A Stiffness Measurement Method and System for Micron-Scale Structures with a Large Aspect Ratio

Abstract

The present invention belongs to the field of instruments and meters, and particularly relates to a method and a system for measuring the stiffness of a micron-scale structure with a large height-to-diameter ratio. The steps of the measurement method are as follows: S1: Fix the sample of the micro-structure to be measured on a horizontal test bench, and arrange a vertical strain probe capable of measuring the deformation amount and / or the lateral compressive stress above the sample. S2: Move the strain probe to a position just in contact with the side wall of the micro-structure to be measured. S3: Move the strain probe towards the micro-structure to be measured, and measure the deformation amount of the micro-structure to be measured, as well as the corresponding deformation amount or lateral compressive stress of the strain probe. S4: Calculate the stiffness of the micro-column corresponding to each moment based on the detection results of the above steps. S5: Fit a test function for characterizing the change of the micro-column stiffness based on the obtained data. S6: Use the function value of the section with a constant slope in the test function as the stiffness of the micro-structure to be measured. The present invention overcomes the problem that the existing measurement methods and instruments cannot accurately measure the stiffness of a micron-scale structure with a large height-to-diameter ratio.

Description

Technical Field

[0001] The present invention belongs to the field of instruments and meters, and particularly relates to a method and a system for measuring the stiffness of a micron-scale structure with a large height-diameter ratio. Background Art

[0002] Stereolithography and photolithography are two laser-based 3D processing technologies. Through these technologies, various three-dimensional microstructures can be prepared using photosensitive polymers such as hydrogels and photoresists as raw materials. These microstructures have very wide applications in the fields of cell mechanics, engineering culture, biomedicine, etc. Among them, mechanical parameters or properties such as the stiffness, Young's modulus, strength, and stress-strain of these microstructures are key parameters for evaluating the structural performance, and are also key indicators for analyzing the properties of the research object during the application process.

[0003] A microstructure refers to a microscopic structure at the micron scale. The mechanical parameters of a microstructure usually need to be measured using specialized instruments. The existing methods for measuring the stiffness of a microstructure are the approximate estimation method and the micro-volume block pressing method. The approximate estimation method measures the magnitude of parameters related to the stiffness of the microstructure through existing displacement or mechanical sensors and other devices, and then estimates an approximate value of the stiffness of the microstructure. This measurement method is simple to operate, does not require specialized testing instruments, and has a low measurement cost; however, the measurement result has poor accuracy and can only be applied to some scenarios with low requirements for the accuracy of stiffness measurement. The micro-volume block pressing method belongs to an indirect measurement method, and the measurement principle is as Figure 1 shown. This method requires first preparing a volume block using the same processing parameters and materials as the microstructure to be measured. For the convenience of measurement, the cross-sectional area of the XY plane of the volume block is usually large, and then an atomic force microscope or a nanoindentation instrument is used to press a corresponding indentation on the volume block. Finally, the nanoindentation instrument calculates the corresponding stiffness value based on relevant parameters such as the pressing force and the pressing indentation. Although the accuracy of the stiffness result of the micro-volume measured by the micro-volume block pressing method is high, the measurement result of this method can only reflect the mechanical parameters of the volume block and cannot accurately reflect the mechanical parameters of the microstructure to be measured; in addition, devices such as atomic force microscopes and nanoindentation instruments used in the micro-volume block pressing method are all expensive precision instruments, and the application cost is high. Most importantly, this measurement method is usually only applicable to measuring the stiffness of microstructures with a relatively large cross-sectional area (radial dimension not less than 10 μm). For special microstructures such as micro-columns, micro-cones, and micro-plates with a large height-diameter ratio (height-diameter ratio greater than 5), the operation difficulty of the micro-volume block pressing method is high, it is difficult for the instrument to form an indentation on the surface of the microstructure, and it is easy to cause the "collapse" of the microstructure. Therefore, the micro-volume block pressing method and corresponding devices such as atomic force microscopes and nanoindentation instruments are basically not applicable to measuring the stiffness of microstructures with a large height-diameter ratio. Summary of the Invention

[0004] In order to overcome the problem that existing measurement methods and instruments cannot accurately measure the stiffness of microstructures with a large height-diameter ratio, the present invention provides a dedicated method and system for measuring the stiffness of micron-scale structures with a large height-diameter ratio.

[0005] The present invention is implemented by the following technical solutions:

[0006] A method for measuring the stiffness of a micron-scale structure with a large height-diameter ratio, the stiffness measurement method comprising the following steps:

[0007] S1: Fix the sample of the microstructure to be measured on a horizontal test bench, and arrange a vertical strain probe above the sample that can measure the deformation amount S and / or the lateral compressive stress F.

[0008] S2: Move the strain probe to a position just in contact with the side wall of the microstructure to be measured, and adjust the height of the strain probe so that the strain probe partially coincides with the microstructure to be measured in the height direction.

[0009] S3: Preset the feed amount x0 for each movement, and move the strain probe successively along a fixed direction in the horizontal plane according to the feed amount x0. And measure the deformation amount S2 of the microstructure to be measured corresponding to different moments, as well as the deformation amount S1 or the lateral compressive stress F corresponding to the strain probe.

[0010] Wherein, the deformation amounts S1 and S2 are respectively the displacements of the strain probe and the microstructure relative to the initial position in the feed direction of the strain probe.

[0011] S4: Based on the detection results of the above steps, calculate the micro-column stiffness K2 corresponding to each moment through any one of the following two formulas:

[0012]

[0013] Or

[0014]

[0015] In the above formula, K1 represents the known material stiffness of the strain probe.

