Integrated meniscus tracking liquid microflow calibration device and method of use thereof

Abstract

The present application relates to the technical field of micro flow calibration, and particularly relates to an integrated meniscus tracking liquid micro flow calibration device and a use method thereof, which comprises a meniscus tracking flow calibration chip, a thermostat and a meniscus tracking device, the meniscus tracking flow calibration chip comprises a glass substrate and a PDMS channel bonded on the surface of the glass substrate, the glass substrate is attached to the thermostat, and the thermostat is used for ensuring the constant temperature of the meniscus chip, the meniscus tracking device comprises a linear motion unit and an image acquisition module, the linear motion unit is located below the meniscus chip and is used for tracking the meniscus in the meniscus tracking flow calibration chip, and the image acquisition module is installed on the linear motion unit and is used for monitoring the meniscus, and the present application solves the problems of calibration and calibration of liquid micro flow sensors and micro injection pumps, and realizes the value traceability of liquid micro flow.

Description

Technical Field

[0001] This invention relates to the field of micro-flow calibration technology, and in particular to an integrated meniscus tracking liquid micro-flow calibration device and its usage method. Background Technology

[0002] In liquid flow rate calibration, existing technical solutions fall into two main categories: the mass method and the volumetric method. The mass method is particularly widely used. Its basic principle is to measure the increase in liquid mass per unit time. During calibration, the instrument under test is connected in series in a pipeline containing a flow generator and a mass measuring device (such as an electronic scale or balance). The measurement accuracy is evaluated by comparing the change in the mass measuring device's reading per unit time with the measured value of the instrument under test. In addition, there are liquid flow rate calibration devices based on the volumetric method. Their principle is to calculate the flow rate based on the change in fluid volume per unit time. A typical example is the volumetric tube. Volumetric tubes are divided into active and passive types based on their power source. The former integrates a power source and can function as a flow generator itself; the latter uses fluid to drive a piston, thereby calculating the flow rate. Existing volumetric tubes typically use carbon steel or stainless steel for the tube body (cylinder) and integrate photoelectric / mechanical sensors to detect piston displacement.

[0003] However, while the mass method can ignore the effects of evaporation and slight vibration when calibrating large flow rates, it becomes non-negligible and a major factor limiting the accuracy of the device when calibrating small flow rates of liquids. Existing volumetric liquid flow calibration devices (such as volume tubes) have complex mechanical structures, typically integrating a large number of valves, transmission structures, and detection elements. As a result, the devices are relatively large and difficult to miniaturize further to meet the needs of small flow rate calibration of liquids. Summary of the Invention

[0004] In view of this, the purpose of this invention is to provide an integrated meniscus tracking liquid micro-flow calibration device and its usage method, so as to solve the existing problems in liquid micro-flow calibration.

[0005] To achieve the above objectives, the present invention provides an integrated meniscus-tracking liquid micro-flow calibration device, comprising a meniscus-tracking flow calibration chip, a thermostat, and a meniscus-tracking device:

[0006] The meniscus tracking flow calibration chip includes a glass substrate and PDMS channels bonded to its surface. The glass substrate is attached to a thermostat, which is used to ensure a constant temperature of the meniscus chip.

[0007] The meniscus tracking device includes a linear motion unit and an image acquisition module. The linear motion unit is located below the meniscus chip and is used to track the meniscus in the meniscus tracking flow calibration chip. The image acquisition module is mounted on the linear motion unit and is used to monitor the meniscus.

[0008] Preferably, the PDMS channel has a serpentine channel structure, including a micro-liquid injection channel, a meniscus measurement channel, and a micro-liquid discharge channel. The micro-liquid injection channel and the micro-liquid discharge channel are respectively connected to both ends of the meniscus measurement channel and are both straight channels. The meniscus measurement channel is composed of a combination of straight channels and arc channels.

[0009] Preferably, the thermostat includes a constant temperature water tank, a micro pump, a cooling fan, a return water pipe, and an outlet water pipe. The constant temperature water tank includes an upper layer and a lower layer, which are separated by a partition and connected at the edge. The micro pump includes two interfaces, which are respectively connected to the return water pipe and the outlet water pipe. The outlet water pipe is connected to the upper layer of the constant temperature water tank in parallel at both ends, and the return water pipe is connected in parallel to the lower layer of the constant temperature water tank.

