2 and interface 1-3 are connected. At this time, the second solenoid valve 7 remains at a low level, and interface 2-2 is connected to interface 2-1 (atmospheric side). However, since the first solenoid valve 5 has isolated interface 1-1 from interface 1-3 on the high-pressure gas source (12) side, the atmospheric passage does not affect the liquid storage chamber 9. The external high-pressure gas source 12 enters the first solenoid valve 5 through interface 1-3, and then delivers the high-pressure gas to the inside of the liquid storage chamber 9 through interface 1-2. The gas pressure in the liquid storage chamber 9 rises rapidly, forming a downward driving pressure on the liquid in the chamber. Under the action of this pressure, the liquid overcomes the surface tension constraint at the nozzle outlet and is slowly squeezed out from the tip of the glass nozzle 4 prepared in the first embodiment, gradually forming a suspended droplet on the outside of the glass nozzle 4. The droplet volume increases with the duration tp of the high-level pulse. The longer tp is, the more liquid is squeezed out of the nozzle, and the larger the droplet volume is formed.

[0045] like Figure 4As shown in Figure b, after the high-level pulse ends and the controller cancels the drive signal to the first solenoid valve 5, the internal gas path of the first solenoid valve 5 immediately switches, and interface 1-2 is connected to interface 1-1. At this time, the gas path connection state is restored to: liquid storage chamber 9 → interface 1-2 → interface 1-1 → interface 2-2 → interface 2-1 (atmosphere). The high-pressure gas in the liquid storage chamber 9 is rapidly released to the outside atmosphere through the above gas path, the gas pressure inside the chamber drops sharply, and a negative pressure is briefly generated due to the inertial release of the gas. Affected by this negative pressure, the neck of the liquid column suspending the droplet on the outside of the nozzle tip is subjected to an inward traction force from the direction of the chamber. Under the combined action of surface tension and transient negative pressure, the liquid column rapidly contracts and narrows, forming a clear bottleneck structure, and breaks in a very short time, and the droplet completely separates from the glass nozzle 4.

[0046] After the droplet separates from the glass nozzle 4, the liquid storage chamber remains continuously connected to the outside atmosphere via interface 1-1 → interface 2-2 → interface 2-1 (atmosphere). The internal air pressure gradually returns to a stable level balanced with atmospheric pressure, and the tip of the glass nozzle 4 returns to standby mode. The separated droplet moves downwards under gravity and spontaneously contracts into an approximately spherical shape under surface tension, ultimately forming a single nanoliter-sized droplet with uniform volume and complete morphology, thus completing one full droplet distribution process.

[0047] In the above three-stage liquid spraying process, the final volume of a single droplet is mainly determined by the following three core parameters: First, the driving air pressure P of the liquid storage chamber precisely set by the pressure regulating valve. The higher the air pressure, the more liquid is squeezed out in a single operation, and the larger the droplet volume. Second, the duration tp of the high-level pulse. The longer tp is, the more liquid is squeezed out of the nozzle, and the larger the droplet volume. Third, the inner diameter of the glass nozzle prepared in the first embodiment. The larger the inner diameter, the more liquid is squeezed out under the same pressure and time conditions.

[0048] By precisely controlling the three core parameters mentioned above, this printing system can use 3 nL, 4 nL, and 5 nL as basic discrete droplet units, and by accumulating and superimposing individual droplets, it can achieve precise combined output of liquids of any target volume in the range of 3 nL to 500 nL, with a minimum dispensing accuracy of 1 nL.

[0049] It is worth noting that in practical applications, the accuracy of droplet volume is also affected by multiple factors, including the stability of air pressure fluctuations, the viscosity and surface tension characteristics of the liquid itself, and the geometry of the nozzle. Different types of liquid media, such as aqueous solutions, organic solvents, solutions containing surfactants, or biological samples, have significantly different viscosity and surface tension parameters, which directly affect the dynamic behavior of droplets during extrusion and separation, thus affecting the consistency and accuracy of the final droplet volume. Therefore, before performing high-precision liquid separation operations on a specific liquid, a systematic calibration test should be conducted for that liquid medium. Droplet volume data should be collected under different combinations of air pressure P and pulse time tp, and the corresponding air pressure-volume relationship curve and correlation coefficient for that liquid should be fitted. The calibration results should be entered into the control system as the parameter basis for subsequent liquid separation operations, thereby ensuring that the error between the actual liquid separation volume and the target volume is always within an acceptable range, fully guaranteeing the accuracy and reliability of the system's liquid separation precision.