[0016] S5: Based on the series of discrete data obtained in the above steps, fit a test function K2(t) for characterizing the change of the micro-column stiffness.

[0017] S6; Take the function value K2 of the section with a constant slope in the test function K2(t) fitted in the above step as the stiffness of the microstructure to be measured.

[0018] As a further improvement of the present invention, the strain probe adopts a force-measuring fiber optic sensor, a displacement and strain-measuring fiber optic sensor or a microcantilever beam sensor.

[0019] As a further improvement of the present invention, in step S3, the deformation amount S1 of the strain probe or the lateral compressive stress F is directly read by a corresponding sensor.

[0020] And / or

[0021] The deformation amount S2 of the micro-structure to be measured is obtained by measuring with a digital scale based on a microscopic image; the microscopic image is an image obtained by photographing along the side surface of the micro-structure and when the main optical axis of the view-finding is perpendicular to the feeding direction of the strain probe.

[0022] The present invention also includes a stiffness measurement system for a micro-structure with a large height-to-diameter ratio. This system uses the stiffness measurement method for a micro-structure with a large height-to-diameter ratio as described above to directly measure the stiffness of the micro-structure. The stiffness measurement system includes: a sample stage, a strain detection mechanism, at least one set of micro-photography mechanisms, and a data processing module.

[0023] Among them, the sample stage is used to fix the sample containing the micro-structure to be measured.

[0024] The strain detection mechanism is located above the sample stage. The strain detection mechanism includes a three-dimensional moving stage and a strain probe, and the strain probe is fixedly connected to the three-dimensional moving stage. The three-dimensional moving stage is used to adjust the spatial position of the strain probe; the strain probe is used to measure its own deformation amount S1 and / or the lateral compressive stress F during the operation process.

[0025] At least one set of micro-photography mechanisms, which are located on the side of the sample stage; the micro-photography mechanisms are used to obtain local images of the sample of the target micro-structure to be measured; the local images of the sample are used to analyze the relative position between the strain probe and the target micro-structure to be measured, and to identify the deformation amount S2 of the target micro-structure to be measured.

[0026] The data processing module is communicatively connected to the strain detection mechanism and the micro-photography mechanism; the data processing module includes a displacement recognition unit and a stiffness calculation unit. The displacement recognition unit is used to analyze, according to the local images of the sample corresponding to each moment, the maximum displacement of the target micro-structure relative to the initial position at the current moment through image recognition and digital scale technology, and use this as the deformation amount S2 of the target micro-structure. The stiffness calculation unit is used to obtain the deformation amount S1 of the strain probe and / or the lateral compressive stress F at each moment. Then through Or Calculate the stiffness value K2(t) corresponding to each moment. Finally, take the average value of the stiffness values K2(t) within the preset sampling period as the stiffness K2 of the micro-structure to be measured. Among them, K1 represents the known material stiffness of the strain probe. The sampling period refers to the intermediate period from the moment when the strain probe contacts the target micro-structure to the moment when the target micro-structure reaches the maximum deformation state.

[0027] As a further improvement of the present invention, the microphotography system includes a camera and a lens system. The lens system is used to optically magnify the target area, and the camera is used to acquire an image of the target area magnified by the lens system.

[0028] As a further improvement of the present invention, the microphotography mechanism further includes a display component or is connected to an external display component. The display component is used to display in real time the image acquired by the camera.

[0029] And / or

[0030] The microphotography mechanism further includes a light source or is connected to an external light source. The light source is used to supplement light to the target area on the sample stage that contains the microstructures to be measured.

[0031] As a further improvement of the present invention, the microphotography mechanism is of a single-group movable type or a multi-group type; the single-group movable type means that the number of the microphotography mechanisms is one group, and the relative position between the microphotography mechanism and the sample stage is adjustable. The multi-group type means that the number of the microphotography mechanisms is not less than two groups, and at least includes two groups of microphotography mechanisms located in the X-axis and Y-axis directions of the plane where the sample stage is located.

[0032] As a further improvement of the present invention, the strain probe adopts a force-measuring fiber optic sensor, a microstrain-measuring fiber optic sensor or a microcantilever sensor.

[0033] As a further improvement of the present invention, the stiffness measurement system further includes a displacement measurement mechanism for measuring the deformation amount S2 of the target microstructure or the deformation amount S1 of the strain probe.

[0034] The displacement measurement mechanism includes a laser, an optical path adjustment component and a monitor; the laser is used to emit a beam of detection laser towards the measurement target, the detection laser is reflected by the target surface and then enters the optical path adjustment component, and finally is reflected to the monitor; the monitor is used to output the deformation amount of the corresponding target according to the position change of the received laser signal.

[0035] As a further improvement of the present invention, when the displacement measurement mechanism is included in the stiffness measurement system, the data processing module simultaneously includes a displacement recognition unit and a stiffness calculation unit, or only includes a stiffness calculation unit.

[0036] And / or

[0037] When the data processing module simultaneously includes a displacement recognition unit and a stiffness calculation unit, the stiffness calculation unit uses the average value of the calculation results of the displacement recognition unit and the displacement measurement mechanism as the required deformation amount S2 of the target microstructure.

[0038] When the data processing module only includes a stiffness calculation unit, the stiffness calculation unit uses the measurement result of the displacement measurement mechanism as the required deformation amount S2 of the target microstructure.