[0010] Preferably, the thermostat also includes a cooling fan, which is fixed to the upper outer wall of the thermostat water bath by a thermally conductive copper sheet.

[0011] Preferably, the linear motion unit includes a stepper motor and a ball screw. The stepper motor is connected to the image acquisition module through the ball screw, and the ball screw drives the image acquisition module to achieve linear motion.

[0012] Preferably, the PDMS channel is made of glass capillary tubes, and the preparation method includes:

[0013] The glass capillary tube was heat-treated in air at 500°C for 1 hour to remove residues on the inner wall.

[0014] The glass capillary was hydrophobically treated with octadecyltrichlorosilane solution. In this process, the OTS solution was slowly injected into the capillary for 90 seconds using a syringe and a soft tube to fully wet the inner wall of the capillary. The remaining solution in the tube was then blown out with nitrogen.

[0015] Place the glass capillary tube on the drying table for drying.

[0016] The present invention also provides a method of using the above-mentioned integrated meniscus tracking liquid micro-flow calibration device, comprising:

[0017] The flow rate to be measured is injected into the PDMS channel to locate the initial position of the image acquisition module so that it can capture the meniscus.

[0018] Using the outer diameter of the meniscus measurement channel in the PDMS channel as a reference, the relationship between image pixels and the real dimensions of the physical world is established. The outer diameter is selected using functions from the OpenCV library. Then, a function is called to return the coordinates of the user-selected region of interest in pixels. The scale is calibrated by the actual size of the outer diameter and the corresponding pixel size.

[0019] The image is subdivided into different regions to simplify image analysis;

[0020] The gradient algorithm is used to determine the contour of the meniscus and return the coordinates of the pixel at the center of the meniscus. The horizontal coordinate of this point is determined in pixels. The actual displacement is calculated using the obtained scale, and the volumetric flow rate of the liquid is obtained using the inner diameter of the channel.

[0021] Preferably, when injecting the flow rate to be measured into the PDMS channel, a heat-insulating film is attached to the outside of the syringe, and the syringe is connected to the meniscus tracking flow calibration chip through a constant temperature pipe.

[0022] The beneficial effects of this invention are:

[0023] 1. Ultra-small flow measurement capability: By using surface modification technology to reduce the meniscus, combined with a gradient operator-based meniscus recognition algorithm (positioning accuracy <5μm), a flow measurement lower limit of 10nL / min is achieved.

[0024] 2. Significantly improved environmental robustness: The integrated constant temperature system reduces temperature sensitivity and can maintain a measurement accuracy of less than 5% even in an unshielded environment.

[0025] 3. High-efficiency automated operation: The closed-loop control system based on machine vision can realize 24 / 7 unattended measurement, and the sampling period can be flexibly adjusted between 1 second and 1 hour.

[0026] 4. Miniaturization and Integration: The core detection unit is integrated into a 20mm×100mm chip using microelectromechanical systems (MEMS) technology (soft lithography). The detection device is also integrated, with a size of less than 400×400×200mm. Attached Figure Description

[0027] To more clearly illustrate the technical solutions in this invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only for this invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0028] Figure 1 This is a schematic diagram illustrating the principle of the meniscus tracking technology according to an embodiment of the present invention;

[0029] Figure 2 This is a comparison image of the meniscus before and after adding a hydrophobic layer in an embodiment of the present invention, wherein... Figure 2 (a) Before adding the hydrophobic layer Figure 2 (b) After adding a hydrophobic layer;

[0030] Figure 3 This is a meniscus position tracking diagram according to an embodiment of the present invention, wherein... Figure 3 (a) is the original image. Figure 3 (b) is an enhanced image. Figure 3 (c) is the algorithm processing diagram. Figure 3 (d) is the coordinate tracking diagram;

[0031] Figure 4 This is a block diagram of the PID position closed-loop control of the meniscus tracking device according to an embodiment of the present invention;

[0032] Figure 5 This is a schematic diagram of the integrated meniscus tracking liquid micro-flow calibration device according to an embodiment of the present invention;

[0033] Figure 6 This is a top view schematic diagram of the integrated meniscus tracking liquid micro-flow calibration device according to an embodiment of the present invention;

[0034] Figure 7 This is a front view schematic diagram of the integrated meniscus tracking liquid micro-flow calibration device according to an embodiment of the present invention;

[0035] Figure 8 This is a schematic diagram of the meniscus tracking flow calibration chip structure according to an embodiment of the present invention.