[0050] The third implementation method: This embodiment provides a maskless flexible printing system and method for microlens arrays based on the linkage of a nanoliter pipette and a three-axis moving platform. Building upon the first and second embodiments, this embodiment further applies pneumatic nanoliter droplet on-demand distribution technology to the direct-write fabrication of microlens arrays. Without the need for any mask templates or molds, microlens array structures of arbitrary sizes can be flexibly constructed on the substrate surface, fundamentally solving the technical problems of insufficient flexibility, high customization costs, and long manufacturing cycles caused by the reliance on fixed masks in traditional fabrication methods.

[0051] like Figure 1 As shown, the printing system consists of five parts: an electronic control unit, a pneumatic control unit, a liquid pipetting unit, a 3D printing platform, and a host computer command control system. Each unit works together to achieve automated direct writing fabrication of microlens arrays.

[0052] The electronic control unit (ECU) is the core control hub of the entire device, mainly composed of an FMC4030 motion controller and dual solenoid valves. The FMC4030 controller is responsible for receiving motion commands from the host computer, driving the stepper motors of each axis of the 3D printing platform to move precisely according to the preset coordinate sequence in real time, and is also responsible for outputting voltage pulse signals to control the opening and closing sequence of the high-speed solenoid valves, thereby coordinating the timing between the platform movement and the droplet ejection action to ensure that each droplet can accurately land at the target coordinate position.

[0053] The pneumatic control unit is responsible for providing a stable and adjustable gas pressure for the droplet ejection process. It consists of a high-pressure gas source 12, a pressure regulating valve 11, and a miniature air pump 6. The high-pressure gas source 12 provides the initial gas pressure, which is then finely adjusted by the pressure regulating valve 11 and output to the liquid storage chamber 9 of the pipetting unit. The introduction of the pressure regulating valve 11 ensures that the actual gas pressure applied to the liquid remains stable at the set level, effectively suppressing droplet volume deviation caused by gas pressure fluctuations. The miniature air pump 6 is used to assist in maintaining a stable gas supply to the system.

[0054] The pipetting unit is the actuating component for droplet generation and ejection, consisting of a liquid storage device 15 and a replaceable glass nozzle 4. The liquid storage device 15 holds the liquid material to be dispensed, and the replaceable glass nozzle is the superhydrophobic capillary glass nozzle 4 prepared in the first embodiment, whose inner diameter directly determines the basic volume range of a single droplet. The glass nozzle 4 is designed for quick disassembly and replacement; when it is necessary to switch liquid types or adjust the droplet volume range, only the corresponding nozzle specification needs to be replaced, making the operation simple and quick.

[0055] The 3D printing platform provides the pipetting unit with precise spatial positioning capabilities across three degrees of freedom. It consists of an operating platform, two X-axis linear screw modules 2 (200 mm stroke), one Y-axis linear screw module 1 (200 mm stroke), and one Z-axis linear screw module 8 (50 mm stroke). The Y-axis linear screw module 1, X-axis linear screw module 2, and Z-axis linear screw module 8 form a three-axis moving platform with three degrees of freedom. The substrate 3 is placed at the target position on the operating platform. The X-axis and Y-axis linear screw modules work together to drive the pipetting unit to achieve arbitrary coordinate positioning within a 200 mm × 200 mm effective printing range in the horizontal plane. The Z-axis linear screw module 8 is responsible for adjusting the vertical distance between the glass nozzle 4 and the substrate 3, ensuring that the working distance between the glass nozzle 4 and the substrate 3 remains consistent even with substrates of different thicknesses or with height differences on the surface of the substrate 3, thus guaranteeing the repeatability of each spraying condition.

[0056] The host computer command control system sends the array printing program to the FMC4030 controller through the software interface. The operator only needs to set parameters such as the number of rows, columns, lens spacing, droplet volume per point, and printing order of the target array in the software, and the system can automatically complete the printing process of the entire array.

[0057] Compared to Figure 6 The maskless flexible printing method provided in this embodiment is as follows: Figure 7 As shown, the specific implementation steps are as follows: like Figure 7As shown in Figure a, the nanoliter pipette prepared according to the first embodiment is fixedly mounted on the end effector of a three-axis precision moving platform. The glass nozzle 4 is vertically oriented towards the surface of the substrate 3 below, maintaining an appropriate working distance from the substrate 3. The substrate 3 has been pre-cleaned. Depending on the material requirements of the target microlens, different types of substrate materials such as glass, silicon wafers, or flexible polymer films can be selected. The array preparation program is pre-input into the system's host computer. The program parameters include the number of rows and columns of the array, the lens spacing, the volume of each printed droplet, and the printing order. All parameters can be modified in real time through the software interface without any hardware modifications.