[0039] The technical solution provided by the present invention has the following beneficial effects:

[0040] In order to solve the problem of stiffness detection of polymer microstructures, the present invention proposes a direct and convenient measurement method, avoiding the problems of poor accuracy of the commonly used theoretical approximation estimation method, inconvenient operation of the indirect measurement method by pressing a micro-volume block, and limitations in the measurement of microstructures with a large height-to-diameter ratio. The lateral touch measurement method provided by the present invention is particularly suitable for the stiffness detection of polymer microstructures with a large height-to-diameter ratio, such as micro-columns, micro-cones, and micro-plates.

[0041] The present invention also designs a special stiffness measurement system for large height-to-diameter ratio micron-scale structures for the proposed stiffness measurement method. In the system, two measurement methods, namely fiber optic force measurement and micro-cantilever beam strain measurement, can be used as the required strain probes, and combined with a micro-photography mechanism to observe and obtain the deformation displacement of the polymer microstructure in real time, and calculate the stiffness of the polymer microstructure. The stiffness measurement system provided by the present invention has a relatively low application cost and simpler operation compared with existing equipment, so it can be widely used in parameter measurement in fields such as cell mechanics, engineering culture, and biomedicine. Description of the Drawings

[0042] The drawings are used to provide a further understanding of the present invention, and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the present invention, but do not constitute a limitation to the present invention. In the drawings:

[0043] Figure 1 It is a schematic diagram of the existing method of measuring the stiffness of a structure by pressing a micro-volume block.

[0044] Figure 2 It is a micrograph of a typical large height-to-diameter ratio micro-column structure targeted by the stiffness measurement method and system of the present invention.

[0045] Figure 3 It is a micrograph of a typical large height-to-diameter ratio micro-cone structure targeted by the stiffness measurement method and system of the present invention.

[0046] Figure 4 It is a micrograph of a typical large height-to-diameter ratio micro-plate structure targeted by the stiffness measurement method and system of the present invention.

[0047] Figure 5 It is a flowchart of the steps of the stiffness measurement method for large height-to-diameter ratio micron-scale structures provided in Embodiment 1 of the present invention.

[0048] Figure 6 It is a schematic diagram of the structure for measurement using a fiber optic sensor as a strain probe in Embodiment 1 of the present invention.

[0049] Figure 7Schematic diagram of the structure for measurement using a microcantilever sensor as a strain probe in Embodiment 1 of the present invention.

[0050] Figure 8 Micro-columns with different mechanical parameters prepared from commercial photoresist SZ2080 under different processing parameters, in different states after processing.

[0051] Figure 9 Microplate structures prepared from commercial liquid photoresist NOA61, in different states after processing due to having two different mechanical parameters.

[0052] Figure 10 Schematic diagram of the structure of a stiffness measurement system for a large aspect ratio micron-scale structure provided in Embodiment 2 of the present invention.

[0053] Figure 11 Schematic diagram of the structure of the displacement measurement mechanism adopted in Embodiment 3 of the present invention.

[0054] Figure 12 For Figure 11 Schematic diagram of the process for measuring the stiffness of a micro-structure using the stiffness measurement system for a large aspect ratio micron-scale structure in the above. Detailed implementation manners

[0055] In order to make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0056] Embodiment 1

[0057] This embodiment provides a method for measuring the stiffness of a large aspect ratio micron-scale structure. This testing method is mainly for measuring the radial stiffness of micro-structures with a relatively small cross-sectional area and a relatively large aspect ratio. In particular, this method can accurately measure the stiffness of micro-structures such as micro-columns, micro-cones, and micro-plates (as Figures 2-4 shown,) with a cross-sectional size less than 10 μm and an aspect ratio greater than 5. This is a measurement task that is difficult to achieve with existing various instruments such as atomic force microscopes and nano-indenters. It should be noted that in micro-columns and micro-cones, the "diameter" in the aspect ratio refers to the cross-sectional scale of the structure, while in micro-plates, the "diameter" in the aspect ratio can be understood as the thickness of the micro-plate.

[0058] As Figure 5 shown, the method for measuring the stiffness of a large aspect ratio micron-scale structure provided in Embodiment 1 of the present invention includes the following steps:

[0059] S1: Fix the sample of the micro-structure to be measured on a horizontal test bench, and set a vertical strain probe above the sample that can measure the deformation amount S and / or the lateral compressive stress F.

[0060] S2: Move the strain probe to a position where it just touches the side wall of the micro-structure to be measured, and adjust the height of the strain probe so that the strain probe and the micro-structure to be measured partially overlap in the height direction.

[0061] S3: Preset the feed amount x0 for each movement, and move the strain probe successively along a fixed direction in the horizontal plane according to the feed amount x0. Measure the deformation amount S2 of the micro-structure to be measured corresponding to different moments, as well as the deformation amount S1 or the lateral compressive stress F corresponding to the strain probe.

[0062] Among them, the deformation amounts S1 and S2 are the displacements of the strain probe and the micro-structure relative to the initial position in the feed direction of the strain probe, respectively.

[0063] S4: Based on the detection results of the above steps, calculate the micro-column stiffness K2 corresponding to each moment through any one of the following two formulas:

[0064]

[0065] Or

[0066]

[0067] In the above formula, K1 represents the known material stiffness of the strain probe.

[0068] S5: Based on the series of discrete data obtained in the above steps, fit a test function K2(t) for characterizing the change of micro-column stiffness.

[0069] S6; Take the function value K2 of the section with a constant slope in the test function K2(t) fitted in the above step as the stiffness of the micro-structure to be measured.