[0036] The following are labeled in the diagram: 1, 2, 3, cooling fan; 4, constant temperature water bath; 5, meniscus tracking flow calibration chip; 5-1, glass substrate; 5-2, micro liquid injection channel; 5-3, meniscus measurement channel; 5-4, micro liquid discharge channel; 6, supplementary light; 7, industrial camera; 8, 10, guide rod; 9, ball screw; 11, water outlet pipe; 12, water return pipe; 13, micro pump; 14, stepper motor. Detailed Implementation

[0037] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments.

[0038] It should be noted that, unless otherwise defined, the technical or scientific terms used in this invention should have the ordinary meaning understood by one of ordinary skill in the art to which this invention pertains. The terms "first," "second," and similar terms used in this invention do not indicate any order, quantity, or importance, but are merely used to distinguish different components. Terms such as "comprising" or "including" mean that the element or object preceding the word encompasses the elements or objects listed following the word and their equivalents, without excluding other elements or objects. Terms such as "connected" or "linked" are not limited to physical or mechanical connections, but can include electrical connections, whether direct or indirect. Terms such as "upper," "lower," "left," and "right" are used only to indicate relative positional relationships; when the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0039] This invention provides an integrated meniscus-tracking liquid micro-flow calibration device, which can realize the digital verification and calibration of liquid micro-flow rates. The device consists of a meniscus-tracking flow calibration chip, a temperature control device, a linear motion unit, a camera, etc., and its working principle is as follows: Figure 1 As shown, during operation, liquid is injected into the meniscus tracking flow calibration chip by a micro-injection pump. As the liquid flows through the chip, a meniscus forms at the front end. Flow data can be obtained by detecting the displacement of the meniscus. Structurally, the device consists of a meniscus tracking flow calibration chip 5, a thermostat, a linear motion unit, an industrial camera 7, and other components.

[0040] Among them, the meniscus tracking flow calibration chip 5 is the site for generating and detecting the liquid meniscus. The chip is fabricated using a soft photolithography process and includes a glass substrate 5-1 and PDMS channels bonded to its surface, such as... Figure 8 As shown, the PDMS channel has a serpentine channel structure, including a micro-liquid injection channel 5-2, a meniscus measurement channel 5-3, and a micro-liquid discharge channel 5-4. A glass substrate 5-1 is attached to the surface of the constant-temperature water bath 4 in the constant-temperature heat exchanger. The micro-liquid injection channel 5-2 and the micro-liquid discharge channel 5-4 are both straight channels, while the meniscus measurement channel 5-3 is a combination of a straight channel and a circular arc channel. The channel width is 0.1–5 mm, and the height is 0.01–0.2 mm.

[0041] Thermostat: Temperature changes can affect the flow of the micro-liquid within the meniscus chip, thus influencing the transmission of values. This device aims to maintain a constant temperature during the circulation of the micro-liquid. This component consists of a thermostatic water tank 4, a micro-pump 13, three cooling fans 1, 2, and 3, a return water pipe 12, and an outlet water pipe 11. The micro-pump 13 has two interfaces: the front connects to the return water pipe 12, and the top connects to the outlet water pipe 11. The outlet water pipe 11 is connected in parallel at both ends to the upper layer of the thermostatic water tank 4. The thermostatic water tank 4 is divided into upper and lower layers, separated by a partition. Three cooling fans 1, 2, and 3 are fixed to the outer wall of the upper layer via thermally conductive copper sheets. The upper and lower layers are connected at the inner edge of the thermostatic water tank 4, and the outlet water pipe 11 is connected in parallel to the outer wall of the lower layer. The thermostatic heat exchange device ensures the constant flow of the meniscus tracking calibration chip 5 through the flow of the internal coolant and the operation of the cooling fans 1, 2, and 3.