[0058] like Figure 7 As shown in Figure b, after the system starts, the three-axis moving platform drives the nanopipette to move sequentially to each target printing position in the X / Y plane according to the array coordinate sequence set in the program. The Z-axis adjusts the distance between the nozzle and the substrate in real time according to the substrate height feedback to ensure that the working distance of each spray is consistent. Upon reaching each target coordinate point, the nanopipette, according to the pneumatic discrete mode of Example 2, precisely controls the number of high-level pulses and gas pressure to spray a preset volume of droplet onto the substrate surface. The droplet spontaneously spreads and stabilizes into a hemispherical shape under the combined action of surface tension and substrate wettability. Figure 7 In Figure b, the solid hemispherical droplets represent the positions that have been printed, and the dashed outlines represent the target positions that are yet to be printed. The moving platform advances step by step along the X direction to complete the precise deposition of droplets column by column.

[0059] like Figure 7 As shown in Figure c, after all the droplets at the array coordinate points have been printed, the substrate is cured. The specific curing method is selected according to the characteristics of the droplet material used, and can be cured by ultraviolet light irradiation, heat curing, or natural drying. After curing, a uniformly arranged, precisely spaced, and highly consistent hemispherical microlens array is formed on the substrate surface. The overall size of the array is completely determined by the printing program parameters.

[0060] and Figure 6Compared with the traditional mask method shown, the fabrication method provided in this embodiment has the following significant advantages: First, no mask templates or molds need to be made throughout the process, eliminating tedious processes such as mask design, processing, and alignment, and shortening the fabrication cycle of the microlens array from several days to less than several hours; Second, the array's row and column specifications, lens spacing, and arrangement can be flexibly adjusted by modifying software program parameters, allowing for the unrestricted fabrication of microlens arrays of any specifications on the same hardware device, greatly reducing the process threshold and cost of customized production; Third, thanks to the high-precision distribution capability of nano-level droplets in Example 2, the volume consistency of each lens unit is good, and the aperture and curvature of each lens in the array are highly uniform, which can meet the optical performance requirements of microlens arrays for applications such as optical sensing, microfluidic chips, and biological detection.

[0061] Fourth implementation method: This embodiment adds a calibration unit to the third embodiment, while the rest remains the same as the first embodiment.

[0062] like Figure 8 The operating platform is equipped with a fixed carrier frame 13, and the base 3 is placed on the carrier frame 13. The printing system also includes a calibration unit, which includes a calibration mark point 10 set on the carrier frame 13 and a laser and a high-definition camera installed at the output end of the Z-axis linear lead screw module 8. The high-definition camera, laser and glass nozzle 4 are arranged side by side, and the central axes of the three are parallel to each other. The calibration mark point 10 is fixed in position and its three-dimensional coordinates are marked as (a, b, c).

[0063] After adding the calibration unit, during step S2, before dispensing the droplets as needed after the glass nozzle 4 is installed, a calibration step is added. The calibration step is as follows: S21: The electronic control unit controls the 3D printing platform to move in three degrees of freedom according to the three-dimensional coordinates of the calibration mark point 10, so that the laser moves to directly above the calibration mark point 10. S22: Then, the electronic control unit controls the laser to turn on, the laser emits laser towards the calibration mark point 10, and at the same time controls the high-definition camera to capture a high-definition image of the laser landing point and the calibration mark point 10 and feeds it back to the electronic control unit. S23: The electronic control unit magnifies the high-definition image at a specific magnification and calculates the offset between the laser landing point and the center point of the calibration mark 10. When the offset distance exceeds the set threshold, the electronic control unit controls the 3D printing platform to stop working and issues a maintenance alarm. Subsequent operations will continue after the deviation is corrected.

[0064] The setting of a specific magnification can be selected according to actual needs, generally not less than 10 times. By magnifying the image, the visibility and intuitiveness of the offset distance between the laser landing point and the center point of the calibration mark 10 are increased. Of course, the offset data obtained after magnification needs to be reduced by the corresponding factor in order to serve as the final offset amplitude, so as to ensure the accuracy of the calibration results. This effectively ensures that the printing system can always maintain high precision during printing, and is not easily affected by the three-axis wear deviation, thus reducing the defect rate of the finished product.