[0070] The principle of the stiffness measurement method for the large aspect ratio micron-scale structure provided in this embodiment is as follows:

[0071] As Figure 6 And Figure 7 Shown, when using a vertical strain probe to touch the micro-structure to be measured from the side, the stiffness of the micro-structure to be measured can be accurately calculated by analyzing the stress and strain conditions between the micro-structure to be measured and the strain probe. Among them, when a force F is applied to the strain probe so that the strain probe and the micro-structure to be measured start to contact until the micro-structure to be measured reaches the maximum deformation state (the critical state of elastic deformation and plastic deformation), the deformation amount S1 corresponding to the strain probe and the deformation amount S2 of the micro-structure to be measured theoretically both satisfy:

[0072] S = S1 + S2

[0073] S is the horizontal distance from the initial position of the strain probe to the position where the strain probe is located when the microstructure to be measured reaches the maximum deformation state. Based on this equivalent relationship, the error evaluation and accuracy test of the deformation variables S1 and S2 measured above can be performed.

[0074] Based on the relationship between force and stress-strain, the stiffness K2 of the microstructure to be measured satisfies the following formula:

[0075] and

[0076] Therefore, the stiffness K2 of the microstructure to be measured can be calculated by only accurately measuring F and S2, or measuring S1 and S2 (wherein the material stiffness K1 of the strain probe is known).

[0077] In the test method provided in this embodiment, in order to accurately obtain the transverse compressive stress F or displacement S1 of the strain probe during the test, a force measuring fiber optic sensor, a micro strain measuring fiber optic sensor or a micro cantilever beam sensor is selected as the required strain probe. The above three sensors are all existing mature sensors for measuring force or precision displacement. For example, in a force measuring fiber optic sensor or a micro strain measuring fiber optic sensor, when the optical fiber interacts with the microstructure, the transverse compressive stress F causes the optical fiber to undergo micro deformation, which causes the refractive index of the fiber core to change. These changes will cause the phase of the light wave in the optical fiber to change. After circuit modulation and demodulation, the data processing unit in the optical fiber sensor can output the corresponding transverse compressive stress F or displacement S1.

[0078] When the micro-cantilever sensor is used, one end is fixed and the other end is suspended. When there is interaction with the sample, the cantilever will swing, thereby realizing precise measurement of three-dimensional morphology, structural characteristics, physical parameters, etc., and is widely used in the field of precision sensing. When the micro-cantilever is used as a strain probe for detection, since the micro-cantilever is extremely sensitive to weak forces and its stiffness K1 is known, the deformation amount S1 of the micro-cantilever can be obtained to calculate the stiffness K2 of the required microstructure to be measured.

[0079] In the practical application of the method of this embodiment, there are many methods for measuring the deformation variable S1 of the micro cantilever beam and the deformation variable S2 of the microstructure to be measured. For example, a microscopic image along the side of the microstructure can be obtained by microscopic photography technology, and the main optical axis when the microscopic photography image is framed is kept perpendicular to the feed direction of the strain probe. Then, the displacement of the target object at different times, that is, the required deformation variables S1 and S2, is measured based on the digital ruler of the microscopic image. In addition to using digital ruler technology, the deformation variables S1 and S2 of the target object can also be indirectly calculated by directly using microscopic images to analyze the pixel position offset of the edge of the target object on the microscopic image at different times.

[0080] In addition, the idea of the "Cavendish experiment" can be borrowed, and a laser and a specially designed optical path are used to amplify the tiny displacement of the target object, and then the displacement of the target object is indirectly measured. The corresponding deformation amounts S1 or S2 of the target object are obtained.

[0081] Compared with the existing measurement methods, the method provided in this embodiment can "directly" measure the stiffness of the micro-structure with higher accuracy. At the same time, the implementation of this method does not rely on various existing expensive precision instruments, and the measurement cost is lower. In the actual application process, the scales of the fiber optic sensor and the micro-cantilever beam sensor are usually significantly larger than the scale of the large aspect ratio micro-structure to be measured (it means that the strain probe is usually thicker than the object to be measured). Therefore, in the actual operation process, it is more convenient to make the two closely contact and apply compressive stress along the fixed side, so as to achieve accurate measurement; all of these improve the operability of the measurement method proposed in this embodiment.

[0082] Embodiment 2

[0083] Figure 8 In the figure are micro-column structures with different structural parameters prepared from commercial photoresist SZ2080 under different processing parameters. The diameter of the micro-columns is 1 μm to 2 μm, and the height is 5 μm to 20 μm. The a structure has a larger stiffness, and the micro-column structure remains upright; in the b structure, the processing exposure dose is greater than that in a, so its structural stiffness is greater than that of the a structure; in the c figure, due to the smaller stiffness, after the structure is subjected to a micro-force, the structure tilts and collapses together; in the d figure, the structural stiffness is smaller, and the structure undergoes plastic deformation after being subjected to a micro-force.

[0084] Figure 9 In the figure are micro-plate structures with different structural parameters prepared from commercial photoresist NOA61 under different processing parameters. The radial dimension (thickness) of the micro-plates is about 0.5 μm to 1 μm, the length is 5 μm to 15 μm, and the height is 3 μm to 10 μm. In the a structure in the figure, the stiffness is larger, and after the structure is subjected to a micro-force, it remains upright; in the b structure, the stiffness is smaller, and it deforms and collapses together after being subjected to a micro-force.