[0042] Linear motion unit: This part enables real-time tracking of the meniscus in the meniscus tracking flow calibration chip 5. The meniscus tracking device is located below the meniscus tracking flow calibration chip 5. A stepper motor 14 fixed on one side is connected to the industrial camera 7 via a ball screw 9. The ball screw 9, guide rod 8, and guide rod 10 drive the industrial camera 7 to achieve linear motion. The industrial camera 7 is fixed on the motion platform of the ball screw 9, and the lens of the industrial camera 7 is directly facing the meniscus measurement channel 5-3 to ensure that the meniscus can be monitored by the camera in real time. For better monitoring, a supplementary light 6 can also be set.

[0043] During the measurement process, the morphology of the meniscus is crucial to the accuracy of displacement measurement. Capillary forces within the channel can cause significant changes in the meniscus. The influence of the hydrophilic / hydrophobic properties of the channel's inner surface was investigated during the invention process. Furthermore, experimental research was conducted on hardware platform design, image recognition, and motion control algorithms. The research content involved in the invention process is as follows:

[0044] 1. Based on numerical simulation and experiments, investigate the relationship between meniscus morphology and liquid and wall properties, determine the channel material parameters of the meniscus tracking system, and establish physical / chemical modification methods for the wall.

[0045] 2. Build a hardware platform for a meniscus tracking liquid micro-flow calibration device, which mainly includes a meniscus tracking flow calibration chip 5, a thermostat, a linear motion unit, an industrial camera 7, etc.

[0046] 3. Construct a meniscus tracking algorithm based on digital image processing technology, and establish a meniscus tracking system by combining motion control technology.

[0047] This invention integrates the core detection unit onto a 20mm×100mm chip using microelectromechanical systems (MEMS) technology (soft lithography). The detection device is also integrated, with a size less than 400×400×200mm.

[0048] This specification also provides the following specific embodiments:

[0049] Example 1:

[0050] 1. The glass capillary tube was heat-treated in air at 500℃ for 1 hour to remove residues on the inner wall. The capillary tube was then hydrophobically treated with an octadecyltrichlorosilane (OTS) solution. This process involved slowly injecting the OTS solution into the capillary tube for 90 seconds using a syringe and tubing to ensure thorough wetting of the inner wall. To prevent clogging, any remaining solution was blown out with nitrogen gas. The capillary tube was then placed on a drying rack for drying. This resulted in the PDMS channel. A comparison of the meniscus before and after adding the hydrophobic layer is shown below. Figure 2 As shown.

[0051] 2. After the flow rate is generated by the Havard micro-injection pump, it is connected to the PDMS channel through a constant temperature pipeline. The industrial camera 7 is mounted on the ball screw 9 driven by the stepper motor 14, so that it can continuously capture the displacement of the meniscus inside the capillary.

[0052] 3. Scale calibration: Using the outer diameter of the capillary tube as a reference, establish the relationship between image pixels and the real dimensions of the physical world. Use OpenCV library functions to select the outer diameter, then call functions to return the coordinates of the user-selected Region of Interest (ROI) in pixels. The scale can be calibrated using the actual size of the outer diameter and the corresponding pixel size.

[0053] 4. Image segmentation: Select an appropriate method to subdivide the image into different regions to simplify image analysis.

[0054] 5. Meniscus Position Determination: The gradient algorithm is used to determine the contour of the meniscus and return the coordinates of the center pixel. The horizontal coordinates of this point are determined in pixels. The true displacement is calculated using the scale obtained in step 3, and the volumetric flow rate of the liquid is obtained through the channel inner diameter. During the processing, the original image (a) is enhanced to form image (b), and the result obtained by the gradient algorithm is shown in Figure (c). The meniscus coordinates are determined by edge recognition, generating a coordinate tracking image (d). Figure 3 As shown;

[0055] The gradient descent algorithm employs the Sobel operator, a classic image processing tool for edge detection. Its core idea is to locate edges (regions of drastic brightness changes) by calculating the brightness gradient (i.e., the rate of change of brightness) at each pixel in the image.