[0065] The above description is merely a preferred embodiment of the present invention; it encompasses all the protection scope of the present invention. Any equivalent substitutions or modifications made by those skilled in the art within the technical scope disclosed in the present invention, based on the technical solutions and improved concepts of the present invention, should be covered within the protection scope of the present invention.

Claims

1. A pneumatic microdroplet on-demand microlens array printing system, characterized in that: The system includes an electronic control unit, a pneumatic control unit, a pipetting unit, a 3D printing platform, and a host computer command control system. The electronic control unit includes a controller and dual solenoid valves, the dual solenoid valves being a first solenoid valve (5) and a second solenoid valve (7). The motion controller receives commands from the host computer and drives the 3D printing platform to move, while simultaneously outputting pulse signals to control the opening and closing sequence of the high-speed solenoid valves. The pipetting unit includes a liquid storage device (15) and a replaceable glass nozzle (4). The glass nozzle (4) is formed by drawing a capillary glass tube, and the outer surface of the nozzle (4) is treated with... Superhydrophobic treatment; the gas control unit includes a high-pressure gas source (12), a pressure regulating valve (11) and a micro air pump (6). The high-pressure gas source (12) is regulated by the pressure regulating valve (11) and output to the liquid storage chamber (9) of the liquid storage device (15). The micro air pump (6) is used to assist in maintaining a stable gas supply in the gas path. The three-dimensional printing platform includes an operating platform and two X-axis linear screw modules (2), one Y-axis linear screw module (1) and one Z-axis linear screw module (8) set on the operating platform. The liquid transfer unit is installed at the output end of the Z-axis linear screw module (8).

2. The pneumatic microdroplet on-demand microlens array printing system according to claim 1, characterized in that: The pneumatic control unit controls the pneumatic path through the coordinated control of two solenoid valves. The first solenoid valve (5) and the second solenoid valve (7) each have a first interface, a second interface and a third interface. The three interfaces of the first solenoid valve (5) are respectively denoted as interface 1-1, interface 1-2 and interface 1-3; the three interfaces of the second solenoid valve (7) are respectively denoted as interface 2-1, interface 2-2 and interface 2-3. The 1-3 interface is connected to the high-pressure gas source (12), the 1-2 interface is connected to the liquid storage chamber (9), and the 1-1 interface is connected to the 2-2 interface; the 2-3 interface is connected to the micro air pump (6), and the 2-1 interface is connected to the outside atmosphere.

3. The pneumatic microdroplet on-demand microlens array printing system according to claim 2, characterized in that: The electronic control unit controls the opening and closing time of the solenoid valve, the number of high-level pulses, and the gas pressure. Using 3nL, 4nL, and 5nL as basic discrete droplet units, it achieves combined output of liquids of any target volume in the range of 3nL to 500nL by accumulating and superimposing individual droplets, with a minimum dispensing accuracy of 1nL.

4. The pneumatic microdroplet on-demand microlens array printing system according to claim 1, characterized in that: The operating platform is provided with a fixed carrier frame (13), and the base (3) is placed on the carrier frame (13). The printing system also includes a calibration unit, which includes a calibration mark point (10) set on the carrier frame (13) and a laser and a high-definition camera installed at the output end of the Z-axis linear lead screw module (8). The high-definition camera, laser and glass nozzle (4) are arranged side by side, and the central axes of the three are parallel to each other. The calibration mark point (10) is fixed in position and its three-dimensional coordinates are marked as (a, b, c).