[0085] It can be seen that even if micro-structures with the same size are processed using the same material, when some processing parameters (such as the exposure dose) in the processing technology are slightly adjusted, there will be obvious differences in the structural properties of the processed samples. Therefore, it is very necessary to measure the performance of the processed samples after the target micro-structure is processed.

[0086] Considering that existing devices usually cannot effectively measure the stiffness and structural parameters of high aspect ratio microstructures such as microcolumns, microcones, and microplates, based on the stiffness measurement method of high aspect ratio micron-scale structures provided in Embodiment 1, this embodiment further provides a corresponding measurement system, that is: a stiffness measurement system for high aspect ratio micron-scale structures. This measurement system is designed based on the stiffness measurement method of high aspect ratio micron-scale structures in Embodiment 1 and can directly measure the stiffness of high aspect ratio microstructures.

[0087] As Figure 10 shown, the stiffness measurement system for high aspect ratio micron-scale structures provided in this embodiment includes: a sample stage, a strain detection mechanism, at least one set of microphotography mechanisms, and a data processing module.

[0088] Among them, in this embodiment, the sample stage is mainly built using various existing optical vibration isolation platforms. The functions of the sample stage include two points: one is to fix the sample containing the microstructures to be measured. The other is to carry other relevant mechanisms or components. In this embodiment, a detachable dedicated sample fixture is set in the center of the sample stage to stably clamp the carrier containing the microstructures to be measured, such as an elastic pressing sheet, etc. And a large number of arrayed screw holes on the tabletop can facilitate the installation of devices such as the strain detection mechanism and the microphotography mechanism.

[0089] The strain detection mechanism is located above the sample stage. The strain detection mechanism includes a three-dimensional moving stage and a strain probe. The strain probe is fixedly connected to the three-dimensional moving stage. The three-dimensional moving stage is used to adjust the spatial position of the strain probe; the strain probe is used to measure its own deformation amount S1 and / or the lateral compressive stress F it bears during the operation. Specifically, the strain probe adopts a force-measuring fiber optic sensor, a microstrain-measuring fiber optic sensor, or a microcantilever beam sensor. Regarding the selection and function of the strain probe, detailed descriptions have been made in Embodiment 1, and will not be elaborated in this embodiment. In this embodiment, the base of the three-dimensional moving stage is installed on the sample stage, and the strain probe is "suspended" on the three-dimensional moving stage and is located above the fixture in the center of the sample stage.

[0090] The three-dimensional moving stage provided in this embodiment can achieve precise position control at the micron level. The operator can control the strain probe to move freely in the X, Y, and Z axis directions through the corresponding joystick or control command to achieve precise position adjustment; and then control the strain probe to approach the structure to be measured and apply a lateral compressive stress to the structure to be measured during the measurement process.

[0091] In the solution provided in this embodiment, the sample stage is fixed, while the strain probe is movable (driven by a three-dimensional moving stage). On the basis of meeting the same test purpose, the sample stage or the sample fixture part therein can also be designed to be movable, while the strain probe is designed to be fixed. Even without considering cost, corresponding three-dimensional moving stages can be designed for both the fixture part and the strain probe part in the sample stage, making the operation process during measurement more convenient. All of these fall within the protection scope of the technical solution provided in this embodiment.

[0092] The microphotography mechanism in this embodiment is located on the side of the sample stage; the microphotography mechanism is used to obtain a local image of the sample of the target microstructure to be measured. Specifically, the microphotography system includes a camera and a lens system. The lens system is used to optically magnify the target area, and the camera is used to obtain an image of the target area magnified by the lens system.

[0093] The target for measurement in this embodiment is usually a micron structure, and it is very difficult to achieve precise operation only by visual inspection of the operator. Therefore, it is necessary to use microphotography to locally magnify the operation area, so that the operator can intuitively observe the positional relationship between the strain probe and the microstructure to be measured.

[0094] It should be noted that the microphotography adopted in this embodiment belongs to an advanced digital microscopy technology, and the local images obtained by this technology can be output through a display or the like. Therefore, the microphotography mechanism in this embodiment further includes a display component or is connected to an external display component. The display component is used to display the image obtained by the camera in real time. Among them, the lens system is a "microscope", and the camera is an image acquisition device. In other simpler solutions, a microphotography system may not be adopted, but an independent microscope may be used instead. In this case, the situation of the object in the target area needs to be directly observed by the operator through the microscope. Of course, this also falls within the protection scope of the equipment provided in this embodiment.

[0095] It should be emphasized that: when observing the target area by visual inspection without using a camera, the image obtained by the camera and the subsequent data processing work based on the microscopic image cannot be carried out, and these works need to be redesigned and implemented.

[0096] In a more optimized solution of this embodiment, the microphotography mechanism further includes a light source or is connected to an external light source. The light source is used to supplement light to the target area on the sample stage containing the microstructure to be measured. The added light source can perform artificial light supplementation when the natural light in the operation area is insufficient, improving the clarity and image quality of the target area during camera or manual observation.

[0097] As mentioned above, the functions of the microphotography mechanism in this embodiment include two points: First, before the strain probe and the micro-structure to be measured come into contact during the measurement process, it is convenient for the operator to understand the relative position between the strain probe and the target micro-structure to be measured in real time, and then apply corresponding manipulation instructions to the three-dimensional moving stage. Second, after the strain probe and the micro-structure to be measured come into contact, it is used to identify the deformation amount of the strain probe and / or the target micro-structure to be measured. Therefore, in theory, the micro-camera needs to simultaneously acquire images along the front and side of the target object. One of these two perspectives is used to observe whether they are approaching and aligned, and the other is used to observe the degree of their deformation.