[0056] This invention uses a horizontal gradient convolution kernel to perform convolution operations on the original image to obtain the horizontal gradient of each pixel region, and determines the position of the meniscus by the gradient value.

[0057] 6. Motion Control: Within one measurement cycle, the linear motion platform remains stationary. After the measurement cycle ends and the system calculates the flow measurement value, the linear motion platform moves directionally within a short time to restore the liquid level to the initial position of the previous cycle. The motion control algorithm is implemented using a PID closed-loop algorithm, and the structure diagram is as follows. Figure 4 As shown, specifically, after one measurement cycle, the position of the meniscus shifts in the field of view. A closed-loop algorithm is needed to drive the line platform carrying the camera, so that the camera moves relative to the capillary tube and moves the meniscus to the initial position. Here, the pixel offset is used as the deviation in the PID algorithm. The P parameter determines the step size of the stepper motor drive based on the magnitude of the deviation. The I parameter eliminates the steady-state error under small deviation conditions. The D parameter improves the dynamic process, making it more stable and faster to reach the predetermined position.

[0058] Example 2:

[0059] 1. Components required for the experimental setup: syringe pump (flow generator), meniscus tracking flow calibration chip 5, syringe, tubing connection cable, LED light, computer and USB camera.

[0060] 2. Set the syringe pump to 10μL / min and the meniscus tracking flow calibration chip channel 5 to 300μm inner diameter.

[0061] 3. First, set up a constant temperature water tank, connect it to the syringe via a tubing, providing a constant temperature environment of 4℃, and attach a layer of insulation film around the syringe. Connect the syringe to the meniscus tracking flow calibration chip via a flexible hose. Manually position the camera initially, capturing the meniscus area. By understanding the distance the meniscus moves over time and the inner diameter of the chip channel, the fluid velocity and its associated uncertainties can be calculated.

[0062] 4. Build a user interface using OpenCV and Pyside libraries. This page should include: Start, End, Canney operator debugging, and scale calibration. Scale calibration sets the relationship between pixels and actual distances.

[0063] 5. The distance between each pixel in the image is 5μm, denoted as M. Let the change in the value of x over a certain time interval be Δx, then the distance L that the capillary tube moves along the meniscus can be expressed as:

[0064] L=Δx·M

[0065] 6. Let the time it takes for the meniscus to move during continuous pumping be ΔT. Given that the inner radius of the capillary tube is r = 150 μm, the volumetric velocity Qv of the pump can be expressed as:

[0066]

[0067] Key aspects of this invention include:

[0068] 1. The present invention performs surface treatment on the inner surface of the channel, thereby changing the hydrophilicity and hydrophobicity of the inner wall of the channel and maintaining the constancy of the geometry of the meniscus, thus producing a stable and easily identifiable meniscus.

[0069] 2. Temperature changes can have a significant impact on the volumetric liquid micro-flow measurement technology. This is mainly because the liquid volume expands and contracts with temperature, which affects the liquid level and leads to deviations in the measurement results. This invention incorporates a thermostat to control the temperature of the liquid being measured, thereby greatly reducing the adverse effects of temperature fluctuations.

[0070] 3. The present invention integrates and automates the device design, enabling continuous measurement over a long period of time without supervision. It is suitable for the actual needs of liquid micro-flow verification and calibration, and does not require staff to be on duty for extended periods.

[0071] 4. This invention uses soft photolithography to process the flow detection chip, creating a micron-level liquid channel. The high processing precision ensures measurement accuracy.

[0072] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of the invention is limited to these examples; within the framework of the invention, the technical features of the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other variations of the different aspects of the invention as described above, which are not provided in detail for the sake of brevity. Any omissions, modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the invention should be included within the scope of protection of the invention.