5. The printing method of a pneumatic microdroplet on-demand distribution microlens array printing system according to claim 4, characterized in that: Includes the following steps: S1: The capillary glass tube is fixed in the drawing equipment and drawn into shape. The outer surface of the nozzle is modified by superhydrophobicity to obtain a glass nozzle with an inner diameter of 10μm to 200μm (4). S2: The glass nozzle (4) is installed in the pipetting unit, and the gas path is controlled by dual solenoid valves to achieve on-demand distribution of nano-level droplets, specifically including:  Liquid suction stage: Control the second solenoid valve (7) to switch to a high-level pulse signal, so that the liquid storage chamber (9) is connected to the micro air pump (6) through the air path. The micro air pump (6) draws out gas to form a negative pressure in the liquid storage chamber (9) and sucks the liquid into the liquid storage chamber (9). During the spraying stage: A high-level pulse signal is applied to the first solenoid valve (5) to connect the high-pressure air source (12) with the liquid storage chamber (9). The liquid storage chamber (9) is pressurized and drives the liquid to be squeezed out from the nozzle to form suspended droplets. Afterward, the high-level pulse signal is removed, and the liquid storage chamber (9) is connected to the atmosphere. The chamber pressure drops sharply, generating a transient negative pressure. The droplets separate and shrink under the combined action of surface tension and negative pressure. S3: Install the pipetting unit on a three-axis precision moving 3D printing platform, and set the number of rows, columns, lens spacing, and droplet volume parameters of the array on the host computer; S4: The three-dimensional printing platform drives the pipetting unit to move sequentially to each target printing position according to the array coordinate sequence set by the program. Each time a target coordinate point is reached, a preset volume of droplets is sprayed onto the substrate (3) surface according to the method described in step S2. S5: After the droplet printing of all array coordinate points is completed, the substrate (3) is solidified to obtain the microlens array.

6. The method for printing a microlens array with on-demand pneumatic microdroplet distribution according to claim 5, characterized in that: The inner diameter of the nozzle (4) is 10μm-200μm; the superhydrophobic treatment is to soak the nozzle in a 1% (by mass) solution of trichlorooctadecylsilane isooctane for 10 to 30 minutes, and during the soaking process, dry inert gas is continuously introduced into the inner cavity of the glass nozzle (4) so ​​that a superhydrophobic modified layer is formed on the outer surface of the glass nozzle (4) while the inner surface retains hydrophilic properties.

7. The method for printing a microlens array with on-demand pneumatic microdroplet distribution according to claim 6, characterized in that: The spraying stage in step S2 specifically includes three consecutive physical stages: droplet extrusion stage, droplet separation stage, and droplet forming stage. Droplet extrusion stage: The first solenoid valve receives a high-level pulse signal, and the high-pressure gas enters the liquid storage chamber (9) through the first solenoid valve. The gas pressure in the liquid storage chamber (9) increases, driving the liquid to be extruded from the nozzle and forming suspended droplets on the outside of the nozzle. Droplet separation stage: The high-level pulse signal is canceled, the first solenoid valve is switched to the low level, the liquid storage chamber (9) is connected to the atmosphere through the cascade gas path of the first solenoid valve and the second solenoid valve, the high-pressure gas in the chamber is released and a transient negative pressure is generated, and the droplet neck contracts and breaks under the combined action of surface tension and negative pressure. Droplet formation stage: The separated droplets shrink into a spherical shape under the combined action of gravity and surface tension.

8. The method for printing a microlens array with on-demand pneumatic microdroplet distribution according to claim 7, characterized in that: In step S4, the volume of each printed droplet is controlled by three parameters: driving air pressure P, high-level pulse duration tp, and nozzle inner diameter. Furthermore, for different liquid media, calibration tests are performed before the formal liquid separation operation to obtain the corresponding air pressure-volume relationship curve for the liquid. The calibration results are entered into the control system as the parameter basis for the liquid separation operation.

9. A pneumatic microdroplet on-demand microlens array printing system and method according to claim 8, characterized in that: In step S5, the curing method is selected from any one of ultraviolet light curing, heat curing, or natural air drying curing, depending on the characteristics of the droplet material.

10. A method for printing a microlens array with on-demand pneumatic microdroplet distribution according to claim 9, characterized in that: In step S2, after the glass nozzle (4) is installed and before the droplets are dispensed as needed, a calibration step is added. The calibration step is as follows: S21: The electronic control unit controls the three-dimensional printing platform to move in three degrees of freedom according to the three-dimensional coordinates of the calibration mark point (10), so that the laser moves to directly above the calibration mark point (10); S22: Then, the electronic control unit controls the laser to turn on, the laser emits laser towards the calibration mark point (10), and at the same time controls the high-definition camera to capture high-definition images of the laser landing point and the calibration mark point (10) and feeds them back to the electronic control unit. S23: The electronic control unit magnifies the high-definition image at a specific magnification and calculates the offset between the laser landing point and the center point of the calibration mark (10). When the offset distance exceeds the set threshold, the electronic control unit controls the three-dimensional printing platform to stop working and issues a maintenance alarm. After the deviation is corrected, subsequent operations continue.

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