[0098] To achieve dual-perspective observation, the microphotography mechanism can be deployed in various ways. Specifically, it includes using a single movable group or multiple groups. The single movable group means that the number of microphotography mechanisms is one group, and the relative position between the microphotography mechanism and the sample stage is adjustable. For example, corresponding slide rails are installed on the sample stage for the microphotography mechanism, and the microphotography mechanism is slid to different positions according to needs during use. In other feasible solutions, the sample stage can also be designed to be rotatable, and then the microphotography mechanism is kept fixed relative to the ground, and the sample stage or the sample fixture is rotated to adjust their relative positions to achieve the purpose of multi-angle observation.

[0099] The best way to achieve multi-angle observation is to adopt the solution of this embodiment, and at least two groups of microphotography mechanisms are set. The two groups of microphotography mechanisms are respectively located in the X-axis and Y-axis directions of the plane where the sample stage is located. In a more preferred solution of other embodiments, a microphotography mechanism located on the Z-axis can also be added above the sample stage. This microphotography mechanism can be used to observe the actual position of the strain probe on the horizontal plane to achieve three-dimensional alignment and measurement.

[0100] In this embodiment, the data processing module is communicatively connected to the strain detection mechanism and the microphotography mechanism; the detection data of the strain probe in the strain detection mechanism is transmitted to the data processing module, and the local image of the sample collected by the camera in the microphotography mechanism is also transmitted to the data processing module. The data processing module at least includes two different functional units, namely a displacement recognition unit and a stiffness calculation unit.

[0101] Among them, the displacement recognition unit is used to analyze the maximum displacement of the target micro-structure relative to the initial position at the current moment through image recognition and digital scale technology according to the local images of the sample corresponding to each moment, and use this as the deformation amount S2 of the target micro-structure. The stiffness calculation unit is used to obtain the deformation amount S1 of the strain probe and / or the lateral compressive stress F borne at each moment. Then through or Calculate the stiffness value K2(t) corresponding to each moment. Finally, take the average value of the stiffness value K2(t) within the preset sampling period as the stiffness K2 of the micro-structure to be measured. Wherein, K1 represents the material stiffness of the known strain probe. The sampling period refers to the intermediate period from the moment when the strain probe starts to contact the target micro-structure to the moment when the target micro-structure reaches the maximum deformation state.

[0102] It can be seen that the data processing module of this embodiment is the data processing center of the entire system. After adopting the method of this embodiment, the data processing module can automatically output the measurement result of the stiffness of the target micro-structure required according to the measurement process. That is: the stiffness measurement system for large aspect ratio micron-scale structures provided by this embodiment is a highly automated instrument, without the need for manual processing of complex calculation tasks.

[0103] Of course, in other embodiments, removing the data processing module used in this embodiment and using manual analysis and processing of the acquired relevant data can also achieve the stiffness measurement task of the target micro-structure. In this case, the stiffness measurement system for large aspect ratio micron-scale structures can be further simplified into a semi-automated measurement device without data analysis and output, which still falls within the scope of the solution protection of the stiffness measurement system proposed in this embodiment.

[0104] Embodiment 3

[0105] Based on Embodiment 2, this embodiment provides a new stiffness measurement system for large aspect ratio micron-scale structures, which can effectively measure parameters such as the stiffness and elastic modulus of such "slender" micro-structures. Specifically, the differences between the solution of this embodiment and the embodiment are as follows:

[0106] In this embodiment, as Figure 11 shown, the stiffness measurement system further includes a displacement measurement mechanism for measuring the deformation amount S2 of the target micro-structure. The displacement measurement mechanism includes a laser, an optical path adjustment component, and a monitor. The laser is used to emit a beam of detection laser to the target micro-structure. The detection laser is reflected by the surface of the target micro-structure and then enters the optical path adjustment component, and finally is reflected to the monitor. The monitor is used to output the corresponding deformation amount S2 of the target micro-structure according to the position change of the received laser signal.

[0107] Among them, after adding the displacement measurement mechanism, the solution of the data processing module in the stiffness measurement system provided by this embodiment can also be adjusted. For example, it can be designed to be the same as in Embodiment 2, and include a displacement recognition unit and a stiffness calculation unit at the same time. It can also be simplified, only including the stiffness calculation unit, and not including the displacement recognition unit based on image recognition and digital scale technology.

[0108] When both a displacement recognition unit and a stiffness calculation unit are included in the data processing module, the stiffness calculation unit uses the average value of the calculation results of the displacement recognition unit and the displacement measurement mechanism as the deformation amount S2 of the required target microstructure. That is: in this embodiment, the deformation amount of the target microstructure is measured by two independent methods respectively, and then the measurement results of the two are fused and used as the final result. This can overcome the influence of the accuracy problem of a single measurement scheme in special situations on the final measurement result. For example, when the image quality of microphotography is poor, a large error may occur in the measurement method based on the microimage. In addition, the results obtained from the two channels can also be used for mutual calibration. For example, when the measurement errors of the two exceed the preset value, it can be determined that at least one of the measurement results is incorrect. At this time, the device can be reset until the errors of the two meet the requirements.

[0109] When only a stiffness calculation unit is included in the data processing module, the stiffness calculation unit uses the measurement result of the displacement measurement mechanism as the deformation amount S2 of the required target microstructure.