Claims

1. An integrated meniscus-tracking liquid micro-flow rate calibration device, characterized in that, Includes a meniscus tracking flow calibration chip, a thermostat, and a meniscus tracking device: The meniscus tracking flow calibration chip includes a glass substrate and PDMS channels bonded to its surface. The glass substrate is attached to a thermostat, which is used to ensure a constant temperature for the meniscus tracking flow calibration chip. The meniscus tracking device includes a linear motion unit and an image acquisition module. The linear motion unit is located below the meniscus tracking flow calibration chip and is used to track the meniscus in the meniscus tracking flow calibration chip. The image acquisition module is installed on the linear motion unit and is used to monitor the meniscus. The PDMS channel has a serpentine channel structure, including a micro-liquid injection channel, a meniscus measurement channel, and a micro-liquid discharge channel. The micro-liquid injection channel and the micro-liquid discharge channel are respectively connected to both ends of the meniscus measurement channel and are both straight channels. The meniscus measurement channel is composed of a combination of straight channels and arc channels. The thermostat includes a constant temperature water tank, a micro pump, a cooling fan, a return water pipe, and an outlet water pipe. The constant temperature water tank includes an upper layer and a lower layer, which are separated by a partition and connected at the edge. The micro pump includes two interfaces, which are connected to the return water pipe and the outlet water pipe, respectively. The outlet water pipe is connected to the upper layer of the constant temperature water tank in parallel at both ends, and the return water pipe is connected in parallel to the lower layer of the constant temperature water tank. The linear motion unit includes a stepper motor and a ball screw. The stepper motor is connected to the image acquisition module through the ball screw, and the ball screw drives the image acquisition module to achieve linear motion. Within one measurement cycle, the linear motion unit remains stationary. After the measurement cycle ends, the linear motion unit moves in a specific direction to restore the meniscus to the initial position of the previous cycle. The motion control algorithm is implemented by a PID closed-loop algorithm. After one measurement cycle, the position of the meniscus shifts in the field of view. The closed-loop algorithm is used to drive the linear motion unit carrying the image acquisition module, so that the image acquisition module moves relative to the capillary of the PDMS channel, moving the meniscus back to the initial position. Here, the pixel offset is used as the deviation in the PID algorithm. The P parameter determines the step size of the stepper motor drive based on the magnitude of the deviation. The I parameter eliminates the steady-state error under small deviation conditions, and the D parameter improves the dynamic process.

2. The integrated meniscus tracking liquid micro-flow rate calibration device according to claim 1, characterized in that, The cooling fan is fixed to the upper outer wall of the constant temperature water tank by a thermally conductive copper sheet.

3. The integrated meniscus tracking liquid micro-flow rate calibration device according to claim 1, characterized in that, The PDMS channel is made of glass capillary tubes, and the preparation method includes: The glass capillary tube was heat-treated in air at 500°C for 1 hour to remove residues on the inner wall. The glass capillary was hydrophobically treated with an octadecyltrichlorosilane solution. In this process, the octadecyltrichlorosilane solution was slowly injected into the capillary for 90 seconds using a syringe and a soft tube to fully wet the inner wall. The remaining solution in the tube was then blown out with nitrogen gas. Place the glass capillary tube on the drying table for drying.

4. A method of using the integrated meniscus tracking liquid micro-flow calibration device as described in any one of claims 1-3, characterized in that, The method includes: The flow rate to be measured is injected into the PDMS channel to locate the initial position of the image acquisition module so that it can capture the meniscus. Using the outer diameter of the meniscus measurement channel in the PDMS channel as a reference, the relationship between image pixels and the real dimensions of the physical world is established. The outer diameter is selected using functions from the OpenCV library. Then, a function is called to return the coordinates of the user-selected region of interest in pixels. The scale is calibrated by the actual size of the outer diameter and the corresponding pixel size. The image is subdivided into different regions to simplify image analysis; The gradient algorithm is used to determine the contour of the meniscus and return the coordinates of the pixel at the center of the meniscus. The horizontal coordinate of this point is determined in pixels. The actual displacement is calculated using the obtained scale, and the volumetric flow rate of the liquid is obtained using the inner diameter of the channel.

5. The method of using the integrated meniscus tracking liquid micro-flow calibration device according to claim 4, characterized in that, When injecting the flow rate to be measured into the PDMS channel, a heat-insulating film is attached to the outside of the syringe, and the syringe is connected to the meniscus tracking flow calibration chip through a constant temperature pipe.

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