[0110] Specifically, the displacement measurement mechanism in this embodiment can not only measure the deformation amount of the target microstructure, but also be used to measure the deformation amount of the strain probe; the measurement principle is the same as above. At the same time, it should be additionally noted that when the surface of the microstructure or strain probe to be measured in this embodiment uses a laser-sensitive material (such as a photocuring material or a material that is easily ablated by a laser), it is not suitable to use the displacement measurement mechanism to measure the deformation amount. The application of this mechanism can be flexibly installed and independently debugged according to the measurement scenario in the actual application process. For example, when using a microcantilever beam sensor as a strain probe, the deformation amount of the microcantilever beam sensor is very suitable for measurement using the displacement measurement mechanism in this embodiment.

[0111] The stiffness measurement system for the large aspect ratio micron-scale structure provided in this embodiment includes two groups of microphotography mechanisms. The two groups of microphotography mechanisms can be used to guide the alignment of the strain probe and calculate the deformation amount of the target microstructure based on the images obtained by the microphotography mechanism. The strain probe uses a microcantilever beam, and the deformation amount of the microcantilever beam is measured by a group of displacement measurement mechanisms.

[0112] Specifically, the test process of measuring the target microstructure using the stiffness measurement system of this embodiment is as follows:

[0113] 1. Prepare a structural body sample containing microcolumns with large aspect ratio characteristics

[0114] Hydrogel is a 3D network composed of hydrophilic polymers that absorb a large amount of water. It has strong deformation ability, and the microstructures of hydrogels processed with different laser parameters have different stiffness characteristics. Therefore, it is very necessary to detect its stiffness. Among the microstructures of hydrogel polymers based on femtosecond laser two-photon printing, the most basic ones are various micro-column elements. In this embodiment, a narrow hydrogel micro-column structure with a diameter of 0.5 - 20 μm and a height of less than 200 μm was printed by femtosecond laser two-photon printing, and this was used as the measurement sample for this experiment.

[0115] The process of femtosecond laser processing is as follows: The hydrogel was dropped onto the cover glass through a pipette. The cover glass was fixed upright on the femtosecond laser two-photon processing platform, and the designed micro-column structure was processed. After the processing was completed, the cover glass was immersed in an ethanol solution for development to remove the uncured part, and the required polymer micro-column structure to be detected was obtained.

[0116] 2. Measure using the stiffness measurement system for microstructures with a large aspect ratio

[0117] In this embodiment, the working process of the stiffness measurement system is roughly as Figure 12 shown, including four stages a - d, which are respectively:

[0118] a. Place the sample cover glass on the sample stage and fix both ends of the cover glass with clamps.

[0119] b. Debug the micro-cantilever beam and the three-dimensional moving platform, and adjust the spatial position of the micro-cantilever beam relative to the target microstructure (micro-column) by manipulating the control knobs in three directions of the three-dimensional moving platform.

[0120] c. The microphotography mechanism obtains the spatial conditions of the sample to be measured and the micro-cantilever beam in real time from the X and Y directions. The operator observes the image and manipulates the three-dimensional moving stage to drive the micro-cantilever beam to move. During the movement, the operator approaches the target microstructure in the X or Y direction in a way that aligns with the vertical center line. When the Z - direction center line of the micro-cantilever beam and the micro-column can be observed to be aligned in the Y - path microimage and there is an overlap in the end space, the real-time distance between the micro-cantilever beam and the micro-column is observed through the X - path microimage.

[0121] d. When the three-dimensional moving stage drives the micro-cantilever beam to approach the micro-column until they come into contact and squeeze each other, due to the interaction of forces, the micro-cantilever beam and the micro-column will each produce micro-deformations.

[0122] When the micro-cantilever beam is used as a strain probe, the micro-cantilever beam is extremely sensitive to weak forces, and its stiffness K1 is known. The micro-cantilever beam is irradiated with a laser and received by a monitor. When the micro-cantilever beam and the polymer micro-column interact and undergo small deformations, the position of the reflected light will change accordingly, and the reflected light beam will also shift. The deformation information S1 of the micro-cantilever beam can be obtained through signal processing by the controller.

[0123] In the detection of the interaction between the beam and the micro-column, the deformation amount S2 of the micro-column can be obtained through analysis of microscopic images. At this time, based on the relationship between force and stress-strain, the stiffness K2 of the micro-structure (micro-column) to be measured can be calculated by the following formula:

[0124]

[0125] The above are only the preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for measuring the stiffness of a micron-scale structure with a large aspect ratio, characterized in that, It includes the following steps: S1: Fix the sample of the microstructure to be measured on a horizontal test bench, and set a vertical strain probe above the sample that can measure the deformation amount S and / or the lateral compressive stress F; S2: Move the strain probe to a position just in contact with the side wall of the microstructure to be measured, and adjust the height of the strain probe so that the strain probe partially coincides with the microstructure to be measured in the height direction; S3: Preset the feed amount x0 for each movement, and move the strain probe successively along a fixed direction in the horizontal plane according to the feed amount x0; and measure the deformation amount S2 of the microstructure to be measured corresponding to different moments, as well as the deformation amount S1 or the lateral compressive stress F corresponding to the strain probe; Wherein, the deformation amounts S1 and S2 are respectively the displacements of the strain probe and the microstructure relative to the initial position in the feed direction of the strain probe; S4: Based on the detection results of the above steps, calculate the micro-column stiffness K2 corresponding to each moment through any one of the following two formulas: Or In the above formula, K1 represents the known material stiffness of the strain probe; S5: Based on the series of discrete data obtained in the above steps, fit a test function K2(t) for characterizing the change of the micro-column stiffness; S6; Take the function value K2 of a section with a constant slope in the test function K2(t) fitted in the above step as the stiffness of the microstructure to be measured.

2. The stiffness measurement method of the micro-scale structure with a large height-diameter ratio according to claim 1, characterized in that: The strain probe adopts a force-measuring fiber optic sensor, a micro-strain measuring fiber optic sensor or a micro-cantilever beam sensor.

3. The stiffness measurement method of the micron-scale structure with a large aspect ratio according to claim 2, characterized in that: In step S3, the deformation amount S1 or the lateral compressive stress F of the strain probe is directly read through the corresponding sensor; And / or The deformation amount of the microstructure to be measured is obtained by measuring with a digital scale based on a microscopic image. The microscopic image is an image obtained by photographing along the side of the microstructure, and the main optical axis of the viewfinder is perpendicular to the feed direction of the strain probe.

4. A stiffness measurement system for a micron-scale structure with a large height-to-diameter ratio, characterized in that: It is used to directly measure the stiffness of the microstructure by using the stiffness measurement method of the high aspect ratio micron-scale structure described in any one of claims 1-3; the stiffness measurement system includes: A sample stage for fixing a sample containing the microstructure to be measured; A strain detection mechanism located above the sample stage; the strain detection mechanism includes a three-dimensional moving stage and a strain probe, and the strain probe is fixedly connected to the three-dimensional moving stage; the three-dimensional moving stage is used to adjust the spatial position of the strain probe; the strain probe is used to measure the deformation amount S1 of itself and / or the lateral compressive stress F during the operation; At least one set of microscopic photography mechanism located on the side of the sample stage; the microscopic photography mechanism is used to obtain a local image of the sample of the target microstructure to be measured; the local image of the sample is used to analyze the relative position between the strain probe and the target microstructure to be measured, and to identify the deformation amount S2 of the target microstructure to be measured; and A data processing module, which is communicatively connected to the strain detection mechanism and the microphotography mechanism; the data processing module includes a displacement recognition unit and a stiffness calculation unit; the displacement recognition unit is configured to analyze, according to the local images of the sample corresponding to each moment, the maximum displacement of the target microstructure relative to the initial position at the current moment through image recognition and digital scale technology, and use this as the deformation amount S2 of the target microstructure; the stiffness calculation unit is configured to obtain the deformation amount S1 of the strain probe and / or the lateral compressive stress F borne at each moment; and then through or calculate the stiffness value K2(t) corresponding to each moment; finally, take the mean value of the stiffness values K2(t) within the preset sampling period as the stiffness K2 of the microstructure to be measured; where K1 represents the known material stiffness of the strain probe; the sampling period refers to the intermediate period from the moment when the strain probe starts to contact the target microstructure to the moment when the target microstructure reaches the maximum deformation state.

5. The stiffness measurement system for the micron-scale structure with a large height-to-diameter ratio according to claim 4, characterized in that: The microscopic photography system includes a camera and a lens system; the lens system is used to optically magnify the target area, and the camera is used to obtain an image of the target area magnified by the lens system.

6. The stiffness measurement system for the micron-scale structure with a large height-to-diameter ratio as claimed in claim 5, wherein: The microscopic photography mechanism further includes a display component or is connected to an external display component; the display component is used to display the image obtained by the camera in real time; And / or The microphotography mechanism further includes a light source or is connected to an external light source, and the light source is used to supplement light to the target area on the sample stage that contains the microstructure to be measured.

7. The stiffness measurement system for the micron-scale structure with a large aspect ratio according to claim 5, characterized in that: The microphotography mechanism is of a single-group movable type or a multi-group type; the single-group movable type means that the number of microphotography mechanisms is one group, and the relative position between the microphotography mechanism and the sample stage is adjustable; the multi-group type means that the number of microphotography mechanisms is not less than two groups, and at least includes two groups of microphotography mechanisms located in the X-axis and Y-axis directions of the plane where the sample stage is located.

8. The stiffness measurement system for the micron-scale structure with a large height-to-diameter ratio as claimed in claim 4, wherein: The strain probe uses a force-measuring fiber optic sensor, a microstrain-measuring fiber optic sensor or a microcantilever sensor.

9. The stiffness measurement system for the micron-scale structure with a large height-to-diameter ratio according to claim 4, characterized in that: The stiffness measurement system further includes a displacement measurement mechanism for measuring the deformation amount S2 of the target microstructure or the deformation amount S1 of the strain probe; The displacement measurement mechanism includes a laser, an optical path adjustment component and a monitor; the laser is used to emit a detection laser beam towards the measurement target, and the detection laser beam enters the interior of the optical path adjustment component after being reflected by the target surface and is finally reflected to the monitor; The monitor is used to output the deformation amount of the corresponding target according to the position change of the received laser signal.

10. The stiffness measurement system for the micron-scale structure with a large height-to-diameter ratio according to claim 9, wherein: When the displacement measurement mechanism is included in the stiffness measurement system, the data processing module includes both a displacement recognition unit and a stiffness calculation unit, or only includes a stiffness calculation unit; And / or When the data processing module includes both a displacement recognition unit and a stiffness calculation unit, the stiffness calculation unit uses the average value of the calculation results of the displacement recognition unit and the displacement measurement mechanism as the deformation amount S2 of the required target microstructure; When the data processing module only includes a stiffness calculation unit, the stiffness calculation unit uses the measurement result of the displacement measurement mechanism as the deformation amount S2 of the required target microstructure.

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